Photocatalytic Degradation of Monolinuron and Linuron in an Aqueous Suspension of Titanium Dioxide Under Simulated Solar Irradiation

The photocatalytic degradation of two phenylurea herbicides, monolinuron (MLN) and linuron (LN), was investigated in an aqueous suspension of TiO2 using simulated solar irradiation. The objective of the study was to compare their photocatalytic reactivity and to assess the influence of various parameters such as initial pesticide concentration, catalyst concentration and photonic flux on the photocatalytic degradation rate of MLN and LN. A comparative study of the photocatalytic degradation kinetics of both herbicides showed that these two compounds have a comparable reactivity with TiO2/simulated sun light. Under the operating conditions of this study, the photocatalytic degradation of MLN and LN followed pseudo first-order decay kinetics. The kobs values indicated an inverse dependence on the initial herbicide concentration and were fitted to the Langmuir-Hinshelwood equation. Photocatalytic degradation rates increased with TiO2 dosage, but overdoses did not necessarily increase the photocatalytic efficiency. The degradation rate of MLN increased with radiant flux until an optimum at 580 W m‑2 was reached and then decreased. Under these conditions, an electron-hole recombination was favored. Finally, the photocatalytic degradation rate depended on pH, where an optimum was found at a pH value close to the pH of the point of zero charge (pH = 6).La dégradation photocatalytique de deux herbicides, le monolinuron (MLN) et le linuron (LN), a été étudiée dans une suspension de TiO2 au contact de lumière solaire simulée. L’objectif de cette étude est de comparer leur photoréactivité et d’évaluer l’influence de différents paramètres tels que la concentration initiale en pesticide, la concentration en catalyseur et le flux photonique sur la cinétique de dégradation du monolinuron. L’étude comparative de la dégradation des deux herbicides a montré que les deux composés présentent une réactivité comparable avec le système TiO2/lumière simulée. Dans les conditions opératoires de cette étude, la dégradation photocatalytique du LN et du MLN suit une cinétique de pseudo ordre 1. La pseudo-constante kobs est inversement proportionnelle à la concentration initiale en pesticide et peut être décrite par une équation de Langmuir-Hinshelwood. L’étude de l’influence de la concentration en TiO2 a permis de montrer que la cinétique de dégradation du MLN augmente avec la dose de catalyseur, mais un surdosage n’est pas nécessaire pour augmenter l’efficacité du procédé. Cette étude a permis également de montrer que la pseudo‑constante d’ordre 1 de dégradation du MLN augmente linéairement avec le flux lumineux jusqu’à 580 W m-2 puis décroît. Dans ces conditions, la recombinaison des électrons trous est favorisée. Enfin, la cinétique de dégradation du MLN en fonction du pH passe par un optimum de pH proche du pH de point de charge nulle (pH = 6)

New Methods for HTR Fuel Waste Management

International audienceConsidering the need to reduce waste production and greenhouse emissions by still keeping high energy efficiency, various 4th generation nuclear energy systems have been proposed. As far as graphite moderated reactors are concerned, one of the key issues is the large volumes of irradiated graphite encountered (1770 m3 for fuel elements and 840 m3 for reflector elements during the lifetime (60 years) of a single reactor module [1]). With the objective to reduce volume of waste in the HTR concept, it is very important to be able to separate the fuel from low level activity graphite. This requires to separate TRISO particles from the graphite matrix with the sine qua non condition to not break TRISO particles in case of future embedding of particles in a matrix for disposal. According to National Regulatory Systems, in case of limited graphite waste production or of short duration HTR projects (e.g. in Germany), direct disposal without separation is acceptable. Nevertheless, in case of large scale deployment of HTR technology, such approach is not economical and sustainable. Previous attempts in graphite management (furnace, fluidised bed and laser incinerations and encapsulation matrices) dealt with graphite matrix only. These are the reasons why we studied the management of irradiated compact-type fuel element. We simulated the presence of fuel in the particles by using ZrO2 kernels. Compacts with ZrO2 TRISO particles were manufactured by AREVA NP. Two original methods have been studied. First, we tested high pressure jet to erode graphite and clean TRISO particles. Best erosion rate reached about 0.18 kg/h for a single nose ending. Examination of treated graphite showed a mixture of undamaged TRISO particles, particles that have lost the outer pyrolytic carbon layer and ZrO2 kernels. Secondly, we studied the thermal shock method by immerging successively graphite into liquid nitrogen and hot water to cause fracturing of the compact. This produced particles and graphite fragments with diameter ranging from several centimetres to less than 500 µm. This relatively simple and economic method may potentially be considered as a pre-treatment step and be coupled with other method(s) before reprocessing and recycling for example

