Degradation of aquatic humic material by ultraviolet light

Abstract

Natural humic water was treated with ultraviolet (UV) light and UV + hydrogen peroxide ( UV H 2 O 2 . The effects on the dissolved organic carbon content (DOC), the UV-absorbance at 254 nm (UV-abs.), the molecular size distribution, pH, and mutagenic activity were monitored, and the identity and concentrations of the most abundant gas chromatographable organic degradation products were determined. The DOC content and the UV-abs. of the water decreased substantially during treatment with UV H 2 O 2 . The decreases were dependent on the time of irradiation (UV dose) as well as on the H 2O 2 dose applied. The humus macromolecules were degraded to smaller fragments during irradiation. At higher UV doses, however, part of the dissolved organic matter (DOM) was found to precipitate, probably as a result of polymerization. Oxalic acid, acetic acid, malonic acid, and n-butanoic acid were the most abundant degradation products detected. These acids were found to account for up to 20% and 80% of the DOM in UV- and UV H 2 O 2- treated waters, respectively. No mutagenic activity was generated by the UV irradiation or the UV H 2 O 2 treatment. It is further concluded that the substantial mutagenic activity formed during chlorination of humic waters cannot be decreased by using UV irradiation as a pretreatment step.