When biomass meet microplastic during dyeing sludge incineration: The impacts on thermal characteristics, gas evolution, and chlorine cycle

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) and burnout (T) temperatures, indicating catalytic degradation by inorganic constituents from biomass. Contrary to expectations, co-combustion of PVC with biomass reduced CO, HO, 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.