The Enhanced Reductive Dechlorination Of Volatile Chlorinated Hydrocarbons In Biocathode

Recently, the Bioelectrochemical systems(BESs) has been environmantal friendly applied for removing the hardly degradable pollutants, such as chlorinated organic compounds, azo dyes, chloramphenicol and so on. Trichloroethylene(TCE) and tetrachloroethylene(PCE) are typical volatile chlorinated aliphatics hydrocarbons(VCHs),which can be accumulated and persiste in the environment continuously resulting in serious ecology burdens and hunman health problems. In order to solve these problems, the article has inoculated urban activated sludge into dual chamber electrochemical cathode systems and cultured abundant specific bacteria on cathode biofilm, which finally strengthen the dechlorination of TCE and PCE. Through Designing different cathode potentials’ conditions and different carbon sources’ conditions on biological cathode systems, the author investigated reductive degradation rules of TCE and PCE, analyzed the bacteria’ and genus’ distribution and abundance on cathode biofilm, and finally explored the effective factors for VCHs’ dechlrination.The study has indicated that cathode biofilm applied with-0.26 V potential(vs.SHE) achieved the highest degradation effect of TCE and PCE compared with others cathode potentials, the corresponding first-order kinetic constants of TCE and PCE degradation are 0.23 and 0.16 seperately, improved to 41 times and 45 times compared with open circuit biological cathode. In electrochemical system, TCE and PCE can be hardly degradated. The evidence proved the biodegradability and high efficiency of biological cathode. PCE first generates intermediate TCE, and finally PCE and TCE dechlorate to Cis-1,2-DCE. With Na HCO3 and acetate switching tests, it is confirmed that the cathde can be used as a sole source of electron donnors, and finally TCE/PCE act as terminal electron acceptor via microo rganism’ transportation.Comparing biological cathode system with different carbon sources, the magnitude relationship between PCE degradation rate and carbon sources is glucose>acetate>Na HCO3, the corresponding degradation rate of PCE is 99.6%, 77.7%, 29.5% when applied with-0.26 V cathode potential at 24 h. The study indicated that organic carbon source provides enough energy supply, enhances microorganisms extracellular electron transfer rate, and promotes reductive degradation capacity.During decomposition,The predominant bacteria in biocathode community consisted of Lactococcus, Bacillus, Geobacter and Pseudomonas. Lactococcus is the main electric related bacteria, while Geobacter and Bacillus are both electric related and reductive dechlorination related. Of all the biocathode samples, the abundance of electro-active bacteria is richer than the abundance of dechlorination bacteria, speculating that electric related bacterias produce electron for reductive dechlorinating microorganism and electro-active bacteria play a leading role in the process. This study provides ideas and methods on bio-electrochemical system remeding chlorinated hydrocarbons contaminations in-situ.