The method of soil washing is currently the only economically feasible cleaning method for PFAS-contaminated soils on large scale.

A total of about 430,000 t of soil contaminated with PFAS and HCs was washed from August 2018 to October 2021 at the site of a former refinery in Bavaria. The cleaned soil could then be refilled at site-specific costs of about EUR 50 per ton. Since September 2022, Züblin Umwelttechnik GmbH has been operating another soil washing plant in Northern Germany, which was specially designed to treat soils contaminated with PFAS. Several hundred thousand tons of sandy soil with around 10% fines will be washed and refilled on site in the next years.

Data obtained from these two large-scale remediation projects are presented. The technical concept and challenges to treat 1,000 to 3,000 t of material per day are discussed, along with regulatory obstacles and the boundary conditions to process these quantities while limiting the emissions. A special focus lies on the heterogeneous nature of input material, with varying contaminant load, soil quality and soil structure as well as affiliated contaminants. In both attempts, the washing water is circulated in a closed water cycle, therefore elaborate treatment of sludge and polluted water is required.

One of the critical issues in soil washing is to optimise the washing process so that the washing liquid serves as the predominant contaminant sink. In this way, steady washing results are achieved, and all output fractions can be successfully processed while water consumption is kept to a minimum.

The complex nature of the contaminant itself, the multitude of singular PFAS substances and precursors, further complicate operation and controlling. Progress shows that soil washing can even be a viable tool to treat the fine fraction, and various strategies in different treatment steps have been tested on multiple scales, including several washing agents.

Since after treatment, the washed soils can be safely reused on site, large emissions from transportation and properly disposing the PFAS-materials is avoided while increasingly limited landfill space is maintained.

Future research is required for expanding the applicability of the method to highly challenging materials such as high fines and/or high organic content. Further projects for washing of PFAS contaminated soils in Europe are already in the planning stage.

How to cite: Faigle, Dr. B., Edel, Dr. H.-G., and Volz, B.: Successful treatment of PFAS-contaminated soils on large scale: practical experience with soil washing., EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-1373, https://doi.org/10.5194/egusphere-egu23-1373, 2023.

Per- and polyfluoroalkyl substances (PFAS) are a diverse group of manmade, fluorinated organic chemicals that gained notoriety for their diverse application, widespread distribution in the environment and toxicity. One of the main sources of PFAS to the environment is through aqueous film forming foam (AFFF), intended for use on fuel fires. AFFF may enter the environment through system testing, training activities, emergency use or accidental release. When AFFF enters the environment PFAS readily adsorb to porous media through hydrophobic and electrostatic interactions. As a result, PFAS impacted porous media may act as a long-term source of contamination to groundwater, potentially influencing water resources and human health. There is a demand for effective treatment of PFAS impacted porous media. Ball milling has emerged as a potential treatment option for PFAS, however, the viability of treating AFFF impacted porous media has been seldom explored. In this work four AFFF formulations were amended onto silica sand and milled without and with the use of potassium hydroxide (KOH) as a co-milling reagent. Six hour milling trials were conducted using a planetary ball mill with stainless steel grinding media. Significant destruction of perfluorosulfonic acids, perfluorocarboxylic acids (PFCAs), fluorotelomer sulfonates, fluorotelomer betaines and fluorotelomer sulfonamido betaines was observed. With the use of KOH as a co-milling reagent the total PFAS destruction percentage in all four AFFFs exceeded 90%. Greater destruction of PFAS was observed in fluorotelomer dominant AFFFs when compared to perfluoroalkyl acid dominant AFFFs. PFCAs and soluble fluoride were identified as destruction byproducts. KOH as a co-milling reagent had the effect of reducing PFCA byproduct formation and increasing fluoride recovery in three of four AFFFs. Fluoride recoveries indicate PFAS molecule defluorination occurs by ball milling. When PFAS in AFFF is compared to PFAS destruction in single analyte trials, less destruction is observed, displaying the necessity of evaluating realistic AFFF contamination events over single or multi analyte mixtures.

How to cite: Turner, L. P., Patch, D. J., Kueper, B. H., and Weber, K. P.: Mechanochemical Destruction of Per-and Polyfluoroalkyl Substances in four Aqueous Film Forming Foam Formulations using amended Silica Sand and Potassium Hydroxide, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2916, https://doi.org/10.5194/egusphere-egu23-2916, 2023.

