Preparation Of BC Immobilized Laccase Environmental Treatment Materials And Its Performance On Degrading Chlorophenol Pollutants

Chlorophenol compounds(CPs)have the characteristics of biotoxicity,bioaccumulation,chemical stability and biodegradation difficultly which can not eliminate easily from the water stream.They are widely found in the environment and easy to accumulate in organisms through the food chain.Human health and ecological safety will be seriously threatened by it,which without effective treatment.Enzymatic hydrolysis is a simple,safe and efficient method in the treatment of refractory organic wastewater.This method provides a new idea for the treatment of chlorophenol pollutants.In this work,bacterial cellulose(BC)was used as the immobilized substrate of laccase.After optimizing the preparation of BC immobilized Laccase environmental treatment material(BC/Laccase),the surface morphology,chemical structure and enzymatic characteristics of the BC/Laccase were studied.It was applied to degrade chlorophenol pollutants in water at the laccase/mediator system(LMS).Specific research contents and experimental conclusions were summarized as follows:1.Preparation and performance evaluation of BC and BC/LaccaseBC substrate with high laccase loading rate was obtained by adjusting fermentation conditions and selecting culture methods.An environmentally friendly,safe and efficient BC/Laccase was prepared by optimizing the fixation process.The results were as follows:The obtained optimal culture conditions for BC substrate were that solution pH 5,culture temperature 28?,culture time 8 d,inoculation volume 10.0%,and yield up to 0.538 g/L.Three immobilized methods:adsorption-crosslinking method,crosslinking method and oxidation method were adopted.After optimization,the optimal immobilization process was obtained.The enzyme activity of BC/Laccase by adsorption-crosslinking,crosslinking and oxidation were respectively 89.87 U/g,78.65 U/g and 55.77 U/g.According to the Michaelis-Menten equation,the Km value of free laccase was 1.018 mM,the Km value of BC/Laccase by adsorption-crosslinking method was 1.086 mM,the Km value of BC/Laccase by crosslinking method was 1.795 mM,and the Km value of BC/Laccase by oxidation method was 3.159 mM.Due to the BC/Laccase by adsorption-crosslinking method has mild preparation conditions,little effect on enzyme molecules,the highest enzyme activity,the minimum Michaelis constant,good storage stability and recycling ability,therefore,this method was selected as laccase immobilization method.2.Degradation performance of BC/Laccase on chlorophenol pollutantsUsing 2-chlorophenol and 4-chlorophenol as simulated chlorophenol pollutants,the degradation ability of adsorption-crosslinking BC/Laccase on chlorophenol pollutants in LMS was studied.The results were as follows:BC/Laccase showed the highest degradation efficiency for 2-chlorophenol and 4-chlorophenol when the mediator was erucic acid.The results proved that BC/Laccase had the same degradation conditions for 2-chlorophenol and 4-chlorophenol.The conditions were medium dose 4 mM,temperature 30?,pH 3 and time 5 h.At this time,the degradation effect of BC/Laccase to 2-chlorophenol under without laccase/mediator system(WLMS)condition was 55.9%,while that of 2-chlorophenol under LMS condition was 79.9%.Under the condition of WLMS,the degradation rate of 4-chlorophenol by BC/Laccase was 53.7%,while under the condition of LMS the degradation rate of 4-chlorophenol by BC/Laccase was 78.2%.After 6 consecuetive cycles of use,the BC/Laccase still retained 84.4%degradation rate of 2-chlorophenol and 83.0%of the degradation rate of 4-chlorophenol which demonstrates the robust reusability.