Insights into the Synergistic Effect and Inhibition Mechanism of Composite Conditioner on Sulfur-Containing Gases during Sewage Sludge Pyrolysis.

Sewage sludge odorous gas release is a key barrier to resource utilization, and conditioners can mitigate the release of sulfur-containing gases. The gas release characteristics and sulfur compound distribution in pyrolysis products under both single and composite conditioning strategies of CaO, FeO, and FeCl were investigated. This study focused on the inhibition mechanisms of these conditioners on sulfur-containing gas emissions and compared the theoretical and experimental sulfur content in the products to evaluate the potential synergistic effects of the composite conditioners. The findings indicated that at 650 °C, CaO, FeO, and FeCl inhibited HS release by 35.8%, 23.2%, and 9.1%, respectively. Notably, the composite of CaO with FeCl at temperatures ranging from 350 to 450 °C and the combination of FeO with FeCl at 650 °C were found to exert synergistic suppression on HS emissions. The strongly alkaline CaO inhibited the metathesis reaction between HCl, a decomposition product of FeCl, and the sulfur-containing compounds within the sewage sludge, thereby exerting a synergistic suppression on the emission of HS. Conversely, at temperatures exceeding 550 °C, the formation of Ca-Fe compounds, such as FeCaO, appeared to diminish the sulfur-fixing capacity of the conditioners, resulting in increased HS emissions. For instance, the combination of CaO and FeCl at 450 °C was found to synergistically reduce HS emissions by 56.3%, while the combination of CaO and FeO at 650 °C synergistically enhances the release of HS by 23.6%. The insights gained from this study are instrumental in optimizing the pyrolysis of sewage sludge, aiming to minimize its environmental footprint and enhance the efficiency of resource recovery.