Biocidal control of legionellae

This paper examines the use of biocides to control the growth of Legionella pneumophila in recirculating cooling-water systems. The reasons for using biocides and their ideal properties are discussed. Comparative studies on several biocides' activity against Legionella are reported together with more detailed laboratory and field studies on one specific biocide, 2-bromo-2-nitropropane-1,3-diol (BNPD). The laboratory data include biocidal and biostatic tests on a range of Legionella species as well as the use of model cooling-water systems. The field studies comprise bacterial counts, fungal counts, Legionella isolation and chemical monitoring of biocide levels. BNPD was effective both in the laboratory and cooling-tower studies. In line with ecological considerations the activity of biocides against specific organisms implicated in supporting the growth of L. pneumophila is stressed. The paper emphasizes the need for field trial data to support laboratory studies in this area of biocide use.