Mise en danger des installations de valorisation énergétiques des biogaz par les siloxanes : la méthanisation agricole est-elle concernée ?

International audienc

Past and present ITRF solutions from geophysical perspectives

International audienceQuestions about the accuracy of the origin of the different versions of International Terrestrial Reference Frame (ITRF), have been regularly raised. In particular the origin drift between ITRF2000 and ITRF2005 (and subsequent ITRF solutions) is well-known to be problematic. Here, we look forward a sort of geophysical evaluation of ITRF solutions. We investigate GNSS vertical velocities provided by the last four ITRF solutions (ITRF2000 to ITRF2014; Altamimi et al., 2005, 2007, 2011, 2016) that we compare with different Global Isostatic Adjustment (GIA) model predictions. We find that each new ITRF solution appears to be more and more consistent with all GIA predictions, except ITRF2014 whose consistency with the GIA models depends on the date of observation. Indeed, GNSS observations and GIA predictions appear consistent at global scale at a level of ~4 mm/yr using ITRF2000 data, ~2.5-3 mm/yr using ITRF2005 data, and ~2 mm/yr using ITRF2008 data (global weighted root mean squares). For ITRF2014, the consistency between GNSS observations and GIA predictions is extremely high in 2000 (~1.5 mm/yr) but seems then to decrease with time (~2 mm/yr in 2013). This discrepancy is due to the recent ice melting effect that is not accounted for in GIA models, but clearly evidenced by ITRF2014 vertical velocities during the last years of observations, in particular in Greenland

UV photolysis and UV/H2O2 photolysis processes for estrogens removal in water

International audienceThis study aimed at investigating the degradation of a mixture of estrogenic hormones (Estrone (E1), β-Estradiol (E2), and 17α-Ethinyl Estradiol (EE2)) in water by UV photolysis and UV/H₂O₂ photolysis. Firstly, the effects of water matrices (drinking water and treated wastewater) and H₂O₂ concentrations (10, 40, and 90 mg/L) were determined. The hormones were added in a UVC (λ=254 nm) pilot system running in semi-batch. Hormones degradation rates were measured by HPLC-UV. Secondly, a single concentration of H₂O₂ (20 mg/L) was tested in order to optimize oxidant cost. Hormones degradation rates as well as changes in estrogenic activity, measured by Yeast Estrogen Screen (YES), were followed at the same time. First results showed negligible degradation of E2 and EE2 by UV photolysis in both matrices. High UV fluences were needed to degrade 80% of E1 in drinking water (1300 mJ/cm²) and treated wastewater (1800 mJ/cm²). All hormones degradation rates were significantly improved in both water matrices at H2O2 concentration as low as 10mg/L. UV fluence of 400 mJ/cm² and 90mg/L of H₂O₂ would enable to remove 80% of all hormones in treated wastewater. Water quality could highly influence the treatment efficiency as shown by higher UV fluences required to reach the same result in treated wastewater than in drinking water. Estogenic activity, measured by YES bioassay, could not be removed by UV photolysis whereas it decreased in the same trend than E2 and EE2 removal rate when combining UV and 20 mg/L of H₂O₂. No high estrogenic by-products were formed. These results pointed out that estrogens removal can be highly enhanced by UV/H₂O₂ photolysis in drinking water and treated wastewater. By combining the approriate concentration of H₂O₂ and UV fluence, it would be possible to design a cost effective treatment for small and midlle sized WTPs

Evidence for postglacial signatures in gravity gradients: A clue in lower mantle viscosity

International audienceThe Earth's surface was depressed under the weight of ice during the last glaciations. Glacial Isostatic Adjustment (GIA) induces the slow recession of the trough that is left after deglaciation and is responsible for a contemporary uplift rate of more than 1 cm/yr around Hudson Bay. The present-day residual depression, an indicator of still-ongoing GIA, is difficult to identify in the observed topography, which is predominantly sensitive to crustal heterogeneities. According to the most widespread GIA models, which feature a viscosity of 2- 3 ×1021 Pa s on top of the lower mantle, the trough is approximately 100 m deep and cannot explain the observed gravity anomalies across North America. These large anomalies are therefore usually attributed to subcontinental density heterogeneities in the tectosphere or to slab downwelling in the deep mantle. Here, we use observed gravity gradients (GG) to show that the uncompensated GIA trough is four times larger than expected and that it is the main source of the North American static gravity signal. We search for the contribution to these GGs from mantle mass anomalies, which are deduced from seismic tomography and are mechanically coupled to the global mantle flow. This contribution is found to be small over Laurentia, and at least 82% of the GGs are caused by GIA. Such a contribution from GIA in these GG observations implies a viscosity that is greater than 1022 Pa s in the lower mantle. Our conclusions are a plea for GIA models with a highly viscous lower mantle, which confirm inferences from mantle dynamic models. Any change in GIA modelling has important paleoclimatological and environmental implications, encouraging scientists to re-evaluate the past ice history at a global scale. These implications, in turn, affect the contribution of bedrock uplift to the contemporaneous mass balance over Antarctica and Greenland and thus the present-day ice-melting rate as deduced from the GRACE space mission. Additionally, studies of the thermo-chemical structure of the lithosphere/crust under North America that exploit gravity or geodetic data should be corrected for a GIA model, which is not the case today

ITRF2014, Earth Figure Changes, and Geocenter Velocity: Implications for GIA and Recent Ice Melting

International audienceUsing a selection of Global Navigation Satellite System vertical velocities from the latest solution of the International Terrestrial Reference Frame (ITRF) ITRF2014, we calculate the degree-1 and degree-2 spherical harmonics coefficients (SHC) of the solid Earth figure changes at different dates, with realistic errors that take into account the inhomogeneity of the network. We find that the SHC are globally close to zero except the zonal coefficients, which show values notably larger than those derived from different glacial isostatic adjustment (GIA) models and which have tended to increase during the time span of observations. We show that these differences are most probably due to global recent ice melting (RIM). Assuming elastic RIM deformation, we then investigate the Earth's geocenter velocity and the geoid oblateness time evolution (J2-rate) derived from our SHC estimations. The obtained geocenter velocity reaches 0.9 ± 0.5 mm/year in 2013 with a z-component of 0.8 ± 0.4 mm/year, which is slightly larger than previous estimations. We compare our J2-rate estimations with observations. Our estimations show a similar acceleration in J2 after 2000. However, our estimates are notably larger than the observations. This indicates either that the J2-rate due to GIA processes is lower than expected (as proposed by Nakada et al., 2015, 2016) or that the deformation induced by RIM is not purely elastic, or both. Finally, we show that viscous relaxation or phase transitions in the mantle transition zone may only partly explain this discrepancy. This raises the question of the accuracy of current mass estimations of RIM and GIA models

Comparatif expérimental des méthodes de détermination du silicium total dans un biogaz et un biométhane.

International audienc

Etat des lieux et comparatif expérimental des méthodes de détermination du silicium total dans un biogaz et un biométhane

Rapport Etude RECORD n°15-0157/1

Treatment of pharmaceuticals by UV/H2O2 process in small wastewater treatment plants: a reed bed constructed wetland case study

International audienc

Effect of Therapeutic Level Ultrasound on Visual Evoked Potentials in the Hypoxic Cat

NRC publication: Ye