Soil Washing Treatment Research Articles

Remediation of soils contaminated with methomyl using electrochemically produced gaseous oxidants

This prospective work focuses on the use of two different gaseous oxidants (chlorine dioxide and ozone) to remediate soil polluted with methomyl in two different applications: ex-situ and in-situ. In the first, the soil washing is integrated with the bubbling of the oxidant, while in the second, the gas was introduced by a perforated pipe located sub-superficially. Regarding the soil washing treatment, results demonstrate that direct use of ozone is not very efficient, although an important improvement is obtained following activation with hydrogen peroxide or UV light. In contrast, chlorine dioxide exhibited complete methomyl depletion from the soil, although with higher energy consumption and technical complexity compared to ozone. The direct dosing of the gaseous oxidants in perforated pipes is effective, achieving methomyl removals of 7.8 % and 9.2 % using ozone and chlorine dioxide, respectively. In these cases, soil conditions are not significantly modified, which becomes an important advantage of the technology as compared with other electrochemically assisted soil remediation process, in which large regions of the treated soil are affected by important changes in the pH or by depletion of ions. This lower impact makes these novel technologies more promising for further evaluations.

Assessing Environmental Sustainability of Phytoremediation to Remove Copper from Contaminated Soils

Phytoremediation stands out as a promising technology for removing heavy metals from contaminated soils. This work focuses on studying the environmental performance of phytoremediation in removing copper from contaminated soil located in an old Spanish mine using the life cycle assessment (LCA) method. For this purpose, Brassica juncea (brown mustard), Medicago sativa (alfalfa) and their rotary cultivation were assessed along with different options for managing biomass (landfill disposal and biomass cogeneration). In addition, soil excavation and soil washing treatments were also compared to phytoremediation. M. sativa proved superior to B. juncea and their rotary cultivation, regardless of the biomass disposal option, achieving impact reductions of 30–100%. This is due to the ability of M. sativa to fix nitrogen, which reduces fertiliser requirements. Among the biomass management alternatives, cogeneration was superior to landfill disposal in all cases by allowing for energy recovery, thereby reducing environmental impacts by 60–100%. M. sativa + cogeneration is the option that presents the best environmental performance of all the studied treatments, achieving reductions up to negligible values in four of eight impact categories due to the impacts avoided by energy production. On the contrary, soil excavation is the less desirable option, followed by soil washing treatment.

Behavior of chlorpyrifos and 3,5,6-trichloro-2-pyridinol (TCP) in a sodium-dodecyl sulphate-electrokinetic soil washing system

Chlorpyrifos (CPF) is widely used around the world as an insecticide to control various insect pests. Numerous studies have shown that CPF and its main metabolite, 3,5,6-trichloropyridinol (TCP) are potential contaminants of soils and water resources. In this work an electro-kinetic soil washing treatment with alternating polarity (EKSW-AP) using the anionic surfactant SDS (4 times CMC) in the washing solution was studied as a possible strategy for CPF remediation in soils. The experiments were performed in two types of soils applying an electric field between the electrodes of 1 V cm−1 during 15 days of operation. The main results of this work showed that SDS does not improve the possibility of mobilization of CPF and TCP in the EKSW-AP treatment, due to the low remaining concentration after its adsorption on soils. In the reference systems, without current application, the recovery of CPF was close to 100% of the added mass whereas in the EKSW-AP systems recoveries reached values near to 80%. Kinetic studies performed in untreated soils revealed only the formation of TCP without any other degradation product. Therefore, EKSW-AP process likely favored the degradation of both compounds CPF and TCP, with the formation of another more polar by-product that was obtained in the collector wells. The results of this study showed that the EKSW-AP with the application of SDS does not significantly alter the physicochemical properties of the soils.

