Effect of temperature on chlorine treatment for elimination of freshwater phytoplankton in ballast water: bench scale test

Chlorine efficacy as a biocide for ballast water treatment was investigated under warm-cold temperatures, across winter and summer seasons. Freshwater phytoplankton samples were collected and acclimated under in situ environmental conditions ranging from 2-22 °C. Samples were exposed to seven chlorine treatments (from 0.02 to 5.0 ppm), in addition to a control (0.0 ppm). Free chlorine concentrations, phytoplankton abundance and photosynthetic efficiency were measured up to 48 h following treatment. After 4 h of treatment at concentrations less than 0.2 ppm, phytoplankton densities were reduced more than 50 % without cell resurgence. Similar reduction was recorded immediately after exposure when chlorine concentrations were higher than 3 ppm. After 8 h, free chlorine neared 0.0 ppm for initial chlorine concentrations below 1.2 ppm irrespective of temperature regime. Winter phytoplankton exhibited slightly lower mortality to chlorine exposure regardless of the temperature although they also exhibited lower photosynthetic efficiency. Despite a general absence of significant effect of temperature on the chlorine decay, our results suggest that higher doses of chlorine or longer exposure times may be required during winter to achieve full treatment effect. Tests at large scales are needed to further confirm these findings.The accepted manuscript in pdf format is listed with the files at the bottom of this page. The presentation of the authors' names and (or) special characters in the title of the manuscript may differ slightly between what is listed on this page and what is listed in the pdf file of the accepted manuscript; that in the pdf file of the accepted manuscript is what was submitted by the author