Surfactant-soil interactions during surfactant-amended remediation of contaminated soils by hydrophobic organic compounds: a review

Impact mechanisms of various surfactants on the biodegradation of phenanthrene in soil: Bioavailability and microbial community responses

The present study was conducted to systematically explore the mechanisms underlying the impact of various surfactants (CTAB, SDBS, Tween 80 and rhamnolipid) at different doses (10, 100 and 1000 mg/kg) on the biodegradation of a model polycyclic aromatic hydrocarbon (PAH) by indigenous soil microorganisms, focusing on bioavailability and community responses. The cationic surfactant CTAB inhibited the biodegradation of phenanthrene within the whole tested dosage range by decreasing its bioavailability and adversely affecting soil microbial communities. Appropriate doses of SDBS (1000 mg/kg), Tween 80 (100, 1000 mg/kg) and rhamnolipid at all amendment levels promoted the transformation of phenanthrene from the very slow desorption fraction (Fvslow) to bioavailable fractions (rapid and slow desorption fractions, Frapid and Fslow), assessed via Tenax extraction. However, only Tween 80 and rhamnolipid at these doses significantly improved both the rates and extents of phenanthrene biodegradation by 22.1-204.3 and 38.4-76.7 %, respectively, while 1000 mg/kg SDBS had little effect on phenanthrene removal. This was because the inhibitory effects of anionic surfactant SDBS, especially at high doses, on the abundance, diversity and activity of soil microbial communities surpassed the bioavailability enhancement in dominating biodegradation. In contrast, the nonionic surfactant Tween 80 and biosurfactant rhamnolipid enhanced the bioavailability of phenanthrene for degradation and also that to specific degrading bacterial genera, which stimulated their growth and increased the abundance of the related nidA degradation gene. Moreover, they promoted the total microbial/bacterial biomass, community diversity and polyphenol oxidase activity by providing available substrates and nutrients. These findings contribute to the design of suitable surfactant types and dosages for mitigating the environmental risk of PAHs and simultaneously benefiting microbial ecology in soil through bioremediation.

Assessing the Impact of Pre-Soaking to Enhance Laundering Efficacy of Firefighter Turnout Gear

Firefighters are exposed to hazardous chemicals at fire scenes, including polycyclic aromatic hydrocarbons (PAHs) among many others, which pose significant health risks. Current laundering practices are ineffective at removing persistent contaminants from turnout gear, necessitating further research to optimize cleaning methods. This study explores the impact of presoaking prior to the laundering process and the factors that can affect its effectiveness, including the presoaking duration and detergent concentration, in PAH removal when laundering. For this, contaminated fabric swatches were subjected to various presoaking durations (1, 3, and 12 h) and detergent concentrations (99:1 and 90:10 water-to-detergent ratios) before undergoing bench-scale washing. The cleaning efficacy was assessed for 16 PAH compounds, including both low-molecular-weight (LMW) PAHs and high-molecular-weight (HMW) PAHs. Moreover, the removal mechanisms of PAHs from turnout gear were fundamentally explained using partition coefficients and standard affinities with different parameters during washing. The results demonstrate that 3 h and 12 h of presoaking lead to 2.8 and 4.3 times greater HMW PAH removal, respectively. After 12 h of presoaking in a 90:10 water-to-detergent ratio, 97% of the LMW PAHs and 78% of the HMW PAHs were removed, compared to only an 11% removal of the HMW PAHs with a 99:1 ratio. Additionally, direct washing with a 90:10 ratio achieved comparable efficacy to that of presoaking with the same water-to-detergent ratio, indicating the crucial role of detergent concentration during laundering. These findings offer valuable insights for optimizing firefighter safety practices, emphasizing the role of presoaking and the appropriate methods to perform presoaking to mitigate firefighters' occupational exposure risks to toxic substances and ensure gear reliability.

Enhanced consolidation and removal of accumulated flocculants in dredged soil via leaching with vacuum preloading

The vacuum preloading coupling flocculation treatment is a widely employed method for reinforcing soils with high water content in practical construction. However, uneven distribution and accumulation of flocculants pose significant damage to the soil environment and result in uneven soil consolidation, leading to severe issues in subsequent soil development and exploitation. To address these concerns, an evolved leaching with vacuum method is developed for facilitating soil consolidation while preventing the accumulation of flocculant in the soil. In this study, five model tests are conducted in which FeCl3 is chosen as the typical flocculant to promote soil consolidation, and deionized water is used for leaching. The final discharged water, settlement, water content and penetration resistance of soil are obtained to evaluate the soil reinforcement effect, while the flocculant removal effect is evaluated by the Fe3+ content in the filtrate and soil. The comprehensive reinforcement and flocculant removal effect show that this method is extremely effective compared to traditional vacuum preloading. The two leaching is clarified as the best choice, resulting in a 22% decrease in the soil water content and a 25% in soil penetration resistance, meanwhile a 12.8% removal rate of the flocculant. The test results demonstrate that leaching with vacuum preloading can contribute to promoting soil consolidation and reducing the accumulation of flocculant in the soil, ensuring the safe and eco-friendly use of the soil for future applications. The conclusions obtained are of significant theoretical value and technical support for practical construction and sustainable development.

Recognizing Functional Groups of MES/APG Mixed Surfactants for Enhanced Solubilization toward Benzo[a]pyrene

Benzo[a]pyrene is difficult to remove from soil due to its high octanol/water partition coefficient. The use of mixed surfactants can increase solubility but with the risk of secondary soil contamination, and the compounding mechanism is still unclear. This study introduced a new approach using environmentally friendly fatty acid methyl ester sulfonate (MES) and alkyl polyglucoside (APG) to solubilize benzo[a]pyrene. The best result was obtained when the ratio of MES/APG was 7:1 under 6 g/L total concentration, with an apparent solubility (Sw) of 8.58 mg/L and a molar solubilization ratio (MSR) of 1.31 for benzo[a]pyrene, which is comparable to that of Tween 80 (MSR, 0.95). The mechanism indicates that the hydroxyl groups (-OH) in APG form "O-H···OSO2-" hydrogen bonding with the sulfonic acid group (-SO3-) of MES, which reduces the electrostatic repulsion between MES molecules, thus facilitating the formation of large and stable micelles. Moreover, the strong solubilizing effect on benzo[a]pyrene should be ascribed to the low polarity of ester groups (-COOCH3) in MES. Functional groups capable of forming hydrogen bonds and having low polarity are responsible for the enhanced solubilization of benzo[a]pyrene. This understanding helps choose suitable surfactants for the remediation of PAH-contaminated soils.

