Desalination Fouling

Aromatic polyamide (aramid) membranes are a copolymer of 1-3 diaminobenzene with 1-3 and 1-4 benzenedicarboxylic acid chlorides. They are usually made into fine hollow fibers, 93 [Lm outer diameter by 43 [Lm inner diameter. Some flat sheet is made for spirals. These membranes are widely used for seawater desalination and to some extent for other process applications. The hollow fibers are capable of veiy high-pressure operation and have considerably greater hydrolytic resistance than does CA. Their packing density in hoUow-fiber form makes them veiy susceptible to colloidal fouling (a permeator 8 inches in diameter contains 3 M fibers), and they have essentially no resistance to chlorine. 

Hyperfiltration (Reverse Osmosis) is a form of membrane distillation or desalination (desalting) operating with membrane pore sizes of perhaps 1 to 10 Angstrom units. The various individual RO component technologies have improved tremendously over the last 20 to 25 years, and resistance to fouling and permeate output rates have benefited. Nevertheless, all RO plants remain susceptible to the risk of fouling, and adequate pretreatment and operation is essential to minimize this problem. 

Chen Y, Dong BZ, Gao NY, Fan JC (2007) Effect of coagulation pre-treatment on fouling of an ultrafiltration membrane. Desalination 204 181-188... 

Juang LC, Tseng DH, Lin HY (2007) Membrane processes for water reuse from the effluent of industrial wastewater treatment plant a study on flux and fouling of membrane. Desalination 202 302-309... 

Green, G and Belfort, G. Desalination 35 (1980) 129. Fouling of ultrafiltration membranes lateral migration and particle trajectory model. 

Jackson, J.M., and Landolt, D., "About the Mechanism of Formation of Iron Hydroxide Fouling Layers on Reverse Osmosis Membranes," Desalination 12, 361-378 (1973). 

Sheppard, J.D., Thomas, D.G., and Channabasappa, K.C., "Membrane Fouling Part IV Parallel Operation of Four Tubular Hyperfiltration Modules at Different Velocities with Feeds of High Fouling Potential," Desalination 11, 385-398 (1972). 

In the case of clarified feeds and low current densities, membrane lifetime can be as long as seven or 10 years for brackish water desalination or drinking water nitrate removal, respectively. However, if the feed solution is fouling or scaling or the ED separation plant has not been well designed or is not properly conducted, membrane lifetime is no longer than a year. 

Grebenyuk, V.D., Chebotareva, R.D., Peters, S., andLinkov, V. 1998. Surface modification of anion-exchange electrodialysis membranes to enhance anti-fouling characteristics. Desalination 115,... 

Lindstrand, V., Sundstrom, G., and Jonsson, A.-S. 2000. Fouling of electrodialysis membranes by organic molecules. Desalination 128, 91-102. 

Schippers, J.C. and Verdouw, J. 1980. The modified fouling index, a method of determining the fouling characteristics of water. Desalination 32, 137-148. 

Hollow fine fiber modules made from cellulose triacetate or aromatic polyamides were produced in the past for seawater desalination. These modules incorporated the membrane around a central tube, and feed solution flowed rapidly outward to the shell. Because the fibers were extremely tightly packed inside the pressure vessel, flow of the feed solution was quite slow. As much as 40-50 % of the feed could be removed as permeate in a single pass through the module. However, the low flow and many constrictions meant that extremely good pretreatment of the feed solution was required to prevent membrane fouling from scale or particulates. A schematic illustration of such a hollow fiber module is shown in Figure 3.47. 

Hasson, D., Drak, A., Komlos, C., Yang, Q. and Semiat, R. (2007) Detection of fouling on RO modules by residence time distribution analyses. Desalination,... 

Another interesting possibility is the use of pressure-driven membrane processes, in particular MF and UF are becoming standard and very efficient pretreatment options for sea- and brackish-water desalination. Also, for wastewater treatment, MF/UF pretreatment technology can efficiently reduce the highly fouling nature of the feed. 

D. Violleau, H. Essis-Tome, H. Habarou, J.P. Croue, M. Pontie, fouling studies of a polyamide nanofiltration membrane by selected natural organic matter an analytical approach, Desalination 173 (2005) 223-238. 

Schafer, A. I., A. G. Fane, and T. D. Waite, "Nanofiltration of Natural Organic Matter Removal, Fouling, and the Influence of Multivalent Ions," Desalination, 118 (1998). 

The most common uses of RO are for desalination of seawater and brackish water for potable and industrial applications. However, as demand for fresh water grows, RO is being pressed into service for wastewater and reuse applications. These will require extensive pretreatment, sometimes involving other membrane technologies such as micro- or ultrafiltration, to minimize fouling of the RO membranes (see Chapter 16). 

Rodriguez C, Sarrade S, Schrive L, Dresh-Bazile M, Paolucci D, and Rios GM. Membrane fouling in cross-flow ultrafiltration of mineral oil assisted by pressurized CO2. Desalination 2002 144 173-178. 

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