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 natural source waters containing natural organic matter produces biodegradable by-products such as organic acids, aldehydes, and ketoacids. These 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 insight into the amount of BDOC that is present. In drinking-water treatment, removal of BDOC can also reduce the formation potential of chlorination disinfection by-products such as trihalomethanes and haloacetic 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 DOC, a 90–100% reduction in aldehydes, and a 40–60% reduction in trihalomethane formation potential. No removal of bromate ion and dibromoacetic acid was observed. A positive correlation was obtained between BDOC and assimilable organic carbon; both parameters indicate a tendency to plateau at an applied ozone/DOC weight ratio of 2:1.