Valorization of sewage sludge via air/steam gasification using activated carbon and biochar as catalysts

The catalytic gasification of sewage sludge was explored using different catalyst particle sizes, bed temperatures, and gasifying agents. Activated carbon and sawdust biochar were used as catalysts in this study. The effects of the porosity of activated carbon on tar adsorption and cracking, and biochar containing alkali and alkaline earth metallic species (AAEMs), which can enhance gasification reactions, were investigated under different conditions. A catalyst bed temperature of 800 °C and particle size of 0.5–1.7 mm showed optimum conditions for increasing H₂ and CO content and decrease CO₂ fraction; however, a higher solid residue (∼38 wt%) was also observed due to the high ash content in sewage sludge. Furthermore, the introduction of steam had a positive effect on the H₂ increment, owing to the presence of inherent AAEMs in the biochar, promoting water gas shift and hydrocarbon steam reforming reactions. The results of this study provide effective measures for using activated carbon and affordable biochar to enhance H₂ production with a parametric effect on the catalyst bed.