Polychlorinated biphenyls affects anaerobic methane production from waste activated sludge through suppressing hydrolysis-acidification and methanation processes

The widespread existence of polychlorinated biphenyls (PCB) in wastewater results in the retention of abundant PCB in waste activated sludge (WAS), which has become a global concern. Till now, the effects of PCB on methane production during WAS anaerobic digestion was still limited. This study aimed to investigate whether and how PCB affects methane production. Results showed that the increased PCB concentration led to the less methane produced. At the highest concentrations of PCB (100 mg/kg DS) in this study, the methane production (112 +/- 6 L CH4/kg VS) was significantly reduced by 26.6 +/- 0.1% compared to the control (153 +/- 7 L CH4/kg VS). Correspondingly, VS destruction at the studied concentrations showed the similar trend. In addition, the dewaterability evaluation indicated that the PCB resulted in the deteriorative sludge dewaterability. The mechanism studies suggested that the decreased methane production with the increased levels of PCB was attributed to the suppression on hydrolysis-acidification and methanation processes. This also was supported by the decreasing key enzymes activities associated with methane production (protease, cellulase, acetate kinase (AK) and coenzyme F-420). The relative activity of F-420 at 100 mg/kg DS of PCB even reduced to 78% +/- 3%.