Studies On Desalination Performance Of Inorganic Salt Solution And Sea Water With Nanofiltration Membranes

Nanofiltration membrane can effectively remove hardness divalent ions, such as Ca²⁺, Mg²⁺, SO₄²⁺, CO₃^2-, and provide high quality feed seawater for desalination. As a result, if it could be applied widely in seawater softening, NF membrane technology would promote the development of seawater desalination industry.The aim of this subject is to give a primary research on the mechanism and feasibility of nanofiltration for softening of seawater. Three kinds of nanofiltration membrane sheets which are NF1, NF2, and NF3, and four kinds of nanofiltration membrane modules which are NFI, NFII, NFIII, and NFIV were chosen to study the performance of NF membranes in single salt solutions,salt mixture solutions and seawater system, respectively. The results of the studies are as follows:For the nanofiltration of single salt solutions, multi-electrolyte solutions, and seawater using membrane sheets, conclusions can be drawn that under the same condition, both the rejection rate and the permeate flux of three membranes become higher as the pressure increases, and the rejection rate gradually come to a limit; the rejection rate and the permeate flux decrease with the increase of feed salt concentration; all the rejection rates of the divalent ions are higher than those of the monovalent ions.The analysis on the performance of NF membranes fouling resistance, accompanied by SEM and streaming potential test on membrane sheets, indicates that although the rejection rate of NF3 is equal to NF2 and lower than NF1, the property of fouling resistance of NF3 is superior. Through the plot study of seawater softening with NF membranes using a pilot setup near the seashore, it can be shown that short-term rejection rate and membrane flux of NFIII and NFIV increase with the increase of the operating pressure and the feed flow rate, and operating pressure plays a main role. Under the same operation condition, the rejections of NFIII on calcium and magnesium ions are much higher than those of NFIV, while NFIV is excellent in...