Removal of emerging pollutants from water using enzyme-immobilized activated carbon from coconut shell

This work reports the removal of diclofenac, amoxicillin, carbamazepine, and ciprofloxacin by utilizing three commercially available granular activated carbons (GACs) (Activated carbon, Silcarbon, and Donau) loaded with laccase. Adsorption was used to successfully immobilize laccase on the GACs, as revealed by scanning electron microscopy and energy dispersive X-ray analysis (SEM-EDX) and Fourier transform infrared spectroscopy (FTIR). In the three types of GACs tested, pH 5, 30 °C, and 2 mg mL⁻¹ laccase content were found to be the optimum immobilization parameters. Laccase immobilization yields of 65.2%, 63.1%, and 62.9% were achieved with activated carbon, Silcarbon, and Donau respectively. The adsorption behaviors of the pharmaceuticals onto the tested activated carbons are best described as a spontaneous endothermic process that follows Langmuir isotherm and first-order kinetics. The reusability of the immobilized enzyme was evaluated using 2, 2′-azino-bis 3-ethylbenzothiazole-6-sulphonic acid (ABTS) as a substrate within six cycles for all adsorbents. In 120 mins, nearly a complete removal of the pharmaceutical compounds (50 mg L⁻¹) was obtained in the case of activated carbon type and more than 90% for other adsorbent types when synergistic adsorption and enzymatic degradation were applied. With adsorption alone, 74% removal was obtained with activated carbon and < 56% for other adsorbents. The finding of this study suggests that biochar produced from coconut shell (same as the one used in this study) can effectively be used as a substrate and adsorbent for pharmaceutical removal. This enzymatic physical removal system has the potential to be applied on a large-scale.