Dark fermentation process response to the use of undiluted tequila vinasse without nutrient supplementation

Abstract

The technical feasibility of valorizing tequila vinasse (TV), a wastewater with high pollution potential, through the production of biogenic hydrogen via dark fermentation, has long been proven in diverse lab‐scale reactors that were operated either in batch or continuous mode. How-ever, such systems have mainly been tested with diluted streams and nutrient supplementation, hindering the techno‐economic attractiveness of the TV‐to‐hydrogen concept at large scale. In this study, the feasibility of producing hydrogen from high‐strength undiluted TV with no added extra nutrients was evaluated under batch mesophilic conditions. Additionally, the use of two different acidogenic inocula obtained either by heat or heat‐aeration pretreatment was investigated to get a greater understanding of the effect of inoculum type on the process. The results obtained showed that the TV utilized herein contained macro‐ and micro‐nutrients high enough to support the hydrogenogenic activity of both cultures, entailing average hydrogen yields of 2.4–2.6 NL H2/L vinasse and maximum hydrogen production rates of 1.4–1.9 NL H2/L‐d. Interestingly, the consumption of lactate and acetate with the concomitant production of butyrate was observed as the main hydro-gen‐producing route regardless of the inoculum, pointing out the relevance of the lactate‐driven dark fermentative process. Clostridium beijerinckii was ascertained as key bacteria, but only in association with microorganisms belonging to the genera Enterobacter and Klebsiella, as revealed by phylogenetic analyses.