Physicochemical Characterisation of Used Engine Oils from Mechanic Workshops in Enugu, South East Nigeria

Used engine oil represents a hazardous waste category that is frequently discarded indiscriminately on soils or drains in mechanic workshops across Nigerian cities, contributing to persistent soil and water contamination that demands systematic characterisation. This study performs physicochemical characterisation of used engine oil samples collected from ten mechanic workshops in Enugu, South East Nigeria. Parameters determined include density, viscosity at 40 and 100 degrees Celsius, flash point, pour point, total acid number, water content, ash content, total base number, and concentrations of trace metals including iron, copper, lead, zinc, barium, and phosphorus using inductively coupled plasma optical emission spectrometry. The degree of oil degradation is assessed by comparing measured parameters against virgin engine oil specifications and identifying metal accumulation patterns indicative of engine component wear. The study also documents oil disposal practices through structured interviews with workshop owners and quantifies volumes discarded monthly to estimate environmental loading in the study area. Results are expected to demonstrate significant increases in metal concentrations and total acid number relative to fresh oil, confirming advanced degradation. Findings provide a technical basis for used oil regeneration feasibility assessments and support advocacy for formalised used oil collection and recycling programmes in the South East zone. Keywords: used engine oil, physicochemical characterisation, trace metals, Enugu, waste oil management