SERI/TR-98372-1 

UC CATEGORY: UC-61a 

ANAEROBIC FERMENTATION 

OF BEEF CATTLE MANURE 

FINAL REPORT 

-A. G. HASHIMOTO 

Y. R. CHEN -

V. H. VAREL 

ROMAN L. HRUSKA U.S. MEAN ' ANIMAL 

, RESEARCH CENTER 

U.S. DEPARTMENT OF AGRICULTURE 

CLAY CENTER, NEBRASKA 

JANUARY 1981 

PREPARED UNDER SUBCONTRACT 

No. 08-9-8372-1 FOR THE 

Solar Energy Research Institute 

A Division of Midwest Research Institute 

1617 Cole Boulevard 

Golden, Colorado 80401 

Prepared for the 

U,S, Department of. Energy 

Contract No, EG-77-C-01-4042 

SERI TECHNICAL MONITOR: 

DAN JANTZEN 
This report describes the results of a research project to produce 

energy in the form of methane and a high protein feed supplement from 

livestock manure. This work was jointly funded by the US Department 

of Agriculture, through the Science and Education Administration, 

and the US Department of Energy, through the Solar Energy Research 

Institute. 

The results of this research indicates that there are many livestock 

operations where thermophillic fermentation of livestock manure would 

be both technically feasible and economically attractive. The development of this technology has now reached the point where a significant 

commercialization effort is needed, aimed at integrating such fermentation units into livestock production operations. 

The USDA and DOE are currently working out arrangements for such a 

program. 

Senior Project Manager 

Biomass Program Office 
g

CH4 production rate. The kinetic model predicted methane production rates of 

existing pilot and full-scale fermentation systems to within 15%. 

The 5.7 

m3 fermentor was operated at: temperatures of 45, 50 and 55°C; 

hydraulic retention times ranging from 12 to 4 days; mixed continuously or 2 

hr/day; and fed once/day or 22 times/day. No difference in methane production 

rate was observed when the fermentor was mixed 2 hr/day versus continuously. 

The methane production rate was about 10% higher when the fermentor was fed 22 

times/day compared with once/day. The highest methane production rate 

achieved by the fermentor was 4.7 L CH4/L fermentor·day. This is the highest 

rate reported in the literature and about 4 times higher than other pilot or 

full-scale systems fermenting livestock manures. 

Assessment of the energy requirements for anaerobic fermentation systems 

showed that the major energy requi rement for a thermophi 1 i c system was for 

maintaining the fermentor temperature. Of the total heating energy required, 

about 89 to 94% was for heating the influent slurry at an ambient temperature 

of 10°C. The next major energy consumption was due to the mixing of the 

influent slurry and fermentor liquor. Mixing amounted to 7.3% of the gross 

methane energy production, assuming continuous mixing. The least energy was 

consumed in pumping. The total energy required for mixing and pumping 

accounted for 10.8 to 11.3% of the gross thermal energy production. 

An approach to optimizing anaerobic fermentor designs by selecting design criteria that maximize the net energy production per unit cost was presented. 

Using this optimization technique, we estimated that a farmer-constructed and 

operated system would be economically feasible for beef feedlots between 1,000 

to 2,000 head without a feed credit assumed for the effluent, and about 300 

head with a feed credit of effluent total solids. Commercial 

"turn-key" systems are only feasible for feedlots larger than 8,000 head with 

no effluent credit, and feedlots between 1,000 to 2,000 head with an effluent 

credit of Based on these results, we bel i eve that the economi cs of 

anaerobic fermentation is sufficiently favorable for farm-scale demonstration 

of this technology. 
LIST OF FIGURES v LIST OF TABLES vi 

1.0 INTRODUCTI ON 1 

2.0 PRINCIPLES OF METHANE PRODUCTION 2 

2.1 INTRODUCTION 2 2.2 MICROBIOLOGY 2 

2.3 ENVIRONMENTAL CONSI DERATIONS 4 

2.3.1 pH 4 

2.3.2 Alkalinity 4 2.3.3 Vol at il e Ac ids 5 2.3.4 Temperature 5 2.3.5 Nutrients 5 2.3.6 Toxic Materi al s 6 

2.4 FERMENTATION KINETICS 7 

2.4.1 Kinetic Models 7 

2.4.2 Ultimate Methane Yield (Bo) 8 2.4.3 Maximum Specific Growth Rate ) 8 

2.4.4 Kinetic Parameter (K) 11 

2.4.5 Application of Kinetic Model 13 

2.5 SUMMARY 13 

3.0 PILOT-SCALE THERMOPHILIC FERMENTOR OPERATION 15 

3.1 INTRODUCTIDN 15 

3.2 EQU I AND PROCEDURES 15 
3.3.1 Start

Up 

20 

3.3.2 Steady-State Operation 20 3.3.3 Comparison of Experimental to Predicted CH4 27 

Production Rates 

3.4 SUMMARY 32 

4.0 ENERGY REQUIREMENTS FOR ANAEROBIC FERMENTATION SYSTEMS 33 

4.1 INTRODUCTION 

4.2 ENERGY AND POWER REQUIREMENTS 

4.2.1 Heating Requirement 

4.2.2 Pumping Power and Energy Requirements 

4.2.3 Mixing Power Requirement 

4.3 DISCUSSION 

33 

33 33 

34 

39 

39 

4.3.1 Comparing Energy Requirements 39 

4.3.2 Effect of Influent Concentration on Net Thermal 42 

Energy Production 

4.3.3 Net Thermal Energy Production of Mesophilic and 42 

Thermophilic Systems 

4. 4 Y 

5.0 ECONOMIC OPTIMIZATION OF ANAEROBIC FERMENTOR DESIGNS 

5.1 INTRODUCTION 

5.2 OPTIMIZED DESIGNS 

5.2.1 Capital Cost 

5.2.2 Net Energy Production Per Unit Cost 

5.3 ECONmlICS 

5.3.1 System Design 

42 

46 46 46 

46 

46 

48 

48 
y 

6.0 

7.0 REFERENCES 

59 

60 
p

p

g

2.3 Effect of influent volatile solids content on the kinetic 12 

parameter K 

3.1 Schematic diagram of pilot-scale anaerobic fermentation system 16 

3.2 Schematic drawing of pilot-scale fermentor 19 3.3 Gas production and pH profiles during start-up 21 

3.4 Total alkalinity and volatile acids profiles during start-up 22 3.5 Changes in total volatile acids with time after feeding 28 3.6 Changes in CH4 and C02 concentration with time after feeding 29 3.7 Changes in CH4 and total gas production with time after feeding 30 

4.1 Comparing net thermal energy production from thermophilic 43 

anaerobic fermentation systems for different influent VS 

concentration 

4.2 Comparing net thermal energy production from mesophilic (35°C) 44 

and thermophilic (55°C) anaerobic systems 

5.1 Effect of fermentor volume on capital cost 47 

5.2 Effect of hydraul i c retenti on time, temperature and influent 49 

concentration on the net energy production per unit cost 

5.3 Effect of plant size on methane production costs 55 5.4 Effect of plant size on electricity production cost 56 
3.1 Beef cattle rations used .throughout the course of the fermentor 17 

operation 

3.2 Summary of steady-state performance of the pilot-scale fermentor 23 

operated at 55°C, mixed continuously, and at different HRT 

3.3 Summary of steady-state performance of the pilot-scale fermentor 24 

operated at different temperatures and HRT 

3.4 Summary of steady-state performance of the pilot-scale fermentor 25 

operated at 50°C, 6 days HRT and mixed continuously and 2 hours 

per day 

3.5 Summary of steady-state performance of the pilot-scale fermentor 26 

operated at 55°C and fed once-per-day or 22 times per day 

3.6 Experimental and predi cted methane producti on rates of the pil ot- 31 

scale fermentor 

4.1 Heating energy requirements and net thermal energy production for 35 

fermentors operating at 55°C 

4.2 Power and energy requirements for pumping effluent and process 37 

slurries (10 hr/day pumping) 

4.3 Power and energy requirements for pumping effluent and process 38 

slurries (3 hr/day pumping) 

4.4 Power and energy requirements for propeller mixing of fermentor 40 

liquor and process slurry 

4.5 Summary of energy producti on and requi rement for anaerobi c systems 41 

fermenting beef cattle manure at 55°C 

5.1 Energy production and requirements for various plant sizes and 51 

energy use options 

5.2 Installed equipment costs for major components of a 1860 m3 52 

anaerobic fermentor 

5.3 Costs for producing methane and electricity at various plant sizes 53 

5.4 Energy production costs for various plant sizes, energy production 57 

options and effluent feed credits 
1. Develop design criteria for optimum production of methane and/or biomass 

from anaerobic fermentation of livestock and crop residues, 

2. Develop efficient methods to recover high protein biomass from the fermented residue, 

3. Evaluate the nutritional value of the biomass as a livestock feed, 

4. Determine the capital and operational costs, and energy, manpower and 

safety requirements for methane fermentation systems associated with 

livestock operations. 

This project was initiated in 1976 and is jointly funded by the U.S. 

Department of Agriculture, Science and Education Administration, Agricultural 

Research and the U.S. Department of Energy, Biomass Energy Systems Branch/ 

Solar Energy Research Institute. The specific objectives of interest to the 

Department of Energy are Objectives 1 and 4 listed above. This report summarizes the completed research on thermophilic, anaerobic fermentation of beef 

cattle manure. Work is continuing on fermentation of crop residue. 
Methane (CH4) is produced in nature through the anaerobic decomposition of 

organic matter. Since bacteria are the predominant species involved in 

methanogenesis, this discussion on the principles of CH4 production deals with 

the bacteria involved in methanogenesis and the factors that affect both the 

rate of CH4 production and the amount of organic matter that can be converted 

to CH4' 

2.2 MICROBIOLOGY 

Methanogenesis has traditionally been viewed as a two-stage process -- the 

acid-forming and CH4-forming stages (Kirsch and Sykes, 1971; Torien and 

Hattingh, 1969). In the first stage, acid-forming bacteria were thought to 

ferment organic materials, like carbohydrates, lipids, and proteins to formate, acetate, propionate, butyrate, ethanol, hydrogen (H2) and carbon dioxide 

(C02). Bryant (1976, 1979) and t·1cI nerny and Bryant (1978) proposed a threestage scheme that attempts to synthesi ze more current i nformati on on methanogenesis from organic matter. In general, the first stage involves species of 

fermentative bacteria which, as a metabolic group, hydrolyze complex carbohydrates, proteins, and lipids and ferment these products to fatty acids, 

H2, and C02' The second metabolic group, called the "H2-producing acetogenic 

bacteri a II produce acetate, C02 and H2 from the fatty aci ds generated in the 

first stage. The third stage involves the methanogenic bacteria that utilize 

the products of the first two stages -- mainly acetate, C02, and H2 to produce 

CH4 and C02' Recently, an additional stage was added to this scheme, as shown 

in Figure 2.1. This metabolic group is called the homoacetogenic bacteria 

which are reported to synthesize acetate using H2, C02, and formate (Zeikus, 1979; Wolfe, 1979). in the gastrointestinal tract of animals 

involves only the first metabolic group and H2 utilization by methanogens 

(Hungate, 1966). Acetogenic bacteria are not significantly involved due to 

the short retention times in these ecosystems. Acetate and other volatile 

acids accumulate in rumen, fecal, and colon fermentations and are utilized as 

major energy sources by herbivorous animal s. 

Most of the information concerning extracellular intermediates important in 

methanogenesis comes from studies of rumen and sewage sludge fermentations 

(Hobson et al., 1974; Hungate, 1966, Torien and Hattingh, 1969; Wolin, 1974). 

Acetate is an important precursor in nature because about 70% of the CH4 

produced in sludge is produced via the methyl group of acetate (Kugelman and 

McCarty, 1965; Smith and Mah, 1966). Mountfort and Asher (1978) found that 

during the first few hours after a beef-manure fermentor is fed, up to 90% of 

the CH4 produced comes from acetate. Reduction of C02 by H2, and to some 

extent by other intermediate electron donors, accounts for the rest of the 

CH4 production. Winfrey et al. (1977) showed that H2 is an important intermediate and a rate-limiting factor in lake sediment methanogenesis. Formate 

is rapidly converted to H2 and C02 by nonmethanogens or is directly utilized 

by methanogens (Hungate, 1966). 
COMPLEX ORGANIC MATTER 

I. HYDROLYTIC BACTERIA 

I ORGANI;'--AC_I_DS_I ___ ----...::>'~ II. HYDROGEN PRODUCiNG-

'ACETDGENIC Bt\CTERIA 

H2t CO2 , FORfili/i.TE 

l 

III. HOMOI1,CETOGENIC 

BACTEHIA ACETATE 

I 

IV. METHANOGENIC BACTER!A 

'f 

Figure 2.1. The four bacterial groups involved in the complete 

anaerobic degradation of organic matter. 
Ethanol and lactate are probably not important intermediates. Organisms produce these products to dispose of electrons generated in glycolysis, but they 

also produce H2' In the natural system, H2-using methanogenic bacteria 

rapidly use the H2' which allows the fermentative bacteria to produce more H2 and acetate and less lactate and ethanol. Thus, in the rumen, ethanol is neither produced nor used, though many bacteri al speci es produce ethanol in 

pure culture (Hungate, 1966). Only under stress of feeding high substrate 

levels does lactate become an important intermediate in the rumen. Wolin 

(1974, 1976) and Bryant (1976, 1979) discussed in detail the research dealing 

with al tered el ectron flow in the di recti on of H2 producti on caused by the 

metabolic interactions of methanogens and nonmethanogens. 

