Assessment of sewage sludge gasification in supercritical water for H₂-rich syngas production

The potential of sewage sludge for hydrogen-rich syngas production from supercritical water gasification (SCWG) was evaluated through thermodynamic analysis and experimental work. The thermodynamic analysis was conducted by using Aspen Plus simulator based on Gibbs free energy minimization. The effect of temperature (380–460 °C), sludge concentration (5–30 wt%), and activated carbon addition (2–8 wt%) on SCWG was experimentally studied. The solid and liquid residues were characterized by Fourier Transform Infrared (FTIR) spectroscopy, Inductively Coupled Plasma-Optical Emission Spectroscopy (ICP-OES), and Total Organic Carbon (TOC) Analyzer. The results showed that higher temperature and lower sludge concentration favored syngas production, leading to higher hydrogen yield. While pressure had no significant effect on the SCWG performance. The TOC and FTIR analyses revealed that organic matters in sewage sludge were decomposed and hydrolyzed into syngas. The addition of activated carbon increased the syngas yield and enhanced the cold gas efficiency. A syngas yield of 6.44 mol/kg containing 38.43% H₂ was obtained from SCWG at 400 °C with the activated carbon loading of 8 wt%. Moreover, the analysis of heavy metals indicated that SCWG had a positive effect on the stabilization of heavy metals and reduced the leaching toxicity of heavy metals in sewage sludge.