GASIFICATION OF MUNICIPAL SEWAGE SLUDGE BY SUPERCRITICAL WATER: A REVIEW

Municipal sewage sludge produced from wastewater treatment plants generally contains 0.25-12% solid materials and around 70-80% organic matter content. Sewage sludge treatment and disposal is the most complicated and expensive step of wastewater treatment, because of the dewatering requirement, costly operations and processes, space requirement, and environmental standards getting more stringent day by day. Gasification of municipal sewage sludge by supercritical water technology is a promising and developing method to concurrently succeed energy recovery and sludge treatment. The objective of this study is to give information about supercritical water gasification and its applicability for hydrogen rich gas production from municipal sewage sludge. Based on the literature data, supercritical water gasification used for hydrogen and methane production from sewage sludge is a new, clean and encouraging technology and it is feasible according to technical and economical evaluations. Two-stage hydrothermal gasification systems and catalytic process concepts achieving optimum hydrogen production at lower temperatures and pressures can be achieved by i) pre-treatment such as steam explosion, electroporation and liquefying, ii) decreasing the particle size by grinder, iii) the selection of an appropriate reactor configuration and appropriate material selection to overcome the corrosion and plugging problems for future applications.