Electrochemical conversion of micropollutants in gray water.

Electrochemical conversion of micropollutants in real gray water effluent was studied for the first time. Six compounds that are frequently found in personal care and household products, namely methylparaben, propylparaben, bisphenol A, triclosan, galaxolide, and 4- methylbenzilidene camphor (4-MBC), were analyzed in the effluent of the aerobic gray water treatment system in full operation. The effluent was used for lab-scale experiments with an electrochemical cell operated in batch mode. Three different anodes and five different cathodes have been tested. Among the anodes, Ru/Ir mixed metal oxide showed the best performance. Ag and Pt cathodes worked slightly better than Ti and mixed metal oxide cathodes. The compounds that contain a phenolic ring (parabens, bisphenol A, and triclosan) were completely transformed on this anode at a specific electric charge Q = 0.03 Ah/L. The compounds, which contain a benzene ring and multiple side methyl methyl groups (galaxolide, 4-MBC) required high energy input (Q ≤ 0.6 Ah/L) for transformation. Concentrations of adsorbable organohalogens (AOX) in the gray water effluent increased significantly upon treatment for all electrode combinations tested. Oxidation of gray water on mixed metal oxide anodes could not be recommended as a post-treatment step for gray water treatment according to the results of this study. Possible solutions to overcome disadvantages revealed within this study are proposed.