Pyrolysis of sewage sludge in a benchtop fluidized bed reactor: Characteristics of condensates and non-condensable gases

Abstract This paper studied influences of temperature and additives on sewage sludge (SS) pyrolysis in a fluidized bed. The maximum condensate yield (17.07 wt%) was observed with Ca-bentonite at 650 °C. The yields of non-condensable gases rose significantly with addition of catalysts (e.g. kaolin). Fourier transform infra-red (FTIR) spectra indicated catalysts led to the appearance of some compounds (e.g. alkanes, ketones, amines) in the pyrolysis oil (PO). Gas chromatography mass spectrometry (GC-MS) revealed that PO mainly contained organo-oxygen species, nitrogen-containing heterocyclic compounds, hydrocarbons and antibiotics. With catalysts addition, the main components in the organo-oxygen species were phenols (1.59%–13.78%) and ketones (1.15%–5.12%). The highest CO2 and CO yields were obtained with kaolin addition, while the lowest CO2 yield was reached by CaO. Nitrogen (N) and chlorine (Cl) mainly existed in char and liquid phase, whereas sulfur (S) was dominated in char, indicating that the existence form of S was stable. CaO had certain N retention ability and S retention capability was up to 99.64%. Ca-bentonite and CaO reduced the release of Cl and all catalysts contributed to reduction of HCN emission.