Remediation of oily soil using acidic sophorolipids micro-emulsion

A sophorolipids (SLs) micro-emulsion in Winsor type I form was used for crude oil contaminated soil washing treatment. The micro-emulsion shows higher oil removal rate than SLs aqueous solution and diesel oil. The type I micro-emulsion with w(SLs) = 6%, w(NaCl) = 1%, w(diesel) = 13.36% gave a high oil removal rate of 95.6% and the eluate remained in type I state. The recovered oil showed lower viscosity, mainly caused by the entering of diesel from the micro-emulsion phase into the oil phase and the lower removal rate of the heavier components, such as the resin and asphaltene. The initial heavily saline-alkaline soil changed into mildly saline-alkaline state after washing treatment, favoring the germination and growth of plants, with ryegrass showing better germination and growth effect than alfalfa. The ryegrass showed good phytoremediation effect on the contaminated soil after SLs micro-emulsion washing. The combination process of SL micro-emulsion washing and ryegrass phytoremediation is prospective for oily soil treatment.

Two-compartment membrane electrochemical remediation of heavy metals from an aged electroplating-contaminated soil: A comparative study of anodic and cathodic processes

In this study, two-compartment membrane electrochemical remediation (MER) based on the anode process and the cathode process strategies were compared for treating a multi metal -contaminated soil. Remediation effect, as well as energy consumption and risk evaluation of the two strategies under different current density conditions of electroplating-contaminated soil suspension were performed, the following conclusions were drawn. MERs based on both the anode and cathode processes exhibited a synergetic effect because the DC electric field and extractants dissolved more metals from the soil phase into the liquid phase of the suspension compared to a usual soil washing treatment. The maximum Cr, Cu, and Ni removal efficiencies of MERs based on the anode process were 79.5%, 86.2%, and 85.0%, respectively, compared to 27.5%, 72.5%, and 65.9% based on the cathode process. Risk assessment results showed lower soil environmental risk after MER based on the cathode process than after MER based on the anode process. In this study, MER based on the cathode process as an evolving soil remediation strategy was found to present high simultaneous remediation ability for soil heavy metals and leaching materials, showing its advantages of environmental friendliness and economic effectiveness.

Polycyclic Aromatic Hydrocarbons: Sources, Toxicity, and Remediation Approaches.

Polycyclic aromatic hydrocarbons (PAHs) are widespread across the globe mainly due to long-term anthropogenic sources of pollution. The inherent properties of PAHs such as heterocyclic aromatic ring structures, hydrophobicity, and thermostability have made them recalcitrant and highly persistent in the environment. PAH pollutants have been determined to be highly toxic, mutagenic, carcinogenic, teratogenic, and immunotoxicogenic to various life forms. Therefore, this review discusses the primary sources of PAH emissions, exposure routes, and toxic effects on humans, in particular. This review briefly summarizes the physical and chemical PAH remediation approaches such as membrane filtration, soil washing, adsorption, electrokinetic, thermal, oxidation, and photocatalytic treatments. This review provides a detailed systematic compilation of the eco-friendly biological treatment solutions for remediation of PAHs such as microbial remediation approaches using bacteria, archaea, fungi, algae, and co-cultures. In situ and ex situ biological treatments such as land farming, biostimulation, bioaugmentation, phytoremediation, bioreactor, and vermiremediation approaches are discussed in detail, and a summary of the factors affecting and limiting PAH bioremediation is also discussed. An overview of emerging technologies employing multi-process combinatorial treatment approaches is given, and newer concepts on generation of value-added by-products during PAH remediation are highlighted in this review.

Removal of chlorinated pesticide contamination by soil washing with sole water

Chlorinated pesticide soil contamination still affects large territories due to past extensive use, poor solubility in water and scarce biodegradability of these agro-chemicals. In particular, this is noticeable for dichloro-diphenyl-trichloroethanes and their derivatives, globally referred as DDX contaminants. Presently, containment or immobilisation is a dominant approach to limit contamination, and remediation has been tried mainly at laboratory scale with contradictory results. Soil washing has been reported as a possible remediation treatment, although environmental effects of employed synthetic co-solvents or surfactants remain unclear. A soil washing treatment with sole water has been set up at laboratory scale, obtaining promising results on a contaminated soil with DDX level of 5050 mg/kg.

