Impact of Change in Water Disinfection Method on Chlorination By-products Occurrence in Raba Water Distribution System in Krakow

The article discusses an impact of the sequence UV irradiation-chlorination on dynamics of by-product formation in water. UV irradiation of raw water can significantly influence the quantity and quality of naturally occurring organic matter (NOM). Consequently, this can affect NOM reactivity with the chlorine. Afew publications on this subject show that chlorine produced electrochemically in water treatment plants contains, beside sodium hypochlorite, other strong oxidants, such as ozone, chlorine dioxide and free radicals. Thus it can influence the quality of organic matter and its potential to form water chlorination by-products. As the subject has been studied only recently, most research has been laboratory based. This article presents results of the research conducted on the real facility (the Raba Water Treatment Plant), where the water disinfection method was recently modernized. Water chlorination was replaced with the sequence of low-pressure UV lamp and chlorine produced electrolytically. Water samples collected from six distribution network endings, before and after the modernization, were taken for studies. The following parameters were measured in the samples: trihalomethanes, haloacetic acids, haloacetonitriles, haloketones, chloropicrin and chloral hydrate. The result analysis showed that the water disinfection modernization caused decrease in the total concentration of analyzed chlorination by-products in Raba water distribution system. However, the increase was observed for chloral hydrate and nitrogen-containing disinfection by-products, especially haloacetonitriles.