Enhanced electrokinetic treatment of marine sediments contaminated by heavy metals and PAHs

AI-assisted systematic review on remediation of contaminated soils with PAHs and heavy metals

This systematic review addresses soil contamination by crude oil, a pressing global environmental issue, by exploring effective treatment strategies for sites co-contaminated with heavy metals and polycyclic aromatic hydrocarbons (PAHs). Our study aims to answer pivotal research questions: (1) What are the interaction mechanisms between heavy metals and PAHs in contaminated soils, and how do these affect the efficacy of different remediation methods? (2) What are the challenges and limitations of combined remediation techniques for co-contaminated soils compared to single-treatment methods in terms of efficiency, stability, and specificity? (3) How do various factors influence the effectiveness of biological, chemical, and physical remediation methods, both individually and combined, in co-contaminated soils, and what role do specific agents play in the degradation, immobilization, or removal of heavy metals and PAHs under diverse environmental conditions? (4) Do AI-powered search tools offer a superior alternative to conventional search methodologies for executing an exhaustive systematic review? Utilizing big-data analytics and AI tools such as Litmaps.co, ResearchRabbit, and MAXQDA, this study conducts a thorough analysis of remediation techniques for soils co-contaminated with heavy metals and PAHs. It emphasizes the significance of cation-π interactions and soil composition in dictating the solubility and behavior of these pollutants. The study pays particular attention to the interplay between heavy metals and PAH solubility, as well as the impact of soil properties like clay type and organic matter on heavy metal adsorption, which results in nonlinear sorption patterns. The research identifies a growing trend towards employing combined remediation techniques, especially biological strategies like biostimulation-bioaugmentation, noting their effectiveness in laboratory settings, albeit with potentially higher costs in field applications. Plants such as Medicago sativa L. and Solanum nigrum L. are highlighted for their effectiveness in phytoremediation, working synergistically with beneficial microbes to decompose contaminants. Furthermore, the study illustrates that the incorporation of biochar and surfactants, along with chelating agents like EDTA, can significantly enhance treatment efficiency. However, the research acknowledges that varying environmental conditions necessitate site-specific adaptations in remediation strategies. Life Cycle Assessment (LCA) findings indicate that while high-energy methods like Steam Enhanced Extraction and Thermal Resistivity - ERH are effective, they also entail substantial environmental and financial costs. Conversely, Natural Attenuation, despite being a low-impact and cost-effective option, may require prolonged monitoring. The study advocates for an integrative approach to soil remediation, one that harmoniously balances environmental sustainability, cost-effectiveness, and the specific requirements of contaminated sites. It underscores the necessity of a holistic strategy that combines various remediation methods, tailored to meet both regulatory compliance and the long-term sustainability of decontamination efforts.

Electrochemical remediation of synthetic and real marine sediments contaminated by PAHs, Hg and As under low electric field values

To date, remediation, protection, and restoration of contaminated sites is a global concern. The current technologies to restore sediments characterized by heterogeneous characteristics, several pollutants, fine grains, and low hydraulic permeability are poorly effective; hence their remediation is still challenging. A promising approach for the sediment's remediation could be the electrochemical route since it is a not-expensive, effective and noninvasive in situ technology. Electrochemical remediation (ER) is commonly studied under relatively high electric fields (E ≥ 1 V cm-1) and using costly processing fluids in a three compartments cell aiming to desorb and transport the contaminants into the processing fluids (secondary dangerous effluent). In this work, contaminated marine sediments were electrochemically treated focusing on the insertion of electrodes directly in the sediments and adopting, for the first time for real sediments, low E values (≤ 0.25 V cm-1) for 4-days period. It was observed that PAHs can be simultaneously transported and degraded in situ preventing the production of a secondary dangerous effluent and reducing the energy consumption. Firstly, clay marine sediments dragged from Capo Granitola Coast (Trapani, Italy) spiked with five PAHs congeners (5PAHs), Hg and As were used as a simplified model matrix and treated to simulate a real case study. A total PAHs removal efficiency of 57% was reached after 96 h of treatment under 0.05 V cm-1. Then, real polluted marine sediments from Augusta Bay (Syracuse) and Bagnoli-Coroglio Bay (Naples) in the southern Italy were treated as real contaminated sediments to be restored, to validate the proposed approach for real cases. A quite good removal efficiency of PAHs was reached after 96 h of electrochemical treatment coupled with a low energetic consumption due to the rather E values adopted. In addition, it was observed that this approach, under the adopted conditions, is unsuitable for the remediation of Hg and As.

Innovative method for the brine treatment by electrokinetic principles integrated with solar photovoltaic plants

With the growing world population and industrial production, the demand for water has been continuously increasing. By 2030, it was estimated that 60.0 % of the world population will not have access to freshwater, which is about 2.50 % of the total global water. For this, a total of over 17,000 operational desalination plants have been constructed worldwide. However, the key barriers to expansion of the desalination treatments are the brine production and energy consumption. In fact, the brine production is 50.0 % higher than the freshwater, and its treatments could account for 5.0-33.0 % of total desalination cost. Here, a new theoretical approach for brine treatments integrated to solar photovoltaic plants (PVs) to supply renewable energy to the whole system has been proposed. This approach consists in combining electrokinetic and electrochemical phenomena to dilute the brine, by using an alkaline clay with high buffering power. This method substantially desalinates the brine to produce new treated seawater, using clean energy, optimizing energetic and management costs. Some hypotheses and secondary effects should validate the model, e.g., relatively high Ca2+ promotes the electro-migration; the Cl2 production reduces the Cl- concentrations; and the production of H2 can be used to store energy. A practical example for PVPs design is shown.

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.

