(514c) Reaction Kinetics for Microcystin -LR Degradation By Ozonation in a Basic Medium

Microcystin-LR (MC-LR) is a cyclic heptapeptide released by some cyanobacteria during algal blooms in eutrophic waters that can bio-accumulate in fish and be transferred to higher organisms. Awareness of the fatal effect of MC-LR in humans began in 1996, when thirty eight patients undergoing dialysis at a renal diseases institute in Brazil died of acute hepatic failure as a result of contamination of the water used for hemodialysis. The cause of the deaths was a mystery initially, until it was reported that the water used for hemodialysis at the institute was contaminated with the toxin MC-LR. In 1988, The World Health Organization set the provisional concentration limit of MC-LR for potable water at 1μg/L. Generally, conventional water treatment methods, such as precipitation, coagulation, flocculation, sand filtration can be effective for removal of intracellular toxins, as intact cells are physically removed, but these processes are ineffective for extracellular toxins released when algal cells lyse. Ozonation can effectively destroy extracellular MC-LR from water at a high pH but it is necessary to predict the extent of degradation after a specified duration of treatment. Studies have shown that pH largely determines the rate of most ozonation reactions. In this study, the rate constants, k₀₃ and k_OH, values will be determined. The probable degradation pathway of MC-LR will be examined using liquid chromatography coupled with mass spectrometry. Membrane filtration using hydrophobic membranes have also been shown to be effective for the removal of MC-LR at high pH, but problems that may arise from this choice of treatment include accumulation of the toxin on the surface of the membrane and cost for disposal of the contaminated membranes. The combination of membrane filtration and ozonation will be further examined to create a treatment process that can be effectively implemented.