Status and prospect of oil recovery from oily sludge: A review

Abstract Oily sludge is a kind of solid emulsified waste produced by the petroleum industry. It is generally composed of water, crude oil, and solid particulate matter. Because it contains large amounts of cycloalkanes, benzene series, polycyclic aromatic hydrocarbons, and other toxic and harmful substances, it poses a substantial threat to human health and the surrounding environment; therefore, it must be treated to reduce its toxicity. However, a large component of oily sludge is crude oil, which has great recycling value. Therefore, various crude oil recovery technologies, such as solvent extraction, pyrolysis, centrifugation, ultrasonic treatment, electronal treatment, flotation, supercritical treatment, and combined processes, have been developed for the treatment of oily sludge. The main purpose of this review is to discuss the development of these recycling technologies and to summarize and compare their advantages, disadvantages, and mechanisms of action. On this basis, the future development direction of recycling technology is prospected.