Reverse Osmosis RO

Membrane Sep r tion. The separation of components ofhquid milk products can be accompHshed with semipermeable membranes by either ultrafiltration (qv) or hyperfiltration, also called reverse osmosis (qv) (30). With ultrafiltration (UF) the membrane selectively prevents the passage of large molecules such as protein. In reverse osmosis (RO) different small, low molecular weight molecules are separated. Both procedures require that pressure be maintained and that the energy needed is a cost item. The materials from which the membranes are made are similar for both processes and include cellulose acetate, poly(vinyl chloride), poly(vinyHdene diduoride), nylon, and polyamide (see AFembrane technology). Membranes are commonly used for the concentration of whey and milk for cheesemaking (31). For example, membranes with 100 and 200 p.m are used to obtain a 4 1 reduction of skimmed milk. 

Reverse osmosis (RO) can be employed to remove and recover heavy metals, particulady nickel. 

Common membrane processes include ultrafiltration (UF), reverse osmosis (RO), electro dialysis (ED), and electro dialysis reversal (EDR). These processes (with the exception of UF) remove most ions RO and UF systems also provide efficient removal of nonionized organics and particulates. Because UF membrane porosity is too large for ion rejection, the UF process is used to remove contaminants, such as oil and grease, and suspended soHds. 

Reverse Osmosis. A reverse osmosis (RO) process has been developed to remove alcohol from distilled spirits without affecting the sensory properties (14). It consists of passing barrel-strength whiskey through a permeable membrane at high pressure, causing the alcohol to permeate the membrane and concentrating the flavor components in the retentate. 

Retention Rejection and Reflection Retention and rejection are used almost interchangeably. A third term, reflection, includes a measure of solute-solvent coupling, and is the term used in irreversible thermodynamic descriptions of membrane separations. It is important in only a few practical cases. Rejection is the term of trade in reverse osmosis (RO) and NF, and retention is usually used in UF and MF. 

Process Description Reverse osmosis (RO) and nanofiltration (NF) processes utilize a membrane that selectively restricts flow of solutes while permitting flow of the solvent. The processes are closely related, and NF is sometimes called loose RO. They are kinetic processes, not equilibrium processes. The solvent is almost always water. 

For organic contaminant removal from surface water packed-tower aeration, granular activated carbon (GAC), powdered activated carbon (PAC), diffused aeration, advanced oxidation processes, and reverse osmosis (RO). 

The technology that competes with ion exchange in wastewater application is reverse osmosis (RO), therefor it is appropriate to make some comparisons. Direct cost comparisons are not straightforward, and requires comparison of some of the hidden cost parameters. Since there appear to be few detailed comparisons in the open literature, there exists the general impression that RO is more economical than ion exchange. Whereas this may be true in a number of applications, as a general rule this is not the case. 

Among the technologies listed in Table 11.1, reverse osmosis RO has gained significant commercial acceptance. Therefore, the remainder of this chapter will discuss RO systems as representative of membrane-separation technologie,s. 

Membranes used for the pressure driven separation processes, microfiltration (MF), ultrafiltration (UF) and reverse osmosis (RO), as well as those used for dialysis, are most commonly made of polymeric materials. Initially most such membranes were cellulosic in nature. These ate now being replaced by polyamide, polysulphone, polycarbonate and several other advanced polymers. These synthetic polymers have improved chemical stability and better resistance to microbial degradation. Membranes have most commonly been produced by a form of phase inversion known as immersion precipitation.11 This process has four main steps ... 

The electrical conductivity of the water is critical to the correct operation of this type of boiler, and the precise level varies with design and power requirements. However, the conductivity is always relatively low (often specifications require a level of below 15-50 p,S/cm), so demineralized or reverse-osmosis (RO) quality FW is usually specified. 

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). 

The use of reverse osmosis (RO), electrodialysis reversal (EDR) and other membrane techniques, and evaporation or demineralization may be applicable when a reduction in the TDS content of the MU water source is required. 

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. 

Ionic silica is not totally removable by DI. Colloidal silica is difficult to remove by both DI and reverse osmosis (RO) it may cause some resin fouling as well as leaking into the treated water. Where the cation effluent is maintained at a pH of 2.0 to 3.0, however, silica tends to both depolymerize and ionize thus enabling its effective removal in strongly basic, anion resin beds. 

Water produced by reverse osmosis (RO) is forced by an osmohc pressure through a semi-permeable membrane which acts as a molecular filter. The difiusion of solubles dissolved in the water is impeded, and those with a molecular weight in excess of 250 do not difftise at all. The process, which is the reverse of the natural process of osmosis, thus removes microorganisms and their pyrogens. Post-RO contaminahon m occur if the plant after the membrane, the storage vessel or the distribuhon system is not kept Ifee Ifom microorganisms. 

An survey of recent developments in membrane processes, involving reverse osmosis (RO), ultrafiltration (UF), microfiltration (MF), electrodialysis (ED), dialysis (D), pervaporation (Pr), gas permeation (GP), and emulsion liquid membrane (ELM), has been provided by Sirkar (1997). 

Reverse osmosis (RO) recovers plating chemicals from plating rinsewater by removing water molecules with a semipermeable membrane. The membrane allows water molecules to pass through, but blocks metallic salts and additives.29... 

---