Influence of moisture content on the direct gasification of dewatered sludge via supercritical water

In the present study, the feasibility of the direct gasification of dewatered sludge in supercritical water and the effect of water content on supercritical water gasification of the dewatered sludge were investigated using a high-pressure autoclave at a constant temperature of 400 °C with residence time of 60 min and by adjusting water content by adding distilled water or using air-dried dewatered sludge. The results showed that dewatered sludge can be directly gasified in supercritical water, with water content ranging from 75 to 95 wt%. The total gas production was increased by decreasing the water content, and the gas yield was decreased. The CO₂ yield was significantly affected by water content, whereas H₂, CH₄, and CO yields were slightly reduced. The liquid residue contained large amounts of organic matter (OM) and total phenols, thereby requiring further treatment before being discharged. The concentrations of OM and total phenols increased with a decrease in water content. Moreover, a serious carbonization reaction happened while carbon particles higher than 10 wt% (char/coke) were being formed in the solid residue.