dairy manure biogas potential report 3-29-09 complete

Dairy Manure Biogas Opportunities in Manica Province, Mozambique

A Preliminary Assessment

Prepared for

Land O’ Lakes International Development

Smallholder Dairy Development Program

in Manica Province, Mozambique

Prepared by

Paul Schwengels Consultant, Climate Change, Clean

Energy and Environment

March 29, 2009

Dairy Manure Biogas Opportunities in Manica Province, Mozambique: A Preliminary Assessment March 27, 2009

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Dairy Manure Biogas Opportunities in Manica Provence, Mozambique: A Preliminary Assessment

Paul Schwengels1

Introduction This report assesses the opportunities for use of biogas digesters to produce and use methane from dairy manure in a number of locations and at three different scales. The assessment was carried out under contract to Land O’ Lakes International Development. With support from the US Department of Agriculture, Land O’ Lakes International Development (LOL/ID) is implementing a project titled Smallholder Dairy Development Program in Manica Province in Mozambique. The main objectives of this private sector-based initiative are to begin rebuilding Mozambique’s dairy industry to meet market demand and to increase incomes for smallholder farmers through participation in a sustainable dairy value chain. The objective of this report is to assess the opportunities for biogas digesters to capture methane from dairy manure within the framework of the overall program. Specifically, the program has identified three different scales of biogas digesters that might be introduced within the framework of this program: 1) household scale - small digesters to provide gas for cooking and lighting plus fertilizer for individual smallholder farmers; 2) milk collection center (MCC) scale - slightly larger digesters that would support a small electricity generator to operate coolers, lights and possibly other small loads at MCCs where smallholders will deliver milk to be held for daily pick-up by the ultimate buyer; and 3) dairy farm scale where a larger digester might provide boiler fuel and electricity for the farm and for a processing plant producing cheese, yogurt and potentially other products. This report is based in part on information provided by the program and participation of the author in a program design visit to Manica province in November 2008. The next section provides background on the dairy development program and the region, as well as the potential benefits of biodigesters. The following three sections discuss the feasibility and possible design options for each of the three different scales of interest to the program. These preliminary assessments consider past experiences, alternative technical designs, costs and benefits, potential problems and solutions, remaining questions and recommended next steps for each of the three possible scales of biogas application in the program. The last section provides a summary discussion of the results, conclusions and recommendations from this preliminary assessment. Background The Smallholder Dairy Development Programme: Manica Province is one of the best areas in Mozambique for livestock farming due to its climate and access to multiple markets. Over a four 1 Independent consultant, climate change, clean energy and environment, [email protected]


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year period, program funds will be used to begin rebuilding the national dairy herd, to train smallholder farmers in feed/fodder techniques, animal husbandry and animal traction, and to establish producer-level cooperatives and milk collection centers to build a sustainable dairy value chain in the region. As a result of the proposed program, household incomes for participating beneficiaries are expected to increase between 100 to 600 percent, milk production to increase significantly, and crop production to increase by at least 30 percent for farms utilizing draft animals. By the program’s end, more than 900 purebred dairy cows will have been distributed. The program also projects that at least 1,000 local cows will be inseminated with dairy cattle genetics. The continued use of dairy cattle genetics over time will help turn local cows into more productive dairy cows. In geographic areas where artificial insemination (AI) is not feasible, purebred dairy bulls will be used to help improve the milk productivity of cows. Ten producer-level cooperatives and three milk collection centers will be formed, located on or near the three commercial farms housing the breeding herds. The centers will be operated under a partnership between the co-ops and the commercial farmers. The centers will be located so they are easily accessible by farmers to assure the milk is transported quickly and efficiently. A large number of smallholder farmers will receive training in fodder and pasture management, animal husbandry, and animal traction. Marketing for expanded products will be included in the program as well. Substantial increases in income are anticipated for smallholder farmers, who can increase their income to $1,050 a year by the end of the program. The program will contribute to the establishment of new milk collection and marketing infrastructure to supply an existing market (the Manica processor) as well as a potential expanded domestic market and future export markets in Malawi, South Africa, Zambia and Zimbabwe. The estimated dollar impact of the program is $2.5 million generated from increases in the amount of milk produced, the value of beef sold (from male calves produced by the restocking program, discussed further in Section 6e), and the asset value of the animals. This economic impact climbs to $6 million after two additional years. Furthermore, improvements in cash crop productivity are expected as a result of introduction and expansion of draft power within Manica Province. In the design of this program, LOL/ID also identified the potential benefit of utilizing dairy manure to produce biogas for the benefit of smallholder farmers and other program participants. Use of biodigester technology can capture methane and provide fuel and improved fertilizer. The initial program proposal called for installation of a digester at one of the milk collection centers to serve as a pilot project for the use of biogas as an energy source to generate electricity to run a milk cooler. This would allow or the collection of data to determine the economic feasibility of this model. If successful, the use of biogas could be expanded, allowing for establishment of additional milk collection centers without reliable access to the electrical grid. As the program planning evolved, it became apparent that biogas digesters could potentially be applied at other points in the program as well. It was decided to evaluate the feasibility of biogas utilization at three separate scales as described above.


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The Case for Biogas Anaerobic digester technology is considered by many experts to be an excellent tool for improving life, livelihoods, and health in the developing world. It is also seen as an economically attractive source of energy and greenhouse gas reductions in developed countries. Dairy manure biogas digester technology has proven to be technically and economically feasible and successful in many applications. There is a long history of biogas technology at several scales and with many alternative designs. There is evidence that biogas was used to heat bath water in Assyria during 10 BC.2 Household scale digesters have been widely used for many years in developing countries, especially India and China, as firewood for cooking has become scarce. Many other countries from Honduras to the tiny South Pacific island nation of Tuvalu, have in recent years also able to harness the methane gas created naturally from decomposing manure and other organic materials. In the last 20 years, biogas technology has been applied at many different scales including community scale digesters for off-grid electricity up to large scale dairy farms processing manure from hundreds or thousands of cows to produce electric power, fuel for machinery and boilers as well as heat for space heating and other processes. Biogas technology can convert a waste management problem into an energy resource. The system uses an anaerobic digester and adapts existing manure management practices to collect biogas. The biogas can be directly combusted as a cooking and lighting fuel, it can be used as a fuel source to generate electricity for on-farm use or for sale to the electrical grid, as a boiler fuel, or for other heating or cooling needs. The biologically stabilized digester effluent provides a high-quality organic fertilizer and other byproducts that can be used in a number of ways, depending on local needs and resources. Successful byproduct applications include use as a crop fertilizer, bedding, and as aquaculture supplements. Beyond energy and fertilizer, the technology offers many additional potential benefits. It can reduce odor and improve sanitation. It can reduce greenhouse gas emissions and improve indoor air quality while creating new jobs and a new business sector. It can reduce the need for firewood and charcoal which in turn helps preserve forested areas and natural vegetation, and can improve quality of life especially for women and children who traditionally gather fuel for cooking. The significance of many of these benefits including respiratory health and sanitation, reducing deforestation and greenhouse gas emissions reductions is staggering. If these “externalities” could be translated into economic value, they would certainly justify the investment costs many times over. A well-maintained digester can last over 20 years and will pay for itself in one-fifth that time. Promoting wide deployment of this technology could result in significant improvements in health and quality of life for rural populations. The range of potential benefits clearly justifies consideration of the opportunities for biogas technologies in a program that seeks to encourage development of the dairy industry.

2 Kangmin and Ho, 2006


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Appendix A provides more detailed technical information on technologies for biogas digesters and related systems, including gas clean up and use in boilers and generators, investment costs and a wide range of monetary and non-monetary benefits. The next three sections provide results of preliminary evaluation of biogas options in three specific contexts of potential applications within the Manica Province program – small households, milk collection centers (MCC) and the Evertz dairy farm that will support a breeding herd and provide central processing of the milk produced in the program into marketable products.


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Household Scale Biogas Opportunities Background As noted above, there is a great deal of interest and enthusiasm for household scale digesters as a key clean energy technology for sustainable rural development in Africa as well as elsewhere in the developing world. The Manica Province program team is commendably considering demonstrations and promotion of household scale digesters for individual small holders. Most of the cows distributed by the project will go to smallholder farmers who will then have one or more cows and possibly other animals. These individual farmers will manage their own dairy cows and transport their milk to collection centers operated by cooperatives. The primary objectives of the program are to build a sustainable dairy industry and to raise the incomes and quality of life of the rural population of Manica Province. Small scale digesters are proven technology that can produce gas for cooking and light in rural households. The residual slurry can be used as high quality fertilizer and could help farmers increase crop production for additional income or fodder to support additional animals. Experience in Asia has shown that widespread deployment of household biodigesters can be highly successful. It is estimated that, at present over 22 million households worldwide receive energy for lighting and cooking from biogas produced in household-scale biogas digesters. This includes 18 million households in China,3 3.7 million households in India, and more than 155,000 households in Nepal; all three countries are world leaders in biogas development and deployment. At the rural, small-scale level, the experience in Nepal exemplifies biogas benefits. Of the installed digesters, more than 95% are in daily use and an estimated 12,000 jobs have been created in the emerging biogas industry. Its use has shown a reduction of workload for women and girls of 3 hours/day/household, annual savings of kerosene of 2.5 liters/household, and annual savings of fuelwood, agriculture wastes and dung of 3 tons/household4. Larger installations have generated income-producing opportunities and based on anecdotal evidence, have also improved rural health. A similar program was started in Vietnam in 2004 and was winner of the Energy World Globe award 2007. More than 25,000 installations have since been built and are now operational.5 Other benefits have also been demonstrated in successful household biogas programs. According to the government, there are 3 million biogas digesters operating in Guangxi Provence, China. This makes the province the largest producer of biogas in the country if not the world. Each biogas digester takes as input animal and human waste, and together they prevent vast amounts of methane from escaping into the atmosphere. The International Fund for Agricultural Development (IFAD) estimates that the Guangxi digesters also replace burning of 8 million tons of standard coal and 3 million tons of firewood each year6. 3 Jingong. 2005 4 USAID 2007 5 Biogas for a Better Life, 2007. 6 Small Farm Permaculture, 2008.


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There is a great deal of activity currently in Africa and other developing countries. The Africa Biogas Initiative, for example, was launched in 2007 with support from more than 20 organizations, including development assistance and African non-profit organizations. The initiative is currently supporting the implementation of a national promotion program in Rwanda; ongoing stakeholder consultations in Ethiopia, Uganda, Kenya, Senegal, Tanzania, and; desk and feasibility studies in about 20 African countries including Sudan, Zambia, Mali, Nigeria7. Appendix B provides more detailed background information on digester types, design issues including rules of thumb for sizing, and lessons learned from international experience. It summarizes relevant experience on economic costs and benefits of household digesters in a number of developing country programs and feasibility studies. The appendix also summarizes a number of lessons learned from prior programs on overcoming financial, technical and institutional barriers to wide deployment of household digesters. Biogas System Design Digester type: There are several types of digesters that have been used successfully in programs in developing countries over the past several decades. Two designs seem most likely to meet the needs of the Manica Province program. The Nepalese GGC 2047 model fixed dome digester is a modification of the design developed in China and used successfully there for many years. It has been promoted successfully in many countries and is being adopted by most, if not all, of the Biogas Africa Initiative countries. Documentation is very good and readily available. This design seems to be somewhat costly in the African context, but very durable and it pays for itself over a few years. The other recommended design is the plastic tubular digester. This has also been implemented very successfully in some countries and is currently being promoted in some African countries, notably Tanzania. It is also very well documented, and installation, operation and maintenance manuals, specifications and other technical information are readily available. This design is much less costly to install but is not expected to be as durable and there are possible operational problems that need study. Another design that might be worth looking at further is the Puxin biodigester digester from China. Depending on results of further investigation this technology might offer an approach to shorten construction time and improve quality and durability of digesters. This is not yet a widely understood and proven technology but depending on the cost of the molds and other parts from the Chinese company and acceptability with participants and installers it might be worth some testing. Digester size: Rules of thumb for various sizes and digester types provide a starting point for initial design. A key point is that the size of plant (and biogas output) has to be based on the

7 Ukpabi, 2008


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amount of available dung as input not on the family size or desired gas output. Some experts suggest that energy for cooking and some lighting for a typical rural family in a developing country would require between 1 and 2 m3/day.8 This would require a digester with an internal volume of 4 m3 or more. The performance of biogas digesters in Monica province conditions remains an empirical question. The program will need carry out demonstrations of one or more digester designs and carefully monitor their performance, including the actual biogas production. This will help to develop a clear understanding of the combinations of numbers of cows, sizes and types of digesters and other factors that will lead to consistently successful results in the Manica Province conditions. It is certainly possible that a single cow digester can provide enough gas to drastically improve a household’s cooking and lighting options. It also seems that 2 cows or 1 cow and other livestock may be a more appropriate to be sure that a family’s needs are completely met. Gas uses: Cook stoves that operate on biogas are widely available in most African countries. In Kenya, biogas cookers are available locally, and local artisans have been able to fabricate new ones or modify LPG stoves to use biogas which is much cheaper.9 However, there is little or no quality control on biogas appliances. This is probably representative of the situation in most African countries including Mozambique. Lanterns using biogas are widely available but not very efficient. As noted in appendix B, one country program in Tanzania10 has identified the need for improved biogas lighting technology as a priority area for research. As with digester technology, this is an area where the Program will need to work with local entrepreneurs, and academic and other organizations to determine what types of technology are currently available and at what cost, and whether the program can or should undertake to stimulate new local businesses and products to supply the needs of the program and subsequent biogas industry development. Economics of Household Digesters A review of experience with household digesters, and of cost benefit calculations and feasibility analyses in several African countries, provides a rough sense of the likely economics of introducing such digesters in Manica Province. Assuming that dung and biogas production, fuel prices, rural income levels are similar, it is likely that fixed dome biogas digesters can be installed and operated at costs that will pay for themselves through savings in fuel and fertilizer cost (or increased crop production) in 3-6 years, and that the societal benefits would be much larger. Installation of plastic tubular digesters could yield similar benefits at lower installation cost, if durability and operational questions are resolved. Household biogas digesters are often financially viable on paper from the perspective of individual farmers in developing countries. However, biogas development on a significant scale has generally required government financed investment subsidies and/or affordable financing

8 TNAU, 2008 9 Biogas for a Better Life, 2007a 10 SGP, 2001


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(for construction and/or maintenance of biogas plants) for small and lower-income farmers.11 The initial capital investment is often an insurmountable barrier for poor rural farmers even though the savings will outweigh the costs in a few years. Except for some cases involving the least expensive designs (e.g., plastic tubular digesters in Vietnam) it has generally been deemed necessary and logical for governments or donors to partially subsidize the initial capital costs. The benefits to society far outweigh the costs of subsidies and program support, and farmers can be convinced to pay half or more of the cost if financing is available. The full capital cost of the fixed dome design is likely to be unaffordable for most poor farmers, but for the plastic tubular design, costs may be low enough that they can be paid fully by farmers after some demonstration and start up support. For wide deployment of any type of digester, however, a financing mechanism is required for farmers to pay back at least part of initial installation costs over time. In the Manica province context, financing through small holder cooperatives seems feasible and could overcome many of the organizational difficulties that have plagued other programs. The MCCs, managed by cooperatives, will be receiving milk from individual farmers and providing payments to these participants based on milk sales. The program concept already envisions that the cooperative would retain a small percentage of the sales revenues from each farmer to cover costs of operation of the Milk Collection Center, medicine and veterinary services as needed, training and other ongoing support services. If the cooperatives were to provide or guarantee loans for the installation of biogas digesters this mechanism could be used to collect monthly payments from individual farmers. It will be important to carry out detailed financial analysis as the program moves forward to determine whether subsidies to bring down the initial capital cost, as is the case in most successful developing country programs to date, will be appropriate to move the biogas digester penetration to significant levels. A number of previous biogas digester promotion programs, successful and not, have illustrated range of possible barriers would need to be overcome to allow for a successful program to promote household digesters in Manica Province. Appropriate technology and financing are two critical prerequisites for success as discussed above but past programs have also identify other technical and institutional barriers to biogas digester deployment and successful operation. Lessons learned include the need for: 1) careful program planning and design, including consultation with key stakeholders; 2) quality digester construction with correct materials by qualified technicians; 3) attention to educating and informing the intended participants and other stakeholders as a part of the program; 4) technical training on installation, quality of materials and maintenance of digesters; 5) certification of trained installers and service personnel, and of materials meeting standards; and 6) a network of technical support and monitoring to ensure long term benefit of the program.

11 USAID, 2007


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The structure of milk production cooperatives and milk collection centers envisioned by the program offers a valuable potential support mechanism not only for financing but for other key aspects of a digester program, including: • Training on biogas digesters can potentially be organized through cooperatives and MCCs

coordinated with dairy management, animal traction and other training that will be a central focus of the overall program. This could include training for installers and entrepreneurs to help establish the capability to deliver and service digesters and biogas appliances on a commercial basis, basic education on digesters for farmers, training on operation and maintenance for farmers and family members interested in participating in the biogas digester option;

• Certification of installers and technicians, standards for materials, etc. could be organized through the cooperatives, though technical expertise will need to be provided by the program initially; and

• Ongoing maintenance and operation could be monitored and addressed with service or training as needed through the cooperatives.

More detail on the calculations, assumptions and other information used to produce the results in this section is provided in appendix B. Conclusions and Recommendations 1. Household scale biogas digesters are definitely an economically, socially and environmentally attractive technology that could be integrated into the overall Manica Province program. It has the potential to contribute to improved health and quality of life for the participants in the program in addition to the other improvements in income and welfare that the program seeks to provide them. Recommendation: The program should move forward with steps to promote household biogas digesters to the maximum degree possible within the framework of its overall smallholder dairy development activities. 2. Many design and feasibility issues need further study. Data collection and consultation with stakeholders are necessary and could take some time. Cost- benefit and affordability analyses should be carried using actual prices, incomes, farming and cooking practices, manure management practices, water availability, etc., that needs to be collected. More credible and detailed information will contribute to further progress in promoting household scale biogas digesters in Manica Province. There is a great deal going on currently in Africa around the promotion of biogas digesters. The Biogas Africa Initiative is one priority contact, as is the Tanzania Program promoting plastic tubular digesters. Kenya has a number of past or ongoing programs, at least one of which has been supported by Land O’ Lakes in the past12. Consultation with all key stakeholders is valuable in gaining better understanding of the best ways to adapt and promote technology and will gain the engagement and ownership of the stakeholders in a 12 Contacts and information for other programs is provided in appendix E.


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successful outcome. A critical need is to identify several entrepreneurs with construction and fabrication skills needed to start businesses installing and maintaining digesters. Recommendations: a) Make contact with other programs promoting biogas in Africa to exchange information and obtain technical advice. b) Consider conducting or supporting a more detailed feasibility assessment including data collection, consultation with potential partners and stakeholders and technical and financial analysis. 3. Demonstrations and tests of selected digester designs are needed, can be carried out in parallel with data collection and analysis, and will generate a great deal of information on digester performance and operation Based on this initial assessment, fixed dome and plastic tubular digester designs are recommended because they are well understood and proven in many countries. However, many design options are available, and it is important for the project to consult with stakeholders and potential installers of digesters and to work with them in the design selection and testing. Technical organizations working with both of these designs in nearby countries can be contacted and information shared with the Manica Province program. Local entrepreneurs should install the demonstrations, and farmers test them, before fixing on a single design or choices to be offered to farmers in a any larger scale distribution. A demonstration and testing phase can: • prove to local participants that the technology works; • train entrepreneurs and technical staff who can serve as installers, trainers and technical

assistance providers in the future; and • determine the needed digester size, number of cows, and digester performance data. Results of these demonstrations combined with a feasibility assessment of wider deployment potential, could allow the program to move forward quickly in whatever directions are chosen. Recommendation: Consider initiating demonstrations of two or more digester types as soon as possible. These demonstrations would likely cost on average under $1000 each even if technical experts need to be brought in from other African countries. Demonstrations could be implemented at or near a training location, such as an MCC, and potentially be integrated with testing of larger versions of similar designs for MCC scale application. These demonstrations could provide a foundation for an expanded program, but even if the Manica Province program determines that support for larger-scale deployment is not possible within the available budget, they can make a lasting contribution. Other biogas initiatives in Africa likely can build on demonstrations and training provided by the program. 4. Beyond demonstration, the Manica Province program could consider a pilot phase for promotion of household biogas digesters in the Chimoio region. The program could provide funds to cover subsidies for some number of installations coordinated through the cooperatives. In parallel, the program could contact other programs and donors in nearby African countries to explore options of partnering with others or handing off implementation of a larger biogas program.


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Except for early demonstration units, digesters should not be given away – farmers need to pay for them to value them. Initially at least, partial subsidies are likely to be needed to make the digester installation costs affordable, particularly if the fixed dome design is adopted. Once a more detailed feasibility assessment and demonstrations have developed more credible estimates of the costs and economic benefits, the program can determine whether and at what level, subsidies are needed to make digesters affordable for smallholder farmers. Recommendation: After completion of demonstrations and further feasibility assessment, consider implementing a second phase to demonstrate the program implementation arrangements that can promote commercial deployment of biogas digesters in Manica Province. If this is not possible look for ways to transfer results to other programs with greater resources focused on promotion of biogas digesters.


