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

• UV-C LEDs were used for the photolysis of anatoxin-a.
• Degradation of anatoxin-a was significantly enhanced on the addition of H2O2.
• Toxicity of the treated water was reduced in comparison to untreated water.
• Treatment process was effective in degrading anatoxin-a in lake water sample.

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 1 μM. During the treatment by UV-C LED, 50% degradation of anatoxin-a was achieved at UV fluence 4032 J/m2. The optimum reaction conditions were: λ = 260 nm, initial pH = 6.4, temperature = 24 °C and distance from water surface = 5 mm. The degradation of anatoxin-a followed the pseudo first order kinetics (k = 2 × 10−4 m2/J). The degradation of anatoxin-a was reduced to 28% in presence of carbonate ions (50 mg/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 0.03 mg/L concentration of DOC was found to be 3 × 10−4 m2/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.