Hydrothermal liquefaction of sewage sludge for biofuel application: A review on fundamentals, current challenges and strategies
Yujie Fan, Ursel Hornung, Nicolaus Dahmen
Abstract
Scientific studies have demonstrated that hydrothermal liquefaction (HTL) can be suggested as a cost-effective and eco-friendly solution for the valorization of sewage sludge in the fields of waste management and renewable energy production. On-going efforts are continued extensively to improve conversion efficiency in order to transform this technology into industrial application. The present review focuses on state-of-the-art of HTL of sewage sludge, systematically, the HTL fundamentals, the influences of the essential operation parameters, main existing challenges and integrated upgrading are evaluated in detail. Opportunities and strategies including pre-treatment, co-liquefaction, post-application of aqueous and solid phases are addressed. Additionally, some available results regarding the continuous-flow tests of sewage sludge are summarized. Finally, further considerations and recommendations are made for improving or completing the economic feasibility of HTL process.