Development of a Compact, Energy-Positive Food Waste Treatment Process

Abstract

This study developed an innovative bioprocess for food waste (FW) treatment by combining a leach bed reactor (LBR) with an anaerobic membrane bioreactor (AnMBR). The two bioreactors were consistently operated at neutral pH and room temperature. The best performance was observed in the LBR run at the conditions of inoculum to substrate ratio 10% and leachate circulation rate 4.4 L/h without any clogging issues in the LBR. In this operating condition, removal of volatile solids (VS) of 88±2%, Hydrogen production of 3.45 L/ kg of VS added and volatile fatty acid yield of 571 g chemical oxygen demand (COD)/ kg of VS added were observed only in a reaction time of 14 d. Part of FW remained in the LBR, accounting for 13-20% of initial FW. LBR leachate (i.e., effluent from the LBR) was further stabilized in the AnMBR, and hydraulic retention time (HRT) related to membrane flux and solid retention time (SRT) were optimized in the AnMBR. Only in 13 d HRT and 75 d SRT, the AnMBR achieved 85% COD removal and complete solid reduction due to membrane separation, along with the specific methane yield of 0.3 L per gram of COD removed. Under this condition, membrane flux was approximately 6 L/m^2-h (LMH) and maintenance cleaning once every five days was required to maintain the flux. Energy balance showed that the combined FW bioprocess is energy-positive with net energy benefit up to 841 kWh per ton of FW treated. The study proved that the newly developed FW process could achieve 79% VS removal of FW only in 20 d of overall reaction time in energy-positive manners.