Remediation of heavily PAHs-contaminated soil with high mineral content from a coking plant using surfactant-enhanced soil washing

This study investigated the effectiveness of various surfactants at different concentrations in removing high concentrations of polycyclic aromatic hydrocarbons (PAHs) from soil with high mineral content, focusing on the impact of surfactant treatment on the mobility of the residual PAHs in soil. The results revealed that the cationic surfactant (CTMAB) inhibited removal of PAHs in the whole tested concentration range of 0.1-8 g/L. In contrast, the non-ionic and anionic surfactants (Triton X-100 and SDBS) significantly enhanced removal of PAHs as their amendment concentrations reached 2 g/L and above. Triton X-100 exhibited steadily increased efficacy with increasing amendment concentrations and maintained favorable solubilization capability when continuously amended, making it the preferable choice for remediating PAHs-contaminated soil. Surfactant and water washing processes altered soil physicochemical properties by removing some clay minerals (e.g., faujasite) and organic matter that can bind or sequester PAHs, potentially increasing their extractability and bioavailability in the washed soil, thereby posing higher ecological risks compared to the original one. Although soil washing decreased retention of the remaining PAHs in soil, it did not significantly impact PAHs release from soil by flowing water. These findings provide insights into the long-term effectiveness and ecological impacts of surfactant-enhanced washing as a potential remediation technique for PAHs-contaminated soil.

Research progress on remediation of organochlorine pesticide contamination in soil

Deteriorated soil pollution has grown into a worldwide environmental concern over the years. Organochlorine pesticide (OCP) residues, featured with ubiquity, persistence and refractoriness, are one of the main pollution sources, causing soil degradation, fertility decline and nutritional imbalance, and severely impacting soil ecology. Furthermore, residual OCPs in soil may enter the human body along with food chain accumulation and pose a serious health threat. To date, many remediation technologies including physicochemical and biological ways for organochlorine pollution have been developed at home and abroad, but none of them is a panacea suitable for all occasions. Rational selection and scientific decision-making are grounded in in-depth knowledge of various restoration techniques. However, soil pollution treatment often encounters the interference of multiple factors (climate, soil properties, cost, restoration efficiency, etc.) in complex environments, and there is still a lack of systematic summary and comparative analysis of different soil OCP removal methods. Thus, to better guide the remediation of contaminated soil, this review summarized the most commonly used strategies for OCP removal, evaluated their merits and limitations and discussed the application scenarios of different methods. It will facilitate the development of efficient, inexpensive and environmentally friendly soil remediation strategies for sustainable agricultural and ecological development.

Main Factors Determining the Scale-Up Effectiveness of Mycoremediation for the Decontamination of Aliphatic Hydrocarbons in Soil

Soil contamination constitutes a significant threat to the health of soil ecosystems in terms of complexity, toxicity, and recalcitrance. Among all contaminants, aliphatic petroleum hydrocarbons (APH) are of particular concern due to their abundance and persistence in the environment and the need of remediation technologies to ensure their removal in an environmentally, socially, and economically sustainable way. Soil remediation technologies presently available on the market to tackle soil contamination by petroleum hydrocarbons (PH) include landfilling, physical treatments (e.g., thermal desorption), chemical treatments (e.g., oxidation), and conventional bioremediation. The first two solutions are costly and energy-intensive approaches. Conversely, bioremediation of on-site excavated soil arranged in biopiles is a more sustainable procedure. Biopiles are engineered heaps able to stimulate microbial activity and enhance biodegradation, thus ensuring the removal of organic pollutants. This soil remediation technology is currently the most environmentally friendly solution available on the market, as it is less energy-intensive and has no detrimental impact on biological soil functions. However, its major limitation is its low removal efficiency, especially for long-chain hydrocarbons (LCH), compared to thermal desorption. Nevertheless, the use of fungi for remediation of environmental contaminants retains the benefits of bioremediation treatments, including low economic, social, and environmental costs, while attaining removal efficiencies similar to thermal desorption. Mycoremediation is a widely studied technology at lab scale, but there are few experiences at pilot scale. Several factors may reduce the overall efficiency of on-site mycoremediation biopiles (mycopiles), and the efficiency detected in the bench scale. These factors include the bioavailability of hydrocarbons, the selection of fungal species and bulking agents and their application rate, the interaction between the inoculated fungi and the indigenous microbiota, soil properties and nutrients, and other environmental factors (e.g., humidity, oxygen, and temperature). The identification of these factors at an early stage of biotreatability experiments would allow the application of this on-site technology to be refined and fine-tuned. This review brings together all mycoremediation work applied to aliphatic petroleum hydrocarbons (APH) and identifies the key factors in making mycoremediation effective. It also includes technological advances that reduce the effect of these factors, such as the structure of mycopiles, the application of surfactants, and the control of environmental factors.

Emulsion-based recovery of a multicomponent petroleum hydrocarbon NAPL using nonionic surfactant formulations

Surfactants can aid subsurface remediation through three primary mechanisms - solubilization, mobilization and/or emulsification. Among these mechanisms, emulsification in porous media is generally not well studied or well understood; particularly in the context of treating sources containing multicomponent NAPL. The objective of this research was to elucidate the processes responsible for recovery of a multicomponent hydrocarbon NAPL when surfactant solutions are introduced within a porous medium to promote the formation of kinetically-stable oil-in-water emulsions. Emulsifier formulations considered here were selected to offer similar performance characteristics while relying on different families of non-ionic surfactants - nonylphenol ethoxylates or alcohol ethoxylates - for emulsification. The families of surfactants have particular environment relevance, as alcohol ethoxylates are often used where replacement of nonylphenol content is necessary. Results from batch and column studies suggest performance of the two formulations was similar. With both, a synergistic combination of emulsification and mobilization led to recovery of a synthetic gasoline NAPL. The relative contribution of solubilization to the recovery was found to be minor. Moreover, the physical processes associated with emulsification and mobilization acted to limit the amount of preferential recovery (or fractionation) of the multicomponent NAPL.

Surfactant-enhanced mobilization of persistent organic pollutants: Potential for soil and sediment remediation and unintended consequences

This review aims to provide an overview of the sources and reactions of persistent organic pollutants (POPs) and surfactants in soil and sediments, the surfactant-enhanced solubilisation of POPs, and the unintended consequences of surfactant-induced remediation of soil and sediments contaminated with POPs. POPs include chemical compounds that are recalcitrant to natural degradation through photolytic, chemical, and biological processes in the environment. POPs are potentially toxic compounds mainly used in pesticides, solvents, pharmaceuticals, or industrial applications and pose a significant and persistent risk to the ecosystem and human health. Surfactants can serve as detergents, wetting and foaming compounds, emulsifiers, or dispersants, and have been used extensively to promote the solubilization of POPs and their subsequent removal from environmental matrices, including solid wastes, soil, and sediments. However, improper use of surfactants for remediation of POPs may lead to unintended consequences that include toxicity of surfactants to soil microorganisms and plants, and leaching of POPs, thereby resulting in groundwater contamination.

