Study of chromate (VI) removal via sequential combined fenton’s process and adsorption by nano-magnesium oxide-modified wood biochar for tannery wastewater treatment

This study explored the combined treatment approach to facilitate the treatment of tannery wastewater through Fenton's reagents and batch adsorption method, which involved the use of low-cost wood biochar. Low-cost adsorbent obtained from thermal conversion of wood biomass (Callistemon citrinus) modified with nano-MgO. Scanning Electron Microscopy, Energy Dispersive X-ray, X-ray diffraction, Fourier transfer-IR, Brunauer–Emmett–Teller–N_2, and Lazer Induced Breakdown Spectroscopy analysis were used to characterize the adsorbent material. Fenton’s reagents, comprising 15 mM of FeSO₄ and 25 mM of H₂O₂, were employed under controlled conditions: pH 3.0, reaction duration of 30 min, a temperature of 30 °C, and agitation at 120 rpm. This process yielded substantial removal percentages for various contaminants, with 82, 79, 67, 72, and 25% removal of COD, NH₃–N, NO₃²⁻, PO₄²⁻, and Cr(VI), respectively. Subsequently, a batch adsorption treatment was conducted within a range of parameters, including pH (1.5–8), contact times (10–240) min, biomass dosages (0.25–2.5) g L⁻¹, and temperature (28–34 °C) range. Significantly, the Fenton treatment substantially enhanced the biodegradability of the system, resulting in an improved efficiency of the subsequent batch adsorption process. This enhancement led to impressive removal percentages of COD, NH₃–N, NO₃²⁻, PO₄²⁻, and Cr(VI),of 93, 88, 79, 8, and 98%, respectively. The equilibrium data exhibited a strong alignment with the Langmuir isotherm model, underscoring a remarkable adsorption capacity of 102.74 mg g⁻¹. Kinetic assessments further indicated conformity with the pseudo-second-order model. Significantly, the uninterrupted series of adsorption and desorption cycles throughout ten iterations highlighted the enduring reusability and robustness of the biochar adsorbent that was prepared. Graphical abstract: (Figure presented.).