Anaerobic Digestion of Animal   ATTRA Wastes: Factors to Consider    A Publication of ATTRA - National Sustainable Agricul...
AgStar. AgStar estimates that anaerobic         Digestion Process                     digestion could be cost-effective on...
been at work in nature for millions of years,     indication that no single system is right forcan be managed to convert a...
Temperature is just one of the many impor-        a deadly poison. It is critical that digester                        tan...
Table 2. Energy Content of Bio-gas from Various Animals                                           Swine          Dairy    ...
generate 70 percent of its electri-      wood chips impregnated with iron oxide                              cal needs wit...
For anyone considering an anaerobic-diges-            desired retention time. The most manage-tion system, the single most...
North Carolina State’s Extension Service            As noted previously, regular—but not                            goes o...
experienced problems that prevented it from      If done right, however, this decision isrealizing its expected revenues. ...
evaluation with a full example of how it should       10. Jones, Don D., John C. Nye, and Alvin C. Dale.          be used....
AgSTAR Handbook and Software                            Manurenet         ...
Lusk, P. 1998. Methane Recovery From Animal       Manures: A Current Opportunities Casebook,       3rd edition. NREL/SR-25...
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Anaerobic Digestion of Animal Wastes: Factors to Consider

  1. 1. Anaerobic Digestion of Animal ATTRA Wastes: Factors to Consider A Publication of ATTRA - National Sustainable Agriculture Information Service • 1-800-346-9140 • www.attra.ncat.orgBy John Balsam Anaerobic digestion is an alternative solution to livestock waste management that offers economicNCAT Energy and environmental benefits. This publication provides an introduction to the technology of bio-gas,Specialist digester design considerations, and system costs with discussion of the digestion process, production,Updated by uses, and risks. Useful tables and further resources are included.Dave RyanNCAT EnergySpecialist Introduction R©2006 NCAT ising energy prices, broader regu- latory requirements, and increasedContents competition in the marketplace are causing many in American agriculture’sIntroduction ..................... 1 livestock sector to consider anaerobic diges-Digestion Process........... 2 tion of animal wastes. They view the technol-Bio-Gas: A Resource ogy as a way to cut costs, address environ-Requiring Care ................ 4 mental concerns, and sometimes generateEnergy Content and new revenues.Relative Value ofBio-Gas ............................... 4 Turkeys. Photo by Jeff Vanuga. While hundreds of anaerobic-digestion sys-Uses of Bio-Gas ............... 5 tems have been installed in Europe and theRefining Bio-Gas into U.S. since the 1970s, it was not until theBiomethane ...................... 6 1990s that better designed, more successfulRisks Associated with projects started to come on line in the U.S.Bio-Gas ............................... 6 Today, an estimated 97 farm-scale projectsDigester Design are in operation, in start-up, or under con-Factors ................................ 6 struction on swine, dairy, and poultry farmsSystem Costs .................... 8 across the country. (1)Summary ........................... 9Assessment Key by-products of anaerobic diges-Resources .......................... 9 tion include digested solids and liquids,References ...................... 10 Sow with piglet. Photo by Scott Bauer. which may be used as soil amendmentsFurther Resources ........ 10 or liquid fertilizers. Methane, the primary component of “bio-gas,” can be used to fuel a variety of cooking, heating, cooling, and lighting applications, as well as to gen- erate electricity. Capturing and using the methane also precludes its release to the atmosphere, where it has twenty-one timesATTRA—National Sustainable more global warming potential thanAgriculture Information Service carbon dioxide. (2)is managed by the National Cen-ter for Appropriate Technology Despite the many benefits, anaerobic diges-(NCAT) and is funded under agrant from the United States tion systems are not appropriate for all farmDepartment of Agriculture’s operations. A cooperative effort among theRural Business-Cooperative Ser-vice. Visit the NCAT Web site Cows and calves. Photo by Lynn Betts. U.S. Departments of Agriculture, Energy( All photos this page courtesy of USDA/ARS. and the Environmental Protection Agencyhtml) for more informa-tion on our sustainable to promote bio-gas projects is known asagriculture projects. ����
