Effects of biochar on the phenol treatment performance and microbial communities shift in sequencing batch reactors

The extensive application of biochar (BC) attracts concerns regarding its environmental effect. Wastewater treatment systems are potential BC recipients; however, the impacts of BC on these systems are still unclear. In this study, effects of BC on the phenol treatment performance and shift in microbial communities in sequencing batch reactor (SBR) were investigated. The phenol degradation rates were enhanced in all BC-treated SBRs during the whole operation due to promotion of key enzymes involved in phenol degradation. The decrease in abundance of intracellular reactive oxygen species (ROS) in SBRs indicated that BC protected microorganisms by ameliorating phenol toxicity, leading to a decrease in the secretion of extracellular polymeric substances (EPS). The functional groups, protein (C=O, -CO-NH), polysaccharide (C-OH, C-O-C, C-O), and nucleic acids (O-P-O) associated bonds of EPS decreased or disappeared in BC-treated SBRs. Miseq sequencing revealed significant decrease in bacterial diversity and remarkable changes in the bacterial community structure in BC-treated SBRs. Abundances of Comamonas and Cupriavidus increased significantly upon BC exposure, which contributed to phenol degradation. Treatment with relatively high BC dosage exhibited considerable inhibition on Thauera. Canonical correspondence analysis (CCA) indicated that the shift in abundances of these genera was closely associated with BC dosage. This study suggested that BC exerted protective effects on sludge microbes of phenol wastewater treatment systems, while it affected the bacterial community structure and diversity at test concentrations. Thus, this study elucidates the comprehensive effects of BC on wastewater treatment process.