Comparative analyses of three olive mill solid residues from different countries and processes for energy recovery by gasification

International audienceBiomass is a renewable energy source which may provide a significant contribution to the reduction of fossil fuels consumption and the associated environmental impacts. The use of agricultural or agro-industrial waste such as solid residues from olive oil production is particularly relevant since it may combine several benefits. Gasification is a promising waste-to-energy technique for this type of lignocellulosic residues. The technology however is adapted to a relatively limited panel of solid waste fuels of defined specifications, which must therefore be characterized properly to assess their adaptation. The purpose of this research was to analyze and compare three different olive mill solid residues by complementary techniques such as Fourier transform infrared spectroscopy (FTIR) and thermochemical methods, in order to characterize these residues as potential fuels for gasification. The results obtained underlined the complex nature of the residues and indicated that they were mainly organic, with very little mineral matter. In addition to the major organic components (cellulose, hemicelluloses and lignin), the presence of several minor organic constituents was shown by thermogravimetry coupled to differential scanning calorimetry and FTIR. The gas produced from pyrolysis was analyzed by gas chromatography and mass spectrometry. It was found to contain several degradation products from lignocellulosic material and olive oil, such as hydroxyacetone, furfural and methoxyphenols. The influence of the olive oil extraction process (two-phase or three-phase) was also demonstrated. It was shown that the thermochemical degradation of olive mill residues followed a complex pathway but the composition of the residues met the requirements for gasification for most parameters

Molecular cloning and biochemical characterization of a Cu,Zn-superoxide dismutase from Scedosporium apiospermum.

A Cu,Zn-superoxide dismutase has been characterized from Scedosporium apiospermum, a fungus which often colonizes the respiratory tract of patients with cystic fibrosis. Enzyme production was stimulated by iron starvation. Purification was achieved from mycelial extract from 7-day-old cultures on Amberlite XAD-16. The purified enzyme presented a relative molecular mass of 16.4 kDa under reducing conditions and was inhibited by potassium cyanide and diethyldithiocarbamate, which are two known inhibitors of Cu,Zn-SODs. Its optimum pH was 7.0 and the enzyme retained full activity after pretreatment at temperatures up to 50 degrees C. Moreover, a 450-bp fragment of the gene encoding the enzyme was amplified by PCR using degenerate primers designed from sequence alignment of four fungal Cu,Zn-SODs. Sequence data from this fragment allowed us to design primers which were used to amplify by walking-PCR the flanking regions of the known fragment. SaSODC gene (890 bp) corresponded to a 154 amino acid polypeptide with a predicted molecular mass of 15.9 kDa. A database search for sequence homology revealed for the deduced amino acid sequence 72 and 83% identity rate with Cu,Zn-SODs from Aspergillus fumigatus and Neurospora crassa, respectively. To our knowledge, this enzyme is the first putative virulence factor of S. apiospermum to be characterized

Controlling the corrosion and cathodic activation of magnesium via microalloying additions of Ge

The evolution of corrosion morphology and kinetics for magnesium (Mg) have been demonstrated to be influenced by cathodic activation, which implies that the rate of the cathodic partial reaction is enhanced as a result of anodic dissolution. This phenomenon was recently demonstrated to be moderated by the use of arsenic (As) alloying as a poison for the cathodic reaction, leading to significantly improved corrosion resistance. The pursuit of alternatives to toxic As is important as a means to imparting a technologically safe and effective corrosion control method for Mg (and its alloys). In this work, Mg was microalloyed with germanium (Ge), with the aim of improving corrosion resistance by retarding cathodic activation. Based on a combined analysis herein, we report that Ge is potent in supressing the cathodic hydrogen evolution reaction (reduction of water) upon Mg, improving corrosion resistance. With the addition of Ge, cathodic activation of Mg subject to cyclic polarisation was also hindered, with beneficial implications for future Mg electrodes

Imaging of concentration distributions and hydrogen evolution on corroding magnesium exposed to aqueous environments using scanning electrochemical microscopy

