Covalently Immobilized Laccase for Decolourization of Glucose-Glycine Maillard Products as Colourant of Distillery Wastewater

Maillard reaction products like melanoidins are recalcitrant, high-molecular-weight compounds responsible for colour in sugarcane molasses distillery wastewater. Conventional biological treatment is unable to break down melanoidins, but extracellular laccase and manganese peroxidase of microbial origin can degrade these complex molecules. In this work, laccase was covalently immobilized on alumina pellets activated with aminopropyltriethoxysilane (APTES). The immobilization yield was 50–60 %, and the enzyme activity (886 U/L) was 5-fold higher compared to the soluble enzyme (176 U/L). The immobilized enzyme also showed higher tolerance to pH (4–6) and temperature (35–60 °C), as well as improved storage stability (49 days) and operational stability (10 cycles). Degradation of glucose-glycine Maillard products using immobilized laccase led to 47 % decolourization in 6 h at pH 4.5 and 28 °C. A comprehensive treatment scheme integrating enzymatic, microbial and membrane filtration steps resulted in 90 % decolourization.