Adsorption dynamique en phase liquide sur charbon actif : comparaison et simplification de différents modèles

L'adsorption en phase liquide sur charbon actif est un sujet très travaillé sur le plan expérimental et de plus en plus dans le domaine de la modélisation. Les tentatives de description des courbes de percée ou de fuite des filtres montrant la saturation du matériau adsorbant remontent aux travaux de BOHART et ADAMS en 1920. D'autres équations avec d'autres approximations ont été proposées par la suite (THOMAS 1944 ; DOLE et KLOLZ 1946), HUTCHINS (1973) ; plus récemment, WOLBORSKA (1989) ou CLARK (1987) ont proposé d'autres modèles. Nous avons essayé de faire le point sur ces différents modèles, de montrer leurs origines communes, souvent à partir des équations de BOHART et ADAMS, les approximations apportées limitant leur domaine d'application, les grandeurs qu'ils permettent de déterminer : capacité maximum d'adsorption, constante cinétique d'adsorption, vitesse de déplacement du front d'adsorption. De tous ces modèles, un seul (CLARK 1987) permet une bonne représentation des courbes de percée. Nous en avons proposé une linéarisaüon qui facilite la détermination des paramètres nécessaires au calcul des courbes de fuite. Tous ces modèles ont été testés sur les résultats expérimentaux obtenus pour l'adsorption d'un tensioactif anionique : le décylsulfonate de sodium et ceci sur cinq petites colonnes de hauteurs différentes de charbon actif. Le modèle de CLARK a également été appliqué à des résultats obtenus au laboratoire (El HANI, 1987) sur l'adsorption et la dégradation biologique des acides humiques sur un filtre de charbon de 1m de haut, sur une période beaucoup plus longue (1 mois) et avec des lavages du filtre. Ce modèle permet de calculer la part qui n'est pas simplement de l'adsorption rapide (dégradation biologique et adsorption lente).Low concentrations of organic contaminants are not easily removed by conventional treatment methods, but activated carbon bas a good affinity for various organics and is used in batch or column reactors.Much has been written concerning the prediction of the performance of powdered activated carbon (PAC) ; adsorptive capacity and equilibrium isotherms determined in « batch » reactor are proposed to simulate the performance of PAC for single or bisolute systems (DUSART et al. 1990, SMITH 1991). Some investigators have attempted to simulate column performance with mathematical models and the aim of this work is to present the principal models and verify how the different models are applied to break-through curves ; parameters which can be evaluated by the different equations will also be compared.As early as 1920 BOHART and ADAMS presented differential equations which govern the dynamics of the adsorption of vapours and gases on fixed beds and the final result, applied to the liquid-solid phase, yields the kinetic adsorption rate (k) and the maximum adsorption capacity (No) (eq. 3). By transposition to the liquid phase, we have calculated the concentration distribution in the bed (eq. 5) by using the kinetic constant k and the maximum adsorption capacity No obtained by equation 4; it was noted that only the low concentration range of the break-through curve can be used. Some approximations from DOLE and KLOTZ (1946) lead to the « Bed Depth/Service-Time (BDST) equation 7 proposed by HUTCHINS (1973) ; the service time of a column tb has a linear relationship with the bed depth Z (fig.3). The activated carbon efficiency No can be estimated and the adsorption rate constant calculated from the slope and the y-intercept.Recently, WOLBORSKA (1989) proposed a rectilinear equation InC/Co = At + B (eq. 10) for the initial segment of the break-through curve. The form of this equation is similar to equation (4) obtained tram the BOHART-ADAMS hypothesis. The mass transfer coefficient, ßa, the maximum adsorption capacity and the migration velocity v (eq.9) of the concentration fronts can be calculated from the constants A and B.The model developed by CLARK (1987) is based on the use of e mass-transfer concept in combination with the Freundlich isotherm (fig.4). The originality of this modal, in comparison to the others, consists in the existence of the equilibrium concentration Ce and the driving force equilibrium « C-Ce ». The general equation is equation (14). Two parameters A and r are determined by regression equations ; we proposed a simple method to calculate A and r by a linearization of the preceding equation (eq. 14). This is equation (16) In [(Co/C)n-1 -1] = In A -rt.Sodium decanesulfonate at a concentration of 20 mg ·l-1 was used as influent and activated powdered carton (200 ≤ ø ≤ 315 µm) as the fixed bed adsorbent layer to illustrate the comparison between the different models. The linear flow rates were 3.0 m . h-1 and the five columns tested were 3.1 ; 4.0 ; 7.5 ; 10.2 ; 12.5 cm high with a 1.45 cm2 cross section. The Freundlich isotherm equation (fig. 4) obtained in a batch system for an equilibrium time (t = 24 h for this activated carbon) gives a « n value » equal to 2.38.Figure 2 presents the experimental break-through curves obtained for the different bed heights ; by using equations (4 or 10) in the system (In C/Co, t) they are represented on the same figure by the dotted line. The agreement is only for the low values of C in the break-through curves.The coefficients A and B (table 1) are determined from the straight lines obtained with the low break-curve concentrations (fig. 1). The kinetic coefficient Sa, and the maximum capacity adsorption No are shown in table 1. The No value is similar to those obtained from the other equations. The migration velocity of the concentration fronts (r = 0,133 cm · h-1) is in good agreement with the experimental value (0,128 cm · h-1).The linearized Clark equation (16) gives a good representation of experimental results (fig. 6) alter the determination of A and r parameters (fig. 5 and table 2). With the use of the two parameters, the break-through curves have been recalculated (fig.6) and compared to experimental results. Their is good agreement. The A parameter is related to the depth Z of the adsorbant : A = Bez ·. B value can be determined with the different columns (fig.7).The Clark model can be applied to filers which have a biological activity ; the results obtained in the laboratory by EL HANI (1987) for the adsorption of humic acids (10 mg · l-1) on a 1m granular activated carton bed were analyzed by the Clark equation (fig. 8). The initial concentrations of humic acids are never obtained in the effluent because of biological degradation and/or slow adsorption in mesopores. From the difference in the area of the two curves, it is possible to calculate the supplementary biological degradation. For 95 cm of activated carbon in the column and after 800 h, the biological degradation represents 55 % of the total elimination. The percentage is constant alter 35 cm depth of the activated carton in agreement with the electon microscopy study that showed that the flora was only present in the 10 first centimeters.The use of this model is facilitated by our linearization and the case of particular phenomena : biological degradation or desorption. in the case of successive muld adsorbates fixation (REYDEMANEUF et al. to be published) can be studied and compared to the only adsorption phenomena.In conclusion, nome of the tested models lead to different parameters by using low break-through curve concentrations or others with the whole range of experimental points, but only one (CLARK) gives a good description of the break-through curves in our actual knowledge

