Study On Removal Of Dissolved Organic Matter In Water By Forward Osmosis

In the study,the sucrose organics such as sucrose and dextran were used as model foulants for neutral hydrophilic small molecules of natural dissolved organic matter?DOM?to examine the purification performance of sugar organics by forward osmosis?FO?.The physical impacts of the initial draw solution concentration?i.e.,initial flux level?and the membrane orientation,operating conditions and the chemical aspects of the character of contaminant?i.e.,initial foulant concentration?types and size?were also investigated.Based on the above research,the purification efficiency of osmosis membranes with separate filtration and tandem filtration of different molecular weight dextran was investigated.The influence of factors such as molecular weight and filtration order on the membrane pores blocking in the support layer of the FO membrane and the continuous filtration of dextran and sucrose after contamination by the FO membrane were studied.The sucrose and other sugar organics could be effectively removed by the FO membrane.It was found that the higher the initial flux level?4mol/L?,the more notable the flux decline.The lower sucrose retention was found at greater draw solution concentrations and in the active-layer-facing-the-draw-solution?AL-facing-DS?orientation.In the AL-facing-DS mode,it was revealed that both the higher initial sucrose concentration?40mg/L?and the larger sugar organic molecules?1000?aggravated the fouling flux decline,and the larger sugar molecules favored higher FO retention?91.2%?.The sucrose salt flux was higher than baseline salt flux was found in this studied.This may be related to the sucrose molecules adsorbed in the support layer,weakening the electrostatic effect in the membrane pores.The permeation drag caused by the water flux probably played a significant role in the retention of sugar organics by the FO membrane.The membrane fouling would be compensated by the reduced ICP level caused by the decreased membrane flux.The FO could reject sugar organic foulants effectively.It was found that the higher the initial flux level?4mol/L?,the more notable the flux decline.The lower sucrose retention was found at greater draw solution concentrations and in the active-layer-facing-the-draw-solution?AL-facing-DS?orientation.In the AL-facing-DS mode,it was revealed that both the higher initial sucrose concentration?40mg/L?and the larger sugar organic molecules?1000?aggravated the fouling flux decline,and the larger sugar molecules favored higher FO retention?91.2%?.It was found that the sucrose salt flux was higher than baseline salt flux.It may be that the sucrose molecules enter the pores of the support layer to weak the electrostatic effect in the pores of the membrane.More adsorption of the small sugar molecules may occur within the porous membrane support layer.The permeation drag caused by the water flux probably played a significant role in the retention of sugar organics by the FO membrane.The membrane fouling would be compensated by the reduced ICP level caused by the decreased membrane flux.It was shown that larger molecular weight?5000,10000?dextran caused more significant reductions in fouling water flux,and 10,000 molecular weight fouling salt fluxes were the lowest,in the process of filtering 1000,5000,and 10000 molecular weight dextran alone.The rejection rate of the three dextran of the FO membrane was over 89%.In the process of filtering two molecular weight dextran in series by FO membrane,through the same membrane clogging situation?the membrane with the same molecular weight dextran has been filtered?and then filtering the different molecular weight dextran for analysis,after the first stage was contaminated with larger molecular weight?5000,10000?dextran,the initial fouling flux level of the second stage was lower,but the flux reduction was smaller than that of the new membrane filtration,while continuing to filter larger molecular weight?10000,5000?The rejection rate of dextran reached over 90%.In addition,according to the blocking of different membranes?the membranes of three kinds of difference molecular weight dextran had been filtered?and then filtering the same molecular weight dextran for analysis,the first stage compared with the smaller molecular weight,the larger molecular weight?10000,5000?The FO membrane after dextran contamination filters a smaller molecular weight of 1000 molecular weight dextran,the fouling flux was reduced,but the first stage after the membrane with a smaller molecular weight?1000?fouling then filters the larger 10,000 molecular weight Dextran still had a flux advantage.In the tandem filtration test,the three molecular weight dextran was subjected to FO membrane sequential filtration?molecular weight from small to large?and reverse filtration?molecular weight from large to small?.The sequential filtration fouling flux was reduced step by step,while the initial filtering flux in the reverse order filtering decreases faster,but the final flux of the two filtering sequences was not much different(about 13L??m²h?^-1).The research on the filtration of small molecule sucrose by the FO membrane after sequential and reverse filtration had shown that the fouling flux level of the membrane after reverse filtration and the sucrose filtration was higher and more stable(about 17 L??m²h?^-1),The reverse salt flux was also high,but the rejection rate of the two filtered FO membranes to sucrose was not much different,both were reached over 96%.When filtering dextran alone,the resistance in the support layer of the FO membrane increases with the increase of molecular weight,and accounts for more than 22%of the total resistance.The blocking of membrane pores by dextran may be more serious.Compared with sequential filtration,the membrane support layer of reverse filtration had a higher surface resistance,and the internal resistance of the support layer was smaller,indicating that the contaminated organic matter in reverse filtration may be more adsorbed on the surface of the support layer or in a shallow position in the layer than in sequential filtration.The larger molecular weight dextran chain structure adsorbed on the support layer may had a certain retention effect on the smaller molecular sucrose that was subsequently filtered.