Agricultural Wastes 4 (1982) 151 158

A N A E R O B I C D I G E S T I O N O F P I G G E R Y W A S T E U S I N G A S T A T I O N A R Y F I X E D F I L M R E A C T O R

K.J . KENNEDY & L. VAN DEN BERG

Division oJ Biological Sciences, National Research Council of Canada,

Ottawa, Ontario, Canada K1A OR6

ABSTRACT

A f ixed film digester with a 35 litre support void volume, treating piggery waste at 35°C, was capable of handling high organic loading rates and short hydraulic retention times without process failure. The digester had a film support made oJfired potter's clay and a surface-to-volume ratio of 157m2m 3. It could be loaded to 18.7kg Volatile Solids (VS) m - 3 day- 1 without substantial increases in volatile acid levels or a reduction in the quality o f the digester gas. Maximum methane gas production was 3"8 m 3 (STP) m - 3 day- 1 and the conversion o[" Volatile Solids into methane decreased with decreasing hydraulic' retention time.

INTRODUCTION

The increasing cost of energy from fossil fuels, as well as from renewable resources, is making anaerobic digestion more attractive to pig growers for energy production, conservation and waste management (Summers & Bousfield, 1980). The economic feasibility of producing methane from piggery waste using anaerobic digestion depends on the capital cost and energy requirements of the process (Morris et al., 1975; Scharer & Moo-Young, 1979). In cold climates a large part of the energy produced is needed for heating (Lapp et al., 1977; Kroeker et al., 1975), which makes it even more important that the efficiency and rate of conversion of organic matter to methane be optimised. Advanced types of anaerobic methanogenic reactor have been designed to increase rates of methane production with little or no loss of conversion efficiency. They have in common the retention of the microbial biomass, which is particularly important for the retention of the methanogenic microorganisms that have mass doubling times of several days or weeks (van den Berg, 1977). The stationary fixed film reactor has been shown to be capable of high

NRCC 19964

151 Agricultural Wastes 0141-4607/82/0004-0151/$02-75 © Applied Science Publishers Ltd, England, 1982 Printed in Great Britain

152 K . J . KENNEDY, L. VAN DEN BERG

rates of methane production using high strength waste with a high suspended solids content (van den Berg et al., 1980; van den Berg & Lentz, 1980).

This paper reports on a study to determine the suitability of the stationary fixed film reactor for the production of methane from pig manure. The study included an assessment of the effect of loading rate on the rate of gas production and on conversion efficiency.

MATERIALS AND METHODS

Fermenter design and operation The design and operation of the fixed film reactor (Fig. 1) has been reported in

detail in previous papers (van den Berg & Lentz, 1979; van den Berg et al., 1980). Briefly, a large glass jar (28.5cm diameter × 90cm tall) was packed with a film support consisting of straight vertical channels about 2.8 × 2.8 cm in cross-section and 66-68 cm tall (Fig. 2). This support was made of potter's clay (Miller 50) fired to 1000°C. The void volume of the digester was 35 litres with a fixed film support surface-to-volume ratio of 157 mZm-3. This included the glass surface adjacent to the packing which also supported a film.

PERISTALTIC PUMP \

\ FEED ~ \ \

LIQUID LEVEL - -

LIQUID DISTRIBUTOR - -

FIXED FILM SUPPORT ~ ~

GLASS JAR ~ I

RECIRCU LATION - ~ \ ~ \\ I

CENTRIFUGAL PUMP ~ \

/ SAMPLING PORTS

/ " WET TEST METER

/ ~ " / / ~ _ S GAS

/ --SYPHON CONTROLLER

~~ /~ --BROKEN SYPHON

/--EFFLUENT

f - -EFFLUENT COLLECTOR /

!

Fig. 1. Set-up of multi-channel fixed film digester.

PIGGERY WASTE DIGESTION WITH A STATIONARY FIXED FILM REACTOR ]53

Fig. 2. Fixed film support (Miller 50 potter's clay).

Feed was pumped in at the top of the reactor intermittently once every 30 min. Effluent was removed from the bot tom of the digester through an intermittent syphon that maintained the liquid level about 5 cm above the film support. Gas exited at the top of the reactor through a wet test gas meter which was used to measure the rate of gas production. To ensure adequate mixing the digester was mixed, for 1 min every 20 min, by pumping the fermenter liquid from the bot tom to the top of the reactor with a centrifugal pump (8 litres rain--1). The digester was located in a temperature controlled room (35 °C).

The reactor was inoculated with sludge from a municipal digester and acclima- tised to pig manure over a period of 8-10 weeks. The reactor was then fed pig manure at a particular Volatile Solids loading rate. Reactors were operated for at least five hydraulic retention times (HRT's) before the data presented here were taken.

