Resumo

Polychlorinated biphenyls (PCBs) are highly toxic recalcitrant compounds. Brazilian government estimates 100,000 tons of equipments containing PCBs were commercialized in Brazil and must be properly destroyed until 2025. In the present work, anaerobic biomass from an UASB reactor treating poultry wastewater has been used as inoculum in batch reactors undergoing fermentative-methanogenic conditions in the presence of six PCBs congeners (PCB 10, 28, 52, 138, 153 e 180). Anaerobic batch reactors (groups C, F and E) were inoculated with 10% (w/v) of biomass under N2 flow (100%) in Angelidaki medium containing ethanol (460 mgL-1), sodium formate (680 mgL-1), polyurethane foam at 12 mg mL-1 (group F) and 0.7 mg mL-1 of an analytical standard of PCBs. Control reactors (A, B and G) did not receive PCBs congeners, and biomass added in reactors of group E (abiotic control) received a heat treatment (121°C – 1 hour, three times) before been inoculated. Reactors were incubated at 30°C, 150 rpm for 60 days. Concentration of PCBs congeners and methane production were monitored throughout the assay. The precise identification of the six congeners was carried out by GC-MS. Change in microbial community during anaerobic digestion was analyzed using PCR-DGGE with specific primers for the domain Archaea and Bacteria. Ethanol and sodium formate favored metabolism of the anaerobic community, evidenced by increased methane production during the period analyzed in reactors supplemented with these co-substrates (B and G). The low yield of methane in reactors containing PCBs (C and F) suggests an inhibitory effect of these compounds over the methanogenic community. Reactors C presented a substantial reduction of the initial concentration of PCBs from 0.7 mg mL-1 to 0.2 mg mL-1 after 60 days of incubation. Characterization of the diversity of the microbial community (domain Bacteria) revealed that the reactors containing PCBs (C and F) were grouped with 86% similarity and only 55% similarity with the reactors without PCBs (A, B, G) indicating a selection of specific population in the presence of PCBs. For the domain Archaea the reactors containing PCBs (C and F) were grouped with 94% similarity and those without PCBs (A, B, G) were grouped 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 domain Bacteria.