Removal of hydrophobic organic pollutants from soil washing/flushing solutions: A critical review

Remediation of soils contaminated by hydrophobic organic compounds: How to recover extracting agents from soil washing solutions?

A lot of soil (particularly, former industrial and military sites) has been contaminated by various highly toxic contaminants such as petroleum hydrocarbons, polycyclic aromatic hydrocarbons (PAHs), polychlorobiphenyls (PCBs) or chlorinated solvents. Soil remediation is now required for their promotion into new industrial or real estate activities. Therefore, the soil washing (SW) process enhanced by the use of extracting agents (EAs) such as surfactants or cyclodextrins (CDs) has been developed for the removal of hydrophobic organic compounds (HOCs) from contaminated soils. The use of extracting agents allows improving the transfer of HOCs from the soil-sorbed fraction to the washing solution. However, using large amount of extracting agents is also a critical drawback for cost-effectiveness of the SW process. The aim of this review is to examine how extracting agents might be recovered from SW solutions for reuse. Various separation processes are able to recover large amounts of extracting agents according to the physicochemical characteristics of target pollutants and extracting agents. However, an additional treatment step is required for the degradation of recovered pollutants. SW solutions may also undergo degradation processes such as advanced oxidation processes (AOPs) with in situ production of oxidants. Partial recovery of extracting agents can be achieved according to operating conditions and reaction kinetics between organic compounds and oxidant species. The suitability of each process is discussed according to the various physicochemical characteristics of SW solutions. A particular attention is paid to the anodic oxidation process, which allows either a selective degradation of the target pollutants or a complete removal of the organic load depending on the operating conditions.

Removal of heavy metals from contaminated paddy soils using chemical reductants coupled with dissolved organic carbon solutions

General acid washing is commonly used to treat heavy metal-contaminated soils, but it is sometimes difficult to achieve remediation aims in severely polluted soils. If we expose the surfaces of Fe oxide minerals to reductive dissolution during washing treatment, more of the metals initially adsorbed to these surfaces will be liberated, which may encourage the removal of heavy metals. Initially, the metal extraction capabilities of nine chemical reductants were compared in ten soil samples polluted by Cr, Cu, Zn, and Ni. Sodium dithionite (Na₂S₂O₄) and ferrous sulfate (FeSO₄) were screened for subsequent intensive research. In summary, the Na₂S₂O₄ solutions had higher Cr, Cu, and Zn removal rates than either the FeSO₄ or acid solution. Application of dissolved organic carbon (DOC) further increased the removal of heavy metals by complexation. About 15%, 86%, 32%, and 52% of the Cr, Cu, Zn, and Ni, respectively, were removed from the representative soil (M-2) by two-stage washing using 0.2 M Na₂S₂O₄ coupled with 1,500 mg L^-1 DOC solution at pH 2.0. Meanwhile, most soil fertility was preserved: ammonium nitrogen was increased 3.9 times; the increase in exchangeable potassium was 33%; and the reduction in available P was only 10%.

Compatibility of nonionic and anionic surfactants with persulfate activated by alkali in the abatement of chlorinated organic compounds in aqueous phase

Surfactant Enhanced In-Situ Chemical Oxidation (S-ISCO) is an emerging technology in the remediation of sites with residual Dense Non-Aqueous Phase Liquids (DNAPLs), a ubiquitous problem in the environment and a challenge to solve. In this work, three nonionic surfactants: E-Mulse3® (E3), Tween80 (T80), and a mixture of Tween80-Span80 (TS80), and an anionic surfactant: sodium dodecyl sulfate (SDS), combined with persulfate activated by alkali (PSA) as oxidant have been investigated to remove the DNAPL generated as liquid waste in lindane production, which is composed of 28 chlorinated organic compounds (COCs). Because the compatibility between surfactants and oxidants is a key aspect in the S-ISCO effectiveness the unproductive consumption of PS by surfactants was investigated in batch (up to 864 h) varying the initial concentration of PS (84-42 mmol·L^-1) and surfactants (0-12 g·L^-1) and the NaOH:PS molar ratio (1 and 2). The solubilization capacity of a partially oxidized surfactant was analyzed by estimating its Equivalent Surfactant Capacity, ESC, (as mmol_{COCs dissolved}g_surf^-1) and comparing it to the expected value for an unoxidized surfactant, ESC_o. Finally, the abatement of DNAPL with simultaneous addition of surfactant and PSA was studied. At the conditions used, a negligible unproductive consumption of PS was found by SDS; meanwhile, PS consumption at 360 h ranged between 70 and 80% using the nonionic surfactants. The highest ratios of ESC/ESC_o were found with SDS and E3 and these surfactants were chosen for the S-ISCO treatment. When oxidant and surfactant were simultaneously applied for DNAPL abatement the COC conversion was more than three times higher with E3 (0.6 at 360 h) than SDS. Moreover, it was obtained that the time needed for the removal of a mass of DNAPL by PSA in the absence of surfactants was notably higher than the time required when a suitable surfactant was added.

A new foam-based method for the (bio)degradation of hydrocarbons in contaminated vadose zone

An innovative foam-based method for Fenton reagents (FR) and bacteria delivery was assessed for the in situ remediation of a petroleum hydrocarbon-contaminated unsaturated zone. The surfactant foam was first injected, then reagent solutions were delivered and propagated through the network of foam lamellae with a piston-like effect. Bench-scale experiments demonstrated the feasibility of the various treatments with hydrocarbon (HC) removal efficiencies as high as 96 %. Compared to the direct injection of FR solutions, the foam-based method led to larger radii of influence and more isotropic reagents delivery, whereas it did not show any detrimental effect regarding HC oxidation. Despite 25 % of HCs were expelled from the treated zone because of high foam viscosity, average degradation rates were increased by 20 %. At field-scale, foam and reagent solutions injections in soil were tracked both using visual observation and differential electric resistivity tomography. The latter demonstrated the controlled delivery of the reactive solutions using the foam-based method. Even if the foam-based method duration is about 5-times longer than the direct injection of amendment solutions, it provides important benefits, such as the confinement of harmful volatile hydrocarbons during Fenton treatments, the enhanced reagents delivery and the 30 % lower consumption of the latter.

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.

Selective removal of phenanthrene for the recovery of sodium dodecyl sulfate by UV-C and UV-C/PDS processes: Performance, mechanism and soil washing recycling

Soil washing is commonly used to remediate PAHs contaminated sites. However, the effluent after washing containing PAHs and surfactant may cause secondary pollution and remediation cost is still high, unless PAHs are selectively removed from the effluent and the surfactant is recovered and recycled. Herein, ultraviolet irradiation (254 nm, UV-C) and its combination with peroxydisulfate (UV-C/PDS) were applied to selectively degrade PHE in the synthetic soil washing effluent. At natural pH of 8.6, 98.2 % of PHE was removed within 30 min under 6 W UV-C irradiation. After adding 2 mM PDS, the time was shortened to 8 min but still achieving 98.7 % PHE removal and less toxic treated effluent than UV-C alone. The ¹O₂ was the main oxidizing species in UV-C alone system, while ¹O₂ as well OH and SO₄^- were responsible for PHE removal in the UV-C/PDS system. The possible intermediates of PHE degradation were recognized using liquid chromatography-mass spectrometry technique and the degradation pathways in both systems were proposed. Soil washing recycling experiments verified the recovered SDS could be reused directly without surfactant supplement and the soil washing efficiency changed insignificantly during three cycles. It indicates UV-C/PDS coupled with soil washing is a promising remediation technology.

