Hydrogenation of waste transformer oil (electrical insulating oils) can produce an oil product that is far better in quality and yield in comparison with fixed bed clay adsorption or reaction with sodium metal. This is proven at Sequoia- client’s facility in Midwestern USA. The 5 million gallon/year throughput naphthenic oil hydrotreater produces oil free of PCBs (polychlorobiphenyls – known carcinogens). The product oil has water-white appearance and low sulphur concentration. Sequoia designed the complete plant, supplied all processing equipment and also supplied a thermal oxidizer for safe disposal of process off-gases from the plant.