Photocatalytic degradation of cyanobacterial microcystin toxins in water

• Published in: Toxicon (Oxford) 1998-12, Vol.36 (12), p.1895-1901
• Main Authors: Shephard, G.S, Stockenström, S, De Villiers, D, Engelbrecht, W.J, Sydenham, E.W, Wessels, G.F.S
• Format: Article
• Language: English
• Subjects: Air. Soil. Water. Waste. Feeding; Animal, plant and microbial ecology; Applied ecology; Applied sciences; Bacterial Toxins - metabolism; Biological and medical sciences; Biotechnology; Catalysis; Cyanobacteria - physiology; Drinking water and swimming-pool water. Desalination; Ecotoxicology, biological effects of pollution; Environment and pollution; Environment. Living conditions; Exact sciences and technology; Freshwater; Fundamental and applied biological sciences. Psychology; In Vitro Techniques; Industrial applications and implications. Economical aspects; Light; Medical sciences; Microcystins; Miscellaneous; Oxidation-Reduction; Oxides - pharmacology; Oxygen - pharmacology; Peptides, Cyclic - metabolism; Peptides, Cyclic - radiation effects; Pollution; Public health. Hygiene; Public health. Hygiene-occupational medicine; Techniques; Time Factors; Titanium - pharmacology; Water Pollutants - metabolism; Water Purification - methods; Water treatment and pollution
• ISSN: 0041-0101; 1879-3150
• DOI: 10.1016/S0041-0101(98)00110-X

The microcystins are hepatotoxins produced by a number of cyanobacterial species (blue–green algae) in fresh water systems. The increasing eutrophication of natural waters has led to an increase in the incidence of algal blooms and the consequent increased risk of microcystin contamination of water resources. The removal of microcystins LR, YR and YA from contaminated water was investigated using an experimental laboratory-scale photocatalytic `falling film' reactor in which an oxygen purge, UV radiation and semiconductor titanium dioxide (TiO 2) catalyst were used to oxidatively decompose the microcystin pollutants. Preliminary studies, using algal extracts spiked into distilled water, indicated that the microcystins were rapidly decomposed in this reactor. The 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 TiO 2 catalyst (0–5 g/l), but only marginally influenced by a change in gas purge from oxygen to compressed air. The use of lake water, rather than distilled water, showed that this process is feasible in natural waters, although increased levels of catalyst (up to 5 g/l) were required to achieve comparable decomposition rates.