Mechanism Study On The Accelerated Biodecolorization Of Azo Dyes By White-rot Fungi Cultured With Lignin

Wastewater containing synthetic dyes has posed serious threat to environment.White-rot fungi(WRF)can degrade various dyes by secreting extracellular lignin-degrading enzymes,which has broad application prospects.Previous studies have found that lignocellulosic crop residues can enhance the efficiency of pollutants removal,in which lignin is supposed to play an important role.In order to analyze the effect of lignin on dyes degradation by WRF,co-metabolism systems containing different lignin and fungi were studied in this paper,and lignin metabolites in these systems was detected and evaluated.The main findings are as follows:The degradation of azo dyes by the WRF Echinodontium taxodii(E.taxodii)with alkali lignin(AL)in the co-metabolism system was studied.The results showed that AL significantly improved and accelerated the decolorization of four different azo dyes,and the acceleration effect was related to the number of azo bonds and the time of treatment.The maxium decolorization rate differences of the four dyes were 25.79%,33.11%,26.42% and 32.59%,respectively.AL accelerated the decolorization rate of the dye.Laccase(Lac)act as a key enzyme in the decolorization and was improved tremendously by AL.AL also changed the way lac act on the dyes.The pH decreased rapidly in the addition of AL,and it was more obvious in the treatment of dyes with more azo bonds.The decolorization of monoazo dyes by WRF Ganoderma Lucidum(G.lucidum)with the enzymatic hydrolysis of mild acid lignin(EMAL)was studied.The results show that EMAL promoted the degradation of monoazo dyes by G.lucidum as well and significantly increased the reaction kinetics of dye decolorization.The promotion effect relieved the inhibition of dyes on the fungal growth and was more remarkable with the refractory Sunset Yellow(SSY).The final decolorization rate difference was 36% higher than that of the control group,while the easily degradable Remazol Brilliant Violet 5R(RBV5)increased by only 13%.Lignin induced lac secretion,enhanced dye degradation,and strengthed the reliance of dye decolorization to laccase activity.EMAL made the pH curve sharper and the change was more significant on RBV5 than that of SSY.The above results reflect that different lignin generally promoted the degradation of various dyes by increasing the secretion of lac from different WRFs.Lignin metabolites were studied using various analytical detection techniques in different culture media.It showed that the solvent extraction was more applicable than the simultaneous distillation and extraction(SED)and solid-phase microextraction(SPME).At the same time,the potato medium was more conducive than the Kirk medium to the production of small molecules related to lignin.Metabolites varied according to fungi and media.and the common metabolites associated with lignin structure were phenol,p-hydroxyphenol,guaiacol,4-ethylguaiacol,4-vinylguaiacol,benzaldehyde,2,4-dimethylbenzaldehyde,phenylacetaldehyde,acetovanillone,vanillin,syringaldehyde,vanillic acid,homovanillic acid and syringic acid.The effect of 30 different lignin model compounds on the degradation of azo dyes by WRFs was studied.The results showed that compounds which promoted the degradation of different azo dyes by E.taxodii increased the lac activity and enhanced the correlation between the decolorization rate and lac activity.They had very different influence on the degradation of two monoazo dyes by G.lucidum.Most of the compounds improved the decolorization of more refractory SSY,but show weaker association between Laccase activity and decolorization.The same compounds that enhanced the decolorization by both fungi were guaiacol,syringyl alcohol,syringaldehyde,trimethoxybenzoic acid,m-hydroxybenzoic acid,p-coumaric acid and o-coumaric acid.They were stable and reactive in structure with low toxicity.In summary,this results show that different lignin enhanced the removal of various azo dyes by WRFs,and the role of lignin metabolites in dye degradation was preliminarily verified.This paper's conclusions provide a certain basis for the future research.on dyes degradation in the co-metabolism system.