Effects of temperature and hydraulic retention time on anaerobic digestion of food waste

A modified three-stage methane fermentation system was developed to digest food waste efficiently. This system consisted of three stages: semianaerobic hydrolysis, anaerobic acidogenesis and strictly anaerobic methanogenesis. In this study, we examined the effects of temperature and hydraulic retention time (HRT) on the methanogenesis. Operation temperature was adjusted from 30°C to 55°C, and the HRTs ranged from 8 to 12 d. The rate of soluble chemical oxygen demand (sCOD) removal correlated with digestion time according to the first-order kinetic model developed by Grau et al. [Water Res., 9, 637–642 (1975)]. With liquor food waste, thermophilic digesters showed a higher rate of sCOD removal than mesophilic digesters. The rates of biogas and methane production by thermophilic digesters were higher than those by mesophilic digesters regardless of HRT. Although maximum biogas production occurred when an HRT of 10 d was used, the methane yield was the highest in the reactor when an HRT of 12 d was used (223 l CH4/kg sCODdegraded). However, digestion stability decreased when an HRT of 8 d was used. The concentration of NH3-N generated in this experiment did not inhibit anaerobic digestion.