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Biogas Opportunities at Milk Collection Centers As a key component of the overall Manica Province program, milk collection centers will be established to accumulate and store milk from individual small farmers until daily pick up by the dairy buyer. The expected schedule is that milk will be collected in the mid-morning, chilled and cool-stored until it is picked up around noon. Then the equipment would be shut down and cleaned and restarted when late afternoon/evening milk deliveries are received. The milk cooler(s) would have to run all night and through the morning until the pick up at noon. Initially, 50-60 farmers would receive cows in a radius around the first MCC. As the project grows, the number of farmers using a single MCC is expected to rise to over 100 farmers. The number could be higher depending on the number of participating farmers in a reasonable travel distance from the MCC. Milk cooler units would be at least 500 liters and could be up to 1500 liters depending on expected usage. Peak electricity demand could be about 2 kW – 5 kW depending on the size and usage. The program is interested in testing the feasibility of using small biogas digesters and generators to provide power for operation of the coolers, lights and possibly other plug loads at milk collection centers. The sites under consideration for the early MCCs are all connected to the power grid, but power supply is not reliable, so some backup generator capacity would be needed with or without biogas, to ensure that large quantities of milk are not lost in the event of a power outage at a critical time in the daily collection, storage and pick up cycle. The global experience with household scale digesters is extensive and successful programs have been implemented in many areas, China, India and Nepal for example. Large scale dairy farm applications are also being widely implemented in developed countries as they provide economically attractive investments and have many environmental benefits. There are fewer examples of the “community scale” digester systems needed for the MCC application –e.g., 10-60 cows, a 25-75 m3 digester, and possibly a 5 kW generator set. This is larger than household scale but very small for a commercial electricity generation application. The economic analysis is somewhat problematic, as power generation at this scale requires relatively expensive capital and it is not possible to capture the economies of scale present at the dairy farm level. One of the key design issues for this project is determining the required manure and corresponding number of cows needed to provide sufficient electricity generation for operation of the coolers and other electricity needs of the MCC. The planned approach for the smallholder program is to initially allocate one cow per farmer, after training and verification that the farmer has prepared the facilities and feed needed. The farmers would then take individual responsibility for their cows and repay the program by turning over the first female calf from their cow – to be provided to another farmer who has completed the necessary training and certification. The farmers will be dispersed around the MCC within a reasonable distance, as they will milk their cows and immediately deliver the milk twice daily. Cooperatives will be established for participating smallholders, and will manage the MCCs and provide other central services (training, testing, veterinary services, insemination, etc.) to members. Moving large volumes of cow manure to a central point does not seem to be a viable,


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sustainable option, however. As discussed in appendix C, there are examples of central collection of manure but this analysis assumes that the cows providing manure input to the MCC digester(s) will be located at the MCC. To demonstrate the use of biogas to power an MCC in the Manica Province program, the program will need to locate a number of cows at the MCC sufficient to provide enough manure to support its power needs - chiller(s) and lights. The program team would prefer to keep this number to a minimum, as locating cows away from the smallholders who are responsible for them is somewhat inconsistent with goals of the program. The desired outcome is establishing individual smallholders as owners and managers of their individual cows, within the framework of a cooperative collection and marketing group. Possibilities for centralizing cows need to be carefully evaluated. One possibility is to locate a small breeding herd at the MCC, managed by the MCC staff. If a sufficient number cannot be achieved in this way, some of the closest smallholders may need to keep their cows at the MCC but remain responsible for care, feeding, milking and management of the cows. At the time of the initial program design visit13on which this report is based, several possible sites had been identified as candidates for an MCC. One possibility is the Instituto Agrario de Chimoio (IAC Agricultural Institute of Chimoio). Chimoio is the capital of Manica Province and its largest city. The smallholder program will be implemented in the countryside around it. The IAC is on the outskirts of town and does have farmers nearby. The campus is very large with facilities for training and lodging trainees, and plenty of room for cows and other MCC facilities. There is room for any sized digester and locating a demonstration here would provide a facility for training on construction and operation of digesters along with other aspects of the training program. Another potential site is a small orphanage, with sufficient land area, close to the dairy farm that will be picking up milk from the MCCs. There are also at least two small to medium sized farms outside the city, that could potentially house parts of the breeding herd, and seem to have a number of willing smallholders around them who could be participants. All of these sites have enough space to locate MCC equipment, digesters and generators, as well as a small breeding herd of cows. Some also have facilities for training and demonstration and all have smallholder farmers in easy walking or bicycling distance. Key decision criteria include likely numbers and willingness of potential smallholder participants around a particular site. Additionally, all of these possible sites have potential uses for extra gas or power if the digester system is sized for growth and in early stages produces more gas than the MCC can use. Another interesting feature is that the sites also have potential to provide other types of organic materials that could be fed into the digester – food waste, night soil (if this is acceptable to local culture), etc. – if desired. Small amounts of such materials, in addition to manure, can significantly increase biogas output of a digester14. Biogas System Design

13 November, 2008 14 House, 2006


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In order to evaluate potential opportunities and designs for biogas at the milk collection centers, key initial issues are: 1) power requirements; 2) type and size of digester; and 3) number of cows to produce the needed amount of manure. The details of technical assumptions and calculations used to produce these estimate are provided in Appendix C along with a great deal of other technical information relevant to community scale digester systems. Results of the calculations are provided below. Power Requirements: Based on the typical power requirements and expected duty cycles of milk coolers the power needs for an MCC would range from 14 kWh/day, for a small facility with one 500 liter cooler, up to 40 kWh/day, for a larger center with 1500 liters of cooler capacity. These power requirements could be met with biogas powered IC engine generator sets using 8.5 to 24 m3 biogas/day. Digester types: Experience with dairy manure biogas digesters of this size is limited, particularly in electric power generation applications. Digester designs that have been constructed or proposed at this scale are either scaled up versions of the household designs or scaled down versions of the dairy farm designs. This initial assessment indicates that the most appropriate designs are relatively low cost technologies scaled up from household scale designs widely and successfully used in developing countries including many in Africa. The fixed dome and plastic tubular digester designs are proven, reliable and relatively low cost technologies. The fixed dome design represents the best known and most reliable technology in the developing world while the plastic tubular is the lower cost approach, but with possible durability and operational problems that need to be examined in more detail. One or both of these technologies should be considered for the first phase of the MCC biogas effort. Some of the proven farm scale digester types could also be scaled down to MCC sizes. Covered anaerobic lagoons are a potentially interesting, low cost, and low maintenance design, but the large volume, land area and water requirements are potential problems. This option is worth further investigation but as a lower priority at the community scale. The water and volume issues raise questions about the potential for wide replication. The plug flow digester design is a well understood and effective technology that plays a key role in farm scale systems in industrialized countries, and may well become important in Africa in the future. It is currently too costly, risky and unfamiliar to be the preferred technology for MCC or community scale applications in Africa. Digester sizes: A fixed dome digester could be developed at a 25 m3 size and should provide at least 9 m3 biogas/day, more than enough for an MCC with one 500 liter cooler. A 25 m3

digester would require about 225 kg manure /day and about 225 liters of water/day as input. A larger fixed dome digester of around 75 m3 should produce at least 25 m3/day and be sufficient to support 1500 liters of cooling capacity and some other electrical loads for the MCC. For a 75 m3

community scale digester, with HRT of 55 days, the manure requirement would be about 675 kg/day with 675 liters of water.

The 8.5 m3 biogas/day required for a small MCC could also be provided by installing two 18 m3

plastic tubular digesters. With a retention time of 55 days, 36 m3 total volume would require


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about 220kg manure and 440 liters of water/day. It is not clear that scaling this design up to the large MCC size would make sense. The logical approach for the Manica Province program for this technology would be to start with the commercially available 18 m3 design and get information on its performance before making decisions about larger scale applications. If this is determined to be an attractive technology, additional 18 m3 units could be added incrementally.

One interesting approach would be to install both fixed dome and plastic tubular designs – possibly both one 18 m3 plastic bag and a fixed dome of 15 m3 to provide the daily biogas needed (8.5 m3/day) to support a small MCC with 500 liters of milk cooling. Number of Cows: The estimates of production of biogas per cow feeding a digester system are quite variable – ranging from 0.5 to 2.8 m3/cow/day. The largest source of variability in this range is the amount of manure that is available for the digester per cow. Based on experience in developing countries and conditions expected in the Manica Province program, the range of 12-25kg manure/cow/day should capture the reasonable expectations for assessment of digester options for the MCC scale. For fixed dome and plastic tubular digesters this translates to 9-19 cows for a small MCC and 27-56 cows for the larger facility. As the variability is primarily due to how much manure on average makes it from one cow into the digester, this uncertainty can be reduced substantially by monitoring actual manure production. Manure should be collected on site and measured before final decisions are made on size of digester and number of cows. Rather than rules of thumb, the number of cows needed can be determined based on actual manure available per cow at a particular site. Electricity Generation: A 2-5kW internal combustion (IC) engine generator set would be a reliable and least cost option for generating electricity to power the MCCs. A dual-fuel biogas/diesel generator set could be specified so that diesel would be available as back up if there should be a temporary disruption of the biogas supply. A 2-3 kW genset would be capable of supplying the power needed for the small MCC configuration while a 5 kW size would support a large MCC. These units are widely available and reliable, and the conversion of a diesel engine generator to run on biogas is easy and inexpensive.

Economic Costs and Benefits Costs: Based on experience and feasibility studies from a number of developing country applications it is estimates that a 25 m3 fixed dome digester producing 8.5 m3 biogas/day would require an investment of $1875 – 2125, and a large MCC scale digester of 75 m3 producing over 25 m3 biogas/day would require $5625 – 6275. The 8.5 m3 biogas/day required for a small MCC could be provided by installing two 18 m3 plastic tubular digesters, at a total cost of $1200-1300.

For power generation, reciprocating engine generator sets for heavy duty use (as opposed to standby use) are available as small as 1 kW and are estimated to cost $500-1,000/kW15 For purposes of this assessment $1,000/kW is a reasonable first approximation of cost. So a generator would cost $2,000-3,000 for a small MCC configuration and $5,000 for the large size. 15 E Source 2007


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Based on the preliminary assessment, total cost, including digester construction and purchase of a generator set, for a small MCC would be at minimum $4,000-6,000 to produce 12 kWh/day and $11,000 – 15,000 for the 40 kWh/day large MCC scale. It should be emphasized that these are very preliminary numbers as a starting point for considering the overall economics of biogas power generation for the milk collection centers in the Manica Province program. Benefits: The small MCC system is sized to produce 12 kWh/day or 4380 kWh/year. Using a reported national average price of $0.08/kWh this would generate savings of $350.40/year from electric power not purchased from the grid. The large MCC system would generate savings 40 kWh/day or 14,600kWh/year. At $0.08/kWh this would save $1168 in a year. Capital costs are $4,000-6,000 to produce 12 kWh/day and 11,000 – 15,000 for the large MCC scale. For this simple calculation operating costs are not considered although there would certainly be some, but not significant relative to the capital. The small MCC calculation shows a simple payback of 11.4 – 17.1 years. For the large MCC, it is 9.4 – 12.8 years. This is basically not attractive as an investment project on strictly financial terms. The avoided cost of power is, of course, higher if part of the alternative is back up power generated with diesel fuel. Based on reported national average diesel fuel price of $0.60/liter, the cost of electricity produced by a diesel generator set is over $0.18kWh. Also, it may not be appropriate to count the full cost of the generator set as a cost of the biogas project, as a back-up generator would be required in any case. Effluent from the digester(s) can be used a fertilizer to improve crop yield or can be sold. These factors along, with more detailed information to replace assumptions and rules of thumb used here, could improve the cost benefit analysis significantly. It may ultimately be a financially viable commercial option. This will not be known until a more detailed feasibility assessment and demonstration(s) are completed. Certainly the investment in biogas systems for this application could be justified based on the wide range of non-energy benefits to society and welfare of participants, even if subsidies are required to make the finances work on an investment basis. If subsidies turn out to be necessary, and the program grows and needs many MCCs, it may be worthwhile looking into carbon credits as a source of some additional cash returns. More detail on the calculations, assumptions and other information used to produce the results in this section is provided in appendix C. Conclusions and Recommendations Preliminary evaluation indicates that biogas electricity generation may not be attractive on strictly financial investment terms given the scale and the duty cycle needed for MCCs. There have been few, if any, demonstrations in applications like this, and uncertainty is very large based on limited information, rules of thumb and assumptions. This leads to two main conclusions:


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1. A serious information gathering effort and more detailed feasibility analysis of biogas opportunities is needed in the next stage of the program. Key information needed includes:

Typical manure produced per cow per day Amount of water used and organic solids flushed from typical MCC operations Cost of materials for digester construction Typical local labor costs for both skilled technicians and unskilled labor Actual electricity and fuel prices delivered to MCC site Delivered cost of diesel-biogas dual fuel generator sets in Chimoio Economic value of fertilizer

In developing and evaluating better information it is important to involve and work with a range of stakeholders who will be involved in implementation and outcomes of the program. This includes farmers, dairy experts, local government, contacts in other African biogas programs, etc. A key group that needs to be engaged is local mechanical and engineering service providers and entrepreneurs who can deliver equipment, installation, training, and maintenance on a commercial basis for both the household and MCC scale digesters in future. This group can provide a great deal of input about what works and doesn’t, what materials and equipment are available and costs, and how to structure designs and programs for acceptance in the region. Recommendation: The program should consider supporting further data collection and assessment, as well as consultation with local stakeholders and other biogas practitioners and programs in Africa as a basis for detailed design of a project 2) A demonstration of biogas power generation at one or more MCCs would be a critical next step to further understanding of the technologies and their economics. It is not reasonable to expect biogas power generation to pay for itself at an MCC at this initial stage. The many currently unquantifiable benefits still make this application attractive from the perspective of the overall economy and society. This is not to suggest, however, that economics should be ignored in a demonstration. In order to develop information and experience that can lead to sustainable commercial technology for the future, it is important to initially design the system to be as close as possible to financially viable. Carefully designed, with appropriate technologies, these systems can be within striking range of that goal. The most likely digester types based on this preliminary assessment are scaled up versions of the household designs, fixed dome digesters and plastic tubular digesters. This project may be able to help define biogas designs and system configurations that maximize net benefits so that the technology becomes closer to financial viability and lower subsidy requirements over time Demonstrations will be valuable as a learning and information gathering exercise, and will provide data that can be helpful for expansion of this program as well as other dairy development programs. They will also prove to local participants that biogas digesters are feasible and provide a training facility that can be useful in supporting implementation of further MCC scale efforts as well as household scale applications. Recommendation: The program should consider constructing at least one MCC biogas electricity project as a demonstration, without expectation of recovering investment costs. .


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Additional conclusions: 3. It is important to plan for phasing in the implementation of a biogas system whether a demonstration or a commercial project. In this case, a diesel generator will be needed from the start as back up to grid power, while any of the digesters recommended will take some time after initial charging before design biogas production is achieved. The diesel generator can be used as needed for back up, and as biogas becomes available it can be used in the generator and increased until the full electricity load is met by biogas generation. 4. There is a great deal of overlap between the next steps for household and MCC scale biogas digester promotion. They are naturally connected because the MCCs could have a key role in organizing and hosting training, technical assistance, and financing for the household scale activities. The same digester types appear to be most likely or both scales and this suggests opportunities for synergies and economies the more the two programs can be integrated at least in the early stages.


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Biogas Opportunities for a Mid-Sized Modern Dairy Operation: Evretz Dairy Farm and Gouda Gold Processing Plant The Evretz Dairy Farm and Gouda Gold Processing Plant, operated by Brendon and Jenny Evans, is a small, relatively modern dairy operation with about 150 cows currently, and ambitious plans for growth and improvement over the next several years. It also includes a modern cheese processing and yogurt production plant that has capacity to expand many times beyond what it is now producing. These expansion plans and capacities are critical to the success of the Land O’ Lakes Smallholder Dairy Development Program in Manica Province. This farm will serve as the home of a breeding herd being introduced into Manica province, and also as the buyer for milk produced by small holder dairy cooperatives established by the by the Land O’ Lakes program. The farm expects to increase its own herd to 500 or more cows over the next 3 years. Given the expected increase in milk production and purchases from small holder cooperatives, the cheese and yogurt production will increase dramatically. The owners are exploring adding new products as well e.g., by adding a long life milk production plant. Currently the farm is milking 120-130 cows and flushes manure from the milk parlor and holding area. This flush volume is estimated at 500 liters/day. This flush water goes into an open culvert and combines with waste water estimated at 2000 liters/day from the cheese and yogurt processing facility. The combined flush water flows about 150m into an unlined open pit and is used sometimes for fertilizing nearby pasture. A paved feeding area is also flushed but the flush water is currently allowed to run off downhill not combined with milking and factory waste. Flush water from the current feeding area is estimated at 100-500 liters/day. Plans are to connect this flush water to current milking and processing waste by means of a new open culvert about 100-130 m. When not in milking or feeding areas the cows are in open lots. Manure in open lots is collected and composted for use as fertilizer on the farm pasture areas. Collected manure could be added to a digester daily. Flush water from a concrete floor feeding area could be directed to digester – currently 100-500l/day. The farmer estimates that roughly 50% of manure from the lactating cows is captured in flush water from the milking parlor, holding area and feeding area. The remainder is collected from fields and open lots. Close to 100% of excreted manure could potentially be available for use in a biogas digester. The cheese processing plant includes a boiler that currently uses 60-70 liters/day diesel fuel. Cost of diesel fuel is estimated at $0.60/liter16. Electricity is provided by the grid with a 60 KVA diesel generator as a backup, as the grid power is unreliable. Also, two borehole pump wells are operated by electricity from the grid to provide water for dairy and cheese processing activities as well as irrigation for some pastures. Average electricity price nationally is reported as $0.08 per kWh and this value is used for preliminary calculations17.

16 Based on published national estimate Metschies, 2005 17 AFDB, 2007


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As noted above, the owners are planning to expand the dairy herd and to make significant improvements in the farm infrastructure over the next few years. The processing plant is expected to increase production greatly as milk from the farm and from smallholder cooperatives increases over several years. Another expansion option under consideration is the addition of a facility for producing and packaging long life milk. The preliminary estimates are that wastewater from the combined processing facilities could increase by more than a factor of 10 -- to 25,000 liters/day – by the time all of the expansions and improvements are implemented over 3-5 years. In the dairy operation, two or more concrete feeding areas may be added, all located uphill and flushed into the open culvert drainage system. The owners are also considering moving to free stalls instead of open lots at some point, which would result in a greater percentage of manure being flushed. The owners are also considering installing a system of settling tanks at the terminus of the culvert system and pumping liquid fertilizer out of the last tank to be sprayed onto a much larger pasture area than is currently fertilized. The owners are interested in exploring options to use biogas technology to capture methane from manure to offset energy costs in the dairy and processing operations. Several options for introducing biogas capture are possible and may be economically attractive. Capital constraints are severe due to a poorly developed banking system in Mozambique (as in many developing countries). This leads to a preference for lower capital cost options, or options where capital cost can be provided incrementally. Given the innovative nature of the farm scale biogas and electricity generation technology in Mozambique, and the substantial greenhouse gas benefits, it would be worth exploring development financing or carbon credits as possible ways of overcoming early capital costs hurdles. Biogas System Design Digester type: As discussed in Appendix D, the anaerobic lagoon type of digester appears appropriate for this dairy farm application. The amounts of flush and wastewater produced by the current and planned operations are well matched with this technology, and it is low cost, reliable and low maintenance. This design requires a large pond, to handle the large volumes of slurry. The minimum depth is 2 m, but lagoons typically have a depth of 4-6 m depending upon ground water levels. Lagoons are usually built with a compacted clay or synthetic (e.g., plastic) liner to prevent leakage and groundwater contamination. An airtight cover system provides the required airtight anaerobic conditions and collects biogas as produced by bacteria in the lagoon. The cover is typically constructed of flexible synthetic materials such as high density polyethylene (HDPE). The design usually includes a mixing tank and pump to ensure an even flow of well mixed slurry into the lagoon. Manure slurry is pumped in one end of the pond and effluent removed at the other while gas is extracted from the top of the flexible cover. The gas can be used to fuel the existing boiler and to generate electric power. Effluent can be used as liquid fertilizer while solids can be separated and used or sold for bedding, compost, etc. Generally a storage lagoon or tank is installed to handle liquid effluent


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until it is used as fertilizer. Fertilizer application occurs unevenly over time and effluent needs to be extracted from the lagoon at a roughly constant rate to keep the lagoon operation and digestion process running smoothly. The settling tanks already being considered could serve this function. Digester size: Based on current and projected numbers of cows and dairy product production, and using available information assumptions and rules of thumb, a series of calculations have been done to illustrate the range of possible anaerobic lagoon sizes and levels of biogas production that could be supported at this farm. A number of scenarios were evaluated reflecting a range in the number of cows, from the current level of about 120 milking cows to the projected target of 500 within a few years, and variation of 50 – 90 % of manure collected. The results show that an anaerobic lagoon would require dedication of substantial area for lagoon use. A small lagoon fed by the current level of 120 cows and capturing 50% of the excreted manure would require a lagoon volume of 375 m3. At 3 m depth this would be equivalent to approximately 125 m2 surface area or 10 m by 12.5 m. At the 500 cow size a lagoon could require volumes of 1900 m3 to 3400 m3, and from 475 m2 of surface area up to 850 m2 (25 m by 35 m) depending on the percentage of manure captured and fed into the lagoon. The results also show that even with the current scale of dairy operations, enough manure is being generated to produce 50-85 m3 biogas/day and if the dairy is successful in its plans to expand to 500 cows, it could produce sizable amounts of biogas, 238 – 425 m3day. Gas use: The highest priority gas use will clearly be fuel for the boiler currently used intermittently in the cheese and yogurt processing operation. The current fuel for the boiler is diesel that is relatively expensive, and the boiler conversion to biogas is simple and inexpensive. The boiler can be configured to run on either biogas or diesel. Diesel can be used as a backup fuel if needed. The boiler use will go up as the processing volume increases. Even with expanded boiler fuel demand, there may to be additional biogas available for other uses. The next most attractive use would be to generate electricity to replace electricity purchased from the grid for use on the farm. It may be possible to adapt the existing backup diesel generator to run on biogas and use this to generate power up to some level. This would be a very low cost option if it is feasible and the generator can operate enough hours to use the excess biogas. If the existing generator cannot be adapted for biogas fuel or is not capable of for heavy use required, a new internal combustion IC engine generator set is the next least cost option. Dual-fuel engine generators are widely available. It appears that a great deal of electric power from the generator could be used on site, particularly if the dairy and processing operations expand and the biogas generated power can be used to operate the borehole pumps as well as the other uses. Depending on the level of trace gases in the biogas and the specific equipment in which it is used, the gas may need to be cleaned before use. Several low cost technologies are available and some information is provided in appendix A. Digester System Economics


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Costs: For the biogas digester system estimates are based on reported costs for comparable systems or components from international experience. Depending on the size of the lagoon in the different possible scenarios evaluated, the investment cost estimates for the digester range from $6,000 from a small lagoon that could produce about 50 m3 of biogas/day to $38,250 for a large lagoon that could handle waste from 500 cows and supply 475 m3 biogas/day. There is no significant investment cost required for converting the boiler to operate on biogas. When power generation with biogas is included there are additional investment costs for the generator set. If the existing backup diesel generator can be retrofit and used for at least the first few years this would keep the initial costs of the generator set are quite low - less that $2000. If it is determined that a new dual-fueled, heavy duty IC engine generator set is needed, than this will raise the initial investment cost substantially, adding $25,000-50,000 to the project costs. Total costs could range from $6,000 for a small digester where the gas is all used in the boiler and no significant gas use equipment investments are necessary, up to as high as $88,250 if a new generator is required and its cost is at the high end of the expected range. Benefits: Substitution of biogas for currently purchased energy – diesel fuel and electricity – is the major monetary benefit of a biogas digester system for this facility. First priority is substitution for diesel fuel to fire the boiler used in the food processing plant. At the current rate of fuel usage and using a reported national average diesel price of $0.60/liter, backing out all current diesel use would save $79/day or $14, 235/year, and require roughly 124 m3/day of biogas.

Table 1: Costs and Benefits of Biogas Options Cases Cost

$ Benefits

$ Simple payback

Years 1. 120 cows, 50% manure capture 6,000 5840* 1.03 2. 120 cows, 90% manure capture 9,150 9855* < 1 3. a. 500 cows, 50% manure capture, no

generator 24,375 27,235* < 1

3.b. 500 cows, 50% manure capture, plus retrofit of existing generator

26,375 19,900

1.2

3.c. 500 cows, 50% manure capture, plus new generator

49,375-74,375

19,900 2.5 – 3.7

4. a. 500 cows, 90% manure capture, plus retrofit of existing generator

40,250 31,667- 39,712

1.1

4 b. 500 cows, 90% manure capture, plus new generator

63,250- 88,250

31,667- 39,712

1.6 – 2.4

*no electricity generation, assumes that all biogas produced can be used to back out diesel fuel for the boiler. Table 1 provides a summary of the information on costs and benefits for each of the scenarios assessed to reflect the Evertz Farm current and projected future situations. More detail on these rough calculations is provided in Appendix D. One initial observation is that all of the proposed


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options appear to be financially attractive, and some could allow recovery of investment costs through saved energy costs in roughly one year or less. This result holds across a range of assumptions about size and technology. Implementation Issues Financing: As noted in the background section above, capital constraints are severe in the current situation. Even though financial returns are very high on paper, it may be difficult to obtain financing for out of pocket investment cost, particularly if the best option includes purchase of a new IC engine generator set. If financing proves to be a barrier to more detailed design and implementation of biogas energy production, initially or later, there are some non-commercial sources that could be explored. Development financing organizations, such as the Global Environment Facility (GEF), United Nations Development Program (UNDP) and development agencies from individual countries may find this project interesting because of the greenhouse gas (GHG) and economic development benefits. As the first of a kind demonstration of a key sustainable energy technology in Mozambique, there is a justification for supporting this project on development assistance grounds, particularly if it can be shown that this project will contribute to the improvement of welfare of poor smallholder farmers in the area around the farm. The UNDP/GEF Small Grants Program has previously provided funding for a dairy farm biogas project in Zimbabwe18 though the justification for this grant was the demonstration of innovative technology, a fuel cell powered with biogas, to produce electricity. Also, the project would have significant and verifiable GHG reductions that could generate marketable emissions reduction credits that could be certified and sold under the Clean Development Mechanism (CDM) or other GHG emissions trading programs. There are at least six biogas projects have been registered with the CDM and a methodology for calculating the baseline and measuring reductions has been approved. Most of the projects to date have been swine farms, but there is great interest in dairy projects as well and a number of project development firms are actively looking for GHG reduction projects. Annex xx provides information on the CDM activities in the biogas area. A quick estimate of the current value of 475 m3, the biogas captured in the largest version of the project shows that emissions reductions would be 79.26 tonnes CH4/yr or 1,664 tonnes CO2 equivalent/year. The price for which carbon credits are being purchase is currently rather unstable as carbon markets are still developing. Prices for credits in the European Union reached levels of over $33.00/tonne in June 2008, while more recently, with the global financial downturn and lower energy prices, the going rate has been as low as $10.00/tonne. This range of prices would translate to a value of $16,640 – 54,912 for the credits that could be generated in a year by Everts Farm with 500 cows. This would be worth looking into as an opportunity to further increase the financial benefit of the project making it even more profitable. It may be possible also that carbon market project developers would be able to help with the up-front 18 SGP, 2006


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investment and technical assistance costs in return for ownership of certified emission reduction credits to be generated after the project is implemented. Phasing: Implementation of a biogas digester project at Evertz Farm can be phased in over time and there are options that would involve fairly low capital investment at the outset if that is desired. In addition, this could be coordinated with the planned expansion of the dairy farm and processing plant as these are planned over several years. 1) Certain relatively low cost improvements can begin at any time while better information and analysis are being obtained. It seems reasonable to start constructing a lagoon and clay liner, mixing, pumping, piping, separation and equipment for pumping liquid fertilizer to fields. These seem to be relatively inexpensive and useful improvements independent of biogas production and will allow for improved utilization of the fertilizer value of the manure.

