Valorized oxalic acid treated onion peel (Allium cepa) and jute stick (Chorchorus olitorius) wastes for dye removal from tannery effluents

Abstract

This study employed bio-adsorbents prepared from agricultural waste onion peel (Allium cepa) and jute stick (Corchorus olitorius) to remove anionic dye (Acid Red 73) from tannery wastewater. Increases in pH and temperature exhibited negative impact on dye adsorption, although the adsorbent dose, initial concentration of dye, and contact time had positive effects on the adsorption process. Equilibrium data were fitted with both the Langmuir and Freundlich isotherm models, and the maximum adsorption capacities of the oxalic acid-modified onion peel (OAOP) and jute stick (OAJS) were 151.51 and 133.33 mg/g, respectively at 298 K. Dye adsorption was shown to follow a pseudo-second-order kinetic model (R2 = 0.961 – 0.997 for OAOP and (R2 = 0.945 – 0.999 for OAJS). The adsorption was spontaneous and favorable at various temperatures. The values of ΔH° for OAOP and OAJS were negative (−54.78 and −53.12 kJ/mol), which signify an exothermic process. Moreover, both the adsorbents, showed multilayered physisorption based on isotherm and thermodynamic studies. The used adsorbents were regenerated, and reused with decreasing capacity (78.32 ± 2.78 – 21.37 ± 1.96 mg/g for OAOP and 84.72 ± 3.08 – 24.76 ± 2.66 mg/g for OAJS). The application of adsorbents in real tannery dyeing effluents along were also evaluated and discussed.