Mass Distribution of Nutrients, Trace Elements, and Heavy Metals Among Particle-Size Fractions of Municipal Solid Waste Compost from Different Regions of the Baltic States

This study assesses the distribution of nutrients, trace elements, and heavy metals across different granulometric fractions of municipal solid waste (MSW) compost from three regions: Kaunas and Alytus (Lithuania) and Daugavpils (Latvia). Samples were collected from mechanical biological treatment plants (MBTPs) and fractionated into six different granulometric fractions (>5 mm, 5–2.5 mm, 2.5–1 mm, 1–0.5 mm, 0.5–0.2 mm, and <0.2 mm). Each fraction was subjected to physicochemical characterization. Macronutrients (Ca, K, Mg, P), trace elements (Al, As, Co, Fe, Mn, Mo), and heavy metals (Cd, Cr, Cu, Ni, Pb, Zn) were analyzed using ICP-OES in triplicate. Results showed that essential nutrients and toxic metals were retained more in the finer fractions (<1 mm). In contrast, undesirable impurities, mainly glass, were retained in the coarse fractions across all the studied areas. All fractions in the compost samples of Kaunas, and coarse fractions (>5 mm, and 5–2.5 mm) of Alytus and Daugavpils are suitable to use as a soil amendment only if the undesirable impurities are removed to the acceptable limits in the coarse fractions. The fine fractions of Alytus have higher levels of heavy metals (Cd, Cr, Cu, Ni, Pb, Zn), while Daugavpils showed higher levels of Cd, Cu, Ni, and Zn, exceeding the EU limits. Regarding physical fractionation, results showed that nutrients and heavy metals increased in the compost as particle size decreased. Our findings suggest that removing particle sizes < 1 mm and large impurities from the coarse fractions can enhance compost quality. Overall, particle-size fractionation can improve the consistency and safety of MBT-derived MSW compost for reuse in circular waste management systems.