An alkaline approach to treating cooling towers for control of Legionella pneumophila

Abstract

Earlier field and laboratory studies have shown that Legionella species survive and multiply in the pH range 5.5 to 9.2. Additionally, the technical feasibility of operating cooling towers at elevated alkalinities and pH has previously been documented by published guidelines. The guidelines indicate that these conditions facilitate corrosion control and favor chlorine persistence which enhances the effectiveness of continuous chlorination in biofouling control. This information suggests that control of Legionella species in cooling towers can be accomplished by operating the towers under alkaline conditions. To test this possibility, we collected water samples over a period of months from a hospital cooling tower. The samples were analyzed for a variety of chemical parameters. Subsamples were pasteurized and inoculated with non-agar-passaged Legionella pneumophila which had been maintained in tap water. Correlation of subsequent Legionella growth with corresponding pH and alkalinity values revealed statistically significant inverse associations. These data support the hypothesis that operating cooling towers outside of the optimal conditions for Legionella growth (e.g., at elevated alkalinities and a pH greater than 9) may be a useful approach to controlling growth in this habitat.

Impact of Water Chemistry, Pipe Material and Stagnation on the Building Plumbing Microbiome

“…Legionella is acid-tolerant [ 78 ] and most isolates have been obtained from environmental sources in the pH range of 2.7–8.3 [ 79 ]. Further, it has been reported in prior studies that Legionella pneumophila has reduced viability and cultivability at higher pH [ 80 , 81 ]. Thus, hypothetically, the high pH level at Utility C (9–10) would have negatively influenced the occurrence of Legionella spp.…”

Factors Stimulating Propagation of Legionellae in Cooling Tower Water

“…Several investigations (15)(16)(17)21) have suggested a relationship between legionella multiplication and certain abiotic factors such as pH, temperature, organic matter, and certain metals, factors considered to play an important role as growth enhancers or inhibitors of legionellae in the environment. On the other hand, legionellae have been shown to be symbiotic bacteria.…”

Survival of Biofilm‐Associated Legionella pneumophila Exposed to Various Stressors

“…The acid-tolerant L. pneumophila bacteria showed no decrease on exposure to pH 3 as expected, but alkaline pH for Legionella bacteria is not a favorable environment, where more than 2 log decrease was recorded. At least one study indicates an inverse association between alkalinity and viability for planktonic Legionella (States et al, 1987). For this reason, States et al recommended elevating alkalinity as a useful approach for controlling Legionella growth where applicable.…”