Biofilm deposits are one of the most difficult challenges your cooling water systems face. They tend to start in areas not accessible to biocide treatments and can quickly grow to form biofouling deposits that can cause corrosion damage, blockages, reduced heat transfer, and amplify the growth of Legionella bacteria. Once they become established, biofilms are incredibly tenacious and difficult to remove.
Even systems with well-regulated biocide programs can experience serious problems because of biofilm deposits. So why are biofilms so difficult to control? What can I do to control them?
Biofilms are Everywhere
Biofilm deposits are communities of surface-attached bacteria growing inside protective microbial secretions. Numerically and by weight, biofilms are the most successful form of life on Earth. They play an important role in the ecology and sustainability of lifeand are found on living and inanimate surfaces in virtually every imaginable environment.
Without extreme control measures, like those used in the pharmaceutical industry, biofilms are inevitable in water systems. In cooling tower systems, biofilm control is especially challenging since systems are continuously inoculated with dust, nutrients, bacteria, and other contaminants during their normal course ofoperation. The only practical objective in cooling water systems is to manage the negative impact of biofilms on corrosion, flow, heat transfer, and disease, not complete elimination.
Biofilms Improve Survival
Over 90% of the world’s population of bacteria are found in biofilms. Why? Bacteria prefer living in biofilms rather than free-floating in the water because it improves their survival.
Unless sterile, all water supplies contain planktonic (free floating) bacteria, most of which cannot be detected by conventional culture testing. If the conditions are favourable, these bacteria will begin producing a protective sticky secretion called EPS (extracellular polymeric substances) within minutes of encountering a surface. Within hours, bacteria can start reproducing inside the biofilm. Within days, mature biofouling deposits can form containing complex communities of problem-causing bacteria and other microorganisms.
The complex structure of biofilms protects the growing microorganisms from environmental hazards, allowing sophisticated communities to develop that can constantly adapt to chemical treatments and even mechanical removal. When conditions become unfavourable, they propagate by releasing bacteria into the bulk water to inhabit other surfaces. Multiple survival mechanisms make biofilms incredibly tenacious and difficult to control.
Why are Biofilms so Hard to Control?
Biofilms tend to start where biocides can't reach such as underneath “muck” in the tower basin or inside dead legs, which are sections of the water system with low or no flow. With their complex piping, redundant equipment, and continuous infusion of dust, nutrients, and bacteria, cooling tower systems provide ideal conditions for biofilm deposits to become established.
Once they become established, biofilms are hard to remove. The Microbial secretions that form biofilms tightly bind the deposit to system surfaces and form a chemically resistant matrix that is extremely difficult for biocides and cleaners to penetrate.
Chlorine or bromine (generally used as primary biocides) oxidising biocide residuals are quickly consumed by reaction with the protective biofilm matrix and can only penetrate the outer layers. If the concentration and contact time is long enough, non-oxidising biocides (generally used as secondary biocides) can diffuse into biofilms, but will only kill certain microorganisms and are prone to deactivation. Microbial populations can also shift over time to favour microorganisms that are not susceptible to the specific non-oxidising biocide used.
What’s worked in the past, may not work in the future. Even high dosages of biocides, dispersants, and cleaners may not be able to effectively remove established biofilms. Unless completely removed, surviving bacteria can rapidly multiply to form new, more resistant and impervious biofilms.
Managing Biofilm Growth Requires a Comprehensive Approach
Effective bio-management is an ongoing battle that requires a lot more than just biocide additions. It requires a comprehensive approach with specialised expertise, maintenance protocols, and technologies to address the unique challenges associated with biofilm remediation and control.
Chem-Aqua’s 360 Approach for Bio-Management defines the key components of an effective program to manage the impact of biofilms on corrosion, flow, heat transfer, and disease in cooling water systems. Our patented bioeXile® cleaning solution and award winning bioDART® biofilm monitor provide the technological advances that you need to help get your systems clean and keep them that way.
For more information, contact Chem-Aqua or visit our Microbiological Control page.