Research on the impact of water-level fluctuations on the remediation of aniline-contaminated soils using surfactants

To explore the impact of water table fluctuation on the effectiveness of surfactant remediation of aniline-contaminated soil in stratified soil, sandy soil and silt soil from a pesticide-contaminated site in Northwest China were selected as research objects. Single-rock-type (sandy soil) and dual-rock-type (sandy soil-silt soil-sandy soil) soil columns were designed. Through indoor experiments, the mass concentrations of aniline in each soil layer and the leachate of the soil columns were determined and analyzed. The influence of water table fluctuation on surfactant remediation of aniline-contaminated soil under different soil column rock types was discussed. The results show that: (1) Water table fluctuation significantly improves the removal efficiency of aniline. The removal efficiencies of single-rock-type sandy soil columns and dual-rock-type soil columns increase by 10% and 13% respectively, and the cumulative removal amount reaches up to 9.63 mg. (2) The difference in rock type of soil layers dominates the migration and distribution of pollutants and the remediation efficiency. The single-rock-type sandy soil promotes vertical migration due to its high permeability, while in the dual-rock-type soil column, the silt soil layer retains pollutants due to its low permeability and strong adsorption, forming a local enrichment zone. Water table fluctuation enhances the hydraulic gradient at the interface between sandy soil and silt soil, overcoming the limitation of silt soil on the remediation efficiency, and increases the aniline removal efficiency of the dual-rock-type soil column by 13% compared to the no-fluctuation condition, with a cumulative removal amount of 9.04 mg. (3) Increasing the frequency of water table fluctuation can accelerate the desorption of pollutants, but it is necessary to balance the flow rate of leachate and the contact time of surfactant to optimize the mass transfer efficiency. The study shows that the dynamic water table management mode can effectively enhance the desorption and migration of aniline in stratified soil by periodically adjusting the leaching parameters. In the remediation and treatment projects of stratified soil contaminated sites (such as the LPZ-HPZ structure of the Hengshan alluvial fan), it is recommended to design differentiated remediation schemes based on the permeability and adsorption characteristics of soil layers to improve economic efficiency and precision.