Strong Hydrophilic Modification And Antifouling Performance Of The Forward Osmosis Membrane For The Treatment Of Emulsified Oil

Conventional pressure driven membrane technologies,such as nanofiltration and reverse osmosis,are difficult to be employed to effectively separate the emulsified oil.The main reason is that oil foulants will cause serious membrane fouling under hydraulic pressure,which makes membrane separation process difficult to continue.As an emerging membrane process that utilizes osmotic pressure as the driving force,forward osmosis(FO)technology possesses several special advantages,such as more reversible fouling propensity and higher water recovery.FO technology has shown great potential application in the advanced treatment of emulsion oil for water reclamation.However,the fabrication of high performance membrane and the control of membrane fouling are still the bottlenecks for FO process to effectively separate the emulsified oil.In this study,novel disulfonated poly(arylene ether sulfone)hydrophilichydrophobic multiblock copolymer(BPSH100-BPS0)were blended with polysulfone to prapred the hydrophilic substrate of the thin film composite(TFC)forward osmosis(FO)membrane.Water flux of these prepared membrane were improved compared to the pristine membrane.On the other hand,TFC FO membranes were modified by grafting the amine-terminated sulfonated poly(arylene ether sulfone)(NH2-BPSH100)to enhance fouling resistance to emulsified oil.Meanwhile,in order to advoid oil fouling induced by charge-charge interaction,TFC FO membranes with neutral and salt-responsive properties were modified by grafting the poly(sulfobetaine methacrylate)(PSBMA)on the polyamide surface.The main contents in the present work are as following:(1)Polysulfone substrates modified by different contents of BPSH100-BPS0 were employed to fabricate the high performance TFC FO membranes.It was found that blending modification with BPSH100-BPS0 could increase the substrate hydrophilicity and porosity;while the tensile strength of the modified substrate(substrate-25.0)was maintained,compared to the control substrate.Futhermore,the FO performance of the TFC membrane(TFC-25.0)was also significantly improved with extremely high pure water flux of 74.4 LMH in the PRO mode and 40.5 LMH in the FO mode when using 2.0 M Na Cl as the draw solution.These results were almost one-fold higher than the TFC membrane without addition of BPSH100-BPS0.It was also found that the surface characteristic of the modified supports could directly affect the surface morphologies and fouling propensities of the TFC FO membranes.Compared with the control TFC FO membrane,the surface of TFC FO film based on BPSH100-BPS0 exhibited lower roughness and fouling trend.However,irreversible fouling was still occured because of their hydrophobic surface.(2)Anti-fouling TFC FO membranes were prepared by in situ surface grafting of nascent polyamide active layer using NH2-BPSH100,over a range of molecular weights(2,10 and 18 kg/mol).Surface characterization using Zeta potential,AFM,and contact angle,displayed that the grafting of NH2-BPSH100 could influence the TFC membrane surface properties.The results showed that compared to the control membrane,zetapotential of the modified membranes became more negative and their surface roughness increased slightly,which could accelerate serious membrane fouling.However,the membrane modified with 10 kg/mol of NH2-BPSH100(10k-g-TFC)showed optimum antifouling performance for separating soybean emulsified oil.This phenomenon could be explained by its superhydrophilic and underwater superoleophobic properties.In the current study,water flux of 10k-g-TFC membrane could maintain as high as 69.8% of its initial value at 80% water recovery of emulsified oil,in direct contrast to 11.0% for the unmodified membrane.(3)Salt-responsive TFC FO membranes were prepared by grafting zwitterionic PSBMA brushes on a commercial FO membrane surface via an ATRP reaction.The optimum modified membrane(i.e.TFC-PSBMA)exhibited superhydrophilic and ultralow oil-adhesion properties.Compared to the TFC-control membrane,the TFCPSBMA membrane exhibited the lower water flux decline,which demonstrated the superior anti-fouling ability of the TFC-PSBMA membrane.Furthermore,multi-cycle FO fouling tests showed that DI water cleaning were not effective to remove the membrane fouling of the modified membrane in long-term use.Hovever,water flux of the modified membrane could be remarkable recovered by using salt cleaning.The saltresponsive properties of the PSBMA brushes were thought to provide a driving force for the removal of oil foulants from the modified membrane surface.(4)The analysis of the foulant on the membrane surface,such as hydraulic resistance and XPS,demenstrated that emulsified oil contributed to the dominant fouling on the membrane surface.On this basis,five kinds of cleaning methods including physical cleaning,osmotic backwash,and chemical cleaning(Na OH solution,citric acid solution and SDBS solution),were selected to evaluate the cleaning efficiency of the modified membrane.The results showed that SDBS solutiong cleaning was the most effective cleaning method to maintain the antifoulig properties of the modified membrane.It also demonstrated that the combination of surface modification and cleaning method was an efficient membrane fouling control strategy for the FO process treating the emulsified oil.