Managing Manure withBiogas Recovery SystemsImproved Performance at Competitive Costs

1EPAUnited States EnvironmentalProtection Agency

The AgSTAR Program

Office of Air and Radiation (6202J)EPA-430-F-02-004www.epa.govWinter 2002

One of the biggest challengesthat livestock producers faceis managing manure andprocess water in a way that

controls odors and protects environ-mental quality. Biogas recovery systemscan help producers meet this challenge.The environmental benefits providedby these systems far exceed those sup-plied by “conventional” liquid andslurry manure management systems(e.g., storage tanks, storage ponds,lagoons). These benefits include odorcontrol, improved air and water quality,improved nutrient management flexi-bility, and the opportunity to reducegreenhouse gas emissions and capturebiogas—a useful source of energy.

About AnaerobicDigestionBiogas recovery systems are sometimesknown as anaerobic digesters, becausethey use a process called anaerobicdigestion. (Conventional lagoons oper-ate on the same biological principle.)During anaerobic digestion, bacteriabreak down manure in an oxygen-freeenvironment. One of the natural prod-ucts of anaerobic digestion is biogas,which typically contains between 60 to70 percent methane, 30 to 40 percentcarbon dioxide, and trace amounts ofother gases.

Biogas and energy. When biogas is cap-tured, it can be used to generate heat,hot water, or electricity—significantlyreducing the cost of electricity andother farm fuels such as natural gas,propane, and fuel oil. Biogas can also

be flared to control odor if energyrecovery is not feasible. Both the flar-ing and use of biogas reducegreenhouse gas emissions. Biogas is arenewable source of energy with muchlower environmental impacts than conventional fossil fuel. The methanegenerated from anaerobic digestionprovides rural electric cooperatives andutilities with a source of “green power”to sell to customers who wish to pur-chase power from renewable sources.Biogas recovery also provides ruralenergy benefits such as distributed generation and voltage support.

High-quality fertilizer and soilamendment. Because anaerobic diges-tion reduces ammonia losses, digestedmanure can contain more valuablenitrogen for crop production. Also, thefiber in digested dairy manure can beused on the farm as bedding or recov-ered for sale as a high-quality pottingsoil ingredient or mulch.

Managing Manure with Biogas Recovery Systems 3

Managing Manure with BiogasRecovery SystemsImproved Per formance at Competitive Costs

Floating gas collection cover on a8,600-hog finishing farm lagoon.

Status of AnaerobicDigestionBiogas recovery systems are a proventechnology. Currently, more than 30 digester systems are in operation atcommercial U.S. livestock farms, and an additional 30 are expected to bein operation by 2003.

How Are BiogasRecovery SystemsDesigned?Biogas recovery systems have four basiccomponents: a digester, a gas-handlingsystem, a gas-use device, and a manurestorage tank or pond to hold the treat-ed effluent prior to land application(see Figure 1). Biogas recovery systemsseparate the treatment and storagefunctions. This design provides severalfinancial benefits to producers,including:

■ Lower total volume requirements,which reduce excavation costs andthe land area required for the wastemanagement system.

■ Lower cover costs because of smallerlagoon surface areas.

This multiple-cell process also improvesenvironmental performance. Theseenvironmental benefits are describedlater in this document.

4 Managing Manure with Biogas Recovery Systems

Creating Energy on the Farm and for theCommunity – The Haubenschild ExperienceIn September 1999, Dennis Haubenschild and sons Tom and Bryan,owners and operators of Haubenschild Farms in Princeton, Minnesota,completed the installation of a heated plug flow digester at their 500-cow freestall dairy. The methane-rich biogas generated by thesystem fuels an engine attached to a 150 kWh generator set.

The Haubenschilds sell the excess electricity produced to their localelectric cooperative, East Central Energy (ECE). Heat, recovered ashot water from the engine and exhaust, is stored in an insulated tank and is used to maintain the digester's temperature and heat themilking parlor floor.

In its first two years of operation, the system produced 1.9 million kWhof power from 46 million cubic feet of biogas. The methane recovery system has produced revenues from the sale of electricity and reducedfarm expenditures by virtually eliminating propane purchases, whilecontributing to the farm's environmentally sound manure managementstrategy. “Its great!” reports Dennis Haubenschild. “My digester systemis working, meeting and exceeding my expectations—particularly myenvironmental expectations.”

Under a power purchase agreement, ECE purchases all excess energy from the Haubenschild farm and resells the energy to othercustomers who participate in the cooperative's renewable energy program.

“We're very pleased to assist the Haubenschilds in the development of this exciting new renewable energy project, and the results are particularly noteworthy,” said Henry Fischer, ECE’s Manager ofBusiness and Community Development. “This project exemplifiesECE's mission, which is to enhance the quality of life and provide premier service to our customers,” Fischer added.

Fischer said, “The Haubenschild Farm project is an excellent exampleof how agriculture, utilities, environmental organizations, communitygroups, and others can effectively pool their resources to developrenewable energy, promote sustainable agriculture, and ensure envi-ronmental stewardship.”

