Bioenergy recovery from biomass by-products is a promising approach for the circular bioeconomy transition. However, the management of agri-food by-products in stand-alone treatment facilities is a challenge for the low-capacity food processing industry. In this study, the techno-economic assessment of a small-scale anaerobic digestion process was evaluated for the management of jabuticaba by-product and the production of biomethane, electricity, heat, and fertilizer. The process was simulated for a treatment capacity of 782.2 m³ y⁻¹ jabuticaba peel, considering the experimental methane production of 42.31 L CH₄ kg⁻¹ TVS. The results of the scaled-up simulated process demonstrated the production of biomethane (13,960.17 m³ y⁻¹), electricity (61.76 MWh y⁻¹), heat (197.62 GJ y⁻¹), and fertilizer (211.47 t y⁻¹). Economic analysis revealed that the process for biomethane recovery from biogas is not profitable, with a net margin of −19.58% and an internal rate of return of −1.77%. However, biogas application in a heat and power unit can improve project feasibility, with a net margin of 33.03%, an internal rate of return of 13.14%, and a payback of 5.03 years. In conclusion, the application of small-scale anaerobic digestion can prevent the wrongful open-air disposal of jabuticaba by-products, with the generation of renewable energy and biofertilizer supporting the green economy toward the transition to a circular economy.

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.