Porous biochars derived from brewery waste for the treatment of Cr(VI)-contaminated water

The use of brewery waste for the removal of pollutants such as chromium has rarely been studied. In the present work, the removal of hexavalent chromium (Cr(VI)) from aqueous solutions was evaluated by brewer's spent grain (BSG), brewing sewage sludge (BSS), and their mixture (MIX), which were obtained from the Bedele Brewery Share Company, Ethiopia. BSG with acid and heat treatment at 600 °C was selected during the preliminary screening experiments and further characterized via FTIR, XRD, and SEM. An adsorption experiment was carried out in batches to study the effectiveness of adsorbents in removing Cr(VI) under different conditions. Factors affecting adsorption, including pH, contact time, adsorbent dosage, and initial Cr(VI) concentration, were analyzed and optimized. The best conditions for the highest efficiency in removing Cr(VI) were a contact time of 7 h, initial solution pH of 2, initial Cr(VI) concentration of 40 mg/L, and adsorbent dose of 2 g/L. The pseudo-second-order (PSO) model, which suggests chemisorption of Cr(VI) on the surface of the adsorbent, describes the kinetics of Cr(VI) removal by the adsorbent (R2 = 0.9570). The Freundlich isotherm was a good fit for the experimental equilibrium adsorption data. The BSG biochar was found to have an approximate adsorption capacity of 31.87 mg/g for Cr(VI). The ability to recycle adsorbents suggests that BSG biochar could be effectively used to treat Cr(VI) in wastewater. As a result, converting industrial waste into useful material is cost effective and beneficial for the protection of the environment. More research is recommended to study how well this adsorbent works in real wastewater samples and during the column adsorption process.