Pyrolysis of sewage sludge digestate with different degrees of digestion: Thermodynamics, kinetics and product characterization

• Published in: Energy conversion and management Vol. 315; p. 118756
• Main Authors: Wang, Zhi, Sun, Xiyue, Li, Jian, Yan, Beibei, Chen, Guanyi
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 01-09-2024
• Subjects: Digestate; Kinetics; Pyrolysis; Sewage sludge; Thermodynamics; Digestate; Pyrolysis; Thermodynamics; Kinetics; Sewage sludge
• ISSN: 0196-8904
• DOI: 10.1016/j.enconman.2024.118756

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•The effects of anaerobic digestion (AD) times on the pyrolysis were investigated.•AD enhanced the thermal stability of sewage sludge, especially in the early stage.•Short AD time promoted the depolymerization of the sludge and the release of gases.•Excessive consumption of volatile via AD reduced the source of gas generation.•The selectivity of non-condensable species was altered by AD.
The disposal of digestate derived from sewage sludge (SS) anaerobic digestion (AD) has been a challenging problem. Pyrolysis is a potential technology for the centralized and sustainable treatment of SS digestate. In this study, the effects of AD times (0, 10, 20 and 30 days) on the pyrolysis of SS digestate, including thermodynamics, kinetics and product characterizations, were investigated. Thermodynamics analysis showed that AD enhanced the thermal stability of SS digestate, particularly in the early stage of AD. Coats-Redfern analysis confirmed that the activation energy of digestate pyrolysis initially decreased, then increased, and decreased again. Online FTIR revealed that functional groups and gases released earlier in short-AD groups, and this boost would disappear in long-AD groups. For the evolution of gas, short AD time was beneficial to the depolymerization of the SS and further promoted the release of gases, while excessive consumption of organic composition via AD reduced the source of gas generation. Additionally, AD affected the non-condensable species of SS digestate pyrolysis, and it was easier to convert large-carbon number species to small-carbon number species. These results can provide theoretical guidance for the pyrolysis treatment of SS digestate.