Traitement d'effluents de tannerie-mégisserie par microfiltration tangentielle

Dans ce travail un procédé de traitement des effluents issus de l'unité de préparation des peaux des animaux au tannage (travail en rivière) en tannerie-mégisserie a été étudié en utilisant la technique de microfiltration tangentielle sur membrane minérale en céramique. Les performances de ce procédé en terme de flux de filtration et de rendement épuratoire dépendent aussi bien des paramètres hydrodynamiques de filtration que de la qualité des effluents (collectés en été et en printemps) issus des différents bains de traitement et de rinçage des peaux dans l'atelier de rivière. Le flux de filtration varie entre 15 l/h.m2 pour l'effluent de printemps et 90 l/h.m2 pour l'effluent d'été. Les paramètres hydrodynamiques optimaux ont également été déterminés: la vitesse de circulation U=3 m/s, la pression transmembranaire Ptm=2 bar et la température T=43°C. L'étude de la microfiltration à concentration variable conduit à des facteurs de concentration volumique (FCV) de 6,5 pour l'effluent de l'été et de 2,4 pour l'effluent de printemps.The leather industry is responsible for the transformation of raw animal skin to a final form as shoes, bags, dresses, etc. This industry was known for centuries as a craft activity, and today with industrial development, environmental regulations and new emerging technologies, it has become necessary to include elaborate processes for its wastewater treatment. These industries consume a great amount of water. In Tunisia, more than 15000 tons of skin are treated per year, and about 600000 m3 per year of effluents are discharged. The waste water contains chemicals, fats, hair and protein, varying in composition depending on the season. Figure 1 represents the preparation of raw skin for the tanning operation and the amount of waste water produced. The amount of water used for the preparation of raw skin is about 70% of the total quantity of water used. This waste water has a significant polluting load (chemicals and organic matter), with 5000 - 7500 mg/l of COD and 100 to 150 mg/l of sulfur. Tunisian legislation and regulations concerning the standards for wastewater disposal are 1000 mg/l for COD, 3 mg/l for sulfur and a pH between 6.5-9. Different techniques for wastewater treatment such as: physico-chemical treatment, treatment by electrochemical oxidation and membrane technology were proposed. Wastewater treatment by microfiltration and ultrafiltration with mineral membranes is advantageous because no chemicals are used and it can be combined easily with other physico-chemical or biological pre-treatments. In this study, we have treated two types of effluents from the leather pre-treatment industry collected in the summer (effluent 1), and the spring (effluent 2) seasons. The physico-chemical characteristics of the two types effluents are given in Table 2. The filtration experiments were made on a test bench (Figure 2) equipped with a feed reservoir, a volumetric pump, a filtration module, flow meter, pressure transducers, a heat exchanger and control valves. Ceramic membranes of tubular geometry (7 channels), 0.08 m2 membrane surface area and of 0.1 µm (mean diameter) pores were used. During the microfiltration experiments, the following physico-chemical parameters were analysed in the permeate and retentate: turbidity, specific conductivity, pH, viscosity, chemical oxygen demand (COD), sulfur (volumetric method), fats (Standard JIS 0102.24.2), protein (using Kjeldahl nitrogen), and organic nitrogen. Hydrodynamic parameters such as temperature (25 < T < 50 °C), transmembrane pressure (1 < Ptm < 2.2 bar) and feed velocity (1 < U < 3 m/s) were fixed for experimentation. The COD concentration in the effluent was adjusted and kept constant at 5000 mg/l. The raw effluent was pre-filtered on a screen filter (150 µm pore size). For experiments with variable concentration, we regularly removed the filtrate and the concentration factor was represented by FCV=Vi / Vr, where Vi was the initial volume and Vr was the volume of the retentate. The performance of the microfiltration (J) was expressed in l/h×m2. The retention rate (TR) was defined by: TR=1 - (Cpermeate) / (Cfeed). The total hydraulic resistance (RT) was defined by Darcy's law: Jf=Ptm / µ RT. After each experiment, the membrane was regenerated following a standard protocol and it was verified by measuring water flux. Figure 3a represents the variation of the filtration flux with time for 4 different temperatures: 25 °C, 43 °C, 45 °C and 50 °C with effluent 1. The flux increased from 90 to 118 l/h×m2 when the temperature increased from 25 °C to 43 °C. After 90 min at 50 °C, the filtration flux was 123 l/h×m2. Table 3 shows that the viscosity of the effluent decreased with temperature, while the turbidity of the filtrate increased from 0.63 NTU at T=25 °C to 1.6 NTU for T=50 °C. The retention rate of COD was always superior to 50 %. On the basis of these results, we chose the optimum temperature of 43 °C for other experiments. Figure 4 summarises the variation of flux with transmembrane pressure at flow velocities of 1 m/s, 2 m/s and 3 m/s. The stabilized fluxes were practically the same for the flow velocities of 1 and 2 m/s (of the order of 80 l/h×m2), but were higher at 3 m/s (110 - 115 l/h×m2 at 2 bar). The physico-chemical characteristics of the raw effluent and the permeate obtained after 90 minutes of filtration are summarised in Table 4. Figure 7a shows the variation of filtration flux for 2 types of effluents. The filtration flux for the same conditions of experimentation and at stabilized conditions (at 90 min) was 118 l/h×m2 for effluent 1 and 20 l/h×m2 for effluent 2. The lower filtration flux for effluent 2 can be explained by high deposits of rejected matter on the membrane and in the pores. Table 5 gives a comparison of the characteristics of effluents 1 and 2 before and after microfiltration. At variable feed concentrations, FCV=6.5 for effluent 1 and FCV=2.4 for the effluent 2 and the stabilized flux was about 90 l/h×m2 for the effluent 1 and 15 l/h×m2 for the effluent 2. The time needed for treatment of effluent 1 was about 6 hours, while more that 16 hours was necessary for effluent 2. Table 6 provides physico-chemical characteristics for the two types of effluents. The contents of fat, protein, nitrogen and sulfur in the effluent were important factors for variation. These results indicate that microfiltration is very sensitive to the quantity of polluting matter present in the effluents, particularly sulfur and fat. Increased polluting matter in effluent 2 could be responsible for the membrane polarization and blocking of pores. The resistance model was used to verify this hypothesis. The irreversible resistance values for effluent 2 were greater, thus confirming the hypothesis that the increased adsorption on the membrane surface and passage of pores by the presence of sulfur and organic polluting matter. These experimental results confirm that the best performance can be obtained at the hydrodynamic conditions of: a temperature of 43 °C; a transmembrane pressure of 2 bar; and a flow velocity of 3 m/s. Seasonal variation changed the quality of effluents, which considerably affects the performances of the microfiltration. Effluent 2, which was obtained from the treatment of sheep skin during the spring season, led to more membrane pore blocking than effluent 1 for the same initial concentration in COD. The interactions of fats and sulfur with the membrane layer appear to play an important role in the formation of a cake layer

