Removal of chromium from synthetic wastewater by electrocoagulation and using natural coagulant (blend of hen eggshell powder with lime): optimization of response surface methodology

Water is a limited natural resource that is essential for both the survival of the environment and all forms of life. Nowadays, heavy metal pollution containing Cr has put serious threat to our environment. It can enter into soil, water, and even particulate matter in air, and can be harmful to human health and wild life. In this work, the removal of Cr from synthetic wastewater by electrocoagulation supported by natural coagulant (eggshell powder) with aluminum electrodes was investigated. The central composite design of the response surface methodology was employed to estimate and optimize process variables, such as initial Cr concentration (225–475 mg/L), solution pH (5–9), and current density (0.35–045 A/m2), and treatment time (30–40 min) with an electrode distance (ED) of 0.5 and 1 cm, respectively. 99.90% and 99.74% of removal efficiencies were observed at initial Cr concentration of 456.11 mg/L, a solution pH of 5.45, with current density of 0.47 A/m2, and treatment time of 36.84 min. The analysis of variance (ANOVA) was performed, and the multiple correlation coefficients (R2) of both ED were found to be 0.9996 and 0.9955, which confirms the significance of the predicted model. Furthermore, X-ray diffraction, Fourier transform infrared spectroscopy, Brunauer–Emmett–Teller analysis, and thermogravimetric analysis were used to characterize the crystal structure, functional groups, specific surface area, and thermal stability of the coagulants (eggshell powder). The findings of this study suggest that using this natural coagulant, synthetic wastewater can be treated in a more cost-effective and simple way than other existing method.