Study On Nanofiltration Using Abandoned Polyamide Reverse Osmosis Membrane And Desalination And Concentration

Aromatic polyamide thin-film composite reverse osmosis(RO)membranes have been widely applied to desalination of seawater and brackish water,because of high salt rejection and permeability.Reverse osmosis(RO)membranes might experience degradation of membrane performance and shorten useful life after disinfection has been applied,or after membrane cleaning,because of hydrolysis and oxidation processes.Therefore,it has an important significance to investigate the degradation mechanism of the waste RO membrane and the condition that waste RO membranes translate into nanofiltration functional membranes.Firstly,changes in the chemical composition,morphology and performance of membranes exposed to NaC lO solution was explored,and the condition that waste RO membranes translate into na nofiltration functional membranes was also explored in this study.Secondly,the separation performance of nanofiltration functional membranes on inorganic salt and organic macromolecular solution was studied,and the separation and antifouling performance of nanofiltration functional membranes on dye and salt mixture solution was also studied.And lastly,the purification and desalination performance of nanofiltration functional membranes in batch constant volume diafiltration process was investigated.Changes in the chemical composition,morphology and performance of such membrane were characterized by Fourier transform infrared spectroscopy(FT-IR),Xray photoelectron spectroscopy(XPS),contact angle measurements,scanning electron microscope(SEM),atomic force microscopy(AFM)and streaming potential measurements.After chlorination,the water flux of RO membrane doubled,and the NaCl and Na2SO4 rejection of the RO membrane decreased to 46.2% and 86.2%,respectively.However,the rejection of congo red,methyl blue and direct red 80 was 99.4%,98.0% and 100%,respectively.This indicates that abandoned RO membranes can be recovered as “nanofiltration functional membranes” after 48000 ppm·h sodium hypochlorite exposure,and be suitable for fractionation purposes.And,the e ffect of operational pressure,feed dye concentrations and salt concentrations on the separation performance of nanofiltration functional membranes was investigated.This result shows that nanofiltration functional membranes have excellent performance of separation and antifouling.At last,the performance of nanofiltration functional membranes in batch constant volume diafiltration process indicates that under the temperature 25? and 0.8 MPa,observed rejection of dye component reach 100%.After six-stage batch diafiltration operation,concentration of dye inc reased 1.65 times,and the concentration of NaC l decreased from 13 g/L to 2.3 g/L.This result indicates that nanofiltration functional membranes in batch diafiltration operation mode are applicable to desalination and concentration of dye and salt mixture solution.