Ex situ pilot scale electrokinetic restoration of saline soil using pulsed current

Hybrid and enhanced electrokinetic system for soil remediation from heavy metals and organic matter

The electrokinetic (EK) process has been proposed for soil decontamination from heavy metals and organic matter. The advantages of the EK process include the low operating energy, suitability for fine-grained soil decontamination, and no need for excavation. During the last three decades, enhanced and hybrid EK systems were developed and tested for improving the efficiency of contaminants removal from soils. Chemically enhanced-EK processes exhibited excellent efficiency in removing contaminants by controlling the soil pH or the chemical reaction of contaminants. EK hybrid systems were tested to overcome environmental hurdles or technical drawbacks of decontamination technologies. Hybridization of the EK process with phytoremediation, bioremediation, or reactive filter media (RFM) improved the remediation process performance by capturing contaminants or facilitating biological agents' movement in the soil. Also, EK process coupling with solar energy was proposed to treat off-grid contaminated soils or reduce the EK energy requirements. This study reviews recent advancements in the enhancement and hybrid EK systems for soil remediation and the type of contaminants targeted by the process. The study also covered the impact of operating parameters, imperfect pollution separation, and differences in the physicochemical characteristics and microstructure of soil/sediment on the EK performance. Finally, a comparison between various remediation processes was presented to highlight the pros and cons of these technologies.

Electrokinetic remediation for the removal of heavy metals in soil: Limitations, solutions and prospection

Electrokinetic remediation (EKR) technology is a promising method to remove heavy metals from low permeability soil, because it is environmentally friendly, efficient and economical, and can realize in-situ remediation. In this paper, the basic principles and related physical and chemical phenomena of EKR are systematically summarized, and three limiting problems of EKR technology are put forward: the weak ability of dissolving metals, focusing effect, and energy consumption. There are many methods to solve these technical problems, but there is a lack of systematic summary of the causes of problems and solutions. Based on various enhanced EKR technologies, this paper summarizes the main ideas to solve the limiting problems. The advantages and disadvantages of each technology are compared, which has guiding significance for the development of new technology in the future. This paper also discusses the dissolution of residual heavy metals, which is rare in other articles. The energy consumption of EKR and the remediation effect are equally important, and both can be used as indicators for evaluating the feasibility of new technologies. This paper reviews the influence of various electric field conditions on power consumption, such as renewable energy supply, new electrode materials and electrode configurations, suitable voltage values and functional electrolytes. In addition, a variety of energy consumption calculation methods are also introduced, which are suitable for ohmic heat loss, energy distribution when there is non-target ion competition, and power consumption of specific ions in various metal ions. Researchers can make selective reference according to their actual situations. This paper also systematically introduces the engineering design and cost calculation of EKR, lists the research progress of some engineering cases and pilot-scale tests, analyzes the reasons why it is difficult to apply EKR technology in large-scale engineering at present, and puts forward the future research direction.

Removal of Pb from Contaminated Kaolin by Pulsed Electrochemical Treatment Coupled with a Permeable Reactive Barrier: Tuning Removal Efficiency and Energy Consumption

Lead contamination in soil has emerged as a significant environmental concern. Recently, pulse electrochemical treatment (PECT) has garnered substantial attention as an effective method for mitigating lead ions in low-permeability soils. However, the impact of varying pulse time gradients, ranging from seconds to hours, under the same pulse duty cycle on lead removal efficiency (LRE) and energy consumption in PECT has not been thoroughly investigated. In this study, a novel, modified PECT method is proposed, which couples PECT with a permeable reaction barrier (PRB) and adds acetic acid to the catholyte. A comprehensive analysis of LRE and energy consumption is conducted by transforming pulse time. The results show that the LREs achieved in these experiments were as follows: PCb-3 s (89.5%), PCb-1 m (91%), PCb-30 m (92.9%), and PCb-6 h (91.9%). Importantly, these experiments resulted in significant reductions in energy consumption, with decreases of 68.5%, 64.9%, 51.8%, and 47.4% compared to constant voltage treatments, respectively. It was observed that LRE improved with an increase in both pulse duration and voltage gradient, albeit with a corresponding rise in energy consumption. The results also revealed that corn straw biochar as a PRB could enhance LRE by 6.1% while adsorbing migrating lead ions. Taken together, the present data highlights the potential of modified PECT technology for remediation of lead-contaminated soil, which provides an optimal approach to achieve high LRE while minimizing energy consumption.

