Decontamination of Petroleum-Contaminated Soils Using The Electrochemical Technique: Remediation Degree and Energy Consumption

High-temperature electrothermal remediation of multi-pollutants in soil

Soil contamination is an environmental issue due to increasing anthropogenic activities. Existing processes for soil remediation suffer from long treatment time and lack generality because of different sources, occurrences, and properties of pollutants. Here, we report a high-temperature electrothermal process for rapid, water-free remediation of multiple pollutants in soil. The temperature of contaminated soil with carbon additives ramps up to 1000 to 3000 °C as needed within seconds via pulsed direct current input, enabling the vaporization of heavy metals like Cd, Hg, Pb, Co, Ni, and Cu, and graphitization of persistent organic pollutants like polycyclic aromatic hydrocarbons. The rapid treatment retains soil mineral constituents while increases infiltration rate and exchangeable nutrient supply, leading to soil fertilization and improved germination rates. We propose strategies for upscaling and field applications. Techno-economic analysis indicates the process holds the potential for being more energy-efficient and cost-effective compared to soil washing or thermal desorption.

A review on the landfill leachate treatment technologies and application prospects of three-dimensional electrode technology

With the expansion of urbanisation, the total amount of solid waste produced by urban residents has been increasing, and the problem of municipal solid waste disposal has also been aggravated. Landfill leachate treatment technologies could be divided into three categories: biological, physical and advanced oxidation treatment technology. Among them, advanced oxidation treatment technology has a good effect on the treatment of landfill leachate with little secondary pollution and has excellent application potential. Three-dimensional (3D) electrode technology, as a new type of advanced oxidation technology, could remove refractory pollutants in water and has attracted considerable attention. This article aims to (1) compare existing landfill leachate treatment technologies, (2) summarise 3D electrode technology application scenarios, (3) discuss the advantages of 3D electrode technology in landfill leachate treatment and (4) look ahead the future directions of 3D electrode technology in landfill leachate treatment. We hope that this article will be helpful to researchers who are interested in the field of landfill leachate treatment.

Identifying active xenobiotics in humans by use of a suspect screening technique coupled with lipidomic analysis

Lipidomic analysis has been proven to be a powerful technique to explore the underlying associations between xenobiotics and health status of organisms. Here, we established a strategy that combined the lipidomic analysis with high-throughput suspect contaminant screening technique with an aim to efficiently identify active xenobiotics in humans. Firstly, in the light of single liquid phase equilibrium of chloroform-methanol-water (15:14:2, v/v/v), we developed an efficient method that was able to simultaneously extract both polar and nonpolar lipids in serum samples. By use of this method, targeted and non-targeted lipid analyses were conducted for n = 120 serum samples collected from Wuxi city, China. Secondly, we established a suspect database containing 1450 contaminants that have been previously reported in human samples, and contaminants in this database were screened in the same batch of serum samples by use of high-resolution mass spectrometry (HR-MS). Thirdly, the underlying associations between suspect contaminants and lipids were explored and discussed, and we observed that levels of some lipids were statistically correlated with concentrations of numerous contaminants. Among these active contaminants, 23 ones were identified on the basis of HR MS¹ and MS² characteristics, and these contaminants belonged to the classes of phthalates, phenols, parabens, or perfluorinated compounds (PFCs). Three active xenobiotics were fully validated by comparison with authentic standards, and they were perfluorooctanoic acid (PFOA), perfluorooctane sulfonate (PFOS), and diethyl phthalate (DEP). There were statistically significant changes in levels of triglyceride (TG), lysophosphocholine (LPC), and sphingomyelin (SM) as peak areas of xenobiotics increase. We also observed that, among target lipid molecules, 18:0 lysophosphatidylethanolamine (LPE(18:0)) was very sensitive, and this lipid responded to exposure of various contaminants. Our present study provides novel knowledge on potential alteration of lipid metabolism in humans following exposure to xenobiotics, and provides an efficient strategy for efficiently identifying active xenobiotics in humans.

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.

Managing soils of environmental significance: A critical review

Globally, environmentally significant soils (ESSs) mainly include acid sulfate, heavy metal(loid)-contaminated, petroleum hydrocarbon-contaminated, pesticide-contaminated, and radionuclide-contaminated soils. These soils are interrelated and have many common characteristics from an environmental management perspective. In this review, we critically evaluate the available literature on individual ESSs, aiming to identify common problems related to environmental quality/risk assessment, remediation approaches, and environmental regulation for these soils. Based on these findings, we highlight the challenges to, and possible solutions for sustainable ESS management. Contaminated land has been rapidly expanding since the first industrial revolution from the industrialized Western countries to the emerging industrialized Asia and other parts of the world. Clean-up of contaminated lands and slowdown of their expansion require concerted international efforts to develop advanced cleaner production and cost-effective soil remediation technologies in addition to improvement of environmental legislation, regulatory enforcement, financial instruments, and stakeholder involvement to create enabling environments. Two particular areas require further action and research efforts: developing a universal system for assessing ESS quality and improving the cost-effectiveness of remediation technologies. We propose an integrated framework for deriving ESS quality indicators and make suggestions for future research directions to improve the performance of soil remediation technologies.

