Evaluation Of MIEX/Enhanced Coagulation In Removing Micro-pollutant And The Process Optimization

Pharmaceuticals and personal care products（PPCPs）received growing attention as emerging contaminants.In last few years,PPCPs,which include antibiotics,endocrine disruptor compounds（EDCs）and persistent organic pollutants（POPs）,have been detected more frequently in surface waters used as drinking water sources in both north and south China,and have possible threats to aquatic environment and human health.So it is important to investigate the PPCPs removals to ensure the safety of water supply.In this study,the concentrations of sulfamethoxazole（SMX）were measured by the ultra-high performance liquid chromatography/tandem mass spectrometer（UPLC-MS/MS）after that SMX was treated by enhanced coagulation,magnetic ion exchange resin（MIEX）adsorption and MIEX-enhanced coagulation integrated process.The effects of different Al-salt species,pH values and natural organic matter（NOM）,such as humic acid（HA）,on SMX removals were evaluated with or without humic acid.And some results are as follows.1.The removal efficiency of SMX by coagulation was relatively low,and it illustrated that inorganic Al-salt coagulants were not suitable for removals of small molecule organic matter.The Al-salt coagulants used in this research were Al₂（SO₄）₃（AS）,poly aluminium chloride（PACl）and Nano AlO₄Al₁₂（OH）₂₄（H₂O）₁₂⁷⁺(Al₁₃).Analysis on mechanism of coagulation,it could be found that the process of coagulation was not a single but more than two mechanisms interacting with each other.In acidic environment,the SMX removal efficiency by AS was higher than that by PACl and Al₁₃ as a whole.It mainly because the monomer aluminum（Ala）were more likely to hydrolyze and precipitate.With the help of adsorption bridging action and sweep flocculation,Ala could form larger flocs and removal SMX.In the neutral and alkaline environment,charge neutralization was believed to play a important role in coagulation process.The neutralization ability of polymeric aluminum（Alb and Alc）was better than the Ala and it would be better to removal SMX.Zeta potencial,residual Al in effluent water and the growth of floc size in different pH were consistent with the results about removal efficiency analysis.The effect of HA on SMX removals by three coagulants was great.The activated groups on humic acid molecules competed with SMX.And they fought for binding site to form chelating ligand combined with Al-salt coagulants.This is the reason for low SMX removal efficiency treated by coagulants.In addition,HA seriously hamper the reaction between Ala and SMX.Zeta potencial,residual Al in effluent water and MW distribution in different pH with the effect of HA were consistent with the results about removal efficiency analysis.2.The SMX removal efficiency by MIEX resin treatment was high.When SMX contacted with MIEX resin,it reacted so quickly that it just needed a short time to complete reaction.And,the regeneration of MIEX resin performed well.the SMX removal rate exceeded 55 % in the pH range of 2-10.Although the different pH values had a small effect on SMX removals.Nevertheless,the removal efficiency of SMX was reached highest（71.2 %）when pH were 5-7.It should not be ignored that the removal efficiency in acid condition was a little higher than that under the neutral and alkaline atmospheres.That was possibly due to the characteristic of SMX and the interference of other ions in the water sample.HCl and NaOH as additions to control pH introduced the chloride ion and hydroxide ion.And it might compete with SMX for exchange sites on the MIEX resin.Meanwhile,HA macromolecular may cause the hole plug by MIEX resin adsorption,and lead to a fall in SMX removal efficiency.When HA added into SMX solution,SMX removal efficiency by MIEX resin treatment was decreased generally compared with that HA did not exist.It could be interpreted that waters with a high HA concentration tend to have a high concentration of anionic species that might compete with SMX for exchange sites on the MIEX resin,thereby impacting SMX removal by ion exchange.Zeta potencial and MW distribution in different pH with the effect of HA were consistent with the results about removal efficiency analysis.3.By studying the removal rates of SMX in different pHs using MIEX-enhanced coagulation integrated process,it could be found that MIEX resin had played a major role in SMX removals by MIEX-enhanced coagulation integrated process.Coagulation process removed SMX rely mainly on the interactions of charge neutralization,adsorption bridging action and sweep flocculation.While MIEX resin removed SMX by ion-exchange adsorption.This is not only related to the Al-salt species and the pH of the solution,but alsodepended on the nature of SMX substance.SMX has a small molecular weight and can be dissolved in the water.This is the reason for low SMX removals by coagulation treatment.SMX shows the nature of anions in the aqueous solution,and has a variety of easily adsorbed functional groups on the molecules.That is conductive to MIEX resin to remove SMX.When HA existed,the performance of MIEX-enhanced coagulation integrated process for SMX removal was lower than that HA wasn’t added to SMX solution.According to the analysis,it can be learned that HA have an impact on removing SMX by enhanced coagulation and MIEX resin adsorption technologies.HA and Al-salt coagulants will have a complex reaction and form the HA-aluminum copolymerization complex.It can consume the amount of Al-salt coagulants and reduce the removal efficiency of SMX.In the process of resin adsorption,HA might compete with SMX for exchange sites on the MIEX resin,thereby impacting SMX removals.