An evaluation of surfactant foam technology in remediation of contaminated soil

Critical evaluation of the performance of rhamnolipids as surfactants for (phyto)extraction of Cd, Cu, Fe, Pb and Zn from copper smelter-affected soil

Rhamnolipids are biosurfactants produced by bacteria belonging to the Pseudomonas genus. They are discussed to complex heavy metal cations stronger than cations of Fe, Ca, Mg. It is therefore suggested to employ rhamnolipids in phytoextraction where their addition to soil should result in preferential complexation of heavy metals that can be taken up by plants, thus enabling rapid and ecological clean-up of contaminated soil. In order to test this concept, we evaluated the rhamnolipid-mediated phytoextraction of heavy metal from soil collected from the vicinity of a copper smelter. The following aspects were investigated: i) selectivity of rhamnolipids towards Cu, Zn, Pb, Cd and Fe during soil washing; ii) phytoextraction efficiency of each ion with respect to the effective concentration of rhamnolipids; iii) possible phytotoxic effects; iv) effect of micro-sized polystyrene amendment. The experiments evaluated soil washing efficiency, BCR (Community Bureau of Reference) sequential extraction to determine the impact of rhamnolipids on the mobility of metal ions, phytoextraction with maize (Zea mays L.) and phytotoxic effects based on dry matter, chlorophyll fluorescence and content. The obtained results indicated that rhamnolipids lack desired selectivity towards heavy metal ions as Fe was complexed more efficiently by 80 % of the available rhamnolipids compared to priority pollutants like Zn, Cu, Pb, which were complexed by only 20 % of the tested rhamnolipids. With increased concentration of rhamnolipids, the soil washing efficiency increased and shifted in favour of Fe, reaching values of approx. 469 mg for Fe and only 118 mg in total of all tested heavy metals. Phytoextraction also favoured the accumulation of Fe, while Cd was not removed from the soil even at the highest applied rhamnolipid concentrations. Considering the selectivity of rhamnolipids and the costs associated with their production, our results suggest the need to search for other alternative (bio)surfactants with better selectivity and lower price.

Effect of in situ mixed micellization of ester-functionalized gemini surfactant at different pHs on solubilization and cosolubilization of various polycyclic aromatic hydrocarbons of varying hydrophobicities

A pH controlled cleavability unfolds the 3-in-1 surfactant feature of an ester-bonded gemini surfactant, 2, 2'-[(oxybis (ethane-1,2-diyl))bis (oxy)]bis (N-hexadecyl-N,Ndimethyl-2-oxoethanaminium) dichloride (C16-C4O2-C16), by reinforcing in-situ mixed micellization between cleaved components at non-neutral pH (pH 3,12). The triplicity is assigned to two mixed-micelle variants at pH 3 and pH 12 besides the unhydrolyzed C16-C4O2-C16 at pH 7. The pH-controlled aggregation of such trichotomic surfactant dramatically enhances the micellar solubilization/cosolubilization of PAHs viz. naphthalene (Np), phenanthrene (Ph), pyrene (Py), perylene (Pe). The cosolubilization of binary/ternary PAH mixtures in such remarkable micellar assemblies at pH 3, 7 and 12 yields intriguing synergistic or antagonistic solubility outcomes correlated to PAH-PAH and PAH-micelle interactions. This study provides valuable insights into the potential applications of the ester-bonded gemini surfactant for the cosolubilization of undesirable hydrophobic compounds at natural sites having variable pH.

Foam Propagation with Flow Reversal

With a view towards modelling the foam improved oil recovery process, fractional flow theory is used to study the dynamics of a foam as it propagates in a porous medium that is initially filled with liquid. In particular, a case is studied whereby, at a certain time, the net pressure driving the foam is decreased below the hydrostatic pressure at depth, leading to a local change in the flow direction. This is known as flow reversal. In both forward and reverse flow, the boundary between foamed gas and liquid is found as a discontinuous jump in liquid saturation. Over a certain thickness in the neighbourhood of this discontinuity, foam is finely textured, and the mobility of foamed gas drops by orders of magnitude relative to either pure gas or pure liquid. In reverse flow, however, the foam mobility itself and also the thickness over which low mobilities apply might differ from the forward flow case. Fractional flow theory reveals that the thickness of the low mobility region, and hence the resistance to motion that it presents, increases directly proportional to the distance travelled. Previous studies recognised this, but assumed the thickness of this region to be just a small fraction of the distance travelled by the discontinuity. Here, however, we demonstrate that the extent of the low mobility region, in both forward and reverse flow, accounts for a considerable fraction of the distance travelled by the foam, despite what was assumed in previous works.

Biodiesel Co-Product enhances microbial stability and beneficial microbial communities along a gradient of soil water content

Biodiesel Co-Product (BCP) is a complex carbonaceous liquid formed during the commercial production of biodiesel. Previously, BCP was shown to decrease nitrogen (N) leaching from the soil, but the effects of BCP on the diversity, composition, and structure of soil microbial communities are not well understood. Here, we applied 1.5 mg BCP-C to acidic soil (pH 3.5) at a range of different water contents (from 40 % to 100 % water holding capacity) to investigate the interactions between BCP and increasing water holding capacity on the diversity, composition, and interactions of soil microbial communities. Distance-based multivariate linear model (DistLM) and non-metric multidimensional scaling (NMDS) analyses showed that BCP caused larger changes in fungal than bacterial communities, while soil water content had a greater effect on bacterial communities relative to fungal communities. Co-occurrence network analyses indicated that BCP amendment produced more robust and complex bacterial networks and more stable fungal ones. BCP significantly increased the OTU numbers of beneficial microbes (e.g., Trichoderma spp.) in all water contents, with fewer OTU numbers of putative pathogenetic species (Fusarium spp. and Aspergillus spp.). These findings indicate that BCP addition may be conducive to the health and stability of soil ecosystems.