Sorption as a rapidly response for oil spill accidents: A material and mechanistic approach

Accidents involving oil transportation has increase due to directly connection with the elevation of global energy demand. The environmental losses are tremendous and brings huge economic issues to remediate the spilled oil. This report presents an up-to-date review on an overall aspects of oil spill remediation techniques, the fundamentals and advantages of sorption, the most applied materials through diverse types of oil spill sites and oils with variety features, highlight to natural materials and future prospective. As the environment preservation progressively becomes a major social concern issue, the achievement of a worldwide distribution process aligned with environmental legislation and economic viability is crucial to the oil industry. For this, a specific preparation considering several scenarios must be carried out regarding minimization of oil spillages. Since the sorbent materials are decisive for sorption, it was approached the main sorbents: natural, graphenic, nano, polymeric and waste materials, and future trends.

A new perspective towards in-situ cold plasma remediation of polluted sites: Direct generation of micro-discharges within contaminated medium

The in-situ treatment of solid wastes might be regarded as cost-effective and minimum environmental fingerprint solution, particularly with reference to contaminated soils, offering several benefits compared to ex-situ methods. In this short communication it is described the study of a lab-scale coaxial dielectric barrier discharge (DBD) plasma reactor simulating the in-situ soil remediation conditions for the first time. In this conceptual design, the contaminated medium is handled as a part of the electrical discharge, while the plasma discharges are produced directly within the contaminated porous medium under treatment, thus scattering reactive species directly in the air contained inside its interconnected pores. The in-situ cold plasma setup was used to remediate bauxite samples highly contaminated by oil sludge contaminants. A very high TOC removal (∼70%) was achieved after 30 min of plasma treatment time with the corresponding energy consumption being 0.53 kWh kg^-1. Carbon balance analysis of the exhaust gases revealed that 61% of the removed pollutant was converted to CO₂, 19% was decomposed to CO, and 20% was emitted as VOCs. The scale-up of the presented in-situ cold plasma approach could lead to a promising alternative for the fast, cost-effective, and green in-situ remediation of granular porous, heavily contaminated with hydrocarbons contaminated sites.

Optimization of electro-kinetic process for remediation of soil contaminated with phenanthrene using response surface methodology

The objective of this work was to investigate the modification of soil contaminated with phenanthrene (PHE) by electro-kinetic remediation (EKR) process using response surface methodology (RSM). The soil sample was obtained from the subgrades (0-30 cm) of an area close to Shahroud City, Northeast of Iran. The effect of variables such as initial pH, voltage, electrolyte concentration, and reaction time on PHE removal was studied. Based on the results obtained from the central composite design (CCD) experiment, the highest and lowest amount of PHE removal was 97 and 20%, respectively. In this study, the variables A, B, C, AB, AC, and C² with a p value < 0.05 were significant model terms and the parameter of the lack of fit was not significant (p value = 0.0745). Findings indicated that the "predicted R-squared" of 0.9670 was in reasonable agreement with the "adj R-squared" of 0.9857 and the plot of residual followed a normal distribution and approximately linear. Also, the kinetic rates of the removal PHE by the EKR process best fitted with a first-order kinetic model (R²: 0.926). Results of the investigation of the effective variables showed that in values of pH 3, time of 168 h, voltage of 3 V, and electrolyte concentration of 4 mg/L, the removal efficiency of PHE reached 96.6%. Graphical abstract.

Assessment of European and hybrid aspen clones efficiency based on height growth and removal percentage of petroleum hydrocarbons-a field trial

