Pyrolysis and subsequent direct combustion of pyrolytic gases for sewage sludge treatment in China

Highlights: • An equipment based on pyrolysis of SS and immediate combustion of pyrolytic gases as energy supplier was developed. • The practical treatment of dry SS was carried out. • Flue gas compositions and leaching behavior of heavy metals were investigated. • Energy and mass balance evaluation was performed based on the treatment of 300 kg/h dry SS. • High temperature flue gas could be utilized for drying wet SS or steam production. - Abstract: An equipment based on pyrolysis and subsequent direct combustion of the pyrolytic gases as energy supplier was developed to treat dry sewage sludge in China. In this system, the pyrolytic gases generated in the pyrolysis room were transported upward to the burning room where they were ignited to release heat energy which irradiated back to sustain pyrolysis of the sewage sludge in the pyrolysis room. Parameters such as the feeding speed and transporting speed of sewage sludge, as well as the temperatures of pyrolysis room and burning room were investigated and optimized. The compositions of the flue gas and leaching behavior of heavy metals in biochar were analyzed to assess their impact on environment. Furthermore, the energy and mass balance was investigated to figure out the efficiency of this equipment and the amount of heat energy preserved in the high temperature flue gas which could be utilized for either drying wet sewage sludge or steam production.