Electrokinetic remediation of estuarine sediments using a large reactor: spatial variation of physicochemical, mineral, and chemical properties

The treatment and beneficial use of polluted or contaminated environmental matrices have become major issues, especially as the world strives toward a zero-waste policy. In this regard, dredged sediments need to be treated before they can be used in an environmentally safe and sustainable manner. Therefore, this work aims to treat estuarine sediments and, more importantly, use physicochemical, mineral, organic, and chemical information to understand the reactions that occur upon treatment. Dredged estuarine sediments were collected from Tancarville (Seine River estuary, France) and subjected to electrokinetic (EK) remediation using a 128-L laboratory-scale reactor. The sediments were treated 8 h per day for 21 days. The electric (voltage and current) and physicochemical (pH and electric conductivity) parameters were monitored during treatment. Sediments were collected from various sections in the reactor at the end of the experiment (lengthwise, widthwise, and depthwise). The spatial variation was investigated in terms of organic, mineral, and metal contents. Statistical analyses proved that the variation occurred only in the lengthwise direction. Furthermore, three main phases described the treatment, which were mainly linked to carbonate dissolution and pH variation. The results also showed that the trace elements Ni and Zn were reduced by 21% and 19%, respectively, without a direct link to pH, while Ca and Mg were only redistributed. The buffering capacity of the anodic sediment was reduced due to carbonate dissolution. The treated sediments showed reduced contents in trace metals without affecting major elements that can be useful in agriculture (i.e., Ca and Mg).

An overview of in-situ remediation for nitrate in groundwater

Faced with the increasing nitrate pollution in groundwater, in-situ remediation has been widely studied and applied on field-scale as an efficient, economical and less disturbing remediation technology. In this review, we discussed various in-situ remediation for nitrate in groundwater and elaborate on biostimulation, phytoremediation, electrokinetic remediation, permeable reactive barrier and combined remediation. This review described principles of each in-situ remediation, application, the latest progress, problems and challenges on field-scale. Factors affecting the efficiency of in-situ remediation for nitrate in groundwater are also summarized. Finally, this review presented the prospect of in-situ remediation for nitrate pollution in groundwater. The objective of this review is to examine the state of knowledge on in-situ remediation for nitrate in groundwater and critically evaluate factors which affect the up-scaling of laboratory and bench-scale research to field-scale application. This helps to better understand the control mechanisms of various in-situ remediation for nitrate pollution in groundwater and the design options available for application to the field-scale.

Remediation of saline-sodic soil by plant microbial desalination cell

Saline-sodic soil is widely distributed around the world and has induced severe impacts on ecosystems and agriculture. Plant microbial desalination cell (PMDC) and soil microbial desalination cell (SMDC) were constructed to migrate excessive salt in the soil in this study. Compared with SMDC, PMDCs generated higher voltage ranging from 150 mV to 410 mV (500Ω) and the maximum power density reached 34 mW/m². Higher desalinization efficiency was obtained by PMDCs, the soil conductivity reduced from initial 2.4 mS/cm to 0.4 ± 0.1 mS/cm and pH decreased from initial 10.4 to 8.2 ± 0.1. Soils desalination in PMDCs was achieved through multiple pathways, including ion migration in PMDCs driven by electrokinetic process, plant absorption and bioremediation by plant roots and anode microorganism activity. Geobacter was the dominant electrogenic bacteria at the PMDC anode. The electrochemical and desalinating performance of PMDCs was enhanced by plants and provided a new method for remediation of saline-sodic soil.

Sustainability in ElectroKinetic Remediation Processes: A Critical Analysis

In recent years, the development of suitable technologies for the remediation of environmental contaminations has attracted considerable attention. Among these, electrochemical approaches have gained prominence thanks to the many possible applications and their proven effectiveness. This is particularly evident in the case of inorganic/ionic contaminants, which are not subject to natural attenuation (biological degradation) and are difficult to treat adequately with conventional methods. The purpose of this contribution is to present a critical overview of electrokinetic remediation with particular attention on the sustainability of the various applications. The basis of technology will be briefly mentioned, together with the phenomena that occur in the soil and how that will allow its effectiveness. The main critical issues related to this approach will then be presented, highlighting the problems in terms of sustainability, and discussing some possible solutions to reduce the environmental impact and increase the cost-effectiveness and sustainability of this promising technology.

Removal of inorganic contaminants in soil by electrokinetic remediation technologies: A review

The soil contaminated by inorganic contaminants including heavy metals, radioactive elements and salts has been posing risks for human health and ecological environment, which has been widely paid attention in recent years. The electrokinetic remediation (EKR) technology is recognized as the most potential separation technology, which is commonly used to clean sites that are contaminated with organic and inorganic contaminants. It is the most suitable remediation technology for low permeability porous matrices. The main transport mechanism of pollutants in EKR include electromigration, electroosmosis and electrophoresis, coupled with electrolysis and geochemical reactions. Although arduous endeavors have been carried out to build optimal operating conditions and reveal the mechanism of EKR process, a systematic theoretical foundation hasn't been sorted yet. A comprehensive review on electrokinetic remediation of inorganic contaminants in soil is given in this study, and a more systematic theoretical foundation is sorted out according to the latest theoretical achievements. This theoretical system mainly focuses on the scientific and practical aspects of the application of EKR technology in soil remediation, by which we try to dig into the core of this technology. It contains key motive power of electric phenomena, side effects, energy consumption and supply, and removal of heavy metals, radioactive elements and salts in soil during EKR. In addition, correlations between dehydration, crystallization effect, focusing effect and thermal effect are disclosed; optimal operating conditions for the removal of heavy metals by EKR and EKR coupled with PRB are discussed and sorted out. Also discussed herein is the relationship between energy allocation and energy saving. According to the related findings, some potential improvements are also proposed.

