What Is Biofilm in Water Systems? Causes, Risks and Control Methods

Biofilm can become a persistent problem in water systems when microbial growth accumulates on equipment, membranes, and other wetted surfaces. In systems with biofilm in water pipes or biofilm in water lines, microbial deposits can contribute to water quality concerns, biological fouling, flow restrictions, and conditions that may promote corrosion or interfere with equipment performance.

Established biofilm can also be difficult to control because microorganisms within the biofilm matrix may be less accessible to disinfectants than free-floating microorganisms in water. If not addressed, continued biological growth can increase cleaning, treatment, and maintenance requirements and may reduce system operating efficiency.

Effective control requires understanding what causes biofilm in water treatment systems and selecting appropriate treatment and maintenance practices. This post explains the causes, risks, detection, prevention, and control methods.

What Is Biofilm in Water?

Biofilm is a structured community of microorganisms that attaches to a surface and becomes surrounded by a self-produced extracellular polymeric substance (EPS) matrix. The microorganisms may include bacteria, fungi, algae, protozoa, and other microbial populations, depending on the water system and environmental conditions.

The EPS matrix contains polymers, proteins, nucleic acids, and other materials that help microorganisms adhere to surfaces and interact with their surroundings. Biofilms can form on pipes, tanks, valves, heat-transfer surfaces, membranes, filters, and other wetted components, with the EPS matrix promoting microbial attachment and persistence.

What Causes Biofilm in Water Systems?

Several factors can create conditions that support biofilm formation in water systems, including:

• Nutrient Availability: Organic carbon, nitrogen, phosphorus, and other nutrients can support microbial growth. Even low nutrient levels may contribute to biofilm formation when microorganisms can attach to surfaces and remain exposed to a continuing nutrient supply.
• Water Temperature: Temperature influences microbial growth and activity. Different microorganisms have different temperature ranges for growth, so temperature conditions can affect biofilm development when other growth requirements are present.
• Stagnation and Low-Flow Conditions: Stagnant or low-flow areas increase contact time between microorganisms, nutrients, and surfaces. Dead legs, poorly circulated sections, storage areas, and infrequently used equipment can therefore support localized biofilm growth.
• Surface Characteristics: Surface material, roughness, damage, deposits, and existing fouling can affect microbial attachment. Rough or fouled surfaces may provide sites where microorganisms can establish and develop biofilms.
• Water Chemistry: pH, dissolved minerals, organic matter, oxygen availability, and other water chemistry parameters can influence microbial activity, surface conditions, and treatment effectiveness. These factors are particularly relevant when evaluating biofilm in well water, where source-water characteristics can vary significantly.
• Disinfectant Limitations: Disinfectants may control microorganisms in bulk water but have limited effectiveness against established biofilms. Inadequate concentration, contact time, distribution, or residual maintenance can further reduce control.

What Are the Risks of Biofilm in Water Systems?

Biofilm can affect water quality, equipment condition, and system performance, with potential impacts including:

• Water Quality Concerns: Biofilm can release microorganisms, organic material, and particles into circulating water as portions detach. This can cause fluctuations in microbial water quality and make consistent water quality control more difficult, particularly in systems with stringent requirements.
• Microbial Protection and Persistence: The EPS matrix can protect microorganisms from environmental stresses and reduce disinfectant access. Microorganisms within established biofilms may therefore persist even when bulk-water microbial levels are reduced.
• Fouling and Flow Restrictions: Biofilm and associated deposits can accumulate on wetted surfaces, contributing to fouling, increased hydraulic resistance, restricted flow passages, and reduced equipment performance.
• Corrosion-Related Impacts: Biofilm can alter localized conditions at metal surfaces and contribute to microbiologically influenced corrosion (MIC). The potential impact depends on the microorganisms, materials, water chemistry, and operating conditions.
• Increased Maintenance Requirements: Persistent biofilm may require additional inspection, cleaning, disinfection, sampling, and treatment adjustments. Recurring growth may also require investigation of underlying system conditions rather than repeated treatment alone.
• Operational Inefficiencies: Biological fouling can affect heat transfer, filtration, membrane performance, and flow. Depending on its extent, this may increase energy, water, chemical, cleaning, and maintenance requirements.

How To Detect Biofilm in Water Systems?