Utilization of a biosurfactant foam/nanoparticle mixture for treatment of oil pollutants in soil

Oil contamination has become a primary environmental concern due to increased exploration, production, and use. When oil enters the soil, it may attach or adsorb to soil particles and stay in the soil for an extended period, contaminating the soil and surrounding areas. Nanoparticles have been widely used for the treatment of organic pollutants in the soil. Surfactant foam has effectively been employed to remediate various soil contaminants or recover oil compounds. In this research, a mixture of biosurfactant foam/nanoparticle was utilized for remediation of oil-contaminated soil. The results demonstrated that the biosurfactant/nanoparticle mixture and nitrogen gas formed high-quality and stable foams. The foam stability depended on the foam quality, biosurfactant concentration, and nanoparticle dosage. The pressure gradient change in the soil column relied on the flowrate (N₂ gas + surfactant/nanoparticle mixture), foam quality, and biosurfactant concentration. The optimal conditions to obtain good quality and stable foams and high oil removal efficiency involved 1 vol% rhamnolipid, 1 wt% nanoparticle, and 1 mL/min flowrate. Biosurfactant foam/nanoparticle mixture was effectively used to remediate oil-contaminated soil, whereas the highest treatment efficiency was 67%, 59%, and 52% for rhamnolipid biosurfactant foam/nanoparticle, rhamnolipid biosurfactant/nanoparticle, and only rhamnolipid biosurfactant, respectively. The oil removal productivity decreased with the increase of flowrate due to the shorter contact time between the foam mixture and oil droplets. The breakthrough curves of oil pollutants in the soil column also suggested that the foam mixture's maximum oil treatment efficiency was higher than biosurfactant/nanoparticle suspension and only biosurfactant.

Viscous froth model applied to the dynamic simulation of bubbles flowing in a channel: three-bubble case

A two-dimensional foam system comprised of three bubbles is studied via simulations with the viscous froth model. Bubbles are arranged in a so-called staircase configuration and move along a channel due to imposed driving back pressure. This flowing three-bubble system has been studied previously on the basis that it interpolates between a simpler staircase structure (a simple lens, which breaks up via so-called topological transformations if driven at high pressure) and an infinite staircase (which sustains arbitrarily large driving pressure without breaking). Depending on bubble size relative to channel size, different solution branches for the three-bubble system were found: certain branches terminate (as for the simple lens) in topological transformations and others reach (as for an infinite staircase) a geometrically invariant migrating state. The methodology used previously was, however, a purely steady state one, and hence did not interrogate stability of the various branches, nor the role of imposing different driving pressures upon topological transformation type. To address this, unsteady state three-bubble simulations are realized here. Stable solution branches without topological transformation exist for comparatively low driving pressures. For sufficiently high imposed back pressures, however, topological transformations occur, albeit with imposed pressure now influencing the transformation type.

Influence of the injection of densified polymer suspension on the efficiency of DNAPL displacement in contaminated saturated soils

Nowadays the remediation of DNAPL contaminated zones near groundwater has gained great prominence in environmental fields due to the high importance of water resources. In this work, we suggest injecting a densified polymer suspension by adding barite particles to displace DNAPL. To evaluate the efficiency of the densification of polymer suspensions on the displacement of DNAPL, various densities of barite-polymer suspension; lower, equal, and higher than the density of DNAPL were prepared and their rheological behavior was analyzed. Then flow experiments were performed using a decimetric-scale 2D tank. The displacement procedure was monitored with an imaging technique and the production and injection process data were recorded by mass balance interpretation. It was shown that the densification of the polymer suspension could improve the displacement efficiency of DNAPL up to four times. The clogging behavior of barite-polymer suspension was assessed in a 1D column. Generalized Darcy's law and the continuity equation were used to numerically simulate the experimental two-phase flow. To take into account the clogging behavior of the suspension, the transport equation of diluted species was implemented into the model. The simulation results show that the model can properly predicts the experimental consequences.

Localized Delivery of Liquid Fertilizer in Coarse-Textured Soils Using Foam as Carrier

Agrochemicals and fertilizers are central to modern agriculture and are credited with the large increase of crop yield as a part of the Green Revolution of the 1960’s. Timely and targeted fertilizer application to crop root zones enhances effectiveness and reduces unintended release to the environment. This is particularly important for highly mobile liquid fertilizers (e.g., nitrate) that can be mobilized with infiltrating water to bypass root-bearing soil volumes. We report a novel liquid fertilizer delivery method using foam as carrier. The high degree of control and mechanical stability of liquid fertilizer foam (defined dispersed gas bubbles in a continuous liquid phase) injection into coarse soils (most susceptible to preferential flows) is proposed a novel delivery method to targeted root zone volumes at concentrations and geometry that promote uptake and reduces losses. This note and preliminary communication meant to serve a proof of concept report comparing foam and conventional liquid fertilizer applications. The results indicate that foam-delivery reduced fertilizer leaching thus improving its retention in soil for similar flow conditions of liquid delivery. Theoretical estimates suggest that the effects of fertilizer retention could be enhanced in more localized (3-D) injection of foam fertilizers and other agrochemicals thus enhancing agronomic efficiency and reducing environmental risk of contamination.

Analysis of a model for surfactant transport around a foam meniscus

A model developed by Bussonnière & Cantat [1] is considered for film-to-film surfactant transport around a meniscus within a foam, with the transport rate dependent upon film-to-film tension difference. The model is applied to the case of a five-film device, in which motors are used to compress two peripheral films on one side of a central film and to stretch another two peripheral films on the central film's other side. Moreover, it is considered that large amounts of compression or stretch are imposed on peripheral films, and also that compression or stretch might be imposed at high velocities (relative to a characteristic velocity associated with physico-chemical properties of the foam films themselves). The actual strain that results on elements within each film might differ from the imposed strain, with the instantaneous film length coupled to the actual strain determining the amount of surfactant currently on each film (and hence also the amount of surfactant that has transferred either from or onto films). Quite distinct surfactant transport behaviour is predicted for the stretched film compared with the compressed one. In particular, when a film is stretched sufficiently at high enough velocity, surfactant flux onto it is predicted to become extremely 'plastic', increasing significantly.