Effect of flux components of lightweight aggregate on physical properties and heavy metal solidification performance

The preparation of lightweight aggregate (LWA) by high-temperature sintering is a promising method for recycling solid waste safely, especially for solidifying heavy metals effectively. The main aim of this research was to systematically evaluate the effects of the flux components on LWA, including Na₂O, MgO, CaO, and Fe₂O₃. The physical properties and chromium solidification mechanism of LWA were characterized and analyzed. The results showed that the addition of Na facilitated LWA preparation and Cr solidification, whereas Ca, Mg, and Fe were deleterious to some extent. Further analysis indicated that increasing the Fe₂O₃ content was not conducive to the reduction of Cr because its decomposition reaction creates an oxygen-rich environment. The results of this research could provide a meaningful guide for regulating the composition of raw materials for the production of LWA to treat industrial Cr-containing solid waste.

Reusable Cyclodextrin-Based Electrochemical Platform for Detection of trans-Resveratrol

A reusable sensor architecture, through the combination of self-assembled monolayers and cyclodextrin supramolecular interactions, is demonstrated for class recognition of hydrophobic analytes demonstrated with trans-resveratrol. The reloadable sensor is based on reversible immobilization of α-cyclodextrin on polyethylene glycol surface. α-cyclodextrins complexes with polyethylene glycols and causes the polymer chains to change their surface configuration. The reproducibility and stability of the sur-face, in the detection of nanomolar concentrations of trans-resveratrol, can be demonstrated by electrochemical impedance spectroscopy, X-ray photoelectron spectroscopy, and Attenuated total reflectance-Fourier transform infrared spectroscopy. We propose that during sensor operation, α-cyclodextrin decouples from the poly-ethylene glycol surface to complex with trans-resveratrol in solution, and after use, the surface regeneration is conducted with a simple α-cyclodextrin soak. To test the nonspecific response, the sensor was also tested with trans-resveratrol spiked human urine.

From aliphatic compounds contaminated soil to active building material: An emerging opportunity for soil remediation and waste utilisation

Soil contaminated with the production wastewater of 4,4'-diaminostilbene-2,2'-disulfonic acid is extremely hazardous and difficult to bioremediate. In this study, a cost-effective method was developed to reduce the risk of contaminated soil and produce building materials through a combination of ultrasonic processing and solidification/stabilisation. Ultrasonic processing conditions of 5 min at 40 kHz were found to significantly improve the compressive strength of bricks. The results of scanning electron microscopy, X-ray diffraction, and thermogravimetric analysis demonstrated that the enhanced strength was due to the ultrasonic processing controlling the shape and scale of the crystals and microstructure of the cement paste. Furthermore, the effect of the activating agent, CaO, on the leaching toxicity of the bricks was closely related to the curing temperature. Under natural dry conditions (10-25 °C), the leaching toxicity decreased along with the reduction of CaO. However, under high artificial temperature conditions (40 °C), increasing the CaO was beneficial for decreasing the leaching toxicity. The addition of 2.91% CaO was suitable for improving brick performance under both natural dry (10-25 °C) and artificial temperature curing conditions (40 °C). The results of GC-MS revealed that 64.8% and 66.7% of organic species and organic volume, respectively, were reduced in the leachate of the bricks, which was produced by CaO activation and ultrasonic treatments. It was demonstrated that the optimal combined process for cost-effectively transforming hazardous soil to active building materials is feasible.

Role of surfactants in spontaneous displacement of high viscosity oil droplets from solid surfaces in aqueous solutions

HYPOTHESIS

Displacement of oil droplets receding from solid surfaces in aqueous solutions plays a critical role in many household activities and industrial operations. Surfactants are often involved in these activities to control the displacement process. We hypothesize that the influence of surfactants on the displacement process of oil is highly dependent on the type and dosage of surfactants, with the mechanisms being elucidated by the analysis using appropriate dynamic wetting models.

EXPERIMENTS

We systematically investigated the spontaneous displacement of a high viscosity oil on curved hydrophilic glass surfaces in aqueous solutions of anionic sodium dodecylbenzene sulfonate, cationic hexadecyl trimethyl ammonium bromide, and nonionic Triton^TM X-100 over a wide range of concentrations.

FINDINGS

The rather different oil displacement behaviors were observed with different surfactant additions. The displacement dynamics of the receding oil droplet was found to be inhibited by surfactant additions and followed two distinct models quantitatively: the power-law model describing the temporal evolution of early-stage displacement, and the molecular kinetic model describing the dependence of the three-phase contact line displacement velocity on the dynamic contact angle at the late stage of oil displacement. The model-based data analysis provided insights on the role of surfactants in controlling the oil displacement dynamics.

Enhanced treatment of the oil-contaminated soil using biosurfactant-assisted washing operation combined with H2O2-stimulated biotreatment of the effluent

A real crude oil-contaminated soil was treated using a two-step method: biosurfactant-assisted soil washing and the biostimulated biotreating of the effluent. The mixture of surfactin and rhamnolipid could enhance the TPH removal from an oil-contaminated soil (32 g/kg) in the soil washing operation. 86% of TPH was removed from the oil-contaminated soil in the soil washing operation under the mixed biosurfactant (surfactin + rhamnolipid) of 0.6 g/L, the soil/water ratio of 20 w/v%, the temperature of 30 °C, and the washing time of 24 h, leaving an effluent containing 5028 mg/L TPH. The effluent was efficiently biotreated in the bioprocess with 5 g/L acclimate biomass daily stimulated with 0.1 mM H₂O₂, and the concentrtion of TPH decreased to 26 mg/L within 17 d corresponding a TPH biodegradation over 99%. The biostimulation with H₂O₂ caused the production of a high amount of peroxidase that could accelerate the biodegradation of TPH. Accordingly, the findings suggest that the biosurfactant-assisted washing operation combined with the H₂O₂-stimulated biodegradation process could be an enhanced green method for efficient treatment of the heavy oil-contaminated soils.

The role of surfactants in colloidal biliquid aphrons and their transport in saturated porous medium

In remediation of dense non-aqueous phase liquids (DNAPLs), colloidal biliquid aphrons (CBLAs) could be added to produce a lower density nonaqueous phase which mitigate downward migration of DNAPL to non-polluted aquifers. There is still a big gap in the application of CBLAs in the remediation of actual polluted sites, especially the absence of relevant studies on its transport behavior in the sites, and its structural model has not been fully verified. These two factors could affect the effectiveness of CBLAs in the underground environment and its effect on density control. In this study, we prepared CBLAs with different surfactants and verified the structural model of CBLA based on their particle size distributions and demulsification performance. We studied the effects of particle concentrations, injection velocities, and porous media size on the migration of CBLA using the breakthrough curves and distribution profiles along the column. Experimental results indicated that surface elasticity of CBLAs was inversely proportional to the concentration of the anionic surfactant sodium dodecyl sulphate (SDS), which led to easier demulsification of CBLA with the increase in SDS concentration. This observation was in agreement with the verified structural model of the CBLA which constitute both internal nonionic and external anionic surfactants. Furthermore, CBLA deposition is mainly caused by interception and is not suitable for application in fine media. Low concentration of CBLA and high injection flow rate help CBLA to form a remediation area with a certain radius. This study solved the problem of DNAPLs in contaminated groundwater from the perspective of density regulation, and made contributions towards the development of combined remediation approaches using CBLAs.

