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Interaction of alkylphenolic and perfluorinated compounds with sewage sludges and soils

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Universitat de Barcelona. Departament de Química Analítica

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[spa] En esta tesis doctoral se ha estudiado la interacción de contaminantes orgánicos persistentes, tales como compuestos alquilfenólicos (APCs) y perfluorados (PFCs) con lodos de depuradora y suelos. Por lo que se refiere a la lixiviación de APCs en muestras de lodo, concretamente de octilfenol (OP), nonilfenol (NP) y nonilfenol-mono-etoxilado (NP1EO), ésta disminuyó después de un tratamiento de secado a 40 °C. Este comportamiento se atribuyó al hecho que, en el lodo fresco, los APCs se encontraban mayoritariamente asociados a la materia orgánica particulada en solución, mientras que el secado condujo a una transformación de la materia orgánica en moléculas más sencillas, provocando que los APCs quedaran mayoritariamente retenidos en la fase sólida del lodo, disminuyendo su lixiviación. En relación con la interacción de APCs en suelos, se evaluó la sorción y desorción de NP y NP1EO en suelos con distintos contenidos del carbono orgánico (OC). La sorción y desorción de estos compuestos fue lineal para el intervalo de concentraciones estudiado y los coeficientes de distribución sólido-líquido (Kd) obtenidos mostraron una buena correlación con el OC, lo que sugirió una interacción hidrófobica entre la cadena alquilo del APC y la materia orgánica de los suelos. La desorción de NP y NP1EO fue inferior a 5% para todas las combinaciones APC-suelo, demostrando una sorción significativamente irreversible de estos compuestos. Los estudios de sorción de PFCs, concretamente de sulfonato de perfluoroctano (PFOS), ácido perfluorooctanoico (PFOA) y sulfonato de perfluorobutano (PFBS), en lodos y suelos llevaron a conclusiones similares a las obtenidas con APCs. Las isotermas de sorción de PFCs también mostraron un comportamiento lineal en ambas matrices ambientales con una buena correlación entre Kd y OC, lo que sugirió una interacción hidrofóbica entre la cadena perfluorada y la materia orgánica. Se observó que la afinidad de sorción de PFCs en lodos y suelos aumentó con la hidrofobicidad del compuesto (PFBS < PFOA < PFOS), mientras que la desorción disminuyó, siendo el PFOS el más irreversiblemente sorbido, lo que permitió concluir que la hidrofobicidad del compuesto gobierna su sorción en lodos y suelos.

# metadata.dc.description.abstract[].value
[eng] In this doctoral thesis the interaction of emergent organic pollutants, such as alkylphenolic and perfluorinated compounds (APCs and PFCs, respectively) with sewage sludge and soil samples was studied. These two families of organic compounds were selected because of their ubiquitous presence and persistence in environmental matrices and to know mechanisms responsible for their interaction. With respect to the behaviour of APCs in sewage sludges, concretely octylphenol (OP), nonylphenol (NP) and nonylphenol-mono-ethoxylate (NP1EO), the application of a leaching test to fresh sludge samples and to samples dried at 40 °C showed that leaching yields of APCs decreased after the drying treatment (from 1.3-35% for fresh sludge samples to 0.8-3.4% for dried samples). This was attributed to differences in the characteristics of sludge organic matter in fresh and dried sludge samples. Thus, in the fresh sludge samples, APCs were mainly associated with the particulate matter in solution, showing high leaching yields. In contrast, drying treatment provoked the transformation of organic compounds into simpler molecules, thus leading to a decrease in the particulate matter in solution, thus favouring the association of APCs with the organic matter of the solid phase, and decreasing the leaching yield. Therefore, sewage sludge drying is recommended before their potential addition to agricultural soils. For studying the sorption behavior of NP and NP1EO in soils, sorption and desorption tests were applied to several soils with different characteristics such as pH, organic carbon (OC) and dissolved organic carbon. Sorption and desorption isotherms of NP and NP1EO were linear within the concentration range studied, and the solid-liquid distribution coefficients (Kd) derived from the isotherms correlated with the OC of soils, suggesting that soil organic matter governed the sorption of NP and NP1EO through a hydrophobic interaction with the alkyl chain of APCs. Exception to this pattern was the sorption of NP1EO in those soils with the highest DOC/OC ratio, which were better described by the Freundlich equation (N>1), due to the competition between the organic matter in solution and that in the solid phase for NP1EO sorption at low initial concentrations. Moreover, Kd values were usually higher for NP than for NP1EO, according with the higher hydrophobicity of NP. Desorption yields of NP and NP1EO were lower than 5 %, thus indicating that the sorption of APCs in soils was considerably irreversible. Sorption behaviour of PFCs, concretely perfluorooctane sulfonate (PFOS), perfluorooctanoic acid (PFOA), perfluorobutane sulfonate (PFBS), in sewage sludge and soil samples led to similar conclusions to those obtained for APCs. Sorption and desorption isotherms showed a linear pattern in the two environmental matrices, with satisfactory correlations between Kd and the organic matter content of the sample, suggesting a hydrophobic interaction between the pefluorinated carbon chain and the organic matter of sewage sludges and soils, predominantly Van der Waals forces. Potential additional role of Ca/Mg ion bridges to overcome the electrostatic repulsions of deprotonated PFCs with negatively charged surface sites of sludges at the sample pH was also suggested. Sorption affinity of the PFCs for the sludge and soil samples increased with the hydrophobicity of the compound, that is, in the sequence: PFBS < PFOA < PFOS. In contrast, PFOS showed the highest irreversibility in the two environmental matrices, whereas PFOA and PFBS were desorbed in higher rates. This suggested that the physicochemical properties of the compound, such as solubility and octanol-water partitioning coefficient, together with the organic matter content of sewage sludges and soils controlled the sorption behaviour of PFCs.

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Tesis Doctorals - Departament - Química Analítica

# metadata.dc.title[].value
Interaction of alkylphenolic and perfluorinated compounds with sewage sludges and soils