Removal of Colour and COD from vegetable tannery wastewater onto bone char– Effect of process parameters, adsorption mechanism, kinetics and equilibrium modelling

ABSTRACT In this study, bone char derived from head bones of cattle was used as an adsorbent in the removal of Chemical Oxygen Demand (COD) and colour from vegetable tannery wastewater. The char was characterized by proximate analysis, pHpzc, FTIR, BET surface area analysis and SEM-EDX spectroscopy. The effects of operational parameters (pH, contact time, adsorbent mass and temperature), the kinetics and isotherms of the adsorption process were investigated. Optimal conditions for maximum adsorption of COD (77.4%) and colour (98.01%) occurred at pH 2 after 60-minute contact time with 50 g of adsorbent at 25°C. The adsorption kinetics were analyzed using Elovich and the pseudo-first and – second-order models. The pseudo-second order model gave the best fit for the kinetic data. Application of the intra-particle diffusion and Boyd models to the kinetic data revealed that COD and colour adsorption onto the bone char were predominantly controlled by film diffusion. The Langmuir, Freundlich, Temkin and Redlich-Peterson isotherm models were applied. The Freundlich model best described the adsorption of COD and colour. The maximum monolayer adsorption capacities for COD and colour were 559.61 mg/g and 2011.76 Pt-Co/g, respectively. These results indicate that bone char can be an effective low-cost adsorbent in wastewater treatment.