Unravelling biocomplexity of electroactive biofilms for producing hydrogen from biomass

Abstract

SummaryLeveraging nature's biocomplexity for solving human problems requires better understanding of the syntrophic relationships in engineered microbiomes developed in bioreactor systems. Understanding the interactions between microbial players within the community will be key to enhancing conversion and production rates from biomass streams. Here we investigate a bioelectrochemical system employing an enriched microbial consortium for conversion of a switchgrass‐derived bio‐oil aqueous phase (BOAP) into hydrogen via microbial electrolysis (MEC). MECs offer the potential to produce hydrogen in an integrated fashion in biorefinery platforms and as a means of energy storage through decentralized production to supply hydrogen to fuelling stations, as the world strives to move towards cleaner fuels and electricity‐mediated transportation. A unique approach combining differential substrate and redox conditions revealed efficient but rate‐limiting fermentation of the compounds within BOAP by the anode microbial community through a division of labour strategy combined with multiple levels of syntrophy. Despite the fermentation limitation, the adapted abilities of the microbial community resulted in a high hydrogen productivity of 9.35 L per L‐day. Using pure acetic acid as the substrate instead of the biomass‐derived stream resulted in a three‐fold improvement in productivity. This high rate of exoelectrogenesis signifies the potential commercial feasibility of MEC technology for integration in biorefineries.

Efficient Conversion of Aqueous-Waste-Carbon Compounds Into Electrons, Hydrogen, and Chemicals via Separations and Microbial Electrocatalysis

“…The end-products of fermentation such as acetate, form substrate for the exoelectrogens and accumulate if an electron sink is not provided such as under open circuit conditions. Thus, the syntrophy between the two groups was clearly illustrated (Lewis et al, 2018).…”

“…The information on complex microbial communities present in bioanode treating mixed substrate feedstocks is limited. Lewis et al recently reported characterization of microbial population treating switchgrass-derived BOAP, which showed a dependence between the fermenters and the exoelectrogens (Lewis et al, 2018). This was one of the first detailed account of the microbial community treating complex feedstocks directly fed into anode.…”

“…While the ultimate goal of the anodic processes is to generate electrons, a synergy between the exoelectrogens and the fermenters and hydrolytic microbes is necessary for effective conversion of wastes. The aqueous phase from pyrolysis, BOAP, has shown to require a high level of synergy between the fermentative organisms and exoelectrogens for effective production of current in the anode (Lewis et al, 2018). This is due to the wide range of compounds present in the BOAP as shown in section Bio-Oil Components and Carbon in Aqueous Waste.…”

“…The microbial population included Firmicutes, Bacteroidetes, and γ-Proteobacteria as the dominant families. These families were reported to use a division of labor strategy to facilitate conversion of the complex feedstock (Lewis et al, 2018).…”

“…The focus is bio-oil derived from biomass via pyrolysis, which is compared with wastes from other biorefinery pathways and food industry processes. The use of BOAP for production of electricity and hydrogen is reviewed with the goal of evaluating the progress toward practical feasibility and achievement of productivities and current densities needed for commercial consideration of BESs Lewis et al, 2018). The findings are compared with those using other waste streams and conversion platforms.…”