Waste-to-Hydrogen pathways: Gas composition and char structure evolution during pyrolysis of food and digestate waste

This study investigates the influence of pyrolysis temperature on the yield distribution and gas composition of biochars derived from food waste (FW) and digestate waste (DW). Pyrolysis experiments were performed at 400–700 °C, and the resulting solid, liquid, and gas fractions were characterised. Gas compositions were quantified using Gas Chromatography (GC), while structural and physicochemical properties of the biochars were evaluated using SEM-EDS, BET, XRD, Raman spectroscopy, and TPO-DTG analysis. The proportion of syngas components, particularly hydrogen (H 2 ), showed a pronounced dependence on temperature and feedstock type. No detectable H 2 was found at 400 °C for either feedstock, whereas a substantial increase occurred with temperature elevation. For FW-derived gas, H 2 increased from 7.41 vol% at 500 °C to 26.57 vol% at 700 °C. Similarly, DW-based gas exhibited an increase from 6.68 vol% to 18.28 vol% across the same temperature range. This rise was accompanied by a reduction in CO 2 and an increase in CH 4 and light hydrocarbons. Raman spectroscopy revealed a temperature-dependent structural transition, indicated by increasing ID/IG ratios from 0.57 to 0.76 in FW biochar and 0.59 to 0.67 in DW biochar, confirming enhanced disorder and defect formation, particularly in FW. Overall, the thermochemical evolution of both feedstocks demonstrates that increasing pyrolysis temperature significantly enhances hydrogen generation capacity, most notably in food waste, where H 2 production increased from undetectable levels at 400 °C to 26.57 vol% at 700 °C, underscoring the strong potential of temperature-driven pathways for producing hydrogen-rich syngas from waste materials. • Pyrolysis temperature strongly governs hydrogen yield from FW and DW wastes. • FW reaches 26.57% hydrogen at 700 °C, outperforming DW in syngas quality. • Char structure evolves with temperature, showing increased disorder and porosity. • DW biochars exhibit higher thermal stability due to mineral-rich composition. • Distinct gas profiles reveal tailored energy and material valorisation pathways.