  2. 2. AgStar. AgStar estimates that anaerobic Digestion Process digestion could be cost-effective on about Anaerobic digestion works in a two-stage 7,000 U.S. farms. (3) A critical issue is process to decompose organic material planning; each system needs to be designed (i.e., volatile solids) in the absence of oxy- to accommodate a variety of factors. This gen. Bio-gas is produced as a waste product publication provides an overview of those of digestion. In the first stage, the volatile factors and identifies resources for addi- solids in manure are converted into fatty acids by anaerobic bacteria known as “acid tional detailed information. Several of these formers.” In the second stage, these acids resources include computational analysis are further converted into bio-gas by more tools to help users determine whether an specialized bacteria known as “methane anaerobic digestion system could be a cost- formers.” With proper planning and design, effective addition to their operation. this anaerobic-digestion process, which has Figure 1. Basic components of an anaerobic-digestion system (4) Gas Receiver Gas Clean-up Compression Equipment Fuel Use or Storage Mixer Manure Slurry Heat Exchanger Effluent Storage or Disposal DigesterPage 2 ATTRA Anaerobic Digestion of Animal Wastes: Factors to Consider
  3. 3. been at work in nature for millions of years, indication that no single system is right forcan be managed to convert a farm’s waste- all or even most into an asset. Starting the digestion process is not dif-There are several types of anaerobic digesters. ficult, but it does require patience. The digester tank is filled with water and thenCovered lagoons—A pool of liquid manure heated to the desired temperature. “Seed”topped by a pontoon or other floating cover. sludge from a municipal sewage treatmentSeal plates extend down the sides of the plant is then added to 20 to 25 percent ofpontoon into the liquid to prevent exposure the tank’s volume, followed by graduallyof the accumulated gas to the atmosphere. increasing amounts of fresh manure overDesigned to use manure with two percent a six to eight-week period until the desiredor less solid content, this type of digester loading rate is reached. Assuming that therequires high throughput in order for the temperature within the system remains rela-bacteria to work on enough solids to produce tively constant, steady gas production shouldgas. Most frequently used in warmer south- occur in the fourth week after start-up. Theern regions, where the atmospheric heat can bacteria may require two to three months to Shelp maintain digester temperatures, this is multiply to an efficient population. (6) tarting thethe least expensive of all designs to installand operate. About 18 percent of all digest- There are two distinct temperature ranges digestion pro-ers presently in use in the U.S. are covered- most suitable for gas production, and differ- cess is notlagoon systems. ent bacteria operate in each of these ranges. difficult, but it does Mesophilic bacteria optimally function in require patience.Complete mix—A silo-like tank in which the 90° to 110°F range. Thermophilicthe manure is heated and mixed, designed bacteria are most productive in the 120°to handle manure with two to ten percent to 140°F range. Thermophilic digestionsolids. This is the most expensive system kills more pathogenic bacteria, but it hasto install and operate, but it’s particularly higher costs due to maintaining higher tem-appropriate for operations that wash out peratures, and thermophilic digesters maymanure. About 28 percent of all digesters be less stable. Bacterial digestion in cov-in use in the U.S. are of this type. ered lagoons at temperatures below 90°F isPlug flow—A cylindrical tank in which called psychrophilic. Psychrophilic meansthe gas and other by-products are pushed a preference for lower temperatures; how-out one end by new manure being fed into ever, digestion slows down or stops com-the other end. This design handles 11 to pletely below 60° or 70°F, so these digest-13 percent solids and typically employs hot- ers do not produce methane all of the time.water piping through the tank to maintain Temperature within the digester is criti-the necessary temperature. Most appro- cal, with