methane recovery from chicken manure digestion

Methane Recovery from Chicken Manure DigestionAuthor(s): C. William Savery and Daniel C. CruzanSource: Journal (Water Pollution Control Federation), Vol. 44, No. 12 (Dec., 1972), pp. 2349-2354Published by: Water Environment FederationStable URL: http://www.jstor.org/stable/25037689 .

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Methane recovery from chicken

manure digestion

C. William Savery and Daniel C. Cruzan

The

large concentration of manure

produced by intensive livestock pro duction units provides an opportunity for

producing the valuable by-product of methane. To provide preliminary design data for a farm total energy system fueled

by methane produced by bacteria, an ex

perimental anaerobic digester was built and

daily gas production rates and composi tions were determined for loadings of fresh chicken manure.

Background

The trend to intensive livestock produc tion units and the increased impact on the local environment are evident. The history,

pollutant nature, imposed legal controls, and waste treatment and disposal alterna tives of the problem of animal wastes have been discussed recently by Loehr1 and Laak.2 Environmental problems associated with poultry production were of concern as

long as 20 yr ago, and, as reviewed by Gates,3 the Long Island duck farms were

subjected to pollution controls in 1954. Loehr 1 estimated that 50 to 80 percent

of the laying hens and most broilers pro duced in the major poultry producing regions are raised in confinement. These

egg and chicken factories have frequently created local odor and groundwater con tamination problems. Poultrymen are in

creasingly facing new restrictions on waste

disposal that inevitably lead to some form of waste treatment. At the same time, however, the large concentration of manure can be exploited to produce methane by the anaerobic digestion process. The me thane produced can be used in a farm total

energy system for heating and production of electricity. Thus, the saving in farm

operating costs for fuel and electricity can

be balanced against the increased capital investment for the anaerobic processing and equipment for the total energy sys tem. The incorporation of an anaerobic

digestion unit to process animal wastes and to produce methane becomes even

more attractive when pollution controls are required.

Of the nine waste treatment systems for enclosed animals described by Loehr,1 three could be integrated with an anaero bic digestion unit. In the system, which consists of water flushing, an anaerobic unit followed by an aerobic unit, and then land

disposal, the anaerobic unit is already a

component, although the design would be different. The other two systems, drying and incineration, both require heat energy,

which is a significant operational cost fac tor. The methane produced by anaerobic

digestion could provide fuel for either a

drying or incineration system. In these variations of the drying and incineration

systems, the drying or incineration system components would be preceded by the anaerobic unit in the process.

It is interesting to consider the energy obtainable if all of the animal wastes in the U. S. were converted to methane by anaerobic digestion. By using Laak's2 1967 estimate of total wet manure pro duced per day from cattle, hogs, and chick ens of 8.4 bil lb (3.8 bil kg), the measured

gas production rate of about 2 cu ft/lb (125 I/kg) of wet manure reacted and a

heating value of 600 btu/cu ft (5.34 kg cal/1), an energy equivalent of about 50,000

BTu/day/cap (12,600 kg-cal/day/cap ) is calculated. This figure is 8 percent of the total energy used in the U. S. in I9604

?Vol. 44, No. 12, December 1972 2349



Savehy and Chuzan

or equivalent to 25 percent of the natural

gas consumed.4 The potential energy source from the anaerobic digestion of animal wastes is enormous, and it will

certainly be closely scrutinized as the

world's petroleum resources are consumed in the next century.5

Experimental Method

The experimental digester was located on the junior author's farm in Bridgeton, N. J., near a neighboring chicken ranch that provided the supply of fresh manure.

The large capacity of the digester, 35 1, and its location in a farm building render the experiment a field test.

The cylindrical digestion chamber is

constructed of steel with a removable sealed lid and is of 35-1 capacity. The di

gester is contained in a thermally insulated,

electrically heated water bath constructed of a modified hot water heater. The gases evolved from the digester were passed continuously through a 2.8-1/hr wet test

meter so that the daily history of gas pro duction could be measured.

