Magnetite-enhanced bioelectrochemical stimulation for biodegradation and biomethane production of waste activated sludge

Abstract Microbial electrolytic cell (MEC) and magnetite (M) have shown excellent performance in promoting anaerobic digestion (AD) of biowastes. In this study, four types of anaerobic systems (i.e. single AD, M-AD, MEC-AD, and M-MEC-AD) were developed to comprehensively investigate the potential effects of magnetite-enhanced bioelectrochemical stimulation on the biodegradation of waste activated sludge (WAS) and methane (CH4) production. Results showed that M-MEC-AD system produced the highest cumulative CH4 yield, 9.4% higher than those observed in MEC-AD system. Bioelectrochemical stimulation enriched electroactive Geobacter, and classical methanogens (Methanosaeta and Methanobacterium), and the proliferation was further promoted when coupling with magnetite. The relative abundance of Geobacter (6.9%), Methanosaeta (0.3%), and Methanobacterium (12.6%) in M-MEC-AD system was about 10.8, 1.2, and 1.2 times of MEC-AD system, respectively. The integration of magnetite could serve as the conductive materials, and promote inherent indirect electron transfer (IET) and emerging direct electron transfer (DET) between methanogens and fermentative bacteria, building a more energy-efficient route for interspecies electron transfer and methane productivity. This study demonstrated the positive promotion of the coupled bioelectrochemical regulation and magnetite on organic biodegradation, process stability and CH4 productivity, providing some references for the integrated technology in sludge treatment and bioenergy recovery.