| Forward Osmosis(FO)and Membrane Distillation(MD)aroused more and more interests for treatment of high salinity wastewater.However,a challenge of the application of FO processes is the lack of suitable membrane and draw solution,resulting in high energy consumption;MD membrane is easily wetted by surfactant pollutants.In our research,we fabricated a FO membrane with high water flux,low reverse salt flux and excellent mechanical properties and developed a Forward Osmosis-Membrane Distillation(FO-MD)integrated systems for high-salinity wastewater treatment based on the fabricated FO membrane.And also the effect of some parameters on FO and MD systems were investigated.Finally,FO-MD integrated systems was applied in wastewater treatment,and the transfer process of the integrated systems is explored.The main results are as follows:(1)The FO membranes with polyacrylonitrile(PAN),polyacrylonitrile/carbon nanotubes(PAN/f-MWCNTs)and polyacrylonitrile/Grapheneoxidation(PAN/GO)substrates were prepared via electrospinning,respectively.The active layer under these substrates was fabricated by Interface polymerization.The effects of film formation,spinning voltage,receiving-distance and composition of the material on the membrane structure were investigated.And also the effects of PAN concentration and MWCNT concentration on the morphologies,hydrophilic and mechanical properties of the membranes were investigated thoroughly.It was found that as the voltage increased,the fiber diameter increased at first and then decreased,and the increases of receiving distance decreased the fiber diameter.The increase of PAN concentration improved the fiber diameter and the mechanical strength,also increased the porosity within a certain range.The addition of MWCNT increased the diameter and mechanical strength of fibers,and decreased membrane toughness.(2)PAN substrates were prepared by phase inversion method and electrospinning respectively.Membrane fabricated by phase transformation method shows greater mechanical strength,but a lower water flux.The PAN/GO and the PAN/MWCNT membrane were prepared by electrospinning.We found that both graphene and carbon nanotubes can increase the water flux,and carbon nanotubes have greater impact on water flux than the graphene.The effects of the concentration of PAN and f-MWCNT on the FO were also studied.The increase of PAN concentration in acertain interval is helpful to improve the water flux and salt rejection of the membrane,and the increase of MWCNT can improve the water flux.When the concentration of PAN and f-MWCNTs is 12% and 1.44% respectively,the prepared membrane exhibits not only high water flux,but also a good salt rejection.With 1 mol/L NaCl as the draw solution and deionized water as feed solution,the water flux reaches 70.1L/(m2.h)with a low reverse salt flux of only 50.4 g/(m2.h).(3)The effects of concentration,temperature and flow rate on the flux and reverse salt flux of the FO process were investigated,and the feed solution temperature in the membrane distillation process was also investigated.The results show that the water flux increases with the increase of draw solution concentration,temperature difference and the flow rate in the FO progress,but the effect of temperature difference on the water flux is greater than other parameters.The increases of temperature difference,the decrease of film thickness,and the increase of the flow rate can improve the water flux of MD process.(4)By comparing with the MD and RO,MD and FO-MD integrated process of wastewater treatment,we found that FO-MD integrated systems shows a stable performance and the treated water exhibits a lower level of contamination.The energy consumption calculated exhibited that the NaCl solution cost lower energy than NH4HCO3,and the NaCl solution can be concentrated effectively during the continuous operate process. |
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