Scaling-up the acid-enhanced electrokinetic remediation of a real contaminated soil

Effective remediation of heavy metals in contaminated soil by electrokinetic technology incorporating reactive filter media

Soil contamination is increasingly a global problem with serious implications for human health. Among different soil decontamination approaches, electrokinetic (EK) remediation is a relatively new technology for treating organic and inorganic contaminants in soil. This research aims to develop an enhanced EK treatment method incorporating a compost-based reactive filter media (RFM) with the advantages of low-cost and strong affinity for heavy metals and test and improve the treatment efficiency for multiple heavy metals in natural soil. A series of EK operations were performed to investigate the performance of EK-RFM under different operating conditions such as the electric current and voltage, processing time, and the amount of RFM. The electric current and treatment time demonstrated a significant positive impact on removing Zn, Cd and Mn ions while changing the amount of RFM had an insignificant impact on the efficiency of heavy metals removal. Overall, 51.6%-72.1% removal of Zn, Cd, and Mn was achieved at 30.00 mA of electric current and 14 days of treatment duration. The energy consumption of the EK process was 0.17 kWh kg^-1. The soil organic matter adversely affected the mobilization and migration of heavy metals such as Cu and Pb during EK treatment. The results are valuable in optimizing the design of the EK-RFM system, which will extend its application to field-scale soil decontamination practices.

Experimental and Numerical studies on remediation of mixed metal-contaminated sediments by electrokinetics focusing on fractionation changes

Electrokinetic remediation technique is widely applied for the removal of heavy metal from contaminated soil, but the soil buffering capacity and fractionation of heavy metals mainly affect the cost and duration of the treatment. This study aims to treat heavy metal-contaminated sediments by electrokinetic remediation (EKR) technique by using various enhancing agents such as EDTA, [Formula: see text], HCI, [Formula: see text], acetic acid and citric acid for optimizing the cost and treatment duration. The optimum molar concentration of enhancing agent for treatment was estimated by batch experiments to maximize the dissolution of target heavy metals and reduce the dissolution of earth metals (Fe, Al and Ca) to maintain soil health. The EKR experiments were performed up to 15 days with the above enhancing agents to reduce the risk associated with heavy metals and the selection of enhancing agents based on removal efficiency was found to be in an order of EDTA > citric acid > acetic acid > [Formula: see text] > HCl [Formula: see text] [Formula: see text]. Also, a numerical model has been developed by incorporating main electrokinetic transport phenomena (electromigration and electroosmosis) and geochemical processes for the prediction of treatment duration and to scale up the EKR process. The model predicts well with experimental heavy metal removal with a MAPD of [Formula: see text] 2-18 %. The parametric study on electrode distance for full-scale EKR treatment was found in this study as [Formula: see text] 0.5 m.

Modeling of electrokinetic remediation combining local chemical equilibrium and chemical reaction kinetics

A mathematical model for reactive-transport processes in porous media is presented. The modeled system includes diffusion, electromigration and electroosmosis as the most relevant transport mechanisms and water electrolysis at the electrodes, aqueous species complexation, precipitation and dissolution as the chemical reactions taken place during the treatment time. The model is based on the local chemical equilibrium for most of the reversible chemical reactions occurring in the process. As a novel enhancement of previous models, the local chemical equilibrium reactive-transport model is combined with the solution of the transient equations for the kinetics of those chemical reactions that have representative rates in the same order than the transport mechanisms. The model is validated by comparison of simulation and experimental results for an acid-enhanced electrokinetic treatment of a real Pb-contaminated calcareous soil. The kinetics of the main pH buffering process, the calcite dissolution, was defined by a simplified empirical kinetic law. Results show that the evaluation of kinetic rate entails a significant improvement of the model prediction capability.

Experimental study on removing heavy metals from the municipal solid waste incineration fly ash with the modified electrokinetic remediation device

The MSWI fly ash which contains a large number of heavy metal substances is a subsidiary product of waste incineration power generation technology. If the MSWI fly ash is disposed improperly, heavy metal pollutants will pose a great threat to environmental safety and human health. Based on the technology of electrokinetic remediation, the feasibility of removing heavy metal pollutants from the MSWI fly ash using a modified electrokinetic remediation device - cylinder device was evaluated in this study. Differing from the traditional cuboid device with the volume ratio of the cathode chamber to the anode chamber being 1:1, the volume ratio of the cathode chamber to the anode chamber of the cylinder device was 16:1. Changes in parameters, such as pH values and conductivity in the cathode and the anode chambers as well as current and voltage in the sample area were analysed under the voltage gradient of 2 V/cm. After the experiment, the average removal efficiencies for Zn, Pb, Cd and Cu in the sample area were 53.2%, 31.4%, 42.3% and 30.7%, respectively. It indicates that the cylinder device is effective in removing heavy metals from the MSWI fly ash. Adopting the cylinder device for the experimental study on the electrokinetic remediation technology could provide a better way of thinking for the future engineering practices and applications.

Aging effects on the mobility of Pb in soil: Influence on the energy requirements in electroremediation

This paper studies the possible differences in the behavior of lead as a contaminant in soil samples when it is present as "naturally-aged" for decades after the contamination, and when it has been spiked in the laboratory. This behavior differences are stablished mainly in two ways: as changes in the fractionation analysis obtained after a sequential extraction procedure (SEP) and as changes in the efficiency of the acid-enhanced electroremediation (EKR) technique. Additionally, aging effects have been studied for almost five years. In the case of the lead-spiked soil the influence of storage conditions on contaminant behavior have also been explored: 1) samples stored in capped containers at constant moisture conditions, and 2) samples in containers open to the atmosphere, with periods of water flooding and drying. Lab-spiked and the "naturally-aged" contaminants show very different behavior with respect not only to SEP analysis but also to EKR experiments. The soil spiked with a soluble lead salt presents a higher percent in the more mobile fractions. Regarding storage conditions, some changes were observed in the lead distribution along the vertical soil profile for samples stored in uncapped containers. The EKR results were also in agreement with those from fractionation analysis. Energy requirements for the remediation were estimated by a mathematical model with important differences obtained for the different soil samples. Results are indicating that it will be very unreliable to draw estimations for the "naturally-aged" soils from contaminant-spiked samples.

The enhancement of synthesized wastewater on non-uniform electrokinetic remediation of a Cd-spiked natural clayey soil

It is usually very difficult to achieve satisfactory extraction efficiencies in electrokinetic remediation of heavy metal-contaminated soils of high acid/base buffer capacity. Enhancement agent is often required. In this study, synthesized citric acid industrial wastewater (CAIW) is used as the enhancement agent to remediate cadmium-spiked natural clayey soil from Shanghai, China. Four electrokinetic extraction experiments were carried out to evaluate the enhancement effects of CAIW on the remediation of metal-spiked clayed soil of high buffer capacity and the effects of treatment time and initial cadmium concentration on the migration of cadmium in the specimen. The results of electrokinetic experiments indicated that CAIW can efficiently enhance the transport of cadmium in comparison with HNO₃ of the same pH. Cadmium mobilization was enhanced with prolonged treatment time from 104 to 261.2 h, but the average cadmium removal efficiency was not significantly enhanced. A non-uniform cadmium distribution in the specimen was observed after the enhanced electrokinetic experiments due to the localized electrical gradients with an electrical gradient of approximately 1 V/cm and a ratio of the distance between electrodes of the same polarity to the outer diameter of electrode of 2.8 (50:18 mm).