Simultaneous Passivation and Removal of Heavy Metals in the Compost of Agricultural Waste and Sediment by the Enhanced Migration of Liquid Media

The study investigated the impact of different liquid media (ultrapure water (UW), citric acid (CA), and ethylenediaminetetraacetic acid disodium (EDTA)) on the composting process and heavy metal (HM) remediation. After 36 days of composting agricultural waste and sediment, the pile underwent enhanced migration with UW, 0.1 M CA, and 0.1 M EDTA. UW increased pH and C/N ratio while reducing total nitrogen (TN) and dehydrogenase activity (DA). In contrast, CA and EDTA reduced pH, TN, and DA, with EDTA also increasing organic matter and TN. The difference in liquid media also influenced the evolution of humic substances (HS). UW reduced HS, fulvic acid, and humic acid, while CA and EDTA enhanced their production, likely due to Fenton-like reactions promoted by chelates formed between EDTA/CA and Fe²⁺, breaking down lignin, and generating HS precursors. Regarding HM removal, EDTA-enhanced migration proved most effective, achieving 38.08% and 51.15% removal of Cr and Cd, respectively. This was attributed to the strong chelating ability of EDTA, forming stable metal complexes that were removed with the liquid media. The enhanced migration also caused a redistribution of HM speciations, with an increase in residual fractions and a decrease in exchangeable and reducible fractions. Overall, the study shows that the EDTA-enhanced migration in compost could combine the passivation and removal in the treatment of heavy metal pollution, which provides a new strategy to remediate the sediments contaminated by HMs.