Study on the synergistic remediation of heavy metal contaminated soil by micro-nano bubbles-ryegrass enhanced system.

Abstract

Conventional phytoremediation of heavy metal-contaminated industrial soils often fails to achieve desired outcomes due to limited metal accumulation capacity and low plant biomass. To overcome these limitations, we developed a synergistic micro-nano bubbles (MNBs)-ryegrass (Lolium perenne L.) remediation system. MNBs supply reactive oxygen species to mobilize heavy metals, thereby optimizing the rhizosphere microenvironment. The results demonstrated that MNBs treatment significantly stimulated both aboveground growth and biomass accumulation in ryegrass. Under high-polluted condition, the shoot length and dry weight increased by 41% and 88%, respectively, compared to the control group, accompanied by a 43% reduction in the root-to-shoot ratio. Under low-polluted condition, MNBs enhanced the plant content of Pb, Cr, Zn, and Cu by 1.9-, 1.9-, 1.2- and 1.2-fold, respectively, reducing the soil residual rates of Cr, Zn, and Cu to below 30%. Furthermore, principal component and correlation analyses revealed that soil heavy metal retention was positively correlated with total dissolved solids (TDSs), and these parameters inversely affected ryegrass growth. Membership evaluation showed the MNBs-treated group scored 0.83, much higher than the control group's 0.17 under metal stress. Ultimately, the synergistic MNBs-ryegrass system emerges as a highly efficient and promising strategy for the practical remediation of industrial soils.