Photocatalytic degradation of microcystin-LR and anatoxin-a with presence of natural organic matter using UV-light emitting diodes/TiO2 process

Abstract

Cyanotoxins are released into water bodies when cyanobacterial blooms occur. Representative cyanotoxins are microcystin-LR (MC-LR), which is one of the most-frequently detected, and anatoxin-a (ANTX), threatening human health through the liver damage and nervous system, respectively. One of the advanced oxidation processes, UV/TiO2 process is effective for MC-LR degradation; however, applying conventional UV lamps is an ongoing issue owing to disadvantages, such as use of mercury and high energy consumption. To resolve these, this study aims to use light emitting diodes (LEDs), developed by the Lumens Co., combined with commercial TiO2 for the removal of two types of cyanotoxins, MC-LR and ANTX. With 0.05 g L−1 of TiO2, over 99.9 % of the MC-LR was degraded in 15 min. Under acidic conditions, MC-LR and TiO2 were converted into MC-LRH− and TiO2+, then, electrostatic attraction was generated between them. Therefore, the degradation rate constant (k) of MC-LR was higher under acidic conditions than neutral or basic conditions. The natural organic matter (NOM) served as a scavenger of OH, reducing the MC-LR degradation rate under UV-LED/TiO2 process. 35%–53.6% degradation of NOM due to the decrease in humic substances and building blocks, and the increase in low molecular weight neutrals and low molecular weight acids. The degradation efficiency of MC-LR was higher than that of ANTX, and both cyanotoxins were completely degraded within 15 min. The k of MC-LR and ANTX were similar but significantly reduced due to the NOM and alkalinity of the water collected from the Han River.