Soils polluted by organic or inorganic pollutants are an emerging global environmental issue due to their toxic effects. A phytoremediation experiment was conducted to evaluate the extraction potential of three European aspen clones (R2, R3, and R4) and seven hybrid aspen clones (14, 27, 34, 134, 172, 191, and 291) grown in soils polluted with hydrocarbons (includes polycyclic aromatic hydrocarbons (PAH) and total petroleum hydrocarbons (TPH)). Height growth, plant survival rates, and .hydrocarbon removal efficiencies were investigated over a 4-year period at a site in Somerharju, Luumaki Finland, to assess the remediation potential of the clones. Hydrocarbon content in the soil was determined by gas chromatography and mass spectrometry. The results revealed that hybrid aspen clones 14 and 34 and European aspen clone R3 achieved greater height growth (171, 171, and 114 cm, respectively) than the other clones in the study. Further, the greatest removals of PAH (90% at depth 10-50 cm) and (86% at depth 5-10 cm) were observed in plot G15 planted with clone R2. Furthermore, the greatest TPH removal rate at 5-10 cm depth (C₂₂-C₄₀, 97%; C₁₀-C₄₀, 96%; and C₁₀-C₂₁, 90%) was observed in plot 117 with clone 134. However, other clones demonstrated an ability to grow in soils with elevated levels of TPH and PAH, which indicates their tolerance to hydrocarbons and their potential capacity for phytoremediation of hydrocarbon-polluted soils. Our study suggests that European aspen and hybrid aspen clones could be used for the remediation of soils polluted with PAH and TPH.

Bioremediation of oil contaminated soil using agricultural wastes via microbial consortium

Agricultural wastes, such as wheat bran and swine wastewater, were used for bioremediation of oil-contaminated soil. Two optimised strains that could degrade oil efficiently were selected. The result showed that the best ratio of strain A to strain B was 7:3. Swine wastewater could be a replacement for nitrogen source and process water for bioremediation. Next, the Box-Behnken design was used to optimise the culture medium, and the optimal medium was as follows: microbial dosage of 97 mL/kg, wheat bran of 158 g/kg and swine wastewater of 232 mL/kg. Under the optimal medium, the oil degradation rate reached 68.27 ± 0.71% after 40 d. The urease, catalase, and dehydrogenase activities in oil-contaminated soil all increased, and the microbe quantity increased significantly with manual composting. These investigations might lay a foundation for reducing the pollution of agricultural wastes, exploring a late model for bioremediation of oil-contaminated soil.

Nutrient drip irrigation for refractory hydrocarbon removal and microbial community shift in a historically petroleum-contaminated soil

An adequate amount of nutrients is required to enable biodegradation of refractory hydrocarbons in petroleum-contaminated soil. In this study, a microcosm experiment was conducted using a drip fertigation method for petroleum-contaminated soil remediation. Nitrogen and phosphorus were homogeneously and periodically sprayed into a historically contaminated soil using a modified horticultural drip irrigation device. Various petroleum hydrocarbon fraction contents were then determined by gravimetry and gas chromatography (GC), and changes in the soil microbial community were analyzed by high throughput sequencing. After 90 days of remediation, the removal efficiencies of total petroleum hydrocarbon (TPH), saturates, aromatics, C7-C30 n-alkanes, and 16 PAHs were respectively enhanced by 21.5%, 25.5%, 12.4%, 10.4%, and 19.6% compared with the use of a single nutrient amendment application. The high throughput sequencing result showed that obvious changes had occurred in the soil microbial community compositions during drip fertigation; however, fungi were more sensitive to drip fertigation than bacteria. The resulting predominant bacterial and fungal genera were Dietzia, Nocardioides, Mycobacterium, Sphaerobacter, Leifsonia, and Aspergillus, Scolecobasidium, and Fusarium, respectively. Remediating polluted soils by regular fertigation ensures the automatic addition of even amounts of nutrients, which achieves high refractory hydrocarbon removal efficiencies. It is expected that this method can be applied in the in-situ remediation of petroleum-contaminated soil on a large scale.

Optimization of aeration enhanced surfactant soil washing for remediation of diesel-contaminated soils using response surface methodology

Surfactant-enhanced soil washing has been used for remediation of organic pollutants for an extended period, but its effectiveness and wide application was limited by the high concentration of surfactants utilized. In this work, the efficiency of conventional soil washing performance was enhanced by 12-25% through the incorporation of air bubbles into the low concentration surfactant soil washing system. Surfactant selection pre-experiment using aerated and conventional soil washing reveals Brij 35 > TX100 > Tween 80 > Saponin in diesel oil removal. Optimization of the effect of time, surfactant concentration, pH, agitation speed, and airflow rate in five levels were undertaken using Response Surface Methodology and Central composite design. The optimum degree of variables achieved was 90 min of washing time, 370 mg/l of concentration, washing pH of 10,535 rpm of agitation speed and 7.2 l/min of airflow rate with 79.5% diesel removal. The high predicted R 2 value of 0.9517 showed that the model could efficiently be used to predict diesel removal efficiency. The variation in efficiency of aeration assisted and conventional soil washing was variable depending on the type of surfactant, organic matter content of the soil, particle size distribution and level of pollutant weathering. The difference in removal efficiency of the two methods increases when the level of organic matter increases and when the particle size and age of contamination decreases.