maximum conversion occurring atpriate for livestock operations that remove approximately 95°F in conventional meso-manure mechanically rather than washing it philic digesters. For each 20°F decrease inout, the plug-flow system accounts for more temperature, gas production falls by approx-than half of all digesters presently in use. imately 50 percent. (7)Fixed film—A tank is filled with a plastic Even more significant is the need to keepmedium that supports a thin film of bacteria the temperature steady. Optimal opera-called a biofilm. This design handles one tion occurs when the methane formers useto two percent solids, and uses a shorter all the acids at approximately the sameretention time, as short as two to six days. rate that the acid formers produce(5) Only about one percent of systems cur- them. Variations of as little as 5°F canrently installed in the U.S. are of this type. inhibit methane formers enough to tip theThere are also a number of hybrid sys- balance of the process and possibly causetems being designed and installed, a strong system failure. (7) ATTRA Page 3
  4. 4. Temperature is just one of the many impor- a deadly poison. It is critical that digester tant factors in successfully starting and systems be designed with adequate venting operating an anaerobic-digestion system. to avoid these dangerous situations. (7) The other key factors include: Storage. Because of the high pressure Loading rate. The system’s design will dic- and low temperature required, it is tate loading rates and contents, but experi- impractical to liquefy methane for use as ence indicates that uniform loading, on a a liquid fuel. Instead, the gas can be col- daily basis, of manure with 6 to 10 per- lected and stored for a period of time until cent solids generally works best. The load’s it can be used. The most common means retention time in the digester will typically of collecting and storing the gas produced range from 15 to 30 days. by a digester is with a floating cover—a weighted pontoon that floats on the liquid Mixing. The loaded manure needs to be surface of a collection/storage basin. Skirt mixed regularly to prevent settling and to plates on the sides of the pontoon extend maintain contact between the bacteria and down into the liquid, thereby creating a seal the manure. The mixing action also pre- and preventing the gas from coming into vents the formation of scum and facilitatesT contact with the open atmosphere. High- he most release of the bio-gas. pressure storage is also possible, but is both common Nutrients. The best digestion occurs with more expensive and more dangerous and means of col- a carbon to nitrogen ratio between 15:1 should be pursued only with the help of alecting and storing and 30:1 (optimally 20:1). Most fresh ani- qualified engineer.the gas produced mal manures fall within this range andby a digester is with require no adjustment. Nutrient imbalance Bio-Gas: A Resource can occur, however, if excessive amountsa floating cover—a of exposed feedlot manure become part of Requiring Careweighted pontoon the load. Adding crop residues or leaves Bio-gas produced in an anaerobic digesterthat floats on the (both can be heavy in carbon) can improve contains methane (60 to 70 percent),liquid surface of a digester performance. carbon dioxide (30 to 40 percent), and various toxic gases, including hydrogencollection/storage Management. Anaerobic digesters require sulfide, ammonia, and sulfur-derivedbasin. regular and frequent monitoring, primar- mercaptans. Bio-gas also typically contains ily to maintain a constant desired tempera- 1 to 2 percent water vapor. ture and to ensure that the system flow is not clogged. Failure to properly manage the digester’s sensitivity to its environment can Energy Content and Relative result in a significant decline in gas produc- Value of Bio-Gas tion and require months to correct. At roughly 60 percent methane, bio-gas Safety. Working with anaerobic digester possesses an energy content of 600 Btu/ bio-gas, and especially with methane (the ft3. For comparison, Table 1 presents the major component of the gas), warrants energy content of several other well-known extreme caution. Methane, when mixed with energy sources. air, is highly explo- sive. In addition, Table 1: Energy Content of Common Fuels because digester gas is heavier than Propane 92,000 Btu/gal Diesel fuel 138,000 Btu/gal air, it displaces Natural Gas 1,000 Btu/ft3 No. 2 fuel oil 138,000 Btu/gal oxygen near the Electricity 3,414 Btu/kWh Coal 25,000,000 Btu/ton g round, and i f Source: Barker, James C. 2001. Methane Fuel Gas from Livestock Wastes: A Sum- hydrogen sulfide mary. North Carolina State University Cooperative Extension Service, Publication is still present, #EBAE 071-80. the gas can act asPage 4 ATTRA Anaerobic Digestion of Animal Wastes: Factors to Consider
