Study On Desalination Of High Salinity Brackish Water Membrane Method

With economic development and population growth,the demand for freshwater resources is gradually increasing.The shortage of freshwater and the safety of drinking water have become one of the biggest constraints to sustainable socio-economic development in the regions with scarce freshwater resources.One has to look inevitably for alternative water resources to alleviate the freshwater crisis.Desalination of brackish water is an important approach to overcoming freshwater shortage.Although85%brackish water contains 1?10 g/L of salt,most current cases of brackish water desalination target brackish water with a low salt content of 1?5 g/L,which has insufficient demonstration significance for desalination of high salinity brackish water.The primary objective of this study was to design and evaluate a membrane-based desalination process for processing high salinity brackish water with a salt content of10 g/L.High-concentration Na Cl single salt solution and Na Cl/Mg SO₄mixed salt solution were used as the feed solutions to simulate brackish water.The desalination performance of the commercially available 4040 nanofiltration membranes?VNF2 and ESNA1?and low-pressure reverse osmosis membranes?ULP100,LP100,and ESPA1?under different operating conditions?including operating pressure,feed flow rate,and salt concentration in feed water?was evaluated in terms of water flux and salt rejection.Series experiments were also conducted to evaluate the feasibility of four integrations of the membrane processes?NF-NF,NF-RO,RO-NF,RO-RO?for the treatment of highly concentrated brackish water.The results demonstrate that the permeation flux and salt rejection of all membranes increase with the increase of operating pressure and feed flow rate,and decrease with the increase of the feed salt concentration.The salt rejection of VNF2can reach more than 90%for monovalent and high-valent salts,while ESNA1 shows a poor retention performance,and the salinity of the produced water is much larger than1g/L.The three RO membranes all showed high rejection,but their retention performance follow the order of LP100>ULP100>ESPA1,and the relationship of permeation flux is just the opposite.The VNF2 and ULP100 membranes have both high water production and salt rejection,which are good options for high salinity brackish water desalination.Series experiments reveal that the ULP100-VNF2 combination mode showed satisfactory results both in terms of total water recovery and water quality.And the desalination process can be conducted at a low pressure range of less than 1.6MPa.Such a pressure allows the desalination system to use inexpensive engineering plastic pipes and valves,avoiding problems of corrosion associated with the use of stainless steel.