Optimizing Acidogenic Process for Achieving High Biomethane Yield from Anaerobic Co-Digestion of Food Waste and Rice Straw Using Response Surface Methodology

Response surface methodology was used to optimize the acidogenic phase parameters for co-digestion of food waste (FW) and rice straw (RS) to obtain high biomethane yield in the methanogenic phase. The organic loading rate (OLR), hydraulic retention time (HRT), feedstock to microorganism ratio (F/M-(VS/VS)) and food waste to rice straw ratio (FW/RS(VS/VS)) were investigated. The maximum volatile fatty acid (VFA) yield in the acidogenic phase was 16,844 mg/L, which was obtained at an OLR of 42.95 g volatile solid (VS)/L, HRT of 7.95 days, F/M-(VS/VS) of 2.12:1, and FW/RS(VS/VS) of 3.88:1. The VFA concentration under optimal conditions was 30.4% higher than the value under center-point conditions, which were the optimal levels derived from one-factor tests. The highest methane yield of 561 mL/g VSadded was achieved when the optimal acidified effluent was digested in the methanogenic phase, which was 27.5% higher than the average value at the center-point condition. Optimizing acidogenic process could highly improve biomethane production in corresponding methanogenic phase. The highest methane yield from anaerobic co-digestion of FW and RS was obtained when the optimal acidified effluent was digested in the methanogenic phase.