Iron slag permeable reactive barrier for PFOA removal by the electrokinetic process

The efficacy of the Standalone Electrokinetic (EK) process in soil PFAS removal is negligible, primarily due to the intersecting mechanisms of electromigration and electroosmosis transportation. Consequently, the redistribution of PFAS across the soil matrix occurs, hampering effective remediation efforts. Permeable reactive barrier (PRB) has been used to capture contaminants and extract them at the end of the EK process. This study conducted laboratory-scale tests to evaluate the feasibility of the iron slag PRB enhanced-EK process in conjunction with Sodium Cholate (NaC) biosurfactant as a cost-effective and sustainable method for removing PFOA from the soil. A 2 cm iron slag-based PRB with a pH of 9.5, obtained from the steel-making industry, was strategically embedded in the middle of the EK reactors to capture PFOA within the soil. The main component of the slag, iron oxide, exhibited significant adsorption capacity for PFOA contamination. The laboratory-scale tests were conducted over two weeks, revealing a PFOA removal rate of more than 79% in the slag/activated carbon PRB-EK test with NaC enhancement and 70% PFOA removal in the slag/activated carbon PRB-EK without NaC. By extending the duration of the slag/AC PRB-EK test with NaC enhancement to three weeks, the PFOA removal rate increased to 94.09%, with the slag/AC PRB capturing over 87% of the initial PFOA concentration of 10 mg/L. The specific energy required for soil decontamination by the EK process was determined to be 0.15 kWh/kg. The outcomes of this study confirm the feasibility of utilizing iron slag waste in the EK process to capture PFOA contaminants, offering a sustainable approach to soil decontamination. Combining iron slag PRB and NaC biosurfactant provides a cost-effective and environmentally friendly method for efficient PFOA removal from soil.

Numerical solutions for the treatment brine by diffusive and migration flux using new brine-clay-seawater system

With the growing world population and industrial production, the demand for water has been continuously increasing. By 2030, 60.0% of the world population will not have access to freshwater, which is ∼2.50% of the total global water. For this, a total of over 17,000 operational desalination plants have been constructed worldwide. However, the key barrier to desalination expansion is brine production, which is 50.0% higher than the freshwater, generating 5.0-33.0% of total desalination cost. In this paper, a new theoretical approach for brine treatments has been proposed. It consists in combining electrokinetic and electrochemical mechanisms by using an alkaline clay with high buffering power. Advanced numerical model has been carried out to estimate the ions concentrations in the brine-clay-seawater system. Analytical analyses have been also carried out to estimate the global system efficiency. Results show the feasibility of the theoretical system, its size, and usability of the clay. This model not only should clean the brine to produce new treated seawater but also it should recover useful minerals thank to the electrolysis and precipitations effects.

Roles of oxidant, activator, and surfactant on enhanced electrokinetic remediation of PAHs historically contaminated soil

Electrokinetic (EK) remediation technology can enhance the migration of reagents to soil and is especially suitable for in situ remediation of low permeability contaminated soil. Due to the long aging time and strong hydrophobicity of polycyclic aromatic hydrocarbons (PAHs) from historically polluted soil, some enhanced reagents (oxidant, activator, and surfactant) were used to increase the mobility of PAHs, and remove and degrade PAHs in soil. However, under the electrical field, there are few reports on the roles and combined effect of oxidant, activator, and surfactant for remediation of PAHs historically contaminated soil. In the present study, sodium persulfate (PS, oxidant, 100 g L-1) or/and Tween 80 (TW80, surfactant, 50 g L-1) were added to the anolyte, and citric acid chelated iron(II) (CA-Fe(II), activator, 0.10 mol L-1) was added to catholyte to explore the roles and contribution of enhanced reagents and combined effect on PAHs removal in soil. A constant voltage of 20 V was applied and the total experiment duration was 10 days. The results showed that the removal rate of PAHs in each treatment was PS + CA-Fe(II) (21.3%) > PS + TW80 + CA-Fe(II) (19.9%) > PS (17.4%) > PS + TW80 (11.4%) > TW80 (8.1%) > CK (7.5%). The combination of PS and CA-Fe(II) had the highest removal efficiency of PAHs, and CA-Fe(II) in the catholyte could be transported toward anode via electromigration. The addition of TW80 reduced the electroosmotic flow and inhibited the transport of PS from anolyte to the soil, which decreased the removal of PAHs (from 17.4 to 11.4% with PS, from 21.3 to 19.9% with PS+CA-Fe(II)). The calculation of contribution rates showed that PS was the strongest enhancer (3.3~9.9%), followed by CA-Fe(II) (3.9~8.5%) (with PS), and the contribution of TW80 was small and even negative (-1.4~0.6%). The above results indicated that the combined application of oxidant and activator was conducive to the removal of PAHs, while the addition of surfactant reduced the EOF and the migration of oxidant and further reduced the PAHs removal efficiency. The present study will help to further understand the role of enhanced reagents (especially surfactant) during enhanced EK remediation of PAHs historically contaminated soil.

Trace element contamination status of surface marine sediments of Greece: an assessment based on two decades (2001-2021) of data

This study is a first attempt to assess the trace element contamination status in the surface sediments of the Hellenic Seas since the first environmental studies in the country commenced in the mid-1970s. All available trace element data from the last 20 years have been collected and assessed using sediment quality guidelines and application of single- and multielement pollution indices. Although Hellenic marine sediments initially appear as anthropogenically enriched in Cr and As, this enrichment is attributed to the natural background. Central Greece appears more polluted, followed by Northern Greece and lastly Southern Greece. The element pollution indices featured the influence of industrial activities such as mining, steel industry and chemical factories, shipyards, and secondarily the influence of port activities.

Electrokinetic combined peroxymonosulfate (PMS) remediation of PAH contaminated soil under different enhance methods

Because of the high hydrophobicity, low volatility, and high sorption capacity of PAHs, their remediation in contaminated soil is challenging. Electrokinetic (EK) enhanced chemical remediation is an emerging dual technology employed in this study, using a new oxidant peroxymonosulfate (PMS) to remediate PAHs contaminated soil. Here, PMS migration under electric field and the remediation efficiency for the PAHs polluted soil were assessed. We observed that the PMS removal efficiencies (59.7%-82.8%) were higher than those with persulfate (PS) (53.9%-78.5%), indicating PMS's superior oxidation capacity for PAHs. Although oxidant PMS can decontaminate PAHs in polluted soils, its removal of PAHs was only 11.0% without the enhanced methods. The enhancements increased the removal efficiency for PAHs from 0.33 to 2.10 times. At fixed catholyte pH of 4, the highest removal efficiency (34.1%) was achieved because it enhanced PMS migration from cathode to anode. These findings suggested that PMS was a potential oxidant for EK remediation, and some enhancements must be applied in EK combined PMS remediation PAHs polluted soil.

