Psychrophilic methanogenesis of food waste in a bio-electrochemical anaerobic digester with rotating impeller electrode

Psychrophilic bio-electrochemical anaerobic digestion (PBEAD) is a promising new technology for improving methane production at low temperatures via supply of low energy. In this study, a PBEAD reactor operating at 19.8 ± 2.9 °C equipped with a low-cost stainless steel (SUS304) rotating impeller electrode was manufactured to observe the efficiency of methane production and changes in archaeal communities at a high organic loading rate (OLR). Stable methane production was achieved without VFA accumulation and pH decrease in the PBEAD reactor up to an OLR of 4.5 kg/m3·d owing to H2-dependent methylotrophic and hydrogenotrophic methanogens, which converted H2 into methane. In the case of an OLR of 6.0 kg/m3·d, methane production decreased significantly due to decreased pH and accumulated VFAs, but recovered on increasing the alkalinity. The maximum energy efficiency of 71.7% confirmed the high performance of the PBEAD reactor equipped with an SUS304 rotating impeller electrode.