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Abstract
The objective of this investigation was to provide a controlled, independent, and scientific evaluation of several classes of nonchemical water treatment devices (NCDs) for controlling biological activity in a model cooling tower system. Five NCDs (magnetic, pulsed electric field, electrostatic, ultrasonic, and hydrodynamic cavitation) were evaluated for efficacy in reducing planktonic and sessile microbial populations. Two model cooling towers were designed and operated to simulate field conditions. One tower served as the untreated control (T1), while the NCD was installed on the second tower (T2). Each trial was conducted over a four-week period. Heterotrophic plate counts (HPC) were used to monitor planktonic and sessile biological growth. Make-up water for both systems was dechlorinated city tap water. No statistically significant difference in planktonic or sessile microbial concentrations (HPC) was observed between the control tower and the tower treated by NCD during any of the five trials. Chemical treatment of the towers with free chlorine generated appreciable reduction in both planktonic (2–3 log) and sessile (3–4 log) microbial growth in these towers. The results of this study conducted under well-controlled conditions indicate that NCDs did not control biological growth under the test conditions in the pilot-scale cooling tower systems.
Acknowledgment
The authors of this study thank Marilyn Wagener for performing statistical analyses of data collected during this investigation.
Scott Duda, MS, is Project Manager. Janet E. Stout, PhD, Member ASHRAE, is Research Associate Professor. Radisav Vidic, PhD, PE, is William Kepler Whiteford Faculty Professor and Chairman.