<p>This study explores the development of high-performance membranes derived from recycled polyethylene terephthalate (rPET) for oil–water emulsion separation, addressing the limitations of existing PET-based membranes, which often suffer from poor fouling resistance, low stability, and limited scalability issues. Using a Simplex Lattice Design (SLD), Zinc Oxide (ZnO) nanoparticles and hydrophilic additives were systematically blended into the rPET matrix, producing an optimized membrane that achieved superior oil rejection (&gt; 99.2%) and consistent flux (5.52 L·m⁻²·h⁻¹) across various emulsions owing to its refined pore structure and improved surface uniformity. Further surface modification with polydopamine (PDA) significantly enhanced the water flux and antifouling performance, with the PDA-modified membrane demonstrating a 93% flux recovery ratio and the lowest irreversible resistance (7%). Statistical model validation confirmed the robustness of the design, with mean percentage errors of 0.27% for the flux and 0.65% for the rejection. Benchmark comparisons showed that the dual-modified rPET membranes outperformed other membranes in terms of rejection efficiency and oil loading. Beyond technical improvements, the reproducibility of the fabrication parameters supports scalability, while the use of post-consumer PET provides environmental and economic relevance. These results establish the novelty and significance of integrating SLD optimization with ZnO and PDA dual modification to develop sustainable and scalable membranes for oily wastewater treatment.</p>