Surfactant-aided Soil Washing Research Articles

Solar‐powered BDD‐electrolysis remediation of soil washing fluid spiked with diesel

AbstractBACKGROUNDThe remediation of a soil spiked with diesel using Unitol L90 and sodium dodecyl sulfate (SDS) in a soil washing process was evaluated. The washing process was followed by an anodic oxidation based on boron doped‐diamond electrolysis (BDD‐electrolysis) to treat the washing liquid, using a solar photovoltaic (PV)‐battery system as a direct electrical power source.RESULTSThe results demonstrate that high concentrations of Unitol L 90 and SDS are required for the surfactant‐aided soil‐washing (SASW) to efficiently extract diesel from the soil. However, Unitol L 90 strongly interacts with the soil due to the adsorption process. The main characteristics of the effluents produced during this soil remediation was low conductivity. Therefore, the addition of 0.05 mol L–1 sodium sulfate (Na2SO4) as an electrolyte, at current density of 30 mA cm−2, was investigated. BDD‐electrolysis demonstrated that total organic carbon (TOC) and total petroleum hydrocarbon (TPH) were removed more effectively using SDS. The key of the treatment is associated to the electrogeneration of S2O82− due to the contribution of the surfactant composition and the addition of 0.05 mol L–1 Na2SO4. Additionally, an average solar irradiation intensity and integration of PV cells produced more than 10 A current and continuous electricity (∼27 V), which was constantly supplied to the electrolytic reactor at all times through a direct current generator.CONCLUSIONSFinally, based on the achieved results, BDD‐electrolysis is an efficient technology approach to remove hydrocarbons from the effluent produced during the soil washing process. © 2019 Society of Chemical Industry

The combined effects of surfactant solubilization and chemical oxidation on the removal of polycyclic aromatic hydrocarbon from soil

A method for the remediation of polycyclic aromatic hydrocarbons (PAHs) contaminated soils was proposed involving a combination of surfactant-aided soil washing and chemical oxidation by activated persulfate (SP). In this study, Triton X-100 (TX-100) and SP was applied to the soil, either concurrently or sequentially. Results indicated that surfactant followed by amendment with a solution of SP, TX-100 + SP(l), was most effective in decreasing PAHs concentrations in a sandy loam soil (SS) and a silty clay soil (NS) from 1220 mg/kg and 2730 mg·kg−1 to 414 mg·kg−1 and 180 mg·kg−1, respectively. Compared with extraction alone and oxidation alone, TX-100 + SP(l) increased the removal of PAHs by 10–20%. TX-100 improved the degradation of 3–4 ring PAHs (M-PAHs) and 5–6 ring PAHs (H-PAHs) in SS, by approximately 8%–11%. The oxygenated polycyclic aromatic hydrocarbons (oxy-PAHs) including furans and xanthene exhibited greater reductions in soil when amended with the TX-100 and SP, than under TX-100 extraction or SP oxidation alone. Overall, increased removal of PAHs in contaminated soil can occur through simultaneous application of TX-100 and SP, relative to the sole use of TX-100 or SP. The sequential combination of surfactant and oxidant was most effective for the elimination of PAHs, especially for M-PAHs and H-PAHs in sandy loam contaminated soil.

Remediation of soils polluted with lindane using surfactant-aided soil washing and electrochemical oxidation

In this work the complete treatment of soil spiked with lindane is studied using surfactant-aided soil-washing (SASW) to exhaust lindane from soil and electrolysis with diamond anodes to mineralize lindane from the soil washing fluid (SWF) waste. Results demonstrated that this technological approach is efficient and allow to remove this hazardous pollutant from soil. They also pointed out the significance of the ratio surfactant/soil in the efficiency of the SASW process and in the performance of the later electrolysis used to mineralize the pollutant. Larger values of this parameter lead to effluents that undergo a very efficient treatment which allows the depletion of lindane for applied charges lower than 15AhL−1 and the recovery of more than 70% of the surfactant for the regeneration of the SWF.

