19-12: Control of Ozone Based on Water Temperature for Reduction of Legionella

In the US, there is an estimated population of 500,000 to 600,000 cooling towers (US Department of Energy by the Pacific Northwest Laboratory, 1995) that provide cooling for both HVAC systems and industrial applications. Based on this number, we can extrapolate that the number of cooling towers worldwide is roughly 1.5 million even though there are no figures to confirm this. Water being an excellent means to transfer and dispose of heat. During this cycle, however, bacteria growth necessarily leads to biofilm deposits within the cooling system, the results of which can be (1) reduced effectiveness of the chiller, and (2) spread of Legionella pneumophilia, a hazardous bacteria.