Box-Behnken approach for optimization of Cr(III) removal from a real tanning effluent using powdered marble

Abstract

During the tanning step, 30-40% of trivalent chromium remains in the solid and liquid wastes, generating highly polluted sewage. In this study, powdered marble was used as a low-cost adsorbent to remove trivalent chromium from a synthetic solution and a real tanning effluent. Batch adsorption experiments on powdered marble were performed. After incubation, samples were filtered and the uptake of chromium was determined. A 3-level Box-Behnken Design was used to study the combined effect of initial chromium concentration, pH values and adsorbent dose on the removal of trivalent chromium. The results showed that the maximum uptake (> 99%) was obtained at a chromium initial concentration of 0.758�g/L, pH = 5.0 and using 6% (w:v) of powdered marble. Adsorption isotherm was satisfactorily described by Langmuir model. The toxicity of the tanning effluent was examined before and after adsorption. Phytotoxicity (Lepidium sativum) assays revealed an improvement of the germination index rising from 0 to 35% before and after adsorption, respectively. Microtoxicity (Escherichia coli) assays showed a decrease in the growth inhibition percentage going from 100 to 31% following the adsorption experiment using raw tanning effluent. Desorption study indicated that nearly 45% of the adsorbed trivalent chromium was recovered using 4% (v:v) HCl. Overall, results showed that powdered marble is an effective and an economical alternative with great potential for trivalent chromium recovery. 2021, Islamic Azad University (IAU).