The impact of preozonation and biodegradation on disinfection by-product formation

Abstract

Ozonation and biological treatment were investigated as a means of controlling the formation of disinfection by-products (DBPs) as measured by total organic halides (TOX) and purgeable organic halides (POX). Organic matter from a groundwater and a river water source were used and chlorine or chloramines were used as the final disinfectant. The amount formed, the formation kinetics and the impact of disinfectant dose were investigated. Chloramination produced significantly less organic halides, especially POX, compared to chlorination. With both disinfectants and for both sources of organic matter, the nonpurgeable organic halide formation rate was found to be much faster than that of POX. Preozonation decreased the amount of organic halide formation by 10–40% upon subsequent chlorination. With chloramines preozonation had no significant impact on the extent of the reaction. Preozonation followed by biotreatment resulted in the least amount of organic halide formation with a reduction of 50–80% when chlorine was used, and greater than 90% with chloramines. In all cases examined, the ratio of organic halides to dissolved organic carbon decreased after biological treatment indicating a selectivity for the potential reactive sites. Based on the results of this bench scale study, pilot studies of biological treatment for DBP control are being made.