Ancient mtDNA Genetic Variants Modulate mtDNA Transcription and Replication

Although the functional consequences of mitochondrial DNA (mtDNA) genetic backgrounds (haplotypes, haplogroups) have been demonstrated by both disease association studies and cell culture experiments, it is not clear which of the mutations within the haplogroup carry functional implications and which are “evolutionary silent hitchhikers”. We set forth to study the functionality of haplogroup-defining mutations within the mtDNA transcription/replication regulatory region by in vitro transcription, hypothesizing that haplogroup-defining mutations occurring within regulatory motifs of mtDNA could affect these processes. We thus screened >2500 complete human mtDNAs representing all major populations worldwide for natural variation in experimentally established protein binding sites and regulatory regions comprising a total of 241 bp in each mtDNA. Our screen revealed 77/241 sites showing point mutations that could be divided into non-fixed (57/77, 74%) and haplogroup/sub-haplogroup-defining changes (i.e., population fixed changes, 20/77, 26%). The variant defining Caucasian haplogroup J (C295T) increased the binding of TFAM (Electro Mobility Shift Assay) and the capacity of in vitro L-strand transcription, especially of a shorter transcript that maps immediately upstream of conserved sequence block 1 (CSB1), a region associated with RNA priming of mtDNA replication. Consistent with this finding, cybrids (i.e., cells sharing the same nuclear genetic background but differing in their mtDNA backgrounds) harboring haplogroup J mtDNA had a >2 fold increase in mtDNA copy number, as compared to cybrids containing haplogroup H, with no apparent differences in steady state levels of mtDNA-encoded transcripts. Hence, a haplogroup J regulatory region mutation affects mtDNA replication or stability, which may partially account for the phenotypic impact of this haplogroup. Our analysis thus demonstrates, for the first time, the functional impact of particular mtDNA haplogroup-defining control region mutations, paving the path towards assessing the functionality of both fixed and un-fixed genetic variants in the mitochondrial genome

