A global model for the combustion of gas mixtures released from forest fuels

International audienc

Skeletal and global mechanisms for the combustion of gases released by crushed forest fuels

International audienc

Determination of the distribution of rare earth elements La and Gd in <i>Daphnia magna</i> via micro and nano-SXRF imaging

While our awareness of the toxicity of rare earth elements to aquatic organisms increases, our understanding of their direct interaction and accumulation remains limited. This study describes the acute toxicity of lanthanum (La) and gadolinium (Gd) in Daphnia magna neonates and discusses potential modes of action on the basis of the respective patterns of biodistribution. Ecotoxicological bioassays for acute toxicity were conducted and dissolved metal concentrations at the end of the tests were determined. The results showed a significant difference in nominal EC50 (immobility) between La (>30 mg L−1) and Gd (13.93 (10.92 to 17.38) mg L−1). Daphnids that were then exposed to a concentration close to the determined EC50 of Gd (15 mg L−1, nominal concentration) for 48 h and 72 h were studied by synchrotron micro and nano-X-ray fluorescence to evaluate the biodistribution of potentially accumulated metals. X-ray fluorescence analyses showed that La was mainly found in the intestinal track and appeared to accumulate in the hindgut. This accumulation might be explained by the ingestion of solid La precipitates formed in the media. In contrast, Gd could only be detected in a small amount, if at all, in the intestinal tract, but was present at a much higher concentration in the tissues and became more pronounced with longer exposure time. The solubility of Gd is higher in the media used, leading to higher dissolved concentrations and uptake into tissue in ionic form via common metal transporting proteins. By studying La and Gd biodistribution in D. magna after an acute exposure, the present study has demonstrated that different uptake pathways of solid and dissolved metal species may lead to different accumulation patterns and toxicity.PeerReviewe

Fate of cadmium in the rhizosphere of Arabidopsis halleri grown in a contaminated dredged sediment

International audienceIn regions impacted by mining and smelting activities, dredged sediments are often contaminated with metals. Phytotechnologies could be used for their management, but more knowledge on the speciation of metals in the sediment and on their fate after colonization by plant roots is needed. This work was focused on a Zn, Cd-contaminated contaminated dredged sediment from the Scarpe river (North of France). Zn, Cd hyperaccumulating plants Arabidopsis halleri from metallicolous and non metallicolous origin were grown on the sediment for five months in a pot experiment. The nature and extent of the modifications in Cd speciation with or without plant were determined by electron microscopy, micro X-ray fluorescence and bulk and micro X-ray absorption spectroscopy. In addition, changes in Cd exchangeable and bioavailable pools were evaluated, and Cd content in leachates was measured. Finally, Cd plant uptake and plant growth parameters were monitored. In the original sediment, Cd was present as a mixed Zn, Cd, Fe sulfide. After five months, although pots still contained reduced sulfur, Cd-bearing sulfides were totally oxidized in vegetated pots, whereas a minor fraction (8%) was still present in non vegetated ones. Secondary species included Cd bound to O-containing groups of organic matter and Cd phosphates. Cd exchangeability and bioavailability were relatively low and did not increase during changes in Cd speciation, suggesting that Cd released by sulfide oxidation was readily taken up with strong interactions with organic matter and phosphate ligands. Thus, the composition of the sediment, the oxic conditions and the rhizospheric activity (regardless of the plant origin) created favourable conditions for Cd stabilization. However, it should be kept in mind that returning to anoxic conditions may change Cd speciation, so the species formed cannot be considered as stable on the long term

Study of lead levels in soils by weathering of metallic Pb bullets used in dove hunting in Córdoba, Argentina

A study of level of Pb in soils of the center-north of the Province of Córdoba, a worldwide recognized tourist region for dove hunting, was performed in this work. The native forest of the region has a great population of doves associated with the grainproductivefields of the surrounding. Contamination of soils due to hunting activities is regulated by national and local norms. The Córdoba Environmental Secretary by resolution no. 1115/2011 approved a new regulation that categorizes this activity as generator of Y31 (Pb) industrial waste. Lead from pellets alloy is deposited on the soil of the shootingfields. Samples were taken at depth of 50 mm from 315 pits referenced by GPS in accordance with local environmental authorities as well as the hunting outfitters companies. Sampling sites are distributed between parallels 31 °S (S31) up to 30 °S (S30) and between meridians W64 up to W63. Soils samples were analyzed by X-rayfluorescence spectroscopy while Pb bullets were analyzed by scanning electron microscopy (SEM) and X-ray diffraction (XRD). The average concentration obtained for Pb in dry soil sieved (200 mesh) was 80 ppm. Powder XRD patterns of crust material removed from the corroded surface of weathered bullets were obtained. Three Pb mineral compounds were identified by XRD analysis and also studied by optical microscopy and SEM.submittedVersionFil: Bonzi, Edgardo Venusto. Universidad Nacional de Córdoba. Facultad de Matemática, Astronomía y Física; Argentina.Fil: Rubio, Marcelo. Universidad Nacional de Córdoba. Facultad de Matemática, Astronomía y Física; Argentina.Fil: Rubio, Marcelo. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina.Fil: Rubio, Marcelo. Ministerio de Ciencia y Tecnología de la Provincia de Córdoba. Centro de Excelencia en Procesos y Productos de Córdoba; Argentina.Física Atómica, Molecular y Química (física de átomos y moléculas incluyendo colisión, interacción con radiación, resonancia magnética, Moessbauer Efecto.

