This paper provides an overview of ASHRAE Research Project 954 findings of the efficacy of specific oxidizing and nonoxidizing biocides examined using a model cooling tower system inoculated with a microcosm containing an environmental isolate of Legionella pneumophila. The activity of three biocides was tested against both planktonic and sessile Legionella against “dirty” systems, with pre-established bacterial microcosms, and also against “clean” systems subsequently drip-fed with a Legionella seed. The findings of the project can be used to better understand the likely reaction of Legionella bacteria to biocide dosage programs and assist in the development of future biocide products and strategies.

Units: SI