Research On The Characteristics Of Nanofiltration Membranes For Water Treatment Of Different Water Sources

In recent years,with social and economic development,people's demand for drinking water quality has been increasing,and the traditional water treatment process has limited effect on the removal of pollutants in water sources,which cannot guarantee the safety of drinking water and meet people's demand for quality drinking water.Nanofiltration process of membrane depth treatment process has high efficiency of pollutant removal,strong applicability and other characteristics,its separation characteristics between ultrafiltration and reverse osmosis,and ultrafiltration compared to the lower retention molecular weight,better decontamination efficiency,compared with reverse osmosis with low operating pressure,high permeate flux characteristics,relatively low operating costs,nanofiltration process in drinking water treatment has a high prospect of application.In this study,the water from Queshan Reservoir,Nanyang Lake water and Yi River water were used as research objects,and the coagulation precipitation+microfiltration pretreatment process was used to investigate the removal efficiency of two types of nanofiltration membranes,NF1 and NF2,on inorganic and organic pollutants in water sources of different water quality,to study the membrane contamination caused by different influent waters and the cleaning effect of chemical cleaning on contaminated membranes,with the aim of providing data references for the selection of membrane processes in water plants of different water sources,and the main conclusions of this study are as follows.The pH of the three water sources is slightly reduced after pretreatment,and pretreatment has a good effect on turbidity removal,but no effect on total hardness,TDS and inorganic ions.The concentration of total hardness and TDS in nanofiltration water is influenced by the water quality of the influent,the water quality of Nanyang Lake is the worst and the concentration of total hardness and TDS in the influent is relatively high,the water quality of Queshan Reservoi is the best and the concentration of total hardness and TDS in the influent is relatively low,the removal effect of NF1 on total hardness and TDS is better than that of NF2.NF1 and NF2 have higher removal effect on both monovalent and divalent ions in the three feed waters,and the removal effect is better than that of NF2;the order of retention of monovalent ions in NF2 is:F^->K⁺>Na⁺>Cl^->NO₃^-,and there is almost no removal effect on NO₃^-;there is no significant difference in the removal effect of divalent ions in NF1 and NF2,and the order of retention of divalent ions is:SO₄^2->Mg²⁺>Ca²⁺,and the water quality of NF2 meets the requirement of drinking water standard,and the desalination rate is moderate.The water quality of NF2 meets the requirements of drinking water standards,and the desalination rate is moderate.Pretreatment mainly removes some of the large molecules of organic matter from the water of 3 different water quality sources.2 types of nanofiltration membranes have a high removal effect on the organic pollutants in different influent waters;NF1 has a better removal effect than NF2 on COD_Mn,UV₂₅₄,TOC,THMFP,CDOC and DOM in 3 kinds of influent waters,and the removal effect is less affected by the concentration and molecular weight of different influent organic pollutants;NF2 has a higher removal effect on COD_Mn,UV₂₅₄,TOC,THMFP,CDOC and DOM in 3 kinds of influent waters.The higher the concentration of influent pollutants,the higher the removal rate of nanofiltration membrane,and the higher the content of organic pollutants in the produced water;large molecule organic pollution can be completely removed by nanofiltration membrane,and the removal effect of LMW organic pollutants is poor;NF1 and NF2 have a higher reduction rate of C1and C3 components of different influent water.The reduction rate of maximum fluorescence intensity of NF1 and NF2 on C1 and C3 components of different influent waters was higher without significant differences,and the reduction effect of maximum fluorescence intensity of NF1 on C2 and C4 components was better than that of NF2,and the highest content of C2component in the influent water of Nanyang Lake,and the reduction rate of maximum fluorescence intensity of NF2 on it was 93.26%,and the highest content of C4 component in the influent water of Yi River,and the reduction rate of maximum fluorescence intensity of NF2 was 98.93%.The surface roughness of the membrane surface increased after the contamination of the NF2 membranes of the three different influent waters,with more inorganic ions in Nanyang Lake and more particulate matter in Yihe River water being the main reasons for the increase in membrane surface roughness.The main reason for the decrease of membrane flux is the presence of a large amount of inorganic pollutants such as calcium carbonate on the membrane surface;the main reason for the decrease of membrane flux due to the intake of water from Yihe River is the formation of a dense filter cake layer by bridging ions and colloids on the membrane surface.The membrane flux recovery effect of alkaline washing followed by acid washing is significantly better than that of acid washing or alkaline washing alone,and is applicable to membrane contamination caused by all three feed waters.