2.3 ENVIRONMENTAL CONSIDERATIONS 

Environmental factors influence the rate and amount of CH4 produced during 

methanogenesis. Some of the major environmental factors are pH, alkalinity, 

volatile acids, temperature, nutrients, and toxic materials. Several authors 

have reviewed the influence of these factors on methanogenesis (Mah et al., 

1977; Wolfe, 1971; Zeikus, 1977; Hobson et al., 1974; Torien and Hattingh, 

1969; Speece and McCarty, 1964; Kirsch and Sykes, 1971). 

2.3.1 EJ:!. 

The methanogenic and acetogenic bacteria seem to be sensitive to pH. The pH, 

in turn, is a function of the bicarbonate alkalinity, the C02 partial pressure, 

and the vol ati 1 e aci ds concentrati on. (1964a). reported that CH4 

production proceeds quite well as long as the pH is maintained between 6.6 and 

7.6, with an optimum range between 7.0 and 7.2. At pH values below 6.2, toxicity is acute. Alkali should be added to maintain the pH above 6.6. High pH 

can be a problem with CH4 production from animal manure because of the high 

levels of ammonia generated at high organic loading rates (Jewell et al., 1976). 

2.3.2 Alkalinity 

Alkalinity is a measure of the buffering capacity of the fermentor contents 

and consists of the bicarbonate, carbonate, ammonia, and hydroxide components. 

Organic acids and acid salts may also contribute to the buffering capacity 

(Am. Public Health Assoc., 1975). (1964a) indicated that a bicarbonate alkalinity in the range of 2.5 to 5.0 g CaC03/L provides a safe buffering capacity for anaerobic treatment of waste. Sievers and Brune (1978) 

and Kroeker et al. (1979) reported on the importance of ammonia in buffering 

animal manure fermentations. The relatively low carbon:nitrogen ratio of animal manures was reported as a major factor in the stability of animal manure 

fermentations. Ammonia was reported to contribute to the process stability by 

increasing the bicarbonate buffering capacity and increasing the pH. 
g

2.3.4 Temperature 

Temperature is an important environmental parameter in anaerobic fermentation 

processes. Faster fermentation rates, faster solid-liquid separation and 

minimization of bacterial and viral pathogens are some benefits attributed to 

thermophilic fermentation (Pfeffer, 1974; Cooney and Wise, 1975). Pfeffer 

(1974) used shredded municipal refuse to establish optimum temperatures. 

The optimum in the mesophilic and thermophilic range was 42 and 60°C, 

respectively. He al so concluded that it Itlas less expensive to produce CH4 at 

the higher temperature. A definite acclimation period was required to initiate thermophilic fermentation. Buhr and Andrews (1977) stated that although 

the literature is contradictory, minor fluctuations in temperature can cause 

problems for thermophilic fermentors. Golueke(1958) found that the total 

volatile acids increased as temperature increased between 35 and 65°C. 

Although the rates of reaction in the thermophilic range are much faster than 

those in the mesophi 1 i c range, most sewage sl udge fermentati on systems have 

operated under mesophilic conditions (McCarty, 1964a). In the past, energy 

requirements to maintain thermophilic temperatures were thought to be 

excessive due to the high water content of sewage sludges. Studies on urban 

refuse indicate that thermophilic temperatures are more economical and efficient for CH4 production (Pfeffer and Liebman, 1976; Pfeffer, 1974). Results 

published in this report show that thermophilic fermentation of beef cattle 

manure is more economical than mesophilic fermentation. 

2.3.5 Nutrients 

Another important envi ronmental conditi on is the presence of the nutri ents, 

like nitrogen, phosphorous, sulfur, and trace nutrients, needed by bacteria 

(Bryant, 1974; Bryant et al., 1971; 1964a). Animal manures and municipal sewage sludges usually contain all the required nutrients in adequate 

quantities, but other substrates may not. Pfeffer and Liebman (1976) found 

that municipal refuse was deficient in nitrogen and phosphorous. McCarty 

(1964b) reported that other elements having stimulatory effects at low concentrations include sodium, potassium, calcium, magnesium, and iron. All of 

these elements can exhibit inhibitory effects at higher concentrations. In 

general, the bacteria involved in methanogenesis have simple nutrient requirements and, although various individual species may require growth factors 

(e.g., B-vitamins, fatty acids, amino acids), these are supplied by other 

bacterial species (Bryant, 1974; Bryant et al., 1971). 

The relative proportion of nutrients is also important in methanogenesis. 

Hills (1979) reported a 60 to 70% increase in CH4 yield when the carbon:nitrogen 

ratio was increased from 8 to 25 by adding glucose or cellulose. Since most 

animal manures have carbon:nitrogen ratios between 6 to 10, the potential to 
inorganic substances vary depending on whether the substr'ates act singly or in 

combination. Certain combinations have synergistic effects, whereas others 

display antagonistic effects 1946b; Kugelman and 1965). 

Several investigators have implicated high concentrations of sulfate in 

retarding CH4 production. But recently, Bryant et al. (1977) and Winfrey and 

Zeikus (1977) have independently proposed that competition for available H2 is 

the mechanism by which sulfate inhibits in natural ecosystems. 

The sulfate-reducing bacteria apparently scavenge the available H2 faster than 

the methanogens. 

Inhibition by ammonia is a significant problem with some high rate fermentation processes, particularly when ammonia-rich manure from swine and poultry 

are fermented, and a proper acclimation period is not permitted (Lapp et al., 

1975; Stevens and Schulte, 1979; Sievers and Brune, 1978; Kroeker et al., 1979; Converse et al., 1977a). fvlcCarty (1964b) reported that at concentrations 

between 1.5 and 3.0 giL of total ammonia nitrogen and at a pH greater than 

7.4, the unionized ammonia may inhibit methanogenesis. At concentrations 

above 3.0 giL, ammonia becomes toxic regardless of pH. However, Lapp et al. 

(1975), Converse et al. (1977a) and Fischer et al. (1979) have reported stable 

CH4 production with ammonia concentrations in excess of 3.0 giL (2.2 to 8.0 

giL). Kroeker et al. (1979) used a urea and acetic-acid substrate to investigate the effect of ammonia inhibition on CH4 production. They concluded that 

CH4 was progressively inhibited as the ammonia nitrogen concentration 

increased above 2 giL; however, toxicity (i.e., complete cessation of CH4 

production) did not occur even at ammonia nitrogen concentrations of 7.0 giL. 

Antibiotics and growth promoters used in livestock rations can inhibit or even 

completely stop methanogenesis. Turnocliff and Custer (1978) reported that operating an anaerobic fermentation system where the antibiotic lincomycin is 

used is probably futile. Fischer et al. (1978) also reported severe fermentor 

instability 'r/hen lincomycin was used in swine rations to control dysentery. 

Hashimoto et al. (1979) reported that chlortetracycline had no adverse effect 

on methanogenesis, but that monensin nearly doubled the time (from 20 to 40 

days) for the start of CH4 production in batch fermentations. After the bacteria adapted to the monensin, however, the fermentation proceeded at rates comparable to batch fermentations without monensin. Three possible mechanisms 

may explain the apparent adaptation of the bacteria to monensin or any other 

antibiotic: a) mutant strains of bacteria develop resistance to the antibiotic; b) microbial populations shift as the result of inhibition of some 

bacteria and increase in others; andlor c) the antibiotic is deactivated 

during the lag period. Chen and Wolin (1979) have evidence suggesting that 

the first two mechanisms listed above explain the role of monensin in the 

rumen. The Rumensin Technical Manual (Eli Lilly Co., 1975) shows that one 

part per million of monensin in soil samples is deactivated in 14 days when 

incubated with animal feces, and in 25 days when incubated without feces. 

Experiments on daily feeding of manure containing monensin to fermentors show 
It is important to understand the kinetics of CH4 fermentation to design and 

operate optimum systems. Several kinetic models have been used to describe 

the anaerobi c fermentati on process. The Monod (1950) ki neti c model has been 

adapted to describe the anaerobic digestion kinetics of sewage sludge 

(OIRourke, 1968; Lawrence and McCarty, 1969; Andrews and Pearson, 1965) and 

animal manures (Morris, 1976; Hill and Barth, 1977). The advantages of the 

Monod type model are that the ki neti c parameters (the mi croorgani sm maximum 

specific growth rate and half-velocity constant) have deterministic connotations that describe the microbial processes, and the model can predict the 

conditions when maximum biological activity occurs and when activity ceases 

(i.e., wash-out). Disadvantages of the Monod model are that one set of kinetic parameters cannot describe the biological process at short and long retention times (Garrett and Sawyer, 1952; Chiu et al., 1972a,b), and that the 

kinetic parameters cannot be obtained for certain complex substrates (Pfeffer, 

1974) . 

To overcome the disadvantages of the Monad model, various forms of the firstorder kinetic model have been used (McKinney, 1962; Eckenfelder, 1963; Grau et 

al., 1975; Grady .et al., 1972; Pfeffer, 1974; Morris, 1976). The advantages 

of the first-order models are that they are simple to use and give good fit of 

experimental data. Disadvantages are that they do not predict the conditions 

for maximum biological activity and system failure. 

The Contois (1959) kinetic model has the advantages and generally avoids the 

di sadvantages inherent in the model. The Contoi s model was adapted to 

describe the kinetics of CH4 fermentation as follows (Chen and Hashimoto, 

1978) : 

where: 

[ 1 - K ] - 1 + K 

Yy = volumetric CH4 production rate, L CH4/L fermentor'day; 

So = influent total volatile solids (YS) concentration, giL; 

Bo =' ultimate CH4 yield, L CH4/9 VS added as e ---7 00; 

e = hydraulic retention time, day; 

= maximum specific growth rate of microorganisms, day-I; 

K = kinetic parameter, dimensionless. 

(2.1 ) 

Equation 2.1 states that for a given loading rate (Sole), the daily volume of 
(i.e., l/e = 0); or 2) incubating a known amount of substrate until a negligible amount of CH4 is produced (long-term batch fermentation). These two 

methods gave similar estimates of Bo for beef cattle manure fermented at temperatures ranging from 30 to 65°C at 5°C intervals (Hashimoto et al., 1979). 

There was no effect of temperature on 

Bo' and 

80 averaged 0.32 ± 0.01 L CH4/9 

VS fed for the steady-state method and 0.328 ± 0.022 L CH4/9 VS fed for the 

batch method. 

For livestock manures, Bo depends on the specie, ration, the age of the 

manure, the collection and storage method, and the amount of foreign material 

(like dirt and bedding) incorporated in the manure. Table 2.1 shows some 

values of Bo determined for beef cattle manure (Hashimoto et al., 1979) .. 

Table 2.1 shows that the manure from cattle fed higher grain rations had 

greater Bo val ues than that from ani'mal s fed hi gher roughage rati ons. Thi s is 

an expected result since rations containing higher levels of roughage would 

contain greater amounts of lignin complexed with cellulose. Table 2.1 also 

shows that chlortetracycline and monensin do not affect 

Bo' but 6 to 8 week 

01 d manU.re from a di rt feedlot has a lower 80 than fresh manure. Based upon the trends noted above, we have estimated Bo (L CH4/9 VS fed) for confined 

beef to be 0.35 ± 0.05, beef manure from dirt lots to be 0.25 ± 0.05; dairy 

manure to be 0.20 ± 0.05; and swine manure to be 0.50 ± 0.05. More studies 

are needed to refine these estimates and to determine other factors that 

affect methane yield. 

2.4.3 Maximum Specific Growth Rate 

Figure 2.2 shows the relationship between temperature and llm' The values of 

shown in Figure 2.2 were estimated by Chen and Hashimoto (1978) from data 

on anaerobic fermentations of sewage sludge (O'Rourke, 1968), municipal refuse 

(Pfeffer, 1974), dairy cattle manure (Morris, 1976; Bryant et al., 1976) and 

beef cattle manure (Varel et al., 1977). 

Figure 2.2 shows that a straight line can be drawn between most of the data 

between 20 and 60°C. This relationship is described by the following 

equation: 

= 0.013 (T) - 0.129 (2.2) 

where T is the temperature between 20 and 60°C. Temperatures above 60°C 

sharply decrease The data that do not conform to Equation 2.2 are those 

of Pfeffer at 40 and 45°C and those of Bryant et al. and Varel et al. at 60°C. 

