Thermo-tolerant anaerobic degradation of volatile fatty acids by digested organic fraction of municipal solid waste

Abstract

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°C or at 35–40°C. OFMSW, digested at either temperatures exhibited comparable methanogenic activities under mesophilic (37°C) and thermophilic (55°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°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°C.