Enhanced biogas production and biodegradation of phenanthrene in wastewater sludge treated anaerobic digestion reactors fitted with a bioelectrode system

The purpose of this study was to investigate the enhanced biogas production and biodegradation of phenanthrene in sludge treated anaerobic digestion (AD) reactors fitted with a bioelectrode system (AD-MEC reactors). Different cathodes were considered for installation in the AD-MEC reactor. The result showed that the maximum methane yield (113.45 L/kg TS) and the highest phenanthrene degradation rate (52.3%) were obtained in a reactor with a carbon paper (CP) cathode; this performance was 30.5% and 83.5% greater, respectively, than that in the AD control reactor. Clostridia spp., bacteria that degrade pollutants, were specifically adsorbed onto the electrodes, and Methanosaeta spp. and Geobacter spp. were enriched on the anode. These results implied that a potential direct electron transfer occurred between Methanosaeta and Geobacter. Two hydrogenotrophic methanogens (Methanospirillum spp. and Methanobacterium spp.) were enriched on the surface of the cathode, which enhanced interspecies H₂ transfer in the AD-MEC reactors.