A simulation study of in-situ NAPL remediation treatment by using surfactant and foam processes in a military base South Korea

Surfactant and foam processes have been widely used to enhance oil recovery from petroleum-bearing geological formations, and also been recently extended to remediate non-aqueous-phase-liquid (NAPL) contaminants from the shallow subsurface. This study investigates the potential of using surfactant and foam processes for the in-situ remediation treatments within a military base in South Korea: first, optimizing the subsurface permeability and net-to-gross (NTG) values based on history matching and machine-learning algorithm; second, performing simulations that successfully predict the surfactant/foam processes applied in the field; and third, expanding simulations that evaluate different scenarios that might have been used for field tests. The site for the pilot-scale testing, located in the existing fuel-distribution facilities within a military base, has 5 m × 5 m treatment area with 3 m depth, prepared with 3 injection wells and 3 extraction wells. The NAPL of interest is a mixture of various oil compounds showing the average oil saturation of 5%. The overall remediation process applied consists of two major steps: the first is a 20-day injection of surfactant solution (Tween 80) to mobilize the oleic phase trapped by capillary force, and the second is a 3-day injection of foam (i.e., gas and surfactant co-injection) to control the mobility of injected gas and overcome the heterogeneity of the underground system. The major findings of this study are (i) surfactant/foam processes can be an effective means of NAPL recovery from shallow subsurface recovering more than 90% of contaminants, and (ii) computer simulations can be a useful tool for evaluating the in-situ treatment and improving the design of similar operations.

Viscous froth model applied to the motion and topological transformations of two-dimensional bubbles in a channel: three-bubble case

The viscous froth model is used to predict rheological behaviour of a two-dimensional (2D) liquid-foam system. The model incorporates three physical phenomena: the viscous drag force, the pressure difference across foam films and the surface tension acting along them with curvature. In the so-called infinite staircase structure, the system does not undergo topological bubble neighbour-exchange transformations for any imposed driving back pressure. Bubbles then flow out of the channel of transport in the same order in which they entered it. By contrast, in a simple single bubble staircase or so-called lens system, topological transformations do occur for high enough imposed back pressures. The three-bubble case interpolates between the infinite staircase and simple staircase/lens. To determine at which driving pressures and at which velocities topological transformations might occur, and how the bubble areas influence their occurrence, steady-state propagating three-bubble solutions are obtained for a range of bubble sizes and imposed back pressures. As an imposed back pressure increases quasi-statically from equilibrium, complex dynamics are exhibited as the systems undergo either topological transformations, reach saddle-node bifurcation points, or asymptote to a geometrically invariant structure which ceases to change as the back pressure is further increased.

Electro-osmotic and viscous effects upon pressure to drive a droplet through a capillary

A charged oil droplet advancing into a charged capillary is considered, assuming the special case in which charges are opposite and equal. The droplet is surrounded by an aqueous phase that wets the capillary wall, such that a thin film adjacent to the wall is laid down as the droplet advances. Electro-osmotic conjoining pressures contrive to make the film even thinner than in an uncharged case. The pressure drop needed to drive the droplet along is examined. The pressure drop is dominated by capillarity but contains electro-osmotic and viscous corrections. The viscous correction is shown to be remarkably insensitive to the presence of electro-osmotic effects. The electro-osmotic pressure correction is negative, reflecting work done by the electro-osmotic conjoining pressure as film is laid down. The negative electro-osmotic correction to pressure drop can far exceed the positive viscous correction. As a result, in the presence of conjoining pressures, a droplet can be driven along a capillary channel with even less pressure drop than is seen for a static uncharged droplet.

Flushing of Soils Highly Contaminated with Cd Using Various Washing Agents Derived from Sewage Sludge

The suitability of sewage-sludge derived washing agents (SS_WAs) (dissolved organic matter DOM; humic-like substances HLS; soluble humic substances SHS), was assessed for removing Cd from highly contaminated (300 mg/kg) sandy clay loam and clay. The soils were remediated via column flushing at two flow rates, 0.5 and 1.0 mL/min. The stability of the flow velocity (FV) depended on the type of SS_WA and decreased in the following order: DOM > HLS > SHS. Cd was most effectively removed during the first hours of flushing, and the process proceeded with a first-order kinetics. The overall process efficiency was higher at flow rate of 1.0 mL/min than at 0.5 mL/min and ranged from 65.7 (SHS) to 75.5% (DOM) for the sandy clay loam and from 64.7% (SHS) to 67.8% (DOM) for the clay. However, all SS_WAs at both flow rates removed the most mobile Cd fraction (F1) with an efficiency above 90%. Flushing improved soil characteristics in terms of the content of organic matter, humic substances and nutrients. Among all SS_WAs, DOM was the most suitable for remediation of highly Cd-contaminated soils due to high efficiency of Cd removal, the high stability of its FV during flushing and the simple manner of DOM recovery from sewage sludge.

