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Biosurfactants, surface-active agents produced by microorganisms, are increasingly studied for their potential use in soil remediation processes because they are more environmentally friendly than their chemically produced homologues. In this work, we report on the use of a crude biosurfactant produced by a bacterial consortium isolated from a PAHs-contaminated soil, compared with other (bio)surfactants (Tween80, Sodium dodecyl sulfate - SDS, rhamnolipids mix), to wash PAHs from a contaminated porous media. Assays were done using columns filled with sand or sand-clay mixtures (95:5) spiked with four model PAHs. The crude biosurfactant showed less adsorption to the [sand] and the [sand + clay] columns compared to Tween 80, SDS and the rhamnolipid mix. The biosurfactant showed the second best capacity to remove PAHs from the columns (as dissolved and particulate phases), both from [sand] and [sand + clay], after SDS when applied at lower concentrations than the other sufactants. The effluent concentrations of phenanthrene (PHE), pyrene (PYR) and benzo[a]pyrene (BAP) increased in the presence of the crude biosurfactant. Compared to the control experiment using only water, the global PAHs washed mass (amount of PAHs removed from the columns) increased between 9 and 1000 times for PHE and BAP in the [sand] column, and between 55 and 6000 times respectively for PHE and BAP in the [sand + clay] columns. Moreover, in the [sand + clay] columns, leaching of a part of the clays was observed in the SDS and the biosurfactant injections assays. This clay leaching resulted in higher PAHs removal, due not to desorption but rather to particulate transport. In the context of washing PAH-contaminated soils in biopiles or subsurface remediation, our results could help in sizing the remediation approach using an environmental friendly biosurfactant, before a pump-and-treat process., Competing Interests: Declaration of Competing Interest The authors declare that they have no competing interests., (Copyright © 2022 Elsevier B.V. All rights reserved.)

Volatilization of hazardous hydrophobic organic compounds is often observed in many water, wastewater and soil treatment (bio)processes. Several models have been developed to quantify and predict gas-liquid pollutant transfer, being the proportionality coefficient model (PCM) one of the most commonly used, particularly in wastewater treatment. The PCM is based on the use of oxygen as a reference compound, which has a low resistance to the transfer in the gas phase. However, this resistance might be important for (semi-)volatile organic compounds - or (semi-)VOCs, which may render the use of the PCM model inaccurate. This study proposes an experimental methodology and a modeling approach for the use of the two-reference compound model (2RCM) that considers both the liquid-side and the gas-side resistances, by using water and oxygen as references. Results showed that the 2RCM predicts more accurately the overall mass transfer coefficients than the PCM for a VOC and two semi-VOCs tested in this study. In addition, the 2RCM was found to be a more robust method to estimate mass transfer coefficient of any compound and its use can be extrapolated to all substances. Finally, the relevance and limitations of both models was established., (Copyright © 2021 Elsevier B.V. All rights reserved.)

Pumping experiments were performed in a 2D tank in order to estimate the recovery yield of pure heavy chlorinated organic compounds (DNAPL; dense non-aqueous phase liquids) by varying different parameters: permeability of the saturated zone, pumping flow rates, addition of surfactant and heating. Surfactant was added to decrease capillary forces involved in the entrapment of DNAPL in porous media while temperature was increased to reduce DNAPL viscosity (and hence increase its mobility). Chemical enhancement was performed with the addition of Sodium Dodecyl Benzene Sulfonate (SDBS) (at its Critical Micelle Concentration, to avoid DNAPL dissolution) and thermal enhancement was performed at 50 °C (to avoid DNAPL volatilization). The experiments were monitored with photography allowing, on the basis of image interpretation, to convert optical densities (OD) into water saturations (S w ). Image interpretations were compared with modelling results. The two-phase flow modelling was performed with the pressure-pressure formulation using capillary pressure and relative permeability functions based on the van Genuchten-Mualem equations. Measured volumes of DNAPL recovered as well as the displacement of the DNAPL-water interface (radius and height of the cone of depression) are consistent with the modelling results. Furthermore, chemical enhancement results in a significant increase in the recovery rates of DNAPL. The observed improvement in the recovery of DNAPL with chemical enhancement is due to the fact that: (i) the residual saturation inside the cone of depression is lower and (ii) the cone of depression radius and height increase. Thermal enhancement had no beneficial effect on DNAPL recovery rate or yield. This study shows that it is possible to accurately determine water and DNAPL saturations by image interpretation during pumping tests in a 2D tank in the laboratory. For field-scale applications, the two-phase flow model allows to determine remediation yields as well as the volumes of the cone of depression according to the different operating conditions., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2020 Elsevier B.V. All rights reserved.)

