EFFECT OF PRE-OZONATION ON ORGANICS REMOVAL BY IN-LINE DIRECT-FILTRATION

A pilot-scale study of the effects of pre-ozonation on the performance of in-line direct filtration was carried out. Performance measures in cluded filtered water turbidity, unit filter run volumes, and organics in filtered waters: DOC, UV254, AOC and DBPs. Continuous operation of four dual media GAC/sand filters with and without pre-ozonation and c hlorinated backwash and a dual media anthracite/sand filter were compa red to full-scale performance. Pre-ozonation frequently results in lon ger filter runs, causes a two-fold increase in raw water AOC and has l ittle effect on raw water DOC. GAC/sand filters consistently reduced t he AOC in the ozone train to levels below that of the full-scale plant and also provided 25 % lower DOC levels as compared to anthracite/san d filters. The effect of ozone and filtration on chlorinated DBPs foll owed overall DOC removal while DBPs created by ozonation followed AOC removal trends.