Fate of organics during treatment of water streams by active chlorine in chemical and electrochemical processes

Abstract In many cases, quality of water bodies is worsening due to the increased concentration of various organics. The chemical and electrochemical treatment of water containing organics by active chlorine species, largely used for disinfection purposes, may give rise to the abatement of organic matters and concurrently to the generation of toxic by-products. Hence, in this work we have systematically compared the ability of chemical and electrochemical chlorination for the treatment of waters contaminated by organics from the points of view of both their removal and the generation of chlorinated by-products. The analysis of many by-products, including various organic substances, such as chlorophenols, carboxylic acids and chloroacetic acids, was performed. Moreover, the production of inorganic by-products, such as chlorate and perchlorate, was analyzed. The electrochemical chlorination was performed at BDD and Ti/IrO 2 -Ta 2 O 5 anodes and Ni and Ag cathodes. It was found that chemical and electrochemical methods allow to remove completely the phenol, used as a model recalcitrant organic molecule, but that both of them give rise to the production of various potentially toxic by-products, comprising chlorophenols, carboxylic acids, chloroacetic acids, chlorate and perchlorate. The production of different by-products depended, for the chemical chlorination, on the concentration of NaClO and, for the electrochemical method, on the nature of both the anode and the cathode. Eventually, it was highlighted that the electrochemical treatment, if performed under suitable operative conditions, can give both a higher abatement of the total organic compounds and phenol and a lower production of toxic by-products with respect to chemical chlorination.