Facile synthesis of core\shell Fe3O4@mSiO2(Hb) and its application for organic wastewater treatment

Treatment of organic wastewater is a challenging task. Biological techniques using biocatalysts have shown their benefits in organic wastewater treatment. In this research, a novel biocatalyst was developed by encapsulation of Fe3O4 microspheres and haemoglobin (Hb) with mesoporous silica, named Fe3O4@mSiO2(Hb). Fe3O4@mSiO2(Hb) exhibited typical mesoporous characteristics (mesoporous silica), magnetic feature (Fe3O4) and peroxidase activity (Hb). The results showed that the immobilization of Hb into Fe3O4@mSiO2 did not affect its activity. In addition, Fe3O4@mSiO2(Hb) exhibited a higher efficiency in the peroxidation of aromatic compounds than free Hb. The peroxidase activity of the synthesized biocatalyst was estimated to be 120 Ug^-1, which was almost four times greater than that of previously reported immobilized Hb. Also, the Km of Fe₃O₄@mSiO₂(Hb) was similar to that of the free Hb and it was estimated to be 4.3 × 10^-4 μM, indicating that the activity of the Hb in the immobilized enzyme was not affected after immobilization. The immobilized enzyme was also found to be stable, recyclable and reusable. Taken together, these results indicate that the Fe₃O₄@mSiO₂(Hb) has good potential to be used for treating organic wastewater containing aromatic compounds. The magnetically separable novel biocatalyst developed in this study provided not only a more suitable microenvironment for retaining the activity of Hb, but also demonstrated enhanced stability and activity under unfavorable conditions.

Investigation of a biosurfactant-enhanced electrokinetic method and its effect on the potentially toxic trace elements in waterways sediments

In this study, the biosurfactant-enhanced electrokinetic method was investigated for the removal of potentially toxic trace elements (As, Ba, Cd, Cr, Cu, Mo, Ni, Pb, Sb, Se and Zn) in waterways sediments. The effect of this method was compared to the removal capacities of deionized water in the same conditions in order to assess its efficiency. After treatment, batch leaching tests have shown that almost toxic elements (As: 81.3%; Ba: 80%; Cr: 97.3%; Cu: 82%; Zn: 94.5%; Mo: 13.8%; Ni: 62.7%; Se: 66.8% and Sb: 9.3%) were less released in waters. On the whole sediment samples, Ba and Cd displayed the highest removal rates (Ba: 71.2% and Cd: 77.5%). The use of biosurfactant enhanced the electrokinetic method by improving the trace elements migration and altering pH and Eh locally generated by the system. Overall, the application of this new approach dredged sediments seems to be promising but needed further investigations for industrial applications.

Enhanced electrokinetic remediation for Cd-contaminated clay soil by addition of nitric acid, acetic acid, and EDTA: Effects on soil micro-ecology

Enhanced electrokinetic remediation (EKR) allows the rapid remediation of heavy metal-contaminated clay, but the impacts of this process on soil micro-ecology have rarely been evaluated. In this study, nitric acid, acetic acid, and EDTA were applied for enhancement of EKR and the effects on Cd removal, soil enzyme activity, and soil bacterial communities (SBCs) were determined. Nitric acid and acetic acid allowed 93.2% and 91.8% Cd removal, respectively, and EDTA treatment resulted in 40.4% removal due to the formation of negatively charged EDTA-Cd complexes, resulting in opposing directions of Cd electromigration and electroosmosis flow and slow electromigration rate caused by low voltage drop. Activities of soil beta-glucosidase, acid phosphatase, and urease, were all reduced by enhanced EKR treatment, especially nitric acid treatment, by 46.2%, 58.8% and 57.7%, respectively. The SBCs were analyzed by high-throughput sequencing and revealed significantly increased diversity for acetic acid treatment, no effect for EDTA treatment, and reduced diversity for nitric acid treatment. Compared with nitric acid and EDTA, acetic acid treatment enhanced EKR for higher Cd removal and improved biodiversity.

Phenanthrene removal from the contaminated soil using the electrokinetic-Fenton method and persulfate as an oxidizing agent

Remediation of soils contaminated with hydrocarbon materials is of particular importance due to their association with food chain. One of the remediation methods, which has been taken into account in recent years by researchers, is the electrokinetic technique. In this study, the electrokinetic method was used in combination with the Fenton technique to remove phenanthrene from clay soil. Oxidizing agent and catalyst used in the Fenton technique greatly influenced the efficiency of the remediation process. To investigate the effect of these two factors on the remediation process, it was made use of three different types of electrodes as catalyst, including graphite, iron, and copper, as well as hydrogen peroxide and sodium persulfate with different concentrations as oxidizing agent. During the 9 experiments designed, factors affecting removal efficiency, such as remediation time, electric current intensity, electroosmotic flow rate, and pH of the cathode and anode reservoirs were also investigated. Overall, the use of the electrokinetic-Fenton method with 15% hydrogen peroxide and copper electrode exhibited a 100% increase in the process efficiency over the same time period required to perform the conventional electrokinetic method and removed 93% of the soil phenanthrene, these findings indicated that combining the Fenton technique with the electrokinetic method enhanced the efficiency of this method in removing organic pollutants from the soil. Also, the use of sodium persulfate as an oxidizing agent in the electrokinetic method increased the removal efficiency by more than 95% over the half time period required to perform the conventional electrokinetic method.

Application of enhanced electrokinetic remediation by coupling surfactants for kerosene-contaminated soils: Effect of ionic and nonionic surfactants

Electrokinetic (EK) by coupling surfactants is an enhanced promising remediation technology to eliminate hydrophobic organic contaminants (HOC_s) from low-permeable soils. It is also applied to remediate kerosene-contaminated soils using anionic (SDS) and non-ionic (Tween 80) surfactants at different concentrations. There was negligible removal efficiency (40%) of kerosene during traditional EK without any enhancement technique. In the present study, the application of 0.005M and 0.01M SDS in EK-SDS-1 and EK-SDS-2 improved the removal efficiency to 50 and 55%, respectively towards the anode. Furthermore, the use of Tween 80 in EK-Tw80-1 and EK-Tw80-2 at 0.1 and 1% concentrations was able to raise kerosene removal gradually from 45% to 52% towards the cathode. These findings suggest that higher concentrations of SDS and Tween 80 contribute to the more effective elimination of kerosene. Thus, in EK-SDS-Tw80-V1.5 and EK-SDS-Tw80-V2, SDS and Tween 80 were used simultaneously at higher concentrations, which led to 63 and 67% kerosene removal, respectively. Considering the maximum removal in EK-SDS-Tw80-V2, the energy consumption in EK-SDS-Tw80-V2 was 178 KWh/m³ due to the higher voltage gradient; whereas without increased voltage in EK-SDS-Tw80-V1.5, this amount was decreased to 84 KWh/m³. It is to be mentioned that the electro-osmotic flow (EOF) played a significant role in minimizing kerosene concentration during the EK process, particularly when combined with surfactants.

