Trihalomethane, chlorite and bromate formation in drinking water oxidation of Italian surface waters

Recent regulations on drinking water have introduced very restrictive limits for oxidation/disinfection by-products (DBPs), particularly total trihalomethane concentrations (TTHMs), chlorite and bromate. Consequently many utilities are closely optimizing their disinfection practices in order to meet the regulation standards. This study evaluates DBPs formation and suggests some applicability criteria for chlorine, chlorine dioxide and ozone for different waters.

Different oxidation batch tests with chlorine, chlorine dioxide and ozone were performed on some raw water samples coming from ten representative sources in Italy: seven artificial lakes and three rivers. TTHMs, chlorite and bromate increase with increasing chlorine, chlorine dioxide and ozone dose, respectively. The Italian standard for TTHMs (30 µg l⁻¹) is fulfilled by 50% of the waters for chlorine doses of 1.1–1.2 mg l⁻¹. Because chlorite concentration is about 60% of chlorine dioxide dose, the Italian standard for chlorite (200 µg l⁻¹) is fulfilled for chlorine dioxide doses lower than 0.3–0.4 mg l⁻¹. The maximum concentration of 10 µg l⁻¹ for bromate can be respected only for waters with very low bromide concentration (lower than 20 µg l⁻¹) (von Gunten 2003).