ANAEROBIC-DIGESTION OF CATTLE WASTE AT MESOPHILIC AND THERMOPHILIC TEMPERATURES

Methanogenesis was studied using stirred, bench-top fermenters of 3-1 working volume fed on a semi-continuous basis with waste obtained from cattle fed a high grain, finishing diet, Digestion was carried out at 40 and 60 degrees C. CH4 production was 11.8, 18.3, 61.9 and 84.5% hi gher in the thermophilic than the mesophilic digestor at the 3, 6, 9 a nd 12 g volatile solids (VS) l(-1) reactor volume loading rates, respe ctively. When compared on an energetic basis CH4 production was 7.4, 1 8.3, 72.9 and 107.3 kJ day higher in the thermophilic than the mesophi lic digestor. CH4 production decreased more rapidly with each increase in VS loading rate and decrease in retention time (RT) in the mesophi lic than the thermophilic digestor. When expressed as l g(-1) VS fed o r as kJ kJ(-1) fed, the amount of CH4 was 49% less at the highest comp ared to the lowest loading rate in the mesophilic digestor. In the the rmophilic digestor the decrease was only 16%. Propionate accumulated i n the mesophilic digestor at the two highest loading rates, reaching c oncentrations of about 50 mM, but were only about 13 mM in the thermop hilic digestor. Isobutyrate, isovalerate plus 2-methylbutyrate, and va lerate also accumulated at the higher loading rates.