Degradation of Microcystins from Microcystis aeruginosa by 185-nm UV Irradiation

Abstract

Microcystins (MCs) are toxic compounds produced by cyanobacteria in eutrophicate water environment and threaten the drinking water quality which often leads to serious sicknesses. MCs are difficult to be removed in water treatment when the concentration is very low but still harmful. When the MC concentration is low (μg/L), filter or some conventional chemical does not work, but UV can keep removing it to a lower level by some active groups. Herein, 185-nm UV irradiation in an immersing mode was used to remove MCs. Compared with the normal radiation mode, the immersing mode showed a remarkable degradation rate of MCs and a greater removal efficiency than the direct radiation. Radicals of ·H and ·OH were produced and strengthened the removal rate, after H2O absorbed 185 nm photons. Three important factors of pH value, initial concentration, and aeration capacity were investigated. When pH was less than 7, a better removal rate by ·H was found, due to the main path of MC degradation and Adda strain removal. When the initial concentration increased, the MC removal ratio decreased because HO· formed near the lamp surface and degraded MC molecules fast. When the aeration capacity improved, the MC removal ratio for the presence of air enforced reaction of dissolved oxygen with hydrated electrons and hydrogen atoms produced in the radiolysis.