  5. 5. Table 2. Energy Content of Bio-gas from Various Animals Swine Dairy Beef Poultry (per (per (per (layers) head) head) head) (per bird) Animal weight (lbs.) 135 1,400 800 4 Expected Energy Content Gross energy content 2,300 27,800 16,600 180 (Btu/head/day) Net energy content (Btu/ 1,500 18,000 10,700 110 head/day) (uses 35% of gross to operate digester) Source: Barker, James C. 2001. Methane Fuel Gas from Livestock Wastes: A Summary. North Carolina State University Cooperative Extension Service, Publication #EBAE 071-80.Putting these energy-content values in thecontext of an anaerobic-digestion system Table 3. Bio-gas Gas Net Returns from Various Animalsmeans the energy production per animal Poultry Swine Dairy Beefcan be estimated, as seen in Table 2. (layers) Electricity Equivalent ----- per head per year -----In Table 3, North Carolina State Univer-sity’s Cooperative Extension Service has kWh (20% combined 32 385 230 2.5 generating efficiency)converted the energy-content figures fromTable 2 into bio-gas net returns relative to Value (@ $.085/kWh) $2.76 $32.73 $19.55 $0.21four other common energy sources. Natural Gas Equivalent Mcf 0.55 6.60 3.90 0.04Uses of Bio-Gas Value (@ $11.04/Mcf) $6.07 $72.89 $43.07 $0.44Because of the extreme cost and difficulty Propane (LP Gas)of liquefying bio-gas, it is not feasible for Equivalentuse as a tractor fuel. Bio-gas has many other Gallons 6 72 43 0.45on-farm applications, however, including Value (@ $2.00/gallon) $12.00 $144.00 $86.00 $0.90virtually anywhere natural gas is used—for No. 2 Fuel Oil Equivalentcooking, heating (space heating, water heat- Gallons 4 48 28 0.3ing, grain drying), cooling, and lighting. In Value (@ $2.00/gallon) $8.00 $96.00 $56.00 $0.60most cases, the equipment designed to burn Source: Barker, James C. 2001. Methane Fuel Gas from Livestock Wastes: A Sum-natural gas will require certain modifica- mary. North Carolina State University Cooperative Extension Service, Publica-tions to accommodate the slightly different tion #EBAE 071-80. Updated to 2006 prices by NCAT.burn characteristics of bio-gas.Bio-gas can also be used to fuel generators 1. A well-insulated, three-bedroomto produce steam and electricity. In some home that requires 900,000 Btu/cases, the electricity can be sold to a local day for heating in cold weatherutility, possibly in a net metering arrange- could be served by 50 dairy cat-ment. This option should be explored early, tle, 600 hogs, or 7,870 layershowever, to make sure the utility is amena- (assuming that around 35 per-ble to such arrangements. cent of the bio-gas produced will be used to maintain theNorth Carolina State University’s Coopera- digester’s temperature).tive Extension Service developed severalspecific examples of how bio-gas can be 2. A dairy using the national aver-applied on-farm: age of 550 kWh/cow/year ATTRA Page 5
  6. 6. generate 70 percent of its electri- wood chips impregnated with iron oxide cal needs with bio-gas (assuming (iron sponge) or through activated carbon. 20 percent generator efficiency and Carbon dioxide can be removed by bub- that around 35 percent of the bio- bling the bio-gas though water in a vertical gas produced will be used to main- column packed-bed scrubber. Finally, tain the digester’s temperature). moisture can be removed by flowing the 3. A swine operation that uses about bio-gas through a refrigerated coil. (9) 55 kWh of electricity and 5.75 gal- lons of LP gas per hog per year Risks Associated with Bio-Gas (including feed mill and incinera- While methane is a very promising energy tor) could supply 40 percent of its resource, the non-methane components of energy needs with bio-gas (assum- bio-gas (hydrogen sulfide, carbon dioxide, ing 20 percent generator effi- and water vapor) tend to inhibit methane ciency and that around 35 per- production and, with the exception of the cent of the bio-gas produced will water vapor, are harmful to humans and/ be used to maintain the digester’s or the environment. For these reasons, theD temperature). igesters are bio-gas produced should be properly installed The number of animals required for a “cleaned” using appropriate