Algae removal performance of UV-radiation-enhanced coagulation for two representative algal species

Algal blooms severely impact the ecological environment and human health, as well as drinking water supplies and treatment systems. This study investigated UV-radiation-enhanced aluminum (Al)-based coagulation for the removal of two representative algal species (Microcystis aeruginosa and Cyclotella sp.) which are responsible for most fresh water algal bloom in different seasons. The results demonstrated that the UV-Al process can enhance algae removal, and simultaneously control algal organic matter (AOM) release. Comparing with Microcystis aeruginosa, Cyclotella sp. was more sensitive to UV irradiation and its activity was severely inhibited by 240 s of UV irradiation; intracellular reactive oxygen species (ROS) increased sharply then decreased rapidly, and SEM images showed cell walls exhibited substantial compression. UV irradiation decreased the zeta potential, which might have contributed to algae removal. Approximately 93.5% of Microcystis aeruginosa cells and 91.4% of Cyclotella sp. cells were removed after 240 s of UV irradiation with 0.4 mmol/L Al. The MCs concentrations after Al coagulation were low (<100 ng/L). The DOC of Microcystis aeruginosa and Cyclotella sp. was also lower (1.2 and 1.6 mg/L, respectively) than the national standard level after UV-Al process. This study highlights the practical application of UV irradiation for enhancing algae removal and simultaneously controlling AOM release in water treatment plants, which is a simple and promising technology. This result also indicates that the water treatment parameters should be adjusted according to the algae species present in different seasons, especially for diatom which needs low UV irradiation and Al dosage.