Degradation of anatoxin-a by UV-C LED and UV-C LED/H₂O₂ advanced oxidation processes

In the present study UV-C LED photolysis and UV-C LED/H₂O₂ treatment processes were investigated for the degradation of anatoxin-a. The initial anatoxin-a concentration in the aqueous solution was kept at 1μM. During the treatment by UV-C LED, 50% degradation of anatoxin-a was achieved at UV fluence 4032J/m². The optimum reaction conditions were: λ=260nm, initial pH=6.4, temperature=24°C and distance from water surface=5mm. The degradation of anatoxin-a followed the pseudo first order kinetics (k=2×10^-4m²/J). The degradation of anatoxin-a was reduced to 28% in presence of carbonate ions (50mg/L) and at higher concentrations of carbonate ions the degradation was completely inhibited. The concentration of anatoxin-a was significantly reduced (62%) in the presence of dissolved organic matter (DOC) depicting the photosensitization effect of humic acid on the direct photolysis of anatoxin-a. The pseudo first order kinetic constant k at 0.03mg/L concentration of DOC was found to be 3×10^-4m²/J. It was also observed that UV-C/H₂O₂ process enhanced the oxidation rate of anatoxin-a by 4.5 times in comparison to direct photolysis by UV-C LED leading to 97% degradation of anatoxin-a. In Pitkäjäärvi lake water, 96% removal of anatoxin-a was achieved by photolysis using UV-C LED and 79% removal was achieved with UV-C/H₂O₂ process. The acute toxicity tests were conducted using Vibrio fischeri. The results indicated a decrease in the acute toxicity of the treated samples, both after the UV-C LED photolysis and UV-C/H₂O₂ process.