Rejection Property Of Forward Osmosis Process To Typical Organic Components In Recycled Water

With the increase of the population in the worldwide and the promotion of living standards of residents,the trend of people's demand for municipal water is increasing year by year.Most of the regions are confronted with severe water shortages and serious water pollution problems at the same time.It is difficult to meet social development requirement by simply relying on traditional surface and undergroud water resources.Therefore,unconventional water resoureces which is represented by recycled water have increasingly widespread applications in social manufacture and daily life.However,the species of toxic organic components in recycled water are complex and diverse,which specific substance content is relatively low,it cannot be ignored that they have long-term comprehensive toxicity to human body.For this reason,the reuse of reclaimed water as drinking water is restricted to some extent.Forward osmosis technology was adopted in this research,recycled water was taken as feed solution and brackish water was taken as draw solution.The retention characteristics of osmotic mambrane to macromolecular organic component such as humic acid(HA)and fulvic acid(FA)and typical small molecular organic component such as endocrine disrupting chemicals(EDCs)and aromatic compounds was systematically evaluated.The main conclusions are given as follows:(1)The rejection efficiency of forward osmosis process to organic compotents in recycled water is mainly associated with molecular weight,electric charge property and hydrophilicity.Because of the larger molecular size,the rejection efficiency of osmosis process to HA and FA which belong to mid-macromolecule was the highest.In initial time(0.5 h)of systems operation,the rejection efficiency to HA and FA was 100% under FO mode(the active layer of osmotic membrane orients towards recycled water)when salt concentration in draw solution was 12.08 g/L,and the rejection efficiency dropped to 99.7% and 98.6% respectively 5.0 hours later.Meanwhile,the water flux of CTA membrane was 2.00 L/(m2?h),and there was no obvious decrease with the increase of running time.(2)Membrane material and membrane orientation can also significantly affect the retention efficiency to organic compotents.Generally,the order of rejection rate is PA membrane-FO mode > CTA membrane-FO mode > CTA membrane-PRO mode > PA membrane-PRO mode.The reason of such differences is mainly related to membrane material and concentration polarization.Taking PA membrane for example,the thickness of it is about 150 ?m,which is 3 times as thick as CTA membrane,and the support layer of PA membrane has certain adsorption property for organic compotents.Under PRO mode,organic compotents flux had been significantly improved because of the occurrence of concentration polarization.While running with FO mode,organic compotents flux was the highest because of its thicker thickness and stronger adsorption property.(3)Under CTA membrane-FO mode,CTA membrane-PRO mode and PA membrane-PRO mode,the order of rejection rate of forward osmosis to EDCs were all in line with estrone(E1)> 17?-estradiol(E2)> estriol(E3)> bisphenol A(BPA)> 17?-ethynyl estradiol(EE2),which was codetermined by Zeta potential(electric charge property),logKow(hydrophilicity),and molecular weight.It was different from CTA membrane that the flux of E3 was the biggest with PA menbrane under FO mode,and the adsorption of PA membrane for organic solute in draw solution was the major cause of such differences.Empirical parameter S had been proposed by integrating above factors,and it can primely indicate the retention characteristics of forward osmosis to each organic matters under all of modes had been mentioned through computational verification.(4)It is different from HA,FA and EDCs that aromatic small molecules are mainly in the form of dissolved state in the water.The rejection efficiency of forward osmosis process to such aromatic compounds is mainly associated with the types of substituents on benzene rings and molecular weight.When the benzene ring was connected with the hydrophobic group,the rejection rate was the highest which was still more than 90% after 7 hours of running.If the branched chain of the benzene ring was hydrophilic group,the rejection efficiency of forward osmosis process to this kind of matters was evidently descendant.Compared with phenolic hydroxyl and amidogen,nitryl has certain electron absorption property.The high membrane-passing ability of 2-nitroaniline and M-dinitrobenzene is related to deviation of their electron atmosphere,and they can combine with hydrogen ion to form hydrogen bond easily,so the molecules are electropositive and they will attract to membrane with negatively charged surface.As a result,the retention rate of this substances is the lowest in forward osmosis process.In summary,the rejection efficiency of FO process to each organic compotents in recycled water is very high.It is effective to control the osmotic amount that organic components permeate to draw solution by controlling concentration factor of recycled water and selecting appropriate membrane material and orientation in the process of system operation.The research has significant meaning in reality to achieve safe reuse of recycled water for drinking purposes,to dilute and utilize the inferior groundwater such as brackish water on the basis of ensuring the quality of effluent,and to solve the problem of drinking water safety in water shortage areas.