Electron Flow Shifts from Anode Respiration to Nitrate Reduction During Electroactive Biofilm Thickening

Abstract

As electrons generated through substrate oxidation compete with electrodes, dissimilatory nitrate reduction to ammonium (DNRA), denitrification in bioelectrochemical systems in the presence of nitrate, and nitrate reduction through an electroactive biofilm (EAB) are unpredictable. We find that pathways of nitrate reduction are related to EAB thickness and that 76 ± 2 μm is the critical thickness of a biofilm at which both the inner and outer layers simultaneously include DNRA, leading to a maximum level of DNRA efficiency of 42%. Fractions of electrons flowing during nitrate reduction are relatively stable, but their distributions between DNRA and denitrification vary with biofilm thickness. Electrons prefer denitrification in an EAB that is 66 ± 2 μm, while DNRA reversely surpasses denitrification when the thickness increases in the range of 76 ± 2 to 210 ± 2 μm. Biofilm thickening enhances the DNRA of all biofilms close to solution, where nirK remains constant and nrfA is significantly upregulated. However, nrfA is downregulated in layers close to the electrode when the biofilm is thicker than 76 ± 2 μm. These findings reveal the spatially heterogeneous reduction of nitrate in thick EABs, highlighting the importance of biofilm thickness to the regulation of end products of nitrate reduction.

Reaction kinetics of anodic biofilms under changing substrate concentrations: Uncovering shifts in Nernst‐Monod curves via substrate pulses

“…This includes positive as well as negative effects and is in accordance with results from Zhou et al. [ 31 ] and Sun et al. [ 32 ] who observed limitations of the current density only after numerous batch cycles when thick biofilms had developed.…”

“…The results indicate that CDWD is not a decisive factor influencing the concentration response behavior for mixed-culture biofilms with CDWD up to 1.1 mg cm −2 as obtained after one to two weeks of cultivation time. This includes positive as well as negative effects and is in accordance with results from Zhou et al [31] and Sun et al [32] who observed limitations of the current density only after numerous batch cycles when thick biofilms had developed. Such limitations can result from concentration gradients that develop in the biofilms [4].…”

Subnanometric alkaline-earth oxide clusters for sustainable nitrate to ammonia photosynthesis

“…Another virtue of using NO 3 − feedstock lies in its rich distribution in wastewater. The abundant nitrate in wastewater offers sufficient reactants for NO 3 − reduction reaction (NO 3 − RR) routes [17][18][19][20] . Instead of the partial reduction of NO 3 − to N 2 for its purification, the eight-electron transfer reaction for NO 3 − to NH 4 + synthesis provides an opportunity for the valueadded conversion of contaminative NO 3 − into ammonia as an economically competitive product.…”

Coupling riboflavin de novo biosynthesis and cytochrome expression for improving extracellular electron transfer efficiency in Shewanella oneidensis

“…Cells on the anodes in the MFC setups were stained with a LIVE/DEAD BacLight bacterial viability kit, showing green or red depending on the cell membrane permeability of live and dead cells (Zhou et al, 2020). We then performed CLSM on the MFCs carbon cloth electrodes of the engineered strains and DL0 strain.…”