## 1 Introduction  
Currently, chlorinated organic compounds are mainly used in industry for degreasing and dry cleaning, but due to improper disposal procedures for the storage tanks, they are released into the environment, making soil and groundwater contaminated by chlorinated organic compounds a common problem [1]. The subsequent disposal of these chlorinated organic compounds usually occurs in hazardous waste disposal sites, especially in urban industrial areas [2]. Among the chlorinated organic compounds, trichloroethylene (TCE) and perchloroethylene (PCE) are volatile organic compounds (Figure 1), which have been approved by the United States Department of Health and Human Services and confirmed to be carcinogenic chemicals [3]. Therefore, in consideration of human health, it is necessary to establish effective remedial methods to protect groundwater plant sites polluted by chlorinated ethylenes, such as TCE and PCE. The densities of TCE and PCE are 1.46 g cm\({}^{-3}\) and 1.62 g cm\({}^{-3}\), respectively [4], and both of these compounds are dense nonaqueous phase liquids (DNAPLs), which are liquids with a density greater than water. The soil gaps in the saturated layers of groundwater systems are all filled with water and are under an anoxic environment, so DNAPLs cannot volatilize into their gas phases. Therefore, once they enter the groundwater system, they will sink to the bottom of the groundwater, increasing the difficulty of groundwater remediation [5]. [PERSON] and [PERSON] [6] pointed out that chlorine-containing organic compound DNAPLs have a tendency to enter and flow through cracks even when the groundwater pores are small. In addition, due to the high density and low solubility of chlorinated organic compounds, TCE and PCE are more likely to diffuse downward through aquifers to form impermeable strata than other soluble pollutants. Therefore, DNAPL remediation is one of the most complex technical challenges faced by environmental engineers [7; 8; 9]. The adsorption of an organic pollutant is usually described through adsorption isotherm, that is, the amount of adsorbate on the adsorbent as a function of its concentration at a constant temperature. At present, many adsorption isotherm models have been developed, among which the Langmuir isotherm and the Freundlich isotherm are the most common models. Therefore, the adsorption experimental data in this study will be interpreted in these two modes. To assess whether there is a risk of exposure to groundwater, the general approach is to monitor the flow of chlorinated organic compounds along the groundwater stream and use the concentration of pollutants and byproducts to explore various natural attenuation (NA) mechanisms, such as physical, geochemical and microbial degradation [5]. The NA of TCE and PCE in natural water bodies mainly occurs through physical dispersion and dilution processes, followed by a biochemical dechlorination process. TCE and PCE are often found together in groundwater because TCE is produced by the reductive dechlorination of PCE [2]. PCE produces TCE through biological reduction and dechlorination, and, after various subsequent reductions, PCE can ultimately be reduced to ethylene, which is not harmful to the environment. However, the NA transformation process is quite slow  
Figure 1: Structures of (**a**) trichloroethylene (TCE) and (**b**) perchloroethylene (PCE). and difficult, and the toxicity and fluidity of the substances produced after NA may be greater than those of the original pollutants [10]. Therefore, technologies for removing pollutants from water evolved from the NA mechanisms to include biological degradation, incineration, condensation, extraction, ion exchange, adsorption, etc. [11]. Among various treatment technologies for removing organic compounds from the environment, adsorption is a simple and effective method. The adsorption operation process is simpler, less expensive and results in less pollution [12; 13].