Coupling of Anodic Oxidation and Soil Remediation Processes: A Review

In recent years, due to industrial modernization and agricultural mechanization, several environmental consequences have been observed, which make sustainable development difficult. Soil, as an important component of ecosystem and a key resource for the survival of human and animals, has been under constant contamination from different human activities. Contaminated soils and sites require remediation not only because of the hazardous threat it possess to the environment but also due to the shortage of fresh land for both agriculture and urbanization. Combined or coupled remediation technologies are one of the efficient processes for the treatment of contaminated soils. In these technologies, two or more soil remediation techniques are applied simultaneously or sequentially, in which one technique complements the other, making the treatment very efficient. Coupling anodic oxidation (AO) and soil remediation for the treatment of soil contaminated with organics has been studied via two configurations: (i) soil remediation, ex situ AO, where AO is used as a post-treatment stage for the treatment of effluents from soil remediation process and (ii) soil remediation, in situ AO, where both processes are applied simultaneously. The former is the most widely investigated configuration of the combined processes, while the latter is less common due to the greater diffusion dependency of AO as an electrode process. In this review, the concept of soil washing (SW)/soil flushing (SF) and electrokinetic as soil remediation techniques are briefly explained followed by a discussion of different configurations of combined AO and soil remediation.

Synergistic Solubilization of Phenanthrene by Mixed Micelles Composed of Biosurfactants and a Conventional Non-Ionic Surfactant

This study investigated the solubilization capabilities of rhamnolipids biosurfactant and synthetic surfactant mixtures for the application of a mixed surfactant in surfactant-enhanced remediation. The mass ratios between Triton X-100 and rhamnolipids were set at 1:0, 9:1, 3:1, 1:1, 1:3, and 0:1. The ideal critical micelle concentration values of the Triton X-100/rhamnolipids mixture system were higher than that of the theoretical predicted value suggesting the existence of interactions between the two surfactants. Solubilization capabilities were quantified in term of weight solubilization ratio and micellar-water partition coefficient. The highest value of the weight solubilization ratio was detected in the treatment where only Triton X-100 was used. This ratio decreased with the increase in the mass of rhamnolipids in the mixed surfactant systems. The parameters of the interaction between surfactants and the micellar mole fraction in the mixed system have been determined. The factors that influence phenanthrene solubilization, such as pH, ionic strength, and acetic acid concentration have been discussed in the paper. The aqueous solubility of phenanthrene increased linearly with the total surfactant concentration in all treatments. The mixed rhamnolipids and synthetic surfactants showed synergistic behavior and enhanced the solubilization capabilities of the mixture, which would extend the rhamnolipids application.

Simultaneously enhanced surfactant flushing of diesel contaminated soil column and qualified emission of effluent

Seven surfactants were selected as candidate agents for in situ soil column flushing. Column flushing lacks the interaction between surfactants and contaminants, so efficiency is not easy to improve. Microbubbles generated in situ may adhere to the contaminant diesel. Thereafter, the bubbles were mobilized to lift the multi-system oil to the top layer. This process must be attributed to the increased column flushing efficiency of diesel removal. Compared with a single solution, using randomly methylated beta-cyclodextrin (RAMEB) and microbubble enhancement, the diesel removal of column flushing increased by 30.7%. Compared with the existing conditions (5.25 × 10^-4cm s^-1), the hydraulic conductivity of loam soil (3.74 × 10^-3cm s^-1) increased by 7.1 times after the continued operation of the two processes. The oil layer was collected for further reuse. After three treatments, the effluent for the RAMEB was more than 85%. The collected effluent was treated with a synthetic absorbent and then qualifiedly discharged with a TOC value of only 2.6 mg L^-1. By combining surfactant flushing with microbubbles and other equipment, not only can the reaction time be effectively saved, but organic pollutants could be concentrated and reused in the soil, so no additional treatment was required.

Synergistic Effects of Carbon Dots and Palladium Nanoparticles Enhance the Sonocatalytic Performance for Rhodamine B Degradation in the Absence of Light

Carbon dot (CD) and palladium nanoparticle (Pd NP) composites are semiconducting materials having tremendous applications in catalysis with suitable band gaps. However, their combination with a suitable polymer matrix in sonophotocatalysis has not been explored. Herein, we have synthesized and characterized a new nanohybrid catalyst from a polyamide cross-linked CD-polymer and subsequent deposition of Pd NPs. A sonocatalytic activity of 99% rhodamine B dye degradation was achieved in mere 5 min in the dark. A model catalyst replacing CDs with benzene and other control studies revealed that the synergistic effects of CDs and Pd NPs enhance the sonocatalytic activity of the nanohybrid catalyst. Interestingly, visible light did not influence the activity significantly. Mechanistic investigations suggest that generation of reactive oxygen species on the surface of the CD-polymer initiated by ultrasound, which is further facilitated by Pd NPs, is the key for remarkable catalytic activity (a rate constant of 0.99 min-1). Recyclable heterogeneous catalysts under ambient conditions are promising for exploring sono-assisted dark catalysis for several avenues.

Desorption process and morphological analysis of real polycyclic aromatic hydrocarbons contaminated soil by the heterogemini surfactant and its mixed systems

Surfactant-enhanced remediation (SER) is an efficient and low-cost technology for polycyclic aromatic hydrocarbons (PAHs) contaminated sites. This study assessed the desorption processes and effects of Heterogemini surfactant (Dodecyldimethylammonium bromide/tetradecyldimethylammonium bromide, DBTB), two traditional surfactants (Hexadecyl trimethyl ammonium bromide, CTAB; Sorbitan monolaurate, Span 20) and their mixed systems on the real PAHs-contaminated soil from an abandoned coking plant, as well they were analyzed micro morphologically. DBTB had greater desorption capability for PAHs and favorable interaction with the traditional surfactants confirmed by reaction parameters β^m and Gibbs. Whether for total PAHs (TPAHs) or different molecular weight PAHs, the mixed system Span 20/DBTB had larger molar solubilization ratio (MSR) and partition coefficient (K_m) than CTAB/DBTB, the highest desorption rate for TPAHs reaching 68.83%. Additionally, microscopic morphology showed micelles of Span 20/DBTB were more dispersed and formed strings easily, explaining its good desorption capability. What resulted demonstrated the feasibility of DBTB, a novel Heterogemini surfactant, and its mixed systems remediating PAHs-contaminated soil of abandoned industrial site.

A review of the application of sea material shells as low cost and effective bio-adsorbent for removal of heavy metals from wastewater

The pollution caused by heavy metal ions in industrial wastewater is of a great concern. Applying effective and low-cost methods is an urgent need for treatment of polluted water and aqueous solutions. Biosorption have received the most attention among the various methods. It has become an alternative technique to conventional technologies due to low cost, simple operation and treatment for heavy metal recovery, and high selectivity. In recent years, sea material shells have been applied as one of the most cost-effective bio-adsorbents due to their special properties. They are environmentally friendly, low cost, and easy to access and have high adsorption capacity. The purpose of this review is to present the application of oyster shell, snail shell, and shrimp shell as low-cost and effective biosorbents for removal of noxious heavy metals from aqueous solutions. In addition, heavy metals, their sources, and ways to remediate them from waste streams and various factors affecting the biosorption process with sea materials shells are also reviewed. Moreover, a brief description and literature review of the equilibrium, kinetic, and thermodynamic behaviors of the heavy metal ion adsorption process on sea material shells have been studied. Finally, further applications of sea materials shell for waste effluents treatment are specially focused.

