Demonstrational gardens with EDTA-washed soil. Part I: Remediation efficiency, effect on soil properties and toxicity hazards

Abstract

The viable chelator-based soil washing has yet to be demonstrated on a larger scale. Soil containing 1850, 3830 and 21 mg kg^-1 Pb, Zn and Cd, respectively, was washed with 100 mmol EDTA kg^-1 in a series of 16 batches (1 ton soil/batch) using the new ReSoil® technology. The ReSoil® recycled the process water and 85% of the EDTA, producing no wastewater and 14.4 kg ton^-1 of waste. The soil washing removed 71, 28 and 53% of Pb, Zn and Cd, respectively, mainly from the carbonate fraction, saturated the soil with basic cations and increased the soil pH by up to 0.5 units. Raised beds (4 × 1 × 0.5 m) with original (contaminated) and remediated soil were constructed as lysmeters, and local produce was grown from July 2018 to November 2019. Throughout the gardening period, the concentration of Pb and Cd in the leachates from the remediated soil was lower and that of Zn was higher than in the original soil. Remediation decreased the concentration of plant-available and mobile toxic metals, as determined by CaCl₂ and NH₄NO₃ extractions, and reduced the bioavailability of Pb, Zn, and Cd in the simulated human gastrointestinal phase by an average of 4.3, 1.7 and 2.7-fold, respectively. Revitalization with vermicompost, earthworms and rhizosphere soil, and spring fertilisation with compost and manure, had no significant effect on the mobility and accessibility of the toxic metals. The ReSoil® is a cost-effective technology (material cost = 18.27 € ton^-1 soil) and showed the prospect of sustainable reuse of remediated soil.

Keywords: Contaminated soil; EDTA; Hazard mitigation; Sustainable remediation; Toxic metals.