Effect of ozone treatment on cultures of Nannochloropsis oculata, Isochrysis galbana, and Chaetoceros gracilis

This research evaluated ozone treatment of three unicellular algal species commonly used in the culture of marine larvae. Isochrysis galbana and Nanno chloropsis oculata were found to be resistant to total residual oxidants (T RO); whereas, Chaetoceros gracilis was relatively sensitive to TRO. Isochry sis galbana remained in log-phase growth after treatment with 0.05 mg/L to 0.50 mg/L TRO, and N. oculata exhibited strong growth after being exposed t o TRO levels up to 0.67 mg/L. Only TRO levels of 0.92 mg/L and 0.90 mg/L re duced cell counts of N. oculata and I. galbana, respectively. Furthermore, algal cultures having higher concentrations at the time of ozone treatment may respond more favorably to the treatment. Initially, C. gracilis was red uced in cell count at TRO levels above 0.06 mg/L, but log-phase growth was resumed 2 d after exposure to TRO levels as high as 0.31 mg/L. It is conclu ded that I. galbana and N. oculata can be successfully treated with ozone i n the mass production stages without hampering the timely production of con centrated cultures. Although C. gracilis was found to be relatively sensiti ve, ozone treatment of starter cultures can be performed routinely with thi s species. We have demonstrated that ozone treatment of algal cultures is a feasible technique, but studies need to be conducted on ozone treatment of other species of unicellular algae and on ozone treatment of varying conce ntrations of algae in order to enhance the applications of this technique. Also, in order to determine the extent of disinfection of algal cultures, b acterial and viral composition of the cultures should be evaluated in futur e studies.