Abstract:Abstract. Fluorescent dyes like uranine (UR) and sulforhodamine B (SRB) have been used for decades as artificial tracers in hydrological studies.
Recently, attempts have been made to trace organic pollutants in soil with such dyes, but the knowledge of the controls of sorption of UR and SRB in soils is still incomplete and poorly standardised.
For this reason, we selectively controlled clay, organic matter (OM) and pH within batch experiments and quantified systematically the impact and possible interactions o… Show more
“…is the molecular weight of the adsorbate, c ref [mol m −3 ] is a reference concentration used for units correction, and (dimensionless) is the isotherm exponent. K d and depend on factors such as the type of adsorbent and adsorbate, temperature, and pH, among others (Skopp 2009;Bork et al 2020). Previous studies (Brownawell et al 1997;John et al 2000;Botella-Espeso et al 2021) proved that the Freundlich isotherm (with different K d and values) is the most suitable isotherm for reproducing adsorption of surfactants in soils, specially for the case of non-ionic surfactants.…”
Section: Transport and Adsorption Modelingmentioning
confidence: 99%
“…Surfactants can be further affected by other processes such as degradation caused by light or microorganisms, which deplete their environmental concentration (Bork et al 2020). A general overestimation of adsorption from laboratory batch experiments when compared with field scale experiments, i.e., infiltration experiments, has also been observed (Botella-Espeso et al 2021).…”
The unsaturated zone, located between the soil surface and the phreatic level, plays an important role in defining the fate of any substance entering the subsoil. In addition to the processes of flow and transport taking place in the liquid phase, surface reactions such as adsorption to the solid phase may occur and increase the residence time of the substance entering the system. In this study, we aim to understand the pore-scale mechanisms that control adsorption in unsaturated systems. We combine 2D pore-scale experimental images with numerical simulations to analyze flow, transport, and adsorption under different liquid saturation degrees. We demonstrate the role of mixing on adsorption at the liquid-solid interfaces by analyzing the deformation in time of a pulse-injected surfactant. We also analyze the impact of the isotherm functional shape and the inclusion of the liquid-gas interfaces as adsorption sites on this surface reaction. The enhancement of mixing as saturation decreases is accompanied by a reduction in the amount of adsorbed mass, located mainly along preferential flow paths, where the solute is primarily transported. For the same isotherm, a nonlinear behavior of adsorption as a function of liquid saturation has been observed. This is explained by the nonlinear variation of the volume fraction of liquid behaving as preferential path or stagnation zone as liquid saturation decreases, despite the linear decrease in the surface area of solids accessible for adsorption.
“…is the molecular weight of the adsorbate, c ref [mol m −3 ] is a reference concentration used for units correction, and (dimensionless) is the isotherm exponent. K d and depend on factors such as the type of adsorbent and adsorbate, temperature, and pH, among others (Skopp 2009;Bork et al 2020). Previous studies (Brownawell et al 1997;John et al 2000;Botella-Espeso et al 2021) proved that the Freundlich isotherm (with different K d and values) is the most suitable isotherm for reproducing adsorption of surfactants in soils, specially for the case of non-ionic surfactants.…”
Section: Transport and Adsorption Modelingmentioning
confidence: 99%
“…Surfactants can be further affected by other processes such as degradation caused by light or microorganisms, which deplete their environmental concentration (Bork et al 2020). A general overestimation of adsorption from laboratory batch experiments when compared with field scale experiments, i.e., infiltration experiments, has also been observed (Botella-Espeso et al 2021).…”
The unsaturated zone, located between the soil surface and the phreatic level, plays an important role in defining the fate of any substance entering the subsoil. In addition to the processes of flow and transport taking place in the liquid phase, surface reactions such as adsorption to the solid phase may occur and increase the residence time of the substance entering the system. In this study, we aim to understand the pore-scale mechanisms that control adsorption in unsaturated systems. We combine 2D pore-scale experimental images with numerical simulations to analyze flow, transport, and adsorption under different liquid saturation degrees. We demonstrate the role of mixing on adsorption at the liquid-solid interfaces by analyzing the deformation in time of a pulse-injected surfactant. We also analyze the impact of the isotherm functional shape and the inclusion of the liquid-gas interfaces as adsorption sites on this surface reaction. The enhancement of mixing as saturation decreases is accompanied by a reduction in the amount of adsorbed mass, located mainly along preferential flow paths, where the solute is primarily transported. For the same isotherm, a nonlinear behavior of adsorption as a function of liquid saturation has been observed. This is explained by the nonlinear variation of the volume fraction of liquid behaving as preferential path or stagnation zone as liquid saturation decreases, despite the linear decrease in the surface area of solids accessible for adsorption.