Material flow analysis and heavy hydrocarbon removal in a full-scale biopile and soil washing plant in northern Italy

This study aimed to assess the mass fluxes and removal efficiencies of heavy hydrocarbons in a full-scale plant located in northern Italy. This plant receives and treats contaminated soil, soils and rocks from construction and demolition activities, incineration slags and street cleaning residues. The plant has three sections, consisting of bioremediation using biopile, a soil washing stage and a stabilization/solidification unit, which can perform independently or together with the others. The material flow analysis showed how the crisis in the construction industry changed the final destination of waste after the treatment: as the market demand for coarse material decreased, waste was sent directly to landfills for inert waste, instead of being recovered. Hydrocarbon mass fluxes showed that a considerable amount of pollutants was removed. In the period 2009-2014, the removal efficiencies of the bioremediation, the soil washing section and the entire plant were respectively 73%, 58% and 62%. The percentages of removal attained at the facility in study were sufficient to ensure the possibility of recovering the waste or disposing of it in different landfill categories, according to the national regulations.

Construction and visible-light-photocatalysis of a novel ternary heterostructure BiOI/(001)TiO2/Ti3C2

Constructing effective heterojunctions between semiconductors and appropriate cocatalysts and exposing highly active crystal facets have been considered an effective approach to obtain efficient photocatalysts. Herein, a novel BiOI/(001)TiO₂/Ti₃C₂ (BTT) hybrid was for the first time synthesized by in situ growing (001)TiO₂ nanosheets on a 2D MXene nanomaterial (Ti₃C₂) and subsequent deposition of flower-like nanoflake BiOI on the obtained (001)TiO₂/Ti₃C₂ hybrid. The BTT hybrid exhibited excellent photocatalytic performance for degradation of Rhodamine B under visible light irradiation, with the highest degradation rate being 6.26, 1.72, and 1.35 times of that of a pure BiOI, BiOI/TiO₂ hybrid, and BiOI/Ti₃C₂ hybrid, respectively. The staggeringly enhanced photoactivity of BTT was attributed to the separation of photogenerated carriers by a multiple charge transfer channels because of the formed p-n and Schottky double junctions. This study demonstrates that (001)TiO₂/Ti₃C₂ obtained by simple hydrothermal oxidation of Ti₃C₂ can be a good cocatalyst for fabricating excellent visible-light-driven photocatalyst.

Formulation of Bio-Based Washing Agent and Its Application for Removal of Petroleum Hydrocarbons From Drill Cuttings Before Bioremediation

Drill cuttings from petroleum exploration and production sites can cause diverse environmental problems. Total petroleum hydrocarbons (TPHs) are a major pollutant from the use of polyolefin-based mud. As an alternative to incineration, this study investigated the application of surfactant-enhanced washing technology prior to bioremediation. The washing step was necessary because the initial TPH concentrations were quite high at approximately 15% (w/w). Washing agents were formulated by varying the concentration of lipopeptide biosurfactant (in foamate or cell-free broth), Dehydol LS7TH (fatty alcohol ethoxylate 7EO, oleochemical surfactant) and butanol (as a lipophilic linker) at different salinities. The most efficient formula produced a Winsor Type I microemulsion (oil-in-water microemulsion) with polyolefin and contained only 20% (v/v) foamate and 2% (v/v) Dehydol LS7TH in water. Due to the synergistic behavior between the anionic lipopeptides and non-ionic Dehydol LS7TH, the formula efficiently removed 92% of the TPHs from the drill cuttings when applied in a jar test. To reduce the cost, the concentrations of each surfactant should be reduced; thus, the formula was optimized by the simplex lattice mixture design. In addition, cell-free broth, at a pH of 10, containing 3.0 g/L lipopeptides was applied instead of foamate because it was easy to prepare. The optimized formula removed 81.2% of the TPHs and contained 72.0% cell-free broth and 1.4% Dehydol LS7TH in water. A 20-kg soil washing system was later tested where the petroleum removal efficiency decreased to 70.7% due to polyolefin redeposition during separation of the washing solution. The remaining TPHs (4.5%) in the washed drilled cuttings were further degraded by a mixture of Marinobacter salsuginis RK5, Microbacterium saccharophilum RK15 and Gordonia amicalis JC11. To promote TPH biodegradation, biochar and fertilizer were applied along with bacterial consortia in a microcosm experiment. After 49-day incubation, the TPHs were reduced to 0.9% by both physical and biological mechanisms, while the TPHs in the unamended samples remained unaffected. With the use of the formulated bio-based washing agent and bioremediation approach, the on-site treatment of drill cuttings could be conducted with an acceptable cost and low environmental impacts.

Surfactant-enhanced aquifer remediation: Mechanisms, influences, limitations and the countermeasures

In recent years, surfactant-enhanced aquifer remediation (SEAR) has attracted increasing interest duo to the high efficiency of removing non-aqueous phase liquids (NAPLs) from aquifer. A thorough understanding of SEAR is necessary for its successful implementation in field remediation. This paper reviewed the SEAR technology in a comprehensive way based on the recent research advances. Firstly, an overview of the basic processes and mechanisms underlying the technology was presented. Secondly, applications of SEAR and the factors that influence the performance were summarized. Thirdly, the key limitations of SEAR, which are downward migration of dense-NAPLs, secondary pollution of surfactants, adsorptive, precipitative and partitioning loss of surfactants, and heterogeneity of the aquifer, were reviewed. Finally, the recent advances in modifying SEAR to overcome the limitations were discussed in detail. The review will promote our understanding of SEAR technology and provide some useful information to improve the performance of SEAR in applications.

Removal of 17β-Estradiol by Activated Charcoal Supported Titanate Nanotubes (TNTs@AC) through Initial Adsorption and Subsequent Photo-Degradation: Intermediates, DFT calculation, and Mechanisms

A low-cost composite of activated charcoal supported titanate nanotubes (TNTs@AC) was developed via the facile hydrothermal method to remove the 17β-estradiol (E2, a model of pharmaceutical and personal care products) in water matrix by initial adsorption and subsequent photo-degradation. Characterizations indicated that the modification occurred, i.e., the titanate nanotubes would be grafted onto the activated charcoal (AC) surface, and the micro-carbon could modify the tubular structure of TNTs. E2 was rapidly adsorbed onto TNTs@AC, and the uptake reached 1.87 mg/g from the dual-mode model fitting. Subsequently, the adsorbed E2 could be degraded 99.8% within 2 h under ultraviolet (UV) light irradiation. TNTs@AC was attributed with a unique hybrid structure, providing the hydrophobic effect, π−π interaction, and capillary condensation for E2 adsorption, and facilitating the electron transfer and then enhancing photocatalytic ability for E2-degradation. In addition, the removal mechanism of E2 was elucidated through the density functional theory calculation. Our study is expected to provide a promising material for environmental application.

