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Optimising load allocation and reduction strategies for sewage treatment plants in urban tropical rivers: Modelling with QUAL2K and GIS

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Abstract

The discharge of pollutant loads from sewage treatment plants (STPs) significantly impacts the quality of tropical rivers. The present study evaluates the impact of projected increases in population equivalent (PE) from STPs on the selected water quality parameters (WQP) of the Kuang River basin (KRB) under the influence of climate stress and advanced treatment. Using the QUAL2K model, discharge was simulated, and scenarios were based on population growth rate (PGR) for the next 10 years, with Low (2.1% PGR), Medium (2.2% PGR) and High (2.5% PGR). The findings indicate that elevated PE affects TSS, NH₃-N, and BOD₅ concentrations with a p-value < 0.05 between the seasons. Under high PGR scenarios in the dry season, concentrations for BOD₅ were 7.82 mg/L, 3.02 mg/L for NH₃-N, and 48 mg/L for TSS. This study suggests reducing pollution loads from STPs by 98.88% (35.59 and 7881.5 kg/day) for BOD₅, 99.44% for NH₃-N (7.16 and 1585.27 kg/day), and 83.93% for TSS (35.25 and 1303.08 kg/day) to meet class II. Additionally, the model’s performance was validated with flow calibration results showing R2 = 0.79-0.94 and NSE = 0.80-0.94. Therefore, this study projected the load allocation for WQP for all identified STPs for sustainable KRB management under future urban growth.

Data availability

The data presented in this article will be available on request. Additional other relevant data can be found in the supplementary files accompanying this publication.

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Acknowledgements

We wish to acknowledge the Ministry of Higher Education Malaysia under Fundamental Research Grant Scheme (FRGS/1/2022/WAB02/UPM/02/1), the Organization for Women in Science for the Developing World (OWSD) and Universiti Putra Malaysia for sponsoring this research. Additionally, we extend our thanks to Indah Water Konsortium and the PLAN Selangor authority for providing essential data for this study. .

Funding

This article was supported by the Ministry of Higher Education Malaysia under Fundamental Research Grant Scheme (FRGS/1/2022/WAB02/UPM/02/1), the Organization for Women in Science for the Developing World (OWSD), and Universiti Putra Malaysia (UPM).

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Authors and Affiliations

  1. Water Resources Laboratory, Department of Environment, Faculty of Forestry and Environment, Universiti Putra Malaysia, Seri Kembangan, Selangor, Malaysia

    Julieth Joseph Balilemwa, Nor Rohaizah Jamil, Noorain Mohd Isa & Syahida Sapia’e

  2. Department of Earth Science, Mbeya University of Science and Technology, Iyunga, P.O. Box 131, Mbeya, Tanzania

    Julieth Joseph Balilemwa

  3. Aquatic Ecosystem and Management Laboratory, International Institute of Aquaculture and Aquatic Sciences (I-AQUAS), Lot 960 Jln Kemang 6, Negeri Sembilan, Port Dickson, Seri Kembangan, 71050, Selangor, Malaysia

    Nor Rohaizah Jamil

  4. Centre for Water Research and Analysis, Faculty of Science and Technology, Universiti Kebangsaan Malaysia, Bangi, 43450, Selangor, Malaysia

    Zaki Zainudin

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  1. Julieth Joseph Balilemwa
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  2. Nor Rohaizah Jamil
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Contributions

Julieth Joseph Balilemwa: Writing – review & editing, Writing – original draft, Validation, Methodology, Investigation, Formal analysis, Data curation, Software, Visualisation, Conceptualization, Funding acquisition. Nor Rohaizah Jamil: Writing – review & editing, Writing – original draft, Supervision, Methodology, Formal analysis, Conceptualization, Project administration, Funding acquisition. Noorain Mohd Isa: Writing – review & editing, Supervision, Methodology, Data curation. Zaki Zainudin: Writing – review & editing, Visualization, Supervision, Methodology, Data curation, Software. Syahida Sapia’e: Writing – review & editing, Methodology, Data curation.

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Nor Rohaizah Jamil.

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Balilemwa, J.J., Jamil, N.R., Isa, N.M. et al. Optimising load allocation and reduction strategies for sewage treatment plants in urban tropical rivers: Modelling with QUAL2K and GIS.
Sci Rep (2026). https://doi.org/10.1038/s41598-026-46763-9

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  • DOI: https://doi.org/10.1038/s41598-026-46763-9

Keywords

  • TMDL
  • Point source
  • Urban growth
  • Climate change
  • Seasonal
  • Spatial analysis

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