The control of disinfection by-product formation by ozonation and biotreatment

The use of disinfection to provide a microbially safe drinking water leads to the formation of disinfection by-products (DBPs), some of which are of health concern. The draft Disinfectant-Disinfection By-Product Rule proposes decreasing the maximum contaminant level (MCL) for trihalomethanes (THMs) from 0.1 to 0.08 mg/L and to set an MCL for the sum of five haloacetic acids (HAAs) at 0.06 mg/L, and an MCL for bromate, an ozonation DBP, at 0.01 mg/L.;Ozone dose and bromide concentrations affect the formation of ozonation DBPs and halogenated DBPs after chlorination. Ozone also increases the biodegradability of organic matter. Biological treatment results in a decrease in the organic matter, which minimizes DBP formation, ozonation DBPs, and control the substrate that would enhance microbial regrowth in the distribution system.;The overall objective of this research was to understand the effect of ozonation and biological treatment on the formation and control of ozone DBPs and chlorination DBPs. Two sources of organic matter were examined: Ohio River water and isolated humic substances from a German groundwater.;Increasing ozone dose increased the yield of organic and inorganic DBPs. Increases in ozone dose and bromide concentrations increased bromate formation. Ozonation resulted in DBP precursor oxidation and affected the relative yields of chloro- and bromo-substituted DBPs. Organic ozonation DBPs, like low molecular weight aldehydes, were found to increase with increasing ozone dose. Ozonation affected the nature and reactivity of organic matter. The dissolved organic carbon (DOC) concentration was not affected, but the UV absorbing components were significantly decreased.;Biological filtration was found to decrease the organic matter in both Ohio River water and the groundwater humic substances. The aldehydes formed by ozonation were found to be very biodegradable. Biological oxidation of the precursors resulted in significant decreases in chlorine demand and in halogenated DBP formation.;Thus, preozonation and biological treatment before final chlorination may be an effective means of controlling DBPs and producing biologically stable water.