SSS7.5

In the last decade, per- and polyfluoroalkyl substances (PFAS) have been added to the list of pollutants of concern because they are persistent and potentially carcinogenic and have a high bioaccumulation rate. PFASs are detected in numerous environmental matrices, confirming their high persistence and mobility in the environment. In addition, the chemical structure of PFAS and their reactivity pose a technological challenge for remediation efforts. SCENARIOS is an H2020 research and innovation project involving 19 partners from 11 countries. The main objective is to fill knowledge gaps and achieve breakthrough TRL advances in toxicological assessment, congener detection and remediation of PFAS with unprecedented energy balance and virtually no external chemical additives, supporting EU countries in decision-making related to environmental safety and human health. The project will evaluate and develop state-of-the-art technologies and strategies for the detection, quantification, control, and elimination of PFAS in soil, vadose zone, and water by targeting outcomes within the 4 remediation quadrants: In-situ Soil, In-situ Water, Ex-situ Soil, and Ex-situ Water. Likewise, the project is developing a set of solutions to control pollution and remediate PFAS contaminated soils (agricultural and industrial) and groundwater. All these solutions will comply with the principle of green chemistry, zeroenergy, sustainability and circular economy. This paper presents the project progress in PFAS detection, monitoring and remediation.

How to cite: Dondero, F. and the SCENARIOS TEAM: PFAS as a test bed for the EU Green Deal zero pollution ambition from refractory and mobile organic chemicals: technologies, solutions and strategies developed under the H2020 project SCENARIOS, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-13566, https://doi.org/10.5194/egusphere-egu22-13566, 2022.

The PROMISCES project aims to understand the origins, routes and fates of industrial persistent, mobile and potentially toxic pollutants (iPM(T)s), including per- and polyfluoroalkyl substances (PFAS). These substances, also called “forever chemicals”, can be harmful to the environment, human health and circular economy resources.

PROMISCES will develop, test and demonstrate, new technologies and innovations to prevent, monitor and remediate iPM(T)s in the soil-sediment-water system under real-life conditions in the field. In this way, PROMISCES will establish more cost-effective, sustainable and ecological technologies for remediating PFAS and iPM(T)s.

The project will support the European Green Deal goals and sustainability roadmap of urbanised areas by reducing the environmental impacts on waters (surface and groundwater, urban runoff, drinking waters, wastewater, landfill leachate), soils (contaminated sites, brownfields) and dredged sediments (river, seaports) and of nutrient and material recovery (from sewage sludge to recovered fertilisers, dredged sediments to valorised materials, reclaimed water to crops).

To pursue this objective, PROMISCES is centered around seven representative case studies in different European regions linked with challenging chemical pollution, including locations in Spain, Italy, Bulgaria, France, Germany and the Danube river basin between Vienna and Budapest.

This Horizon2020-Green Deal project will address key technological challenges while also developing recommendations for implementing relevant EU plans - such as the Zero Pollution Action Plan, the Circular Economy Action Plan and the EU chemicals strategy for sustainability - and EU policy directives, such as the Sewage Sludge Directive and the Water Framework Directive.

How to cite: Lions, J., Miehe, U., Zhiteneva, V., Togola, A., Groot, H., Bakker, M., van Hullebusch, E. D., Dulio, V., Zjip, M., Heine, N., Track, T., Sperlich, A., Zessner, M., Bosch, C., Fatone, F., Colombano, S., Fernandez-Rojo, L., and Negrel, P.: Establishing a zero-pollution circular economy: an overview of the Horizon2020-Green Deal project PROMISCES, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3821, https://doi.org/10.5194/egusphere-egu22-3821, 2022.