Piggery waste The pig waste used in the experiment consisted of urine and faeces from pigs fed a

corn-rich finishing diet. The piggery waste was obtained from a grower not using antibiotics in his finishing ration. To minimise pumping and line-blockage problems, the waste was screened through a 10 mesh (wire diameter 0.0011 mm, width of opening 1-83 mm) stainless steel cloth. The composition of the filtered waste was determined (Table 1) and the waste was then stored at - 20 °C until used.

154 K. J. KENNEDY, L. VAN DEN BERG

TABLE 1 C O M P O S I T I O N OF P I G G E R Y W A ST E USED IN REACTORS

Minimum Maximum Average

Total Solids (g litre- 1) 21.0 28.8 26.4 Total Volatile Solids (g litre- 1) 14.1 20.1 18.2 Total Suspended Solids (g litre - 1) 14.5 21.2 18.0 Volatile Suspended Solids (g litre - 1) 8.3 15.1 13.0 Total chemical oxygen demand, COD (g 0 2 per litre) 27-0 51.0 39.2 Soluble chemical oxygen demand (g 0 2 per litre) 10.6 17.8 14.6 Ammonia-nitrogen (mg litre-1) 2100 3800 2700 Volatile acids (mg litre-1)

Acetic acid 2950 4100 3500 Propionic acid 850 1100 950

A n a l y s e s

R o u t i n e m e a s u r e m e n t s i nc luded ra te o f gas p r o d u c t i o n a n d gas c o m p o s i t i o n , volat i le fa t ty ac id c o n t e n t o f the d iges ter l iqu id , chemica l oxygen d e m a n d ( C O D ) , a m m o n i a - n i t r o g e n , T o t a l Sol ids (TS), S u s p e n d e d Sol ids (SS) a n d Volat i le Solids (VS) o f the effluent a n d feed. M e t h a n e a n d vola t i le fa t ty acids were d e t e r m i n e d dai ly by a g a s - c h r o m a t o g r a p h i c m e t h o d ( K h a n & Tro t t i e r , 1978), a n d solids, a m m o n i a n i t r o g e n a n d C O D once or twice a week acco rd ing to s t a n d a r d m e t h o d s ( A m e r i c a n Pub l i c Hea l th Assoc ia t ion , 1975). V o l u m e s o f m e t h a n e were cor rec ted to s t a n d a r d

t e m p e r a t u r e (0°C) a n d pressure (1 a tm) (STP) .

RESULTS AND DISCUSSION

The fixed film reactor was capable of digesting piggery waste at an Hydraul ic Re ten t ion T i m e ( H R T ) as shor t as 1 d a y (Tab le 2). At this h igh l oad ing rate (18.7 kg VS m -3

TABLE 2 EFFECT OF H Y D R A U L I C RETENTION TIME O N PE RFO RMANCE OF THE FIXED FILM REACTOR

Hydraulic Retention Time (Days)

1"0 1"7 2"7 3"7 8"0

18.7 10.2 6.6 4.6 2.5

0.12 0.064 0-041 0"029 0.016 70 70 71 71 71

3.8 2.6 2.2 2.1 1-4

0.024 0-017 0.014 0.013 0.009

710 480 490 675 610 250 90 100 100 55

2100 2600 - - 2500 3500

Volatile Solids loading rate (kg VS m -3 day -1)

Film surface loading rate (kg VS m - 2 day - 1)

Methane content of digester gas (%) Volumetric rate of methane

production (m a (STP) m -3 day 1) Methane production rate Of film

(m 3 (STP) m -2 day 1) Volatile acids (mglitre-1)

Acetic acid Propionic acid

Ammonia-nitrogen (mg litre - t)

P I G G E R Y WASTE DIGESTION W I T H A S T A T I O N A R Y FIXED FILM R E A C T O R 155

day - 1) the reactor produced 3.8 m 3 CH4(STP) m - 3 day- 1. Methane content of the digester gas was not significantly affected by hydraulic retention time. Even at the high loading rate total volatile acids levels were low (below 1000mg litre-1) with propionic acid levels below 300 mg litre-1

The conversion of Volatile Solids into methane was markedly affected by the Volatile Solids loading rate (Fig. 3). At long HRT's (8.0 days) the conversion was 70 % of the theoretical maximum value of 0.75 m 3 C H 4 (STP) kg 1 VS but at a short HRT (1 '0 day) the conversion rate dropped to 0.20 m 3 C H 4 (STP)kg-1 VS. These results indicate that bacteria other than the methane formers were limiting methane production.

To determine more precisely the limiting steps in the digestion of pig manure, each of the three steps of anaerobic digestion liquefaction, acid formation and methane formation were studied. The degree of completeness of each of these steps was calculated according to van Velsen (1977):

(A) Liquefaction The breakdown of suspended organic solids into soluble material. Liquefaction (%) = 100 (G + S)/M.

