Tackling microplastics and their ecological risks in industrial wastewater: Evaluation of the removal efficiency of continuous-flow activated sludge and sequencing batch reactors

Abstract

Microplastics (MPs) are recognized as emerging contaminants in wastewater due to their persistence and ecological risks. This study assessed the abundance, morphology, polymer composition, removal efficiency, and ecological risk of MPs in the industrial wastewater treatment plant which operates Continuous-Flow Activated Sludge (CFAS) and Sequencing Batch Reactor (SBR) systems. Sampling spots over winter season included influent, grit chamber, chemical removal, anaerobic tanks, effluent, and sand filtration. MPs were extracted using Fe(II)/H2O2 digestion and ZnCl2 density separation, quantified by stereomicroscopy, and characterized via micro-Raman spectroscopy. Influent MPs ranged from 237.5 to 455 MPs/L, mostly fibers (up to 65) from textile and packaging sources. Removal efficiencies of CFAS and SBR were 72-88 and 86-96, respectively, with SBR showing superior fragment removal. Polyethylene, polypropylene, and polystyrene dominated (>80). Ecological risk assessment indicated moderate to considerable risks, with PLI >1, PHI medium to high, and ERI exceeding 1200 in some months. Given that treated effluents are reused for irrigation, residual MPs may threaten ecosystems and human health. Findings highlight the need for improved treatment technologies and stricter management to reduce MP release from industrial wastewater.