Energy and Environmental Performance of Biodiesel Derived From Waste Vegetable and Animal Oils: Integrated Energy Balance, Process Optimization, and Feasibility Assessment

Abstract

This study quantifies the full energy and environmental performance of biodiesel produced from waste vegetable and animal oils (WVO/WAO) using a rigorously defined system boundary that covers feedstock collection and transport to the processing site, pre-treatment, transesterification, phase separation, and washing/drying up to the plant gate. A transparent energy accounting framework was developed to apportion primary energy inputs associated with methanol consumption, transport diesel, electricity, and catalyst use, while explicitly propagating ±5% measurement uncertainty into the net energy ratio (NER). Experiments and reconciled calculations based on representative 75-gal feedstock batches produced approximately 70–75 gal of specification-compliant biodiesel (ASTM/EN), with glycerin co-product credits treated conservatively. The representative batch yielded a Net Energy Ratio (NER) of 7.67, while sensitivity and optimization scenarios indicate that NER can approach approximately 7.8–8.2 (median ≈8.0), confirming a strong positive energy return that exceeds typical values reported for biodiesel derived from virgin vegetable oils and remains substantially higher than fossil diesel benchmarks.