Assessing polychlorinated biphenyl degradation by an anaerobic microbial consortium in batch reactors with biofilm

Anaerobic biomass was used as inoculum in batch reactors undergoing fermentative-methanogenic conditions aiming to removal PCBs congeners (0.7 mg mL-1). Ethanol (460 mg L-1) and sodium formate (680 mg L-1) was used as co-substrate and polyurethane foam (PF) as support for biomass immobilization. Control reactors (RWCS, RCS and RCS-PF) did not contain PCBs, and biomass received a heat-treatment (RCS-PCB-HT). Ethanol and sodium formate stimulate the metabolism of biomass, since there was an increased methane production in reactors RCS and RCS-PF. The low yield of methane in reactors RCS-PCB and RCS-PCB-PF suggests an inhibitory effect of PCB over the methanogenic community. Reactors RCS-PCB presented a substantial reduction of the initial concentration of PCBs from 0.7 to 0.2 mg mL-1 after 60 days. For domain Bacteria, the reactors with PCBs (RCS-PCB and RCS-PCB-PF) were grouped with 86% similarity and only 55% with free-PCBs reactors (RWCS, RCS and RCS-PF) suggesting a selection of specific population in the presence of PCBs. For Archaea domain the reactors RCS-PCB and RCS-PCB-PF were grouped with 94% similarity and those without PCBs (RWCS, RCS and RCS-PF) with 86%. However, between these groups the similarity was 59% indicating that besides the selection of specific populations induced by PCBs the variation was not as evident as observed for the Bacteria domain. Reactors containing PCBs (RCS-PCB and RCS-PCB-PF) had an increased prevalence of Firmicutes and Chloroflexi phyla and, a pronounced relative abundance of Sedimentibacter, (7.4 and 12.4, respectively) a bacterium correlated with reductive dechlorination of PCBs.