Etude d'un réacteur aérobie à culture concentrée couplé à une séparation par micro ou ultra-filtration tangentielles sur membranes minérales. Première approche d'une application en dépollution

La réduction de la pollution organique des eaux usées, urbaines ou industrielles, fait le plus souvent appel à des procédés biologiques anaérobies ou aérobies. Dans ce dernier cas, les procédés à boues activées sont parmi les plus courants mais nécessitent de grands volumes de bassinsLes bioréacteurs à membranes présentent l'avantage de la compacité et permettent l'obtention d'un effluent de très bonne qualité, constante, même à très forte charge.Le système étudié ici est un bioréacteur faisant corps avec le module de filtration utilisé, avec injection d'oxygène dans la boucle, supprimant ainsi tout bassin conventionnel. Une eau usée synthétique y est traitée en aérobiose sur membranes minérales à une température de 30 °C, soit par ultrafiltration à 500 Å, soit par microfiltration à 0,2 µm. Le problème de l'encrassement des membranes est étudié et certains de ses mécanismes en présence d'une biomasse concentrée sont mis en évidence. L'encrassement est évitable en utilisant un décolmatage à flux inverse et en pratiquant des purges de boues régulières. La qualité de l'effluent obtenu en sortie est en tout point comparable ou supérieure à celle d'une station à boues activées travaillant en aération prolongée. La comparaison n'inclut pas les aspects économiques, et la nitrification est incomplète.Urban or industrial waste water organic pollution is must often treated by aerobic biological systems. In this case, commonly used activated sludge plants need large tanks. Membrane bioreactors would give compactness and very high and constant quality effluent. Up to now, organic membranes have been mainly utilized for polishing effluents from conventional secondary treatment. MEMCOR process, using hollow fibers membranes, allows permeate fluxes of 100 l/h.m2 for several months under a 1 bar pressure. Chaize (1990), using inorganic membranes for urban waste water treatment, reached high organic and nitrogen removal. Biomass was about 10 to 20 g/l and permeate fluxes of 20 and 28 l/h.m2 at 1.1 and 1.4 bar transmembrane pressure with residuals less than 20 ppm COD and SSM and 5 ppm TKN.Materials and methods :The pilot studied here combined in the same module a compact bioreactor and a filtration membrane. A synthetic waste water has been treated by crossflow micro or ultrafiltration with aerobic microorganisms and pure oxygen injection. This effluent had a DCOIDBO ratio of 1.5 with very low suspended solid matters (38 mg/l). a-Alumina (pore size : 0.2 µm) or Zirconium oxide (pore size : 500 Å) inorganic membranes have been used. As membrane fouling is the main weakness of this processes, two treatments have been experimented with both membranes :1. total biomass recycling without back flush system ;2. excess biomass draining with back-flush system operating.Experiments lasted continuously for 3 to 7 days.Crossflow velocity was about 3.8 m/s, pH was regulated at 7.0 by concentrated sodium hydroxide addition.Heat generated by pumps needed heat exchange with tap water in order to maintain temperature around 30 °C, wich was considered optimal for biological reactions.Permeate COD and nitrogen, biomass Suspended Volatile Matters (SVM) and Suspended Solid Matters (SSM) have been monitored.Results and discussion :1) Effluent quality was constant and better than for conventional extended aeration. The two membranes retained the whole of SSM and bacteria, permeate COD was less than 30 mg/l, even under high load conditions (5 to 20 kg COD/kg SVM.d), elimination rates reached 98 % BOD and 97 % COD. Biomass production and oxygen consumption were lower than for high load activated sludge process, tact reported to pure oxygen utilization and unfloculated bacteria predominance. Nitrification remained very low due to short sludge age (< 90 h).2) Membranes cleaning state at the beginning of the tests didn't modify stabilized permeate fluxes. Particulate fouling predominated with 0,2 µm membrane, problem solved using back-flush system, but fast slime fouling developed in the first 24 h. Electron microscopy membrane surface examination shown heavy fouling by a biofilm which real composition remains unknown, and by numerous small particles (site range from 0.04 to 0.3 mm).With total biomass recycling, permeate fluxes were very low for both types of membranes : 15 l/h.m2 for 500 Å membrane and 2 l/h.m2 for 0.2 µm membrane. Treatment had to be stopped alter only 99 h. Biomass concentration increased up to 32 g/l in 3 days. When using back flush system and regularly draining excess biomass, becter stabilized permeate fluxes could be observed : 35 l/h.m2 for 500 Å membrane and 24 l/h.m2 for 0.2 µm membrane. Mean biomass concentration was about 15 g/l.Enzymatic digestion of slimes on fouled membranes pointed out the role of bacteria colt walls and proteins. These compounds were thought to be produced mainly under substrate limitation conditions. Fouling could thus be avoided by regularly draining excess biomass.Technology of inorganic membranes is still recent and involves relatively high costs. However, as it may ha interesting for soma industrial effluents, tests are carried on to confirm chose results

Exercise-induced bronchoconstriction and atopy in Tunisian athletes

<p>Abstract</p> <p>Background</p> <p>This study is a cross sectional analysis, aiming to evaluate if atopy is as a risk factor for exercise induced bronchoconstriction (EIB) among Tunisian athletes.</p> <p>Methods</p> <p>Atopy was defined by a skin prick test result and EIB was defined as a decrease of at least 15% in forced expiratory volume in one second (FEV1) after 8-min running at 80–85% HRmaxTheo. The study population was composed of 326 athletes (age: 20.8 ± 2.7 yrs – mean ± SD; 138 women and 188 men) of whom 107 were elite athletes.</p> <p>Results</p> <p>Atopy was found in 26.9% (88/326) of the athletes. Post exercise spirometry revealed the presence of EIB in 9.8% of the athletes including 13% of the elite athletes. Frequency of atopy in athletes with EIB was significantly higher than in athletes without EIB [62.5% vs 23.1%, respectively].</p> <p>Conclusion</p> <p>This study showed that atopic Tunisian athletes presented a higher risk of developing exercise induced bronchoconstriction than non-atopic athletes.</p

