Halonitromethanes formation in wastewater treatment plant effluents.

Halonitromethanes (HNMs) constitute one class of emerging disinfection by-products with high potential health risks. This study investigated the formation and occurrence of HNMs under different disinfection scenarios and the presence of their precursors in municipal wastewater treatment plant (WWTPs) effluents. Formation potential tests performed on WWTP effluents revealed that HNM formation occurred in the order of ozonation-chlorination >> ozonation-chloramination > chlorination > chloramination. Ozonation alone did not produce any HNM. Municipal WWTP effluents contained some reactive HNM precursors, possibly the by-products of biological treatment processes and/or some moiety of industry or household origin. No effects of nitrate on the formation of HNMs were observed in this study, and nitrification in WWTPs appears to remove appreciable portion of HNM precursors, especially those reactive to chlorine. UV disinfection using low pressure lamps in municipal WWTPs had negligible impact on HNM formation potential. HNM concentrations in the effluents of selected WWTPs were either non-detectable or less than minimum reporting level, except for one WWTP that gave trichloronitromethane concentrations in the range of 0.9-1.5 microg L(-1). No HNMs were observed in the effluents disinfected with UV radiation. Therefore, it appears the typical wastewater disinfection processes involving chlorination or UV treatment in WWTPs do not produce significant amounts of HNMs.

Halonitromethane formation potentials in drinking waters.

Halonitromethanes (HNMs) are highly cyto- and genotoxic nitrogenous disinfection by-products (DBPs) that have been detected in some water distribution systems. In this study, a systematic investigation was conducted to examine the formation potential of HNMs in drinking waters under different oxidation conditions. Formation potential tests of samples obtained from various drinking water sources showed that ozonation-chlorination produced the highest HNM yields followed by in the order of chlorination, ozonation-chloramination, and chloramination. Similar or higher HNM yields were observed in the treated waters (i.e., after conventional water treatment) than in the raw waters, indicating that hydrophilic natural organic matter (NOM) components that are not effectively removed by conventional treatment processes are likely the main precursors of HNMs. This was further confirmed by examining HNM formation potentials of NOM fractions obtained with resin fractionation. Hydrophilic NOM fractions (HPI) showed significantly higher HNM yields than hydrophobic (HPO) and transphilic (TPH) fractions. The correlation analysis of HNM formation potentials during ozonation-chlorination with various water quality parameters showed the best correlation between the HNM yields and the ratio of dissolved organic carbon to dissolved organic nitrogen concentrations in the water samples tested.