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., (Copyright © 2020 Elsevier B.V. All rights reserved.)

Biosurfactants are surface-active agents produced by microorganisms whose use in soil remediation processes is increasingly discussed as a more environmentally friendly alternative than chemically produced surfactants. In this work, we report the production of a biosurfactant by a bacterial community extracted from a polluted soil, mainly impacted by PAHs, in order to use it in a soil-washing process coupled with bioremediation. Nutrient balance was a critical parameter to optimize the production. Best conditions for biosurfactant production were found to be 20 g/L of glucose, 2 g/L of NH 4 NO 3 , and 14.2 g/L of Na 2 HPO 4 , corresponding to a C/N/P molar ratio equal to 13/1/2. Purification of the produced biosurfactant by acidification and double extraction with dichloromethane as a solvent allowed measuring the Critical Micellar Concentration (CMC) as equal to 42 mg/L. The capacity of the purified biosurfactant to increase the apparent solubility of four reference PAHs (naphthalene, phenanthrene, pyrene and benzo[a]pyrene) was completed. The solubilisation ratios, in mg of PAH/g of biosurfactant for phenanthrene, pyrene and benzo[a]pyrene are 0.214, 0.1204 and 0.0068, respectively. Identification of the bacteria found in the colony producing the biosurfactant showed the presence of bacteria able to produce biosurfactant (Enterobacteriaceae, Pseudomonas), as well as, others able to degrade PAHs (Microbacterium, Pseudomonas, Rhodanobacteraceae)., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2018 Elsevier B.V. All rights reserved.)

Chemical and thermal enhanced recovery of pure heavy chlorinated organic compounds (DNAPL; dense non-aqueous phase liquids) was investigated by using lab-scale 1D cells. Temperature was increased to reduce DNAPL viscosity (and hence increase its mobility), while surfactant was added to decrease capillary forces involved in the entrapment of DNAPL in porous media. Laboratory scale experiments, based on mass balance and indirect monitoring methods (i.e., permittivity, electrical resistivity and optical density), were conducted to quantify the effects of these enhancements. Heating the DNAPL up to 50 °C decreased its viscosity by a factor of two. The addition of a surfactant; i.e., Sodium Dodecyl Benzene Sulfonate (SDBS), at its Critical Micelle Concentration (to prevent DNAPL solubilization), decreased interfacial tensions by a factor of 12. Drainage-imbibition experiments performed in 1D cells provided retention curves (capillary pressure as a function of water saturation) of a two-phase (DNAPL-water) system in experimental glass bead porous media. The observed reduction of residual saturation (S rn ) obtained with SDBS was 28% for 0.5 mm-diameter glass beads (GB) and 46% for 0.1 mm GB. No significant decrease in S m was observed with thermal enhancement. The van Genuchten - Mualem model was found to satisfactorily reproduce the measured retention curves. Indirect measurements of water saturations (S w ) showed that: i. measured permittivities were very close to values modeled with the Complex Refractive Index Model (CRIM); ii. Archie's Law was less successful in reproducing measured electrical resistivities; iii. optical densities provide accurate estimations of S w . At field scale, the combined monitoring of electrical resistivity (which provides a global picture) and permittivity (which yields locally precise but spatially limited information) is expected to significantly improve the collection of information on residual saturations S rn ., (Copyright © 2019 Elsevier B.V. All rights reserved.)

