Characteristics of Natural Organic Matter and Formation of Chlorinated Disinfection By-Products from Two Source Waters that Respond Differently to Ozonation

Abstract

This study investigated the characteristics of natural organic matter (NOM) in two different raw surface water sources that respond differently to ozonation: one for which ozonation decreases the disinfection by-product (DBP) formation potentials (i.e., Capilano Reservoir, Vancouver, Canada), and one for which ozonation does not (i.e., South Thompson River, Kamloops, Canada); and evaluated the effect of ozonation on these characteristics and on the DBP formation potential of the different size and polar fractions of the NOM. Although the South Thompson River and the Capilano Reservoir waters had relatively similar total organic carbon concentrations, the characteristics of the NOM (e.g., size and polar distribution, specific UV absorption), in these water sources differed significantly. In general, no clear and consistent trend was observed with respect to the tendency of different size and polar fractions of NOM to generate DBPs. Nonetheless, the results from the present study suggest that hydrophobic NOM has a higher tendency to form DBPs. In addition, when considering individual size and polar fractions, specific UV absorption was a good overall indicator of the DBP formation potential for a given water source. The effect of ozonation on South Thompson River and Capilano Reservoir waters also differed significantly. For both source waters, ozonation appeared to have a greatest effect on the more hydrophilic fractions, generally increasing the DBP formation potential of the smaller more hydrophilic NOM, while generally decreasing that of the larger more hydrophilic NOM. The beneficial effect of ozonation on reducing haloacetic acid (HAA) formation potentials was due to a reduction in both the dichloroacetic acid (DCAA) and trichloroacetic acid (TCAA) formation potentials, while the negative effect of ozonation on increasing HAA formation potentials was due to an increase in the DCAA formation potentials. The results from the present study clearly indicate that the use of ozone as a primary disinfectant does not necessarily reduce the DBP formation potential of NOM in all water sources, further demonstrating the complex structure of NOM and the fact that NOM from different sources cannot be simply treated as one entity and compared with one another.