Reverse osmosis challenges

Because of the challenging environment in which ultrafiltration membranes are operated and the regular cleaning cycles, membrane lifetime is significantly shorter than that of reverse osmosis membranes. Ultrafiltration module lifetimes are rarely more than 2-3 years, and modules may be replaced annually in cheese whey or electrocoat paint applications. In contrast, reverse osmosis membranes are normally not cleaned more than once or twice per year and can last 4-5 years. 

The ability to determine the pore size and pore size distribution for porous membranes has existed for a number of years (11,40-42). Recent advances have permitted the determination of pore size and distribution for finely porous ultrafiltration membranes (, 1 ). Determination of i j, (the average cross-sectional area of the transport corridor) for the skin layer of reverse osmosis and tight ultrafiltration membranes as well as pervaporatlon membranes at present remains a challenge, although advances are being made in this direction (9,10,48-50). 

Greenlee LF, Lawler DF, Freeman BD, Marrot B, and Moulin P, Reverse osmosis desalination Water sonrces, technology and today s challenges. Water Research 2009,43,2317-2348. 

L.F. Greenlee, D.W. Lawler, B.D. Freeman, B. Marrot, P. Moulin, Reverse osmosis desalination water sources, technology, and today s challenges, Water Res. 43 (2009) 2317-2348. 

The material science of long-term membrane compaction in asymmetric membranes is not well reported. This phenomenon has been observed in gas separations including this report, but also in reverse osmosis [6] and organic solvent nanofiltration [38]. How to accurately predict multi-year performance in the field with short-term lab tests is a continuing challenge. 

The formed-in-place membrane is compatible with a wide variety of contaminants often encountered in hazardous wastewater steams. Many ccmventional reverse osmosis membranes are made from materials such as cellulose acetate and exhibit poor conqmtibility with reactive substances often encountered in hazardous wastes. These cmventiaial membranes will degrade and become inoperative when challenged with many organic cmnpounds. The compatibility problem becomes more critical as the level of concentration increases. The formed-in-place membrane is stable under most chemical environments and will not degrade even at high contaminant concentrations. 

Deowan, A.S., Hoinkis, J. Patzold, C. (2008) Low-energy reverse osmosis membranes for arsenic removal from groundwater. In Battacharya, P, RamanaOian, A.L., Bundschuh, J., Keshari, A.K. Chandrasekharam, D. (eds.) Groundwater for sustainable development problems, perspectives and challenges. CRC Press, Boca Raton, FL. pp. 275-386. 

N. Misdan, W.J. Lau, and A.R Ismail, Seawater Reverse Osmosis (SWRO) desalination by thin-film composite membrane—Current development, challenges and future prospects, Desalination 287 (2012) 228-237. 

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