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.

Enhancing remediation of residual DNAPL in multilayer aquifers: Post-injection of alcohol-surfactant-polymer mixtures.

Although polymer-surfactant injection is an effective remediation technology for multilayer aquifers contaminated by Dense Non-Aqueous Phase Liquids (DNAPL), the existence of residual DNAPL after treatment is inevitable. This study evaluates the efficiency of the post-injection of alcohol-surfactant-polymer (ASP) mixtures containing 1-propanol/1-hexanol, sodium dodecylbenzenesulfonate (SDBS), and xanthan in enhancing remediation of residual DNAPL in layered systems. A range of experimental devices, including batch, rheological measurements, centimetric 1D column, and decametric 2D tank experiments, were employed. Batch experiments revealed that the inclusion of 1-hexanol swelled the DNAPL volume due to alcohol partitioning. Conversely, with only 1-propanol present in the alcohol-surfactant (AS) mixture, DNAPL dissolved in the aqueous phase. The co-presence of 1-hexanol along with 1-propanol in AS mixture favored 1-propanol's partitioning into the DNAPL phase. Column experiments, following primary xanthan-SDBS (XS) injections, demonstrated that ASP mixtures with 1-hexanol (regardless of presence of 1-propanol) underwent a mobilization mechanism. DNAPL appeared in the effluent as an organic phase after the post-injection of 0.3 pore-volumes (PV), by a reduction trend in its density. In contrast, mixtures with solely 1-propanol exhibited a solubilization mechanism, with DNAPL dissolving in the aqueous phase and emerging in the effluent after approximately 1 PV. 2D tank experiments visualized mobilization and solubilization mechanisms in multilayered systems. Post-injection of the ASP mixture with solely 1-propanol led to DNAPL solubilization, demonstrated by a dark zone of varied DNAPL concentrations, followed by a clearer white zone indicating significant DNAPL dissolution. Injecting ASP mixture containing both 1-propanol and 1-hexanol mobilized swollen DNAPL ganglia throughout layers, with these droplets coalescing and migrating to the recovery point. The darkness of mobilized droplets was faded as more DNAPL was recovered. The solubilization ASP mixture enhanced the recovery factor by 0.02 while the mobilization ASP mixture led to a 0.08 increase in the recovery factor.

Remediation of multilayer soils contaminated by heavy chlorinated solvents using biopolymer-surfactant mixtures: Two-dimensional flow experiments and simulations.

To assess the efficiency of remediating dense non-aqueous phase liquids (DNAPLs), here heavy chlorinated solvents, through injection of xanthan solutions with or without surfactant (sodium dodecylbenzenesulfonate: SDBS), we conducted a comprehensive investigation involving rheological measurements, column (1D) and two-dimensional (2D) sandbox experiments, as well as numerical simulations on two-layers sand packs. Sand packs with grain sizes of 0.2-0.3 mm and 0.4-0.6 mm, chosen to represent the low and high permeable soil layers respectively, were selected to be representative of real polluted field. The rheological analysis of xanthan solutions showed that the addition of SDBS to the solution reduced its viscosity due to repulsive electrostatic forces and hydrophobic interactions between the molecules while preserving its shear-thinning behavior. Results of two-phase flow experiments depicted that adding SDBS to the polymer solution led to a reduced differential pressure along the soil and improvements of the DNAPL recovery factor of approximately 0.15 and 0.07 in 1D homogeneous and 2D layered systems, respectively. 2D experiments revealed that the displacement of DNAPL in multilayer zones was affected by permeability difference and density contrast in a heterogeneous soil. Simulation of multiphase flow in a multilayered system was performed by incorporating non-Newtonian properties and coupling the continuity equation with generalized Darcy's law. The results of modeling and experiments are very consistent. Numerical simulations showed that for an unconfined soil, the recovery of DNAPL by injection of xanthan solution can be reduced for more than 50%. In a large 2D experimental system, the combination of injecting xanthan with blocking the contaminated zone led to a promising remediation of DNAPL-contaminated layered zones, with a recovery of 0.87.

The effects of water table fluctuation on LNAPL deposit in highly permeable porous media: A coupled numerical and experimental study.

