Production of Bio-Based Hydrogen Enriched Methane from Waste Glycerol in a Two Stage Continuous System

In the present work, a continuous process was developed aiming at the production of bio-based hydrogen-enriched methane, from waste glycerol (WG) in a two-stage reactor system. In the first step, biohydrogen production was studied, using an attached mixed acidogenic consortium in an up-flow column bioreactor. Cylindrical porous ceramic beads with a surface area of 600 m2L−1 were used as attachment matrix of bacterial cells. The hydrogen yield, the substrate consumption and the distribution of soluble metabolites were investigated for two different substrate concentrations in the feed, i.e. 20 and 25 g WG/L. SEM pictures of the biofilm formed on the ceramic beads revealed that bacilli dominated in the reactor. Subsequently, RISA methodology showed that Klebsiella sp. and Clostridium sp. were among the dominant microorganisms. In parallel, a methanogenic reactor was started up and operated in continuous mode using initially commercial glycerol, and subsequently WG as carbon sources. In the sequel, the effluent of the hydrogenic reactor was fed to the methanogenic reactor (constituting thus the second stage in a two-stage process), and the effect of organic loading on the methane yield was studied. It was shown that the reactor managed to generate up to 73 % of the theoretically expected methane based on COD removal, corresponding to 256.0 ± 2.6 L CH4/kg WG. Moreover, simulation of the experimental data of the methanogenic reactor via the Anaerobic Digestion Model ADM1 revealed that the model was able to successfully describe the performance of the digester, even under dynamic conditions.