Analysis of Pfeffer's data shows a large variation in Bo and K with 

temperature, indicating a variation in composition of the refuse fed to the 

various fermentors. The high values of for the data of Bryant et al. and 

Varel et al. may have resulted from the limited amount of data (three 

relatively short hydraulic retention times: 3, 6 and 9 days) available to 
TABLE 2.1. EFFECT OF TYPE AND RATION CONSTI TUENTS 

ON UL TIMATE YIELD (Bo)a 

Ration, % Dry Matter 

r,1anure Type Corn Silage Corn Antibiotic 

Bo 

L VS fed 

1 day 01 d 91.5 0 none 0.173b 

1 day 01 d 40.0 53.4 none 0.232c 

1 day 01 d 7.0 87.6 none O.290 d 

1 day 01 d 7.0 87.6 Chlortetracycline 0.294d 

1 day 01 d 7.0 87.6 Monensin 0.267 d 

6-8 weeks old from 7.0 87.6 Chlortetracycline 0.210 b 

di rt lot & Monensin 

aFrom Hashimoto et al., 1979. 

b,c,dMeans without a common superscript differ (P<0.05). 
1.0 

I 

>. 

a 

'U 

... W 0.8 t- A 

<! 

0::: 

I 

l- ~\ S 0.6 

0 \ 0:::: 

(9 \ 

\ 

<-) \ 

tL 0.4 \ 

0 \ 

LJ.J \ 0.. V U) 

~ 

:J 0.2 JJm =0.13 (T) - 0.129 ~ 

X 0 c::{ 0 ~ 

o.o ________ ~ ________ ~ ______ ~~ ______ ~ ________ ~ ______ ~ 

10 20 30 40 50 60 70 

TEMPERATURE, °C 

Figure 2.2. Effect of temperature on maximum specific growth rate (0 - O'Rourke. 1968; • - Morris, 1976; 

V - Chen et al., 1979;.6. - Pfeffer, 1974; A - Vare1 et al., 1978; 0 - Bryant et al., 1976). 

I-' 

a 
system than the bacteria can effectively use); inhibitory substances (e.g., 

volatile acids, ammonia, heavy metals, and salts) exceeding threshold levels; 

or reduced mass transfer of substrate, products, or both, because of the 

higher solids concentration. 

Figure 2.3 shows the effect of influent volatile solids (YS) concentration on 

K for swine manure at 35°C, and cattle manure at 32.5 and 60°C. The K values 

for swine manure were calculated from the data of Summers and Bousfield 

(1980). We estimated the Bo for their manure to be 0.36 L CH4/9 YS fed by 

plotting the CH4 yield (L CH4/9 YS fed) versus lie and extrapolating to an 

infinite e. This Bo is lower than what we suggest for U.S. swine manure (0.50 

L CH4/9 YS fed), which may have been caused by the diet (barley rather than 

corn) and the use of bedding (sawdust) to house the swine. Also, the lower YS 

content (70% rather than the 80 to 85% for fresh swine manure in the U.S.) of 

their manure suggests that some YS were destroyed before fermentation or that 

a larger portion of the VS in the ration was used by the swine. Both of these 

factors would decrease 

Bo' 

The values for Bo "'Jere 0.245 L CH4/9 VS fed for dairy cattle manure at 32.5°C 

(data of Morrois, 1976), 0.169 L CH4/9 VS fed for dairy cattle manure at 60°C 

(data of Bryant et al., 1976), and 0.280 L CH4/9 VS fed for beef cattl e manure 

at 60°C (data of Chen and Hashimoto, 1978). ° 

We estimated the values for using Equation 2.2; we calculated K by substituting the cited values of 

Bo' So and e for each data set into Equation 2.1 and solving for K. 

Figure 2.3 shows that K is relatively constant (about 0.6) at low So' but 

increases at different So depending upon the fermentation temperature and 

manure type. The value of K begins increasing at 35 g VS/L for swine manure 

at 35°C, 40 9 VS/L for cattle manure at 32.5°C and 60 g VS/L for cattle manure 

at 60°C. This behavior of K seems logical, because overloading a fermentor 

inhibits CH4 formation, and thermophilic fermentors can sustain a higher 

loading rate than mesophilic fermentors before onset of inhibition (Varel et 

al., 1980). The effect of manure type on K may be caused by differences in 

ration digestible energy, differences in digestion (rumen versus monogastric) 

and/or the presence of inhibitory substances in the swine ration (e.g., the 

swine ration contained 200 ppm of copper). 

Figure 2.3 should be used with caution because several data sources ,,,ere used 

and these experiments were not planned to evaluate the kinetic parameters. A 

systematic study using identical apparatus and procedures is necessary to 

verify the preliminary results shown in Figure 2.3. Also, the presence of 

inhibitory substances in the manure would cause K to increase at a lower So 

than shown in Figure 2.3. 
0:: 

W 

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w 

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B 

n:: 4 

a: 

o 

t--

W 

Z 

~ 2 

CATTLE" 60° C 

SWINE, 35° C 

CATTLE t 32.5° C 

~ 

O __________ ~ ________ ~ __________ .~ ____ ~ __ ~ __________ ~ ________ ~.d 

o 25 50 75 100 125 150 

INFLUENT VOLATILE SOLIDS CONTENT, g VS/L 

Figure 2.3. Effect of influent volatile solids content on the kinetic parameter K (e - Summers et al., 

1980; II - Morris, 1976; T - Bryant et al.,1976; A - Varel et a1.) 1977). 

...... 

N 
Table 2.2 shows the experimental and predicted Yy along with the operational 

and kinetic parameters used to estimate Yv. It al so shows the ratio of the 

predicted to experimental Yv. Most of the predicted values are within 15% of 

the experimental value of Yy except for the dairy manure fermented at 60°C. 

This predictive capacity is quite good, considering that and K, and Bo in 

most instances, were independently determined and had not been adjusted to fit 

the experimental data. 

2.5 SUMMARY 

This Section summarizes the major biological and operational factors involved 

in methanogenesis. A kinetic model that describes the fermentation process 

was presented and applied as a starting point in understanding and optimizing 

the fermentation process. Substrate biodegradability, fermentation 

temperature, and influent substrate concentration were shown to have significant effects on CH4 production rate. The CH4 production rates of existing 

pilot and full-scale fermentation systems were predicted to within 15% using 

this kinetic model. 
TABLE 2.2. EXPERII~ENTAL MJD PREDICTED VOLUlvlETRIC METHANE PRODUCTION RATES 

B a Temp a S a a ea y~,a L CH4/L'day Ratio 0 llm 0 K Specie L CH4/9 VS fed °C day-l 9 VS/L day ~ Pred Pred/Exp Source of Data --

Dai ry 0.20 35 0.326 64.7 1.05 10.4 0.94 0.86 0.92 Converse et al., 1977b 

Dai ry 0.20 60 0.651 65.2 0.60 6.2 1.41 1. 76 1.25 Converse et al., 1977b 

Swine 0.50 35 0.326 31.5 0.60 15 0.95 0.90 0.96 Kroeker et al . , 1975 

Swine 0.50 35 0.326 31.5 0.60 15 0.89 0.90 1.01 Kroeker et al . , 1975 

Swine 0.50 35 0.326 31.5 0.60 30 0.57 0.49 0.86 Kroeker et al . , 1975 

Swine 0.50 35 0.326 31.5 0.60 30 0.50 0.49 0.98 Kroeker et a 1 . , 1975 I-' 

Swine 0.50 35 0.326 43.5 0.75 15 1.08 1.22 1.13 Fi scher et a 1 . , 1975 +:0 

Swine 0.50 35 0.326 39.2 0.70 15 1.07 1.11 1.03 Fi scher et al . , 1975 

Swine 0.50 35 0.326 46.8 0.90 15 1.17 1.27 1.08 Fischer et a 1 • , 1975 

Swine 0.50 35 0.326 60.0 1. 70 15 1.36 1.39 1.02 Fischer et al . , 1975 

Swine 0.36 35 0.326 23.1 0.60 10 0.69 0.66 0.95 Summers et a 1 . , 1980 

aSymbols are defi ned in Equation 2.1 
Thermophil i c anaerobi c fermentati on of 1 i v'estock manures has several advantages 

that make it attractive for more detailed investigation. This system has the 

potential for significantly higher CH4 production rate, with resultant savings 

in capital expenditures. Also, the residue is sanitized; therefore, disease 

transmission is minimized. This is especially important if the product is to 

be refed to livestock. Laboratory studies have demonstrated higher CH4 production rates at thermophilic than mesophilic temperatures. Augenstein et al. 

(1976) showed about four times higher CH4 production rates at 60°C than at 37°C 

for anaerobic cultures being fed C02 and H2' Likewise, Pfeffer (1974) showed 

a four-fold increase in reaction rate at 60°C compared to 35°C for cultures 

fed domestic refuse. Varel et al. (1977) reported the highest CH4 production 

rate (4.5 L CH4/Lfermentor'day) for beef cattle manure fermented at 60°C. 

Converse et al. (1977b) compared the pilot-scale anaerobic fermentation of 

dairy waste at mesophilic (37°C) and thermophilic (60°C) temperatures. Their 

thermophilic CH4 production rate was lower than the laboratory results 

reported by Varel et al. (1977) and close to those obtained by their mesophilic fermentor. They proposed the following possible explanations for the 

unexpectedly low gas yields of their thermophilic fermentor: insufficient 

mixing; wide temperature fluctuations in fermentor; less efficient microflora 

in their system; less biodegradable manure in their system; lower system efficiency because of improper scale-up factors. 

The need for improved design criteria and scale-up factors for thermophilic, 

anaerobic fermentation systems is apparent. One of the objectives of this 

project was to determine the design factors necessary to achieve the high gas 

yields obtained by laboratory-scale thermophilic fermentors. 

3.2 EQUIPMENT AND PROCEDURES 

3.2.1 Pilot-Plant Facilities 

Figure 3.1 is a schematic diagram of the pilot-scale fermentation system. The 

pilot-scale facilities were constructed under contract with Hamilton Standard 

Division of United Technologies, Inc. Manure (1 to 10 days old) was gathered 

daily from steers housed on partially roofed, concrete-floored pens. The 

steers weighed from 340 to 570 kg, depending on the season. Table 3.1 shows 

the rations fed to the cattle over the 1319 days of fermentor operation. 

The manure was transported to the pilot plant by a small front-end loader and 

dumped into the s1 urry tank. Itlater was added to the materi alto form a sl urry 

of 12 to 14% total solids (TS). The slurry i'laS mixed by a 1-kltl variable speed 

mixer. Based upon the TS and volatile solids (VS) analyses, a given amount of 

slurry was pumped into a 1-m3 tank on a platform scale, the weight of the slurry transferred was recorded, and water was added to dilute the slurry to a specified VS concentration. 
o = PUMP 

.. SLURRY 

FEEDLOT ... TANK 

J" 

LAND 

DRYER 

: 

,~ 

FEED 

PRESSURE 

_..4i11e--i R ELI E F 

VALVE 

..... 

GAS 

CHROMATOG 

GAS 

METER 

kV~ WEIGHT kV ~ HEAT 

TANK EXCHANGER j~ 

_4 CENTRATE 

"'" 

CENTRIFUGE 

._ CAKE ..... J J~ 

,,- ... ~ ~ p P 

CONDENSATE 

a FOAM TRAP 

11/0 

, 

FERMENTOR 

'if 

Figure 3.1. Schematic Diagram of Pilot-Scale Anaerobic Fermentation System 

....... 

0'1 
TABLE 3.1. BEEF CATTLE RATIONSa USED THROUGHOUT THE COURSE OF THE FERMENTOR OPERATION 

Day of Operation (inclusive dates) 

0-125 126-436 437-463 464-809 810-1319 

Item (11 /30/76-4/4/77) (4 /5 /77 -4 /9 /78) (4 /10 /77 -5/5/78) (5 /6 /78-2/17 /79) (2/18/79-7 /11 /80 ) 

Yellow Corn 

Corn Sil age 

Al falfa Haylage 

Soybean ~1ea 1 

Limestone 

Dicalcium Phosphate 

Salt 

Trace Mineralsb 

Vitamin ADE c 

Chlortetracyclined 

83.6 

4.0 

4.2 

7.0 

0.9 

0.1 

+ 

+ 

+ 

aExpressed on a dry matter basis 

90.8 

6.9 

2.3 

b9. 9 9 Arizona-chelated trace minerals per kg dry ration 

90.8 

6.9 

1.9 

0.3 

0.1 

0.1 

+ 

+ 

+ 

c29 •3 g (ADE supplement of 8.8 x 106 IU Vito A/lb) per kg of dry ration 

90.8 

6.9 

1.9 

0.3 

0.1 

0.1 

+ 

+ 

°10.8 9 chlortetracycline (110 9 chlortetracycline/kg carrier) per kg of dry ration 

85.0 

13 .0 

1.6 

0.2 

0.1 

0.1 

+ 

+ 

I-' 

-..... 
248 days of operation and 5.1 

m3 for the remainder of the study. The fermentor had four baffles equally spaced around the tank and the mixer consisted of 

a 1.5 kW variable-speed motor and two, 3-blade, stainless steel, marine propellers on a stainless steel shaft. The following geometric relationships 

were used: fermentor diameter (T) to propeller diameter (D) ratio, T/D = 5.6; 

propeller spacing of 2.50; baffle width (W) of-T/W = 14; and spacing between 

baffle and fermentor wall W/2. 