Performance evaluation of a biotrickling filter for the removal of gas-phase 1,2-dichlorobenzene: Influence of rhamnolipid and ferric ions

The aim of this study was to evaluate the influence of rhamnolipid (RL) and ferric ions on the performance of a biotrickling filter (BTF) for the removal of gas-phase 1,2-dichlorobenzene (o-DCB). A comprehensive investigation of microbial growth, pollutant solubility, extracellular polymeric substances (EPS) and enzymatic activity in o-DCB degradation by an isolated strain Bacillus cereus DL-1 with/without RL and Fe³⁺ were carried out using batch microcosm experiments. In addition, o-DCB removal performance, biofilm morphology, and microbial community structures in two identical lab-scale biotrickling filters (named BTF1 and BTF2) inoculated with strain DL-1 were studied. The batch microcosm experiments demonstrated that 120 mg L^-1 RL and 4 mg L^-1 Fe³⁺ could enhance the biodegradation of o-DCB, which may be due to promotion on bacterial growth, o-DCB solubilization, C₁₂O enzyme activity, and polysaccharide (PS) and protein (PN) in EPS. Fourier transform infrared (FTIR) spectra indicated that the addition of RL with Fe³⁺ had notable effects on the functional groups of PS and PN in EPS. The experimental results in BTFs indicate that the removal efficiency of o-DCB decreased from 100% to 56.4% for BTF1, which was not fed with RL and Fe³⁺, and from 100% to 80.3% for BTF2, which was fed with RL and Fe³⁺, when the inlet loading rate increased from 4.88 to 102 g m^-3 h^-1 at an empty bed residence time of 60 s. In addition, the microbial adhesive strength and the microbial community structure were different among both BTFs, highlighting the positive effects of RL and Fe³⁺.

Combined effects of soil particle size with washing time and soil-to-water ratio on removal of total petroleum hydrocarbon from fuel contaminated soil

In this study, total petroleum hydrocarbon (TPH) removal from fuel-contaminated field soil was investigated. The influence of the washing method (washing before/after sieving), washing time, soil-to-water ratio, and soil particle size on TPH removal efficiency was evaluated under constant stirring speed. Washing the whole contaminated soil is more efficient than separating the soils into particle size fractions and separately washing the fractions. Particles with differing diameters would be more in contact with each other resulting in detachment of contaminants from the soil particle surface. Effects of soil washing time and soil-to-water ratio on TPH removal were not significant in coarse soil particles (greater than 0.15 mm diameter) but significantly affected TPH removal in fine particles (less than 0.15 mm diameter). This study suggests a threshold washing time of 1 h and a threshold soil-to-water ratio of 1:6 for the whole soil in soil washing. However, soil particles less than 0.075 mm (<75 μm) should be separated after washing to meet the Korean soil TPH limit of less than 500 mg/kg. This study demonstrates the importance of finer soils as debrading media and particle size fraction composition of fuel-contaminated soil in soil washing.

Distribution Characteristics of Bacterial Communities and Hydrocarbon Degradation Dynamics During the Remediation of Petroleum-Contaminated Soil by Enhancing Moisture Content

Microorganisms are the driver of petroleum hydrocarbon degradation in soil micro-ecological systems. However, the distribution characteristics of microbial communities and hydrocarbon degradation dynamics during the remediation of petroleum-contaminated soil by enhancing moisture content are not clear. In this study, polymerase chain reaction and high-throughput sequencing of soil microbial DNA were applied to investigate the compositions of microorganisms and alpha diversity in the oil-polluted soil, and the hydrocarbon removal also being analyzed using ultrasonic extraction and gravimetric method in a laboratory simulated ex-situ experiment. Results showed the distribution of petroleum hydrocarbon degrading microorganisms in the petroleum-contaminated loessal soil mainly was Proteobacteria phylum (96.26%)-Gamma-proteobacteria class (90.03%)-Pseudomonadales order (89.98%)-Pseudomonadaceae family (89.96%)-Pseudomonas sp. (87.22%). After 15% moisture content treatment, Actinobacteria, Proteobacteria, and Firmicutes still were the predominant phyla, but their relative abundances changed greatly. Also Bacillus sp. and Promicromonospora sp. became the predominant genera. Maintaining 15% moisture content increased the relative abundance of Firmicutes phylum and Bacillus sp. As the moisture-treated time increases, the uniformity and the richness of the soil bacterial community were decreased and increased respectively; the relative abundance of Pseudomonas sp. increased. Petroleum hydrocarbon degradation by enhancing soil moisture accorded with the pseudo-first-order reaction kinetic model (correlation coefficient of 0.81; half-life of 56 weeks). The richness of Firmicutes phylum and Bacillus sp. may be a main reason for promoting the removal of 18% petroleum hydrocarbons responded to 15% moisture treatment. Our results provided some beneficial microbiological information of oil-contaminated soil and will promote the exploration of remediation by changing soil moisture content for increasing petroleum hydrocarbon degradation efficiency.

A dynamic model to evaluate the critical loads of heavy metals in agricultural soil

Estimation of critical load (CL) is important for soil environmental management and pollution prevention. We developed a mass balance-based dynamic critical load (DCL) model, which improved the model performance, applicability and functionality compared with the traditional one. Paddy soils in two typical fields in central south China and two scenarios were chosen as case studies. The result of case study showed that atmospheric deposition was the main source of Cd, Cu, Pb, and Zn in the soils, with percentage contributions ranging from 59.9 to 79.8%. Crop uptake, particularly the rice straw harvest, was the primary output pathway, accounting for 35.1-71.2% of the total output flux. The critical loads also known as annual input limits (I_max) of heavy metals in the paddy soils were calculated by the developed DCL model. For example, the Imax of Cd was recommended as 0.05 kg ha^-1 in the paddy soils under the default scenario for a protection period of 40 years, and that became 0.12 kg ha^-1 and 0.17 kg ha^-1 under the straw removal scenario in the two typical fields, respectively. The scenario simulation suggested that the straw removal strategy reduced the total concentrations of heavy metals (C_t) in the soils and notably increased the I_max. Meanwhile, the sensitivity analysis indicated that the changes of C_t and I_max can be controlled by adjusting the partition coefficient (K_d), plant uptake factor (PUF) and input flux. The mass balance-based DCL model provides a reference method to establish the standard for controlling heavy metal inputs to agricultural soil, this will be helpful to develop strategies for the prevention of soil contamination.

Research on Treatment of Oily Sludge from the Tank Bottom by Ball Milling Combined with Ozone-Catalyzed Oxidation

Difficult separation of oil-solid phase and high fine content of the recovered oil were two problems in the treatment of oily sludge from the tank bottom by the hot water-based extraction process. To solve the problems, one technology with "ball milling + ozone-catalyzed oxidation" as the core was studied, and the process parameters of ball milling and ozone-catalyzed oxidation were respectively optimized. After ball milling treatment, the oil content of dry oily sludge decreased from 33.9 to 10.2%. Then, an ozone catalytic oxidation treatment technology with aluminum ore as the catalyst was developed to further treat this stubborn oily sludge. Under the optimal conditions, the oil content of oily sludge could be further reduced to 0.28%, which met the treatment and disposal requirements stipulated in GB4284-2018. For further research on the contribution of the catalyst to the ozone catalytic oxidation system, the reaction activation energy and reaction rates of ozone oxidation and ozone catalytic oxidation were compared from the perspective of kinetics. The results showed that, with the catalyst addition, the reaction rate constants increased about three times and the reaction activation energy reduced 82.26%, which showed the effectiveness of the catalyst on the kinetics quantitatively. The combined process with "ball milling + ozone-catalyzed oxidation" as the core can solve the two problems in the treatment of oily sludge from the tank bottom by hot water-based extraction and provides a reference for the harmless and resourceful treatment of oily sludge from the tank bottom.

