| Due to the high moisture content of raw sewage sludge, a drying or pyrolysis processat relatively low temperatures is recognized as an essential pre-treatment step forsubsequent thermal utilization processes. The release of odorous gases to some extent limitthe development of sludge pyrolysis technology. Among the odorous gases during sewagethermal treatment, sulfur-containing gases have been identified as the main odorants, inaddition to nitrogen compounds, benzene series and other. Therefore, this study aims toinvestigate the release of organic sulfur in sludge as sulfur-containing odorants at150-450°C. To understand the effect of organic sulfur type on release of sulfur-containingodorants, pyrolysis experiments of raw sludge and sludge samples loaded with variousorganic sulfur compounds were performed.The sulfur in sewage sludge is present in both organic and organic forms. Inorganicsulfur includes mainly sulfates and sulfides. Organic sulfur in sludge mainly has four types:aromatic sulfur, aliphatic sulfur, sulfoxide and sulfone. The raw sludge and char sampleswere characterized by XPS. The results showed that the proportion of organic sulfur in rawsludge reached74.15%.In the raw sludge pyrolysis process primarily aliphatic (150-250℃) and aromaticsulfur (＞350℃) decomposed. When the temperature is higher than250℃sulfates has asmall amount of decomposition, while the sulfone and sulfoxide sulfur content changedlittle during pyrolysis. Five kinds of sulfur-containing gases were detected in the Gaseousproducts, respectively H2S, SO2, COS, CS2and CH3SH. Which H2S content is the highest,SO2followed, the emissions of COS and CS2are very small. Sulfur-containing gasemission increases with the temperature is gradually increased.In order to understand the effect of organic sulfur type on release of sulfur-containinggases, pyrolysis experiments of raw sludge and sludge samples loaded with various organicsulfur compounds were performed. Compared to those of raw sludge, the concentrations ofsulfur-containing gases show a significant increase for the Aliphatic Sulfur-loaded andAromatic Sulfur-loaded sludge. H2S emissions increased sharply while the other four kinds of sulfur-containing gases increase relatively less, which the CS2only slightly increased.This shows that the aliphatic and aromatic sulfur decomposed mainly to generate H2S.Wherein the aliphatic sulfur begins to decompose between150-250℃, the decompositiontemperature of aromatic sulfur is relatively high (350℃). However, Sulfone-loaded andThiophene-loaded sludge samples show the close concentrations of sulfur-containing gasescompared to raw sludge at all temperatures in this study. Therefore, desulfurization ofsulfone and thiophene does not seem to occur at temperatures below450℃. |