Light Non-Aqueous Phase Liquid (LNAPL) flow on the water table is highly mobile and is sensitive to the fluctuation of groundwater. This process is highly complex and involves the migration of three immiscible phases (i.e. water, LNAPL and air) which need the explicit definition of multiple parameters. A coupled experimental and numerical simulation methodology is performed by using Time Domain Reflectrometer (TDR) and multiphase simulation of a controlled environment to mimic the water table fluctuation and its effect on the LNAPL residual saturation. TDR probes are installed in different locations of a 2D tank (i.e. a cuboid box with relatively low off-plane thickness) and the bulk permittivity of the phases are measured through artificially imposed boundary conditions. The bulk permittivity is then translated into saturation of the three different phases. The translated residual saturations along with the previously measured porous media properties (e.g. porosity and saturated permeability) are then inserted into the numerical simulator (i.e. COMSOL Multiphysics®) and the migration of the three phase in porous media is simulated. The numerical exponents and entry pressures needed for the simulation of the multiphase flow are estimated using the temporal experimental values. The exponents of water LNAPL relative permeability were estimated to be around 2 while the exponents gas LNAPL relative permeability were estimated to be closer to 3. The results, simulated with the optimized parameters, are then evaluated with pictures taken from the transparent face of the 2D tank different stages of the experiment. The temporal evolution of different phase saturation has been compared and validated between the experimental results obtained and interpreted by the TDR probe measurements and the simulations. The relative error stays in the 5 % confidence level for most reported points and only in the highly dynamic flow time steps the error reaches around 12% which are discussed in the text and is accepted due to the highly nonlinear nature of the problem.

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.

Relating mercury occurrence in soil gases at establishments hosting children to historical mercury-using activities in Paris, France.

Volatile pollutants from former industrial sites can degrade the buildings' indoor air quality that were built after the industrial activities. Since 2010, environmental assessments have been conducted in French establishments hosting sensitive populations identified as being on or near potentially contaminated former industrial sites. These projects are based on historical studies traditionally carried out as part of managing contaminated sites, to determine which substances should be analyzed. They pinpoint former activities likely to have stored or used pollutants. We show that the historical information collected is not effective in targeting sites with increased probability of mercury being present in soil gases. Environmental history has demonstrated the existence of large-scale artisanal contamination, both prior to and concomitant with the industrial era. Classic historical studies would not take into account artisanal activities, which are less documented than industrial activities. We carried out additional research for three schools located in three different Parisian districts. Although information on activities which could have emitted mercury was relatively imprecise (in terms of location, type and duration of activities) and uncertainties exist about the completeness of the archival documents available, our investigations identified several mercury-using activities that had not been identified during the classic historical study. However, we have shown that the number of activities identified does not provide information on how mercury has affected soil gas. Consequently, although a more extensive historical research improves knowledge about the presence of potential mercury-using activities, our study shows that a systematic analysis of mercury as part of the assessment of establishments hosting sensitive populations remains relevant. This approach should be applied to other cities around the world.

"You helped me keep my head above water"-experience of bereavement research after loss of a loved one in the ICU: insights from the ARREVE study.

PURPOSE: Bereavement research has helped to improve end-of-life practices in the ICU. However, few studies have explored bereaved relatives experience of research participation in this context. We aimed to explore the experience of bereaved relatives' participation in the ARREVE study which included three telephone follow-up calls to complete several quantitative tools. METHODS: Volunteer relatives who participated in the 12-month follow-up call completed a questionnaire about research participation that included ten open-ended questions so that respondents could use their own words and thoughts. These open-ended questions were analyzed using qualitative analysis that examines themes within the data. RESULTS: 175/311 relatives completed the questionnaire. Three themes were derived from the thematic analysis: (1) struggling: reactivation of emotional distress associated with the ICU experience and the loss is frequent, specifically during the 1st follow-up call. (2) Resilience: as time goes by, research participation becomes increasingly positive. The calls are a help both in giving meaning to the relatives' experience and in accepting the loss. (3) Recognition: research calls can compensate for the absence of support during bereavement. CONCLUSION: Although some emotional difficulties must be acknowledged, bereavement research is overall associated with benefits, by facilitating emotional adjustments, meaning-making and resilience. Lack of support and social isolation during bereavement are frequent experiences, revealing that support strategies for bereaved relatives should be developed after the loss of a loved one in the ICU.

Correction to: Terminal weaning or immediate extubation for withdrawing mechanical ventilation in critically ill patients (the ARREVE observational study).

Correction to: Intensive Care Med (2017) DOI 10.1007/s00134-017-4891-0.

Terminal weaning or immediate extubation for withdrawing mechanical ventilation in critically ill patients (the ARREVE observational study).

