Pilot-scale electro-kinetic remediation of lead polluted field sediments: model designation, numerical simulation, and feasibility evaluation

Abstract

Background: The accumulation of lead (Pb) in sediments from anthropogenic activities possesses serious threats to ecosystem and human health. Recycling of sediments for agricultural plantation is politically encouraged while their applications are still limited due to the high cost and poor environmental compatibility of existing remediation techniques. Electro-kinetic remediation (EKR) enhanced with electrode polarity inversion (EPI) strategy was an effective technique for Pb decontamination from low permeable matrix. However, lacking full understanding of the interactions between Pb and sediment constituents restricts the wide application of this technology. Results: In this study, an innovative approach based on model simulation and feasibility analysis was proposed for guiding the pilot-scale remediation and recycling of Pb-polluted sediments. Initially, a specific two-dimensional (2D) model that consisted of transport-reactive modules was designed, with assumptions of operating parameters and reaction equations. A three-step sequential non-iterative split-operator computation scheme was implemented to simulate the electrochemical variables of EKR. The predicted results indicated that the electrode reversal should be conducted around 48 h to avoid pH polarization and Pb precipitation. In addition, 12 h was suggested to be the preferable EPI duration as the shortest time required (226 h) to remove the target level of sediment Pb. Afterwards, a comparative study was performed between the experimental and simulated data to validate the model accuracy. Good agreements were achieved in spite of minor discrepancies which suggested the designed model could approximately predict the performance of EPI-enhanced EKR. Finally, the feasibility analysis was conducted based on a parametric study. In consideration of energy utilization efficiency, concentration of 220 mg/kg was determined as the lower limit of safety threshold for Pb removal. In this level, the maximum energy consumption (EC), materials, electrolyte post-treatment, and labor expenditure for sediments remediation were 110 $/m3, 450 $/remediation unit, 2 $/L, and 300 $/remediation unit, respectively, and the agricultural eco-environment was safe during the recycling process. Conclusion: We believed that the methodology and results in this study could be employed as an useful tool to support the designation of full-scale EKR and the reutilization of contaminated sediments.