THE ECONOMICS OF BIOGAS TECHNOLOGY: A SET - UP PROJECT FOR SMALLENTERPRISE DEVELOPMENT 1

MARIA C. HERNANDEZ , MS, Assistant Professor IIQuirino State University , Diffun, Quirino 3401 Philippines

ABSTRACT

The Department of Science and Technology through the Small EnterpriseDevelopment Upgrading Program (DOST SET-UP) as one of the strategic programs underthe National S and T Plan has provided funds for the establishment of the project entitled“Waste Utilization Through Methane Production”, and to implement the project inaccordance with the approved technological intervention. An integrated system aims todemonstrate an eco-friendly approach towards improve animal production and is tangible tocounteract environmental pollution. The heart of the system is the biogas process, it has thepotential to seed self-reliance.

The project provides the socio-economic and environmental aspects of biogas for SETUP farmer beneficiary in the province of Quirino. Pig husbandry has significantly contributedto the households’ income. Pig producers have long experienced in husbandry with relativelyhigh production but positive awareness of environmental issues.

The support provided by the DOST and the Government policies have successfullyattained the achievements not only in manure management in the husbandry sector but also inmany aspects of sanitation, environment, job creation and energy security importantly in thedevelopment of livestock enterprises in the province.

The dome type digester has attained higher net benefit ratio compared to the plasticbag one. The greater profitable levels are promising with higher utilization levels of biogasand slurry.

The biogas programs should encourage the installation without any financial supports, shiftingthe funding resource towards further high target of promoting the issuance of certified emissionreductions in the community.

____________1 A Development Paper presented during the PAEDA Convention held at CentralMindanao State University, Musuan , Maramag Bukidnon, October 23-25, 2013

INTRODUCTION

Manure residues from livestock industries have long been identified as a major sourceof environmental pollution. Traditionally, these wastes have been disposed of, directly or aftercomposting, as soil amendments in the agricultural industry. Since this practice has resulted indegradation of air, soil, and water resources, new regulations for protecting the environmenthave been promulgated to control land application of animal manure. The nitrate-directive,regulates input of nitrate on farmland, aiming to protect ground and surface waterenvironments from nitrate pollution, and includes rules for the use of animal manure andchemical fertilizers. In principle, not more than 170 kg of animal manure N may be appliedper ha per year, as long as this is not in conflict with application standard for total P.

Implementation of these environmental measures entails a high cost of manuredisposal for livestock farmers, which impairs profitability of farming. As such, livestockindustries and regulatory agencies are seeking alternatives for managing manure residues in aneconomically feasible and environmentally- friendly manner.

Several studies have shown that anaerobic digestion (AD) of organic wastes has thepotential to manage these problems in a cost effective and environmentally sustainablemanner.( Solomie A. Gebrezgabher, 2010)

Interest has recently been growing in using the AD of organic waste of farm origin,such as manure, crop residues and organic residues from food and agro-industries, to generaterenewable energy and Processing manure to biogas through AD recovers energy thatcontributes no net carbon to the atmosphere and reduces the risk from pathogens from landspreading, as thermophilic or mesophilic AD with a sanitization step destroys all or virtuallyall pathogens. Besides biogas, AD produces digestate, which consists of a mixture of liquidand solid fractions. Applying digestate to land is the most attractive option in terms ofenvironmental issues, because it allows nutrients to be recovered and reduces loss of organicmatter suffered by soils under agricultural exploitation. A reliable and generally acceptedmeans of disposing of the comparatively large amounts of digestate produced is of crucialimportance for the economic and environmental viability of a biogas plant.

Objectives

1. To demonstrate an eco-friendly approach of animal production through methaneproduction.

2. To reduce cost on fuel and labor utilizing waste products as biofuel.

POTENTIAL IMPACT/BENEFICIARIES

ECONOMIC BENEFIT OF BIOGAS TECHNOLOGY

The development of biogas production from animal manure can generate benefits both at anational and household level.

In rural areas , people mostly use firewood for cooking and heating purposes and for obtaininghot water. The uncontrolled forest cutting that took place in the country over the past decade greatlyincreases the risk of dangerous phenomena, such as avalanches, landslides. Besides, woodstoves thatpeople use are of very low efficiency.

When considering the benefits of replacing wood as energy source with biogas , one should takeinto account the contribution this will make up to the value of the standing forest that is saved.

Moreover, the development of biogas production will generate GHG reductions by decreasingmethane emissions and replacing wood as energy source.

