Towards utmost bioenergy conversion efficiency of food waste: Pretreatment, co-digestion, and reactor type

Food waste (FW), which contains a large amount of easily biodegradable organic matter, has great potential for methane production using anaerobic digestion (AD). However, the bioenergy conversion efficiency in this method is not ideal because FW has a long hydraulic retention time (HRT) of > 20 days, low organic loading rate (OLR) of 1-6 g VS /L.d and low bioenergy conversion rate 40-70%. To improve the efficiency of bioenergy conversion, pretreatment technologies, co-digestion with other organic wastes and the effect of reactor types are reviewed and discussed. Enzymatic pretreatment and co-digestion of FW with landfill leachate are preferable for hydrolysis of organic solids, enhancement of methane production and stability improvement of the AD system. Based on the discussion and our preliminary experiment results, the feasibility of FW treatment using a third generation anaerobic reactor is proposed and analyzed. If the proposed concept can be applied practically in the future, more than 90% of the organic matter in FW could be recovered as bioenergy with an OLR greater than 20 kg COD/m3 d.