2) The first major investment cost for the biogas production is the lagoon cover and gas collection system. Once this investment has been made, some biogas should begin to flow fairly soon. As soon as biogas is available, the boiler can be modified and gas can begin displacing diesel fuel with clear financial benefit.

3) Once the biogas production has fully replaced the need for diesel fuel for the boiler, the electricity generation phase of the project can be considered. If the existing standby generator can be adapted and used for some significant amount of power generation, then the investment cost will again be low and the pay very quick through avoided electricity purchases.

4) If it is determined at this point or subsequently that a new generator is needed then this incremental project can probably be designed so that it pays back investment in a couple of years. Each of these phases of investment should pay for itself fairly quickly and each one can be implemented independently, with no commitment as to when or if the next stage will be undertaken. More detail on the calculations, assumptions and other information used to produce the results in this section is provided in appendix D. Conclusions and recommendations. 1. This very preliminary assessment indicates that biogas energy at this Evertz Farm would be a highly attractive investment with some options likely to pay for themselves in one year. The assessment is by necessity crude and subject to large uncertainties. A biogas digester project is well worth pursuing further. In addition to the financial returns for the Evertz Farm/Gouda Gold operation, the recognition as a leader in promoting “green technology” could have value for marketing, dealing with government, etc. Failure to follow through to implementation of a biogas to energy project in this situation would be an opportunity lost.


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Recommendation: The Evertz Farm/Gouda Gold owners should move ahead with next steps toward development of a biogas digester system if at all possible. 2. Significant effort needs to be directed toward assembling and developing better information and analysis to support design and implementation of a successful investment project. The needs include:

• Collection of better data, including o local fuel prices, o current on-site energy use -- diesel, power – amounts, prices and total monthly cost o fertilizer prices, practices

• Measurements such as o manure/cow/day -- % flushed and otherwise collected o volume of flush water/day o volume of food processing waste water flow, % solids

• Analysis o engineering/technical design advice on specific technologies/systems o improved calculations and projections of energy, water, manure management and

other data with expansion o credible feasibility study including technical, engineering and financial IRR

components Recommendation: a) Evertz Farm/Gouda Gold should consider carrying out data collection and analysis to respond to the above list. This should move toward completing a feasibility assessment and design specifications for one or more preferred biogas digester system options. b) The Manica Province program should consider providing expert technical assistance to the farm operators (e.g., International experts brought in for training and design of the household and MCC scale biogas demonstrations, may be able to provide technical assistance to the farm at very low incremental cost). 3. If financing is a barrier, initially or in later stages, there are some non-commercial sources that could be explored. Development financing organizations, such as the Global Environment Facility (GEF), United Nations Development Program (UNDP) and development agencies from individual countries may find this project interesting because of the greenhouse gas (GHG) and economic development benefits. Also, the project would have significant and verifiable GHG reductions that could generate marketable emissions reduction credits to be certified and sold under the Clean Development Mechanism (CDM) or other GHG emissions trading programs. Recommendation: Explore possibilities of proposals to development assistance organizations currently active in biogas in Africa, and also make contact with carbon trading project developers to see if there is interest in a dairy farm biogas project. (Appendix E provides some information and contacts in this area.) 4. Consider integrating biogas system development into the long term phased strategy for expansion of the dairy farm and milk product processing. This will allow investments to be made incrementally and begin to pay for themselves before the next increment of investment is


26

required. This will help to ensure that the biogas production is implemented efficiently and with maximum return per dollar invested.


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Overall Conclusions This report has presented results of a preliminary evaluation of opportunities for biogas digester systems to provide energy, fertilizer and other benefits within the framework of the Land O’ Lakes Smallholder Dairy Development Program in Manica Province. These results are based largely on data, rules of thumb and assumptions drawn from published literature on biogas digesters and adapted to the Manica Province situations. The quantitative results should be considered indicative, and need to be verified and refined using actual data from the program locations before major investment decisions are made. 1. At all three scales of projects evaluated, there are positive opportunities for anaerobic digesters that should be explored in more detail. Household scale biogas digesters are definitely an attractive technology that could be integrated into the overall Manica Province Program and add to the income and welfare benefits that the program seeks to achieve for participants. For the milk collection center (MCC) scale, the Manica Province program could make a major contribution by carrying out a demonstration(s) of biogas power options at one or more sites. At the dairy farm scale, there are very financially attractive options for implementing a biogas digester system at different sizes and with different uses for the gas.

2. Proven, reliable and low cost digester designs have been identified for all three applications, and these should provide a basis for moving ahead with both further assessment and with design of demonstration or commercial projects. At the household and the MCC scale, two well tested household designs - The fixed dome digester and the plastic tubular digester - are obvious choices. At the dairy farm scale, the recommended design is the covered anaerobic lagoon, the lowest cost and lowest maintenance option at this scale 3. Better data and analysis is needed to verify and refine the preliminary assessment results provided in this report. These results of this preliminary assessment clearly suggest that the modest investment by the program in more detailed assessment using more accurate data and measurements as input is justified by very large potential benefits. 4. Involvement of stakeholders is important at all levels. A centrally important category of stakeholders is potential commercial partners who can sell, install and service digesters and related biogas systems at the household and MCC scales. Firms, shops and entrepreneurs that have skills in mechanical, small construction, engineering and equipment service areas should be contacted and those interested engaged in the program design and planning process. Long run success will depend heavily on the availability of trained and certified commercial vendors, suppliers and service firms that can make money on successful biogas digesters. These partners can become the engine for sustainable growth of the market, with initial financial support from the program and potentially from government or other donors.. 5. If successful, the Milk Collection Centers (MCCs) and smallholder dairy cooperatives planned to support the dairy development operations central to the program can be an enormous resource for development and improvements in health and welfare in the program region. For biogas digester deployment, this structure can provide a framework that will help overcome barriers that


28

have been encountered in previous programs, through training, technical support, financing, etc. This would increase the likelihood of long term success for household and MCC scale biogas and could strengthen the cooperatives by giving them an additional type of benefit to offer their participants. 6. At all scales, the recommended biogas digester systems and current conditions will allow for phasing investments and project implementation over time. This can have several benefits, allowing for learning from initial stages to inform refinements in design of later stages; reducing the requirement for up-front investment from the program and participants to more manageable levels; and allowing some of the benefits of early investments to begin to flow before the next phase of investment is required. 7. The availability of capital for the initial investments is likely to be a barrier to implementation and financing assistance may be needed at all levels. Most successful household biogas digester programs around the world have included capital subsidies, special financing arrangements or both. Large farm scale dairy farm projects in the US and Europe also frequently receive financial subsidies of one kind or another as incentives to move ahead with projects. The MCC scale biogas technology will need full funding for demonstration and this should provide a great deal of information on costs, benefits and technical design. These projects all provide wider social and environmental benefits beyond those that accrue directly to the investors. 8. Although it was considered only peripherally in this assessment, the program managers and partners should explore working with carbon credit project developers. Certifying and selling emissions reductions under the Clean Development Mechanism or other greenhouse gas trading programs could increase the profitability of biogas energy investments. It is also possible that some developers may provide capital and expertise at the outset in return for rights to emissions reductions to be certified later. This is initially an obvious option for the farm scale system, but could eventually provide support for MCC and household scale programs as well. Recommendation It is recommended that the Smallholder Dairy Development Program in Manica Province carry out and support biogas energy development at all three scales if possible and consider the following actions as next steps in this process: 1. Contact other manure biogas energy initiatives and projects in Africa. These programs can provide access to experience technical experts, organizations and equipment providers as well as lessons learned from past experience. This may also lead to partnerships down the road with some of the organizations that can support expansion of the biogas elements of the program and will add to its long term impact on improved health and welfare for participants (see Appendix E). 2. Support more detailed study and analysis to improve data and technical basis for design and implementation of biogas energy strategies at all three levels. This should include engagement of


29

local stakeholders. Among the most important stakeholders are engineering, small construction and mechanical services firms who can become commercial installers and service providers. 3. Support a few demonstrations of small digester designs as quickly as possible. This can be done in parallel with improving analysis on the long tern directions. It may be possible and efficient to carry out demonstration of household and MCC scale designs initially at a single MCC/training location. 4. Encourage and support the Evertz Dairy Farm and Gouda Gold Dairy Processing Plant in refining the assessment provided in this report and exploring specific biogas investment options. This could include some assistance and support in identifying sources of development or carbon financing if necessary.


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References

African Development Bank (AFDB) Group. 2007. Mozambique Electricity II Project Project Performance Evaluation Report (PPER) Operations Evaluation Department, 8 February http://www.afdb.org/fileadmin/Uploads/afdb/Documents/Evaluation-Reports/12550249-En-Mozambique-Electricity-II.pdf

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Appendix A: Biogas Digesters – General Technical Background

Biogas Digester Technology19 The basic principles of biogas digester technology are simple and consistent across a range of scales and applications. A digester consists of one or more airtight reservoirs into which organic feedstock – dairy manure, human waste, food processing waste, etc. - is introduced either in batches or continuously. The anaerobic environment (oxygen is excluded) causes different bio-chemical reactions to occur than would happen in open air. Anaerobic digestion is a process that occurs naturally in cows’ stomachs and anaerobic bacteria already present in the manure ferment the waste, producing heat and gas. Digestion is accomplished in two general stages. First, acidogenic bacteria turn biomass into volatile fatty acids and acetic acid. Then methanogenic bacteria metabolize these compounds into a combination of methane-rich gas and odorless phosphorus- and nitrogen-laden slurry, which makes excellent fertilizer. The end product is about 50–80% methane and 20–40% CO2, with small amounts of hydrogen sulfide and other impurities. Small-scale digesters for household use are commonly made of concrete, bricks, metal, fiberglass, or plastic. Larger commercial biogas digesters are made mainly of bricks, mortar, and steel. Biogas burns like liquefied petroleum gas and has an energy value of approximately 600 to 800 BTU per cubic foot (17.7-23.6 kJ/m3).20 It can be used to produce heat through direct, external combustion, a household stove for cooking, a light fixture with a gauze mantle for lighting, or to other appliances connected with simple natural gas plumbing, or it can heat a boiler or other larger and more technologically advanced combustion equipment. The gas can run also internal combustion engines, gas turbines and other technologies that power generators to produce electricity. A typical biogas system consists of the five basic components: 1) manure collection, 2) the anaerobic digester vessel, 3) effluent storage, 4) gas handling, and 5) gas use.

Manure collection Livestock facilities use manure management systems to collect and store manure because of sanitary, environmental, and farm operational considerations. Manure is collected and stored as liquids, slurries, semi-solids, or solids. Small farmers in developing countries may collect manure for use as fuel or to be spread on fields. For household scale digesters manure is collected manually and shoveled into the digester at least daily. In large dairy farms manure is collected through flush, scrape, and vacuum systems. A water flushing system will generally reduce the concentration of manure from 12 percent solids, “as excreted,” to less than one percent solids in the flush water. Flush systems are more economical and less labor-intensive than scrape or vacuum systems. Scrape systems simply collect the

19 Adapted from Brown,2006; Biogas for a Better Life, 2007; TNAU 2008; US EPA, undated. 20 U.S. EPA, undated.


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manure by scraping it to a sump. Under normal weather conditions the scraped manure has approximately the same consistency as the “as excreted” manure. During the warm dry summer (often the case in Manica Province) manure may lose water on the slab. Vacuum systems collect “as excreted” manure with a vacuum truck and haul it to a digester or disposal site rather than to an intermediate sump. Vacuum collection is a slow and tedious process. The collected manure is undiluted and approximately equal to the “as excreted” concentration. Pre-processing: For many digester types manure must be mixed before entering the digester. If thick slurries are processed in an anaerobic digester, intense mixing is required to maintain the solids in suspension. In large scale systems this is done with mechanical mixers and pumps. In the household systems this is done by hand with a shovel. Sometimes in large systems some of the solids are removed through screens or gravity separation prior to entering the digester. The purpose is to remove sand, straw or other extraneous materials that might clog the digester process. However, removal of solids also results in the removal of some of the organic material through screening and sedimentation and will reduce the quantity of organic solids that can be converted to gas in the digester. The preferred approach is to manage the dairy, bedding and manure collection systems to minimize contaminants. In large farms, toxic materials such as fungicides and antibacterial agents can have an adverse effect on anaerobic digestion. The anaerobic process can handle small quantities of toxic materials without difficulty but amounts should be kept as small as possible. Storage containers for fungicides and antibacterial agents should be placed at locations that cannot leak into the anaerobic digester. Anaerobic digester The digester is the component of the manure management system that optimizes naturally occurring anaerobic bacteria to decompose and treat the manure while producing biogas. Digesters are covered with an air-tight impermeable cover to trap the biogas for on-farm energy use. Hydraulic Retention Time (HRT) is the average number of days a volume of manure remains in the digester, that is the volume of the digester/the daily input. Depending on temperature, moisture content and the type of digester, HRT can be 6 days up to 60 days to fully process manure.21 (Simpler digesters may take longerand can be up to 70-90 days in cooler climates.22) Methane producing bacteria require a neutral to slightly alkaline environment (pH 6.8 to 8.5) in order to produce methane. Specific technical design options for digesters are different depending on the scale. These are discussed in detail in the appendices that deal with the 3 scales relevant to this program. Effluent storage The products of the anaerobic digestion of manure in digesters are biogas and effluent. The effluent is a stabilized organic solution that has value as a fertilizer and other potential uses. Waste storage facilities are required to store treated effluent because the nutrients in the effluent generally cannot be applied to land and crops evenly year round. The size of the storage facility and storage period must be adequate to meet farm requirements during the non- 21 Brown, 2006. 22 Devkota, 2003


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growing season. Facilities with longer storage periods allow flexibility in managing the waste to accommodate weather changes, equipment availability and breakdown, and overall operation management. The digested slurry, or effluent, is automatically discharged from the outlet, is an excellent bio-fertilizer, rich in humus. The anaerobic fermentation increases the ammonia content by 120% and quick acting phosphorous by 150%. Similarly the percentage of potash and several micro-nutrients useful to the healthy growth of the crops also increase. The nitrogen is transformed into ammonia that is easier for plant to absorb. This digested slurry can either be taken directly to the farmer’s field along with irrigation water or stored in a slurry pits (attached to the digester) for drying or directed to a compost pit for making compost along with other waste biomass. The slurry and also the sludge contain a higher percentage of nitrogen and phosphorous than the same quantity of raw organic material fed into the digester.23 Sometimes the final products are separated into a liquid stream and a solid stream. The liquid stream will contain inorganic nitrogen as ammonia and a small amount of phosphorus. The solid stream will contain organic nitrogen and a vast majority of the phosphorus. Both the solid and liquid streams will be fully stabilized and odorless. Large dairy farms in the industrialized countries often sell the solids or compost them for bedding. Gas handling A gas handling system removes biogas from the digester and transports it to the end-use, such as an engine or boiler. The gas system can include the digester cover, pressure and vacuum relief devices, water trap, flame trap, pressure regulator, gas meter, check valve, pressure gauges, piping, gas pump or blower; condensate drain(s), waste gas burner and a gas holder,. Biogas produced in the digester is trapped under an airtight cover placed over the digester. The biogas is removed by pulling a slight vacuum on the collection pipe (e.g., by connecting a gas pump/blower to the end of the pipe), which draws the collected gas from under the cover. A gas meter may be used to monitor the gas flow rate. The biogas coming from the digester is saturated with water vapor. This water vapor will condense at the walls of the pipeline. If this condensed water is not removed regularly, it will ultimately clog the pipeline. Hence, a condensate drain has to be placed in the pipeline. The position of the water drain should be vertically below the lowest point of the pipeline so that water will flow by gravity to the trap. Water can be removed by opening the drain. As this has to be done periodically, the drain must be well accessible and protected in a well, maintained drain pit. Flame traps are emergency devices installed in gas lines to prevent flames travelling back up the gas line (flashback) and reaching the digester. The flame trap generally consists of a box filled with stone or a metal grid. If a flame develops in the gas line, the temperature of the flame is reduced below the ignition point as it passes through the trap and the flame is extinguished.24

A mixture of biogas and air can be explosive. Methane gas in concentrations of between 5% and 15% in air by volume is explosive. Operating staff on waste treatment plants should ensure that no air is allowed to enter the digester or gasholder. All piping and equipment must be sealed

23 Energysaving.com 24 Russell, 2008


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properly to prevent gas from escaping to the outside. There must be no smoking and all electrical installations, including light switches, torches etc must be of the explosion-proof type, as the smallest spark could ignite escaped gases.25

Biogas Clean-up: All biogas produced in a digester contains methane, carbon dioxide and small amounts of trace gases. These trace gases can include hydrogen, hydrogen sulfide (H2S), non-methane volatile organic carbons (NMVOC), nitrogen and halocarbons. The presence of non-burnable substances in the biogas, like water and carbon dioxide, reduces the conversion efficiency. The major concern, however, is hydrogen sulfide that can be 0.3 to 2% of biogas. When burned, hydrogen sulfide combines with oxygen to produce sulfur dioxide, which reacts with moisture to produce sulfuric acid. This not only has a corrosive effect on equipment, but contributes to the acid rain problem as well. Using the biogas in technologies like IC engines for conversion of biogas to energy may require either a method to remove toxic and corrosive contaminants, or special procedures to accommodate the deleterious effects of contaminants in the biogas stream. One common on-farm approach is changing oil (in IC engines) frquently (numerous operators change oil weekly). This practice can prevent equipment damage without removing the trace H2S. To successfully burn biogas that has not had the H2S removed, a boiler should be operated continuously. When biogas containing H2S is burned, the H2S is converted into oxides of sulfur (S) (primarily sulfur dioxide (SO2) and sulfur trioxide (SO3)). These sulfur compounds are regulated as air pollutants in the United States, and air emission permits are required depending on the amount released by a facility. When exhaust gases containing SO2 and SO3 cool below the dew point temperature, the moisture that condenses in the gas stream will combine with these compounds to form highly corrosive sulfuric acid (H2SO4). It is the formation of H2SO4 following the combustion of biogas that contains H2S that results in severe equipment corrosion. A method commonly employed when operating boilers on biogas containing H2S is to operate the boiler continuously at a temperature above dew point. By maintaining the boiler temperature above the dew point of the gas steam, H2SO4 is not formed inside the boiler and corrosion is avoided. Since SO2 will reduce the dew point of the gas stream, the greater the H2S level of a biogas, the higher the boiler temperature that must be maintained to avoid H2SO4 formation. Biogas with a 1,000 parts per million H2S concentration will require exhaust gas stream temperatures of around 150 degrees Celsius (302 ºF) to remain above dew point. Of course, wherever the exhaust gas stream cools to dew point outside of the boiler, H2SO4 will be formed. Thus, it is very important to direct exhaust gases away from any equipment, personnel, or livestock. Since H2SO4 will form when the boiler is shut down, cautionary measures must be taken to avoid any cycling of the boiler on and off when burning H2S-laden biogas to avoid corrosion.26

25 Russell, 2008 26 USDA, 2007


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There are many types of devices to “scrub” the biogas of corrosive compounds contained in the biogas (e.g., hydrogen sulfide). These scrubbers range from very simple and low cost to more sophisticated devices. A biogas scrubber can be as simple as that shown in figure 1, a simple low cost device designed for use with household scale digesters.27 Most digesters at this scale do not include gas cleaning and the biogas stoves and lighting technologies in rural households are generally able to function well despite H2S problems. Some designers, however, recommend use of simple scrubbers like this one. This device consists of a 20-gallon (80 liter) drum filled with about 15 gallons (60 liters) of water. Biogas from the digester is piped into a low connection on the drum. It bubbles up through the water to reduce the CO2 and SO2 content of the biogas. The gas is then piped off at a top connection to a storage container. Another simple technique used in Europe is to add a small amount of oxygen in the head space of the digester to combine with the hydrogen sulphide to produce a precipitate, thus removing most of the hydrogen sulphide. The biogas is then transferred to the engines underground, so most of the moisture would condense out of the gas.28 A similar gas cleaning approach in the North America is limited to removal of H2S by introduction of air into the gas line with a simple condensation removal system.29

Figure1: A Simple Biogas Scrubber

Source: Forst, 2002

Many biogas producers use “Iron Sponge” (iron impregnated wood chips) as a filter to remove contaminants (principally hydrogen sulfide, H2S) from biogas before introduction of into the energy converter. One higher technology biogas purification system removes sulfuric components and humidity from biogas in three steps. In the first step most of the biogas humidity 27 Forst, 2002 28 House, 2006 29 RETScreen,


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is removed, by a recipient where the water is condensed. In the second step, biogas is directed to purification system, composed of two molecular screens, removing the remainder humidity and the sulfíde components (H2S). In the third step, biogas passes through an amount of iron chip, removing remaining H2S.30 There are numerous chemical, physical and biological methods utilized for removal of H2S from a gas stream and new approaches are being developed currently. Recent research31 has indicated that cow-manure compost mixed with wood chips can be used for removal of H

2S from biogas in

small-scale reactors. Testing has also been carried out that suggests that addition of food wastes to the anaerobic digestion of manure can lead to lower concentrations of H

2S in the biogas.

