Comparative Evaluation of Mesophilic and Thermophilic Anaerobic Digestion for Microbrewery Waste Streams: Process Integration, Internal Neutralization, and CO2 Scrubbing

This study explores a circular bioeconomy strategy for microbrewery waste by characterizing and valorizing its primary waste streams: sugar mash water (A), spent yeast with hops (B), spent yeast without hops (C), and alkaline cleaning wastewater (D). The biochemical methane potential of the acidic organic blend (E, from A-C) was assessed under mesophilic (38 °C) and thermophilic (55 °C) conditions, revealing significant substrate-specific temperature sensitivity. The highly acidic blend E (pH 4.16) was effectively neutralized to pH 7.0 using the on-site alkaline wash water (D, pH 12.03). Mesophilic anaerobic digestion of the neutralized blend achieved a high methane yield of approximately 500 mL/g VS. Furthermore, the alkaline wash water successfully served as an in situ CO2 scrubber, upgrading biogas to ~100% methane content. This integrated approach demonstrates a viable, closed-loop pathway for microbreweries to achieve simultaneous energy recovery from organic wastes and chemical-free treatment of acidic and alkaline effluents. The findings also highlight the importance of substrate-specific thermal management and provide a robust framework for microbreweries to achieve energy independence and internal CO2 neutralization–wastewater treatment.