Foam flushing with soil vapor extraction for enhanced treatment of diesel contaminated soils in a one-dimensional column

A limitation of soil vapor extraction (SVE) remediation for total petroleum hydrocarbons (TPHs) in the unsaturated zone is the inability to remove the less volatile petroleum mixture compounds in diesel fuel. SVE combined with foam flushing may have the potential to enhance dissolution or mobilization of soil sorbed diesel and allow mobilized diesel to move to the SVE extraction well. A nonionic surfactant polyoxyethylene (20) sorbitan monooleate (TW80) was selected for generating foam, and a procedure to incorporate the oxidant sodium persulfate (SPS) in generating TW80/SPS foam to deliver chemical oxidation, was also studied. Both TW80 and TW80/SPS foams exhibited 96-98% quality under 8-32 mM of TW80 and 10-50 mM of SPS. The addition of SPS in TW80 solution resulted in elevated ionic content and degradation of TW80, which may reduce the foam stability and have minor effects on foam quality. Through analysis of interrelationships among column flushing experimental parameters, it was shown that the foam quality was reduced to 42-47% when foam flushed through a diesel contaminated soil column. Moreover, the results of column flushing tests operated for 12 h indicated that the effectiveness of removal of diesel by different foams followed the order of TW80 foam (53%) > TW80/SPS foam (37%) >N₂ gas flow alone (3%). It was shown that foam flushing could be an alternative approach, rather than using N₂ gas flow alone (SVE), in enhancing SVE for reducing diesel contamination in the unsaturated zone.

Experimental study of foam propagation and stability in highly permeable porous media under lateral water flow: Diverting groundwater for application to soil remediation

Foam propagation and stability in highly permeable porous media, encountered in soil pollution applications, are still challenging. Here, we investigated the application of foam for blocking the aquifer to divert the flow from a contaminated zone and, therefore, ease the remediation treatments. The main aim was to better understand the critical parameters when the foam is injected into a highly permeable aquifer with high groundwater flow velocity (up to 10 m/day). A decimetric-scale 2D tank experimental setup filled with 1 mm glass beads was used. The front part of the 2D tank was made of transparent glass to photograph the foam flow using the light-reflected method. The water flow was generated horizontally through injection and pumping points on the sides of the tank. The pre-generated foam was injected at the bottom center of the tank. Water streamlines (using dye tracing) and water saturation were investigated using image interpretation. Results show that 100% of the water flow was diverted during the injection of the foam. Foam stability in porous media depends significantly on the horizontal water flow rate. Recirculating water containing the surfactant increases foam stability. The main mechanism of destruction was identified as the dilution of the surfactant in water. However, the head-loss measurements showed that despite foam destruction, the relative permeability of the water phase in the media remained quite low. Injection of foam increases the radius of gas propagation, thanks to foam's high viscosity, compared to a pure gas injection case. These results are new highlights on the efficiency of foam as a blocking agent, showing that it can also serve as a means for gas transport more efficiently in porous media, especially for soil remediation applications.

Microbial Biosurfactant: A New Frontier for Sustainable Agriculture and Pharmaceutical Industries

In the current scenario of changing climatic conditions and the rising global population, there is an urgent need to explore novel, efficient, and economical natural products for the benefit of humankind. Biosurfactants are one of the latest explored microbial synthesized biomolecules that have been used in numerous fields, including agriculture, pharmaceuticals, cosmetics, food processing, and environment-cleaning industries, as a source of raw materials, for the lubrication, wetting, foaming, emulsions formulations, and as stabilizing dispersions. The amphiphilic nature of biosurfactants have shown to be a great advantage, distributing themselves into two immiscible surfaces by reducing the interfacial surface tension and increasing the solubility of hydrophobic compounds. Furthermore, their eco-friendly nature, low or even no toxic nature, durability at higher temperatures, and ability to withstand a wide range of pH fluctuations make microbial surfactants preferable compared to their chemical counterparts. Additionally, biosurfactants can obviate the oxidation flow by eliciting antioxidant properties, antimicrobial and anticancer activities, and drug delivery systems, further broadening their applicability in the food and pharmaceutical industries. Nowadays, biosurfactants have been broadly utilized to improve the soil quality by improving the concentration of trace elements and have either been mixed with pesticides or applied singly on the plant surfaces for plant disease management. In the present review, we summarize the latest research on microbial synthesized biosurfactant compounds, the limiting factors of biosurfactant production, their application in improving soil quality and plant disease management, and their use as antioxidant or antimicrobial compounds in the pharmaceutical industries.

Effect of Sodium Dodecyl Sulfonate on the Foam Stability and Adsorption Configuration of Dodecylamine at the Gas-Liquid Interface

In this study, the effect of sodium dodecyl sulfonate (SDS) on the foam stability of dodecylamine (DDA) and on its adsorption configuration at the gas-liquid interface was investigated. Froth stability experiments, surface tension measurements, time-of-flight secondary-ion mass spectrometry measurements, and molecular dynamics simulation calculations were performed in this investigation. The results revealed that the foam stability of DDA solution was extremely strong, and the addition of SDS could decrease the foam stability when the concentration of DDA was less than a certain value. The decrease in foam stability could be ascribed to several reasons, namely, the big cross-sectional area of SDS at the gas-liquid interface and low adsorption capacity of surfactants at the gas-liquid interface, the high surface tension, the change in the double-layer structure, the small thickness of the gas-liquid interfacial layer, the weak interaction intensity between the head groups of the surfactants and the water molecules, the strong movement ability of the water molecules around the head groups, and the sparse and less upright arrangement configuration of molecules at the gas-liquid interface. These findings can greatly help in solving the strong foam stability problem in DDA flotation and provide a method for reducing foam stability.

Breakdown of similarity solutions: a perturbation approach for front propagation during foam-improved oil recovery

The pressure-driven growth model has been employed to study a propagating foam front in the foam-improved oil recovery process. A first-order solution of the model proves the existence of a concave corner on the front, which initially migrates downwards at a well defined speed that differs from the speed of front material points. At later times, however, it remains unclear how the concave corner moves and interacts with points on the front either side of it, specifically whether material points are extracted from the corner or consumed by it. To address these questions, a second-order solution is proposed, perturbing the aforementioned first-order solution. However, the perturbation is challenging to develop, owing to the nature of the first-order solution, which is a similarity solution that exhibits strong spatio-temporal non-uniformities. The second-order solution indicates that the corner’s vertical velocity component decreases as the front migrates and that points initially extracted from the front are subsequently consumed by it. Overall, the perturbation approach developed herein demonstrates how early-time similarity solutions exhibiting strong spatio-temporal non-uniformities break down as time proceeds.