There are several ways to detect biofilm in water systems, including:

• Visual Indicators: Visible slime, discoloration, deposits, unusual surface films, or accumulated biological material can provide initial indications of biofilm or biological fouling.
• Water Quality Testing: Microbiological and water chemistry testing can help evaluate conditions associated with biological growth. Parameters such as microbial counts, organic matter, nutrients, pH, temperature, and other system-specific measurements can provide useful information when interpreted together with operating conditions.
• ATP Monitoring: Adenosine triphosphate (ATP) testing can provide a rapid indication of biological activity by measuring ATP associated with living or recently living biological material.
• Microbial Testing: Microbiological testing can help determine the types and concentrations of microorganisms present in water or samples collected from system surfaces.
• Surface Sampling: Swab, coupon, scraping, or other surface-sampling methods can help evaluate biological accumulation directly on equipment surfaces. Surface sampling may provide information that bulk-water testing does not capture because microorganisms in an established biofilm can differ substantially from those measured in circulating water.
• Performance Monitoring: Changes in flow, pressure drop, heat-transfer performance, differential pressure, membrane performance, or other operating parameters can indicate progressive fouling. 

How to Prevent Biofilm Formation in Water Systems?

Preventing biofilm requires a combination of proper system design, water quality control, effective disinfection, and routine monitoring.

System Design and Flow Management

• Minimize Stagnation: Avoid conditions where water remains stationary for extended periods. Adequate use, circulation, and storage practices can reduce areas where microorganisms can accumulate and establish biofilm.
• Eliminate Dead Legs: Unnecessary dead-end piping and poorly connected sections can create stagnant zones. Minimizing dead legs during system design can reduce localized conditions that support microbial growth.
• Maintain Circulation: Consistent circulation helps distribute treated water and maintain more uniform system conditions. Flow should remain within the operating range required for effective system performance.

Water Quality Management

• Control Nutrients: Limiting biodegradable organic matter and other nutrients can reduce resources available for microbial growth. Monitoring water quality can help identify changes that increase biological growth potential.
• Evaluate Source Water: Source water may introduce microorganisms, nutrients, organic matter, and suspended solids. Understanding source-water quality and variability helps determine appropriate pretreatment and biological control requirements.
• Optimize Treatment: Treatment should be matched to the system's water chemistry, microbial conditions, equipment materials, and operating requirements. Regular evaluation can help maintain treatment effectiveness and avoid unnecessary or inadequate chemical use.

Disinfection Programs

• Maintain Disinfectant Residuals: Where residual disinfection is used, maintaining an appropriate concentration throughout the system can help control planktonic microorganisms and limit biological growth. Requirements depend on the disinfectant and application.
• Use Appropriate Biocides: Oxidizing and non-oxidizing biocides can be used for biological control in suitable applications. Selection should consider target organisms, water chemistry, materials compatibility, contact time, and operating conditions.

Monitoring and Preventive Maintenance of Biofilm

• Conduct Routine Inspections: Inspect tanks, piping, heat-transfer surfaces, filters, membranes, valves, and other wetted components for biological deposits and fouling. Early identification can help prevent more extensive accumulation.
• Establish Testing Programs: Routine microbiological, water chemistry, and operational testing can help identify changes in biological activity and treatment conditions. Testing should reflect the system's specific control objectives.
• Track System Trends: Monitor parameters such as microbial activity, ATP, disinfectant residuals, pressure drop, flow, temperature, and equipment performance. Trending can help identify gradual changes and support timely treatment adjustments.

Removing Method of Established Biofilm 

• Mechanical Cleaning: Brushing, flushing, scrubbing, or other physical methods can remove accessible biological deposits. Mechanical cleaning is an important consideration when removing biofilm from water pipes, particularly where the biofilm matrix limits chemical penetration.
• Chemical Cleaning: Chemical cleaning can remove biological material and associated deposits when the selected chemistry is compatible with the equipment. Cleaning agents should be selected based on the deposit, surface material, and manufacturer's requirements.
• Shock Disinfection: Shock disinfection uses an intensified disinfectant treatment for a defined period to address elevated microbial activity. Effectiveness depends on concentration, contact time, distribution, and access to affected surfaces.
• Follow System-Specific Procedures: Established biofilm may require a combination of mechanical cleaning, chemical cleaning, flushing, and disinfection. The appropriate procedure depends on system design, materials, deposit characteristics, and operating conditions.

Improve Biofilm Management Across Water Treatment Systems

Effective biofilm management helps maintain water quality and reliable system operation. Cannon Water Technology provides water treatment equipment for cooling towers, boilers, process water, and other commercial and industrial applications. These solutions can support programs addressing biofilm in water treatment systems, depending on application requirements.