Adaptation of acidogenic sludge to increasing glycerol concentrations for biohydrogen production

Abstract

Hydrogen is a promising alternative as an energetic carrier and its production by dark fermentation from wastewater has been recently proposed, with special attention to crude glycerol as potential substrate. In this study, two different feeding strategies were evaluated for replacing the glucose substrate by glycerol substrate: a one-step strategy (glucose was replaced abruptly by glycerol) and a step-by-step strategy (progressive decrease of glucose concentration and increase of glycerol concentration from 0 to 5 g L(-1)), in a continuous stirred tank reactor (12 h of hydraulic retention time (HRT), pH 5.5, 35 °C). While the one-step strategy led to biomass washout and unsuccessful H2 production, the step-by-step strategy was efficient for biomass adaptation, reaching acceptable hydrogen yields (0.4 ± 0.1 molH2 mol(-1) glycerol consumed) around 33 % of the theoretical yield independently of the glycerol concentration. Microbial community structure was investigated by single-strand conformation polymorphism (SSCP) and denaturing gradient gel electrophoresis (DGGE) fingerprinting techniques, targeting either the total community (16S ribosomal RNA (rRNA) gene) or the functional Clostridium population involved in H2 production (hydA gene), as well as by 454 pyrosequencing of the total community. Multivariate analysis of fingerprinting and pyrosequencing results revealed the influence of the feeding strategy on the bacterial community structure and suggested the progressive structural adaptation of the community to increasing glycerol concentrations, through the emergence and selection of specific species, highly correlated to environmental parameters. Particularly, this work highlighted an interesting shift of dominant community members (putatively responsible of hydrogen production in the continuous stirred tank reactor (CSTR)) according to the gradient of glycerol proportion in the feed, from the family Veillonellaceae to the genera Prevotella and Clostridium sp., putatively responsible of hydrogen production in the CSTR.

Microbial ecology of fermentative hydrogen producing bioprocesses: useful insights for driving the ecosystem function

“…In the first pathway, hydrogen production occurs through the oxidation of reduced ferredoxin (Fd red ) with a ferredoxin-dependent hydrogenase (Fd-[FeFe]). This pathway is mainly used by obligate anaerobic microorganisms, such as Clostridia, which, under special conditions, are able to reoxidate directly the NADH generated during glycolysis to produce additional hydrogen molecules through two other hydrogenases, i.e., NADH-dependent (NADH-[FeFe]) and bifurcating NADH-Fd red -dependent hydrogenase (NADH-Fd red -[FeFe]) (Tapia-Venegas et al 2015). Therefore, if all the NADH are reoxidated a total of 4 molecules of H 2 could be obtained from the fermentation of one molecule of glucose.…”

“…This pathway is used by facultative anaerobes, such as Enterobacteria (Cai et al 2011). Depending on the microorganism involved, this reaction can occur through [NiFe] hydrogenase (Ech hydrogenase) or formate-dependent [FeFe] hydrogenase (Tapia-Venegas et al 2015). Organisms that only have the PFL pathway cannot access NADH for hydrogen production and thus theoretically are limited to 2 mol of hydrogen per mole of glucose (Hallenbeck, Abo-Hashesh and Ghosh 2012).…”

“…Interestingly, in CSTR fed with a mix of glucose and glycerol, Clostridium sp. were minor community members during the progressive adaptation to increasing glycerol concentrations, but became dominant and putatively responsible for hydrogen production when glycerol was the only substrate (Tapia-Venegas et al 2015).…”

Impact of the microbial inoculum source on pre-treatment efficiency for fermentative H2 production from glycerol

“…This demonstrates a better adaptability for H 2 production of untreated aerobic sludge compared to anaerobic sludge in a continuous system using glycerol as substrate. As already reported, untreated anaerobic sludge may require more time to adapt to glycerol [53]. Besides, although no methane production was observed in any reactor, a part of H 2 could have been consumed by other H 2consuming microorganisms present in the untreated anaerobic sludge such as homoacetogens or hydrogenotrophic methanogenic archaea.…”

Evaluation of A Novel Split-Feeding Anaerobic/Oxic Baffled Reactor (A/OBR) For Foodwaste Anaerobic Digestate: Performance, Modeling and Bacterial Community

“…Band a1 belonged to phylum Actinobacteria , most of which are heterotrophs, indicating that it might play an important role in reducing organic carbon 34 . Bands a8 and c1 were close to Prevotella sp., which was considered as a hydrogen-producing microorganism from organics and could also consume by-products such as acetate, succinate, or lactate 35 . Flavobacterium (band a4) as well as Pseudomonas were significant genera of flocforming bacteria due to its production of glue-like extracellular polymers and ability to bind cells together 36 .…”