Degradation Of Dyeing Wastewater By Coupling Of Photocatalysis With Immobilized Laccase

The dyeing wastewater has always been a hot topic in the world due to its complex composition,high content of organic compounds and difficultly degradation.Photocatalytic oxidation has been favored in the treatment of dyeing wastewater,but its treatment efficiency is low,and it is difficult to deal with large amount of wastewater with high concentration of pollutant.Laccase has great potential in the treatment of dyeing wastewater because of its high efficiency and economy.However,recycling of free laccase is difficult and laccase catalytic reaction needs to add the intermediate mediator which will lead to the limitations to applications.In this paper,photocatalytic oxidation technology was used as pretreatment method,and then coupled with immobilized laccase for dyes decolorizing degradation.By comparing with the degradation of dyes in single photocatalytic oxidation and single enzymatic oxidation,the effect of photocatalytic pretreatment to the degradation of dye by immobilized laccase was discussed.Enzyme activity and environmental stability of free laccase were studied using two kinds of laccase sources:industrial-grade and reagent-grade.The results showed that the enzyme activity of laccase by ABTS method was 3-4 times higher than that of DMP method;The optimal reaction conditions of two laccases were pH = 3,temperature = 40℃;85.2%enzyme activity of reagent-grade was deactivated under the environment of pH = 3 in 3 h,and 60.5%of industrial-grade;25.1%enzyme activity of reagent-grade was deactivated under the environment of temperature = 40℃ in 3 h while industrial-grade did not appear deactivation.Aminated mesoporous silica was used as carrier to immobilize industrial-grade laccase,the immobilization conditions were optimized,and the activity of immobilized laccase was also discussed.The mesoporous silica was first prepared by hydrothermal synthesis,and then modified by the addition of APTES under anhydrous toluene.The laccase was then immobilized by covalent binding method using glutaraldehyde as crosslinking agent.The results showed that the enzyme activity of immobilized laccase was 1.13 U/g when average pore size of silica = 3.72 nm,glutaraldehyde concentration = 2%,activation time = 2 h and immobilization time = 12 h,the laccase immobilization efficiency could reach a maximum of 45.2%.Macroporous resin was used as carrier to immobilize industrial-grade laccase,the immobilization conditions were optimized.enzyme activity,environmental stability and reuse of the immobilized laccase were analyzed.Results showed that the immobilization efficiency of amino resin was significantly higher than that of epoxy resin,the optimum immobilization conditions of amino resin were follows:glutaraldehyde concentration = 2%,activation time ＝2 h,immobilization time = 12 h,under these conditions the laccase immobilization efficiency was 78.7%,the enzyme activity of immobilized laccase was 1.97 U/g,and this activity keeps intact basically after being reused for 6 times.Using Reactive Black 5,Reactive Brilliant Red X-3B,Malachite Green,Rhodamine B dyes as pollutants,photocatalytic oxidation as the pretreatment methods,the immobilized laccase by macroporous resin was coupled to degrade the dyes.By comparing with single photocatalytic oxidation and single enzymatic oxidation,the effect of photocatalytic oxidation was studied.The results showed that using enzyme catalysis only,four kinds of dyes could not be degraded without intermediate mediator,but decolorization of four kinds of dyes reached 66.0%,96.5%,98.3%,89.9%respectively with intermediate mediator;however,the decolorizing rate of Reactive Brilliant Red X-3B by immobilized laccase increased by 5 times after photocatalytic pretreatment of titanium dioxide,and this reaction did not need to add additional intermediate mediator.