Investigation on co-combustion behavior of domestic waste and sewage sludge using TG-FTIR-Py-GC/MS: Thermal behavior and gaseous pollutants emission

The rapid increase of domestic waste (DW) and sewage sludge (SS) has made their co-combustion a promising approach for sustainable waste management. In this work, the combustion characteristics, dominant interaction mechanisms, evolution of gaseous pollutants, and product distribution of DW, SS and their blends were studied using the TG-FTIR-Py-GC/MS approach. The results indicated that the positive interaction effects occurred during the co-combustion of the DW and SS blends, which improved their co-disposal efficiency. Meanwhile, the ignition index (D_i) exhibited non-linear behavior, the comprehensive combustion index (CCI) increased up to a 20 % SS blending ratio, and flame stability (F_i) rose linearly with higher SS blending ratios, indicating that co-combustion of DW with SS improved overall combustion performance. The FTIR identified that the evolving gaseous products were HCN, CO₂, CO, HCl, CH₄, NO, SO₂ and H₂O. The total gaseous emissions of CO₂, CO, H₂O, and other pollutants from DW were substantially higher than those from SS, due to distinct combustion characteristics. Adding DW to SS effectively reduced CO₂, CO, H₂O, and other pollutants emissions, indicating that the co-combustion of DW and SS was an advantageous treatment. Further analysis showed that co-combustion of DW with 20 % SS resulted in the lowest emissions of CO₂, CO, H₂O, and other hazardous pollutants. The GC/MS analysis revealed that the ash catalysis effect during the co-combustion of DW with varying SS blending ratios effectively suppressed aromatic hydrocarbon production and enhanced the yield of aliphatic hydrocarbons and ketones. Furthermore, the overall O-containing groups showed a decreasing trend. This study provides the fundamental reference for practical application of waste to energy.