Sewage sludge-based activated carbon: its application for hexavalent chromium from synthetic and electroplating wastewater in batch and fixed-bed column adsorption

As-prepared activated carbons (ACs) were utilized as an adsorbent for removal of Cr (VI) ions from aqueous solution. The effects of different operating parameters such as adsorbent dosage, pH, contact time, initial Cr (VI) concentration and temperature were conducted by batch experiments. According to experimental results, the equilibrium time, the optimum pH, and adsorbent dosage were found 120 min, pH 3, 5 g/l, respectively, with 2.5 g H 3 PO 4 of carbonized sample and post-treatment step by refluxing with HCl and NaOH and autoclaved with HF (arAC) with the BET surface area of 472 mg/g. The equilibrium adsorption data were fitted well by Langmuir and Freundlich adsorption model with a monolayer maximum adsorption capacity of 12.8 mg/g. The rate of Cr (VI) adsorption onto the AC was reasonably explained by the pseudo-second-order kinetic model. In addition, the thermodynamic parameters of the adsorption process such as standard Gibb's free energy (G), standard enthalpy (H) and standard entropy (S) were evaluated. In a fixed-bed column adsorption, the effects of bed height, flow rate and initial ion concentration on the breakthrough curve were investigated, on which the predictions were found to be satisfactory both by the Yan models. The results showed that a maximum of adsorption capacity was 94.54 mg.g -1 by the sample of the arAC. Finally, we found out the sewage sludge-based AC was an efficient low-cost adsorbent for Cr (VI) removal from electroplating industrial wastewater.