Using CO2 and oxidants for in situ regeneration of permeable reactive barriers for leachate-contaminated groundwater.

Groundwater contamination near landfills is commonly caused by leachate leakage, and permeable reactive barriers (PRBs) are widely used for groundwater remediation. However, the deactivation and blockage of the reactive medium in PRBs limit their long-term effectiveness. In the current study, a new methodology was proposed for the in situ regeneration of PRB to remediate leachate-contaminated groundwater. CO2 coupled with oxidants was applied for the dispersion and regeneration of the fillers; by injecting CO2 to disperse the fillers, the permeability of the PRB was increased and the oxidants could flow evenly into the PRB. The results indicate that the optimum filler proportion was zero-valent iron (ZVI)/zeolites/activated carbon (AC) = 3:8:10 and the optimum oxidant proportion was COD/Na2S2O8/H2O2/Fe2+ = 1:5:6:5; the oxidation system of Fe2+/H2O2/S2O82- has a high oxidation efficiency and persistence. The average regeneration rate of zeolites was 72.71%, and the average regeneration rate of AC was 68.40%; the permeability of PRB also increased. This technology is effective for the remediation of landfills in China that have large contaminated areas, an uneven pollutant concentration distribution, and a long pollution duration. The purification mode of long-term adsorption and short-time in situ oxidation can be applied to the remediation of long-term high-concentration organically polluted groundwater, where pollution sources are difficult to cut off.

Adsorptive removal of heavy metal anions from water by layered double hydroxide: A review.

High-valence heavy metals with high ecotoxicity are generally found in water in the form of anions, and this increases heavy metal pollution intensity and treatment difficulty. Recent studies have pointed to the potential efficiency of layered double hydroxides (LDHs) to meet this challenge. In this review, we retrospectively research the development of LDHs using a Java application called CiteSpace. We describe the unique layer structure, highly adjustable chemical properties, and diverse synthesis methods of LDHs, all of which decide the effective adsorption of heavy metal anions by LDHs. Subsequently, we focus on discussing the adsorption mechanism of LDHs on heavy metal anions, as well as the current state of research and future directions for microscopic interaction mechanisms. For practical applications, it is critical to improve the adsorption selectivity and stability. We then recommend solutions to improve the adsorption selectivity and stability after identifying the influencing mechanism. Finally, we provide our perspectives on the future development of LDHs adsorption of heavy metal anions.