Single-Step Modification of Brewer’s Spent Grains Using Phosphoric Acid and Application in Cheese Whey Remediation via Liquid-Phase Adsorption

Brewer’s spent grains (BSG) are a significant by-product of beer production, and its improper disposal poses environmental challenges. This study investigated the use of BSG for activated carbon production with phosphoric acid as a chemical activator and its application in cheese whey remediation through liquid-phase adsorption. The adsorbent was thoroughly characterized through using techniques such as FTIR, SEM, N2 isotherms, and surface charge distribution. The adsorbent exhibited substantial pores, a high surface area (605.1 m2 g–1), good porosity, and positive surface charges that facilitated favorable interactions with cheese whey compounds. Equilibrium was achieved in 330 min for lactose, BOD5, and COD. The maximum adsorption capacities were 12.77 g g–1 for lactose, 3940.99 mg O2 g–1 for BOD5, and 12,857.92 mg O2 g−1 for COD at 318 K. Removing these adsorbates from cheese whey effluent reduces its organic load, enabling water reuse in the manufacturing unit, depending on its intended use. The adsorption process was spontaneous and endothermic, with ΔH° ≥ 265.72 kJ mol−1. Additionally, the activated carbon produced demonstrated impressive regeneration capability with sodium hydroxide, maintaining 75% of its adsorption capacity. These results emphasize the potential of activated carbon as an effective adsorbent for cheese whey remediation, providing a sustainable solution for waste management in the dairy industry and water reuse.