scrubbing and digester system to be cost effective depends separation techniques. primarily upon your situation and upon what you wishfor economic and/or to get out of the digester. Some dairy opera- In addition, the methane itself representsenvironmental rea- tions with as few as 100 cows have installed a serious danger, as it is odorless, color-sons. cost effective digester systems for odor con- less, and difficult to detect. Methane is also trol that also produce digested solids. (8) highly explosive if allowed to come into con- tact with atmospheric air at proportions of 6 Refining Bio-Gas into to 15 percent methane. For these reasons, it is recommended that buildings be well ven- Biomethane tilated; motors, wiring, and lights should The bio-gas produced in the methane be explosion-proof; flame arrestors should digester is primarily methane and car- be used on gas lines; and alarms and gas- bon dioxide, with traces of hydrogen sul- detection devices should be used. fide, and other gasses. Bio-gas by itself can be used as-is for heating and for cooking. However, use of raw bio-gas in Digester Design Factors heating equipment and in internal com- Digesters are installed primarily for eco- bustion engines will cause early failures nomic and/or environmental reasons. because of the corrosive nature of the Digesters represent a way for the farmer to hydrogen sulfide and water vapor. Carbon convert a waste product into an economic dioxide in the bio-gas lowers the heating asset, while simultaneously solving an envi- value of the gas. It should be noted that the ronmental problem. Under ideal conditions, bio-gas from the digestion of animal wastes an anaerobic-digestion system can convert does not have some of the contaminants of a livestock operation’s steady accumulation bio-gas from landfills or municipal waste of manure into a fuel for heating or cooling water treatment plants and is therefore eas- a portion of the farm operation or for fur- ier to clean up. ther conversion into electricity for sale to a Hydrogen sulfide is corrosive and smelly. It utility. The solids remaining after the diges- can be removed from the bio-gas by inject- tion process can be used as a soil amend- ing less than six percent volume of air into ment, applicable on-farm or made available the bio-gas in the gas reservoir, by add- for sale to other markets. Unfortunately, ing iron chloride to the digester influent such ideal conditions seldom exist, in part stream, or by flowing the bio-gas through because of faulty planning and design.Page 6 ATTRA Anaerobic Digestion of Animal Wastes: Factors to Consider
  7. 7. For anyone considering an anaerobic-diges- desired retention time. The most manage-tion system, the single most important able of these factors is retention time; lon-point to understand is that each farmer’s ger retention times mean more completesituation is unique, and as such, requires breakdown of the manure contents, butcareful consideration of many factors. require a larger tank. Table 4, developedAnaerobic-digestion systems can be quite by North Carolina State University’s Coop-costly to install, so the owner should fully erative Extension Service, presents one setunderstand the purpose of the system and of recommended loading rates and dilutionits economics. ratios for different animals. Other sourcesThe size of the system is determined pri- provide similar yet different recommen-marily by the number and type of ani- dations, underscoring the importance ofmals served by the operation, the amount working with an individual experienced inof dilution water to be added, and the designing anaerobic-digestion systems. Table 4. Energy Content of Bio-gas from Various Animals Poultry Swine Beef Dairy (per (layers) (per (per head) (per head) head) bird) Design Criteria Animal weight (lbs) 135 1,400 800 4 Total fresh manure & urine 1.35 12.5 6.1 0.032 (gal/day) Solids content (%) Before dilution 10.0 15.0 15.0 25.0 After dilution 6.7 8.0 8.0 8.0 Total waste volume after 2 24 12 0.1 dilution (gal/day) Volatile solids production 1 12 5 0.038 (VS lbs/day) Digester loading rate (lbs 0 0 0 0.125 VS/ft3 digester/day) Digester volume (ft3/head) 5 47 19 0.3 Retention time (days) 20 15 13 22.5 Probable VS destruction 50 35 45 60 (%) Anticipated Gas Yield Yield (per ft3 digester vol- 1 1 1 1 ume) Yield (ft3/head/day) 4 46 28 0.29 Gross energy content (Btu/ 2,300 27,800 16,600 180 head/day) Net energy content (Btu/ 1,500 18,000 10,700 110 head/day) (uses 35% of gross to operate digester) Source: Barker, James C. 2001. Methane Fuel Gas from Livestock Wastes: A Summary. North Carolina State University Cooperative Extension Service, Publication #EBAE ATTRA Page 7
