When biomass meet microplastic during dyeing sludge incineration: The impacts on thermal characteristics, gas...

Co-combustion of dyeing sludge (DS) and biomass enables energy recovery and conventional pollutant passivation, yet biomass's impact on microplastics (MPs) degradation remains uncharacterized. This study investigates three representative biomass fuels-crab shell (CS; Ca-rich), pitaya peel (PP; K-rich), and rice husk (RH; Si-rich)-on polyvinyl chloride (PVC) MPs combustion via integrated analysis of combustion characteristics, gas evolution, kinetics, and residue chemistry / mineral analysis. Biomass additives shifted PVC mass loss to lower temperatures and reduced ignition (T_i) and burnout (T_f) temperatures, indicating catalytic degradation by inorganic constituents from biomass. Contrary to expectations, co-combustion of PVC with biomass reduced CO₂, H₂O, and HCl yields. CS achieved 95.70 % HCl suppression (0.35PVC/CS) versus pure PVC. PVC-CS interactions accelerated ignition while suppressing gas emissions, particularly HCl. Co-combustion kinetics remained PVC-dominated, with biomass increasing activation energy (E) for PVC dehydrochlorination (inhibiting HCl release) while decreasing E for devolatilization / char combustion (catalyzing degradation). Among biomass additives, CS demonstrated superior chlorine fixation capacity (443.44 mg/g) through formation of chlorine-bearing minerals (hydroxylapatite, hydrophilite, sylvite) via Ca/K-HCl reactions, with calcium providing the predominant contribution. Collectively, co-combustion of DS with calcium-rich biomass represents a promising waste management strategy for simultaneous MPs degradation and chlorine emission mitigation.