Abstract
Furanic and phenolic compounds are 20 lignocellulose-derived compounds known to
inhibit to H2- and ethanol- producing microorganisms in dark fermentation. Bioelectrochemical
conversion of furanic and phenolic compounds to electricity or H2 has recently been
demonstrated as a productive method to use these compounds. However, potential inhibitory
effect of furanic and phenolic compounds on exoelectrogenesis in bioelectrochemical systems is
not well understood. This study systematically investigated the inhibitory effect of furfural (FF),
5-hydroxymethylfurfural (HMF), syringic acid (SA), vanillic acid (VA), and 4-hydroxybenzoic
acid (HBA) on exoelectrogenesis in the bioanode of a microbial electrolysis cell. A mixture of
these five compounds at an increasing initial total concentration from 0.8 to 8.0 g/L resulted in
current decrease up to 91%. The observed inhibition primarily affected exoelectrogenesis,
instead of non-exoelectrogenic biotransformation pathways (e.g., fermentation) of the five compounds. Furthermore, the parent compounds at a high concentration, as opposed to their
biotransformation products, were responsible for the observed inhibition. Tests with individual
compounds show that all five parent compounds contributed to the observed inhibition by the
mixture. The IC50 (concentration resulting in 50% current decrease) was estimated as 2.7 g/L for
FF, 3.0 g/L for HMF, 1.9 g/L for SA, 2.1 g/L for VA and 2.0 g/L for HBA. Nevertheless, these
compounds below their non-inhibitory concentrations jointly resulted in significant inhibition as
a mixture. Catechol and phenol, which were persistent biotransformation products of the
mixture, inhibited exoelectrogens at high concentrations, but to a lesser extent than the parent
compounds. Recovery of exoelectrogenesis from inhibition by all compounds was observed,
except for catechol, which resulted in irreversible inhibition. The reversibility of inhibition, as
well as the observed difference in recovery rates, suggest different modes of exoelectrogenesis
inhibition, related to the hydrophobicity of the inhibiting compounds.