Production of biogas through anaerobic co-digestion of ice cream plant wastewater and ice cream production residue

The primary objective of this study is to determine whether it is possible to dispose of ice-cream production residue (off-spec) and ice-cream wastewater together and to recover energy by anaerobic co-digestion process. Mesophilic batch anaerobic digestion tests were performed under laboratory conditions to evaluate production of methane (CH4) from these substrates. It was found out that it was possible to obtain a high methane yield of 0.338 L CH4 g-1 CODremoved from anaerobic digestion of wastewater alone, with almost 70 % of methane in biogas, while anaerobic digestion of off-spec alone did not seem feasible, due to particular characteristics of the off-spec. When wastewater and off-spec were mixed at a ratio of 9:1 (WW:O) by weight, a methane yield of 0.131 L CH4 g-1 CODremoved could be observed. Lower methane yields for anaerobic co-digestion of wastewater and off-spec could be attributed to high concentrations of sulfate and oil & grease coming from off-spec. Since both ice-cream wastewater and off-spec had variable pH ranges and a poor buffering capacity, adequate amount of buffer must always be present in the anaerobic system to sustain anaerobic degradation.