Integrated valorization of vinasse and spent brewer's yeast co-digestion into bioenergy and biochemical products: A zero-waste biorefinery approach

Abstract

This study demonstrates an integrated zero-waste biorefinery for valorizing vinasse and spent brewer's yeast through two-stage anaerobic co-digestion with cascading product recovery. A bench-scale system operated continuously for 90 days achieved stable hydrogen yield (37.62 mL/g-VS; 14.9 kJ/L·d) and methane yield (301.8 mL/g-VS; 30.22 kJ/L·d). Microbial community analysis revealed functional segregation: Bifidobacterium sp., Caproiciproducens sp., and Lactobacillus sp., dominated the hydrogen stage, while Paludibacter sp., Candidatus Cloacimonas, Methanoculleus sp., and Methanosarcina sp., were enriched in the methane stage. Techno-economic analysis of a 1000 m³/d facility demonstrated viability with net present value of 2,376,686 USD, 6-year payback period, and 14.5 % internal rate of return over 20 years. Following circular biorefinery principles, hydrogenic effluent was converted to polyhydroxybutyrate using Cupriavidus necator TISTR 1335, achieving 72.40 % PHB content (2.78 g/L) with 80.65 % chemical oxygen demand removal. Anaerobic digestate was valorized into biofertilizer pellets compliant with Thai organic fertilizer standards. Green Oak lettuce cultivation trials showed the optimal biofertilizer pellet formulation (BPF-1) achieved 116.8 g fresh weight/plant, representing 96 % of chemical fertilizer performance. This integrated approach successfully produces four value-added products biohydrogen, biomethane, bioplastic, and biofertilizer, while achieving 97.2 % COD reduction from original vinasse feedstock. The system demonstrates complete waste valorization aligned with circular economy principles, providing a sustainable solution for agro-industrial waste management with proven economic viability and environmental benefits.