Modéliser pour prévoir les flux de polluants émis par un dispositif contenant des déchets

Une méthodologie d'étude du comportement en scénario de valorisation de déchets minéraux solidifiés/stabilisés est présentée. La méthodologie est basée sur des outils expérimentaux (des tests paramétriques et des essais de simulation du scénario) et des modèles de comportement. Le cas d'un bassin de stockage d'eau construit avec un matériau contenant des résidus d'épuration des fumées d'incinération d'ordures ménagères est présenté. L'influence de la carbonatation du lixiviat par le CO2 atmosphérique sur le relargage des éléments de constitution du matériau est étudiée. Un modèle de comportement est mis en place pour le cas étudié; il comporte trois niveaux : 1) le matériau (chimie et diffusion), 2) le lixiviat (chimie et convection), 3) l'absorption du CO2 dans le lixiviat. Plusieurs échelles d'expérimentation (tests de laboratoire, pilote de laboratoire, pilote de terrain) ont été mises en place pour l'étude du scénario et pour la validation du modèle de comportement. Le rôle de la modélisation est mis en avant par les résultats prévisionnels des simulations. Ainsi, pour le cas étudié, la carbonatation du système diminue la concentration du plomb dans l'eau du bassin par rapport à un scénario "bassin couvert". La carbonatation ne modifie pas le relargage des éléments solubles (Na, K, Cl) et détermine la spéciation du Ca dans le bassin et à la surface du matériau.The reuse of wastes and industrial residues should only be considered if we can assure that the environmental risks related to the planned use remain acceptable. The assessment and development of methodologies and tools used in evaluating the long-term release of pollutants from materials containing wastes is an area of research that is expanding. These methods depend on not only the characteristics of the materials (especially physical structure and composition) but also contact with both water and the reactive atmosphere.The methodological standard ENV 12 920 is fundamental in the definition of the European approach, which involves the intrinsic and dynamic characterisation of the material/scenario couple in order to model the time-dependent source term. The main steps of the methodology are: 1) definition of the problem and the solution sought; 2) description of the scenario; 3) description of the waste; 4) determination of the influence of parameters on leaching behaviour; 5) modelling of leaching behaviour and 6) behavioural model validation.The reuse scenario considered in the paper was a storage tank open to the atmosphere including material leaching, carbonation and contact with air. The reservoir content was composed of a mixture of hydraulic binders and air pollution control residues from a Municipal Solid Waste Incinerator. Modelling of the source term (the reservoir material) was performed in several steps ranging from the physico-chemical characterisation of the material to the validation of the proposed model by field simulation devices.An experimental "toolbox" consisting of equilibrium dissolution tests and a dynamic leaching test was used. The experimental data supplied by the tests are the necessary input parameters for the behavioural model and give information about the release mechanisms. Identification of the main transfer mechanisms indicates that the release of soluble pollutants is the combined result of diffusional transfer of pollutants in the solution and the physico-chemical specificity of the species.A physico-chemical and transport model has been developed for the long-term prediction of environmental leaching behaviour of porous materials containing inorganic waste solidified with hydraulic binders and placed in a reuse scenario. The model includes the source term, the leachate and the gas/liquid interface. The source term considers the main chemical equilibria (a simplified system) occurring in the interstitial water of the porous material. The consideration of the base content of the material, and the experimental determination of the solubility of heavy metals in the pore water, ensure a good representation of the metal release. The source term also includes diffusion in the porous system, which is considered the main transport phenomenon.The leachate component considers chemical reactions that occur in the leachate. Many competitive dynamic processes (fluxes of mobile species coming from or penetrating into the material, gas absorption) take place in the leachate. Mass transport by convection of the leachate is also considered. Finally, the gas/liquid interface includes absorption with chemical reactions of carbon dioxide.The physico-chemical parameters (initial element content, lead solubility and diffusion coefficient) of the model with respect to the source term were estimated using laboratory leaching tests. The gas/liquid mass transfer coefficient was estimated for each pilot. The simulation results agree with the two scales of experimental data: laboratory scale (volume of reservoir 80 L) and field tests (20 m3). No scale effect was observed as the intensity of the absorption phenomenon was virtually the same.Experimental data and simulations show the main trends for the release of elements contained in the material: 1) The results obtained show that air carbonation of the leachate does not fundamentally change mass transfer mechanisms of easily soluble species (especially for alkaline metals). For these species, the use of the apparent diffusional model is a satisfactory solution for the prediction of long-term leaching behaviour. 2) The release of Ca and Pb was governed by chemical equilibria in pore water and diffusion whereas their speciation in the leachate was determined by pH and the presence of carbonate ions. 3) A carbonation front appears at the leachate/material interface and progresses into the material. 4) The target metal (lead) has a weak release (non-detectable by the analytical method used) for the study period. 5) Simulations of similar scenarios but without carbonation (a closed reservoir) predicts a higher concentration of lead than in the studied scenario.Model estimations may be enhanced by a better knowledge of the source term (particularly the mineralogy and chemistry) and by an exhaustive listing of external factors acting in each scenario. In this study, factors such as the biological activity or temperature fluctuations were not taken into account. The general methodology used is based on several indispensable steps that lead to an environmental assessment of materials containing wastes destined for reuse scenarios. The necessary tools (experimental tests and mathematical models) are however specific for categories of materials (wastes) and types of scenarios.A new generation of decision-making tools, based on modelling and simulation results, can complete, or even replace, the normalised procedures that mainly focus on laboratory experimental data

