Abstract

The aim of the study was to determine the effectiveness of in-situ-formed monochloramine for the control of Legionella growth in a real cooling tower system. The cooling tower utilizes an industrial water (makeup) made of by blending industrial raw water and decarbonated raw water. A generator device injecting in-situ-formed monochloramine into the cooling system was installed. The detection of Legionella, heterotrophic plate count (HPC - 22#xB0;C) and continuous monitoring of oxidation reduction potential (ORP) were carried out to check the efficacy of monochloramine. Water samples were monthly collected for 6 months from the makeup, two collecting basins and the blow-down. Monochloramine was injected at 4 mg/L for 60 days to achieve a mean residual concentration of 0.145 mg/L in the blow-down. Over time, at the same pumping rates, a greater monochloramine residual was achieved so the dosage was decreased at 2.5 mg/L. L. pneumophila (SG 7-14) decreased from an initial load gt;10.000 cfu/L to undetectable levels and remained stable till the end of the experimental period while HPC decreased slowly (mean count lt;10.000 cfu/ml) after the first 60 days.