Greener approach for microplastics detection in wastewater sludge using multimodal spectroscopic techniques

Primary wastewater sludge from a municipal wastewater treatment facility in Toronto, Canada, was subjected to analysis (10 mL; n = 3 non-independent replicates) using an environmentally friendly analytical workflow. This workflow integrated Ferro-sonication (Fe-UlS), recyclable ZnCl₂ density separation (1.90 g/mL), and multimodal Laser Direct Infrared (LDIR) spectroscopy/Optical Photothermal Infrared (O-PTIR) spectroscopy. The Fe-UlS method achieved a reduction of up to 98% in total suspended solids within 30 min. The reuse of ZnCl₂ over five cycles resulted in a density decrease from 1.90 to 1.59 g/mL, with recovery efficiency declining from 100% to 89% due to Polytetrafluoroethylene (PTFE) loss below its buoyancy threshold. LDIR detected 316 particles (10-500 μm; Limit Of Detection (LOD) 14.2 μm), predominantly composed of polyurethane (56%), while O-PTIR identified high-density PTFE and Polycarbonate (PC) down to 6.4 μm. The limit of detection was 60 particlesL^-1. This integrated workflow reduced reagent consumption and processing time compared to conventional 12-24 h digestion protocols, thereby demonstrating enhanced eco-efficiency while maintaining analytical robustness.