Dechlorination of trichloroethylene by immobilized autotrophic hydrogen-bacteria and zero-valent iron.

The efficiency of removing trichloroethylene (TCE) using co-immobilized zero-valent iron and autotrophic hydrogen-bacteria has been studied in this research. Laboratory results show that the combined physicochemical and biological system is much superior to either physicochemical or biological system alone in dechlorination of TCE. In addition to catalyzed hydrogenolysis reactions occurring between hydrogen gas and zero-valent iron particle surface, as well as autotrophic dechlorination of hydrogen-bacteria, the FeS produced by sulfate-reducing bacteria also contributes to the catalytic dechlorination mechanisms. In the presence of hydrogen gas, corrosion of iron powder is somewhat alleviated, thus extending the useful life of iron powder for treating pollution. The results of membrane feeding substrate bioreactor (MFSB) reveal that the TCE removal rate of the combined system is 3.5 times faster than the zero-valent iron method, and 5 times faster than the biological treatment method in removing TCE. The potential of using co-immobilized zero-valent iron and autotrophic hydrogen-bacteria to clean up sites contaminated by chlorinated hydrocarbons is demonstrated by the results presented in this paper.

Reductive dechlorination of trichloroethylene by combining autotrophic hydrogen-bacteria and zero-valent iron particles.

The objective of this study was to evaluate the dechlorination rate (from an initial concentration of 180 micromol l(-1)) and synergistic effect of combining commercial Fe(0) and autotrophic hydrogen-bacteria in the presence of hydrogen, during TCE degradation process. In the batch test, the treatment using Fe(0) in the presence of hydrogen (Fe(0)/H(2)), showed more effective dechlorination and less iron consumption than Fe(0) utilized only (Fe(0)/N(2)), meaning that catalytic degradation had promoted transformation of TCE, and the iron was protected by cathodic hydrogen. The combined use of Fe(0) and autotrophic hydrogen-bacteria was found to be more effective than did the individual exercise even though the hydrogen was insufficient during the batch test. By the analysis of XRPD, the crystal of FeS transformed by sulfate reducing bacteria (SRB) was detected on the surface of iron after the combined treatment. The synergistic impact was caused by FeS precipitates, which enhanced TCE degradation through catalytic dechlorination. Additionally, the dechlorination rate coefficient of the combined method in MFSB was 3.2-fold higher than that of iron particles individual use. Results from batch and MFSB experiments revealed that, the proposed combined method has the potential to become a cost-effective remediation technology for chlorinated-solvent contaminated site.

Reductive dechlorination of 2-chlorophenol in a hydrogenotrophic, gas-permeable, silicone membrane bioreactor.

A gas-permeable silicone membrane bioreactor was used to cultivate the biofilm under hydrogenotrophic condition for reductive dechlorination of 2-chlorophenol (2-CP). The anaerobic sludge obtained from a swine wastewater treatment plant was immobilized by polyvinyl alcohol (PVA) so as to form a biofilm on the surface of the silicone tube. After acclimating for about 4 months, the bioreactor showed a high dechlorinating performance. Under the condition of continuous feeding with 2-CP at 25 mg/l and the hydraulic retention time of 15 h, the 2-CP removal efficiency reached 92.8% (2-CP decay rate: 0.67 g/m(2)d of surface area of silicone tube). H(2) was used as electron donor for dechlorinating 2-CP, and produced the dechlorinating intermediate, phenol. Both nitrate and sulfate played important roles in inhibiting 2-CP dechlorination through different biological mechanisms. Nitrate can be easily utilized as an electron acceptor by the biofilm, while sulfate cannot. Results of this study demonstrated that nitrate competed with 2-CP as the electron acceptor, while sulfate retarded the activity of hydrogen-dechlorinating bacteria and thus inhibited the 2-CP dechlorination.