In-situ tar reduction and catalytic reforming in sewage sludge gasification using steel slag oxygen carrier

Tar formation during sewage sludge gasification severely reduces process efficiency and causes operational and environmental problems. In this work, FeO-rich steel slag was employed as a low-cost oxygen carrier to assist sludge gasification, and the transformation behaviour of major tar compounds was systematically investigated. Under optimal conditions, the total tar yield decreased by over 70 %, and syngas production reached about 3.5 m³/kg with an H₂/CO ratio close to 1:1. Besides, sludge-derived aliphatics and oxygenated organics preferentially evolved into phenolic and N-containing tars, whose polar functional groups and conjugated structures were removed by >80 %, accompanied by fluorescence quenching and blue-shift. Theoretical calculation revealed that FeO promotes adsorption (-1.2 to- 2.4 eV) and CC/CH/CN bond cleavage via lattice-oxygen migration and redox pathways, thereby suppressing heavy tar formation and enhancing gas yield. These findings provide molecular-level guidance for in-situ tar control and syngas upgrading in sludge gasification.