Enhanced anaerobic digestion model no.1 for high solids fermentation: Integrating homoacetogenesis and chain elongation

The production of volatile fatty acids (VFA) through high-solids anaerobic fermentation of organic waste offers a promising route for resource recovery. This study used a batch-mode anaerobic leach bed reactor (LBR) with leachate circulation to ferment the organic fraction of municipal solid waste, producing high concentrations of butyric acid, along with notable amounts of lactic and caproic acids. These results provide valuable insights and underscore the need for process optimization within conventional fermentation systems. To better model the LBR's complex dynamics, the Anaerobic Digestion Model No.1 (ADM1) was modified and extended to account for slow hydrolysis in dry fermentation conditions, thermodynamic constraints imposed by Gibbs Free Energy and hydrogen partial pressures, as well as lactic acid production and chain elongation pathways including homoacetogenesis and caproic acid formation. These enhancements provided deeper insights into high-solids anaerobic fermentation, advancing strategies for improved process control and system optimization.