Assessment of a particle size fractionation as a technology for reducing heavy metal, salinity and impurities from compost produced by municipal solid waste

• We operated a physical fractionation of low grade composted municipal solid wastes (MSW).
• Nutrient and heavy metal distributions in particle size fractions were assessed.
• Salinity and heavy metals were associated to particles with size <0.8 mm.
• Nutrients were more evenly distributed among the particle size fractions.
• Removal of particles <0.8 mm can improve the compost quality and allow its safe use.

A physical fractionation of a compost obtained by municipal solid wastes (MSW) was conducted by dry-sieving process, to quantify coarse impurities and assess the distribution of nutrients, heavy metals and salinity values in particle size fractions of 2, 1.2–2, 0.8–1.2, 0.4–0.8, 0.2–0.4, 0.1–0.2 and <0.1 mm diameter. The whole unfractionated compost and all physical fractions were analyzed for the same chemical parameters. The results showed that the studied compost was of a low grade due to high salinity and heavy metal concentrations, and the presence of coarse impurities, mainly glass. The physical fractionation analysis showed that heavy metal and base cations concentrations, and salinity values significantly increased with decreasing of particle size, whereas macro nutrients such as C, N and P were more evenly distributed among the different particle size fractions. Overall, our results showed that the removal of selected particle size fractions <0.8 mm and coarse impurities (e.g. glass impurity >2 mm) could significantly improve the compost quality without reduce its fertilization potential. We concluded that particle size fractionation is a feasible and sustainable approach to improve composted MSW materials for their safe recycle in agriculture.