Les micropolluants organiques (MPO) tels que les HAPs, PCBs et NP sont sous la surveillance étroite des différentes agences de santé et de l'environnement à cause de leurs effets toxiques, cancérigènes et perturbateurs endocriniens sur les organismes vivants. Dans l'environnement, ils se retrouvent dans le sol, les aquifères, les eaux usées, et en raison de leurs propriétés hydrophobes, ces MPO sont principalement associés aux compartiments matière organique dans les boues d'épuration et les sédiments de rivières. La digestion anaérobie, procédé de stabilisation des boues, présente un potentiel pour l'abattement de ces composés. Les deux principaux mécanismes qui régissent l'abattement dans ces conditions des MPO sont le cométabolisme et la biodisponibilité. Leur double influence est évaluée dans ce travail, avec un focus fort sur l'étude des interactions MPO-matrice, la détermination de la distribution des MPO dans les compartiments physiques de la matrice (libre, sorbé à la matière dissoute et colloïdale (DCM) et sorbé aux particules) et avec une caractérisation fonctionnelle, physique et chimique détaillée de la matrice. Pour cela, des réacteurs anaérobies continus et batch ont été mis en œuvre avec des boues de caractéristiques différentes. L'abattement des MPO varie considérablement en fonction des caractéristiques des boues s'expliquant soit par des variations du niveau de cométabolisme, soit par les différents niveaux de biodisponibilité ; ceci suggère qu'une caractérisation détaillée de la matrice boue pourrait aider à prévoir les niveaux d'abattement des MPO. Par ailleurs, les cinétiques en batch montrent que l'abattement des MPO est associé aux premières étapes de la digestion anaérobie, conjointement à leur transfert du compartiment des particules vers le compartiment aqueux. L'abattement des MPO s'observe simultanément dans les trois compartiments libre, sorbé à la DCM et sorbé aux particules. Il est aussi noté l'importance du compartiment DCM sur l'abattement des MPO de haut poids moléculaire. Les coefficients de partage KDOC et Kpart ont été calculés pour étudier les interactions MPO-matrice., Ces données couplées à celles de caractérisation fonctionnelle de la matrice par fluorescence 3D ont permis de construire un modèle explicatif et prédictif des interactions MPO-matrice à l'aide de la méthode de régression partielle des moindres carrés (PLS). Il a été constaté que le compartiment type acide humique a un rôle important dans les interactions MPO-matrice, principalement dans la phase aqueuse, et dans la phase particulaire, les protéines complexes régissent les interactions. Enfin, des modèles PLS explicatifs et prédictifs d'abattement total des MPO ont été construits. Il en ressort que l'abattement des MPO est favorisé par tous les paramètres du cométabolisme (abattement des divers compartiments matière) et par la concentration des MPO en phase aqueuse ce qui tenterait à confirmer que ce compartiment correspond au compartiment biodisponible. Le modèle prédictif basé sur les caractéristiques des boues initiales a identifié les concentrations initiales de MPO (libre, sorbé à la DCM et aux particules) comme les variables les plus importantes qui permettent de prédire l'abattement total des MPO. Cette étude contribue ainsi à mieux comprendre la répartition des MPO dans les matrices boue, et son implication dans le devenir des MPO, de prévoir cette répartition par une caractérisation fonctionnelle de la matrice et de proposer des stratégies pour optimiser l'abattement des MPO au cours de la digestion anaérobie. / Organic micropollutants (OPs) such as PAHs, NP and PCBs, are nowadays looked as environmental pollutants by environmental and health agencies because of their toxic, carcinogenic and endocrine disrupting effect on living organisms. Within the environment, they can deposit to soil, water bodies and sewage system and due to their hydrophobic properties, they are mainly associated with hydrophobic compartments such as organic matter in sewage sludge. Anaerobic digestion has been shown as a potential biological process for removing these compounds. The two main mechanisms that govern their anaerobic removals are the cometabolism and the bioavailability. In this work, cometabolism and bioavailability influences were evaluated focusing mainly on the study of the OP-organic matrix interactions, the determination of the OPs distribution among the physical compartments (free, sorbed to dissolved and colloidal matter (DCM) and sorbed to particles) combined with a detailed physical, chemical and functional matrix