ZnO-Functionalized Chitosan-Based Composite Hydrogel Beads for Fat, Oil, and Grease Mitigation in Sewer Systems

Abstract Effective mitigation of fat, oil, and grease (FOG) accumulation is essential for sustainable sewer management. Zinc oxide (ZnO)-functionalized chitosan hydrogel beads were fabricated via controlled alkaline gelation. Coordination between ZnO, amino, and hydroxyl groups of chitosan reinforced the polymer network, while poly(vinyl alcohol) (PVA) and polyvinylpyrrolidone (PVP) further enhanced structural stability and FOG sequestration. Among all materials, PVA-ZnO@chitosan demonstrated the most stable postexposure surface charge (+36.08 mV). Incorporation of ZnO and hydrophilic polymers significantly improved water uptake, with PVP-ZnO@chitosan exhibiting the highest swelling degree (249.39%), indicating enhanced diffusion pathways for the FOG interaction. Chitosan beads showed a low initial control efficiency and limited long-term stability. In contrast, ZnO-polymer composites demonstrated enhanced durability and sustained FOG control, achieving removal efficiencies of up to 55.84%. Solid fat content analysis demonstrated efficient FOG mitigation, with PVA-ZnO@chitosan achieving the highest reduction in the solid fat fraction (73.9%), followed by PVP-ZnO@chitosan (72.3%). Inductively coupled plasma mass spectrometry (ICP–MS) analysis further confirmed reduced calcium ion availability, with the Ca2+ concentration decreasing from 143.33 ppb in untreated FOG to 61.06 ppb after PVP-ZnO@chitosan treatment, thereby suppressing calcium soap formation. These results establish ZnO-polymer-chitosan hydrogel beads as robust and effective platforms for mitigating FOG accumulation, offering a scalable strategy for improving sewer system resilience and sustainability.