Optimization of energy consumptions of oxidation tanks in urban wastewater treatment plants with solar photovoltaic systems

This paper combines solar photovoltaic (PV) to wastewater treatment plants (WWTPs). A new methodology is proposed to design solar PV to reduce energy consumptions of aeration thanks in WWTPs. New analytical equations and parameters, based on the air temperatures, solar irradiations, biological kinetics, dissolved oxygens, mechanical oxygenations, are introduced to obtain the peak power of PV that maximize the auto-consumptions of aeration blowers installed in the oxidation tanks of WWTPs. The method allows a direct preliminary design and a calibrated estimation for energy power. To justify this method, three aspect are mainly discussed: (i) the oxidation tanks consume up to 30% of the energy of a WWTP; (ii) the temperature of wastewater is variable during the year, in the smaller WWTPs; (iii) the dissolved oxygen reduces, increasing temperature of wastewater. This methodology will support the sector in making decision over PV investments, helping wastewater utilities to consider sustainable management practices. Therefore, a further contribute to develop the integration of renewable energy sources combined with wastewater sectors is activated.

Insights into the remediation of cadmium-pyrene co-contaminated soil by electrokinetic and the influence factors

The remediation of cadmium-pyrene co-contaminated soil by electrokinetic (EK) and the influence factors were investigated in this study. The artificial contaminated soils were treated for 20 days in EK experimental setups without electrolyte solution reservoirs, to simulate in-situ remediation of unsaturated soil. The results indicated that polarity-reversing electric field had maintained soil pH in the range of 7.27-7.67. Cadmium (Cd) contaminant would aggregate near electrodes, and the average Cd concentration in these areas had reached 72.21 mg/kg (original 51.6 mg/kg), while the value in soil farthest away from electrodes was 33.58 mg/kg. The reasons for Cd aggregated were: the insoluble hydroxide formations attribute to the frequently alternation of acid-base environment, and the decrease of pH and water holding capacity in soil away from electrodes would promote the dissolved Cd movement by electro-osmosis flow. Although the applied electric field could promote the growth and activity of pyrene-degrading microorganisms (PDM), the soluble Cd would be the restriction factor, especially in soil near electrodes. However, the highest (56.38%) pyrene removal efficiency (PRE) was achieved near electrodes due to the synergistic effect of electric filed and PDM, and PRE was positively correlated with the PDM number in soil away from electrodes.

Enhanced electrokinetic remediation of multi-contaminated dredged sediments and induced effect on their toxicity

Electrokinetic (EK) remediation is often developed for metal decontamination but shows limitations for polycyclic aromatic hydrocarbons (PAHs) and polychlorobiphenyls (PCBs) which are nonionic and involve low aqueous solubility. This paper reports many laboratory studies devoted to the investigations of EK efficiency on the mobility and the removal of metals, PAHs and PCBs from dredged sediments, using a mixture of chelating agent and surfactants. The results showed that increasing chelating agent concentration was favorable for both metal and PAH removal. Applying a periodic voltage gradient associated to a low concentration of additives provided the best removal of Zn, Cd and Pb and also the 16 priority PAHs. The tested fresh harbor sediment was highly resistant to metals and organics mobilization and transport because of an aged contamination, a high buffering capacity, a very low hydraulic permeability and a high organic matter content. However, experiments performed on a former sediment which was deposited many years ago provided better removal results, involving low organic matter and carbonates content. The efficiency of the EK process was also assessed by measuring the acute toxicity of the EK-treated sediment on the copepod Eurytemora affinis exposed to sediment elutriates.

State of the art and future challenges for polycyclic aromatic hydrocarbons is sediments: sources, fate, bioavailability and remediation techniques

Polycyclic aromatic hydrocarbons (PAHs) are amongst the most abundant contaminants found in the aquatic environment. Due to their toxicity and carcinogenicity, their sources, fate, behaviour, and cleanup techniques have been widely investigated in the last several decades. When entering the sediment-water system, PAH fate is determined by particular PAH and sediment physico-chemical properties. Most of the PAHs will be associated with fine-grained, organic-rich, sediment material. This makes sediment an ultimate sink for these pollutants. This association results in sediment contamination, and in this manner, sediments represent a permanent source of water pollution from which benthic organisms may accumulate toxic compounds, predominantly in lipid-rich tissues. A tendency for biomagnification can result in critical body burdens in higher trophic species. In recent years, researchers have developed numerous methods for measuring bioavailable fractions (chemical methods, non-exhaustive extraction, and biomimetic methods), as valuable tools in a risk-based approach for remediation or management of contaminated sites. Contaminated sediments pose challenging cleanup and management problems, as conventional environmental dredging techniques are invasive, expensive, and sometimes ineffective or hard to apply to large and diverse sediment sites. Recent studies have shown that a combination of strategies including in situ approaches is likely to provide the most effective long-term solution for dealing with contaminated sediments. Such in situ approaches include, but are not limited to: bioaugmentation, biostimulation, phytoremediation, electrokinetic remediation, surfactant addition and application of different sorbent amendments (carbon-rich such as activated carbon and biochar) that can reduce exposure and limit the redistribution of contaminants in the environment.

Treatment technologies for PAH-contaminated sites: a critical review

To reduce environmental and human health risks of contaminated sites, having a comprehensive knowledge about the polycyclic aromatic hydrocarbon (PAH) removal processes is crucial. PAHs are contaminants which are highly recognized to pose threats to humans, animals, and plants. PAHs are hydrophobic and own two or more benzene rings, and hence are resistant to structural degradation. There are various techniques which have been developed to treat PAH-contaminated soil. Four distinct processes to remove PAHs in the contaminated soil, thought to be more effective techniques, are presented in this review: soil washing, chemical oxidation, electrokinetic, phytoremediation. In a surfactant-aided washing process, a removal rate of 90% was reported. Compost-amended phytoremediation treatment presented 58-99% removal of pyrene from the soil in 90 days. Chemical oxidation method was able to reach complete conversion for some PAHs. In electrokinetic treatment, researchers have achieved reliable results in removal of some specific PAHs. Researchers' innovations in novel studies and advantages/disadvantages of the techniques are also investigated throughout the paper. Finally, it should be noted that an exclusive method or a combination of methods by themselves are not the key to be employed for remediation of every contaminated site but the field characteristics are also essential in selection of the most appropriate decontamination technique(s). The remedy for selection criteria is based on PAH concentrations, site characteristics, costs, shortcomings, and advantages.

