Decolorization of remazol brilliant blue R with immobilized laccase in spent coffee ground biochar

The amount of recalcitrant compound such as synthetic dye can be a threat to sustainability of the environment. Biocatalytic treatment using oxidoreductase enzyme such as laccase has been considered as environmentally benign method. However, the enzyme has some limitations for the applications especially the reusability and stability which required the enzyme to be immobilized to overcome the limits. In this study the laccase, one of oxidoreductase enzyme produced from Megasporoporia sp., was immobilized into spent coffee ground biochar with alkali modification. The spent coffee ground itself has huge source since it was discharge as a waste from one of the most consumed beverages. Meanwhile the alkali modification using potassium hydroxide for biochar activation can improve some characteristics (porosity, surface area, functional group) that can support the immobilization of laccase into spent coffee ground biochar. In addition, the result of spent coffee ground biochar was characterized using BET, FTIR, and SEM analysis. The immobilization was optimized by varying immobilization time, concentration of enzyme and glutaraldehyde and give the optimum condition at 2 hours incubation, 0.6 U initial enzyme and 1% of glutaraldehyde. The immobilized laccase into SCGB was further used for RBBR decolorization and the optimization was undergone in pH range 2.0-7.0 and temperature range 30-70°C, the thermostability of immobilized laccase was improved compare to free laccase and after 6 cycles the immobilized laccase could maintain its decolorization more than 50%. The phytotoxicity of decolorization product from immobilized laccase was less harmful for mung bean and sweet corn seeds. This research emphasized the valorization of spent coffee ground waste for laccase immobilization and applied for RBBR decolorization to provide the alternative method that eco-friendlier and more sustainable.