Surfactant foam injection for remediation of diesel-contaminated soil: A comprehensive study on the role of co-surfactant in foaming formulation enhancement.

Aqueous foam injection is a promising technique for in-situ remediation of soil and aquifers contaminated by petroleum products. However, the application efficiency is strongly hindered by foam's instability upon contact with hydrocarbons. Addressing this, we propose a new binary surfactant mixture of Sodium Dodecyl Sulfate (SDS) and Cocamidopropyl Hydroxysultaine (CAHS). This study investigates CAHS's role as a co-surfactant in enhancing foam stability against antifoaming diesel oil under static and dynamic conditions. Using a dynamic foam analyzer (DFA-100), we assessed static foam's stability by monitoring decay profiles and bubble growth over time. The results revealed that the highest stability can be reached at a CAHS to SDS ratio of 50:50, increasing the half-life of the foam by 7.7 times. Remarkably, our analyses at bulk and bubble scales also elucidated the mechanisms behind the enhanced foam stability of the proposed binary surfactant mixture in the absence and presence of diesel. Additionally, in a 1D sand column, the SDS-CAHS mixture demonstrated more than twofold improvement of the Resistance Factor, attributed to the better survival of the lamellae due to the reduced rate of their destruction. This formulation also yielded a recovery improvement of >10 % compared to SDS foam. The significant improvements in stability and performance of the SDS-CAHS (50:50) mixture were credited to a robust pseudo-emulsion film formation, creating a higher oil entry barrier. This reinforcement and the surfactant molecules' synergistic interactions at the gas-liquid-oil interface significantly contributed to the overall effectiveness.

Impact of both desiccation and exposure to an emergent skin pathogen on transepidermal water exchange in the palmate newt Lissotriton helveticus .

Amphibians are the vertebrate group most affected by global change. Their highly permeable skin is involved in maintaining homeostasis (e.g. water and electrolyte equilibrium), which makes them particularly vulnerable to climate warming and skin pathogens. This study focused on the impacts of both desiccation (as a potential consequence of climate warming) and exposure to Batrachochytrium dendrobatidis (Bd), an emergent skin pathogen of amphibians. Bd causes chytridiomycosis, a lethal skin disease of amphibians, and is responsible for mass mortality events in several regions of the world. Because Bd colonizes the superficial layers of the epidermis, it is assumed to affect water transfer across the skin. We investigated the behavioural postures of the palmate newt Lissotriton helveticus expressed in response to desiccation and their influence on transepidermal water loss (TEWL) rate. We also investigated the effects of repeated 24 h exposure to Bd (i.e. every 4 d for 16 d) on the TEWL and ventral water absorption (VWA) rates of these newts. Our results suggest an efficient behavioural water-conserving mechanism, i.e. an 'S'-shaped posture associated with a restricted activity rate, not affected by repeated exposure to Bd. Similarly, TEWL was not significantly affected in exposed newts. VWA was significantly reduced after just 24 h exposure to Bd without modification until the end of the experiments. Our results suggest that Bd could rapidly inhibit rehydration of L. helveticus through fungal toxins and disrupt an essential function for survival.

Aquifer recharge by stormwater infiltration basins: Hydrological and vadose zone characteristics control the impacts of basins on groundwater chemistry and microbiology.

