Reverse osmosis fractional water recovery

The treatment so far has heen based on a particular feed concentration, Q , in the reverse osmosis cell (Figure 6.3.28 (a)). As time progresses, water from the feed solution will be removed as permeate therefore the feed concentration of species i, e.g. NaCl, will increase. If we require the process to yield a particular concentration of salt in the permeated water, then the salt rejection required of the membrane, / i,reqd> will have to increase. Further, since the osmotic pressure of the feed solution increases with time, either the solvent flux will go down with time or the driving pressure difference, AP, has to go up. To these factors, one has to add the complication of concentration polarization. To illustrate the effect of increasing feed salt concentration with time, we will ignore first the effect of any concentration polarization and then focus on the consequence of different values of fractional water recovery, re. For the reverse osmosis cell shown in Figure 6.3.28(a), it is defined as... 

Consider the spiral-wound module for reverse osmosis desalination described in Example 7.2.3. Determine the fractional water recovery if the feed brine has 10 000 ppm salt. All other conditions are as in the Example 7.2.3. What will be the fractional recovery if the feed brine has 20 000 ppm salt ... 

Consider reverse osmosis desalination in a spiral-wound module for a feed having negligible osmotic pressure. If the fractional water recovery, re, is such that the osmotic pressure of the concentration from the reverse osmosis process still has a negligible osmotic pressure vis-a-vis the liquid pressure, derive the result (7.2.44), i.e. 

Membrane technology may become essential if zero-discharge mills become a requirement or legislation on water use becomes very restrictive. The type of membrane fractionation required varies according to the use that is to be made of the treated water. This issue is addressed in Chapter 35, which describes the apphcation of membrane processes in the pulp and paper industry for treatment of the effluent generated. Chapter 36 focuses on the apphcation of membrane bioreactors in wastewater treatment. Chapter 37 describes the apphcations of hollow fiber contactors in membrane-assisted solvent extraction for the recovery of metallic pollutants. The apphcations of membrane contactors in the treatment of gaseous waste streams are presented in Chapter 38. Chapter 39 deals with an important development in the strip dispersion technique for actinide recovery/metal separation. Chapter 40 focuses on electrically enhanced membrane separation and catalysis. Chapter 41 contains important case studies on the treatment of effluent in the leather industry. The case studies cover the work carried out at pilot plant level with membrane bioreactors and reverse osmosis. Development in nanofiltration and a case study on the recovery of impurity-free sodium thiocyanate in the acrylic industry are described in Chapter 42. 

Cross-flow filtration (CFF) also known as tangential flow filtration is not of recent origin. It began with the development of reverse osmosis (RO) more than three decades ago. Industrial RO processes include desalting of sea water and brackish water, and recovery and purification of some fermentation products. The cross-flow membrane filtration technique was next applied to the concentration and fractionation of macromolecules commonly recognized as ultrafiltration (UF) in the late 1960 s. Major UF applications include electrocoat paint recovery, enzyme and protein recovery and pyrogen removal. 

Applications of reverse osmosis in the dairy industry include water treatment, fractionation, product and chemical recovery, concentration and denaturing. The concentration of process streams from around 10% total solids to 25% can be achieved at a lower cost than by evaporation. Also there is a considerable reduction in volatile flavour component losses and in adverse changes to heat sensitive... 

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