Thermal behaviour of sewage sludge in pyrolysis process

Municipal wastewater treatment results in the production of large quantities of sewage sludge. The proper treatment and disposal of sewage sludge is one of the important environmental issues. The pyrolysis of three samples of sewage sludge was studied by a thermogravimetric analyser and a fixed bed reactor at the temperature of 30- 800 degrees C. Sewage sludge was collected from Shaoxing wastewater treatment plant in China. The heating value of sewage sludge was at the range of 10.8-12.9 kJ g(-1). The rate of pyrolysis as a function of temperature was obtained for different heating rates. The results showed that the pyrolysis of sludge can be divided into four stages: evaporation, decomposition of small molecular weight matter, main decomposition and final decomposition range. Gas chromatographic analysis showed that the gas released during the pyrolysis process mainly included H2O, CO, CO2 and CH4. The effect of metal oxides (CaO, Fe2O3) on the pyrolysis of sewage sludge was also investigated.