Scanning Electrochemical Microscopy (SECM) is presented as an essential tool for the local characterization of the still uncertain mechanism for magnesium corrosion. The reaction leading to magnesium release and hydrogen evolution from separated magnesium cathodes and anodes has been imaged using an adequate combination of the operation modes available in SECM. Magnesium ion selective microelectrodes (Mg-ISME’s) were used for the visualization of the heterogeneously distributed release of magnesium (II) species. Antimony microelectrodes detected the pH gradients in the adjacent electrolyte resulting from either water or magnesium electrolysis, whereas platinum microdiscs were used to monitor the concomitant local evolution of hydrogen. Alkalization and H2 generation were observed over the magnesium strip polarized as cathode, whereas a small local acidification was observed above the strip polarized anodically, at which extensive heterogeneous magnesium release was also image

Reducing the corrosion rate of magnesium via microalloying additions of group 14 and 15 elements

A characteristic of magnesium (Mg) dissolution is that dissolution is accompanied by a concomitant increase in the hydrogen evolution reaction (HER), a phenomenon known as cathodic activation. When magnesium undergoes free corrosion or forced dissolution in response to anodic polarisation, cathodic activation is manifest, which allows magnesium dissolution to readily proceed. However, recent work revealed that alloying magnesium with micro additions of arsenic, As (a group 15 element) was capable of retarding cathodic activation, resulting in a significant reduction in the corrosion rate of Mg-As alloys. As such, in the pursuit of elements with similar chemical and electrochemical properties to arsenic, but with less toxicity, a number of group 14 and 15 elements were alloyed with magnesium and reported herein. Based on the binary alloying additions studied herein, it was revealed that Bi, Ge, Pb, Sb and Sn, demonstrated suppression of cathodic activation of Mg following anodic polarisation (about one order of magnitude lower based on the cyclic galvanostatic-potentiostatic testing), in addition to lower free corrosion rates (about one order of magnitude based on the mass loss and hydrogen evolution testing). Employing a number of corrosion rate assessments, including online atomic emission spectroelectrochemistry, it was shown that reduction in Mg corrosion rates – historically considered difficult to achieve – can be robustly demonstrated. The present work has implications for the development of more corrosion resistant Mg alloys, Mg anodes for cathodic protection, or for the use of Mg as a primary battery electrode

Simultaneously improving the corrosion resistance and strength of magnesium via low levels of Zn and Ge additions

Satisfactory corrosion resistance remains an issue in the widespread implementation of magnesium (Mg). The use of alloying to improve mechanical properties of Mg generally accelerates corrosion due to microstructural heterogeneity. However, recent works have revealed that additions of elements serving as ‘cathodic poisons’ such as arsenic (As) and germanium (Ge) can reduce cathodic reaction rates and suppress cathodic activation - imparting corrosion resistance. The effect of Ge was translated into a ternary (and mechanically relevant) Mg-alloy system for the first time, revealing an alloy system with a balance of properties, and low rate of corrosion relative to Mg-alloys to date

The effect of iron re-deposition on the corrosion of impurity-containing magnesium

This article provides a contribution towards the mechanistic understanding of surface phenomena observed during the corrosion of Mg-based substrates particularly in the low anodic polarization range. The concept considers the recent literature explaining cathodic hydrogen evolution from noble acting areas even during global anodic polarization. Heavy metal impurities in the ppm range or intermetallics are always present even in highly pure magnesium. Their potential effect was investigated here in more detail. The experimental results contribute to understanding the role of iron impurities in dark area formation and suggest a way for linking the observed phenomena to the recent literature. The shown enhanced cathodic activity of dark areas especially at the corrosion front and the superfluous hydrogen are linked to an iron re-deposition mechanism due to iron reduction. The proposed mechanism is based on the results obtained from innovative characterisation techniques using magnetic fields, diffraction experiments and transmission electron microscopy, which show the formation of iron rich zones, especially at the corrosion front offering "in statu nascendi" metallic Fe films acting as active cathodes for hydrogen reduction

Dealloying of Al2Cu, Al7Cu2Fe, and Al2CuMg intermetallic phases to form nanoparticulate copper films

International audienceCopper rich intermetallic particles are common in technical aluminum alloys. When exposed to an aggressive electrolyte, these particles undergo a transformation into a pure copper phase due to a selective dissolution or dealloying mechanism. In this work, the kinetics of this transformation have been investigated using synthetic intermetallic phases of Al2Cu, Al7Cu2Fe, and Al2CuMg in 2M H2SO4 as commonly used in the anodization process. The elementary dissolution rates for Al, Mg, Cu, and Fe were measured as a function of time and potential using atomic emission spectroelectrochemistry (AESEC). From this data, it was possible to measure the degree of selective dissolution for the individual elements in the different potential domains. Mg and Fe dissolve simultaneously with Al during the overall polarization. Al dissolution is activated in the presence of Mg and inhibited in the presence of Fe. This work demonstrates the utility of atomic emission spectroelectrochemistry for the direct measurement of dealloying reactions and the indirect measurement of residual films