Figure 1. Schematic showing thecomponents and products of a biogasrecovery system.

Is a Biogas RecoverySystem Right for My Farm? To determine if a biogas recovery systemis right for your facility, you will needto consider the following factors: howmanure is handled at your facility, thefrequency of manure collection, andthe options available for using therecovered biogas.

■ Manure handling. Biogas digestersystems can accommodate manurehandled as a liquid, slurry, or semi-solid (with little or no beddingadded). The total solids content ofthe manure—a measure of manurethickness—determines these classifi-cations. Figure 2 shows the manurecharacteristics and handling systemsthat are appropriate for specific typesof biogas digester systems.

■ Frequency of manure collection.Facilities best suited for biogasdigester systems typically have stableyear-round manure production, andcollect at least 50 percent of themanure daily.

■ Gas use. Several gas-use options areavailable, including engines, chillers,and boilers, or gas can simply beflared. When choosing among theseoptions, you will need to take intoaccount how the option affects a sys-tem's financial performance, thelabor requirements associated with

the option, and the skills needed tomaintain and repair energy produc-ing equipment.

What Kind ofDigester Will Workon My Farm?Three different types of biogas recoverysystems have been commercialized formanaging manures, and several othertypes of biogas recovery systems arecurrently being developed. The mostsuitable type of system for your opera-tion depends on how you collectmanure and on the total solids contentof the collected manure.

■ A covered lagoon digester is an earth-en lagoon fitted with a cover thatcollects biogas as it is produced fromthe manure. These digesters are best

Managing Manure with Biogas Recovery Systems 5

A compact, clean, low-maintenancewaste management system.

Figure 2. Appropriatemanure characteristics andhandling systems forspecific types of biogasdigester systems.

Farrowing Building

Digester

FlareEngine Room

suited for flush or pit rechargemanure collection systems with atotal solids content of 0.5 to3 percent.

■ A complete mix digester is a heatedtank, constructed of either rein-forced concrete or steel, with agas-tight cover. The digester contentsare mixed periodically, either by amotor-driven impeller or a pump.This digester type works best withslurry manure and with a total solidscontent of 3 to 10 percent.

■ A plug flow digester is a long, rela-tively narrow, heated tank, oftenbuilt below ground level, with a gas-tight cover. Plug flow digesters areused only for dairy manure. Thistype of digester requires thickmanure ranging between 11 and 13percent total solids. Plug flowdigesters can tolerate some bedding,but the amount should be mini-mized, and sand bedding must beavoided.

Plug flow and complete mix digestersare heated systems that operate at aconstant temperature year-round, pro-ducing stable gas flows that supportgas-to-energy applications in all cli-mates. Covered lagoon digesters are notheated, and this can affect gas flow. Inwarmer climates, gas flows are relativelystable during all seasons, and the sys-tems produce enough biogas tofinancially justify energy gas uses.However, in northern climates, gasflows are lower during winter months,so gas use is likely to be limited toflares, with odor control and green-house gas reductions as themanagement objective.

AgSTAR provides several project sup-port products about each of thesedigester systems. They are available freeof charge from the AgSTAR programat 1-800-96AgSTAR (1-800-952-4782)or on the AgSTAR Web site atwww.epa.gov/agstar.

The EnvironmentalBenefits ofAnaerobic DigestionSystemsLivestock confinement facilities gener-ate large amounts of animal waste thatcan create serious environmental con-cerns. The concentrated waste productfrom decomposing livestock manurecan be environmentally detrimental ifit enters rivers, streams, or groundwatersupplies. Decomposing manure alsocauses air quality concerns associatedwith odor, ammonia emissions, and thecontribution of methane emissions toglobal climate change. Anaerobic diges-tion offers a number of air and waterquality benefits, including:

■ Odor control. The effluent odorfrom anaerobic digesters is signifi-cantly less than odors fromconventional manure managementsystems. Odor reduction usinganaerobic digestion can be very cost-effective when compared toother alternatives such as aeration.

6 Managing Manure with Biogas Recovery Systems

Complete mix digester.

Plug flow digester.

■ Greenhouse gas reduction.Conventional liquid and slurrymanure management practices emitlarge amounts of methane, a green-house gas that contributes to globalwarming. Biogas recovery systemscapture and combust methane, thusreducing greenhouse gas emissions.In addition, by off-setting energythat would otherwise be derivedfrom fossil fuels, biogas recovery anduse can help reduce overall quanti-ties of carbon dioxide, anothercritical greenhouse gas.

■ Ammonia control. Ammonia emis-sions from livestock manures—especially emissions from anaerobiclagoons used in the treatment andstorage of these manures—are agrowing environmental concern. Tocontrol ammonia emissions, produc-ers can cover manure storage tanks.Because gas handling is not required,the storage structures of anaerobicdigester systems, which separatetreatment and storage, are smallerand easier to cover than the largerstructures of traditional systems.

