New research supported by ASHRAE indicates that non-chemical devices (NCD) marketed to control the growth of biological agents, such as Legionella in cooling towers, may not materially reduce biological growth.
Research project No. 1361, Biological Control in Cooling Towers Using Non-Chemical Water Treatment Devices, a two-year project recently completed by Dr. Radisav Vidic at the University of Pittsburgh, evaluated five non-chemical devices using different technologies to control biological activity in a model cooling-tower system. The devices studied included a hydrodynamic cavitation device, pulsed and static electric field devices, an ultra-sonic device and a magnetic device.
In Dr. Vidic’s research, none of the non-chemical devices measurably reduced planktonic or sessile microbial populations in comparison to no-treatment tests and to a conventional chemical microbial control treatment protocol. The findings appear to be inconsistent with previous research by non-chemical device manufacturers and some independent researchers on some of the same devices tested in the ASHRAE study. Those other studies reported measurable degrees of biological control within the parameters of testing conducted.
“These results suggest that equipment operators, building owners and engineers should consider taking more frequent water sample tests for their systems that rely on NCDs for biological control. If the testing shows an issue, one possible measure is to add chemical treatment capability to their system to prevent a potential health hazard from developing until additional research and field testing can resolve this question,” according to Dr. Vidic.
The study results are still subject to final approval by the sponsoring technical committee, TC 3.6 – Water Treatment. ASHRAE anticipates formal approval and the release of the final report for this project at its 2010 Annual Meeting Conference in June.