Removal Of Typical Antibiotics And Estrogens By Nanofiltration And Reverse Osmosis Membranes

Antibiotics and estrogens,as toxic organic micropollutants,are frequent occurrence in the natural environment.Conventional water treatment technologies have limited ability to remove antibiotics and estrogens in wastewater,which cause potential harm to the ecological environment and human health.In this paper,the removal characteristics of typical antibiotics and estrogens in nanofiltration and reverse osmosis(NF/RO)membrane were mainly studied.First,the establishment and optimization of solid phase extraction coupled with liquid chromatography tandem mass spectrometry(SPE-LC-MS/MS)were to accurately determine the low concentration of antibiotics and estrogens in various water matrices.Secondly,the retention performance and removal mechanism of NF/RO on antibiotics and estrogens were explored.Finally,the effect and mechanism of complex water conditions on the removal of antibiotics and estrogens were explored.The main conclusions are as follow:(1)SPE-LC-MS/MS method was used to determine nine kinds of sulfonamide antibiotics,namely sulfadiazine(SDZ),sulfathiazole(STZ),sulfamerazine(SMR),sulfamethazine(SMT),sulfamethizole(SFZ),sulfamethoxypyridazine(SMP),sulfachloropyridazine(SCP),sulfamethoxazole(SMX),sulfamonomethoxine(SMM).The limits of detection(LODs)for nine antibiotics ranged between 0.4 and 3.0 ng/L.(2)SPE-LC-MS/MS method was developed and validated for the determination of six estrogens and estrogen mimics,namely estriol(E3),bisphenol A(BPA),17β-estradiol(E2),estrone(E1),ethynyl estradiol(EE2)and dienestrol(DIE).The SPE conditions were optimized as the selection of C18 as cartridges and MeOH as an eluent,and the control of solution pH at 9.0.The method was validated by satisfactory recoveries and intra-day and inter-day precision,LOD,limit of quantification(LOQ)and excellent linearity for calibration curves.The effects of matrix background on the determination were evaluated in four different water matrices.Matrix effects by tap water were negligible,while the matrix effects by surface water and wastewater could not be negligible.Finally,the sum of target estrogenic compounds in Jinze reservoir(Shanghai),the influent and effluent of wastewater in an onsite swine wastewater treatment plant(Jinshan district,Shanghai),river water,and the influent and effluent of a wastewater treatment plant in the campus were within 17-9462 ng/L.(3)The retention performance and removal mechanism of NF/RO on antibiotics and estrogens were explored.The self-degradation of antibiotics and estrogens was investigated.The concentration of DIE decreased significantly by 11.5%within 8 hours,and it has a certain degree of self-degradation.Other estrogens and antibiotics hardly self-degrade.In the initial stage of filtration,adsorption of antibiotics and estrogens by membranes resulted in their high retention rate.Both antibiotics and estrogens reached adsorption equilibrium after 3 hours,adsorption of antibiotics accounted for 10%-30%,and adsorption of estrogens accounted for 6%-23%.Since estrogens have stronger hydrophobic properties than antibiotics,they have stronger affinity and hydrophobic repulsion with four hydrophilic membranes,which makes estrogens more easily to be adsorbed at the initial stage of filtration and to reach adsorption equilibrium later.When adsorption reached saturation,the retention rate of antibiotics and estrogens remained stable.For antibiotics,the removal rates of XLE,NF90,DL and NF270 were 94%-98%,88%-98%,30%-75%,and 45%-85%,respectively.For estrogens,the removal rates of XLE,NF90,DL and NF270 were 95%-100%,96%-100%,16%-60%,and 25%-60%,respectively.For dense membranes NF90 and XLE,size exclusion is the dominant mechanism for the removal of antibiotics and estrogens.For the loose membranes NF270 and DL,electrostatic repulsion and size repulsion are both important mechanisms for the removal of antibiotics and estrogens.The normalized molecular size(MW/rp and rs/rp)of antibiotics and estrogens was correlated to the removal rate.The cut-off values of normalized molecular size,MW/rp was 741 and rs/rp was 1.2,which further proved that size repulsion and electrostatic repulsion were significant mechanisms for the removal of antibiotics and estrogens.(4)The effect and mechanism of humic acid(HA)and calcium(Ca)on the removal of antibiotics and estrogens were explored.Under the condition of HA,the hydrophobicity of NF270 membrane surface was increased,and the hydrophilicity of NF90 membrane surface was increased.The negative charges on NF270 and NF90 membrane surface were reduced,and the water flux was reduced,and the rejection rates of antibiotics and estrogens were significantly reduced.Under the coexistence system of HA and Ca,more obvious fouling layers were formed on the membrane surface.With the increase of Ca concentration,the hydrophobicity of NF270 membrane surface was gradually decreased.At 1 mM Ca,the apparent critical concentration of calcium on NF270 membrane surface accounted for 2.4%.The negative charges on NF270 and NF90 membrane surface were reduced even more.The rejection rates of NF270 and NF90 to neutral molecule boric acid were lower than that under HA condition.The maximum decrease in water flux of NF270 and NF90 were 29.5%and 25.8%,respectively.The removal rate of antibiotics by NF270 and NF90 decreased with the increase of calcium ion concentration.Ca combines with the carboxyl group of HA to form a macromolecular complex.Ca could complex with the carboxyl functional group on the membrane surface to play a charge neutralization effect,aggravate membrane fouling,and lead to a decrease in water flux and rejection.Membrane fouling mechanisms can be divided into four types:Complete blocking,Intermediate blocking,Standard blocking and Cake layer blocking.Under the synthetic water operation for 36 hours,NF270 and NF90 were mainly affected by complete blocking and intermediate blocking,while cake layer blocking has not yet been completely formed on the membrane surface.