Unveiling Hydrogen Fluoride Emission Mechanisms in Municipal Solid Waste Incineration Using a Machine Learning...

Hydrogen fluoride (HF) emissions from municipal solid waste incineration (MSWI) pose significant environmental and health risks. However, their complex formation mechanisms remain poorly understood. This study presents an integrated machine learning framework combining XGBoost for HF prediction, SHAP for feature interpretation, structural equation modeling (SEM) for mechanistic analysis, generalized additive models (GAMs) for threshold identification, and self-adaptive nondominated sorting genetic algorithm II (SA-NSGA-II) for multiparameter optimization. Using over 150,000 high-frequency (5 s interval) sensor records from a waste-to-energy plant in Hainan Province, China (June 1-10, 2024), the XGBoost model showed the best performance among the evaluated models (R² = 0.755, RMSE = 0.041 mg/m³, MAE = 0.031 mg/m³) via 5-fold cross-validation. SHAP analysis identified flue gas temperatures─especially the second flue right side (10.97%) and first flue top (10.19%)─as dominant factors. SEM confirmed the grate incineration zone as the primary HF source (path coefficient = 1.058, p < 0.001). GAM identified location-specific critical temperature thresholds for HF emission control, specifically 767 °C at the upper second flue gas pass, 875 °C at the first flue top, and 212 °C at the low-temperature economizer inlet. SA-NSGA-II optimization, validated with June 11 data, reduced HF emissions in 89.74% of cases, achieving a 17.61% average reduction (0.1176 mg/m³). This framework advances mechanistic understanding and provides data-driven strategies for sustainable MSWI operation and pollution mitigation.