| Recently,forward osmosis(FO)has become a research hotspot because it possesses the merits of low membrane fouling tendency,slight concentration polarization effect,good product water quality as well as no damage to environment.FO is a green separation technology which employs the osmotic pressure difference as the driving force.The osmotic pressure provided by draw solution can make water molecule permeate spontaneously from the feed solution side into the draw solution side.As one of the critical elements in the FO process,draw solution exploration has attracted much attention.A series of compounds have been synthesized and used as draw solution in recent years.Synthetic draw solution surpasses the conventional draw solution in terms of low reverse solute flux in FO process and low energy consumption in recovery processes.However,the problems of complicated synthesis process,low water flux and severe concentration polarization(CP)still exist in most synthetic draw solutes which restrict its further applications in the FO processes.This study aims to prepare a series of high performance draw solution through moderate synthetic processes,and investigate its FO desalination and wastewater treatment efficiency.Two kinds of OA chromium complexes with high water solubility have been synthesized through one-pot reaction under room temperature.A novel draw solution of OA chromium complex in the form of tetramethyl-ammonium salt(N(CH3)4-Cr-OA)was designed for the first time.The newly designed OA chromium complexes possess the properties of multi-charged anions and multiple cations in aqueous and Cr-centred octahedral structure which ensure them appropriate to be draw solutes.The effects of different operation conditions on their FO performance were investigated systematically,and the comparison with two conventional draw solutes of NH4HCO3 and NaCl was also carried out.The experimental results showed that N(CH3)4-Cr-OA draw solution can produce the highest water flux and the lowest reverse solute flux,such as,a reverse solute flux less than 0.08 gMH was acquired when employing 1.0 M N(CH3)4-Cr-OA as draw solution,while a reverse salt flux of 10.64 gMH was produced by NH4HCO3 draw solution under the same conditions.Two super hydrophilic carboxylate functionalized imidazolium ionic liquids were synthesized via quaternary amination reaction,and its FO performance was tested by employing home-made high performance hollow fiber composite membrane as FO membrane under different conditions.The experimental results showed that the water fluxes produced by 1,2-dimelty-3-sodium acetate imidazole iodide ionic liquid(IL-1)draw solution increased dramatically with the draw solution concentration,a high water flux of 63.63 LMH was achieved when 0.8 M IL-1 was used as draw solution under the PRO mode which was two times of that of NaCl draw solution.In addition,the temperature of draw solution can significantly affect its FO performance,when the temperatures of the 0.2 M IL-1 draw solution increased from room temperature to 55 ?,the water fluxes increased from 21.3 LMH to 42.9 LMH,the water production efficiency increased by 50%.Newly designed N(CH3)4-Cr-OA and IL-1 draw solution were applied on the FO processes for wastewater treatment and seawater desalination,respectively.FO efficiency for wastewater treatment was investigated by using model multi component copper containing electroplating wastewater as feed solution,a 76.94%increased in FO efficiency by replacing NH4HCO3 draw solution with N(CH3)4-Cr-OA was achieved.And high copper rejections above 99.9%were observed in all experiments,which surpass the best performance reported for copper ion removal.In addition,a water flux of 8.27 LMH was acquired in FO seawater desalination with 0.8 M IL-1 as the draw solution which was five times of that of NaCl draw solution under the same conditions.All of the above demonstrate the superiority of these two kinds of draw solution in the FO processes and the feasibility of them in FO water treatment. |
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