Enhanced low C/N nitrogen removal in an innovative microbial fuel cell (MFC) with electroconductivity aerated membrane (EAM) as biocathode

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

• High No systematic study of cathode potential vs current density relationship; cathode potential remained at 0.18 V vs SHE across all loads, suggesting it may be limited by biofilm kinetics or mass transfer rather than electrochemistry.

  Authors note 'large energy loss occurred at the cathode' and attribute it to overpotential, intermediate products (NO₂, N₂O), and microbial maintenance, but do not vary cathode potential independently or measure N₂O.

  Try. Potentiostatic control of cathode at 0.0, −0.1, −0.2, −0.3 V vs SHE; measure NO₂⁻ and N₂O accumulation; quantify electron recovery to N₂ vs N₂O.

• High No measurement of N₂O production or quantification of N₂ as final product; nitrogen balance incomplete.

  Authors assume N₂ is the final product in coulombic efficiency calculation (Eq. 4, n=5 for NO₃⁻) but provide no gas chromatography or isotope data. Nitrite accumulation (2.32 mg L⁻¹) suggests incomplete reduction; N₂O may be produced.

  Try. Gas-phase sampling (GC-ECD or IRMS) for N₂O and N₂; nitrogen balance closure; test at different cathode potentials and DO levels.

• Medium Aeration intensity tested at only two levels (30 kPa, 20 kPa); no systematic optimization of DO setpoint for SND vs power generation trade-off.

  Authors state 'The dissolved oxygen of the cathode liquor was controlled at 0.2-0.5 mg L⁻¹ throughout the study' but Table 1 shows only two aeration pressures tested, with minimal difference in anode CE (0.34% decrease). Optimal DO window for SND is known to be 0.3–0.8 mg L⁻¹ from prior work (Munch, Pochana–Keller cited).

  Try. Vary DO setpoint from 0.1 to 1.0 mg L⁻¹ in 0.1 mg L⁻¹ increments; measure TN removal, power density, NO₂⁻ and N₂O accumulation at each level.

• Medium No investigation of HRT effect on nitrogen removal and electrochemical denitrification; only one HRT (12 h) tested.

  HRT is a critical operating parameter for SND and biofilm kinetics. Authors operated at fixed 12 h HRT; no data on shorter (6–8 h) or longer (18–24 h) retention times.

  Try. Test HRT 6, 9, 12, 15, 18 h at constant current density (e.g., 4 A m⁻²); measure TN removal rate, NO₂⁻ accumulation, and biofilm thickness.

• Medium No characterization of biofilm composition or microbial community; mechanisms of SND inferred but not verified.

  Authors propose layered biofilm with nitrifiers in inner aerobic zone and denitrifiers in outer anaerobic zone (Fig. 6), but provide no microscopy, 16S rRNA, or functional gene data.

  Try. FISH or 16S rRNA sequencing of cathode biofilm at different depths; quantify nitrifier and denitrifier abundance; correlate with NO₂⁻ accumulation and current density.

• Low C/N ratio in influent is fixed at 2.8 g COD g⁻¹ N; no variation to test the claimed 'low C/N' capability or identify the minimum C/N at which the system fails.

  Authors claim advantage at 'low COD/N ratio of 2.8' but do not test lower ratios (e.g., 1.5, 1.0) or higher ratios (e.g., 4, 5) to establish operating window.

  Try. Vary influent C/N from 1.0 to 5.0 g COD g⁻¹ N; measure TN removal efficiency, NO₂⁻ accumulation, and power density; identify threshold below which performance degrades.