Patent mining on soil pollution remediation technology from the perspective of technological trajectory

Recent years have seen a marked growth in soil environmental problems, however, the research & development (R&D) direction of soil pollution remediation technology (SPRT) for addressing related challenges to the global ecosystem is still unclear. Patent is the most effective carrier of technological information. Therefore, this study investigates the status and future direction of SPRT through the analysis and mining of 14,475 patents from 1971 to 2020. In 2006-2020, 14,435 SPRT patents (79% of the total) were published, which is in the development stage. By measuring the proportion of high-value patents, determined by the ratio of the number of patent families containing two or more patents (PF2) to that containing at least one patent (PF1), we found that United States (PF2/PF1 = 0.711), Japan (PF2/PF1 = 0.500), and South Korea (PF2/PF1 = 0.431) hold a monopoly. International patent organizations serve as a bridge for technology transfer. Patent CN101947539-A measured by structural hole index (Effective size = 98.194, Efficiency = 0.926) has the most significant technological influence. Therefore, in order to accomplish the technological transition and improve the soil remediation capacity, more attention should be paid to the microbial-assisted phytoremediation technology related to inorganic pollutants, hyperaccumulators and stabilizers. Additionally, patents CN102834190-A (Effective size = 23.930, Efficiency = 0.855, Constraint = 0.141, Hierarchy = 0.089) and CN105855289 (Effective size = 21.453, Efficiency = 0.795 Constraint = 0.149, Hierarchy = 0.086) are both at the location of structural holes. So, more research should be carried out on green and cost-effective solutions for reducing organic pollutants in soil remediation. The current study identifies opportunities for innovations and breakthroughs in SPRT and offers relevant information on technological development prospects.

Surfactant-sodium dodecyl sulfate enhanced degradation of polystyrene microplastics with an energy-saving electrochemical advanced oxidation process (EAOP) strategy

Microplastics have been identified as a kind of emerging pollutant with potential ecological risks, and it is an urgent endeavor to find proper technologies for their remediation. Electrochemical advanced oxidation process (EAOP) technology has exhibited robust performance in the removal of various refractory organic pollutants. In this study, we explored a new remediation strategy for polystyrene microplastics (PS MPs), introducing sodium dodecyl sulfate (SDS) to enhance its degradation performance in boron-doped diamond (BDD) anode adopted EAOP. At first, we investigated the degradation behaviors of SDS in the BDD electrolysis. According to the SDS half-life under various current densities, the SDS addition strategy into EAOP is proposed; that is, supplement SDS to 500 mg/L at every half-life during electrolysis except the last cycle. Results indicated that SDS addition greatly enhanced MPs degradation rate in 72 h of EAOP, about 1.35-2.29 times higher than that in BDD electrolysis alone. The SDS assisted EAOP also led to more obvious changes in the particle size, morphology, and functional groups of the MPs. After treatment, a variety of alkyl-cleavage and oxidation products were identified, which attributed to the strong attack of oxidants (i.e., persulfate) on the MPs. The enhanced persulfate generation and oxidants adsorption on MPs can explain the enhancement effect in the EAOP strategy. Cost analysis results showed the surfactant only accounts for < 0.05% of the total operating costs in the SDS assisted EAOP. In general, the current study provided new insight into the effective way to improve the EAOP efficiency of microplastics.

Factors Influencing the Bioavailability of Organic Molecules to Bacterial Cells-A Mini-Review

The bioavailability of organic compounds to bacterial cells is crucial for their vital activities. This includes both compounds that are desirable to the cells (e.g., sources of energy, carbon, nitrogen, and other nutrients) and undesirable compounds that are toxic to the cells. For this reason, bioavailability is an issue of great importance in many areas of human activity that are related to bacteria, e.g., biotechnological production, bioremediation of organic pollutants, and the use of antibiotics. This article proposes a classification of factors determining bioavailability, dividing them into factors at the physicochemical level (i.e., those related to the solubility of a chemical compound and its transport in aqueous solution) and factors at the microbiological level (i.e., those related to adsorption on the cell surface and those related to transport into the cell). Awareness of the importance of and the mechanisms governing each of the factors described allows their use to change bioavailability in the desired direction.

Coupling surfactants with ISCO for remediating of NAPLs: Recent progress and application challenges

Non-aqueous phase liquids (NAPLs) pose a serious risk to the soil-groundwater environment. Coupling surfactants with in situ chemical oxidation (ISCO) technology is a promising strategy, which is attributed to the enhanced desorption and solubilization efficiency of NAPL contaminants. However, the complex interactions among surfactants, oxidation systems, and NAPL contaminants have not been fully revealed. This review provides a comprehensive overview on the development of surfactant-coupled ISCO technology focusing on the effects of surfactants on oxidation systems and NAPLs degradation behavior. Specifically, we discussed the compatibility between surfactants and oxidation systems, including the non-productive consumption of oxidants by surfactants, the role of surfactants in catalytic oxidation systems, and the loss of surfactants solubilization capacity during oxidation process. The effect of surfactants on the degradation behavior of NAPL contaminants is then thoroughly summarized in terms of degradation kinetics, byproducts and degradation mechanisms. This review demonstrates that it is crucial to minimize the negative effects of surfactants on NAPL contaminants oxidation process by fully understanding the interaction between surfactants and oxidation systems, which would promote the successful implementation of surfactant-coupled ISCO technology in remediation of NAPLs-contaminated sites.

Experimental study on remediation of low permeability Cu-Zn contaminated clay by vacuum enhanced leaching combined with EDTA and hydrochloric acid

To improve the washing efficiency for low permeable clay, the method of vacuum enhanced washing technology was proposed. In this study, ethylene diamine tetraacetic acid (EDTA) and hydrochloric acid (HCl) as eluents, the experiments of remediation of Cu-Zn contaminated cohesive soil by traditional soil column leaching and vacuum enhanced leaching was carried out. Results show that compared with traditional leaching method, the vacuum enhanced leaching method can significantly shorten the leaching time and prominently improve the removal rate of heavy metals Cu-Zn. When concentration of EDTA is 0.1 mol/L, the removal rate of Cu-Zn can reach 95.7% and 82.9%, respectively by vacuum-enhanced leaching. When concentration of HCl is 0.2 mol/L, the removal rate of Cu-Zn by vacuum enhanced leaching method can reach 96.2% and 90.2%, respectively. Whereas, the higher the concentration of EDTA and HCl, the slower the leaching rate. At the same concentration, the leaching rate of HCl was faster. After HCl leaching, the soil structure was seriously corroded, and the relative content of mineral composition changed considerably. After EDTA leaching, the corrosion of soil structure is light, and the relative content of mineral composition changes little. The conclusions obtained are of crucial theoretical value and technical support for environmental engineering.

Aquifer flushing using a SDS/1-butanol based in-situ microemulsion: Performance and mechanism for the remediation of nitrobenzene contamination

In-situ microemulsion flushing is an effective remediation technology for the removal of dense non-aqueous phase liquids (DNAPLs) from aquifers. Nitrobenzene (NB) is a typical DNAPL pollutant that is responsible for the serious contamination of many groundwater systems, while its removal using the flushing method has rarely been studied. In this study, bench scale, 1-D column and 2-D tank experiments were conducted to establish an efficient salt-free sodium dodecyl sulfate (SDS)/1-butanol based in-situ microemulsion flushing system for NB contaminated aquifers. Results showed that the NB/SDS/1-butanol/water microemulsion increased dissolved NB concentrations by more than 15-fold compared to the SDS-only solution. The formulation also presented good solubilization capacity at low temperature (5 ℃) and with clay media. NB was effectively removed from the aquifer by solubilization and mobilization via the formation of the microemulsion with the injected SDS/1-butanol solution. The flushing system also reduced the tailing phenomenon in later remediation stages, and exhibited weak reagent adsorption onto aquifer media. Furthermore, the vertical DNAPL migration to deeper aquifer was effectively controlled. Therefore, the constructed in-situ microemulsion flushing system is a highly efficient treatment method for NB contaminated aquifers, with this study providing valuable reference information on the optimal reagent parameters and the remediation mechanism.

