Biofilm in water refers to a community of microorganisms, such as bacteria, fungi, and algae, that attach to a surface and embed themselves in a protective, self-produced slimy matrix. This microbial layer can form on virtually any surface exposed to water, existing as either a thin film or isolated patches. Biofilms are complex, organized communities.
Biofilm Formation and Composition
Biofilm development begins when free-floating microorganisms, known as planktonic cells, attach to a submerged surface. This initial attachment can occur rapidly, sometimes within hours, especially on new pipe materials. Once attached, these microorganisms multiply and excrete extracellular polymeric substances (EPS), a sticky, gel-like matrix often described as slime. The EPS matrix is primarily composed of polysaccharides, proteins, lipids, and DNA, forming a protective scaffold that holds the microbial community together.
This matrix allows the biofilm to grow into a three-dimensional structure, creating a favorable microenvironment for microbial communities. Within this protective layer, microorganisms are shielded from external threats like disinfectants and changes in environmental conditions. The continuous flow of water introduces new microorganisms and nutrients, which can further colonize and strengthen existing biofilms.
Common Locations of Water Biofilms
Biofilms form in both natural and engineered water environments. In natural settings, they can be found on stones in streambeds, rivers, and lakes, contributing to ecological processes. They also readily colonize various manufactured water systems.
Common examples include the internal surfaces of water pipes, water storage tanks, and household plumbing fixtures like taps and showerheads. They are also found in industrial systems like cooling towers, filters, and other water-handling equipment. Even newly installed water systems can develop stable biofilms within weeks, particularly if water stagnates or temperatures are conducive to microbial growth.
Consequences of Water Biofilms
The presence of biofilms in water systems can lead to undesirable consequences, impacting both human health and infrastructure. A concern is their ability to harbor and protect pathogenic microorganisms, such as Legionella pneumophila and Pseudomonas aeruginosa. Embedded pathogens become more resistant to disinfectants, posing a risk of waterborne infections like pneumonia or urinary tract infections if ingested or inhaled.
Beyond health risks, biofilms contribute to infrastructure problems. They can cause biocorrosion, leading to the degradation of pipes and other metallic surfaces, which shortens the lifespan of water systems. Biofilm accumulation also reduces the internal diameter of pipes, resulting in decreased water flow efficiency and potential blockages. This can lead to increased pumping costs and operational challenges in water distribution networks.
Biofilms can also negatively affect water quality by causing aesthetic issues. They are frequently responsible for the discoloration of water and can impart unpleasant tastes and odors. Their slimy appearance is often a visual indicator, signaling a deterioration in water quality.
Strategies for Control and Removal
Controlling and removing biofilms from water systems involves approaches aimed at preventing their formation and dislodging established communities. Physical methods include mechanical cleaning, such as scrubbing or flushing pipes, to disrupt and remove the attached biofilm layer. Regular flushing of water systems can help prevent the accumulation of stagnant water, which promotes biofilm growth.
Chemical treatments are also employed, utilizing disinfectants like chlorine, chlorine dioxide, ozone, or UV radiation to kill microorganisms within the biofilm and in the water column. However, the protective EPS matrix makes established biofilms highly resistant to these chemicals, often requiring higher concentrations or longer contact times than for free-floating bacteria. Some newer approaches investigate quorum quenching molecules to prevent biofilm development in its initial stages.
Design considerations play a role in preventing biofilm formation in new systems. Selecting materials that are less conducive to microbial attachment and designing systems with smooth surfaces and minimal dead legs can reduce opportunities for biofilm growth. Maintaining consistent water flow and avoiding prolonged stagnation are also preventive measures.