Laboratory study on the mobility of major species in fly ash–brine co-disposal systems: up-flow percolation test

Apart from the generation of fly ash, brine (hyper-saline wastewater) is also a waste material generated in South African power stations as a result of water re-use. These waste materials contain major species such as Al, Si, Na, K, Ca, Mg, Cl and SO4. The co-disposal of fly ash and brine has been practiced by some power stations in South Africa with the aim of utilizing the fly ash to capture the salts in brine. The effect of the chemical interaction of the species contained in both fly ash and brine, when co-disposed, on the mobility of species in the fly ash–brine systems is the focus of this study. The up-flow percolation test was employed to determine the mobility of some major species in the fly ash–brine systems. The results of the analysed eluates from the up-flow percolation tests revealed that some species such as Al, Ca and Na were leached from the fly ash into the brine solution while some species such as Mg, Cl and SO4 were removed to some extent from the brine solution during the interaction with fly ash. The pH of the up-flow percolation systems was observed to play a significant role on the mobility of major species from the fly ash–brine systems. The study showed that some major species such as Mg, Cl and SO4 could be removed from brine solution using fly ash when certain amount of brine percolates through the ash.Web of Scienc

Potential hazards from waste based/recycled building materials

International audienceThis chapter presents the main waste categories used in construction materials with a focus on aggregates and cement-based materials. The chemical composition and properties of the selected wastes are presented in relation to their intrinsic toxic or ecotoxic hazard potential. The factors influencing the leaching of hazardous substances and the toxicity of construction materials in relation to their utilisation scenario are discussed. Methods and tools (including leaching and ecotoxicity tests and models) for assessing the toxic/ecotoxic properties of construction materials are presented and their relevance and application are discussed through practical case examples available in the literature

Wood preservatives

International audienc

Wood preservatives

International audienc

Environmental Assessment of Anammox Process in Mainstream with WWTP Modeling Coupled to Life Cycle Assessment

Conference: Frontiers International Conference on Wastewater Treatment (FICWTM)Location: Univ Palermo, Palermo, ITALYDate: MAY 21-24, 2017This work aims to assess the environmental balance of this process by an integrated approach consisting in modeling the WWTP and life cycle assessment. In this way two models were developed to represent HRAS and PN/A in one single stage with oxygen limitation. These models have been calibrated with literature data, and validated by modeling Strass WWTP (Austria). Finally, the models were used to compare the mainstream application to a reference WWTP. The LCA have been conducted at Endpoint and Midpoint level with different emission factors of nitrous oxide. In this way the threshold value of emission factor until the process is still interesting, from an environmental point of view, can be determined

Biofuels, electrofuels, electric or hydrogen?: A review of current and emerging sustainable aviation systems

International audienceClimate neutrality is becoming a core long-term competitiveness asset within the aviation industry, as demon-strated by the several innovations and targets set within that sector, prior to and especially after the COVID-19 crisis. Ambitious timelines are set, involving important investment decisions to be taken in a 5-years horizon time. Here, we provide an in-depth review of alternative technologies for sustainable aviation revealed to date, which we classified into four main categories, namely i) biofuels, ii) electrofuels, iii) electric (battery-based), and iv) hydrogen aviation. Nine biofuel and nine electrofuel pathways were reviewed, for which we supply the detailed process flow picturing all input, output, and co-products generated. The market uptake and use of these co-products was also investigated, along with the overall international regulations and targets for future aviation. As most of the inventoried pathways require hydrogen, we further reviewed six existing and emerging carbon-free hydrogen production technologies. Our review also details the five key battery technologies available (lithium-ion, advanced lithium-ion, solid-state battery, lithium-sulfur, lithium-air) for aviation. A semi-quantitative ranking covering environmental-, economic-, and technological performance indicators has been established to guide the selection of promising routes. The possible configuration schemes for electric propulsion systems are documented and classified as: i) battery-based, ii) fuel cell-based and iii) turboelectric configura-tions. Our review studied these four categories of sustainable aviation systems as modular technologies, yet these still have to be used in a hybridized fashion with conventional fossil-based kerosene. This is among others due to an aromatics content below the standardized requirements for biofuels and electrofuels, to a too low energy storage capacity in the case of batteries, or a sub-optimal gas turbine engine in the case of cryogenic hydrogen. Yet, we found that the latter was the only available option, based on the current and emerging technologies reviewed, for long-range aviation completely decoupled of fossil-based hydrocarbon fuels. The various chal-lenges and opportunities associated with all these technologies are summarized in this study