Using Calcination Remediation to Stabilize Heavy Metals and Simultaneously Remove Polycyclic Aromatic Hydrocarbons in Soil

Co-contaminated soils containing heavy metals and polycyclic aromatic hydrocarbons (PAHs) are an environmental and human health risk. Research into the remediation of these soils is imperative. In this paper, a novel investigation utilizing calcination technique to stabilize heavy metals and simultaneously remove PAHs in soil was conducted. Calcination temperature (300–700 °C) was observed to play a dominant role in heavy metal stabilization and PAH removal in soils. However, calcination time (0.5–8 h) had no significant effect on these contaminants during calcination at different temperatures. Considering the remediation cycle requirements and economic costs of engineering, we suggested that the optimal calcination condition for Zn, Cu, naphthalene, and fluoranthene was at 700 °C for 0.5 h, and the corresponding stabilization or removal efficiency values were 96.95%, 98.41%, 98.49%, and 98.04%, respectively. Results indicate that calcination as a remedial strategy exhibits a bright future for practical applications in the simultaneous stabilization of heavy metals and PAH removal from co-contaminated sites.

Application of a crustacean bioassay to evaluate a multi-contaminated (metal, PAH, PCB) harbor sediment before and after electrokinetic remediation using eco-friendly enhancing agents

Electrokinetic (EK) remediation can be a suitable technology for treating contaminated dredged harbor sediment, stored on terrestrial disposal sites. Citric acid (CA) and biosurfactants (rhamnolipids and saponin) were chosen as enhancing agents for simultaneous metal (Cd, Cr, Cu, Pb, Zn) and PAH/PCB removal by EK because of their potential low toxicity with a view to site restoration. Three EK runs were performed using a periodic voltage (1Vcm^-1) and various concentrations of agents. The best combination of CA (0.2molL^-1) and saponin (0.85gL^-1) did not remove high amounts of metals (4.4-15.8%) and provided only slightly better results for PAH and PCB removal (29.2% and 38.2%, respectively). The harbor sediment was highly resistant to metal and organics mobilization and transport because of an aged contamination, a high buffering capacity, a very low hydraulic permeability and a high organic matter content. The efficiency of the EK process was also assessed by measuring the acute toxicity of the EK-treated sediment on E. affinis copepods exposed to sediment elutriates. Fortunately, the use of CA and biosurfactants did not significantly impact on sediment toxicity. Some treated sediment sections, particularly those near the anode compartment, were statistically more toxic than the raw sediment. More particularly, E. affinis copepods were significantly sensitive to low pH values and oxidative conditions, to Cu, and to a lesser extent to Pb amounts. The speciation of these metals probably changed in these pH and redox conditions so that they became more easily leachable and bioavailable. In contrast, toxicity was negatively correlated to PAH and PCB amounts after EK treatment, probably due to the production of oxidized metabolites of PAHs and PCBs.

Remediation of electronic waste polluted soil using a combination of persulfate oxidation and chemical washing

Laboratory experiments were conducted to investigate the efficiency of a simultaneous chemical extraction and oxidation for removing persistent organic pollutants (POPs) and toxic metals from an actual soil polluted by the recycling activity of electronic waste. Various chemicals, including hydroxypropyl-β-cyclodextrin (HPCD), citric acid (CA) and sodium persulfate (SP) were applied synchronously with Fe²⁺ activated oxidation to enhance the co-removal of both types of pollutants. It is found that the addition of HPCD can enhance POPs removal through solubilization of POPs and iron chelation; while the CA-chelated Fe²⁺ activation process is effective for extracting metals and degrading residual POPs. Under the optimized reagent conditions, 69.4% Cu, 78.1% Pb, 74.6% Ni, 97.1% polychlorinated biphenyls, 93.8% polycyclic aromatic hydrocarbons, and 96.4% polybrominated diphenylethers were removed after the sequential application of SP-HPCD-Fe²⁺ and SP-CA-Fe²⁺ processes with a duration of 180 and 240 min, respectively. A high dehalogenation efficiency (84.8% bromine and 86.2% chlorine) is observed, suggesting the low accumulation of halogen-containing organic intermediates. The remediated soil can satisfy the national soil quality standard of China. Collectively, co-contaminated soil can be remediated with reasonable time and capital costs through simultaneous application of persulfate oxidation and chemical extraction.

Simultaneous electrodialytic removal of PAH, PCB, TBT and heavy metals from sediments

Contaminated sediments are remediated in order to protect human health and the environment, with the additional benefit of using the treated sediments for other activities. Common for many polluted sediments is the contamination with several different pollutants, making remediation challenging with the need of different remedial actions for each pollutant. In this study, electrodialytic remediation (EDR) of sediments was found effective for simultaneous removal of heavy metals and organic pollutants for sediments from Arctic regions - Sisimiut in Greenland and Hammerfest in Norway. The influence of sediment properties and experimental settings on the remediation process was studied by employing multivariate analysis. The importance of the variables studied varied with the pollutant and based on these results it was possible to assess removal processes for the different pollutants. Desorption was found to be important for the removal of heavy metals and TBT, while photolysis was significant for removal of PAH, PCB and TBT. In addition, dechlorination was found to be important for the removal of PCB. The highest removal efficiencies were found for heavy metals, TBT and PCB (>40%) and lower removal efficiencies for PAH (<35%).

Effect of tea saponin on phytoremediation of Cd and pyrene in contaminated soils by Lolium multiflorum

Tea saponin (TS), a kind of green biosurfactant produced by plants, was added into the Cd-pyrene co-contaminated soils to evaluate its influence on phytoremediation of Cd and pyrene by Lolium multiflorum. The results showed that the accumulation of pyrene in L. multiflorum was significantly promoted by the TS. Compared with no TS treatments (PL and ML), the aboveground concentrations of pyrene in TS treatments (PLT and MLT) increased by 135 and 30%, respectively, and the underground concentrations of pyrene in TS treatments (PLT and MLT) increased by 40 and 25%. The concentrations of Cd in the aboveground and underground parts in single contaminated treatments were all significantly more than those in co-contaminated treatments, while the situation of pyrene was quite the reverse. Besides, the addition of TS enhanced activities of dehydrogenase and polyphenol oxidase in soils and increased the biomass of L. multiflorum. The micromorphology of L. multiflorum was not affected by TS. The study suggests that the use of L. multiflorum with TS is an alternative technology for remediation of Cd-pyrene co-contaminated soils.