Stormwater infiltration systems (SIS) are designed to collect and infiltrate urban stormwater runoff into the ground for flood risk mitigation and artificial aquifer recharge. Many studies have demonstrated that infiltration practices can impact groundwater chemistry and microbiology. However, quantitative assessments of the hydrogeological factors responsible of these changes remain scarce. Thus, the present study aimed to quantitatively test whether changes of groundwater chemistry and microbiology induced by SIS were linked to two factors associated with vadose zone properties (vadose zone thickness, water transit time from surface to groundwater) and one factor associated with groundwater recharge rate (assessed by groundwater table elevation during rain events). To evaluate changes in chemistry (NO3-, PO43- and dissolved organic carbon concentrations), groundwater samples were collected in wells located in SIS-impacted and non-SIS-impacted zones during experimental periods of 10 days. During the same periods, clay beads were incubated in the same wells to measure changes of groundwater microbial biofilms (microbial biomass, dehydrogenase and hydrolytic activities) induced by SIS. Results showed that changes in PO43- supplied to groundwater during stormwater infiltration was negatively correlated with vadose zone thickness. A short water transit time from surface to groundwater increased dissolved organic carbon concentrations in the aquifer which, in turn, increased biofilm biomasses in groundwater. The groundwater recharge rate during rain events (assessed by groundwater table elevation) diluted NO3- concentrations in the aquifer but also influenced the changes of biofilm activities induced by SIS. Groundwater recharge rate during rain events probably increased the fluxes of water and dissolved organic carbon in groundwater, stimulating the activity of microbial biofilms. Overall, the present study is the first to quantify conjointly several factors and processes (water transfer, dilution, solute fluxes) that could explain the impact of stormwater infiltration on chemistry and/or microbiology in groundwater.

3D modelling of solute transport and mixing during managed aquifer recharge with an infiltration basin.

Artificial basins are used to recharge groundwater by many municipalities to improve the sustainability of storm water management. Despite its increasing operational implementation, artificial recharge still raises numerous questions related to its impact on groundwater quality. In this paper, a 3D numerical model of MAR basin/aquifer system was implemented in order to simulate the fate of water and pollutants. It was used to illustrate the complex distribution in time and space of a tracer contaminant injected in the basin. The model was based on a well instrumented storm water infiltration basin located in Chassieu (Lyon area, France). The well-known Richards model was used to simulate the water flow in the saturated and unsaturated zone of the study site. The transfer of solutes in the basin/aquifer system was modelled by the advection-dispersion-equation (ADE). The model was calibrated during a rain event using hydraulic head and electric conductivity data from a set of piezometers located around the basin. The flow model was validated on a one month period of basin operation presenting several rain events. The model was then used to simulate the fate of a solute pollutant considered as a tracer during a high intensity rain event. This simplified test case illustrated the mechanism of capillary trapping in the vadose zone and the effect of sampling point location on concentration measurements. Three main results were obtained: (1) capillary trapping promoted a retention of up to 20% of the injected tracer in the vadose zone, (2) 0 to 24% of the injected solute concentration could be recovered depending on the piezometer location, (3) the averaged concentration decreased by 50% if the measuring device is lowered by 5 m under the water table. These results were strongly site and event dependant but observed trends should be considered while discussing punctual water quality measurements used to monitor MAR systems. It also allowed to suggest some guidelines for sampling point positioning.

Assessment of spatial representativity of X-ray tomography to study Vertical Flow Treatment wetlands.

French Vertical Flow (VF) treatment wetlands receive raw wastewater and provide simultaneous sludge and wastewater treatment. For proper sludge handling, the treatment wetland must be designed adequately and specific operational conditions must be maintained. When these conditions are not met, accumulation of biosolids may lead to clogging. Filtration in French VF Treatment wetlands is governed by mechanisms at the pore-scale. They must be better understood to predict reliably biosolid accumulation. X-ray Computed Tomography (Xray-CT) is a promising technique to characterize in detail the morphology of the filtering media in treatment wetlands. In order to set a solid basis for the use of Xray-CT, the spatial representativity of measurements must be assessed. This issue is addressed in this study by successively analyzing spatial properties at the filter scale using Frequency Domain Electromagnetic Measurements (FDEMs), and at the pore scale using Xray-CT. A map of the electric conductivity at the surface of a French VF Treatment wetland is obtained by FDEM that indicates a homogeneous distribution of biosolids to which electrical conductivity is highly correlated. Different morphological properties were computed from Xray-CT after phase segmentation: phase volume fraction profiles, Specific Surface Area profiles and pore size distributions. Samples show several similarities of pore scale properties obtained by Xray-CT independently of the sampling region and especially the same vertical gradients. FDEM measurements and Xray-CT analysis are in agreement to indicate a good influent distribution at the surface of a full-scale mature French VF Treatment wetland. A criterion to define the limits of the deposit layer and gravel layer is introduced. This division allows to compare layers independently. Finally, a 2D-REV analysis suggests that the selected sample diameter of 5 cm is large enough to be representative of the heterogeneous distribution of phases at the pore-scale as long as no Phragmites are present.

