Electro-Kinetic-Enhanced Phytoremediation for the Restoration of multi-Metal(loid) Contaminated Soils

摘要

Soil heavy metal(loid) contamination from anthropogenic activities has become a serious global environmental problem. In recent years, there have been growing interests in finding new and innovative solutions for the efficient removal of heavy metal(loid)s from contaminated soil. Phytoremediation is a sustainable and green technology which basically use plants and associated soil microbes to reduce the concentrations or toxic effects of heavy metal(loid)s in the environments. Phytoextraction is the main and most useful phytoremediation strategy. Hyperaccumulator plants with greater metal(loid)s accumulation capacity are suggested for the remediation purpose. However, at high concentrations, these metal(loid)s might show phytotoxicity and stress symptoms, which include seed germination, growth rate, biomass, photosynthetic pigments, changes in antioxidant enzymes and antioxidants. In addition, phytoavailability of heavy metal(loid)s is another critical factor for the efficiency of phytoextraction and amendments are added to increase metal dissolution in soil. Compared to conventional physical and chemical technology, phytoremediation is a green technology which is more cost-effective and eco-friendly. However, on one hand, it is difficult to find hyperaccumulators with favorable accumulation ability of multiple heavy metals. On the other hand, to increase the phytoavailability of soil metal(loid)s is not easy. Therefore, electro-kinetic remediation (EKR) is developed to increase the soil heavy metal mobility and uptake by plants, and prevent their leaching into groundwater. Electro-kinetic (EK) enhanced phytoremediation generally contains the application of a low intensity electric field adjoined to growing plants in contaminated soil. The electric field may enhance the removal of the heavy metal(loid)s by increasing the bioavailability of the heavy metal(loid)s by desorption and transportation. Furthermore, the electric field also has beneficial effects on plant growth and rhizospheric activities. Key electrical variables such as electric field intensity, modes of voltage application, electrode materials and electrodes configurations have decisive influence on the effectiveness of EK enhanced phytoremediation. Since dramatic changes such as soil pH and contaminants speciation also occur during the remediation, assisted amendments such as chelatants, complexing agents, organic agents and fertilizer are applied to improve metal(loid)s bioavailability, control soil pH with the favorable range and facilitate plants growth (Figure 1). The purpose of this chapter is to address the mechanisms of the new integrated green technology with current state-of-art studies, appraise the advantages and disadvantages and then issue the future research directions.