Biocides in cooling water systems

Kaur, K., 1990, Ozone as a biocide in cooling water systems PhD Thesis, University of Birmingham. 

In spite of high effectiveness of oxidizing biocides in cooling water systems, it is sometimes difficult to control problem organisms just with oxidizers alone. High reactivity and low persistence of most of oxidizers can leave some microorganisms unharmed, especially those that proliferate in biofilms. Therefore, the need exists in other classes of biocides that are more persistent and aimed at organisms less effected by oxidizers. 

Tributyl(tetradecyl)phosphonium chloride was developed specifically (26,27) as a broad-spectmm biocide for the control of biological fouling in cooling water systems where it is particularly effective (see Industrialantimicrobialagents). 

Donohue, J.M., A.J. Piluso, and J.R. Schreiber. 1966. Acrolein — a biocide for slime control in cooling water systems. Mater. Protect. 5 22-24. 

Kurtz, John B. Bartlett, Christopher Tillet, Hilary Newton, Ursula. Field Trial of Biocides in Control of Legionella Pneumophila in Cooling Water Systems. Ecology and Environmental Control, UK, 1983. 

It should be noted that the new biocide has an excellent microbicidal activity against Legionella pneumophila in cooling-water systems. [8]... 

Bott, T. R., 1998. Techniques for reducing the amount of biocide necessary to counteract the effects of biofihn growth in cooling water systems. Applied Thermal Engineering 18, 1059-1066. 

Microbiocide H-130 is registered by the Environmental Protection Agency (EPA Registration No. 10445-12) as a biocide for use in cooling water systems. 

In cooling water applications, great importance is placed on activity against Legionella pneumophila, the causative agent of Legionnaires disease. Bromochloro dimethylhydantoin has been shown to rapidly hydrolyze in water with the formation of hypobromous acid (21). The pKa of hypobromous acid is 8.8, whereas the pK of hypochlorous acid is 7.4. Because the undissociated hypohalous acid is the active biocide, the hypobromous-generating chemical is more active in alkaline systems. 

Where chlorine dioxide is used in large process cooling systems, it is not uncommon for significant levels of sulfides to be present in the cooling water system. A benefit of chlorine dioxide biocide is its additional ability to readily oxidize this sulfide however, good monitoring and control is necessary, as high initial sulfide levels can result in mineral acid formation and the potential for corrosion to occur ... 

Many of the nonoxidizing biocides employed in cooling systems today were originally developed for other applications, such as slimicides for pulp and paper, biostats for cosmetics, or sanitizers for food factories. The experience gained for these applications has proved to be useful for cooling water systems. Some products that have been available for several years have been, or are being, launched into new and different markets, especially where environmental concerns have a high profile. 

Apart from the primary components of a cooling water system, all ancillary equipment such as level controllers, bleed systems, dosing and control systems, low-level alarms, pH controllers, and on-site biocide generation systems should be regularly inspected, cleaned, calibrated, and maintained in good working order. 

Chlorine has been a preferred biocide for many years on account of its effectiveness and its relatively low cost. It has been used particularly in once through cooling water systems where large volumes of water are used, in order to minimise the cost of treatment. It is effective against micro- and macro-organisms. 

A number of papers have been published on the merits and application of ozone in industrial cooling water systems. Claims made in a patent [Humphrey et al 1979] are that ozone in concentrations of 2 - 20 mg/l prevents scale formation and removes existing scale, passivates metal surfaces to inhibit further corrosion and disinfects the water to prevent algae growth. Edwards [1983, 1987] and Edwards and Sellers [1991] have published valuable reviews of ozone technology and cooling water. As well as biocidal activity the benefits of using ozone include ... 

The use of tributyltin and copper biocides may not be a matter of concern for ocean going vessels where the dilution is infinite, but the use of these biocides in conjunction with say cooling water systems, is not recommended because of the toxic effect and environmental risks. In order to utilise the technique for heat exchangers therefore, it would be necessary to develop suitable biocides that may be incorporated in the resin matrix and still be effective in controlling biofilm formation and growth, without detrimental effects. 

Fig. 16.3 gives the flow sheet of a cooling water system commonly used in power generation that is also used in the process industries. Chemicals such as acids, biocides, scale and corrosion inhibitors and dispersants are added to control problems of fouling in the recirculating system (described elsewhere in this book). The technique is generally applicable where the make-up water is generally of low hardness and silica and low concentration factors are employed. 

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