Adsorptive Removal of Chromium from Tannery Wastewater Using Biochar Derived From Organic Fraction of Municipal Solid Waste

Abstract

This work aimed to investigate the potential use of pyrolysed organic fraction of municipal solid waste as an adsorbent agent for removal of Cr (VI) from aqueous and tannery wastewater. We adopted a pyrolytic process to produce biochars from dried organic fraction of municipal solid waste at different temperatures (350oC, 450oC and 700°C). Cr (VI) adsorptive potential of the manufactured biochars was assessed via batch adsorption experiment. The influence of contact time, co-existing ions, effect of pyrolytic temperature, the initial chromium concentration, pH and adsorbent doses were assessed. The model fitness was determined using Langmuir and Freundlich isotherm model as well as kinetic equilibrium experiments. In this study removal efficiency increased with time until equilibrium time reached at 30 min. The adsorption of Cr (VI) on the biochars was greatly dependent on the pH of the solution. Optimum pH for maximum Cr (VI) removal was at 2. The amount of Cr6+ ions adsorbed increase until it reached the optimum dose 1g, and it became constant with increasing the dose of the adsorbent from 2g to 10 g. Maximum removal efficiency of 98.2%, 99.5% and 98.8% for Cr (VI) was achieved using 1g/L of BC-350oC, BC-450oC and BC-700oC respectively. The removal efficiency of Cr (VI) decreased from (99.9 to 51%), (100 to 56.6%) and (99.9 to 52.5%) with increasing the initial Cr6+ concentration from 1mg/L to 40mg/L for BC-350oC, BC-450oC and BC-700oC respectively. Anions such as phosphate, nitrate, chloride and their mixture had affected the adsorption of Cr (VI) ions on the biochars. The influence of phosphate ions was higher when compared with other anions, but lower than their mixtures effect. Desorption of Cr (VI) increased as the concentration of NaOH increased from 0.1 to 1M solution. The Cr (VI) adsorption kinetics data followed the pseudo-second order equation with the correlation coefficient, R2 >0.99, for all adsorbents. The equilibrium adsorption data was well described by Freundlich isotherms with correlation coefficient R2 value of greater than 0.98 for all tested biochars. Overall the study results indicated that the potential use of biochar derived from OFMSW as adsorbent for Cr6+ removal are feasible.