Porous silsesquioxane cage and porphyrin nanocomposites: sensing and adsorption for heavy metals and anions

A porous silsesquioxane cage/porphyrin nanocomposite was designed as a dual fluorescent probe for the sensing and adsorption of both heavy metal ions and anions.

Electrochemically reversible foam enhanced flushing for PAHs-contaminated soil: Stability of surfactant foam, effects of soil factors, and surfactant reversible recovery

Although surfactant foams enhanced-remediation for PAHs-contaminated soil has been proved to be an effective method, lack of simple/economic surfactant recovery methods from the eluent solutions limit its further remediation application for organic contaminated soil. Here, we prepared a electrochemically reversible ferrocene surfactant FcCH₂N⁺(CH₃)C₁₂H₂₅ (Fc12), then investigated the foaming ability and foam stability of Fc12 under its reduced (active state) and oxidation (inactive state) states and explored the flushing efficiency of reduced Fc12 foam for PAHs-contaminated soil and the recovery efficiency of collected eluent solution. The results showed that the foaming ability and foam stability of reduced Fc12 are greatly higher than those of oxidized Fc12, which is indicative of a well reversibly switchable characteristic of Fc12. The contaminated soil flushing efficiencies of reduced Fc12 for phenanthrene and pyrene were 65.28% and 46.45%. The respective desorption efficiency of phenanthrene and pyrene from collected eluent solutions were calculated to be 74.94% and 72.75% by electrochemical oxidation control, which indicates that Fc12 can be well recovered by simple electrochemical control. This study provides a feasible method for the recovery of surfactants from surfactant-enhanced remediation processes by simply electrochemical control.

Mechanisms that influence the interactions between remediation agent injection and contamination plume variation

To study the interactions between remediation agent injection and hydrodynamic dispersion as well as the expansion of a contamination plume, a two-dimensional sandbox experiment was conducted to simulate and monitor the mixing of a remediation agent in the contamination plume and the expansion of the contamination plume over time. Potassium permanganate is a purple solution, and it represents the remediation agent; Perchloroethylene (PCE), is dyed green and was used to observe the migration and diffusion of the contaminant and the overlap of contamination and the agent-plume. Six quantitative characterization parameters: migration distance, (d_M), migration area, (A_M), initial area ratio, (K_i), spreading speed difference, (SSD), area ratio, (K_A) and migration distance ratio, (K_d), are proposed to comprehensively analyse the influence of the three factors of injection pressure, particle size and viscosity change on the mixing of a remediation agent and the expansion of the contamination plume over time. The results show that these six parameters can effectively characterize the mixing of the remediation agent and the expansion of the contamination plume, where d_M, A_M and K_i characterize the expansion and the other three parameters characterize the mixing. The factors increasing the expansion of the contamination plume follow the order: 40 cm > 30 cm > 20 cm, for injection pressure (water head); coarse sand > medium sand > fine sand for particle size; and no polymer added > added polymer 200 mg/L > added polymer 800 mg/L > added polymer 400 mg/L for viscosity adjustment. The factors that intensify the mixing of the remediation agent in the contamination plume follow the order: 20 cm > 30 cm > 40 cm (water head); coarse sand > medium sand > fine sand; and added polymer 400 mg/L > added polymer 200 mg/L > no polymer added> added polymer 800 mg/L. Finally, conclusions from the TOPSIS method show that under optimal injection conditions, mixing is enhanced without increasing plume expansion and that the optimum injection conditions are injection pressure = 20 cm, use of a coarse sand medium, and added polymer concentration = 400 mg/L.

Effective exploitation of anionic, nonionic, and nanoparticle-stabilized surfactant foams for petroleum hydrocarbon contaminated soil remediation

Contaminated environments posed serious threats to the ecosystems and their living beings. Suitable preventive approaches should be adopted for effective remediation of contaminated environments to remove or lower their health and environmentally-related hazardous aspects. Petroleum or traces of petroleum contamination from oil fields and refineries to exposed soil in the form of gasoline, petrol, diesel, and used motor oil are a rich source of potential damage to the environment. Conventional ways of treatment and management of hydrocarbon are complicated, insufficient, and expensive. Herein, we reviewed a smart approach for the removal of petroleum source contamination from exposed soil using environment-friendly chemical surfactants and nanoscale surfactant system. The host/guest complexes formation of surfactants with the hydrocarbons (hydrophobic contaminants) of soil and water by the encapsulation mechanism of hydrophobes into the (micelles) a self-assembly aggregation of surfactants. Recently, surfactants stabilized by nanoparticles (NPs) acquired more importance and popularity over surfactant alone. The persistence of diverse hydrocarbon-based contaminants and the mechanisms of removal using pristine surfactants or NP-stabilized surfactant foams are discussed with suitable examples. In summary, herein, an effort has been made to present the notable potentialities of pristine surfactants and NP-stabilized surfactant foams to remediate the petroleum hydrocarbon contaminated soil for a greener and sustainable ecosystem.

Performance Evaluation of Novel Polymers for CO2 Foam Enhanced Oil Recovery

The oil recovery from foam flooding mainly depends on the stability of the foam flow in porous media. At severe reservoir conditions, CO2 foam becomes unstable due to water drainage and gas diffusion through the lamella. The petroleum industry is using several foaming agents to produce and stabilize the CO2 foams. These are mainly water-soluble surfactants, CO2 soluble surfactants, nanoparticles, and water-soluble polymers. Addition of a water-soluble polymer in a conventional foam can increase foam stability, viscosity, and oil tolerance. Most of the previous studies utilized partially hydrolyzed polyacrylamide (HPAM) for CO2 foam stabilization. However, the data on CO2 foam stabilization using other polymers is limited.

