Effect of inorganic ions on the solar detoxification of water polluted with pesticides

Abstract

The effect of eleven inorganic ions (Cl −, NO 3 −, SO 4 2−; PO 4 3−, Na +; NH 4 +, Ca 2+, Mg 2+, Zn 2+, Cu 2+ and Al 3+) on the photo-Fenton elimination of pesticides has been investigated. Phosphate and chloride have been demonstrated to have an inhibitory role; on the other hand, the reaction was accelerated in the presence of Cu 2+, most probably due to a copper-driven Fenton-like process. The solar photo-Fenton treatment of a mixture of four commercial pesticides was studied at pilot plant scale in the presence of chlorides. Samples with coincident dissolved organic carbon (DOC) showed similar chemical composition, which resulted in a comparable biocompatibility, however longer irradiation periods were needed to reach the desired mineralization when Cl − was present. It was demonstrated that the chemical process was able to improve significantly the biocompatibility of the effluent, as shown by the inhibition of respiration of activated sludge, BOD/COD ratio and Zahn–Wellens test.