Water softening reverse osmosis

Makeup. Makeup treatment depends extensively on the source water. Some steam systems use municipal water as a source. These systems may require dechlorination followed by reverse osmosis (qv) and ion exchange. Other systems use weUwater. In hard water areas, these systems include softening before further purification. Surface waters may require removal of suspended soHds by sedimentation (qv), coagulation, flocculation, and filtration. Calcium may be reduced by precipitation softening or lime softening. Organic contaminants can be removed by absorption on activated carbon. Details of makeup water treatment may be found in many handbooks (22—24) as well as in technical Hterature from water treatment chemical suppHers. 

The individual membrane filtration processes are defined chiefly by pore size although there is some overlap. The smallest membrane pore size is used in reverse osmosis (0.0005—0.002 microns), followed by nanofiltration (0.001—0.01 microns), ultrafHtration (0.002—0.1 microns), and microfiltration (0.1—1.0 microns). Electro dialysis uses electric current to transport ionic species across a membrane. Micro- and ultrafHtration rely on pore size for material separation, reverse osmosis on pore size and diffusion, and electro dialysis on diffusion. Separation efficiency does not reach 100% for any of these membrane processes. For example, when used to desalinate—soften water for industrial processes, the concentrated salt stream (reject) from reverse osmosis can be 20% of the total flow. These concentrated, yet stiH dilute streams, may require additional treatment or special disposal methods. 

Hardness Calcium, magnesium, barium and strontium salts expressed as CaCOa Chief source of scale in heat exchange equipment, boilers, pipe lines, etc. forms curds with soap interferes wKh dyeing, etc. Softening, distillation, internal boiler water treatment, surface active agents, reverse osmosis, electrodialysis... 

Provision of pretreatment The initial fill volume and MU supply is almost always pretreated in some manner. Because of the large volume of water in these systems, even low-hardness waters can produce sufficient quantities of calcium carbonate scale to severely impede heat transfer thus, for MTHW pretreatment, the use of ion-exchange softeners is the norm. For HTHW, some form of demineralization such as reverse osmosis (RO) or deionization by cation-anion exchange is typically preferred. 

Chemical treatment is apphcable usually to raw, mains and softened water, but is also used to treat the storage and distribution systems of distilled and deionized water and of water produced by reverse osmosis (seetion 3.5). 

In modern high-pressure systems, blowdown water is normally of better quality than the water supply. This is because plant intake water is treated using clarification, filtration, lime/lime soda softening, ion exchange, evaporation, and in a few cases reverse osmosis to produce makeup for the boiler feedwater. The high-quality blowdown water is often reused within the plant for cooling water makeup or it is recycled through the water treatment and used as boiler feedwater. 

Reverse osmosis is a process used by some plants to remove dissolved salts. The waste stream from this process consists of reverse osmosis brine. In water treatment schemes reported by the industry, reverse osmosis was always used in conjunction with demineralizers, and sometimes with clarification, filtration, and ion exchange softening. 

Feed water Portable, softened, or deionized water Water for injection (distilled, reverse osmosis) or purified water... 

Other grades of water may be present in parenteral facilities for use as initial rinses and detergent cleaning. The water utilized for these purposes is generally of relatively low bioburden and is often deionized, softened, ultra-filtered, or in some instances prepared by distillation or reverse osmosis, resulting in chemical purity similar to, if not identical to, WFI. Systems for the preparation of this water are subject to qualification, validation, and routine analysis to assure consistent quality. 

In some regions of the southwest United States, the water is very hard. For example, in Las Cruces, New Mexico, the tap water contains about 560 /xg of dissolved solids per milliliter. Reverse osmosis units are marketed in this area to soften water. A typical unit exerts a pressure of 8.0 atm and can produce 45 L of water per day. 

In general, water is softened in three ways chemical precipitation, ion exchange, and reverse osmosis. Only the chemical precipitation method is discussed in this chapter. 

Conventional softening treatment plant may not remove the impurities in water to the recommended permissible level. Demineralised or reverse osmosis technique is needed for removal of TDS from water but is costly. Water purification in the process house normally consists of floculation, sedimentation, filtration and ion-exchange. Hard water is normally softened using one or combination of methods the details of each process is given in many text books. 

Fluoride intoxication was reported in 1980 in eight patients from a single dialysis unit. The patients developed nausea, vomiting, diarrhea, itching, hypotension, and substemal pain. One patient died. The incident was traced to the spillage of a large amount of hydrofluosilicic acid into the district s water purification plant because of the failure to close a valve. The dialysis unit in question used a water softener only and did not employ reverse osmosis or deionization (All). 

After the break tank, process water is treated using various equipment and technologies depending on its intended use and the water analysis. Some of the technologies are multimedia filtration, water softening, activated carbon adsorption, UV treatment, deionization, ultrafiltration, reverse osmosis, final filtration and distillation. 

Water is softened to remove the scale-forming hardness elements. Soft water is required for boilers, water heaters, cooling towers, reverse osmosis systems, etc. Softening is an ion-exchange process which replaces almost all of the metallic or cations by sodium ions and sometimes, the anions with chlorine ions. Therefore, a constant supply of salt is required. 

Sodium ions may naturally be present in drinking water if the supply is brackish, like many water sources in Central Asia and the Middle East. Above about 300-400 ppm of sodium chloride, the water is unpalatable on account of its chloride content, and special purification measures, such as reverse osmosis (see below Section 6) are required. Naturally soft water frequently contains sodium rather than the hardness cations calcium and magnesium, while water softening artificially in domestic water softeners has the hardness cations replaced by sodium (see below Section 5). Even though... 

---