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Optimal Loading Rates and Economic Analyses forAnaerobic Digestion of Poultry WasteAlan R. Collins a , Jason Murphy a & Danny Bainbridge ba Division of Resource Management , West Virginia University , Morgantown , USAb West Virginia University Extension Service, Freelance Technical Associates, Inc. ,Fairmont , USAPublished online: 27 Dec 2011.

To cite this article: Alan R. Collins , Jason Murphy & Danny Bainbridge (2000) Optimal Loading Rates and EconomicAnalyses for Anaerobic Digestion of Poultry Waste, Journal of the Air & Waste Management Association, 50:6,1037-1044, DOI: 10.1080/10473289.2000.10464147

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Collins, Murphy, and Bainbridge

Volume 50 June 2000 Journal of the Air & Waste Management Association 1037

ISSN 1047-3289 J. Air & Waste Manage. Assoc. 50:1037-1044

Copyright 2000 Air & Waste Management Association

TECHNICAL PAPER

Optimal Loading Rates and Economic Analyses for AnaerobicDigestion of Poultry Waste

Alan R. Collins and Jason MurphyDivision of Resource Management, West Virginia University, Morgantown

Danny BainbridgeWest Virginia University Extension Service, Freelance Technical Associates, Inc., Fairmont

ABSTRACTFour combinations of litter and carcasses from broilerchickens were examined utilizing a thermophilic, stirred-tank digester of demonstration size of approximately10,000 gal. Under computed optimal loading rates, lit-ter with paper bedding had the highest daily produc-tion of methane over an 8-day retention period. Thegreatest methane production per lb of volatile solids wasachieved over 10 days with litter and paper bedding com-bined with carcasses. This research found that sufficientpoultry litter is generated within 20 mi (32 km) ofMoorefield, WV, to support a commercial-sized digesteroperation. However, anaerobic digestion of poultry wastecannot be financially supported by methane productionalone. To be financially viable, anaerobic digestion re-quires a disposal fee for poultry waste and/or the sale ofthe digested solid effluent as an organic fertilizer to re-tail markets.

INTRODUCTIONThe poultry industry is West Virginia’s largest agriculturalenterprise, totaling 51% of the state’s agricultural cash re-ceipts in 1997. Much of this industry is concentrated inthe Potomac Headwaters region (Grant, Hampshire, Hardy,Mineral, and Pendleton counties). This concentrated pro-duction is supported almost exclusively by imported feed,

IMPLICATIONSInvestments in anaerobic digestion of poultry waste re-quire more than monetary returns from methane gas aloneto pay for themselves. When computed under optimalloading rates, present value calculations of the revenuegenerated from methane production did not cover theestimated investment cost of a digester facility. This facil-ity would need additional revenues, such as a disposal feefor the poultry litter or revenue from the sale of digestedlitter as a soil amendment, to make up for the shortfall.

resulting in a large surplus of nutrients contained in thewaste products. Seven million lb of nitrogen and phos-phorus are produced in the 160,000 tons (145,000 met-ric tons) of poultry litter generated annually in thefive-county region. Numerous concerns have been raisedabout the potential for water quality impacts from landdisposal of this litter, particularly in regard to nitrogenand phosphorus flowing into the Potomac River and theChesapeake Bay.1,2

To address such concerns about poultry litter, anaero-bic digestion technology has been promoted as onemethod to transform poultry litter into both energy anda fertilizer product with a lower potential for nutrient run-off. To encourage this technology, the West Virginia De-partment of Agriculture awarded a contract to Olin Corp.in September 1994 to conduct a demonstration project ofOlin’s unique process for anaerobic digestion.

Prior research has demonstrated the technical feasibil-ity of anaerobic digestion of animal wastes, including poul-try waste.3,4 Operational parameters have been establishedto provide for optimal production.5 However, the economicfeasibility of digestion using poultry litter has not been fa-vorable.6 Economics of size for methane production arevery important. Large-scale digestion (for example, han-dling poultry manure from over 500,000 chickens) has amuch higher rate of return on capital investment for meth-ane production than do smaller operations.6

Given the above prior research, the objectives of thisstudy are to

(1) determine the optimal loading rates for poultrywaste mixtures within a demonstration-sizedigester to maximize methane production fromanaerobic digestion; and

(2) project the poultry waste requirements for, andeconomic feasibility of, expanding this demon-stration digester into a larger, more commerciallyviable size.