In this work, CO2 foam stability was assessed using several novel polymers. The foam was generated using alpha olefin sulfonate (AOS) surfactant at a constant concentration. These polymers were mainly acrylamide-based sulfonated polymers that contain thermally stable monomers that increase salt tolerance and thermal stability. The foamability, foam stability, foam diameter and bubble count per unit area of different foaming systems were measured using a dynamic foam analyzer.

The result showed that the addition of polymers enhanced foam stability and reduced liquid drainage. Novel sulfonated polymers showed much better performance compared to the conventional HPAM polymer. Reduction in liquid drainage rate was much higher for sulfonated polymers compared to the conventional HPAM due to viscosity of the foaming solutions. For HPAM, the viscosity of the solution reduced at high temperature in presence of salts whereas sulfonated polymers maintained a high viscosity in the presence of salts that resulted in less liquid drainage and enhanced foam stability. The foam stability was also assessed using foam structure analysis.

This is the first systematic study on the application of sulfonated polymer with varying molecular weight and structure for CO2 foam stabilization. This study helps in understanding the role of polymer molecular structure, molecular weight, and degree of hydrolysis on foam stabilization for CO2 -EOR.

Comparative assessment of a foam-based oxidative treatment of hydrocarbon-contaminated unsaturated and anisotropic soils

In situ delivery of liquid reagents in vadose zone is limited by soil anisotropy and gravity. The enhanced delivery of persulfate (PS) as oxidant, using a new foam-based method (F-PS) was compared at bench-scale to traditional water-based (W-PS) and surfactant solution-based (S-PS) deliveries. The goal was to distribute PS uniformly in coal tar-contaminated unsaturated and anisotropic soils, both in terms of permeability and contamination. Water was the less efficiently delivered fluid because of the hydrophobicity of the contaminated soils. Surfactant enhanced PS-distribution into contaminated zones by reducing interfacial tension and inverting soil wettability. Regardless of coal tar contamination contrasts (0 vs. 5 and 1 vs. 10 g kg _soil^-1) or strong permeability contrasts, PS-solution injection after foam injection led to the most uniform reagents delivery. While PS-concentration varied more than 5-times between zones using W-PS and S-PS methods, it varied less than 1.6-times when the F-PS one was used. Finally, despite unfavorable conditions, the foam-based method did not show any detrimental effect regarding the oxidation of hydrocarbons compared to the W-PS and S-PS methods carried out in ideal conditions. Moreover, hydrocarbon degradation rates were slightly higher when using F-PS than S-PS due to a lower surfactant content in the targeted zone.

A review on the application of chemical surfactant and surfactant foam for remediation of petroleum oil contaminated soil

Soil, exposed to petroleum oil contaminants (in the form of petrol, diesel, gasoline, crude oil, used motor oil), may cause potential damage to the environment, animal and human health. In this review article, mechanisms of the petroleum oil contaminant removal from soil by chemical surfactant systems such as surfactant solution, surfactant foam and nanoparticle stabilized surfactant foams are explained. Laboratory based research works, reported within the last decade on the application of similar systems towards the removal of petroleum oil contaminant from the soil, have been discussed. It is an important fact that the commercial implementation of the chemical surfactant based technology depends on the environmental properties (biodegradability and toxicity) of the surfactants. In recent times, surfactant foam and nanoparticle stabilized surfactant foam are becoming more popular and considered advantageous over the use of surfactant solution alone. However, more research works have to be conducted on nanoparticle stabilized foam. The impact of physicochemical properties of the nanoparticles on soil remediation has to be explored in depth.

Evaluation of a new strategy in the elaboration of culture media to produce surfactin from hemicellulosic corncob liquor

The biosurfactant production is characterized by high costs with substrates, which does not make them sufficiently competitive against synthetic surfactants. The insertion of alternative sources of low cost, especially agro-industrial residue, is an excellent alternative to make this competitiveness viable. An alkaline pretreatment was used to extract the hemicellulose from corncob in order to enhance its C5 fraction, common to vegetable biomasses. The hemicellulosic corncob liquor was used with glucose and mineral salt solution as carbon and nutrients sources in a fermentation process for the growth of Bacillus subtilis. It was performed a 2³ full factorial design to determine the best conditions for the surfactin production in relation to the following response variables: surface tension reduction rate (STRR) and emulsification index (EI₂₄), from which were obtained two optimized bioproducts under specific conditions. The optimized biosurfactants found to be effected presenting a critical micelle concentration of 100 mg.L^-1 and a maximum bioremediation potential of 85.18%, as well as maximum values of 57.38% and 65.30% for STRR and EI₂₄ variables, respectively. Overall results pointed for a successful commercial application for the surfactin produced.

Characteristics and Treatment Methods of Medical Waste Incinerator Fly Ash: A Review

Medical waste incinerator fly ash (MWIFA) is quite different from municipal solid waste incinerator fly ash (MSWIFA) due to its special characteristics of high levels of chlorines, dioxins, carbon constituents, and heavy metals, which may cause irreversible harm to environment and human beings if managed improperly. However, treatment of MWIFA has rarely been specifically mentioned. In this review, various treatment techniques for MSWIFA, and their merits, demerits, applicability, and limitations for MWIFA are reviewed. Natural properties of MWIFA including the high contents of chlorine and carbonaceous matter that might affect the treatment effects of MWIFA are also depicted. Finally, several commendatory and feasible technologies such as roasting, residual carbon melting, the mechanochemical technique, flotation, and microwave treatment are recommended after an overall consideration of the special characteristics of MWIFA, balancing environmental, technological, economical information.

