MESSAI.iO

AI summary

72% confidence

This study integrated a vertical subsurface-flow constructed wetland (VSF-CW) with a microbial fuel cell (MFC) to treat ammonia-rich domestic wastewater at high organic loading (4.2 mg COD/h·L, COD:N = 10:1). Over 28 days of acclimation, planted systems at pH 7.0 achieved 43.4% NH4+ removal and 79% COD removal, with ~60% of ammonia oxidation occurring in the anode chamber. Nitrite accumulated slightly (max <0.25 mg/L) and nitrate remained below detection, indicating predominantly anaerobic conditions. Coulombic efficiency peaked at only 0.16% and power density remained low, suggesting the microbial electrochemical community was still developing.

Key insights

  • Mechanism Approximately 60% of NH4+ removal occurred in the anode chamber versus cathode, indicating the anaerobic anode is the primary site for ammonia oxidation in this coupled system.

    So what. Design anode chambers with sufficient residence time and surface area for electrochemically-active ammonia-oxidizing bacteria; do not rely on the cathode for primary nitrogen removal in this configuration.

  • Threshold Influent pH 7.0 yielded 43.4% NH4+ removal in planted systems, significantly better than pH 6.0 (31.8%) and pH 8.0 (28.5%), establishing a narrow optimal operating window.

    So what. Maintain influent pH at 7.0 ± 0.2 for optimal ammonia removal; pH drift above or below this window reduces performance by ~30%.

  • Trade-off Nitrite concentration dropped >80% across the anode chamber but then increased at the cathode and outlet, especially at pH 7.0, suggesting nitrification in the aerobic surface layer counteracts anammox in the anode.

    So what. Expect nitrite accumulation at the outlet; if N2O or NO3− formation is a concern, suppress cathode-zone nitrification by reducing surface aeration or increasing HRT in the upper layer.

  • Performance Coulombic efficiency remained very low (max 0.16%) after 28 days, and power density was still rising, indicating the electrochemically-active microbial community had not reached steady state.

    So what. Plan for acclimation periods of several months, not weeks; consider pre-inoculation with electrochemically-active sludge or lower external resistance to accelerate biofilm development.

  • Mechanism COD removal (72–81%) was independent of pH and plant presence, but >60% occurred in the anode chamber, showing that organic oxidation is decoupled from nitrogen removal pathways.

    So what. To improve power recovery, increase COD:N ratio above 10:1 or supplement with additional carbon source; nitrogen removal does not require high COD oxidation in the anode.

Opportunity areas6

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

  • High No N2O or N2 measurements reported; anammox pathway is inferred but not confirmed. Nitrogen balance incomplete.

    Text states 'Môi trường yếm khí trong các buồng anode có khả năng xúc tiến quá trình oxy hóa NH4+ bởi NO2− với vai trò xúc tác của vi khuẩn anammox giải phóng N2' but provides no gas chromatography or isotope data.

    Try. Measure N2 and N2O in headspace or via 15N-labeled NH4+ tracer; quantify nitrogen balance to close the gap between inlet NH4+ and outlet NH4+ + NO2− + NO3−.

  • High Coulombic efficiency and power density remain very low after 28 days; acclimation period may be insufficient or external resistance (50 Ω) may be suboptimal.

    Text: 'Hiệu suất coulomb (CE) cao nhất đạt 0,16%... Thời gian thích nghi của các hệ thống MFC thông thường có thể kéo dài trong vài tháng' and authors suggest lower external resistance as a strategy.

    Try. Test external resistance range 10–500 Ω and extend acclimation to 60–90 days; measure power density and CE as functions of resistance and time.

  • Medium COD:N ratio fixed at 10:1; no exploration of higher ratios to improve power recovery while maintaining nitrogen removal.

    Text: 'Nhu cầu tiêu thụ COD cao của vi sinh ở buồng anode cho thấy hiệu suất thu hồi điện sinh học của hệ thống có thể được cải thiện với nước thải có tỷ lệ COD:N cao hơn.'

    Try. Test COD:N = 15:1, 20:1, 25:1 at same loading rate; measure power density, CE, and NH4+ removal to find the trade-off.

  • Medium HRT not explicitly varied; only one flow rate (3–4 mL/min) tested. Residence time effect on nitrogen removal pathways unknown.

    Methods state 'lưu lượng cố định ở mức 3 - 4 mL/phút' but do not report actual HRT or test its effect on nitrification vs. anammox balance.

    Try. Test HRT 4, 8, 12, 24 h by varying flow rate; measure NH4+, NO2−, NO3− profiles and power output to identify optimal residence time for each pathway.

  • Medium Dissolved oxygen profile not measured; aerobic/anaerobic boundary location and dynamics unknown.

    System design includes surface water layer and plant roots (oxygen transport) but no DO measurements reported; nitrification location inferred only from outlet NO2− increase.

    Try. Profile dissolved oxygen vertically at 5 cm intervals using microelectrodes; correlate with nitrification and anammox rates at each depth.

  • Low Single plant species (Cenchrus setaceus) tested; generalizability to other wetland plants and their oxygen release rates unknown.

    Text: 'Cỏ hồng (Cenchrus setaceus) được chọn làm thực vật trồng' but no comparison with other species or quantification of oxygen release.

    Try. Compare 2–3 plant species with different radial oxygen loss rates; measure oxygen profiles and nitrogen removal efficiency.

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What they did

System
MFC

What worked

Coulombic efficiency0.16%
COD removal79.0%best of 2

Abstract

Global challenges on water and energy crisis have pressurized on water treatment industry to put into practice advanced technologies for ensuring a suitable supply of either water or energy services. Compared with other biological treatment technologies, constructed wetland (CW) is widely considered as an efficient eco-technology for wastewater treatment with the advantages of low cost, simple operation and maintenance. Microbial fuel cell (MFC) technology is the recently emerging approach in environmental engineering. The integration of MFCs within vertical up-flow CW systems (VSF-CW) as a sustainable technology, therefore, could provide dual benefits in nitrogen removal of wastewaters and energy recovery simultaneously. This study has preliminarily evaluated the acclimation performance of VSF-CW-MFC systems at the high loading rate (4.2 mg COD/h.L; COD:N = 10:1) of domestic wastewaters containing ammonia. Results demonstrated the potential of VSF-CW-MFC systems in achieving electricity generation and ammonia removal of domestic wastewaters at the high loading rate. The plant presence and influent pH of 7.0 could improve the performance efficiency. Average removal efficiencies of NH4+ and COD in planted microcosms with the influent pH of 7.0 were 43.4% and 79%, respectively.

Keywords

Microbial fuel cellWastewaterSewage treatmentConstructed wetlandWetlandAcclimatization

Identifiers

DOI
10.32508/stdjet.v4isi1.909
Journal
Science & Technology Development Journal - Engineering and Technology
Year
2021
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Extraction

Reported parameters

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