Effect of alkali addition on sulfur transformation during low temperature pyrolysis of sewage sludge

Odorous sulfur-containing gases released during sewage sludge processing cause significant environmental pollution. This study investigates the effect of alkali addition on sulfur transformation as well as the release of the sulfur-containing gases during sewage sludge pyrolysis at 150−450 °C. The presence of alkali can promote the transformation of unstable organic aliphatic and aromatic sulfurs into more stable sulfoxides and sulphonic acid at low temperatures (i.e., 250 °C). Alkalis also fix the inorganic sulfide and sulphate in char. Therefore, the release of the sulfur-containing gases can be greatly reduced with alkali addition. Stronger alkalis show more significant effect on the reduction of sulfur-containing gases, likely because of more OH radicals generated for the transformation of organic sulfurs.