Removal of pendimethalin from soil washing effluents using electrolytic and electro-irradiated technologies based on diamond anodes

This work describes the treatment of soil polluted with the herbicide pendimethalin by the combination of surfactant-aided soil-washing (SASW) and electrochemical advanced oxidation processes. Results show that it is possible to completely extract the herbicide from soil using SDS (sodium dodecyl sulfate) solutions as soil washing fluid (SWF) and ratios SWF/soil higher than 10dm3kg−1. Soil washing effluents obtained after the application of the SASW consisted of a mixture of surfactant (high concentration) and pesticide (low concentration) and their degradation by electrolysis, photo-assisted electrolysis (photoelectrolysis) and sonoelectrolysis with diamond anodes has been compared with that obtained by the application of single photolysis and sonolysis. Opposite to photolysis and sonolysis, the different electrolytic techniques allow decreasing the concentration of herbicide and surfactant in the effluents. Competition between the surfactant and the herbicide oxidation is important and irradiation of high-frequency ultrasound or UV light do not seem to outperform very importantly the results obtained by single electrolysis in the effluents of the SASW obtained with low SDS/soil ratios. Opposite, photoelectrolysis becomes the most efficient technology for the treatment of SWF obtained at high SDS/soil ratios (those required for an efficient SASW). Catalytic effect of the sulfate released during the degradation of SDS (in particular the formation of sulfate radicals) can help to explain the differences observed. The removal efficiency is higher during sonoelectrolysis, reaching a final removal of the pesticide after 8h of treatment of 86.22%. Photoelectrolysis (57.59%) shows higher efficiencies for the removal of SDS followed by sonoelectrolysis (52.64%) and, finally, electrolysis (48.29%), after 8h of treatment.

Treating soil-washing fluids polluted with oxyfluorfen by sono-electrolysis with diamond anodes

This works is focused on the treatment by sono-electrolysis of the liquid effluents produced during the Surfactant-Aided Soil-Washing (SASW) of soils spiked with herbicide oxyfluorfen. Results show that this combined technology is very efficient and attains the complete mineralization of the waste, regardless of the surfactant/soil radio applied in the SASW process (which is the main parameter of the soil remediation process and leads to very different wastes). Both the surfactant and the herbicide are completely degraded, even when single electrolysis is used; and only two intermediates are detected by HPLC in very low concentrations. Conversely, the efficiency of single sonolysis approach, for the oxidation of pollutant, is very low and just small changes in the herbicides and surfactant concentrations are observed during the tests carried out. Sono-electrolysis with diamond electrodes achieved higher degradation rates than those obtained by single sonolysis and/or single electrolysis with diamond anodes. A key role of sulfate is developed, when it is released after the electrochemical degradation of surfactant. The efficient catalytic effect observed which can be explained by the anodic formation of persulfate and the later, a sono-activation is attained to produce highly efficient sulfate radicals. The effect of irradiating US is more importantly observed in the pesticide than in the surfactant, in agreement with the well-known behavior of these radicals which are known to oxidize more efficiently aromatic compounds than aliphatic species.

Treatment of ex-situ soil-washing fluids polluted with petroleum by anodic oxidation, photolysis, sonolysis and combined approaches

In this research, the treatment of soil spiked with petroleum was studied using a surfactant-aided soil-washing (SASW) process followed by sonolysis (US), photolysis and boron doped diamond electrolysis (BDD-electrolysis) for washing liquid treatment. Results clearly demonstrate that SASW is a very efficient approach in the treatment of soil, removing completely the petrochemical compounds by using dosages about 5g of extracting surfactant (sodium dodecyl sulfate (SDS)) per kg of soil. The main characteristics of the effluents produced in this soil remediation technology as well as the efficiency of the treatment (US, photolysis and BDD-electrolysis) depend on the dosage of SDS. Depollution of the effluents (degradation and mineralization of the organic matter) is related to the reduction in size of micelles formed by SDS and petroleum, and it depends on the treatment used. US and photolysis were inefficient decontamination processes, while BDD-electrolysis favors the complete depletion of micelles. However, the intensification of the efficiency was attained by synergic degradation effects when UV light irradiation and US were coupled with BDD-electrolysis, US/BDD-electrolysis and photo/BDD-electrolysis, respectively. Sulfate (coming from SDS) ions play an important role during the BDD-electrolysis, US/BDD-electrolysis and photo/BDD-electrolysis because persulfate and persulfate radicals are produced (by sulfate activation applying US or photolysis), improving the efficiency of the processes.

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.

