Characterization of bio-oil and biochar from high-temperature pyrolysis of sewage sludge

The influence of temperature (550-850°C) on the characteristics of bio-oil and biochar from the pyrolysis of sewage sludge (SS) in a horizontal tube reactor was investigated. Results showed that when the pyrolysis temperature increased from 550°C to 850°C, the yield of bio-oil decreased from 26.16% (dry ash-free basis) to 20.78% (dry ash-free basis). Main components of bio-oil were phenols, esters, cholests, ketones, amides, indoles, and nitriles. Besides, the elevated heating rate of 25°C/min was demonstrated to favour the complete combustion of bio-oil. Moreover, caused by the increase in temperature, the yield of biochar decreased from 54.9 to 50.6 wt%, Brunauer-Emmet-Teller surface area increased from 48.51 to 81.28 m2/g. Furthermore, pH was increased from 5.93 of SS to 7.15-8.96 of biochar. The negative ζ-potential was also strengthened (-13.87 to -11.30 mV) and principal functional groups on the surface of biochar were -OH, C=O, C=C, -NO2, and S=O.