Characterization and comparison of groundwater quality and redox conditions in the Arakawa Lowland and Musashino Upland, southern Kanto Plain of the Tokyo Metropolitan area, Japan.

Groundwater is essential for the Earth biosphere but is often contaminated by harmful chemical compounds due to both anthropogenic and natural causes. A key factor controlling the fate of harmful chemicals in groundwater is the reduction/oxidation (redox) conditions. The formation factors for the groundwater redox conditions are insufficiently understood. In this study, long-term groundwater quality beneath one of the world megacities was monitored and evaluated. We measured and compared hydrogeochemical conditions including groundwater quality (35 chemical parameters) and redox conditions of five aquifers in the Arakawa Lowland and Musashino Upland, southern Kanto Plain of the Tokyo Metropolitan area, Japan. Monitoring results suggested the following: The main origin of groundwater is precipitation in both the Lowland and Upland areas. The three aquifers in the Arakawa Lowland are likely fully separated, with one unconfined and two confined aquifers under iron reducing and methanogenic conditions, respectively. Oppositely, in the Musashino Upland, the water masses in the two aquifers are likely partly connected, under aerobic conditions, and undergoing the same groundwater recharge and flow processes under similar hydrogeological conditions. The different groundwater redox conditions observed are likely caused by the very different groundwater residence times for the Arakawa Lowland and Musashino Upland.

Assessment of X-ray Computed Tomography to characterize filtering media from Vertical Flow Treatment Wetlands at the pore scale.

Computed Tomography is a non-destructive technique often used in earth sciences for the description of porous media at the pore scale. This paper shows the feasibility of this technique to obtain 3D descriptions of filtering media in Vertical Flow Treatment Wetlands (VFTW). Three different samples from two full-scale VFTW were scanned. The samples vary in moisture content and gravel size distribution. The 3D images show three characteristic phases of unsaturated media: voids, fouling material and gravel. The gray contrast level is good enough to perform phase segmentation successfully using region growing algorithms. In this study the results from segmentation are used (i) to compute profiles of phase volume fraction and specific surface at high resolution, (ii) to observe 3D distribution of isolated elements, (iii) and to draw the void's skeleton and to perform a percolation pathway study. This method highlights the presence of a transition zone between the deposit cake and the dense gravel layer. In this zone, mechanical interactions between gravels and filtered solids tend to promote a heterogeneous layer of gravel, fouling material and open porosity. The presence of isolated gravels in the deposit layer is clearly evidenced. The effect of drying to enhance the contrast between phases has been analyzed for one sample by a direct comparison of images obtained before and after drying. The resulting opening of the void phase tends to increase significantly the void-fouling material specific surface and the number and size of percolating pathways computed as the skeleton of the void phase. Finally, a first analysis of filtration processes is proposed. It consists in analyzing the percolation pathways for a class of void size by applying the distance map and skeleton concepts to the void phase.

Alternative solutions for the bio-denitrification of landfill leachates using pine bark and compost.

