Electrochemical Inactivation of Triclosan with Boron Doped Diamond Film Electrodes

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Abstract
This research investigated an electrochemical method for inactivating contaminated stockpiles of the biocidal agent, triclosan. The goal of the electrolysis was to produce products that were amenable to treatment in conventional activated sludge treatment systems. Triclosan oxidation in electrochemical cells with boron doped diamond (BDD) film anodes was investigated in aqueous solutions at a pH value of 12. Chronoamperometry experiments showed that direct oxidation of triclosan occurred at potentials below those for H2O, Cl-, or OH- oxidation. Measurable rates of triclosan oxidation began at potentials above 0.4 V with respect to the standard hydrogen electrode (SHE), while potentials of 0.5, 1.3, and 1.8 V were required to obtain measurable oxidation rates of H2O, Cl-, and OH-, respectively. At anode potentials below 2 V, the dominant electrode reaction involved direct triclosan oxidation, while indirect oxidation was the dominant pathway at higher potentials. However, cyclic voltammetry experiments showed that direct oxidation of triclosan resulted in the formation of a passivating film on the electrode that could only be removed by oxidation at potentials above 3 V. Direct triclosan oxidation showed a very weak potential dependence, suggesting that its oxidation was limited by chemical dependent factors rather than by an outer-sphere electron transfer reaction. Organic triclosan oxidation products consisted primarily of chlorinated acetic acids and chlorinated phenolic compounds. Although the byproducts of triclosan oxidation became increasingly less reactive with increasing electrolysis time, triclosan could be completely oxidized to CO2 at current densities above 2 mA/cm2. Microtox testing indicated that residual triclosan accounted for nearly all the toxicity in the treated water, despite the fact that chlorinated byproduct concentrations were significantly higher than those of triclosan itself.

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