Evaluation of biocidal efficacy of Chloramine T trihydrate on planktonic and sessile bacteria in a model cooling tower water system

Abstract

A model cooling tower system was experimentally seeded with Legionella pneumophila and real industrial cooling tower (CT) water has been run at the closest to full-scale system operating conditions. The water/biofilm samples were taken from the model system monthly, and the effectiveness of the different concentrations of Chloramine T trihydrate biocide was evaluated in terms of its ability to control both planktonic/sessile microbial populations. Although Chloramine T is a recommended commercial formulation for disinfecting CTs, there is a lack of published data on the efficacy of this compound against both planktonic and sessile populations in the cooling tower. Biocide response in both sessile/planktonic bacteria counts varied according to months. Tested biocide concentrations provided the clean tower conditions by reducing the concentration of heterotrophic plate count (HPC) below <10(4) cfu mL(-1), L. pneumophila <10 cfu mL(-1) and of adenosine triphosphate (ATP) values <300 relative light units (RLU), after 1, 3 and 24 h of exposure, during a 6-month period. There were no statistically significant differences in efficacy between concentrations in terms of reduction in the number of bacteria, decrease in ATP value and viability. The results revealed that Chloramine T can effectively control biofouling in cooling systems according to the limit values of the successful control program.