Preparation And Application Of Novel Biopolymer Magnetic Resin In Perchlortate Removal And Anaerobic Reduction

As a great agricultural country,China has a large scale of crop cultivation and abundant straw resources.Improve the comprehensive transformation and utilization efficiency of crop straw resources,that is conducive to promoting the adjustment of Chinese agricultural structure,reducing the pressure of atmospheric pollution,increasing the income of rural economy,and promoting the realization of Sustainable Development Strategy.Crop straw contains a large number of reactive functional groups,such as hydroxyl,carboxyl,and peptide chains,which provide a structural basis for the chemical modification of biomass.The high specific surface area produced by the porous structure of plant ensures the material conditions for the preparation of biosorbent from the raw straw.Based on the above,we used the low-cost corn stalks as the main raw material and developed a novel magnetic amine-crosslinked biopolymer based corn stalk(MAB-CS)by magnetization and chemical modification.The novel biosorbent(MAB-CS)is environmentally friendly,easy to be separated and has high adsorption efficiency for perchlorate pollutants,which effectively improves the comprehensive utilization efficiency of biomass resources and realizes the high-value utilization of crop stalk.The paper optimized the modification methods and reaction conditions for MAB-CS preparation.In order to determine the adsorption characteristics of MAB-CS for perchlorate,we discussed static and dynamic adsorption-desorption of perchlorate by MAB-CS.Based on the characterization of biosorbent and experimental data of perchlorate removal,we investigated the relationship between structure of MAB-CS and perchlorate removal.and then revealed the adsorption mechanism of MAB-CS for perchlorate pollutants.Additionally,due to the biodegradability of perchlorate,this study domesticated and used mixed anaerobic bacteria to reduce perchlorate which was concentrated on the surface of the adsorbent.In conclusion,these results indicated that the reduction of concentrated perchlorate could be achieved simultaneously with the biosorbent bio-regeneration.The main research conclusions were summarized as follows:1.After adjusting the order of magnetization and amination and balancing the magnetization intensity and amination degree in the process of corn stalk-based adsorbent preparation,we fund out the key functional structure and physicochemical properties of biosorbent,and then determined the optimal preparation conditions for magnetic amine-crosslinked biopolymer based corn stalk:corn stalk 3 g,total iron concentration 0.2?0.25 mol L-1,NH3,H2O 20 mL,DMF 20 mL,epichlorohydrin 20 mL,ethylenediamine 6 mL and triethylamine 20 mL.2.This paper investigated the physicochemical composition,structural morphology,magnetic properties and functional group characteristics of MAB-CS,which show that the corn stalk can be endowed with magnetic properties by in-situ coprecipitation magnetization process with saturation magnetization of 6.25 emu g-1.After chemical modification by epichlorohydrin,ethylenediamine and triethylamine,the pore channels on biomass surface and proportion of mesopores were significantly increased.Additionally,a large number of positively charged quaternary ammonium groups were introduced into the cellulose structure of corn stalk,resulting in a significant increase in N content(9.00%)and surface Zeta potential(PZC=8.2)3.The results of static perchlorate adsorption by MAB-CS show that MAB-CS can quickly adsorb and remove perchlorate from water.The process of perchlorate removal can be divided into three stages,namely rapid adsorption stage(0-90 min),slow adsorption stage(90?180 min)and stationary stage(180?240 min).The static adsorption of perchlorate in first 90 min is consistent with intraparticle diffusion model,indicating that the main control step of perchlorate adsorption reaction is intraparticle diffusion in the first reaction stage.During the 90?360 min phase of the static perchlorate adsorption reaction,the reaction data conforms to the pseudo-second-order kinetic model,indicating that chemisorption is the main adsorption reaction occurred in the solution.Therefore,the