Pyrolysis kinetics of sewage sludge and its biochar characteristics

In this study, a comprehensive research was conducted for pyrolysis kinetics and biochar characterization with sewage sludge. Pyrolysis kinetics were investigated using thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) using sludge samples divided into four particle size ranges. Also, surface properties and Cu(II) adsorption capacities were determined for biochars produced at 300, 500, 600, 700, and 900 °C. Similar thermogravimetric analyzer (TGA) profiles were observed with the tested particle size ranges (<2 mm). Using a reaction model, estimated kinetic parameters indicated that sludge particle size and heating rate affected activation energy. In biochar characterization study, it was observed that the surface chemical functional groups of biochar was reduced with increasing pyrolysis temperature. The maximum BET surface area was measured from biochar produced at 600 °C as 92.3 m2/g. Also, the biochar produced at 600 °C showed the maximum Cu(II) adsorption capacity (146.7 mg/g biochar). Electrostatic adsorption was the main mechanism of Cu(II) adsorption for biochar produced at 600 °C, but complexation/precipitation was the main mechanism of Cu(II) adsorption for biochar produced at 300 °C and 900 °C. These adsorption results indicated that the adsorption mechanism and capacity of biochar could be modified by controlling pyrolysis temperature.