  8. 8. North Carolina State’s Extension Service As noted previously, regular—but not goes on to provide several good examples necessarily continuous—mixing of the (see Table 5) of how digester tank sizes digester’s contents is important to maxi- can be computed using the information mize gas production. This mixing can in Table 4. be performed by a mechanical mixer; Digesters must be airtight and situated so by a compressor, which bubbles the col- that they can be heated, usually with hot- lected gas back through the digester; or water piping running in and out of the by a closed-circuit manure pump. (10) digester tank. It may be possible to heat the Purdue University’s Cooperative Exten- water using the methane produced by the sion Service suggests that the mechani- digester. The tank should also be insulated cal mixer works well, as long as a good to help it retain optimal operating tempera- air seal is maintained. Purdue Extension tures. Many practitioners take advantage of also provides the following formula to deter- the soil’s insulating effect by at least par- mine the horsepower needed to mix the tially burying the digester tank in a pit or digester contents: piling the soil up against the tank’s sides. hp = .185 x % total solids x liquid capacity (in 000s of ft3) Table 5. Configuring Digester Tank Size Example 1: 100 cow dairy herd As an example, a 10,000-ft 3 digester containing waste with 6 percent solids Fresh manure @ 15% solids 1,250 gal/day would require an 11.1-hp mixer (.185 x 6% Milk center wash water 500 gal/day x 10). Dilution water required for 8% solids 600 gal/day Total waste volume generated 2,350 gal/day System Costs Digester retention time 15 days The cost of an anaerobic-digestion system Tank capacity (15 x 2,350) 32,250 gal can vary dramatically depending on its Suggestion: Round tank 18 ft. diam. x 18.5 ft. tall size, intended purposes, and sophistication. Example 2: 200 sow farrow-to-finish operation Covered lagoon system cost can be as low Fresh manure @ 10% solids 2,830 gal/day as $25,000 for 150 animals (swine) and as high as $1.3 million for 5,000 animals Additional water from leaking waterers, 1,415 gal/day (dairy). Plug flow digesters range from foggers, etc. $200,000 for 100 dairy cows, to $1.8 mil- Total waste volume generated 4,245 gal/day lion for 7,000 dairy cows. (11) Digester retention time 20 days These costs, of course, must be weighed Tank capacity (20 x 4,245) 84,900 gal against revenue streams developed with Suggestion: Round tank 24 ft. diam. x 25 ft. tall digestion’s by-products. In 1998, Mark Example 3: 50,000 bird layer operation Moser, Richard Mattocks, Stacy Gettier, Fresh manure @ 25% solids 1,620 gal/day PhD, and Kurt Roos—all highly regarded Dilution water required for 8% solids 3,440 gal/day experts in the anaerobic-digester field— Total waste volume generated 5,060 gal/day studied the economic returns of seven AgSTAR digester projects. Revenues Digester retention time 22.5 days came from electric generation, and sale Tank capacity (22.5 x 5,060) 113,850 gal of digested fiber for compost, and from Suggestion: Round tank 7 ft. diam. x 26.5 ft. tall reduced costs for natural gas and propane, Source: Barker, James C. 2001. Methane Fuel Gas from Livestock Wastes: A as well as reduced bedding costs. Costs Summary. North Carolina State University Cooperative Extension Service, and annual revenues of four of these proj- Publication #EBAE 071-80. ects are available from the Minnesota Proj- ect. Of the remaining three projects, two were developed primarily for odor control rather than financial payback, and the thirdPage 8 ATTRA Anaerobic Digestion of Animal Wastes: Factors to Consider
