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This study demonstrates that electrostatic fields (0.2–0.67 V/cm) in anaerobic bioelectrochemical reactors enrich bulk-solution electroactive bacteria (ammonium-oxidizing exoelectrogens and denitritating electrotrophs) that simultaneously remove NH₄⁺ and NO₂⁻ via direct interspecies electron transfer (DIET). Total nitrogen removal rate increased from 106.1 to 166.3 mg N/g VSS·d as field strength rose from 0.2 to 0.67 V/cm, with stabilized cycle times dropping from 9 to 6 days. Electron recovery to N₂ improved from 73.8% to 93.5% at higher field strength, competing with Anammox performance while avoiding slow-growing Anammox bacteria.

Key insights

  • Performance Total nitrogen removal rate increased 57% (from 106.1 to 166.3 mg N/g VSS·d) as electrostatic field strength tripled from 0.2 to 0.67 V/cm, with stabilized cycle time dropping from 9 to 6 days.

    So what. Operators should target the highest feasible field strength (0.67 V/cm) to maximize throughput and minimize residence time, but must verify electrode spacing and power cost trade-offs at scale.

  • Threshold Nitrite requirement for ammonium oxidation (0.80–1.15 mg NO₂-N/mg NH₄-N) remained consistently lower than the Anammox stoichiometry of 1.32, indicating incomplete reduction or side reactions.

    So what. Design systems to maintain NO₂⁻ above depletion threshold (Figure 2 shows removal stops when NO₂⁻ drops), but do not over-dose; electron balance shows 73.8–93.5% goes to N₂, rest to CH₄ and biomass.

  • Trade-off Electron recovery to N₂ gas increased from 73.8% to 93.5% as field strength rose from 0.2 to 0.67 V/cm, while side reactions (CH₄, biomass) fell from 21% to 0.6%.

    So what. Higher field strength suppresses methanogenesis and improves nitrogen selectivity; this is a key advantage over conventional anaerobic processes and suggests field strength is a control lever for product selectivity.

  • Mechanism Pseudomonas caeni abundance jumped from 6.6% (BENR20) to 21% (BENR67), and Thiopseudomonas denitrificans rose from <1% to 2.8%, showing field-dependent enrichment of key electroactive species.

    So what. Monitor microbial community composition (16S rRNA) as a diagnostic for field strength adequacy; low Pseudomonas abundance may signal insufficient field or suboptimal conditions.

  • Threshold Alkalinity requirement (1.11–1.42 mg CaCO₃/mg NH₄-N) was 2.4–5.9× higher than Anammox (0.24–0.47), suggesting bicarbonate is consumed as carbon source for autotrophic growth, not just pH buffering.

    So what. Budget alkalinity as a growth substrate, not just a buffer; systems with low alkalinity feed will require supplementation or recirculation to sustain biomass and avoid pH drift.

Opportunity areas6

Specific gaps in this paper, with an experiment that would close each.

  • High No test of field strength above 0.67 V/cm or below 0.2 V/cm; upper and lower operating windows are undefined.

    Paper states field strength range 0.2–0.67 V/cm tested; linear trend in removal rate and cycle time suggests saturation or optimum may exist beyond 0.67 V/cm, but not explored.

    Try. Test 1.0, 1.5 V/cm (or 0.1 V/cm) while monitoring N removal rate, redox peak height, and power consumption to identify diminishing returns or inhibition threshold.

  • High No measurement of dissolved oxygen, pH drift, or H₂ evolution during operation; cathode chemistry is opaque.

    Paper mentions 'anaerobic' but does not report DO, final pH, or gas composition beyond N₂/CH₄/CO₂; cathode potential and proton availability are not characterized.

    Try. Log pH, DO, and cathode potential continuously; measure H₂ in biogas; correlate with field strength to identify if water reduction competes with NO₂⁻ reduction.

  • Medium No variation of C/N ratio, HRT, or initial NO₂⁻ concentration; only field strength is the independent variable.

    Alkalinity requirement is high (1.11–1.42 mg CaCO₃/mg N) and varies with field strength, but no test of whether lower C/N or shorter HRT can reduce it or improve selectivity.

    Try. Hold field at 0.67 V/cm; vary initial NO₂⁻ (150–400 mg/L) and HRT (3–12 d) to map the operating window and identify NO₂⁻ limitation and washout thresholds.

  • Medium No detection or quantification of N₂O; only N₂, CH₄, CO₂ measured in biogas.

    Denitrification intermediates (NO₂⁻, NO, N₂O) are not tracked; N₂O is a potent greenhouse gas and may accumulate at certain field strengths or pH values.

    Try. Use gas chromatography with electron capture detector (ECD) or FTIR to measure N₂O in headspace across all three field strengths; correlate with redox peak potentials.

  • Medium Batch mode only; no continuous-flow or fed-batch operation tested.

    All experiments are sequential batch with 30 min settling; residence time, mixing, and biofilm formation differ fundamentally from continuous systems.

    Try. Operate BENR67 in continuous mode at HRT 6–12 d with constant field; measure steady-state N removal rate, effluent NO₂⁻/NO₃⁻, and biomass washout.

  • Low No test of electrode material, spacing, or geometry; only copper foils with dielectric coating at fixed 3 cm spacing.

    Paper uses surface-insulated electrodes to promote bulk DIET; no comparison to bare electrodes, different materials, or variable spacing to optimize field distribution.

    Try. Test electrode spacing 1–5 cm and compare field uniformity (via simulation or potential mapping) against N removal rate and redox peak height.

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What they did

System
MNRC
Substrate
real wastewater

What worked

No outcome metrics extracted yet.

Abstract

The effect of electrostatic fields on the bioelectrochemical removal of ammonium and nitrite from nitrogen-rich wastewater was investigated at strengths ranging from 0.2 to 0.67 V/cm in bioelectrochemical anaerobic batch reactors. The electrostatic field enriched the bulk solution with electroactive bacteria, including ammonium oxidizing exoelectrogens (AOE) and denitritating electrotrophs (DNE). The electroactive bacteria removed ammonium and nitrite simultaneously with alkalinity consumption through biological direct interspecies electron transfer (DIET) in the bulk solution. However, the total nitrogen (ammonium and nitrite) removal rate increased from 106.1 to 166.3 mg N/g volatile suspended solids (VSS).d as the electrostatic field strength increased from 0.2 to 0.67 V/cm. In the cyclic voltammogram, the redox peaks corresponding to the activities of AOE and DNE increased as the strength of the electrostatic field increased. Based on the microbial taxonomic profiling, the dominant genera involved in the bioelectrochemical nitrogen removal were identified as Pseudomonas, Petrimonas, DQ677001_g, Thiopseudomonas, Lentimicrobium, and Porphyromonadaceae_uc. This suggests that the electrostatic field of 0.67 V/cm significantly improves the bioelectrochemical nitrogen removal by enriching the bulk solution with AOE and DNE and promoting the biological DIET between them.

Keywords

NitriteAmmoniumNitrogenVolatile suspended solidsWastewaterInorganic chemistry

Identifiers

DOI
10.3390/en13123218
Journal
Energies
Year
2020
Extraction

Reported parameters

84 extracted values

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