Effect Of Pre-deposited Layer Of Nano-sized Adsorbent Materials On Membrane Fouling Control Of Ultrafiltration Membrane Systems

The global shortage of water resources and serious water pollution problems become increasingly prominent,research and development of energy-efficient water treatment technology is particularly necessary.When the traditional water treatment processes can not meet the needs of the current situation,people begin to focus on a variety of new water treatment technologies and advanced treatment technologies,so the hybrid membrane filtration processes attract people's attention.Among them,ultrafiltration membrane is a kind of low-pressure membrane with moderate price and high interception efficiency,which has been widely used in practice for its comprehensive performance.However,for a variety of membranes used in water treatment,membrane fouling is the biggest bottleneck in the application of membrane technology.Natural organic matter?NOM?in surface water is not only the precursors of disinfection by-products,but also the substances which may cause membrane fouling.Therefore,the strategies to effectively reduce the membrane fouling,and the energy consumption of treatment process,which means achieving both of energysaving and emission reduction of the water treatment process,especially to reduce membrane fouling caused by NOM,are urgent scientific problems to be solved.In this work,a simple pre-deposition method was used to pre-deposit an adsorption layer composed of nano-materials on the surface of the ultrafiltration membrane to form a pre-deposited-ultrafiltration membrane system for the treatment of representative types of NOM in surface water and to investigate the effect of membrane fouling reduction.Firstly,the prepared aluminum sulfate solution was heated for different time to form suspension containing nano-particles.The suspension was then pre-deposited on the surface of ultrafiltration membrane by ultrafiltration cup filter to study the removal and flux decline of the pre-deposition layer-ultrafiltration membrane system on humic acid?HA?,sodium alginate?SA,polysaccharide?and bovine serum albumin?BSA,protein?.The results showed that the pre-deposited nano-particles were heated for different heating times from 1to 30 min,the flux decline rate gradually decreased,which indicated that the degree of membrane fouling decreased.For HA,SA and BSA,the removal efficiencies of the three pollutants is preferable for 10-min heating of the pre-deposited nano-particles,and the degree of membrane fouling is lower,and the energy can be saved compared with the heating of 30 min.The results show that the heating process leads to the transformation of primary nanoparticles from amorphous aluminum hydroxide to aluminum oxide?AlOOH,boehmite?in microcrystals.In addition,with the heating time increasing,the average size of the nanoparticles gradually decreased from about 60 nm to 20 nm.In addition,we studied the calcination of the nanoscaled biomass material–bacterial cellulose?BC?to be carbon nanofibers?CNF?at high temperature under argon atmosphere,and pre-deposited them onto the surface of ultrafiltration membrane to form the CNF pre-deposited layer-ultrafiltration membrane system.The removal efficiency of the two organic pollutants,SA and BSA,and the flux decline were studied under the conditions of different CNF loadings.In addition,CNFs were prepared by immersing and stirring in ethanol and N-methylpyrrolidone?NMP?for 24 hours to prepare the modified CNF adsorbent?M-CNF?,which was also pre-deposited on the surface of the ultrafiltration membrane to form the pre-deposited M-CNF-ultrafiltration membrane system,and compared with unmodified CNF system.The results show that the higher loading of M-CNF can achieve the better adsorption performance,and the more significant effect of reducing membrane fouling.Finally,the Fe-Mn mixed nano-particles prepared by FeCl₃ and K₂MnO₄ were pre-deposited on the surface of the ultrafiltration membrane to form the Fe/Mn bimetallic pre-deposited layer-ultrafiltration membrane system.The Fe?OH?₃ nanoparticles were prepared by pre-depositing FeCl₃ on the surface of the ultrafiltration membrane to form the Fe?OH?₃ pre-deposited layer-ultrafiltration membrane system.And we compared the two systems mentioned above to investigate their performance on fouling control.The results showed that the membrane fouling performance of the simulated water samples containing SA and BSA and the samples containing heavy metal trivalent chromium.The results showed that the adsorbents of different adsorption capacities had different performance for different adsorption systems.When the solution of BSA and SA was treated by Fe deposition layer-ultrafiltration membrane system,the best effect was obtained when the concentration of flocculant ferric hydroxide solution was 5 mM and 2 mM.When the bovine serum albumin solution was treated with the Fe/Mn bimetallic-ultrafiltration membrane system,a better removal effect was obtained with the flocculant concentration of10 mM.When the sodium alginate solution was treated with 5 mM flocculant concentration,it can obtain the best comprehensive benefits.When Fe/Mn bimetallic sedimentation-ultrafiltration membrane system treats the heavy metal chromium ion in the water and the treatment solution has the acidity gradually to become neutral,changes again alkalescence,the flocculant best processing concentration increased gradually.When the Fe pre-deposited layer-ultrafiltration membrane system treats the heavy metal Cr³⁺and the treatment solution changes from the acidic to the neutral,and then becomes the alkalinity,the best concentration of the flocculant is generally decreasing,which may be related to the oxidation of the hydroxide iron flocculants are more stable in alkaline conditions.