Nanobubble-Assisted Coagulation–Flocculation–Flotation: Mechanistic Insights into PVC Micro/Nanoplastic Separation

The presence of polyvinyl chloride (PVC) micro/nanoplastics (MNPs) in water poses significant environmental and public health challenges, making their effective removal a pressing research problem. This study investigates the integration of air nanobubble pretreatment with conventional coagulation–flocculation–flotation as a strategy for PVC MNP remediation. The novelty of this study lies in validating nanobubbles as dual-function agents, serving simultaneously as chemical surface modifiers and physical flotation enhancers, within an integrated treatment process. Nanobubble exposure altered the physicochemical properties of PVC particles by reducing particle size, decreasing the magnitude of their negative zeta potential, and introducing oxygenated functional groups that enhanced surface reactivity and subsequent coagulation–flocculation. Among the tested coagulant/flocculant systems, polyaluminum chloride (PAC) combined with polyacrylamide (PAM) achieved the highest clarification efficiency, removing approximately 88–90% of turbidity. In comparison, Alum–PAM and ferric chloride (FeCl3)–PAM systems exhibited lower removal efficiencies of 72–75% and 68–70%, respectively, under the tested flotation conditions. Flotation further promoted separation through nanobubble–particle and bubble–floc interactions. Fourier-transform infrared spectroscopy (FTIR) confirmed surface oxidation and changes in the interfacial chemistry of the recovered PVC-containing flocs. According to the results, the integrated process effectively combines physicochemical surface modification, electrostatic destabilization, polymer-assisted aggregation, and bubble-assisted flotation, with PAC–PAM under nanobubble pretreatment emerging as the most efficient configuration. Future research should focus on scaling to pilot/full-scale systems, testing real wastewater matrices, and evaluating long-term stability and energy efficiency.