Role of coke-bounded environmentally persistent free radicals in phenanthrene degradation by hydrogen peroxide

Emission of polycyclic aromatic hydrocarbons (PAHs) is accompanied with the discharge of carbonaceous particles during the coke production. To degrade the adsorbed PAHs, hydrogen peroxide (H₂O₂) was applied as an oxidising agent, which might be activated by the inherent environmentally persistent free radicals (EPFRs) on coke particles. The transformation of phenanthrene (PHE), selected as model molecule, was achieved in H₂O₂/coke particle system without the addition of additional activating agent. This process consumed the particle-bounded EPFRs, inducing the decreasing of spin density from 1.92 × 10¹⁸ to 4.4 × 10¹⁷ spins g^-1 in 30 min of reaction time. Electron paramagnetic resonance (EPR) technique coupled with spin-trapping agent 5, 5-dimethyl-1-pyrroline-N-oxide (DMPO) was used to probe the potential formation of reactive oxygen species. A higher capture [[Formula: see text]] concentration was observed with larger decreases in EPFRs concentration, indicating that EPFRs were the main contributor to the formation of [Formula: see text]. The obtained results suggested that the activation of H₂O₂ by EPFRs on coke particles resulted in the generation of hydroxyl radical ([Formula: see text]), which then back-reacted with adsorbed PHE. The finding of this study shed light on a new remediation technology for toxic carbonaceous byproducts discharged during the coke production.

Soil washing in combination with electrochemical advanced oxidation for the remediation of synthetic soil heavily contaminated with diesel

Sequential soil washing and electrochemical advanced oxidation processes (EAOPs) were applied for the remediation of synthetic soil contaminated with diesel. The surfactant Tween 80 was used to enhance the extraction of diesel from synthetic soil, and diesel extraction efficiency was improved with the increase of Tween 80 concentration. Under conditions of 180 min washing time, 10 g synthetic soil with 100 mL surfactant solution and two times of soil washing, about 75.2%, 80.0% and 87.9% of diesel was extracted from synthetic soil with 5.0, 7.5 and 10.0 g L^-1 Tween 80. The degradation of diesel in soil washing effluent was carried out by two EAOPs, electro-oxidation (EO) and electro-Fenton (EF) using boron-doped diamond (BDD) anode and carbon felt cathode cell. After 360 min EO treatment, 72.7-83.0% of diesel was removed from the effluent after soil washing with 5.0-10.0 g L^-1 Tween 80 while higher removal efficiencies (77.7-87.2%) were attained with EF process. Parallel factor analysis (PARAFAC) of excitation emission matrix (EEM) fluorescence spectroscopy was conducted to analysis the transformation of fluorescent components in diesel during the treatment by two EAOPs.

Bioremediation of PAH-Contaminated Soils: Process Enhancement through Composting/Compost

Bioremediation of contaminated soils has gained increasing interest in recent years as a low-cost and environmentally friendly technology to clean soils polluted with anthropogenic contaminants. However, some organic pollutants in soil have a low biodegradability or are not bioavailable, which hampers the use of bioremediation for their removal. This is the case of polycyclic aromatic hydrocarbons (PAHs), which normally are stable and hydrophobic chemical structures. In this review, several approaches for the decontamination of PAH-polluted soil are presented and discussed in detail. The use of compost as biostimulation- and bioaugmentation-coupled technologies are described in detail, and some parameters, such as the stability of compost, deserve special attention to obtain better results. Composting as an ex situ technology, with the use of some specific products like surfactants, is also discussed. In summary, the use of compost and composting are promising technologies (in all the approaches presented) for the bioremediation of PAH-contaminated soils.

AOPs-based remediation of petroleum hydrocarbons-contaminated soils: Efficiency, influencing factors and environmental impacts

Petroleum hydrocarbons are a class of anthropogenic compounds including alkanes, aromatic hydrocarbons, resins, asphaltenes and other organic matters, and soil pollution caused by petroleum hydrocarbons has drawn increasing interest in recent years. Multiple advanced oxidation processes (AOPs) are emerging to remediate petroleum hydrocarbons-contaminated soils, while very few studies have focused on the features of AOPs applied in soils. This review aims to provide an updated overview of the state of the science about the efficiency, influencing factors and environmental implications of AOPs. The key findings from this review include: 1) cyclodextrin and its derivatives can be used to synthesize targeting reagents; 2) soil organic matter (SOM), glucose and cement can activate persulfate; 3) SOM affects redox circumstance in soil and could be further developed for enhancing the catalysis effect of transition metals; 4) non-thermal plasma and wet oxidation are promising methods of AOPs to remove petroleum hydrocarbons from soil; 5) the occurrence, fate, and transformation of intermediates during the degradation of petroleum hydrocarbons in soil should be considered more. Overall, this review reveals an urgent need to develop the cost-effective remedial strategies for petroleum hydrocarbons contaminated soils, and to advance our knowledge on the generation, transport and propagation of radicals in soils.

Photoelectrolysis of clopyralid wastes with a novel laser-prepared MMO-RuO2TiO2 anode

This paper studies the applicability of a novel laser-prepared mixed metal oxide (MMO-RuO₂TiO₂) anode in the photoelectrochemical degradation of clopyralid, a toxic and biorefractory herbicide. Results are compared to those obtained using the well-known boron-doped diamond (BDD) anode and demonstrate that, although the electrolysis with diamond is more effective than that obtained with the new electrode, the irradiation of UVC light makes the novel MMO material more effective in chloride media. It was explained in terms of the homolysis of hypochlorous acid/hypochlorite to form chloride and hydroxyl radicals. Photoelectrochemical degradation with MMO produced a marked synergistic effect in TOC removal, especially in the presence of chloride ions. On the contrary, for the BDD anode, at the tested conditions, antagonisms were found in both sulfate and chloride media. These important synergisms allows finding conditions in which the novel anode can be competitive with the BDD.

Electrochemically assisted dewatering for the removal of oxyfluorfen from a coagulation/flocculation sludge

This work focuses on the evaluation of the electrochemical dewatering of sludge obtained in the coagulation of wastes polluted with oxyfluorfen. To do this, sludge samples were treated, aiming not only to reduce the sludge volume, but also to facilitate the degradation of oxyfluorfen contained in the cake via electrolysis with a boron-doped diamond anode. Results show that water can be effectively recovered through three sequential stages. First, a gravity-driven stage, that can recover around 60% of initial volume and where no oxyfluorfen is dragged. Then, a second stage that involves the application of pressure and which accounts for the recuperation of an additional 25% of the total volume of the water removed and in which oxyfluorfen also remained in the cake. Finally, an electrochemical stage, which involves the application of electricity with increasing electric fields (1.0, 2.0, 4.0, and 16.0 V cm^-1), accounting for the recovery of the rest of water released and where an electrolytic degradation of oxyfluorfen is obtained, whose extension depends on the electrode configuration used in the electro-dewatering cell. This electrode configuration also influences the retention or loss of oxyfluorfen from the cake, being the optimum choice the placement of the cathode downstream, next to the outlet of the dewatering cell.