Daily gas samples were taken in 10-ml

syringes and were subsequently analyzed in the Combustion Kinetics Laboratory at

Drexel University, Philadelphia, Pa. Gas

analysis was performed on a gas Chromato

graph equipped with a thermal conductiv

ity detector. The gas Chromatograph used a parallel 100-cm X 3.2-mm diam silica gel and 122-cm X 3.2-mm diam molecular sieve column arrangement. The columns were

maintained at 32 ?C, and the helium carrier

gas flow rate was 0.75 cu cm/min. The

gas samples were injected into the liquid sample ports, and the partial pressures of carbon dioxide and methane were deter

mined by comparison of peak areas with those from a calibration mixture. Other

components in the sample were neglected. Five separate experimental runs were

made. In Run 1, 2.8 kg of fresh chicken

manure, initially at 14 ?C, was placed in the

digester. No seed material was added. The water bath heater was then started and the controller set for 51 ?C. Run I

was operated as a batch process for 9 days. Daily temperature, total gas flow, and gas

2350 Journal WPCF

samples were taken. The digester was not

stirred during the duration of the run.

Run 2 was similar to Run 1, except that the water bath was initially at the new

setpoint of 29?C and the loading was 3.1

kg. This batch run also was not stirred. It was intentionally stopped after 8 days be fore digestion was complete.

The other three runs were attempts to establish operation of the digester as a

continuous-flow reactor. Runs 3, 4, and 5 were maintained at 51 ?C. In each run the fresh loading of manure was operated as a batch for 3 days. Then, in Run 3, approxi

mately 15 percent by volume of the di

gester contents was removed and replaced daily with fresh manure. In Run 4, 20

percent by volume and in Run 5, 25 per cent by volume were fed daily. These feed rates correspond to hydraulic retention times of 4, 5, and 6.7 days. The lid was

removed for feeding and the digester con tents were hand-stirred before removal and

again after feeding. The meter reading and gas samples were taken before the

feeding operation. The feeding process was continued on a daily basis for several

days. In any run the water bath temperature

varied less than 5?C and the digester con

tents varied as much as 2?C. It would have been desirable to have measured pH, alkalinity, ammonia, total nitrogen, total volatile acids, and weight and chemical

oxygen demand (cod) of suspended solids

(ss) periodically as done by other investi

gators in their comprehensive laboratory studies.6'7 However, in this field test only the daily total gas production and com

position were measured.

Results

The total gas production histories of Runs 1 and 2 are shown in Figure 1. Run 1 was a batch process maintained in the

thermophilic bacteria range at 51 ?C, and Run 2 was a batch process maintained in the mesophilic range at 29?C. The gas production history during start-up is similar for the two runs, except that the 29?C run

lags the 51 ?C run by about 12 hr.



Methane Recovery

"4 Y TOTAL

TOTAL GAS

qioo

H80 a*

z o

60 o <

?J

40 JE tu

20 '

ORUN I., 5l?C,2.8Kg LOADING

oRUN2.,29?C,3.l Kg LOADING

2 3 4 5 6 7

TIME SINCE STARTUP, DAYS

8 9

FIGURE 1.?Total gas production and daily gas sample com

position histories for batch operation at 51? and 29?C.

Run 1 shows a distinct decrease in the rate of gas production during Day 3. There is a corresponding dip in the daily methane

fraction during Day 3 of Run 1. This same

start-up phenomenon is shown in Figure 2

where the summary of data for the at

tempted continuous-flow digester operation at 51 ?C for various hydraulic retention times is shown. In Runs 3, 4, and 5, shown in Figure 2, the start-up conditions were

the same as in Run 1 because the digesters were not fed until after the data for Day 3 were recorded. Run 2 (Figure 1), which

was the only one maintained in the meso

philic range, showed no temporary de crease in the rate of gas production during its history. With the exception of the temporary de

crease in the methane fraction noted, the methane fraction steadily increased during the history of the two batch runs shown in

Figure 1. The samples obtained at the

end of the histories were almost totally methane.

