Steering Anaerobic Digestion toward Coproduction of Biomethane and Short-Chain Carboxylic Acids

Anaerobic digestion is a key technology for converting organic waste into energy sources and biofertilizers, yet the potential to simultaneously produce industrial value-added products is largely untapped. Thus, this study aims to explore the anaerobic bioprocessing concept of producing short-chain carboxylic acids from agricultural residues and manure combined with biomethane production. Four semicontinuous anaerobic reactors with a working volume of 5 L were operated under mesophilic conditions (37 °C) and continuously mixed at 60 rpm. Two reactors (MS1 and MS2) were fed with cow manure and straw, while the other two reactors (MSF1 and MSF2) were fed with cow manure, straw, and food waste slurry. The results showed that at a high organic loading rate (7 gvs/L·d), microorganisms produced short-chain carboxylic acids, reaching up to 25 ± 5 mM (2.0 ± 0.2 g/L) in each reactor. Simultaneously, biomethane production persisted at a rate of 5318 ± 281 mL/d (152 ± 8 mL/gvs·d) for MS1 and MS2, and 6801 ± 29 mL/d (194 ± 1 mL/gvs·d) for MSF1 and MSF2. These findings demonstrate that optimizing anaerobic digestion for both energy carriers and industrial chemical precursors enhances the economic value of organic waste, thereby advancing green technologies for renewable chemical production and offering valuable insights for the development of efficient biorefinery processes.