PURPOSE: The relative merits of immediate extubation versus terminal weaning for mechanical ventilation withdrawal are controversial, particularly regarding the experience of patients and relatives. METHODS: This prospective observational multicentre study (ARREVE) was done in 43 French ICUs to compare terminal weaning and immediate extubation, as chosen by the ICU team. Terminal weaning was a gradual decrease in the amount of ventilatory assistance and immediate extubation was extubation without any previous decrease in ventilatory assistance. The primary outcome was posttraumatic stress symptoms (Impact of Event Scale Revised, IES-R) in relatives 3 months after the death. Secondary outcomes were complicated grief, anxiety, and depression symptoms in relatives; comfort of patients during the dying process; and job strain in staff. RESULTS: We enrolled 212 (85.5%) relatives of 248 patients with terminal weaning and 190 relatives (90.5%) of 210 patients with immediate extubation. Immediate extubation was associated with airway obstruction and a higher mean Behavioural Pain Scale score compared to terminal weaning. In relatives, IES-R scores after 3 months were not significantly different between groups (31.9 ± 18.1 versus 30.5 ± 16.2, respectively; adjusted difference, -1.9; 95% confidence interval, -5.9 to 2.1; p = 0.36); neither were there any differences in complicated grief, anxiety, or depression scores. Assistant nurses had lower job strain scores in the immediate extubation group. CONCLUSIONS: Compared to terminal weaning, immediate extubation was not associated with differences in psychological welfare of relatives when each method constituted standard practice in the ICU where it was applied. Patients had more airway obstruction and gasps with immediate extubation. TRIAL REGISTRATION: ClinicalTrials.gov identifier: NCT01818895.

ICU physicians' and nurses' perceptions of terminal extubation and terminal weaning: a self-questionnaire study.

PURPOSE: Terminal extubation (TE) and terminal weaning (TW) are the methods available for withdrawing mechanical ventilation. Perceptions of TE and TW by intensive care unit (ICU) staff may influence bedside practices and the feasibility of studies comparing these methods. METHODS: From January to June 2013, 5 nurses and 5 physicians in each of 46 (out of 70, 65.7 %) French ICUs completed an anonymous self-questionnaire. Clusters of staff members defined by perceptions of TE and TW were identified by exploratory analysis. Denominators for computing percentages were total numbers of responses to each item; cases with missing data were excluded for the relevant item. RESULTS: Of the 451 (98 %) participants (225 nurses and 226 physicians), 37 (8.4 %) had never or almost never performed TW and 138 (31.3 %) had never or almost never performed TE. A moral difference between TW and TE was perceived by 205 (45.8 %) participants. The exploratory analysis identified three clusters defined by personal beliefs about TW and TE: 21.2 % of participants preferred TW, 18.1 % preferred TE, and 60.7 % had no preference. A preference for TW seemed chiefly related to unfavorable perceptions or insufficient knowledge of TE. Staff members who preferred TE and those with no preference perceived TE as providing a more natural dying process with less ambiguity. CONCLUSION: Nearly two-fifths of ICU nurses and physicians in participating ICUs preferred TW or TE. This finding suggests both a need for shared decision-making and training before performing TE or TW and a high risk of poor compliance with randomly allocated TW or TE.

Strategy for recruitment and factors associated with motivation and satisfaction in a randomized trial with 210 healthy volunteers without financial compensation.

BACKGROUND: The aim was to describe a strategy for recruitment of healthy volunteers (HV) to a randomized trial that assessed the efficacy of different telephone techniques to assist HV in performing cardiac massage for vital emergency. Participation in the randomized trial was not financially compensated, however HV were offered emergency first-aid training. We also studied factors associated with HV motivation and satisfaction regarding participation in the trial. METHODS: Strategy for recruitment of 210 HV aged 18 to 60 years was based on: (1) the updated records of all telephone number since January 2000 of HV registered in the Rouen Clinical Investigation Centre HV database, (2) a communication campaign for the general public focussing on posters and media advertisements. Data on the recruitment, socio-demographics, motivation and satisfaction of the 210 HV were collected by anonymous self-administered questionnaire. RESULTS: Of the 210 HV included, 63.3% (n = 133) were recruited from the HV database and 36.7% (n = 77) by the communication campaign. On the one hand, the HV database enabled screening of 1315 HV, 54.8% (n = 721) of whom were reached by phone, 55.2% (n = 398) of these latter accepted to participate in the study and 10.1% of the initial screening (n = 133) were finally included. One the other hand, for the 77 HV not recruited from the HV database, word-of-mouth (56.1%) was the main means of recruitment. The male/female ratio of the 210 HV was 0.5 and mean age 43.5 years (Standard Deviation = 12.4). The main motivations given for participating in the trial were to support research (87.6%) and receive emergency first-aid training (85.7%). Overall satisfaction with the welcome process was significantly higher for older HV (46-60 years) (adjusted odds ratio (AOR): 3.44; 95% confidence interval (95% CI): 1.48-7.99), and for HV in management jobs (AOR: 4.26; 95% CI: 1.22-14.87). Satisfaction with protocol management was higher for women (AOR: 2.33; 95% CI: 1.18-4.60) and for older HV (46-60 years) (AOR: 4.76; 95% CI: 1.97-11.52). CONCLUSIONS: Recruitment of non-compensated HV required broad screening with a primary HV database alongside word-of-mouth communication which seemed more efficient than media advertising. To enhance HV recruitment to randomized trials without financial compensation it seems crucial to provide them not only with a direct interest but also to ensure their satisfaction.