2003 © American Water Works Association YAVICH ET AL | PEER-REVIEWED | 95:4 • JOURNAL AWWA | APRIL 2003 159 Use of Ozonation and FBT to control THM precursors This study evaluated ozonation in combination with biological fluidized-bed treatment (FBT) for control of trihalomethane (THM) precursors in drinking water. THM precursors were represented by several surrogate parameters, including total organic carbon, ultraviolet absorbance measured at 254 nm, humic substances, and THM formation potential. The study was conducted using a continuously operated ozonation–FBT system. No pretreatment was provided. In addition, biofiltration and bench-scale ozonation systems were used to compare the biodegradation efficiency of FBT with that of biofiltration and to investigate the effect of ozonation on biodegradation efficiency. The study showed that the combined ozonation–FBT process was effective in removing THM precursors and reducing turbidity in drinking water. Preliminary cost estimates indicate that the ozonation–FBT process may be a viable alternative to conventional coagulation processes that require additional steps, such as ozonation and biological activated carbon filtration for the control of disinfection by-products in drinking water. BY ALEX A. YAVICH AND SUSAN J. MASTEN he formation of disinfection by-products (DBPs) is a major concern of drinking water utilities. Trihalomethanes (THMs), the dominant DBP species formed during chlorination, have been identified as potential carcinogens in both toxicological and epidemiological studies (Black et al, 1996). Under Stage 1 of the Disinfectants/DBP Rule, the US Envi- ronmental Protection Agency (USEPA) reduced the THM maximum contaminant level in finished water from 100 to 80 μg/L (USEPA, 1998). The agency has pro- posed regulations to further limit levels of THMs and other DBPs (Arora et al, 1997; Pontius, 1995; USEPA, 1994). Nearly 70% of surface water utilities will be affected by these regulations (Black et al, 1996), and the consequences for small utilities are of particular concern. In compliance with the Safe Drinking Water Act amendments, USEPA is required to identify technologies that are technically and economically feasible for small systems serving up to 10,000 people (NRC, 1997). The addition of ozone prior to chlorination has been identified as an impor- tant step in the minimization of THM formation to meet current and future USEPA standards (Ozone News, 1997). These more-stringent water quality reg- ulations have resulted in an increase in the acceptance of ozone by US water providers (Urfer et al, 1997). Since the early 1980s, the number of US drinking water treatment plants employing ozone has risen rapidly from about 10 to approximately 300 (Ozone News, 1997). T