Soil washing for the remediation of dioxin-contaminated soil: A review

Dioxin-contaminated soil has attracted worldwide attention due to its potential negative impacts on human health and the ecosystem. Thus, technological development aiming at high treatment efficiency and low cost for dioxin-contaminated soil is largely needed. In this review, approximately 200 documents were involved to summarize up-to-date scientific achievements of soil washing technology for the remediation of dioxin-contaminated soil. The mechanisms, advantages, and limitations of physical separation techniques (e.g. mechanical stirring, mechanical shaking, ultrasonication, and froth flotation) and washing solutions (e.g. organic solvents, edible oils, and surfactants) used for chemical extraction were comprehensively reviewed. Froth flotation is very promising for field-scale soil washing, whereas organic solvents show high removal efficiencies (up to 99%) of dioxins from contaminated soil. Further, the combination of physical separation and chemical extraction can help enhance dioxin removal efficiency (from 1.5 to 2 times), reducing energy consumption and cost (about 2 times). Among available remediation technologies for dioxin-contaminated soil, soil washing is truly promising since it has shown high removal efficiency (66-99% different remediation scales) with reasonable cost (46 - 250 USD per metric ton). However, the washed solution and volatile organic compounds generated during the process remain a concern and should be addressed in future research.

Application of Soil Washing and Thermal Desorption for Sustainable Remediation and Reuse of Remediated Soil

Global governance of soil resources as well as revitalizations and remediation of degraded areas seem to be necessary actions for sustainable development. A great deal of effort has gone into developing remediation technologies to remove or reduce the impact of these contaminants in the environment. However, contaminated soil remediations in stringent conditions deteriorate soil properties and functions and create the need for efficient soil revitalization measures. Soil washing (SW) and thermal desorption (TD) are commonly used to remediate contaminated soil and can significantly reduce the contaminant, sometimes to safe levels where reuse can be considered; however, the effects of treatment on soil quality must be understood in order to support redevelopment after remediation. In this review, we discussed the effects of SW and TD on soil properties, including subsequent soil quality and health. Furthermore, the importance of these techniques for remediation and reclamation strategies was discussed. Some restoration strategies were also proposed for the recovery of soil quality. In addition, remediated and revitalized soil can be reused for various purposes, which can be accepted as an implementation of sustainable remediation. This review concludes with an outlook of future research efforts that will further shift SW and TD toward sustainable remediation.

Certain Soil Surfactants Could Become a Source of Soil Water Repellency after Repeated Application

Repeated application of soil surfactants, or wetting agents, is a common practice for alleviating soil water repellency associated with soil organic coatings. However, wetting agents are organic compounds that may also coat soil particle surfaces and reduce wettability. For this experiment, hydrophobic sands from the field and fresh, wettable sands were collected and treated with either a polyoxyalkylene polymer (PoAP) or alkyl block polymer (ABP) wetting agent, or water only treatments served as a control. Following repeated treatment application and sequential washings, dissolved and particulate organic carbon (OC) were detected in the leachates of both sand systems. The total amount of OC recovered in leachates was 88% or less than the OC introduced by the wetting agents, indicating sorption of wetting agent monomers to soil particle surfaces regardless of soil hydrophobicity status. While ABP treatment did not alter solid phase organic carbon (SOC) in the sands studied, PoAP application increased SOC by 16% and 45% which was visible in scanning electronic microscopy images, for hydrophobic and wettable sands, respectively. PoAP application also increased the hydrophobicity of both sands that were studied. In contrast, ABP treatment increased the wettability of hydrophobic sand. Our results provide strong evidence that certain wetting agents may increase soil hydrophobicity and exacerbate wettability challenges if used repeatedly over time.

Micro-bubbles enhanced removal of diesel oil from the contaminated soil in washing/flushing with surfactant and additives

Diesel removal of contaminated soil by washing/flushing was enhanced with micro-bubbles and selected surfactants based on their solubilization properties and decontamination capacities. The influencing factors were studied to aim for increasing washing/flushing efficacy. The mixture solution of saponin and cyclodextrin increased the removal efficiency significantly compared to the single-agent solution flushing with an increasing range of 20%-31%. Meanwhile, micro-bubble enhancement increased over 20% of the diesel removal for the sandy soil flushing. As the flushing process may cause soil eroded, the TDS and soil solute in flushing solution were measured to evaluate the circulation time. The 90 min flushing time ensured the cleaning goal and reserved the soil solute by circulation flushing. The soil solute, especially the electron acceptor (NO₃^-) , was remained in the soil, which was highly demanded for residual diesel biodegradation of loam soil. It is concluded that mixed agents, circulation of flushing solution, and micro-bubbles increased the diesel removal, and the circulation flushing could be very promising in practical applications.

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.

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.

Co-presence of the anionic surfactant sodium lauryl ether sulphate and the pesticide chlorpyrifos and effects on a natural soil microbial community

There is a growing concern about the simultaneous presence in the environment of different kinds of pollutants, because of the possible synergic or additive effects of chemical mixtures on ecosystems. Chlorpyrifos (CPF) is an organophosphate insecticide extensively used in agricultural practices. The anionic surfactant sodium lauryl ether sulphate (SLES) is the main component of several commercial products, including foaming agents used in underground mechanised excavation. Both compounds are produced and sold in high amounts worldwide and can be found in the environment as soil contaminants. The persistence of SLES and CPF in agricultural soils and their possible effects on the natural microbial community was evaluated in microcosms. The experimental set consisted of soil samples containing the autochthonous microbial community and treated with only SLES (70 mg/kg), only CPF (2 mg/kg) or with a mix of both compounds. Control microcosms (without the contaminants) were also performed. Soil samples were collected over the experimental period (0, 7, 14, 21 and 28 days) and analysed for CPF, SLES and the main metabolite of CPF (3, 5, 6-trichloropyridinol, TCP). The half-life time (DT50) of each parent compound was estimated in all experimental conditions. At the same time, the abundance, activity and structure of the microbial community were also evaluated. The results showed that the co-presence of SLES and CPF did not substantially affect their persistence in soil (DT50 of 11 and 9 days with co-presence and 13 and 10 days, respectively, when alone); however, in the presence of SLES, a higher amount of the metabolite TCP was found. Interestingly, some differences were found in the bacterial community structure, abundance and activity among the various conditions.

