Biohydrogen production from winery effluents: control of the homoacetogenesis through the headspace gas recirculation

BACKGROUND Fermentative hydrogen production has an inherent limitation caused by hydrogen‐consuming metabolic pathways such as homoacetogenesis related to high hydrogen partial pressures. In this study, a strategy based on recirculating the headspace gas was applied to increase the hydrogen release from the liquid to the gas phase in an upflow anaerobic sludge blanket(UASB) reactor fed with winery effluents. The influence of the gas upflow recirculation velocity on hydrogen production, hydrogen consumption by homoacetogenesis, and microbial community structure was evaluated. RESULTS Under the control condition (only liquid recirculation), the hydrogen productivity was as much as 22 mL H 2 L −1 h −1 . Conversely, the hydrogen productivity increased up to 62 mL H 2 L −1 h −1 when the reactor was operated with an upflow gas recirculation velocity of 28.6 m d −1 . The increase in mass transfer, due to the gas recirculation, produces a decrease (up to 70%) in the hydrogen consumption rate associated with homoacetogenesis. High‐throughput 16s rDNA sequencing characterization showed that the gas recirculation strategy promoted the development of hydrogen‐producing microorganisms related to Megasphaera elsdenii and decreased the abundance of hydrogen‐consuming bacteria related to Clostridium carboxidivorans and C. ljungdahlii . CONCLUSION The results indicated that headspace recirculation at gas upflow velocities higher than 17.8 m d −1 increased the hydrogen production rate concomitantly with the reduction of both the homoacetogenic activity and the abundance of H 2 ‐consuming bacteria. The study demonstrated that headspace recirculation could be a promising way to control homoacetogenesis, and therefore, to increase the biohydrogen productivity from complex substrates such as winery effluents.