There is some disagreement among experts over how likely it is that boilers and IC engine generators can operate on biogas without cleaning. According to one authoritative source: “In general, it would be unwise to burn ‘as produced’ gas in expensive equipment unless it is engineered to be capable of handling the trace H2S.” 32 According to the EPA AgStar Handbook, however, “Gas treatment is not usually necessary if proper maintenance procedures are followed.”33 The best advice may be, according to one good practice manual “The best advice is to choose the appropriate equipment, consult the manufacturer as to the best methods for specific plant requirements, and ensure that anyone using it is fully trained to operate it efficiently.”34 Gas storage: In many cases, the biogas produced in a digester is stored in the headspace of the digester vessel, often under a flexible cover. Biogas can also be stored separately for on-farm uses in some cases. In practice most biogas is used as it is produced and the need for biogas storage is usually of a short term or temporary nature, e.g., at times when production exceeds consumption or during maintenance of digester equipment. Several simple and inexpensive low pressure storage options are available and can be added to the biogas system if needed. These included flexible gas bags made of material similar to digester covers, floating roof storage tanks and water sealed gas holders.35 Gas use. Recovered biogas can be utilized in a variety of ways. Gas of this quality can be used to generate electricity; it may be used as fuel for a boiler, space heater, or refrigeration equipment; or it may be directly combusted as a cooking and lighting fuel. Since the composition of this gas is different, the burners designed for coal gas, butane or LPG when used, as ‘biogas burner’ will give lower efficiency. Therefore specially designed biogas burners are used which give a thermal efficiency of 55-65%36. Biogas is a very stable gas, which is non-toxic, colorless, tasteless and odorless. However, as biogas has a small percentage of hydrogen sulfide, the mixture may smell

30 Coelho, et al., 2006 31 Scott, 2006 32 British Biogen, 1997. 33 USEPA AgStar Handbook 34 British Biogen, 1997. 35 Krich, et al., 2005 36 USEPA AgStar Handbook


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very slightly of rotten eggs, which is not often noticeable especially when being burned. When the mixture of methane and air (oxygen) burn a blue flame is emitted, producing large amount of heat energy. Because of the mixture of carbon dioxide in large quantity the biogas becomes a safe fuel in rural homes as this will prevent explosion. Boilers: Diesel fired boilers can be adjusted to operate on biogas relatively easily and also can be set up to operate on either fuel. This will allow diesel to be used as a back-up fuel in the event there is a disruption of the biogas supply. Boilers normally require very little biogas cleaning and conditioning prior to use, and boiler efficiency has been reported to average 75 percent when burning biogas. Boilers will operate on very low gas pressures in the range of 5 to 10 inches of water.37 While burning biogas with large amounts of H2S will decrease the useful life and increase the maintenance of the equipment, it is still commonly done. The lower the concentration of H2S in the biogas, the longer the boiler life. One recommendation for operating a boiler with high levels of H2S is to operate the boiler continuously as the H2S converts to sulfuric acid and causes corrosion when the temperature drops below the dew point. IC Engine or Gas Turbine generators: Both IC engines and gas turbine driven generators sets are being used to generate electricity from biogas. IC Engine. Natural gas or propane engines are easily converted to burn biogas by modifying carburetion and ignition systems, essentially to handle larger volumes of fuel due to the CO2 in biogas. Engines may also be modified to accept higher levels of contaminants in the incoming air stream (versus the consistency of natural gas). A biogas fueled engine generator will normally convert 18 - 25 percent of the biogas BTUs to electricity, depending on engine design and load factor. Gas treatment is not necessary if proper maintenance procedures are followed. Biogas engines less than 200 horsepower (150 kW) generally meet stringent air pollution limits without modification if run with a lean fuel mixture. Gas Turbines. Small gas turbines that are specifically designed to use biogas are also available. An advantage to this technology is lower NOx emissions and lower maintenance costs, however turbines cost substantially more per kW than IC engines.38 These components of a biomass system are included in some form in biogas digester systems at all scales. However the detailed designs of the digester and other components vary depending on the size of the system, the applications for the gas, location and other factors. The report will describe each of the three scales that can potentially apply in the program and the technology available for each. For each scale the report will briefly discuss relevant experience in other countries, assess in rough terms the costs and benefits, and present options and recommendations for each potential application Digester Sizing and Performance Usually in dairy biogas design situations one knows roughly the number of head of dairy cattle that will be producing manure. Determining the size of digester needed and the expected biogas production, will require an understanding of the likely biogas production per cow. This value is a result of several intermediate steps. First, there is considerable uncertainty about the manure 37 USDA, 2007. 38 Goldstein, 2006


43

produced per cow per day. As shown in table 1, estimates range from 25 to nearly 80 kg manure per cow. This range is affected by breed and condition of dairy cattle, amount and types of feed, water availability, climate, etc. Second, the calculations that follow assume that close to 100% of manure excreted is captured and delivered to the digester. If this is not the case rules of thumb will need to be adjusted to account for the percentage of total manure captured. Finally, there is some variation in the rate of production of biogas per unit of manure. This is a measure of efficiency of the digester, dependent on digester design, maintenance, quality of manure and other materials in feedstock, local temperature and other conditions, etc. Most “rule of thumb” calculations use a figure of 25 m3 biogas/tonne of manure. All of these uncertainties combine to give a range of 0.625 to 2.8 kg per cow. The upper end of this range appears to be representative of recent, well designed and maintained projects at large dairy farms. Table 2 provides measured results from several existing dairy manure projects in North America. Some experts suggest that a major factor contributing to these relatively high numbers/head may be due to larger than expected production of manure from cows in intensively managed dairy farms39.

Table 1: Literature estimates of Biogas Production per Dairy Cow Excretal

output Number of cows to proeduce 1 tonne

Biogas per tonne manure

Biogas per head

Units kg/hd/d Head m3/tonne m3/hd/dy

DEFRA 200540 53 19 25 1.2-1.4

Practically Green, 200741 25-50 20-40 25 0.635-1.25

Schanbacher, 200742 45.4-79.45 13-22 23.4-27.9 1.3- 2.7

The literature on small scale household digesters, offers a range of estimates of manure and biogas production per cow. Most of these estimates are toward the lower end of the overall range as might be expected given issues of lower quality and amounts of feed, incomplete collection of manure and less than optimal digester performance in small scale digesters typical of developing country situations. Experts suggest that energy for cooking and some lighting for a typical rural family in a developing country would require a minimum of 1 m3 biogas/day. There are some technical

39 Nelson and Lamb, 2002, 40 DEFRA, 2005 41 Practically green, 2008 42 Schanbacher, 2007


44

sources43 that suggest that a single cow might provide sufficient manure and urine to produce 1 m3 biogas/day. Several sources 44 suggest that 2 cows are a minimum while others45 argue that 4 or more cows are necessary to ensure support for a family’s biogas needs. The higher numbers of cows needed for a household digester assume use of the widely practiced livestock management system, where cattle feed widely in communal areas during the day and are only penned (corralled) at night so that only a fraction of the total manure is collected. Medium or community scale digester systems tend to be very similar to household systems. They will then have more or less the same performance characteristics (manure input, gas yield and fertilizer production per m3 of digester content) as the smaller systems46.

Table 2: Dairy Manure Digester performance examples47 Project # of

Cows Biogas m3/day

m3/cow /day

Methane Content %

Elect Gen kW-‐kWh/yr

kWh/cow/ year

Digester type/size

Cobden, Ontario, Canada

140 400 2.8 55 complete mix mesophilic

Castellani, California

<1,500 3,300 2.2 70 c Unheated covered anaerobic lagoon

Haubenschild Farms (dairy)

840 2400 2.9 135-1,095,000

1304 combined phase, mesophilic, plug-flow, flexible cover

Gordondale Farms (dairy)

875 135-‐876,000

1208 two phase, mesophilic, mixed plug-flow loop, fixed cover/ 350,000 gl (1325 m3)

New Horizons

1,400 3220 2.3 260-1,500,000

1,071 combined phase , mesophilic, plug-flow (x2) flexible cover

Tinedale Farms (dairy)

2,400 5600 2.3 375 combined phase mesophilic complete-mix (converted TPAD) b

fixed cover b. Temperature-phased anaerobic digester c. avg 2130 m3 biogas/day used to generate avg. 4172 kWh/day – 0.51 m3/kWh or 1m3 yields 1.96 kWh

Obviously these rules of thumb are useful for rough estimates only. Before development of any project generating methane from manure, the developers need to collect dung or monitor quantities for at least several days to determine average daily dung production. On this basis, the appropriate size biogas digester plant can be calculated. 43 Last, 2007, Brown, 2006, 44 Forst, 2002, Biogas for a Better Life. 2007 45 Biogas for a Better Life, 2008 46 GEF Egypt 2008 47 Cobden data from RETScreen, 2008, Castellani Brothers data from Martin 2008, all others from Kramer, 2004.


45

Once daily input of manure is estimated then there are recommended approaches for developing a first estimate of the size of the digester - organic loading rate and hydraulic retention time (HRT).of sizing a digester design. For large scale dairy farm digesters, there are two approaches commonly used.48

1) Loading Rate method uses a 'rule of thumb' that 6kg dry matter/day requires 1 cubic meter of digester. For dairy manure, as excreted, 12 % of the total weight is solids. Therefore for high solids digesters the amount of manure is multiplied by 0.12 to give the number of m3 of digester capacity needed. This method is appropriate for high solids digesters only.

2) Hydraulic Retention Time (HRT) method is a very simple calculation that applies to most large scale digesters. This method requires an estimate of the volume of the daily input in m3 and an estimate of the HRT which for dairy cattle is mainly a function of the type of digester and in some cases the local climate.

Note a tonne (1000kg) of water has a volume of 1 cubic meter (1000Litres) by definition. For most approximations, liquid food and farm wastes have a density close to that of water. To estimate the range of possible sizes for most high solids digesters, use a retention time (average residence time in the digester ) of 15 days with a limit of +/- 7 days for a wide range of materials. For low density digesters, e.g., anaerobic lagoons, the retention times are longer in the range of 40 days. For example, a high solids digester handling 10 tonnes of manure would convert to 10 m3/day multiplied by 15 days would require a 150 m3 digester. A lagoon handling the same volume of manure would have input of 40 m3/day - 10 m3 manure/day multiplied by 4 to reflect dilution by flush water to 3% solids or less. The retention time would be 40 days so volume required is 40m3/day x 40days HRT = 1600 m3 lagoon volume. For household scale digesters, sizing is specific to the particular design with some designs calling for digesters as small as 3 m3 to supply biogas for a household up to some suggesting that 8 m3 is the minimum size for a household digester. Required size for household and community scale digesters are determined by input volume and HRT and specific design. This will be explained in more detail in later sections for specific designs. Economics of digester projects Biogas digester projects as all scales are evaluated first in terms of financial viability. This is a function of monetary costs and benefits. The costs are mainly capital costs of the digester and any other equipment needed for the system including gas using technology like cookstoves and boilers, electric power generators, manure and gas handling and storage equipment, piping, clean up and safety equipment. Operating costs are also considered, though in most cases they are

48 This discussion is adapted from Practically Green. 2008


46

low, as the basic feedstock is essentially free. There are maintenance and operation costs, however, at all levels. Energy benefits: Monetary benefits are primarily the value of the energy produced using the biogas, whether that is direct combustion, offsetting another fuel like wood, diesel, kerosene, etc., or the generation of electricity that offsets purchases from the grid, and sometimes actually is sold to the grid when not needed on the farm. Fertilizer Benefits: The second category of monetary benefits comes from the sale of, or avoided purchase of, fertilizer, compost, bedding and other products that are derived from the effluent or digested manure coming out of the digester. In the process of anaerobic digestion, the organic nitrogen in the manure is largely converted to ammonium. Ammonium is the primary constituent of commercial fertilizer, which is readily available and utilized by plants.49

Manure is already widely spread on fields as a soil amendment. Anaerobic digestion can increase the value of manure as a fertilizer. Carbon or “organic” compounds are undesirable bulk when manure is used as fertilizer. The high proportion of organic substances in cow manure ordinarily inhibit the action of beneficial microbes. Anaerobic digestion turns 70 to 90 percent of the carbon present in manure into methane and carbon dioxide, reducing what is called ‘organic loading’ and allowing the beneficial microbes to work. The digestion process converts organic nitrogen into an inorganic form (ammonia or nitrate nitrogen) that can be taken up more quickly by plants. These nitrogen compounds are far less obnoxious and far more useful as fertilizers. Timing of the plant uptake of ammonia and nitrate nitrogen, similar to that of commercial fertilizers, is more predictable than the plant uptake of organic nitrogen from raw manure. Nearly odorless, these compounds are much more readily utilized by plants, and, if applied properly, much less likely to run off and contaminate ponds, lakes and waterways. In rural developing countries, the by-product slurry has twice the nitrogen content of composted dung because open-air composting allows much of the nitrogen to escape in the form of volatile compounds. The remaining bulky organic substances can be separated out, greatly reducing storage needs. With the addition of a solids separation system, the final products are a solid, fibrous material and a liquid with the consistency of milk—both nearly odorless. The fiber can be used as animal bedding, a soil amendment or as a high-quality potting soil. The liquid can be stored and applied to fields as high-quality fertilizer. After solids separation, the effluent can still be spread on the fields, retaining about 75 percent of the total nutrients of the original manure. Weed seeds in manure subjected to anaerobic digestion can exhibit reduced germination and viability compared to weed seeds contained in untreated manure.50 Unlike decomposing dung, digester effluent is odorless and does not attract flies or mosquitoes. Farmers in India have reported that it actually repels termites, and inhibits weed growth.51 However, nitrogen in ammonia form can easily be

49 TNAU, 2008 50 TNAU, 2008 51 Sampat, 1995


47

lost to the air (called volatilization), where it is a pollutant (see below). Therefore, care must be taken to handle the digested manure to minimize nutrient leaching and volatilization.52 In many cases digester effluent used as fertilizer can replace otherwise purchase commercial products, or be sold to other users, creating a readily determined market value that can be included in the economic benefit analysis. In others, it is used to replace fertilization with raw manure or to expand the use of fertilizer on existing farms, and the benefit would be increased productivity from the fertilized areas. This is harder to quantify and value. Likewise with solids separation, if fiber products are sold a market value can be included, but often they are used on farm and economic value of hard to determine. These costs and benefits are really quantifiable only in the context of the scale and type of digester, the conditions around the farm or other location of the digester and the normal practices in the base case situation. These costs and benefits are examined in more detail below in the discussion of options at each of the three scales of interest in the Manica Province program – household scale, milk collection center or community scale, and modern dairy farm scale. Non-Monetized Benefits of Biogas Recovery and Use As illustrated in the previous section, accounting of financial benefits for biogas projects is usually limited to the energy value of the biogas and the value of digested effluent as fertilizer or other products, but there are many other benefits that are not captured in this analysis. Properly designed and used, a biogas digester can mitigates a wide spectrum of social and environmental problems: it can improve the quality of life for rural households, it can mitigate respiratory health problems associated with wood, charcoal and dung fueled cookstoves; it improves sanitation; it reduces greenhouse gas emissions; it reduces demand for wood and charcoal for cooking, and therefore helps preserve forested areas and natural vegetation; Social and Gender Benefits: The switch to biogas fuel for cooking and lighting can have a profound effect on the quality of life and opportunities for rural families especially for women. Just gathering the fuel takes several hours a day -- work that, in sub-Saharan Africa, is done almost entirely by women and children. Women also do most of the housework that can be significantly reduced by a switch from dung or fuelwood to biogas. In Sri Lanka, it has been reported that women and children, freed from firewood collection and from cleaning smoke-blackened utensils and the disposal of animal waste, gain some two hours a day for other activities. About 80% now use this time to earn extra income that currently accounts for approximately 24% of the family's monthly income.53 In Tanzania a government program distributed and installed 46 plastic digesters in several villages. After the digesters had been running for five months, respondents said they were doing an average of five fewer hours of housework (including fuel collection) per day. In rural areas where there is otherwise no

52 Nelson and Lamb, 2002 53 Ho, 2005


48

electricity supply, biogas has enabled women to engage in evening study, literacy classes and other home and community activities.54 Respiratory Health Benefits: For the rural poor in the developing world, biogas’s greatest benefit may be that it can help alleviate a very serious health problem: poor indoor air quality. Some 2 billion people around the world, including 89% of the sub-Saharan African population, use biomass for cooking and heating.55 Where combustible biomass is the chief energy source, life often revolves around an indoor cookstove or open fire that likely has no vent to the outdoors. Figure xx illustrates the relative levels of emissions of two of the most serious indoor pollution health risks from the possible fuels that can be used for cooking and lighting in rural areas. Women do most of the cooking and they and their children are exposed to cookstove smoke far more than men. Their respiratory health suffers accordingly. In 2000, burning solid fuels caused 1–2 million deaths, comprising 3–4% of total global mortality.56 In 2002 the World Health Organization (WHO) reported that indoor air pollution much of it stemming from biomass burning may increase the risk of acute lower respiratory infections in children, chronic obstructive pulmonary disease in adults, tuberculosis, low birth weight, asthma, ear infections, and even cataracts.57 The Global Health Council, an international group of health care professionals and organizations based in Washington, DC, reported that of all infectious diseases worldwide, those in the lower respiratory tract are the leading cause of death.58 Switching to biogas has resulted in a smoke-free and ash-free kitchen, so women and their children are no longer exposed to the risks of respiratory infections and other effects of indoor pollution, and can look forward to longer, healthier lives

54 Brown, 2006 55 Flavin and Auek, 2005 56 Martinot, 2005 57 Who, 2002 58 Brown, 2006


49

Figure xx: Local pollutant emissions along the energy ladder

(source: Biogas for a Better Life, 2008) Sanitation and disease: With the switch to biogas in smallholder farms, cattle dung is no longer stored in the home or the farm yard, but is fed directly to the biogas digester, with a significant improvement in sanitation. The anaerobic digestion process also destroys pathogens reducing the likelihood of disease. According to the Global Health Council, almost 40% of deaths in Africa are due to diarrheal diseases. There is no question that animal waste is loaded with pathogens that are transmitted via the oral–fecal route and can cause diarrhea, abdominal cramps, dehydration, fever, vomiting, and—in vulnerable populations such as infants, children, the elderly, and immunocompromised persons—death.59 Even though the biodigestion process naturally reduces the pathogen load, handling biogas feedstock and using biogas slurry as fertilizer does carry some risk of infection. It is not entirely clear whether slurry from household scale digesters can still harbor enough pathogens to infect humans who handle it or eat crops fertilized with it, though the risk of infection is certainly greatly reduced. A Cape Town, South Africa–based alternative energy company, has reported that once people see a digester in action and are trained in proper hygiene, such as washing their hands while working with it, they realize that health risks associated with operating a biodigester are relatively minor. This company has installed a number of biogas systems in rural areas.60 If latrines can be connected to the household scale digesters, this can also have great sanitation and health benefits. Whether or not this is an option depends on cultural factors. In Nepal very

59 Ibid.

60 Brown, 2006


50

few households were initially interested in latrines, but more than 60% have now had them installed.61 Large, farm-scale digesters also reduce pathogens dramatically. Heated digesters reduce pathogen populations dramatically in a few days. Lagoon digesters isolate pathogens and allow pathogen kill and die-off prior to entering storage for land application. These processes have the potential to practically eliminate many, but not all, kinds of pathogens, greatly reducing this potential source of water pollution. The effectiveness of a particular digester in pathogen destruction will vary. Biogas digesters in industrialized countries are required to meet fairly stringent standards for use of effluents as fertilizer of any other discharge. Generally digesters can be operated so that they meet these standards without requiring further treatment of the effluent. Reduced Surface and Groundwater Contamination: Digester effluent is a more uniform and predictable product than untreated manure. The higher ammonium content allows better crop utilization and the physical properties allow easier land application. Properly applied, digester effluent reduces the likelihood of surface or groundwater pollution. Anaerobic digestion greatly reduces Total Oxygen Demand (TOD), is a measure of how much oxygen could potentially be consumed by breaking down organic matter, such as that found in manure. This is an issue if there is a catastrophic spill of manure that enters surface water. If too much oxygen in the water is used to break down manure that spills into a stream, natural stream life will suffer or be killed. Reduced Odors: Biogas systems reduce offensive odors from manure storage facilities. These odors impair air quality and may be a nuisance to nearby communities. Biogas systems reduce these offensive odors because the volatile organic acids, the odor causing compounds, are consumed by biogas producing bacteria. One study showed that anaerobic digestion reduced odor by 97 percent over fresh manure.62For some projects, odor control is a primary reason for installing a digester, especially covered lagoon systems. Fly propagation is also extremely limited in digested manure compared to fresh manure. Reduced greenhouse gas emissions: Methane is a greenhouse gas more potent than carbon dioxide in causing global warming. By capturing and burning the methane produced from animal manure, anaerobic digesters help to slow down the rate of global warming. (Note: manure management systems that result in aerobic decay of manure, such as grazing systems and dry manure packs, do not produce significant amounts of methane; thus the benefit of methane reduction reported here is only in comparison to other anaerobic systems of treating manure, such as a lagoon system). In addition to the environmental benefit, this ability to provide verifiable greenhouse gas reductions can be a source of revenues to help with the up front capital costs. In developing countries verified greenhouse gas reductions can be registered as certified emissions reductions (CERs) under the Clean Development Mechanism (CDM). This is outside the scope of this report and probably not relevant in the early stages of the program, but could be worth exploring if the program leads to scaled up numbers of digesters in the future. 61 Biogas for a Better Life, 2007. 62 Nelson and Lamb, 2002


51

Preservation of forested areas and natural vegetation. By substituting biogas for fuelwood anaerobic digestion reduces demand for wood and charcoal for cooking, and therefore reduces the degradation of forest and vegetation. That, and the practice of containing livestock for manure collection, which might otherwise graze in the forest, both contribute to protecting the remaining forests and allowing the forests to regenerate.


1

Appendix B: Household Scale Digester Systems Household Biogas Digester Designs The three most common types of systems that have been extensively used are: 1) Fixed dome, 2) Floating drum (or dome) and 3) Plastic tubular. Fixed dome digester: Developed and extensively deployed in China the standard fixed dome design consists of a gas-tight chamber constructed of bricks, stone or poured concrete (see figure xx). Both the top and bottom are hemispherical and are joined together by straight sides. The fermentation (digester) chamber and the gasholder are one unit. The inside surface is sealed by many thin layers of mortar to make it gas-tight; earlier designs showed gas leakages. The hemispherical top and bottom are designed to withstand high structural forces. The basic design keeps the ratios of key dimensions constant, e.g. diameter to height of the cylinder is 2:1. This design works according to the principle of constant volume, changing pressure. When the rate of gas production is higher than that of gas consumption, pressure inside the digester rises and expels some digester contents into the overflow compartment. When the consumption is higher than production, pressure inside the digester falls and the expelled materials in the outlet compartment run back to digester. Changing pressure of gas delivered into home varies causes variations in heat produced by cooking elements. Some systems use separate gas storage that can help to maintain constant gas pressure.

Figure 3. Schematic of fixed dome digester63

Chinese designs are resource conserving, compact, and adaptable to whatever building materials is locally available. Attempts to replicate the Chinese results outside the People’s Republic of 63 Kangmin and Ho, 2006


2

China (PRC) have yielded very uneven results. High quality materials and trained installers are needed to build this kind of digester and this can be expensive. Building materials, such as cement, lime and quarried stones, which are produced locally in China, can be expensive in other countries. The construction of the dome can be difficult unless an experienced technical expert is involved. Creating a water and gas tight digester vessel can be difficult and can take some time. The design also requires continuous checking for leaks and repair whenever they occur. Although it is required only rarely, Chinese bioreactors are also difficult to clean. Some firms provide digester-cleaning services at a cost as part of their business. Depending the level of maintenance, a digester may need cleaning every 1 to 2 year.64 A variation of the fixed dome model biogas plant has been designed and optimized in the Institute of Fuel Research and Development (IFRD), Bangladesh Council of Scientific and Industrial Research (BCSIR), Dhaka. This model is durable (25-30 years), easy to construct with locally available construction materials and has a better performance. It has been patented and disseminated throughout Bangladesh with satisfactory operational results65.

A very popular adaptation of the Chinese model is the fixed-dome digester GGC 2047, developed in Nepal. Based on the principles of fixed dome model from China, the Gobar Gas and Agricultural Equipment Development Company (GGC) of Nepal developed this design and has been popularizing it since the early 1990s. The design uses a standardized concrete dome and has been developed to minimize construction cost and to maximize durability and performance.66 This design has proved its performance and reliability in Nepal and several other Asian countries. This design is being promoted currently in some African countries (e.g. Ethiopia, Rwanda, etc. under the Biogas for Africa Initiative) and has been adapted for use in South Africa.67

Building and installation of this unit still requires skill, and some have developed technical problems because of poor workmanship and installation by unqualified persons. The unit requires that the water trap and other fittings be checked regularly for leaks. Also, water condensing in along the fittings, and at times in the cookers, can be an issue, but the inlet pipes can easily be modified with several water traps to ameliorate this problem and help identify leakages.68 Well designed and constructed, and well maintained, any of these fixed dome digesters should have a lifetime of at least 15-20 years. The hydraulic retention time (HRT), for cow manure, is 35-55 days. At total solids concentrations of 5-8% it produces 0.2-0.3m3 biogas/m3 of biodigester volume/day.69

64 USAID 2007 65 BCAS, 2006 66 FAO, 1997 67 Biogas for a Better Life, 2008 68 Biogas for a Better Life, 2007a 69 USAID, 2007, Devkota, 2003.


