## 6 Sustainability and Economic Viability of Waste Cooking Oil Valorization
### Challenges Associated with Waste Cooking Oil Vaporization and Future Direction  
Despite the clear environmental and economic advantages of waste cooking oil vaporization, it still faces some challenges hindering its widespread implementation and industrial scalability, which are stated as follows:  
1. Supply chain constraints. One of the most critical issues is the inconsistency in WCO supply. The lack of a well-established and organized collection infrastructure often results in significant quantities of WCO being improperly discarded. In many regions, over half of the used cooking oil is released into sewage systems, leading not only to environmental pollution but also to the loss of valuable raw materials that could otherwise be repurposed. Establishing robust collection networks involving households, restaurants, and food processing industries is essential for ensuring a steady and reliable feedstock supply for industrial applications. 2. Variability in oil properties. WCO quality varies depending on the source (households, restaurants, industries), frying duration, and type of food cooked. WCO is therefore highly heterogeneous, with its physicochemical properties varying widely depending on the type of oil used, the cooking duration, the temperature, and the nature of the food materials fried. Contaminants include water, food particles, polymers (from repeated heating), and heavy metals, which affect processing and catalyst performance. This variability can significantly influence the efficiency and outcome of conversion processes such as transesterification. Therefore, preliminary laboratory assessments of each collected WCO batch are necessary to determine key parameters such as acidity, moisture content, and fatty acid composition. 3. Cost of Collection, Transportation, and Processing  
The economic viability of WCO valorization depends not only on the low cost of the raw material but also on the logistics associated with its collection, storage, and transport. In decentralized collection systems, the cost per liter of collected WCO can increase substantially, especially in remote areas. Thus, techno-economic analysis is critical to identify cost bottlenecks and optimize the overall process, particularly when aiming for applications in high-performance sectors such as transformer insulation. 4. Carbon Emissions During the Conversion Process  
While WCO valorization is generally considered environmentally beneficial, the conversion process, especially transesterification, can be a significant source of carbon emissions. Studies have shown that this stage alone accounts for a substantial proportion of the total carbon footprint of the entire process. According to Refs. [179; 180], the transesterification stage can be responsible for approximately 68% to 75% of the total carbon emissions during WCO processing. This indicates the need for greener processing technologies. One promising alternative is the supercritical methanol process, which has been reported to produce fewer GHG emissions compared to conventional alkali-catalyzed methods [181; 182]. Although this method requires higher energy inputs, it eliminates the need for catalysts and simplifies post-reaction purification, which can offset its energy demands and reduce overall environmental impacts. 5. Research and Development Needs  
Ongoing research is essential to improve the environmental performance and scalability of WCO valorization technologies. This includes developing low-energy, low-emissionprocessing methods, refining supply chain logistics, and exploring catalytic systems that enhance conversion efficiency while minimizing waste and emissions. Life cycle assessment (LCA) and techno-economic analysis (TEA) should be applied in tandem to identify optimization opportunities across the value chain and guide policy interventions that promote the use of WCO as a mainstream industrial feedstock.