Multispecies reactive transport modelling of electrokinetic remediation of harbour sediments

We implemented a numerical model to simulate transport of multiple species and geochemical reactions occurring during electrokinetic remediation of metal-contaminated porous media. The main phenomena described by the model were: (1) species transport by diffusion, electromigration and electroosmosis, (2) pH-dependent buffering of H⁺, (3) adsorption of metals onto particle surfaces, (4) aqueous speciation, (5) formation and dissolution of solid precipitates. The model was applied to simulate the electrokinetic extraction of heavy metals (Pb, Zn and Ni) from marine harbour sediments, characterized by a heterogeneous solid matrix, high buffering capacity and aged pollution. A good agreement was found between simulations of pH, electroosmotic flow and experimental results. The predicted residual metal concentrations in the sediment were also close to experimental profiles for all of the investigated metals. Some removal overestimation was observed in the regions close to the anode, possibly due to the significant metal content bound to residual fraction.

Simultaneous application of chemical oxidation and extraction processes is effective at remediating soil Co-contaminated with petroleum and heavy metals

Chemical extraction and oxidation processes to clean up heavy metals and hydrocarbon from soil have a higher remediation efficiency and take less time than other remediation processes. In batch extraction/oxidation process, 3% hydrogen peroxide (H₂O₂) and 0.1 M ethylenediaminetetraacetic acid (EDTA) could remove approximately 70% of the petroleum and 60% of the Cu and Pb in the soil, respectively. In particular, petroleum was effectively oxidized by H₂O₂ without addition of any catalysts through dissolution of Fe oxides in natural soils. Furthermore, heavy metals bound to Fe-Mn oxyhydroxides could be extracted by metal-EDTA as well as Fe-EDTA complexation due to the high affinity of EDTA for metals. However, the strong binding of Fe-EDTA inhibited the oxidation of petroleum in the extraction-oxidation sequential process because Fe was removed during the extraction process with EDTA. The oxidation-extraction sequential process did not significantly enhance the extraction of heavy metals from soil, because a small portion of heavy metals remained bound to organic matter. Overall, simultaneous application of oxidation and extraction processes resulted in highly efficient removal of both contaminants; this approach can be used to remove co-contaminants from soil in a short amount of time at a reasonable cost.

Performance of electroremediation in real contaminated sediments using a big cell, periodic voltage and innovative surfactants

The present work focused on evaluating the electrokinetic (EK) treatment of real contaminated sediments with toxic metals and polycyclic aromatic hydrocarbons (PAHs), using a big laboratory EK cell, periodic voltage and recently tested non-ionic surfactants. The results indicated that the "day on-night off" application mode of voltage, in conjunction with the selected solubilising agents, favoured the overall EK process. Arsenic, nickel and chromium exhibited the highest removal percentages, obtaining 83%, 67% and 63%, respectively, while zinc and lead attained 54% and 41% at the maximum. Furthermore, in the experiments where the non-ionic surfactants were introduced in the electrolyte chambers, there was a major uniformly removal of PAHs from the entire sediment across the EK cell, indicating the high solubilisation capacity of the enhancing agents. Essentially, transport and in some cases removal of PAHs (particularly from sections adjacent to the electrolyte compartments) also occurred in the unenhanced EK run, mainly due their negative charge, their potential weak bonds to the soil matrix and to the periodic application of voltage. Maximum removal was obtained by the use of Nonidet P40 where app. 1/3 (ca. 6498μg out of 20145μg) of the total initial amount of PAHs were removed from the cell.

Degradation of phthalate esters and acetaminophen in river sediments using the electrokinetic process integrated with a novel Fenton-like process catalyzed by nanoscale schwertmannite

The main objective of this study was to develop and establish an in situ remediation technology coupling nano-schwertmannite/H2O2 process and electrokinetic (EK) process for the removal of phthalates (PAEs) and acetaminophen in river sediments. Test results are given as follows: (1) injection of nano-schwertmannite slurry and H2O2 (collectively, "novel oxidant") into the anode reservoir would yield ·OH radicals that then will be diffused into the sediment compartment and further transported by the electroosmotic flow and/or electrophoresis from the anode end toward the cathode to degrade PAEs and pharmaceuticals in the sediment if any; (2) an electric potential gradient of 1.5 V cm(-1) would help the removal of PAEs and acetaminophen in the blank test, which no "novel oxidants" was added to the remediation system; (3) the practice of electrode polarity reversal would maintain neutral pH for sediment after remediation; (4) injection of equally divided dose of 10 mL novel oxidant into the anode reservoir and four injection ports on the top of sediment chamber would further enhance the removal efficiency; and (5) an extension of treatment time from 14 d to 28 d is beneficial to the removal efficiency as expected. In comparison, the remediation performance obtained by the EK-assisted nano-SHM/H2O2 oxidation process is superior to that of the batch degradation test, but is comparable with other EK integrated technologies for the treatment of same contaminants. Thus, it is expected that the EK-assisted nano-SHM/H2O2 oxidation process is a viable technology for the removal of phthalate esters and pharmaceuticals from river sediments in large-scale operations.

Ligand-enhanced electrokinetic remediation of metal-contaminated marine sediments with high acid buffering capacity

The suitability of electrokinetic remediation for removing heavy metals from dredged marine sediments with high acid buffering capacity was investigated. Laboratory-scale electrokinetic remediation experiments were carried out by applying two different voltage gradients to the sediment (0.5 and 0.8 V/cm) while circulating water or two different chelating agents at the electrode compartments. Tap water, 0.1 M citric acid and 0.1 M ethylenediaminetetraacetic acid (EDTA) solutions were used respectively. The investigated metals were Zn, Pb, V, Ni and Cu. In the unenhanced experiment, the acid front could not propagate due to the high acid buffering capacity of the sediments; the production of OH(-) ions at the cathode resulted in a high-pH environment causing the precipitation of CaCO3 and metal hydroxides. The use of citric acid prevented the formation of precipitates, but solubilisation and mobilisation of metal species were not sufficiently achieved. Metal removal was relevant when EDTA was used as the conditioning agent, and the electric potential was raised up to 0.8 V/cm. EDTA led to the formation of negatively charged complexes with metals which migrated towards the anode compartment by electromigration. This result shows that metal removal from sediments with high acid buffering capacity may be achieved by enhancing the electrokinetic process by EDTA addition when the acidification of the medium is not economically and/or environmentally sustainable.

