Using cow dung and mineral vermireactors to produce vermicompost for use as a soil amendment to slow Pb2+ migration

The widespread existence of lead (Pb) contamination in soil has received extensive attention. To effectively slow lead-ion (Pb²⁺) migration and promote plant growth in heavy metal-contaminated soil as well as to realize the resource utilization of solid waste, vermireactors were used to obtain vermicompost using cow dung mixed with modified mineral (MM) as feedstock material for Eisenia fetida. Vermicompost was characterized first, and then its slowing effect on Pb²⁺ migration in soil was further evaluated through pot experiments. The results demonstrated that earthworms could grow well in cow dung and mineral vermireactors, and earthworm activity increased the cation exchange capacity (CEC), total nutrient content and surface area but decreased the pH, carbon to nitrogen ratio (C/N) and organic matter content in the vermicompost. The addition of MM resulted in an increase in the pH, CEC, and surface area but a decrease in the C/N of the vermicompost. X-ray diffraction analysis showed that the addition of MM increased the contents of quartz, CaCO₃, CaO and MgO in the vermicompost. Fourier transform infrared spectroscopy analysis indicated that comparatively less carbohydrates, lipids and polysaccharides and more aromatic compounds existed in the vermicompost, and the addition of MM increased the number of Me-O groups. Pot experiments showed that the application of vermicompost from cow dung and mineral vermireactors significantly promoted the growth of celery cabbage and reduced the Pb content in its edible parts and the Pb bioavailability in soil. Thus, it is possible to use cow dung and mineral vermireactors to optimize the properties of vermicompost for its use as a soil amendment to remediate Pb contamination.