Rejection efficiency

The experiments determined that the membrane is not stable to bromine and like chlorine, dissolved bromine would have to be removed prior to membrane separation. However, the membrane did not lose rejection efficiency immediately, suggesting that it provides some resilience to bromine. In the event of bromine contact with the membrane, it is anticipated that the membranes will not be irreparably damaged, provided that the situation is corrected within a short time. 

In the separation tests with the use of a UF membrane, the rejection efficiency for the Cjg cationic surfactants was found to be in the range 90-99%, whereas for the C12 surfactants it ranged from 72 to 86%, when the feed concentration of each surfactant was greater than its corresponding CMC value. Therefore, UF rejection efficiency seems to be dependent on the respective hydrated micelle diameter and CMC value. In conclusion, the study showed that for cationic surfactants removal, if the feed concentration of a surfactant is higher than its CMC value, then the UF membrane process is found to be the best. However, if the feed concentration of a surfactant is less than its CMC value, then ion exchange is the best process for its removal. 

RO is not 100% effective, and some particles will pass through the membranes. The membranes will have a higher rejection efficiency for some particles than for others. 

Rejection efficiency was defined as the change in total concentration for these contaminants between the feed and the permeate ... 

Two usual definitions of partial efficiency are the "rejection efficiency" and the "acceptance efficiency" or recovery index. The rejection efficiency, relevant in classification of powders, is considered as the mass of coarse product greater than the cut size (the limiting size dividing a particle size distribution into fines and coarse fractions) related to the mass of feed solids greater than the same cut size. According to this, in Equation 10.21 Xj would represent the cut size (X50) and X2 would be the maximum particle size in the feed. The rejection efficiency E, can be expressed as a function of cumulative oversize (coarse) percentage and the cumulative percentage of coarse fraction in the feed F, as... 

With regard to the acceptance efficiency, it may be considered opposite to the rejection efficiency in the sense that the undersized particles are those considered as the reference for defining such efficiency. In this case, Xi in Equation 10.21 would represent zero, while X2 would be taken as the cut point. The acceptance efficiency can be expressed as a function of cumulative undersized (fines) percentage Ff and the cumulative percentage of fines fraction in the feed F, as... 

Rejection efficiency Screen efficiency Total efficiency Reduced total efficiency... 

The commercially available membrane RO elements today are of standardized diameters and length and salt rejection efficiency. Standard membrane elements have limitations with respect to a number of performance parameters such as feed water temperamre (45°C), pH (minimum of 2 and maximum of 10), silt density index (less than 4), chlorine content (not tolerant to chlorine in measurable amounts), and feed water pressure (maximum of 80-100 bars). 

The curves between sihca rejection efficiency and SWE in the beginning show a high sUica rejection plateau as the SWE decreased, which evenmaUy gives way to deterioration in product sUica at lower SWE values (Fig. 13.13). The rudimentary requirement is to operate the EDI modules at high SWE (low current efficiency) to attain the desired product water quahty in terms of resistivity and sUica rejection performance for a given feed water conductivity and temperature. 

A is often referred to as the water permeability constant. Note that if the soluble spedes rejection is not complete, the osmotic pressure difference across the membrane must be related to the osmotic pressure difference between the feed and the permeate streams, instead of that between the feed and pure water. Another factor commonly reported for membrane performance is the salt or solute rejection efficiency (ratio), R, defined as... 

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