3

Floating drum (or dome) digester: This design has been developed, standardized and widely disseminated in India and works on the principle of constant pressure, changing volume. Figure xx shows a current popular version of this basic design. The digester includes a cylindrical section, commonly made from brick and cement that is covered with a gas tight steel cylinder which moves up when gas production is higher than consumption and comes down under the reverse conditions. The life spans of these digesters vary widely, and are dependent upon the quality of labor and materials used in construction, as well as management and maintenance. In Bangladesh, one study reported that the durability of floating dome biogas plant is only 4-6 years. The floating drum, made of mild steel sheet, was prone to rapid corrosion, and replacement or repair was difficult in the target rural areas where welding and workshop-facilities were often not available70. Other researchers have shown that high quality, well-managed floating drum digesters can last for over 40 years, though there are some failures – largely because of poor management and maintenance. On the average, it is safe to say that floating drum digesters, if built with high

Figure 4. Floating Dome (Indian Design) Type Digester71

70 BCAS, 2006 71 USAID, 2007


4

quality materials and well managed, can give service of at least 15-20 years providing cooking gas, lighting and fertilizer. Good maintenance includes the need for repainting of all metal parts every few years to ensure that they are protected from corrosion.72 Fabrication and installation of floating drum digesters requires technicians who are well trained and fairly experienced technical workers. There are kits that can be installed by the end user, with instructions to guide the installation, and that could significantly reduce costs. However, this installation still requires pre-existing technical knowledge to self-build.73 The Shenzhen Puxin Science & Technology Co. Ltd. has developed a variation of this floating drum concept intended to simplify the construction process while also improving quality and standardization of the digesters. The company markets a product composed of a number of steel molding boards, used to construct a poured concrete digester. According to the company’s website, the molds allow a 6 or 10 m3 Puxin biogas digester to be built within 48 hours. The steel mold can be reused over 2000 times and lasts over ten years. It is easy to build the concrete digester, as the workers do not need a blueprint, and require only limited training to work with the steel mold. The other key component marketed by the company is a glass fiber reinforced plastic gasholder that serves as the floating drum, to collect and store the biogas produced in the digester. The gasholder has a volume of 1.0 m3 (for 6m3 plant) or 1.2 m3 (for 10m3 plant) and can last over 10 years. Compared traditional fixed and floating dome designs the company advertises that this design is easy to build with a 100% success rate, requires no skilled labor, is less likely to leak throughout the life of the plant, and can be built in much less time – 2 days compared to up to 15 days, with leak testing and repairs, for a traditional fixed dome design. Because the digester is cast concrete, the durability and maintenance issues are less of a problem.74 Plastic tubular digester: The bag digester was developed in the 60’s in Taiwan to solve the problem of high costs experienced with brick, concrete and metal digesters. The first designs used nylon and neoprene but they proved relatively costly. In the 1970s, poly vinyl chloride (PVC) was combined with the residue from aluminum refineries to produce the product named "red mud PVC". This was later replaced by less costly polyethylene which is now the most common material used in Latin America, Asia and Africa. The tubular digester is basically a long cylindrical polyethylene or PVC bag, half-buried longitudinally in the ground, fed with fresh cow dung slurry at one end and discharged at the other. Figure xx shows a plastic tubular digester and its integration into a rural farm system. With the formation of gas, the bag swells like a balloon and the gas is led out to the point of use through a pipe by putting pressure on the balloon from outside. The gas can be stored in a reservoir after leaving the digester. Gas storage reservoirs can be large plastic bags or more substantial vessels, like a floating drum tank.

72 Biogas for a Better Life, 2007a 73 Ibid. 74 Shenzhen Puxin, 2008


5

While the polyethylene bags are much cheaper than the above designs, they are also less durable and certain parts can require replacement every 2-3 years. Experience has shown that a bag digester could be successful where materials and fabrication facilities are easily available, and with the right design and quality control. 75 In Vietnam, and several other developing countries (including India, Colombia, Ethiopia, Tanzania, Cambodia and Bangladesh) this digester has been promoted to reduce production cost, utilize local materials and simplify installation and operation. The low-cost digester has been well received by poor farmers, especially when farmers participate fully in the necessary maintenance and repair work. In the Vietnam program, in less than ten years, over 20,000 polyethylene digesters were installed and mainly paid by the farmers themselves76.

Figure 5: Low-cost plastic tubular biodigester77

Tanzania a UNDP funded project is promoting polyethylene bag digesters and has worked with farmers to install more than 1000 such systems.78 The digester design produces gas for cooking and lighting for a household and can be installed in about 4 hours by a trained technician with local labor support. The digester requires the excreta from 1-2 cows, 5-8 pigs or 4 able-bodied people on a daily basis as well as an adequate water supply, ideally operating on 2 parts water for one part manure. Interestingly, this project has connected with an existing program, “Heifer-in-Trust,” under which a farmer is loaned an in-calf heifer, and agrees to give the first two female 75 GEF Egypt 2008. 76 Ho, 2005 77 An, et al, 1994 78 SGP, 2001


6

calves to neighbors. UNDP project has trained 50 technicians in Uganda as well as in Tanzania to install and repair biogas systems, but still identifies the scarcity of adequately trained technicians as a technical barrier limiting the rate at which digesters can be disseminated. Other opportunities for improving the technology, such as integrating rain water harvesting with biogas systems, improving durability, and developing an improved biogas-powered lighting system have been identified and are being addressed. In Kenya, a recent study79 found that success rates for tubular bag digesters have been low to date. In 2006 a Kenyan plastics company adapted international designs and started manufacturing and selling UV treated, pressure resistant plastic tubular digesters of between 9 m3 and 18 m3. Since then, about 200 units have been installed countrywide. The study found that although the technology seems simple and quick to install and use there are complex technical issues that must be addressed during installation, use and maintenance. Four of the five digesters actually visited had some technical or operational problems. These problems were easily solved by trained personnel, but point to the need to review the technology and technical support system. The digester performance also seems to vary with effects of temperature more than other household scale digesters that are fully buried underground.

A modification of the low-cost plastic biodigester system to help the durability of the digestion chamber involves constructing it from bricks and concrete. The design is a cross between an underground fixed dome (Chinese) model and a plastic-bag model. The main digestion chamber is a rectangular (flat-topped) low-depth underground concrete tank. There is no pre-digestion/ mixing chamber, but instead a siphon-type input with active and continuous scum-breaking action is used.80 This design has not had widespread deployment and needs further study. Another interesting design, the “Horizontal biogas digester,” operates in a very similar manner as the polyethylene tubular digester. It is really a slightly inclined cylinder that can be constructed by welding together 3 or more 200 liter drums with the lids and bottoms removed from the drums except on the 2 ends. Manure slurry is introduced on the upper end and the effluent flows out of the lower end. Gas is extracted through a pipe at the topmost point of the digester and collected in a storage container that could be a flexible bladder or a more substantial vessel such as a floating drum container. This is an inclined plane continuous flow digester. Organic material that is entered into the upper end of the digester exits the lower end. When fed 2% of its volume per day, the process takes about 50 days for a volume to pass through. During this process, about 50% of the carbon in the material is converted into methane and carbon dioxide81. This design can be also constructed at very low cost and may be more durable than the plastic digesters. All of these designs are fed semi-continuously (e.g., once a day). There are small scale digesters that operate in a “batch mode”, filled once and then left to produce gas until the methanogenesis process is complete then emptied and refilled. These have not been used in any significant

79 Biogas for a Better Life, 2007a. 80 GEF Egypt, 2008 81 Forst, 2002


7

programs with dairy manure82. Many other designs or variations have also been developed but those described above are considered the most appropriate for the Manica Province program. Biogas digesters are usually built underground to protect them from temperature variations and also to prevent accidental damage. The exception is the plastic tubular digesters that are not completely buried and hence more affected by temperature and exposed to damage. Typically, in developing nations, biogas digesters are constructed in a pit which is excavated by a trained laborer with assistance from one or more members of the household or community. Digester Sizing It is important to correctly size a digester in order to obtain the maximum biogas production per unit of reactor volume while maintaining low capital construction costs. For larger plants (e.g. for 400 or more cattle), a number of empirically based calculation methods are available but small family-size digesters have primarily relied on sizing tables based on long experience with trial and error. Tables 3 and 4 below are from the Nepalese Construction Manual for the GGC 2047 Fixed Dome Digester, published in 1994 and an updated training manual from this program released in 2003. This sizing information has proven reliable for many years and is still reproduced and recommended in technical reports on biogas digesters.83

Table 3

S.N. Size of Plant m3

Daily Fresh Dung (kg)

Daily Water Liters

Approx. No. Cattle Required

1. 4 24 24 2 - 3 2. 6 36 36 3 – 4 3. 8 48 48 4 – 6 4. 10 60 60 6 – 9 5. 15 90 90 9 – 14 6. 20 120 120 14 and more

* Plant size is the sum of digester volume and gas storage ** Based on a hydraulic retention time of 70 days

(Source: Bajgain, 1994 )

Table 4: Size, volume and gas production of fixed dome plant

82 USAID, 2007 83 USAID, 2007


8

Size (cum) Digester Gas storage Daily dung Retention Gas production/ vol.(Cum) vol. (Cum) feeding (kg) time (Day) day (Cum)

4 2.8 1.2 25 80 1.4 6 4.4 1.7 40 75 1.8 8 5.8 2.2 48 83 2.2

(Source Devkota, 2003)

One concern in all digesters is under loading (from oversizing the digester, or disruption of the flow of inputs). The construction manual for the Nepalese GGC 2047 fixed dome digester cautions: “If a plant is underfed, the gas production will be low; in this case, the pressure of the gas might not be sufficient to displace the slurry in the outlet chamber. This means that amount of slurry fed into the digester is more than the amount of slurry thrown out from the outlet. This will cause the slurry level to rise in the digester; gasholder and it may eventually enter to the gas pipe and sometimes, to the gas stove and lamp while opening the main valve.”84 While the mechanisms may be different, all of the digester designs will perform poorly if they are built significantly too large for the manure supply, or for any reason are loaded at substantially less than the design input. On the other hand, it is also a concern if the digester is overloaded so that the slurry moves through the chamber too quickly. According to a recent USAID report: “Optimal gas production per m3 however, must allow a margin of safety in size, equal to several days’ additional retention beyond “optimum”, to ensure viable growth for the methanogenic microbes... and must be large enough to avoid “washout.”85 If the quantity of methanogenic bacteria carried out of the digester with the effluent flow is greater than the their growth rate inside the digester then this will “wash out” the population of bacteria in the digester and slow the methane production process. Before deciding the size of any biogas digester no matter which design, it is necessary to collect dung for several days to determine the average daily dung production. The amount of dung daily available helps in determining the capacity of the plant. The key point is that the size of plant has to be based on the amount of available dung as input not on the family size or desired gas output. This report provides rules of thumb for various sizes and digester types as a starting point for initial design, but the program will need carry out demonstrations and carefully monitor their performance to develop a clear understanding of the combinations of number of cows, size and type of digesters and other factors that will lead to consistently successful results in the Manica Province conditions. Based on the results of data collection and testing, the program will develop an understanding of whether a single well-managed dairy cow will provide sufficient manure to support a biogas digester sized to provide cooking and lighting for a household. If not, some households may still 84 Bajgain, 1994 85 USAID, 2007


9

be able to purchase and install the system at their house if they own other livestock, and they could then, using the manure from their own livestock, use the effluent on their own land and use the gas in their own kitchen. There may also be some cases where two or more households may “pool” their resources (manure) for a single digester and will have to agree on how to divide the effluent and the gas among the participating households. Some experts suggest that energy for cooking and some lighting for a typical rural family in a developing country would require a minimum of 1 m3 biogas/day.86 Other estimates of gas required for cooking -- 0.3- 0.4m3/day/person – and for lighting -- 0.10-0.12M3/hr/100candle power light -- suggest that this requirement could be between 1 and 2 m3/day.87 The literature on small scale household digesters, offers a range of estimates of manure and biogas production per cow. Most of these estimates are toward the lower end of the overall range as might be expected given issues of lower quality feed, incomplete collection of manure and digester performance in small scale, developing country situations. There are some technical sources88 that suggest that a single cow might provide sufficient manure and urine to produce 1 m3 biogas/day. Several sources 89 suggest that 2 cows are a minimum while others90 argue that 4 or more cows are necessary to ensure support for a family’s biogas needs. The higher numbers of cows needed for a household digester assume use of the widely practiced livestock management system, where cattle feed widely in communal areas during the day and are only penned (corralled) at night so that only a fraction of the total manure is collected. As noted above, biogas includes trace elements that can create problems in some gas using equipment. Most household biogas systems assume that cookstoves and other simple household equipment will not require biogas cleaning, but there are simple designs for gas cleaning that can be added if this turns out to be necessary.91 Economics of Household Digesters Costs: There are a large range of estimates of the cost of construction of a digester sufficient to supply the cooking and lighting needs of a household – depending on the design, size, materials, location, etc. It is generally agreed that the fixed and floating dome designs are more costly that the plastic tube option – although they have much longer lifetimes. Costs have been reduced as designs have been standardized and improved through the 1980s and 1990s.92

86 Kangmin and Ho, 2006 87 TNAU, 2008 88 Last, 2007, Brown, 2006, 89 F orst, 2002, Biogas for a Better Life. 2007 90 Biogas for a Better Life, 2008 91 See Forst, 2002 e.g. 92 BCAS, 2006


10

Recent estimates of the cost of a digester sufficient for a household’s cooking and lighting needs are around $260 in China93 and $200-250 in India,94 $250-390 in Nepal,95 and $200 in Vietnam.96 In Africa, recent estimates of costs for the same designs and sizes are much higher. A recent GEF project document97 estimates that the cost of either fixed or floating dome digesters in Egypt would be about $90/m3. This would be $540 for a 6m3 digester and $720 for 8m3. In 2007 and 2008 several researchers associated with the Biogas Africa Initiative estimated costs for a 6 m3 fixed dome digester in South Africa at $900-1150, Rwanda at $860, Uganda at $770-1000 and Kenya at $575.98 The differences in cost are most importantly due to the estimated local costs of materials – cement, brick, piping – which can be 4 times higher, or more, in African countries. Labor costs are also somewhat higher in the African countries. Some of this cost difference can be explained by the difference in cost for locally manufactured materials in Asia versus those imported into Africa. Indeed some of the highest cost estimates include significant import duties and VAT that raise the delivered cost of materials. Some of the labor costs are also valuation of in-kind labor contributions of participating households. Some of the differences may also be due to exchange rates at the times of the calculations. If programs like the Biogas Africa Initiative are successful at promoting widespread deployment of manure biogas technologies, it is possible that typical costs of digester installation can come down substantially over time. If a substantial biogas industry develops, cost may come down over time due to local manufacture of materials and scale economies. A combination of government policy, technology improvements, and other measures will also help to encourage a growing market and lower costs. However, it appears likely that, in the near term, construction of household scale fixed or floating dome digesters in Manica Province will cost a minimum of $500-600 out of pocket. Plastic tubular digesters are less expensive and easier to install. In Vietnam, costs have been reported to be $40 or less for a full system (materials only).99 In Tanzania, different projects have estimated total costs including installation at $100 or less.100 This is clearly much more manageable for small farmers in terms of up-front costs. In Kenya, a locally manufactured plastic bag digester is sold at around $400 for an 8 m3 digester, possibly over $500 with installation. The key issue with the plastic digesters is how long they will last and how much maintenance and operation is required. Cost Benefit Analysis: From the point of view of a small holder who might invest in a digester, there are two products - biogas and fertilizer – that can yield quantified monetary benefits. There

93 Greengadget, 2008 94 Last, 2008, TNAU, 2008 95 Ashden, 2005 96 Biogas for a Better Life, 2007a 97 GEF Egypt 2008 98 South Africa and Rwanda, Biogas for a Better Life 2008; Uganda and Kenya, Biogas for a Better Life 2007a 99 An, et al., 1996 100 Brown, 2006, SGP 2001


11

are different approaches for the evaluation of these products of the biogas plant, but a fairly straightforward one is to use the value of products for which these substitute. The gas should be valued at the cost of fuels for which it substitute. In cooking it may be compared with firewood, butane, charcoal or possibly with dried dung. In lighting it may be compared with kerosene or candles. For example, box xx shows some sample calculations created by researchers in India.101 This example estimates annual energy and fertilizer benefits of over 15,000 rupees (over $300), from 3 m3 fixed dome digester that costs Rs. 12000 (about $250). The benefit cost ratio is 15, 608.05/1954 = 7.99. In this example, the critical component of the benefit is the avoided firewood cost so the result would be very sensitive to the cost of firewood and whether the individual farmer actually purchases all of his cooking fuel or if some or all of it is collected by family members. If dung is used directly for cooking fuel it is difficult to get monetary values but there are still clear benefits. 12.3 kg of dried dung cakes is equivalent to 61.5 kg wet dung, assuming 20 per cent solids in the wet dung. If this dung were processed in a gas plant, it would be expected to produce 2 m3 of gas (calorific value about 20 MJ/m3) which is double the amount of heat obtained from the dung cakes (calorific value about 8.8 MJ/kg), taking into account the efficiency of the biogas stove which is about 60 per cent in comparison to the efficiency of the cattle dung stove (open hearth) which is usually less than 10 per cent. 12.3 x 8.8 = 108.24 MJ energy from dung x 0.10 eff = 10.8MJ energy from dung. 20 x 2 = 40 MJ energy from Biogas x 0.60 eff = 24 MJ energy from biogas. So the biogas would provide more than twice the energy value of dried dung plus the full value of the fertilizer. When the dung is burned of course there would be none available for fertilizer. The quality of life and health benefits would be very large also in this case, although they are not able to be expressed in monetary terms for the farmers. A study in South Africa102 provides some detailed data on cooking fuels and costs among the rural poor in 3 provinces in that country. Based on data from a household statistical survey on use of 3 fuels – paraffin, LPG and wood – for cooking, it concludes that “in South Africa, many of the poor have to resort to using paraffin or wood” and calculates the average avoided fuel costs per year for a household for the three provinces at ZAR 744 (US$ 106). This is very conservative estimate as the total cooking energy costs indicated by the households which were surveyed is between ZAR 90 and ZAR 172 per month in the three provinces. Fertilizer benefits were estimated at ZAR 285 (US$41)/year. This study uses a cost of $1050 for a 6 m3 fixed dome digester and with loan interest and maintenance cost annualized the internal rate of return is positive, 16% without government subsidies. It is important to note that in this case, monthly loan repayments would exceed current monthly fuel costs for individual farmers. A study in Burkina Faso103 reported typical fuel use for a rural family of 10 people at 5400 kg/year fuel wood, valued at $68, 480 kg/year charcoal, valued at $44, and 36 liters/year of 101 TNAU, 2008

102 Biogas for a Better Life, 2008 103 Gtz, 2007


12

kerosene at $36 for a total of $148/year fuel costs. Capital costs of a 6 m3 fixed dome digester that could substitute biogas for all of these fuels, were calculated at $821 (plus in kind labor). The internal rate of return was calculated using annualized capital and interest plus annual maintenance costs against benefits of energy use for cooking fuel and lighting only for a family of 10 people. This study found a positive but somewhat low IRR of 10.25% in this case. It also considered the benefit of carbon credits under the Clean Development Mechanism (CDM) which raised the IRR to 21.18%. A recent similar analysis in Egypt104 found a 14% IRR for the investment and simple payback of 6.1 years. It should be noted, however, that the results are sensitive to the estimated value of the fertilizers and the value of the fuel the biogas is replacing, namely whether it is LPG, kerosene or a mix of them and what is considered as the real or perceived value added for the reduced need for transporting kerosene or LPG over the distances, which sometimes can add significantly to the final price of these fuels.

104 GEF Egypt, 2008


13

A financial and economic analysis of biogas digesters was carried out recently for the Biogas Africa Initiative which plans to promote biogas digesters in more than 20 countries across the

Box 1: Example of Economic Benefits Researchers in India1 have calculated the values of energy and fertilizer for a household scale digester. Energy value is calculated starting with firewood and kerosene fuel offset per m3 biogas produced based on a number of assumptions:

1. 70 per cent of the gas will be used, instead of wood, for cooking and 30 per cent, instead of kerosene for lighting.

2. the calorific values are biogas (20MJ/m3), kerosene (38 MJ/litre) and firewood (20 MJ/kg), 3. stove efficiencies of 60 per cent for the biogas and 10 per cent for the firewood 4. the same lamp efficiency for biogas and kerosene 5. average cost of Rs.10/litre for kerosene and Rs.3/- kg for firewood 6. the digester produces 3 m3 biogas/day all used for cooking and lighting.

For firewood in cooking 1 kg of firewood contains the same energy as 1 m3 of biogas, but the gas stove is 6 times more efficient than the typical wood stove so 1m3 offsets 6 kg firewood valued at Rs 3/kg or Rs 18. For kerosene in lighting the equivalent values are 38MJ/20MJ or 0.53 litre biogas valued at Rs. 10/litre or Rs. 5.3 offset for each m3 biogas.

From these figures it is easy now to calculate the annual benefits of using biogas instead of kerosene and firewood as follows: Kerosene Rs. 5.30/m3 x 0.9 m3/day (30% of 3 m3/day) x365day = Rs. 1,741.05/year. Firewood Rs. 18/ m3 x 2.1 m3/day (70% of 3 m3/day) x 365 days = Rs. 13,797.00 The total value of biogas as energy is then Rs. 15,538.05 (US$ 318.40)/year. Value of fertilizer in digester effluent in comparison to the raw or the cow dung Assumptions: 1) the fresh dung has initially 0.10% nitrogen; 2) for each m3 of biogas produced 25 kg of cattle dung is used per day (i.e. 9125 kg/year) and 3) commercial urea fertilizer has 46% nitrogen and costs Rs. 3.45/kg The value of 1 kg nitrogen is Rs. 3.45/kg fertilizer divided by .46 (%N) = Rs. 7.50 Annual N in manure is 9125 kg dung at 0.10 per cent nitrogen = 9 kg nitrogen Value of nitrogen in cattle dung for 3 m3/day biogas plant = 9 x 3.0 x 7.50 = Rs. 202.50/year In the current method of making manure (piling the dung for 30 days before use) the manure value of

nitrogen decreases by about 50 per cent. Value of usable nitrogen in dung = 202.50 x 0.5 = Rs. 101.25. If, the new practice of drying the effluent is adopted, then only 15 per cent of the nitrogen will be lost.

Accordingly, the value of nitrogen = 202.50 x 0.85 = Rs. 172.13. The improved nitrogen value of the manure = 172.12 - 101.25 = Rs.70.80/yr Total energy and fertilizer value in this example is Energy Rs. 15,538.05 + fertilizer Rs. 70.80 = Rs.

15,608.05 (US$ 319.85)/year. 1 TNAU 2008


14

continent.105 The outcome was positive, but strongly depended on the price of firewood. Biogas is always a very attractive option from the broad societal or economy-wide perspective, but less so for households. At the macro-economic level, the study found biogas programs to be profitable even when overall program costs are more than 20%. Additional benefits from better health and sanitation are not quantified in these calculations but would add significant benefits from the perspective of society. Other quality of life and productivity benefits from savings of time and effort for fuel gathering, would also accrue to women in particular. At this stage it is possible to look at analyses from other developing countries, especially African countries as indicative of the costs and benefits of household scale digesters in Manica Province. In order to accurately calculate costs and benefits for the Manica Province application it is necessary to collect better data on current energy sources and fertilizer practices and their costs to the farmers. Implementation of Household Digester Programs Financing: Although household biogas digesters are often financially viable on paper from the perspective of individual farmers in developing countries, biogas development on a significant scale has required government financed investment subsidies and/or affordable financing (for construction and/or maintenance of biogas plants) particularly for small and lower-income farmers.106 The initial capital investment is often an insurmountable barrier for poor rural farmers even though the savings will outweigh the costs in a few years. Except for some cases involving the least expensive designs (e.g., plastic tubular digesters in Vietnam) it has generally been deemed necessary and logical for governments or donors to partially subsidize the initial capital costs. The benefits to society far outweigh the costs of subsidies and program support and farmers can be convinced to pay half or more of the cost if financing is available. In China for example, the central government pays half the price of building a $260 fixed dome biogas digester. India provides substantial subsidies through a complicated formula that takes into account location, social grouping and income to ensure that the neediest participants receive the most help from the government.107 The very successful program in Nepal has been used as a model program by experts around the world. The program is managed by a dedicated central government organization, the Biogas Support Programme (BSP). This program administers subsidies to reduce and level the costs of a 6 m3 fixed dome plant – the Nepal GGC 2047 design also used as a model around the world. Construction costs for the plant vary between $250-325 depending on the location of the plant. Additional costs of transporting materials raise the cost for remote, hilly areas. The BSP subsidy program operates on a sliding scale so that each plant owner pays the same amount, equivalent to about $180. One third of the owner contribution is paid in kind, by the family providing labor 105 Biogas for a Better Life, 2007 106 USAID, 2007 107 Gtz, undated


15

and materials, but the remaining $120 is still a significant amount of money for rural Nepali farmers. The participants are willing to pay this amount because they have seen the long-term benefits that these plants have brought to their neighbors. They are also able to finance biogas plants, considered a safe investment in Nepal, where over 80 banks and micro- finance organizations will provide loans. Most families pay back their loan within about eighteen months: those who previously purchased fuelwood will have saved more than the cost of the biogas plant within this time.108 In Tanzania, where a UNDP funded project is promoting low cost plastic tubular digesters, financial barriers still exist in obtaining the biogas systems. Each system costs $100-120 with appliances and installation, and the system more than pays for itself over a short time through income generation and savings on fuel purchase. Nonetheless, this up-front cost represents a large percentage of many farmers’ yearly income. Micro-finance systems have been developed to ensure the spread of this technology. In one region, a women’s organization has established a revolving credit fund with support from the project. Each family contributes a set amount of savings per month, and farmers then can then acquire credit on a revolving basis.109 In the Manica province context, financing through small holder cooperatives seems feasible and could overcome many of the problems that have created problems for other programs. These organizations will be receiving milk from individual farmers and providing payments to these participants based on milk sales. The program concept already envisions that the cooperative would retain a small percentage of the sales revenues from each farmer to cover costs of operation of the Milk Collection Center, medicine and veterinary services as needed, training and other ongoing support services. If the cooperatives were to provide or guarantee loans for the installation of biogas digesters this mechanism could be used to collect monthly payments from individual farmers. It will be important to carry out detailed financial analysis as the program moves forward to determine whether subsidies to bring down the initial capital cost, as is the case in most successful developing country programs to date, will be appropriate to move the biogas digester penetration to significant levels. Technical and Institutional Issues: A number of previous biogas digester promotion programs, successful and not, have illustrated the need for systematic efforts to identify and overcome a range of possible barriers that could undermine long term program success. Appropriate technology and financing are two critical prerequisites for success as discussed above but past programs have also identify other technical and institutional barriers to biogas digester deployment and successful operation. In the early stages of India's biogas development programs results were disappointing to some experts. With government incentives such as subsidies and tax benefits to encourage biogas use, a large number of digesters were being installed. In 1995, however, Dr. Rajendra Pachauri, Director of the Tata Energy Research Institute, stated that only two-thirds of the installed plants are actually functioning (although official figures at the time placed this figure at 89 percent).

