ABSTRACT
Papain is used to modify the surface of a low-cost adsorbent, charred citrus fruit peel (CCFP) for adsorptive removal of mercury (II). The immobilization condition of papain on CCFP is optimized using response surface methodology considering initial concentration of papain, pH, and weight of CCFP as independent factors and specific enzymatic activity as response. The immobilized sample obtained at optimum condition is termed as charred citrus fruit peel immobilized papain (CCFPIP). Comparative study shows that commercial activated carbon, CCFP, and CCFPIP can remove 21.55%, 21.37%, and 99.92% mercury (II), respectively, when they have been used individually to treat synthetic wastewater containing 5 mg/L mercury (II) under identical condition. The removal process of mercury (II) by CCFPIP has been optimized using RSM, considering initial concentration of mercury (II), weight of CCFPIP, pH, and temperature as input factors and percentage removal of mercury (II) as response. Theoretically predicted percentage removal (83.76%) matches well with the experimental observation (85%) at optimum condition. CCFPIP is equally able to treat industrial wastewater. Finally, recovery study with spent CCFPIP shows better (66.68%) recovery at lower pH (4) than at higher pH (7 and 9).