A growing body of site investigations have demonstrated that vadose zones serve as significant long-term sources of PFAS to groundwater. Quantifying PFAS leaching in the vadose zone and mass discharge to groundwater is therefore critical for characterizing, managing, and mitigating long-term contamination risks. Recently, mathematical models representing the PFAS-specific transport and retention processes, including surfactant-induced flow, and rate-limited, nonlinear adsorption at solid-water and air-water interfaces, have been developed. While these advanced models provide fundamental insights into the primary processes controlling the long-term retention of PFAS, they are less suitable for screening-type applications due to significant computational cost and the requirement for detailed input parameters. To address this knowledge gap, we develop a simplified model by assuming steady-state infiltration and linear solid-phase and air-water interfacial adsorption; a two-domain model is used to represent kinetic solid-phase adsorption. We derive novel analytical solutions for the simplified model allowing for arbitrary initial conditions. The newly derived analytical solutions are then validated by application to miscible-displacement experiments under a wide range of conditions and by comparisons to a state-of-the-art comprehensive model under both experimental and field conditions applicable to PFAS-contamination sites. Overall, the simplified analytical model provides an efficient and accurate screening-type tool for quantifying long-term PFAS leaching in the vadose zone.

How to cite: Guo, B., Zeng, J., Brusseau, M., and Zhang, Y.: A screening model for quantifying PFAS leaching in the vadose zone and mass discharge to groundwater, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6328, https://doi.org/10.5194/egusphere-egu22-6328, 2022.

The topic of per- and polyfluoroalkyl substances (PFASs) is a late-breaking issue due to its high environmental relevance (toxicity, persistence and bio accumulation) and due to the detection of PFASs as contaminants in various environmental compartments including groundwater, surface water and soil. PFASs enter the environment for instance through industrial, agricultural, and house-hold activities. Restricted PFASs like PFOA by the Stockholm Convention 2019 have often been replaced by molecules of the same family with shorter carbon chains, and nowadays around 4000 different molecules of PFASs can be found in the environment. Although PFASs have been manufactured since the 1940s, the fate of these chemicals in soils was not studied until the late 1990s.
These studies have shown that the retention of PFASs in soils depends on various factors such as the PFASs type (e.g. molecular structure and carbon chain length), the soil properties (e.g. amount of organic carbon), and the pore water (e.g. degree of saturation, pH). Still, the retention – and release – mechanisms of PFASs on soil constituents are not completely elucidated, and a generic model able to predict the transport of PFASs in the subsoil is not available yet.
In this work, building on a recently developed approach coupling nuclear magnetic resonance (¹⁹F - NMR) and modeling [1], we used magnetic resonance imaging (¹⁹F - MRI) to obtain quantitative information of the spatial and temporal distribution of a fluorinated substance inside a porous medium during transport experiments. We validated the performance of our approach by comparing MRI profiles obtained during flow-through experiments in sand columns tracing the transport of sodium fluoride (NaF) – a fluorinated non-reactive tracer – with traditional breakthrough curve and numerical simulations. These results pave the way for the application of this innovative MRI/modeling approach PFASs and conclusively to improve our understanding and modeling capability of PFASs fate in porous media.

[1] Courtier-Murias, D., Michel, E., Rodts, S., & Lafolie, F. (2017). Novel Experimental-Modeling Approach for Characterizing Perfluorinated Surfactants in Soils. Environmental Science and Technology, 51(5), 2602–2610. https://doi.org/10.1021/acs.est.6b05671

How to cite: Fries, E., Courtier-Murias, D., Gil Roca, J., Peyneau, P.-E., Michel, E., and Béchet, B.: 19F-MRI and numerical modeling as a combined method for the measurement and prediction of fluorinated substances (e.g. PFASs) transport in porous media, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1288, https://doi.org/10.5194/egusphere-egu22-1288, 2022.

A 2-dimensional and dynamic numerical model of PFAS fate in unsaturated porous media is developed by accounting for the most important PFAS flow and mass-transfer mechanisms: convective flow, hydrodynamic dispersion, adsorption on solid grains and adsorption on air/water interfaces. Experimental measurements of the transient evolution of the shape of pendant and sessile drops are combined with image analysis software to develop equations describing the dynamics of the surface tension [1] and contact angle, associated with the surfactant (PFAS) sorption on the air/water interfaces, and formulate relevant models. Likewise, equilibrium and kinetic studies of PFAS sorption on soil grains are used to estimate all relevant (Langmuir, Freundlich, 1^st-order, 2^nd-order) sorption parameters [2]. Earlier work conducted on the immiscible two-phase flow in glass-etched pore networks [3] and soil columns [4] is used to model the dependence of capillary pressure and gas/water relative permeability curves on gas and water capillary numbers, regarded as dynamic parameters expressing the transient variation of the ratio of viscous to capillary forces. All aforementioned information is incorporated into the numerical code (JavaScript) so that a true-to-the physics model is obtained. The algorithm is developed in the platform of Comsol Multiphysics®.

