Microbiological Control in Industrial Water Treatment
In industrial water treatment programs, effective microbiological control is one of the essential pillars — alongside scale inhibition and corrosion mitigation — needed for maintaining system integrity and efficiency. These three elements form a “three-legged stool” of water treatment. If any one of the legs is deficient, the entire system’s performance and reliability can be compromised. Below is an in-depth look at the importance of microbiological control, key microorganisms of concern, detection methods, and the chemical strategies Chemstar WATER employs to ensure robust microbiological management.
The Role of Microbiological Control
Microorganisms can proliferate in cooling towers, closed-loop systems, and other water-handling equipment, leading to a variety of operational and health-related issues. Unchecked microbial growth promotes:
- Biofilm formation – Biofilms can reduce heat transfer efficiency, increase energy consumption, and accelerate corrosion.
- Under-deposit corrosion – Bacterial colonies can create localized corrosive conditions, especially in areas where scale or deposits accumulate.
- Health hazards – Certain bacteria (e.g., Legionella pneumophila) pose significant risks if aerosolized and inhaled. For additional details, see our Legionella section.
Comprehensive microbiological control strategies focus on effectively monitoring and suppressing bacterial populations to mitigate these deleterious effects.
Key Microorganisms of Concern
1. Legionella in Cooling Systems
Legionella pneumophila is a well-known pathogenic bacterium that can proliferate in cooling towers and evaporative condensers when water temperatures and nutrient levels are conducive to growth. For a thorough discussion on Legionella monitoring and control, please visit
Chemstar WATER’s Legionella Page or refer to the CDC’s Legionella Resources for additional external guidance.
2. Iron-Reducing Bacteria (IRB)
Iron-reducing bacteria (IRB) are commonly found in closed-loop systems. These microorganisms can alter the oxidation state of iron for survival, forming iron-rich deposits that promote localized corrosion and reduce system efficiency.
- Impact: IRBs create tubercles or deposits that can occlude flow paths and encourage pitting corrosion.
- Environment: They thrive in low-oxygen, nutrient-rich areas, often found in closed loops where dissolved iron is abundant.
3. Sulfate-Reducing Bacteria (SRB)
Sulfate-reducing bacteria (SRB), also prevalent in closed loops, utilize sulfate (SO42−) as an electron acceptor under anaerobic conditions. Their metabolic processes produce hydrogen sulfide (H2S), which is highly corrosive to steel and other metals.
- Impact: SRBs are notorious for causing aggressive pitting corrosion known as Microbiologically Influenced Corrosion (MIC).
- Environment: SRBs thrive in anaerobic or near-anaerobic conditions, often in stagnant pockets or under deposit layers.
4. Mycobacteria
Mycobacteria, though sometimes overlooked, are increasingly recognized in industrial water systems. These organisms can form biofilms and may exhibit resistance to certain disinfectants, making them persistent contaminants.
- Impact: Some species are opportunistic pathogens; others fortify biofilm structures, complicating disinfection.
- Environment: Mycobacteria can persist in aerobic and low-oxygen conditions, requiring combined or enhanced disinfection strategies for comprehensive control.
Detection and Monitoring Methods
Chemstar WATER employs multiple analytical and microbiological techniques to identify and quantify bacterial populations that threaten system performance. Routine monitoring is crucial to detect early signs of microbial growth and adjust treatment programs proactively.
- BART™ Tests (Biological Activity Reaction Tests)
- IRB-BART™ and SRB-BART™ kits allow for on-site screening of iron- and sulfate-reducing bacteria, respectively.
- These tests provide a semi-quantitative assessment of bacterial activity through visual metabolic indicators in a proprietary medium.
- For more information on BART™ testing, visit Chemstar WATER Services or the manufacturer’s FAQ.
- Culture-Based Laboratory Testing
- Traditional plate counting methods and dip slides are used for routine bacterial enumeration.
- Culture-based methods remain a cornerstone for determining colony-forming units (CFU) and identifying specific bacterial species.
- Polymerase Chain Reaction (PCR) Testing
- For Legionella and other fastidious organisms, PCR-based assays offer rapid, sensitive detection.
- PCR reduces false negatives and enables swifter response compared to culture methods.
- Additional Selective Media & Biochemical Assays
- Targeted media for pseudomonads, mycobacteria, or other specific bacterial groups may be applied, depending on system risk factors.
- Biochemical assays confirm metabolic traits (e.g., sulfate reduction, nitrate reduction) that guide the correct control strategy.
Biocide Strategies for Effective Microbial Management
No single biocide can address all microbial challenges. Chemstar WATER leverages a dual approach — combining oxidizing and non-oxidizing biocides — to achieve broad-spectrum, long-lasting control.
1. Oxidizing Biocides
- Examples: Chlorine, bromine, and chlorine dioxide.
- Mode of Action: Rapid oxidation of cellular components, effective against bacteria, algae, and fungi.
- Advantages: Fast-acting, cost-effective, and readily available.
- Considerations: Possible increased corrosion rates if overdosed, byproduct formation (e.g., halogenated organics), and pH-dependent efficacy.
2. Non-Oxidizing Biocides
- Examples: Glutaraldehyde, isothiazolinones, DBNPA, and quaternary ammonium compounds.
- Mode of Action: Disruption of cell membranes, protein synthesis, or enzyme function.
- Advantages: Sustained release, more selective modes of action, and effective where oxidizers are less suitable.
- Considerations: Potential foaming, handling constraints, and compliance with discharge regulations.
3. Synergistic Application
By alternating or simultaneously applying oxidizing and non-oxidizing biocides, we minimize the risk of microbial adaptation and biofilm formation. This synergistic approach addresses a broad spectrum of microorganisms — including IRBs, SRBs, mycobacteria, and Legionella — ensuring comprehensive system protection.
A Continuous, Adaptive Process
Microbiological control is a dynamic, ongoing endeavor. It demands continuous monitoring and periodic reassessment. System operating conditions (temperature, pH, residence time), makeup water quality, and process changes can alter microbial activity. Chemstar WATER’s integrative approach ensures that:
- Online monitoring tools and periodic testing strategies detect shifts in microbial populations.
- Chemical dosages are optimized for efficacy while mitigating secondary issues such as corrosion or scale.
- Treatment plans are routinely reviewed and updated to reflect changes in system demands, regulatory guidelines, and best-in-class technologies.
Conclusion
Microbiological control is a critical “leg” of the water treatment “three-legged stool,” underpinning the reliability and safety of industrial water systems. Through advanced detection methods (BART™ tests, culture-based tests, PCR) and integrated biocide strategies (oxidizing and non-oxidizing agents), Chemstar WATER delivers the robust, adaptive solutions necessary for effective microbial management.
By understanding the roles of key microorganisms — from IRBs and SRBs in closed loops to Legionella in cooling systems, and emerging concerns such as mycobacteria — facilities can establish proactive, scientifically informed water treatment programs. This comprehensive approach preserves asset life, optimizes operational efficiency, and safeguards public health, reflecting both technical excellence and compliance in every aspect of industrial water management.
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