Effect of EDTA, EDDS, NTA and citric acid on electrokinetic remediation of As, Cd, Cr, Cu, Ni, Pb and Zn contaminated dredged marine sediment

In recent years, electrokinetic (EK) remediation method has been widely considered to remove metal pollutants from contaminated dredged sediments. Chelating agents are used as electrolyte solutions to increase metal mobility. This study aims to investigate heavy metal (HM) (As, Cd, Cr, Cu, Ni, Pb and Zn) mobility by assessing the effect of different chelating agents (ethylenediaminetetraacetic acid (EDTA), ethylenediaminedisuccinic acid (EDDS), nitrilotriacetic acid (NTA) or citric acid (CA)) in enhancing EK remediation efficiency. The results show that, for the same concentration (0.1 mol L(-1)), EDTA is more suitable to enhance removal of Ni (52.8 %), Pb (60.1 %) and Zn (34.9 %). EDDS provides effectiveness to increase Cu removal efficiency (52 %), while EDTA and EDDS have a similar enhancement removal effect on As EK remediation (30.5∼31.3 %). CA is more suitable to enhance Cd removal (40.2 %). Similar Cr removal efficiency was provided by EK remediation tests (35.6∼43.5 %). In the migration of metal-chelate complexes being directed towards the anode, metals are accumulated in the middle sections of the sediment matrix for the tests performed with EDTA, NTA and CA. But, low accumulation of metal contamination in the sediment was observed in the test using EDDS.

Degradation of oil products in a soil from a Russian Barents hot-spot during electrodialytic remediation

A highly oil-polluted soil from Krasnoe in North-West Russia was used to investigate the degradation of organic pollutants during electrodialytic remediation. Removal efficiencies were up to 70 % for total hydrocarbons (THC) and up to 65 % for polyaromatic hydrocarbons (PAH). Relatively more of the lighter PAH compounds and THC fractions were degraded. A principal component analysis (PCA) revealed a difference in the distribution of PAH compounds after the remediation. The observed clustering of experiments in the PCA scores plot was assessed to be related to the stirring rate. Multivariate analysis of the experimental settings and final concentrations in the 12 experiments revealed that the stirring rate of the soil suspension was by far the most important parameter for the remediation for both THC and PAH. Light was the second most important variable for PAH and seems to influence degradation. The experimental variables current density and remediation time did not significantly influence the degradation of the organic pollutants. Despite current density not influencing the remediation, there is potential for degrading organic pollutants during electrodialytic removal of heavy metals, as long as a stirred set-up is applied. Depending on remediation objectives, further optimisation may be needed in order to develop efficient remediation strategies.

Effects of saline-alkaline stress on benzo[a]pyrene biotransformation and ligninolytic enzyme expression by Bjerkandera adusta SM46

Benzo[a]pyrene (BaP) accumulates in marine organisms and contaminated coastal areas. The biotreatment of waste water using saline-alkaline-tolerant white rot fungi (WRF) represents a promising method for removing BaP under saline-alkaline conditions based on WRF's ability to produce ligninolytic enzymes. In a pre-screening for degradation of polycyclic aromatic hydrocarbons of 82 fungal strains using Remazol brilliant blue R, Bjerkandera adusta SM46 exhibited the highest tolerance to saline-alkaline stress. Moreover, a B. adusta culture grown in BaP-containing liquid medium exhibited resistance to salinities up to 20 g l(-1). These conditions did not inhibit fungal growth or the expression of manganese peroxidase (MnP) or lignin peroxidase (LiP). The degradation rate also became higher as salinity increased to 20 g l(-1). Fungal growth and enzyme expression were inhibited at a salinity of 35 g l(-1). These inhibitory effects directly decreased the degradation rate (>24%). The presence of MnSO4 as an inducer improved the degradation rate and enzyme expression. MnP and LiP activity also increased by seven- and fivefold, respectively. SM46 degraded BaP (38-89% over 30 days) in an acidic environment (pH 4.5) and under saline-alkaline stress conditions (pH 8.2). Investigating the metabolites produced revealed BaP-1,6-dione as the main product, indicating the important role of ligninolytic enzymes in initializing BaP cleavage. The other metabolites detected, naphthalene acetic acid, hydroxybenzoic acid, benzoic acid, and catechol, may have been ring fission products. The wide range of activities observed suggests that B. adusta SM46 is a potential agent for biodegrading BaP under saline conditions.

Remediation of Pb/Cr co-contaminated soil using electrokinetic process and approaching electrode technique

Electrokinetic process has emerged as an important tool for remediating heavy metal-contaminated soil. The process can concentrate heavy metals into smaller soil volume even in the absence of hydraulic flow. This makes it an attractive soil pre-treatment method before other remediation techniques are applied such that the chemical consumption in the latter stage can be reduced. The present study evaluates the feasibility of electrokinetic process in concentrating lead (Pb) and chromium (Cr) in a co-contaminated soil using different types of wetting agents, namely 0.01 M NaNO3, 0.1 M citric acid and 0.1 M EDTA. The data obtained showed that NaNO3 and citric acid resulted in poor Pb electromigration in this study. As for Cr migration, these agents were also found to give lower electromigration rate especially at low pH region as a result of Cr(VI) adsorption and possible reduction into Cr(III). In contrast, EDTA emerged as the best wetting agent in this study as it formed water-soluble anionic complexes with both Pb and Cr. This provided effective one-way electromigration towards the anode for both ions, and they were accumulated into smaller soil volume with an enrichment ratio of 1.55-1.82. A further study on the application of approaching cathode in EDTA test showed that soil alkalisation was achieved, but this did not provide significant enhancement on electromigration for Pb and Cr. Nevertheless, the power consumption for electrokinetic process was decreased by 22.5%.

Enhanced-electrokinetic extraction of heavy metals from dredged harbor sediment

In this study, the feasibility of an ex situ electrokinetic (EK) process combined with pre-oxidation using hydrogen peroxide (H2O2) and pre-washing using ethylenediaminetetraacetic acid (EDTA) was investigated in enhancing the extraction of Cu, Pb, and Zn from actual dredged harbor sediment. H2O2 pre-oxidation led to a change in the fractionation of Cu bound to organic matter and the sulfide fraction in the Fe-Mn oxides to the exchangeable fraction, but was not effective at removing metals. In contrast, EDTA pre-washing changed the Fe-Mn oxide-bound fractions of Cu and Pb into easily extractable fractions; 20.1, 27.5, and 32.8% of Cu, Pb, and Zn were removed, respectively. During EK treatment, metals were transported toward the anode by electromigration of negatively charged complexes such as metal-EDTA and metal-citrate. However, EK treatment did not significantly enhance the removal of metals because metals accumulated near the anodic region with an increase in the exchangeable fraction due to the short EK operating duration and low voltage gradient. Therefore, it is necessary to extend the EK operating duration and/or increase the voltage gradient for effective transportation and removal of metals from sediment.