(B) Acid format ion--The breakdown of soluble organics into volatile fatty acids, carbon dioxide and hydrogen. Acid formation ~"/~ = 100 (G + V)/M.

(C) Methane formation--Conversion of the end products of acid formation into methane. Methane formation (%) = 100 G/M

Where: G = COD removed via methane gas (g 0 2 per litre of manure). S = COD supernatant (g 0 2 per litre).

M = Total manure COD (g 0 2 per litre of manure). V = COD, corresponding with the VFA concentration in the digester

effluent (g 0 2 per litre).

The results of these calculations, presented in Fig. 4, showed that all three processes were similarly affected by the loading rate. This, in turn, indicated that the first step, the liquefaction, was the rate-limiting step in the process and that the residence time was too short for complete liquefaction. Increased ammonia nitrogen concentration at longer HRT's (Table 2) also indicated that liquefaction was limited by HRT. Maki (1954), Hobson et al. (1974) and van Velsen (1977) also suggested that liquefaction was the rate-limiting step in the digestion of piggery waste. Data published by van Velsen (1977) showed that when the hydraulic retention time was greater than the doubling times of the methanogens, liquefaction was the rate-limiting step; however, when retention times were less than the doubling time of the methanogens, methane formation became the rate-limiting step of the process, probably due to the washout of these slow growing bacteria.

156 K . J . K E N N E D Y , L. VAN D E N B E R G

4 .0

a

~" 3.o I-- ( f)

%

Z 0 p 2.0

0 0 Q::

-r"

h i

U.. 0 ,,, 0 ; I---

ILl r n

I I I I I I I I I • J O ~O

• . .

0.75 ~,~

", • • 70.50 • g

0 a s N

(/3

I I I I I I ~- 4 8 12 16 20 <~

0 VOLATILE SOLIDS LOADING RATE (KG VS/M3/DAY) >

Fig. 3. Effect of Volatile Solids loading rate on the volumetric rate of methane production, (O); and methane production per kilogramme of Volatile Solids added, (A).

Microbial liquefaction becomes a more critical step in the fixed film fermenter, since the washout of the methanogens is minimal (van den Berg & Lentz, t1980).

A single clay support was removed from the reactor during steady state operation at a 1.0 day HRT. The clay support was covered with a thin microbial film, 2-4 mm thick, which was evenly distributed over the entire support area. The microbial film was 5-8 ~o non-soluble organic solids. Fermenter performance based on the amount of microbial film was 1.1 1-4 g C O D removed per gramme per day. This film activity was similar to that reported by van den Berg & Lentz (1980) for polyvinyl chloride and clay support materials.

The stability of the fixed film reactor at high loading rates was rather remarkable. An HRT of 1.0 day was maintained for thirty-five retention times without a reactor upset occurring. Also, the reactor could be changed from one HRT to another, whether up or down, without a problem or a long adaptation period. Some of the results obtained during mechanical failure suggest that a once a day feeding or drastic overloading may easily be tolerated. While the results presented here were obtained using recirculation ( l m i n out of 20min), limited tests without re- circulation showed that, although the reactor could be operated reasonably well, it probably would not obtain the high Volatile Solids loading rates obtained with recirculation. Where severe overloading did occur it was found that propionic acid

P I G G E R Y WASTE DIGESTION W I T H A STATIONARY FIXED FILM R E A C T O R 157

Fig. 4.

o (..)

LI.I

<F 9o r r

{ /3

N 8o 113 b-

0 70

a

z 6 0

UA o 5 0 z

x ~ 40 0

o 3 0

~, 2o

z IO 0 if3 CE UA

Z

8

Effect

I00 i i I I I I I I [ I

0 [ 0 4

/ - LIQUEFACTION

~ ~ - ~ / / ACID FORMATION

I J I l I I J [ I 8 12 16 20 24 28 32 36 40 44

FERMENTER LOADING RATE (KG COD/M3/DAY)

of f e rmen te r l o a d i n g ra t e o n l i que fac t ion , ac id f o r m a t i o n a n d m e t h a n e f o r m a t i o n .

concentrations increased much faster than the acetic acid concentration, suggesting that a high propionic acid level in the reactor was an indication of impending digester upset. Propionic acid levels in the fixed film reactor were never high enough to cause a major digester failure. These results are in agreement with those of Hobson et al. (1974) and Summers & Bousfield (1980) who also reported that reactor stability was best controlled by monitoring propionic acid concentrations in the digester.

C O N C L U S I O N S

Comparison of results with those in the literature showed that the stationary fixed film reactor was capable of handling larger loading rates and had higher rates of methane production than partially or fully mixed tank reactors (Hobson & Shaw, 1972; Robertson et al . , 1975; Lapp et al . , 1975; van Velsen, 1977; Summers & Bousfield, 1980; Scharer et al . , 1980), or plug flow reactors (Jewell et al . , 1978). Results also indicated that microbial liquefaction of organic solids was the rate- limiting step of the process in terms of conversion efficiency.