characterization. For this, continuous and batch anaerobic reactors were fed with different sludge samples. It was found that the OPs removals varied greatly as a function of sludge characteristics and that greater or lesser removal might be explained either by variations in cometabolism or by different levels of bioavailability, suggesting that a detailed characterization of the feed may help to predict the OPs removals. Additionally, batch kinetics demonstrated that OPs removals are coupled to the first step of the anaerobic digestion, jointly to the OPs transfer from the particules to the aqueous compartment. The OPs are simultaneously removed from the three physical compartments (free, DCM and particules). Moreover, it was highlighted the importance of the DCM fraction on the removal of the high molecular weight OPs. KDOC and Kpart partition coefficients were calculated to study the OP-organic matrix interactions coupled to a functional characterization by 3D fluorescence of the matrix in order to construct an explicative and predictive model of the OP-organic matrix interactions using partial least square regression (PLS). It was found that the humic acid-like compartment has a great role in the OP-organic matrix interactions mainly in the aqueous phase, and in the particulate phase, the complex proteins govern the interactions. Finally, explanatory and predictive PLS models of total OPs removals were constructed. It was concluded that OPs removals are favored by all cometabolic parameters (substrates removals) jointly to the aqueous OPs concentration which tends to confirm that this compartment corresponds to the bioavailable one. The predictive model based on the initial sludge characteristics, identified the initial OPs concentrations (free, DCM and particulate) as the most important variables that predict the total OPs removals. This study contributes to better understand the OPs distribution among the sludge compartments and its role in the fate and removal of the compounds, to predict this distribution through matter functional characterization and to propose strategies in order to optimize the OPs removals under anaerobic conditions.

Doctor of Philosophy / Department of Civil Engineering / David R. Steward / Groundwater contamination with arsenic (As), a naturally occurring metalloid, is a worldwide problem. Over 100 million people are at health risk due to arsenic contaminated groundwater, especially in the Bengal Basin in south-east Asia. Dissolved organic matter (DOM), geology and geomicrobiology are important factors affecting arsenic mobility. This study focuses on interactions of different aspects of natural organic matter in arsenic-contaminated environments. A literature review specifically includes past studies done on fundamentals of arsenic geology, geomicrobiology, DOM characterization and relevant analytical methods and tools. Based on background information already collected, this research is focused on specific research questions and corresponding hypotheses. The overarching goal of this investigation is to better understand the mechanisms by which DOM influences arsenic mobilization. The specific goals of this research are: 1) to evaluate role of oxidized humic quinones in reductive dissolution of Fe-As minerals and subsequent arsenic mobilization via electron shuttling, 2) to quantify the rate of microbially mediated reductive dissolution in the presence of oxidized humic quinones, 3) to evaluate DOM-Fe-As ternary complex formation and its influence on arsenic mobility and 4) to characterize DOM in the arsenic-contaminated aquifers of West Bengal, India and evaluate its role in arsenic mobilization using groundwater flow and contaminant transport modeling approach. Results of this study revealed that oxidized quinone like moieties (such as fulvic acids) serve as an electron shuttle and enhance the reductive dissolution process under reducing conditions, hence mobilize the arsenic in groundwater. Another key result from this study suggested that arsenic binds with non-aromatic portion of the humic-like DOM under reducing conditions and increases its solution concentration. A field study conducted in West Bengal, India revealed that the mechanisms studied in the laboratory exists in reducing aquifer. A groundwater flow and reactive transport model was created to explain multiple interactions of DOM and arsenic spatial scales. Broader impacts of this study include significant addition to scientific knowledge about subsurface biogeochemistry and the role of DOM in biogeochemical reactions in the subsurface.

