Application of Bioelectrochemical System in Nitrogen Removal via Simultaneous Autotrophic Nitrification and Denitrification from Wastewater
Parisa Ebrahimzadeh, Nahid Navidjouy, Hassan Khorsandi, Mostafa Rahimnejad
AI summary
78% confidenceThis study demonstrates a two-chamber bioelectrochemical system (BES) performing simultaneous nitrification and denitrification (SND) in the cathode to remove ammonium and nitrogen while oxidizing organic matter in the anode. Operating the cathode in sequential 24 h aerobic then anoxic phases achieved 83.4% total nitrogen removal at COD 10,000 mg/L and NH₄⁺-N 50 mg/L, with 100% ammonium removal. However, higher ammonium concentrations (100 mg/L) reduced total nitrogen removal to 61%, and increased COD concentration decreased COD removal efficiency (81.2% → 77.9%) while boosting nitrogen removal, revealing a trade-off between organic and nitrogen removal driven by pH acidification and electron availability.
Key insights
Trade-off Total nitrogen removal increased from 66.1% to 83.4% when COD rose from 2,000 to 10,000 mg/L at constant NH₄⁺-N 50 mg/L, but COD removal efficiency fell from 81.2% to 77.9%.
So what. Operators must choose between maximizing nitrogen removal (high COD feed) and organic matter removal (moderate COD feed); high substrate causes anode acidification (pH 7.4→6.2) that inhibits microbes.
Threshold Ammonium removal efficiency decreased from 92% to 75% and total nitrogen removal from 86% to 61% as initial NH₄⁺-N concentration increased from 25 to 100 mg/L at COD 2,000 mg/L.
So what. Design for low to moderate ammonium feeds (≤50 mg/L) to maintain >80% removal; high ammonium loads exceed the electron and H⁺ supply from the anode.
Trade-off Power density dropped from 87.78 to 22.32 mW/m² as NH₄⁺-N increased from 25 to 100 mg/L at COD 10,000 mg/L, indicating energy consumption by nitrification and denitrification.
So what. High ammonium loads consume most cathode electrons for treatment, leaving little surplus power; do not expect net electricity generation at NH₄⁺-N >50 mg/L.
Mechanism Sequential 24 h aerobic then 24 h anoxic operation reduced ammonium from 25 to 2 mg/L in the aerobic phase, then reduced nitrate and nitrite below 1 mg/L in the anoxic phase.
So what. Maintain strict aerobic (DO 2–3 mg/L) and anoxic (DO <2 mg/L) phases; the two-phase cycle is essential to prevent nitrite/nitrate accumulation and achieve complete nitrogen removal.
Mechanism At COD 10,000 mg/L and NH₄⁺-N 50 mg/L, 100% ammonium removal was achieved but total nitrogen removal was only 83.4%, implying 16.6% of nitrogen remained as nitrate or nitrite.
So what. Complete ammonium oxidation does not guarantee complete denitrification; ensure sufficient anoxic residence time and electron availability to reduce all oxidized nitrogen to N₂.
Contradictions1
Tensions the paper itself points to. Each side quotes the passage it comes from.
Within the paper Ammonium removal reaches 100% but total nitrogen removal plateaus at 83.4%, implying incomplete denitrification despite complete nitrification.
One sideAmmonium removal efficiency (25 and 50 mg/L) was obtained in the maximum value (100%)
“Ammonium removal efficiency (25 and 50 mg/L) was obtained in the maximum value (100%)”
Other sidethe maximum removal efficiency of nitrogen compounds was 83.4% at COD 10000 mg/L and the initial ammonium concentration was 50 mg/L
“the maximum removal efficiency of nitrogen compounds was 83.4% at COD 10000 mg/L and the initial ammonium concentration was 50 mg/L”
Authors’ reading. Authors attribute this to insufficient electron and H⁺ supply during the anoxic denitrification phase; nitrification consumes O₂ but denitrification requires electrons from the cathode, which may be rate-limiting.
Opportunity areas6
Specific gaps in this paper, with an experiment that would close each.
High No measurement of N₂O accumulation or speciation during the anoxic phase; only final N₂ is inferred from mass balance.
The paper lists N₂O formation (Equations 7–8) as part of the denitrification pathway but provides no data on N₂O concentration, yield, or whether it accumulates at high ammonium loads or low cathode potential.
