Reverse-osmosis concentration advantages

The freeze concentration process is based on the partial solidification of water into ice in a fluid food product followed by the removal of the solid ice phase from the concentrated liquid phase. This process has some inherent advantages over evaporation and reverse osmosis for concentrating fluid foods as well as other process streams (1). One advantage is that essentially none... 

A second potential application is pressure-driven desalination. When a pressure difference is applied across the membrane, the concentrated ionic groups in the ion exchange domains are swept through the membrane, producing a salt-enriched permeate on the low-pressure side. This process, usually called piezodialysis, has a number of conceptual advantages over the alternative, conventional reverse osmosis, because the minor component (salt), not the major component (water), permeates the membrane. 

Membrane distillation offers a number of advantages over alternative pressure-driven processes such as reverse osmosis. Because the process is driven by temperature gradients, low-grade waste heat can be used and expensive high-pressure pumps are not required. Membrane fluxes are comparable to reverse osmosis fluxes, so membrane areas are not excessive. Finally, the process is still effective with slightly reduced fluxes even for very concentrated solutions. This is an advantage over reverse osmosis, in which the feed solution osmotic pressure places a practical limit on the concentration of a salt in the feed solution to be processed. 

An interesting alternative development is that of forward osmosis. Whereas in reverse osmosis a high pressure is required to oppose the natural tendency of freshwater to move across such a membrane via osmosis to dilute the seawater, in forward osmosis the system takes advantage of this natural tendency. Here, salt water sits on one side of the membrane, but the freshwater on the opposite side is transformed into a high-concentration solution by adding NH3 and CO2. Water naturally flows from the salt water to what is now the draw solution, which can have a solute concentration as high as 10 times that of the salt water. There is no need for an external pressure. The diluted draw solution is then heated to evaporate off the CO2 and NH3 for reuse, leaving behind freshwater. (See Patel-Predd, 2006). 

Nanofiltration or reverse osmosis treated water is needed in the most demanding places of the null such as for the high-pressure showers in a paper machine. Surface water used in the mill as intake freshwater may also need NF or RO treatment. Permeation of monovalent ions, in particular chloride ions, is both an advantage and a disadvantage of NF compared to RO. Monovalent salts cause significant osmotic pressure when retained in RO. In NF their permeation keeps the osmotic pressure lower and thus the transmembrane pressure needed to overcome the osmotic pressure is lower. The permeation of chloride ions in NF may restrict the reuse of the permeate because of concerns regarding corrosion caused by chloride. On the other hand, the concentrate then contains less chloride and its reuse or incineration is safer. 

As a method of concentrating organic matter from water, reverse osmosis has the advantage of utilizing ambient conditions to minimize the possibility... 

The major advantages of the tubular reverse osmosis configuration are the ability to tolerate high suspended solids concentrations in the feed and the possibility of mechanical membrane cleaning. The disadvantages are the excessive number of tube end fittings in proportion to the active membrane area in each pressure vessel, the bulkiness of the reverse osmosis plant and the high cost. 

The extract solution of 3%-5% solid content obtained according to the aforementioned method is concentrated by means of multieffect tube-evaporators or a reverse osmosis membrane. This concentration by reverse osmosis has the advantages of the flavor not disappearing and the deterioration due to heat is small, since mild operating temperatures are employed. It is preferable to concentrate the solution at a temperature of about 25 C, since water flux can be too low at lower temperatures. The solids content in the extract solution is increased from 10% to 30%. 

Despite its advantages, reverse osmosis is seldom used in analytical procedures. However, diluted sample solutions can be concentrated. Not only high molecular weight substances, but also low molecular weight substances, are rejected by ultrafiltration... 

Numerous endeavors have been implemented in fermentation process development in order to alleviate the solvent-induced inhibitory effects and thus improve the fermentation productivity. Usually, the selective removal of fermentation products was integrated simultaneously into the fermentation process in order to maintain a low solvent concentration in the fermentation broth. Many online butanol removal techniques have been reported with various advantages and efficiencies, including liquid-liquid extraction, perstraction, gas stripping, pervaporation, adsorption, reverse osmosis, etc. 

The High Efficiency Reverse Osmosis, or HERO (HERO is a trademark of Debasish Mukhopadhyay) takes advantage of the elevated concentrations of silicates at very high pH (Figure 7.5) and removes metals as part of the HERO process to eliminate the potential for forming metals silicates at high pH on the RO membranes. See Chapter 16.5 for more on the HERO process. 

Instead of drawing off juice, it is now possible to eliminate water directly from the grape must (Section 11.5.1). Two methods currently exist the first circulates the must across membranes which retain water by reverse osmosis (Degre-mont, Inc.) the second evaporates water in a low-temperature (20-24°C) forced vacuum (Entropie, Inc.). These techniques have the additional advantage of increasing the sugar concentration, thns eliminating the need for chaptaUzation in some cases. 

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