Potential role of sulfide precipitates in direct interspecies electron transfer facilitation during anaerobic digestion of fish waste

Abstract

Fish waste (FW) contains large amounts of protein and is a challenging feedstock for biogas production due to possible H₂S and ammonia generation. Adding FeCl3 to an anaerobic digester can precipitate H₂S. Mackinawite and greigite are conductive and magnetic substances formed from H₂S precipitation. Direct interspecies electron transfer (DIET) can be stimulated by developing these conductive materials and by applying an external magnetic force. In this study, FW was digested in batch reactors and exposed to magnets magnetic fields from 3 to 115 mT. The results showed that the use of magnetic fields could increase the biomethane yield by up to 36 %. XRD analyses showed that mackinawite and greigite were accumulating in the solid phase in digesters added FeCl3. Genetic analysis of the microbial community suggested that applying a magnetic field not only increased the relative abundance of protein-hydrolyzing bacteria but also potentially improved methane production through DIET.