Lac Supérieur | EPFL Graph Search

Le lac Supérieur est le plus grand des Grands Lacs d’Amérique du Nord. Sa superficie () en fait le plus vaste lac d'eau douce au monde. Il est à cheval entre les États-Unis et le Canada. Géographie vignette|gauche|250px|Accumulation de glace en hiver, sur le littoral sud (Minnesota). Le lac Supérieur s'étend sur , partagée entre le Canada (28 750 km², ce qui le met au second rang des superficies lacustres canadiennes après le lac Huron) et les États-Unis (53 600 km²). Le lac Supérieur est plus vaste que la République tchèque ; ses longueurs et largeurs maximales sont respectivement de et . Sa profondeur moyenne est de et atteint un maximum de . Le lac Supérieur contient d’eau (12 232 milliards de mètres cubes - 10 % de l'eau douce libre de surface de la Terre) et compte de rivages, y compris ses îles. La durée de rétention de 191 ans correspond à un apport moyen de 2030 m3/s Il baigne la province de l'Ontario (Canada) au nord, et les États du Minnesota, du Wisc

N-removal optimization by various aeration strategies

Simon Taillard

In order to improve the purification capacity of an aerobic granular sludge, two aeration strategies were designed and tested. The goal was to optimize the nitrogen removal performances via various oxygen patterns in the aeration phase of the reactor cycle. The main process driving theses patterns is that a difference between oxygen concentrations in the reactor will modify the size of the anoxic inner zone of a granule. The first aeration was based on a succession of oxygen peaks (50%DO) and semi anoxic valleys (5%DO). The second was based on a short pulse of oxygen followed by the hermetical isolation of the reactor and a continuous recirculation of the pulse. The objective was to get an n-removal superior to 82%, results of a previous article, and if possible better than 88%, results of a previous experiment in the lab. The succession of oxygenated peaks strategy worked well and gave good results, as the n-removal was increasing with the sludge bed height and time. However, due to laboratories problem and to the shortness of the time-slots available to experiment, the system could not have the time to stabilize and no constant removal value could be found. Therefore, the average n-removal was equal to 69% for 40 days of experimentation, with some peak over 80%. The highest value observed was 88% of n-removal. The recirculation strategy gave unsatisfactory results, actually unexplained. The first recirculation led to the disappearance of high nitrification capacity, giving an n-removal percentage of 48%. The second attempt was worse, as the oxygen concentration started to behave incoherently and over-oxygenated the system. This behavior still lacks a proper explanation and only hypotheses can actually be proposed. Besides these mains results, the surveillance of the sludge in the reactors allowed the discovery of a bias in the evaluation of the suspended biomass measurement. It was explained by the fact that heavier granules tend not to mix well, and therefore the system could not be considered homogenous. The bias was created because measurements were made at different height between the two reactors. In order to remove it, a linear transformation was developed and tested. The first results seem to be consistent, but due to the lack of experimenting time, the working hypothesis could not be deepened. Another bias that was spotted is the possible influence of the operator during the aeration cycle measurement. Three of four off-trend points in the first experiment originated from a cycle measurement. The data set was too small to draw strong conclusions upon the bias. An extended survey of the cycle measurement and their supposed off-trend consequences in previous and future experiments could clarify the situation.

2009

Hyphenated Analytical Techniques for Studying the Speciation and Fate of Contaminants and Nanoparticles in Waste Treatment and Bioenergy Processes

Debora Foppiano

The widespread use of nanoparticles (NPs) and other potentially ecotoxic chemical compounds to enhance the quality of consumer products has raised concern about their fate in the environment. Indeed, those products have to be ultimately disposed of and along with them also NPs and contaminants could end up in landfills or in facilities where waste and nano-waste, as well as biomass products, are stored and/or treated. Among the possible pathways involving their release in the environment, this thesis' focus is in particular on gaseous emissions during two main applications, namely waste treatment and bioenergy generation. In this frame, the effect of contaminants is considered not only in terms of their toxicity but also in terms of their effect on energy efficiency or potential damages caused to the facilities along the process chain. For this purpose, new online and offline methods were developed by using hyphenated analytical techniques to achieve complementary and superior power of investigation. Firstly, the speciation of siloxane compounds were studied during bio-methane production from manure and agricultural waste. The samples were collected using a liquid quench (LQ) sampling system that concentrates condensable and non-condensable compounds in a liquid solvent in continuous contact with the gas probed, for an improved time resolution. The offline investigation required a complete method development for the combination of a separation technique, such as gas chromatography (GC), and detectors able to provide chemical information. The novelty was represented by the simultaneous use of GC with a flame ionization detector (FID) and inductively coupled plasma mass spectrometry (ICP-MS), which could fulfill the requirements of recent regulations for the specific application, with lower detection limits compared to existing methods. Secondly, the fate of zinc oxide (ZnO) NPs were investigated during the combustion of impregnated wood, as a model of nano-waste. ZnO was specifically considered because of its use in paints and waterproofing agents. The potential release of NPs during nano-waste treatment was investigated with an online method that combines an RDD (rotating disk diluter) used as conditioning and dilution unit, an SMPS (scanning mobility particle sizer) providing the particle size distribution and ICP-MS used as a multi-elemental analytical technique. An initial assessment of the performances of the RDD-SMPS-ICP-MS was required, to correct some major assumptions used in the SMPS data treatment. The technique was successfully applied even to heterogeneous matrices. The particular capability of performing online sampling and simultaneous size-resolved and elemental analysis on the off-gases produced during wood combustion was providing the needed insights to verify the predicted mechanism of reduction and further re-oxidation of ZnO nano-objects. Thanks to the calibration strategy coupling a TGA (thermogravimetric analyzer) with RDD-ICP-MS, a successful determination of their concentration was also possible. In conclusion, the development of specific hyphenated techniques was proven to be crucial to improve the capabilities of the already existent state-of-the-art methods and to develop new ones that could give more insight on the two main scientific questions that were the driving force of this thesis.

EPFL2019

A Gibeon meteorite yields a high-performance water oxidation electrocatalyst

Wiktor Stefan Bourée, Paul Joseph Dyson, Aswin Gopakumar, Nestor Guijarro Carratala, Florian Le Formal, Arnaud Magrez, Mathieu Steven Prévot, Kevin Sivula, Charlotte Marie Sornay, Julie Voit

Examining the electrocatalytic performance of naturally-occurring metallic minerals is of interest for energy conversion applications given their unique atomic composition and formation history. Herein, we report the electrocatalytic function of an iron-based Gibeon meteorite for the oxygen evolution reaction (OER). After ageing under operational conditions in an alkaline electrolyte, an activity matching or possibly slightly superior to the best performing OER catalysts emerges, with stable overpotentials as low as 270 mV (for 10 mA cm(-2)) and Tafel slopes of 37 mV decade(-1). The Faradaic efficiency for the OER was unity and no deterioration in performance was detected during 1000 hours of OER operation at 500 mA cm(-2). Mechanistic studies suggest an operando surface modification involving the formation of a 3D oxy(hydroxide) layer with a metal atom composition of Co0.11Fe0.33Ni0.55, as indicated by Raman and XPS studies and trace Ir as indicated via elemental analysis. The growth of the catalyst layer was self-limiting to

2016