Food waste treatment through anaerobic co-digestion: Effects of mixing intensity on the thermohydraulic performance and methane production of a liquid recirculation digester

Abstract

This paper investigates the thermohydraulic performance and methane production of a Liquid recirculation Mesophilic Digester with Submerged solid waste (LMDS) under different mixing strategies. A combination of food waste and cow dung was used as a substrate in the co-digestion experiments. After 24 days of digestion, we reported a higher specific methane yield (301.84 Nm3 CH4 tvs−1) when gentle mixing was adopted, compared to intense mixing (221.32 Nm3 CH4 tvs−1). As for the unmixed co-digestion, it produced the lowest methane yield (112.88 Nm3 CH4 tvs−1). Furthermore, the thermal study showed that the gentle mixing caused less heat loss from the LMDS (20.90 kWh) compared to the intense mixing (40.21 kWh). Moreover, CFD results showed that intense mixing caused a higher pumping energy consumption (through increasing pressure drop) without inducing a significant improvement in the mixing inside the LMDS. Additionally, the liquid flow fields, force distribution, and percolation of the submerged waste were qualitatively evaluated for the considered mixing strategies. Based on these findings, we presented several recommendations aimed at reducing thermal and hydraulic energy losses while guaranteeing optimal methane production in LMDS digesters.