ANAEROBIC BIODEGRADATION OF SLUDGE AND FOG

The anaerobic biodegradability of municipal primary and secondary sludge with increasing levels of partially dewatered fat, oil and grease (FOG) was assessed using a mixed methanogenic culture at 35°C. Under batch conditions with an acclimated and enriched microbial population, the sludge loading was 3 kg VS/m3 and the highest FOG loading tested was 1.5 kg VS/m3, resulting in a methane yield of 245 mL methane/g sludge VS added at 35°C and 1,010 mL methane/g FOG VS added at 35°C. Under semicontinuous feeding conditions, the sludge and sludge plus FOG loading tested were 3 and 3.75 kg VS/m3-day, respectively. Within 23 days of operation, the VFA concentrations were reduced below 200 mg COD/L (187 mg/L as acetic acid). Enhancement of sludge digestion was observed in those reactors where co-digestion of sludge and FOG took place, attributed to a higher level of microbial activity maintained in these reactors as a result of FOG degradation. The results of this study demonstrate that beneficial use of FOG through co-digestion with municipal sludge is feasible.