Effect of ozonation and UV irradiation with direct filtration on disinfection and disinfection by-product precursors in drinking water treatment

Pilot plant studies were conducted to evaluate the effect of pre-ozonation and ultraviolet irradiation on disinfection, disinfection by-product precur sors and water quality in a direct filtration water treatment system. Disin fection parameters including total coliforms, faecal coliforms and heterotr ophic plate count were investigated. Total organic carbon (TOC), trihalomet hanes (THMs), total organic halides (TOX), filtered water turbidity and col our were also evaluated. It was found that advanced pre-oxidation processes (ozonation and UV irradiation) significantly increase the level of disinfe ction of raw water. Removal of total trihalomethanes and total organic hali des precursors improved with ozonation and UV irradiation, compared to no o xidation treatment in direct filtration and/or in conventional water treatm ent. All coliforms (total and faecal) were completely destroyed by ozonatio n alone, and also with ozonation in conjunction with UV irradiation. Howeve r, the heterotrophic plate count was not significantly reduced at an ozone residual concentration of 0.1 mg 1(-1). This suggests that disinfection eff iciency is strongly influenced by competition reactions of organic and inor ganic compounds with ozone. Precursors of total trihalomethanes and total o rganic halides were reduced by 90% and 98%, respectively, with advanced pre -oxidation processes. Water quality parameters were improved by the pre-ozo nation and UV irradiation treatment system.