Thermochemistry of sulfur during pyrolysis and hydrothermal carbonization of sewage sludges

Sulfur (S) is an abundant and redox-active element in urban wastewater systems plays a critical role both the sludge treatment processes. This study comparatively characterized transformation of S several closely associated metals (Cu, Zn, Fe) during pyrolysis (250 to 750 °C) hydrothermal carbonization (HTC, 150 275 treatments sewage sludge. S, Fe, Cu K-edge X-ray absorption spectroscopy was applied quantitatively evaluate fate contribution different species regulating metal speciation. During pyrolysis, aliphatic-S sulfonate were preferentially degraded at low temperature (below 350 sulfate thermochemically reduced above 450 °C, while sulfides (up 27%) thiophenes 70%) increasingly formed. Similar process, 40% 200 formed HTC. The degradation thiols organic sulfide, as well reduction, released sulfide strongly affected For example, almost all half Zn transformed into Cu-Fe- or Zn-Fe-sulfides HTC, whereas they partially desulfidized pyrolysis. High abundance (S?1 S?2) hydrochars may contribute their strong reductive adsorption Cr(VI). Results from this work reveal thermochemical reactions driving transformations its results provide fundamental knowledge for selecting techniques value-added applications products.