Digestate is an organic by-product of biogas production via anaerobic digestion processes and has a great potential as soil fertilizer due to concentrated nutrients. In this study, we examined digestate as a potential nutrient and microbial seeding for bioremediation of weathered (aged) petroleum hydrocarbon contaminated soils. We analysed 6 different treatments in microcosm using two industrial soils having different textures: a clay rich soil and a sandy soil. After 30 days of incubation, the highest total petroleum hydrocarbons (TPH) removal was observed in microcosms containing digestate together with bulking agent (17.8% and 12.7% higher than control in clay rich soil and sandy soil, respectively) or digestate together with immobilized bacteria (13.4% and 9% higher than control in clay rich soil and sandy soil, respectively). After digestate application microbial respiration was enhanced in sandy soil and inhibited in clay rich soil due to aggregates formation. After bulking agent addition to clay rich soil aggregates size was reduced and oxygen uptake was improved. Application of digestate to soil resulted in the development of distinct microbial groups in amended and non-amended soils. Genera containing species able to degrade TPH like Acinetobacter and Mycobacterium were abundant in digestate and in soil amended with digestate. Quantification of alkB genes, encoding alkane monoxygenase, revealed high concentration of these genes in digestate bacterial community. After application of digestate, the level of alkB genes significantly increased in soils and remained high until the end of the treatment. The study revealed great potential of digestate as a nutrient and bacteria source for soil bioremediation., (Copyright © 2019. Published by Elsevier B.V.)

Hydrophobic organic compound (HOC)-contaminated soils are a great environmental and public health concern nowadays. Further research is necessary to develop environmental friendly biotechnologies that allows public and private sectors to implement efficient and adaptable treatment approaches. Aerobic soil-slurry bioreactor technology has emerged as an effective and feasible technique with a high remediation potential, especially for silt and clay soil fractions, which often contain the highest pollutant concentration levels and are usually difficult to remove by implementing conventional methods. However, the mechanisms involved in the HOC removal in bioslurry reactor are still not completely understood. Gas-liquid and solid-liquid mass transfer, mass transport and biodegradation phenomena are the main known processes taking place in slurry bioreactors. This review compiles the most up-to-date information available about these phenomena and tries to link them, enlightening the possible interactions between parameters. It gathers the basic information needed to understand the complex bioremediation technology and raises awareness of some considerations that should be made., (Copyright © 2017. Published by Elsevier B.V.)

Tar oil contamination is a major environmental concern due to health impacts of polycyclic aromatic hydrocarbons (PAH) and the difficulty of reaching acceptable remediation end-points. Six tar oil-contaminated soils with different industrial histories were compared to investigate contamination characteristics by black particles. Here we provide a simple method tested on 6 soils to visualize and identify large amounts of black particles (BP) as either solid aggregates of resinified and weathered tar oil or various wood/coke/coal-like materials derived from the contamination history. These materials contain 2-10 times higher PAH concentrations than the average soil and were dominantly found in the sand fraction containing 42-86% of the total PAH. The PAH contamination in the different granulometric fractions was directly proportional to the respective total organic carbon content, since the PAH were associated to the carbonaceous particulate materials. Significantly lower (bio)availability of PAH associated to these carbonaceous phases is widely recognized, thus limiting the efficiency of remediation techniques. We provide a conceptual model of the limited mass transfer of PAH from resinated tar oil phases to the water phase and emphasize the options to physically separate BP based on their lower bulk density and slower settling velocity., (Copyright © 2017 Elsevier B.V. All rights reserved.)

Zinc (Zn) leaching yields and kinetics from three different zinc plant leach residues (ZLR) generated in different periods (ZLR1>30 years, ZLR2 5-30 years and ZLR3<2 years) were investigated. The factors affecting the Zn leaching rate such as solid to liquid ratio, temperature, acid concentration and agitation were optimized. Under optimum conditions, 46.2 (±4.3), 23.3 (±2.7) and 17.6 (±1.2) mg of Zn can be extracted per gram of ZLR1, ZLR2 and ZLR3, respectively. The Zn leaching kinetics of ZLRs follow the shrinking core diffusion model. The activation energy required to leach Zn from ZLR1, ZLR2 and ZLR3 were estimated to be 2.24kcal/mol, 6.63kcal/mol and 11.7kcal/mol, respectively, by the Arrhenius equation. The order of the reaction with respect to the sulfuric acid concentration was also determined as 0.20, 0.56, and 0.87 for ZLR1, ZLR2 and ZLR3, respectively. Zn was selectively recovered from the leachates by adjusting the initial pH and by the addition of sodium hydroxide and sodium sulfide. More than 90% of Zn was selectively recovered as sphalerite from the ZLR polymetallic leachates by chemical sulfide precipitation., (Copyright © 2016 Elsevier B.V. All rights reserved.)

