Sustainability in the Brewing Industry: A Review of Brewing Waste Valorization and Wastewater Treatment

The brewing industry is one of the largest food and beverage sectors worldwide and generates approximately 16–23 kg of solid by-products per hectoliter of beer and significant quantities of wastewater throughout the production processes. Major solid by-products include brewers’ spent grains (BSG), which account for approximately 85% of total solid residues, brewer’s spent yeast (BSY), and hot trub, all of which are rich in proteins, fibers, carbohydrates, bioactive compounds, and minerals. At the same time, brewery wastewater is characterized by high organic load, elevated chemical oxygen demand (COD) ranging from 2000 to 6000 mg/L, and biochemical oxygen demand (BOD) ranging from 1200 to 3600 mg/L, while the sector is known for substantial water consumption requirements. Growing environmental concerns and policy initiatives, including the EU Circular Economy Action Plan and the United Nations Sustainable Development Goals (SDGs 6, 12, and 13), have strengthened the need for sustainable waste management, resource recovery, and wastewater treatment in the brewing industry. This review critically examines the physicochemical characteristics of brewery solid wastes and wastewater and evaluates current and emerging technologies for their treatment and valorization. This narrative review synthesizes literature published between 2011 and 2026, identified through Scopus, Web of Science, and Google Scholar. Particular emphasis is placed on the use of brewery by-products in animal feed, agricultural soil amendments, bioenergy and biofuel production, biotechnological applications, and the development of biodegradable packaging materials and bioplastics. In parallel, the review discusses conventional and advanced wastewater treatment technologies, including anaerobic and aerobic processes, membrane-based systems, advanced oxidation processes, microbial fuel cells, and wastewater reuse practices, while highlighting the high operational costs and scalability challenges associated with emerging technologies. Quantitative findings indicate that anaerobic wastewater treatment can achieve COD removal efficiencies of 65–90%, while combined anaerobic–aerobic systems can reach up to 98% under suitable operating conditions. Furthermore, BSY processing through enzymatic hydrolysis and fractionation enables the recovery of proteins, peptides, and other valuable compounds, although the degree of protein enrichment depends on the processing conditions. These results demonstrate the potential for pollutant removal and resource recovery, although reported performances depend on substrate characteristics, treatment conditions, and process scale. However, variability in waste composition and economic feasibility challenges highlight the need for further pilot-scale validation and Life Cycle Assessment studies.