Size-resolved and seasonal assessment of the undersized fraction of municipal solid waste: Resource potential and...

The undersized fraction of municipal solid waste (UFMSW), typically <100 mm and produced during mechanical-biological treatment (MBT), remains an underutilised stream despite its considerable volume and resource potential. This study presents a seasonally and granulometrically resolved characterisation of stabilised UFMSW from a Hungarian MBT facility. Coarse fractions (20-60 mm), representing the largest mass share (36-45 w/w%), were rich in plastics and paper and exhibited high heating values (up to 22.7 MJ/kg), indicating strong suitability for mechanical, construction-related and chemical valorisation. In contrast, fine fractions (<10 mm), constituting 21-38 w/w% of the bulk, showed substantial accumulation of toxic metals (e.g., Cd 6.01 mg/kg, Pb 423 mg/kg), frequently exceeding regulatory thresholds and posing environmental risks that limit their potential for biological utilisation or material recovery. Thermal analysis confirmed size-dependent decomposition behaviour, with finer particles igniting earlier and coarser fractions displaying diffusion-limited combustion. Hazardous materials (3-12 w/w%) were detected across all size classes, underscoring deficiencies in upstream selective collection. Overall, the findings highlight a clear size-dependent distinction between highly contaminated fines and resource-rich coarse fractions. Effective granulometric separation is therefore essential to enable safe and efficient UFMSW valorisation within circular economy strategies.