High-loading food waste and blackwater anaerobic co-digestion: Maximizing bioenergy recovery

In this study, food waste (FW) was added into source-diverted blackwater (BW) to enhance biomethane production using an upflow anaerobic sludge blanket (UASB) reactor at 35 °C. Increasing amount of FW was introduced into the BW according to the BW:FW volatile solids (VS) mixing ratios ranging from 1:0.3 (BW:FW) to 1:1.5. The optimal biomethane recovery efficiency was achieved when BW:FW VS mixing ratio was 1:1, corresponding to an organic loading rate (OLR) of 10.0 (±0.5) kg chemical oxygen demand (COD)/m3/day, which is 2.5 times of the highest OLR reported in the literature for BW treatment (4.1 kg COD/m3/day). Under this condition, a methane production rate of 2.42 (±0.15) L/L/day (highest biomethane recovery efficiency for BW treatment studies reported to date) was achieved, which represented 96.8 MJ/m3/day heat recovery. The enhanced biomethane production was attributed to the significantly improved solid substrate hydrolysis efficiency (85.9% higher than BW only) and microbial activities (sludge hydrogenotrophic methanogenic activities 2.4 times higher than BW only). Further OLR increase with more FW addition led to a reduction in methane production due to insufficient sludge retention. It can be concluded that anaerobic co-digestion of BW and FW is an attractive approach to maximize biomethane recovery efficiency from domestic wastewater in future decentralized wastewater treatment facilities.