Short Communication

A Note on Anaerobic Digestion of Cattle and Poultry Wastes

Pilot-plant digestion of cattle and poultry wastes has shown that sign!licant reductions in polluting power, including reduction in odour, can be obtained. Spee(fJc gas production, and methane content, is lowerj?om cattle than,l?om poultry wastes. For both wastes detention times approaching 20 days seems optimal. With cattle wastes digestion is better at higher than lower solMs contents, while the reverse is true

jor poultry wastes. These eJJZ, cts are probably caused by the ammonia content q[ the wastes.

IN I 'ROI)U( 'TION

Anaerobic digestion of sludges from domestic sewage works is a comparatively old process but it is only recently that digestion of other wastes as a method of pollution control and energy production has been seriously considered. Previous reports from these laboratories have been concerned with digestion of piggery wastes or piggery wastes plus other materials such as silage liquor (Bousfield et al. 1974). These results have been essentially confirmed by others (e.g. van Velsen, 1977), but there are fe~ data available on mesophilic, high-rate digestion of cattle and poultry wastes, although cattle wastes have been used for many years in the small digesters of India and other eastern countries.

We present here some preliminary data on digestion of cattle and poultry wastes.

ME I~|tOI)S

Digestio, Digestion was carried out in 1501itre single-stage digesters, with continuous

mechanical stirring. The digesters were maintained at 35°C by a water jacket 161

.4~ricultural 14"a,s'te,~ (I) (1979) ~' Applied Science Publishers Lid, England. 1979 l'rinted ill Great Britain

162 SHEILA BOUSFIELD, P. N. HOBSON, R. SUMMERS

supplied f rom an electrically heated, thermostat ical ly controlled unit. The slurries were fed to each digester f rom a stirred tank via a Lina-flow pump operat ing at intervals o f f rom about 10 to 20 min according to the detention time of the digester.

A n a l y s e s

Analyses were made as previously described (Hobson & Shaw, 1973) by s tandard methods.

Wastes

Cattle wastes were f rom fattening cattle on various experimental diets containing concentrates, hay, silage and dried grass. The mixed faeces and urine were collected f rom under slats and diluted with water to give slurries o f the required solids concentrat ions.

Poul t ry droppings, wi thout litter, were scraped from under caged laying birds and slurried with water to the required consistency.

RESULTS AND DISCUSSION

With both wastes digester running has been cont inuous, various measurements being made at daily, two or three-daily or weekly intervals. After a change in slurry consistency or other parameter , results over the first two or three detention times were discarded to allow for digester stabilisation and analyses then continued for some months to obtain good averages or to see if there was any slow decline in digester performance.

c a t t l e w a s t e s

The results in Table 1 indicate that a near 20-day detention time is, overall, better for cattle wastes than the 10-day detention optimal for piggery wastes (Summers &

TABLE 1 EFFECT OF DETENTION TIME ON DIGESTION

Poultry waste digestion a Cattle waste digestion ~ Detention time (day's) Detention time (days)

15 2O 10 2O

o~ reduction BOD 81.3 84. l 45.7 71-4 °/o reduction COD 40-0 48.4 16.1 20.6 ~o reduction TS 17-5 22.6 17.0 23-3 ~,i reduction VFA 69.7 83-3 65-2 77.6 Gas produced per

kilogramme TS added 0.362m "~ 0.380m ~ 0.195m 3 0.215m 3

° A t 6 ~ o TS input Ammonia nitrogen levels unchanged.

ANAEROBIC DIGESTION OF CATTLE AND POULTRY WASTES [ 63

Bousfield, 1976). Gas production is lower than that from piggery wastes (0.300 In 3

(kg TS added) 1) and the methane content at 55 60 ",~, is lower, possibly due to the lower fat content of the cattle slurry. There is little change in COD, but much of this and the solids would be lignified plant fibres, the residues of rumen digestion.

Table 1 also shows a 20-day detention time to be suitable for poultry slurry. The gas contains about 70 o; methane and gas production was higher than from piggery waste.

Figure 1 shows that while cattle waste digestion improved as solids input increased, poultry waste digestion was affected in reverse fashion. A possible reason

8

- - 6 u9 I--

1 2 -

IO :/ 0.2

, I ~ , , , i , , ~ , I

0.3 O-Z. O- 5 Gas (m 3 )

Fig. 1. Effects of solids loading on gas production. Total Solids (TS) in input sludge, gas production (m 3) per kilogramme TS added to digesters. Cattle waste digestion O; poultry waste digestion [~. For gas

analyses see text. Twenty-day detention time.

(Hobson & Shaw, 1976) is that the poultry waste digestion was being inhibited by the high ammonia concentrations (4900mglitre 1 at 12"/oTS). Low ammonia concentrations (500 mg litre- 1) in the cattle waste of 5 %0 TS could cause less than optimum digestion. An effect of low ammonia concentration on rumen microbial activity has recently been noted (Mehrez et al., 1977).

The digested sludges were much improved in odour and the results show that significant reductions in pollution power can be obtained by digestion of cattle and poultry wastes. Whether the gas production would give useful energy returns depends, of course, on the size of the unit.

SHEILA BOUSFIELD, P. N. HOBSON & R. SUMMERS. Rowett Research Institute, Bucksburn,

Aberdeen, Scotland, Great Britain

164 SHEILA BOUSFIELD, P. N. HOBSON, R. SUMMERS

REFERENCES

BOUSFIELD, S., HOBSON, P. N. & SUMMERS, R. (1974). Pilot plant high rate digestion of piggery and silage wastes. J. Appl. Bact. 37, xi.

HOaSON, P. N. & SHAW, B. G. (1973). The anaerobic digestion of waste from an intensive pig unit. Water Res. 7, 437 49.

HOnSON, P. N. & SHAW, B. G. (1976). Inhibition of methane production by Methanobacterium formicicum. Water Res. 10, 849 52.

MEHREZ, A. Z., ORSKOV, E. R. & MCDONALD, I. (1977). Rates of rumen fermentation in relation to ammonia concentration. Brit. J. Nutr. 38, 437 43.

SUMMERS, R. & BOUSF1ELO, S. (1976). Practical aspects of anaerobic digestion. Proc. Biochem. ! 1(5), 3 6. VAN VELSEN, A. F. M. (1977). Anaerobic digestion of piggery waste. 1. The influence of detention time

and manure concentration. Neth. J. Agr. Sci. 25, 151 69.