Preparation And Application Of Composite Nanofiltration Hollow Fiber Membranes For Dye Desalination And Concentration As Well As Electroplating Wastewater Treatment

This study focused on the application of composite nanofiltration (NF) hollow fiber membranes formed by interfacial polymerization using piperazine (PIP) and trimesoylchloride (TMC) as functional monomers on polysulfone/polyethersulfone (PS/PES) hollow fiber supporting membranes for dye desalination and concentration as well as electroplating wastewater treatment.The prepared composite NF hollow fiber membranes had an isoelectric point at a pH value of 6.6, and possessed a molecular weight cut-off (MWCO) approximately 520 Da. The optimized preparation conditions of the composite NF hollow fiber membrane are described as following. The concentration of PIP and TMC is 2.0 w/v%and 0.5 wt%, respectively, the water phase processing time is 10 min, the interfacial polymerization time is 50 s, heat-treatment temperature is 70 ℃, and heat-treatment time is 10 min. At 0.4 MPa, the rejection rate and permeate flux of the optimized composite NF hollow fiber membrane for Na2SO4 reached 95.9% and 43.2 L/m2 h, respectively.Due to the steric hindrance and Donnan exclusion effects, rejection rates of the anionic dyes reactive brilliant blue X-BR and acid red B at 0.4 MPa by the prepared composite NF hollow fiber membranes were 99.99% and 99.90%, respectively. Then the prepared NF hollow fiber membranes were applied to the process of dye desalination and concentration using an X-BR and NaCl mixed aqueous solution as the pollutant. After finishing the process, the volume of retentate was concentrated 6.25 times, and the dye concentration in the retentate reached 2854.8 mg/L. Moreover, the recovery rate of dye was up to 91.4%, and over 95.3% NaCl was removed from the dye/salt mixtures, which indicated that the prepared composite NF hollow fiber membranes could be successfully applied to the dye desalination and concentration process.The prepared composite NF hollow fiber membranes were used to treat actual electroplating industry wastewater. And the performance for the removal of heavy metals from electroplating wastewater under different operating conditions was investigated. At 0.4 MPa, the rejection rates of chromium, copper, and nickel ions by the composite NF hollow fiber membranes reached 95.76%,95.33%, and 94.99%, respectively. With a rise in feed temperature, the permeate flux increased while the rejection rates of heavy metals did not significantly change. It was evident that the feed pH greatly affected the permeate flux and heavy metal rejection as well. In addition, the membrane rejection rates for chromium, copper, and nickel ions were over 94.8% throughout the concentration process.