  9. 9. experienced problems that prevented it from If done right, however, this decision isrealizing its expected revenues. (12) not a simple one. It should involve careful planning and design, preferably with inputThe AgSTAR Program evaluators believe from an engineering professional and/anaerobic digestion can be cost-competitive or someone well experienced with anaer-relative to conventional waste-management obic-digestion systems. This planningpractices (e.g., storage tanks, storage ponds, process must consider a long list of factors.lagoons). When the bio-gas produced by thesystem is put to work, digesters can report- Factors to Consideredly have payback periods of three to sevenyears, substantially more attractive than • The specific benefits to be derivedthe sunk costs typically associated with • The number and kind of animals to beconventional approaches. (13) served • Where the system might be placed Construction Costs and Annual Benefits • How the manure and other inputs will be collected and delivered to the system Barham Covered $289,474 $46,000 A Farm Lagoon per/year • How the required temperatures will be maintained naerobic Martin Covered $95,200 $16,000 Family Lagoon per/year • How all the risks associated with the pro- digesters Farm cess, some of which are substantial, will be are installed mitigatedOther digester case studies can be found for various rea- • How the outputs will be handled sons—as a meansat • The amount of monitoring and manage- to resolve environ- ment time required mental problems,Summary as a means to eco-Anaerobic digesters are installed for vari- Assessment Resources nomically re-use anous reasons—as a means to resolve environ- Because anaerobic digesters are expen- otherwise wastedmental problems, as a means to economi- sive to install and manage, the above con- resource, and as acally re-use an otherwise wasted resource, siderations and many others should be source of additionaland as a source of additional revenue. All researched and then factored into an eco-of these factors typically play a role in an revenue. nomic-feasibility assessment. A number ofowner’s decision to install a system. resources have been developed to guide a prospective system owner through this assessment process: • AgSTAR Program, the premier U.S. resource for information and assistance relating to methane digesters. • Manurenet, the leading Canadian resource that also includes projects and providers in the U.S. and other countries. • Various sources offer self-evaluation forms to estimate the potential of aCow and calf. Photo by Lynn Betts. successful digester system installa-Courtesy of USDA/NRCS. tion. The Cooperative Extension Service at Purdue University’s Department of Agricultural Engineering offers a ATTRA Page 9
  10. 10. evaluation with a full example of how it should 10. Jones, Don D., John C. Nye, and Alvin C. Dale. be used. ( 1980. Methane Generation from Livestock Waste. 105.html). Though somewhat dated (published Publication #AE-105. Purdue University Cooper- in 1980), the steps in the worksheet and most of ative Extension Service, West Lafayette, IN. 15 p. the values used should still be valid. Only some of the dollar values, such as the current price pubs/methane.htm of energy, will need to be updated. Another 11. U.S. Environmental Protection Agency. Guide evaluation tool can be found at Environomics. to Operational Systems. AgSTAR Program. 4 p. _screening_ form.htm 12. Moser, Mark A., Richard P. Mattocks, Dr. Stacy Gettier, and Kurt Roos. 1998. Benefits, Costs andReferences Operating Experience at Seven New Agricultural1. AgStar Digest Winter 2006 Anaerobic Digesters. U.S. Environmental Protec- tion Agency. 7 p.2. Environmental Protection Agency Methane Web Page 13. U.S. Environmental Protection Agency. 2002.3. AgStar - Market Opportunities for Biogas Managing Manure with Biogas Recovery Systems: Recovery Systems Improved Performance at Competitive Costs. 8 p. ems_screenres.pdf Further Resources4. Hansen, R.W. 2001. Methane Generation from AgSTAR Program Livestock Wastes. Publication #5.002. Colorado State University Cooperative Extension Service. Ft. Collins, CO. 6 p. Introduction to Systems and Concepts farmmgt/05002.html Contains fact sheets that introduce the types of gas recovery systems currently in use. The fact5. AgStar Digest Winter 2003 sheets describe the systems and provide brief case study snapshots of operating systems (still6. Jones, Don D., et al. 1980. Methane Digestion in development). from Livestock Waste http://pasture.ecn.purdue. AgSTAR Digest edu/%7Eepados/swine/pubs/methane.htm Barker, James C. 2001. Methane Fuel Gas from Contains all editions of the program’s annual newsletter (starting in 1998). Livestock Wastes: A Summary. Publication #EBAE 071-80. North Carolina State University Industry Directory for On-Farm Biogas Recovery Systems Cooperative Extension Service, Raleigh, NC. 10 p. (2nd ed., July 2003) Helps farm owners and others interested in on-farm biogas recovery publicat/wqwm/ebae071_80.html systems identify appropriate consultants, proj- ect developers, energy services, equipment8. The Minnesota Project. Anaerobic Digester Sys- manufacturers and distributors, and commod- tems for Mid-Sized Dairy Farms. ity organizations. It provides company descrip- tions and contact information for each listed %20update.pdf business.9. Sustainable Conservation. Biomethane from AgSTAR Press Dairy Waste: A sourcebook for the Production and Use of Renewable Natural Gas in California. Contains news and media articles on digester systems from BioCycle, Agri News, and Chapter_3.pdf other resources.Page 10 ATTRA Anaerobic Digestion of Animal Wastes: Factors to Consider
