Microbial Communities in Flexible Biomethanation of Hydrogen Are Functionally Resilient Upon Starvation

Washington Logroño,Hauke Harms,Sabine Kleinsteuber,Paul Kluge,Marcell Nikolausz,Denny Popp

doi:10.3389/fmicb.2021.619632

Washington Logroño, Hauke Harms + Show 4 more

Open Access

https://doi.org/10.3389/fmicb.2021.619632

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Abstract

Ex situ biomethanation allows the conversion of hydrogen produced from surplus electricity to methane. The flexibility of the process was recently demonstrated, yet it is unknown how intermittent hydrogen feeding impacts the functionality of the microbial communities. We investigated the effect of starvation events on the hydrogen consumption and methane production rates (MPRs) of two different methanogenic communities that were fed with hydrogen and carbon dioxide. Both communities showed functional resilience in terms of hydrogen consumption and MPRs upon starvation periods of up to 14 days. The origin of the inoculum, community structure and dominant methanogens were decisive for high gas conversion rates. Thus, pre-screening a well performing inoculum is essential to ensure the efficiency of biomethanation systems operating under flexible gas feeding regimes. Our results suggest that the type of the predominant hydrogenotrophic methanogen (here: Methanobacterium) is important for an efficient process. We also show that flexible biomethanation of hydrogen and carbon dioxide with complex microbiota is possible while avoiding the accumulation of acetate, which is relevant for practical implementation. In our study, the inoculum from an upflow anaerobic sludge blanket reactor treating wastewater from paper industry performed better compared to the inoculum from a plug flow reactor treating cow manure and corn silage. Therefore, the implementation of the power-to-gas concept in wastewater treatment plants of the paper industry, where biocatalytic biomass is readily available, may be a viable option to reduce the carbon footprint of the paper industry.

Highlights

The growing share of variable renewable energy, mainly photovoltaics and wind power, generates temporary surplus electricity that leads to an energy storage problem
volatile fatty acids (VFAs) concentrations in the liquid phase were analyzed by high performance liquid chromatography (HPLC)
The resulting amplicon sequencing variants (ASVs) for 16S rRNA genes were classified against the MiDAS database v2.1 (McIlroy et al, 2017) trimmed to the region covered by the 341f and 785r primers

Summary

INTRODUCTION

The growing share of variable renewable energy, mainly photovoltaics and wind power, generates temporary surplus electricity that leads to an energy storage problem. Methanation can be performed by a catalyst-based chemical reaction, known as the Sabatier reaction, or in a microbial process employing the CO2-reductive pathway of hydrogenotrophic methanogenesis. Ex situ biomethanation is a microbial process that uses point sources of CO2 or the CO2 fraction of biogas to produce high quality biomethane. It can be carried out by methanogenic pure cultures (Rittmann et al, 2015) or mixed cultures (Angelidaki et al, 2018). Acetate can be converted to hydrogen and CO2 by syntrophic acetate-oxidizing bacteria (SAOB), provided the hydrogen partial pressure is kept sufficiently low due to immediate consumption (Eq 5) This reaction relies on the syntrophic cooperation of SAOB with hydrogenotrophic methanogens (Eq 2) (Hattori, 2008). We assessed the effect of the inoculum source on the performance of the biomethanation process and propose a concept to implement the P2G approach for biogas upgrading in wastewater treatment plants

Experimental Setup

Analytical Methods

RESULTS AND DISCUSSION