Understanding how per- and poly-fluoroalkyl substances (PFAS) are transported is critical to site characterization, monitoring, risk assessment, and remediation planning.  This includes an understanding of PFAS retention and release at air-water interfaces.  These interfaces exist throughout the vadose zone, but can also exist as trapped air bubbles created by water table fluctuations, recharge, and biogenic gas production.  In addition to being directly applicable to transport through trapped gas zones at PFAS-impacted sites, laboratory experiments using emplaced trapped gas (quasi-saturated conditions) provide a controlled method to investigate PFAS behavior, including the effects of different PFAS, concentrations, and mixtures. 

In this study, a series of laboratory experiments was conducted using one-dimensional sand-packed columns (20 cm × 7 cm dia.).  Trapped air was emplaced by sequential drainage and imbibition to create quasi-saturated conditions.  Each experiment included separate injections of non-reactive tracer (NaCl) and PFAS solutions through both water-saturated and quasi-saturated columns.  A clean, low organic carbon sand was used to eliminate solid-phase sorption (verified through comparison of non-reactive tracer and PFAS breakthrough in the water-saturated columns) and to isolate the effect of air-water interfaces.  Experiments were conducted using single-component solutions of PFOA, PFOS and 6:2 FTS, as well as mixtures of those PFAS, at concentrations of 0.1-1 mg/L.  Experiments were also conducted using diluted aqueous film-forming foam (AFFF) solutions.  Measured retardation factors in triplicate experiments were used to estimate air-water partitioning coefficients.

The results showed that PFAS breakthrough was significantly delayed in the presence of trapped air bubbles.  Breakthrough delay was greater for PFOS than for PFOA or 6:2 FTS, and was greater for lower PFAS concentrations, for the range of concentrations used in these experiments.  For PFAS mixtures, differences in retention were sufficient to completely separate breakthrough (i.e., PFOA and 6:2 FTS achieved complete breakthrough prior to any PFOS arrival) even over short (20 cm) distances.  However, the behavior of each PFAS tested was altered by the presence of other PFAS, with PFOA and 6:2 FTS experiencing earlier breakthrough at higher concentrations (concentration overshoot) in the presence of PFOS.  Mixture effects were also observed for branched and linear PFOS isomers, and for AFFF solutions, which was further complicated by the presence of hydrocarbon surfactants.  The experimental results will be presented along with numerical simulations of PFAS transport subject to air-water partitioning, both to interpret the behavior of PFAS mixtures in experimental systems and to explore the implications of mixture transport in more complex field scenarios.

How to cite: Mumford, K. G., Abraham, J. E. F., Patch, D. J., Kibbey, T. C. G., and Weber, K. P.: PFAS transport through quasi-saturated porous media: Laboratory experiments and mixture effects, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7942, https://doi.org/10.5194/egusphere-egu23-7942, 2023.

The fate of emerging contaminants from runoff/storm waters in urban areas has aroused widespread concern as it poses a threat to the water managing. Contaminated water can reach, for instance, the river that passes through the area, contributing to the degradation of the aquatic ecosystem, or the aquifer that supplies drinking water to the community. In this framework, one of the objectives of the URBANWAT project is to evaluate the capacity of the Barcelona urban soil to retain the contaminants of emerging concern from runoff waters in order to propose an improvement of tools and criteria for groundwater management in urban areas.

To this aim, a set of batch and packed soil column experiments were performed. The soil selected for the study is located in the Barcelona urban area at 20 m depth and composed of 48 % quartz, 28 % albite and 24 % microcline. It is constituted by 91 % sand, 7 % silt and clay and 2 % gravel, being the sand particle size dimension the one selected to perform the column experiments. The resident water in contact with the soil was analysed by ICP-MS and has a conductivity of 723 µS/cm and pH of 7.9. A list of representative emerging contaminants has been selected from diverse pharmaceutical families and UV filters based on the concentration values found in the runoff waters of the Barcelona urban area.

