Pii: S0043-1354(97)00066-3

-This paper presents the results obtained from oxidation with 03 and O3/H20,_ of a residual water coming from the production of dicofoi and tetradifon pesticides, where chlorobenzenes, DDTs and its metabolites and other organochloride compounds were found. The oxidation processes were carried out using ozone (03) in basic medium (pH 9.4) at low dosage (0--1.5 g O~ g-L initial TOC) and in the presence of hydrogen peroxide (H_,O_,), with a 0,5 H_,O_,/O3 molar ratio. During the treatment, many compounds were removed (dichlorobenzophenone, tetradifon, chlorobenzene, trichlorobenzene) and their change in concentration at different ozonation contact time was monitored. Other compounds like DDE remained practically invariable. This study investigated the formation of first ozonation by-products (FOBPs) in the wastewater, specifically chlorophenols, by means of gas chromatography/mass spectrometry (GC/MS) and gas chromatography/electron capture detection (GC/ECD) analysis in terms of the amount of time the 03 has been in contact with the processed sample, o-Chlorophenol, p-chlorophenol, benzenemethanol, n-chlorohydroxibenzaldehyde, n-chlorobenzenemethanol, chlorobenzoic acid, etc., were formed during the treatment, due to the mechanism of fast and non-selective oxidation which ozone has through OH radicals, formed by the decomposition of the 03 molecule and accelerated by the presence of H_~O2 in water. ;f~. 1997 Elsevier Science Ltd Key words--organochloride compounds, pesticides, ozone, hydrogen peroxide, chlorobenzenes, dicofol, tetradifon, by-products, wastewater.