Self-heating of dried wastewater sludge

► Significant self-heating (up to 90 °C) of dried sludges from wastewater treatment was reproducibly observed. ► Air significantly support the self-heating, while some water is an important cofactor. ► Direct or indirect heating in drying does not affect the self-heating behavior. ► Unsteady (start-up, shut down) drying operations may yield sludges that evolve into spontaneous combustion. ► Due to the specific industrial origin, some original chemistry is likely to occur.