158 K.J . KENNEDY, L. VAN DEN BERG

The poorer conversion of waste to methane at very short HRT's may make the choice of an intermediate HRT desirable. It should be pointed out that with a more concentrated waste than used in these tests, higher rates of methane production may be possible because of the longer HRT for the same Volatile Solids loading rates. This, as well as factors such as continuous versus once-a-day-feeding and reactor overloading, is being studied.

REFERENCES

AMERICAN PUBLIC HEALTH ASSOCIATION (1975). Standard Methods for the Examination of Water and Wastewater. (14th ed) Washington, DC.

HOBSON, P. N. & SHAW, B. G. (1972). The anaerobic digestion of waste from an intensive pig unit. Water Research, 7, 437-49.

HOBSON, P. N., BOUSFIELD, S. & SUMMERS, R. (1974). Anaerobic digestion of organic matter. CRC Crit. Rev. Environm. Control (June), 131 91.

JEWELL, W. D. et al. (1978). Anaerobic fermentation of agricultural residue: Potential for improvement and implementation, Final Report, US Department of Energy. HCPT/2981-07.

KHAN, A. W. & TROTTIER, T. M. (1978). Effect of sulphur-containing compounds on anaerobic degradation of cellulose to methane by mixed cultures obtained from sewage sludge. Applied and Environmental Microbiology, 35, 1027-34.

KROEKER, E. J., LAPP, H. M., SCHULTE, D. D. & SPARLING, A. I . (1975). Cold weather energy recovery from anaerobic digestion of swine manure. In: Energy, agriculture and waste management. (Jewell, W. J. (Ed.)) Proc. Cornell Univ. Agric. Waste Management Conf., 337 52.

LAPP, H. M., SCHULTE, D. O., SPARL1NG, A. A. & BUCHANAN, L. C. (1975). Methane production from animal wastes. I. Fundamental considerations. Can. Agric. Eng., 17, 97-102.

LAPP, n . M., HALIBURTON, J, D. & STEVENS, M. A. (1977). The energy balances in a pilot-scale anaerobic digester. Annual Meeting Can. Soc. Agric. Eng., Guelph, Ontario. 77, 409 20.

M AKI, L. W. (1954). Experiments on the microbiology of cellulose decomposition in a municipal sewage plant. Antonie van Leeuwenhoek 20, 185.

MORRIS, G. R., JEWELL, W. J. and CASLER, G. L. (1975). Alternative animal waste anaerobic fermentation designs and their costs. Proc. Cornell Univ. Agric. Waste Management Conf. 317-36.

ROBERTSON, A. M., BURNETT, G. A., HOBSON, P. N., BOUSFIELD, S. & SUMMERS, R. (1975). Bioengineering aspects of anaerobic digestion of piggery wastes. Proceedings of the International Symp. on Livestock Wastes, Managing Livestock Wastes, 544-8.

SCHARER, J. M. & Moo-YOUNG, M. (1979). Methane generation by anaerobic digestion of cellulose- containing wastes. Adv. Biochem. Eng. II , 85-101.

SCHARER, J. M., Moo-YouNG, M., FUJITA, M. & BYTHELL, D. (1980). Methane production of anaerobic digestion of agricultural wastes. Proceedings Second Bioenergy Research and Development Seminar, Ottawa, Canada, 295-99.

SUMMERS, R. & BOUSFIELD, S. (1980). A detailed study of piggery waste anaerobic digestion. Agric. Wastes, 2, 61-78.

VAN DEN BERG, L. (1977). Effect of temperature on growth and activity of a methanogenic culture utilizing acetate. Can. J. Microbiol. 23, 898-902.

VAN DEN BERG, L. & LENTZ, C. P. (1979). Comparison between up- and down-flow anaerobic fixed film reactors of varying surface-to-volume ratios for the treatment of bean blanching waste. Proc. 34th Purdue Industrial Waste Conf. 319-25.

VAN DEN BERG, L., LENTZ, C. P. & ARMSTRONG, D. W. (1980). Anaerobic waste treatment efficiency comparisons between fixed film reactors, contact digesters and fully mixed continuously fed digesters. Proc. 35th Purdue Industrial Waste Conf.

VAN DEN BERG, L. & LENTZ, C. P. (1980). Effects of film area-to-volume ratio, film support, height and direction of flow on performance of methanogenic fixed film reactors. Proc. U.S. Dept. oJ Environm. Workshop~Seminar on Anaerobic Filters, Howey-in-the-Hills, Florida.

VAN VELSEN, A. F. M. (1977), Anaerobic digestion of piggery waste. I. The influence of detention time and manure concentration. Neth. J. Agric. Sci., 25, 151-69.