Raw water

Waste from steam systems. If steam is used as a hot utility, then inefficiencies in the steam system itself cause utility waste. Figure 10.9 shows a schematic representation of a steam system. Raw water from a river or other source is fed to the steam system. This is... 

A fourth mechanism is called sweep flocculation. It is used primarily in very low soflds systems such as raw water clarification. Addition of an inorganic salt produces a metal hydroxide precipitate which entrains fine particles of other suspended soflds as it settles. A variation of this mechanism is sometimes employed for suspensions that do not respond to polymeric flocculants. A soHd material such as clay is deUberately added to the suspension and then flocculated with a high molecular weight polymer. The original suspended matter is entrained in the clay floes formed by the bridging mechanism and is removed with the clay. 

Fixed investment includes cooling tower, boiler feedwater treatment, raw water ammonia storage as minimum off-sites requirement. 

Water reuse is usually a question of the tradeoff between the costs of raw water and the costs associated with treatment for reuse and for discharge. If biological treatment is to be employed, several factors must be considered. These are an increase in concentration of organics, both degradable and nondegradable. This may have a negative effect in terms of final effluent toxicity. An increase in temperature or total dissolved soHds may adversely affect the performance of the biological process. 

Suspended matter in raw water suppHes is removed by various methods to provide a water suitable for domestic purposes and most industrial requirements. The suspended matter can consist of large soflds, settleable by gravity alone without any external aids, and nonsettleable material, often colloidal in nature. Removal is generally accompHshed by coagulation, flocculation, and sedimentation. The combination of these three processes is referred to as conventional clarification. 

Table 1 Hsts a number of common inorganic coagulants. Typical iron and aluminum coagulants are acid salts that lower the pH of the treated water by hydrolysis. Depending on initial raw water alkalinity and pH, an alkah such as lime or caustic must be added to counteract the pH depression of the primary coagulant. Iron and aluminum hydrolysis products play a significant role in the coagulation process, especially in cases in which low turbidity influent waters benefit from the presence of additional colHsion surface areas.

Precipitation softening processes are used to reduce raw water hardness, alkalinity, siHca, and other constituents. This helps prepare water for direct use as cooling tower makeup or as a first-stage treatment followed by ion exchange for boiler makeup or process use. The water is treated with lime or a combination of lime and soda ash (carbonate ion). These chemicals react with the hardness and natural alkalinity in the water to form insoluble compounds. The compounds precipitate and are removed from the water by sedimentation and, usually, filtration. Waters with moderate to high hardness and alkalinity concentrations (150—500 ppm as CaCO ) are often treated in this fashion. 

Hot Process Softening. Hot process softening is usually carried out under pressure at temperatures of 108—116°C. At the operating temperature, hot process softening reactions go essentially to completion. This treatment method involves the same reactions described above, except that raw water COg is vented and does not participate in the lime reaction. The use of lime and soda ash permits hardness reduction down to 0.5 g/gal, or... 

Alkalinity Reduction. Treatment by lime precipitation reduces alkalinity. However, if the raw water alkalinity exceeds the total hardness, sodium bicarbonate alkalinity is present. In such cases, it is usually necessary to reduce treated water alkalinity in order to reduce condensate system corrosion or permit increased cycles of concentration. 

Treated Water Quality. Predicted analyses of a typical raw water treated by various lime and lime—soda softening processes are presented in Table 3. Treatment by lime converts the sodium bicarbonate in the raw water to sodium carbonate as follows ... 

Factor Raw water Removal of calcium alkalinity cold-lime Lime—soda softening (cold) Lime—soda softening (hot) Lime softening (hot) ... 

Removal of SiOg by the hot process, to the levels shown, may require the feed of supplemental magnesium oxide. Sludge recirculation is necessary. All raw water constituents will be diluted by the steam used for heating by approximately 15% if the process is hot. 

Lower alkalinity, raw water, silica, and CO2 removal required... 

High sodium, raw water, existing 2-bed system, low leakage required... 

Color can be removed effectively and economically with either alum or ferric sulfate at pH values of 5—6 and 3—4, respectively. The reaction is stoichiometric and is a specific reaction of the coagulant with the color to form an insoluble compound (17). The dosage required may be as high as 100—150 mg/L (380—570 mg/gal). Raw-water colors may be as high as 450—500 units on the APHA color scale. The secondary MCL (maximum contaminant level) for color in the finished water is 15 units, although most municipal treatment plants produce water that seldom exceeds 5 units. 

The two principal methods of softening water for municipal purposes are addition of lime or lime-soda and ion exchange. The choice method depends upon such factors as the raw-water quaUty, the local cost of the softening chemicals, and means of disposing of waste streams. 

Formerly, water was accepted by a second user for reuse while it was still under control of the first user (5). Today, the used water is treated in such a manner that it can be used again before ultimate disposal. Furthermore, a distinction can be made between direct reuse, where the water is reclaimed without dilution or natural purification, and indirect use, where treated used water is returned to the environment for subsequent utilization as a raw water supply. 

Figure 19-72 illustrates a dissolved-air flotation plant flowsheet for water treatment. The flowsheet shows that the incoming raw water is... 

Let s consider an industrial boiler. You may need at least three of these previous mentioned o-rings just to prevent leaks and drips in a simple hydronie or steam boiler. Raw water comes into the boiler room with pipes, gauges, valves and instrumentation. All these fittings would probably use Nitrile rubber o-ring seals to give long-term leak free service. 

Next, the raw water must be treated before it can be pumped into the boiler. Treating the boiler water does three things. First it controls the... 

The fluid being pumped is often not well defined. Terminology like well water, industrial effluent, raw water, boiler feed water, condensate water, etc., is usually the only definition we have of the fluid being pumped. Any of these fluids can contain several concentrations of. solids that cause erosion and wear inside the pump. 

Figure 20-14 shows the protection of a gravel filter in the treatment of raw water. The 200-m internal surface was coated with 300 jlm of tar-pitch epoxy resin. Long-term experiments indicated that at = -0.83 V, no cathodic blisters were formed, but were formed at more negative potentials (see Section 5.2.1.4). TiPt anodes 400 and 1100 mm in length, 12 mm in diameter, and with an active surface of 0.11 m were installed [29]. 

The RO system removes 90-95 % of the dissolved solids in the raw water, together with suspended matter (including colloidal and organic materials). The exact percent of product purity, product recovery and reject water depends on the amount of dissolved solids in the feedwater and the temperature at which the system operates. 

The number and complexity of unit processes and in turn unit operations comprising a water purification or wastewater treatment facility are functions of the legal and operational requirements of the treated water, the nature and degree of contamination of the incoming water (raw water to the plant), and the quantities of water to be processed. This means then, that water treatment facilities from a design and operational standpoints vary, but they do rely on overlapping and even identical unit processes. 

Hardness leakage is also dependent on the raw water characteristics. If the Na/Ca ratio and calcium hardness are very high in the raw water, leakage of the hardness ions will be higher. 

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