■ Water quality protection. Anaerobicdigestion provides several waterquality benefits. When an anaerobicdigester system, especially a coveredlagoon, is properly managed, phos-phorous and metals, such as copperand zinc, will settle out in theprocess cells, thus reducing phospho-rous and metals loadings to surfacewaters when manure is land-applied.Digester systems, especially heateddigesters, isolate and destroy disease-causing organisms that mightotherwise enter surface waters andpose a risk to human and animalhealth. Anaerobic digestion alsohelps protect ground water.Synthetic liners provide a high levelof groundwater protection formanure management systems. Theseprotective liners are a more afford-able option with anaerobic digestersystems than with conventionallagoons, because the multiple-celldesign of anaerobic digesters requires

less volume and, therefore, less lin-ing material is needed. The concreteor steel tanks used in plug flow andcomplete mix digesters also effective-ly prevent untreated manure fromreaching ground water.

How Much Do TheseBenefits Cost? Livestock producers can choose from awide range of waste managementoptions provided by a variety of agri-cultural engineers, vendors, andequipment suppliers. The costs of theseoptions can vary greatly, in terms ofboth initial investment and annualoperation and maintenance. For exam-ple, the cost of a typical manure storagefacility can range between $60 perAnimal Unit (AU) for a typical pondto $300 per AU for an above-groundprefabricated tank. (An AU equals1,000 pounds live animal weight, orapproximately the weight of one beef

Managing Manure with Biogas Recovery Systems 7

What AgSTAR Provides

To find out more about the opportunities that digester technologycan offer the livestock industry, AgSTAR provides information andtools to help swine and dairy producers make informed decisionsabout these technologies:

■ The AgSTAR Handbook, a comprehensive manual developed toprovide guidance on developing biogas technology at commercialfarms.

■ FarmWare, an expert decision-support software package that you can use to conduct biogas recovery system prefeasibilityassessments.

■ The AgSTAR Industry Directory, which you can use to identify consultants, project developers, energy services, equipment manufacturers and distributors, and commodity organizations.

■ The AgSTAR Web site (www.epa.gov/agstar), which contains alibrary where you can download the resources listed above. Inaddition, the Web site includes information on farm-scaledigesters currently operating at commercial livestock farms in the U.S., as well as articles and case studies.

Contact an AgSTAR representative at 1-800-952-4782 or visit theAgSTAR Web site at www.epa.gov/agstar.

cow.) Similarly, an open-air conven-tional lined lagoon that combines bothtreatment and storage functions canrange between $200 to $400 or moreper AU, depending on annual rainfalland process water use at the facility.

Anaerobic digestion is cost-competitivewhen compared to conventional wastemanagement practices. For example,the installed cost of both a coveredlagoon and heated digester (includingan attached storage pond) rangesbetween $200 and $450 per AU. Thesesystems can also have financially attrac-tive payback periods of 3 to 7 yearswhen energy gas uses are employed.

Conventional waste systems, in con-trast, do not provide this paybackopportunity and become sunk costs tothe farm enterprise.

The Environmental Effectiveness Tableabove compares conventional wastemanagement options to their environ-mental benefits. The table is intendedto provide livestock producers with aneasy-to-use tool to understand the envi-ronmental performance that they canachieve with their investment dollar.This type of comparison can help pro-ducers make informed businessdecisions related to the environmentand the neighboring community. (TAB1)

8 Managing Manure with Biogas Recovery Systems

Environmental Effectiveness of Manure Management Options

Greenhouse Water Cost Range††

Options Odor Gas Quality (per 1,000 lbs/Control Reduction Protection live weight)

Covered lagoon digesters with open storage ponds E H G $150-400

Heated digesters (i.e., complete mix and plug flow) with E H G $200-400open storage tanks

Aerated lagoons with open storage ponds† G-E H F-G $200-450

Separate treatment lagoons and storage ponds F-G L G $200-400(2-cell systems)

Combined treatment lagoons and storage ponds P-G L F-G $200-400

Storage ponds and tanks P-F M-H P-F $50-500

Key: P=poor, F=fair, G=good, E=excellent, L=low, M=medium, H=high†Aerated lagoon energy requirements add an additional $35-50 per 1,000 lbs/year.††Cost ranges do not include annual operation and maintenance (O&M) costs.

Here’s what some digesterowners have to say abouttheir biogas recoverysystems:

“Community and consumer-owned electric systems canrealize benefits fromdistributed generation, whilesupporting biogas projectsthat conserve energy andprovide economic andenvironmental solutions forfarmers and ruralcommunities.”

Greg Booth, Power Manager,Tillamook People’s Utility District,

Oregon

“I want my operation toproduce and exist withoutmy neighbors even knowingI'm there. And I want toleave the environment inbetter shape than I found it.”

Julian Barham, speaking aboutthe environmental benefits of the

covered lagoon digester at his4,000-sow farrow-to-wean

operation in North Carolina

For more information about methanerecovery technologies, contact anAgSTAR representative at:

1-800-95AgSTAR (1-800-952-4782)(Hours of Operation: 9:00am to5:00pm EST)

www.epa.gov/agstar