ISSN print edition: 0366-6352 ISSN electronic edition: 1336-9075 Registr. No.: MK SR 9/7 Published monthly

Resource recovery from the supernatant of recycled sludge discharge in high-turbidity river water treatment plants

Xiaosan Song, Wenjing Sun, Qingchao Shen, Peiqiang Liu, and Hairong Yan

Key Laboratory of Yellow River Water Environment in Gansu Province, Lanzhou Jiaotong University, Lanzhou, China

E-mail: songxs@mail.lzjtu.cn

Received: 20 May 2025  Accepted: 19 January 2026

Abstract:

The direct discharge of sludge water from water purification plants in recent years has led to serious environmental pollution and considerable waste of recoverable resources. This study investigates the resource-oriented reuse of the supernatant derived from sludge discharge water in high-turbidity river water treatment plants. Single-factor experiments combined with an orthogonal experimental design were conducted to systematically evaluate the effects of coagulant dosage, reflux ratio, and supernatant turbidity on coagulation performance, thereby identifying optimal reuse conditions. Under the determined optimal parameters (PAC dosage of 4 mg/L, reflux ratio of 2%, and turbidity of 67.5 NTU), key water quality indicators, including effluent turbidity, chroma, ammonia nitrogen, and total phosphorus, were analyzed to assess the safety of sludge water reuse. The results indicate that reuse of sludge water markedly improves coagulation efficiency, with turbidity and chroma removal rates increasing by 5.53% and 10.48%, respectively. Following reuse, the permanganate index satisfied the relevant standards, while concentrations of manganese and arsenic showed slight increases but remained well below the limits specified in drinking water quality standards. Moreover, under appropriate reuse conditions, turbidity as well as aluminum and iron concentrations in the settled water all met effluent water quality requirements. Finally, the mechanisms underlying the enhanced coagulation performance were elucidated through analyses of zeta potential, floc morphology, and particle size distribution. Overall, this study provides a scientific reference for the resource utilization of supernatant from sludge discharge water in high-turbidity river water treatment processes.

Graphical abstract

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Keywords: High-turbidity rivers; Water treatment plant; Sludge water; Supernatant reuse

Full paper is available at www.springerlink.com.

DOI: 10.1007/s11696-026-04686-9

Chemical Papers 80 (4) 4231–4248 (2026)