Inhibitory Effect of Furanic and Phenolic Compounds on Exoelectrogenesis in a Microbial Electrolysis Cell Bioanode

The objective of this study was to systematically investigate the inhibitory effect of furfural (FF), 5-hydroxymethylfurfural (HMF), syringic acid (SA), vanillic acid (VA), and 4-hydroxybenzoic acid (HBA), which are problematic lignocellulose-derived byproducts, on exoelectrogenesis in the bioanode of a microbial electrolysis cell. The five compound mixture at an initial total concentration range from 0.8 to 8.0 g/L resulted in an up to 91% current decrease as a result of exoelectrogenesis inhibition; fermentative, nonexoelectrogenic biotransformation pathways of the five compounds were not affected. Furthermore, the parent compounds at a high concentration, as opposed to their biotransformation products, were responsible for the observed inhibition. All five parent compounds contributed to the observed inhibition of the mixture. The IC₅₀ (i.e., concentration resulting in 50% current decrease) of individually tested parent compounds was 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. However, the parent compounds, when tested below their respective noninhibitory concentration, jointly resulted in significant inhibition as a mixture. Catechol and phenol, which were persistent biotransformation products, inhibited exoelectrogenesis only at high concentrations, but to a lesser extent than the parent compounds. Exoelectrogenesis recovery from inhibition by all compounds was observed at different rates, with the exception of catechol, which resulted in irreversible inhibition.