108 Ashden, 2005 109 SGP, 2001


16

Several technical and institutional problems were undermining the long term use of digesters. The early programs were standardized, and managed top down for the entire country. Across-the-board implementation policies led to the construction of plants in areas unsuited to biogas production. In cooler or drought-prone regions, or in villages with insufficient cattle, projects often failed. Plants that encountered technical difficulties were sometimes abandoned when project technicians failed to follow up. Conventional fuels like diesel, kerosene and LPG were also highly subsidized in rural areas, reducing the incentive to make the switch to biogas or to continue its use in the face of technical difficulties.110 These problems have been addressed through the use of a formula that includes regional location and income in allocating subsidies to individuals, and by decentralized implementation 111now managed by the states and local government organizations. In addition, training and technical support systems have been enhanced, and the Indian program has become one of the world’s successful models. Several programs in Africa have had disappointing past experience with operation of digesters after installation. Tanzania began distributing heavily subsidized concrete and steel digesters costing $1400 each in 1982. By 1991, only a few of these digesters were still in operation.112 Subsequently, the UNDP funded program described above has been more successful by focusing on much less expensive plastic tubular digesters and including more involvement of local organizations and technical support113. In Kenya biogas digesters have been promoted by donors, government and NGOs for fifty years, and trained Kenyan technicians have built hundreds of biogas digesters in the country. Evaluations showed that a high proportion of digesters appear to operate below capacity, are dormant or in disuse after construction because of management, technical, socio-cultural and economic problems. In Egypt, plants have been installed in the past with significant donor support, but without significant follow-up and technical support. Many were later abandoned or found to be operating at low levels. Technical experts visiting some still operating plants were able to increase gas production immediately by 5-6 times through technical improvements.114 Greater investments in training, education and technical support were needed to keep many of the plants operating at satisfactory levels. Lessons learned include the following:115 • Program planning and design: Program planners or promoters need to have a clear

understanding of the purpose, implementation strategy and expected benefits of the program – Why is this a good idea for the society at large? Why is it good for the participants? Are the necessary inputs – e.g., manure and water, construction materials – likely to be available in the require quantities and at acceptable cost? Are there adequate uses/markets for the products – biogas and fertilizer? Program planning needs to address, for example, how to

110 Sampat, 1995 111 GEF Egypt 2008 112 Brown, 2006 113 SGP, 2001 114 GEF Egypt 2008 115 This summary of lessons learned adapted from Biogas for a Better Life 2007a


17

reach customers with marketing, installation and technical follow-up in areas where there are no private and often no public means of transport to potential customers combined with impassable roads.

• Technology design and construction: biogas digesters are not as simple as they look. They

must be properly designed and constructed by a qualified technician(s). The digester must be sized and designed to fit the resources, conditions and needs of the particular location. It is often the case that scarcity of trained technical experts can hamper the ability to scale up programs. Identification and training of sufficient numbers of technicians and verification of availability of materials and construction equipment need to be built into a plan for deployment of digesters. Shortages of trained personnel can result in delays in implementation, and worse, inadequately trained installers may be used leading to failures, operational problems and long term acceptance issues for digesters. A related issue is the need to establish clear standards for technology, materials, certification of technicians, and quality control procedures.

• Education and promotion of technology: Large scale programs to deploy biogas digesters need to pay attention to educating and informing the intended participants and other stakeholders as a part of the program. There is a need for a sustained awareness creation campaign to educate potential users on the uses and benefits of biogas. Where possible this should include some survey, stakeholder consultation, or other research to identify potential acceptance problems, positive features that should be emphasized, and approaches that fit local culture. For example, the re-charging of the digester may be seen as a dirty job and hence leads to poor ownership responsibility by users.116

• Technical Training: Technicians need to be trained in installation, quality of materials and maintenance of digesters. Some certification system should be established if possible so that participants can identify trained technical experts. Installers may also need training on marketing and business management. Farmers should be trained on proper utilization of biogas and correct application of equipment. Digesters are built without proper explanation to users on how to care for them.

• Technical support for operation and maintenance: A lot of proper operation and maintenance is a function of education and training of the owners and local technicians. However, there are inevitably problems that arise that cannot be solved by individual farmer-owners of household scale digesters. In addition, there is a tendency for some participants to become less conscientious over time. With so many competing uses for rural farm labor, management of the digesters can suffer without adequate technical backstopping occurring during further operation. It is a lesson of many successful and failed programs that a network of technical support and monitoring can make a huge difference is the long term benefits of the program.

116 Biogas for a Better Life, 2007a


18

In planning and implementing the Manica Province program, some of these lessons are critically important while others may not be relevant at least in the near term.


1

Appendix C: Milk Collection Center (MCC) Scale Digester Systems MCC Power requirements Some very preliminary calculations provide a rough estimate of the power and manure requirements at an MCC in order to back out the number of cows needed and to suggest the sizing and design of the possible system components. Table C-1 contains some typical power requirements for chillers likely to be used for the MCCs. The first option used is the 500 l chiller. This might be sufficient for the first MCC and additional chillers could be added as the milk collections increase over time. This allows for incremental investment and also for sequencing of the peak demand from multiple chillers to smooth out the load if necessary.

Table C-1 MCC Chiller power requirements

Tank

size (l) Voltage, Freq (phases) Refrigeration

Capacity Watts

Run

current Max

current Run

KVA* Run

kW** Peak

KVA** Peak

kW**

500 220 -240 V, 50 Hz, (S) 2227W, 1.2 Hp 5.99 A 7.26A 1.3777 1.171 1.7424 1.481

1000 220 -240 V, 50 Hz, (S) 5706W, 2,5 Hp 14.1A 26.3A 3.243 2.757 6.312 5.365

1000 380 -400 V, 50 Hz, (3) 5706W, 2.5 Hp 5,.27A 8.1A 3.555+ 3.022 5.605 4.764

1500 220 -240 V, 50 Hz, (S) 7276W, 3 Hp 19.8 A 27A 4.554 3.871 6.48 5.502

1500 380 -400 V, 50 Hz, (3) 7276W, 3 Hp 7.52A 9.21A 5.074 4.313 6.373 5.417

* Run KVA =Middle of voltage range (e.g., 230v or 390v X run current in amps / 1000. ** kW = KVA x .85 power factor *** Peak = highest voltage (240, 400) X peak current in amps/1000 + 3 phase KVA = v X a X 1.73 This assumes that the chiller will be operating at full load for periods of 3 hours when milk deliveries are coming in and milk temperatures need to be lowered to standard levels quickly. The rest of the time that the chiller is on, it is assumed that the cooling components will be coming on intermittently to maintain temperature but not running continuously. The estimate is that this will require 20% of full power on average over long periods. Power needs – 500 liters $100% = 1.2 kW 20%= 0.28 Usage – 10 AM- 1PM = 100% 3hrs 1-4PM = 0 4-7PM = 100% 3hrs 5PM-10AM = 20% 15hrs 6hrs X 1.2= 7.2 kWh + 15hrs X 0.24= 3.6 kWh = Total 10.8 kWh/day Thus to be sure that power needs of one 500 liter cooler and a few other small loads can be met, the digester needs to produce biogas sufficient to generate around 12 kWh/day.


2

For one 1,500 liter cooler on the same duty cycle the MCC would require 6 X 4.3 kW = 25.8 kWh 15 X 0.86 kW = 12.9 kwh Total 38.7 kWh This would imply generation of 40 kWh/day Estimates of electric power production from biogas range from 1.7-2.35 kWh/m3117 due to the quality of biogas, efficiency of conversion technology and other factors. Given the small scale and developing country setting of this program, it is appropriate to use the lower end of the range for these estimates. To produce 14 kWh/day, the digester must provide 12/1.7=8.3 m3 biogas/day. 40 kWh/day would require 40/1.7= 23.5 m3 biogas. Though one 500 liter cooler should be enough to handle milk from a cooperative group of 50-60 farmers each with one cow, it is likely that these MCCs would expand over time and need to receive milk from larger numbers of cows. The Monica Province program staff estimate that an individual farmer with one dairy cow under the expected conditions could deliver up to 8 liters/day to the MCC. This would happen if the farmer manages and feeds his cow well, and delivers all of the milk to the MCC (not holding any out for his own family’s use). Using this value, 50-60 farmers would deliver a maximum of 440-480 liters/day. However, it is envisioned that MCCs could grow over time to support 100 or more farmers, each with at least one cow. It may be a important to plan for possible expansion in the design of an MCC biogas system. One possibility is that an MCC might start with 1 500 liter cooler sufficient to support its first group of 50-60 farmers. Then as the group grows another 500 liter cooler or even 2 could be added over time. Or the MCC could initially install a 500 liter or 1500 liter cooler. Another strategy would be to install a 500 liter cooler at the outset then to swap it for a larger cooler as the cooperative grows and pass on the small one to another MCC starting up. Digester design needs to consider what would be required to support up to 1500 liters of cooling and other small loads. The construction of a digester would definitely be better done only once. One larger digester would be less costly and difficult to construct and operate than two or more smaller digesters. To support an MCC with1500 liter cooling capacity would require roughly 40 kWh/day and 24 -25 m3 biogas/day for either three 500 liter coolers or one 1500 liter cooler. Digester types and sizes Experience with dairy manure biogas digesters of this size is limited, particularly in electric power generation applications. In straightforward investment project evaluation in developed countries, dairy manure projects generally need to be at a larger scale - usually several hundred cows – in order to justify the capital costs of digester and generation equipment. The AgStar Program in the U.S. recommends that dairy farms consider investment in biogas electricity

117 Estimates are from DEFRA 2005: Davies, 2007


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generation if they have 500 head or more118. In Europe smaller scale digesters have been implemented119 (with support of active renewable energy programs and financial incentives) and the AgStar program has more recently supported research on smaller scale diary manure biogas economics120. Nonetheless, there are few projects as small as would be envisioned for the MCC applications in Manica Province. A recent GEF project proposal121 has evaluated community scale anaerobic digestion as an option for Egypt. This evaluation concluded that community digester systems can be very similar to household systems. They will then have more or less the same performance characteristics (manure input, gas yield and fertilizer production per m3 of digester content) as the smaller systems. The reference community scale digester for this evaluation is 130 m3 in volume and fed by roughly 100 cows. The fixed dome digester described in the previous section has proven to be reliable and effective in many successful household scale biogas programs and is currently being promoted in several African countries. The literature from the Nepalese Biogas Promotion Program (BSP),122 provides specifications and instructions for construction of a fixed dome digesters up to a 50 m3 size that is expected to produce at least 15 m3 biogas/day. A community scale fixed dome digester, like the one described for the GEF project in Egypt, at 130 m3 would produce at least 39 m3 biogas/day. Fixed dome household digesters are usually fed with equal amounts of manure and water and use a hydraulic retention time (HRT) of somewhere around 55 days in warm flat areas. Using rules of thumb provided for household scale digesters in appendix B, a fixed dome digester could be developed at a 25 m3 size and should provide at least 9 m3 biogas/day, more than enough for an MCC with one 500 liter cooler. A 25 m3 digester would require about 225 kg manure /day and about 225 liters of water/day as input. A larger fixed dome digester of around 75 m3 should produce at least 25 m3/day and be sufficient to support 1500 liters of cooling capacity and some other electrical loads for the MCC. For a 75 m3 community scale digester, with HRT of 55 days, the manure requirement would be about 675 kg/day with 675 liters of water.

The plastic tubular digester, commonly used at the household scale, described in some detail in the previous section, is a possible low cost approach for the MCC scale. Very inexpensive household scale tubular plastic biogas digesters have been installed in many countries, in recent 118 US AgStar Handbook: The first screening criterion listed: “Is Your Confined Livestock Facility (Dairy or Hog) “Large”? For screening purposes, livestock facilities with at least 500 head of dairy cows/steers or 2,000 sows or feeder pigs in confinement, where at least 90 percent of the manure is collected regularly, are potential candidates. Facilities of this size produce enough manure to generate the biogas required to support a financially viable project. It should be noted, however, that this size criterion is not absolute. Smaller confined facilities could potentially support successful recovery projects, given certain site-‐specific and market conditions. “ 119 Harold K. House, 2006. 120 Philip R. Goodrich. 2005. 121 GEF Egypt, 2008 122 Devkota, 2003


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years -- e.g., 800 plastic digesters were installed in Viet Nam in 3 years. These digesters have a volume of about 5 m3 and cost under $100 USD. They are generally fabricated on site by installers using commonly available polyethylene sheeting. No examples of plastic tubular digesters of this design at sizes needed to support an MCC have been found, but this is theoretically possible. The concerns about plastic tubular digesters are durability and possible operational problems.

Since 2006, a Kenyan company, Pioneer Technologies, Ltd., has been manufacturing and selling an improved, UV treated, pressure resistant plastic tubular digesters up to 18 m3 capacity. To support an MCC, a higher quality product would be advisable, so the assuming the costs of manufactured, heavy duty models from Kenya seems to be the safer option. The 8.5 m3 biogas/day required for a small MCC could be provided by installing two 18 m3 plastic tubular digesters. With a retention time of 55 days, 36 m3 total volume would require about 220kg manure and 440 liters of water/day.

It is not clear that scaling this design up to the large MCC size would make sense. Certainly the logical approach for the Manica Province program to this technology would be to start with the smaller design and get information on its performance before making decisions about larger scale applications. If this is determined to be an attractive technology, additional 18 m3 units could be added incrementally. Another approach that has been proposed is to scale down a design that is normally used in projects for large (at least 200 cows) dairy farms. There are two farm-scale digester designs that could be considered for the MCC applications – plug flow digester and covered anaerobic lagoon. The plug flow digester is commonly used in the large dairy applications where manure is collected is by scraping and is fed into the digester in near “as excreted” condition, with about 10-13% solids. This type of digester is heated so that the methanogenesis process is relatively rapid and HRT is relatively low about 20-30 days. Because it takes less diluted manure as input and has a lower HRT, this is the most compact of the designs considered here. It is somewhat more to expensive and complex to construct and operate as it requires heating of the digester and premixing of the manure prior to the input to the digester. A typical design for a plug-flow system includes a manure collection system, a mixing pit and the digester itself. The liquids and solids from the dairy cows are scraped to a collection pit at least twice per day. A prop type mixer is used to agitate the manure, then a pump loads manure into the digester. In the mixing pit, the addition of water adjusts the proportion of solids in the manure slurry to the optimal consistency. The digester is a long, rectangular container, often built below-grade, with an airtight, expandable cover. New material added to the tank at one end pushes older material to the opposite end. Coarse solids in ruminant manure form a viscous material as they are digested, limiting solids separation in the digester tank. As a result, the material flows through the tank in a "plug." Anaerobic digestion of the manure slurry releases biogas as the material flows through the digester. The flexible, impermeable cover on the digester traps the gas. Inside the digester, suspended heating pipes allow hot water to circulate. The hot water heats the digester to keep the slurry at 25°C to 40°C (77°F to 104°F), a


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temperature range suitable for methane-producing bacteria. The hot water can come from recovered waste heat from an engine generator fueled with digester gas or from burning digester gas directly in a boiler. A 70 m3 plug flow digester has been proposed to provide biogas for power generation and heat in Bangladesh.123 A unit of this size, heated to 40oC, with a typical HRT of 20 days, would require at least 3 tones of manure/day as input and could produce at least 70 m3 biogas/day. A large plug flow digester in the US can produce 1.5 m3 biogas/m3 of digester volume124. If a 70 m3 digester in a developing country could approach this efficiency it would produce over 100 m3/day of biogas more than four times what would be needed for a large MCC. To support a large MCC, a plug flow digester of roughly 18 m3 could produce more than 24 m3 of biogas/day. With a design retention time of 20 days, the digester would require about 900 liters input/day of manure mixed with small amounts of water, say 800 kg manure. Because of the complexity and cost, a plug flow digester would probably not be an attractive option for any smaller size than this, so it has not been evaluated for the small MCC, 8-9 m3 biogas/day scale. A covered anaerobic lagoon is the least expensive and most easily operated of the large digester designs but requires considerable area, and water input. The waste is washed into the lagoon by flushing the animal pens with water. Solid waste, particularly the fibrous type of cows, is sometimes separated before the wastewater enters the lagoon to prevent the buildup of solid material. Anaerobic organisms naturally present in the manure and the environment decompose the waste in the anaerobic conditions of the lagoon. Anaerobic lagoons have a longer hydraulic retention time (about 40 days) and are generally slightly less efficient in converting manure to biogas. The lower efficiency is less of an issue in tropical climates, where temperature remains high enough for anaerobic bacteria to function well all year round without heating. The covered anaerobic lagoon volume required is calculated for 8.5 and 24m3 biogas/day to cover the range of possible MCC scale options. For anaerobic lagoons the size is determined by the daily loading volume times the hydraulic retention time (HRT). A typical HRT for an lagoon is 40 days. An anaerobic lagoon is best suited for organic wastes with a total solid concentration of 0.5%-3%. To dilute manure, with 12 % solids as excreted, 3-11 times the volume of waste water from the MCC would need to be added (dilute 12% solids to 3 - 1% solids). A lagoon with volume of around 150 m3 with would produce about 8.5 m3 biogas/day, sufficient to support the small MCC. With a 40 day retention time this would require daily flow of 3.6 m3/day at 1% solids this would be equivalent to 340 kg manure/day. This would require a minimum of 1000 liters/day to dilute the slurry to 3% solids and 3800 liters to dilute to 1% solids.

123 Khan, 124 Nelson and Lamb, 2002; Kramer 2008


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A lagoon of roughly 450 m3 would produce about 24 m3 biogas/day for a large MCC with 1500 liters of milk cooling capacity. With HRT of 40 days, this size lagoon would require about 4 m3 input flow/day at 1% solids this would be equivalent to 950 kg manure/day. A minimum depth of two meters is necessary for anaerobic conditions, but the depth should not exceed 6 meters. Sometimes a secondary lagoon is used to accept wastes while the primary lagoon is undergoing maintenance or for other purposes. For the small MCC size, a lagoon of 3 m depth would require a surface area of 50m, e.g., 5 m by 10 m. For the large MCC size a lagoon of 4 m depth, would need an area of 112.5 m – e.g., 8m by 14 m. A lagoon may possibly be appropriate for MCCs as extra water will be used to clean equipment and facilities daily between milk pickup and late afternoon deliveries so extra water along with some organic waste from cleaning will be readily available. It would only make sense for an MCC application if the operations of the facility produced large amounts of waste water or if the manure is flushed into a collection system, and if the site has plenty of space. The amount of wastewater that would be generated daily by normal operation of the MCC is a critical input to this analysis and should be verified through measurement after the first MCC is in operation, before moving toward this option. Number of cows needed This analysis assumes that the cows feeding an MCC digester(s) will be located at the MCC. Transporting manure is much more cumbersome and difficult than modest amounts of milk. It may be technically feasible, but does not seem attractive as a sustainable model for replication. In developed countries centralized digesters and power generation projects are being developed at a very large scale where substantial amounts of manure are transported by truck to central facilities.125 This model is clearly not appropriate to the scale and conditions of the MCC. There are not many examples to be found of successful projects involving manure transport at the MCC scale and in developing countries. One interesting exception is a proposed Global Environment Facility (GEF) project to promote biomass energy in Egypt126. Among other technologies, this project is proposing to promote community scale biodigesters in the 100 cow size range, where dispersed farmers would bring manure to the central digester and pick up fertilizer for their own use. The project document does not give much detail on how this would work, but it is worth watching to see if this can be successful. At some future point, the Manica Province program may want to reconsider this approach at the MCC scale. The estimates of production of biogas per cow feeding a digester system are quite variable – ranging from 0.5 to 2.8 m3/cow/day. This makes it difficult to determine the size of digester to install for a given number of cows. Or, as in the case of the MCC scale digester, as the amount of biogas needed is roughly known and it is difficult to estimate the number of cows needed to produce this level of output for different types of digesters. 125 AgStar Handbook, 126 GEF Egypt Project Document, 2008


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Several design documents aimed at smaller scale digesters give estimates in the range of 0.65-1.4 m3/cow/day.127 The ranges are primarily due to variations in the amount of manure produced per cow, the percent of manure actually collected and fed into the digester, and the effectiveness of the digester in converting volatile solids in the manure to biogas. The largest source of variability in this range is the amount of manure that is fed into the digester per cow. For milking cows in developed country situations a figure of 50kg manure/cow/day might be appropriate, where virtually all of the manure is collected and used in the digester. 20-25 kg/cow/day is usually the lower end of the range used in the industrialized world.

Table C-2: Estimates of manure and cows needed to feed MCC digesters Type Manure input for

small MCC Cows needed for

small MCC Manure input for

large MCC Cows needed

for large MCC Fixed Dome 225kg/day 9-19 675kg/day 27-56

Plastic Tubular 220kg/day 9-19 Plug Flow 800kg/day 32-67 Anaerobic

Covered Lagoon 340 kg/day 13-29 950 kg/day 38-79

Biogas programs in developing countries use still lower figures, around 10-12 kg/cow/day.128 These developing country rules of thumb appear to be general estimates that represent the average breed, management and feeding practices and include dairy and non-dairy cows. It is likely, therefore that the manure production of the cows distributed by the Manica Province project will be somewhat higher. These cows will be a more productive breed and will be managed and fed in ways that will produce more milk than average dairy cows. Milk production is proportional to manure production and the cows will likely be managed at the MCC so that a higher proportion of the excreted manure will be captured than is normally the case in developing countries. Based on all of these factors one would expect that the daily manure input to the digester per cow would be somewhere between the developing country rule of thumb and the typical figures for dairies in the industrialized world. The range of 12-25kg manure/cow/day should capture the reasonable expectations for assessment of digester options for the MCC scale. Table C-2 provides estimates of cows needed based on estimated manure requirements of the different digester design options considered. The good news is that the variability is primarily due to how much manure on average makes it from one cow into the digester. Manure production can and should be collected on site and carefully measured before final decisions are made on size of digester and number of cows. This is true for any digester design. Rather than rules of thumb, the digester design can be adjusted to match actual manure available for a particular site and number of cows.