Electro-osmotic Treatment of Dredged Sediment by Different Power Supply Modes: Energy Consumption and Electro-osmotic Transport Volume

Laboratory model tests were conducted in constant-voltage mode and constant-current mode for the one-dimensional electro-osmotic treatment of dredged sediment, with an approximately consistent initial electric power. The voltage, current, drainage rate, electro-osmotic transport volume, and energy consumption coefficient during the electro-osmotic process were measured and calculated. After treatment, the final soil moisture at designated positions in the test samples was measured to investigate the effects of different power supply modes. Further, the divergent phenomena observed with constant voltage and constant current were discussed. Based on an analysis of the measured energy consumption coefficients with time, we obtained a linear relationship between the applied/equivalent voltage and energy consumption coefficient. Furthermore, the electro-osmotic processes are divided into four stages by equal drainage quantity to obtain the energy consumption and electro-osmotic transport volume under different working conditions. The results reveal that the energy consumption of electro-osmosis is mainly determined by the applied voltage or the equivalent voltage for dredged sediment, while the value of electro-osmotic transport volume depends mainly on the change in soil water content rather than power supply modes. The drainage rate in constant-current mode was observed to be relatively steady, maintaining an approximately constant rate until the soil moisture was dramatically reduced. In other words, constant-current mode shows the advantages of being powerful and persistent in electro-osmotic treatment.

A pore-scale investigation of heavy crude oil trapping and removal during surfactant-enhanced remediation

The presence of nonaqueous phase liquid (NAPL) in the subsurface presents significant challenges for soil and groundwater remediation. In particular, heavy crude oil, coal tar and/or bitumen present unique difficulties for removal and cleanup due to associated high viscosities, low aqueous solubilities, and limited mobility extraction potential. Although surfactant-enhanced aquifer remediation (SEAR) techniques have shown some promise for source removal, overall remediation (mobilization) performance will depend significantly on interfacial effects between the fluid and solid phases. A pore-scale study, implementing synchrotron X-ray microtomography (SXM), was conducted to understand and quantify the trapping and mobilization mechanisms and in-situ emulsification processes of heavy crude oil distributed within increasing complexity (i.e. physical heterogeneity) unconsolidated sands during surfactant flushing events. Pore-scale imaging analyses were conducted to quantify the changes in oil blob morphology before and after surfactant flushing events to assess the primary factors controlling the recovery. Results showed relatively low (10%) net recovery from the homogeneous sand after 5 pore volumes (PVs) of surfactant flushing and may be, in part, due to the more connected ganglia (i.e. single continuous) oil-phase. Such a condition may have limited the surfactant/oil contact resulting in relatively low interfacial activity and correspondingly inefficient oil mobilization and recovery. Negligible net oil recovery was achieved from the mildly-heterogeneous-sand and is likely due to the lower associated permeability of this particular porous medium. Furthermore, the oil-phase distribution within this medium primarily consisted of small disconnected blobs more readily exposed (in contact with) the surfactant solution. For the highly-heterogeneous-sand experiments, an average of 20% heavy-oil recovery resulted after each flushing event (total of ~37% after 5 PVs) and was attributed to more efficient reduction of interfacial tension associated with the increased surfactant-oil contact. The associated higher pH sand/fine‑carbonate system may have aided in maintaining a water-wet porous medium, a condition more conducive to higher oil recovery and displacement efficiency.

A Review of Libyan Soil Databases for Use within an Ecosystem Services Framework

Ecosystem services (ESs) are increasingly being used by many countries around the world as a framework for addressing the United Nations (UN) Sustainable Development Goals (SDGs). This review article of the usability of Libyan soil databases for ESs and SDGs is the first of its kind for North Africa. The objectives of the article are to: describe the available soil resources of Libya in relation to an ES framework; provide examples of the usability of Libyan soil databases for ES applications (e.g., provisioning, Healthy Eating Plate), and describe some of the typical disservices in the country. Desertification, salinization, and limited freshwater resources are the largest challenges (disservices) for agriculture and future development in Libya. Seawater intrusion in coastal areas due to rising sea levels has resulted in high concentrations of salts in irrigation waters, which can lead to low soil productivity. These challenges can be addressed by integrating Libyan soil resources into a market that transforms resources into goods and services to meet human demand in a sustainable manner, with non-market institutions mediating the interactions between humans and the environment. If Libyan soil resources are taken into account by both market and non-market institutions, it will lead to more efficient use of soil resources and also should enable the implementation of innovative strategies, such as integrated farming systems, non-soil-based agricultural production (e.g., hydroponics), and alternative farming practices.