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PROJECT DESCRIPTIONThe demonstration digester developed by Olin was de-signed to process up to 1 ton of waste (loaded daily) andproduce up to 2000 ft3 of methane daily. The demonstra-tion digester tank holds 9635 gal (36,472 L). With 16.67%reserved for air space, this leaves 8030 gal (30,397 L) ofliquid holding capacity.

The Olin digester uses a state-of-the-art, fully auto-mated microprocessor control operated by a program-mable logic controller along with a process/recipe stationfor operator input.7 Limited operator intervention in thedigestion process is required. Specific operations, such asdigester loading, recirculation, and mixing, can be accom-plished by remote access to the process computer. Thetechnology is a thermophilic, stirred-tank design. Heatincreases the rate of bacteria reproduction, destroys patho-gens, and reduces the retention time needed to digest theslurry. Stirring releases gases trapped by scum layers thatform in the digester and also mixes the anaerobic bacte-ria into the incoming slurry. This reduces the time requiredfor the new material to begin methane generation.

Prior to loading in the digester, the size and density ofpoultry waste are reduced by grinding to increase thesurface area available for bacterial action. Water is addedin a mixing tank to form a semi-liquid slurry with less than7% total solids. This slurry is heated to 132 °F in a heater.Digestion occurs in a three-step process. First, enzymesconvert complex organic compounds into simpler, solublecompounds. These compounds are then converted by acidbacteria into soluble simple organic acids, mainly aceticacid. Finally, methane bacteria convert the organic acidsinto methane and carbon dioxide. This process also gener-ates small amounts of hydrogen sulfide and ammonia.Upon discharge, some of the gas and liquid effluent arereintroduced into the tank along with new material to con-tinue the process. After separation, the remaining solid andliquid effluents can be used as fertilizers.

Construction of the demonstration digester north ofMoorefield began in February 1995 and was completed byJune 1995. The digester was purged of oxygen, and a starterculture of microbes was introduced. Tests and pilot opera-tions were conducted throughout 1995, until the digesterreached design processing and methane generation capac-ity in early 1996. The digester was operated for a period ofapproximately 8 months during 1996. Four trials of broilerchicken waste material inputs were examined: (1) litter withpaper bedding, (2) litter with wood chip bedding, (3) litterwith paper bedding and chicken carcasses, and (4) litterwith paper bedding and twice the amount of carcasses asin trial 3. Due to operational problems with the grindingand loading of poultry waste slurry at the demonstrationdigester, the loading rates varied considerably (from 0 to870 gal) during this 8-month trial period.

METHODSObjective 1

The variations in loading rates and mixtures during thefour trials enabled determination of an optimal loadingrate through estimation of multiple regression models.To explain methane production, a single model was de-veloped to forecast the maximum gas production withthe digester operating at optimal loading rates. Daily re-port data of loading and gas production from the demon-stration digester were used in model estimation.7

The dependent variable for the regression model wasdaily methane production in cubic feet. During the firstthree trials of waste inputs, the volume of gas productionfrom the digester was measured by a mechanical flowmeter. During the fourth trial, an electronic flow meterwas used in addition to the mechanical one. The elec-tronic flow meter produced much higher and more accu-rate estimates of gas output than the mechanical meter.To adjust the previous three trials for projected electronicflow estimates, a linear relationship was derived betweenelectronic and mechanical flow meter estimates in ft3/day.The estimated coefficients for this linear relationship wereelectronic flow = 151.81 + 1.5008 * mechanical flow. Theadjusted R2 was 0.663. This linear relationship was cor-rected for autocorrelation between error terms (Rho =0.3575), and two observations were dropped because theywere obvious outliers in the data. To determine the quan-tity of methane gas produced, the electronic flow esti-mates were multiplied by the measured percentage ofmethane in the daily gas production.

To explain methane production, various indepen-dent variables were examined. The primary variable uti-lized was reduction in volatile solids, RVS, measured asthe daily reduction in pounds of volatile solids withinthe digester. The theoretical basis for this variable camefrom research by Morris et al.8 As shown, RVS was com-puted as a ratio of two calculations: (1) a reduction involatile solids that were fed into the digester in the nu-merator, and (2) the average retention time (in days) inthe denominator.