main factor that controlled the adsorption reaction is the chemical bond between perchlorate and the active sites on adsorbent surface.4.The static adsorption of perchlorate by MAB-CS accords with the Langmuir isotherm adsorption model,which indicates that the adsorbate is homogeneous monolayer adsorbed on the surface of MAB-CS,and the interaction between the adsorbates adsorbed on the surface of the adsorbent are not occurred in this process.The maximum adsorption capacity(qm)of MAB-CS for perchlorate is 119.05 mg g-1,126.58 mg g-1 and 178.57 mg g-1 at 20 ?,30 ?,40 ?,respectively.Thermodynamic parameters of perchlorate adsorption,such as ?H(16.10?63.80 kJ/mol),AS(0.12-0.28 kJ/mol)and ?G(-22.11?16.51 kJ/mol),show that the adsorption of perchlorate used by MAB-CS is an endothermic reaction that can be spontaneously carried out.5.The XPS spectra of MAB-CS before and after adsorption of perchorate show that the perchlorate removal by MAB-CS mainly depends on the ion exchange reaction To be specific,perchlorate can be removed and adsorbed on the surface of MAB-CS by ion exchange reaction with Cl" that was from the quaternary ammonium group on the surface of MAB-CS.Both NaCl and HCl solutions can effectively recover the adsorption capacity of MAB-CS for perchlorate.The regeneration efficiencies of NaCl and HCl solutions are 83.5%?90.4%and 87.6%-89.5%,respectively.MAB-CS can be effectively seperated from solution no matter before and after chemical regeneration.6.The dynamic adsorption of perchlorate by MAB-CS are affected by bed depth,soluiton flow rate and the pH of solution.The adsorption capacity of MAB-CS can be enhanced by increasing the adsorbent bed depth from 0.95 cm to 2.15 cm.But the dynamic adsorption rate(KTh)of perchlorate would be decreased from 1.644 mL min-mg-1 to 1.196 mL min-1 mg-1.Additionally,insufficient contact between MAB-CS and adsorbate would be ocurred by accelerating the flow rate of solution from 5 mL min-1 to 12 mL min-1 which would decrease 36.8%of breakthrough volume for perchlorate.Under weakly acidic conditions(pH=4.02),MAB-CS has a higher adsorption capacity for perchlorate(22.7 mg/g).In addition,MAB-CS is more conducive to the treatment of low concentration perchlorate solution,and its adsorption breakthrough curve is basically in line with the Thomas model.Therefore,the perchlorate adsorption reaction conforms to the pseudo second-order kinetic model and the Langmuir isotherm model.In the mixed solution,perchlorate has the strongest binding ability to the surface functional group of MAB-CS,which can be exchanged with the loaded nitrate and phosphate,and eventually adsorbed on the surface of MAB-CS.7.The seed activated sludge of domestication used in this study was the activated sludge from the bioreactor in domestic sewage treatment plant.After 20 days of anaerobic domestication,the mixed perchlorate reducing bacteria were obtained and dominated by Dechloromonas sp.strain(Rhodocyclales).The results of three-level three-factor Box-Behnken Design model show that the interaction influence of two factor on perchlorate reduction was in the order:interaction between pH and acetate>interaction between pH and temperature>interaction between temperature and acetate.Box-Behnken Design model predicted a maximum perchlorate reduction efficiency of100%under the optimal conditions of pH = 7.5,308 K,and 0.51 mg L-1 of acetate.8.It needs an average of 24 h to reduce perchlorate that concentrated on the surface of MAB-CS.When the solution pH=7.4,the bio-regeneration efficiency of MAB-CS loaded with perchlorate can be obtained more than 99%.With the increasing biomass of activated sludge,bio-regeneration efficiency of adsorbent is also gradually increasing.When the biomass of activated sludge is 4.02 g L-1,more than 92%adsorption sites on MAB-CS are released and restored accordingly.In the mixed slution,the co-existing anions enriched on the surface of the adsorbent will disperse the perchlorate reducing bacteria to reduce the concentrated perchlorate significantly.Results of this study supported the applicability of adsorption-microbial reduction for perchlorate removal,which can achieve effective bio-regeneration of adsorbent simultaneously with efficient reduction of concentrated perchlorate.