Elimination de colorants de l'industrie textile par des sciures de bois

L'élimination de la couleur de rejets de petites industries textiles peut être réalisée à l'aide de sciures d'essences de bois diverses dont le choix est fait après étude de leur relargage dans l'eau (couleur et DCO); les sciures de chêne, de châtaignier, de pin Douglas conduisent à des relargages de substances fortement colorées correspondant à des DCO d'environ 60 mg d'oxygène par gramme de sciures sèches et ceci en réacteur discontinu. Par contre, les sciures de hêtre, bouleau, sapin et peuplier relarguent nettement moins de produits colorés ou non et conduisent à des DCO plus faibles, excepté pour le bouleau (30 mg d'O2.g-1).Le pH de l'eau est également modifié par addition de sciures et l'on obtient des valeurs de pH d'équilibre atteint en 10 min., de 4,3; 5; 5,8 et 7 pour le bouleau, le sapin, le hêtre et le peuplier respectivement.L'élimination de colorants à 25 mg.l-1 dans l'eau par des doses de sciures de 50 g.-1 pour 2 h de temps de contact, montre qu'une meilleure décoloration (98 à 100 %) est obtenue pour le colorant cationique Basic Red 22 avec les quatre sciures sélectionnées, qu'avec les colorants anioniques (ou acides) dont les valeurs de rétention, variables selon les sciures (de 4 à 8 %) peuvent être très bonnes également.Les isothermes d'adsorption permettent de déterminer les capacités d'adsorption à saturation; à titre d'exemple, des valeurs de 0,1 à 0,2 mmol.g-1 sont obtenues sur des sciures de peuplier et de hêtre pour le colorant BR 22 et de 4 à 8.10- mmol.g-1 pour le colorant anionique Acid Blue 25, sur ces mêmes sciures. Contrairement à d'autres matériaux, on observe que les résultats obtenus ne dépendent que très peu de la température (entre 15 et 35 °C).Une étude dynamique sur colonne confirme les écarts pour les deux types de colorants, mais les résultats dépendent de la vitesse de passage : des pourcentages d'élimination de 0,4 à 1 % en masse peuvent être obtenus pour l'AB 25 le BR 22 sur la sciure de hêtre. Il faut cependant signaler que les produits minéraux et organiques contenus dans les effluents colorés industriels diminuent l'efficacité des sciures par rapport à leur efficacité sur des solutions de colorants purs.Anticipated water pollution regulations require textile dye industries to reduce substantially the amount of colour in their effluents. One possible method of colour removal is through adsorption techniques. The most commonly used adsorbent for treatment of textile effluents is activated carbon. The capability of sawdust for removing colour was recognised some time ago (POOTS et al. 1978; ABO-ELELA and EL-DIB, 1987; ASFOUR et al., 1985) as were those of peat and of charred woollen fiber treatments (PERINEAU et al., 1983). Sawdust has recently received more attention (ASFOUR et al., 1985) owing to its economic advantages when the sawmills are near the textile mills. In order to measure the real efficacy of some types of sawdust, evaluation of the released coloured products and their influence on the effluent water pH are never described. The aim of the present work is to study and evaluate the behaviour of types of sawdust from Limousin woods (released COD and pH of solutions) and the discolouring power of the selected sawdust (beech, poplar, birch and fir trees) with respect to textile dyes in dilute solutions and industrial effluents.MATERIALS AND METHODSExperiments were conducted using sawdust from beech, chestnut, poplar, oak, birch, fir and Douglas pine, in doses of 50 g.l-1 of water. The industrial sawdust particle site was between 0.5 - 1.5 mm.The dyestuffs