Multistimuli-Responsive Foams Using an Anionic Surfactant

In this work, we report a novel class of a commercially available surfactant which shows a multistimuli-responsive behavior toward foam stability. It comprises three components-a hydrophobe (tristyrylphenol), a temperature-sensitive block (polypropylene oxide, PO), and a pH-sensitive moiety (carboxyl group). The hydrophobicity-hydrophilicity balance of the surfactant can be tuned by changing either the pH or temperature of the system. At or below pH 4, the carboxyl functional group is dominantly protonated, resulting in zero foamability. At higher pH, the surfactant exhibits good foamability and foam stability marked with a fine bubble texture (∼200 μm). Foam destabilization could be achieved rapidly by either lowering the pH or bubbling CO₂ gas. At a fixed pH in the presence of salt, increasing the temperature to 65 °C resulted in rapid defoaming because of the increased hydrophobicity of the PO chain. This stimuli-induced stabilization and destabilization of foam were found to be reversible. We envisage the use of such a multi-responsive foaming system in diverse applications such as foam-enhanced oil recovery and environmental remediation where spatial and temporal control over foam stability is desirable. The low-cost commercial availability of the surfactant further makes it lucrative.

Field demonstration of foam injection to confine a chlorinated solvent source zone

A novel approach using foam to manage hazardous waste was successfully demonstrated under active site conditions. The purpose of the foam was to divert groundwater flow, that would normally enter the source zone area, to reduce dissolved contaminant release to the aquifer. During the demonstration, foam was pre generated and directly injected surrounding the chlorinated solvent source zone. Despite the constraints related to the industrial activities and non-optimal position of the injection points, the applicability and effectiveness of the approach have been highlighted using multiple metrics. A combination of measurements and modelling allowed definition of the foam extent surrounding each injection point, and this appears to be the critical metric to define the success of the foam injection approach. Information on the transport of chlorinated solvents in groundwater showed a decrease of contaminant flux by a factor of 4.4 downstream of the confined area. The effective permeability reduction was maintained over a period of three months. The successful containment provides evidence for consideration of the use of foam to improve traditional flushing techniques, by increasing the targeting of contaminants by remedial agents.

Plasmid-Mediated Bioaugmentation for the Bioremediation of Contaminated Soils

Bioaugmentation, or the inoculation of microorganisms (e.g., bacteria harboring the required catabolic genes) into soil to enhance the rate of contaminant degradation, has great potential for the bioremediation of soils contaminated with organic compounds. Regrettably, cell bioaugmentation frequently turns into an unsuccessful initiative, owing to the rapid decrease of bacterial viability and abundance after inoculation, as well as the limited dispersal of the inoculated bacteria in the soil matrix. Genes that encode the degradation of organic compounds are often located on plasmids and, consequently, they can be spread by horizontal gene transfer into well-established, ecologically competitive, indigenous bacterial populations. Plasmid-mediated bioaugmentation aims to stimulate the spread of contaminant degradation genes among indigenous soil bacteria by the introduction of plasmids, located in donor cells, harboring such genes. But the acquisition of plasmids by recipient cells can affect the host’s fitness, a crucial aspect for the success of plasmid-mediated bioaugmentation. Besides, environmental factors (e.g., soil moisture, temperature, organic matter content) can play important roles for the transfer efficiency of catabolic plasmids, the expression of horizontally acquired genes and, finally, the contaminant degradation activity. For plasmid-mediated bioaugmentation to be reproducible, much more research is needed for a better selection of donor bacterial strains and accompanying plasmids, together with an in-depth understanding of indigenous soil bacterial populations and the environmental conditions that affect plasmid acquisition and the expression and functioning of the catabolic genes of interest.

Surfactant- and Aqueous-Foam-Driven Oil Extraction from Micropatterned Surfaces

Liquid-infused surfaces are rough or patterned surfaces in which a lubricating fluid, such as oil, is infused, which exhibits various original properties (omniphobicity, biofouling, drag reduction). An outer flow in a confined geometry can entrain the oil trapped between the pattern of the surfaces by shearing the oil-water interface and cause the loss of the omniphobic properties of the interface. Starting from the theoretical analysis of Wexler et al. (Shear-driven failure of liquid-infused surfaces. Phys. Rev. Lett. 2015, 114, 168301), where a pure aqueous solution is the outer phase, we extend the predictions by introducing an extraction efficiency parameter α and by accounting for new dynamical effects induced by surfactants and aqueous foams. For surfactant solutions, decreasing the oil-water interfacial tension (γ_ow) not only enhances oil extraction as expected but also modifies the dynamics of the receding oil-water interface through the variations of the receding contact angle (θ) with the capillary number (Ca), which is the ratio between the viscous and the capillary forces at the oil-water interface. For aqueous foams, the extraction dynamics are also influenced by the foam flow: oil is sheared by the thin film between the bubbles and the lubricating layer, which imposes a stronger interfacial shear compared to pure aqueous solutions. In both surfactant and foam cases, the experimental observations show the existence of nonuniform extraction dynamics related to the surfactant-induced instability of a two-fluid shear flow.

Insights on Flow Behavior of Foam in Unsaturated Porous Media during Soil Flushing

  One-dimensional column and two-dimensional tank experiments were carried out to determine (1) the physics of foam flow and propagation of foaming gas, foaming liquid, and foam; (2) the pressure distribution along foam flow and the effect of media permeability, foam flow rate and foam quality on foam injection pressure; and (3) the migration and distribution property of foam flow in homogeneous and heterogeneous sediments. The results demonstrated that: (1) gas and liquid front were formed ahead of the foam flow front, the transport speed order is foaming gas > foaming liquid > foam flowing; (2) injection pressure mainly comes from the resistance to bubble migration. Effect of media permeability on foam injection pressure mainly depends on the physics and behavior of foam flow; (3) foam has a stronger capacity of lateral spreading, besides, foam flow was uniformly distributed across the foam-occupied region, regardless of the heterogeneity of porous media.