Investigating the use of synthetic humic-like acid as a soil washing treatment for metal contaminated soil

Humic acid can effectively bind several metals and is regarded as a promising soil washing agent. Previous studies indicate that carboxylic groups dominate metal binding to humic acid. In this study, a synthetic humic-like acid (SHLA) with high COOH content (5.03 mmol/g) was used as a washing agent to remove metals (Cu, Zn, Ni, Pb, As) from two contaminated agricultural soils (Soil 1 (pH: 6.17 ± 0.11; organic carbon: 5.91 ± 0.40%; Cu: 302.86 ± 3.97 mg/kg; Zn: 700.45 ± 14.30 mg/kg; Pb 323.56 ± 4.84 mg/kg; Ni: 140.16 ± 1.59 mg/kg) and Soil 2 (pH: 9.83 ± 0.01; organic carbon: 2.52% ± 0.25%; Cu: 242.81 ± 10.66 mg/kg; Zn: 841.00 ± 22.31 mg/kg, Pb 451.21 ± 1,92 mg/kg, As: 242.23 ± 5.24 mg/kg)). The effects of solution pH (4 to 11), liquid/solid ratio (L/S ratio, 5:1 (mL:g) to 80:1 (mL:g)), SHLA concentration (100 mg/L to 2000 mg/L), and contact time (0 to 1440 min) on % metal removal were investigated and optimum conditions identified: pH of 9, L/S ratio of 1:80, SHLA concentration of 1500 mg/L at 25 °C for 4 h. Under optimum conditions, a single washing removed 45.2% of Cu, 34.6% of Zn. 42.2% of Ni and 15.6% of Pb from Soil 1, and 30.6% of Cu, 28.1% of Zn. 14.6% of As and 18.1% of Pb from Soil 2. A modified BCR extraction of the two soils before and after washing indicated that the SHLA mainly removed metals in the exchangeable and acid soluble fraction and reducible fraction, which could effectively reduce bioavailability and environmental risk of metals. On a molar basis, SHLA was a more effective washing agent than commercial humic acid, Na2EDTA, citric acid and tartaric acid. Overall, SHLA shows great potential for use as a soil washing agent.

Ethylenediamine-N,N'-Disuccinic Acid (EDDS)-Enhanced Flushing Optimization for Contaminated Agricultural Soil Remediation and Assessment of Prospective Cu and Zn Transport.

This paper presents the results of an experimental study aimed at investigating the effect of operative parameters on the efficiency of a soil flushing process, conducted on real contaminated soil containing high amounts of Cu and Zn. Soil flushing tests were carried out with Ethylenediamine-N,N′-disuccinic acid (EDDS) as a flushing agent due to its high biodegradability and environmentally friendly characteristics. Process parameters such as Empty-Bed Contact Time (EBCT) and EDDS solution molarity were varied from 21–33 h and from 0.36–3.6 mM, respectively. Effects on the mobility of cations such as Fe and Mn were also investigated. Results showed that very high performances can be obtained at [EDDS] = 3.6 mM and EBCT = 33 h. In these conditions, in fact, the amount of removed Cu was 53%, and the amount of removed Zn was 46%. Metal distribution at different depths from the top surface revealed that Cu has higher mobility than Zn. The process results were strongly dependent on the exchange of metals due to the different stability constants of the EDDS complexes. Finally, results from a comparative study showed that soil washing treatment reached the same removal efficiency of the flushing process in a shorter time but required a larger amount of the EDDS solution.

SOIL-WASHING AND THERMAL PLASMA TREATMENT FOR DECONTAMINATION OF DREDGED MARINE SEDIMENTS FROM THE MIDIA PORT - ROMANIA

The aim of this paper is to show the results of two methodological approaches applied for decontamination of the Midia Port dredged sediment to assess their potential reusability. Firstly, the sediment samples were defined in physical, chemical, microbiological and ecotoxicological terms. The results were compared to the limit values established by environmental regulations for dredged sediment management. Some sediment samples exposed a very high concentration of hydrocarbons; the sediments were classified in three categories on the basis of their level of organic/inorganic pollutants. The polluted sediment samples were subjected to the soil-washing treatment. The post treatment analysis revealed that the coarse silty and sandy fractions resulted unpolluted. The soil-washing induced the physical concentration of pollutants (i.e. C>12) in the silty-clay fraction. The wastewater from the treatment plant, once treated, showed no critical issues. After soil-washing treatment, the sediment samples were exposed to a laboratory scale 30kW RF thermal plasma source. Two types of plasma assisted treatments have been performed: the carbothermal process (to evaluate the technical feasibility of silicon extraction during material inertization) and the vitrification process (only for material inertization). Scanning electron microscopy (SEM), energy dispersion spectroscopy (EDS) withal X-ray fluorescence (XRF) and leaching tests were used to investigate the obtained material. The acquired results revealed a decontamination of the collected sediments with leaching test results below legal limits. EDS analysis showed the increment of silica (SiO2) content by about 5-7 % after the plasma treatment and that the localized extraction of silicon by the carbothermal reduction process has been obtained.