The batch experiments were carried out first to verify if the soil already contained the target contaminants and second to know the soil sorption capacity. The target contaminants have different properties (pka, charge) that cause them to be sorbed with variable efficiency by the soil tested (80-100 % sorption for Paroxetine and Venlafaxine, 60-80 % for Cocaine and Caffeine, 40-60 % for Tradadol and Climbazole and low sorption (< 40 %) for a list of more than 15 emerging contaminants). Sorption capacities obtained in the batch experiments were also identified in the percolation tests, obtaining significantly different breakthrough curves for the studied target contaminants. By means of the percolation column experiments, the effect of the flow rate on the soil retention capacity was evaluated and the two main processes involved in the pollutants retention mechanism (sorption and biodegradation) were quantified to verify the specific contribution of each process to the global procedure. 

How to cite: Luquot, L., Garcia Rios, M., Duporte, G., and Gomez, E.: Evaluation of the Barcelona urban soil capacity for retention of emerging contaminants, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6762, https://doi.org/10.5194/egusphere-egu23-6762, 2023.

A novel aerobic process has been developed for the passive cometabolic treatment of contaminant mixtures in groundwater.  Our studies have focused on Rhodococcus rhodochrous ATCC 21198 that can concurrently oxidize 1,4-dioxane (1,4-D) and diverse mixtures of chlorinated aliphatic hydrocarbons (CAHs). We found that the short chain alkane monoxygenase (SCAM) responsible for the cometabolism of the contaminants is induced after grown on 1-butanol and 2-butanol, permitting the use of Slow Release Compounds (SRCs) that slowly hydrolyze to produce these alcohols.  Methods were developed to co-encapsulate the SRCs and ATCC 21198 in gellan-gum hydrogel beads. ATCC 21198 grows within the gellan-gum beads and upon diffusion into the beads the contaminants are transformed. In batch reactors containing the gellan-gum beads successive additions of a mixture of  1,1,1-trichloroethane (1,1,1-TCA_, cis-dichloroethene (cis-DCE), and 1,4-D were transformed for over 300 days, with the rates of cometabolism correlated with the rates of alcohol release, oxygen consumption and CO₂ production. Continuous flow tests have been performed with columns packed with the gellan-gum beads. The columns mimic passive treatment that might be achieved using an in-situ permeable reactive barrier (PBR) constructed with the gellan-gum beads.  Over 99% removal of a mixture of 1,1,1-TCA, cis-DCE, and 1,4-D, each at influent concentration of 250 µg/L, was achieved with a hydraulic residence time of approximately 12 hours  The columns effectively transformed the contaminant mixture for over 600 pore volumes (300 days). The columns performance was negatively affected when cis-DCE was replaced by 1,1-dichloroethene (1,1-DCE), due to 1,1-DCE transformation product toxicity.  The column containing the SRC that produced 2-butanol was more negatively impacted by 1,1-DCE due to the lower biomass that developed in the gellan-gum beads. Studies are currently being performed in a 3-D physical aquifer model using a funnel-and-gate system with the co-encapsulated gellan-gum beads used to create a cometabolic permeable reactive barrier. 

How to cite: Semprini, L., Azizian, M., Wortkoetter, J., and Rasmussen, M.: Hydrogels that Co-Encapsulate Slow Release Compounds and Rhodococcus rhodochrous ATCC 21198 for the Aerobic Cometabolic Treatment of 1,4-Dioxane and CAHs, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10942, https://doi.org/10.5194/egusphere-egu23-10942, 2023.

Ultraviolet filters (UVFs) are contaminants of emerging concern (CECs) produced and used in large quantities worldwide. They are constituents of a large number of personal care and hygiene products and other consumer goods. Benzophenones, such as benzophenone-3 (BP-3), benzophenone-4 (BP-4) and avobenzone (AVO), are among the most used. These compounds are characterized by being photo-stable and lipophilic. Although it is highly known the lipophilicity of these compounds, their monitoring in porous media is centered in the aqueous phase. Nevertheless, their high logK_ow make foreseeable the accumulation in more lipophilic phases such as biofilm or sedimentary organic matter. For that, in this work we have highly characterized a Managed Aquifer Recharge system with a very intensive monitoring of benzophenones and transformation products in the three phases: water, biofilm and sedimentary organic matter. Furthermore, we have contrasted our results with a numerical model, which was based on the partition of UVFs under equilibrium conditions. Our results show that biofilm acted as an additional environmental compartment favoring the retention and degradation of UVFs in porous media. Indeed, it played a central role in the fate of these compounds, controlling both sorption and biodegradation. With this we believe that the current understanding of the organic compounds fate should incorporate it as a new compartment capable of bio-accumulate these compounds.

