Martín Barragán-Trinidad, Julián Carrillo-Reyes, Germán Buitrón
The use of ruminal fluid as a source of hydrolytic microorganisms for the pretreatment of a native consortium of microalgae (essentially Senedesmus) was investigated. The hydrolytic enzyme activity of the ruminal culture was first enriched in a bioreactor. Then, using the enriched culture, the effect of the microalgae to the ruminal fluid ratio (S/X) on the hydrolysis and subsequent production of methane was investigated. An S/X ratio of 0.5 showed the best hydrolysis efficiency (29%) reaching in a second stage process a methane yield of 193 mL CH4 g COD−1. The processing time (pretreatment plus methanization) was only 7 days. The predominant ruminal hydrolytic bacteria selected in the enrichment were principally Clostridium, Proteocatella and Pseudomonas.
Carlos Alberto Contreras-Dávila, Hugo Oscar Méndez-Acosta, Luis Arellano-García, Felipe Alatriste-Mondragón, Elías Razo-Flores
Lignocellulosic biomass is a promising alternative energy source, which after pretreatment can be efficiently used as feedstock for biological production of second generation biofuels. Hydrogen is considered an ideal biofuel and its production through dark fermentation has been recognized as a sustainable process. However, more studies with continuous systems are needed for its application at industrial scale. In this study, enzymatic hydrolysate of Agave tequilana bagasse was used for long-term continuous hydrogen production in both, a continuous stirred tank reactor (CSTR) and a trickling bed reactor (TBR), which were operated up to 87 days under different organic loading rates (OLR) ranging from 17 to 60 g COD/L-d. Volumetric hydrogen production rate (VHPR) and hydrogen molar yield (HMY) in CSTR displayed an inverse correlation with maximum values of 2.53 L H2/L-d and 1.35 mol H2/mol substrate, attained at OLR 52.2 and 40.2 g COD/L-d, respectively. In contrast, increasing OLR up to 52.9 g COD/L-d simultaneously enhanced VHPR and HMY in TBR, attaining values of 3.45 L H2/L-d and 1.53 mol H2/mol substrate, respectively. Acetate and butyrate were the main metabolites in both reactors, while lactate and propionate were detected in minor concentrations. Metabolites distribution, electron balances and hydrogen production trends obtained from both reactors suggest that CSTR may be more susceptible to inhibition by hydrogen accumulation than TBR. Apparent hydrogen consumption and susceptibility to high solids load were found to limit further OLR increments in CSTR and TBR, respectively.