Study Of Modified Polysulfone Membrane For Surface Water Treatment In Coagulation-ultrafiltration Process

Antibiotics have been widely used in many aspects of life.Due to excessive and irregular use,the antibiotics detected in surface water are mainly tetracycline Ultrafiltration(UF)technology can achieve the separation and purification of surface water,but there are serious membrane fouling problems.The membrane fouling can be effectively alleviated by hydrophilic modification and coagulation.However,humic acid(HA)in surface water has an effect on the removal of antibiotics in water,and the interaction mechanism between the two is still unclear.In this study,membrane surface modification was applied in the coagulation-ultrafiltration(C-UF)process to research the effect of modified layers on the properties of PSf membrane Assisted by the self-polymerization of polydopamine(PDA)on the membrane surface under weak alkalinity,nano titanium dioxide(TiO2)particles could be hydrolyzed with ammonium fluotitanate((NH4)2TiF6)solution under acidic conditions,and the hydrophilic group of TiO2 was introduced onto the PSf membrane surface to form a double-modified layer.Polydimethyl diallyl ammonium chloride(PDMDAAC)and polyaluminum chloride(PAC)were used as flocculants.Meanwhile,the relationship model between coagulation,floc characteristic and membrane fouling was established The influence mechanism of different coagulation systems and modified pH conditions on the performance of C-UF combined process was analyzed.The difference of hydrophilicity and anti-fouling properties of PSf membrane before and after modification was clarified.In addition,HA and HA-CTC were selected for C-UF treatment to study the effect of the presence of HA on the removal of CTC.The application prospect of the interaction mechanism between HA and antibiotics was clarified.This study obtained the following main research contents and results:(1)Study on different coagulation systems of PAC and PDMDAAC:PAC was added followed by PDMDAAC(PAC/PDMDAAC).PAC and PDMDAAC were mixed to produce the composite flocculant PAC-PDMDAAC.These two coagulation systems were selected in this study.The results showed that the PDMDAAC in the PAC/PDMDAAC coagulation system had stable branch structure and high surface charge density.PDMDAAC could fully play the role of charge neutralization and adsorption bridging,the system showed better coagulation efficiency.(2)Study on membrane properties under different modified pH conditions:The characterization results showed that the hydrophilicity of the modified PSf ultrafiltration membrane was significantly enhanced,and a stable modified layer was formed between PDA and TiO2 through coordination.Under acidic conditions,with the(NH4)2TiF6 solution pH increased,more Ti02 particles were adsorbed on the surface of PDA,and the hydrophilic group was successfully introduced into the membrane surface.Under the modified condition of pH 5,PDA/Ti02 modified membrane had the best performance.The surface of modified layer formed a hydrophilic layer,which prevented the adsorption of pollutants on the membrane surface.The recovery rate of water flux was up to 90%,and most effectively reducing the membrane fouling at pH 5(3)Study on the interaction mechanism between HA and CTC in C-UF combined process:There were hydrogen bonds or ?-? stacking interaction between HA and CTC to agglomerate,resulting in the increase of particle size of the composite pollutant and the increase of Zeta potential.The presence of HA effectively improved the removal efficiency of CTC in C-UF combined process.PAC/PDMDAAC system was used to treat HA,CTC and HA-CTC simulated water samples.The results presented that the active sites between HA-CTC compound pollutant and flocculant increased.The removal efficiencies of HA and CTC in HA-CTC water samples were higher than that in a single water sample.The agglomeration between HA and CTC could reduce the small molecules remaining in the coagulation water and mitigate the membrane hole blockage.(4)Study on the effect of different initial pH on the efficiency of HA-CTC water samples treated by C-UF combined process:The results showed that pH affected the flocculant to play different coagulant roles.Under neutral and slightly acidic conditions,PAC/PDMDAAC system mainly played the role of electrical neutralization,accompanied by bridging and sweep,resulting in forming large and loose flocs.The loose flocs had more contact surfaces and could absorb more small flocs.Under neutral conditions,large and puff flocs formed loose and porous filter cake layer on the PSf membrane surface,increasing the passage of water molecules.Flocs had higher recovery performance,which further adsorbed small molecular substances in water,preventing membrane pore blockage.Therefore,organic matter removal efficiency was the highest and membrane pollution was the lowest under neutral conditions.