Effects of garden waste on the reduction of sewage sludge pyrolysis process and the change of carbon-containing substances

Due to the high water content, high ash content, high energy consumption in pyrolysis, and low product quality of municipal sewage sludge (SS), it has become a bottleneck restricting the application of SS pyrolysis resource technology. Garden waste (GW) with higher calorific value and organic matter content was added to SS for co-pyrolysis. The reduction effect and material composition were determined through thermogravimetric analyzer, gas chromatography-mass spectrometer, etc., and the pyrolysis kinetics was analyzed using Coats-Redfern method. The results showed that the co-pyrolysis process of SS and GW was mainly divided into three stages: water loss, volatile decomposition, and decomposition of refractory organic matter. After co-pyrolysis of GW and SS, the activation energy could be reduced, and the pyrolysis reaction was shifted towards the low-temperature range. When GW dosage was 50%, the activation energy in the volatile decomposition stage (155-380 ℃) was 4.64 kJ/mol, which was 10.25% less than that of SS pyrolysis alone. In addition, co-pyrolysis could also reduce the generation of secondary pollutants. When GW dosage was 50%, the contents of organic carbon oxides and aliphatic hydrocarbons in the pyrolysis oil after pyrolysis were reduced from 376 and 94 mg/g in the case of individual pyrolysis to 252 and 30 mg/g, respectively. Based on the above research results, it was indicated that GW could reduce the energy input for SS pyrolysis and decrease the generation of pollutants, providing theoretical support for the reduction and resource utilization practical projects of SS and GW.