Removal of oxyfluorfen from ex-situ soil washing fluids using electrolysis with diamond anodes

In this research, firstly, the treatment of soil spiked with oxyfluorfen was studied using a surfactant-aided soil-washing (SASW) process. After that, the electrochemical treatment of the washing liquid using boron doped diamond (BDD) anodes was performed. Results clearly demonstrate that SASW is a very efficient approach in the treatment of soil, removing the pesticide completely by using dosages below 5 g of sodium dodecyl sulfate (SDS) per Kg of soil. After that, complete mineralization of organic matter (oxyflourfen, SDS and by-products) was attained (100% of total organic carbon and chemical oxygen demand removals) when the washing liquids were electrolyzed using BDD anodes, but the removal rate depends on the size of the particles in solution. Electrolysis of soil washing fluids occurs via the reduction in size of micelles until their complete depletion. Lower concentrations of intermediates are produced (sulfate, chlorine, 4-(trifluoromethyl)-phenol and ortho-nitrophenol) during BDD-electrolyzes. Finally, it is important to indicate that, sulfate (coming from SDS) and chlorine (coming from oxyfluorfen) ions play an important role during the electrochemical organic matter removal.

The role of particle size on the conductive diamond electrochemical oxidation of soil-washing effluent polluted with atrazine

Soil washing using surfactant solutions is a very effective and widely used technique for the remediation of polluted soil. However, it is not a finalistic technology and once the pollutant is transferred to the washing-solution, the resulting aqueous waste has to be treated. In this work, the feasibility of Conductive-Diamond Electrochemical-Oxidation (CDEO) to treat the effluent of a surfactant-aided soil washing process was studied and some important mechanistic aspects were pointed out. Atrazine was selected as the model pesticide and sodium dodecyl sulfate (anionic surfactant) was used as washing agent. Besides COD, TOC, and pollutants concentration, the changes of z-potential and particle size were monitored during electrolysis in order to clarify the degradation mechanisms involved in the electrochemical treatment of emulsions. The results show that CDEO enables a complete reduction in the organic load of the waste. However, the process efficiency seems to be influenced by the size of particles present in the reaction media, which decreases continuously during the treatment. Steric hindrance of the large micelles (mean size 1100 um) seems to prevent direct oxidation of micelles on the anodic surface and hence only mediated processes can explain the results obtained. In this case, it may be assumed that peroxocarbonate (from carbonate salts added as supporting electrolyte) and peroxosulfate ions (formed from the oxidation of sulfate ions released from SDS molecule) are the main species expected according to the washing fluid composition.

Ultrasonically Enhanced Effectiveness of Various Surfactants on Diesel Removal from Contaminated Soil

The use of ultrasound to enhance the efficiency of surfactant-aided soil washing was investigated with a series of laboratory tests on diesel-contaminated soil. Test conditions included the power and duration of sonic energy, the surfactant type, and mixing time. The results of the study show that the use of ultrasound in the soil washing process significantly enhanced the remediation of the contaminated soil. The degree of enhancement varied with sonication energy, treatment time, and mixing duration.

Influence of Triton X-100 and SDBS on the Sorption of Streptomycin Sulfate from Soil

Although surfactants have been considered in surfactant-aided soil washing systems, there is little information on the adsorption of the impact of surfactant on the adsorption of antibiotic, and this may have significant implications for the soil. In this study, Triton X-100 and SDBS were selected to study its effect on the sorption of Streptomycin sulfate from soil under equilibrium sorption. The adsorption of Streptomycin sulfate on soils in surfactant free and surfactant solutions of different critical micelle concentrations (CMCs) has been studied .The applied surfactant concentrations (X) ranged from below the (nominal) CMC to 5 times the CMC. For relatively water-soluble Streptomycin sulfate, the distribution coefficients with anionic surfactant (Kd*) deceeded those without surfactant (Kd), while non-ionic (Kd*) all exceeded those without surfactant (Kd). The Kd*/Kd ratios were used to evaluate the efficiency of surfactants and it was found that anionic surfactant is a better choice for remediation of contaminated soils whereas non-ionic surfactants leads to poor remediation efficiency.

The use of a combined process of surfactant-aided soil washing and coagulation for PAH-contaminated soils treatment

Polycyclic aromatic hydrocarbons (PAHs) persist in soils due to their low volatility, low water solubility and low biodegradability, all of which make it difficult to remove this type of compound from soils. The work described here involved the study of a combined surfactant-aided soil washing (SASW) process and coagulation treatment, using iron and aluminium salts, to remediate a low-permeability PAH-polluted soil. Phenanthrene was selected as the model PAH and three different types of surfactants (anionic, cationic, and non-ionic) were used as washing agents. The results show that the anionic surfactant is the most effective washing fluid because efficiencies higher than 90% can be achieved. Non-ionic and cationic surfactant efficiencies were 70% and 30%, respectively. In addition, only the anionic wastewater can be satisfactorily treated with this technology, with COD removals greater than 90% achieved. Variation of pH, zeta-potential and the dose of aluminium required seem to indicate that a charge-neutralization mechanism is the main process involved in the emulsion break-up obtained in the treatment of aqueous surfactant wastes. In addition, the effects of surfactant concentration and that of the pH of the soil-washing wastewater seem to have a greater influence on the performance of the coagulation process.