Temporal Evolution of PAHs Bioaccessibility in an Aged-Contaminated Soil during the Growth of Two Fabaceae

Polycyclic aromatic hydrocarbons (PAHs) are health-concerning organic compounds that accumulate in the environment. Bioremediation and phytoremediation are studied to develop eco-friendly remediation techniques. In this study, the effects of two plants (Medicago sativa L. and Trifoliumpratense L.) on the PAHs’ bioaccessibility in an aged-contaminated soil throughout a long-term rhizoremediation trial was investigated. A bioaccessibility measurement protocol, using Tenax^® beads, was adapted to the studied soil. The aged-contaminated soil was cultured with each plant type and compared to unplanted soil. The bioaccessible and residual PAH contents were quantified after 3, 6 and 12 months. The PAHs’ desorption kinetics were established for 15 PAHs and described by a site distribution model. A common Tenax^® extraction time (24 h) was established as a comparison basis for PAHs bioaccessibility. The rhizoremediation results show that M. sativa developed better than T. pratense on the contaminated soil. When plants were absent (control) or small (T. pratense), the global PAHs’ residual contents dissipated from the rhizosphere to 8% and 10% of the total initial content, respectively. However, in the presence of M. sativa, dissipation after 12 months was only 50% of the total initial content. Finally, the PAHs’ bioaccessible content increased more significantly in the absence of plants. This one-year trial brought no evidence that the presence of M. sativa or T. pratense on this tested aged-contaminated soil was beneficial in the PAH remediation process, compared to unplanted soil.

Enhanced phytoremediation of PAHs-contaminated soil from an industrial relocation site by Ochrobactrum sp

Nowadays, the remediation of polycyclic aromatic hydrocarbons (PAHs)-contaminated soil has received wide attention. In this work, Ochrobactrum sp. (PW) was isolated through selective enrichment from PAHs-contaminated soil in coking plant of Beijing, and the effects of PW on phytoremediation of that soil by alfalfa (Medicago sativa L.) and ryegrass (Lolium multiflorum Lam.) were investigated through pot experiments. Plant biomass, peroxidase (POD) activity, malondialdehyde (MDA) contents, soil enzyme activity (polyphenol oxidase and dehydrogenase activity), and residual concentration of PAHs in soils were determined to illustrate the ability of PW for enhancing the degradation of PAHs by plants. The results showed that the fresh weight of ryegrass and alfalfa inoculated with PW was significantly (p < 0.05) increased while the activity of POD and MDA contents were notably (p < 0.05) reduced than that without inoculation. Additionally, PW enhanced the activity of polyphenol oxidase and dehydrogenase in soil significantly (p < 0.05), and further enhanced the degradability of the system to PAHs. Different treatment methods could be ranked by the following order according to the degradability: SP (alfalfa + PW) > RP (ryegrass + PW) > PW (PW) > S (alfalfa) > R (ryegrass). The combined action of PW and alfalfa/ryegrass could accelerate the degradability of PAHs from soil contaminated by coking plants. PW could be used as potential bacteria to promote phytoremediation of the soil contaminated by PAHs.

Assessment of Pesticide Residue Content in Polish Agricultural Soils

Pesticides belong to a group of xenobiotics harmful to humans and wildlife, whose fate and activity depends on their susceptibility to degradation. Therefore, the monitoring of their residue level in agricultural soils is very important because it provides very valuable information on the actual level of soil contamination and environmental risk resulting from their application. The aim of this study was to evaluate contemporary concentrations of organochlorine (OCPs) and non-chlorinated pesticides (NCPs) in arable soils of Poland as an example of Central and Eastern European countries. The results were assessed in relation to Polish regulations, which are more restrictive compared to those of other European countries. The sampling area covered the territory of arable lands in Poland (216 sampling points). The distribution of sampling points aimed to reflect different geographical districts, conditions of agricultural production, and various soil properties. The collected soil samples were extracted with organic solvents in an accelerated solvent extractor (ASE 2000). The OCPs, including α-HCH, β-HCH, γ-HCH, and p,p’DDT, p,p’DDE, and p,p’DDD, were extracted with a hexane/acetone mixture (70:30 v/v) and determined by gas chromatography with an electron capture detector (GC-μECD). NCPs included atrazine, carbaryl, and carbofuran were extracted with a dichloromethane/acetone mixture (50:50 v/v), while maneb was extracted by intensive shaking the sample with acetone (1:1 v/v) and ethylenediamine-tertraacetic acid. The NCPs were identified by a dual mass- spectrometry (GC-MS/MS). The total content of individual OCPs ranged from 0.61 to 1031.64 µg kg⁻¹, while the NCP concentrations were significantly lower, from 0.01 to 43.92 µg kg⁻¹. DDTs were detected in all soils samples (p,p’DDD (23.60 µg kg⁻¹) > p,p’DDT (18.23 µg kg⁻¹) > p,p’DDE (4.06 µg kg⁻¹), while HCHs were only in 4% of the analyzed samples (β-HCH (339.55 µg kg⁻¹) > α-HCH (96.96 µg kg⁻¹) > γ-HCH (3.04 µg kg⁻¹)), but in higher values than DDTs. Among NCPs, higher concentration was observed for carbaryl (<0.01–28.07 µg kg⁻¹) and atrazine (<0.01–15.85 µg kg⁻¹), while the lower for carbofuran (<0.01–0.54 µg kg⁻¹). Maneb was not detected in analyzed soils. Assessment of the level of soil pollution based on Polish regulations indicated that several percentages of the samples exceeded the criterion for OCPs, such as ∑3DDTs (14 samples; 6.5% of soils) and HCH congeners (α-HCH in one sample; 0.5% of soils), while NCP concentration, such as for atrazine, carbaryl and carbofuran were below the permissible levels or were not detected in the analyzed soils, e.g., maneb. The obtained results indicated that residues of the analyzed pesticides originate from historical agricultural deposition and potentially do not pose a direct threat to human and animal health. The behavior and persistence of pesticides in the soils depend on their properties. Significantly lower NCP concentration in the soils resulted from their lower hydrophobicity and higher susceptibility to leaching into the soil profile. OCPs are characterized by a high half-life time, which affect their significantly higher persistence in soils resulting from affinity to the soil organic phase.

Oil mobilization and solubilization in porous media by in situ emulsification

HYPOTHESIS

For a wide range of subsurface engineering processes, such as geological carbon sequestration and enhanced oil recovery, it is critical to understand multiphase flow at a fundamental level. To this end, geomaterial microfluidic devices provide visual data that can be quantified to explain the physics of multiphase flow at the length scale of individual pores in realistic rock structures. For surfactant enhanced oil recovery, it is the underlying geometrical states of the capillary trapped oil that dictates the recovery process and the degree to which oil is recovered through either mobilization or solubilization during in situ emulsification.

EXPERIMENTS

A novel geomaterial microfluidic device is fabricated and its integrity is checked using light microscopy and X-ray micro-computed tomography (μ-CT) imaging. Subsequently, alkaline surfactant (AS) flooding of an oil saturated device is studied for enhanced recovery. The recovery process is analyzed by collecting 2D radiographic projections of the device during water flooding and in situ emulsification. 3D μ-CT images are also collected to quantify the geometrical states of the fluids after each flooding sequence.

