Oxydation humide des polluants organiques par l'oxygène moléculaire activée par le couple H²O²/Fe²+: Optimisation des paramètres opératoires

L'oxydation humide par l'oxygène moléculaire (procédé WAO) activée par le couple (H202/Fe2+) a été mise en oeuvre pour l'oxydation de la pollution organique aqueuse à travers deux composés modèles: l'acide succinique, normalement oxydable, et l'acide acétique, réputé réfractaire. L'influence des différents facteurs a été étudiée par la planification d'expériences. Après leur recensement, une étape préliminaire de criblage a été menée à bien en utilisant une matrice de Plackett et Burman. Seuls les paramètres les plus influents ont été gardés pour l'étape ultérieure d'établissement de modèles prévisionnels à partir d'une matrice composite centrée orthogonale. Les modèles établis ont été validés et ont permis de déterminer les conditions optimales de fonctionnement. L'effet de la température fait apparaître un optimum, à environ 200 °C, au-delà duquel la décomposition du peroxyde devient trop rapide. L'effet de la quantité de peroxyde d'hydrogène introduit est déterminant et l'ajout de moins de 20 % de la quantité stoechiomé- trique permet d'obtenir à 200 °C, avec environ 10 ppm de sels de fer, une efficacité de traitement d'environ 70% pour un composé normalement oxydable. Dans des conditions analogues, le procédé conventionnel sans promoteur conduit à une efficacité inférieure à 5 %.Wet air oxidation (WAO) is a liquid phase oxidation process using molecular oxygen at high temperature (250-300°C) and high pressure (50-150 bar). It can help treating toxic organic aqueous wastes from chemical industries with efficiencies up to 98% after 1 hour. The process can also help treating sludges from domestic sewage treatment facilities. It is usually very cost effective because of the very high operating pressure.This paper deals with the promoted wet air oxidation of acetic acid, rnodel compound for refractory wastes, and succinic acid, model for readily oxidized wastes. The study was conducted in order to determine the promoting effect when adding small dosages of hydrogen peroxide (with iron salts) during oxidation by molecular oxygen. It was previously shown that the initiating step is very temperature dependent (Reaction I) and limits the overall oxidation process The addition of small amounts of H2O2/Fe2+ (Fenton's reagent) can promote the forrnation of very reactive OH• radicals able to develop R• radicals (Reaction IV), even at a low temperature. Then, the oxidation (Reactions VI and VII) continues using molecular oxygen, but the peroxide should be added continuously during a batch test in order to maintain the initiating step.An optimal design methodology was used in order to assess the dependency of the oxidation effrciency on the various parameters and mainly on the promotors. At frrst, a Plackett and Burman design of experiments (PE1) was used to screen the most important variables among those likely to have an effect. The design of experiments, the conditions of the runs and the results (tables 1 to 3) allowed the determination of a new experimental domain and the selection of the four most important variables for the further design of experiments. At the same time, the effect of an addition of phenol (able to reduce iron to the ferrous species, more efficient) was considered. For succinic acid oxidation, a central composite optimal design (PE2) was used (tables 4 and 5). The results allowed us to establish a predictive model (Relationship lX, table 6 and figure 2) and typical results are presented in figures 3 and 4. Approximately 50% oxidation efficiencies could be obtained at 200°C; without peroxide addition, only 5% efficiency is obtained under similar conditions. Moreover, it was observed that the optimum temperature is around 205°C and that phenol is not compatible with peroxide as a promotor. A third optimal design (PE3) was used to predict the efficiency of the method for the treatrnent of acetic acid, a model for a refractory waste. It is composed only of a fractional factorial design (table 7 and 8) and the bias corresponds to the main quadratic effect of temperature (Relationship XIII and table 10). The optimum temperâture is also 205°C and greater than 20% oxidation efficiencies are obtained; at such a temperature, acetic acid cannot be oxidized with the conventional process.The results obtained for the two model compounds validate this oxidation technique. The addition of about 10 ppm of ferrous iron and of less than 20% of the stoichiometric amount in hydrogen peroxide can turn a high pressure WAO process into a medium pressure one

Oxydation en voie humide de la pollution organique aqueuse par le peroxyde d'hydrogène Procédé « Wet Peroxide Oxidation » (WPO®) Étude de nouveaux catalyseurs