% VS input * % TS input * loading rate * % reduction in VS * 8.345 lb/gal

8030 gal (digester capacity) / loading rateRVS =

(1)

where % VS input is the percentage of volatile solids ofpoultry waste input; % TS input is the percentage of totalsolids of poultry waste input; % reduction in VS is thetotal reduction of volatile solids; and loading rate is theaverage daily gal of poultry waste and water mixture addedto the digester.

The measurements of loading rate, % VS input, and% TS input were based on averages over a 7-day periodprior to the daily methane production. This time period

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was selected based on research by Jenner et al.,9 who foundthat nearly 80% of the total RVS occurred during the first7 days of digestion. The % reduction in VS was computedas an average over each trial period.7

In addition to RVS, other independent variables wereexamined in multiple regression models: (1) a 7-day aver-age loading rate variable, (2) a squared RVS variable toaccount for the possibility of a nonlinear impact on meth-ane production from RVS, and (3) dummy variables toaccount for slope and intercept impacts of different typesof waste inputs on methane production (trial 1 was thebase period to which the other three trials were compared).Both linear and log-linear functional forms were explored,with ordinary least-squares regression used to estimatecoefficients.

Objective 2The primary benefit of digestion is the generation of meth-ane to be utilized either directly to generate heat or forconversion into electricity. The costs and benefits of uti-lizing the digested litter have not commonly been con-sidered in prior economic analyses of digestion,10,11 sincepoultry litter—particularly broiler litter—without diges-tion has a positive monetary value for either fertilizer orlivestock feed. Digestion of litter for methane productiondoes not substantially alter this fertilizer value. Thus, iflitter is accorded a zero value when put into the digester,then ignoring the economic value of digested litter is logi-cal from an economic standpoint.

Two analyses were projected over 20-year periods toexplore different uses for the methane: (1) stand-alonedigestion, and (2) cost savings associated with industrialuse of methane production to replace an existing gasenergy source. Under the stand-alone analysis, methanewould be produced for recovery by a natural gas truck-ing firm that provides the necessary methane process-ing (dehydrating, cleaning, and compressing). A naturalgas trucking industry has developed in West Virginia torecover methane from coal mines. Information providedby Marlin Gas Transport, Inc.12 indicated that the mini-mum-sized facility to receive such a service would needto produce 500,000 ft3 (14,158 m3) of methane daily. Thequoted price for trucked methane in 1997 was $5/1000ft3 (MCF).

The cost savings analysis was conducted utilizing thissame level of methane production. An industrial facilityusing the methane directly would realize cost savings fromreduced utility payments. Mountaineer Gas Co. is thenatural gas service provider in the Moorefield area. In1997, their commercial rate for natural gas was $5.53 perMCF plus an $18.50 per month service fee. They operateon regulated 3-year price moratoriums, and their last priceincrease equaled 1.6%.

Accurate data were not available on the capital re-quirements and operating costs of this demonstrationdigester. Regardless, cost data from the demonstrationproject would not be comparable to a facility producing500 MCF of methane daily due to the research nature ofthis digester. Approximate capital investment costs for adigester facility to meet the daily requirement of 500 MCFof methane were derived from available information onother operating biogas digester facilities. Information wasgathered from two comparable biogas digester facilitiesdescribed by CADET IEA/OECD on their Web site.13 Thesefacilities are located in Nistelrode, The Netherlands, andNorre Nebel, Denmark. The Nistelrode facility uses chickenand pig manure, and the Norre Nebel facility uses a com-bination of livestock manure, organic industrial waste,and sewage sludge.

Three adjustments were made to relate the invest-ment costs from these two facilities to an approximateinvestment cost of a commercial facility in West Virginia.The following adjustments were made: (1) costs in U.S.dollars were derived using foreign exchange rates appli-cable at the times of construction for the Nistelrode andNorre Nebel facilities, (2) costs in 1997 dollars were com-puted using the producer price index for the chemicalindustry, and (3) economics of size were accounted forbased upon size and per-unit investment cost relation-ships found by Bravo-Ureta and McMahon.11 The esti-mates of investment cost from comparable facilities werecalculated on a per MCF of daily methane productionand multiplied by 500.

