The Experimental Study Of Nanofiltration With Brackish Water

Due to the unique nature,geological conditions and hydrological cycle in the western region,brackish water is widely distributed.Brackish water contains high concentrations of salt,not only has bad taste,but also causes digestive diseases in long-term drinking,gastrointestinal disorders,and may even cause stones and cancer.In addition,because brackish water contains a variety of soluble inorganic salts,the chemical properties are lively,and it is not suitable as a direct water source for industrial production.Desalination treatment is required.Therefore,how to develop and use brackish water reasonably and effectively becomes an important solution to alleviate water shortages,reduce disease,and promote development.Since the advent of nanofiltration technology,nanofiltration has become a hot spot in the field of high salt water treatment because nanofiltration removes impurities and some soluble substances in water while effectively retaining some elements and other components beneficial to humans in water.First,all countries have invested a large amount of human and material resources to research nanofiltration technology,and China is also actively involved in development.However,due to the late start,the main research object at present is the import of membranes,but less research and application of domestic nanofiltration membranes.Based on this,this article selects two kinds of domestic nanofiltration membranes,performs basic research on brackish water desalination,and provides data support for in-depth study of domestic nanofiltration membranes and practical engineering applications.This paper mainly measured the characteristic parameters?pure water permeability coefficient LP,reflection coefficient?and solute permeability coefficient Ps?and structural parameters?film hole radius?of two domestic nanofiltration membranes;In addition,the effects of nanofiltration membranes on the retention of common anions and cations in brackish water were investigated.The interactions between the ions were analyzed.The operating pressure,influent concentration,and temperature were studied by single factor and orthogonal experiments.The effect of pH on the performance of nanofiltration membranes to desalinate brackish water and optimize operating conditions.Concluded as follow:?1?The characteristic parameters and structural parameters of nanofiltration membranes NF1 and VNF2 were characterized by NaCl solution retention experiment.The experimental results show that the reflection coefficient of nanofiltration membrane NF1 is?=0.6782,the solute permeability coefficient Ps=18.05×10^-6m/h,the membrane pore radius rp=3.46×10^-10m,and the reflection coefficient?=0.9301 of nanofiltration membrane VNF2.The solute permeability coefficient Ps=1.5403×10^-6m/h and the film hole radius rp=1.78×10^-10m.The membrane pore radius of NF1 is larger than that of VNF2,and its retention capacity for solute is smaller than that of VNF2 membrane.?2?The experimental results of single-component inorganic salt retention showed that:under the same conditions,the two membranes desalinated NaCl solution have the largest flux and the smallest rejection,indicating that the solute radius is the influence of membrane flux and rejection rate.Key factor.The rejection rate of various solute by nanofiltration membrane can be obtained as follows:The order of annihilation of anion and cation for each solute of NF1 nanofiltration membrane is as follows:For cations:Mg²⁺>Ca²⁺>Na⁺,for anion:HCO3^->SO4^2->Cl^-;and nanofiltration membrane VNF2 the anodic and cation rejection rate of each solute sequence:pairs of cations:Mg²⁺>Ca²⁺>Na⁺,for the anion:SO₄^2->HCO₃^->Cl^-.The difference in the order of anion retention between the two nanofiltration membranes is due to the effect of electroosmotic effects on the pore size of the nanofiltration membrane.?3?Two-component and multi-component inorganic salt retention experiments showed that when the nanofiltration membrane retains the inorganic salt solution,the nanofiltration membrane has a higher retention rate for divalent ions than monovalent ions and exists between the same type of charged ions.The competitive effect makes the retention of ions in the mixed solution by the nanofiltration membrane generally smaller than the retention rate when the nanofiltration membrane retains the single component solution.When the nanofiltration membrane NF1 was desalinated in the NaCl/Na2SO4 mixed solution,the concentration of Cl-in the permeate was higher than that in the water,and the maximum concentration reached 205%of the influent.For the nanofiltration membrane VNF2,the effect of this competition was small,and there was no phenomenon that the concentration of ions in the permeate was greater than that of the water,indicating that the membrane pore size was the decisive factor for the retention of the nanofiltration membrane.The competition of the same charge ions also shows that the larger the difference between the diffusion coefficient and the hydration radius between the ions,the more competitive the interaction between them,and the greater the change in rejection,the smaller the difference between the diffusion coefficient and the hydrated ion radius.The smaller the competition is,the smaller the change of rejection rate is;and the impact of high-valence ions on low-valence ions is significantly greater than that of the same-valent ions.?4?Single-factor experiments showed that the experimental influent water concentration increased?influent from 1000mg/L to 5000mg/L?,the flux and rejection of nanofiltration membranes NF1 and VNF2 were reduced,and the nanofiltration membrane NF1 was The interception rate changes little with the influence of the influent concentration,and is relatively stable.In the process of increasing the experimental temperature from 10°C to 25°C,both the flux and the rejection of NF1 and VNF2 increase,but the interception of VNF2increases.The rate changes little with the influence of inlet water temperature;in the influent pH range?pH rises from 6 to 9?,the membrane flux of the nanofiltration membrane NF1decreases,while the membrane flux of the VNF2 changes little,while the pH The impact of changes on the rejection of NF1 and VNF2 is also different.The rejection of VNF2 increases with increasing pH,and the rejection of NF1 is greatest at pH=7;within the experimental operating pressure variation,the operating pressure Increase the increase in flux and rejection rates that are beneficial to both membranes.?5?Orthogonal experimental studies show that:in the experimental range,the order of the factors affecting the membrane flux of the nanofiltration membrane NF1 is operating pressure>influent concentration>temperature>pH,and the best condition for maximum membrane flux is The water concentration was 1000 mg/L,the operating pressure was 0.4MPa,the influent pH was 6 and the temperature was 20°C.The order of factors affecting the rejection rate was the operating pressure>temperature>influent concentration>pH,and the best conditions for maximum rejection.The influent concentration was 1000 mg/L,the operating pressure was 0.4 MPa,the pH was 7 and the temperature was 20°C.The order of the factors affecting membrane flux of nanofiltration membrane VNF2 is operating pressure>influent concentration>temperature>pH,and the optimal conditions for maximum membrane flux are influent concentration 1000 mg/L,operating pressure 0.4 MPa,pH For 6,the temperature is 20°C;the order of factors affecting the rejection rate is influent concentration>operating pressure>pH>temperature,and the best condition for maximum rejection is influent concentration 1000 mg/L,operating pressure 0.4 MPa,and pH 8,the temperature is 20°C.?6?Comprehensive consideration should be given to membrane flux and rejection rate.The optimum conditions for nanofiltration membranes NF1 and VNF2 are operating pressure of 0.4 MPa,temperature of 20°C,and pH of 7.