Optimized anaerobic-aerobic sequential system for the treatment of food waste and wastewater

•Successful treatment of combined wastewater and food waste.•High removal efficiency and methane generation.•Stable anaerobic operation at ammonia levels below a tipping point.•Average strain rate magnitude indicative of ammonia conversion potential. Considering that modern wastewater and solid waste processing facilities seek efficient energy recovery methods, this study investigates anaerobic-aerobic sequential systems for combined treatment of raw wastewater with food waste. The optimum loading rate was found to be 1.6mgVSL−1d−1 resulting in a stable operation of the anaerobic compartment. Yet, the increase in ammonia concentration resulted in gradual accumulation of VFA, until reaching a tipping point of 3000mgL−1 beyond which an abrupt increase in VFA to above 6000mgL−1 was observed, with acute stability loss and performance deterioration. The aerobic system was modeled using computational fluid dynamics methods. Optimum performance was achieved at an average strain rate magnitude of 12.7s−1 yielding a DO concentration of 4mgL−1 which have resulted in 74% conversion of ammonia nitrogen. Under optimum conditions, the studied AASS yielded high total removal rates of 93% VS and 94% COD, with a high specific methane yield of 845LkgVS−1 and a CO2-to-CH4 ratio of 0.63.