Enhancement Of Jute By Laccase And Removal Of Methylene Blue,Congo Red And Cd²⁺ From Water

The pollution of organic and heavy metal ions has become a new form of environmental pollution.It is of great significance to explore effective materials and methods for the removal of various pollutants from aqueous solutions for the prevention and protection of the environment and human health.In this study,laccase was loaded in segment jute（SJ）matrix,and a series of laccase-jute composite materials（0.1%L-SJ,0.5%L-SJ,1%L-SJ,5%L-SJ）were produced.The removal performance and regeneration performance of SJ and L-SJ were studied by the batch experiments under the conditions of single methylene blue（MB）,congo red（CR）,heavy metal Cd²⁺and MB+Cd²⁺compound pollution,and the effect of laccase dosage,temperature,p H and ionic strength were studied.Furthermore,the produced samples was characterized by Fourier Transform Infrared Spectroscopy（FTIR）,Scanning Electronic Microscopy（SEM）,and the surface charge for the sake of exploring the mechanism of different pollutants removal by samples.The main objective of this study was to provide a theoretical basis for the application of L-SJ in wastewater treatment and a new idea for the application of laccase enhanced jute in wastewater treatment.The main conclusions were as follows:（1）The laccase-loaded jute exhibited enhanced MB removal ability compared with that of raw jute.The order of MB removal was followed by 1%L-SJ>5%L-SJ>0.5%L-SJ>0.1%L-SJ>SJ,exhibiting a trend of first increasing and then decreasing.Additionally,the kinetic process of MB removal accorded with pseudo first-order kinetic model and pseudo second-order kinetic model respectively,reached dynamic equilibrium in about 120 min.The isotherm removal curves conformed to the Sips adsorption isotherm model,where 1%L-SJ exhibited the highest removal capacity(1097.11 mmol·kg^-1).Furthermore,the removal process was spontaneous,exothermic and entropy decreasing.The increase in temperature and ionic strength,and a decrease in p H were not conducive to MB removal.Finally,1%L-SJ maintained a removal rate of 76.66%after being regenerated four times.The mechanism of MB removal was found to the synergistic action of jute adsorption and laccase enzymatic hydrolysis.Jute adsorption contributed to 91.12%,involving electrostatic interaction,surface adsorption and hydrogen bonding.Accordingly,laccase enzymatic hydrolysis contributed to8.88%,whereas laccase improved the MB removal by enzymatic hydrolysis and altering the jute structure.（2）SJ and L-SJ had a lower removal rate of CR,and the removal rule was SJ>>0.5%L-SJ≈1%L-SJ≈0.1%L-SJ≈5%L-SJ.The removal capacity of L-SJ decreased greatly due to the crosslinking of glutaraldehyde,which was much higher than that of Na OH modification and laccase loading,so the removal performance of SJ was better than that of L-SJ,and laccase loading increased the enzymatic hydrolysis reaction of L-SJ to CR.The kinetic processes of SJ and L-SJ fitted the pseudo first-order and pseudo second-order kinetic equations severally,and achieved dynamic equilibrium in about 300 min.The adsorption of SJ was dominated by the surface monolayer adsorption process dominated by rapid adsorption,while the removal by L-SJ not only had monolayer adsorption,but also had a certain chemical reaction（enzymatic hydrolysis reaction）.Besides,the isotherm removal curves of SJ and L-SJ corresponded with the Sips isotherm adsorption model.Moreover,the CR removal reaction was spontaneous,endothermic and entropy increasing.The CR removal increased with the rise of temperature and ionic strength,while the CR removal first increased and then decreased following the move up of p H.The adsorption mechanism of SJ was mainly surface adsorption（includedπ-πstacking,hydrogen bonding and dispersion force）.The removal mechanism of L-SJ was mainly surface adsorption（the same as SJ）,supplemented by enzymatic hydrolysis.Lastly,the difference of CR removal rate and removal performance between SJ and L-SJ mainly came from the difference of charge between CR and MB.（3）Laccase loading was beneficial to the removal of Cd²⁺,the order of Cd²⁺removal was0.1%L-SJ>5%L-SJ>0.5%L-SJ>1%L-SJ>SJ.The removal of Cd²⁺by SJ and L-SJ could complete the removal process within 100 min,which were suitable for the pseudo-second-order kinetic model.The fitting of the isothermal removal curve were in line with the Langmuir model,and the removal of Cd²⁺was a monolayer adsorption behavior.Additionally,the removal of Cd²⁺by SJ and L-SJ was exothermic,spontaneous and entropy increasing phenomenon.Specifically,the increase of temperature,the decrease of p H and the increase of ionic strength cut down the removal performance.Mechanism of Cd²⁺removal by L-SJ included the adsorption of SJ,the increase of specific surface area after Na OH pretreatment exposed more adsorption sites,the augment of adsorption sites by the-CHO of glutaraldehyde,the degradation of lignin by laccase and the interaction between laccase and Cd²⁺.The contribution rates of the four groups were 61.38%,13.70%,18.66%and 6.26%,respectively.The adsorption of SJ was the main mechanism,which mainly included electrostatic action,complexation and hydrogen bonding.Na OH,glutaraldehyde and laccase had auxiliary removing effects.（4）SJ,0.1%L-SJ and 1%L-SJ were selected to study the removal rule of MB+Cd²⁺under the compound condition.The presence of Cd²⁺inhibited the removal of MB,in the meantime,the presence of MB promoted the removal of Cd²⁺,which was 2.67 times,1.72 times and 1.60times higher than that of single Cd²⁺.The isothermal removal curves of MB and Cd²⁺were propitious to Langmuir model and Freundlich model in the compound system.The effect of temperature,p H and ionic strength on the removal of MB were consistent with the removal rule of single and compound conditions,which proved that the presence of Cd²⁺did’t change the removal rule of MB,but would impressed the removal performance of MB.The removal by temperature and ionic strength were slightly different under single and compound conditions of Cd²⁺.The presence of Cd²⁺inhibited the removal of MB,and the presence of Cd²⁺competed with MB for the limited adsorption sites.Meanwhile,the presence of Cd²⁺might co-precipitate with laccase,reduced the activity of laccase and lead to the reduced removal ability of MB.The presence of MB promotesd the removal of Cd²⁺,Cd²⁺contended for the adsorption sites of the ion-exchangeable part of MB.MB and Cd²⁺could make up a six-membered ring chelate,as well as MB adsorbed on jute surface could also provide more adsorption sites.The removal efficiency of SJ and L-SJ for MB,CR and Cd²⁺was in the order of Cd²⁺>MB>CR.On the whole,laccase-jute composites are attractive and economically feasible materials for MB and Cd²⁺.