Etude de la dégradation de quelques composés organochlorés volatils par photolyse du peroxyde d'hydrogène en milieux aqueux

Le travail a eu pour but d'étudier l'efficacité de la photolyse du peroxyde d'hydrogène sur la dégradation de quelques composés organochlorés aliphatiques saturés (chiorométhanes et chloroéthanes) en milieu aqueux (pH 7,5). Les expériences ont été réalisées en réacteur statique, avec une Lampe basse pression à vapeur de mercure et avec des concentrations initiales en produit chloré de l'ordre de 10-6 mol l-1 et en H202 comprises entre 10-5 et 10-3 mol L-.Les résultats montrent que le système H202/UV peut oxyder les composés organochlorés étudiés à l'exception des composés ne possédant pas d'atome d'hydrogène (CCL4 et C2 CL6). Les rendements d'oxydation obtenus avec Le réacteur utilisé dépendent du temps de réaction, de la concentration initiale en H202, du flux photonique et peuvent être nettement diminués par la présence de pièges à radicaux (ions bicarbonates) dans le milieu réactionnel.Par ailleurs, une étude cinétique de la photolyse du peroxyde d'hydrogène en absence de matière organique est également présentée.The aim of this work was to study oxidation of certain volatile polychlorinated hydrocarbons, using hydrogen peroxide photoactivated by UV. This research was carried out with different mixtures of diluted aqueous solutions of chloromethanes (CHCl3, CCl4) and chloroethanes (C2H3Cl3, C2H2Cl4, C2HCl5, CCl6), which are typical halogenated compounds most frequently found in contaminated groundwater. The effect of the hydrogen peroxide concentration, the light intensity and the bicarbonate concentration on the rate of 1,1,2-trichloroethane (TCE) oxidation was determined. A kinetic study on hydrogen peroxide photolysis in a solution free of organic compounds was also carried out.EXPERIMENTATIONExperiments were conducted in a batch reactor (V = 4 l), equipped with an immersed mercury low-pressure lamp. The intensity emitted at 253.7 nm was roughly 2 1019 photons s-1. The temperature of the reaction mixture was maintained with a regulation system at 16 ± 0.5 °C (figure 1).The solutions were prepared in a phosphate buffer µ = 2 10-2 M, pH = 7.5). The outer surface of the lamp was masked with strips of aluminium, so as to obtain various percentages of initial energy (20 to 100 %).The concentration of the hydrogen peroxide of the samples was determined by spectrophotometry and the chlorinated compounds were analysed by electron capture gas chromatography.RESULTKinetics of hydrogen peroxide photolysis : H202 was decomposed by UV tb produce two hydroxyl radicals. In diluted solutions ([H202] < 10-3 M), the concentration decreases in accordante with a first order law. The rate constant depends on the initial light intensity (Io), on the characteristics of the reactor (volume and distance between the lamp and the watt. of the reactor) and on the motar extinction coefficient of the irradiated solution (equation C). The decomposition rate appears to be dependent on pH, the rate of constant rire has been found to be proportional to the dissociation of hydrogen peroxide into its basic form (EH2O2 = 20 mol-1 cm-1,EH2O2_ = 240 mol-1 cm-1) (figure 2 and 3).Oxidation of the chlorinated compounds : H202/UV is very efficient for the removal of organic compounds. Preliminary experiments showed that both UV and H2O2 treatments do not decompose halogenated compounds. Hydroxyl radicals are extremly reactive and attack organic compounds preferentialty by abs-tracting a hydrogen atom from an organic molecule. This is confirmed by the results which show that chloromethanes and chloroethanes with an H atom are eliminated, but net compounds such as tetrachloride and hexachloroethane (figure 4 to 7).The effectiveness of an H202/UV system depends on various parameters. Studies on the TCE elimination show that the oxidation yields an increase when the reaction time, the UV irradiation dose (figure 9b) and the hydrogen peroxide concentration (figure 8) increase. However, the efficiency decreases in the presence of radical traps such as bicarbonate and carbonate ions (figure 10)

Effect of cocoa pod decomposition on earthworm density in agroforestry systems of the Dominican Republic

