Anaerobic Biological Dechlorination Of Polychorinated Biphenyls Coupling With Organic Matter Mineralization In Paddy Soil

Polychlorinated biphenyls (PCBs) are typical chlorinated organic pollutants, with the effects of carcinogenesis, teratogenesis and mutagenesis. It has become one of the priority control pollutants in Stockholm Convention on Persistent Organic Pollutants. Paddy soils are important accepters of PCBs. It has been found that many chlorinated organic pollutants, including high-chlorinated PCBs, can been naturally dechlorinated in paddy soils. The coupling process between the organic matter mineralization and the electron transfer in the dechlorination of PCBs in anaerobic paddy soils may be an important mechanism for the biological dechlorination of PCBs. Few researches have been focused on it. Further researches in coupling mechanism between the two processes should be carried out.In this study, the anaerobic biological dechlorination processes of Aroclor1260 and PCB116, PCB153 were stimulated in paddy soil slurries. The dechlorination performance in the natural and enhanced-mineralization condition were compared. Possible mechanisms of dechlorination of PCBs were speculated through variation characteristics of environmental factors, electron donors, and organic matters. The enrichment methods of the PCBs microbial dechlorination cultures were established. The coupling process between mineralization and dechlorination and the microbial structures were studied afterward. Main results of this study are as follows:(1) The dechlorination of Aroclorl260 in the anaerobic paddy soil slurry was verified in the 105 days of cultivation, and it mainly happened in Hexa-CBs and Hepta-CBs. The dechlorination microbes consumed the mineralization products, making pH increase and maintaine between 7.0 to 7.5, proper for the PCBs dechlorination. The consumption of mineralization products made the hydrogen partial pressure of the dechlorination treatment lower than that of the mineralization treatment. The dissolved organic carbon (DOC) in paddy soil slurries supply enough carbon sources and substrates for microbes inside. The consumption of more mineralization products in the dechlorination treatment also made characteristic peaks in the FT-IR spectra weakened more significantly.(2) The dechlorination of PCB116 and PCB153 in the anaerobic paddy soil slurry was verified in the 124 days of cultivation. The eliminating rates suggested that the enhanced organic matter condition had promoting function on both the two typical high-chlorinated PCB congeners. The input of extraneous source organic matters created the proper growing environment for the PCBs dechlorination microbes rapidly, and provided sufficient electron donors for the dechlorination continuously, which promted the dechlorination of PCBs. The concentration of DOC in the intensified dechlorination treatment was much higher than in the the natural dechlorination treatment, which provided more carbon sources and substrates for microbial growth. The promoted PCBs dechlorination had a larger promoting function on the mineralization process, making characteristic peaks in the FT-IR spectra of the intensified dechlorination treatment weakened much more significantly.(3) The enrichment methods of the PCBs microbial dechlorination cultures in the methane production condition were established. They were seperated from typical PCBs-polluted paddy soils and sediments. The growth of PCBs dechlorination becteria was induced with 2,6-BB and Aroclor1260. The cultures were transferred every 60 days. The eliminating rates of Aroclor1260 in culture-Ⅲ were higher than those in culture-II, suggesting the steady multiplication of microbes inside. The eliminating rates in the cultures with acetic acid as substrates were significantly higher than that with methanol as substrates. The methane-production activity in culture-Ⅲ steadily rose before falling. The stimulation and inhibition of methane-production caused by PCBs were more obvious in the cultures with acetic acid. There might be amounts of microbes belonging to Firmicutes and Chloroflexi related with PCBs dechlorination in the cultures. The genuses identified in cultures distributed widely. Dehalobacterium and Dehalobacter, which were directly related with dechlorination of chlorinated aromatic organic pollutants, were identified in the cultures.