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Sustainable – Low-Cost - Upgrade of Activated Sludge Process for Nitrogen and Phosphorus (N&P) Removal from Wastewater
Many municipal wastewater treatment plants (WWTPs) in developing countries were designed primarily for organic matter and suspended solids removal and therefore face increasing difficulty in meeting modern nitrogen (N) and phosphorus (P) discharge requirements. Conventional biological nutrient remov...
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AUC Knowledge Fountain
2026
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| Summary: | Many municipal wastewater treatment plants (WWTPs) in developing countries were designed primarily for organic matter and suspended solids removal and therefore face increasing difficulty in meeting modern nitrogen (N) and phosphorus (P) discharge requirements. Conventional biological nutrient removal upgrades commonly require additional reactor volume, recirculation systems, aeration energy, and capital investment. Accordingly, sustainable retrofit strategies that improve nutrient removal within existing treatment footprints are increasingly needed, particularly in water-scarce and land-constrained regions.
This study investigated the integration of water hyacinth (Eichhornia crassipes) into the aeration stage of an activated sludge process as a hybrid nature-based enhancement for nitrogen and phosphorus removal. A pilot-scale activated sludge system was operated at Madinaty Wastewater Treatment Plant (MWWTP), Egypt. Two parallel lines were evaluated under identical hydraulic and operational conditions: a conventional activated sludge control line and a plant-integrated line incorporating water hyacinth within the aeration tank. Six experimental runs were conducted using real municipal wastewater, and performance was assessed through total nitrogen (TN), ammonia (NH₃), nitrite (NO₂⁻), nitrate (NO₃⁻), total Kjeldahl nitrogen (TKN), organic nitrogen (ON), and total phosphorus (TP).
The plant-integrated system achieved stronger nutrient removal than the conventional activated sludge control line. Average final TN decreased from 20.49 mg/L in the control to 13.15 mg/L in the plant-integrated line, increasing TN removal efficiency from 57.7% in the control to 72.8% in the plant-integrated line. Ammonia also decreased from 4.75 mg/L in control to 2.93 mg/L in plant, while TKN showed a more pronounced reduction from 13.33 mg/L in control to 2.77 mg/L in plant, indicating improved removal of reduced nitrogen forms. Nitrogen transformation analysis suggested enhanced apparent ammonia oxidation, reduced-nitrogen removal, and oxidized nitrogen formation in the plant-integrated reactor, likely due to root-associated biofilms, plant uptake, biomass assimilation, and improved solids capture. TP removal improved moderately from 23.6% in control to 29.4% in plant, reflecting limited but positive phosphorus uptake and particulate phosphorus retention. Ammonia volatilization was recognized as a possible secondary pathway but was not quantified because pH, temperature, airflow-specific stripping, and gaseous NH₃ emissions were not measured.
The plant-associated differential removal capacity was estimated at 0.425 g NH₃-N, 2.47 g TKNN, and 1.71 g TN per kg wet water hyacinth per day. Full-scale extrapolation for a 50,000 m³/day WWTP indicated that achieving equivalent TKN performance by conventional expansion would require approximately 2,677 m³ of additional aerobic volume, 1.57 million kWh/year of extra aeration energy, and 17.8 million EGP of avoided CAPEX, while maintaining the four-hour aeration hydraulic retention time and avoiding major process modification in the pilot configuration. Overall, water hyacinth integration offers a practical, low-cost, and sustainable retrofit strategy for upgrading existing WWTPs. |
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