Under this objective, the amount of poultry wastethat would be required to provide feedstock for an eco-nomically sized digester facility was calculated. Using theresults from the multiple regression model for optimalmethane production, two procedures were utilized to es-timate the pounds of broiler litter input needed to pro-duce 500 MCF (14,158 m3) of methane per day. In thefirst procedure, the number of 10,000-gal (37,854 L) di-gesters was computed along with a daily input loadingrequired. The second procedure utilized a computationfor the total volatile solids necessary from poultry litterto produce 500 MCF daily. These two procedures wereutilized as a comparison check for accuracy. The formulasfor daily input of poultry waste are shown below:

Procedure 1

500 MCF methane/day

ft3 of methane/digester

optimal input/gal * % TS input * 8.345 lb/gal

% solid*

(2)Procedure 2

500 MCF methane/day

ft3 of methane/lb of VS

1

% solid * % VS input* (3)

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Cubic feet of methane production per 10,000-gal di-gester and per lb of volatile solids loaded were derivedfrom calculations utilizing the multiple regression modelresults. Trial averages for % TS input and % VS input fromTable 1 were used in each procedure. The % solid repre-sents the percentage of solids in poultry waste. This per-centage was estimated to be 66.3% for both trials, basedon litter-testing data obtained from the West VirginiaDepartment of Agriculture. Both procedures computed thepounds of poultry waste input required. Pounds were con-verted to tons and multiplied by 350 days to compute anannual tonnage of poultry litter waste.

Data from trials 1 and 3 were selected to computepoultry waste requirements. Trial 1 (broiler litter withpaper bedding) was selected because it showed the high-est methane production at optimal input. Trial 3 (broilerlitter with paper bedding and poultry carcasses) was alsoselected because this input had the largest methane pro-duction per lb of volatile solid input.

RESULTSA total of 103 days of data from the digester were avail-able between March and October 1996 over the four trialperiods. Visual inspection of a plot of RVS and methaneproduction showed a curvilinear relationship betweenthese two variables (Figure 1). This relationship was con-firmed with a statistically significant F statistic at aboutthe 7% level (F1,94 = 3.584) for the addition of a squaredRVS variable to the regression model.

The multiple regression model selected had a linearfunctional form (Table 2). A log-linear form explained lessvariation in the dependent variable. All independent vari-ables, with the exception of one intercept dummy vari-able, had statistically significant coefficient estimates inthe selected model. The loading rate variable had a coeffi-cient estimate that was not statistically different from zeroand was dropped from the regression model. The modelshown in Table 2 had autocorrelation problems (i.e., afirst-order relationship between error terms). The Durbin-Watson statistic was statistically significant for positiveautocorrelation (Rho = 0.3952). This result is a violationof the multiple regression assumption that error terms

should be independent, and it causes biased estimationof coefficients. This autocorrelation problem was pre-sumed to be the result of overlapping components of theRVS variable estimate.

To correct for this autocorrelation, an iterative Praisand Winston algorithm was used. As evidenced by theimproved Durbin-Watson statistic, the autocorrelationproblem was eliminated (Table 3). Coefficients from thiscorrected model were utilized to determine optimal load-ing input. The coefficient estimates in Table 3 were inter-preted in the following manner. The intercept term andintercept dummy variables for trials 2, 3, and 4 representan underlying steady-state level of methane production,which was between 120 (3.4 m3) and 1500 ft3 (42.5 m3)per day depending upon the type of feed input. Broilerlitter with paper bedding and poultry carcasses had thehighest, and broiler litter with paper bedding only hadthe lowest steady-state level. The statistically significantpositive coefficient for RVS showed that the more poundsof volatile solids reduced per day, the more methane pro-duction increased. The RVS impact was highest for trial 1of broiler litter with paper bedding, as the slope dummyvariables (slope trials 2, 3, and 4) had negative coefficients.The statistically significant coefficient for the squared RVSshowed a curvilinear relationship between RVS and meth-ane production. Thus, the impact of RVS on methane pro-duction initially increased at a declining rate, reached amaximum, and then declined (Figure 1).

