A Review on the Role of Microorganisms and Its Control in Industrial Cooling Water System

Abstract

Water plays a significant role in many industrial processes may it be the manufacturing process for semiconductors or the creation of steam for electricity generation or even the production of drugs in the pharmaceuticals industry. The water in an open recirculating cooling system is continuously infested with a variety of nuisance microorganisms introduced for the most part in wind-blown dust. Essentially all of these microorganisms are indigenous to soil; they include bacteria, algae, fungi and protozoa in addition to a few multicellular bacterial predators. This infestation in the cooling water system is majorly controlled by introduction of oxidizing biocide such as chlorine while sodium hypochlorite, bromine, chlorine dioxide and ozone are gaining popularity owing to their benefits. Underfeed of the biocide will result in microbiological growth whereas overfeed of the biocide can lead to elevated chemical utilization and cost and also potential damage to the system metallurgy (corrosion) or the cooling tower (wood delignification). Laboratory screening procedures are coupled with maintaining a residual level of the biocide to ensure the maximum "kill" rate. This method has typically resulted in a periodic underfeed, leading to organism growth, or overfeed, adding unneeded expense and potential component damage, but typically all microbiological control programs are designed to eliminate 99% or more of the organisms in the water, as well as prevent any future growth from occurring. Oxidation Reduction Potential (ORP) can be implemented to rectify the underfeed and the overfeed problems. This ORP value is a direct reading of the activity of the oxidizing as well as reducing agents in the water. Measurement of ORP offers major improvements over treatment programs using residual control of an oxidizing microbiocide, resulting in improved life for heat exchangers and cooling towers, minimal usage of treatment chemicals for chlorinating and dechlorinating, and increased efficiency of plant processes that utilize the cooling water for heat exchange purposes. This review work will provide an insight to the vital destruction being created by the microorganisms in the industrial cooling water system. Also the mode of action of the biocides and importance of ORP measurements are discussed briefly.