The wide use and the incomplete metabolism of antibiotics, along with the poor removal efficiency of current treatment systems, results in the introduction of large quantities of antibiotics to the environment through the discharge of treated and untreated wastewater. If not treated or attenuated near the source of discharge, the antibiotics can be distributed widely in the environment. In this research, sulfamethoxazole (SMX), a common sulfonamide antibiotic, was selected as a model compound due to its presence in the environment and its resistance to remediation and natural attenuation. Among the various entry routes, discharges from on-site disposal systems are of particular interest due to the wide use of these systems. The complex nature of subsurface transport downstream of these systems adds difficulties to the removal of SMX from subsurface discharges. For this research, two processes that impact SMX removal, biodegradation and sorption, were examined to determine the primary factors governing the elimination of SMX from septic effluent discharges in the subsurface. To characterize the biodegradation of SMX, batch experiments were conducted with SMX in the presence of septic effluent and soil for both aerobic and anoxic conditions. Results showed that SMX removal was limited in the septic effluent but increased in the presence of soil, demonstrating the important role of the soil in SMX removal in both aerobic and anoxic conditions. Addition of external nutrients (ammonium and sulfate) had small effects on SMX removal, although SMX removal was enhanced under aerobic condition with increased dissolved organic carbon. To overcome the limited sorption of SMX on soil, soil amendments were developed and evaluated using biochar, a green and cost-effective adsorbent. Biochars produced from different types of feedstock were characterized for different pyrolysis temperatures, and their adsorption behaviors were examined and compared with commercial biochar and activated carbon (AC). Adsorption isotherms were developed and adsorption kinetics of soil, biochar and AC were studied. Results showed that adsorption on soil, biochar and AC followed three different kinetics models and their equilibrium isotherms followed the Freunlich model. Higher adsorption rates were achieved with biochars prepared at the higher temperature. A lab-engineered biochar with pine sawdust at 500 °C achieved comparable sorption capacity to AC. SMX transport in subsurface was also explored with saturated soil columns filled with soil that was mixed with biochar at different percentages. Significant SMX removal (including complete elimination at a low flowrate and over 90 % elimination at a high flowrate) for all cases was primarily attributed to biodegradation. These results provide insight into the transport and transformations affecting SMX, and then provide a basis for developing low-cost approaches for the mitigation of SMX.

L'assainissement non collectif concerne 12 à 15 millions de personnes en France. La filière classique de ce mode d’assainissement se compose généralement d'un prétraitement anaérobie par une fosse septique recevant l’ensemble des eaux usées domestiques suivi d’un système d’infiltration dans le sol ou d’un filtre à sable. Le filtre à sable vertical drainé met à profit le pourvoir épuratoire qui est principalement lié à la présence d’une biomasse sous forme d’un biofilm. Cette dynamique de la croissance de la biomasse ou du biofilm est soumise à l’impact de la nature de matériaux filtrants. L’écoulement insaturé dans ces systèmes conditionne également cette croissance du biofilm. Dans ce contexte, l'objectif du travail de la thèse est d’appréhender les mécanismes mis en jeu et particulièrement l’impact des matériaux dans le fonctionnement des filtres en comparant notamment deux types de matériaux: les sables de rivière et les agrégats concassés. Pour cela, une étude expérimental sur une unité pilote composé des réacteurs de filtration du diamètre de 30cm et différents épaisseurs de garnissage (15, 30 et 70cm) a été construite. Les réacteurs garnis de deux sables roulés et deux agrégats concassés, sont alimentés en effluent septique avec une charge volumique 12cm/jour par 10 bâchés par jour. Suite des matériaux, une étude de la performance épuratoire avec le suivi des composants biochimiques de la biomasse totale et de la matrice extracellulaire du biofilm est réalisée en comparant notamment les deux types de matériaux filtrants. / The onsite wastewater treatment systems concern 12 to 15 million of people in France. The treatment plant is generally composed by a septic tank as pretreatment, followed by soil infiltration field or sand filtration bed. The vertical drained sand filter provides the purification capacity thanks to the presence of a biomass in form of the biofilm. The dynamic of the biomass growth or the biofilm development is under the impact of filter materials’ nature. In this context, the objective of this work is to understand the mechanisms involved and especially the impact of medium in the functioning of the filtration reactor by comparing two types of packing materials: river sands and crushed aggregates. For this purpose, an experimental study is conducted with pilot unity composed by filtration reactors of 30cm of diameter and different packing thicknesses (15, 30 and 70cm). The reactors packed with two river sands and two crushed aggregates are fed with septic effluent with a volumic hydraulic charge of 12cm/day by 10 batches per day. Based on a characterization of materials, a study of purification performance with biochemical components monitoring of the total biomass and the extracellular matrix of the biofilm is realized by comparing two types of filter materials. The purification performance has presented similar efficiencies of particulates and organic matters removals by fine river sand and fine crushed aggregate. The nitrogen pollutants removals are more effective in the fine river sand which presents the finest granulometry with an alternative of aerobic and anoxic phases along the reactor depth and with a biomass more abundant. The distribution and the quality of the total biomass and the extracellular matrix differentiate between the river sand and the crushed aggregates. As the reference material, the fine river sand presented an earlier stabilization of total biomass growth with a less important production of extracellular exudates compared to the crushed aggregates. The origin of impacts brought by the crushed aggregates might be due to the higher fine particles content which created microenvironments poor in substrates or in oxygen and also due to a more heterogeneous mineralogy. The extracellular components of highest percentage in the biofilm of crushed aggregate are polysaccharides type substances.