The proliferation of bacteria, algae, and fungi on surfaces can result in microbiological fouling within cooling water systems. While such issues tend to develop more rapidly and extensively in open-loop systems, closed recirculating systems also pose a significant risk for microbial growth and fouling deposits.

Unchecked microbiological growth can swiftly lead to the formation of biofilms on wetted surfaces. These biofilms provide an environment for both aerobic and anaerobic bacteria to thrive, adversely impacting equipment performance, accelerating wood deterioration, and promoting metal corrosion.

Effectively managing biological agents such as bacteria and algae is fundamental in any robust cooling water treatment strategy. Biocides play a crucial role in controlling these factors, falling into two primary categories:

1. Oxidizing Biocides: Chlorine-based compounds, bromine, and ozone are the main oxidizing biocides that offer broad control over biological agents. The effectiveness of most oxidizing biocides may be influenced by the pH level of the water.

2. Nonoxidizing Biocides: Typically used in closed systems, these chemicals work to suffocate, starve, or impede the reproduction of bacteria. They have a very short half-life at the standard operating pH of closed systems, necessitating close monitoring.

Controlling bacterial levels in closed water systems should begin from the initial fill. Flushing and chemical pretreatment are essential practices to prevent the proliferation of bacteria, algae, and fungi on pipe surfaces, ensuring the integrity and efficiency of the system.