Photocatalytic processes assisted by artificial solar light for soil washing effluent treatment.

Contaminated soil has become a growing issue in recent years. The most common technique used to remove contaminants (such as metals) from the soil is the soil washing process. However, this process produces a final effluent containing chelating agents (i.e., ethylenediaminedisuccinic acid, also known as EDDS) and extracted metals (i.e., Cu, Fe, and Zn) at concentrations higher than discharge limits allowed by the Italian and Brazilian environmental law. Therefore, it is necessary to develop further treatments before its proper disposal or reuse. In the present study, soil washing tests were carried out through two sequential paths. Moreover, different artificial sunlight-driven photocatalytic treatments were used to remove Cu, Zn, Fe, and EDDS from soil washing effluents. Metal concentrations after the additional treatment were within the Brazilian and Italian regulatory limits for discharging in public sewers. The combined TiO2-photocatalytic processes applied were enough to decontaminate the effluents, allowing their reuse in soil washing treatment. Ecotoxicological assessment using different living organisms was carried out to assess the impact of the proposed two-step photocatalytic process on the effluent ecotoxicity. Graphical Abstract ᅟ.

UV assisted electrochemical technologies for the removal of oxyfluorfen from soil washing wastes

In this work, it is studied the treatment of soil polluted with oxyfluorfen by Surfactant-Aided Soil-Washing (SASW) and after that, photo-electrolysis was used for the treatment of the soil-washing fluid produced. This liquid waste is characterized by the high concentration of micelles of pesticide and surfactant (sodium dodecyl sulfate, SDS), whose initial size depends on the ratio soil-surfactant used in the soil washing treatment. The waste treatment is studied in terms of the decrease in size of the particles and the depletion of the pollutants. Results clearly demonstrate that photo-electrolysis with diamond electrodes is a very effective treatment technology with results that overcome those obtained by single photolysis and/or single electrolysis with diamond electrodes. The greater improvements attained by combining UV irradiation to the electrolysis were observed in the removal of the pesticide while the removal of the surfactant was little affected. Electrolysis does not only deplete the complete concentration of pesticide but it also shows to be very efficient in the depletion of the surfactant, preventing its potential recycle. The significant concentration of sulfate released during the attack to the surfactant and the effect of the peroxosulfate anions that are formed from the anodic oxidation of that anion, explain the improved performance of the technology in the treatment of washing fluids with higher concentrations of SDS.

Screening of biosurfactant-producing bacteria from offshore oil and gas platforms in North Atlantic Canada

From offshore oil and gas platforms in North Atlantic Canada, crude oil, formation water, drilling mud, treated produced water and seawater samples were collected for screening potential biosurfactant producers. In total, 59 biosurfactant producers belong to 4 genera, namely, Bacillus, Rhodococcus, Halomonas, and Pseudomonas were identified and characterized. Phytogenetic trees based on 16S ribosomal deoxyribonucleic acid (16S rDNA) were constructed with isolated strains plus their closely related strains and isolated strains with biosurfactant producers in the literature, respectively. The distributions of the isolates were site and medium specific. The richness, diversity, and evenness of biosurfactant producer communities in oil and gas platform samples have been analyzed. Diverse isolates were found with featured properties such as effective reduction of surface tension, producing biosurfactants at high rate and stabilization of water-in-oil or oil-in-water emulsion. The producers and their corresponding biosurfactants had promising potential in applications such as offshore oil spill control, enhancing oil recovery and soil washing treatment of petroleum hydrocarbon-contaminated sites.

