Assessment of Small-Settlement Wastewater Discharges on the Irtysh River Using Tracer-Based Mixing Diagnostics and Regularized Predictive Models

Anapyanova, Samal; Kolpakova, Valentina; Kulisz, Monika; Nabiollina, Madina; Yeremeyeva, Yuliya; Nurbayeva, Nailya; Sherov, Anvar

doi:10.3390/w18020232

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Assessment of Small-Settlement Wastewater Discharges on the Irtysh River Using Tracer-Based Mixing Diagnostics and Regularized Predictive Models

by

Samal Anapyanova

^1,2

,

Valentina Kolpakova

²,

Monika Kulisz

^3,*

,

Madina Nabiollina

¹,

Yuliya Yeremeyeva

^2,*

,

Nailya Nurbayeva

⁴ and

Anvar Sherov

⁵

¹

Department of Water Resources and Melioration, Faculty of Water Resources and Information Technology, Non-Profit Joint Stock Company Kazakh National Agrarian Research University, Almaty 050010, Kazakhstan

²

Center for Competence and Technology Transfer in Water Management and Water Use, School of Architecture, Construction and Energy, Non-Profit Joint Stock Company “D. Serikbayev East Kazakhstan Technical University”, Ust-Kamenogorsk 070004, Kazakhstan

³

Department of Organization of Enterprise, Faculty of Management, Lublin University of Technology, 20-618 Lublin, Poland

⁴

Department of Ecology, Institute of Forestry and Environment, Non-Profit Joint Stock Company “S. Seifullin Kazakh Agro Technical Research University”, Astana 010011, Kazakhstan

⁵

Department of Use of Hydromelioration Systems, Faculty of Hydromelioration, Tashkent Institute of Irrigation and Agricultural Mechanization Engineers, National Research University, Tashkent 100000, Uzbekistan

^*

Authors to whom correspondence should be addressed.

Water 2026, 18(2), 232; https://doi.org/10.3390/w18020232

Submission received: 18 November 2025 / Revised: 22 December 2025 / Accepted: 9 January 2026 / Published: 15 January 2026

(This article belongs to the Special Issue Eco-Engineered Solutions for Industrial Wastewater)

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Abstract

An integrated field–analytical framework was applied to quantify the impact of two small-settlement treatment facilities (TF1 and TF2) on the Irtysh River (East Kazakhstan). The main objective of this study is to quantify effluent-driven dilution and non-conservative changes in key water-quality indicators downstream of TF1 and TF2 and to evaluate parsimonious models for predicting effluent-outlet BOD and COD from upstream measurements. Paired upstream–downstream control sections are sampled in 2024–2025 for 22 indicators, and plant influent–effluent records are compiled for key wastewater variables. Chloride-based conservative mixing indicated very strong dilution (approximately D ≈ 2.0 × 10³ for TF1 and D ≈ 4.2 × 10² for TF2). Deviations from the mixing line were summarized using a transformation diagnostic θ. At TF1, several constituents exceeded mixing expectations (θ ≈ 13 for COD, θ ≈ 42 for ammonium, and θ ≈ 6 for phosphates), while nitrate shows net attenuation θ < 0. At TF2, θ values cluster near unity, indicating modest deviations. Under a small-sample regime (N = 10) and leave-one-out validation, regularized regression provided accurate forecasts of effluent-outlet BOD and COD. Lasso under LOOCV performed best (BOD_after: RMSE = 0.626, MAE = 0.459, and R² = 0.976; COD_after: RMSE = 0.795, MAE = 0.634, and R² = 0.997). The results reconcile strong reach-scale dilution with constituent-specific local departures and support targeted modernization and operational forecasting for water-quality management in small facilities.

Keywords: Irtysh river; anthropogenic load; water quality; domestic wastewater; small sewage treatment facilities

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MDPI and ACS Style

Anapyanova, S.; Kolpakova, V.; Kulisz, M.; Nabiollina, M.; Yeremeyeva, Y.; Nurbayeva, N.; Sherov, A. Assessment of Small-Settlement Wastewater Discharges on the Irtysh River Using Tracer-Based Mixing Diagnostics and Regularized Predictive Models. Water 2026, 18, 232. https://doi.org/10.3390/w18020232

AMA Style

Anapyanova S, Kolpakova V, Kulisz M, Nabiollina M, Yeremeyeva Y, Nurbayeva N, Sherov A. Assessment of Small-Settlement Wastewater Discharges on the Irtysh River Using Tracer-Based Mixing Diagnostics and Regularized Predictive Models. Water. 2026; 18(2):232. https://doi.org/10.3390/w18020232

Chicago/Turabian Style

Anapyanova, Samal, Valentina Kolpakova, Monika Kulisz, Madina Nabiollina, Yuliya Yeremeyeva, Nailya Nurbayeva, and Anvar Sherov. 2026. "Assessment of Small-Settlement Wastewater Discharges on the Irtysh River Using Tracer-Based Mixing Diagnostics and Regularized Predictive Models" Water 18, no. 2: 232. https://doi.org/10.3390/w18020232

APA Style

Anapyanova, S., Kolpakova, V., Kulisz, M., Nabiollina, M., Yeremeyeva, Y., Nurbayeva, N., & Sherov, A. (2026). Assessment of Small-Settlement Wastewater Discharges on the Irtysh River Using Tracer-Based Mixing Diagnostics and Regularized Predictive Models. Water, 18(2), 232. https://doi.org/10.3390/w18020232

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Assessment of Small-Settlement Wastewater Discharges on the Irtysh River Using Tracer-Based Mixing Diagnostics and Regularized Predictive Models

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