Solving the biofilm threat in industrial cooling water systems
Solenis ’ Christina Moering discusses biofilm challenges and a treatment programme that proactively protects industrial cooling towers from biofilm
Industrial cooling water systems provide perfect conditions for the growth of microorganisms , because the cooling water temperature is ideal , and the water contains nutrients from natural debris and contaminants introduced from process leaks . Biofilm forms when planktonic ( i . e ., free-floating ) microorganisms begin to adhere on surfaces , such as pipe walls , heat exchangers and cooling tower fill , and begin secreting extracellular polymeric substances . The resulting slimy extracellular matrix protects the community of microorganisms that has adhered to the surface from environmental stresses and increases their potential to survive and reproduce in the cooling water environment . Biofilm formation in cooling water systems tends to start in areas not accessible to microbiological control treatments , such as dead ends or low-flow areas . Therefore , it is not easy to detect . Biofilm in industrial cooling water systems is undesirable both for human health reasons , as it can provide a habitat for pathogenic organisms , such as Pseudomonas and Legionella , and also for operational reasons . Because biofilm is composed mostly of water , it is more insulating than typical mineral scales ( Figure 1 ). The insulating effect of biofilm negatively reduces the cooling capacity of heat exchangers : a biofilm layer that is only 20 µ m thick can increase heat transfer resistance by 7 %. Microbiologically induced corrosion represents another often-neglected threat that can lead to downtime for costly maintenance and repair .
Figure 1 - Thermal effect of biofilm and typical mineral scales
It is estimated that 20 – 50 % of all corrosion originates from microorganisms . The fact is that biofilm causes many more problems in industrial cooling water systems than individual microorganisms ( Figure 2 ). For companies operating a cooling water system , early detection and effective protection against biofilm are imperative to ensure maximum operating efficacy and reliability . Solenis ’ ClearPoint biofilm detection and control programme brings together a novel biofilm analyser and a proprietary chlorine stabiliser chemistry to address biofilm growth in industrial cooling water systems .
Real-time biofilm measurement Often , biofilm is detected only when operational problems occur or when a slimy matrix is tangible or visible on easily accessible surfaces in cooling towers . Common analytical methods , such as the determination of total bacteria counts ( laboratory analysis , dip slides ), have limited our ability to predict possible biofilm growth on surfaces because these methods cover only planktonic and not sessile microorganisms . An additional disadvantage is that it takes several days to deliver results . Sessile coupons can predict biofilm growth on a surface , but coupons take even longer to deliver results , prolonging the time until corrective actions can be taken . None of these techniques clearly quantify the amount of biofilm . The OnGuard 3B analyser provides the earliest detection and most accurate measurement of biofilm growth possible in industrial cooling water systems , enabling detection and monitoring of biofilm in real time . The Karlsruhe Institute of Technology and the Center for Biofilm Engineering at Montana State University have both independently validated its biofilm early detection capability and measurement accuracy . The analyser uses a patented ultrasonic sensor that detects
12 SPECIALITY CHEMICALS MAGAZINE ESTABLISHED 1981