Les effluents aqueux pollués par des matières organiques provenant d'industries chimiques présentent souvent une faible biodégradabilité. Dans certains domaines de concentration (DCO = 0,5 - 15 g/l), le procédé WPO® développé au laboratoire se substitue avantageusement à l'incinération pour traiter ce type d'effluents. La réaction, qui met en œuvre le réactif de Fenton à température élevée, conduit parfois à la formation de quantités importantes d'acides carboxyliques légers. Nous avons donc développé des systèmes catalytiques originaux remplaçant les sels de fer et conduisant à une oxydation totale des acides carboxyliques. Le système le plus efficace constitué de sels de fer, de cuivre et de manganèse permet d'obtenir, en 1 h à 100 °C, l'oxydation totale d'un mélange synthétique de ces acides (COT = 5 g/l) avec 1,5 fois la quantité de peroxyde théoriquement nécessaire à l'oxydation. Le catalyseur précipité et séparé en fin de traitement peut être recyclé et conserve la môme activité. Les unités industrielles permettant d'effectuer le traitement WPO® avec les nouveaux catalyseurs, recyclés ou non, seront similaires à celle déjà réalisée pour le traitement de « points noirs » industriels.There is an important concern about the problems occuring with wastes elimination, specially the industrial liquid wastes. Te face the problem of organic aqueous wastes coming front various branches of industry, the WPO® (wet peroxide oxidation) process was developed at the laboratory. In the WAO process (wet air oxidation), which uses gaseous oxygen, the limiting step is usually oxygen transfer. In this new process, this problem is suppressed by using a liquid oxidising agent (hydrogen peroxide). This process is adapted from the classical Fenton's reaction and iron salts are used as the catalyst in order to promote the formation of •OH radicles which are the main active species. But the reaction is carried out at about 120 °C; so, a very significant TOC (total organic carton) removal efficiency is obtained (60 to 90 %) in comparison with the low efficiency of the classical Fenton's reagent (typically 25 % at room temperature).Significant amounts of free fatty acids are formed during the reaction. They are namely oxalic, malonic, succinic and acetic acids, which are common by products obtained during audition of most industrial organic pollutants. In order to comply with the regulations requirements, it was necessary to improve the efficiency of the original process. It was also very important to obtain an efficient elimination at a temperature not greater than 100 °C in order to avoid to pressurize the treatment reactor. This could be obtained by using new catalysts which are described in this paper.Because of the related field, precious metals like Pt and potentially toxic ones like Cr were not considered. One needs a treatment process as cheap and as reliable as possible. So, only Fe, Cu, Co, Ni and Mn were used as salts in order to test their calalytic activity in the treatment by hydrogen peroxide of a synthetical mixture of oxalic, malonic, succinic and acetic acids (O, M, S, A). The experimental device is a stirred tank reactor where the organics and the catalyst are batch loaded. It is continuously fed, for 1 hour, with hydrogen peroxide. The total amount injected is 1.5 the stoechiometric amount. In table 1, it can be seen that any metal has a satisfactory activity when used alone (TOC removal efficiency cannot exceed 22 %). In table 2, it is clear that, in soma cases, the association of two or three metals with each other can lead to very important synergetic effects. When using a mixture of Fe, Cu and Mn, the removal efficiency can increase to 91 %. This Fe/Cu/Mn catalyst is studied with further details in table 4. It appears to have its best efficiency at about 100 °C because of a parasitic decomposition of the peroxide at higher temperatures. For an organic mixture coutaining 5 g TOC/l, 100 ppm of each metal is a convenient concentration. This new catalyst still needs an acidic pH, from 3 to about 5, but the dependency is not so strict than with Fe alone (original process) which needs a value from 3 to 3.5. In addition, it was observed that the treatment time could be easily reduced (down to 45 minutes) as well as the amount of peroxide injected.Very similar results have been obtained with synthetic solutions of pollutants and with real industrial ones, thus establishing the ability of the Fe/Cu/Mn mixture to catalyse the oxidation of a large variety of species and not only carboxilic acids. The difference between the efficiency of this new catalyst and the conventional one is shown in table 5. Figures 1 and 2 are related to an Industrial WPO® unit which is commonly used with the conventional catalyst (Fe). It has been possible to improve its efficiency by using the new one without any significant modification. The Fe/Cu/Mn catalyst can be easily separated alter reaction (coprecipitation effect). Thus, the treated water meets the regulation requirements and the recovered catalyst can be easily resolubilized and recycled

Nouveaux procédés d'oxydation chimique pour l'élimination des rejets aqueux phénolés

