THERMO-TOLERANT ANAEROBIC DEGRADATION OF VOLATILE FATTY-ACIDS BY DIGESTED ORGANIC FRACTION OF MUNICIPAL SOLID-WASTE

The effect of temperature on the methanogenic and volatile fatty acid degrading activity of the digested organic fraction of municipal solid waste (OFMSW), was studied in bench-scale experiments. Digested OFMSW samples were obtained from pilot plants of a BIOCEL dry anaerobic batch digestion process which was operated either at 25-30-degrees-C or at 35-40-degrees-C. OFMSW, digested at either temperatures exhibited comparable methanogenic activities under mesophilic (37-degrees-C) and thermophilic (55-degrees-C) conditions. The mesophilic methanogenic activity was not affected by a thermophilic digestion period of 1 month. Such a thermo-tolerant property was not observed in digesters which were inoculated with mesophilic granular sludge (MGS) from a full scale UASB reactor. In contrast to MGS, digested OFMSW showed high acetate conversion rates at the subthermophilic temperature range (45-50-degrees-C). However, for propionate and butyrate conversion the thermo-tolerance was less pronounced. Digested OFMSW was used as seed material for the start-up of a thermophilic anaerobic high rate reactor. After 5 months of continuous operation the cultivated sludge showed a temperature optimum for acetate degradation at 60-65-degrees-C.