A numerical framework to predict the performances of a tubular photobioreactor from operating and sunlight conditions

International audienceA framework model is proposed to evaluate the actual overall growth rate of microalgae in an outdoor tubular photobioreactor. A Monte Carlo-based radiative transfer modeling approach describes the local distribution of light energy inside the broth as a function of static (reactor geometry, location) and dynamic solar radiation parameters (angle of incidence, direct and diffuse solar contribution, incident radiation intensity). The light fields are coupled to a Lagrangian discrete random walk tracking of the cells to give the light variations experienced by each microalga for different broth flow rates. The cell light experiments are combined with a dynamic biological model to statistically calculate the actual overall growth rate. Using this model, 380 numerical experiments were performed for a wide range of geographic, light, biomass concentration, and broth flow turbulence conditions. Correlations for a normalized growth rate, Gamma, relating the actual overall growth rate to its asymptotic behaviors (i.e., the instantaneous response and the full integration response), are proposed. The results clearly show that, for a fixed broth flowrate, Gamma does not change with cell concentration variation. Under given light conditions, the level of turbulence linearly manages Gamma, and thus the efficiency of sunlight utilization by the photobioreactor biomass can be tuned by the broth flow rate in the tubular photobioreactor. Gamma also increases linearly with the diffuse fraction of solar radiation. A simple correlation is proposed for fast calculation of the actual overall growth rate

Life cycle assessment of a parabolic solar cooker and comparison with conventional cooking appliances

International audienceCooking is a basic human need and is realised worldwide using several kinds of appliances, many of them requiring the direct or indirect use of fossil fuels to operate. It thus creates large amount of greenhouse gas emissions in addition to other damages to the environment and human health. Life Cycle Assessment (LCA) helps at quantifying the potential environmental impacts and at identifying the sustainable cooking practices. Here, LCA was used to evaluate the environmental performances of three western conventional cooking appliances (induction hob, electric plate and gas hob) and to compare them with those of a parabolic solar cooker declined with several materials (10 models in total). The functional unit was defined as to heat 2 L of water from room temperature to boiling temperature, three times a day, every day during 40 years. Experiments were performed to quantify the Energy consumption and the devices' composition. LCA was performed with Umberto LCA+ software with ecoinvent database, and ReCiPe method was used to for the impacts assessment with both end-point and mid-point approaches. The worst solar cooker (made on Chinese aluminium) has a cradle-to-grave climate change impact of 264 kgCO2eq while the solar device made in wood and recycled aluminium performs the best with 58 kgCO2eq. Concerning the conventional devices, the less impacting is the induction hub (847 kgCO2eq) followed by the electric plate (1085 kgCO2eq) and gas hob with the worst impact (3736 kgCO2eq), on a cradle-to-grave base. The construction stage contributes with 463, 266 and 85 kgCO2eq for the gas hob, the electric plate and the induction hob respectively. These results demonstrate that the energy consumption in the use stage is the most contributors to climate change impact. The absence of energy consumption with the solar cookers also prevent from other impacts like particulate and oxidant formation and damages on human health. Globally, the device with the highest cradle-to-grave impacts on most of the mid-point indicators (11 out of 18) is the electric plate. In comparison, the solar cookers always have lower impacts than the conventional ones except for the agricultural land occupation where the wood and Chinese aluminium parabola dominates. The impact of the latter is 161 m2·yr mainly due to the use of wood (156 m2·yr) against 95 m2·an which is the highest for the conventional cookers (electric plate). In terms of end points, the overall aggregated cradle-to-grave damage of the worst solar cooker is 25 points (Chinese aluminium), while for the cleaner conventional device is 112 points (induction hob). Among the 10 models of solar cookers, those made on wood and recycled aluminium strongly reduce the impacts compared to those fully made on aluminium. Additionally, a sensitivity analysis was performed by varying the lifespan of the cookers, the grid's carbon intensity, the annual energy consumption for cooking and the lifespan of the structure of the aluminium solar cooker. Finally, the conditions for an ecological benefit of solar cooking were analysed as well as the economic accessibility. Overall, in almost all scenarios, the solar cooker is ecologically beneficial, although its environmental performance depends on the composing materials and the frequency of use. These results demonstrate that solar cooking can be considered as a credible sustainable cooking practice