used in all the experiments are reported in table 1. The initial concentration of colouring matter was 25 mg.l-1 and determined spectrophotometrically at maximum absorbance wavelength. In a batch system the time required for equilibrium was 2 hours (or less).RESULTS AND DISCUSSIONKinetic rejections of the sawdust are shown in figure 1; four types of sawdust are suitable : beech, poplar, birch, and fir were selected for further experiments. The absorbance depends on the wavelength and becomes maximum near UV range (as shown in fig. 2 and 3). The COD of the released products is particularly important for chestnut, oak, Douglas pine (60 mg.O2.g-1; table 2) and also for birch (31 mg.O2.g-1). These data have never been mentioned in published works where the wood was not submitted to any form of pre-treatment.Sawdust contains some acidic or basic groups that modify the pH of water (fig. 6, 7) which becomes more acidic; the phenomenon can be used to neutralize textile fixing effluents loaded with carbonate ions (pH : 10). Batch results (table 3) indicate that the tour selected types of sawdust give good colour removal for the 8 dyes; particularly, the cationic dye : Basic Red 22 is discoloured with very good yield (96 to 99.5 %) on beech and on birch sawdust.A variation of temperature between 15 and 35 °C does not change significantly the adsorption results and at pH = 2, the release decreases (table 2) and the adsorption increases (table 4).Equilibrium conditions of adsorption of basic and acidic dyes on four types of dust were studied using the Langmuir equation; this equation was also used for the determination of the « ultimate capacity » Г∞ and the equilibrium constant K (STUMM and MORGAN, 1981). The resulting Г∞ and K for some dyes (AB 25, BR 22, NLB) on fir, beech, poplar, and birch sawdust are given in table 5. The best results were obtained for the cationic dye BR 22 which showed an ultimate capacity of 0.210 and 0.06 mmol.g-1 on beech and on birch sawdust respectively. [The result for other dyes is in the order of 0.005 mmol.g-1]. The results obtained by extrapolation of the linearized Langmuir equation are somewhat different from those obtained by the experimental saturation curve (fig. 8) for BR 22 on polar sawdust. For AB 25, the saturation curve shows a great increase of the adsorption capacity for concentrated solutions (2 - 2.25 g.l-1), this is probably due to a micellary process as shown on figure 9 : the critical micellary concentration is between 1.5 and 3.3 g.1-1.DYNAMIC STUDYFlow tests using small columns (3 - 7 cm of height) are used with beech sawdust for determining the breakthrough curves (rate : 1.03 m.h-1). The concentrations of AB 25, BR 22 and their mixture are 25 mg.l-1 (close to industrial waste-water concentration). The adsorption capacity deduced from the « Bed Depth Service Time » model is 0.4 % and 0.8 % for each dye respectively.Glass columns (4 cm diameter) containing 20 g or 30 g of beech sawdust were also used. The values of adsorption for a rate of 3.1 m.h-1 are 0.45 mg.g-1 (0.04 %) for AB 25 and 13 mg.g-1 (1.3 %) for BR 22. Approximately 650 litres of this dye can be treated by this sawdust (fig. 10 and 11).Industrial effluents (unknown composition) are less discoloured, probably due to the presence of many other compounds.Batch experiments adsorption of dyes on wood sawdust can lead to different measurements of the efficiency of the sawdust depending on rejection by the adsorbent of chemical species in the bulk solution. These substances modify the pH, the adsorbance of the solution and the amount of adsorbed dyes by competitive reaction

