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 degrees 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 degrees 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. (C) 2016 by The Combustion Institute. Published by Elsevier Inc.