Research progress and prospect of low-carbon biological technology for nitrate removal in wastewater treatment

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

• High No quantitative operating windows provided for cathode potential, anode potential, or current density in photoelectrotrophic denitrification (PEDeN) systems; paper mentions PEDeN as 'emerging' but provides no electrochemical parameters, pH ranges, or HRT values.

  Section 1 and abstract highlight PEDeN as a key emerging technology, but the body text (truncated at 32,000 chars) does not contain detailed electrochemical operating conditions, suggesting this section was cut off or underdeveloped.

  Try. Vary cathode potential (-0.4 to -1.0 V vs. Ag/AgCl), anode potential (0 to +0.8 V), current density (0.5–5 A/m²), pH (6–8), and HRT (4–24 h) in a photoelectrotrophic denitrification reactor; measure NO₃⁻ removal, N₂O selectivity, and electron recovery.

• High No systematic comparison of N2O accumulation risk across SAD, HAD, and n-DAMO under varying C/N ratios, dissolved oxygen, or catholyte pH; paper states SAD reduces N2O by 96% but does not specify operating conditions (HRT, temperature, influent NO₃⁻ concentration) under which this is achieved.

  Section 2.1 claims N2O reduction but does not provide the operating window (e.g., HRT, C/N, DO, pH) that ensures this performance; Section 3 and 4 do not quantify N2O or nitrite accumulation risk.

  Try. Test SAD, HAD, and n-DAMO reactors at C/N ratios of 2–10, HRTs of 4–48 h, influent NO₃⁻–N of 50–500 mg/L, and pH 6.5–8.5; measure N2O, NO₂⁻, and N2 production rates to define safe operating windows.

• Medium Nitrite accumulation risk in PN-n-DAMO-anammox is mentioned qualitatively ('does not have excessive nitrate accumulation') but no quantitative threshold or control strategy is provided; no data on NO₂⁻ concentration limits or feedback control.

  Section 4.1 states nitritation-n-DAMO 'does not have excessive nitrate accumulation and N2O emission' but provides no numbers, setpoints, or control logic for maintaining stable nitrite levels.

  Try. Operate PN-n-DAMO-anammox at varying aeration rates (0.5–2 kg O₂/kg N) and measure steady-state NO₂⁻ concentration; define the maximum tolerable NO₂⁻ level before n-DAMO or anammox inhibition occurs.

• Medium No data on the effect of temperature on HAD or n-DAMO kinetics and H₂ or CH₄ solubility; paper mentions 10 °C stability for n-DAMO but does not compare performance across 5–35 °C range or provide activation energy estimates.

  Section 4.1 reports 10 °C performance for n-DAMO but does not systematically vary temperature; Section 3 does not address temperature effects on H₂ solubility or HAD kinetics.

  Try. Operate HAD and n-DAMO reactors at 5, 10, 15, 20, 25, and 30 °C; measure denitrification rate, H₂/CH₄ solubility, and microbial community composition to define optimal temperature windows.

• Medium Sulfammox process is mentioned as a method to reduce sulfate production in SAD but is described as 'limited and remains at the proof-of-concept stage'; no pilot or full-scale data provided, and no comparison of sulfammox performance under varying S/N ratios or HRTs.

  Section 2.3 states 'sulfammox is limited and remains at the proof-of-concept stage' but provides no quantitative performance data, operating windows, or engineering design criteria.

  Try. Operate a SAD-sulfammox coupled reactor at S/N ratios of 0.5–2.0 and HRTs of 8–48 h; measure sulfate production, ammonia oxidation rate, and nitrite accumulation to establish design guidelines.

• Medium No comparison of electron recovery or coulombic efficiency in MEC-based HAD systems (MEC-MBfR, MEC-PRB) versus standalone HAD or heterotrophic denitrification; paper reports total nitrogen removal but not energy efficiency or electron balance.

  Table 2 reports nitrogen removal efficiency (>90%, 97.8%, 80.6%, 85%) but does not provide cathode potential, current density, applied voltage, or coulombic efficiency, making it impossible to assess energy cost per kg N removed.

  Try. Operate MEC-MBfR at applied voltages of 0.5–2.0 V and measure cathode potential, current density, H₂ production rate, and nitrogen removal rate; calculate coulombic efficiency and energy cost per kg NO₃⁻–N removed.