FINANCIAL VIABILITY OF BIOGAS PRODUCT

The dome type digester has attained higher net benefit ratio compared to the plastic bag one.

The greater profitable levels are promising with higher utilization levels of biogas and slurry. Theevaluation of the financial viability of biogas uses a discount rate of 21% and a lifetime of 25years. The financial calculations assume that 20% of investments would be the responsibility of

farmers(co financing). The remaining 80% would be covered by the SET UP Program .Share of

farmers=20% ; Interest on Loans=0 % Payback period=7 years

ESTIMATION OF GREENHOUSE GASES (GHGS) ABATEMENT POTENTIAL

In order to calculate the net GHG reduction, the baseline scenario includes emissionsfrom manure as well as emission from existing fuel.(e.g. wood) The alternative case includesthe emission from biogas.

Methanecontentin Biogas

MethaneDensityin kg/m5

Methane

Globalwarmingpotentialin CO2equivalent

Heatcontentof

Biogas

MJ/m3

Bio gasemissionfactor

tC/TJ

Heatcontentof wood

Wood,density

t/m3

Woodemissionfactor

tC/TJ

50%. 0.710 21 22.500 30.6 13.198 0.569 29.9

Source:UNDP

Table 1 Gas Yield per Feed Stock

Fermentedmaterial

Amt. ofwaste perday

Drymatter(%)

CarbonNitrogenRatio

Gas Yieldof theFeedstock(liter/kg/day

ManureCow 15-20 18-20 24-25 15-32Buffalo 18-25 16-18 24-25 15-32Pig 1.2-4.0 24-33 12-13 40-60Poultry 0.02-0.05 25-50 5-15 50-60Human 0.18-0.34 20-34 2.9-10 60-70Dry PaddyStraw

80-85 48-117 1.5-2.0

Source: SNV Biogas program inVietman

ECONOMIC ANALYSIS OF BIOGAS (ESTIMATED FOR ONE YEAR OPERATION)

Case 1 Concrete Dome Type Digester

Basic Assumptions:

Pig Manure Amount of Waste /Day Gas Yield of the Feedstock/liter/kg/day

1.2-4.0 kg 40-60 liter/kg

Per kilogram Cost of LPG Php 63.64

Biogas Production Inputs ( Substrate) Gas Yield TOTAL

3 heads breeder swine= 12kg/day 480 liters/kg Php 30,547.00

Monthly Gas Yield 360 kg 14,400 li/kg Php 916,416.00

Capital Investment Costs

Biogas digester Construction ( fo r 8 cubic meter digester including

labor cost ) Php 250,000.00

Operation and maintenance cost

Breeder Cost (3 heads @ 12,000/hd) PhP 36,000.00

Feeds 3,250 consumption ( 1320 @50 kgs ) 85,536.00

Medicines/vaccines/dewormers 5,000.00

Labor 100/day rate ( family labor-non-Cash) ( 36,000.00)

Income (B)

Sales from piglets ( 2 breeding cycle/yr) Php 75,000.00

GROSS INCOME (A +B) 991,416.00

TOTAL PRODUCTION COST PhP 371,536.00

Depreciation Cost of 1%/year 2,500.00

NET INCOME 619,880.00

ROI 1.66%

Cost and Return Analysis of Tubular Polyethylene Digester

*Only LPG Consumption of a single household was considered

* Environmental as well as social benefits are not considered

Assumptions

5 years lifespan of a digester in concrete trench

2 LPG consumption of 8 member of household

Total expenses is P6,784.88

Net Income 25,560.00

ROI 376.77%

Payback Period(year) 1.16

IRR 750%

BCR 2.08

NPV 7,312.70

Source: Technology Adoption and Commercialization of Low Cost and Environment Friendly Biogassystem ,QSC RDET,2000

ENVIRONMENTAL BENEFIT

When considering the benefits of replacing wood as an energy source with biogas, oneshould take into account the contribution this will make to the value of the standing forest thatis saved. This “ shadow price ” of afforestation /reforestation has been estimated for differentprojects develops ( but not yet implemented) in Quirino. The cost of 1 m3 wood varies in therange of P150-200 and it is expected to increase in areas where forest is very scarce.

The conservation of forests plays an important role for local communities with regard toflood control and water protection. Uncontrolled cutting and logging, which took place during

the last decade, has led to a decrease of underground water resources and initiated soil erosiveprocesses in many regions which have resulted in serious damage.

