Application Of Laccase In Wastewater Treatment

Laccases,which have important value in some industrial fields such as bioremediation,and have been highly studied recently,belong to the multicopper oxidase(MCO)family.In this study,we chose the high laccese-producing Cerrena sp.HYB07 as the object studied,figured out how metal ions work to the inhibition on laccase activity firstly,then made up immobilized laccases,studied its enzymatic properties and built enzymatic reactor,ending up applying it to wastewater treatment,which would provide theoretical foundation in laccases’ application of wastewater treatment.The result is as follows:1.Laccase is resistant to many metal ions except for Ag+,Li+,Pb2+and Hg2+,whose inhibition were all reversible on the laccase.Hgg+had the lowest/C50 value on the laccase activity,followed by Ag+,Li+ and Pb2+.The inhibition type on laccase activity was mixed type for Ag+ and Li+,competitive for Pbr0,and noncompetitive for Hg2+.The inhibition kinetic model of Hg2+ on laccase activity was established by using the kinetic method of substrate reaction.The microscopic forward inhibition rate constant(K+-))of Hg2+was 3.26×10-2 s-1 and the microscopic reverse inhibition rate constant(k-o)was 1.36×10-3 s-1.Hg2+ reduces the pH and thermal stability of the laccase.The fluorescence emission spectra showed that Hg2+has a laccase binding site.2.Laccase was immobilized by five methods:GAC adsorption,AB-8 macroporus resin adsorption cross-linking,magnetic Fe3O4-chitosan co-crosslinking,alginate-Pac coadsorption and alginate-glutaraldehyde adsorption cross-linking.The enzyme immobilization rates were 90.3%,92.7%,78.0%,44.3%,and 43.0%.The immobilized enzyme has good thermal stability and anti-inhibito stability compared with free enzyme.It is concluded that the five cycle modes are all better than their batch mode,using five immobilized enzymes above to discolor RBBR in the system of Packed Bed Reactor,and GAC adsorption immobilized laccase is superior to the other four immobilized enzymes.3.The best conditions of dyeing wastewater treatment of free laccase:pH 6.0,35℃,0.5 U/mL of enzyme dosage,reaction time 4 h,decolorization rate was 58.63%,and 18.18%.The best conditions of dyeing wastewater decolorization of GAC immobilized laccase:pH 6.0,25-35℃,0.5 U/mL of enzyme dosage,reaction time 12 h.Its decolorization rate was 91.43%,and clearance rate 77.18%.After 3 times of dyeing wastewater treatment,the immobilized enzyme activity still retained 86.97%.The COD degradation rate of dyeing wastewater was 13.49%and 69.17%,applying free laccase and GAC immobilized laccase to treat dyeing wastewater respectively in the optimization of decolorization conditions.4.Tobacco seeds and human aortic endothelial cells were used for toxicological experiments.The conclusion is that laccase can effectively reduce the toxicity of dyeing wastewater.The above studies show that laccase has great potential for application in the treatment of wastewater.