How to cite: Rodriguez-Escales, P., Jou, S., Carrera, J., Martinez, L., Diaz-Cruz, S., Sunyer, A., Quitana, G., and Valhondo, C.: The role of biofilm as a bio-accumulator of Ultraviolet Filters in porous media, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12632, https://doi.org/10.5194/egusphere-egu23-12632, 2023.

The role of dissolved organic matter (DOM) in the transport of trace organic pollutants through the soil profile remains controversial. Several studies reported enhanced transport for nonpolar pesticides and other pollutants such as pharmaceuticals (e.g., Borgman & Chefetz 2013). It is generally hypothesized that DOM modifies the sorption properties of the contaminants through co-sorption and/or cumulative sorption (Totsche et al. 1997). Co-transport with DOM can also enhance the mobility of pollutants (Chabauty et al. 2016). Other authors reported little effect of DOM on both sorption or desorption of herbicides (e.g., Barriuso et al. 2011). To help elucidating the multiple roles of DOM, we developed the PolDOC model implemented in the VSoil modeling platform of INRAE. We took advantage of the modularity of the platform to couple available 1D water flow and solute transport models with novel reactivity modules for organic pollutants and DOM. Indeed, sink/source terms in the transport equation have been used to calculate the interactions between pollutants, DOM and the soil solid phase.

The model was designed to simulate the transport of organic pollutants in intact soil cores sampled in the Bt horizon of a cultivated Albeluvisol to which either a synthetic soil solution without DOM (SYNTH), a soil solution extracted from the top horizon (CONTROL) or a soil solution extracted from the top horizon of a neighbour plot receiving sewage sludge and green waste compost (SGW) were applied (Chabauty et al., 2016). In PolDOC, the organic pollutants can be transported either free or associated with DOM. To describe the multiple roles of DOM in the transport of organic pollutants we first simplified the wide spectrum of organic molecules which constitute DOM and distinguished two types of DOM with different reactivity: DOM_Bt produced by depolymerization of the organic matter in the Bt soil horizon, and DOM_SURF, produced by depolymerization of the organic matter of the surface horizon.

The model was used to simulate the transport of both DOM types and three different organic pollutants: isoproturon (ISO), a mobile herbicide, epoxiconazole (EPX), a moderately mobile fungicide and sulfamethoxazole (SMX), a mobile antibiotic. Since pollutants are applied at the soil surface, we considered that organic pollutants will be more prone to interact with DOM_SURF, which is rich in phenolic compounds. Physical non-equilibrium transport conditions were identified and quantified with PolDOC. Model showed that the Bt horizon acted as a sink to partly retain DOM_SURF. While differences in ISO and SMX transport could be explained by different sorption reactivity with the soil solid phase, the increased leaching of EPX in presence of DOM_SURF required the activation of co-transport with DOM_SURF.

References:

Barriuso, E., Andrades, M.-S., Benoit, P., and Houot, S. (2011) Biogeochemistry 106, 117–133.

Borgman, O., and Chefetz, B. (2013) Water Research 47, 3431–3443.

Chabauty F., Pot V., Bourdat-Deschamps M., Bernet N., Labat C., and Benoit P. (2016) Environmental Science and Pollution Research, 23, 7, 6907-6918.

Totsche, K.U., Danzer, J., and Kögel-Knabner, I. (1997). Journal of Environment Quality 26, 1090–1100.

How to cite: Pierre, B., Jeanne, D., François, L., Florian, C., and Valérie, P.: Assessing the multiple effects of dissolved organic matter on the transport of organic pollutants in subsoil horizons through a modular modeling approach, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12446, https://doi.org/10.5194/egusphere-egu23-12446, 2023.