Pour faire face au problème posé par les rejets aqueux chargés en phénol, deux procédés d'épuration par voie chimique sont proposés. Les deux méthodes font appel au peroxyde d'hydrogène. Celui-ci joue le rôle de promoteur de radicaux lors de l'oxydation de la charge organique par l'oxygène moléculaire dans le premier procédé qui s'inspire de la technique « Wet Air Oxidation » et constitue l'agent oxydant dans le second procédé intitulé « Wet Peroxide Oxidation ».L'introduction en continu de peroxyde d'hydrogène permet d'initier la réaction d'oxydation du phénol par l'oxygène moléculaire et de réduire considérable-ment les conditions de température et de pression de fonctionnement de la technique WAO classique. La réduction de la Demande Chimique en Oxygène de l'effluent dépasse 95 % à 160 °C en introduisant du peroxyde d'hydrogène à raison de 10 % de la quantité stoechiométrique nécessaire pour l'oxydation complète du phénol. Le second procédé consiste à utiliser l'oxydation par le peroxyde d'hydrogène en présence de fer ferreux (réactif de Fenton) dans des conditions de température (environ 120 °C) conduisant à un abattement important de la charge organique de l'effluent. A température élevée, la compétition entre la réaction de décomposition du peroxyde en oxygène moléculaire inactif et celle de décomposition en radicaux qui développent le processus d'oxydation engendre des conditions opératoires optimales pour lesquelles l'efficacité du procédé est maximale.Ces deux procédés apportent une solution technique satisfaisante pour traiter, avec un abattement important de la demande chimique en oxygène et du carbone organique, les effluents aqueux assez fortement chargés en composés phénolés.Despite of a growing concern about the problems of wastes elimination during the previous years, there is still a lack of processes in order to treat industrial aqueous wastes. Organic aqueous wastes and specially phenolic wastes, that can be either nonbiodegradable or toxic, give rise to one of the main problems. Landfilling disposal and related methods are a priori rejected as they appear to leaving the legacy of a problem we have net been able to solve rather than to considering our environment as being borrowed from the future mankind. Various oxidation techniques are suited for the elimination of this class of wastes. But, because of the environmental and economical drawbacks of incineration, it seems that liquid phase oxidation techniques should be preferred.The paper reviews : two liquid phase purification techniques using the chemical oxidation route; phenol being used as a test compound. The first technique is adapted from the wet air oxidation (WAO) process and uses molecular oxygen as the oxidizing agent. In the meantime, hydrogen peroxide is added at a low dosage and promotes the radicle reactions. Thus, the reaction temperature and pressure can be set at lower values (typically 160 °C, 25 bar) than usually. In this way, the conventional WAO process, which is very capital intensive because of temperature and pressure constraints is turned into a more affordable process. The second technique uses hydrogen peroxide as the oxidizer. it is associated to a ferrous salt as in the Fenton's reagent but it is run out under temperature (about 120 °C) so that a very important total organic carbon (TOC) removal efficiency con be obtained. This technique was named wet peroxide oxidation (WPO) process. As opposed to WAO, WPO needs only limited capital but generates higher running colts. Yet, both techniques can be regarded as efficient and economically satisfying in order to treat organic aqueous wastes containing fair amounts of phenol or phenolic compounds.The test compound was selected considering the frequent occurrence of phenol within the wastewaters of refineries, steel works and chemical industries. Their biological treatment is still very difficult for high concentrations despite of an important research activity. Treatment times and efficiencies of physicochemical methods are not but seldom satisfactory. Then, liquid phase oxidation methods have their whole interest. As it was reported that phenolic compounds (methylphenols, chloro-phenols) oxidation proceeds in a similar way than for phenol, the last molecule was considered for assessing the efficiency of both oxidation methods.The first method (WAO) was tested using a completely mixed batch reactor (stirred autoclave): The cold reactor was loaded with a phenol (2100 mg. 1-1) and ferrous sulfate (10 mg. l-11) solution al the convenient pH value (3.5). After heating at the rated temperature, the run was started by injecting instantaneously a large amount of oxygen (10 times the amount necessary). At the same time, a dosing pump was started and fed continuously hydrogen peroxide within the reactor all along the run (90 minutes). The total amount injected was usually 10 % of the amount necessary for a stoechiometric oxidation. The promoting effect of hydrogen peroxide on molecular oxygen is evidenced on figure 2 where the initiating period is shortened and on figure 3 where the oxidation efficiency actually obtained (curve 3) is greater than expected by adding the efficiencies of molecular oxygen and hydrogen peroxide oxidations if separated (curve 2). WAO promoted with hydrogen peroxide gave after 90 minutes better oxidation efficiencies at 160 °C than conventional WAO at 220 °C, then turning into a medium pressure process a high pressure one. The promoting effect of the peroxide is more marked at 160 °C than above 200 °C where a rapid decomposition occurs; dosages greater 15 % do not significantly increase the efficiency and dosages as small as 0,2 % have already a significant affect (see figure 5). Various compounds have been identified and the oxidation sequence is as follows : phenol -> dihydroxy-benzenes -> maleic acid -> oxalic, formic, acetic acids. Most of the remaining chemical oxygen demand (COD) of the oxidized solutions is acetic acid. Only more drastic experimental conditions allow its total removal.The WPO runs (second oxidation method) were conducted into a similar reactor. It was batch loaded with the phenol (2300 mg. 1-1) and ferrous sulfate (30 mg. l-1) solution at pH 3.5. After heating at 120 °C, the run was started and hydrogen peroxide was continuously fed using a dosing pump. The total amount injected all along the run (60 minutes) was the amount necessary for a stoechiometric oxidation. A similar oxidation sequence than reported hereon was observed; pyrocatechol, bydroquinone and oxalic acid were evidenced (figure 9) but, in this case, only very limited amounts of formic and acetic acids were detected. For the two processes, tables 2 and 3 summarize the material balances of the various products as a function of the oxidation time. A 90 % COD removal efficiency and a 70 % total organic carbon (TOC) removal efficiency is reported on figure 10. This result has to be compared with the TOC removal efficiencies (< 25 %) reported for the usual Fenton’s reagent at room temperature. The changes of the pH value and of the COD/TOC ratio (figure 11) during the run are easily explained by considering that oxalic acid is quite the sole product remaining after oxidation contrarily to promoted WAO where acetic acid is the major remaining product. Besides the production of radicles that bring on the oxidation process, a side-reaction decomposes hydrogen peroxide into molecular oxygen which is net active at such a low temperature. The competition between the two reactions makes optimum operating conditions to exist and to lead to a maximum efficiency of the process.Both processes bring on new methods in order to treat fairly concentrated phenolic solutions with a typical 90 % COD removal efficiency. The products remaining after oxidation (mainly acetic acid or oxalic acid) should not be regarded as a drawback of these processes. In actual fact, such compounds can be easily treated by adding a biological post-treatment unit to the chemical oxidation

