Single and two-stage anaerobic digestion for hydrogen and methane production from acid and enzymatic hydrolysates of Agave tequilana bagasse

A comparison study on the energy recovery from single and two-stage anaerobic digestion of Agave tequilana bagasse hydrolysates is presented in this contribution. Firstly, the A. tequilana bagasse was acid or enzymatically hydrolyzed and then both hydrolysates were digested at different concentrations (20-100% v/v) in batch reactors. Results showed that the two-stage anaerobic digestion outperformed the single-stage process. During the acidogenesis phase of the two-stage process, high hydrogen yields were reached with the enzymatic hydrolysate at a concentration of 40% (3.4 mol H2/mol hexose); whilst during methanogenic phase, the highest methane yield was obtained at a concentration of 20% for both hydrolysates (0.24 L CH4/g COD). The overall energy recovery analysis demonstrated that the two-stage process outperformed 3.3 times the single-stage process when comparing the highest energy recoveries obtained in each process. This is the first study that reveals such enhancement for the anaerobic digestion of lignocellulosic hydrolysates.