Optimization of Ammonia Nitrogen and Phosphorus Removal Performance and Analysis of Microbial Community Structure in Microbial Fuel Cells

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

• High No measurement of N2O or NO2− accumulation during optimization; paper does not report whether nitrification proceeds to NO3− or accumulates at intermediate oxidation states.

  Section 3.1.2 mentions 'simultaneous nitritation/denitritation (SND)' as a potential pathway but provides no data on NO2− or N2O concentrations. High ammonia (>40 mg/L) is known to inhibit NOB, which could lead to NO2− accumulation, but this is not measured.

  Try. Measure NO2−-N, NO3−-N, and N2O in effluent across the HRT and ammonia concentration ranges tested (12–24 h, 20–80 mg/L); quantify whether NOB inhibition at high ammonia leads to incomplete nitrification or N2O production.

• High No explicit measurement of cathode potential, anode potential, or current density during optimization; paper does not report electrochemical operating window.

  Methods section states 'copper wire between the two electrodes and a 200 Ω fixed resistor were connected' but no potentiostat data, voltage profiles, or current density (A/m²) are reported. Nitrogen removal mechanisms (nitrification, denitrification, electrochemical reduction) depend on electrode potentials.

  Try. Measure cathode and anode potentials (vs. Ag/AgCl) and current density (mA/m²) at each HRT and ammonia concentration condition; correlate with NH4+-N and NO3−-N removal rates to identify electrochemical vs. biological contributions.

• High No investigation of dissolved oxygen (DO) concentration in cathode chamber; paper does not report whether aerobic nitrification or oxygen-limited denitrification dominates.

  Methods state 'The cathode chamber was aerated and oxygenated with an air pump' but no DO setpoint, measurement, or profile is given. DO is critical for nitrification kinetics and for distinguishing nitrification from electrochemical reduction pathways.

  Try. Measure DO in cathode chamber (mg/L or % saturation) at each condition; vary DO setpoint (e.g., 2, 5, 8 mg/L) to determine optimal window for nitrification vs. denitrification and to assess trade-off between power generation and nitrogen removal.

• Medium No measurement of catholyte pH during operation; paper does not report pH profile or buffer capacity, which affect nitrifier activity and ammonia speciation (NH3 vs. NH4+).

  Synthetic wastewater includes 750 mg/L NaHCO3 buffer, but no pH data are reported during the 85 d operation. Nitrification consumes alkalinity and lowers pH; high pH favors NH3 (toxic to nitrifiers) while low pH favors NH4+ (less bioavailable). This is a critical control variable.

  Try. Monitor catholyte pH continuously or daily across the optimization range; measure ammonia speciation (NH3 vs. NH4+) using pH-dependent equilibrium calculations; determine if pH drift limits nitrification at high ammonia concentrations.

• Medium No analysis of phosphorus speciation or mechanism of TP removal; paper does not distinguish between biological uptake, chemical precipitation, or electrochemical reduction.

  TP removal is reported (59.39%) but no data on PO4³−, HPO4²−, or H2PO4− concentrations, nor on whether phosphorus is removed via biomass accumulation, struvite precipitation, or cathode reduction. Mechanism is unclear.

  Try. Measure soluble reactive phosphorus (SRP) and particulate phosphorus in effluent; perform mass balance on phosphorus in biomass and precipitate; test whether TP removal correlates with Mg²+ or Ca²+ concentration (struvite/apatite formation).

• Medium No long-term stability or repeated batch testing; paper reports only 85 d operation and does not assess whether optimized conditions are sustainable or if microbial community shifts over longer timescales.

  Microbial community analysis is performed at day 85 only; no time-series data on community succession or performance drift. Optimization is validated over 3 days of continuous operation, which is short for assessing robustness.

  Try. Operate optimized systems for ≥6 months; sample microbial community and measure NH4+-N, TP, NO2−, NO3− removal rates weekly to assess long-term stability and identify any community drift or performance degradation.