Inhibition of Algal Growth in Water Purification Process by UV Irradiation and Observation of Damage Level on Algal Cell

Rapid algal growth in the water purification process often causes problems such as turbidity leak. We investigated whether the application of ultraviolet (UV) radiation (254 nm) was effective in controlling algal growth. The objective of this study is to investigate the effect of UV irradiation on some isolated algae at a conventional UV dose (50-200 mJ cm-2) or a high UV dose (500-1000 mJ cm-2) . Three algae that obstruct water purification, that is, diatoms of Cyclotella, green algae of Dictyosphaerium, and flagellate of Cryptomonas, were selected and cultivated. As a result, it was observed that the cell concentration was reduced or maintained during one week after conventional UV dose irradiation in all algae. Dictyosphaerium exhibited higher resistance or faster growth compared with Cyclotella and Cryptomonas. Moreover, it was observed that algal cells exposed to a high UV dose were simultaneously broken, and the cell number was reduced in the cases of Cryptomonas and Dictyosphaerium. On the other hand, for Cyclotella, the cell content was changed but the shape of the cell was not. In conclusion, a conventional UV dose inhibited algal growth and a high UV dose injured cellular contents directly and induced cytolysis in some algal species.