The performance of a new water treatment isothiazolone based biocide in recirculating cooling towers was evaluated through a field trial performed on two cooling towers at an Eastern United States steel mill. The biocide was tested alone on one tower and in combination with an oxidizing biocide (chlorine) on the other tower. The biocide was slug fed into each system two times per week for time periods of nine weeks and five weeks. Low use rates of the isothiazolone biocide were effective in preventing accumulation of a range of green algae and cyanobacteria on both cooling tower decks. Only when the biocide treatment was discontinued did an algal biomat form on both decks. In combination with chlorine (fed daily), the biocide maintained the aerobic bacterial plate counts measured from the cooling tower water at low levels throughout the trial. Performance of the new biocide was also compared with that of terbuthylazine in laboratory recirculating cooling tower studies.
Keywords: algaecide, biocide, biotilm, chlorophyll, cyanobacteria, diatoms, green algae, dichloro-n-octyl-isothiazolone, triazine