Micelles as Soil and Water Decontamination Agents

Contaminated soil and water pose a serious threat to human health and ecosystem. For the treatment of industrial effluents or minimizing their detrimental effects, preventive and remedial approaches must be adopted prior to the occurrence of any severe environmental, health, or safety hazard. Conventional treatment methods of wastewater are insufficient, complicated, and expensive. Therefore, a method that could use environmentally friendly surfactants for the simultaneous removal of both organic and inorganic contaminants from wastewater is deemed a smart approach. Surfactants containing potential donor ligands can coordinate with metal ions, and thus such compounds can be used for the removal of toxic metals and organometallic compounds from aqueous systems. Surfactants form host-guest complexes with the hydrophobic contaminants of water and soil by a mechanism involving the encapsulation of hydrophobes into the self-assembled aggregates (micelles) of surfactants. However, because undefined amounts of surfactants may be released into the aqueous systems, attention must be paid to their own environmental risks as well. Moreover, surfactant remediation methods must be carefully analyzed in the laboratory before field implementation. The use of biosurfactants is the best choice for the removal of water toxins as such surfactants are associated with the characteristics of biodegradability, versatility, recovery, and reuse. This Review is focused on the currently employed surfactant-based soil and wastewater treatment technologies owing to their critical role in the implementation of certain solutions for controlling pollution level, which is necessary to protect human health and ensure the quality standard of the aquatic environment.

Ex-Situ Remediation Technologies for Environmental Pollutants: A Critical Perspective

Pollution and the global health impacts from toxic environmental pollutants are presently of great concern. At present, more than 100 million people are at risk from exposure to a plethora of toxic organic and inorganic pollutants. This review is an exploration of the ex-situ technologies for cleaning-up the contaminated soil, groundwater and air emissions, highlighting their principles, advantages, deficiencies and the knowledge gaps. Challenges and strategies for removing different types of contaminants, mainly heavy metals and priority organic pollutants, are also described.

Evaluation of foam surfactant for foam-flushing technique in remediation of DDT-contaminated soil using data envelopment analysis method

With an aim to select the most appropriate foaming surfactant for remediation of DDT-contaminated soil by foam-flushing technique, the performances of nonionic and anionic surfactant in several aspects were observed in this study. SDS had the best foam static characteristic among the four experimental surfactants. The solubilizing ability for DDT followed the order of Tween80 > TX100 > SDS > Brij35. The adsorption loss of SDS onto soil was the lowest. The order of desorption efficiency for DDT followed as TX-100 > Tween80 > Brij35 > SDS. Based on these experimental investigations, the overall performances of foaming surfactants were evaluated by data envelopment analysis method. The results indicated that SDS was the optimal alternative for remediation of DDT-contaminated soil by foam-flushing technique. This conclusion was reached with the consideration of the cost, foam static characteristic, surfactant adsorption loss, solubilizing ability, and desorption efficiency of surfactant for DDT.

Application of colloidal gas aphron suspensions produced from Sapindus mukorossi for arsenic removal from contaminated soil

Colloidal gas aphron dispersions (CGAs) can be described as a system of microbubbles suspended homogenously in a liquid matrix. This work examines the performance of CGAs in comparison to surfactant solutions for washing low levels of arsenic from an iron rich soil. Sodium Dodecyl Sulfate (SDS) and saponin, a biodegradable surfactant, obtained from Sapindus mukorossi or soapnut fruit were used for generating CGAs and solutions for soil washing. Column washing experiments were performed in down-flow and up flow modes at a soil pH of 5 and 6 using varying concentration of SDS and soapnut solutions as well as CGAs. Soapnut CGAs removed more than 70% arsenic while SDS CGAs removed up to 55% arsenic from the soil columns in the soil pH range of 5-6. CGAs and solutions showed comparable performances in all the cases. CGAs were more economical since it contains 35% of air by volume, thereby requiring less surfactant. Micellar solubilization and low pH of soapnut facilitated arsenic desorption from soil column. FT-IR analysis of effluent suggested that soapnut solution did not interact chemically with arsenic thereby facilitating the recovery of soapnut solution by precipitating the arsenic. Damage to soil was minimal arsenic confirmed by metal dissolution from soil surface and SEM micrograph.

Removal of Hg from Real Polluted Sediments Using Enhanced-EK Decontamination: Verification of Experimental Methods and Batch-Test Preliminary Results

The aim of the research is to apply a biosurfactant-enhanced-EK technology to marine sediment contaminated by high level of Hg. In this work, data from batch-tests using different novel biosurfactant agents were reported. In addition, a dedicated EK bench-scale apparatus was designed and carried out. Technical test was also performed to evaluate the optimal operating features of the EK bench-scale apparatus, assessing the influence of applied voltage and treatment time on the current intensity and electroosmotic flow. Batch experiments were conducted using two sugar esters as biosurfactants and EDTA salt at different concentrations. Results showed that the maximum extraction efficiency was observed for the biosurfactant Olimpicon GC (15%), for which the Hg extraction was shown to be 3.6-fold higher than for 0.2 M EDTA. From technical tests, the observed reduction of current intensity and electroosmotic flow with time highlights the necessity of using conditioning agents during the treatment. Data demonstrates also the good working features of the experimental apparatus. Preliminary results show that EK treatment jointly with biosurfactants such as sugar esters could be a better choice for the remediation of Hg-polluted sediments. The results obtained are of scientific and practical interest and can be used for further researches.

Fast and complete in situ mineralization of contaminated soils using a novel method for superoxide generation

Our remediation technology is by far superior to any previous technologies for soil purification from hydrocarbons and petroleum products.