Clean conversion of pig manure via supercritical water gasification: Hydrogen-enriched syngas generation, mechanisms analysis, and environmental impacts

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The energy potential of pig manure (PM) has garnered attention. Supercritical water gasification (SCWG) is proposed to convert PM to H 2 -enriched syngas without the drying process for wet materials. This paper studied the effect of diverse parameters on H 2 -enriched syngas production . The results revealed that higher temperatures and alkaline catalysts elevated total gas yield and H 2 yield, with the addition of K 2 CO 3 at 620 °C, 30 min, and 6 wt% feed concentration generating the highest total gas yield (36.55 mol/kg), H 2 yield (18.89 mol/kg), and mole fraction (51.55%), accompanied by a high gasification efficiency (87.59%). Based on product characterization and thermodynamic analysis, reaction mechanisms were proposed to provide insight into enhancing syngas production, indicating that the suppression of polymerization reactions between cyclic compounds and the promotion of CH 4 , C 2 H 6 , and long-chain alkanes conversion were essential. Further, the environmental impact evaluation showed that heavy metals (Cu, Cr, As, and Zn) were concentrated in solid products by adsorption and passivation. The solid products exhibited negligible environmental hazards. This work showed that PM SCWG realized syngas production as well as heavy metals enrichment and stabilization, which could provide an alternative solution to the clean conversion of other types of organic wastes, especially with high heavy metals content, such as oily sludge and sewage sludge. • Pig manure was converted into H 2 -enriched syngas at moderate conditions. • The carbon gasification efficiency reached 90.30%. • High H 2 yield (18.89 mol/kg) and mole fraction (51.55%) were obtained at 620 °C. • Gasification mechanisms were proposed to promote H 2 -enriched syngas production. • The solid products exhibited negligible environmental hazards.