Influence of washing treatment on the qualities of heavy metal–contaminated soil

Soil washing is an efficient method to remove heavy metals from contaminated soils; however, soil properties can be altered during remediation processes. Therefore, changes in physicochemical properties after soil-washing treatments were examined to investigate their effects on the ecological properties of soil. Two types of washing processes using different physical separation methods and extraction reagents were applied to Pb- or Zn-contaminated soil. The physicochemical properties of soil changed following physical separation and chemical extraction processes, resulting in deterioration of soil fertility. Soil texture and particle size showed more uniformity regardless of the original properties. Although sorting improved, water-holding capacity decreased because of an increase in sand content. The ecological properties of soil could not be improved completely after the removal of metals due to adverse changes in the physicochemical properties of soil. Therefore, the decision to reuse or recycle remediated soils should reflect changes in soil quality.

A kinetic study of the simultaneous removal of EDDS and cupric ions from acidic aqueous solutions by TiO2-based photocatalysis under artificial solar light irradiation and deaerated batch conditions

The removal of cupric ions from aqueous solutions containing N,N′-ethylenediamine-disuccinic acid (EDDS) is carried out in batch conditions to simulate a possible treatment of water streams coming from soil washing treatment units for heavy metal decontamination. The reduction of cupric ions to zero-valent copper and the oxidation of EDDS species is observed with the achievement of low degrees of mineralization.A mathematical model has been developed to simulate and predict the concentration profiles of both total EDDS and cupric ions under specified experimental conditions. A series of experimental investigations have been carried out and the results have been used to build a reaction network. Kinetic models have been developed to describe the system behavior in a variety of operating starting conditions (such as different photocatalyst load, cupric ions and EDDS starting concentrations, pH). One of the mathematical models proposed has allowed to estimate the best numerical values of the unknown kinetic constants through an optimization process. A good alignment with the values reported in literature for similar reactions has also emerged for some kinetic constants. Model validation has been carried out successfully. The mathematical model proposed could be useful for the design of a photo-reactor, capable of purifying the solutions coming from soil washing procedure.

Combination of surfactant enhanced soil washing and electro-Fenton process for the treatment of soils contaminated by petroleum hydrocarbons

In order to improve the efficiency of soil washing treatment of hydrocarbon contaminated soils, an innovative combination of this soil treatment technique with an electrochemical advanced oxidation process (i.e. electro-Fenton (EF)) has been proposed. An ex situ soil column washing experiment was performed on a genuinely diesel-contaminated soil. The washing solution was enriched with surfactant Tween® 80 at different concentrations, higher than the critical micellar concentration (CMC). The impact of soil washing was evaluated on the hydrocarbons concentration in the leachates collected at the bottom of the soil columns. These eluates were then studied for their degradation potential by EF treatment. Results showed that a concentration of 5% of Tween® 80 was required to enhance hydrocarbons extraction from the soil. Even with this Tween® 80 concentration, the efficiency of the treatment remained very low (only 1% after 24 h of washing). Electrochemical treatments performed thereafter with EF on the collected eluates revealed that the quasi-complete mineralization (>99.5%) of the hydrocarbons was achieved within 32 h according to a linear kinetic trend. Toxicity was higher than in the initial solution and reached 95% of inhibition of Vibrio fischeri bacteria measured by Microtox® method, demonstrating the presence of remaining toxic compounds even after the complete degradation. Finally, the biodegradability (BOD5/COD ratio) reached a maximum of 20% after 20 h of EF treatment, which is not enough to implement a combined treatment with a biological treatment process.

Influence of solubilizing agents (cyclodextrin or surfactant) on phenanthrene degradation by electro-Fenton process – Study of soil washing recycling possibilities and environmental impact