The gas produced during the fermentation passed through condensate-foam traps, 

a temperature-compensated gas meter, and a pressure relief valve. The condensate-foam trap consisted of a cylindrical tank, 0.53 m in diameter and 

1.73 m high, with a siphon calibrated to discharge when the pressure exceeds 

0.25 m of water column. This has reduced the frequency of draining condensate 

from the gas flow meters and has eliminated the need to disassemble and clean 

the gas line after excessive foaming. The CH4 and C02 concentration is 

measured by a gas chromatograph several times each day. 

The pilot-plant facilities are housed in a 14 x 8.5 m building which also contains an office and laboratory facilities for determining solids, pH and 

a 1 k ali n ity • 

3.2.2 Methods 

Before adding fresh slurry to the fermentor, a specified volume of fermented 

slurry, corresponding to the desired hydraulic retention time (HRT) , was 

removed. The fermented slurry was either mixed directly with other feed 

ingredients for livestock feeding trials or centrifuged. The centrate flowed 

to a lagoon for ultimate land applicatibn, and the centrifuge cake was dried 

at 70°C, then used as a feed ingredient for livestock feeding trials. 

Samples of slurries fed and withdrawn from the fermentor were routinely analyzed for various constituents. Total, volatile, fixed and suspended solids, 

ammonia (distillation method), chemical oxygen demand, alkalinity (to pH 3.7), 

pH, and total volatile acids (TVA, silicic acid method) were determined by the 

methods outlined in Standard Methods (APHA, 1975). Total Kjeldahl nitrogen 

was determined using Technicon block digestors and Auto-Analyzer II as 

described by Wael and Gehrke (1975). 

Daily gas production was measured by an American AL-175 gas meter with temperature compensati on capabi 1 i ty. Gas vol ume was corrected to standard temperature (O°C) and pressure (1 atmosphere). CH4 and C02 concentrations were 

measured using an on-line, Gow Mac Series 550 gas chromatograph with thermal 

conductivity detectors. The stainless steel column (0.64 by 183 cm) was 

packed with 60/80 mesh chromosorb 102. Injector, oven and detector temperatures were 102, 100 and 131°C, respectively, with a bridge current of 100 

m.a. Helium carrier gas flow was 60 ml/min. 
VARIBLE SPEED MIXER 

2 .13 f'I') 

BAFFLE 

-

o:::t 

co 

o 0.07 

0.15 

k-o 

ALL DIMENSIONS IN METERS 

Figure 3.2. Schematic Drawing of Pilot-Scale Fermentor. 

o 

± 

,..... 

C\J 

o 
tion and decrease in TVA. Daily charging of manure began on day 9 with a 

loading of 1.6 kg YS/m3 of tank contents. 

Figure 3.3 shows the change in pH and accumulated gas production during 

start-up. After 6 days, the gas production increased dramatically. Figure 

3.4 shows that the alkalinity increased during start-up and that the TVA 

increased to 3.5 gil as HOAc at day 6 of operation, then steadily decreased to 

below 1 gil after 10 days. Within 9 days, significant gas production was 

achieved. This agrees with the experiences of Varel et al. (1977) for their 

laboratory-scale fermentors. 

The fermentor loading was gradually increased from 1.6 to 2 .. 4 kg YS/m3 between 

days 9 and 37 of operat1on. On day 38, the fermentor reached the desired 

operating volume (5.4 m ) and daily effluent withdrawal commenced. The 

hydraul i c retenti on ti me (HRT) was gradually decreased to 20 gays on day 56. 

The temperature was raised to 55°C and loading of 5.4 kg VS/m on day 63. The 

loading was decreased to 3.4 kg YS/m3 on day 73 because the TVA began to increase. 

3.3.2 Steady-State Operation 

The fermentor performance was eval uated at vari ous operati ng conditions to 

define optimum design criteria. The fermentor was operated at each condition 

for at least four HRT before steady-state data were recorded. 

Tables 3.2, 3.3, 3.4 and 3.5 summarize the steady-state performance of the 

fermentor under different operating conditions. These tables .show that the 

volumetric CH4 production rate increases as the loading rate increases; the F,S 

in the effluent was close to the influent FS, indicating that the fermentor 

contents were completely mixed; and that little nitrogen was lost during 

fermentation. 

Table 3.2 summarizes the fermentor performance at 55°C, fed once daily and mixed 

continuously. It shows that the CH4 yield (L CH4/9 VS fed (VSf») decreased as 

the HRT decreased, and that the L CH4/9 YS used (VS

u) averaged 0.54. 

Table 3.3 summarizes the fermentor performance at 45 and 50°C, fed once daily 

and mixed continuously. The first three steady-states in Table 3.3 (So = 

65.3, 61.5 and 77.1 g VS/L) showed unusually low yields of 0.36, 0.39 and 0.30 

L CH4/9 YS

u' These low yields prompted an intensive search for gas leaks from the fermentor and gas handling system. The search revealed a small leak 

around the packed bearing of the propeller shaft and a significant leak 

through the secondary gas-relief valve. The last steady-state in Table 3.3 

(So = 80.2 g VS/L) shows the fermentor performance after the gas leaks were 

sealed. The CH4 yields were much higher than the three previous steady-state 

yields. 
I 7 Q. 

14 

t t t t 

12 4.3 0.8 2.3 2.3 LIME ADDED, Kg 

r0 t f t E 

Z .... 10 

0 

ft.) 

::) 8 

0 

0 

0:: 

0- 6 

(f) 

c:::r: 4 

<..9 

2 

o 

2 4 6 8 10 12 

DAYS 

Figure 3.3. Gas Production and pH Profiles During Start-Up. 
6 

---'---

/ '" / ''v/ 

5 I r TOTAL ALK. (pH 3.7) 

. as Co C03 

4 (______ I en 

.. I '",) z 

0 I VOLATILE - ACIDS as HOAc 0:: 3 

r-- I z w 

u 

Z 2 0 START DAILY U FEEDING 

o 2 4 6 8 10 12 

DAYS 

Figure 3.4. Total Alkalinity and Volatile Acids Profiles During Start-Up. 
I nf., gIL 

Eff., giL 

Volatile Solids 

Inf., giL 

Eff., gIL 

Fixed Solids 

Inf., giL 

Eff., giL 

COD 

Inf., gIL 

Eff., giL 

Tota 1 Nitrogen 

Inf., giL 

Eff., giL 

Ammonia-N 

I nf., giL 

Eff., giL 

Volatile Acids 

I nf., giL 

Eff., giL 

Alkalinity 

Inf., giL 

Eff., giL 

pH 

Inf. 

Eff. 

Methane, Methane Production 

LIL'day 

Llg VSf Llg VS u 

70.1±5.4 

36.6±2.7 

61. 8±S. 3 

29.2±2.8 

8.3 

7.4 

74.9±13.2 

40. 2±7.1 

4.32±0.37 

3. 93±0. 38 

1.13±0.12 1.89 ±D. 05 

6.95±0.79 

1.15±0.23 

4.06±1.18 

8.59±0.42 

5.2±0.26 

7.9±0.OB 

55.0±4.9 

1.59±0.30 

0.31 0.58 

74.4±7.3 

43. 0±3. 8 

68. 7±8. 7 

37. 0±4. 6 

5.7 

6.0 

73.8±3.1 

47. 2±3. 5 

3.69 to. 41 

3.B2±0.03 

1. 02 ±D. 28 1.82±0.07 

6. 75±0. 74 

1.82±0.21 

3.26±0.54 

8.53±0.55 

4.8±0.29 

7.9±0.07 

52.1±3.0 

2.73±0.12 

0.23 0.50 

67.7±4.7 

43. 8±1. 7 

59.5±4.5 

35.B±1.5 

8.2 

7.9 

73.0±3.6 

47.B±2.4 

3.81±0.10 

4.14±0.23 

1.50±0.26 1.90±0.07 

4.56±0.85 

2.55±0.19 

5.43±0.45 

9.23±0.11 

7.65±0.36 

7.93±0.12 

52.2±2.1 

3.28±0.24 

0.22 

0.55 

92.4±2.7 

47.0±0.8 

82.6±2.1 

37.1±0.5 

9.8 9.9 

93.1±11 

55.0±3.6 

4.25±0.32 4.19±0.03 

0.93±O.07 

1. 61±0.16 

7.85±0.66 

1. 27±0. 07 

3.73±0.48 

8. 26±0. 51 

4.85±O.21 

7.87±0.04 

49.9±O.7 

3.47±0.20 

0.29 

0.53 

aData presented as mean ± 1 standard deviation, steady-state assumed after 

4 HRT 
I nf. , gil 74.8±9.4 70.1±3.9 85.1±11.2 92.0±3.1 

Eff. , gil 38.5±6.8 39.5±0.5 42.3±5.9 53.8±5.6 

Vol at i1 e So 1 ids 

I nf. , gIL 65.3±9.4 61.5±3.6 77 .1±10. 2 80.2±2.9 

Eff. , gil 30.0±0.6 30.8±0.5 33. 8±0. 5 42.1±0.S 

Fixed Solids 

I nf. , gil 9.5 8.6 8.0 11.8 

Eff. , gil 8.5 8.7 8.5 11. 7 

COD 

I nf. , gil 72. 4±4. 8 73.9±3.3 76. 5±10.4 94. 3±5. 2 

Eff. , gIL 42.7±2.7 42. 8±1. 6 43.6±5.7 56. 5±5. 5 

Total Nitrogen 

I nf. , gil 2.68±0.10 2.81±0.16 2. 97±0. 38 3.44±0.21 

Eff. , gIL 2.80±0.06 2.98±0.10 3.20±0.07 3.66±0.08 

Ammonia-N 

Inf. , gIL 0.58±0.04 0.62±0.05 O. 72±0. 06 1.23±0.05 

Eff. , gil 1. 21±0. 02 1. 33±0. 03 1. 37±0. 01 1.49±0.02 

Vol at i1 e Ac ids 

I nf. , gil 6. 44±0. 51 6.60±O.62 8. 06±0. 39 . 6. 41±1. 38 

Eff. , gil 1. 47 to. 09 0.87 to. 05 1.17±0.13 1.68±0.07 

A 1 kal i nity 

I nf. , gil 2. 88±0. 56 2.88±0.35 3. 98± 1. 42 5.05±0.38 

Eff. , gil 6.93±0.09 7.34±0.15 7.53±0.20 10.23±0.34 

pH 

Inf. 4.88±0.28 4.71 ±O.ll 4.81±0.35 5.44±0.22 

Eff. 7.61±O.04 7.76±0.07 7.78±0.10 7.91±0.06 

tvlethane, % 52.7 ±3. 7 58 .1±1. 3 53.9±1.4 59.4±O.7 

Methane Production 

L/l'day 1.43±O.15 2.01±0.1l 2.14±0.21 3.85±0.06 

L!g VSf 0.20 0.20 0.17 0.29 L/g YS u 0.36 0.39 0.30 0.60 

aOata presented as mean standard devi a ti on, steady-state assumed after 4 HRT 
I nf • , giL 67.7±3.3 69.6±4.1 Eff. , giL 34.4±0.4 33.1±0.8 

Vo 1 at il e So 1 ids 

I nf • , giL 59.8±3.0 61.4±3.6 

Eff. , gIL 26.5±0.3 25.1±0.8 

Change, % -55.7 -59.1 

Fixed Solids 

I nf., giL 7.9 8.2 

E ff., giL 7.9 8.0 

COD 

I nf • , giL 68.9±3.5 70.2.±6.9 

Eff. , giL 34.0±4.3 34.8±5.1 

Total Nitrogen 

I nf. , giL 2.42±0.17 2.61±0.24 

Eff. , giL 2.65±0.06 2.54±0.03 

Ammonia-N 

I nf. , giL 0.73±0.02 0.78±0.04 

Eff. , giL 1.24±0.06 1. 29±0.02 

Vol at il e Ac ids 

I nf. , giL 5.07±0.70 6.72±0.82 

Eff. , giL 0.62±0.10 O. 92±0. 35 

Alkalinity 

Inf., giL 3.33±0.15 3.19±0.26 

Eff. , giL 6.57±0.22 6.79±0.27 

pH 

Inf. 5.45±0.37 4.80 ±0.04 

Eff. 7. 50±0. 04 7.5110.05 

Methane, % 52.5±0.8 53.9 ±4. 7 

Methane Production 

L/L'day 2.59±0.06 2.6010.19 

l/g VSf 0.26 0.25 l/g VS u 0.47 0.43 

aData presented as mean ± 1 standard deviation, steady-state 

assumed after 4 HRT 
Inf., g/L 

Eff., gIL 

Volatile Solids 

Inf., g/L 

Eff., g/L 

Fixed Solids 

I nf., g/L 

Eff., g/L 

COD 

Inf., g/L 

E ff " g/L 

Total Nitrogen 

Inf., g/L 

Eff., g/L 

Ammonia-N 

Inf., g/L 

Eff., g/L 

Vol at il e Ac ids 

Inf., g/L 

Eff., g/L 

Alkalinity 

Inf., g/L 

Eff., g/L 

pH 

Inf. 

