Co-pelletization of refuse-derived fuel and sewage sludge for synergistic combustion and in-situ chlorine retention.

Refuse-derived fuel (RDF) and sewage sludge (SS) were co-pelletized to produce S-RDF with sludge blending ratios ranging from 0 to 40% by weight. The effects of sludge addition on pellet properties, combustion behavior, kinetics, and chlorine retention were systematically investigated. Results showed that sludge-derived extracellular polymeric substances enhanced pelletization, increasing compressive strength by 12% at a sludge blending ratio of 40%. At blending ratios of 30% or less, the lower ignition temperature and catalytic inorganic minerals in sludge jointly promoted synergistic combustion, increasing the comprehensive combustion index by 38.05% while reducing activation energy. Furthermore, phosphorus- and aluminum-rich minerals derived from sludge substantially promoted chlorine stabilization via the formation of chlorapatite, calcium chlorophosphate, and aluminosilicate phases. At a 40% sludge incorporation level, this led to a 4.37-fold increase in chlorine retention in bottom slag at 800 °C compared with pure RDF, highlighting the effectiveness of sludge minerals in in-situ chlorine immobilization. These findings demonstrate the multifunctional role of sewage sludge in improving fuel quality, combustion performance, and in-situ chlorine stabilization, providing a sustainable strategy for waste-to-energy applications.