With the coefficient estimations in Table 3, an opti-mal loading rate in gallons was computed. This compu-tation was possible when % VS input and % TS inputwere set at the trial averages shown in Table 1. A partialderivative of methane production with respect to theloading rate from eq 1 was set equal to zero to derive theoptimal loading rate. Complete derivations of the opti-mal loading rates for each trail are presented in the ap-pendix. With this optimal loading rate in gallons, digester

Table 1. Trial averages for waste input into digester.

% Total Solids % Volatile % Reduction in

Solids Volatile Solids

Trial 1 6.56 76.81 67.117

Trial 2 5.2 74.85 59.669

Trial 3 4.01 76.51 74.411

Trial 4 5.50 79.44 80.814

Table 2. Multiple regression results for the relationship between methane produc-

tion (dependent variable) and RVS (n = 103).

Variable Estimate (B) SE (B) t-Statistic p-Value

RVS 120.35 23.805 5.06 <0.0001

RVS (squared) –1.4445 0.763 –1.89 0.061

Slope Trial 2 –51.078 12.514 –4.08 <0.0001

Slope Trial 3 –76.504 14.014 –5.46 <0.0001

Slope Trial 4 –45.681 19.219 –2.38 <0.02

Trial 2 775.27 162.98 4.76 <0.0001

Trial 3 1149.70 166.14 6.92 <0.0001

Trial 4 385.05 353.42 1.09 0.279

Intercept 375.62 132.99 2.82 0.006

Note: R = 0.79, R2 = 0.62, Durbin-Watson Statistic = 1.262

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calculations for each trial were made for (1) optimal re-tention time in days, (2) pounds of volatile solids percubic foot of waste input, (3) optimal daily methane pro-duction from a 10,000-gal digester, and (4) methane andbiogas produced per lb of volatile solids loaded into thedigester (Table 4).

Poultry Waste RequirementsTable 5 shows that the computed poultry waste quanti-ties from the two procedures correspond closely withone another. For trial 1, approximately 28,000 tons(25,400 metric tons) of broiler litter would be requiredannually. The computed requirements for a 500-MCF-per-day facility were a 1.9-million-gal capacity for di-gestion (190 demonstration-size digesters) and 81,700lb (37,058 kg) of volatile solids per day. For trial 3, lesswaste would be required annually, about 19,000 tons(17,200 metric tons) of broiler litter and poultry car-casses. The computed requirements for a 500-MCF-per-day facility were (a) 2.63 million gal capacity fordigestion (263 demonstration-size digesters), and (b)55,600 lb (25,220 kg) of volatile solids per day. Lesswaste and volatile solids but more digesters were re-quired for broiler litter and carcasses because of thelower percentage of solids utilized and the longer di-gestion period for optimal methane production.

Table 6 illustrates the poultry (mainly broiler) litterthat is potentially available from the area surroundingthe digester demonstration project. The tonnage estimates

Table 3. Prais and Winston correction for autocorrelation of error terms in the

multiple regression estimation in Table 2.

Variable Estimate (B) SE (B) t-Statistic p-Value

RVS 120.11 29.231 4.109 <0.0001

RVS (squared) –1.6588 0.866 –1.914 <0.056

Slope Trial 2 –42.656 17.228 –2.476 0.013

Slope Trial 3 –66.576 19.493 –3.415 0.0006

Slope Trial 4 –39.202 23.349 –1.679 0.09

Trial 2 625.41 227.29 2.752 0.006

Trial 3 1021.40 244.56 4.177 <0.0001

Trial 4 275.42 428.53 0.643 0.52

Intercept 444.59 189.09 2.351 0.019

Note: Corrected Durbin-Watson = 2.0394, Rho = 0.3952

Figure 1. Observed and fitted data for methane gas production for the four poultry waste material trials.

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are a function of the number of poultry houses withinthe various radii adjacent to the current site. Based uponTable 5 calculations, a more than sufficient quantity ofpoultry litter exists within 20 mi (32 km) of Moorefield tosupport a commercial-size digester facility.

