Water treatment systems

Apart from sodium hypochlorite and sodium bromide solutions, almost all other liquid biocides (or biocide intermediates) are nonoxidizer types. Most nonoxidizers are manufactured by specialist chemical companies, who sell these branded products for scores of different sanitizing or disinfection applications, of which cooling water system treatment is only one. These chemicals may be merely renamed (according to subregistration permits) or they may be blended with other biocides or inhibitors to form new and different products with accordingly modified properties. Some biocides may only be available from the primary manufacturer, often as extremely concentrated and hazardous materials. These chemicals will then usually require some form of dilution, stabilization, and quality verification before being incorporated into a service company s product line. 

Sludge disposal typically can be responsible for 25 to 40 percent of the operating costs of a biological treatment system. Treatment of sludge is aimed primarily at reducing its volume. This is so because the sludge is usually 95 to 99 percent water and the cost of disposal... 

Sequestration forms the basis for detergent and water-treatment appHcations of polyphosphates. Sequestration of hardness ions by sodium tripolyphosphate used in detergent formulations prevents the precipitation of surfactants by the hardness ions. Sodium polyphosphate glass (SHMP) may be added to water system to prevent the formation of calcium or magnesium scales by reducing the activity of the hardness ions. However, if the ratio of cation to polyphosphate is too high at a given pH, insoluble precipitates such as may result instead of the soluble polyphosphate complexes. The... 

Saline Water for Municipal Distribution. Only a very small amount of potable water is actually taken by people or animals internally, and it is quite uneconomical to desalinate all municipally piped water, although all distributed water must be clear and free of harmful bacteria. Most of the water piped to cities and industry is used for Htfle more than to carry off small amounts of waste materials or waste heat. In many locations, seawater can be used for most of this service. If chlorination is requited, it can be accompHshed by direct electrolysis of the dissolved salt (21). Arrayed against the obvious advantage of economy, there are several disadvantages use of seawater requites different detergents sewage treatment plants must be modified the usual metal pipes, pumps, condensers, coolers, meters, and other equipment corrode more readily chlorination could cause environmental poUution and dual water systems must be built and maintained. 

Wood preservatives ate appHed either from an oil system, such as creosote, petroleum solutions of pentachlorophenol, or copper naphthanate, or a water system. Oil treatments ate relatively inert with wood material, and thus, have Htde effect on mechanical properties. However, most oil treatments require simultaneous thermal treatments, which ate specifically limited in treating standards to preclude strength losses (24). 

The wash water mixed with paint which is a strong waste can be transferred (periodically, if the water curtain system is a closed cycle rather than a continuous running water system) to the effluent treatment plant for further treatment, as shown in Figure A13.12. 

A National Primary Drinking Water Regulation (NPDWR or primary standard) is a legally-enforceable standard that applies to public water systems. Primary standards protect drinking water quality by limiting the levels of specific contaminants that can adversely affect public health and are known or anticipated to occur in water. They take the form of Maximum Contaminant Levels (MCL) or Treatment Techniques (TT). 

Lead and copper are regulated by a Treatment Technique that requires systems to control the corrosiveness of their water. If more than 10% of tap water samples exceed the action level, water systems must take additional steps. For copper, the action level is 1.3 mg/L, and for lead is 0.015 mg/L. 

In the case of a closed water system, once the correct water treatment is provided, the incidence of microbiological fouling or corrosion is virtually eliminated, provided that the addition of fresh water is not a frequent occurrence. It is, however, essential to have water tests carried out at regular intervals by a water laboratory. 

Chemical consumption Chemical consumption will be associated with boiler feed make-up water-treatment plant, dosing systems for feedwater and boiler system, treatment of cooling water circuits and effluent treatment. Typical chemical requirements for a thermal power plant are given in Table 15.9. 

For food and drink, medical, pharmaceuticals and cosmetics production the microbiological quality of the water becomes paramount. Even in applications where biological quality is not directly important, uncontrolled growth can be a damaging nuisance. Warm-water systems and cooling circuits in particular are a potential hazard (e.g. from Legionella). Some water treatment or conditioning is commonly required. 

It is worthwhile drawing attention to health hazards associated with film infected water systems which also cause corrosion. Two of the most common are Legionnaires disease and so called humidifier fever . Because of strong adhesion of biofilms and diffusion rates through the film treatment based on cleaners and chemical sterilisers such as chlorine often fail similar considerations apply to other systems in industry, e.g. food, paint, oil and gas are examples where biofilm activities have given massive problems. 

Industrial Cooling Water Systems Waters used for recirculating cooling systems can either be scaling or corrosive. Corrosive waters are treated with corrosion inhibitors which require monitoring for overall assessment of the treatment programme. 

To limit the potential for waterside problems throughout the steam-water system cycle a balance of water treatment processes is required with external items of capital equipment providing primary duty for FW pretreatment and internal specialty chemicals providing a supporting, polishing function. 

Where water softening is provided and there is no reduction in system water TDS, treatments are primarily based on inorganic corrosion inhibitor blends (nitrite, molybdate, etc.). Under these circumstances, there is no benefit in using an expensive organic oxygen scavenger to keep the TDS level low, and a common chemical such as catalyzed sodium sulfite may be used. 

For more than 50 years, magnetic devices and other devices have been regularly tested and compared with other water treatment methods, notably chemicals. Although irrefutable, documented evidence of their beneficial effect in industrial water systems still seems sadly lacking, they have enjoyed a profitable share of the water treatment market. 

As discussed in the introduction, boiler water (BW) treatment programs enable the waterside chemistry of boilers and their associated systems to be controlled within certain agreed upon and relevant parameters and specifications. They provide a countermeasure against a wide range of adverse conditions that may strive to develop and hinder efficient boiler operation or cause serious damage. 

BSI recommends in the table of water treatment for hot water systems that chromate inhibitors should not be used because of their undesirable impact on the environment. It should also be noted that some treatment chemicals are microbiologically degraded in storage. 

Table 12.9 (BS 2486 1997 table 1) Water treatment for hot water systems... 

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