Optimizing hydrogen production from wastewater-derived sewage sludge via alkali-catalyzed supercritical water gasification

The increasing global wastewater generation and reliance on fossil fuels for energy production necessitate sustainable treatment and energy recovery solutions. This study explores supercritical water gasification (SCWG) of sewage sludge from municipal wastewater as a hydrogen production pathway, focusing on the role of alkali catalysts (KOH, K₂CO₃, Na₂CO₃). The effects of temperature (450–550°C), reaction time (5–30 min), and catalyst type on gas yield and efficiency were analyzed. At 550°C, the highest carbon efficiency (61 %), gas efficiency (69 %), and hydrogen yield (41 mol/kg) were observed. After 30 min, the gas composition reached H₂ (58 %), CO₂ (26 %), CH₄ (11.7 %), and CO (4 %). Among catalysts, Na₂CO₃ exhibited superior H₂ yield (29 mol/kg), carbon efficiency (58 %), and gas efficiency (51 %). This study highlights SCWG as a viable technology for hydrogen-rich gas production, contributing to sustainable energy solutions and wastewater valorization. • SCWG efficiently converts sewage sludge into syngas at 450–550°C. • Higher temperatures (550°C) enhance carbon and gasification efficiencies. • Na₂CO₃ catalyst improves hydrogen yield (29 mol/kg) over other catalysts. • CO₂, CH₄, CO, and H₂ ratios peak after 30 min of reaction time. • KOH and K₂CO₃ show comparable hydrogen generation efficiency.