Evaluation of disinfectant efficacy against biofilm and suspended bacteria in a laboratory swimming pool model

Laboratory reactor systems designed to model specific environments enable researchers to explore environmental dynamics in a more controlled manner. This paper describes the design and operation of a reactor system built to model a swimming pool in the laboratory. The model included relevant engineering parameters such as filter loading and turn-overs per day. The water chemistry in the system's bulk water was balanced according to standard recommendations and the system was challenged with a bacterial load and synthetic bather insult, formulated to represent urine and perspiration. The laboratory model was then used to evaluate the efficacy of six chemical treatments against biofilm and planktonic bacteria. Results showed that the biofilm was able to accumulate on coupons and in the filter systems of reactors treated with either 1–3 mg/L free chlorine or 10 mg/L polyhexamethylene biguanide (PHMB). All the treatments tested resulted in at least a 4 log reduction in biofilm density when compared to the control, but shock treatments were the most effective at controlling biofilm accumulation. A once weekly shock dose of 10 mg/L free chlorine resulted in the greatest log reduction in biofilm density. The research demonstrated the importance of studying a biofilm in addition to the planktonic bacteria to assess the microbial dynamics that exist in a swimming pool model.