Preliminary Kinetic Studies on the Degradation of the Textile Dye Methyl Blue by Trichoderma asperellum LBKURCC1 Laccase without Mediators

Abstract

Laccases are multicopper-containing oxidases that can catalyze the oxidation of a wide variety of phenolic compounds, benzenethiols, diamines, and aromatic amines without requiring hydrogen peroxide. Several fungal laccases can degrade synthetic dyes, and therefore are important for the bioremediation of dye-containing waste. Methyl Blue (MB), also known as Cotton Blue and Acid Blue 93, is a widely used textile dye in the denim and other textile industries. MB is an acidic dye that is hard to degrade naturally, and if untreated, can pollute the environment, causing high chemical oxygen demand (COD). It is also toxic if ingested by mammals and fish in large quantities. Therefore, it is important to remove MB from textile waste effluents before releasing the effluents into the environment. This research aims to determine the kinetics of the enzymatic degradation of MB by Trichoderma asperellum LBKURCC1 crude laccase extracts at room temperature (±30 RC), without the addition of any mediator molecules. MB solutions with concentrations of 25 ppm and 50 ppm were incubated in the dark with crude extracts of the laccase enzyme (activity 0.007 U/mL or 0.014 U/mL). The absorbance of the colored solution was measured at 594 nm at various time points. Preliminary results show that MB degradation by the laccase crude extracts follows Michaelis-Menten kinetics. A two-fold increase in the MB concentration increased its degradation rate by T. asperellum LBKURCC1 laccase. Likewise, increasing the enzyme activity also increased the degradation rate of MB by the laccase. A buffer control (pH 5.5) of 50 ppm MB solution without adding enzyme showed no decrease in color after four days incubation at room temperature (±30 RC). After four days of incubation at room temperature, the addition of 0.014 U/mL laccase activity could decrease 69% of the 50 ppm MB solution color. However, a heat-denatured laccase solution could decrease 39% of the same MB solution color, showing that the crude enzyme may contain non-enzymatic components that can also contribute to the degradation of MB.