The main reason for using anaerobic digestion which generates biogas as a by-product, isto treat wastes. According to the Governments Ecological White Paper issued in 2005, thetotal amount of livestock and poultry wastes generated in the country reached 2.485 billiontones in 1995, some 3.9 times the total industrial solid wastes. These wastes are preciousresources if used properly, but constitute major pollution when discharged into rivers andlakes. The second main reason for anaerobic digestion is that methane is a major greenhousegas, second to carbon dioxide in amount generated, but with a global warming potential 22times that of carbon dioxide. Using biogas not only removes polluting wastes, but alsomitigates global warming.(Biogas Bonanza for Third World Development).

Using biogas solves the most serious problem of energy supply in rural areas, wherepeople traditionally forage for fuel wood in forest. A 10m3 digester in rural areas can save2,000 kg of fuel wood which is equivalent to reforesting 0.24-4 ha.-Fuel wood gathering wasa major cause of forest depletion. Unlike firewood, biogas burns without smoke, thus alsosaving women and children from respiratory distress and diseases.

Biogas is a combustible mixture of gases produced by micro-organism when livestockmanure and other biological waste are allowed to ferment in the absence of air in closedcontainers. Wikipedia biogas refers to a gas produced by the biological breakdown of organicmatter in the absence of oxygen. Organic waste such as dead plant and animal material ,animal dung, and kitchen waste can be converted into a gaseous fuel called biogas. Biogasoriginates from biogenic material and is a type of biofuel.

The major constituents of biogas are methane ( CH4, 60 percent or more by volume) andcarbon dioxide (CO2, about 35%) but small amounts of water vapour , hydrogen sulphide(H2S) carbon monoxide (CO), and Nitrogen (N2) are also present. The composition of biogasvaries according to the biological material. The methane content of biogas produced fromnight soil (human excreta), chicken manure and wastewater from slaughter house sometimescould reach 70% or more. The concentration of H2S in biogas produced from chicken andmolasses could be as high as 4000 mg/m3, and from alcohol water even higher at10,000mg/m3. Biogas is mainly used as fuel, like natural gas, while the digester mixture ofliquids and solids “bio-sludge” are mainly used as organic fertilizer for crops. But there arenumerous other sources for biogas, bio- slurry and bio-sludge. ( Prof. Li Kangman and Dr.Mae Wan –Ho).

The gases methane, hydrogen , and carbon monoxide (CO) can be combusted oroxidized with oxygen. The energy release allows biogas to be used as fuel. Biogas can be usedas fuel for any heating purpose, such as cooking. It can also be used in anerobic digesterswhere it is typically used in a gas engine to convert the energy in the gas into electricity and

heat. Biogas can be compressed, much like natural gas, and used to power motor vehicles. Inthe UK, for example biogas is estimated to have the potential to replace around 17% vehiclefuel. Biogas is a renewable fuel, so it qualifies for renewable energy subsidies in some parts ofthe world. Biogas can also be cleaned and upgraded to natural gas standards when it becomesbiomethane.

Biogas can potentially help reduce global climate change. Normally, manure that is leftto decompose releases two main gases that cause global climate change; nitrouse dioxide andmethane. Nitrous dioxide ( N02) warms the atmosphere 310 times more than carbon dioxideand methane 21 times more than carbon dioxide. Furthermore by converting manure intomethane biogas instead of letting it decompose, we would be able to reduce warming gases byninety-nine million metric tons or four percent (ISIS Report 2010).

SOCIAL IMPACTS OF BIOGAS TECHNOLOGY

In addition, biogas utilization will also generate social benefits. People will spend less orno time, energy and finances on wood collection; indoor pollution will be reduced; whenbiogas is used for electricity production, it will contribute to the improvement of educationlevels. Other benefits derived from biogas are reduced GHG emissions. Based on the energybalance data for 2001( the amount of electricity generated by hydro power plants (HPPS), bythermal power plants (TPPs) amount of fuel combusted in TPPs.

(Source: ICF Consulting: Carbon Sequestration through Afforestation.)

FIG. 1 BIOGAS DIAGRAM

leads to greater causes

leads to the creation of

needed for

creates

negatively affects

creates

The model diagram represents people , plants, and human structures. The figuresshows how a simplistic society can function just as well as a complex society. The biogascoincides with the social system and the ecosystem. In this day in age, we focus too muchon technology and not enough fact that we need to survive can be found in environment.

