Evaluation of municipal waste compost in relation to the environmental retention of heavy metals

This study investigates the performance of municipal compost as a heavy metals adsorbent 1 for environmental protection systems. The performed assays test the effects of pH (2-9) and contact time (5-250 minutes) on metal retention. To simulate leaching in natural systems, the soluble organic fraction was removed, leading to variations in the surface properties, including a 10% increase of cation exchange capacity (CEC) and 242% increase in the BET specific surface area, accompanied by a small decrease in the surface charge (characterized by a less negative zeta potential values) of the washed municipal compost (WMC). Notably, these variations, which have not been found in previous research, yielded an improved retention of Cu(II) and Zn(II) compared to the raw municipal compost (RMC) attaining 96% for Cu(II) and 97% for Zn(II) at pH ca 6.8-7.2 for a contact time of 120 minutes. The vast availability, cost-effectiveness, and resistance to desorption make municipal compost a viable option, in a circular economy context for mitigating metal pollution in various environmental conditions. It is worth noting that this study can serve as a proxy for the expected outcomes in long-term exposure to environmental protection systems, enhancing the practical relevance of using compost for metal retention purposes.This work was financially supported by the Interreg VA Spain-Portugal Programme (EU) through the project Res2ValHum (0366_RES2VALHUM_1_P). Thanks are due to Fundação para a Ciência e Tenologia (FCT) and FEDER (European Fund for Regional Development)-COMPETE- QRENEU for financial support through the Chemistry Research Centre of the University of Minho (UID/QUI/00686/2020). This paper was also financed by National Funds of the FCT – Portuguese Foundation for Science and Technology within the project UID/ECO/03182/201