BIODEGRADATION PROCESSES OF CHLORINATED ORGANICS UNDER ANAEROBIC ENVIRONMENTS

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Under anaerobic environments anaerobic bacteria reductively dechlorinated 2,4,6-trichlorophenol (2,4,6TCP) and decomposed it into 4-chlorophenol (4CP) and 2-chlorophenol (2CP) via 2,4-dichlorophenol (2,4DCP). About 95% of initial 2,4,6TCP were converted into 4CP and the remaining 5% were into 2CP. Although 2CP was further dechlorinated and converted into phenol, 4CP was not degraded and accumulated in the reactor.By investigating the involvement of methane producing bacteria (MPB) and sulfate reducing bacteria (SRB) in the reductive dechlorination of 2,4,6TCP, it was made clear that the dechlorination of 2,4,6TCP into 4CP and 2CP was conducted by SRB but the further dechlorination of 2CP was done by MPB. The dechlorination activity of MPB, however, was affected by the sulfate reduction by SRB, and it was greatly decreased when 50mg/L sulfate were reduced into hydrogen sulfide (HィイD22ィエD2S) and completely ceased at 100mg/L sulfate.Additionally, studied was the relation between 2CP dechlorination and nitrate reduction (denitrification) in the presence of nitrate under anaerobic condition. When acetate is available as electron donor, 2CP was reductively dechlorinated and converted into phenol independent of the presence of nitrate. Also, when the MPB activity was inhibited by chloroform or BESA in the presence of nitrate, nitrate was reduced into nitrogen gas but 2CP was not decomposed at all. This means that MPB are primary bacteria associated with the 2CP dechlorination. On the other hand, when no electron donor is present, 2CP was not decomposed without nitrate but oxidatively degraded by coupling with nitrate reduction in the presence of nitrate. It was shown that 2CP could be degraded reductively in the presence of electron donor or oxidatively by coupling with nitrate reduction without electron donor.