Effect of ozone on algae as precursors for trihalomethane and haloacetic acid production.

The effect of ozone on the trihalomethane (THM) and haloacetic acid (HAA) formation of two algae species was investigated. Scenedesmus quadricauda (green alga) and Cyclotella sp. (diatom) were cultured under controlled conditions and harvested in the log or late log growth phase. Experiments examined the formation of disinfection byproducts (DBPs) from the algal suspensions with and without preozonation. Preozonation with 1 mg/L increased chloroform formation from Scenedesmus by 17-44%. For Cyclotella, chloroform production increased by 5-26% with 1 mg/L ozone and by 39-109% with 3 mg/L ozone. Chlorinated HAA yields were not significantly increased after 1 mg/L ozone but increased by 38-76% for Cyclotella after 3 mg/L ozone. As compared to other sources of organic matter, algae under bloom conditions may contribute significantly to the DBP precursor pool. However, the majority of the DBP precursors (70%) were attributable to the cellular material, and thus removal of algae cells from a drinking water supply priorto oxidation will substantially reduce algal precursor concentrations.