127 Defra, 2005; Practically Green Environmental Services. 2008, FACE 2008. 128 Bajgain, 2003


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As discussed above, it may be necessary to clean the gas before it goes to a power generator. The hydrogen sulfide (H2S) in particular, present in small amounts in biogas can form sulfuric acid in the combustion process and damage equipment. Testing of the actual composition of produced biogas and consultation with equipment suppliers will determine whether cleanup is needed. If so, there are several simple scrubbing technologies that can be built into the digester system design or purchased commercially. Electricity Generator For the MCC scale the primary generation option would be an internal combustion (IC) engine generator. Reciprocating engines drive the vast majority of on-site generation. They are mass-produced by many manufacturers around the world, cost less than other distributed generation technologies, and have a fully developed sales, maintenance, and repair infrastructure. All of these factors, combined with market familiarity, decreasing exhaust emissions, extended service intervals, and long engine life, continue to make reciprocating engines the most commonly used technology. Often in agricultural systems, a standard diesel or spark engine is modified to burn the biogas to turn a generator to produce electricity. A biogas fueled engine generator will normally convert 18 - 25 percent of the biogas energy to electricity, depending on engine design and load factor. Gas treatment my or may not be needed as described earlier. Dual-fuel engines are growing in popularity. These units use a small amount of diesel for start-up and then run on natural gas. Emissions are reduced nearly to the level of natural gas engines. These units can be operated on 100 percent diesel fuel at times when natural gas is not available. A number of engine manufacturers make dual-fuel units, and existing diesel gensets can also be retrofitted to dual-fuel at a reasonable cost.129 A Stirling engine generator is another option that has been proposed for small scale distributed generation in developing country applications. A Free Piston Stirling engine has logistic benefits with external combustion of biogas and also is somewhat more efficient. However, this technology is likely to be significantly more expensive and sales and service are less likely to be readily available in rural areas of developing countries. 130 A 2-5kW IC engine generator set would be a reliable and least cost option for generating electricity to power the MCCs. A dual-fuel biogas/diesel generator set would be recommended so that diesel would be available as back up if there should be a temporary disruption of the biogas supply. A 2-3 kW genset would be capable of supplying the power needed for the small MCC configuration while a 5 kW size would support a large MCC. Economics of MCC System Cost of biogas electricity system 129E Source, 2006. 130 Khan, 2007; E Source, 2006.


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One estimate of cost for constructing a community scale digester, using household scale designs such as the Nepalese fixed dome, is that the household scale costs roughly $90 per m3 and with economies of scale this would go down to $70/m3 for a 130 m3 digester.131 These numbers represent a mid range estimate for fixed dome digester construction costs. Some estimates in Asia are as low as $60-65 m3 for a household scale digester, while some African countries estimate $140-170/m3 for the same design.132 For the MCC possible sizes – 25 m3 and 75 m3 – a range of $75-85/m3 seems appropriate. A 25 m3 digester producing 8.5 m3 biogas/day would require an investment of $1875 – 2125, and a large MCC digester of 75m3 producing over 25 m3 biogas/day would require $5625 – 6275.

The retail price for the 18m3 plastic tubular digester in Kenya is at least $600, but could be higher with costs associated for installation, including some form of protection over the plastic bag. Household scale programs in Asia and elsewhere133 have reported costs of under $100 for digesters about one third this size. To support an MCC, a higher quality product would be advisable, so the Kenyan cost numbers are probably more appropriate for the Manica Province program. The 8.5 m3 biogas/day required for a small MCC could be provided by installing two 18 m3 plastic tubular digesters, costing $1200-1300.

In the US small plug flow digester estimated investment costs are rarely less that $1000/m3 of digester volume. 134 This would require an investment of $18,000 for a unit to support the large MCC. Even if costs in a developing country can be reduced (and this is not necessarily the case for a relatively advanced technology not widely used in Africa) the cost would still be very high for the MCC application. Covered anaerobic lagoons are the least costly large scale design in industrialized countries. The metric of $/m3 of volume is not appropriate for this technology as the lagoon volume could vary dramatically across the range of solids concentrations (0.5-3%) that could be encountered at different digester sites. A more useful measure is $/cow input to the lagoon. Lagoons in the U. S. typically require investment of $100-200/cow135. Applying this rule of thumb to the sizes required for the MCC application yields $1200 – 5800 for a small MCC digester and $3800 – 15,800 for a large MCC. While this range is very large and suggests caution and considerable further study before any decision, it does also suggest that at the lower end of the cost range, with careful design and management, an anaerobic lagoon could be roughly equivalent in cost per m3 biogas provided to the scaled up household scale technologies – fixed dome and plastic tubular digesters. The primary concerns about the anaerobic lagoon technology are the need for large amounts of water and the land area required.

131 USAID, 2007 132 Greengadget, 2008 ,estimates for China; Ashden, 2005 for Nepal; Biogas for a Better Life, 2007a estimates for Rwanda and South Africa. 133 Columbia, Ethiopia, Tanzania, Viet Nam, Cambodia and Bangladesh are documented in An, et al., 1996 134 Goodrich, 2005; USDA, 2007. 135 USDA, 2007


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For power generation, reciprocating engine generator sets for heavy duty use (as opposed to standby use) are available as small as 1 kW and are estimated to cost $500-1,000/kW136 For purposes of this assessment $1,000/kW is a reasonable first approximation of cost. So a generator would cost $2,000-3,000 for a small MCC configuration and $5,000 for the large size. Total cost, including digester construction and purchase of a generator set, for a small MCC would be at minimum $4,000-6,000 to produce 12 kWh/day and $11,000 – 15,000 for the large MCC scale. These are very preliminary numbers and need to refined through collection of better data, more detailed analysis, and actual demonstration and measurement. They are a starting point for considering the overall economics of biogas power generation for the milk collection centers in the Manica Province program. Benefit Cost Analysis The financial analysis of the MCC biogas/power options is complicated. The primary benefit is the cost of avoided electricity. There is great uncertainty about the cost of digesters at this scale and some questions about the incremental cost of the biogas option relative to an uncertain baseline of MCC cost without biogas. What values to use for electricity and fuels replaced by the biogas is also a question. For example using a recent analysis of a proposed community scale biogas digester in Egypt used a subsidized power price of $0.03/kWh and also a more realistic marginal cost based price of $0.09/kWh. This makes a huge difference in the financial viability of a community scale digester and power generation project. At the lower price the project is not viable but at the higher commercial tariff which might be obtained directly from the targeted customers, the IRR is 7% and a simple payback period is 9.1 years. A recent report from the African Development Bank (AFDB) stated that the national average electricity tariff for Mozambique was equivalent to $0.08/kWh, while the while the long run marginal cost was $0.091/kWh.137 This means that electricity prices on average are lower than cost, or subsidized. The report also indicates that there are different tariffs for different geographical regions and different classes of customers that include substantial cross subsidies. The actual price paid by a residential or commercial customer could vary significantly from the national average. The other value that can be used is the avoided cost of diesel fuel which would be the typical fuel for back-up power when grid power is not available. In the Egypt study, substitution of biogas for diesel provided a positive IRR of 8% and simple payback of 8.6 years even with a low government subsidized diesel price. With an unsubsidized diesel price or by providing a similar subsidy for biogas, the IRR would jump to 30% with a simple payback of 3 years. For the MCC applications in Manica Province, there are several factors that are specific to this location and application. The actual power and fuel prices of course need to be determined and used for a credible calculation. In addition, because of the nature of the MCC electricity demand the generator will not be used at full load most of the time. Generally in a biogas power project, the

136 E Source 2007 137 AFDB, 2007


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financial logic is to size the generator so that it can run at near full load as much of the time as possible, so that the capital costs can be spread across as many kWh of power produced as possible. In the MCC case, a key objective is to limit the number of cows that will need to be located at the MCC to support the digester. Plus the duty cycle expected for the milk cooling equipment inherently results in a small amount of time where the load will require near full load of the generator, and many hours of low load. Finally, the scale of this project is smaller than most commercial biogas power project and this also makes it more difficult for the project to be financially viable. As a result one would expect that this overall investment project would be less attractive than other biogas power projects. The small MCC system is sized to produce 12 kWh/day or 4380 kWh/year. Using the national average price of $0.08/kWh this would generate savings of $350.40/year from electric power not purchased from the grid. The large MCC system would generate savings 40 kWh/day or 14,600kWh/year. At $0.08/kWh this would save $1168 in a year. Capital costs are $4,000-6,000 to produce 12 kWh/day and 11,000 – 15,000 for the large MCC scale. For this simple calculation operating costs are not considered although there would certainly be some, but not significant relative to the capital. The Small MCC calculation shows a simple payback of 11.4 – 17.1 years. The large MCC shows 9.4 – 12.8 years. This is basically not attractive as an investment project on strictly financial terms. The avoided cost of power is, of course, higher if the alternative is back up power generated with diesel fuel. Reported national average retail diesel prices in Mozambique fluctuated between $0.43 and $0.79/liter from 2000-2004 and a value of $0.60/liter is about the average.138 A diesel generator produces about 3.2 kWh for each liter of fuel it uses up. Value of avoided fuel use assuming that 100% power would have been from a diesel generator: For the small MCC system - 12 kWh/3.2 = 3.75 liters/day x $0.60 = $2.25 per day = $821.25 per year. The simple payback would be 4.9 – 7.3 years. For the large MCC - 40 kWh/3.2= 10.7 liters/day x $0.60 = 6.42 per day = $2343.30 per year and the simple payback 4.6 – 6.4 years. Clearly the assumption of 100% diesel generator power offset by biogas is not realistic, but rather an upper bound on the financial benefit of the biogas substitution. This might be a useful indicator of the value of a biogas system if an MCC were to be developed in a rural off-grid location in the future. Another way to think about this financial analysis is to assume that the MCC would require a backup diesel generator of roughly equivalent capital cost even without a decision to invest in biogas. A standby generator designed to run much less than full time might be somewhat less costly than what might be required for the biogas system, but not drastically less. Assuming that the generator cost is not counted against the biogas project the costs of the MCC systems would be $2,000-3,000 for a small digester and $6,000-$10,000 for a large system. This would bring the simple paybacks to

138 Metschies, 2005


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Small MCC 5.1 – 8.6 years

Large MCC 4.5 – 22.8 years Another limitation of these preliminary calculations is that they do not include any financial benefit for the high quality fertilizer that will be produced from the biogas digesters. This is clearly a real benefit, but there is not readily available market information that would allow for a quantitative estimate of the value. Of course there are many of the other non-monetary benefits that are discussed in an earlier section of this report – improvements in odor and sanitation, local air quality, greenhouse gas emissions reductions, etc.


1

Appendix D: Diary Scale Digester Systems Digester Type and Design Box D-1 summarizes the digester types most commonly used in large dairy farm operations in the U.S. These are all proven, cost-effective and reliable designs, but the appropriate design for the Evertz Farm/Gouda Gold application is the covered anaerobic digester. This is the least cost design of the four digester types and is suited for low concentrations (less than 3 percent) of solids. It is best suited to dairy farms with flush systems for manure collection like the Evertz Farm flush manure management system and the waste water from the Gouda Gold processing facility. Anaerobic lagoons are perhaps the most trouble free, low maintenance systems available for treatment of animal waste from large dairy farms. A properly designed, constructed and operated anaerobic lagoon is very forgiving and not likely to create emergency situations that can be expected with many alternative waste management systems. Adding methane recovery to the system increases maintenance but even in the event of failure of the gas collection system, it will not interrupt the waste stream and digestion process. The main advantages of covered anaerobic lagoons are the low capital cost compared to other digester types, fairly simple construction design, and ease of management. The disadvantage of covered anaerobic lagoons is the large footprint (land area requirement), solids settling issues, and the dependency of biogas production on climate. Anaerobic lagoons operate at ambient temperature and a principal drawback of this design in the US is that it is not as well suited for cooler climates. This is not a problem in Manica Province.

Figure D-1: Covered Anaerobic Lagoon Digester139

Solids introduced into a lagoon are prone to settle and require removal at some interval because of the large dilution volume and long HRT associated with covered anaerobic lagoons. Appropriate sludge removal intervals will depend on the loading of the lagoon and the

139 Burke, 2002


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concentrations of inorganic solids and indigestible fiber in the wastewater. Nuisance odors may


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Box D-1: Farm Scale Digester Types1

There a few primary types of anaerobic digesters currently in wide use in North America. The choice of which digester to use is driven by the existing (or planned) manure handling system at the facility. The digester must be designed to operate as part of the facility’s operations. One of the basic options will generally be suitable for most conditions. Exhibit 1-1 summarizes the main characteristics of these digester technologies: Covered Lagoon Digester. Covered lagoons are used to treat and produce biogas from liquid manure with less than 3 percent solids. Generally, large lagoon volumes are required, preferably with depths greater than 2 meters. The typical volume of the required lagoon can be roughly estimated by multiplying the daily manure flush volume by 40 to 60 days. Covered lagoons for energy recovery are compatible with flush manure systems in warm climates. Complete Mix Digester. Complete mix digesters are engineered tanks, above or below ground, that treat slurry manure with a solids concentration in the range of 3 to 10 percent. These structures require less land than lagoons and are heated. Complete mix digesters are compatible with combinations of scraped and flushed manure. Plug Flow Digester: Plug flow digesters are engineered, heated, rectangular tanks that treat scraped dairy manure with a range of 11 to 13 percent total solids. Swine manure cannot be treated with a plug flow digester due to its lack of fiber. Fixed Film Digester. Fixed-film digesters consist of a tank filled with plastic media. The media supports a thin layer of anaerobic bacteria called biofilm (hence the term "fixed-film"). As the waste manure passes through the media, biogas is produced. Like covered lagoon digesters fixed-film digesters are best suited for dilute waste streams typically associated with flush manure handling or pit recharge manure collection.

. 1Source: U.S. EPA, AgStar Handbook


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be generated while cleaning the lagoons.140 The effluent from the digester is a valuable source of nitrogen for plants that can be field applied for improved crop production. Placing a cover over the lagoon for collecting biogas virtually eliminates odor from the lagoon. Odor from field application of effluent from covered lagoons is much reduced from what might be expected when applying untreated or uncovered lagoon effluent. Periodic sludge removal can be achieved either by temporary removal of all or part of the cover, or by providing gas tight openings around the cover perimeter to access the lagoon. Generally, large lagoon volumes are required. The minimum depth is 2 m, but lagoons typically have a depth of 4-6 m depending upon ground water levels. Covered anaerobic lagoons are usually built with a compacted clay or synthetic (e.g., plastic) liner to prevent leakage and groundwater contamination. Facilities on sites with high ground water will need to be avoided or tile drained. The lagoon is constructed with slightly sloping sides. The volume of the required lagoon can be roughly estimated by multiplying the daily manure flush volume by hydraulic retention time (HRT), normally 40 to 60 days.141 Slurry with solids content of 0.5-3% is appropriate for treatment in a lagoon.142 The cover of the lagoon serves to create the airtight, anaerobic conditions needed for methane formation and also serves as the gas storage and collection area. Covers are typically constructed of flexible synthetic materials including high density polyethylene (HDPE), linear low-density polyethylene (LLPE), ethylene propylene diene monomer rubber (EPDM), polypropylene (PP), or reinforced polyethylene (RPE). These materials have a life-span of more than 20 years and are easily repaired. Biogas is collected in pipes along the top of the cover and moved using a low vacuum pump to the point of use. In some cases, excess biogas is flared (burned off without being used for other energy needs) from covered anaerobic lagoons. Biogas from covered anaerobic lagoons has been utilized quite successfully and economically to fuel boilers and generate electricity.143 Flush water from the milking process and other wastewater, such as from the food processing activities, typically moves through drains that empty into a manure mix tank. At this point other manure scraped or hand collected from barns and pastures can be added so long as there is sufficient water coming in to maintain a solids content of 3% or below. Generally, an agitator device mixes the tank and a chopper pump moves the slurry to the lagoon. In some cases solids may be screened and removed prior to entering the lagoon. The slurry may be pumped through a separation process (separator screens and/or gravity separation) to remove non-degradable solids like straw and sand that can interfere with methane production and lead to more frequent cleaning of the lagoon. However, a considerable amount of energy potential is lost with the 140 NIWA, 2008 141 In colder climates such as North America, HRT can be much longer, up to 8 months. Usually these lagoons are used strictly for waste handling and odor control,and methane is often flared. 142 US EPA AgStar Handbook 143 USDA, 2007; NIWA, 2008


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removal of particulate solids, so it is preferable to manage the dairy and manure handling operations in ways that avoid the presence of extraneous solids and skip the separation step if possible.144 Effluent processing: Solids separation may be done after effluent flows out of the lagoon. This would provide a liquid, easily used, high quality fertilizer, and a solid product that can be used or possibly sold for bedding, soil amendments, etc. If this is done, or for other reasons, a liquid storage tank/lagoon for slurry fertilizer would be needed. If fertilizer application occurs unevenly, as is likely in this case, effluent would need to be extracted from the lagoon at the same rate that influent is put in to keep the lagoon operation and digestion process running smoothly. Part of the design of the digester system should include development of a plan for use of the processing and use of the effluent, or the volumes could quickly overwhelm the storage capacity and cause problems. Sufficient areas need to be identified for application of the liquid effluent to avoid overflow or waste. If solids are separated, as is usually the case in dairy farm scale operations, then uses should be identified. Solids can be spread on cropland, composted and exported off the farm, recycled as bedding, or otherwise used. Size and Biogas Production In order to determine the correct size of a covered anaerobic lagoon and potential biogas production, the number of cows needs to be multiplied by the kg manure/cow/day, and % of manure captured. The Evertz Farm calculations also need to account for the other organic solids coming from cheese and yogurt processing. The manure as excreted contains 12 % solids so the total manure captured is multiplied by 0.12. Solids in the processing waste stream should be estimated and added to give the total solids entering the lagoon/day. This is combined with the flow of flush water/day to give the total volume of slurry/day. Sufficient liquids must be added to dilute the slurry to 3% solids or less. This daily flow is multiplied by the hydraulic retention time (HRT) to determine the total volume needed for the lagoon. Typical manure produced per day by a dairy cow in the US is about 50 kg. Evertz Farm is in a developing country with a normally warm, dry climate and feed practices that may not be as intense as US dairies, so a conservative assumption is 30 kg/cow. Anaerobic lagoons normally have a relatively long HRT of 40-60 days and 50 days is used here as an estimate. The calculations are a crude effort to get a sense of the potential and economics of biogas capture and use. The lower bound calculations assume the current situation of about 120 cows being milked and that the system will capture manure flushed from the milk parlor and holding area, and that the flush water from the paved feeding area will be connected to the waste stream if a digester is installed. This gives a figure of 50% of total manure captured in flush water . The second calculation is for the same 120 cows but assumes that a mixing tank is installed and that manure

144 Burke, 2002


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collected from fields is combined with the flushed slurry mixed and pumped into the lagoon. That would allow 90% of the manure to be utilized. In both of these cases current levels of cheese and yogurt processing are assumed and that wastewater is included. The second set of estimates are for the medium term projected numbers of 500 milking cows with greatly expanded cheese, yogurt and long life milk processing. The two cases again assume 50% and 90% capture of manure respectively. The results show that even with the current operation enough manure is being generated to produce 50-85 m3 biogas/day and if the diary is successful in its plans to expand to 500 cows, it could produce sizable amounts of biogas – 238 – 425 m3. This would also require dedication of substantial area for lagoon use. At the 500 cow size a lagoon could require 475 m2 of area up to 850 m2 depending on the percentage of manure captured and fed into the lagoon. Gas Handling: Biogas is collected in the headspace of the anaerobic lagoon under the flexible biogas collection cover. Covers can typically function as reservoirs for biogas storage for some time at low pressures. It is particularly important to ensure that excessive amounts of air do not enter the gas collection system. Depending on the methane concentration of the biogas, explosive mixtures are created when air is mixed with biogas such that 6 to 12 percent of the mixture is CH4. Safety precautions, including adequate flame traps and pressure reducers, should be used on biogas delivery lines. A gas meter to monitor rate of flow, and pump will be required to move the gas through piping to the boiler, generator and any other possible uses. Ordinarily, with lagoons the biogas storage capacity under the lagoon flexible cover is sufficient to hold all the gas produced until it is used. It may be preferable to locate gas storage closer to the end uses and this can be accomplished with a simple storage container – e.g., a flexible rubber/plastic bag or simple floating drum – that will hold gas near the end uses at a constant pressure. There is some question as to the need for gas treatment, in particular scrubbing to remove hydrogen sulfide (H2S). Once biogas starts to be produced, it can be tested to determine the H2S content and the equipment in which it will be used can be evaluated to determine whether it will be able to accept this level of contaminants. Boilers and IC engine generators, for example, often are able to operate on biogas without cleaning before use. Gas Uses The highest priority gas use will clearly be fuel for the boiler currently used intermittently in the cheese and yogurt processing operation. The current fuel for the boiler is diesel and it is estimated that 50-60 liters are used per day on average. This will also increase as the expansion plans are implemented. Diesel fuel is relatively expensive and operating a boiler is a very simple and efficient use of biogas. Most likely the boiler can be modified to operate on biogas relatively easily and also can be set up to operate on either fuel. This will allow diesel to be used as a back-up fuel in the event there is a disruption of the biogas supply. Boilers normally require very little biogas cleaning and conditioning prior to use, and boiler efficiency has been reported to average 75 percent when burning biogas. While burning biogas with large amounts of H2S


7

will decrease the useful life and increase the maintenance of the equipment, it is still commonly done. The lower the concentration of H2S in the biogas, the longer the boiler life. If H2S is slightly high, one approach is to change oil and clean the boiler frequently.145 Once H2S

145 Scott, 2005.


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Box D-2: Calculations of Lagoon Size and Biogas Production

Case 1. 120 cows x 15kg/cow/day (30 kg manure 50% recovered) = 1800 kg, 12% solids = 216 + flush water 1000 liters/day + processing waste water 2000 liters/day = 4800 liters assume that processing waste water contains 1% organic solids =20kg total solids = 226

Total volume of slurry needs to be 7530 liters/day to dilute to 3% solids. In addition to the estimated flow of 4800 liters 2730 liters/day more water is needed to achieve minimum flow = 7530 liters/day

7.53 m3/day x 50 days = 376.5 m3

375 m3 lagoon volume at 3 m depth – approximately 125 m2 surface area or 10m by 12.5 m

estimated biogas production is 2 tonnes (1.8 manure + 0.2 equiv from food processing waste x 25 m3

biogas/tonne manure = 50 m3 biogas/day

Case 2. 120 cows 90% manure captured = 3240 kg manure/day = 388.8 kg solids + 20 kg solids from food processing = 408.8 kg solids @ 3% soilds this equals 13,627 liters/day total flow.

