Treatment Efficiency For SDS Based Enhanced Ultrafiltration Of O-toluidine And Tricyclazole From Water

Due to the environmental hazards and industrial values of pesticides and their raw material compounds,it is necessary and meaningful to study relevant pollution control technologies to reject them for not being discharged into environmental water,and meanwhile to recycle them.Micellar enhanced ultrafiltration(MEUF)process is based on the conventional ultrafiltration and surfactants and can remove small molecular compounds.A surfactant is added to aqueous solutions in such concentrations as to form micelles into/onto which the small molecular compounds are bound.The micellar streams containing pollutants can be retained by UF membranes with smaller pore sizes than micelles.Then,MEUF process has the advantages of both high selectivity of reverse osmosis(RO)and nanofiltration(NF)and high permeate flux of ultrafiltration(UF).In this study,tricyclazole(TC)and o-toluidine(OT)were chosen as target pollutants to be removed,which is a pesticide commonly used in recent years and the raw material compound to manufacture TC,respectively.Filtration experiments were conducted using polyethersulfone(PES)hollow-fiber membrane and sodium dodecyl sulfate(SDS)as a surfactant to create micelles.Effects of various operating factors on the treatment of OT/TC by MEUF were investigated,and optimization experiments for treatment efficiency of both pollutants were also carried out.Additionally,mathematical models were also constructed to predict the declines of permeate fluxes in the filtration process.Furthermore,solubilizing mechanisms of OT and/or TC in SDS micelles were discussed.Finally,the efficiency of separation and recovery for SDS and pollutants in the retentate was examined.This study herein lays a foundation and provides a helpful reference for the practical application of MEUF in the treatment of organic wastewater.Firstly,three kinds of surfactants including SDS,CTAB(cetyl trimethyl ammonium bromide)and TX-114(Triton X-114)were assayed prior to the selection of SDS for removing OT/TC through MEUF in the preliminary experiments.Effects of various influencing factors on the treatment of single pollutant were examined.Results showed that in the process of determining the dosage of surfactant and the concentration of feed pollutant,concentration ratio and adsorption rate were better to reflect micelle binding abilities to the pollutant comparing to rejection rate,and then they were favorable to determine corresponding concentrations.The excessive dosage of surfactant had only limited effect on the rejection rate and the concentration rate of each pollutant but could further decrease the permeate flux.Nearly all of OT is completely removed by 6 k Da UF membrane using SDS,and tricyclazole reached the best removal efficiency of 91%in near-neutral p H condition.Sodium compounds can lead to the rise of rejection of SDS,but the increased rejection was adsorbed and/or deposited on the UF membrane.The addition of Na₂CO₃can reduce the removal of OT in MEUF process.To investigate the interactions of various influencing factors and optimize the treatment of OT and TC in binary solution by MEUF using SDS as a surfactant.Polynomial regression models were developed to predict the treatment performance indexes of both pollutants by MEUF based on the experiment of response surface methodology.The best rejections of OT and TC could reach values of more than 99%and 87%,respectively at optimum conditions.Utilizing the mixed surfactants solutions(SDS-TX-114/SDS-TX-100)could improve significantly the fluxes,the rejection of TC slightly increased at appropriate concentations of mixed surfactants,but the rejection of OT decreased to different extent.The addition of sodium compounds can improve the rejection of SDS with adjusting solution p H to the optimum p H value(p H 4.7),and the increased mount of SDS rejected was not adsorbed/deposited on the membrane,the rejection of both pollutants was also not affected by that condition.The models of partial least-squares regression(PLS),Back Propagation Neural Network(BPNN)and coupling model of Partial Least Square Regression and Artificial Neural Network(PLS-BP)were constructed to predict the flux as a function of volume concentration factor(VCF)and to discern the membrane fouling extent in MEUF process.BPNN showed the best performance for flux predication with the mean absolute percentage error and mean square error of 3.11%and 0.67,repectively,when the 3-8-1 type network was constructed using SDS feed concentration,transmembrane pressure and VCF as input factors.Mechanisms of SDS micelles solubilizing OT and/or TC were analyzed and discussed from the view of macro level of micelles and micro level of surfactant molecules,respectively through applying the dynamic light scattering(DLS)technique and nuclear magnetic resonance(NMR)technique.Results showed that OT could reduce the repulsive force among the negatively charged head groups of SDS through electrostatic attraction and lead to the increase in the aggregation performance of SDS micelles.The micelle sizes became lager after solubilizing pollutants.OT was mainly solubilized in the shell region of SDS micelles,and meanwhile partially resided in the core,but it did not penetrated into the sites close to terminal methyl.TC was mainly solubilized in the core of SDS micelles and resided close to bulk methylene and terminal methyl in the deeper region of micelles.OT and TC were solubilized in the core of the micelles when they were simultaneously solubilized in SDS micelles,and OT migrated to?-methylene to some extent.Additionally,types and rules in the process of SDS micelles solubilizing OT and TC simultaneously were examined under the optimized acidic solution condition(p H 4.7).Solubilization isotherms were analyzed to indicate that monolayer adsorption was more favorable than multilayer adsorption for binary system.The solubilization was a spontaneous endothermic process through investigating the thermodynamic rules.Processes of SDS micelles solubilizing OT and TC followed pseudo-second order and pseudo-first order kinetics,respectively.Finally,the separation and recovery efficiency of surfactant and organic pollutants in the retentate was examined with the treatments of chemical precipitation and of precipitation by lowering temperature.The former method could attain the best recovery of around 81%for SDS with each pollutant content of 10?30%for their respective initial amount.The latter method just attained the best recovery of 66%for SDS,but OT and TC contents in the reclaimed SDS were only 10%and 5%respectively for their initial values,which were lower than those through chemical precipitation.The best recovery of SDS reached 90%when the retentate was treated by chemical precipitation after it was treated initially through precipitation by lowering temperature.The coupled method possesses the advantages of both high purity of reclaimed SDS for precipitation by lowering temperature without adding chemicals and high SDS recovery efficiency for chemical precipitation.