First, forced imbibition in a soil column is simulated by considering the injection of uncontaminated water at a constant flow rate, until reaching the residual non-wetting phase (air) saturation. Then the water is replaced by PFAS-contaminated water, the flow rate is kept identical, and changes caused on the temporal and spatial distribution of water saturation and PFAS concentration across the soil column are mapped. Parametric analyses are done with respect to the type and concentration of PFAS, water injection flow rate, soil properties, and water composition. The numerical results could be used as a database for assessing the spreading of PFAS in vadose zone under varying conditions. The numerical model could be calibrated with regard to corresponding results from soil column tests, when such data become available.

Acknowledgements

This work was performed under Grant Agreement 101037509 — SCENARIOS — H2020-LC-GD-2020 / H2020-LC-GD-2020-3 (project title: “Strategies for health protection, pollution Control and Elimination of Next generAtion RefractIve Organic chemicals from the Soil, vadose zone and water” - acronym “SCENARIOS”) supported by the European Commission.

Literature

[1] Berry, J.D., Neeson, M.J., Dagastine, R.R., Chan, D.Y.C., Tabor, R.F., “Measurement of surface and interfacial tension using pendant drop tensiometry”,J. Coll. Interface Sci. 454 (2015) 226-237.

[2] Stavrinou, A., Aggelopoulos, C.A., Tsakiroglou, C.D.,“Exploring the adsorption mechanisms of cationic and anionic dyes onto agricultural waste peels of banana, cucumber and potato: Adsorption kinetics and equilibrium isotherms as a tool”,J.Env. Chem. Eng. 6 (2018) 6958–6970.

[3] Tsakiroglou, C.D., Avraam, D.G., Payatakes, A.C., “Transient and steady-state relative permeabilities from two-phase flow experiments in planar pore networks”, Adv. Water Res. 30 (2007) 1981-1992.

[4] Tsakiroglou, C.D., “The Correlation of the Steady-State Gas / Water Relative Permeabilities of Porous Media with Gas and Water Capillary Numbers”, Oil & Gas Science and Technology - Revue d' IFP Energies nouvelles 74 (2019) 45, 11p.

How to cite: Bali, N., Ntente, C., Stavrinou, A., Melitsiotis, A., Karavasilis, M., Theodoropoulou, M., and Tsakiroglou, C.: Numerical simulation of dissolved PFAS transport in unsaturated soil columns, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1886, https://doi.org/10.5194/egusphere-egu22-1886, 2022.

Increasing environmental awareness and still countless cases of polluted environmental compartments have led to a wide range of publications on chemical remediation methods in recent years. Many of them are devoted to advanced oxidation processes (AOPs) in water, with increasing attention for the remediation of persistent pollutants in surface-, ground- and waste waters with sulfate radicals. Processes based on activation of the oxidants peroxydisulfate (PS) and peroxymonosulfate (PMS) are becoming more and more popular especially for in-situ remediation strategies for aquifers contaminated with perfluorinated alkyl substances (PFAS).

In contrast to hydroxyl radicals, sulfate radicals are able to attack the carboxylate group in many PFAS. Our main focus of attention lies on the heterogeneous activation of PS for sulfate-radical generation in order to exploit pollutant enrichment at active surfaces. In the present study, the activation of PS with various iron minerals was investigated. From the pool of iron minerals tested, iron(II)-sulfide (FeS) proved to be a powerful activator for PS. A more detailed investigation of the FeS/PS system (e.g. pH dependence of the reaction, long-term performance of FeS as activator for PS and determination of radical yield and activation energy) led to the hypothesis of an activation mechanism via homolytic bond cleavage and to the assumption that FeS acts as a true catalyst with a considerable lifetime and not, as would be expected, as a reagent.