Social System

Population

Demand forClean Fuel

Food

Job

Quality of Life

BIOGAS

ecosystem

Wood burning

Smoke

Cow Dung/Swinemanure

Methane

Compost

MODEL PROJECT RESULT

Biogas plant

Biogas digester ( or fermentation tank) and a gas holder were constructed. The digesteris a cube-shaped or cylindrical water proof (dome-like) with a diameter of eight (8) cubicmeter with an inlet into which the fermentable mixture is introduced in the form of a liquidslurry. The gas holder is normally an airproof steel container that, by floating like a ball on afermentation mix, cuts off air to a digester ( anaerobiosis) and collects the gas generated. Thegas holder is equipped with a gas outlet, while the digester is provided with an overflow pipeto lead the sludge out into a drainage pit. The digester reactors are constructed from concreteHollow blocks, cement, and steel.

Fig.1.1 EIGHT (8) CU. METER BIOGAS DIGESTER (Plant lay-out)

EIGHT (8) cu. meter BiogasDigester Plant Lay-out

Table 1 Production Cost of Biogas Plant and other Facilities and Equipment

Quantity Item of expenditures Amount

1 unit biogas system 170,000.00

1 unit water system 50,000.00

1 unit HP motor 10,000.00

1 unit weighing scale 20,000.00

Total 250,000.00

Enhanced Water System FacilitiesOne (1) HP motor was installed and 1,000 liter water tank capacity was fabricated .The Water source is adueqate and enough to sustain the water requirement from dayto day activity in the project site . ( to include the water consumption for the familyand the animals; swine, poultry , etc.)

Enhancement of Piggery HouseThe existing wooden frames used in the roofing of the pens was enhanced throughusing steel bars and angular bars. Due to typhoon Qiel and Sendong last year byheavy winds and rain. devastated the area .

Other Support Activities

TRAININGS

One (1) Training and Biogas Assessment were conducted at Diffun Quirino by theDOST ITDI representatives attended by Biogas farmer operators in the province toassessed the on-going biogas projects established. Some biogas operators wereidentified and helped through technical experts coming from the ITDI , Taguig,Metro Manila.

Fig. Javonillo Biogas Farm, San Antonio, Diffun, Quirino

Student and Farmer traineesvisited the Allias BiogasFarm at Diffun, Quirino

Student and Farmer traineesvisited the Allias BiogasFarm at Diffun, Quirino

Fig Allias Biogas Farm, Aurora West, Diffun, Quirino

Some of the findings were the following:

1. Established biogas projects were functional but the problem still on the sludgearea where sludge is directly flowing in the river ( biogas established at SanAntonio, Diffun, Quirino .owned by Captain Javonillo. There is a need to divertthe sludge area to lessen contamination and pollution near the river banks.

2. The problem on the pressure of the biogas system to operate the water pump (biogas used as electricity by Michael Allias at Aurora West , Diffun

3. Quirino. Some technical measures to again make a wider sludge area open sludgeto increase pressure .

4. The problem on leak ( during rainy and dry season) to limit oxygen or air insidethe tank ) .

PROJECT MANAGEMENT ACTIVITIES ( BIOGAS OPERATION ANDUTILIZATION)

ACTIVITIES Mo.

1

Mo.

2

Mo.

3

Mo.

4

Mo.

5

Mo.

6

Mo.

7

Mo.

8

Mo.

9

Mo.

10

Mo.

11

Mo.

12

Procurement ofEquipment

Installation ofEquipment

Trial Run

Training

ActualOperation andMonitoring

SUMMARY AND CONCLUSIONS

The implementation of this environmentally friendly technique depends widely on apolitical framework that creates and provides an economically attractive incentive for running

biogas (Anaerobic Digester) plants. The Philippine Council for Industry and Energy andEmerging Technology Research and Development ( PCIEERD) , DOST/ITDI renewablepolicy has been widely dessiminated for having been too supportive to provide sufficientfunds for research investments in renewable energy technologies.

The widespread awareness on the importance and manner in which energyutilization a can be introduce and become part of the daily operations of Small Enterprises

For biogas plants to be profitable without a subsidy is to look for alternative revenuesfor small farm businesses to survive and sustain operation.

Implications and Recommendation

The following factors impede or delay the establishment of biogas

1.Time Table affected due to some delays in the construction of the biogas digester due to

heavy rains and typhoons that water flows into the septic tank .

2. Daily amount of manure less than 20 kg

3. Difficulties in manure collection

4. High Construction costs

5. Low income of farmers

6. Low qualification of constructors

7. The lack of strategy to finance biogas projects and the absence of credit lines for farmers

impede the take off of biogas production in the province.

