Many industries including the food, chemical, pharmaceutical, paint, oil processing and manufacturing, and engineering industries uses water either in the process or as a utility (cooling, lubrication etc). The water source contains all the naturally occurring living organisms and nutrients that are responsible for uncontrolled multiplication of the living organisms. The cooling water systems provide the ideal condition (32-38 ºC in the water temperature and 8-9 in pH) for the biofouling. The growth of living organisms like bacteria, algae & fungi on the surface which comes in contact with water for a period of time leads to biofouling.
This process begins with the formation of a thin layer of micro organisms on the solid surface. A number of organisms including bacteria, protozoa, amoebae, fungi, barnacles and other organisms have been shown to form bio-films that create nuisances in man-made environments after the equipment functioning. These bio-films are formed as results of gummy substances excreted by microorganisms, having a property of adherence. Bio-films are reservoirs of pathogenic organisms giving protection against disinfectant action. The metabolic activities of these organisms results into formation of acidic environment which enhances the dissolution of material from the surfaces. The organic acids that are waste products of bacterial metabolism get between the biofilm and the heat exchanger surface and corrode the surface. The growth of a bio-film can progress to a point where it provides a foundation for the growth of seaweed, barnacles, and other organisms. This bio-film results into bio-fouling.
Power generation stations are frequent targets of fouling invertebrates, including zebra mussels, colonial hydroids, bryozoans, and sponges. An optimal combination of abundant food, warm temperatures, flowing water can result in serious growths in the intake chambers, filters, condenser tube sheets, and other structures. While the populations may die off seasonally, they leave behind dormant reproductive bodies capable of producing a new, larger generation when conditions are favorable. Microbial fouling with direct or indirect corrosive effects and interference in re-circulation is controlled by using chemicals collectively known as biocides, which have either cidal or inhibitory action on microorganisms. Various factors influence biocidal activities of these chemicals and among these, development of resistance and immunity is the most important one and is mainly responsible for inactivation of biocides. Bacteria can develop resistance to destroy biocides by:
- producing enzymes
- change in internal structure of cell
- change in permeability of the cytoplasmic membrane
- change in the composition of cell wall and mutations and genetic transfer
Effect of biofouling on Human health & process equipment:
Biofouling is the important contributor to impaired heat transfer causing decrease in efficiency and increased power consumption. In fact, it has been unequivocally demonstrated that because of the unique surface characteristics of bio-films, their hydrodynamic and insulating properties far exceed those of an equivalent thickness of inorganic scales or corrosion deposits. Biofouling can destroy cooling tower lumber. Apart from biofouling; the biological growth plays an important role in promoting corrosion through the formation of acid metabolic products resulting in corrosion and damages the heat transfer and other process equipments, pipelines, water conducting system.
More seriously, such contaminants can be harmful to humans coming in contact like operational and maintenance personnel. The most notable example has been the outbreaks of Legionnaires' disease, affected people in hotels, hospitals, office buildings and other locations, who had come into contact with cooled air from an air conditioning system contaminated from cooling tower water of the air conditioning plant. According to the Center for Disease Control, when bacterial populations reach or exceed 500,000 colonies per ml there is an enhanced risk of Legionella growth.
In today's world of expensive energy, it is more vital than ever for, heat exchange equipment to be kept free of bio-films that result into high energy consumption due to reduced thermal efficiency. Usually, biofouling is only detected after it has already caused considerable damage. The challenge thus lies in finding a solution to prevent the formation of biofouling rather than treating it after it has caused damage to the systems.
More information on Biofouling
- Biology of Cooling Waters
- Steps in Biofilm Formation
- Our solution : HyCator® BFP for prevention of Biofouling