Application of spectral induced polarization for characterizing surfactant-enhanced DNAPL remediation in laboratory column experiments

The widespread presence of entrapped dense non-aqueous phase liquid (DNAPL) in the subsurface poses a continuing challenge to groundwater remediation. Cost-effective and high-resolution subsurface characterization is a critical issue for further DNAPL recovery due to the complexity of DNAPL source zone architecture (SZA). Geophysical techniques provide a noninvasive, spatially continuous and cost-effective way for monitoring the DNAPL remediation process. In particular, the spectral induced polarization (SIP) method has shown great potential in environmental problems. In this study, we performed real-time SIP measurements on DNAPL contaminated soil in columns to quantitatively assess the ability of SIP method for monitoring surfactant-enhanced DNAPL remediation process. Chemical data was simultaneously collected during the remediation process to verify the results obtained by SIP method. Taking account into the variations of subsurface environment, we conducted a series of column flushing experiments under different flow rate, surfactant concentrations and fluid salinities. The results highlight that SIP method is able to effectively monitor the DNAPL remediation process, as well as to evaluate the remediation efficiency under different conditions. The variations in the flow rate, the concentration of surfactant and the salinity of pore water not only affect remediation effectiveness, but also have an impact on the SIP signatures. This study shows that SIP performs better for monitoring DNAPL remediation at a relatively low flow rate of ~ 0.4 m/d, low surfactant concentration of 5000 mg/L and high salinity of 1.0 S/m, with an error of saturation estimation (RMSE_S) <0.1.

Remediation of hexachlorobenzene-contaminated soils with alkyl glycoside-enhanced desorption and zero-valent iron-EDTA-air treatment

In this work, the use of a coupled process, alkyl glycoside (APG) enhanced soil desorption followed by the zero-valent iron-ethylenediaminetetraacetic acid (EDTA)-air (ZEA) Fenton-like system, was investigated for the remediation of a simulated hexachlorobenzene (HCB)-contaminated diatomite soil and a real HCB-contaminated soil. Three surfactants with different concentrations were studied to obtain the suitable soil desorption agent. Compared with APG0810 and Triton x-100, APG0814 showed a better solubilization effect due to its lower critical micelle concentration. With addition of 3000 mg L^-1 APG0814, 35% of HCB was removed from contaminated diatomite soil, and a small amount of residual APG in diatomite soil was found to be beneficial for the soil dispersion. After treatment with the ZEA system, the removal efficiency of HCB in the diatomite soil desorption solution reached 76% in 2 h; we observed that a small amount of APG retained in the desorption solution accelerated the HCB removal. A real HCB-contaminated soil was used to verify the remediation effects. This study demonstrates that our approach is a feasible alternative for remediating soil contaminated with hydrophobic organic compounds.

Adsorptive removal of tetracycline by sustainable ceramsite substrate from bentonite/red mud/pine sawdust

In this study, a novel, sustainable and efficient ceramsite substrate of constructed wetlands (CWs) were prepared for tetracycline (TC) removal by employing bentonite (Ben) and red mud (Rm) as the main materials and pine sawdust (Ps) as the additive. The optimal parameters for Ben/Rm/Ps ceramsite preparation were obtained via orthogonal and one-factor experimental designs, and the optimal parameters were presented as follows: mass ratio of Ben: Rm: Ps = 4:1:0.9, preheating temperature = 240 °C, preheating time = 20 min, calcining temperature = 1150 °C, and calcining time = 14 min. The properties of Ben/Rm/Ps-op ceramsite (obtained at the optimal condition) were first analyzed, including XRD and SEM, and demonstrated a microporous structure with some crystal strength components. Neutral condition and higher temperature were indicated conducive to improve the TC removal efficiency, while coexisting ions (Na⁺ or Ca²⁺) showed adverse effect for TC adsorption by Ben/Rm/Ps-op. In addition, adsorption kinetics and isotherm could be well described by the second-order kinetics and linear isothermal model, respectively, which suggested chemisorption and multilayer adsorption thickness increased infinitely. The theoretical maximum TC adsorption capacity of Ben/Rm/Ps-op at 20 °C reached up to 2.5602 mg/g. In addition, Ben/Rm/Ps-op could effectively remove TC as the CWs substrate under a dynamic flow condition. Further, Ben/Rm/Ps-op exhibited high reusability capability and stability for TC removal, and the adsorption amount still remained for 2.13 mg/g (C₀ = 80 mg/L) after three consecutive cycles.

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.

Soil washing remediation of heavy metal from contaminated soil with EDTMP and PAA: Properties, optimization, and risk assessment

Soil washing is a rapid and efficient remediation technique for soil contaminated by heavy metals. In this study, Cd, Pb, and Zn were removed from contaminated soil by ethylenediamine tetra (methylene phosphonic acid) (EDTMP) and polyacrylic acid (PAA). We then investigated the effect of varying the concentration, pH and duration of the washing processes. Single-factor experiments suggest that the PAA washing process may be dominated by electrostatic adsorption, and is suitable for remediation under weak acid and neutral conditions. Meanwhile, EDTMP remediation might be dominated by chelation, which is favorable in strong acid and alkaline environments. In a quadratic saturation D-optimization design (QSDD), we optimized the washing parameters and further explored the washing mechanism including primary factor, principal effect, interaction effect, and the optimal washing conditions, with simultaneously changing multiple influencing factors. The optimum efficiencies of Cd, Pb, and Zn removal were 92.74%, 96.14%, and 50.76% respectively in EDTMP remediation, and 84.62, 79.24, and 41.66% respectively in PAA remediation. The washing processes effectively reduced the availability of Cd, Pb, and Zn in contaminated soil, without noticeably affecting soil chemical properties. Therefore, the washing incurred little ecological risk. EDTMP and PAA are suitable remediation agents of soil contaminated by heavy metals.

FerrateVI oxidation of polycyclic aromatic compounds (PAHs and polar PACs) on DNAPL-spiked sand: degradation efficiency and oxygenated by-product formation compared to conventional oxidants

In situ chemical oxidations are known to remediate PAH contaminations in groundwater and soils. In this study, batch-scale oxidations aim to compare the PAC (polycyclic aromatic compound) degradation of three oxidation processes traditionally applied for soil treatment: permanganate, heat-activated persulfate (60 °C) and Fenton-like activated by magnetite, to results obtained with ferrates (Fe^VI). Widely studied for water treatments, ferrates are efficient on a wide range of pollutants with the advantage of producing nontoxic ferric sludge after reaction. However, fewer works focus on their action on soil, especially on semi-industrial grade ferrates (compatible with field application). Oxidations were carried out on sand spiked with dense non-aqueous phase liquid (DNAPL) sampled in the groundwater of a former coking plant. Conventional 16 US-EPA PAHs and polar PACs were monitored, especially potential oxygenated by-products that can be more harmful than parent-PAHs. After seven reaction days, only the Fenton-like showed limited degradation. Highest efficiencies were obtained for heat-activated persulfate with no O-PAC ketones formed. Permanganate gave important degradation, but ketones were generated in large amount. The tested ferrates not only gave slightly lower yields due to their auto-decomposition but also induced O-PAC ketone production, suggesting a reactional pathway dominated by oxidoreductive electron transfer, rather than a radical one.

