Study on the Characterization and the Removal Efficiency of Cd²⁺ by the Substrate Residues From Cow Dung-Shell Powder Vermireactors

The widespread existence of cadmium (Cd) contamination in soil environment has obtained extensive attention. There is growing interest to use organic wastes to remediate heavy metal pollution to achieve recycle of organic solid waste and the safe utilization of heavy metal contaminated soil. In this study, the vermireactors containing cow dung and shell powder were set up to obtain substrate residues for the removal of Cd²⁺ from aqueous solutions. The results demonstrated that earthworms showed considerably good survival rate with shell powder or modified shell powder addition. The earthworm treatment could reduce pH, C/N, lipid material and polysaccharide substance contents of substrate residues but increase its cation exchange capacity and the specific surface area, alcohol or carboxylic acids substance, aromatic substance, silicate, and soluble salts. Similarly, the addition of shell powder or modified shell powder could increase pH, cation exchange capacity and the specific surface area of substrate residues. The addition of shell powder added CaCO₃, while the modified shell powder addition increased the content of CaCO₃, CaO and Ca(OH)₂ in substrate residues. The adsorption test showed that the removal efficiency of Cd²⁺ was the best for the substrate residues from cow dung and modified shell powder after earthworm treatment, and the adsorption rate was 59.9%. Therefore, it is feasible to set up the vermireactors containing cow dung and modified shell powder to produce substrate residues for the removal of Cd²⁺ in environment.