Supercritical water gasification of sewage sludge by continuous flow tubular reactor: A pilot scale study

Abstract

• The pilot scale, continuous flow tubular reactor was designed, specially produced. • Effects of temperature, feed concentration, and KOH catalyst were studied. • Temperature, sludge concentration and KOH had great effect on the system yield. • SCWG is a promising and efficient technology for the gasification of wet biomass. • Unlike conventional gasification methods, no hazardous emissions. Treatment and disposal of sewage sludge constitute one of the major problems of wastewater treatment plants due to high water content and more stringent environmental regulations. Supercritical water gasification (SCWG) technology is accepted as a promising method for sustainable sludge disposal because of the elimination of need for costly water reduction and drying processes before disposal by conventional methods. The aim of this study is to determine the effect of temperature (450–650 °C), solid matter content (1–2%) and catalyst addition (0.5–2% KOH) on supercritical gasification of sewage sludge in a continuous-flow pilot scale tubular reactor. The results indicate that the gasification efficiency is generally temperature dependent. Furthermore, catalyst addition improves the gasification efficiency at high solids content. The produced gas contains 60% of H 2 and 22% of CH 4 at experimentally determined optimal conditions (650 °C, 2% solid matter content, 2% KOH). The resulting gas contains H 2 S and CO below detection limits and there is no need for additional treatment. Consequently, SCWG technology provides complete decomposition of organic matter in a short time, clean gas formation with higher energy content, and volumetric reduction compared to conventional methods.