Electrochemical degradation reductive dechlorination

In activated sludge, 80.6% degraded after a 47-h time period (Pal et al., 1980). Chemical/Physical. Zhang and Rusling (1993) evaluated the bicontinuous microemulsion of surfactant/oil/water as a medium for the dechlorination of polychlorinated biphenyls by electrochemical catalytic reduction. The microemulsion (20 mL) contained didodecyldi-methylammonium bromide, dodecane, and water at 21, 57, and 22 wt %, respectively. The catalyst used was zinc phthalocyanine (2.5 nM). When PCB-1221 (72 mg), the emulsion and catalyst were subjected to a current of mA/cm on 11.2 cm lead electrode for 10 h, a dechlorination yield of 99% was achieved. Reaction products included a monochlorobiphenyl (0.9 mg), biphenyl, and reduced alkylbenzene derivatives. 

Direct electrolytic dechlorination of 9-chloroanthracene at a mercury electrode occurs at about -1.65 V (see) in a layer of adsorbed cetyltrimethylammonium bromide on the electrode surface233. Similarly, electrochemical degradation of trichloroethylene in acetonitrile resulted in quantitative conversion to chloroacetylene, which was reduced further to acetylene at a more negative reduction potential (-2.8 V) in 96% yield234. Reductive destruction of 1,3,5-trichlorobenzene in the cathode compartment could be observed235. Electrochemical methods presumably can be used for decontamination of chemical warfare agents such as mustard derivatives as an alternative to the chemical methods such as base-catalyzed dehydrohalogenation236. 

Figure 19.9. Electrochemically enhanced microbial reductive dechlorination of perchloro-ethene (PCE) and oxidative degradation of vinyl chloride (VC). Stimulated biodegradation is indicated by a chloride increase during electrochemical treatment.

Electrochemical degradation utilizes the high redox potential at an anode and the low redox potential at a cathode to oxidize or reduce contaminants. Most applications of electrochemical degradation involved cathodic reduction or anodic oxidation of chlorinated organic contaminants. Schmal et al, (55) showed that pentachlorophenol was sequentially dechlorinated (i.e. reduced) at a carbon fiber cathode. Experiments conducted by Cheng et al. (34) indicated that the composition of the cathode was critical for cathodic reduction of 4-... 

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