One of the aims in soil washing treatment is to reuse the extracting agent and to remove the pollutant in the meantime. Thus, electro-Fenton (EF) degradation of synthetic soil washing solutions heavily loaded with phenanthrene was suggested for the first time. Two solubilising agents hydroxypropyl-beta-cyclodextrin (HPCD) and Tween 80® (TW 80) were chosen as cyclodextrin (CD) and surfactant representatives, respectively. In order to reuse HPCD and to degrade the pollutant simultaneously, the following optimal parameters were determined: [Fe2+] = 0.05 mM (catalyst), I = 2000 mA, and natural solution pH (around 6), without any adjustment. Only 50% of TW 80 (still higher than the critical micelle concentration (CMC)) can be reused against 90% in the case of HPCD while phenanthrene is completely degraded in the meantime, after only 180 min of treatment. This can be explained by the ternary complex formation (Fe2+-HPCD-organic pollutant) (equilibrium constant K = 56 mM−1) that allows OH to directly degrade the contaminant. This confirms that Fe2+ plays an important role as a catalyst since it can promote formation of hydroxyl radicals near the pollutant and minimize HPCD degradation. After 2 h of treatment, HPCD/phenanthrene solution got better biodegradability (BOD5/COD = 0.1) and lower toxicity (80% inhibition of luminescence of Vibrio fischeri bacteria) than TW 80/phenanthrene (BOD5/COD = 0.08; 99% inhibition of V. fischeri bacteria). According to these data, HPCD employed in this integrated (soil washing + EF degradation) approach gave promising results in order to be reused whereas the pollutant is degraded in the meanwhile.

Urban Mining: Quality and quantity of recyclable and recoverable material mechanically and physically extractable from residual waste

The mechanically sorted dry fraction (MSDF) and Fines (<20mm) arising from the mechanical biological treatment of residual municipal solid waste (RMSW) contains respectively about 11% w/w each of recyclable and recoverable materials. Processing a large sample of MSDF in an existing full-scale mechanical sorting facility equipped with near infrared and 2-3 dimensional selectors led to the extraction of about 6% w/w of recyclables with respect to the RMSW weight. Maximum selection efficiency was achieved for metals, about 98% w/w, whereas it was lower for Waste Electrical and Electronic Equipment (WEEE), about 2% w/w. After a simulated lab scale soil washing treatment it was possible to extract about 2% w/w of inert exploitable substances recoverable as construction materials, with respect to the amount of RMSW. The passing curve showed that inert materials were mainly sand with a particle size ranging from 0.063 to 2mm. Leaching tests showed quite low heavy metal concentrations with the exception of the particles retained by the 0.5mm sieve. A minimum pollutant concentration was in the leachate from the 10 and 20mm particle size fractions.

Current views on EDDS use for ex situ washing of potentially toxic metal contaminated soils

The paper presents a mini-review on EDDS use for ex situ chemical washing of potentially toxic metal contaminated soil. The attention is focused, initially, on studies aimed at verifying the biodegradability and the toxicity of free EDDS and metal-EDDS complexes. Free EDDS is found to be highly biodegradable. Metal-EDDS complexes, instead, are indicated as having variable biodegradability, but their toxicity is found to be always very low. The results obtained during soil washing treatments are successively reviewed. Removal percentages as high as 80–90 % are indicated as maximum obtained values. The extraction process is initially very fast, and then tends to slow down reaching the final equilibrium in about 1 week or even more. Generally acidic conditions are favourable to enhance the process. The influence of organic matter on process efficiency and the interactions between EDDS and soil minerals are also considered, revealing variable effects of the organic matter presence depending on its characteristics, and highlighting the possibility of iron and aluminium washing off during the remediation treatment.

Remediation of Used Motor Engine Oil Contaminated Soil: A Soil Washing Treatment Approach

The increasing contamination of soil by used motor oil is very common and of great concern to our society because of the possible harm that it can cause the environment. Remediation of contaminated soil is the application of suitable techniques in the removal of contaminants present in soil. Contaminants like heavy metals and aromatic hydrocarbons are found in used motor oil as a result of reactions in motor engines occurring during use of motor oil. The study determined the effect of soil washing using detergent as a remediation technique for soils contaminated with used motor oil. Detergent solution was added to soil contaminated by used motor oil. After twenty four (24) hours, the concentration of heavy metals (Cr, Zn, Cd, Pb, Ar, and Cu) and Polyaromatic Hydrocarbons (PAHs) in the soil residue were determined. A control experiment was carried out for a soil sample with no used motor oil added to it. The control experiment indicated that PAHs were not present in the soil before introduction of used motor oil. The removal rate of contaminants for this technique was 63.8% for Zn, 100% for Ar, 52.9% for Cd, 67.3% for Cr, 89.2% for Pb, 43.4% for Cu and 95.6% for PAHs. Soil washing was found to be effective in remediation of soils contaminated by low concentrations of used motor oil.