Investigaciones esperimentales [sic] sobre la acción fisiológica y terapéutica del fosfato de cal

Copia digital : Junta de Castilla y León. Conserjería de Cultura y Turismo, 201

Differential Fault Analysis on A.E.S.

We explain how a differential fault analysis (DFA) works on AES 128, 192 or 256 bits

Regular graphs of large girth and arbitrary degree

For every integer d > 9, we construct infinite families {G_n}_n of d+1-regular graphs which have a large girth > log_d |G_n|, and for d large enough > 1,33 log_d |G_n|. These are Cayley graphs on PGL_2(q) for a special set of d+1 generators whose choice is related to the arithmetic of integral quaternions. These graphs are inspired by the Ramanujan graphs of Lubotzky-Philips-Sarnak and Margulis, with which they coincide when d is prime. When d is not equal to the power of an odd prime, this improves the previous construction of Imrich in 1984 where he obtained infinite families {I_n}_n of d+1-regular graphs, realized as Cayley graphs on SL_2(q), and which are displaying a girth > 0,48 log_d |I_n|. And when d is equal to a power of 2, this improves a construction by Morgenstern in 1994 where certain families {M_n}_n of 2^k+1-regular graphs were shown to have a girth > 2/3 log_d |M_n|.Comment: (15 pages) Accepted at Combinatorica. Title changed following referee's suggestion. Revised version after reviewing proces

Oxidative stress and proinflammatory cytokines contribute to demyelination and axonal damage in a cerebellar culture model of neuroinflammation

Background: Demyelination and axonal damage are critical processes in the pathogenesis of multiple sclerosis (MS). Oxidative stress and pro-inflammatory cytokines elicited by inflammation mediates tissue damage. Methods/Principal Findings: To monitor the demyelination and axonal injury associated with microglia activation we employed a model using cerebellar organotypic cultures stimulated with lipopolysaccharide (LPS). Microglia activated by LPS released pro-inflammatory cytokines (IL-1β, IL-6 and TNFα), and increased the expression of inducible nitric oxide synthase (iNOS) and production of reactive oxygen species (ROS). This activation was associated with demyelination and axonal damage in cerebellar cultures. Axonal damage, as revealed by the presence of non-phosphorylated neurofilaments, mitochondrial accumulation in axonal spheroids, and axonal transection, was associated with stronger iNOS expression and concomitant increases in ROS. Moreover, we analyzed the contribution of pro-inflammatory cytokines and oxidative stress in demyelination and axonal degeneration using the iNOS inhibitor ethyl pyruvate, a free-scavenger and xanthine oxidase inhibitor allopurinol, as well as via blockage of pro-inflammatory cytokines using a Fc-TNFR1 construct. We found that blocking microglia activation with ethyl pyruvate or allopurinol significantly decreased axonal damage, and to a lesser extent, demyelination. Blocking TNFα significantly decreased demyelination but did not prevented axonal damage. Moreover, the most common therapy for MS, interferon-beta, was used as an example of an immunomodulator compound that can be tested in this model. In vitro, interferon-beta treatment decreased oxidative stress (iNOS and ROS levels) and the release of pro-inflammatory cytokines after LPS stimulation, reducing axonal damage. Conclusion: The model of neuroinflammation using cerebellar culture stimulated with endotoxin mimicked myelin and axonal damage mediated by the combination of oxidative stress and pro-inflammatory cytokines. This model may both facilitate understanding of the events involved in neuroinflammation and aid in the development of neuroprotective therapies for the treatment of MS and other neurodegenerative diseases