Biological remediation technologies are an environmentally friendly approach for the treatment of polluted soils. This study evaluated through a pot experiment four bioremediation strategies: a) natural attenuation, b) phytoremediation with alfalfa (Medicago sativa L.), c) bioaugmentation with Pseudomonas aeruginosa and d) bioaugmentation-assisted phytoremediation, for the treatment of a co-contaminated soil presenting moderate levels of heavy metals (Cu, Pb and Zn at 87, 100 and 110mgkg(-1) DW, respectively) and petroleum hydrocarbons (3800mgkg(-1) DW). As demonstrated by plant biomass and selected physiological parameters alfalfa plants were able to tolerate and grow in the co-contaminated soil, especially when soil was inoculated with P. aeruginosa, which promoted plant growth (56% and 105% increase for shoots and roots, respectively) and appeared to alleviate plant stress. The content of heavy metals in alfalfa plants was limited and followed the order: Zn>Cu>Pb. Heavy metals were mainly concentrated in plant roots and were poorly translocated, favouring their stabilization in the root zone. Bioaugmentation of planted soil with P. aeruginosa generally led to a decrease of plant metal concentration and translocation. The highest degree of total petroleum hydrocarbon removal was obtained for bioaugmentation-assisted phytoremediation treatment (68%), followed by bioaugmentation (59%), phytoremediation (47%) and natural attenuation (37%). The results of this study demonstrated that the combined use of plant and bacteria was the most advantageous option for the treatment of the present co-contaminated soil, as compared to natural attenuation, bioaugmentation or phytoremediation applied alone., (Copyright © 2015 Elsevier B.V. All rights reserved.)

The release of hydrophobic organoxenobiotics such as polycyclic aromatic hydrocarbons, petroleum hydrocarbons or polychlorobiphenyls results in long-term contamination of soils and groundwaters. This constitutes a common concern as these compounds have high potential toxicological impact. Therefore, the development of cost-effective processes with high pollutant removal efficiency is a major challenge for researchers and soil remediation companies. Soil washing (SW) and soil flushing (SF) processes enhanced by the use of extracting agents (surfactants, biosurfactants, cyclodextrins etc.) are conceivable and efficient approaches. However, this generates high strength effluents containing large amount of extracting agent. For the treatment of these SW/SF solutions, the goal is to remove target pollutants and to recover extracting agents for further SW/SF steps. Heterogeneous photocatalysis, technologies based on Fenton reaction chemistry (including homogeneous photocatalysis such as photo-Fenton), ozonation, electrochemical processes and biological treatments have been investigated. Main advantages and drawbacks as well as target pollutant removal mechanisms are reviewed and compared. Promising integrated treatments, particularly the use of a selective adsorption step of target pollutants and the combination of advanced oxidation processes with biological treatments, are also discussed., (Copyright © 2015 Elsevier B.V. All rights reserved.)

Low cost materials (sugar beet pulp, corncob, corncob char, perlite, vermiculite, sand, sediment) have been tested for their ability to quickly sorb copper, glyphosate, diuron and 3,4-dichloroaniline (3,4-DCA) as single or mixed compounds. Tests have been performed in increasingly complex liquid matrices: ultra pure water (UPW), runoff water (RW) and sediment extract medium (SEM). Highest sorption levels in UPW are achieved with corncob char for Cu (93%), glyphosate (74%), diuron (98%) and 3,4-DCA (99%). Other ready-to-use adequate sorbents are sugar beet pulp for Cu and sand for glyphosate, diuron and 3,4-DCA. Sorption levels obtained in UPW are significantly altered in SEM as a result of its higher dissolved organic carbon concentration, tenuous changes being obtained with RW. Interactions between herbicides and Cu are pointed out: higher sorption level is observed for glyphosate in mixture with Cu, as it is observed with diuron and 3,4-DCA when mixed with all other pollutants. Langmuir model has been found to better fit the data for copper, whereas Freundlich one has been found more relevant for diuron and 3,4-DCA. Our results stress the need for studying adsorption in different matrices when searching for sorbents to be used in field conditions., (2010 Elsevier B.V. All rights reserved.)