Nitrified leachate may still require an additional bio-denitrification step, which occurs with the addition of often-expensive chemicals as carbon source. This study explores the applicability of low-cost carbon sources such as garden refuse compost and pine bark for the denitrification of high strength landfill leachates. The overall objective is to assess efficiency, kinetics and performance of the substrates in the removal of high nitrate concentrations. Garden refuse and pine bark are currently disposed of in general waste landfills in South Africa, separated from the main waste stream. A secondary objective is to assess the feasibility of re-using green waste as by-product of an integrated waste management system. Denitrification processes in fixed bed reactors were simulated at laboratory scale using anaerobic batch tests and leaching columns packed with immature compost and pine bark. Biologically treated leachate from a Sequencing Batch Reactor (SBR) with nitrate concentrations of 350, 700 and 1100 mgN/l were used for the trials. Preliminary results suggest that, passed the acclimatization step (40 days for both substrates), full denitrification is achieved in 10-20 days for the pine bark and 30-40 days for the compost.

Liquid and gas permeabilities of unsaturated municipal solid waste under compression.

A novel set of experimental apparatus was designed and constructed to study the changes in the fluid-flow properties of municipal solid waste (MSW) related to the physical evolution of its structure under compression. The vertical liquid and gas permeabilities of MSW samples were measured in a laboratory-constructed cell termed an oedopermeameter. Another original device, a gas pycnometer, was employed to assess the volumetric gas content of the porous medium. Finally, the horizontal gas permeability of the compressed MSW sample was measured using another laboratory-constructed cell called a transmissivimeter. The results made it possible to characterise the intrinsic gas permeability as a function of porosity. Additionally, gas permeability measurements of samples with different liquid contents allowed the derivation of gas permeability correlations as functions of the physical parameters of the medium. A unique relationship was found between the gas permeability and the volumetric gas content.

Characterisation of the physico-mechanical parameters of MSW.

Following the basics of soil mechanics, the physico-mechanical behaviour of municipal solid waste (MSW) can be defined through constitutive relationships which are expressed with respect to three physical parameters: the dry density, the porosity and the gravimetric liquid content. In order to take into account the complexity of MSW (grain size distribution and heterogeneity larger than for conventional soils), a special oedometer was designed to carry out laboratory experiments. This apparatus allowed a coupled measurement of physical parameters for MSW settlement under stress. The studied material was a typical sample of fresh MSW from a French landfill. The relevant physical parameters were measured using a gas pycnometer. Moreover, the compressibility of MSW was studied with respect to the initial gravimetric liquid content. Proposed methods to assess the set of three physical parameters allow a relevant understanding of the physico-mechanical behaviour of MSW under compression, specifically, the evolution of the limit liquid content. The present method can be extended to any type of MSW.

Effect of pine bark and compost on the biological denitrification process of non-hazardous landfill leachate: focus on the microbiology.

In an attempt to optimize the cost-efficiency of landfill leachate treatment by biological denitrification process, our study focused on finding low-cost alternatives to traditional expensive chemicals such as composted garden refuse and pine bark, which are both available in large amount in South African landfill sites. The overall objective was to assess the behaviour of the bacterial community in relation to each substrate while treating high strength landfill leachates. Denitrification processes in fixed bed reactors were simulated at laboratory scale using anaerobic batch tests with immature compost and pine bark. High strength leachate was simulated using a solution of water and nitrate at a concentration of 500 mg l(-1). Results suggest that pine bark released large amounts of phenolic compounds and hydroxylated benzene rings, which both can delay the acclimatization time and inhibit the biological denitrification (only 30% efficiency). Furthermore, presence of potential pathogens like Enterobacter and Pantoea agglomerans prevents the applicability of the pine bark in full-scale operations. On the other hand, lightly composted garden refuse (CGR) offered an adequate substrate for the formation of a biofilm necessary to complete the denitrification process (total nitrate removal observed within 7 days). CGR further contributed to a rapid establishment of an active consortium of denitrifiers including Acinetobacter, Rhizobium, Thermomonas, Rheinheimera, Phaeospirillum and Flavobacterium. Clearly the original composition, nature, carbon to nitrogen ratio (C/N) and degree of maturity and stability of the substrates play a key role in the denitrification process, impacting directly on the development of the bacterial population and, therefore, on the long-term removal efficiency.