Application And Mechanism Of Magnetic Resin In The Advanced Treatment Of Municipal Wastewater

This paper focused on the actual demand of advanced treatment and reuse of municipal effluent.In view of the further removal of dissolved organic matter(DOM),the DOM of the secondary effluents from four typical wastewater treatment plants was analyzed and characterized deeply.The DOM removal by the five new magnetic acrylic anion exchange resins with quaternary armonium functional groups were investigated.Based on the study of the interaction between the DOM and the magnetic anion exchange resins,the combination process of the resin and the Na-modified zeolite to remove ammonia-nitrogen and DOM simultaneously and efficiently were developed.The exploration of the removal of potential pathogens and antibiotic resistance genes by the magnetic resin with quaternary ammonium functional groups were operated.The main research contents were as followed:(1)We have preliminarily mastered some common characteristics of such DOM,such as low content of aromatic compounds and poor biodegradability.The molecular weight distribution of the DOM is characterized by the "three peak distribution",and the molecular weight distribution is relatively narrow.The existence of protein like fluorescent substances in DOM is one of the characteristics of these secondary effluents.Hydrophobic acids(HPO-A)and hydrophilic fractions(HPI)are the major organic components and there are acidic groups in the structure of HPO一A and transition hydrophilic acids(TPI-A)while C-O bond of polysaccharide,alcohol or ether and β-glucosidic bonds in the structure of HPI.Hydrophobic neutral(HPO-N)and transition hydrophilic neutral compounds(TPI-N)have similar infrared characteristics and have obvious fat carbon chain structures.The content of unsaturated double bonds or aromatic rings was higher in the hydrophobic components,but less in the hydrophilic components.The strong acidity of the components is HPI>HPO-A>TPI-A>HPO-N>TPI-N.(2)In order to improve the removal efficiency of DOM in the municipal secondary effluents,this study discussed the influence of the characteristics of the resins on the adsorption of DOM.NDMP-A to NDMP-E resins with 0 to 20.7%iron oxide content were chosen as the adsorbents.With the improvement of iron oxide content,the water content of the resins were also increased from 42.8%to 68%.From the kinetic curves of adsorption for humic acid and DOM,FTIR spectroscopy and UV spectrum after adsorption,it could be concluded that the higher water content,the better adsorption efficiency except NDMP-E with 20.7%iron oxide content.The resin with high magnetism could not contact with the water completely.The kinetic curves of adsorption for humic acids and DOM can be fitted well by pseudo-second order model.(3)From the point of the influence of organic matter on the adsorption,the result indicated the molecular weight of organic matter affected the adsorption rate and adsorption capacity of the resin.In the experiment of adsorption of humic acid simulated wastewater,it was found that the adsorption rate from fast to slow was as followed:molecular weight(2500～10000 Da)>(1000～2500 Da)>(>10000 Da)>(<1000 Da)and the equilibrium adsorption capacity from high to low was as followed:molecular weight(2500～10000 Da)>(>10000 Da)>(1000～2500 Da)>(<1000 Da).The order of equilibrium adsorption capacity is the same as that of the Zeta potentials of the humic acids in the pH range of 6 to 9 and the electrostatic interaction between humic acid and the resin played a significant role.The results of GPC also proved that the resin had a poor removal efficiency on the organic matters with Lower molecular weight in the actual wastewater.The three-dimensional fluorescence results showed that after the treatment of NDMP-D resin,the high fluorescence intensity of the protein-like,fulvic-like and other substances were significantly decreased.In the further dynamic analysis of fluorescence spectra,we found that these substances almost all reached adsorption equilibrium in 20-30 minutes.And the comparison of the fast adsorption stage within 5 minutes found that the peak intensity of the protein-like substances,fulvic-like acid substances and humic-like substances declined almost equivalently.Because the excitation wavelength of the components with high fluorescence intensity is 230 nm,so in the following RPHPLC-FLD experiments,the excitation wavelength was fixed to 230 nm and multiple emission wavelengths were scanned.Different hydrophobic components were separated by HPLC and the different components reached equilibrium at the same time in the resin kinetic experiments.The equilibrium time is 30 minutes,and there is no difference occurs due to the different hydrophobicity.The different hydrophobicity fractions separated by DAX-8 and XAD-4 resins were treated by NDMP-D resin,respectively.The removal efficiency of hydrophobic substances(HPO-A and HPO-N)and TPI were higher than that of HPI.But after many times batch testes,the removal efficiency of HPO-N fraction decreased more faster,indicating that the resin had poor continuous adsorption capacity for this fraction.(4)In the advanced treatment of the actual wastewater,the application conditions of the magnetic resin and the zeolite were optimized firstly.The results showed that with the increase of the resin dosage,the removal efficiency of organic matter,nitrate nitrogen and phosphorus increased.When the dosage was 20 mL/L,the removal efficiency of UV254,NO3-N and PO3-P reached 70%,77%and 70%,respectively.In order to remove ammonia-nitrogen efficiently,we modified the natural zeolite.The results showed that sodium chloride modification improved the cation exchange capacity of natural zeolite,reduced impurities and improved the quality of zeolite.In the experiment of simulated wastewater,the thermodynamic and kinetic experiments of the zeolite indicated that humic acid had a negative effect on the removal of ammonia nitrogen,the higher the molecular weight,the greater the influence.The adsorption thermodynamic data of ammonia nitrogen by zeolite can be better fitted by the Freundlich model in the absence of humic acid and can be fitted well by Langmuir model in the presence of humic acid,which may show that humic acid changed the surface morphology of the zeolite and occupied the exchange site.Regardless of the presence or absence of humic acid,all the kinetic data can be better fitted by the peseudo-second order kinetics equation.Humic acid has no effect on the equilibrium time,but shortened the time controlled by the intra particle diffusion alone.Secondly,in the experiment of combination of resin and zeolite,the four processes of"NDMP-D alone","the zeolite alone","NDMP-D resin followed by the zeolite" and"the zeolite followed by NDMP-D",were compared.The results showed that the application of magnetic resin prior to the Na-form zeolite can further improve the reduction efficiency of ammonia-nitrogen and extended work cycle of the zeolite obviously.The best regeneration agents of the zeolite is "10%NaCl+0.6%NaOH".After ten times of regeneration,the NDMP-D resin and the modified zeolite maintained relative removal efficiency of organic matter and ammonia nitrogen.(5)The experiment found that the magnetic ion exchange resin also exhibited high removal efficiency on the total bacterial counts and the total coliform in secondary effluent and the removal efficiency reached 57%and 87%,respectively when the resin dosage was 10 mL/L.This process was very rapid and the equilibrium was achieved in 5 min and 1.5 min,respectively.The magnetic resin made the species of the potential pathogens reduced from 39 to 19 and the relative abundance of total potential pathogens decreased by 60%.The magnetic resin also made the type of antibiotic resistance genes(ARGs)reduced from 14 to 8 and the relative abundance of the total ARGs decreased by 79%.The reduction rates of the relative abundance of tetracycline ARGs,sulfonamide ARGs,multidrug ARGs,Aminoglycoside ARGs,β-lactam ARGs and Bacitracin ARGs were 85%,72%,80%,89%,84%and 46%,respectively.The adsorption of magnetic resin was more efficient than the combined process of coagulation and sand filtration.