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

Sequential bio–photocatalytic system for efficient dye degradation using cost-effective photocatalyst: performance, optimization, and circular economy assessment

V. Kant, S. Prabhudesai, J. Panchal, K. Reddy, K. Y. A. H. Alkhoori, S. Vincent, S. Mutnuri, and B. G. P. Kumar

Department of Chemical Engineering, Birla Institute of Technology and Science, Dubai International Academic City, Dubai, United Arab Emirates

E-mail: vincent@dubai.bits-pilani.ac.in

Received: 8 December 2025  Accepted: 4 May 2026

Abstract:

Textile dye-contaminated wastewater contains high colour intensity and refractory organic pollutants, which are difficult to degrade using conventional processes alone. This study presents, for the first time, a sequential Moving Bed Biofilm Reactor (MBBR)-photocatalysis system using Medical Waste Fly Ash (MWFA) as a standalone photocatalyst for the degradation of Sunfix Red dye in municipal wastewater. Real wastewater was spiked with 100 ppm dye to stimulate realistic effluent conditions. The MBBR achieved ~ 75% COD removal and considerable initial colour reduction, improving the biodegradability and reducing the load on the photocatalytic stage. Subsequent MWFA-based photocatalysis achieved 99.26% colour removal and 95.2% COD removal, demonstrating strong synergy between biological pretreatment and advanced oxidation. Process optimization using Response Surface Methodology (RSM) identified the most influential variables, enabling maximized dye degradation with ultra-low-cost operation at 0.09 g L⁻¹. Material was Characterized by XRD, FESEM-EDS, UV-DRS, BET and XPS, confirming the presence of naturally occurring metal oxides in MWFA, enabling photocatalytic activity without doping. Circular economy analysis showed that at a loading of 1 kg of MWFA can treat 11.11 kL of wastewater, with a 94% lower cost compared to commercial TiO₂. This integrated and optimized system demonstrates a scalable, low-cost solution using a medical waste-derived photocatalyst, contributing to SDG-6 and SDG-12.

Graphical Abstract

Keywords: Wastewater treatment; Photocatalysis; Moving Bed Biofilm Reactor (MBBR); Circular economy; Medical waste fly ash; Waste reuse; Textile dye degradation

Full paper is available at www.springerlink.com.

DOI: 10.1007/s11696-026-05011-0

Chemical Papers 80 (9) 10365–10379 (2026)