Assessment of left ventricular diastolic function in children after successful repair of aortic coarctation

The purpose of the study was an assessment of left ventricular diastolic function in children after the successful repair of aortic coarctation (CoA). The prospective study concerned 32 pediatric patients after the CoA surgery. Tissue Doppler imaging parameters including strain and strain rate and the conventional echocardiographic indexes were analyzed in patients and healthy controls. Analysis of mitral annulus velocities, E–E′ ratio, strain, and strain rate of left ventricular mid-cavity segments and conventional indexes of mitral inflow showed the worsening of left ventricular diastolic mechanics in the study group compared to healthy controls. The E/E′ ratio was significantly higher in the study group compared to the control group (8.30 ± 3.24 vs. 6.95 ± 1.36; p < 0.05). The early diastolic strain rate to late diastolic strain rate ratio as well as early to late diastolic strain ratio of the left ventricular mid-cavity segments were significantly lower in the study group compared to healthy controls (1.81 ± 0.63 vs. 3.74 ± 1.53; p < 0.001 and 1.20 ± 0.49 vs. 3.41 ± 1.26; p < 0.001). No differences of the pulmonary venous flow parameters between those two groups were observed. The left ventricular diastolic mechanics in hypertensive patients after CoA repair did not differ from normotensive subjects. Hypertensive and normotensive children after surgical repair of CoA are found to have worsening of the left ventricular diastolic mechanics suggesting the impairment of the active myocardial relaxation

Balanced gene losses, duplications and intensive rearrangements led to an unusual regularly sized genome in Arbutus unedo chloroplasts

Completely sequenced plastomes provide a valuable source of information about the duplication, loss, and transfer events of chloroplast genes and phylogenetic data for resolving relationships among major groups of plants. Moreover, they can also be useful for exploiting chloroplast genetic engineering technology. Ericales account for approximately six per cent of eudicot diversity with 11,545 species from which only three complete plastome sequences are currently available. With the aim of increasing the number of ericalean complete plastome sequences, and to open new perspectives in understanding Mediterranean plant adaptations, a genomic study on the basis of the complete chloroplast genome sequencing of Arbutus unedo and an updated phylogenomic analysis of Asteridae was implemented. The chloroplast genome of A. unedo shows extensive rearrangements but a medium size (150,897 nt) in comparison to most of angiosperms. A number of remarkable distinct features characterize the plastome of A. unedo: five-fold dismissing of the SSC region in relation to most angiosperms; complete loss or pseudogenization of a number of essential genes; duplication of the ndhH-D operon and its location within the two IRs; presence of large tandem repeats located near highly re-arranged regions and pseudogenes. All these features outline the primary evolutionary split between Ericaceae and other ericalean families. The newly sequenced plastome of A. unedo with the available asterid sequences allowed the resolution of some uncertainties in previous phylogenies of Asteridae

Dynamic control of a single-server system with abandonments

In this paper, we discuss the dynamic server control in a two-class service system with abandonments. Two models are considered. In the first case, rewards are received upon service completion, and there are no abandonment costs (other than the lost opportunity to gain rewards). In the second, holding costs per customer per unit time are accrued, and each abandonment involves a fixed cost. Both cases are considered under the discounted or average reward/cost criterion. These are extensions of the classic scheduling question (without abandonments) where it is well known that simple priority rules hold. The contributions in this paper are twofold. First, we show that the classic c-μ rule does not hold in general. An added condition on the ordering of the abandonment rates is sufficient to recover the priority rule. Counterexamples show that this condition is not necessary, but when it is violated, significant loss can occur. In the reward case, we show that the decision involves an intuitive tradeoff between getting more rewards and avoiding idling. Secondly, we note that traditional solution techniques are not directly applicable. Since customers may leave in between services, an interchange argument cannot be applied. Since the abandonment rates are unbounded we cannot apply uniformization-and thus cannot use the usual discrete-time Markov decision process techniques. After formulating the problem as a continuous-time Markov decision process (CTMDP), we use sample path arguments in the reward case and a savvy use of truncation in the holding cost case to yield the results. As far as we know, this is the first time that either have been used in conjunction with the CTMDP to show structure in a queueing control problem. The insights made in each model are supported by a detailed numerical study. © 2010 Springer Science+Business Media, LLC

Phylogenomic analysis of the Chlamydomonas genome unmasks proteins potentially involved in photosynthetic function and regulation

Chlamydomonas reinhardtii, a unicellular green alga, has been exploited as a reference organism for identifying proteins and activities associated with the photosynthetic apparatus and the functioning of chloroplasts. Recently, the full genome sequence of Chlamydomonas was generated and a set of gene models, representing all genes on the genome, was developed. Using these gene models, and gene models developed for the genomes of other organisms, a phylogenomic, comparative analysis was performed to identify proteins encoded on the Chlamydomonas genome which were likely involved in chloroplast functions (or specifically associated with the green algal lineage); this set of proteins has been designated the GreenCut. Further analyses of those GreenCut proteins with uncharacterized functions and the generation of mutant strains aberrant for these proteins are beginning to unmask new layers of functionality/regulation that are integrated into the workings of the photosynthetic apparatus