Power Generation and Microbial Communities in Microbial Fuel Cell Powered by Tobacco Wastewater

Tensions the paper itself points to. Each side quotes the passage it comes from.

• Within the paper Trichococcus dominance contradicts typical MFC exoelectrogen composition

  One side

  Trichococcus reached 72.40% abundance in R1 and was present at high abundance in all MFCs, with authors suggesting it may serve as a novel exoelectrogen

  “Trichococcus may serve as a novel exoelectrogen for power generation, demonstrating remarkable performance in the MFC at high abundance (72.40%)”

  Other side

  Authors state: 'in the vast majority of studies on wastewater treatment of MFC, the highest abundance in the bioanode is of the Geobacter or Desulfobulbaceae, which act as typical exoelectrogens and play a major role in MFCs for electrical energy generation; however, their presence was not detected in this study'

  “in the vast majority of studies on wastewater treatment of MFC, the highest abundance in the bioanode is of the Geobacter or Desulfobulbaceae, which act as typical exoelectrogens and play a major role in MFCs for electrical energy generatio”

  Authors’ reading. Authors acknowledge the atypical community composition and propose Trichococcus as a substrate-adapted alternative exoelectrogen for tobacco wastewater, supported by presence of EET genes (dmkA, fmnB, ndh2) and Fe(III)-reducing ability, but lack direct electrochemical proof.

• Within the paper Carbon source addition improves treatment metrics but worsens electrical efficiency

  One side

  Glucose supplementation achieved maximum power density (717.04 mW/m²) and highest COD removal (75.97%), with authors concluding 'the addition of extra carbon sources could increase the voltage output, COD, and nitrogen removal efficiency'

  “the addition of extra carbon sources could increase the voltage output, COD, and nitrogen removal efficiency”

  Other side

  Coulombic efficiency with glucose (7.75%) was lower than without supplementation (11.16%), and authors state 'the addition of carbon sources did not enhance the coulombic efficiencies of the MFCs (R1–R4) in comparison with R5'

  “the addition of carbon sources did not enhance the coulombic efficiencies of the MFCs (R1–R4) in comparison with R5. This indicated that not all electrons released from the oxidation of the carbon source were transferred to the anode”

  Authors’ reading. Authors resolve this by noting that electrons from added substrates are diverted to biomass synthesis and denitrification rather than power generation, making the MFC a treatment device rather than a power generator when supplemented.

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

• High No measurement of nitrite (NO₂⁻) or N₂O accumulation during denitrification; only TN and NH₄⁺-N reported

  Nitrogen removal pathways are inferred from microbial community and KEGG predictions, but intermediate nitrogen species are not quantified. Section 3.1 reports only TN and NH₄⁺-N removal; no mention of NO₃⁻, NO₂⁻, or N₂O. This is critical for understanding whether denitrification is complete or if N₂O is being released.

  Try. Measure NO₃⁻, NO₂⁻, and N₂O (via gas chromatography or ion chromatography) at days 0, 1, 2, 3, 6, 9 of each cycle for all carbon source treatments; correlate with Brevundimonas and denitrification gene abundance.

• High No cathode potential or anode potential control; only external resistance varied in Stage I and fixed at 1000 Ω in Stage II

  Operating window for nitrogen cycling is unknown. Section 2.1 states external resistances were 47–1000 Ω in Stage I and fixed at 1000 Ω in Stage II. Cyclic voltammetry (Figure 3) shows redox peaks at −0.05, +0.25 V (oxidation) and −0.30, +0.1 V (reduction), but no potentiostatic operation or anode potential measurement is reported. Cathode potential and dissolved oxygen are not controlled or measured.

  Try. Operate MFCs at fixed anode potentials (−0.3, −0.2, −0.1, 0.0 V vs. Ag/AgCl) and measure TN, NO₃⁻, NO₂⁻, N₂O, and power output; separately control cathode potential and measure dissolved oxygen to assess nitrification vs. denitrification windows.

• Medium No measurement of dissolved oxygen (DO) in anode or cathode compartments; anaerobic conditions assumed but not verified

  Section 2.1 states 'all reactors were aerated with N₂ for 15 min to maintain an anaerobic environment' but no DO measurements are provided. Nitrification requires oxygen, yet TN removal is observed; unclear whether residual DO or cathode oxygen diffusion enables nitrification.

  Try. Measure DO in anode and cathode compartments daily using a DO probe; test effect of cathode oxygen supply (air vs. inert) on nitrification and denitrification rates.

• Medium No measurement of pH in anode compartment during Stage II; only cathode pH shown in Figure 2c, and interpretation of pH rebound is speculative

  Figure 2c shows pH dynamics in anode, with rapid decline days 0–2 and rebound after day 2. Authors attribute this to degradation of glucose into organic acids, but no mechanistic explanation for the rebound is provided. Anode pH affects nitrification/denitrification kinetics and microbial activity.

  Try. Measure anode pH continuously or daily; correlate with COD, TN, NO₃⁻, NO₂⁻, and volatile fatty acid (VFA) concentrations to identify the source of pH rebound (e.g., ammonia production, denitrification, or organic acid consumption).

• Medium No variation of hydraulic retention time (HRT); all Stage II cycles fixed at 9 days

  Section 2.1 states 'each cycle lasted for nine days' with no justification or sensitivity analysis. Nitrogen removal plateaued at ~47% TN; unclear whether longer HRT would improve removal or if 9 days is optimal for this wastewater and microbial community.

  Try. Test HRT of 6, 9, 12, and 18 days with butyrate supplementation (best nitrogen removal); measure TN, NO₃⁻, NO₂⁻, N₂O, power output, and coulombic efficiency to identify optimal operating window.

• Medium No measurement of influent NO₃⁻ concentration or C/N ratio; only initial COD and TN reported

  Section 3.1 reports initial COD (1645.33 mg/L for R5) and TN removal (46.95% for R4), but does not specify initial TN concentration, NO₃⁻ vs. NH₄⁺-N split, or C/N ratio. This limits reproducibility and comparison with other MES studies. KEGG predictions suggest denitrification, but substrate availability for denitrification is not quantified.

  Try. Measure initial and final NO₃⁻, NO₂⁻, NH₄⁺-N, and organic nitrogen separately; calculate C/N ratio and test effect of C/N ratio (10:1, 20:1, 30:1) on nitrogen removal and power output.