OZONE ENHANCED REMOVAL OF NATURAL ORGANIC-MATTER FROM DRINKING-WATER SOURCES

The use of ozone as a pre-oxidant or intermediate oxidant in drinking- water treatment is becoming increasingly common. The ozonation of natu ral source waters containing natural organic matter produces biodegrad able by-products such as organic acids, aldehydes, and ketoacids. Thes e organic by-products serve as carbon source for bacteria, potentially causing regrowth problems in distribution systems. The measurement of biodegradable dissolved organic carbon (BDOC) provides quantitative i nsight into the amount of BDOC that is present. In drinking-water trea tment, removal of BDOC can also reduce the formation potential of chlo rination disinfection by-products such as trihalomethanes and haloacet ic acids. Removal of BDOC was optimal at an applied ozone:DOC ratio of 2:1 (mg/mg) for source waters containing DOC levels ranging from 3 to 6 mg/liter. The use of biotreatment resulted in a 40-50% decrease in DOG, a 90-100% reduction in aldehydes. and a 40-60% reduction in triha lomethane formation potential. No removal of bromate ion and dibromoac etic acid was observed. A positive correlation was obtained between BD OC and assimilable organic carbon; both parameters indicate a tendency to plateau at an applied ozone/DOC weight ratio of 2:1. (C) 1997 Else vier Science Ltd.