Progressive Purkinje Cell Degeneration in tambaleante Mutant Mice Is a Consequence of a Missense Mutation in HERC1 E3 Ubiquitin Ligase

The HERC gene family encodes proteins with two characteristic domains: HECT and RCC1-like. Proteins with HECT domains have been described to function as ubiquitin ligases, and those that contain RCC1-like domains have been reported to function as GTPases regulators. These two activities are essential in a number of important cellular processes such as cell cycle, cell signaling, and membrane trafficking. Mutations affecting these domains have been found associated with retinitis pigmentosa, amyotrophic lateral sclerosis, and cancer. In humans, six HERC genes have been reported which encode two subgroups of HERC proteins: large (HERC1-2) and small (HERC3-6). The giant HERC1 protein was the first to be identified. It has been involved in membrane trafficking and cell proliferation/growth through its interactions with clathrin, M2-pyruvate kinase, and TSC2 proteins. Mutations affecting other members of the HERC family have been found to be associated with sterility and growth retardation. Here, we report the characterization of a recessive mutation named tambaleante, which causes progressive Purkinje cell degeneration leading to severe ataxia with reduced growth and lifespan in homozygous mice aged over two months. We mapped this mutation in mouse chromosome 9 and then performed positional cloning. We found a G⇔A transition at position 1448, causing a Gly to Glu substitution (Gly483Glu) in the highly conserved N-terminal RCC1-like domain of the HERC1 protein. Successful transgenic rescue, with either a mouse BAC containing the normal copy of Herc1 or with the human HERC1 cDNA, validated our findings. Histological and biochemical studies revealed extensive autophagy associated with an increase of the mutant protein level and a decrease of mTOR activity. Our observations concerning this first mutation in the Herc1 gene contribute to the functional annotation of the encoded E3 ubiquitin ligase and underline the crucial and unexpected role of this protein in Purkinje cell physiology

Human Mesenchymal Stem Cells Prolong Survival and Ameliorate Motor Deficit through Trophic Support in Huntington's Disease Mouse Models

We investigated the therapeutic potential of human bone marrow-derived mesenchymal stem cells (hBM-MSCs) in Huntington's disease (HD) mouse models. Ten weeks after intrastriatal injection of quinolinic acid (QA), mice that received hBM-MSC transplantation showed a significant reduction in motor function impairment and increased survival rate. Transplanted hBM-MSCs were capable of survival, and inducing neural proliferation and differentiation in the QA-lesioned striatum. In addition, the transplanted hBM-MSCs induced microglia, neuroblasts and bone marrow-derived cells to migrate into the QA-lesioned region. Similar results were obtained in R6/2-J2, a genetically-modified animal model of HD, except for the improvement of motor function. After hBM-MSC transplantation, the transplanted hBM-MSCs may integrate with the host cells and increase the levels of laminin, Von Willebrand Factor (VWF), stromal cell-derived factor-1 (SDF-1), and the SDF-1 receptor Cxcr4. The p-Erk1/2 expression was increased while Bax and caspase-3 levels were decreased after hBM-MSC transplantation suggesting that the reduced level of apoptosis after hBM-MSC transplantation was of benefit to the QA-lesioned mice. Our data suggest that hBM-MSCs have neural differentiation improvement potential, neurotrophic support capability and an anti-apoptotic effect, and may be a feasible candidate for HD therapy