Experimental Observations on the Thermal Degradation of a Porous Bed of Tires

In this paper, an experimental study on the forward combustion of a bed of tires and refractory briquettes is presented. Temperature measurements within the reactor were obtained as a function of time as well as the evolution of the fuel bed. The products of combustion were cooled down and usable liquid fuel was recovered and measured. The reaction was found to become unstable for fuel concentrations lower than 50%. The results show that the airflow and tire concentration define different modes of combustion while the reaction remains oxygen limited. Oil production is maximized when an increase in airflow leads to a transition from a rate-limited reaction to a heat transfer-limited propagation. Variation of the tire concentration shows the importance of the inert in achieving high conversion rates

Determination of the Burning Characteristics of a Slick of Oil on Water

Research journal paper published in Spill Science and Technology Bulletin 2003The burning rate of a slick of oil on a water bed is characterized by three distinct processes, ignition, flame spread and burning rate. Although all three processes are important, ignition and burning rate are critical. The former, because it defines the potential to burn and the latter because of the inherent possibility of boilover. Burning rate is calculated by a simple expression derived from a onedimensional heat conduction equation. Heat feedback from the flame to the surface is assumed to be a constant fraction of the total energy released by the combustion reaction. The constant fraction (c) is named the burning efficiency and represents an important tool in assessing the potential of in-situ burning as a counter-measure to an oil-spill. By matching the characteristic thermal penetration length scale for the fuel/water system and an equivalent single layer system, a combined thermal diffusivity can be calculated and used to obtain an analytical solution for the burning rate. Theoretical expressions were correlated with crude oil and heating oil, for a number of pool diameters and initial fuel layer thickness. Experiments were also conducted with emulsified and weathered crude oil. The simple analytical expression describes well the effects of pool diameter and initial fuel layer thickness permitting a better observation of the effects of weathering, emulsification and net heat feedback to the fuel surface. Experiments showed that only a small fraction of the heat released by the flame is retained by the fuel layer and water bed (of the order of 1%). Ignition has been studied to provide a tool that will serve to assess a fuels ease to ignite under conditions that are representative of oil spills. Two different techniques are used, piloted ignition when the fuel is exposed to a radiant heat flux and flash point as measured by the ASTM D56 Tag Closed Cup Test. Two different crude oils were used for these experiments, ANS and Cook Inlet. Crude oils were tested in their natural state and at different levels of weathering, showing that piloted ignition and flash point are strong functions of weathering level

Evaluation of the Extinction Factor in a Laminar Flame Established over a PMMA Plate in Microgravity

A methodology for estimating the extinction factor at wavelength of 530 nm in diffusion flames is presented. All experiments have been in microgravity and have as their objective the production of quantitative data that can serve to evaluate the soot volume fraction. A better understanding of soot formation and radiative heat transfer is of extreme importance to many practical combustion related processes such as spacecraft fire safety. The experimental methodology implements non-axisymmetric configurations that provide a laminar diffusion flame at atmospheric pressure. PMMA is used as fuel and the oxidizer flows parallel to its surface. Optical measurements are performed at the 4.74 s ZARM drop tower

Interactions between Soot and CH* in a Laminar Boundary Layer Type Diffusion Flame in Microgravity

A three-dimensional laminar non-buoyant diffusion flame was studied with the objective of improving the understanding of the soot production. The flame originated from a porous ethylene burner discharging into a laminar boundary layer. Soot volume fractions were measured using Laser-Induced Incandescence (LII) and the spontaneous emission from CH* was determined using chemiluminescence. The main parameter varied was the oxidizer flow. CH* measurements allowed to identify the reaction zone, while LII measurements permitted the tracking of soot. It was observed that soot volume fractions are inversely proportional to the global residence time. This is in contradiction to previous studies on axi-symmetric non-buoyant diffusion flames. The combined measurements allowed to establish that the apparently contradictory behaviour can be explained by an analysis of the influence of the flow field on the ratio of soot production to oxidation