Economic Feasibility CalculationsThese analyses were conducted using methane as the onlyeconomic output from a digester facility. At $5 per MCF,a stand-alone facility with a daily production capacity of500 MCF (14,158 m3) would have an annual productionof 175,000 MCF (4,955,448 m3) and generate $875,000 inrevenue. At a 7% discount rate over 20 years, the presentvalue of this annual revenue stream would be approxi-mately $9.3 million. For the cost savings analysis, yearlycost savings for a facility utilizing 500 MCF per day rangedfrom $970,000 to $1.1 million when assuming increasesof 1.6% every 3 years over 20 years. The present value ofthese annual cost savings at a 7% discount rate is approxi-mately $10.6 million.

The investment cost of a commercial-size digestionfacility ranged from $5.1 million to $12.7 million (Table7). Given its relative closeness in size to 500 MCF andmore recent construction, the Norre Nebel estimate of$12.7 million was judged to be the more accurate repre-sentation of the investment cost that would be requiredfor such a facility in West Virginia. In both analyses, thepresent value of revenue streams fell short of the esti-mated investment cost from the Norre Nebel facility.

Even without considering operating costs, the revenuegenerated from methane production would not coverthe estimated investment cost of a poultry waste digesterfacility. A digester facility would need additional rev-enues, such as a disposal fee for the poultry litter or rev-enue from the sale of digested litter as a soil amendment,to make up for this shortfall.

CONCLUSIONSSufficient poultry litter is available to support a commer-cial-size digester operation in the Moorefield area. Theresults of this research show that, from an economic stand-point, anaerobic digestion of poultry waste cannot besupported solely by the production of methane. Both thestand-alone and the cost-savings analyses indicated thatrevenues at optimal production levels of methane wouldnot financially support the investment cost of a digestionfacility. To be financially viable, anaerobic digestion re-quires positive monetary returns from the other servicesand products provided by digestion. Thus, a disposal feefor the poultry waste brought into the facility is needed,and/or the digested solid effluent must be converted intoan organic fertilizer product with a retail or commercialmarket value above that of poultry litter.

Under current market conditions, a disposal fee forpoultry litter, particularly broiler litter, seems unlikely. Lit-ter serves as a valuable fertilizer for pasture and cropland

Table 6. Potentially available poultry litter in the area surrounding the digester

demonstration project.

Radius in Miles Poultry Houses Tons of Litter

(km) within Radius Generated Annuallya

(Metric Tons)

2 (3.2) 4 700 (635)

5 (8.0) 38 6650 (6033)

10 (16.1) 107 18,725 (16,987)

20 (32.2) 229 40,075 (36,355)

Note: aCalculation based on each broiler house generating approximately

175 tons (158.76 metric tons) per year over 7 production cycles.

Table 4. Summary of optimal digester performance estimated from the multiple

regression model in Table 3. Each of the four trials was based on 8030 liquid gal

(30,397 L) capacity of the digester with the average per trial for total and volatile solids

percentages in the influent.

Optimal Digester Operation

Daily Loading Retention Period Lb VS / ft3

Rate in Gal (L) in Days (kg/m3)

Trial 1 1015 (3842) 7.9 0.57 (9.13)

Trial 2 984 (3725) 8.2 0.43 (6.89)

Trial 3 825 (3123) 9.7 0.28 (4.49)

Trial 4 815 (3085) 9.8 0.40 (6.41)

Maximum Daily Production of Methane

(assuming 60% methane)

Methane in ft3/lb VS

ft3 (m3) (m3/kg VS)

Trial 1 2619 (74) 6.14 (0.38)

Trial 2 1974 (56) 6.18 (0.39)

Trial 3 1898 (54) 8.99 (0.56)

Trial 4 1707 (48) 5.74 (0.36)

Table 5. Tons of poultry waste input required annually for a digester facility pro-

ducing 500 MCF (14,158 m3) of methane daily.

Procedure 1 Procedure 2

Estimate in Tons Estimate in Tons

(Metric Tons) (Metric Tons)

Trial 1 28,171 (25,556) 28,079 (25,472)

Trial 3 19,149 (17,371) 19,169 (17,389)

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or as feed for cattle. A recent survey of West Virginia poul-try growers revealed that 70% of respondents were ableto sell some or all of their (chicken or turkey) litter at anaverage price of $5.79 per ton.14 However, disposal feescould become a reality under one scenario—if total maxi-mum daily loads (TMDLs) were implemented and enforcedfor the South Branch of the Potomac and several of itstributaries, resulting in reductions in farmland spreadingin these watersheds.