Syndromics: A Bioinformatics Approach for Neurotrauma Research

Substantial scientific progress has been made in the past 50 years in delineating many of the biological mechanisms involved in the primary and secondary injuries following trauma to the spinal cord and brain. These advances have highlighted numerous potential therapeutic approaches that may help restore function after injury. Despite these advances, bench-to-bedside translation has remained elusive. Translational testing of novel therapies requires standardized measures of function for comparison across different laboratories, paradigms, and species. Although numerous functional assessments have been developed in animal models, it remains unclear how to best integrate this information to describe the complete translational “syndrome” produced by neurotrauma. The present paper describes a multivariate statistical framework for integrating diverse neurotrauma data and reviews the few papers to date that have taken an information-intensive approach for basic neurotrauma research. We argue that these papers can be described as the seminal works of a new field that we call “syndromics”, which aim to apply informatics tools to disease models to characterize the full set of mechanistic inter-relationships from multi-scale data. In the future, centralized databases of raw neurotrauma data will enable better syndromic approaches and aid future translational research, leading to more efficient testing regimens and more clinically relevant findings

Intravenous alteplase for stroke with unknown time of onset guided by advanced imaging: systematic review and meta-analysis of individual patient data

Background: Patients who have had a stroke with unknown time of onset have been previously excluded from thrombolysis. We aimed to establish whether intravenous alteplase is safe and effective in such patients when salvageable tissue has been identified with imaging biomarkers. Methods: We did a systematic review and meta-analysis of individual patient data for trials published before Sept 21, 2020. Randomised trials of intravenous alteplase versus standard of care or placebo in adults with stroke with unknown time of onset with perfusion-diffusion MRI, perfusion CT, or MRI with diffusion weighted imaging-fluid attenuated inversion recovery (DWI-FLAIR) mismatch were eligible. The primary outcome was favourable functional outcome (score of 0–1 on the modified Rankin Scale [mRS]) at 90 days indicating no disability using an unconditional mixed-effect logistic-regression model fitted to estimate the treatment effect. Secondary outcomes were mRS shift towards a better functional outcome and independent outcome (mRS 0–2) at 90 days. Safety outcomes included death, severe disability or death (mRS score 4–6), and symptomatic intracranial haemorrhage. This study is registered with PROSPERO, CRD42020166903. Findings: Of 249 identified abstracts, four trials met our eligibility criteria for inclusion: WAKE-UP, EXTEND, THAWS, and ECASS-4. The four trials provided individual patient data for 843 individuals, of whom 429 (51%) were assigned to alteplase and 414 (49%) to placebo or standard care. A favourable outcome occurred in 199 (47%) of 420 patients with alteplase and in 160 (39%) of 409 patients among controls (adjusted odds ratio [OR] 1·49 [95% CI 1·10–2·03]; p=0·011), with low heterogeneity across studies (I2=27%). Alteplase was associated with a significant shift towards better functional outcome (adjusted common OR 1·38 [95% CI 1·05–1·80]; p=0·019), and a higher odds of independent outcome (adjusted OR 1·50 [1·06–2·12]; p=0·022). In the alteplase group, 90 (21%) patients were severely disabled or died (mRS score 4–6), compared with 102 (25%) patients in the control group (adjusted OR 0·76 [0·52–1·11]; p=0·15). 27 (6%) patients died in the alteplase group and 14 (3%) patients died among controls (adjusted OR 2·06 [1·03–4·09]; p=0·040). The prevalence of symptomatic intracranial haemorrhage was higher in the alteplase group than among controls (11 [3%] vs two [<1%], adjusted OR 5·58 [1·22–25·50]; p=0·024). Interpretation: In patients who have had a stroke with unknown time of onset with a DWI-FLAIR or perfusion mismatch, intravenous alteplase resulted in better functional outcome at 90 days than placebo or standard care. A net benefit was observed for all functional outcomes despite an increased risk of symptomatic intracranial haemorrhage. Although there were more deaths with alteplase than placebo, there were fewer cases of severe disability or death. Funding: None