Membrane fouling reducer

Membrane Fouling Fouling is the reduction in membrane permeability [= flux divided by pressure expressed in L/(m - h - bar)]. Typically, the transmembrane pressure (TMP) has to be increased to keep the flux at a constant level (Fig. 9.8). Thus, membrane fouling reduces productivity by increasing TMP, which in turn increases maintenance and operational costs. 

Automatic periodic membrane flush to remove recent surface deposits, thus reducing the risk of membrane fouling... 

Pretreatment Requirements for RO In addition to CIP and other fouling control systems constructed within the main body of the RO frame, it is vital that all due consideration be given to providing the correct kinds of RO RW pretreatment, in order to further reduce risks of membrane fouling. Options for pretreatment include ... 

Membranes UF membranes consist primarily of polymeric structures (polyethersulfone, regenerated cellulose, polysulfone, polyamide, polyacrylonitrile, or various fluoropolymers) formed by immersion casting on a web or as a composite on a MF membrane. Hydrophobic polymers are surface-modified to render them hydrophilic and thereby reduce fouling, reduce product losses, and increase flux [Cabasso in Vltrafiltration Membranes and Applications, Cooper (ed.). Plenum Press, New York, 1980]. Some inorganic UF membranes (alumina, glass, zirconia) are available but only find use in corrosive applications due to their high cost. 

To increase the solubility of calcium carbonate and reduce its potential for precipitation and hence membrane fouling, the pH of the feed water is lowered through the addition of acid (Greenlee et al. 2009). Sulphuric acid and hydrochloric acid are most commonly used. Acid treatment can also help to improve the coagulation of colloids and slightly increase the solubility of silica (Bergman 2007). 

Membrane fouling due to adsorption of polyelectrolytes (such as humic acids, surfactants, and proteins) may severely reduce ion permeability, especially in the anion-exchange membranes. However, exhausted anion-exchange membranes used in the ED of molasses, whey, citric acid, or sodium dodecyl-benzenesulfonate can be reactivated by circulating simultaneously an acidic solution in one compartment and an alkaline solution in the other one, both solutions at titres greater than 0.1 kmol/m3 (Tokuyama Soda Co., 1983). 

The main disadvantages of contactors are related to the nature of the membrane interface. The membrane acts as an additional barrier to transport between the two phases that can slow the rate of separation. Over time, the membranes can foul, reducing the permeation rate further, or develop leaks, allowing direct mixing of the two phases. Finally, the polymeric membranes are necessarily thin (to maximize their permeation rate) and consequently cannot withstand large pressure differences across the membrane or exposure to harsh solvents and chemicals. In many industrial settings, this lack of robustness prohibits the use of membrane contactors. 

Because most of the established membrane polymers can not meet all the performance requirements for a membrane dedicated to a particular application, membrane modifications are gaining rapidly increasing importance. Membrane modification is aimed either to minimize undesired interactions, which reduce membrane performance (e.g., membrane fouling), or to introduce additional interactions (e.g., affinity, responsive or catalytic properties) for improving the selectivity or creating an entirely novel separation function [3]. Three general approaches can be distinguished ... 

In addition to the MF pretreatment, used to remove particulates and microorganisms from raw water, reducing membrane fouling in the successive steps, the NF step is able to reduce water hardness decreasing osmotic pressure of the RO feed, allowing operation at higher water recovery level. 

With the aim to avoid or to reduce the membrane fouling, which causes the membrane flux decline, another type of membrane module configuration of PMR,... 

In addition to fluid dynamics, surface modification of the membrane can reduce the attractive forces or even create repulsive ones between potential fouling solutes and the membrane (Belfort, Davis, and Zydney, 1994). 

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