In Runs 3, 4, and 5, the digester was fed with fresh manure after the data were re

corded for Day 3. The daily feed rates were 15, 20, and 25 percent, respectively, of the digester volume for Runs 3, 4, and 5. The digester became upset in each of these runs, as can be seen by the decreased total gas production rate during Day 4 and the severe drop in methane fraction from 85 to 25 percent by the day following the initiation of feeding. There is very little difference among the data shown on

Figure 2 for the different feed rates. The average gas composition was 69 per

cent methane and 31 percent carbon di

oxide, and the methane production rate was 89 1/kg of wet manure reacted for Run 1. Run 2 produced 50 percent methane and 50 percent carbon dioxide, and the

methane production rate was 46 1/kg of

?Vol. 44, No. 12, December 1972 2351



S a very and Cruzan

5000

(0 4000

3 3000|

o > L?

?g 2000! o

< O H 1000

Cr^ FRACT.

TOTAL GAS

o RUN 3f H YD. RET TIME 6.7 DAYS a RUN 4, HYD. RET. TIME 50 DAYS Q RMN 5, HYP. RET. TJME 4j0DAYS

100

80 ^o

z o

60S OC Li_

L? Z < X

40

20

< o

I 8 2 3 4 5 6 7 TIME SINCE STARTUP, DAYS

FIGURE 2.?Total gas production and daily gas sample com

position histories for attempted continuous-flow operation at

51?C

wet manure reacted. Because Run 2 was

deliberately stopped after 8 days and com

plete digestion typically takes approxi mately 20 days at this temperature, the

methane production rate for complete di

gestion would be much higher than that in

dicated by this result.

Discussion

The total gas yield of the batch run in

the thermophilic range of 51 ?C was 130

1/kg of wet manure reacted. If Laak's 2

figures of 0.07 lb total solids (Ts)/day (0.032 kg Ts/day), volatile solids (vs) 77

percent of ts, and 0.24 lb/day (0.11 kg/ day) wet manure for a 5-lb (2.3-kg) laying hen are used, vs are computed to constitute 22.4 percent of the wet manure weight.

With this computed fraction, the total gas

yield becomes 8.9 cu ft/lb vs (560 1/kg vs).

2352 Journal WPCF

This compares favorably with the best gas

yield of 5.14 cu ft/lb vs (320 1/kg vs) ob tained by Pohland and Bloodgood6 in a

series of continuous-flow wastewater sludge digestion experiments at 126?F (52?C). The methane fraction in the gas was 69

percent in this investigation and 65.5 per cent in that of Pohland and Bloodgood.6

The efficiency of waste stabilization can

be estimated as follows. Laak2 gives fig ures of 0.29 mg BOD/mg vs and 1.1 mg

coD/mg vs for an average 5 lb (2.3 kg) chicken. By using these manure char acteristics and the methane yield from the batch run at 51 ?C, an actual waste sta bilization of 4.39 cu ft of methane/lb total oxygen demand (tod) (27.4 1/kg tod) is determined. This is 78 percent of the 5.62 cu ft/lb tod stabilized (35.1 1/kg tod) theoretical prediction given by Mc

Carty.8



Methane Recovery

In Runs 3, 4, and 5, where it was at

tempted to establish a continuous-flow di

gester mode of operation, the digester be came upset, and retarded operation fol lowed. The indicators were decreased total gas production and an increasing per

centage of carbon dioxide in the gas. The

additional indicators of volatile acid con

centration and pH recommended by Mc

Carty 8 were not monitored. Furthermore,

no attempts were made to control the di

gester when it became upset. Pohland and

Bloodgood6 noted that the normal diges tion of wastewater sludge that they ob served in their mesophilic digestion stud ies was not obtained in their studies at

126?F (52?C). The results of this in

vestigation with continuously fed chicken manure at 51 ?C confirm their observations of retarded digestion in the thermophilic range.

