[Microbial reductive dechlorination of TCE with nano iron serving as electron donor]

A trichloroethylene (TCE) dechlorinating enrichment (Dehalococcoides spp.), which was isolated from soil of chlorinated ethene contaminated site, was used to investigate whether nano-scale zero valent iron (NZVI) could serve as electron donor for this consortium via cathodic H2 production during anaerobic corrosion. The results show that in the presence of methanol serving as electron donor, dechlorinating culture of 25 fold dilution [(2.0 +/- 0.44) x 10(5) cell/mL] degraded 20 mg/L TCE completely in 96 h, which was accompanied by the production of 2.706 micromol ethene in 190 h. Methanol-free control caused partial degradation of TCE to primarily cis-DCE in 96 h, with only 0.159 micromol ethene produced in 190 h. This indicates bacteria cannot reduce TCE to ethene without electron donor. But when 4 g/L NZVI was added as sole electron donor, this dechlorinating culture degraded 20 mg/L TCE into ethene and vinyl chloride (VC) in 131 h at a speed higher than that by NZVI alone. Compared to 2.706 micromol ethene produced by Dehalococcoides spp. with methanol added as the electron donor, there was only 1.187 micromol ethene produced by bacteria with NZVI serving as the electron donor, which means NZVI has a potential toxicity on Dehalococcoides spp.. At the meantime, 0.109 micromol acetylene was produced in 190 h, which was relatively lower than 0.161 micromol produced by NZVI alone, indicating bacteria competed with NZVI under electron deficient condition. In conclusion, NZVI could serve as electron donor and support dechlorination activity for Dehalococcoides spp. which could enhance the application of NZVI and usage of dechlorinating culture as a polishing strategy in future ground water remediation.