Eff. 

% 

Methane Production 

L/l'day 

L/g VSf 

l/g VS u 

92.8±8.9 

46.4±1.9 

84.9±8.4 

39.8±1. 7 

7.9 

6.6 

93.7±11 

52.9±5.2 

3.62±0.31 3.88±0.29 

O.94±O.13 

1.44±0.03 

6.89±0.34 

1.64±0.12 

2.95±0.59 

6.12±0.32 

4.61±0.31 

7.70±0.05 

51.9±1.4 

4.23±0.49 

0.25 

0.47 

94. 7±5. 9 

51.6±2.0 

83.8±5.1 

41. 5±1. 7 

10.9 10.1 

96.1±13.1 

56. 9± 9.2 

4.25±0.20 4.27±0.18 

1.12±0.16 1.85±0.14 

7.70±1.14 

2.39±0.33 

4.37±0.25 

8.63±0.63 

5.65±0.30 

7.71±0.12 

55±2.3 

4.65±0.22 

0.28 0.55 

95.0±9.9 

50.2±1.6 

82.3±8.6 

38. 8±1. 2 

12.7 11.4 

102.2±9.7 

53.0±5.3 

3.95±0.12 

4.01±0.08 

0.79±0.02 

1. 72±0. 07 

9. 04±1. 01 

2.12±0.85 

3.24±0.24 

9.50±0.48 

4.41±0.04 

7.70±0.16 

56.6±0.3 

4. 70±0. 32 

0.29 0.54 

88.8±2.6 

51. 2±0. 7 

76.0±5.1 

37.8±0.4 

12.8 

13.4 

95.9±12.1 

55.3±4.6 

4.25±0.10 4. 22±0. 08 

O. 92±0. 02 

2.07±0.02 

11.42±0.42 

3.34±0.08 

4.35±0.46 

10.08±1.31 

4.71 to. 24 

7.84 to. 06 

57. 3±0. 4 

4.30±0.16 

0.25 

0.51 

aOata presented as mean ± 1 standard deviation, steady-state assumed after 

4 HRT 
decrease in effective fermentor volume affects important operational parameters 

such as HRT and loading rate. Thus, the mixing requirement for fermentation 

systems may be based on the materials handling and fermentor design aspects 

rather than maximum CH4 production rates. More research is needed on the 

materials handling function of mixing systems in anaerobic fermentors. 

Table 3.5 compares the fermentor performance when fed once daily or 22 times 

per day. At a HRT of 5 days and similar influent YS concentration, the CH4 

production rate was about 10% higher when the fermentor was fed 22 times per 

day compared to being fed once per day. The lower CH4 production rate at once 

per day feed; ng may have resul ted from the dai ly shock loadi ng of the 

fermentor, especially at the short HRT of 5 days. Figure 3.5 and 3.6 show the 

variation in TVA, and percent CH4 and C02, respectively, with time after 

feeding when the fermentor was operated at 55°C andHRT of 12 days. There was 

a 250% increase in TVA 2 hr after feeding, then a gradual decrease in TVA. 

The CH4 concentration decreased to about 46% 4 hr after feeding, increased to 

66% 14 hr after feeding, and remained at that concentration for the rest of 

the day. Figure 3.7 shows the change in hourly total gas and CH4 production 

rate with time after feeding. The hourly total gas production rate was 7 

times higher and the CH4 production rate was 6 times higher 1 hr after feeding 

compared to 22 hr after feeding. Since the results shown in Figures 3.5 to 

3.7 were for the fermentor operated at 12 days HRT and loading rate of 5.2 kg 

. YS/m

3'day, we that the magnitude of a daily shock loading at 5 days HRT 

and 16.5 kg VS/m 'day loading rate would be much greater, and this shock 

loading may be the reason for the lower CH4 production rate for the daily fed 

operation compared to the 22 hr/day feeding. 

3.3.3 Comparison of Experimental to Predicted CH4 Production Rates 

One of the major reasons for operating the pilot-scale fermentor was to obtain 

data that could be used to design full-scale systems. 

In the design and scale-up of the fermentation systems, it is important to be 

able to predict the performance of the fermentor under different operating 

conditions in order to optimize the systems. Equation 2.1 was used to predict 

the CH4 production rate (Yy) of the fermentor. Figure 2.2 was used to estimate at 50 and 55°C and Figure 2.3 was used to estimate K. Since Figure 

2.3 has relationships between K and So only at 32.5 and 60°C, the values for K 

at 50 and 55°C were assumed to vary as they do at 60°C (this assumption seems 

to be valid based on preliminary results from our laboratory). The value of 

Bo was assumed to be 0.35 L CH4/9 YSf' since long-term (114 to 186 day) batch 

fermentations of the fermentor influent yielded Bo ranging from 0.32 to 0.40 L 

CH4/9 YSf· 

Table 3.6 shows the experimental and predicted Yy from the fermentor, along 

with the operational and kinetic parameters used to predict YV' The mean 
1.6 

-0 

0 

<! 

0 

-+-

(J) 

0 

« 1.2 

(j) 

0 

-' ""'-

01 

.. (f) 

0 0.8 

0 

« 

lJJ 

-' 

t( 0.4 -' 0 

> 

-' 

~ 5 

l- 0.0 

0 6 12 18 24 

TIME AFTER FEEDING, hours 

Figure 3.5. Changes in Total Volatile Acids with Time After Feeding (T = 55°C, HRT = 12 days, Loading 

Rate = 5.2 kg VS/m3'day) 

N 

(X) 
,. 

70 

0 ~ 60 .. Z 

0 

~ 50 

a:: 

IZ 

w 

(.) 

z 

o· 

U 

30 

C\I 

0 

() 

0:: 20 

0 

~ 

I 10 U 

o~------------~------------~------------~------------~ o 6 12 18 24 

TIME AFTER FEEDING, hours 

FigUl~e 3.6. Changes in CH4 (0) and C02 (0) Concentration with Time Afte\~ Feeding (T = 55°C. HRT = 

12 days. Loading Rate = 5.2 kg VS/m3·day). 

N 

\.0 
"'7 ""-

o 

2.0 

l- 1.0· 

o 

:J 

C) 

o 

0:: 

(L 

(j) 

« 0.5-

(9 

TOTAL GAS 

O.O,."........,.. ______ """'-________ I-________ J.. ___ ,-'"-_""""'"" 

o 

Figure 3.7. 

6 12 18 24 

TIi\!lE A~FTER FEEDii\JG, hours 

Changes in C.~ and Total Gas Production with Time After Feeding (T = 55°C, HRT = 12 days. 

Loading Rate = 5.2 kg VS/m3.day). 

w 

o 
TABLE 3.6. EXPERH1DJTAL AND PREDICTED t

J

1ETHANE PRODUCTION RATESa OF THE PILOT -SCALE FERMENTOR 

Feeding t1i xi ng Tempe ra tu re HRT So YY..2. L CH~l/L' day Ratio llm K x/day h/day °C day-1 day 9 VStlL Exp Pred Pred/Exp --

1 24 55 0.586 12 61.8 0.60 1. 59 1.64 1.03 

1 24 55 0.586 6 68.7 0.65 2.73 3.18 1.16 

1 24 55 0.586 4 59.5 0.60 3.28 3.60 1.10 

1 24 55 0.586 7 82.6 0.80 3.47 3.61 0.95 

1 24 50 0.521 6 80.2 0.80 3.85 3.08 0.88 w 

...... 

1 24 50 0.521 6 59.8 0.60 2.59 2.62 1.05 

1 2 50 0.521 6 61.4 0.60 2.60 2.69 1.07 

1 24 55 0.586 5 85.0 0.85 4.23 3.85 0.98 

22 24 55 0.586 5 84.0 0.85 4.65 3.81 0.88 

22 24 55 0.586 5 82.3 0.80 4.70 3.86 0.87 

22 24 55 0.586 4.5 76.0 0.70 4.30 3.89 0.96 

aAssumes Bo = 0.35 L CH4/9 VSf 
12 to 4 days; mixed continuously or 2 hr/day; and fed 1 or 22 times/day. No 

difference in CH4production rate was observed when the fermentor was mixed 2 

hr/day versus continuously. The CH4 production rate was about 10% higher when 

the fermentor was fed 22 times/day as compared with once/day. The highest CH4 

production rate achieved by the fermentor was 4.7 L CH4/L fermentor·day. This 

was the highest rate reported in the literature and about four times higher 

than other pilot- or full-scale systems fermenting livestock manure. 
This section discusses the power and energy requirements for m1x1ng, pumping, 

and heati ng the i nfl uent sl urry and fermentor 1 i quor. Th; s di-scussi on is 

necessary in order to maximize the net energy production of anaerobic fermentation systems. 

4.2 ENERGY AND POWER REQUIREMENTS 

4.2.1 Heating Requirement 

The total heat required to maintain the fermentor liquor at a desired temperature can be expressed as follows: 

QT = Qf + Qw + Qg + Oi - Or (4.1) 

where: OT = total fermentor heat requirement, J/day; 

Of = heat loss through fermentor walls, floor and top, J/day; 

Ow = heat loss due to evaporation, J/day; 

Qg = heat loss due to the gas leaving fermentor, J/day; 

O' = heat required to rai se the influent slurry to the desired -1 

fermentor temperature, J/day; and 

Or = heat of reaction from methane fermentation, J/day. 

The heat loss through the fermentor wall s (Of) is the sum of the heat loss 

through the top, side walls, and bottom of the fermentor, which can be calculated from the overall heat transfer coefficients of top, side walls and bottom of the fermentor. 

The heat loss due to evaporated water (Ow) is the sum of the sensible heat 

loss of the steam and the heat of evaporation of water. The sensible heat loss with the dry biogas leaving the fermentor (Og) is the sum of the sensible 

heat in CH4 and C02' Ashare et ala (1978) have dlscussed in detail the calculation of Og and Ow' 

The heat required to raise the influent slurry to the fermentor operating temperature can be calculated from: 

Qi = W Cp (t - ts) (4.2) 

where t is the fermentation temperature (OC), ts is the influent slurry temperature (OC), H is the total weight of slurry to be added to the fermentor 
Pirt (1978) suggested that in an anaerobic process, 3% of the available heat 

is liberated in the reaction. However, using our experimental data from 6 

days HRT and a volatile solids loading rate of 15 kg/m

3'day, we found that 102 

MJ/m

3'fermentor'day of heat energy was available from the influent fed to the 

5.1 

m3 fermentor. The fermentor, however, produced 122 moles of CH4/ 

m3'fermentor'day, which contained a heat energy of 107.7 MJ/m

3·fermentor o day. 

Since the heat energy in the CH4 is essentially equal to the substrate heat 

energy, we concluded that the heat of reaction (Or) was negligible. 

In the following calculations, fermentors with total working volume up to 785 

m3 were assumed to have worki ng tank hei ght to di ameter rati os of 1. 0, thu s 

limiting tank height to 10 m. Tanks larger than 785 

m3 were designed with a 

maximum tank height of 10 m and sufficient diameter to accomodate the volume. 

The maximum tank diameter was assumed to be 80 m, resulting in a maximum tank 

volume of 5027 

m3. Systems requiring volumes greater than 5027 

m3 were 

designed with multiple tanks. The top, sides, and bottom of each fermentor 

were assumed to be insulated with materials having an overall heat transfer 

coefficient of 2.04 KJ/h·m

2.oC. 

Table 4.1 gives the thermal energy requirements for fermentation systems 

operating at 55°C, 5 days HRT and 80 g VS/L influent concentration along with 

their gross methane energy production. Using B = 0.35 L CH4/g VS for beef 

cattle manure, maximum specific growth rate of 0.586 day-l (for 55°C) and 

kinetic parameter (K) of 0.8, the volumetric methane production rate (rV) of 

3.96 

mj CH4/m3'fermentor'day is obtained (Hashimoto et al., 1980). 