  11. 11. AgSTAR Handbook and Software Manurenet A comprehensive manual (8 chapters; 8 man_digesters.html appendices; glossary) developed to provide Selecting a Digester System guidance on developing biogas technology for commercial farms. The Handbook also con- man_digesters.html#Selecting tains FarmWare, an expert decision support Access to six articles addressing the software package that can be used to conduct details involved in selecting a methane- pre-feasibility assessments. digester system.USDA-NRCS Biogas Interim Standards Cogeneration Power Sources Available in Appendix F of the Handbook. digesters.html#Co-Generation Access to 11 articles discussing engines andTechnical and Environmental Articles other technologies used with a methane- digester system to generate power. Contains an array of technical, economic, and science-based publications, including European, Canadian, and U.S. Digester Programs, an excellent article titled Benefits, Costs and Projects, and Providers/Consultants Operating Experience at Seven New Agricul- tural Anaerobic Digesters. man_digesters.html#European Report: Haubenschild Farms Anaerobic Digester man_digesters.html#Canadian Haubyrptupdated.pdf man_digesters.html#U.S.A.%20Digester The Minnesota Project’s final report for Numerous instructional articles, case studies, the Haubenschild Dairy manure-to- and reports detailing the development methane digester. and operation of methane-digester systems forManaging Manure with Biogas Recovery Systems: various animals on different levels throughout Improved Performance at Competitive Costs the world. Provides background information about anaer- Agricultural Utilization Research Institute obic digestion and explains how the methane produced from this process can be captured (AURI) site that helps evaluate the benefits and used to generate heat, hot water, and elec- of an on-farm digester. Also has a checklist tricity. Also includes information for dairy to use to determine if a digester is a viable and swine farmers to help them determine if a option. biogas-recovery system is right for their farm. BioCycle Magazine Describes the environmental benefits of anaer- obic-digestion systems and provides a table that compares the cost and environmental Energy Efficiency and Renewable Energy, U.S. effectiveness of conventional animal-waste Department of Energy. 2002. Methane (Biogas) systems to anaerobic-digester systems. from Anaerobic Digesters. Consumer Energy Information: EREC Reference Briefs. Merri-Minnesota Project field, VA. 5 p. The Minnesota Project is a nonprofit organiza- Cooperative Extension Service. 2001. Anaerobic tion dedicated to environmental protection and Digesters and Methane Production Questions sustainable development in greater Minnesota. that need to be asked and answered before investing your money. Publication #A3766. University of Wisconsin, Discovery Farms. 6 ATTRA Page 11
  12. 12. Lusk, P. 1998. Methane Recovery From Animal Manures: A Current Opportunities Casebook, 3rd edition. NREL/SR-25145. Prepared by Resource Development Associates, Washing- ton, DC, under contract to the National Renew- able Energy Laboratory. Golden, CO. 5 p., Charles, Dennis Sievers, and James R. Fischer. 1993. Generating Methane Gas From Manure. University of Missouri Cooperative Extension Service, Columbia, MO. 8 p. agguides/agengin/g01881.htmMazza, Patrick. 2002. Biogas. Climate Solutions Special Report. Olympia, WA. 4 p. University of Florida Civil Engineering Labora- tory developed an activity course with informa- tion about how to build a small scale digester system for educational purposes: Anaerobic Digestion of Animal Wastes: Factors to Consider By John Balsam NCAT Energy Specialist Updated by Dave Ryan NCAT Energy Specialist ©2006 NCAT Paul Driscoll, Editor Cynthia Arnold, Production This publication is available on the Web at: and IP219 Slot 218 Version 102506Page 12 ATTRA