Environmental Risks and Sustainable Management Pathways for Used Lubricating Oils: A Structured Review with Conceptual Spill Risk Analysis

Used lubricating oils (ULOs) represent one of the largest hazardous liquid waste streams globally and pose significant environmental risks if improperly managed. This study presents a structured review of ULO management pathways, including regeneration, reprocessing, and energy recovery technologies, within a sustainability and circular economy framework. The review systematically categorizes treatment options based on recovery efficiency, waste generation, environmental performance, and technical feasibility. To contextualize environmental risk, a conceptual numerical spill dispersion analysis using the SIMOIL model is included as an illustrative case study under simplified marine conditions. The simulation highlights the rapid dispersion potential of ULOs in coastal environments, reinforcing the need for preventive management strategies. The analysis indicates that refining technologies generally offer higher material circularity potential, while thermochemical processes provide viable alternatives for heavily contaminated oils. The study identifies critical gaps in technoeconomic comparability, regulatory harmonization, and source segregation practices. Strengthening integrated management systems is essential to minimize environmental impact and enhance resource recovery.