Operation And Optimization Of Nanofiltration/Reverse Osmosis Process For Desalination Of Brackish Water

Brackish water(BW),because of its high salt content,seriously affects the production and life of the residents who take it as the drinking water source.However,the new water treatment desalination technology mainly based on nanofiltration(NF)/ reverse osmosis(RO)technology is receiving more and more attention.In this paper,the nanofiltration / reverse osmosis technology is used to optimize the membrane parameters,pretreatment process and pilot operation of brackish water,so as to provide some reference for the practical application of nanofiltration / reverse osmosis.Through wave and imsdesign simulation,the operation efficiency of nanofiltration / reverse osmosis system under different recovery conditions was investigated,which provided theoretical guidance for the selection and optimization of membrane parameters in subsequent pilot tests.Recovery rate refers to the percentage of water produced in the membrane system in the influent water.In principle,the greater the recovery rate,the better the water production effect of the membrane system.However,the simulation results show that when the recovery rate increases from 50% to 80%,the average desalination rate of nanofiltration membrane decreases from 93.10% to 85.16%,the average desalination rate of reverse osmosis membrane decreases from 99.30% to 97.58%;the average permeability of nanofiltration membrane decreases from 6.48 LMH / bar to 5.02 LMH / bar,and the average permeability of reverse osmosis membrane decreases from 3.31 LMH / bar to 2.75 LMH / bar;the average power consumption per ton of nanofiltration membrane increased from 0.29 kwh to 0.36 kwh,and the average power consumption per ton of reverse osmosis membrane increased from 0.54 kwh to 0.62 kwh.If the method of concentrated water reflux is adopted to improve the recovery rate,the concentrated water volume of the corresponding reflux will increase,the concentration of the permeate before the membrane will also increase,the energy consumption will increase correspondingly,and the water production effect will also become worse,but the water consumption per unit of raw water will decrease,which can provide reference for water shortage areas.Three pretreatment processes,bank filtration(BF),powdered activated carbon(PAC)adsorption and ultrafiltration(UF),were investigated to study the pollution control performance of the membrane.The results showed that the removal rate of total organic carbon(TOC)was 41.50%,40.37% and 48.15% respectively,and the effect of ultrafiltration was better than that of bank filtration.In terms of the specific flux of the nanofiltration membrane after 50 hours of operation,the specific flux of shore filtration and nanofiltration is 0.785,that of powder activated carbon adsorption and nanofiltration is 0.778,and that of ultrafiltration and nanofiltration is 0.793.Ultrafiltration is still the best way to alleviate membrane pollution.Through comparison,the ultrafiltration pretreatment process,due to the better quality of the produced water,has better mitigation effect on the subsequent membrane pollution,and the produced water quality is stable,which is applicable to a wide range of water quality,so it can be selected as the pretreatment scheme for the subsequent pilot test.Combined with the theoretical experience of software simulation on the optimization of nanofiltration / reverse osmosis membrane parameters and laboratory small-scale test on the optimization of pretreatment process,the pilot test compares the water production performance and economic difference of nanofiltration / reverse osmosis system with integrated ultrafiltration as pretreatment.The results showed that when the recovery increased from 50% to 80%,the average desalination rate of nanofiltration membrane decreased from 97.25% to 94.07%,the desalination rate of reverse osmosis membrane decreased from 99.43% to 99.05%;the average permeability of nanofiltration membrane decreased from 5.44 LMH / bar to 4.61 LMH / bar,the average permeability of reverse osmosis membrane decreased from 2.90 LMH / bar to 2.53 LMH / bar;the average power consumption of nanofiltration membrane increased from 0.64 kwh to 0.76 Kwh,the average power consumption of RO membrane increased from 1.91 kwh to 2.06 kwh.Compared with reverse osmosis,nanofiltration has higher water yield,lower energy consumption,water quality can meet the water standard,and its construction cost and operation cost are more economic,so it is more appropriate to choose nanofiltration as the local advanced water treatment process.In addition,the change of membrane flux before and after adding scale inhibitor was compared in pilot test.The results show that the addition of scale inhibitor can significantly slow down the membrane pollution and ensure the operation of nanofiltration / reverse osmosis system at a higher flux,which has a certain reference significance for the optimal operation of the actual nanofiltration / reverse osmosis membrane system.