FINDINGS

Our study reveals the processes of oil cluster mobilization and solubilization in porous media. After water flooding there are numerous oil clusters that are relatively large, extending over multiple pores, forming various loop-like structures. These clusters are mobile under AS flooding accounting for 75% of the recovered oil. The less mobile smaller clusters, isolated to single pores, forming no loop-like structures are immobile. These clusters are solubilized during AS flooding accounting for 25% of the recovered oil. The mobilized clusters coalesce forming an oil bank prior to total solubilization. The remaining oil clusters after AS flooding are highly non-wetting, as indicated by contact angle measurements and would only be recoverable after further solubilization.

Soil heterogeneity and surfactant desorption influence PAH distribution during electroremediation at a tar oil-contaminated site

After a field experiment utilising electroosmosis and non-ionic surfactant Tween 80 as a remediation effort on the removal of polycyclic aromatic hydrocarbons (PAHs) from a long-term asphalt-contaminated soil, the PAH heterogeneity in the soil was yet extensive. This study come as a follow-up to address the following questions: (i) was PAH (re)distribution a consequence of the treatment? and (ii) to what extent does the surfactant affected PAH desorption and subsequent bioavailability? To answer question (i), we selected random soil samples from different locations of the field site before in situ remediation took place, and quantified and characterised soil organic matter by elemental analysis and solid-phase ¹³C nuclear magnetic resonance spectroscopy and PAH concentrations. Finally, batch desorption experiments with selected contaminated soil samples were carried out with and without 1% Tween 80 in the solution phase to address question (ii). Data shows that PAH concentrations were related neither to organic matter content nor to a high aromaticity of the organic matter, which serves as a proxy for the presence of tar oil. Soil heterogeneity is likely to be the cause of PAH heterogeneous distribution, but it is inferred that remediation causes weathering of the tar oil phase, resulting in the release and subsequent transport and sorption of PAH to inherent organic material. The results of the batch desorption experiments demonstrate PAH desorption up to 146 times when surfactant is present. However, Tween 80 does not enable biodegradation, since desorbed PAH molecules are entrapped inside surfactant micelles.

Desorption kinetics and isotherms of phenanthrene from contaminated soil

BACKGROUND

Prediction of polycyclic aromatic hydrocarbons (PAHs) desorption from soil to estimate available fraction regarding to initial concentration of the contaminant is of great important in soil pollution management, which has poorly been understood until now. In the present study estimation of fast desorption fraction which is considered as available fraction was conducted by evaluating desorption kinetics of phenanthrene (a three ring PAH) from artificially contaminated soils through the mathematical models.

METHODS

Desorption rate of phenanthrene (PHE) was investigated by using the nonionic surfactant Tween80 in a series of batch experiments. The effects of reaction time from 5 to 1440 min and initial PHE concentration in the range of 100-1600 mg/kg were studied.

RESULTS

Available fractions of the contaminant were achieved within the first hour of desorption process as the system reached to equilibrium conditions. Experimental data were examined by using kinetic models including pseudo-first-order, pseudo-second-order in four linearized forms, and fractional power. Among the models tested, experimental data were well described by pseudo-second-order model type (III) and (IV) and fractional power equation. Fast desorption rates, as Available fractions were determined 79%, 46%, 40%, 39%, and 35% for initial PHE concentrations of 100, 400, 800, 1200, and 1600 mg/kg respectively. Among the evaluated isotherm models, including Freundlich, Langmuir in four linearized forms, and Temkin, the equilibrium data were well fitted by the first one.

CONCLUSION

Applying the nonionic surfactant Tween80 is a useful method to determine available fraction of the contaminant. This method will provide the management of contaminated sites by choosing a proper technique for remediation and predicting achievable treatment efficiency.

Rapid and versatile pre-treatment for quantification of multi-walled carbon nanotubes in the environment using microwave-induced heating

The concerns regarding potential environmental release and ecological risks of multi-walled carbon nanotubes (MWCNTs) rise with their increased production and use. As a result, there is the need for an analytical method to determine the environmental concentration of MWCNTs. Although several methods have been demonstrated for the quantification of well-characterized MWCNTs, applying these methods to field samples is still a challenge due to interferences from unknown characteristics of MWCNTs and environmental media. To bridge this gap, a recently developed microwave-induced heating method was investigated for the quantification of MWCNTs in field samples. Our results indicated that the microwave response of MWCNTs was independent of the sources, length, and diameter of MWCNTs; however, the aggregated MWCNTs were not able to convert the microwave energy to heat, making the method inapplicable. Thus, a pre-treatment process for dispersing bundled MWCNTs in field samples was crucial for the use of the microwave method. In the present paper, a two-step pre-treatment procedure was proposed: the aggregated MWCNTs loaded environmental samples were first exposed to high temperature (500 °C) and then dispersed by using an acetone-surfactant solution. A validation study was performed to evaluate the effectiveness of the pre-treatment process, showing that an 80-120% recovery range of true MWCNT loading successfully covered the microwave-measured MWCNT mass.

Nanohybrid Layered Double Hydroxides Used to Remove Several Dyes from Water

For the preparation and characterization of several layer double hydroxides (LDH) with inorganic interlayer anions (carbonate and nitrate) and nanohybrids, two organo-LDHs were studied in detail. The dodecylbenzene sulfonate (DBS) was used as an organic interlayer anion to modify the hydrophilic nature of the interlayer. The aim of the modification of the layered double hydroxides (LDH) was to change the hydrophilic character of the interlayer to hydrophobic with the purpose of improving its ability to adsorb several (anionic and cationic) dyes from water. These compounds have been used as adsorbents of amaranth (Am), diamine green B (DGB) and brilliant green (BG) dyes. Adsorption tests were conducted using variable pH values, contact times and initial dye concentrations (adsorption isotherms) to identify the optimum conditions for the intended purpose. Adsorbents and adsorption products were characterized by several physicochemical techniques. The results of the adsorption tests showed that the organo-LDH nanohybrids could be efficient adsorbents in the removal of studied dyes from water. Thus, it can be concluded that nanohybrids studied in this work might act as suitable supports in the design of adsorbents for the removal of a wide spectrum of dyes with the aim of reducing the adverse effects on water resources.

Comparing storage battery and solar cell in assisting Eucalyptus Globulus to phytoremediate soil polluted by Cd, Pb, and Cu

Metal decontamination and leaching alleviation capacity of Eucalyptus globulus with and without electric field were investigated using ICP-MS. The biomass production of the chosen plant increased from 0.87 kg in planting control without electrokinetic treatment to 1.16 and 1.42 kg in experiments with electric field supplied by storage battery and solar cell, respectively. Under the influence of electric field with a voltage of 6.5 V, significantly more Cd, Pb and Cu were extracted by the species. Precipitation simulation was performed to evaluate the capacity of battery and solar panel to intercept leaching. The total volume of leachate gathered from the control decreased from 1012 mL to 299 and 336 mL in containers treated by storage battery and solar cell, respectively. In addition to reduction of leachate, the leaching mass of Cd, Pb and Cu was decreased significantly by electric fields (both battery and solar cell) treatments. The effect of remediation and environmental risk alleviation by solar cell was comparable with storage battery, at least during the 30-day experimental period. On the basis of the present study, solar cell should be a suitable substitute for conventional power supply to improve metal polluted soil when considering phytoremediation efficiency and energy consumption.