Table 4.1 shows that for plant sizes ranging from 1 to 1,000 TS/day, Of 

increases from 0.186 to 36.2 GJ/day; Ow + 

08 increases from 0.089 to 89.0 GJ/day; and Oi increases from 1.910 to 1,91 GJ/day. The total heat energy 

requirement, however, decreases from 39.7% to 37.0% of the gross methane 

energy production, assuming a boiler efficiency of 70% and an ambient temperature of 10°C. Of the total heating requirement, 87.4% to 93.9% is for 

heating the influent, while heat loss through the fermentor walls accounts for 

1.8% to 8.5% of the total heat requirement. The percent of heat required to 

compensate for the surface heat loss varies inversely with the size of the 

fermentor. 

The net thermal energy production, i.e., the amount of CH4 energy production 

minus heat energy requirement, ranges from 4.73 GJ/day for the 1 Mg TS/day 

plant to 4,950 GJ/day for the 1,000 TS/day plant. 

4.2.2 Pumping Power and Energy Requirements 

The rheological properties of the slurry being pumped and mixed have a direct 

influence on the power requirements. Livestock waste slurries and fermentor 

liquor generally display non-Newtonian, pseudoplastic behavior. We previously 

used a power-law formula to describe the relationship between shear stress (T) 
TABLE 4.1. HEATING ENERGY REQUIREMENTS AND NET THERtvlAL ENERGY 

PRODUCTION FOR FERt~ENTORS OPERATING AT 55°Ca 

PLANT SIZE (Mg TS/day) 

PARM1ETER 1 10 100 

Each Fermentor Volume (m3) 53.2 532 2660 

Number of Tanks 1 1 2 

Gross Thermal Energy Production 7.85 78.5 785 

(GJ Iday) 

Fermentor Surface Heat Loss 0.186 0.862 5.19 

(GJ I day) 

Heat Loss Through Gas Line 0.089 0.890 8.90 

(GJ I day) 

Heating Influent (GJ/day) 1.910 19.10 191.0 

Total Heat Loss (GJ/day) 2.185 20.85 205.1 

Heat Required (GJ/day) 3.12 29.79 293.0 

Net Thermal Energy Production 4.73 48.8 493 

(GJ Iday) 

aInfluent TS = 94 giL; influent VS = 80 giL; % CH4 = 50; influent slurry temperature lOoC 

Ambient temperature 10°C, Overall heat transfer coefficient = 2.04 KJ/h·m2.oC 

YV = 3.96 m3 CH4/m3 fermentor' day, HRT = 5 days. 

1000 

13300 

4 

7850 

36.2 w 

(jl 

89.0 

1910 

2035 

2907 

4950 
The method of calculating the pumping power requirement for a pseudoplastic 

slurry was described previously (Chen and Hashimoto, 1976). He have found 

that the onset of turbulence in pumping livestock waste slurry was delayed 

until the General i zed Reynol ds number (NRe I) for 1 i vestock waste sl urry was 

over 3,100. The Generalized Reynolds number is defined by: 

(4.5) 

where P = slurry density, kg/m3; 

o = pipe diameter, m; 

v = slurry flow speed, m/sec/ 

To prevent solid particles from settling in the pipe and to have better heat 

transfer characteristics when a heat exchanger is used to recover effluent 

heat, the piping should be designed to maintain turbulent flow (NRe > 4,300)' 

In our calculation, however, the pipe size is chosen so that the NRe l is close 

to but does not exceed 5,000, and the pipe size is no smaller than 0.0191 mID. 

Table 4.2 lists the pipe diameter, pumping rate, number of pumps and the total 

influent and effluent volume to be pumped. The plants were assumed to operate 

at 5 days HRT and 80 g VS/L influent concentration (9.4% T5 concentration). 

The effective pumping length was assumed to be 300 m, which does not include 

the pressure head due to the liquid height of the above-ground tank. The same 

pump used to pump the i nfl uent was al so used to pump the effl uent. Effl uent pumpi ng was not necessary for the 1000 r,1g TS/d pl ant because there was sufficient head to use gravity flow. 

The rheological properties were assumed to be: K = 0.61 Pa·s n and n = 0.54 

for the 10% T5 influent; and K = 0.33 Pa's n and n = 0.5 for the 5% TS 

effluent. 

Table 4.2 shows that the power required to pump the influent is 0.70 kW for 

the 1 Mg T5/day plant and 95.4 kW for the 1,000 Mg T5/day plant. The power 

requirement per unit volume of slurry pumped decreases from 65.8 W/m3 for the 

1 Mg T5/day plant to 8.97 H/m3 for the 1,000 Mg TS/day plant. Because of the 

low viscosity of the fermentor liquor and use of gravity flow in the large 

plant, the power required to pump the effluent ranged from 3.55 to 0 kW for 

plants ranging from 1 to 1,000 TS/day. The total energy required to pump 

the influent and effluent increased from 0.0345 GJ/day for the 1 Mg TS/day 

plant to 3.44 GJ/day for the 1,000 TS/day plant. 

Table 4.3 shows that if the pumping time for the influent slurry and the 
TABLE 4.2. POWER AND ENERGY REQUIREMENTS FOR PU~1PING EFFLUENT AND PROCESS SLURRIES a 

PLANT SIZE (Mg TS/day) 

PARAMETER 1 10 100 1000 

Volume of Slurry to be Pumped 1.064 10.64 106.6 1064 

per 1·lou r (m3 /hr) 

Pipe Diameter 

(m) 0.0191 0.0381 0.1016 0.2286 

Generalized Reynolds Number for 495 2740 2783 4234 

Influent Pumping w 

Number of Pumps 1 1 2 4 '" 

b Influent Power (kW) 0.70 4.31 12.90 95.4 

Power/Volume (W/m3) 65.8 40.5 12.12 8.97 

Effluent Power {kW)b 0.26 3.55 1.61 0 

Power/Volume (VJ/m 3 ) 24.2 33.4 1. 513 0 

Total Ener9Y Required (GJ / day) 0.0345 0.283 0.524 3.44 

a10 hours pumping. Influent assumed: 10% TS, K = 0.61 Pa's n, n = 0.54; Effluent assumed: 5% TS, 

K = 0.33 Pa's n, n = 0.50. Effective length 300 m including the effective length due to sucti on. 

expansion, contraction of flow. 

b Pump efficiency = 50% assumed. 
TABLE 4.3. POWER AND ENERGY REQUIREMENTS FOR PUMPING EFFLUENT AND PROCESS SLURRIES a 

PLANT SIZE (~1g TS/day) 

PARAf'lIETER 1 10 100 1000 

Volume of Slu3ry to be Pumped 3.55 35.5 355 3550 

per Hour (m /hr) 

Pipe Diameter 

(m) 0.0254 0.0635 0.1778 0.330 

Generalized Reynolds Number for 1446 4711 4260 4084 

Influent Pumping 

Number of Pumps 1 1 2 4 w 

co 

Influent b Power (kW) 2.10 14.21 19.21 33.0 

Power/Volume (W/m3) 197.4 133.6 18.05 3.10 

Effl uent b Power (kW) 1.20 8.92 0 0 

Power/Volume (H/m3) 11. 28 83.8 0 0 

Total Ener9Y Required (GJ I day) 0.0358 0.250 0.415 2.854 

a3 hours pumping. Influent assumed: 10% TS, K = 0.61 Pa's n, n = 0.54; Effluent assumed: 5% TS, 

K = 0.33 Pa's n, n = 0.50. Effective length 300 mincluding the effective length due to suction, 

expansion, contraction of flow. 

b Pump efficiency = 50% assumed. 
4.2.3 Mixing Power Requirement 

The pilot-scale fermentor liquor (at about 5% TS) and the influent slurry (at 

about 12% TS) were agitated by mixers equipped with dual, 3-blade marine 

propell ers. Adequate agitati on was achi eved at rotati onal speeds of 140 rpm 

for the fermentor liquor and 316 rpm for the influent slurry. 

The net power consumption was estimated from the plots of power number (N p) and Reynolds number (NRe) for mixing beef cattle manure (Chen and Hashimoto, 

1979). The net power consumption for mixing the fermentor liquor was 86.7 W 

for one propeller and 156.2 W for dual propellers, using a factor of 1.8 for 

dual propellers (Bates et a1., 1966). This gives a net power consumptiDn per 

volume of 28.8 W/m3. 

The net power consumpti on for mi xi ng the i nfl uent sl was esti mated usi ng 

the same procedure, and was calculated to be 152 W/m for single propeller and 

213 W/m3 for dual propellers. A factor of 1.4 for dual propellers is used 

because the separation of these two propellers is only one propeller diameter 

(Bates et al., 1966). 

To maintain the same quality of mixing in large scale fermentation systems, 

the power consumption per unit volume should be preserved (Johnstone and 

Thri ng, 1957). 

Table 4.4 shows the pov,er and energy requirement for mixing fermentor liquor 

and i nf1 uent sl urry for different pl ant si zes. I;Jith conti nuous mi xi ng, the 

fermentor mixing energy requirement increased from 0.222 to 222.0 GJ/day for 

plant sizes ranging from 1 to 1,000 Mg TS/day. For mixing the influent 

slurry, the power and energy requirement are 48% higher than those for the 

fermentor liquor. 

4.3 DISCUSSION 

4.3.1 Comparing Energy Requirements 

Table 4.5 summarizes the energy requirements for systems fermenting beef 

cattle manure operating at 55°C,S days HRT, and 80 g VS/L influent 

concentration. The energy requirements for C02 scrubbing and CH4 compression are also listed in Table 4.5. Ashare et al. (1978) concluded that the water 

scrubbing of C02 is the simplest and cheapest way to clean the biogas.The 

power requ i red was es ti mated to be 5.88 vJ /m3 / day of the bi ogas flow rate. The 

net power required to compress the methane gas from 101.3 kPa (1 atmosphere) 

to 861 kPa (8.5 atmosphere) was used. Assuming an ideal gas and adiabatic 

process, the total power required to compress the CH4 is 4.94 vl/m3/day (Perry 

and Chilton, 1973) with a compressor efficiency of 70%. 

Table 4.5 shows that the heating required to maintain the fermentor at 55°C 
TABLE 4.4. POWER AND ENERGY REQUIREMENTS FOR PROPELLER MIXING OF FERMENTOR LIQUOR a AND PROCESS SLURRyb 

PLANT SIZE (~1g TS/day) 

PARAMETER 1 10 100 1000 

Fermentor Liquor 

Vo 1 ume (m3) 53.2 532 5320 53200 

Power Required (kW)c d 2.567 25.67 256.7 2567 

Energy Required (GJ/day) 0.222 2.220 22.20 222.0 

Influent Sl urry ~ 

0 

Vo 1 ume (m3) 10.64 106.4 1064 10640 

Power Required (kW)c d 3.80 38.0 380 3800 

Energy Required (GJ/day) 0.329 3.29 32.9 329 

Total Energy Required {GJ/day)d 0.551 5.51 55.1 551 

aFermentor Liquor: 5% TS, K = 0.33 Pa·s n and n = 0.5. 

bInfluent Slurry: 10% TS, K = 0.61 P a . 5 n, n = 0.54. 

CMotor Efficiency 80%. 

d24hours mixing. 
TABLE 4.5. SUMMARY OF ENERGY PRODUCTION AND REQUIREMENT FOR ANAEROBIC 

SYSTEMS FERMENTING BEEF CATTLE MANURE AT 55°Ca 

PLANT SIZE (r~g TS / day) 

PARM1ETER 1 10 100 

Gross Methane Energy Production 7.85 78.5 785 

(GJ /day) 

Heating Energy Requiredb (GJ/day) 3.12 29.79 293.0 

Heating Energy Requiredb w/50% 1. 757 16.15 156.5 

Effluent Heat Recovery (GJ/day) 

Pumping Energy RequiredC (GJ/day) 0.0345 0.283 0.524 

Mi xi ng Energy Requiredd (GJ / day) 0.551 5.51 55.1 

C02 Scrubbing (GJ / day) 0.2142 2.142 21.42 

CH4 Compression (GJ/day) 0.0900 0.900 9.00 

aInfluent concentration 80 9 VS/L, HRT = 5 days, Yv = 3.96 013 CH4/m3·fermentor·day. 

bAmbient and process slurry temperature, 10°C. 

c10 hours of pumping, 300 01 effective length. 

d24 hours of mixing. 

1000 

7850 

2907 

1543 

3.44 

551 

205 

90.0 
The next major energy consumption is mlxlng. It amounts to 7.3% of the total 

CH4 energy production. Our laboratory and pilot studies showed that the CH4 

production did not vary with the duration of daily mixing of the fermentor 

liquor, indicating that the minimum mixing requirement for fermentation 

systems may be based on the slurry and effluent handling aspects. The energy 

consumption of mixing can be cut at· least one half by reducing the mixing 

time. 

The least energy is consumed in pumping. Pumping energy depends less on the 

plant size because larger pipes can be used for handling larger volumes of the 

slurry. Energy consumed per volume pumped decreases as pipe size increases. 

