The Impact of Waste Compost-Based Soil Amendments on the Leaching Behavior of a Heavy Metal Contaminated Soil

The application of waste compost-based soil amendments to remediate contaminated land for soft-end use is an emerging technology that is cost-effective, simple to implement, and sustainable. This concept is tested in this paper in which a heavy metal contaminated soil is amended with two waste-based composts, with and without a zeolite additive fraction. The effect of the amendments is assessed in terms of the leachability of the amended soil. Fresh soil and soil that had been used in pot experiments were tested and compared. The results from batch and column leaching tests are presented and compared in terms of the leachability of Zn²⁺, Cd²⁺, Cl⁻, NO₃ ⁻, and SO₄ ²⁻ . The results show that green waste compost reduced the leachate concentrations of both Cd²⁺ and Zn²⁺ from 0.15 mg dm⁻³ and 4.7 mg dm⁻³ to 0.07 mg dm⁻³ and 2.3 mg dm⁻³ respectively, but only for Zn²⁺ did these concentrations fall below its World Health Organization (WHO) drinking water standard of 3 mg dm⁻³. The use of composted sewage sludge had the opposite effect and increased the leachate concentration of Zn²⁺ to 9.8 mg dm⁻³, which was to up to 3.3 times its WHO standard, and increased the leaching concentration of NO₃⁻ to 395.4 mg dm⁻³ (10 times its WHO standard). Batch leaching tests leached a larger quantity of metals than column leaching tests, while the leaching of anions was similar. The column test also showed that initial leaching concentrations of metals and anions can be much higher than those obtained with the batch test but these decline quickly as leaching continues.