The organism always wins. This is the challenge of biofilm control. Microbial biofouling and its root cause, biofilm, cannot be totally prevented, at least for a practical length of time in industrial settings. We have many approaches to keep it at bay but it will always be with us.
In industrial water treatment, our goal is to keep biofouling under control. We should target treatments that keep the effects of biofilm below a detectable “threshold of interference” (i.e., the point at which an industrial process is impacted negatively). When biofilm growth reaches the problematic threshold it becomes biofouling.
Biofilm Mission Control
So, keeping a cooling tower clean and operating efficiently is a never-ending job. In a recent article*, Professor Hans-Curt Flemming, founder of the Biofilm Centre in the Aquatic Microbiology Institute at the University of Duisburg-Essen (Germany) and a leader in the field, identifies what we are doing ineffectively in biofilm control in industrial water treatment: detection, diagnosis, and monitoring of biofouling; removal of biofouling – not just killing of microbes; and use of oxidizing biocides.
Detection of biofouling often occurs after first observing its negative effects on the process or product being controlled/produced with the aid of cooling water. Diagnosis of the problem can be ineffective when the bulk water alone is sampled. This gives an inaccurate view of the location and extent of the fouling problem on internal surfaces where it matters most. This information is critical in clean-up and control treatments. In addition to detection and analysis of biofouling problems, effective biofouling control should include a monitoring program for ongoing detection and analysis of a clean system in order to maintain it in that state (below the “threshold of interference”) and provide efficient and cost-effective operations.
Killing is not cleaning. Since microorganisms are the root cause of biofouling it makes sense that killing them will solve the problem. However in reality, it is impossible to completely disinfect a system and maintain it that way for a practical length of time. Killing microbes in the bulk water using standard oxidizing and non-oxidizing biocides is relatively easy, but killing sessile, surface-bound biofilm microbes with biocides alone is much more difficult.
Surviving biofilm microbes released into the bulk water continuously re-inoculate the system. Dead/non-viable biofilm microbes continue to foul surfaces, reducing heat transfer and accelerating under-deposit corrosion. Only removal of biofouling deposits from system surfaces restores a process to optimum performance. All biocides will result in some removal of biofilm as microbes near the deposit-water interface are killed, and the top layer of the deposit sloughs into the bulk water. The effectiveness of these biocides can be significantly enhanced, however, if they are used in conjunction with chemicals which penetrate biofilm and disrupt deposits. This combination of biocide-plus-penetrant/dispersant yields the ideal result of clean surfaces and low bulk water microbe populations.
Oxidizing biocides may lead to other problems. In the process of killing microbes, oxidizers also react with the biomass and break it up into more readily metabolized pieces. That is, in a system where biofilm growth is being controlled, does it make sense to be making nutrients more available for its growth?
Flemming proposes that a single solution will not control the various challenges of biofouling, but “an appropriate strategy includes the selection of low-adhesion, easy-to-clean surfaces, good housekeeping, early warning systems, limitation of nutrients, improvement of cleaners, strategic cleaning and monitoring of deposits.”
AMSA provides products that penetrate, disperse, and clean organic deposits and when used with biocides provide a critical part of an effective biofilm control program. Killing is not cleaning. Pairing a dispersant such as BCP™ 1015 (DTEA II™) with a biocide provides an effective approach.