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

In this study,the natural surface water of Bailang River Reservoir in Shandong Province and the dissolved organic matter in the filter influent and filter backwash water of Bailanghe Water Plant were taken as the research objects.The characteristics of natural dissolved organic matter were analyzed.The effects of draw solution concentration,initial total organic matter concentration,membrane orientation,cross flow velocity and ionic strength on the retention efficiency of forward osmosis were systematically studied.On this basis,the efficiency of the filtration of different water samples in the series by forward osmosis process was further investigated,and the effect of the relative molecular weight distribution of natural organic matter on membrane fouling occurred on the membrane surface or within the membrane porous support layer were also evaluated.The initial flux level of forward osmosis increases nonlinearly with the increased of the draw solution concentration.The higher initial flux level(～33.13 L?（m~2h）^-1)resulted in severe fouling flux loss and lower organics retention.When the support layer of the forward osmosis membrane faces feed solution,the membrane fouling flux of the concentrated water sample significantly reduced.The alternative membrane orientation showed a lower and stable water flux as a result of the more severe internal concentration polarization.The fouling flux level significantly reduced when decreasing the cross-flow flow rate(～100 m L?min^-1)and increasing the calcium concentration(～6.3 mmol?L^-1).The forward osmosis membrane can effectively remove natural organic matter.The removal rate of dissovled organic matter in three water samples is more than98%,and the retention rate of natural organic matter is higher（more than 94%）.The permeation drag caused by water flux plays an important role in the adsorption of small molecular weight natural organics in the porous support layer of forward osmosis membrane.The fouling occurred when the membrane support layer facing the feed solution would be compensated by the reduced ICP level induced by the decreased membrane flux.When filtering natural surface water and water samples of the water plant process,the fouling flux of water samples with higher proportion of small molecular organics decreases more significantly.In the filtration of feed water and backwash water of filter in the series by forward osmosis process,when the backwash water containing less medium and small molecules is filtered first and then the filtration of feed water of filter followed,the membrane fouling occurred was less severe,i.e.,the first filtration in the series of water samples containing less medium and small molecular organics could favour the higher continuous filtration efficiency of the forward osmosis process.The filtration sequence had minor effect on the retention of organic matter by the forward osmosis membrane,and the retention rate was above 96%.Based on the observation of the fouled membrane by scanning electron microscope and confocal laser scanning microscope,a small amount of algal cells and polysaccharides adsorbed on the membrane surface,and more protein organic substances adsorbed within the membrane support layer.