Screening of variable importance for optimizing electrodialytic remediation of heavy metals from polluted harbour sediments

Using multivariate design and modelling, the optimal conditions for electrodialytic remediation (EDR) of heavy metals were determined for polluted harbour sediments from Hammerfest harbour located in the geographic Arctic region of Norway. The comparative importance of the variables, current density, remediation time, light/no light, the liquid-solid ratio and stirring rate of the sediment suspension, was determined in 15 laboratory-scale EDR experiments by projection to latent structures (PLS). The relation between the X matrix (experimental variables) and the Y matrix (removal efficiencies) was computed and variable importance in the projection was used to assess the influence of the experimental variables. Current density and remediation time proved to have the highest influence on the remediation of the heavy metals Cr, Cu, Ni, Pb and Zn in the studied experimental domain. In addition, it was shown that excluding the acidification time improved the PLS model, indicating the importance of applying a limited experimental domain that covers the removal phases of each heavy metal in the specific sediment. Based on PLS modelling, the optimal conditions for remediating the Hammerfest sediment were determined; operating in the experimental domain of 0.5-0.8 mA/cm(2) and a remediation time after acidification of 450-570 h met acceptable levels according to Norwegian sediment quality guidelines.

Application of biosurfactants and periodic voltage gradient for enhanced electrokinetic remediation of metals and PAHs in dredged marine sediments

Dredged harbor sediment co-contaminated by heavy metals and polycyclic aromatic hydrocarbons (PAHs) was subjected to enhanced electrokinetic treatments, using a mixture of a chelating agent (citric acid CA) and a surfactant as additives in the processing fluids. We tested various operating conditions (at 1 V cm(-1)): different CA concentrations, applying a periodic voltage gradient, pre-conditioning the sediment with the additives, and replacing the synthetic surfactant Tween 20 (TW20) by biosurfactants. Increasing the CA concentration was favorable for both metal and PAH removal. Applying a periodic voltage gradient associated to a low concentration of CA and TW20 provided the best results for Zn, Cd and Pb removal and also for removal of the 16 priority PAHs. Promising results were obtained with solutions containing rhamnolipids (0.028%) and a viscosin-like biosurfactant produced by Pseudomonas fluorescens Pfa7B (0.025%), associated to a periodic voltage gradient. Although the rhamnolipid and the viscosin-like compounds involved a higher electrical current than TW20, metals were less removed from the sediment. The electroosmotic flow was lower when we used biosurfactants, hence a less effective effect on PAH removal.

Removal of Hg from Real Polluted Sediments Using Enhanced-EK Decontamination: Verification of Experimental Methods and Batch-Test Preliminary Results

The aim of the research is to apply a biosurfactant-enhanced-EK technology to marine sediment contaminated by high level of Hg. In this work, data from batch-tests using different novel biosurfactant agents were reported. In addition, a dedicated EK bench-scale apparatus was designed and carried out. Technical test was also performed to evaluate the optimal operating features of the EK bench-scale apparatus, assessing the influence of applied voltage and treatment time on the current intensity and electroosmotic flow. Batch experiments were conducted using two sugar esters as biosurfactants and EDTA salt at different concentrations. Results showed that the maximum extraction efficiency was observed for the biosurfactant Olimpicon GC (15%), for which the Hg extraction was shown to be 3.6-fold higher than for 0.2 M EDTA. From technical tests, the observed reduction of current intensity and electroosmotic flow with time highlights the necessity of using conditioning agents during the treatment. Data demonstrates also the good working features of the experimental apparatus. Preliminary results show that EK treatment jointly with biosurfactants such as sugar esters could be a better choice for the remediation of Hg-polluted sediments. The results obtained are of scientific and practical interest and can be used for further researches.

Health risk assessment linked to filling coastal quarries with treated dredged seaport sediments

Dredged seaport sediments raise complex management problems since it is no longer possible to discharge them into the sea. Traditional waste treatments are poorly adapted for these materials in terms of absorbable volumes and cost. In this context, filling quarries with treated sediments appears interesting but its safety regarding human health must be demonstrated. To achieve this, a specific methodology for assessing health risks has been developed and tested on three seaport sediments. This methodology includes the development of a conceptual model of the global scenario studied and the definition of specific protocols for each of its major steps. The approach proposed includes in particular the use of metrological and experimental tools that are new in this context: (i) an experimental lysimeter for characterizing the deposit emissions, and (ii) a geological radar for identifying potential preferential pathways between the sediment deposit and the groundwater. The application of this approach on the three sediments tested for the scenario studied showed the absence of health risk associated with the consumption of groundwater for substances having a "threshold effect" (risk quotient <1), and an acceptable risk for substances having a "non-threshold effect", with the notable exception of arsenic (individual risk equal to 3.10(-6)).

Electrokinetic-enhanced bioremediation of organic contaminants: a review of processes and environmental applications

There is current interest in finding sustainable remediation technologies for the removal of contaminants from soil and groundwater. This review focuses on the combination of electrokinetics, the use of an electric potential to move organic and inorganic compounds, or charged particles/organisms in the subsurface independent of hydraulic conductivity; and bioremediation, the destruction of organic contaminants or attenuation of inorganic compounds by the activity of microorganisms in situ or ex situ. The objective of the review is to examine the state of knowledge on electrokinetic bioremediation and critically evaluate factors which affect the up-scaling of laboratory and bench-scale research to field-scale application. It discusses the mechanisms of electrokinetic bioremediation in the subsurface environment at different micro and macroscales, the influence of environmental processes on electrokinetic phenomena and the design options available for application to the field scale. The review also presents results from a modelling exercise to illustrate the effectiveness of electrokinetics on the supply electron acceptors to a plume scale scenario where these are limiting. Current research needs include analysis of electrokinetic bioremediation in more representative environmental settings, such as those in physically heterogeneous systems in order to gain a greater understanding of the controlling mechanisms on both electrokinetics and bioremediation in those scenarios.