Decolorization and degradation of toxic Malachite green dye using laccase immobilized biochar

Abstract

Biochar produced from pyrolysis of waste pine needles was acid functionalized and used as a support for immobilization of laccase enzyme. Laccase was immobilized through adsorption and immobilization was optimized using single variable approach. Successful immobilization of biochar was confirmed via FTIR and high laccase binding of 64.4U/g was achieved. Increased pH, thermal and storage stability was displayed by immobilized enzyme as compared to free enzyme.The immobilized laccase retained more than 50% relative activity in the pH range 2-7, more than 45% relative activity at 65°C and more than 55 % relative activity at 4°C for 5 weeks. The re-usability of immobilized enzyme was checked with 2, 2′-azino-bis 3-ethylbenzothiazoline-6-sulphonic acid (ABTS) substrate and enzyme retained 53% of its activity after 6 cycles. Immobilized laccase was used for the degradation and decolorization of azo dye malachite green in aqueous solution. More than 85% removal of malachite green dye (50mg/L) was observed within 5hr and presence of degradation products (Leuco Malachite Green and Methanone, [4-(dimethyl amino)pheny]phenyl ) in GC-MS analysis confirmed degradation. Phytotoxicity analysis indicated that the enzymatic degradation resulted in lesser toxic metabolites than the original dye. Thus, lac case immobilized biochar can provide a sustainable solution through simultaneous decolorization and degradation and can be used as an efficient biocatalytic agent to remove dye from water.