A TMDL represents the maximum amount of a pol-lutant that can be discharged or deposited into a streamand still maintain water quality standards. TMDLs are re-quired under the federal Clean Water Act and are beingimplemented in West Virginia under the settlement of a1995 lawsuit against EPA by the Ohio Valley Environmen-tal Council. The TMDL for the South Branch of thePotomac covers fecal coliform levels and could requirethat the watershed’s agricultural industry decrease its con-tribution of fecal coliform bacteria into the Potomac andfive tributaries by 30–50%.

Even if TMDLs were enforced, anaerobic digestionwould need to compete with alternative uses for poultrylitter, such as composting or palletizing. The compostingoption is currently being explored in the market by fourcommercial-size composting facilities in West Virginia thatutilize poultry litter.

ACKNOWLEDGMENTSThis research was sponsored by a grant from the NationalResearch Center for Coal and Energy located at West Vir-ginia University, Morgantown. Data for this research wereobtained from the West Virginia Power Project inMoorefield, a collaborative effort between the West Vir-ginia Department of Agriculture and Olin Corp.

REFERENCES1. Ator, S.W.; Blomquist, J.D.; Brakebill, J.W.; Denis, J.M.; Ferrari, M.J.;

Miller, C.V.; Zappia, H. Water Quality in the Potomac River Basin, Mary-land, Pennsylvania, Virginia, West Virginia, and the District of Colum-bia, 1992–96; U.S. Geological Survey Circular 1166, 1998; accessed athttp://water.usgs.gov/pubs/circ1166, July 1999.

2. Ward, K. Threat to the Nation’s River? State’s Poultry Industry Seenby Some as Threat to Environment; Sunday Gazette-Mail, Charleston,WV, October 12, 1997, p 1a.

3. Hills, D.J.; Ravishanker, P. Methane Gas from High Solids Digestionof Poultry Manure and Wheat Straw; Poultry Science 1984, 63, 1338-1345.

Table 7. Comparable digester facility information and estimated investment cost for a digester facility producing 500 MCF (14,158 m3) of methane daily.

Facility Year Facility Size Investment Cost per Investment Cost per Estimated Total

Built (MCF/day) Daily MCF of Daily MCF, Adjusted Investment Cost for a

Methane Production for Facility Size in 500 MCF/Day Facility

1997 Dollars in West Virginia

Norre-Nebel 1992 290 $24,780 $25,340 $12,700,000

Nistelrode 1986 23 $14,186 $10,123 $5,060,000

4. Safley, L.M.; Vetter, R.L.; Smith, L.D. Management and Operation ofa Full-Scale Poultry Waste Digester; Poultry Science 1987, 66, 941-945.

5. Stafford, D.A.; Hawkes, D.L.; Horton, R. Methane Production from WasteOrganic Matter; CRC Press: Boca Raton, FL, 1980.

6. Bravo-Ureta, B.E.; McMahon, G.V. The Economic Feasibility of Electric-ity Generation on Cage Layer Operations; Research Report 79, Storrs Ag-ricultural Exporting Station, College of Agriculture and NaturalResources; The University of Connecticut: Storrs, CT, 1984.

7. Olin Services. Final Report on the Operational Demonstration of the WestVirginia Power Project Moorefield, West Virginia; submitted to the WestVirginia Department of Agriculture; St. Petersburg, FL, 1996.

8. Morris, G.R.; Jewell, W.J.; Loehr, R.C. Anaerobic Fermentation of Ani-mal Wastes: Design and Operation Criteria; In Food, Fertilizer andAgricultural Residues; Loehr, R.C., Ed.; Ann Arbor Science: Ann Arbor,MI, 1977; pp 395-413.

9. Jenner, M.W.; Maatta, J.; Sievers, D.M. Evaluation of Methane GasProduction in a Simultaneous Regression System. In Proceedings ofthe Kansas State University Conference on Applied Statistics in Agricul-ture; Department of Statistics, Kansas State University, Manhattan,KS, 1991; pp 62-74.

