508 / 2018-09-13 21:53:47

Effects of CaO on the emission of aromatics during sewage sludge pyrolysis

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CaO is considered a promising additive to help achieve a clean thermal disposal of sewage sludge, because it can diminish the emissions of nitrogen oxide, sulfide gas as well as arsenic during the heating process. Emission of aromatics during sludge thermal treatment is also a non-negligible problem. However, the effects of CaO on the emission of this carcinogenic pollutant are still unclear enough. Before the additve was large-scale used in the process of sludge thermal treatment, understanding the effects of the material on the fate of aromatics shall be extremely necessary. In this study, volatiles released from sewage sludge with or without CaO mixed were collected and then analyzed with the combination of Gas Chromatography-Mass Spectrometer (GC-MS), Ultraviolet fluorescence spectrophotometer (UV-F) and advanced Electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry (ESI FT ICR-MS). It is found that CaO showed various effects during sewage sludge pyrolysis. The addition of CaO not only facilitated the cracking of large compounds to generate small molecules, but also leaded to the polymerization of fatty acids to form ketones. With the help of CaO, the aromatic degree of heavy components in the volatiles was reduced while the generation of simple polycyclic aromatic hydrocarbons (PAHs) were improved. Overall, CaO significantly promoted the aromatic degree of the volatiles and therefore increased the emission of aromatics from sewage sludge at 450℃ and 850℃.