Review of Literature

Biogas Production by Anaerobic Digestion Natural Energy

Anaerobic digestion is a natural process which takes place in the absece of oxygen.Organic materials ia digested by bacteria in a closed reactor vessel and biogas is produced.This controlled process normally accelerated by increasing the reactor temperature into themesphilic range ( normally between 30-37 oC.; or into the thermophilc range ( normallybetween 55-654oC.The decomposition of the material consists of the following basicprocesses ( Dohanyos, et al., 2000).

Since the anaerobic digestion process is usually carried out in a single reactor vesselthe process described above run concurrently biogas consists of 45 -85% methane(CH4) and12-45% Carbon dioxide(CO2).with the exact proportions depending on the productionconditions and processing techniques. In addition, hydrogen sulphide (H2S) , ammonia,(NH3)and nitrogen gas (N2)may be present in small amounts.(Dohanyos, et al., 2000)

Livestock House and Biogas System

To build a biogas system associated with livestock raising is one of the importantcontents of a energy Demonstration Base. Livestock feeding can make use of the agriculturalgrain production, stalk, and othe biomas, which are produced by the base. And the system canalso supply meat and other animal products. The agricultural waste materials such as dung,and distillers grains from ethanol production are better materials to produce biogas. Thebiogas is a kind of high quality fuel which can provide heat energy for the base.(FAOCorporate Documentary Repository produced by Natural Resources Management).

Biogas Production

Materials of Biogas Production

Two kinds of materials are used to produced biogas in this base: Dung (pig waste) anddistillers grains. In a small pig farm, the quantity of dung collection is 4 kg/head. There are90 heads of pigs in the base, so the quantity of dung in each equals to 360 kg/hd. The totalsolods (TS) is 18%. If the fermentation materials entering the digester are calculated by 8% ofTS concentration, the quantity if input mixed materials of digester is 810 kg. In the differentfermentation process and digester construction, the outputs of biogas are different.(NaturalResources Management, 2000).

What is Biogas ?

Biogas is a combustible mixture of gases produced by micro-organism when livestockmanure and other biological waste are allowed to ferment in the absence of air in closed

containers. Wikipedia biogas refers to a gas produced by the biological breakdown of organicmatter in the absence of oxygen. Organic waste such as dead plant and animal material ,animal dung, and kitchen waste can be converted into a gaseous fuel called biogas. Biogasoriginates from biogenic material and is a type of biofuel.

Biogas can potentially help reduce global climate change. Normally, manure that is leftto decompose releases two main gases that cause global climate change; nitrouse dioxide andmethane. Nitrous dioxide ( N02) warms the atmosphere 310 times more than carbon dioxideand methane 21 times more than carbon dioxide. Furthermore by converting manure intomethane biogas instead of letting it decompose, we would be able to reduce warming gases byninety-nine million metric tons or four percent (ISIS Report 2010).

ENVIRONMENTAL OPERATIONAL CONSIDERATIONS OF A BIOGAS PLANT

Raw materials/Influent solids

Raw materials may be obtained from a variety of sources-livestock and poultrywastes. Daily collection of animal waste will be facilitated to reduce the timneof the digester to become operational.

The raw material ratio to water should be 1:1 ( 100 kg of excrete to 100 kg ofwater. In the slurry , this corresponds to a total solids concentration of 8-11percent by weight.

Loading

The size of the digester depends upon loading which determined by the influentsolid content, retention time and the digester temperature. Otpimum loading ratesvary with different digesters and their sites of location. Higher loading rates havebeen used when the ambient temperature is high. The loading rate should be(a)the weight of the total volatile solids (TVS) added per day unit volume of thedigester, or (B) the weight of the TVS assessed per day unit weight of the TVS inthe digester

Seeding

Common practice involves seeding with an adequate population of both the acid-forming and methanogenic bacteria. Actively sludge from a sewage plantconstitutes ideal”seed material. The seed material should be twice the volume of

the fresh manure slurry during the start –up phase, with a gradual decrease inamount added over a three-week period. If the digester accumulates volatile acidsas a results of overloading, the situation can be remedied by reseeding, or byaddition of lime or other alkali.

Ph

Low ph inhibits the growth of the methanogenic bacteria and gas generation andis often the result of overloading. A successful ph range for anaerobic digestionis 6.0-8.0 efficient digestion occurs at ph nears neutrality. A slightly alkalinestate is an indication that ph fluctuations are not too drastic. Low ph may beremedied by dilution or by addition of lime.

