微生物と電気の力でアンモニウムの再生に成功～サステイナブルな窒素循環社会の実現に期待～

2026-09-15 北海道大学

環境中へ大量に散逸する硝酸（NO₃^–）を生物電気化学的にNH₄⁺へ戻し、再生肥料化する。

＜関連情報＞

• https://www.hokudai.ac.jp/news/2026/09/post-2443.html
• https://www.sciencedirect.com/science/article/pii/S1385894726091734

水溶性電子伝達体を用いた生物電気化学プロセスによる硝酸のアンモニウム再生 Soluble-electron mediator assisted bioelectrochemical reduction of nitrate to ammonium for nitrogen recovery

Yunjeong Choi, Nichika Takahashi, Satoshi Okabe, Mamoru Oshiki
Chemical Engineering Journal  Available online: 7 September 2026
DOI:https://doi.org/10.1016/j.cej.2026.181710

Highlights

• First demonstration of soluble-mediator-assisted bioelectrochemical NO₃⁻ reduction to NH₄⁺
• High NO₃⁻ reduction activity; 10.9 mmol-N L⁻¹ day⁻¹ and Ks = 0.19 mM
• Efficient NO₃⁻ reduction in natural water matrices at 1 mM NO₃⁻
• Faradaic efficiency in natural water matrices; 50–59%
• Electricity consumption in natural water matrices; 188–192 kWh kg-NO₃⁻-N⁻¹

Abstract

Bioelectrochemical reduction of dilute nitrate (NO₃⁻; sub-mM) to ammonium (NH₄⁺) is a promising route toward circular nitrogen management from nitrate-contaminated groundwater and surface waters. However, conventional bioelectrochemical systems (BES) rely on extracellular electron transfer through electrode-attached biofilms, restricting catalysis to a few electroactive bacteria in direct contact with the electrode. Here, we developed a soluble-mediator-assisted BES in which a diffusible mediator shuttles electrons to suspended cells throughout the catholyte, enabling weakly electroactive bacteria to serve as nitrate-reduction catalysts. Three biocatalysts (Escherichia coli, Shewanella oneidensis, and Candidatus Brocadia sinica), nine soluble mediators spanning viologens, quinones, and phenazines, cathodic potentials from −0.3 to −0.9 V, and pH 6.5 to 8.5 were screened, and NO₃⁻ reduction to NH₄⁺ was confirmed using a ¹⁵NO₃⁻ tracer. With E. coli cells and methyl viologen, NO₃⁻ was reduced to NH₄⁺ at a maximum volumetric rate of 10.9 mmol-N L⁻¹ day⁻¹ and a low NO₃⁻-affinity constant (K_s = 0.19 mM). This rate was 8-fold higher than previously reported biofilm-based systems, and NO₃⁻ reduction was repeated over three successive NO₃⁻ additions during 48 h of operation. Furthermore, the soluble-mediator-assisted BES showed high performance even in natural groundwater and surface water, with a Faradaic efficiency of 50–59% and an electricity consumption of 188–192 kWh kg-NO₃⁻-N⁻¹, substantially lower than metal-catalyst systems at comparable NO₃⁻ concentration. These findings demonstrate that soluble-mediator-assisted BESs provide an energy-efficient platform for converting NO₃⁻ in natural water into a recoverable NH₄⁺ form, with full nitrogen recovery additionally requiring downstream NH₄⁺ concentration or separation.