Thermogravimetry-Fourier transform infrared spectrometry-mass spectrometry technique to evaluate the effect of anaerobic digestion on gaseous products of sewage sludge sequential pyrolysis

Pyrolysis is considered as one promising technology for anaerobic digestate treatment, due to its great potential generating useful bio-oil and biochar with enhanced quality. In the present study, an online thermogravimetry (TG)-Fourier transform infrared spectrometry (FTIR)-mass spectrometry (MS) technology was used to investigate the effect of anaerobic digestion (AD) on gaseous products from sewage sludge pyrolysis. Compared with the raw sludge, the anaerobically digested sludge had similar derivative TG (DTG) profiles and evolved gaseous composition, but its weight loss and releasing amount of most of gaseous compounds during the pyrolysis was lower. AD caused a decrease in the emission of N-containing and Cl-containing gaseous groups by 22.4-87.6%, but an increase in one possible S-containing group by 20.1%. The generation of more-than-186-m/z gaseous components showed a low reduction and even a slight increase after AD, possibly ascribed to thermal decomposition of some large refractory polysaccharide like and aromatic substances. Some gaseous compounds such as CH4, CH3COOH, and CH3CHO obtained from the sludge pyrolysis reduced significantly after AD, which might enable to conveniently and quickly evaluate sludge anaerobic biodegradability. The findings imply that the TG-FTIR-MS supplies new insights about the influence of AD on sludge pyrolysis on the account of gaseous products.