PHOTOCATALYTIC DEGRADATION OF CYANOBACTERIAL MICROCYSTIN TOXINS IN WATER

The microcystins are hepatotoxins produced by a number of cyanobacteri al species (blue-green algae) in fresh water systems. The increasing e utrophication of natural waters has led to an increase in the incidenc e of algal blooms and the consequent increased risk of microcystin con tamination of water resources, The removal of microcystins LR, YR and YA from contaminated water was investigated using an experimental labo ratory-scale photocatalytic 'falling film' reactor in which an oxygen purge, UV radiation and semiconductor titanium dioxide (TiO2) catalyst were used to oxidatively decompose the microcystin pollutants. Prelim inary studies, using algal extracts spiked into distilled water, indic ated that the microcystins were rapidly decomposed in this reactor. Th e decomposition followed first order reaction kinetics with half-lives of less than 5 min with the reactor operating in a closed-loop mode. Reaction rates were strongly dependent on the amount of TiO2 catalyst (0 5 g/l), but only marginally influenced by a change in gas pul-ge fr om oxygen to compressed air. The use of lake water, rather than distil led water, showed that this process is feasible in natural waters, alt hough increased levels of catalyst (up to 5 g/l) were required to achi eve comparable decomposition rates. (C) 1998 Elsevier Science Ltd. All rights reserved.