Ion exchange, reverse osmosis

The pre-boiler, FW supply should normally be of demineralized quality, such as may be provided by ion exchange, reverse osmosis (RO), or similar process. Extremely efficient mechanical deaeration also is required because the path length from the FW tank to the boiler is usually quite short, and thus the contact time is generally inadequate for the sole use of chemical oxygen scavengers (even catalyzed scavengers). 

Ion exchange Reverse osmosis Nano-filtration Electro dialysis Crystallization Evaporation Acid Base Heat treatment UV light Chemical oxidation... 

Chemical precipitation has traditionally been a popular technique for the removal of heavy metals and other inorganics from wastewater streams. However, a wide variety of other techniques also exist. For example, ion-exchange, reverse osmosis, evaporation, freeze crystallization, electrodialysis, cementation, catalysis, distillation, and activated carbon have all been used for removal of inorganics. 

Low-volume waste sources include water treatment processes that prevent scale formation such as clarification, filtration, lime/lime soda softening, ion exchange, reverse osmosis, and evaporation. Also included are drains and spills from floor and yard drains and laboratory streams. 

This technology removes dissolved metals from liquid wastes at a lower cost then other treatment options, such as precipitation followed by clarification and conventional filtration, ion exchange, reverse osmosis, and electrolysis. An advantage of the DuPont/Oberlin microfiltration technology is that it produces a dry, stabilized cake that can be landfiUed when used in conjunction with a filter aid/cake stabilizing agent. 

Table 1 shows treatment costs for the technology (based on a processing rate of 20 gpm) in comparison to other groundwater treatment technologies (i.e., chemical reduction and precipitation, chemical precipitation with sedimentation or filtration, activated carbon adsorption, ion exchange, reverse osmosis, and electrodialysis) (D168869, Table 13). 

Metal removal from surface water, groundwater or wastewater streams is more straightforward than that from soils. Typically, removal is achieved by concentration of the metal within the wastestream using flocculation, complexation, and/or precipitation. For example, the use of lime or caustic soda will cause the precipitation and flocculation of metals as metal hydroxides. Alternatively, ion exchange, reverse osmosis, and electrochemical recovery of metals can be used for metal removal (Chalkley et al., 1989 Moore, 1994). Unfortunately, these techniques can be expensive, time-consuming and sometimes ineffective, depending on the metal contaminant present. 

Water quality is usually defined in terms of chemical and bacteriological purity, particulate matter content, and endotoxin levels. Potable water is normally from the municipal water system, which may have been treated with chlorine to control microbiological growth. Soft water and deionized water have undergone ion exchange or similar treatment to eliminate unwanted ionic species, such as Mg2+ and/or Ca2+. Purified water, water for injection, and other types of water meeting compendial specifications are produced by ion exchange, reverse osmosis, distillation, or a combination of such treatments. 

Technology Ion Exchange Reverse Osmosis Biological Denitrification Catalytic Reduction... 

Tertiary treatments.These are used to convert chemicals diflficult to convert or not converted by secondary treatments, and when more stringent water quality is required examples are active carbon adsorption, ion exchange, reverse osmosis and the AOPs. 

Ion exchange, reverse osmosis, ultrafiltration, and air stripping can also be used for separating waste components, especially for waste-water treatment. 

The quality attributes of water for injection (WFI) are stricter than for purified water. Consequently, the preparation methods typically vary in the last stage to ensure good control of quality of WFI. Methods for the production of WFI are the subject of current debate. The PhEur 2005 indicates that only distillation would give assurance of consistent supply of the appropriate quality. However, the PhEur 2005 permits distillation, ion exchange, reverse osmosis, or any other suitable method that complies with regulations on water intended for human consumption laid down by the competent authority. 

Distfllation, ion exchange, reverse osmosis, and ultraviolet oxidation are processes used to prepare reagent grade water. In practice, water is often filtered before any of these processes are used. 

Purified water is typically prepared by ion exchange, reverse osmosis or a combination ofthe two treatment processes. Purified water is intended for use as an ingredient in the preparation of compedial dosage forms. It contains no added substances, and is not intended for use in parenteral products. It contains no chloride, calcium, or sulfate, and is essentially free of ammonia, carbon dioxide, heavy metals, and oxidizable substances. Total solids content will be no more than 10 ppm, pH will be 5-7, and the water will contain no coliforms. The United States Pharmacopoeia National Formulaiy (USP) requires that purified water comply with EPA regulations for bacteriological purity of drinking water (40 CFR 141.14, 141.21). Table 4 is a quantitative interpretation of United States Pharmacopoeia XXI standards for purified water. ... 

Senior engineers shall decide whether the water treatment facilities will be operated round the clock (all 24 h of a day, 7 days a week) or for about 8-12 h only per day. This will need bigger units for filtration, softeners, ion exchangers, reverse osmosis plants, etc. 

Today, various treatment techniques and processes have been used to remove the metallic ions from the wastewater, including precipitation, evaporation, solvent extraction, ion exchange, reverse osmosis, membrane separation, and so on. Most of these methods suffer from some drawbacks such as high capital and operational costs for the treatment and disposal of the residual metal sludge [32-34]. Therefore, efforts are made to develop low-cost materials to remove contaminants from aqueous solutions. Fortunately, recent development of nanotechnique has shed a light on this field. Nanoparticles, often characterized by a significant amount of surfaces, have been attracting much interest because of their unique properties and potential applications. 

Nowadays, numerous methods (physieal and ehemical processes) have been proposed for efficient heavy metal removal from waters, including but not limited to chemical precipitation, ion exchange, ultrafiltration, adsorption, ion-exchange, reverse osmosis, oxidation, ozonation, coagulation, flocculation, membrane filtration proeesses, sonication [175, 20] and electroehemieal teehnologies [55, 204, 144, 109, 57]. 

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