Algicidal and chemical effect of u.v.-radiation of water containing humic substances

Abstract

u.v.-Radiation is increasingly used to disinfect drinking water. In addition to an effect on microorganisms, both artificial and natural u.v.-radiation transforms chemicals in water. The effect of u.v. on humic substances (HS) in water acquires increasing relevance because of the anticipated increase in global radiation, as a consequence of the reduced O 3 content in the stratosphere. We conducted experiments with typical surface water with HS. The results show that u.v.-radiation of humus water changes the chemical composition of water, including acidity and charge density and also inhibits the growth of the alga Selenastrum capricornutum. Inhibition increases with increased “u.v.-dose” from a mercury-lamp. The algicidal effect apparently lasts for several weeks. The observed action of u.v.-treated humus water may be explained by photon-initiated interactions of HS and other chemicals in the water which results in the formation of oxidizing reagents such as OH radicals; these inturn oxidize organic materials by hydrogen abstraction.