A biofilm is a community of microorganisms, such as bacteria, fungi, protozoa, or algae, that attach to a surface and encase themselves in a self-produced slimy layer. This layer, often referred to as an extracellular polymeric substance (EPS), holds the microbial community together. Biofilms are a common occurrence wherever moisture and a surface for attachment are present, appearing anywhere within a water system.
The Formation Process of Biofilms
Biofilm formation begins with the attachment of free-floating microorganisms (known as planktonic cells) to a wet surface. This initial contact is often reversible, but if conditions are favorable, the microbes will start to form a monolayer and attach more firmly.
Once attached, these microorganisms multiply and colonize the surface, forming microcolonies. As the colony grows, the microbes produce the extracellular polymeric substance (EPS), a slimy matrix composed of polysaccharides, proteins, and nucleic acids. This EPS acts as a protective barrier, making the biofilm highly resistant to external threats like disinfectants and environmental changes. The biofilm develops into a complex, three-dimensional structure, with some cells eventually detaching to colonize new areas.
Where Biofilms Thrive in Water Environments
Biofilms are commonly found in household water environments where surfaces are consistently wet. These microbial communities frequently accumulate inside plumbing pipes, where the inner surfaces provide ample space for attachment. Showerheads and faucets are also typical locations, as lingering water droplets after use create suitable breeding grounds for microorganisms.
The “pink slime” often seen in toilet bowls or around drains is a common example of biofilm. Pet water dishes and refrigerator water dispensers, which have consistent water exposure, are also prone to biofilm development. Humidifiers, with their standing water, present another environment where biofilms can flourish. Beyond the household, hot tubs and swimming pools can develop biofilms on their surfaces and within their filtration systems.
Associated Risks of Biofilms in Water
Biofilms in water systems present various risks to human health and infrastructure. A significant concern is their ability to harbor and protect harmful pathogens, shielding them from typical disinfection methods. Pathogens such as Legionella pneumophila (which causes Legionnaires’ disease) and Pseudomonas aeruginosa (a common cause of infections in vulnerable individuals) can thrive within biofilm structures. Other bacteria like certain coliforms or Mycobacterium avium complex (MAC) can also be found, posing potential health issues through ingestion or inhalation of contaminated aerosols.
Beyond health implications, biofilms contribute to infrastructure problems and aesthetic issues. They can lead to microbially influenced corrosion (MIC) in pipes, where microbial activity accelerates the deterioration of metal surfaces, potentially causing pitting, crevice corrosion, and even leaks. Extensive biofilm growth can also reduce water flow by narrowing pipe diameters, leading to clogs and decreased system efficiency. Biofilms can produce compounds that impart unpleasant tastes and odors to drinking water, affecting its palatability.
Removal and Prevention of Water Biofilms
Removal of biofilms in water systems typically involves a two-step approach. The primary step focuses on physical or mechanical removal to break apart the protective extracellular polymeric substance (EPS) matrix. This can be achieved through scrubbing, scraping, or high-pressure flushing, which physically dislodges the microbial community from surfaces. For larger systems, techniques like water jetting or ultrasonic cleaning are employed to disrupt the biofilm.
Once the biofilm structure is disrupted, disinfection with appropriate chemical cleaners becomes more effective. Common disinfectants such as chlorine dioxide, hydrogen peroxide, or peracetic acid can then penetrate and eliminate the exposed microorganisms. To prevent future biofilm formation, regular cleaning of susceptible surfaces is advised, along with preventing water stagnation by flushing infrequently used lines. Maintaining proper disinfectant levels in systems like pools and spas, and ensuring water filters are changed according to manufacturer recommendations, also helps inhibit microbial growth.