Volatile Organic Silicon Compounds in Biogases: Development of Sampling and Analytical Methods for Total Silicon Quantification by ICP-OES

International audienceCurrent waste management policies favor biogases (digester gases (DGs) and landfill gases (LFGs)) valorization as it becomes a way for energy politics. However, volatile organic silicon compounds (VOSiCs) contained into DGs/LFGs severely damage combustion engines and endanger the conversion into electricity by power plants, resulting in a high purification level requirement. Assessing treatment efficiency is still difficult. No consensus has been reached to provide a standardized sampling and quantification of VOSiCs into gases because of their diversity, their physicochemical properties, and the omnipresence of silicon in analytical chains. Usually, samplings are done by adsorption or absorption and quantification made by gas chromatography-mass spectrometry (GC-MS) or inductively coupled plasma-optical emission spectrometry (ICP-OES). In this objective, this paper presents and discusses the optimization of a patented method consisting in VOSiCs sampling by absorption of 100% ethanol and quantification of total Si by ICP-OES

Micro-particules organiques synthétiques : sources, transfert,quantification et impacts des micro- et nano-plastiques au sein deshydrosystèmes urbains - Etat de l’art des connaissances scientifiques

De nombreux produits plastiques en fin d’usage échappent aux filières de traitement et de valorisation et se retrouvent, volontairement ou involontairement dans les différents compartiments de la biosphère, dont l’exutoire final, l’océan. Depuis une quinzaine d’années, la présence de macro- et microparticules (MPs) plastiques a également été mise en évidence dans les écosystèmes continentaux : les eaux terrestres, l’air et les sols. Leurs impacts sur les hydrosystèmes urbains en interaction avec le cycle de l’eau font l’objet de questionnements scientifiques.L’objectif de cette action de recherche multidisciplinaire est de réaliser un état des lieux sur les sources, les caractéristiques (tailles, forme, nature des polymères), les occurrences des microparticules synthétiques présentes dans les hydrosystèmes urbains et d’évaluer leur devenir (stockage, transfert, conversion, interaction avec le biotope), en particulier dans les rejets urbains par temps de pluie. Les méthodes d’échantillonnage et d’analyse permettant leur collecte, leur caractérisation et leur quantification ont également été investiguées. A l’issue de la synthèse bibliographique, il ressort que les principales sources des MPs sont les eaux pluviales (eaux de ruissellement, rejets des déversoirs d’orage) et les rejets domestiques (vecteurs de MPs présentes dans les produits cosmétiques et rejets des machines à laver). Les MPs ont des tailles inférieures à 5 mm et se présentent principalement sous trois formes différentes : les fibres, les fragments et les billes. Les mécanismes à la base de leur transfert sont les mêmes que ceux qui gouvernent les autres types de particules, à savoir l’advection, la dispersion (du fait de la turbulence), la sédimentation et la remise en suspension. Les MPs s’accumulent principalement dans les sédiments des ouvrages de gestion des eaux pluviales et les boues des stations de traitement des eaux urbaines. Leur présence dans les eaux de nappe et leur bioaccumulation au sein des organismes aquatiques sont avérées, ce qui augure d’un impact sanitaire sur l’homme. Leur écotoxicité au sein des hydrosystèmes urbains est en cours d’investigation.Les principales pistes de recherche identifiées concernent (i) l’harmonisation des protocoles d’échantillonnage et d’analyse des MPs, (ii) leur réactivité notamment avec la matière organique et les autres types de polluants présents au sein des matrices liquides (eaux usées et pluviales) et solides (sédiments et boues), (iii) leur transfert au sein des hydrosystèmes de gestion des eaux urbaines, notamment leur dispersion au passage des déversoirs d’orage, leur comportement au sein des dispositifs de rétention et d’infiltration des eaux urbaines (techniques alternatives, bassins d’infiltration/rétention, filtres plantés de roseaux). Les investigations sur l’écotoxicité des MPs doivent également se poursuivre