10. Ashok Kumar, N. Economics of BioGas Evaluation; The Times ResearchFoundation: Opp. Modi Baug, India, 1988.

11. Bravo-Ureta, B.E.; McMahon, G.V. A Capital Budgeting Analysis ofElectricity Generation on Egg Farms; J. Northeastern Agricultural Eco-nomics Council 1983, 12(1), 41-48.

12. Marlin Gas Transport, Inc. http://www.marlingas.com (accessed May1999).

13. CADDET Renewable Energy. http://www.caddet-re.org (accessed May1999).

14. Basden, T. Personal interview; West Virginia University CooperativeExtension Service, Morgantown, WV, June 9, 1999.

APPENDIX: CALCULATION OF OPTIMAL LOADINGRATE FOR EACH TRIALThe following methodological steps were applied:

(1) Use the coefficient estimates from Table 3 to finda partial derivative of methane production withrespect to RVS. Set this partial derivative equal tozero.

(2) Replace the RVS variable with the following equa-tion:

RVS =8030 gal digester capacity/X

% VS input * % TS input * X * % reduction in VS * 8.345 lb/gal

(3) Use trial averages for % VS input, % TS input,and % reduction in VS to solve for X (optimalloading rate in gal).

(4) Use optimal loading rate and trial averages tocompute RVS from the above equation.

(5) Multiply the RVS computed in step 4 by the esti-mated regression coefficients from Table 3 toproject methane production at the computedoptimal loading rate.

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Collins, Murphy, and Bainbridge

1044 Journal of the Air & Waste Management Association Volume 50 June 2000

Trial 1Optimal loading rate (gal) = ((2 * 120.11)/(4 * (–1) *(–1.6588) * (0.7681 * 0.0656 * 0.67117 * 8.345 lb/gal/8,030gal)))0.5 = 1015 gal

RVS = 0.677117 * 0.7618 * 0.0656 * 8.345 lb/gal * (1015 gal)2

8030 gal= 36.204 lb

Optimal methane production = 444.59 + 120.11 * 36.204– 1.6588 * (36.204)2 = 2618.8 ft3

Trial 2Optimal loading rate (gal) = ((2 * 77.45) / (4 * (–1) *(–1.6588) * (0.7485 * 0.052 * 0.5967 * 8.345 lb gal/8030gal)))0.5 = 983.5 gal

RVS = 8030 gal

0.5967 * 0.7485 * 0.052 * 8.345 lb/gal * (983.5 gal)2= 23.346 lb

Optimal methane production = 1070 + 77.45 * 23.346 –1.6588 * (23.346)2 = 1974.1 ft3

Trial 3Optimal loading rate (gal) = ((2 * 53.53) / (4 * (–1) *(–1.6588) * (0.7651 * 0.041 * 0.7441 * 8.345 lb/gal/8030gal)))0.5 = 824.7 gal

RVS = 8030 gal

0.7441 * 0.7651 * 0.041 * 8.345 lb/gal * (824.7 gal)2= 16.136 lb

Optimal methane production = 1466 + 53.53 * 16.136 –1.6588 * (16.136)2 = 1897.9 ft3

About the AuthorsAlan R. Collins is an associate professor in the Division ofResource Management, P.O. Box 6108, West Virginia Uni-versity, Morgantown, WV 26506. His research interests in-clude poultry litter management, water quality, pesticide useon orchards, and watershed management. DannyBainbridge was a research assistant with the West VirginiaUniversity Extension Service at the time of this research.He is currently president, Freelance Technical Associates,Inc., Fairmont, WV 26554. Jason Murphy is an undergradu-ate student in Agribusiness Management and Rural Devel-opment within the Division of Resource Management at WestVirginia University, Morgantown, WV 26506.

Trial 4Optimal loading rate (gal) = ((2*80.91) / (4 * (–1) * (–1.6588)* (0.7944 * 0.055 * 0.8081 * 8.345 lb/gal/8030 gal)))0.5 =815.2 gallons

RVS = 8030 gal

0.8081 * 0.7944 * 0.055 * 8.345 lb/gal * (815.2 gal)2= 24.338 lb

Optimal methane production = 720 + 80.91 * 24.388 –1.6588 * (24.388)2 = 1,706.6 ft3

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