Biofouling Control Strategies for Industrial Cooling Water Systems
Biofouling control should connect microbiological conditions with surface cleanliness and heat transfer performance. Visually clear water can still contain microorganisms that form biofilm on tubes, basins, or low-flow sections of the system. An effective program combines biocide selection, contact time, cleaning, and monitoring. This article discusses microfouling caused by biofilm and macrofouling considerations for systems that draw water from natural sources.
Biofilm develops on surfaces
Microorganisms attached to surfaces form a matrix of extracellular polymeric substances (EPS). This matrix can trap particles and limit biocide access to cells within it. Biofilm layers impede heat transfer, restrict flow paths, and can increase pressure drop. Circulating water samples mainly describe planktonic organisms; the results should be complemented by examination of surface-attached organisms. [1]
Biofilm can also create local conditions that support microbiologically influenced corrosion (MIC). However, the presence of bacteria alone does not establish the cause of corrosion. Deposit analysis, metallurgical examination, and operating data are needed to assess the relationship between microbiological activity and material damage. [2]
Selecting a biocide
Oxidizing biocides include chlorine- or bromine-based programs and, for certain applications, chlorine dioxide or ozone. Their effectiveness depends on pH, oxidant demand, contact time, and residual distribution throughout the system. At higher pH, the proportion of hypochlorous acid (HOCl) decreases. Bromine chemistry can be a candidate under alkaline conditions, but should still be assessed against water quality, materials, and discharge limits. [3]
Non-oxidizing biocides, including glutaraldehyde, isothiazolinones, and DBNPA, have different application conditions. Selection should consider target organisms, pH, retention time, and program compatibility. Biodispersants can help disrupt or release biological deposits, but the effectiveness of combinations must be assessed; increasing a single dose does not automatically improve penetration into mature biofilm. [1]
pH changes free chlorine speciation
The following table is a simplified equilibrium calculation assuming an HOCl pKa of approximately 7.5 under conditions near 25 °C. The proportions are calculated from the acid–base relationship between HOCl and OCl⁻. These values describe speciation, rather than microorganism kill percentages or biocide dosage setpoints. [4]
Water pH | Approximate HOCl | Approximate OCl⁻ |
|---|---|---|
7.0 | 76% | 24% |
8.0 | 24% | 76% |
8.5 | 9% | 91% |
Measured free chlorine includes HOCl and OCl⁻. These species have different levels of activity; describing OCl⁻ as completely inactive is incorrect. Interpretation of test results should consider pH, temperature, contact time, and interference from other oxidants. Residual measured at the injection point also does not represent residual at the end of the network or in low-flow areas. [3,4]
Cleaning and monitoring complement the program
Mechanical cleaning helps remove established biofilm. After deposits are released, microbiological control and solids removal should be managed to prevent redeposition elsewhere. Establish sampling points that represent the basin, supply and return lines, and locations prone to deposits.
Monitor ATP or microbial count trends using the selected method, surface or coupon inspections, biocide residual, pH, and heat transfer indicators. Different microbiological methods do not produce directly interchangeable values. For cooling towers, a Legionella control program should manage sediment and biofilm, temperature, water age, and disinfectant residual. CDC recommends offline cleaning and disinfection at least annually, with additional frequency according to operating conditions. [5]
At river or seawater intakes, macrofouling by larger organisms requires identification of species and seasonal occurrence patterns. Screening, intake inspection, cleaning, and appropriate treatment can be included in the program. Results for particular species in other countries cannot directly establish dosage or contact time targets for a site in Indonesia.
An evaluation with Harvest Chemical can begin with the make-up water source, flow configuration, deposit history, and residual data. The technical objective is to maintain surface cleanliness and stable heat transfer using a chemical program suited to plant materials and operation.
References
All reference links were checked on 10 October 2026.
Comments