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International audience; Methane is a strong greenhouse gas, 21 times more potent than carbon dioxide. Landfills are one of the most important anthropogenic source of methane trough biogas production. For small or old landfills it is not possible install energy recovery systems and in several cases it is impossible to use flares as well. In these situations biofiltration represents a valid alternative for biogas treatment. In biofilters methane is oxidized by methanotrophic bacteria. The aim of this work is the evaluation of the efficiency of such a biofilter, through the development of a mathematical model which describes the biological oxidation process. To calibrate the model an experimental setup on a biological methane oxidation column is presented. The column was designed to reproduce at lab-scale a real biofilter trying to consider the more probable landfill boundary conditions. Although the methane oxidation efficiency in the column was lower than the expected (around 35%), an appropriate model implementation showed an acceptable agreement between the outcomes data of the model simulation and the experimental data (with a Theil's Inequality Coefficient value of 0.08). The factors that mostly affect the process and which actually regulate the entire process have been highlighted in this work. Specifically, it was found that temperature, flow and methane concentration are the most important parameters that influence the system.

A series of control and abatement systems must be provided to minimize the environmental impact that may derive from landfills (during the management or during the postmanagement). In the landfills the decomposition processes of organic substances under anaerobic conditions lead to the production of biogas which is usually composed mainly of methane (CH4) and carbon dioxide (CO2). Both are classified as greenhouse gases. In the atmosphere the concentration of CH4 has increased from a pre-industrial value of about 715 to 1732 parts per billion (ppb) in the early 1990s, and was 1774 ppb in 2005. The atmospheric concentration of CH4 in 2005 far exceeded the natural range of the last 650 000 years (320 to 790 ppb) as determined from ice cores. In the last years the values of methane concentration are due to continuing anthropogenic CH4 emissions. Several studies have demonstrated that the contribution of methane to climate change is 18% of the totalradiative forcing by all long-lived greenhouse gases. In the United States the methane originated from landfills is the second largest anthropogenic CH4 emission source: the emission of CH4 from US landfills in 2007 was about 6.329 Tg. Also in Europe, in 2006, the methane from landfills was the second largest source of anthropogenic CH4 (22%) with an estimated CH4 emission of 3.373 Tg from waste disposal. If the contribution of all the landfills in the world is considered, the amount of methane released is between 35 and 69 Tg year–1 of CH4. Obviously all these data do not originate from measurements on site but are projections based on estimated rates of CH4 production in relation with the national statistics about (landfilled) waste.In relation with the environmental problematics related to the global warming, in the last few years many countries have recognized the treatment of biogas as an important step to lower the emission of greenhouse gasses. In all the developed countries new landfills must provide for a biogas extraction system linked with an energy recovery plant. However there are different situations, such as small waste disposal sites or old landfills in which is not possible or not cost-effective making a new LFG (landfill gas) extraction system or a new energy recovery plant. For these situations there are different way to treat the biogas in order to lower the methane concentration content in the flow.Flares represent a system to reduce the methane present in the biogas. The methane is oxidized to carbon dioxide and water through combustion. Technical specifications for flares available on the market indicate a minimum flow of 50 Nm3/h and a methane concentration of 30% v/v. If these parameters are not respected the incomplete combustion would lead the production of other gaseous pollutants (hydrocarbons, nitrogen oxides, carbon monoxide etc.). In many cases the flow and the methane concentration in the gas arelow for any flares.Biofiltration is a biologic treatment for the biogas and represent a reliable system for those situations characterized by low flow quantity (less than 50 Nm3/h) and low methane concentration (less than 30%). The process consist in a biologic oxidation occurred by the methanotrophic bacteria. These bacteria are able to use the methane content in the gas flow as carbon source. The biofilter is an aerobic reactor in which the biochemical reaction described before is occurring, so called microbial aerobic methane oxidation (MAMO). Generally biofilters are containers filled with material that allows the methanotrophic bacteria to develop. The filling material is the heart of the system and different studies were focused to find the best composition to oxidize the methane. Wood chips are considered a good material to support and sustain the development of a methanotrophic biofilm. From a technical point of view the LFG is conveyed and conducted by a piping system to the biofilter. To avoid preferential pathways in the bottom of the container there is an empty space in which theLFG can be distributed uniformly over the entire oxidation surface.As for all the biological processes many environmental factors influence the methane oxidation efficiency. The temperature is an important parameter that control this process. The optimal range for these bacteria is around 25 – 35 °C, while 31°C is mentioned as the optimal temperature. However, methane oxidation can occur down to 1–2 °C. The moisture of the filling material is also important for the nutrient transport and it has to be between 10- 20% w/w. If the water content is higher the methane oxidation efficiency goes down (molecular diffusion in water is about 100 times slower than in the air). If this value is under the threshold value of 5% the bacteria activity is drastically reduced as the water stress in the system influences the nutrient supply. The pH value for the methane oxidation must be between 5.5 and 8.5. Exopolymeric substances (EPS) can also influence the methane oxidation efficiency. EPS accumulation in the biofilm reduces the CH4 oxidizing capacity.In conclusion the biogas treatment for small or landfills in advanced stages of post management is a challenging task. The biofiltration is a good solution because it is not affected by the low LFG flow or by the low methane concentration in the biogas. The development of a mathematical model to manage and control the biofiltration process is very important in order to optimize the performance of a biofilter.The aim of the thesis concerns the development of a full scale biofilter considering all the phases: mathematical model development, lab. scale calibration, sensitivity analysis, design of full-scale biofilter, construction of the full-scale biofilter, installation in a real landfill., J’ai effectué ma recherche au laboratoire d’Ingénierie Sanitaire de l’école d’Ingénierie de l’Université des études de Basilicate. J’ai travaillé d’abord sur l’état de l’art. Par le biais de recherches approfondies, j’ai repéré les groupes de travail s’occupant du même thème, afin de centrer ma recherche sur un aspect de la problématique qui n’avait pas encore été traité : la gestion du méthane présent dans les décharges petites et/ou « en fin de vie » : débit de biogaz inferieur à 50Nm3/h, concentration de méthane inférieur à 30% v/v. L’idée était de développer un procédé biologique permettant aux exploitants des décharges de traiter le biogaz ayant des caractéristiques non exploitables avec les solutions les plus communes (production d’énergie, torchère etc.). Le procédé que nous avions choisi est un procédé biologique qui, grâce à des bactéries aérobies, les « méthanotrophes», dégrade le méthane présent dans le biogaz (les méthanotrophes utilisent le méthane comme source de carbone et d’énergie). Au niveau technique la solution que nous avons choisie était la mise en œuvre d’un biofiltre, placé à l’intérieur d’un container (pour le rendre le plus possible adaptable et reproductible). Je me suis occupé personnellement de la construction et de l’installation du biofiltre à échelle réelle. Dans ce but, un travail de coordination entre les différents intervenants a été nécessaire. J’ai travaillé avec les techniciens préposés à la construction et au montage des pièces du biofiltre et les collègues de la faculté d’agronomie sont intervenus afin d’optimiser la réalisation biologique du système. De plus, j’ai géré la partie administrative en lien avec l’obtention des autorisations de la part des administrations locales pour l’installation du système dans les décharges. Concernant l’aspect financier de ce projet, j’ai demandé et obtenu le support de l’entreprise Entsorga Italia SRL qui a entièrement financé le cout totale de la réalisation du biofiltre.Dans un deuxième temps, je me suis occupé de la modélisation mathématique du procédé biologique et de la calibration du modèle. Pour cela, entre janvier et septembre 2014, j’ai intégré le groupe de recherche du laboratoire d’eau et écotechnologies (LIWET) rattaché au département de sciences biologiques et industrielles de l’Université de Gand (Belgique). L’expérience du laboratoire dans le domaine de la modélisation m’a permis d’approfondir et d’améliorer le modèle construit autour du biofiltre. Nous avons aussi travaillé sur la calibration du modèle à échelle de laboratoire. Le résultat de ma recherche a donc abouti à la mise en œuvre d’un biofiltre à échelle réelle actuellement installé dans la décharge de Venosa (Italie).

International audience; Landfills must be equipped with systems capable of reducing the impacts during both phases of management and post-management. A series of control and abatement systems must be provided to minimize the environmental impact that may derive from landfills. The processes of decomposition of organic substances occur by means of anaerobic bacteria, which are present in landfills, and lead to the production of leachate and landfill gas (LFG). Their diffusion in the environment would cause pollution of soil, water (surface and groundwater) and atmosphere. Landfill gas, which is mainly composed by methane and carbon dioxide, is the final product of the anaerobic degradation of organic waste. The production of biogas continues until the organic material has not been completely degraded and can also continue for decades. CH4 and CO2 are classified as greenhouse gases (GHGs). Many countries, in recent years, have recognized the contribution of landfill gas emission to the global climate change due to the greenhouse effect. Consequently most of the industrialized countries provide by law the extraction and treatment of landfill gas, especially in recently constructed installations. At the same time, scientific research has focused its attention on the development of new technologies that are able to balance the cost/benefit ratio and, at the same time, to adapt themselves to different scenarios. In recent decades, considerable research and testing laboratory have been conducted with the aim to identify a solution to the problem of inapplicability of traditional systems. A good solution can be represented by the biological filtration. The biofilter is a biological reactor classified as "immobilized biomass". Structurally it consists of a metal casing (biocontainer) containing a filling material, on which the methanotrophic biomass can