Two-phase mesophilic anaerobic co-digestion of food waste and sewage sludge: effect of hydraulic retention time

The impact of hydraulic retention time (HRT) on two-phase mesophilic (35 degrees C) anaerobic co-digestion of food waste and sewage sludge was studied under mixing ratio of 1:1 on the TS basis. Laboratory-scale, two-phase anaerobic digestion systems were employed with each system consisting of an acidogenic reactor and a methanogenic reactor linked in series. For the acidogenic phase, an increase of volatile fatty acid (VFA) concentration was observed as HRT increased from id to 5d and the HRT of 5d was recommended for significantly higher VFA production and less propionate percentage, which could provide stable and favourable substrates for the methane reactor. Under acidogenic HRT of 5d, 20d was proved to be the optimum TART for methanogenic phase with the methane content, methane production rate, methane yield and two-phase VS removal rate reached 71%, 0.7L/(L.d), 0.69L/gVS(removed) and 64.7%, respectively. Results verified that the constraints of conventional anaerobic digestion for food waste or sewage sludge separately could be overcome by synergistic effect of co-digestion strategy and two-phase treatment.