Effects of Pre-Ozonation of High Humic Content Waters on Direct Filtration in a Pilot Plant

Abstract

Direct filtration and the effects of pre-ozonation on direct filtration performance were evaluated and compared with conventional water treatment performance in a pilot plant study. Performance measures including coagulant demand, turbidity, colour, total organic carbon, head loss development, filter run time, back wash water consumption, filtration solids volume and iron and manganese were examined for a water source with low turbidity and high organic matter content. The optimal coagulant dosage established for in-line direct filtration was much lower than that required for conventional treatment of the same raw water. Direct filtration preceded by ozonation achieved similar, or substantially higher, turbidity removal efficiencies with a significantly lower alum coagulant dosage. Pre-ozonation was effective in lowering turbidity, colour, head loss development and iron and manganese levels but was not significant in removing TOC. Pre-ozonation increased filter run time by about 7% when compared with the case of no ozonation treatment. The back wash consumption was 5% of total water produced and solids volume produced by coagulation and direct filtration alone was 8% of the back wash water used. There were no significant differences for the latter two parameters by pre-ozonation treatment.