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Efficacy and limitations of the A2O process in simultaneous removal of surfactants and nutrients from municipal wastewater

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Abstract

This study evaluated the efficacy of the Anaerobic-Anoxic-Oxic (A2O) process for the simultaneous removal of organic pollutants, specifically surfactants (detergents), and nutrients (nitrogen and phosphorus) from municipal wastewater. Sampling was conducted over a 12-month period from September 23, 2023 to September 22, 2024, at a monthly frequency. During each sampling event, grab samples were collected from multiple points within the treatment train: the raw influent wastewater, the influent and effluent streams of the anaerobic, anoxic, and aerobic tanks, and the final effluent from the secondary clarifier. The anionic surfactants (as methylene blue active substances, MBAS), ammonium-nitrogen (NH₄⁺-N), nitrate-nitrogen (NO₃⁻-N), nitrite-nitrogen (NO₂⁻-N), and total phosphorus (TP)—were quantified in accordance with Standard Methods for the Examination of Water and Wastewater. The mean final effluent concentrations were 0.22 ± 0.05 mg/L for linear alkylbenzene sulfonate (LAS), 13.18 ± 3.7 mg/L for nitrate (as NO₃-N), and 4.46 ± 0.18 mg/L for phosphorus (as P). Process performance data indicated that the oxic tank was the primary site for LAS and phosphorus removal, while the anoxic tank facilitated the most significant nitrate reduction. While the Anaerobic-Anoxic-Oxic (A2O) process proficiently removes surfactants and phosphorus via microbial metabolism, its performance in nitrate elimination is constrained. Inadequate denitrification in the anoxic stage, frequently due to a limited biodegradable carbon source or improper redox conditions, indicates a need for process optimization.

Data availability

The datasets used and/or analyzed during the current study are available from the corresponding author on reasonable request.

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Acknowledgements

The authors thank Shahid Sadoughi University of Medical Sciences.

Funding

No funding was received for this manuscript.

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Authors and Affiliations

  1. Student Research Committee, School of Public Health, Shahid Sadoughi University of Medical Sciences, Yazd, Iran

    Tahereh zarei Mahmoudabadi & Amir Hossein Bagheri

  2. Environmental Sciences and Technology Research Center, Department of Environmental Health Engineering, School of Public Health, Shahid Sadoughi University of Medical Sciences, Yazd, Iran

    Tahereh zarei Mahmoudabadi, Fahimeh Teimouri & Amir Hossein Bagheri

  3. Center for Healthcare Data Modeling, Department of Biostatistics and Epidemiology, School of Public Health, Shahid Sadoughi University of Medical Sciences, Yazd, Iran

    Sara Jambarsang

Authors

  1. Tahereh zarei Mahmoudabadi
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  2. Fahimeh Teimouri
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Contributions

Fahimeh Teimouri and Tahereh Zarei Mahmoudabadi designed the study. Sampling and experiments were performed by Tahereh Zarei Mahmoudabadi and Amir Hossein Bagheri. Data analysis was conducted by Sara Jambarsang, and data interpretation was performed by Fahimeh Teimouri. The first draft of the manuscript was written by Tahereh Zarei Mahmoudabadi, and the finalization of the manuscript was carried out by Fahimeh Teimouri. Supervision was the responsibility of Fahimeh Teimouri. These are the authors’ roles.

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Fahimeh Teimouri.

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zarei Mahmoudabadi, T., Teimouri, F., Bagheri, A.H. et al. Efficacy and limitations of the A2O process in simultaneous removal of surfactants and nutrients from municipal wastewater.
Sci Rep (2026). https://doi.org/10.1038/s41598-026-45194-w

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  • DOI: https://doi.org/10.1038/s41598-026-45194-w

Keywords

  • Wastewater treatment
  • Nutrients
  • Surfactants
  • Biological process

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