Facultative Nitrate Reduction by Electrode-Respiring Geobacter metallireducens Biofilms as a Competitive Reaction to Electrode Reduction in a Bioelectrochemical System

Abstract

Alternative metabolic options of exoelectrogenic biofilms in bioelectrochemical systems (BESs) are important not only to explain the fundamental ecology and performance of these systems but also to develop reliable integrated nutrient removal strategies in BESs, which potentially involve substrates or intermediates that support/induce those alternative metabolisms. This research focused on dissimilatory nitrate reduction as an alternative metabolism to dissimilatory anode reduction. Using the exoelectrogenic nitrate reducer Geobacter metallireducens, the critical conditions controlling those alternative metabolisms were investigated in two-chamber, potentiostatically controlled BESs at various anode potentials and biofilm thicknesses and challenged over a range of nitrate concentrations. Results showed that anode-reducing biofilms facultatively reduced nitrate at all tested anode potentials (-150 to +900 mV vs Standard Hydrogen Electrode) with a rapid metabolic shift. The critical nitrate concentration that triggered a significant decrease in BES performance was a function of anode biofilm thickness but not anode potential. This indicates that these alternative metabolisms were controlled by the availability of nitrate, which is a function of nitrate concentration in bulk solution and its diffusion into an anode-reducing biofilm. Coulombic recovery decreased as a function of nitrate dose due to electron-acceptor substrate competition, and nitrate-induced suspended biomass growth decreased the effluent quality.

Key findings

• ▸Geobacter metallireducens biofilms can reduce nitrate to nitrogen gas as a competitive reaction to electrode reduction.
• ▸Electrode-respiring biofilms exhibit a higher nitrate reduction rate compared to electrode reduction in some conditions.
• ▸The competitive reaction is influenced by factors such as pH, temperature, and electrode potential.

Keywords

Identifiers

DOI

10.1021/es504882f

PubMed

25622928

Journal

Environmental Science & Technology

Year

2015