Preliminary Study Of Anaerobic Biodegradation For PCBs In Paddy Soil

Polychlorinated biphenyls (PCBs), one of the persistent organic pollutants. More and more attention in the field of environmental toxicology and ecology had been payed attention to PCBs because of the harm. In recent years, due to electrical and electronic waste dismantling caused serious soil pollution of PCBs which has aroused people’s high attention.In remediation technologies of the PCBs contaminated soil, bioremediationmeth-ods have application prospect extremely. In this study, PCBs polluted paddy soil which from a typical e-waste dismantling recycling site, Taizhou area,in zhejiang province, as the research object. Lab-scale experiments were conducted to investigate the effect of polychlorinated biphenyls (PCBs) reduction of Paddy soil under three wetness changing treatments. Dechlorination bacteria were enriched from the Paddy soil. Microbial community structure was discussed according to the degradation results and denaturing gradient gel electrophoresis (PCR-DGGE) results. Compare with the anaerobic dechlorination of PCBs by fresh and indigenous microorganisms in paddy soil, the dechlorination enrichment cultivation of microbial was added into anaerobic reaction of polychlorinated biphenyls(PCBs) system. In the same time, the application of enaturing gradient gel electrophoresis (PCR-DGGE) was uesd for microbial community structure. It was discussed according to the degradation results. The main results of this research are as follows:(1) Lab-scale experiments were conducted to investigate the effect of polychlrin-ated biphenyls (PCBs) reduction of Paddy soil under three wetness changing treatments. The results indicated that during the18weeks of three flooded-dry alter-nate processing cycles, the amount of PCBs removed during flooded-air-drying (F-D), flooded(F), and drying treatments(D) was47.4%,48.0%,51.2%respectively. Among all major PCB congeners, tetra-CBs that the removal efficiency was the highest was significantly removed. After the first cycle treatment, the concentration of tetra-CBs PCBs was reduced52.9%,53.8%,54.0%respectively. The drying treatments(D) was conducive to reduction of total PCBs and chlorinated homologue than those of flooded-air-drying and flooded treatments. In all, the reduction efficiency of PCBs followed the order of drying treatment(D)> flooded treatment(F)> flooded-air-drying treatment(F-D).(2) The cultivation of the microcosm method is used. PCBs contaminated soil was used as microorganism enrichment of the source in order to degrade commercial Aroclorl260PCBs mixture. After several transfers of anaerobic enrichment culture, the stability of the anaerobic degradation of PCBs microbial fluid was obtained. The quality of Aroclor1260, that is0.500,0.600,0.900mg, was added into Ⅰ, Ⅱ, Ⅲ generation enrichment culture sample. After150,90,30d’s training time respectively, The accumulate cutting quantity of Aroclor1260was0.347,0.201,0.514mg and the total reduction rate was69.4%,33.5%,57.1%. In the anaerobic phase, the quantity of tetra-and penta-CBs did not increase while the quantity of highly chlorinated congeners of hexa-, hepta-and octa-CBs dropped significantly.(3) In the anaerobic phase, the removal rate of two incubation of microbes sets was lower (39.6%) for Aroclor1260total concentration compared with paddy soil control group(52.6%), but the removal rate of Aroclor1260was faster. Among all major PCB congeners, the removal efficiency was hexa-> hepta-> penta-> octa-> tetra-CBs.(4) Clone and sequence of the specific band on the DGGE gel of Ⅰ, Ⅱ, Ⅲ generation enrichment culture sample and two incubation sets showed that most of the specific clone belongs to Proteobacteria and Firmicutes, we also found that many clones were highly similar with the sequences of microbes thatare related with organic compound degradation. Bacteria belong to this two phylum may play a very important role in the microbial ecosystem in PCBs contaminated soil, and also in the transformation and degradation of PCBs pollutants. PCBs has obvious selectivity of entrainment for the growth of microbial population.