Influence of sludge properties on the direct gasification of dewatered sewage sludge in supercritical water

In the present study, ten different types of dewatered sewage sludges were treated in supercritical water in a high-pressure autoclave under a given condition (at 400 °C, 60 min and 23 MPa). The feasibility of direct gasification and the effect of sludge properties on the gasification of dewatered sewage sludge with various properties in supercritical water were investigated. The results showed that dewatered sewage sludge with various water contents (73.48–88.51 wt%), organic matter contents (29.25–73.02 wt%, on dry basis) and inorganics can be directly gasified in supercritical water. The total gas and phenol production increased linearly with the increment of organic matter content in dewatered sewage sludge. The difference in hydrogen content in the gaseous product may be related to the content of water and inorganic as well as pH value of the sludge. The char/coke formed in the solid residue increased with decrement of water content, which inhibited the gasification reaction and resulted in the carbonization reaction.