Anatoxin-a degradation by Advanced Oxidation Processes: Vacuum-UV at 172 nm, photolysis using medium pressure UV and UV/H2O2

Two Advanced Oxidation Processes, namely vacuum-ultraviolet (VUV) photolysis at 172 nm and ultraviolet/hydrogen peroxide (UV/H2O2) were investigated for the degradation of anatoxin-a in aqueous solutions. Solutions of anatoxin-a-fumarate were treated with VUV light at 172 nm with a UV dose of 200 mJ/cm2, where fumaric acid served as a reference compound for a competition kinetics analysis. The second-order rate constant for the reaction between anatoxin-a and the hydroxyl radical was found to be (5.2 ± 0.3) × 109 M−1 s−1 and was independent of pH, temperature, and initial concentration of anatoxin-a. The direct photolysis of anatoxin-a using a medium pressure (MP) UV lamp was also investigated, in which case a UV dose of 1285 mJ/cm2 was required to degrade anatoxin-a by 88% and 50% at concentrations of 0.6 mg/L and 1.8 mg/L of toxin, respectively. Treatment of anatoxin-a with a low pressure (LP) UV lamp in the presence of 30 mg/L of H2O2 was examined, where it was found that more than 70% of toxin could be degraded at a UV dose of 200 mJ/cm2. The degradation arises from the oxidation of the toxin by hydroxyl radicals. The addition of H2O2 clearly enhanced the degradation of anatoxin-a, up to a concentration of 40 mg/L, after which addition of more H2O2 had little effect on the degradation kinetics of anatoxin-a. The effect of background constituents in the water on the degradation of anatoxin-a was also investigated using natural and synthetically produced model waters.