Chemical oxidizers for disinfection

Chemical Oxidizers for Disinfection of Reverse Osmosis Systems... 

This chapter deals with the same topic of chemical oxidation and disinfection, but at the advanced level. Specifically the engineering design and applications of chlorination processes for treatment of wastewater, biosolids, and septage are introduced in detail. 

Chemistry. Chemical processes are used to treat water and wastewater, to control air pollution, and for site remediation. These chemical treatments include chlorination for disinfection of both water and wastewater, chemical oxidation for iron and manganese removal in water-treatment plants, chemical oxidation for odor control, chemical precipitation for removal of metals or phosphorus from wastewater, water softening by the lime-soda process, and chemical neutralization for pH (acidity) control and for scaling control. 

Propylene oxide is a useful chemical intermediate. Additionally, it has found use for etherification of wood (qv) to provide dimensional stabiUty (255,256), for purification of mixtures of organosiUcon compounds (257), for disinfection of cmde oil and petroleum products (258), for steriliza tion of medical equipment and disinfection of foods (259,260), and for stabilization of halogenated organics (261—263). 

UV radiation is also the basis of several chemical oxidation technologies where the action of radiation and free radicals generated in the process allow for a high degree of micropollutant degradation and/or disinfection. Similar to ozonation or hydrogen peroxide oxidation, UV radiation may act on the matter present in water in two dilferent ways direct photolysis or indirect photolysis (e.g., free radical oxidation). 

A 30 or 40 per cent by volume hydrogen peroxide is used as bleach for silk, wood, Wool, bones, teeths, feathers, mother of pearl, hom, hair, coral, gelatine, oils and fats. In medical science it is an excellent disinfectant and is also essential for sterilizing water for municipal use and preserving milk. Apart from this, hydrogen peroxide is used in the chemical industries for the manufacture of persalts and in laboratories for oxidation. 

In addition to dioxygen, many other chemical oxidants are used for water and waste treatment purposes. Not surprisingly, they also tend to be powerful microorganism deactivators (and thus good disinfectants) because they may induce abnormal redox processes in cells that kill or deactivate them (or else prevent their reproduction) by the following possible mechanisms attack or alteration of the cell wall, of the cell contents (nucleic acids, protoplasm), or of the cell functions and processes (protein synthesis, redox processes, enzymatic activity). 

Polyamide membranes are also not resistant to the strong oxidizing actions of disinfectants such as hydrogen peroxide and hypochlorite. Acids used to the clean membrane system must be rinsed out thoroughly before application of hypochlorite for disinfection as hypochlorite at low pH can cause corrosion in stainless steel. The pH of the chemical cleaning solution must fall within the tolerable range of pH 1-13 for polysulfone membranes and pH 3-8 for CA membranes (87). 

Chlorine in elemental or hypochlorite salt form is a strong oxidizing agent in aqueous solution and is used in water treatment for disinfection, and in industrial waste treatment facilities primarily to oxidize cyanide. Chlorine and hypochlorites can also be used to oxidize phenol-based chemicals, but their use is limited because of the formation of toxic chlorophenols if the process is not properly controlled. 

Chemical redox is a full-scale, well-established technology used for disinfection of drinking water and wastewater, and it is a common treatment for cyanide (oxidation) and chromium [reduction of Cr(VI) to Cr(III) prior to precipitation] wastes. Enhanced systems are now being used more frequently to treat hazardous wastes in soils. Figure 4 shows a typical site remediation project involving the use of chemical redox (chemical reduction/oxidation) for removal of chromium from the environment (22). 

Chemical oxidation shows several potential benefits compared to other treatment options. The main advantage is the possible minerahzation of organic substances to carbon dioxide and water. The substance can be completely de-structed and is not only simply enriched or shifted into another phase [33]. Furthermore, there is also a disinfecting effect if ozone is used. Ozonation is the oxidative treatment process most widely spread in drinking water treatment—though it is mainly implemented for disinfection and the oxidation is only considered a beneficial side effect [28]. 

A number of chemical oxidants are currently being used either as disinfectants for potable or swimming pool waters, or for the destruction of organic and inorganic chemical species found in wastewaters. The most commonly used oxidants for the above purposes are ozone, hydrogen peroxide, chlorine, chlorine dioxide, sodium and calcium hypochlorite, and potassium permanganate. 

Disinfection byproducts Side reactions can occur in water when chemical oxidants such as chlorine and ozone are used to control potentially pathogenic microorganisms. These reactions can form low levels of disinfection byproducts, several of which have been regulated for potential adverse human health effects. 

---