Changes in the microbial consortium during dark hydrogen fermentation in a bioelectrochemical system increases methane production during a two-stage process

Kengo Sasaki,Akihiko Kondo,Daisuke Sasaki,Yota Tsuge,Masahiko Morita

doi:10.1186/s13068-018-1175-z

Kengo Sasaki, Akihiko Kondo + Show 3 more

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https://doi.org/10.1186/s13068-018-1175-z

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Abstract

BackgroundBioelectrochemical systems (BESs) are an innovative technology developed to influence conventional anaerobic digestion. We examined the feasibility of applying a BES to dark hydrogen fermentation and its effects on a two-stage fermentation process comprising hydrogen and methane production. The BES used low-cost, low-reactivity carbon sheets as the cathode and anode, and the cathodic potential was controlled at − 1.0 V (vs. Ag/AgCl) with a potentiostat. The operation used 10 g/L glucose as the major carbon source.ResultsThe electric current density was low throughout (0.30–0.88 A/m2 per electrode corresponding to 0.5–1.5 mM/day of hydrogen production) and water electrolysis was prevented. At a hydraulic retention time of 2 days with a substrate pH of 6.5, the BES decreased gas production (hydrogen and carbon dioxide contents: 52.1 and 47.1%, respectively), compared to the non-bioelectrochemical system (NBES), although they had similar gas compositions. In addition, a methane fermenter (MF) was applied after the BES, which increased gas production (methane and carbon dioxide contents: 85.1 and 14.9%, respectively) compared to the case when the MF was applied after the NBES. Meta 16S rRNA sequencing revealed that the BES accelerated the growth of Ruminococcus sp. and Veillonellaceae sp. and decreased Clostridium sp. and Thermoanaerobacterium sp., resulting in increased propionate and ethanol generation and decreased butyrate generation; however, unknowingly, acetate generation was increased in the BES.ConclusionsThe altered redox potential in the BES likely transformed the structure of the microbial consortium and metabolic pattern to increase methane production and decrease carbon dioxide production in the two-stage process. This study showed the utility of the BES to act on the microbial consortium, resulting in improved gas production from carbohydrate compounds.

Highlights

Bioelectrochemical systems (BESs) are an innovative technology developed to influence conventional anaerobic digestion
Methanogenesis was inhibited in the BES and non-bioelectrochemical system (NBES) by loading the artificial medium at a pH of 6.5, which contained glucose as the major carbon source, and the pH was maintained at ≥ 6.2 (Table 1)
These results showed that a hydrogen-consumption reaction occured in the BES, the ratio of hydrogen to carbon dioxide in the gas was unchanged in the BES and NBES

Summary

Introduction

Bioelectrochemical systems (BESs) are an innovative technology developed to influence conventional anaerobic digestion. BESs have been used in anaerobic digestion of organic matter to influence the structure and/or metabolism of the microbial consortium and boost hydrogen production [7], methane production [8,9,10], and biohythane production [11]. Gaseous fuels such as hydrogen and methane, which can be used in heat and/or electricity production and for transport, are often obtained via two-stage fermentation [12, 13]. Research on the twostage approach involving bioelectrochemical hydrogen fermentation and methane fermentation is limited [7]

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