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Abstract
The removal of hexavalent chromium from aqueous solution was examined by the adsorption process using non-living activated sludge as an absorbent. The kinetics of the hexavalent chromium removal were examined in batch experiments for the concentrations between 1 and 20 mg/L hexavalent chromium solutions. The adsorbent dosage applied was 0.1 g dry weight of adsorbent/250 mL for the non-living activated sludge. Four different mixing times ranging from 30 to 120 min and six different pH values between 2 and 7 were assessed to find out the optimum mixing time and pH value. The removal efficiencies were above 56% for all hexavalent chromium concentrations and mixing times. The 250-rpm shaker speed at pH 2 gave the highest removal efficiency. The adsorption kinetics can be described by the pseudo-first-order and pseudo-second-order kinetic models. The rate constants were evaluated for all hexavalent chromium concentrations. This study showed that the hexavalent chromium adsorption kinetics of the non-living activated sludge fitted quite well to the pseudo-second-order kinetic model than the pseudo-first-order kinetic model. This reveals that it is comparative to the square of the concentration of chromium adsorption rate. These results show that non-living activated sludge could be effectively used as a low-cost and alternative absorbent for the removal of hexavalent chromium from aqueous solution.