Comparative performance of ZnO-functionalized SiC membranes and polymeric membranes for oil-in-water emulsion filtration

This study evaluates the performance of ZnO-functionalized SiC and polymeric membranes for the filtration of a surfactant-stabilized oil-in-water emulsion (soybean oil, 1 g/L; SDS, 2 mM), focusing on permeance, turbidity-based oil rejection, fouling behavior, and regeneration potential. Dead-end filtration experiments were conducted using membranes with different pore sizes and surface properties under membrane-specific transmembrane pressures (0.10-0.75 bar). Separation efficiency was determined from turbidity measurements, and chemical cleaning with an alkaline solution was applied to assess the ceramic membranes' regeneration. A clear trade-off between permeance and separation efficiency was observed. Polymeric membranes exhibited higher initial permeance, reaching up to 603.56 L/h.m².bar for PVDF 0.2 µm, whereas ceramic membranes showed lower initial permeance (P0 ≈ 18-26 L/h.m².bar), and two samples exhibited low end-of-run permeance (P180 ≈ 0.27-0.54 L/h.m².bar). Nevertheless, most membranes achieved high turbidity-based oil rejection efficiencies (>95%), except hydrophobic PTFE (1 µm) and two membranes that showed lower rejection under the tested conditions (SiC‑ZO1 and PES 10 kDa). Separation performance was governed by membrane wettability, with hydrophilic membranes promoting water transport and turbidity-based oil rejection, while hydrophobic PTFE membranes at 1 µm showed reduced efficiency (as low as 22%). Alkaline vacuum-assisted cleaning restored SiC performance and enabled recovery from a severely blocked state (P180 as low as 0.27 L/h.m².bar), recovered up to 73.3 L/h.m².bar while maintaining ~99% rejection. Although polymeric membranes provided higher short-term permeance, the ZnO-functionalized SiC membranes combined high turbidity-based rejection, operational stability, and strong post-cleaning recovery, supporting their potential for oily wastewater treatment where durability and aggressive regeneration are required.