A variety of hydrogenotrophic enrichment cultures catalyze cathodic reactions

Journal article, 2019

Biocathodes where living microorganisms catalyse reduction of CO2 can potentially be used to produce
valuable chemicals. Microorganisms harbouring hydrogenases may play a key role for biocathode
performance since H2 generated on the electrode surface can act as an electron donor for CO2 reduction.
In this study, the possibility of catalysing cathodic reactions by hydrogenotrophic methanogens,
acetogens, sulfate-reducers, denitrifiers, and acetotrophic methanogens was investigated. The cultures
were enriched from an activated sludge inoculum and performed the expected metabolic functions. All
enrichments formed distinct microbial communities depending on their electron donor and electron
acceptor. When the cultures were added to an electrochemical cell, linear sweep voltammograms
showed a shift in current generation close to the hydrogen evolution potential (−1 V versus SHE)
with higher cathodic current produced at a more positive potential. All enrichment cultures except
the denitrifiers were also used to inoculate biocathodes of microbial electrolysis cells operated with
H+ and bicarbonate as electron acceptors and this resulted in current densities between 0.1–1 A/m2.
The microbial community composition of biocathodes inoculated with different enrichment cultures
were as different from each other as they were different from their suspended culture inoculum. It was
noteworthy that Methanobacterium sp. appeared on all the biocathodes suggesting that it is a key
microorganism catalysing biocathode reactions.