LRCH Proteins: A Novel Family of Cytoskeletal Regulators

Background: Comparative genomics has revealed an unexpected level of conservation for gene products across the evolution of animal species. However, the molecular function of only a few proteins has been investigated experimentally, and the role of many animal proteins still remains unknown. Here we report the characterization of a novel family of evolutionary conserved proteins, which display specific features of cytoskeletal scaffolding proteins, referred to as LRCHs. Principal Findings: Taking advantage of the existence of a single LRCH gene in flies, dLRCH, we explored its function in cultured cells, and show that dLRCH act to stabilize the cell cortex during cell division. dLRCH depletion leads to ectopic cortical blebs and alters positioning of the mitotic spindle. We further examined the consequences of dLRCH deletion throughout development and adult life. Although dLRCH is not essential for cell division in vivo, flies lacking dLRCH display a reduced fertility and fitness, particularly when raised at extreme temperatures. Conclusion/Significance: These results support the idea that some cytoskeletal regulators are important to buffer environmental variations and ensure the proper execution of basic cellular processes, such as the control of cell shape

Simulating the midlatitude atmospheric circulation: what might we gain from high-resolution modeling of air-sea interactions?

Purpose of Review. To provide a snapshot of the current research on the oceanic forcing of the atmospheric circulation in midlatitudes and a concise update on previous review papers. Recent findings. Atmospheric models used for seasonal and longer timescales predictions are starting to resolve motions so far only studied in conjunction with weather forecasts. These phenomena have horizontal scales of ~ 10–100 km which coincide with energetic scales in the ocean circulation. Evidence has been presented that, as a result of this matching of scale, oceanic forcing of the atmosphere was enhanced in models with 10–100 km grid size, especially at upper tropospheric levels. The robustness of these results and their underlying mechanisms are however unclear. Summary. Despite indications that higher resolution atmospheric models respond more strongly to sea surface temperature anomalies, their responses are still generally weaker than those estimated empirically from observations. Coarse atmospheric models (grid size greater than 100 km) will miss important signals arising from future changes in ocean circulation unless new parameterizations are developed

A SARS-CoV-2 protein interaction map reveals targets for drug repurposing

The novel coronavirus SARS-CoV-2, the causative agent of COVID-19 respiratory disease, has infected over 2.3 million people, killed over 160,000, and caused worldwide social and economic disruption1,2. There are currently no antiviral drugs with proven clinical efficacy, nor are there vaccines for its prevention, and these efforts are hampered by limited knowledge of the molecular details of SARS-CoV-2 infection. To address this, we cloned, tagged and expressed 26 of the 29 SARS-CoV-2 proteins in human cells and identified the human proteins physically associated with each using affinity-purification mass spectrometry (AP-MS), identifying 332 high-confidence SARS-CoV-2-human protein-protein interactions (PPIs). Among these, we identify 66 druggable human proteins or host factors targeted by 69 compounds (29 FDA-approved drugs, 12 drugs in clinical trials, and 28 preclinical compounds). Screening a subset of these in multiple viral assays identified two sets of pharmacological agents that displayed antiviral activity: inhibitors of mRNA translation and predicted regulators of the Sigma1 and Sigma2 receptors. Further studies of these host factor targeting agents, including their combination with drugs that directly target viral enzymes, could lead to a therapeutic regimen to treat COVID-19