Cocoa-based agroforestrysystems (Cocoa AFS), that combine at least onecropin association withcocoa trees, often aim at optimizing ecological and economical interactions among their components. CocoaAFS have been widely described in the literature for their high taxonomic and functionaldiversity, includingthe soil biota. However, in these agrosystems the interactions between agricultural practices and earthworm communities are poorly documented. A common harvestingpractice all over cocoa producing countries consists in piling the harvested cocoapods on a determined area of the plantation floor before opening them. The cocoa beans are extracted and carried out of the plantationsfor further post-harvesting processes, but pod husks remain and decompose on the ground.We compared earthworm densities and some morphological traits (length and body mass) under cacao pods and leaf litterin 42cocoa AFS distributed among 4 age classes:0-3, 4-10, 11-25 and > 70 yearsin the Dominican Republic. The TSBF method was implemented: extraction of 25 x 25 cm, 20 cm depth soil monolith and hand sorting of earthworms (total of 120 TSBF). Earthworm densities were calculated and morphological traits measured. Earthworm densities were significantly higher under cacao pods than leaf litter.Earthworm lengths were slightly higher under cacao pods than under leaf litter in 11-25 years age class. Cocoa pods decomposition lead to earthworm densities increasing and, consequently,to a stimulation of ecological functions that they provide. Further studies are needed to confirmthese results, that could lead toa recommendation to spread pod husks over the plantation floor when harvesting cocoa, taking into accountthe current sanitary recommendations for harvesting

Harvesting practices and their influence on soil macrofauna in cocoa-based agroforestry systems

Agroecological approaches require a complete understanding of the agroecosystems by considering complex and countless interactions. Agroforestry systems, that combine at least one ligneous perennial with at least one crop or cattle species, often aim at optimizing ecological and economical interactions among their components. They encompass highly contrasted agroecosystems, from mechanized input-intensive plantations intercropping only two species to family grown, highly diverse and ecologically intensive agroforests. Cocoa-based agroforestry systems have been widely described in the literature for the high taxonomic and functional diversity of the soil biota, especially of larger-sized organisms such as earthworms and macroinvertebrates. However, the interactions between farmer's practices and soil macrofauna are poorly documented. A common practice all over cocoa producing countries consists in piling the harvested pods on a determined area of the plantation floor before opening them. The cocoa beans are extracted and carried out of the plantations, but pod husks remain on the floor. In this study, we compared pod harvesting sites and sites free of pod husks for the diversity of soil macrofauna in the leaf-litter, the 0-10 cm and the 10 – 20 cm soil layers. Based on 60 soil and leaf litter samples, we compared mature (aged 11-25 years) with old (aged > 70 years) cocoa-based agroforestry plantations in the Dominican Republic. We found that under the cocoa pods, macrofauna density and taxa richness were significantly higher and bulk density was lower. This result is enhanced by the age of the cocoa plantation, as the accumulation of pod husks on a determined harvesting arena tends to be higher over time. The trade-off between a recommendation to spread pod husks over the plantation floor when harvesting cocoa and the current sanitary recommendations for harvesting is discussed

Entre pratique et discours : les villes de la région parisienne face au secret au début du XVe siècle

L’étude de l’utilisation du secret dans l’espace politique à l’époque de la guerre civile entre Armagnacs et Bourguignons montre qu’il est un moyen de conquête et de conservation du pouvoir, non seulement par la dissimulation d’information, mais aussi par la révélation des secrets. Celle-ci est souvent performative, et est utilisée pour disqualifier son adversaire. Aussi le désordre créé par la pratique du secret amène-t-il les autorités à prendre des mesures de prévention et de protection

Écorçage des arbres fruitiers

La consommation de l’écorce des arbres par les ovins peut interrompre le trajet de la sève, et impacter négativement la santé et la croissance des vergers. Cet écorçage peut se produire de manière soudaine, massive et inexpliquée après plusieurs semaines de pâturage sans incident. Cette fiche présente les résultats d’expérimentations et d’enquêtes auprès de producteur.rices menées dans le cadre du projet ECORCE pour mieux comprendre l’origine de l’écorçage, et tenter d’identifier des mesures de protection efficaces

État des lieux réglementaire et juridique

Cette fiche technique est le résultat des enquêtes et ateliers de travail réalisés auprès d’arboriculteur-trices et d’éleveur-ses, mais aussi des retours de technicien-nes et professionnel-les. Elle présente les règlementations de base à avoir en tête avant de mettre en place un pâturage sous verger, que ce soit sous l’angle de la production fruitière ou animale ou de la gestion du partenariat