TP87-06: Methods for Evaluating the Efficacy of Biocides Against Sessile Bacteria

Dual pilot plant cooling towers were designed and constructed to conduct comparative evaluations of biocides in water systems. The towers were built with instrumentation used to control and monitor environmental parameters. The control of parameters such as pH and conductivity can be used to determine the impact of environmental conditions on biocidal activities. In this paper, we describe the cooling towers and give examples of methods that we have developed and incorporated into our cooling systems to detect biological fouling. These methods include a sessile (attached) bacteria monitor, an annular differential pressure device for calculating biological and/or inorganic fouling thicknesses, and an algae collection surface used for gravimetric analysis. We have concentiated on detecting biological fouling because it is the sessile microorganisms that present the majority of the problems in cooling towers. These problems include pitting corrosion, reduced heat transfer efficiency, restricted flow, and reduced cooling tower performance(l,2,3,4).