Three hours pumping has higher Reynolds number but requires larger pumps and 

pipes than 10 hours pumping and therefore involves higher capital cost (Tables 

4.2 and 4.3). 

The total energy consumption, including C02 scrubbing and CH4 compression, but 

excluding heating energy, accounts for 11.3% of the gross CH4 energy production for the 1 Mg TS/day plant and 10.8% for the 1,000 Mg TS/day plant. 

4.3.2 Effect of Influent Concentration on Net Thermal Energy Production 

Equation 2.1 and Figures 2.2 and 2.3 were used to calculate the gross CH4 

production from which the heating requirement was subtracted to determine the 

net thermal energy production. In calculating the CH4 production at 55°C, m 

of 0.586 day-1 and K = 0.6, 0.65, 0.8, and 1.3 for So = 60, 70, 80, and 100 g 

VS/L, respectively, were used. Figure 4.1 shows that at long HRT, higher 

influent concentration will produce more net thermal energy for the same plant 

size. However, at HRT less than 12 days, the net thermal energy production 

increases with So only if So is less than 80 g VS/L. As So increases to 100 g 

VS/L, the net thermal energy production has a decreases sharply. 

4.3.3 Net Thermal Energy Production of tvlesophilic and Thermophilic Systems 

Figure 4.2 compares the net thermal energy production from systems fermenting 

beef cattle manure at mesophilic (35°C) and thermophilic (55°C) temperatures 

with an influent concentration of 80 g VS/L. At 35°C and So = 80 g VS/L, = 

0.326 day-1 and K = 1.7 were used. 

Figure 4.2 shows that, at long HRT, mesophilic systems may produce more net 

thermal energy than thermophil ic systems, but at short HRT, thermophil ic 

systems wi 11 produce more. The advantage of thermophil i cover mesophil i c 

systems will increase if the effluent heat is recovered for influent slurry 

heating. 

4. 4 

This section discussed the energy requirements for anaerobic fermentation 
......... ~ 

0 90 

-0 

"'-

-::> 

<..9 

'--'" 

".. 75 - z 

0 

l0 

~ 60 - 0 

0 

0::: 

0..-

r 45 - (9 

n:: 

w 

Z 

W 

30 

-.J 

<I: 

~ 

0::: 

W 

I 15 

JrW 

Z 0 

0 

Figure 4.1. 

So = 100 9 V8/L 

:= 

80 =70 g VS/L 

SO= 60 9 VS/L 

5 10 15 20 25 

HYDRAULIC RETENTION TIME, (days) 

Comparing net thermal energy production from thermophilic anaerobic fermentation systems for 

different influent VS concentration (fermentation temperature 55°C) plant size 10 Mg TS/day, ambient temperature 10°C, and 80 = 0.35 L CH4/g VS). 

.j::>. 

w 
-- 100 ~ 

a 

"'0 

:::s 

(9 

.......... 

.... 80 - z 

0 

tO 

::J 

0 

0 60 0:: 

t'1-

>- <..9 

0:: 

W 40 Z 

LLI 

~ 

<t 

~ 

et: 20 

lLJ 

I 

r1-

w a z 0 

Figure 4.2. 

5 10 15 20 25 

HYDRAULIC RETENTION TIME, (days) 

Comparing net thermal energy production from mesophilic !35°C) and thermophilic (55°C) anaerobic 

systems lplant size 10 Mg TS/day, ambient temperature 10 C, So = 80 g VS/L, and 90 = 0.35 L CH4/9 

VS. A: 35°C without effluent heat recovery, B: 35°C with 50% heat recovery, C: 55°C without 

effluent heat recovery, D: 55°C with 50% heat effluent heat recovery). 

~ 

..J::> 
and fermentor liquor. Mixing amounted to 7.3% of the gross methane energy 

production, assuming continuous mixing. The mixing energy can be reduced 

greatly if the mixing time is reduced. 

The least energy was consumed in pumping. Pumping energy did not increase 

when the pumping time was shortened from 10 to 3 hours. Three hours of 

pumping has a higher Reynolds number but requires a larger pump and bigger pipes. 

The total energy consumption excluding thermal energy consumption accounts 

10.8 to 11.3% of the gross thermal energy production. 

Using the kinetic constants given for different influent concentration and 

fermentation temperature, it was found that for HRT less than 12 days, the net 

thermal energy production increased with the influent concentration up to 80 g 

VS/L and began to drop at influent concentration greater than 80 g VS/L. 

Also, a longer HRT will produce more net thermal energy at the same influent 

concentration. 

The net thermal energy production for 35° and 55°C were also compared for an 

influent concentration of 80 g VS/L. This comparison showed that a thermophilic (55°C) system will produce more thermal energy than a mesophilic 

(35°) system unless the fermenter is operated at a very long HRT. 
It is apparent from this report and reports published elsewhere that producing 

methane (CH4) from livestock manures is technically, and sometimes economically, feasible. The maximum amount of CH4 per unit weight of substrate is 

obtained at long hydraulic retention times (HRT); however, long HRT require 

very large fermentor volumes and high capital costs. This section presents 

our approach to optimizing fermentor designs, based on maximizing the net 

energy production per unit fermentor cost. 

5.2 OPTIMIZED DESIGNS 

5.2.1 Capital Cost 

Figure 5.1 shows the capital cost for various anaerobic fermentation systems 

plotted against the fermentor volume (Ashare et al., 1977; Burford et al., 

1977; Coppinger et al., 1979; Fischer 'et al., 1978; Hashimoto and Chen, 1979; 

and Hayes et al., 1979). The capital cost included all equipment and facil,ity 

costs for the fermentation system (including installation labor), except costs 

for effluent treatment or storage (e.g., centrifugation, filtration, 

lagooning) and biogas handling or use (e.g., C02 scrubbing and electrical generation). 

Several important relationships should be noted from Figure 5.1. For fermentors larger than 100 m3, there are two apparent cost-volume relationships 

(high and low capital costs), and both relationships show that capital cost 

increases with volume to the 0.7 power. Also, the high capital cost systems 

cost three times more than the low capital cost systems, and the capital costs 

for the plug-flow systems, reported by Hayes et al. (1979), resembles that for 

the same si ze conventi onal fermentor. The hi gh capi tal cost systems represent 

"turn-keyll systems that are desi gned, constructed and started-up by pri vate 

contracting firms. The low capital cost systems represent farmer-contracted 

systems with partial construction labor provided by farm personnel. 

5.2.2 Energy Production Per Unit Cost 

The method we selected to optimize the design of anaerobic fermentation 

systems is to maximize the net thermal energy production per unit of capital 

cost. vie cal cul ated the gross energy producti on by usi ng the ki neti c equati on and parameters presented in Section 2.0. The net thermal energy production 

was calculated by subtracting the heating requirements of the system from the 

gross energy production as described in Section 3.0. 

Si nce the cost of the fermentation system is rel ated to the fermentor vol ume 

,to the 0.7 power (Figure 5.1), the net thermal energy production per unit of 

relative capital cost (NEPC) was calculated as follows: 
-W-10 6 

... l-

(/) 

0 

U 

-1 

~ -J:::>o 

'-J 

0.. 

<t 105 

() 

104~·~~~~~~--~--~~~~--~~~~~--~~~~~~--~~~~~ 

10 10 2 103 104 105 106 

FERMENTOR VOLUME m3 I t 

Fi gure 5.1. Effect of Fermentor Vol ume on Capital Cost (0, Ashare et a 1.. 1977; ., Burford et a 1.. 1977; 

0, Coppinger et al., 1979; ", Fischer et al., 1978;!J., Hashimoto et al., 1979; and 0, Hayes 

et a 1 ., 1979). 
are 10

C and that 50% of the effluent heat is recovered. Figure 5.2 shows that 

the design conditions are optimum at 55°C, with HRT between 4 and 5 days and 

influent concentrations between 80 and 100 g VS/l. Under these conditions, 

the thermophilic system had about twice the NEPC of the mesophilic systems. 

5. 3 

5.3.1 System Design 

Using the optimum design conditions determined in the preceeding subsection, 

Y./e made an economi c assessment to determi ne the economic feas i bi 1 i ty of us; ng 

anaerobic fermentation systems in beef cattle enterprises. Beef cattle enterprises were selected because more information is available on the kinetic 

parameters of cattle manure fermentation systems than other livestock manures 

(Section 2.0), and because we have experience in operating a pilot-scale (5 m3 ) 

thermophilic, anaerobic fermentor close to these optimum conditions 

(Section 3.0). Based on the discussion in Section 3.0, we used the following 

kinetic parameters: Pm = 0.586 day-1 at 55°C and K = 1.0 at an influent concentration of 90 9 VS/l. These kinetic parameters yield a CH4 production rate 

of 4.15 l CH4/l fermentor'day assuming a 80 of 0.35 l CH4/9 VS. This CH4 pro- duction rate is achievable since we have obtained a rate of 4.7 l CH4/l 

fermentor'day in our pilot-scale fermentor. We assumed a CH4 concentration of 

55% in the biogas. 

In the proposed fermentation system, manure from a confinement feedlot is 

scraped into a mi xi ng tank where water is added to produce a sl urry of 90 g 

VS/l (assuming VS = 85% of TS). The mixing tank is equipped with a mechanical 

mixer, degritting mechanism, qnd piping to heat the slurry to the desired temperature. The slurry is then pumped to the fermentor, which is mixed for 12 

hr/day. The effluent is pumped through the piping in the mixing tank to 

recover about 50% of the heat. The effluent is then incorporated with other 

ration ingredients and fed back to the cattle. Supplemental heating of the 

i nfl uent is provi ded by a hot y./ater heat-exchanger. Operati on of the enti re 

system is controlled by a microprocessor-controller. 

We evaluated several options for biogas handling (with and without C02 removal) 

and use (heat or electricity) in this assessment, as follows: 

Option Energy Use CO2 Removed 

A On-site Heating No 

B Sale as Natural Gas Yes 

C El ectri city No 

0 El ectri ci ty Yes 
l'f) 

E 

'-. 

J 120 (9 

.... 1-

U) 55 Q C 

0 90 g VS/L 0 100 -

lZ 

~ 

0:: 

80 

liJ 

0-

Z 

0 60 - 60 g VSI -

~-

0 35°C :) 80 g VS/L 0 -0 40 Ct: 

0.. 

>- (9 

G:: 20 w 

Z 

W 

IW 0 

Z 0 2 4 6 8 10 

HYDRAULIC RETENTION TIME, days 

Figure 5.2. Effect of Hydraulic Retention Time, Temperature and Influent Concentration on the Net Energy 

Production Per Unit Cost. 

..p. 

1.0 
p

p

p

1 ate the vol ume and number of fermentors and energy requi rements are presented 

in Section 4.0. 

Since the efficiency of an internal combustion engine to convert CH4 into useful work increases as the engine size increases, the engine-generator efficiency 'v-/as estimated by the following equation (assuming a 95% efficient 

generator and engine efficiencies published by Evans et al., 1973): 

Engine-generator efficiency (%) = 4.18 1n (E) + 11.61 (5.2) 

where E is the gross energy input to the engine (GJ/day) and the maximum efficiency is 38%. Equation 5.2 only applicable for engines fueled with 100% 

CH4; therefore, Equation 5.2 is applicable only for Option D. The enginegenerator efficiencies for Option C were assumed to be 60% of that calculated 

from Equation 5.2, since the useful work output per unit energy input of a 

high compression engine, receiving gas containing 55% CH4, is 60% of an engine 

receiving 100% CH4 (Neyeloff and Gunkel, 1975). 

The net CH4 production, shown in Table 5.1, was calculated by subtracting the 

net heating requirement from the gross energy production. The net electrical 

production was calculated by subtracting the electrical energy requirements 

from the electrical energy produced by the engine-generator. Option 0 produced more net electrical energy than Option C because the higher enginegenerator efficiency of Option 0 was sufficient to offset the increased energy for C02 removal. 

We assumed that the waste heat from the engine would be used to heat the 

fermentor. This assumption is justified since the net heating requirement is 

only about 20% of the total energy production, and between 20 to 30% of the 

gross energy consumed by the engine can be recovered from the jacket cooling 

system. Since an additional 26 to 30% of the heat can be recovered from the 

engine exhaust, Options C and 0 can be a source of low temperature (75 to 

85°C) process It/ater, as well as electricity. We did not assume any use of the 

excess waste heat from the engine generator in our energy balance, nor did we 

assess any credit for the excess heat generated. 