Isolation and characterization of novel bacterial strains for integrated solar-bioelectrokinetic of soil contaminated with heavy petroleum hydrocarbons

This study investigated the isolation and characterization of three novel bacterial strains; Acinetobacter calcoaceticus, Sphingobacterium multivorum, and Sinorhizobium, isolated form agriculture land. From three hundred strains of bacteria, the three isolates were identified for their superior diesel degradation ability by a series of bench-scale tests. The isolates were further investigated in bench tests for their ability to grow in different diesel fuel concentrations, temperature and pH; degrade diesel fuel in vitro; and for the identification of functional genes. Semi-pilot bioelectrokinetic tests were conducted in three electrokinetic cells. An innovative electrode configuration was adopted to stabilize the soil pH and water content during the test. The genes expressed in the diesel degradation process including Lipases enzymes Lip A, LipB, Alk-b2, rubA, P450, and 1698/2041 were detected in the three isolates. The results showed that the solar panel voltage output is in agreement with the trapezoid model. The temperatures in the cells were found to be 5-7 °C higher than the ambient temperature. The electrode configuration succeeded in stabilizing the soil pH and water content, preventing the development of a pH gradient, important progress for the survival of bacteria. The diesel degradation in the soil after bioelectrokinetic tests were 20-30%, compared to 10-12% in the controls. The study succeeded in developing environmentally friendly technology employing novel bacterial strains to degrade diesel fuel and utilizing solar panels to produce renewable energy for bioelectrokinetics during the winter season.

Mitigation of soil contaminated with diesel fuel using bioelectrokinetics

This study investigated the effectiveness of bioelectrokinetics in rehabilitating a silty clayey sand contaminated with diesel fuel using three novel bacterial strains; Acinetobacter calcoaceticus, Sphingobacterium multivorum, and Sinorhizobium, isolated form agriculture land. Three electrokinetic bioremediation cells were used to conduct the tests and a novel electrode configuration technique was used to stabilize pH and water content in the soil specimen. Solar photovoltaic panels were used to generate sustainable energy for the process. The tests were carried out in outdoors for 55 days. Applied voltage, current passing through the electrokinetic cell, and the temperature of the soil specimen were recorded periodically during the test. The pH, water content, and diesel concentration were determined at the end of the tests. Over the test period, the voltage typically increased from zero before sunrise, remained relatively stabilized for about 4 h, and then started to decrease and dropped to zero by sunset. The temperatures in the cells were found to be 5-7 °C higher than the ambient temperature. The innovative electrode configuration succeeded in keeping the pH of soil to remain the same and thereby prevented the development of a pH gradient in the soil, an important development for survival of the bacteria. The diesel degradation in the soil after bioelectrokinetics were 20-30%, compared to 10-12% in the control test. The study was successful in developing environmentally friendly technology employing novel bacterial strains to degrade diesel fuel and utilizing solar panel to produce renewable energy for bioelectrokinetic during the winter season.

Environmental assessment on electrokinetic remediation of multimetal-contaminated site: a case study

In this study, an environmental assessment on an electrokinetic (EK) system for the remediation of a multimetal-contaminated real site was conducted using a green and sustainable remediation (GSR) tool. The entire EK process was classified into major four phases consisting of remedial investigations (RIs), remedial action construction (RAC), remedial action operation (RAO), and long-term monitoring (LTM) for environmental assessment. The environmental footprints, including greenhouse gas (GHG) emissions, total energy used, air emissions of criteria pollutants, such as NOx, SOx, and PM10, and water consumption, were calculated, and the relative contribution in each phase was analyzed in the environmental assessment. In the RAC phase, the relative contribution of the GHG emissions, total energy used, and PM10 emissions were 77.3, 67.6, and 70.4%, respectively, which were higher than those of the other phases because the material consumption and equipment used for system construction were high. In the RAO phase, the relative contributions of water consumption and NOx and SOx emissions were 94.7, 85.2, and 91.0%, respectively, which were higher than those of the other phases, because the water and electricity consumption required for system operation was high. In the RIs and LTM phases, the environmental footprints were negligible because the material and energy consumption was less. In conclusion, the consumable materials and electrical energy consumption might be very important for GSR in the EK remediation process, because the production of consumable materials and electrical energy consumption highly affects the GHG emissions, total energy used, and air emissions such as NOx and SOx.