Efficacy of Indigenously Prepared Sugarcane and Pineapple Wine Solvents for Washing Highly Dioxin-Contaminated Field Soils

Poly-chlorinated dibenzo-p-dioxins (PCDDs) and poly-chlorinated dibenzo-furans (PCDFs) negatively affect human health and are often found as unwanted by-products of chemical handling and manufacture procedures. While commercial solvents have been used to remove dioxins from contaminated soil, these solvents themselves may adversely affect soil health. In this study, we examined the effects of washing highly PCDD/F contaminated field-soil with two natural solvents (sugarcane and pineapple wine) under ambient temperature. Performing an initial three-washing-cycle experiment, we found that sugarcane wine more effectively removed the contaminants than pineapple wine (removal, 60% vs. 50%) and chose it to perform a six-washing-cycle experiment facilitated by mechanical stirring and ultrasonication. Sugarcane wine was found to have a high removal efficiency (almost 80%), largely due to its higher alcohol and acid content. We believe that both wines can be used in soil remediation tasks without further damage to soil health. This is the first study employing naturally made wines as soil washing solvents in treating highly PCDD/F contaminated field soil. After soil washing processes, the winery solvents are believed to be beneficial to (if necessary) bioremediation methods and/or monitored natural attenuation.

Identification of surfactants and its correlation with physicochemical parameters at the confluence region of Vembanad Lake in India

The present study describes the monitoring of some of the major classes of surfactants in water. The separation, identification, and the quantitative estimation of the compounds were achieved using LC-Q-ToF-MS. The analyses revealed the presence of variety of surfactants including linear alkylbenzene sulfonate (LAS), alcohol ethoxysulfates (AES), and alcohol ethoxylates (AE). Further, emphasis was given to AES as they are one of the most produced and consumed surfactants in the world. And as far as India is concerned, the present study is one of the most significant attempt regarding the identification and quantification of AES. The data obtained during the analysis revealed that the average concentration of AES C12Ex varied from 0.7 to 13.6 μg L^-1 while that of C14Ex ranged between 1.3 and 10.4 μg L^-1. The risk assessment revealed that higher chain AES are capable of posing medium level risk to the aquatic compartment. In addition, the study also included the physicochemical analysis of water from the selected area. Water was found to be acidic in nature and the salinity, TDS, and EC values were found to be high during the pre-monsoon season. The order of the levels of anionic constituents was of Cl^->SO₄^2-SO₄^2->F^->NO₃^2- ≅ PO₄^2- while that of cations were Na⁺ > Mg²⁺ > K⁺ > Ca²⁺. Results of correlation analysis showed that statistically negative correlation exists between AES homologs and pH while slight positive correlations were found between AES and other parameters including TDS and EC. The suitability of this water for domestic and agricultural purposes has been examined on the ground of basic quality indices such as the water quality index (WQI) and sodium adsorption ratio (SAR). The WQI measurements also revealed that the water quality of the region falls under the "very poor" category especially during the pre-monsoon season. The study could explore the cumulative share of these canals in the quality impairment of the receiving Vembanad Lake.

Surfactant-enhanced bioremediation of DDTs and PAHs in contaminated farmland soil

Field-scale bioremediation of dichlorodiphenyl trichloroethanes (DDTs) and polycyclic aromatic hydrocarbons (PAHs) contaminated farmland soil from the Shenyang North New Area of China was studied using the bacteria Arthrobacter globiformis. The additive effects of different concentrations of biosurfactant rhamnolipids (RLs) and anionic-nonionic mixed surfactant (SDBS-Tween 80) were evaluated. DDT and PAH removal rates by A. globiformis after 150 days of remediation were 52.1% and 21.9%, respectively. At the optimum RL concentration of 5 mg kg^-1, DDTs and PAHs had removal rates of 64.3% and 35.6%, respectively, at 150 days. This was 60.7% and 29.3% higher than the control; 36.9% and 19.8% higher than soil with RL-5 alone; and 12.2% and 13.8% higher than the A. globiformis treatment alone. RL-5 can enhance soil enzyme activity and A. globiformis reproduction during the DDT and PAH biodegradation processes. This study illustrates a highly efficient, low-cost in situ soil bioremediation technology that could have practical utility.

Soil water repellency of the artificial soil and natural soil in rocky slopes as affected by the drought stress and polyacrylamide

Soil water repellency (SWR) causes reduced soil water storage, enhanced runoff and reduced ecosystem productivity. Therefore, characterization of SWR is a prerequisite for effective environmental management. SWR has been reported under different soils, land uses and regions of the world, particularly in forest land and after wildfires; however, the understanding of this variable in the artificial soil of rocky slope eco-engineering is still rather limited. This study presented the characterization of SWR in the artificial soil affected by the polyacrylamide (PAM) and drought stress. There were two molecular weights of PAM, and the CK was without PAM application. Three types of soil were studied: natural soil and two types of artificial soil which have been sprayed for 1y and 5y, respectively. The drought stress experiments had three drought gradients, lasted for three weeks. Water repellency index (WRI) and soil-water contact angle (β) were determined using intrinsic sorptivity method by measuring the water sorptivity (S_W) and ethanol sorptivity (S_E) in all soil samples. The results showed that (1) Polyacrylamide treatments significantly increased S_W by 3% to 38%, and reduced S_E by 1% to 15%, WRI by 6% to 38%, β by 3% to 23% compared to the control group. Polyacrylamide treatments also increased water-stable aggregates content and total porosity by 22% to 33%, 11% to 20% relative to the control, while PAM with a higher molecular weight performed best. (2) The interaction between PAM and drought stress had a significant effect on WRI and β for all soil types (P<0.01) while it only had a significant effect on S_W and S_E for the artificial soil (P<0.01). (3) The artificial soil had a greater WRI and β than the natural soil.

In situ long-term modeling of phenanthrene dynamics in an aged contaminated soil using the VSOIL platform

Management and remediation actions of polycyclic aromatic hydrocarbons (PAH) contaminated sites require an accurate knowledge of the dynamics of these chemicals in situ under real conditions. Here we developed, under the Virtual Soil Platform, a global model for PAH that describes the principal physical and biological processes controlling the dynamics of PAH in soil under real climatic conditions. The model was applied first to simulate the observed dynamics of phenanthrene in situ field experimental plots of industrial contaminated soil. In a second step, different long-term scenarios of climate change or bioavailability increase were applied. Our results show that the model can adequately predict the fate of phenanthrene and can contribute to clarify some of unexplored aspects regarding the behavior of phenanthrene in soil like its degradation mechanism and stabilization. Tested prospective scenarios showed that bioavailability increase (through the addition of solvent or surfactants) resulted in significant increase in substrate transfer rate, hence reducing remediation time. Regarding climate change effect, the model indicated that phenanthrene concentration decreased by 54% during 40years with a natural attenuation and both scenarios chosen for climatic boundaries provided very similar results.