Photodegradation of 2,2′,4,4′-tetrabromodiphenyl ether in nonionic surfactant solutions

Recently, polybrominated diphenyl ethers (PBDEs) contaminated soils in electronic waste (e-waste) disposal sites of China have been reported and aroused concern. Since surfactant-aided soil washing followed by photodestruction has been suggested as a promising technology for soil remediation, the photodegradation of 2,2′,4,4′-terabromodiphenyl ether (BDE-47) in nonionic surfactant solutions under UV-irradiation at 253.7 m was studied in the present work. The investigation was carried out on the effect of the type and concentration of surfactants, initial pH, and the addition of cations and acetone on BDE-47 photodecay. BDE-47 photodegradation all well followed pseudo-first-order kinetics under various conditions, and the decay rate was 0.4–1.3 times greater in the presence of surfactants than that in water alone. It was found that BDE-47 photodegradation was hardly affected through varying initial pH levels and retarded due to the presence of cations and acetone. The primary decay pathways in all surfactant micelles were shown to be reductive photodebromination, in which tri- to mono-BDEs were formed through a consecutive loss of bromine atoms. 2,4,4′-tribromodiphenyl ether (BDE-28), 4,4′-dibromodiphenyl ether (BDE-15), and 4-monobromodiphenyl ether (BDE-3) appeared sequentially as the predominant photoproducts over reaction time. Polybrominated dibenzofurans (mono- to tri-) were tentatively identified as additional intermediates for BDE-47 photodegradation in surfactant micelles.

Particle-Size Dependent Sorption and Desorption of Pesticides within a Water−Soil−Nonionic Surfactant System

Although nonionic surfactants have been considered in surfactant-aided soil washing systems, there is little information on the particle-size dependence of these processes, and this may have significant implications for the design of these systems. In this study, Triton-100 (TX) was selected to study its effect on the sorption and desorption of two pesticides (Atrazine and Diuron) from different primary soil size fractions (clay, silt, and sand fractions) under equilibrium sorption and sequential desorption. Soil properties, TX sorption, and pesticide sorption and desorption all exhibited significant particle-size dependence. The cation exchange capacity (CEC) of the bulk soils and the soil fractions determined TX sorption capacity, which in turn determined the desorption efficiency. Desorption of pesticide out of the clay raction is the limiting factor in a surfactant-aided washing system. The solubilization efficiency of the individual surfactant micelles decreased as the amount of surfactant added to the systems increased. Thus, instead of attempting to wash the bulk soil, a better strategy might be to either (1) use only the amount of surfactant that is sufficient to clean the coarse fraction, then separate the fine fraction, and dispose or treat it separately, or (2) to separate the coarse fractions mechanically and then treatthe coarse and fine fractions separately. These results may be applicable to many other hydrophobic organic compounds such as polyaromatic hydrocarbons (PAHs) and polychlorinated biphenyls (PCBs) strongly sorbed onto soils and sediments.

Effect of Ultrasound on Surfactant-Aided Soil Washing

The use of ultrasound as an enhancement mechanism in the surfactant-aided soil-washing process was examined by conducting desoption tests of soils contaminated with naphthalene or diesel-oil. The experiments were conducted to elucidate the effect of ultrasound on the mass transfer from soil to the aqueous phase using naphthalene-contaminated soil. In addition, the use of ultrasound for the diesel-oil-contaminated soil was investigated under a range of conditions of surfactant concentration, sonication power, duration, soil/liquid ratio, particle size and initial diesel-oil concentration. The ultrasound used in the soil-washing process significantly enhanced the mass transfer rate from the solid phase to the aqueous phase. The removal efficiency of diesel-oil from the soil phase generally increased with longer sonication time, higher power intensity, and large particle size.