Phenanthrene degradation using Fe(III)-EDDS photoactivation under simulated solar light: A model for soil washing effluent treatment

In this work, for the first time, the nonionic surfactant polyoxyethylene-(20)-sorbitan monooleate (Tween 80, C₆₄H₁₂₄O₂₆) aided soil washing effluent was treated by enhanced activation of persulfate (PS) using Fe(III)-EDDS (EDDS: ethylenediamine-N, N-disuccinic acid) complexes under simulated solar light irradiation. The performance of this system was followed via the production and reactivity of radical species (SO₄^-, HO, Cl₂^-) and degradation of phenanthrene (PHE) used as a model pollutant in soils. Different physico-chemical parameters such as the concentration of reactive species and pH were investigated through the PHE degradation efficiency. The second-order rate constants of the reactions for generated radicals with PHE and Tween 80 in solution were identified through competitive reaction experiments under steady-state conditions and application of nanosecond laser flash photolysis (LFP) as well. A kinetic approach was applied to assess the selectivity and reactivity of photo-generated radicals in aqueous medium in order to explain the observed degradation trends. This work proposes an innovative technology of management of soil washing solutions using Fe(III)-EDDS complexes and solar light for the activation of persulfate.

Heterogeneous Fenton-like catalyst for treatment of rhamnolipid-solubilized hexadecane wastewater

The treatment of wastewater containing hydrophobic organic pollutants solubilized by surfactants is of great environmental importance. In this work, the removal of rhamnolipid-solubilized hexadecane via a salicylic acid-methanol-acetone modified steel converter slag (SMA-SCS) catalyzed Fenton-like process was studied. First, we investigated the adsorption of rhamnolipid and hexadecane onto SCS and SMA-modified SCS. Compared to that of SCS, SMA-SCS exhibited better adsorption performance with maximum adsorption capacities of 0.23 and 0.28 mg/g for hexadecane and rhamnolipid, respectively. Degradation experiments showed that hexadecane was more readily degraded by the Fenton-like process than rhamnolipid. Up to 81.1% of hexadecane removal was achieved over 20 g/L of SMA-SCS within 24 h, whereas only 36% of rhamnolipid was degraded. On the other hand, the results indicated that increased rhamnolipid concentration had a negative effect on the degradation of hexadecane. During the oxidation reaction, the pH value of solution remained between 6.0 and 6.72. All these results demonstrated that the SMA-SCS/H₂O₂ Fenton-like process could be a cost-effective and promising approach for the treatment of surfactant-solubilized hydrophobic organic compounds.

How to accurately assess surfactant biodegradation-impact of sorption on the validity of results

Surfactants not only are widely used in biotechnological processes but also constitute significant contaminants of the modern world. Among many reports, there is a shortage of works which summarize the issue of surfactant sorption to biomass in a way that would elucidate the biological factors for analysts and analytical factors for microbiologists. The main factor, which is not as obvious as one would expect, is associated with the susceptibility of analytical approaches to errors resulting from incorrect handling of biomass. In case of several publications reviewed in the framework of this study, it was not possible to establish whether the decrease of the analytical signal observed by the authors actually resulted from biodegradation of the surfactant. This review emphasizes the necessity to consider the possibility of surfactant sorption to microbial cells, which may result in significant detection errors as well as conceptual inconsistency. In addition, a reference study regarding representative surfactants (cationic, anionic and non-ionic) as well as yeast, Gram-negative, Gram-positive bacteria, and activated sludge was provided to highlight the possible errors which may arise from disregarding sorption processes when determining degradation of surfactants. This particularly applies to systems which include ionic surfactants and activated sludge as sorption may account for 90% of the observed depletion of the surfactant. Therefore, a systematic approach was proposed in order to improve the credibility of the obtained results. Finally, the need to employ additional procedures was highlighted which may be required in order to verify that the decrease of surfactant concentration results from biodegradation processes.

Regeneration of Washing Effluents for Remediation of Petroleum-Hydrocarbons-Contaminated Soil by Corncob-Based Biomass Materials

Surfactant-enhanced soil washing is an effective remediation method for petroleum-hydrocarbons-contaminated soil. The residual petroleum hydrocarbons in the washing effluents reduce the elution ability of the washing effluents and cause secondary pollution to the environment. In this work, modified corncobs were prepared and used as selective adsorbents to remove the residual petroleum hydrocarbons in washing effluents. The structure of adsorbent was characterized and the adsorption conditions were optimized. With the adsorption by corncob-based adsorbents, washing effluents can be regenerated and recycled. After five cycles, the recovery efficiency of the washing effluents is still as high as 75.4%. The optimal adsorbent linear alkylbenzene sulfonates (LAS-Cb) also exhibited excellent recyclability, which can be recycled five times. The selective adsorption mechanism of the LAS-Cb for petroleum hydrocarbons in washing effluents, related to its huge hydrophobic core and surface electronegativity, is proposed.

Enhanced electrolytic treatment for the removal of clopyralid and lindane

In this work, it is evaluated the more critical point of a new electrochemical technology for the removal of organic pollutants based on the regeneration of granular active carbon (GAC) (that can be used efficiently to concentrate aqueous wastes) with methanol and in the electrochemical treatment of methanol with conductive diamond electrochemical oxidation (CDEO). The system proposed was studied with lindane and clopyralid. Results show that it is possible the complete removal of the raw pesticides and intermediates formed by electrolyzing these species in methanol media and that both sodium chloride and sodium hydroxide can be used as supporting electrolyte to increase the conductivity of methanol. The cell voltages obtained are quite similar to those obtained during the electrolysis of aqueous wastes. The electrolysis of these dilute solutions does not generate significant concentrations of intermediates and the depletion of the raw pollutant fits well to a pseudo-first order kinetic model. Oxidants capable to oxidize iodide to iodine are produced during the electrolysis in methanol media and they have an important influence on the degradation of the pollutants. The new technology, based on the concentration of the pollutant before electrolysis, allows to remove completely pollutants from soil and soil washing fluids in a more efficient way, although the concentration of pollutant attained and, hence, the efficiency of the overall removal process depends on the adsorption equilibria of the pollutant in aqueous and methanol media.

Advanced Oxidation Based Treatment of Soil Wash Water Contaminated with Sulfolane

This study investigates advanced oxidation processes (AOPs) as post-treatment techniques to degrade sulfolane in soil washing water. Soil washing experiments were conducted with different soil/water ratios, shaking times, and number of extraction cycles. The soil wash water containing sulfolane was treated with four AOPs including H2O2/ultraviolet (UV), O3/UV, alkaline ozonation, and neutral Fenton reagent. Results show that sulfolane can be effectively removed from the soil using water as a washing solvent, where optimum conditions were found with 30 min of vigorous shaking, using 1:2 soil/water mass ratio, and a three-cycle extraction procedure. Moreover, the sulfolane in the soil wash water was also effectively degraded using appropriate AOPs. Among the four AOPs investigated, neutral Fenton was the least effective method to treat sulfolane in the wash water, while H2O2/UV, O3/UV, and alkaline ozonation can achieve more than 99% of sulfolane degradation within 1 h.