Methylene Blue Removal from Aqueous Solution using Biochar of Brewery Spent Grain

In this study, biochars were produced from solid wastes collected from breweries, municipal wastewater treatment plants, and the metal processing industry. Preliminary experiments showed that biochar derived from brewery spent grain (BSG) is the most effective (90.93%) in removing methylene blue (MB) from aqueous solution. The pyrolysis time and temperature were optimized in the BSG biochar preparation. The properties of the biochar, such as surface functional groups, crystallinity, morphology, and surface area, have been determined by using FTIR, XRD, SEM, and BET. The surface area of BSG biochar is 1.48 m²/g at 300 °C, which is significantly lower than the 69.87 m²/g at 500 °C. This increase in surface area at higher temperatures results from greater pore formation and the release of volatile substances during pyrolysis. Batch adsorption experiments were conducted to optimize the effects of pH, contact time, initial MB concentration, and adsorbent dose. Under optimum conditions, more than 99.7% of MB was removed. The kinetic data are best described by the pseudo-first-order model (R 2 = 0.98481and χ 2 = 0.126). Similarly, the isotherm data are best explained by Freundlich's model (R 2 = 0.954 and χ 2 = 2.675), suggesting that MB adsorption may involve multiple interactions, including electrostatic attraction, π-π interactions, and hydrogen bonding. The findings of this study confirmed that biochar derived from BSG is an effective adsorbent for removing MB from industrial sewage and is useful in waste valorization. • Brewery spent grain (BSG) biochar was successfully produced. • Carbonization temperature affects the surface area and porosity of BSG biochar. • BSG offers an eco-friendly alternative for wastewater treatment. • Recycling waste promotes the circular economy and supports waste valorization.