Development and assessment of an innovative soil-washing process based on the use of cholic acid-derivatives as pollutant-mobilizing agents

Surfactant-aided soil washing is often proposed for the restoration of aged organic pollutant-contaminated soils. As many of commercial surfactants have been found to be toxic and recalcitrant, the opportunity to use in this process cheap, non-toxic, and biodegradable pollutant-mobilizing agents, such as deoxycholic acid (DA), bovine bile (BB), and the residue resulting from DA extraction from BB (BBR), was studied in this work. A soil historically contaminated by chlorinated anilines and benzenes, thiophenes, and several polycyclic aromatic hydrocarbons was suspended at 15% w/v and washed in water or water amended at 1.0% (w/v) with DA, BB, BBR, or Triton X-100 (TX). The resulting effluents were supplemented with nutrients and subjected to aerobic bioremediation. The biogenic agents enhanced the water pollutant elution potential by 230/440%. TX enhanced the same parameter by about 540%; however, it mediated a lower depletion of the initial soil ecotoxicity and a more extensive mobilization of soil constituents with respect to the biogenic agents. Furthermore, TX adversely affected the biotreatability of resulting effluents, by adversely affecting the growth of cultivable bacterial biomass and the structure of eubacterial community of the effluent. On the contrary, the biogenic agents, and in particular DA and BB, enhanced the effluents bioremediation, by sustaining the growth and increasing the complexity of the effluent eubacterial communities. Thus, DA and BB are very promising additives for an effective and environmental friendly soil washing treatment of aged (chloro)organics contaminated soils.

Amphoteric Effect of Humic Acids in Surfactant-Aided Photolysis of Polychlorobiphenyls

Polychlorobiphenyls (PCBs) are one of the most environmentally problematic organic contaminants present in soils and sediments due to their long-life in direct disposal or spills in soil. It is known that surfactant-aided soil washing followed by a photodechlorination process has the ability to separate PCBs from the soil and decompose them all in one step. However, the influence of humic substances on the removal of PCBs in surfactant-aided ultraviolet systems is of special interest because of the involvement of humic materials in the soil-washing process. A PCB congener, 4,4′-dichlorobiphenyl (DCB), was used as a probe in this study. At low humic acid (HA) concentrations, humic substances promote the photochemical reaction, but a high dose of HA leads to retardation of the DCB decay. A mechanism for the amphoteric effect of HA on the photodecay of DCB is proposed in this study, and two mathematical models are developed to successfully rationalize the amphoteric effect of HA in the photolysis process.

Remediation of Contaminated Soils by Surfactant-Aided Soil Washing

This paper provides reviews and updates of surfactant-aided subsurface remediation. Experimental measurements were made of various systems comprising two non-ionic surfactants, five soils of different fractional organic carbon contents, and several typical hydrophobic organic compounds ~HOCs!. Soil-washing performance was quantified using reciprocal surfactant-soil solubilization coef- ficients (1/Kd), and two phases of soil-washing mechanisms were identified depending on the presence of surfactant micelles. Reciprocal surfactant-soil solubilization coefficients (1/Kd), octanol-water partition coefficients (Kow), fractional organic carbon content of the soil ( f oc), and surfactant concentration were correlated for the soil-washing process using a proposed surfactant-aided soil-washing model.

The mechanism of the surfactant-aided soil washing system for hydrophobic and partial hydrophobic organics

A surfactant-aided soil washing mechanism is proposed in this study by examining nine common organic contaminants, which were divided into two groups, hydrophobic compounds and partial hydrophobic compounds, depending on the respective soil partitioning of contaminants, K oc . The presence of a free non-aqueous phase liquid in the soil washing system is critical to determine the soil washing performance curves. A mathematical model is proposed to describe soil-washing performance at various surfactant concentrations. The resulting slopes and intercepts from the model for the performance prediction are linearly related to K oc . In addition, a transition zone between the hydrophobic and partial hydrophobic compounds was observed, and has been used in verifying the proposed mechanism successfully by overdosing and underdosing the contaminants in the system.

Modeling the sequential photodechlorination of hexachlorobenzene in surfactant micelles

A five-stage consecutive irreversible model is derived to predict the photodegradation of hexachlorobenzene (HCB) in a surfactant solution, which was proven to be a useful treatment process following the surfactant-aided soil washing or remediation. The photodegradation of HCB in surfactant micelles is dominated by photodechlorination, which sequentially removes chlorides one at a time. The minor pathways of photoisomerization and photochlorination were neglected in the kinetic model. The results show that the derived consecutive irreversible model can accurately predict the decay of HCB and the formation (and decay) of its less-chlorinated congeners. The initial rate approach was used to identify the proper range of decay rate of each chlorinated benzene; so the overall rate constants can be determined easier by trial. The decreased performance of a completely mixed flow reactor (CMFR) with continuous input is also quantified compared to a batch reactor.