Surfactant-enhanced flushing enhances colloid transport and alters macroporosity in diesel-contaminated soil

Soil contamination by diesel has been often reported as a result of accidental spillage, leakage and inappropriate use. Surfactant-enhanced soil flushing is a common remediation technique for soils contaminated by hydrophobic organic chemicals. In this study, soil flushing with linear alkylbenzene sulfonates (LAS, an anionic surfactant) was conducted for intact columns (15cm in diameter and 12cm in length) of diesel-contaminated farmland purple soil aged for one year in the field. Dynamics of colloid concentration in column outflow during flushing, diesel removal rate and resulting soil macroporosity change by flushing were analyzed. Removal rate of n-alkanes (representing the diesel) varied with the depth of the topsoil in the range of 14%-96% while the n-alkanes present at low concentrations in the subsoil were completely removed by LAS-enhanced flushing. Much higher colloid concentrations and larger colloid sizes were observed during LAS flushing in column outflow compared to water flushing. The X-ray micro-computed tomography analysis of flushed and unflushed soil cores showed that the proportion of fine macropores (30-250μm in diameter) was reduced significantly by LAS flushing treatment. This phenomenon can be attributed to enhanced clogging of fine macropores by colloids which exhibited higher concentration due to better dispersion by LAS. It can be inferred from this study that the application of LAS-enhanced flushing technique in the purple soil region should be cautious regarding the possibility of rapid colloid-associated contaminant transport via preferential pathways in the subsurface and the clogging of water-conducting soil pores.

Biosurfactant-enhanced removal of o,p-dichlorobenzene from contaminated soil

Surfactant-enhanced remediation is less applicable for the treatment of dichlorobenzene (DCB)-contaminated soil. In this study, water solubility enhancements of o-dichlorobenzene (o-DCB) and p-dichlorobenzene (p-DCB) by micellar solutions of biosurfactants (saponin, alkyl polyglycoside) and chemically synthetic surfactant (Tween 80) were measured and compared. Solubilities of o,p-DCB in water were greatly enhanced in a linear fashion by each of Tween 80, saponin, and alkyl polyglycoside. Solubility enhancement efficiencies of surfactants followed the order of Tween 80 > saponin > alkyl polyglycoside. However, the ex situ soil washing experiment demonstrated the opposite result. The removal efficiency of o,p-DCB by biosurfactant saponin and alkyl polyglycoside was higher than that of chemically synthetic surfactant Tween 80 in contaminated soil. This difference may be due to the different adsorption behaviors of the surfactants onto soil. In addition, elution kinetics for o,p-DCB were relatively fast, with apparent elution equilibrium reached within 360 min, and can be described by a pseudo first-order kinetic equation. The elution process of o,p-DCB in soil-aqueous systems obeyed four-parameter biphasic first-order kinetic model including rapid and slow phases. The results confirmed potential application of saponin and alkyl polyglycoside in elution solution for enhanced remediation of DCB-contaminated soil.

Removal mechanisms in aerobic slurry bioreactors for remediation of soils and sediments polluted with hydrophobic organic compounds: An overview

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.

Evaluation of the influence of surfactants in the bioaccumulation kinetics of sulfamethoxazole and oxazepam in benthic invertebrates

The potential ecotoxicological effects of mixtures of contaminants in the aquatic environment are generating a global concern. Benthic invertebrates, such as the crustacean Gammarus fossarum, are key in the functioning of aquatic ecosystems, and are frequently used as sentinel species of water quality status. The aim of this work was to study the effects of a mixture of the most frequently detected surfactants in the bioconcentration kinetics of two pharmaceuticals in G. fossarum, evaluating their potential enhancing or suppressing effects. Laboratory exposure experiments for both pharmaceuticals and surfactants (concentration ratio 1:25) were set up for two individual compounds, the anxiolytic oxazepam and the antibiotic sulfamethoxazole. Gammarid samples were processed using microQuEChERS (Quick, Easy, Cheap, Effective, Rugged, and Safe) extraction. Pharmaceuticals concentration in the organisms was followed-up by means of nanoliquid chromatography coupled to tandem mass spectrometry (nanoLC-MS/MS). Results indicated a similar mode of action of the surfactants in the bioconcentration kinetics of both drugs, decreasing the accumulation rate in the organism. Oxazepam showed a higher accumulation potential than sulfamethoxazole in all cases. Depuration experiments for oxazepam also demonstrated the high depurative capacity of gammarids, eliminating >50% of the concentration of oxazepam in <6h.

The use of ultrasound-assisted anaerobic compost tea washing to remove poly-chlorinated dibenzo-p-dioxins (PCDDs), dibenzo-furans (PCDFs) from highly contaminated field soils

The remediation of dioxin-contaminated soil of a specific coastal area previously employed for the manufacture of pentachlorophenol (PCP) in southern Taiwan's Tainan City has attracted much attention of researchers there. This work addresses the possibility of providing an effective and environmentally friendly option for removing PCDD/Fs from soil in that field. Soil screening/sieving was first conducted to assess particle distribution. Fine sand was observed to be the major component of the soil, accounting for more than 60% of the total mass. A combination of ultrasonification and mechanical double-blade agitation was used to facilitate the washing of the soil using the biosurfactant anaerobic compost tea. More than 85 and 95% of total removal efficiencies were achieved for moderately and highly contaminated soils after 6 and 10 washing cycles, respectively, under ambient temperature, a soil/liquid ratio 1:2.5, 700 rpm, and over a relatively short duration. These results were achieved through the collision and penetration effects of this combined treatment as well as PCDD/F partitioning between the particles and anaerobic compost tea. This study represents the first to report the use of anaerobic compost tea solvent to wash soil highly contaminated by dioxin. It was concluded that anaerobic compost tea, rich in non-toxic bio-surfactants (e.g., alcohols, humic acids), can be used to improve bioavailability and bioactivity of the soil making bio-attenuation and full remediation more efficient.

Advanced technologies for the remediation of pesticide-contaminated soils

The occurrence of pesticides in soil has become a highly significant environmental problem, which has been increased by the vast use of pesticides worldwide and the absence of remediation technologies that have been tested at full-scale. The aim of this review is to give an overview on technologies really studied and/or developed during the last years for remediation of soils contaminated by pesticides. Depending on the nature of the decontamination process, these techniques have been included into three categories: containment-immobilization, separation or destruction. The review includes some considerations about the status of emerging technologies as well as their advantages, limitations, and pesticides treated. In most cases, emerging technologies, such as those based on oxidation-reduction or bioremediation, may be incorporated into existing technologies to improve their performance or overcome limitations. Research and development actions are still needed for emerging technologies to bring them for full-scale implementation.

Effects of rhamnolipids on the cell surface characteristics of Sphingomonas sp. GY2B and the biodegradation of phenanthrene

The mechanism of the interaction of rhamnolipids on strain GY2B.