Waste cooking oil to sustainable aviation fuel: A review of pretreatment technologies

Abstract

The valorization of waste cooking oil (WCO) into sustainable aviation fuel (SAF) represents an important strategy for reducing the carbon footprint of the aviation sector. However, raw WCO is highly heterogeneous, containing triglycerides and diverse impurities (e.g., suspended solids, phospholipids, free fatty acids, metals, and oxidation products) that can severely compromise the activity, stability, and longevity of hydrotreatment catalysts. While effective, conventional WCO pretreatment operations suffer from drawbacks such as high energy and chemical consumption, substantial wastewater generation, spent adsorbent disposal issues, and neutral oil loss, underscoring the need for eco-friendly, energy-efficient WCO pretreatment systems. This review examines the sources, collection, and recovery of WCO, its compositional characteristics, and key physicochemical properties relevant to SAF production. We critically summarize recent advances in WCO pretreatment technologies, emphasizing impurity removal mechanisms, process performance, operational limitations, and engineering applicability. Furthermore, we highlight the potential of emerging approaches, including membrane separation, enzymatic degumming, advanced adsorbent-based treatment, and coalescence separation, to overcome the limitations of traditional processes. Where direct WCO-specific evidence remains limited, selected studies on related lipid systems are considered only to provide transferable mechanistic and technological insights. Finally, we outline the primary technical challenges and future perspectives for developing green WCO pretreatment systems. This review provides a focused framework into WCO feedstock upgrading, supporting the development of sustainable, scalable SAF production pathways.