Significant Reduction of Systematic PAH and NPAH Discharges from Hazardous Waste Treatment by the Advanced Scrubbing and Circular GASMILD Combustion

This study systematically investigates the application of sludge and fly ash circular combustion (SFACC) under gasification-moderate or intense low-oxygen dilution (GASMILD) incineration in a hazardous waste thermal-treatment system (HAWTTS) to achieve significant reductions in hazardous air pollutants. The aim of this research is to evaluate whether integrating residue reinjection into a closed-loop GASMILD system can enhance the net removal efficiency of polycyclic aromatic hydrocarbons (PAHs) and nitro-PAHs (NPAHs), while revealing critical insights into pollutant behavior and control. The research demonstrates that while conventional incineration effectively destroys a substantial portion of polycyclic aromatic hydrocarbons (PAHs, 98.7% destruction) and nitro-PAHs (NPAHs, 89.2% destruction), and air pollution control devices (APCDs) further reduce their emissions (63.9% and 88.1% reduction, respectively), pollutant migration and concentration in sludge and fly ash significantly diminish overall system removal efficiency (6.1-43.2%). Crucially, implementing SFACC achieved a closed-loop system, demonstrably enhancing the net reduction of PAHs and NPAHs to 99.2% and 93.7%, respectively, by eliminating solid residue discharge. Detailed particle size distribution analysis in the stack flue gas provided valuable insights into respiratory health risks. The investigation discovered that their absolute emission levels remained low while SFACC increased particulate matter concentrations and the relative content of more toxic, higher molecular-weight PAHs and NPAHs. These findings provide strong scientific evidence supporting the use of SFACC under GASMILD incineration as a novel and effective approach to achieving comprehensive, system-wide control of hazardous air pollutants from hazardous waste incineration.