Biocides, oxidizing chlorine dioxide

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 ... 

Nevertheless, chlorine dioxide does have a valuable role to play. It is a useful chemical tool for solving particular, tough, combined biocidal and oxidation problems. 

Biocides are used widely in industry. There are at least three main classes of industrial chemical biocides. The first class includes the oxidizing and bleaching agents, such as chlorine dioxide, hydrogen peroxide, and sodium hypochlorite. The oxidizing action may directly kill bacteria or fungi or weaken the cell walls so that they are more susceptible to other classes of biocides (see below). Sodium... 

Typical biocides include hypochlorous acid, chlorine dioxide, hypobromus acid, hydrogen peroxide, ozone, ultraviolet-light treatment, phenolics, aldehydes, and quaternary ammonium compounds (Ref 73, 80). A brief description of each follows (Ref 73, 80). Hypochlorous acid is probably the most commonly used biocide and also one of the most powerful oxidizing agents. The sources of hypochlorous acid are chlorine gas and sodium hypochlorite. In aque-... 

Helz, G. R., R. Y. Hsu, and R. M. Block. 1978. Bromoform production by oxidative biocides in marine waters. In R. G. Rice and J. A. Cotruvo, Eds. Ozone-Chlorine Dioxide Oxidation Products of Organic Materials. (Cleveland, OH Ozone Press Inti.), pp. 68-76. 

Biocides such as chlorine dioxide and bromine compounds (oxidizers) are used for sterilization. The biocides might interfere with the performance of inhibitors and hence the concentration of biocides must be controlled. 

The following sections discuss the primary biocide used today, chlorine, and alternative physical and chemical techniques to address membrane biofouling control. The most common alternative techniques examined here include chloramine, chlorine dioxide, ozone, UV, and non-oxidizing biocides such as DBNPA and isothiazolone. Table 8.12 summarizes advantages and limitations of these techniques (adapted from Kim, 2009). It is important to note that some of these biocides/disinfectants can contact the membranes, and others must be removed or destroyed before the water is introduced to the membrane system itself. 

Chlorine dioxide is also an oxidizing biocide. Over the last 20 to 30 years, its use has increased significantly for disinfection, color reduction, and taste and odor control. While it minimizes the production of THMs by oxidizing the THM precursors, it does form chlorite and chlorate, both of which are considered disinfection by-products (DBPs). Note that the EPA has established a maximum contaminant level goal (MCLG) for chlorite of 0.8 ppm because 75% of chlorine dioxide that is applied to water forms chlorite, the maximum chlorine dioxide concentration allowable is... 

Other, safer alternative oxidizing solutions, such as ammonium persulfate, hydrogen peroxide, dilute peracetic acid, or a citric nitrate solution, should be considered. Another possible approach is the use of a nonoxidizing biocide such as hexamethylene biguanide or other environmentally safe biocides. These are free of the hazards associated with chloiine, h)q)ochlorite, chlorine dioxide, and other halogenated agents. 

Chlorination to residual chlorine content of a few tenths of a ppm is the usual treatment for control of biological growths in open recirculated systems. In order to discourage the development of chlorine-resistant strains, it is advisable to surprise the microbes at irregular intervals with other biocides (e.g., quaternary amines). Other oxidizing biocides (e.g., chlorine dioxide and ozone) used in municipal waters are normally too expensive for cooling water systems. 

The first point to emphasize is that crevice corrosion of passive alloys does not occur in environments deprived of oxidizing species other than water. Generally, it does not occtrr in deaerated solutions. On the contrary, oxidizing agents such as many biocides (hypochlorite, chlorine, chlorine dioxide, etc.) may catrse crevice corrosion. 

Biocides are commonly used for many industrial applications such as industrial water systems. Biocides may be divided into two categories (a) oxidizing agents such as chlorine, ozone, and chlorine dioxide and (b) nonoxidizing agents such as bisthiocyanate, isothiazolines, acrolein, dodecylguanidine hydrochloride, formaldehyde, glutaraldehyde, chlorophenols, and quaternary ammoniiun salts. 

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