Inactivation and degradation of Microcystis aeruginosa by UV-C irradiation

In this study, the mechanisms and factors affecting the inactivation and degradation efficiency during UV-C irradiation of Microcystis aeruginosa, a harmful cyanobacteria strain, were investigated. Under different experimental conditions, the concentrations of three bioactivity materials, including protein, phycocyanin and chl-a, were measured, and fluorescence regional integration (FRI) was used to quantify the results of excitation emission matrix fluorescence spectroscopy. Furthermore, any alternation occurring in cell ultrastructure was determined using transmission electron microscopy. Results showed that UV-C could effectively damage the M. aeruginosa cells, most likely via a 3-step procedure, including impairment of photosynthesis system, decomposition of cytoplasmic inclusions, and cell cytoclasis. Comparison of FRI values and biochemical parameters in the presence of H₂O₂ and HCO3- under the UV-C irradiation revealed the importance of photolysis and reactive oxygen species (ROS)-induced oxidation. UV-C/H₂O₂ treatment was more efficient due to enhanced ROS generation, while adding HCO3- inhibited the ROS-induced oxidation, resulting in suppression on reaction. Humic acid and NO3-, two common water solutes, somewhat inhibited the inactivation and degradation processes, due to the ROS scavenging and " inner filter" effect.