“…However, the high discrepancy between the retention of conservative tracers ( , ) and UR at F.3 revealed that UR ought to be considered as a non-conservative tracer with respect to its sorption properties. This was described previously for UR application in soils with comparable OC content, texture and pH 44 , 61 , 62 . Figure 2 Breakthrough curves (BTCs) of the tracers bromide, chloride, UR, SRB and the biocides diuron, terbutryn, OIT and the sum of biocides (diuron+terbutryn+OIT; represented by diamonds).…”
Section: Resultsmentioning
confidence: 99%
“…At this temperature OC had been transformed to 91 . Additionally, sorption isotherms for UR and SRB were produced according to OECD guideline 106 92 described in 62 and linear sorption coeffients ( -values) were calculated.…”
Groundwater quality in urban catchments is endangered by the input of biocides, such as those used in facade paints to suppress algae and fungal growth and washed off by heavy rainfall. Their retention in storm water infiltration systems (SIS) depends, in addition to their molecular properties, on chemical properties and structure of the integrated soil layer. These soil properties change over time and thus possibly also the relevance of preferential flow paths, e.g. due to ongoing biological activity. To investigate the mobility of biocides in SIS, we analyzed the breakthrough of differently adsorbing tracers (bromide, uranine, sulforhodamine B) and commonly used biocides (diuron, terbutryn, octhilinone) in laboratory column experiments of undisturbed soil cores of SIS, covering ages from 3 to 18 years. Despite similar soil texture and chemical soil properties, retention of tracers and biocides differed distinctly between SIS. Tracer and biocide breakthrough ranged from 54% and 5%, to 96% and 54%, respectively. We related the reduced solute retention to preferential transport in macropores as could be confirmed by brilliant blue staining. Our results suggest an increasing risk of groundwater pollution with increasing number of macropores related to biological activity and the age of SIS.
“…Estudos acerca dos mecanismos de controle de adsorção de uranina em sedimentos ainda são incompletos e pouco sistematizados (BORK et al, 2020). Portanto, a avaliação de possíveis interações físicas entre o traçador e o material sólido pelo qual ele percolará deve, preferencialmente, preceder sua apli-cação no aquífero, de modo a antever possíveis perdas de massa.…”
A aplicação de substâncias fluorescentes como traçadores hidrogeológicos pode fornecer informações relevantes acerca da dinâmica das águas subterrâneas. Para um melhor controle na aplicação dos traçadores in situ, é pertinente definir possíveis interações dessas substâncias nos solos e sedimentos através de experimentos de bancada, a fim de prever seu comportamento durante a injeção no aquífero. O objetivo do trabalho corresponde à quantificação da adsorção e determinação do fator de retardamento do traçador fluorescente uranina em sedimentos quaternários da porção rasa do aquífero São Paulo. Os coeficientes de partição água/sedimento para uranina foram obtidos por meio de ensaios do tipo batch-test. Os experimentos consistiram em misturar sedimento orgânico, argiloso e grosso (arenoso) com soluções contendo uranina em cinco concentrações iniciais (5, 10, 50, 100 e 150 µg/L) em água deionizada e água do aquífero. Etapas de agitação, repouso e centrifugação precederam as medições de fluorescência. Através do ajuste de isotermas lineares, os valores do coeficiente de partição e fator de retardamento calculados para o sedimento grosso foram, respectivamente: 2,60x10-3 L/g ± 0,22x10-3 e 1,51 ± 0,13 (água deionizada), e 1,80x10-3 L/g ± 0,12x10-3 e 1,35 ± 0,09 (água do aquífero). Para o sedimento orgânico e argiloso, a fluorescência aparente gerada pelas partículas em suspensão nas soluções contendo uranina se sobrepôs à fluorescência real do traçador, impossibilitando a aferição dos coeficientes de partição e dos fatores de retardamento. Em meio sólido poroso com alto conteúdo de matéria orgânica e argilominerais, a uranina exibe alta susceptibilidade aos fenômenos de sorção. Contudo, sua utilização é indicada para a aferição de propriedades hidráulicas em aquíferos francamente quartzosos, uma vez nestes sedimentos a uranina apresentou um baixo fator de retardamento.
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