Gasification of Sewage Sludge—A Review

The increasing amount of sewage sludge produced demands new methods of its management to minimize socioeconomic and environmental problems related to its current treatment. An effective solution may be the thermochemical conversion of sewage sludge through gasification. First, the most known sewage sludge gasification processes are presented along with the challenges that they face. Then the detailed characteristics of sewage sludge are discussed from the point of view of its use in the gasification process, as well as research on the kinetics of gasification of sewage sludge char using various models. As scientific reports on sewage sludge gasification focus on the influence of process parameters on gas yield and composition (especially H2 and tar content), the main part of the work is devoted to the discussion on the influence of temperature, type, and amount of the gasifying agent and the presence of a catalyst on these parameters. Moreover, the co-gasification of sewage sludge as well as advanced gasification methods, i.e., supercritical water gasification and plasma gasification, are analyzed. Finally, the possibilities of utilization of sewage sludge gasification process by-products were discussed and the impact of the process on the environment was assessed. The review concludes with indications of directions for further research.