Try. Measure N₂O in cathode outlet gas and liquid at NH₄⁺-N 50–100 mg/L and COD 10,000 mg/L; vary cathode potential (−0.2 to −0.6 V vs SHE) to identify N₂O emission risk.
High No explicit cathode or anode potential control or measurement; only voltage across the cell is reported.
The paper does not state the applied or measured cathode potential, anode potential, or whether potentials were controlled. This is critical because denitrification pathway (NO₃⁻ → NO₂⁻ → N₂O vs N₂) is potential-dependent.
Try. Operate at fixed cathode potentials (−0.3, −0.5, −0.7 V vs Ag/AgCl) and measure nitrite accumulation, N₂O yield, and total nitrogen removal at COD 10,000 mg/L, NH₄⁺-N 50 mg/L.
High Catholyte pH is not reported; only anode pH is shown. Nitrification and denitrification kinetics are pH-sensitive.
The paper states 'the pH of the nutrient solution for nitrifying and denitrifying bacteria was set in the range of 7/60.2' but does not report actual cathode pH during operation or how it changes with COD and ammonium load.
Try. Monitor cathode pH continuously at COD 2,000–10,000 mg/L and NH₄⁺-N 25–100 mg/L; correlate pH drift with nitrite accumulation and nitrogen removal efficiency.
Medium Hydraulic retention time (HRT) is fixed at 48 h (24 h aerobic + 24 h anoxic); no variation of HRT or phase duration is tested.
The paper states 'the reactor was operated with these conditions during three consecutive periods' but does not explore whether shorter or longer phases improve denitrification or reduce nitrite accumulation.
Try. Test phase durations of 12, 24, 36 h aerobic and anoxic at COD 10,000 mg/L, NH₄⁺-N 50 mg/L; measure nitrite and nitrate at phase boundaries.
Medium No investigation of C/N ratio optimization; only two C/N ratios are tested (40 and 200).
The paper notes 'with the change of COD concentration in the anode chamber, the C/N ratio will also change' and shows C/N 40 gives 66.1% TN removal vs C/N 200 gives 83.4%, but does not test intermediate ratios or explain the mechanism.
Try. Test C/N ratios of 40, 80, 120, 160, 200 at constant NH₄⁺-N 50 mg/L by varying COD; measure electron flow to cathode and denitrification rate.
Medium Dissolved oxygen (DO) in cathode is maintained at 2–3 mg/L during aerobic phase but no variation of DO is tested.
The paper states 'The required dissolved oxygen in the cathode container was provided in the range of 2–3 mg/L through an air injection pump' but does not explore whether lower DO (e.g., 1 mg/L) reduces N₂O or higher DO (e.g., 4–5 mg/L) improves nitrification.
Try. Vary aerobic-phase DO from 1 to 5 mg/L at COD 10,000 mg/L, NH₄⁺-N 50 mg/L; measure nitrification rate, nitrite accumulation, and N₂O yield.
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Abstract
Abstract Bioelectrochemical systems (BES) is a new and expanding technology that can simultaneously convert chemical energy into electrical energy by removing nutrients. The present study investigated the BES in removing nitrogen compounds and produce electricity. To this end, a BES reactor with two chambers of cathode and anode and nafion 117 membrane was used as a separator between the two chambers. Then, the BES performance at different concentrations of COD and primary ammonium at different retention times was investigated to remove nitrogen compounds and organic matter. Voltage, current and power density were measured. The results showed that the maximum COD removal efficiency was 73.2 % for the substrate concentration of 2000 mg/L, which decreased to 72.6 % when the substrate concentration increased to 10000 mg/L. The maximum removal efficiency of nitrogen compounds was 83.4 % at COD 10000 mg/L and the initial ammonium concentration was 50 mg/L. The maximum voltage, current and power density in this phase were 391 mV, 460 mA/m 2 , 63/48 mW/m 2 , respectively. The results of the study showed that BES can be used as a suitable method to remove high amounts of ammonium in wastewater and organic materials and simultaneously produce electricity.
Keywords
Identifiers
- Journal
- ChemElectroChem
- Year
- 2024
No 3D model is mapped to this paper yet. Parameter ranges above still place reported values on the literature distribution.