Dissolved organic matter (DOM) is a central component of the global carbon cycle. Thus, small changes to the amount of DOM imported, processed and produced within lakes can have a large effect on regional carbon budgets. In addition to being a vital energy source at the base of the aquatic food web, DOM is physico-chemically reactive. However, identifying and understanding the controls of DOM processing has remained challenging due to the complex composition of DOM. DOM comprises a mixture of decomposition by-products of terrestrial origin as well as newly synthesized material from in situ production. DOM compounds form gradients of reactivity to biogeochemical processes, such as photodegradation, biodegradation, and flocculation, and they perform a suite of functions in aquatic systems. The overarching goal of this thesis was to investigate controls of DOM processing in Swedish lakes. We do this in two ways: 1) by characterizing the molecular-level composition of DOM in lakes, and 2) by investigating interactions between very labile and relatively recalcitrant DOM. The first three chapters utilize ultrahigh resolution mass spectrometry to show that the detailed chemical composition of DOM varies along a hydrology gradient, and secondarily along a temperature gradient that co-varies with agriculture and nutrients. Next, we illustrate the coherence between molecular-level characteristics and bulk optical characteristics. Together, these studies suggest that protein-like fluorescence, aliphatic compounds, and N-containing compounds are either resistant to degradation or tightly cycled in the system, and thus persist at long water residence times. The most oxidized compounds, such as vascular plant-derived polyphenolic compounds, are abundant in areas with high precipitation and are lost with increasing water residence time. Vascular plant-derived polyphenolic compounds were most strongly related to DOM with high apparent molecular weight, suggesting that hydrophobic interactions drive aggregate formation. Furthermore, the association of high molecular weight DOM with polyphenolic compounds suggests that aggregates are hotspots of reactivity in aquatic systems. Finally, we find no indication that the addition of labile organic matter enhances the biodegradation of less reactive DOM. Thus, we suggest that in freshwaters, intrinsic molecular properties, such as the basic structural features of compounds, dominate over extrinsic factors.

Dissolved organic matter (DOM) is the largest pool of organic carbon in aquatic systems and an important component of the global carbon cycle. Large amounts of DOM are decomposed within lakes, resulting in fluxes of CO2 and CH4 to the atmosphere. Therefore, there is a considerable interest in understanding the controls of DOM decomposition in freshwaters. There is evidence that in lakes intrinsic controls related to DOM composition are of primary importance, yet our knowledge about molecular drivers of DOM degradation is limited. This thesis addresses the link between chemical composition and reactivity of lake DOM by applying an experimental approach, molecular-level DOM characterization, and kinetic modeling of DOM decay. The first study shows that photoinduced transformations and partial removal of colored aromatic components of DOM have profound effects on DOM degradation kinetics, mediated by the shifts in the relative share of rapidly and slowly degrading DOM fractions. Two following studies estimate exponential decay coefficients for each individual molecular formula identified within bulk DOM. A continuous distribution of exponential decay coefficients is found within bulk DOM, which directly corroborates the central and previously empirically untested assumption behind the reactivity continuum model of DOM decay. Further, individual decay rates are evaluated in connection to specific molecular properties. On average, highly unsaturated and phenolic compounds appear to be more persistent than compounds with higher aromatic content (plant polyphenols and polycondensed aromatics), and aliphatic compounds demonstrate the highest decay rates. The reactivity of aromatics additionally increases with increasing nominal oxidation state of carbon. Molecular analysis further indicates that increasing reactivity of DOM after UV exposure is caused by disintegration of supramolecular complexes. Study IV shows that changes in relative proportion of terrestrial versus algal DOM control degradability of DOM through seasons. Under ice, when algal-derived DOM is maximally depleted, DOM degradation potential converges to similarly low levels, regardless of lake type (productive or humic), and bacterial respiration primarily relies on terrestrial carbon. This suggests a general pattern of baseline metabolism across boreal lakes. I conclude that DOM is a dynamic reactivity continuum and a tight link exists between DOM behavior and compositional properties.