Based on the experiences made, the FeS/PS system was optimized and specifically designed for degradation of PFOA (perfluorooctanoic acid), one of the most prominent PFAS representatives being in the focus of regulatory attention. Due to surface-mediated processes, the target reaction, PFOA degradation, can be carried out even in real groundwater samples, even additionally doped with typical water constituents, such as humic acid. These results are remarkable, as it is known that not only dissolved iron, but also chloride and dissolved organic matter (DOM) effectively quench free sulfate radicals. The presentation will inform about reaction products, yields and pathways under various reaction conditions. By mechanistic insight into the activation of PS via heterogeneous activation, this work breaks new ground for novel remediation approaches using PS for in-situ and ex-situ water treatment.

Based on the promising lab results, a field test of the FeS/PS system, as a part of the Intraplex^® technology, was conducted at a contaminated site in western Germany. The main contaminants were the perfluorinated carboxylic acids with a total concentration of 0.6 µg/L. Using a combination of permanent injection points and direct push injections, an injection transects was carried out to apply the material across the main downstream direction of the PFAS plume. The effects of the pilot test were studied by an intensive monitoring program which determined the concentration of pollutants, transformation products and hydrogeochemical parameters. Preliminary results will be presented.

How to cite: Sühnholz, S., Bosch, J., Mackenzie, K., and Qian, L.: Iron minerals as catalytic activators for persulfate for PFAS degradation, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1629, https://doi.org/10.5194/egusphere-egu22-1629, 2022.

In the region Rastatt/Baden-Baden in the Upper Rhine Valley, Germany, approximately 1000 ha of predominantly agricultural land is contaminated with per- and polyfluoroalkyl substances (PFASs). About one decade ago, paper-fibre biosolids mixed with compost were applied as fertiliser. This affects various land uses and the underlying aquifer as the main drinking water resource for surrounding cities and municipalities. Besides perfluorinated carboxylic and sulfonic acids, the soil pollution is characterised by high contents of polyfluorinated precursors.

Remediation attempts have been limited to date, particularly due to the large spatial extent of the contamination and the related high costs. Currently, the possibility to immobilise the PFASs in the soil material is discussed. One strategy is an in-situ approach: substances with a high sorption capacity would be applied on the ground surface and mixed with the soil. The altered soil should still fulfil its original purpose (e.g., for agriculture). In this project, two soil mixtures treated with different active carbon-based products are used. Another strategy could be to remove the contaminated soil and use it for construction (e.g., noise protection embankment) after treatment with the immobilisation agents. This is tested with a liquid soil mixture and a concrete mixture.

The purpose of this research is to develop a test strategy to evaluate the long-term leaching characteristics of treated soils. Therefore, tests on three scales (batch experiments, column experiments, lysimeters) including different saturation conditions (saturated, variably saturated) are conducted. Effluent concentrations are monitored over time with different analytical methods (target analysis, determination of sum parameters (EOF/AOF), Total Oxidisable Precursor Assay (TOP)). In Hydrus-1D, mathematical models are employed to evaluate the appropriateness of various processes (e.g., equilibrium sorption) and the leaching behaviour for time scales larger than laboratory experiments can reproduce. The measured and modelled time-series of effluent concentrations serve as the basis for a simple and cost-effective method for the experimental testing of immobilisation measures for PFASs.

The current data illustrate significant reductions in PFAS desorption rates in the soils treated with active carbon-based additives. The immobilisation efficacy is chain-length dependent with less retention for short-chain carboxylic acids (PFBA, PFPeA); similar characteristics are observed in all experimental methods. In the variably saturated lysimeter experiments, delayed elution of short-chain PFAS in treated soils indicate additional processes (such us biotransformation).

The presentation focuses on the illustration and interpretation of PFAS desorption characteristics in the differently treated soils, on a data-based comparison of the experimental methods and challenges in the numerical simulations. 

How to cite: Bierbaum, T., Klaas, N., Braun, J., Haslauer, C., Lange, F. T., Nürenberg, G., and Scheurer, M.: Testing PFAS-Immobilization, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-325, https://doi.org/10.5194/egusphere-egu22-325, 2022.