Insights into in-situ sulfur retention by co-combustion of dyeing sludge and wood sawdust

Dyeing sludge (DS) incineration is a promising strategy to achieve waste reduction and waste-to-energy conversion efficiency; however, the poor-combustion performance and high-emission level of the gaseous sulfur of DS limit its applications. This study attempts to introduce wood sawdust (WS) to improve combustion performance and inhibit the sulfur emission during DS incineration. The combustion characteristics and release behavior of sulfur gas products of DS-WS mixtures were investigated using thermogravimetry and mass spectrometry (TG-MS), as well as the influence of WS on sulfur fate of DS and the in-situ retention mechanism to sulfur were revealed by ash analysis. Results indicated that WS addition restrained the devolatilization of light volatiles and facilitated the degradation of heavy volatiles and fixed carbon. WS addition improved the combustibility, burnout performance and combustion stability of DS. Organic sulfur species occupied most sulfur-containing compounds in DS, the thermal degradation of organic matter was responsible for emitting SO2, CH3SH, H2S, COS. SO2 contributed > 40% of sulfurous gas emissions. WS addition (30%) significantly reduced the normalized sulfur content from DS, and the in-situ retention ratio to sulfur reached 16.72%. The in-situ retention mechanism to sulfur was explained as potassium iron sulfate and calcium hydrogen sulfate jointly retained the release of sulfur. Moreover, Ca-based sulfate was more stable, indicating that the newly formed mineral contributed to preventing the re-emission of sulfur from incineration residue.