Reverse Osmosis and Ion Exchange

The preceding example of a reverse osmosis industrial application at a refinery showed that the process is capable of  

Reverse osmosis also has been used to treat municipal water supplies for industrial purposes even though these supplies are generally low in turbidity, suspended solids and dissolved solids. A large number of reverse osmosis systems have been installed in industrial plants to prepare industrial process water with municipal water as the feed source. A significant number of these industrial applications are to either replace ion exchange demineralization or to pretreat municipal supplies prior to ion exchange demineralization. 

Reverse osmosis systems now commercially available will remove 95% or more of the dissolved solids normally removed in ion exchange, and as will be discussed later, a few that are not. The ionized solutes are not all removed to the same degree by reverse osmosis any more than ion exchange resins have the same effect on all solutes. Divalent and multivalent ions, such as calcium, magnesium, sulfate, iron and manganese, can be rejected to greater than 99%. So- 

An important factor to be remembered is that in some cases water supplies unsatisfactory for processing to high purity water may be the only sources available. Preliminary demineralization by reverse osmosis will make this water suitable for subsequent demineralization by ion exchange. It is thus apparent that such an economically important factor as plant site location, which may be dependent on the availability of suitable water, can be made more flexible through the use of reverse osmosis. It may be possible now to utilize seawater as a source of industrial process water. 

During the 1960 s, reverse osmosis was compared with other methods of demineralization. It was indicated in these comparisons that reverse osmosis could not compete favorably with ion exchange at dissolved solids concentrations below 700 mg/fi and that its most favorable area of use would be from about 1,200 to 5,000 mg/6 dissolved solids. This idea has been totally refuted because some of the most successful applications of reverse osmosis, particularly as part of the process to produce high purity water, have been in treating low dissolved solids water. Water containing 200 mg/ dissolved solids or less has been treated at costs equal to or lower than those of ion exchange alone. 

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Recycling of wastes is the preferable waste management method after source reduction opportunities have been exhausted. Recycling can be performed within the process itself, within the plant, or off-site, and can involve reuse of the entire waste stream, or recovery of a part of it. Recovery of the stream s metal content can be achieved through operations such as electrolytic recovery, reverse osmosis, and ion exchange. 

Other methods to achieve bitartrate stability, rarely used in the North Coast, are addition of metatartaric acid, electrodialysis, reverse osmosis, and ion exchange. Concern with potential bitartrate instability varies from winery to winery. Some enologists prefer to keep the processing of wine to a minimum. They rely solely on cool fermentation and winter storage temperatures to precipitate excess bitartrates. They trust their customers will overlook any additional bitartrate crystals that precipitate out in bottled wines. 

Iron and manganese may be removed by reverse osmosis and ion exchange. The unit operation of reverse osmosis was discussed in a previous chapter the unit process of ion exchange is discussed in a later chapter. This chapter discusses the removal of iron and manganese by the unit process of chemical precipitation. 

One of the most innovative industrial uses of reverse osmosis is at the Petromin Refinery in Riyadh, Saudi Arabia. The refinery takes an unusable municipal wastewater, secondary effluent from the Riyadh sewage treatment plant, and by using lime clarification, filtration, reverse osmosis and ion exchange demineralization, it converts that useless waste into the entire process water requirements for the refinery. Figure 4.16 is the process flow schematic for the refinery water treatment plant. 

Lipnizki, J. et al.. Water treatment Combining reverse osmosis and ion exchange. Filtration and Separation, 2012.49(5) 30-33. 

Co-continuous blend structures find industrial application in selective, reverse osmosis and ion exchange membranes requiring specific functional properties. For example, PA/polyester blends could be appropriate for hydrophilic microporous separation and filtratirMi membranes when the phases form a co-continuous structure with domain sizes ranging from 0.01 to 10.0 pm (Harrats and Makhilef 2006a). 

Krause [13] reviewed empirical evidence of the activity of microdomains in block copolymer membranes such as those used for reverse osmosis and ion exchange processes. Depending on whether they are dispersed or continuous, the microphases may either sequester compatible solutes or serve as channels for their transport through the membrane. Partitioning of solutes into the microdomains was found to be a complex function of solute structure and microdomain structure and composition and could not easily be predicted quantitatively. 

Coker, S. D., Beardsley, S. S., and Whipple, S. S. (1994). An economical comparison of demineralization with reverse osmosis and ion exchange technology. Power-Gen Americas. Las Vegas, Nevada. 

Xylose is obtained from sulfite Hquors, particularly from hardwoods, such as birch, by methanol extraction of concentrates or dried sulfite lyes, ultrafiltration (qv) and reverse osmosis (qv), ion exchange, ion exclusion, or combinations of these treatments (201). Hydrogenation of xylose is carried out in aqueous solution, usually at basic pH. The Raney nickel catalyst has a loading of 2% at 125°C and 3.5 MPa (515 psi) (202,203). 

To understand the sorption of small organic molecules containing no major hydrophilic groups by a reverse osmosis or ion exchange membrane, and thus the transport of these molecules through the membrane, it is necessary to consider the interaction of the hydrophobic molecule with only the hydrophobic portion of the membrane polymer. 

For those laboratories producing in-house LC-giade water it is important that the proper filters/iesins (e.g., carbon, reverse osmosis [RO], ion exchange) are installed to yield the correct level of purity. Many different systems are commercially marketed, and a detailed list of laboratory needs and uses will help the manufacturer of the system assemble the correct configuration (i.e., the order of the filters as well as the type). 

Desalination (0011-9164) (1873-4464). Desalination covers all desalting fields—distillation, membranes, reverse osmosis, electrodialysis, ion exchange, freezing, water purification, water reuse, and wastewater treatment—and aims to provide a forum for any innovative concept or practice. 

The final step is the tertiary treatment. It is used for specific contaminants which cannot be removed by the secondary treatment. This phase is not always present in a WWT, it depends on the origin of the sewage and the final use of the water output. Individual treatment processes sometimes are necessary to remove nitrogen, phosphorus, additional suspended solids, refractory organics, heavy metals and dissolved solids. The technologies to be used depend on the contaminants which must be removed, i.e. filters and separation membranes, systems for dechlorination and disinfection, reverse osmosis systems, ion exchangers, activated carbon adsorption systems and physical-chemical treatments. 

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. 

Indian Ion Exchange and Chemical Industries - Produces reverse osmosis and demineralization systems, base exchange softeners, clarifiers and filters, degassers and de-aerators, filtration and micro filtration systems, effluent treatment plant...http //www.indianionexchange.com. ... 

For removing low levels of priority metal pollutants from wastewater, using ferric chloride has been shown to be an effective and economical method [41]. The ferric salt forms iron oxyhydroxide, an amorphous precipitate in the wastewater. Pollutants are adsorbed onto and trapped within this precipitate, which is then settled out, leaving a clear effluent. The equipment is identical to that for metal hydroxide precipitation. Trace elements such as arsenic, selenium, chromium, cadmium, and lead can be removed by this method at varying pH values. Alternative methods of metals removal include ion exchange, oxidation or reduction, reverse osmosis, and activated carbon. 

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. 

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. 

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. 

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