5.3.2 Capital Cost 

Table 5.2 shows the installed equipment costs for major components of a 1860 

m3 anaerobi c fermentati on system, usi ng the vari ous bi ogas handl i ng and use 

options identified above. The costs shown in Table 5.2 were used as the basis 

to estimate the total capital cost at various plant sizes. Total capital 

costs were estimated by using engineering and inspection fees, contingency, 

escalation and start-up costs of 14, 10, 18 and 10% of installed equipment 

costs, respectively. To estimate the total capital costs for different plant 

sizes, the scale-up factor of digester volume to the 0.7 power, as shown in 
TABLE 5.1. ENERGY PRODUCTION AND REQUIREMENTS a FOR VARIOUS 

PLANT SIZES AND ENERGY USE OPTIONS 

PLANT SIZE, Mg TS/day 

PARAiv1ETER 1 10 

Working volume, m3 47 472 

Gross energy producti on, MJ /day 7,300 73,000 

Energy requirements, MJ/day 

Net heating 1,550 14,100 

Mixing 143 1;430 

Pumping 21 129 

Gas compression 152 1,520 

Scrubbing pump 111 1,110 

Electrical generator efficiency, % 

Option C 12 18 

Option D 20 30 

Net CH4 productionb, MJ/day 

Options A & B 5,750 58,900 

Net el ectri ca 1 producti an b, / day 

Option C 574 10,100 

Option D 1,030 17,400 

100 

4,720 

730,000 

136,000 

14,300 

635 

15,200 

11 , 100 

24 

38 

594,000 

145,000 

236,000 

aAssumes 50% effluent heat recovery, 12 hr/day mixing of influent and fermentor, 

10 hr/day pumping of influent and effluent, and ambient and influent temperature of 10°C. 

bGross production minus requirement (thermal or electrical energy). 
TABLE 5.2. INSTALLED EOUIPfY1ENT COSTS FOR COMPONENTS 

OF A 1860 m3 ANAEROBIC FERMENTOR 

COST (i n $1000 ) 

A B C 

Premix & degrit 50 50 50 

Pump 30 30 30 

Fermentor w/mixer 250 250 250 

Heat exchanger 20 20 20 Piping 10 10 10 

Microprocessor-controller 20 20 20 

Gas cleaner 50 50 50 

CO2 scrubber 200 

Compressors & storage tanks 100 50 100 

Boiler 30 30 

Engine-generator w/heat exchangers 100 

TOTAL INSTALLED EQUIPMENT COST 560 710 630 

D 

50 

30 

250 

20 

10 

20 

50 

200 

50 

100 

780 
PLANT SIZE, Mg TS/day 

PARM1ETER 1 10 100 

Capital costs, $1000 

Option A 65 327 1,640 

Option B 83 417 2,090 

Option C 73 365 1,830 

Option D 91 454 2,270 

Labor costs, $1000/yr 11 22 43 

Fixed costs, $1000/yr 

Opti on A 16 79 394 

Option B 20 100 501 

Option C 17 87 439 Option D 22 109 546 

Uti 1 ity costs, $1000/yr 

Option A 1.7 17 164 

Option B 2.2 22 220 

Option C 0.1 1 11 Option D 0.1 1 11 

Total annual costs, $1000/yr 

Option A 29 117 600 Option Ala 10 48 306 

Option B 34 144 764 

Option Bla 12 62 398 

Option C 29 111 492 

Option Cia 9 36 168 Option D 33 132 600 Option D'a 10 43 204 

aLow cost option assumes labor and fixed costs to be 25% and 33%, respectively, 

of high cost option. 
Mg TS/day plant. 

Fixed costs were calculated assuming an interest rate of 14% and a 20-year 

straight-line depreciation of the total capital cost. Taxes, insurance, and 

repair and maintenance were estimated to be 3, 1.5 and 3% of the installed 

equipment cost, respectively. 

Utility costs were calculated based upon the energy requirements in excess of 

that produced. Utility rates were assumed to be $14/GJ (5\1/kv/h) for electricity and $0.11/m3 for make-up water. The utility costs shown for Options A 

and 8 reflect electricity and water charges. The only utility cost charged to 

Opt; cins C and 0 was for make-up water, si nee the engi ne-generator produced 

more el ectri city and waste heat than needed by the fermentati on system. 

Table 5.3 also shows the total annual costs for the low cost, farmercontracted and operated systems. The capital costs for these systems were 

assumed to be one-third the cost of a comparably sized, "turn-key" plant 

(Figure 5.1). The labor costs were assumed to be one-quarter of the high cost 

system. This low level of labor can be justified because of the use of 

microprocessor-controllers to operate and monitor much of the routine 

operation. 

5.3.4 Energy Production Costs 

Energy production costs were calculated by dividing the total annual cost for 

each opti on by the annual net energy (CH4 or el ectri city) produced by each 

option. The effect of plant size on CH4 production costs for the high cost 

systems (Options A and 8) and the low-cost systems (Options AI and 

81 ) are 

shown in Figure 5.3. The plant size at which CH4 production costs equal the 

current natural gas prices of $3/GJ would be 75, greater than 300, 4.2 and 6.7 

Mg TS/day for Options A, 8, AI and 

81 , respectively. Thus, although there is 

only about a three-fold difference in total annual cost between Option A and 

AI, there is about an 18-fold difference in break-even plant size. 

Fi gure 5.4 shows the effect of plant si ze on el ectri ci ty producti on costs. 

The plant sizes at which the electricity production costs equal the current 

electricity rate of $14/GJ (5\1/kWh) would be 43, 22, 5.3 and 2.8 Mg TS/day for 

Options C, 0, 

CI and 

0 1 , respectively. These results show that there is an 

eight-fold difference in break-even plant size between the low-cost and highcost systems, and that the increased electricity generation efficiency, caused 

by scrubbing C02 from the biogas (Options 0 and 

0 1 ), more than compensates for 

the increased total annual costs. 

Table 5.4 lists the energy production costs for the various options at different plant sizes (1, 10 and 100 Mg TS/day) and an effluent feed credit of 

S60/Mg effluent TS. The production costs with effluent feed credit were 

calculated by subtracting the feed credit from the total annual cost and by 
J 

~ -tIT 

12 

r: 

(/) 

0 

u 

z 

0 

I- 8 <-) 

::> 

a 

0 

0:: 

ll. 

LlJ B Z 

« 4 A I 

ilLl 8' ~ 

A 

20 40 60 80 100 

PLANT SIZE, Mg TS/day 

Figure 5.3. Effect of Plant Size on Methane Production Costs (Temperature = 55°C, HRT = 5 days, So = 

90 9 VS/L. A = High Cost, no C02 Removal; n = High Cost, C02 removal; A' = Low Cost, no 

C02 Removal; 8' = Low Cost, C02 Removal). 

01 

01 
140 

J 

(9 120 

"'-

4:A-

... t- 100 (I) 

0 

0 

Z 

0 80 

1-

() 

:J 

0 

0 60 . cr: 

(L 

>-

t- 40 .. 0 

cr: 

~ 

0 

w 20-

-.J 

W 

20 40 

PLANT SIZE, Mg 

J 

60 

TS/day 

80 100 

Figure 5.4. Effect of Plant Size on Electricity Production Cost (Temperature = 55°C, HRT = 5 days, So = 

90 9 VS/L. C = High Cost, no C02 Removal; 0 = High Cost, C02 Removal; C' = Low Cost, no 

C02 Removal; 01 = Low Cost, C02 Removal). 

CJ1 

0"1 
TABLE 5.4. ENERGY PRODUCTION COSTS a FOR VARIOUS PLANT SIZES, ENERGY 

PRODUCTION OPTIONS AND EFFLUENT FEED CREDITS 

PLANT SIZE, Mg TS/day 

1 10 100 

Feed Credit Feed Credit Feed Credit 

OPTION $O/Mg $60/Mg $0 $60/Mg $O/Mg $60 

A 13.71 8.01 5.46 -0.11 2.77 -2.76 

AI 4.67 -1.04 2.26 -3.32 1.41 -4.11 

B 15.88 10.23 6.67 1.14 3.49 -1.99 

BI 5.57 -0.09 2.83 -2.70 1.82 -3.66 

C 138.36 81.18 29.98 -2.46 9.31 -13,35 CI 41.87 -15.31 9.68 -22.76 3.17 -19.49 

0 88.68 56.74 20.83 1. 94 6.96 -6.94 0 1 27.19 -4.75 6.76 -12.13 2.36 -11. 54 

aCosts expressed as $/GJ. 
moderate plant sizes (3 to 6 Mg TS/day) when farmer-constructed and operated 

systems are used or when "turn-key" systems use an effl uent feed credit of 

effluent TS. Assuming that 2.8 kg TS/day can be recovered from a confined steer, the break-even plant size discussed above would serve feedlots 

between 1,000 to 2,000 cattle. If the farmer-constructed and operated systems 

also fed the fermentor effluent, then anaerobic fermentation systems would be 

economically feasible for feedlots of less than 300 cattle. 

In this assessment, we assumed that all of the energy produced would be used. 

Lipper et al. (1976) reported that the energy requirements for energy-intensive 

commercial feedlots in Kansas were 2.2 GJ/head'yr for natural gas and 0.32 

GJ/head'yr for electricity. The net energy production from a plant receiving 

manure from a 1,000-head feedlot would be about 6.2 GJ/head'yr of CH4 (Options 

A and B) or 0.9 (Option C) and 1.6 GJ/head"yr (Option D) of electricity. 

Thus, more energy would be produced by these systems than could be used by the 

livestock enterprise. Strategies must be developed to utilize this excess 

energy. Conscientious effort must be exercised to adjust energy use to producti on at the enterpri se level, and there must be the opportuni ty to sell the 

surplus energy. 

5. 4 Y 

We have presented our approach to optimizing anaerobic fermenter designs by 

selecting design criteria that maximize the net energy production per unit 

cost. Using this optimization technique, we estimate that a farmer-constructed and operated system would be economically feasible for beef feedlots between 

1,000 to 2,000 head without an effluent feed credit, and about 300 head with 

an effl uent feed credi t of eff1 uent TS. Commerci a 1 "tu rn-key" systems 

are only feasible for feedlots larger than 8,000 head when an effluent credit 

is not used, and for feedlots between 1,000 to 2,000 head when an effluent 

feed credit of $60/Mg effluent TS is used. Based on these results, we believe 

that the economics of anaerobic fermentation is sufficiently favorable for 

farm-scale application of this technology. 
Moira Wilhelm. 
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89. Zeikus, J. G. 1977. Biology of methanogenic bacteria. Bacteriol. Rev. 

41:514. 

90. Zeikus, J. G. 1979. Microbial populations in anaerobic digesters. 

First International 'Symposium on Anaerobic Digestion, University Industry 

Center, University College, September 17-21, Cardiff, Wales. 
9. Performing Organization Name and Address 

Roman L. Hruska U.S. Meat Animal Research Center 

U.S. Department of Agriculture 

Clay Center, Nebraska 

12. Sponsoring Organization Name and Address 

Solar Energy Research Institute 

1617 Cole Boulevard 

Golden, Colorado 80401 

15. Supplementary Notes 

SERI Technical Honitor: Dan Jantzen 

10. Project/Task/Work Unit No. 

3335.01 11. Contract (C) or Grant (G) No. 

(C) DB-9-8372-l 

(G) 

13. Type of Report & Period Covered 

Technical Report 

14. 

16. Abstract (Limit: 200 words) This report summarizes the research to convert livestock manure 

and crop residues into methane and a high protein feed ingredient by thermophilic 

anaerobic fermentation. The major biological and operational factors involved in 

methanogenesis were discussed, and a kinetic model that describes the fermentation 

process was presented. Substrate biodegradability, fermentation temperature, and 

influent substrate concentration were shown to have significant effects on CH4 pro- duction rate. The kinetic model predicted methane production rates of existing 

pilot and full-scale fermentation systems to within 15%. The highest methane production rate achieved by the fermenter was 4.7 L CH4/L fermenter day. This is the I highest rate reported in the literature and· about 4 times higher than other pilot 

or full-scale systems fermenting livestock manures. Assessment of the energy requirements for anaerobic fermentation systems showed that the major energy requirement for a thermophilic system \Vas for maintaining the fermenter temperature. 

The next major energy consumption was due to the mixing of the influent slurry and 

fermenter liquor. An approach to optimizing anaerobic fermenter designs by selecting design criteria that maximize the net energy production per unit cost was presented. Based on the results, we believe that the economics of anaerobic fermentation is sufficiently favorable for farm-scale demonstration of this technology. 

17. Document Analysis 

a.DescriptorsAnaerobic Conditions:Ql; Animal Foods; Biomass; Economics; Fermentation: 

Tl,Q2; Methane:T3; Recovery:Q3; Thermophilic Conditions: Agricultural Wastes; Alkanes; Cryogenic Fluids; Energy Sources; Fluids; Food; Hydrocarbons; Organic Compounds; Renewable Energy Sources; Solid 

Wastes; Hastes 

c. UC Categories 

61a 

18. Availability Statement 

National Technical Information Service 

U.S. Department of Commerce 

5285 Port Royal Road 

Sorinofiplr1 Vir9'in.<1 22161 

Form No. 8200-13 (6-79) 

19. No. of Pages 

76 

20. Price 

$6.00