Enhancement of sulfur control by conditioners during sewage sludge pyrolysis: Focusing on screening and in-situ sulfur fixation mechanism based on model compounds

Utilizing conditioners is effective to reduce S-containing gases during sludge pyrolysis. Revealing the relationship between conditioners of different prices and multiple S control factors under similar conditions is key for efficient screening. However, a detailed performance comparison of conditioners remains unavailable. This study, for the first time, comprehensively compared the S control effect of six typical conditioners, and the model compounds of organic-S were used to reveal the in-situ S fixation mechanism of the conditioners. Results show that the total release of gas-S (especially H2S) decreased by 34.4–54.2 % after the addition of CaO, Fe2O3, and FeCl3. These conditioners (especially Fe2O3) can enhance the stepwise oxidation of easily decomposed organic-S (especially aliphatic-S) into stable sulfoxide-S and sulfone-S. Additionally, sulfide-S and sulfate-S can be generated via the capture of S-containing intermediates (i.e., ·SH) by conditioners (especially CaO). The presence of Cl can react with inorganic sulfide-S or organic-S via replacement, leading to the re-release of H2S. Among all conditioners, CaO, followed by Fe2O3 and FeCl3, showed the best comprehensive performance, especially in terms of price and effective H2S control temperature range. This work can guide the selection of conditioners for the synergistic control of S-containing gases in the integrated treatment of sludge.