@ 50 days HRT = 680 m3 lagoon volume at 4 meters depth – approximately 170 m2 surface area or 10 m by 17m

3.2 tonnes + 0.2 from food processing solids 3.4 tonnes x 25 m3/tonne = 85 m3 biogas/day

Case 3: 500 cows – 30 kg manure/day 50% captured --7500 kg (12% solids) = 900 kg solids Food processing waste water = 25 m3 day a 1% solids = 250 kg solids total solids 1150 kg/day diluted to 3% = 38 m3 minimum daily flow @ 50 days HRT =

l 1900 m3 lagoon volume at 4 m depth – approximately 475 m2 surface area or 19m by 25 m. 9.5 tonnes manure/day x 25 m3/tonne = 238 m3 biogas/day Case 4: 500 cows x 30kg manure/cow/d ay 90% captured -- 15 tonnes/day – 12% = 1800 kg solids Food processing waste water = 25 m3 day a 1% solids = 250 kg solids, total solids 2,050 kg/day diluted to 3% = 68,340 liters 68 m3/day minimum flow @ 50 days HRT

3400 m3 lagoon volume at 4 m depth approximately 850 m2 surface area or 25 m by 34 m 17 tonnes (manure + food solids) x 25 m3/tone = 425m3 biogas/day


9

concentrations can be determined, the managers of the plant can make a judgment as to whether some biogas cleaning is needed. This can be added into the gas handling system at any time without much difficulty. Once the boiler is converted and operating satisfactorily on biogas, there is like to be additional biogas available for other uses in the farm and processing operations. The next most financially attractive use for the gas would be to generate electricity to supply the on-site needs and back out purchased electricity from the grid. The least cost option would be to retrofit the existing diesel fired IC engine generator set to operate on either diesel or biogas. This 60 KVA generator is currently used as back-up power for the unreliable local grid and would need some evaluation to determine if it is durable enough to run nearly for long periods of time to generate enough power to offset all or most of the on-site electricity needs. If the existing generator cannot be adapted for heavy use and biogas fuel, then a new IC engine generator set is the next least cost option. Dual-fuel engine generators are widely available. These units use a small amount of diesel for start-up and then run on gas. Emissions are reduced nearly to the level of natural gas engines. These units can be operated on 100 percent diesel fuel at times when natural gas is not available. A number of engine manufacturers make dual-fuel units, and existing diesel gensets can also be retrofitted to dual-fuel at a reasonable cost.146 If the existing genset cannot be utilized, a new generator would be required and this would add considerably to the capital cost of the system. It appears at first look, that a great deal of electric power from the generator could be used on site, particularly if the biogas generated power can be used to operate the borehole pumps as well as the other uses. As the overall expansion plan of the farm and processing plant is implemented over time, and/or as existing equipment ages and becomes less reliable, additional options for using the biogas can be considered. Depending on how much power, boiler fuel and process heat are needed it may make sense to expand the system and to install a new and larger generator, possibly in a cogeneration configuration so that the waste heat from the electric power generation could be used to heat water to supplement the boiler, or for other uses. In addition to IC engines, several newer technologies could be considered at that point as well. Micro turbine generators, Stirling engines and fuel cells have all been used or proposed for biogas generation projects.147 Economics The estimated costs of the digester system: The costs of an anaerobic lagoon are composed of the 1) lagoon construction, 2) the flexible cover and gas collection system and 3) various additional smaller scale components. No detailed cost estimates have been available for construction of anaerobic lagoons in Africa or other developing countries. Cost estimators have been derived from costs reported in the US and other industrialized countries. These cost factors have been adjusts a bit, in a fairly crude way, to reflect lower labor and construction costs one would expect in Mozambique, and slightly higher costs that may be 146 Esource, 2006. 147See for example Esource, 2006, Goldstein, 2006


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Box D-3: Anaerobic Lagoon Cost Estimates

Based on US experience with large lagoons, estimated costs for lagoon cover and gas collection system are between $16 and $25 per m2 surface area. Balance of the system (mainly lagoon construction, etc.) runs between $0.80 and $1.5 per m3 lagoon capacity.1 Another analysis from New Zealand breaks down cost components of a new anaerobic digester system.1 These costs are similar ($20-25/m2) for the cover and gas collection but considerably higher ($8-10/m3) for balance of system including construction of the lagoon. As the lagoon construction and other components are likely to be largely labor, and use local materials these costs may be somewhat lower in Mozambique, a medium to low figure of $5/m3 is used for lagoon excavation and other costs. Conversely, the flexible cover and gas collection system may need to be imported so a higher figure of $25/m2 of surface area is used. There are other analyses that show higher costs and identify additional components that may be included in the above estimates. To be conservative it is assumed that an additional $1000 - $5000 is needed to cover adjustments to the boiler, additional equipment, piping, etc.

Case 1. 120 cows 50% manure captured: 50 m3 biogas/day Costs are estimated to be: 125 m2 surface area x $25/m2 = 3125 375 m3 lagoon volume x $5/m3 = 1875 Additional system components = 1000 Total cost = $6,000

Case 2. 120 cows 90% manure captured 85 m3 biogas/day Costs are estimated to be: 170 m2 surface area x $25/m2 = $4250 680 m3 lagoon volume x $5/ m3 = $3400 Additional system components = $1500 Total cost = $9,150 Case 3: 500 cows – 30 kg manure/day 50% captured 238 m3 biogas/day Costs are estimated to be: 475 m2 surface area x $25/m2 = $11,875 1900 m3 lagoon volume x $5/m3 = $9,500 Additional system components = $3,000 Total cost = $24,375

Case 4: 500 cows x 30kg manure/cow/d ay 90% 425m3 biogas/day Costs are estimated to be: 850 m2 surface area x $25/m2 = $21,250

3400 m3 lagoon volume x $5/m3 = $17,000 Additional system components = $5,000

Total cost = $38,250


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incurred for items, like the flexible cover, that likely to be imported. Box 3 provides “ball park” estimates of cost for the 4 size/configuration cases developed earlier. The investment cost estimates range from $6,000 from a small lagoon that could produce about 50 m3 of biogas/day to $38,250 for a large lagoon that could handle waste from 500 cows and supply 475 m3 biogas/day, likely more than enough to supply boiler fuel and a good deal of electricity generation needed for the farm and processing plant.

It is likely that the existing diesel boiler could be adapted to run on either biogas or diesel fuel without significant cost. This is a common practice on biogas projects around the world and is assumed to add no significant cost. This, like other assumptions in this assessment should be examined in more detail as part of the of a project design process if the decision is made to move forward. Generator costs: If the existing diesel generator can be retrofitted and used for at least the first few years this would keep the initial costs of the system are quite low. If it is determined that a new dual fueled, heavy duty IC engine generator set is needed, than this will raise the initial investment cost substantially. It is conservative to estimate that the retrofit of the existing generator plus increase maintenance could cost $2000. Also, it is assumed that biogas from the smaller sized lagoons would be entirely used to supply boiler fuel, as backing out diesel is the most economically valuable gas use. If it is determined that a new generator is required, the range for a standard dual fuel IC engine generator set of 50 kW (roughly equivalent to 60KVA current unit) at $500-1000/kW would be $25,000-$50,000. Total costs: For the smaller scale lagoons, the gas production would all go into offsetting boiler fuel, no generation technology costs would be needed and the total cost would equal the digester costs in Box D-2. For the two larger lagoon cases cost estimates are more complicated. 1) The 1900 m3 lagoon producing 238 m3 biogas/day would be:

a. lagoon and digester system only $24,375, if all of the gas could be used as boiler fuel due to expanded operations; b. lagoon and digester system $24,375 + generator upgrade $2000 = 26,375; c. lagoon and digester system + new generator = $49,375-74,375

2) The 3400 m3 lagoon producing 475 m3 biogas/day would be:

a. lagoon and digester system $38,250 + generator upgrade- $2000 = $40,250 b. lagoon and digester system + new generator = $63,250- 88,250

Financial benefits: Substitution of biogas for currently purchased energy – diesel fuel and electricity – is the major monetary benefit of a biogas digester system for this facility. First priority is substitution of biogas for the existing use of diesel fuel to fire the boiler used in the


12

food processing plant. An initial estimate from the plant manager is that the boiler currently uses 60-70 liters/day supporting the processing plant. A recent report indicated that diesel prices in Mozambique have been between $0.40-$0.80/liter in the early 2000s.148 $0.60/liter is a conservative value used for these calculations. If purchase of 65 liters/day of diesel at a price of $0.60/liter is avoided the savings would be $39/day or $14,235/year. Substitution of this amount of diesel fuel would require at most124 m3 biogas/day. The remaining biogas available, as much as 475-124 = 351 m3, could be used for power generation and/or expanded operation of the boiler. The cheese, yogurt and long life milk processing is expected to ramp up with expansion of the dairy operations and increasing milk purchases from the smallholder dairy cooperatives. If the boiler fuel demand expands, this would be the first priority for use of additional biogas. It is the highest value use, and does not require any further capital investment. The power generation at 1.7 kWh/m3 could be in theory as much as 597 kWh/day. It is not clear at this point whether this much power could be productively used on a daily basis, and this should be further evaluated. At an electricity price of $0.08/kWh (reported to be the national average electricity tariff in Mozambique.149 This of course needs to be recalculated using actual on-farm figures for price and daily use) would save roughly $47.76/day or $17,432/year. If the boiler fuel requirement doubled with the expansion, the diesel substitution could save $28,470/year and the remaining 227 m3 biogas could produce up to 385 kWh/day at $0.08/kWh worth $30.80/day or $11,242/year. Total energy savings for the largest lagoon option are 14,235 + 17,432 = $31,667 with replacement of current diesel use only, plus power 28,470 + 11,242 = $39,712 with replacement of double diesel use, plus power. With existing generator total costs = $40,250 the best case provides for a simple payback of slightly over 1 year. With a new generator, costs would be $63,250– $88,250 and simple

Table D-1: Costs and Benefits of Biogas Options

Cases Cost $

Benefits $

Simple payback years

1. 120 cows, 50% manure capture 6,000 5840* 1.03 2. 120 cows, 90% manure capture 9,150 9855* < 1 3. a. 500 cows, 50% manure capture, no

generator 24,375 27,235* < 1

3.b. 500 cows, 50% manure capture, plus retrofitted generator

26,375 19,900

1.2

3.c. 500 cows, 50% manure capture, plus new generator

49,375-74,375

19,900 2.5 – 3.7

148 Metschies, 2005 149 AFDB, 2007


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4. a. 500 cows, 90% manure capture, plus retrofitted generator

40,250 31,667- 39,712

1.1

4 b. 500 cows, 90% manure capture, plus new generator

63,250- 88,250

31,667- 39,712

1. – 2.4

*no electricity generation, assumes that all biogas produced can be used to back out diesel fuel for the boiler. payback would be 1.6 to 2.8 years. Costs and benefits were calculated in the same way for all cases and results are shown in Table D-1. These economic calculations do not include monetized value for the anaerobic lagoon effluent used as fertilizer or other products. These benefits could be substantial as the effluent is much higher quality fertilizer than the raw manure and could be sold or could increase productivity significantly if applied to pastures or crops on the farm. However, the value of these products is difficult to determine at this time. More detailed analysis may be able to quantify some of these benefits, further improving the financial attractiveness of the project. On the other hand, there are some costs that clearly are not captured in this preliminary analysis. No effort has been made to include operation and maintenance (O&M) costs, sometimes estimated as 5-6% of annualized capital costs in the US.150 This figure would include O&M for the digester systems and also any increases in O&M for equipment like the boiler and IC engine generator. Some additional components e.g., piping systems, may add costs not included in the analyses used to derive cost estimators. More detailed analysis of the individual components – biogas cleaning, tanks, pumps, valves, buildings, etc -- could show higher costs than those embedded in the general cost estimators used in this analysis. This is particularly an issue for imported equipment. There is also some cost associated with more detailed study possibly up to a full engineering feasibility study that will be necessary to move this project forward. May be possible for the Manica Province program to support some additional consulting/engineering services as a next step. It is also possible to seek development funding, e.g., GEF small grants program or CDM project developers. Despite the uncertainties and limitations of the financial analysis in this report, it seems unlikely that better data and analysis will change the fundamental conclusion that biogas opportunities here are economically attractive. There are options for using initial increments of biogas that appear to save more than their cost in the first year. Most of the size and technology configurations appear to payback in under 3 years which is generally considered a very attractive rate of return on investment. Phasing of project investments

150 USDA, 2007.


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The components of the proposed digester and biogas utilization system are all proven commercial products or items that can be produced locally. However, the overall system is somewhat complex and the interactions between the components need to be timed and planed carefully to avoid waste and disruption. Notably, the anaerobic lagoon digester will take some time to begin operation and stabilize daily biogas production. It would be wasteful to make an investment in generation technology that would sit idle or underutilized waiting for the biogas supply to be available. Similarly, the construction and operation of the lagoon must be timed to fit with the expansion plans of the dairy so that the lagoon can be fed by the necessary head of cows when it begins filling for operation. Another reason for careful planning and phased investment is that capital scarcity is a major constraint for the project as described above. Ideally, parts of the project can be implemented at relatively low cost and begin to show financial benefits quickly, then additional component investments can be made as possible. Fortunately, this project has several aspects that will make phasing relatively easy and may allow capital costs to be held lower than most similar projects. Project investment can be phased in several ways. First, it would be worth considering phased development of anaerobic lagoon capacity. Depending on the rate at which expansion of the dairy and food processing operations is expected, it may be many years before the volume of daily manure and wastewater flows will be sufficient to support a full scale 3400 m3 lagoon capacity. It may make sense to build this as two lagoons of half this size, 1900 m3 volume. The first could be scheduled for completion and operation at a point where the dairy herd will be at roughly 250 cows and the food processing waste water will increase somewhat, but not to full expected flows. This would lower the initial investment cost and spread some of the investment into future years, but would allow for some savings to be generated quickly by substituting biogas for diesel fuel. It might also have an advantage down the road when the lagoon needs to be cleaned of sludge. One half could be cleaned at a time so that the flow of biogas would not be completely disrupted. This option would clearly forgo some economies of scale and increase overall cost. Pros and cons need to be evaluated in more detail. A second opportunity for lowering initial investment costs is lies in the existence of the boiler used for food processing and very likely easy and inexpensive to adapt for use of biogas to replace some or all of the existing diesel fuel. This is a low cost option that generates high returns as diesel fuel is the most expensive energy option that can be replaced. The other interesting option for phasing is the possibility of adapting the existing diesel fired back-up generator to biogas and running it for sufficient periods to offset some of the farms purchase of electricity from the grid. This is a lower value opportunity that replacing diesel fuel but could add to savings and help the early investments to pay for themselves very quickly. Some modest improvements in the manure handling system could also begin fairly quickly and be spread over long periods avoid lumpiness of capital investment. It would be useful to consider replacing or adapting the open culvert system for moving manure from the milking parlor and other flush areas to the lagoon. These distance are fairly long and it is possible that some of the energy value in the slurry is being lost through volitization in the current system. Adding PVC piping or some similar material into the existing culverts would eliminate this


15

problem without a huge investment. It also reduces odor. Add drain pipes from the existing feeding area to lagoon location. A mixing tank, pumps and settling tank(s) will be necessary for full operation of the lagoon digester, and could be introduced earlier with benefits for the manure management system before the full operation of the digester system. Acquisition of a fertilizer pumping vehicle could allow some of the fertilizer benefits to be obtained before the biogas energy benefits are fully in place.


1

Appendix E: Biogas Program Information and Contacts There are a great many programs that are currently promoting or have recently promoted biogas digester systems in African countries. Some of the programs that have been cited in this report, and appear to have the greatest relevance to the Manica Province program, are listed below. Where possible contact information is provided. Regional - Biogas for Better Life, An African Initiative (also referred to as Biogas Africa Initiative) http://www.biogasafrica.org/index.html Communication Contact: Chudi Ukpabi +31(0) 652 033 141 Email: [email protected] Biogas Initiative Ambassador: Hauwa Ibrahim Plot 2261, Ndola Crescent, Wuse Zone 5, Abuja, Nigeria. Phone: +234 9 523 6663; Fax: +234 9 523 8271 Email: [email protected] On May 20-23, 2007 representatives from 27 countries in Africa, and 37 in all, met in Nairobi, Kenya to formally launch the Biogas for Better Life Initiative. This meeting follows an exploratory workshop organized in Amsterdam in October 2006. During this 3-day event participants discussed how to carry forward the objectives of the broader Initiative. A number of country national biogas program pre-feasibility and feasibility studies are already completed or underway, and programs are already being launched in Rwanda and Ethiopia. Twenty-one founding organizations, international and African, are listed with websites at http://www.biogasafrica.org/AllItems.aspx.html Kenya Sustainable Community Development Services Programme (SCODE) is a non-profit making Non-Governmental Organization (NGO). It was formed in 1996 and has its registered office and community training resource centre in Nakuru. The NGO SCODE operates in Nakuru district and is currently the leading installer of biogas systems in Kenya with 200 installed systems. Most systems have been installed cash, but SCODE has also developed a structure with an internal revolving fund, with seed money from 3 donors. SCODE is a member of the East African Energy Technology Development Network (EAETDN). EAETDN was established in 1998 and has 35 members in Kenya who work in various areas of energy development. The goal of the network is to reduce poverty among communities in East Africa through use of appropriate clean energy technologies. SCODE is the Chair and Focal Point of the EAETDN in Kenya. John Maina (Executive Co-ordinator) Email via Household Energy Network Site: http://www.hedon.info/SCODEKenya

Renewable Energy Engineering Contractors (REECON) Email: [email protected]


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REECON was established in 1998 and registered in Kenya in 1999. It is involved in development, fabrication and installation of renewable energy systems and technologies that are environmentally friendly. REECON has highly qualified technicians who have been involved in the biogas sector for over 15 years. Pioneer Technologies Ltd is a local company incorporated in Kenya and operated by Kenyans. It started biogas business as an offshoot of a plastic business they have been running. It ventured into biogas because of two major reasons – problems of energy especially in the rural areas, and the need to conserve forests/trees. They had also recognised the logical option of using already existing resources – cow-dung and plastics and that at least 60 percent of rural households have livestock, which can give sufficient dung to be used in production of methane. Currently, Pioneer Technologies Ltd receives support from Land O’lakes and has entered into research collaboration with Jomo Kenyatta University of Agriculture and Technology (JKUAT). Land O’Lakes gives financial support to the company in the production of biogas digesters. JKUAT is supposed to carry out investigations into issues arising from the use of the technology, with focus on how the technology can be improved, made more efficient, etc. Pioneer Technologies partnered with the USAID Dairy Development for Kenya project completed in 2008 by Land O; Lakes, Inc. The project supported the private-sector service-provider of biogas, to re-introduce an affordable olythene/tubular biogas technology to smallholder dairy farmers with appropriate training and technical back-up in place to ensure sustainability. Land O; Lakes contact in Kenya: Mulinge Mukumbu and/or Joe Carvalho

Land O’Lakes, Inc. – Kenya Office Phone: +254-20 3748685 Fax: +254-20 3745056 E-mail: [email protected]

In the business model for biogas under the Breathing Space project in Kenya, financial institutions (the KUSSCO umbrella organization of Kenyan SACCOs, and KWFT) are supported to promote loans for biogas systems. The biogas systems are installed by technicians managed and trained by partner companies SCODE and REECON. IT Power also has the responsibility to check on the quality of the systems. Biogas for a Better Life. 2007a. Promoting Biogas Systems in Kenya: A Feasibility Study. October, 2007. http://www.biogasafrica.org/Documents/Kenya-Feasibility-Study.pdf South Africa AGAMA Energy, a Cape Town, South Africa–based alternative energy company Greg Austin, director AGAMA Energy (Pty) Ltd 9b Bell Crescent Close Westlake Business Park Westlake, 7945 Phone: +27 (0)21 701 3364 Fax : +27 (0)21 701 3365 http://agama.co.za/


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(email can be sent through the website) AGAMA Energy is a leading renewable energy consulting business in Southern Africa. Established in 2000, it is a privately owned company with many years of project experience that covers a wide range of more sustainable energy solutions. We have undertaken research and consulting projects over the past decade for a diverse range of local and international clients and pioneered the delivery of more sustainable energy services. Strategic focus areas include

• green buildings and sustainable developments • energy management services • carbon related projects • bioenergy project development and implementation (mainly biogas) • the marketing and sale of green power certificates

BiogasPower Shelby Tyne South Africa [email protected] Business +27-31-7811981 Mobile +27-83-6428229 Description: Manufactures and designs cheap and cost effective bio-plant designs that provide sustainable and renewable energy. Zero Waste Livestock Farming Website Address:http://www.biogaspower.co.za Biogas for a Better Life. 2008. South Africa: Household Biogas Feasibility Study, January

2008 http://www.biogasafrica.org/Documents/South-Africa-Feasibility-Study.pdf Tanzania Foundation for Sustainable Rural Development, or SURUDE (NGO) Implementing Organization: UNDP/GEF Small Grants Program Project: Biogas Technology in Agricultural Regions, Tanzania SURUDE – Biogas and sustainable energy projects - http://www.superflex.net/tools/supergas/surude.shtml Dr. Sebastian V. Sarwatt Executive Secretary Foundation for Sustainable Rural Development (SURUDE) P.O.Box 3087 MOROGORO, TANZANIA Tel: 255 – 744-411 968 E-mail: [email protected] Website: www.superflex.dk/surude Founded in 1994, SURUDE is a membership organization currently involving about 250 farmers. SURUDE’s main office is located in Turiani, about 200 km west of Dar Es Salaam. Five sub-centers are being established in the various regions of Tanzania in an effort to


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further spread the use of biogas technology incorporated with farming and livestock practices. Cows can provide a steady supply of manure, and farmers are helped to obtain them through a “Heifer-in-Trust”scheme under which a farmer is loaned an in-calf heifer, and agrees to give the first two female calves to neighbors. A Danish company called Superflex has helped produce and distribute the tubular plastic biogas digester. http://www.superflex.net/tools/supergas/index.shtml Egypt UNDP/GEF Project: Bioenergy for Sustainable Rural Development Project Documen Posted on the Global Environment Facility Web Site, July 14, 2008 http://www.gefweb.org/Documents/Council_Documents/GEF_C28/documents/1335PIMS2284EgyptBioenergyProjectDocument_Final0205Rev206.pdf Project Contact Person: Vesa Rutanen Date: 9 July 2008 Tel. and Email: +358 50 320 9287 [email protected] GEF Project – This project has evaluated and plans to promote, among other biomass technologies, household, community scale, and farm scale biogas digester systems. Bukina Faso GTZ, 2007. Feasibility Study for a National Domestic Biogas Programme in Burkina Faso. Prepared By Deutsche Gesellschaft Für Technische Zusammenarbeit (Gtz) Gmbh for the Biogas For A Better Life African Initiative, June. http://www.biogasafrica.org/Documents/Biogas-Feasibility-Study-Burkina-Faso.pdf Institut de Recherche en Sciences Appliquées et de Technologie (IRSAT) Contacts: Dr. Oumar Sanogo and Gombila Kaboré 03 BP 7047 Ouagadougou 03 Burkina Faso Phone: 226-50-36-3790 Fax: 226-50-36-37901 NETwork for the development of Sustainable Sanitation in Africa (NETSAF) (Réseau de développement à l'échelle des approches durables d'implémentation de l'assainissement en Afrique) Burkina Faso Contact: Patrick Bracken Clean Development Mechanism/Carbon Credit References/Contacts Mozambique Designated National Agency


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Ministério para a Coordenação da Acção Ambiental (MICOA) Av. Acordos de Lusaka nº 2115 P.O. Box nº 2020 Maputo Mozambique Ms. Marília Telma António Manjate ([email protected] ) Phone: (258-21)46 5849/46 6245 Fax: (258-21)46 6495 http://www.micoa.gov.mz/ Carbon Limits (former ECON Carbon), Oslo South Africa Contact: Torleif Haugland Contact: Randall Spalding-Fecher Biskop Gunnerius' gate 14A P.O. Box 34107 P.O. Box 5 Rhodes Gift, 7707 N-0051 Oslo South Africa Norway [email protected] [email protected] Phone: +27 82 857 9486 Phone: +47 90 55 11 37 Fax: +47 22 42 00 40 http://www.carbonlimits.no/ Based in Oslo, Norway, Carbon Limits is an active player in the emerging carbon market. With substantial experience in all phases of the carbon market, as well as energy and development, Carbon Limits assist clients in monetizing carbon benefits. A;though details are confidential the website indicates that in 2007 the company initiated development of CDM project in Mozambique Small project to use natural gas locally for power production and possible extension of gas use into manufacturing industries. Cleaner Climate - an international carbon solutions company whose expertise lies in the commercialisation of carbon, that can help farmers install and operate such systems in South Africa. Headquartered in the United Kingdom, Cleaner Climate has a global network of operations in over 6 countries. www.cleanerclimate.com. Kerry Wright, director of Cleaner Climate South Africa 27 De Winaar Street, Halfway House Midrand, 1682, South Africa [email protected] International Mozambique GEF UNDP Small Grants Programme (SGP) is part of the global SGP which is a GEF corporate programme that aims to deliver global environmental benefits through


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community based approaches. It covers the GEF focal areas of biodiversity, climate change, international waters, persistent organic polutants and land degradation. It doesn't intervene in GEF focal area of ozone layer depletion. Its guided under the principle that community action can maintain the fine balance between human needs and environmental imperatives. Grants are also made directly to community groups and NGOs in recognition of the key role they play as a resource and constituency for environment and development concerns.

Augusto Correia Rua Francisco Barreto, nº322 Maputo 4595 Mozambique Tel: +258 (0)1 491 409 Fax: +258 (0)1 492 325 [email protected]. www.undp.org/sgp Shell Foundation Breathing Space Project: Karen Westley, Shell Foundation, Shell Centre, London SE1 7NA, United Kingdom E-mail: [email protected] In 2001, the Shell Foundation committed US$10 million to its Breathing Space programme with the goal of reducing health risks associated with IAP suffered by 1 million women and children in developing countries by 2008. In the business model for biogas under the Breathing Space project in Kenya, financial institutions (the KUSSCO umbrella organization of Kenyan SACCOs, and KWFT) are supported to promote loans for biogas systems. The biogas systems are installed by technicians managed and trained by partner companies SCODE and REECON. IT Power also has the responsibility to check on the quality of the systems.