INACTIVATION AND REPAIR STUDY OF MICROCYSTIS VIRIDIS AND TETRASELMIS SUECICA FOLLOWING MP-UV IRRADIATION

Abstract

The transfer of invasive organisms by ballast-water discharge has become a growing concern. UV treatment has become an attractive ballast water treatment technology due to its effective, no harmful disinfection byproducts and easy to handle. Two robust algae strains Microcystis viridis and Tetraselmis suecica were selected as indicator organisms to determine efficiency of medium-pressure (MP) UV-treatment on ballast water. Inactivation and potential repair of these two algae strains following UV irradiation were assessed under various turbidity, TOC and salinity conditions. The range of UV doses was from 25 to 500 mJ/cm2. For M. viridis, results indicated that disinfection efficiency was negatively correlated with all of these three factors at low doses (25-200 mJ/cm2). Photoreactivation and dark repair were promoted at high TOC levels (6-15 mg/L) with about 6-25% higher repair levels compared with those in distilled water, whereas no significant impacts were identified for turbidity and salinity. For T. suecica, increased turbidity and TOC levels both hindered the effect of UV irradiation at high doses (200-500 mJ/cm2). Suppressive effect on photoreactivation and dark repair was consistently observed with changes of all of the three factors. In conclusion, generally these three factors result in repressive effects on UV disinfection efficiency, and TOC plays a more significant role in the levels of reactivation than the other two. The response of T. suecica to these three factors is more sensitive than M. viridis.