Utilization of thermally treated sludge for the removal of hexavalent chromium from drainage wastewater: a laboratory and field study

Nowadays, wastewater treatment is a huge challenge, especially with the increasing of human caused pollution. The recent study introduced new adsorbents based on thermal treatment of wastewater sludge to eliminate hexavalent chromium from wastewater. The new adsorbents were characterized by different chemical and physical tools, such as sludge pH, total solids, elemental concentration, FTIR, TGA, SEM, XRD, and PET surface area. The adsorption efficiency of sludge samples toward Cr (VI) from aqueous media was studied using the batch method. Various parameters, such as solution initial concentration, pH, time, and adsorbent dose, have been studied. The sludge samples showed high efficiency for Cr (VI) adsorption in aqueous media, with removal efficiency reaching 98.4%, 75%, and 98.4% for SI, SII, and SIII, respectively. The Cr (VI) adsorption occurred via electrostatic attraction in acidic medium. The adsorption data is well-fitting to pseudo-second order and Elovich kinetics models as well as the Freundlich isotherm, which reflect the Cr (VI) favorability adsorption on the hetero-energetic active sites of sludge samples. Additionally, a field investigation of the thermcally treated sludge adsorbent (SIII) application on real wastewater samples from Egyptian wastewater treatment plants and drainage revealed the high removal efficiency of over 67% for TSS, 80% for BOD, 75% for COD, and 100% for Cr (IV), Ni (II), and Fe (II).