Plants produce a diverse array of toxic compounds which may be released by precipitation, that explains their wide occurrence in surrounding soil and water. This study presents the first mechanistic model for describing the generation and environmental fate of a natural toxin, viz.  ptaquiloside (PTA), a carcinogenic phytotoxin produced by bracken fern (Pteridium aquilinum L. Kuhn). The newly adapted DAISY model was calibrated based on two-year monitoring performed in the period 2018-2019 in a Danish bracken population located in a forest glade. Several functions related to the fate of PTA were calibrated, covering processes from toxin generation in the canopy, wash off by precipitation and degradation in the soil. Model results (2018-2019) show a good description of observed bracken biomass and PTA contents, indicating that toxin production can be explained by biomass and bracken development stage. The wash off is maximum in the middle of summer, coinciding with the moment of maximum biomass, fully developed canopy and highest PTA content. Model results show that only 4.4 % of the PTA produced in bracken is washed off by precipitation, from both canopy and litter. Once in the soil, PTA degrades rapidly, especially during summer due to the high soil temperatures. Leaching takes place in form of pulses directly connected to precipitation events, with maximum simulated concentrations up to 4.39 µg L^-1 at 50 cm depth. Macropore transport is responsible for the events with highest PTA concentrations, contributing to 72% of the total mass of PTA leached. Based on the results, we identify areas with high precipitation and soils characterized by fast transport, as the most vulnerable to surface and groundwater pollution by phytotoxins

How to cite: Diamantopoulos, E., García-Jorgensen, D. B., Holbak, M., Abrahamsen, P., and Bruun Hansen, H. Chr.: Modeling the environmental fate of the natural toxin ptaquiloside: production, release and leaching to groundwater, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12856, https://doi.org/10.5194/egusphere-egu23-12856, 2023.

The anthropogenic organic contaminants contemplated in the environmental legislation, as well as those of emerging concern, threaten the quality of water resources to a degree that remains largely unknown. Contaminant exposure in the aquatic environment is a crucial element if a full understanding of the risk is pursued. There are still many uncertainties about the occurrence of organic contaminants and their behavior in the hydro(geo)logical media in large scale areas. The case study of the unconfined aquifer of the Granada Plain (approximately 200 km²) is presented here. Two groundwater and surface water monitoring campaigns were conducted (March 2017 and June 2018). Water samples were analysed for (i) 171 organic contaminants (e.g., pesticides, pharmaceuticals, drugs of abuse, PAHs); (ii) major and minor ions (Ca²⁺, Mg²⁺, Na⁺, K⁺, Cl^-, SO₄^2-, HCO₃^-, NO₃^-) and (iii) isotopes of the water molecule (δ¹⁸O, δ²H) and δ¹³C from the dissolved inorganic carbon. Additionally, in situ measurements of physico-chemical parameters (pH, temperature, electrical conductivity, redox potential and dissolved oxygen) were carried out. In total, 41 organic pollutants were detected, at least once: 17 pharmaceuticals or drugs of abuse, 21 pesticides or their metabolites and three PAHs. Statistical tests confirmed the significance of seasonal changes for some of these parameters (e.g., EC, Cl^-, F^-, δ¹⁸O, δ¹³C), revealing the influence from snowmelt water input on streams and the intensification of irrigation. In March 2017, the group of pesticides (largely represented by triazines) predominated, whereas the frequency of detection of pharmaceuticals increased substantially in June 2018. Based on the obtained results, a qualitative evaluation has been made to suggest four main factors affecting the spatial and seasonal variation of organic pollutants in the aquifer: (i) the variation of the unsaturated zone thickness; (ii) the river-groundwater hydraulic connection; (iii) the hydraulic gradient; and (iv) the anthropogenic factor determining the period of contaminant release throughout the year and wastewater management practices. The river-groundwater hydraulic connection can be especially important in the case of those contaminants whose main path of entry into the aquatic environment occurs through wastewater discharge into streams (i.e., pharmaceuticals).

How to cite: Llamas, M. I., Jiménez-Gavilán, P., Luque-Espinar, J. A., Benavente-Herrera, J., Candela, L., Sanmiguel-Martí, M., Rambla-Nebot, J., Aranda-Mares, J. L., and Vadillo-Pérez, I.: Hydrogeological, hydrodynamic and anthropogenic factors affecting the spread of pharmaceuticals and pesticides in water resources of the Granada plain (Southern Spain), EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-15414, https://doi.org/10.5194/egusphere-egu23-15414, 2023.