A preliminary design analysis of a total

energy system for a 60,000-chicken poultry operation was performed by a group of

engineering students.9 Their principal re

sults were that the methane yield measured in this investigation was sufficient for sup

plying the manure digestion process heat

ing and farm electrical power requirements and that the estimated capital costs of the anaerobic digester and total energy system

were six times the current annual farm electrical power costs.

Now that the feasibility of a total energy system for a poultry operation has been

established by this student group design project,9 the following plan for implemen tation of the study results is outlined. The incentive for development of methane pro

duction as a poultry by-product will most

certainly be great when poultry emissions, odor, and wastewater are subjected to con

trols. It is recommended that preliminary designs of poultry production facilities in

corporating alternate types of pollution controls x and total energy systems fueled

by anaerobic digestion of chicken manure

be performed. A comparison of these de

signs with respect to estimated process re

quirements, capital costs, and operating costs will indicate the most promising ar

rangement. After one design has been

selected as most promising, a full-scale pro cess should be designed in detail and built.

Only by actual construction and operation can operational problems and requirements be determined. In addition, actual con

struction and operating costs can be ob tained. Thus, the practicality of the system can be demonstrated.

Conclusions

Fresh chicken manure was digested in an

experimental 35-1 capacity anaerobic di

gester. Batch reactor operation in the

thermophilic bacteria range at 51 ?C pro duced 130 1 of gas (69 percent methane)/ kg of wet manure reacted. Attempts to

operate the anaerobic digester at 51? C in a

continuous-flow, well-stirred mode with

hydraulic retention times of 4, 5, and 6.7

days resulted in retarded digester opera tion. It was estimated that 78 percent of the tod was stabilized by this process.

Anaerobic processing in conjunction with aerobic digestion, drying, or incineration offers promise of economic waste treat

ment of chicken manure, particularly if in

corporated with a farm total energy sys tem fueled with the recovered methane.

Acknowledgments

C. William Savery is assistant professor, Thermal and Fluid Sciences, Drexel Uni

versity, Philadelphia, Pa., and Daniel C. Cruzan is associated with Cruzandale

Farms, Bridgeton, N. J. Daniel C. Cruzan was a senior mechanical engineering stu

dent, Drexel University, at the time of the

preparation of this paper.

References

1. Loehr, R. C, "Alternatives for the Treatment

and Disposal of Animal Wastes." Jour. Water Poll. Control Fed., 43, 668 (1971).

2. Laak, R., "Cattle, Swine and Chicken Manure

Challenges Waste Disposal Methods." Water

? Sew. Works, 117, 134 (1970). 3. Gates, C. D., "Treatment of Long Island Duck

Farm Wastes." Jour. Water Poll Control

Fed., 35, 1569 (1963). 4. Landsburg, H. H., and Schurr, S. H., "Energy

in the United States: Sources, Uses and

Policy Issues." Random House, New York, N. Y. (1968).

?Vol. 44, No. 12, December 1972 2353



Savery and Cruzan

5. "Resources and Man, A Study and Recom

mendations." Committee on Resources and

Man, National Academy of Sciences, W. H.

Freeman and Co., San Francisco, Calif.

(1969). 6. Pohland, F. G., and Bloodgood, D. E., "Lab

oratory Studies on Mesophilic and Thermo

philic Anaerobic Sludge Digestion." Jour. Water Poll. Control Fed., 35, 11 (1963).

7. Lawrence, A. W., and McCarty, P. L., "Kinetics of Methane Fermentation in Anaerobic Treat

ment." Jour. Water Poll. Control Fed., 41, Rl (1969).

8. McCarty, P. L., "Anaerobic Waste Treatment

Fundamentals: I. Chemistry and Micro

biology; II. Environmental Requirements and

Control." Pub. Works, 95, 9, 107; 95, 10, 123 (1964).

9. Aglira, T., et al, "Digestion of Poultry Manure

for Methane Recovery." Project Design Re

port, Dept. of Mech. Eng., Drexel Univ.,

Philadelphia, Pa. (1971).

2354 Journal WPCF



methane recovery from chicken manure digestion

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