Reverse osmosis membranes fouling/scaling

Sahachaiyunta et al. [38] conducted dynamic tests to investigate the effect of silica fouling of reverse osmosis membranes in the presence of minute amounts of various inorganic cations such as iron, manganese, nickel, and barium, which are present in industrial and mineral processing wastewaters. Experimental results showed that the presence of iron greatly affected the scale structure on the membrane surface when compared to the other metal species. 

Xu, P., C. Bellona, and J. E. Drewes. 2010. Fouling of nanofiltration and reverse osmosis membranes during municipal wastewater reclamation Membrane autopsy results from pilot-scale investigations. J. Memb. Sci. 353 111-121. 

Membrane filters are made in a wide variety of pore sizes (Fig. 1). The effective pore size for membranes vary, and membranes can be used in reverse osmosis (RO), nanofiltration (NF), ultrafiltration (UF), and microfiltration (MF). RO membranes are widely used in water treatment to remove ionic contaminations from the water. These membranes have an extreme small pore size and, therefore, require excellent pretreatment steps to reduce any fouling or scaling of the membrane, which would reduce the service lifetime. RO membranes are used by extensive pressures on the upstream side of the filter membrane to force the liquids through the pores. 

The separations feasible by filtration have expanded enormously over the last generation. The developments this symposium has commemorated, and the individuals it has honored, have been largely responsible. The removal of dissolved solutes or other low-molecular-weight substances from water by hyperfiltration or reverse osmosis, which the Loeb-Sourlrljan membrane made technically and economically feasible, has become an industrial-scale operation. Ultrafiltration of colloids and filtration of coarser materials from liquids have become much more efficient with the use of cross flow of liquid to slow the buildup of flltercake appreciation of the benefits from shear at the Interface has become much more general from the necessity of controlling concentration polarization and fouling in salt filtration. 

Electrodialysis (ED) is used to remove ionized substance from hquids through selective ion-permeable membranes. ED is the most widely commercialized electromembrane technology. Desalination of brackish water is the area of electrodialysis application with the largest number of installations. This chemical-free technology competes with reverse osmosis. Electrodialysis shows better resistance to fouling and scaling. It also has an economical advantage in desalination of low-salinity solutions [13]. Also, it should be kept in mind that because of small material consumption ED is the most environmental friendly process for solution desalination [14]. 

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