Brewery Byproducts as Bioenergy Sources: A Review of Biohydrogen and Biomethane Production

Abstract This review synthesizes recent advances in the biological production of hydrogen and methane from brewery by-products, including spent grain, spent yeast, hot trub, and brewery wastewater. It examines anaerobic systems, encompassing single- and two-stage configurations and mono- and co-digestion strategies. The physicochemical characteristics of brewery waste were discussed regarding suitability for renewable energy generation. Although brewery residues represent a promising feedstock for sustainable bioenergy production, their bioproduction to biohydrogen and biomethane remains challenging due to substrate recalcitrance, imbalanced carbon-to-nitrogen (C/N) ratios, and inhibitory compounds, which may compromise process stability and energy yields. Reported production values showed variability, with biomethane production ranging from 65 to 447 L kg −1 VS (or up to 573 L kg −1 COD) and biohydrogen production ranging from 25 to 198 L kg −1 VS (equivalent to 139–758 L kg −1 COD). These variations may be associated with differences in substrate composition, pretreatment approaches, and operational conditions, as reported in the literature. Overall, this review highlights the technical feasibility and environmental relevance of valorizing brewery waste through anaerobic digestion within a circular economy. By converting organic waste into high-added-value products, anaerobic digestion supports waste volume reduction, on-site energy recovery, and resource utilization, contributing to lower fossil energy demand and reduced environmental impacts in brewery operations. Graphical Abstract