Determination of methane potential of mixtures composed of sewage sludge, organic fraction of municipal waste and grease trap sludge using biochemical methane potential assays. A comparison of BMP tests and semi-continuous trial results

Abstract

The main objective of this study was to evaluate the effect of simultaneous addition of grease trap sludge and organic fraction of municipal waste on anaerobic digestion of sewage sludge. Batch experiments were performed under mesophilic conditions to determine the biochemical methane potential and methane production rate of raw material as well as their mixtures. The optimum mixing ratio of sewage sludge with grease trap sludge and organic fraction of municipal waste was 4:3:3. For this mixture methane yield was 327 LCH4/kg VS, which is higher by approximately 130% than that of sewage sludge alone. Additionally, selected models were used to analyze the kinetics of anaerobic co-digestion.Despite the significant differences in the methane yields reported for the BMP assays and the semi-continuous trial, for the estimated profit of thermal energy and the theoretical thermal/electric power production for both experimental procedures similar trends were observed (values increasing with the gradual increase in the share of the co-substrate in the mixtures). Moreover the estimated degree in which electric energy obtained from the combustion of biogas covers the energy demand of the wastewater treatment plant showed that the addition of both co-substrates may lead to a value of 125% for this parameter.