Recycling biochar derived from tannery liming sludge for chromium adsorption in static and dynamic conditions

Abstract

In tannery industry, unhairing and liming (termed as liming) are indispensable but it is a very polluting part of process when producing quality leather. Expelled wastewater from liming generates significant amounts of liming sludge. In this study, efficacies of liming sludge biochar derived for adsorption of chromium from tannery wastewater are described. The biochar was characterized by FTIR, SEM, EDX, and BET technologies, and pHzpc. Surface area and responsible functional groups of biochar were as follows: 9.2 m2/g and C-H, C-N, C-O, C=C, N-H, S=O, and O-H. EDX analysis revealed chromium adsorption and SEM images led to changes in surface morphology. pHzpc for dry liming sludge and biochar were 4.1 and 6.1, respectively. Batch adsorption was verified by assorted parameters including biochar dose, shaking speed, contact time, and dilution factor. Column study results confirm the highest chromium adsorption efficiencies of 408.12 and 533.41 mg/g for 3 cm and 5 cm bed height, respectively. Regression coefficient suggested that adsorption obeys the Freundlich isotherm and pseudo-second order kinetics in batch mode, while it follows the Yoon–Nelson model in column mode. The physicochemical parameters of tannery wastewater prior and post-adsorption revealed good removal efficiencies for chloride content (Cl), chemical oxygen demand (COD), and biochemical oxygen demand (BOD) were, respectively, 50.5%, 80.1%, and 85.5%. Desorption process recovers 69.37 mg/g Cr from adsorbed biochar which could be reused in the tanning process. Consequently, an innovative state-of-the-art tannery liming sludge biochar can satisfactorily use in tannery wastewater treatment by following wealth-from-waste principle.