Temperature

With a mesophilic flora, digestion proceeds nest at 30-40 C; with thermophils,the optimum range is 50-60 C. The choice of the temperature to be used isinfluenced by climatic considerations. In general, there is no rule of thumb, butfor optimum process stability, the temperature should be carefully regulatedwithin the narrow range of the operating temperature. In warm climate with nofreezing temperatures, digesters may be operated without added heat. As a safetymeasure, it is common practice either to bury the digesters in the ground onaccount of the advantageous insulating properties of the soil, or to use agreenhouse covering. Heat requirements and, consequently ,costs can beminimized through the use of natural materials.

Stirring

The maintenance of optimum microbial activity in the digester is crucial to gasgeneration and consequently is related to nutrient availability. Two mostimportant nutrients are carbon and nitrogen and the critical factor for rawmaterial choice is the overall C/N ratio.

Animal and poultry waste are examples of N-rich materials that providenutrients for the growth and multiplication of the anaerobic organisms. On theother hand, N-poor materials like green grasses corn stubble are rich incarbohydrates substances that are essential for gas production.

Retention Time

Other factors such as temperature, dilution, loading rate , etc. Influence retentiontime. At high temperature bio-digestion occurs faster reducing the time

requirement. A normal period for the digestion of dung would be two to fourweeks.

COLLABORATING AGENCIES FUNCTIONS AND DUTIES

1. Department of Science and Technology shall:

1.1 Facilitate the acquisition/fabrication of all equipment/ materials .

1.2 Monitor, evaluate and document project activities, alternative courses of action to

address problems met, if any during the implementation of the project.

2. Hernandez Swine Production shall:2.1 Coordinate and collaborate with DOST RO2 in the acquisition /fabrication of all

the equipment/materials .2.2 Implement the above project in accordance with the approved technological

intervention2.3 Provide the Site and building to house the equipment and other needed in the

implementation of the project2.4 Coordinate and collaborate with DOST RO2 all activities to be undertaken in

relation to project implementation2.5 Notify DOST RO2 of any deviation in the activities and plan during the

implementation of the project2.6 Be responsible for the day to day operation of the project and ensure that it

progresses to a commercial scale in the shortest time possible.

References

P. Weiland, E. Hassan, Production of biogas from forage beets

Proceedings of the Ninth World Congress, Anaerobic Conversion for Sustainability,Antwerpen, Belgium (2001), pp. 631–633

Martin J.H., Report submitted to US Environmental Protection Agency. EPA Contract No. 68(2003)

T. Birkmose, The Danish Agricultural Advisory Centre, The National Department of CropProduction (2000)

X. Gomez, M.J. Cuetos, A.I. Garcıa, A. Moran, Evaluation of digestate stability fromanaerobic process by thermogravimetric analysis Thermochim. Acta, 426 (2005), pp. 179–184

P. Borjesson, M. Berguld, Environmental systems analysis of biogas systems—Part I: fuel-cycle emissions Biomass Bioenergy, 30 (2006), pp. 469–485

P. Weiland, E. Hassan, Production of biogas from forage beets

PP. Weiland, E. Hassan ,Production of biogas from forage beets,Proceedings of the NinthWorld Congress, Anaerobic Conversion for Sustainability, Antwerpen, Belgium (2001), pp.631–633

Martin J.H., Report submitted to US Environmental Protection Agency. EPA Contract No. 68(2003).

T. Birkmose, The Danish Agricultural Advisory Centre The National Department of CropProduction (2000)

X. Gomez, M.J. Cuetos, A.I. Garcıa, A. Moran,Evaluation of digestate stability fromanaerobic process by thermogravimetric analysis Thermochim. Acta, 426 (2005), pp. 179–184

P. Borjesson, M. Berguld Environmental systems analysis of biogas systems—Part I: fuel-cycle emissions Biomass Bioenergy, 30 (2006), pp. 469–485

P. Weiland, E. Hassan, Production of biogas from forage beets Proceedings of the NinthWorld Congress, Anaerobic Conversion for Sustainability, Antwerpen, Belgium (2001), pp.631–633

Phillippine Council For Industry, Energy and Emerging Technology and Development(PCIEERD), Annual Report, 2012

QSC-RDET ,Technology Adoption and Commercialization of Low Cost and EnvironmentFriendly System,(2000)