Necrotrophism Is a Quorum-Sensing-Regulated Lifestyle in Bacillus thuringiensis

How pathogenic bacteria infect and kill their host is currently widely investigated. In comparison, the fate of pathogens after the death of their host receives less attention. We studied Bacillus thuringiensis (Bt) infection of an insect host, and show that NprR, a quorum sensor, is active after death of the insect and allows Bt to survive in the cadavers as vegetative cells. Transcriptomic analysis revealed that NprR regulates at least 41 genes, including many encoding degradative enzymes or proteins involved in the synthesis of a nonribosomal peptide named kurstakin. These degradative enzymes are essential in vitro to degrade several substrates and are specifically expressed after host death suggesting that Bt has an active necrotrophic lifestyle in the cadaver. We show that kurstakin is essential for Bt survival during necrotrophic development. It is required for swarming mobility and biofilm formation, presumably through a pore forming activity. A nprR deficient mutant does not develop necrotrophically and does not sporulate efficiently in the cadaver. We report that necrotrophism is a highly regulated mechanism essential for the Bt infectious cycle, contributing to spore spreading

The PlcR Virulence Regulon of Bacillus cereus

PlcR is a Bacillus cereus transcriptional regulator, which activates gene expression by binding to a nucleotidic sequence called the ‘PlcR box’. To build a list of all genes included in the PlcR regulon, a consensus sequence was identified by directed mutagenesis. The reference strain ATCC14579 sequenced genome was searched for occurrences of this consensus sequence to produce a virtual regulon. PlcR control of these genes was confirmed by comparing gene expression in the reference strain and its isogenic Δ-plcR strain using DNA microarrays, lacZ fusions and proteomics methods. The resulting list included 45 genes controlled by 28 PlcR boxes. Forty of the PlcR controlled proteins were exported, of which 22 were secreted in the extracellular medium and 18 were bound or attached to cell wall structures (membrane or peptidoglycan layer). The functions of these proteins were related to food supply (phospholipases, proteases, toxins), cell protection (bacteriocins, toxins, transporters, cell wall biogenesis) and environment-sensing (two-component sensors, chemotaxis proteins, GGDEF family regulators). Four genes coded for cytoplasmic regulators. The PlcR regulon appears to integrate a large range of environmental signals, including food deprivation and self cell-density, and regulate the transcription of genes designed to overcome obstacles that hinder B. cereus growth within the host: food supply, host barriers, host immune defenses, and competition with other bacterial species. PlcR appears to be a key component in the efficient adaptation of B. cereus to its host environment

The Secret Life of the Anthrax Agent Bacillus anthracis: Bacteriophage-Mediated Ecological Adaptations

Ecological and genetic factors that govern the occurrence and persistence of anthrax reservoirs in the environment are obscure. A central tenet, based on limited and often conflicting studies, has long held that growing or vegetative forms of Bacillus anthracis survive poorly outside the mammalian host and must sporulate to survive in the environment. Here, we present evidence of a more dynamic lifecycle, whereby interactions with bacterial viruses, or bacteriophages, elicit phenotypic alterations in B. anthracis and the emergence of infected derivatives, or lysogens, with dramatically altered survival capabilities. Using both laboratory and environmental B. anthracis strains, we show that lysogeny can block or promote sporulation depending on the phage, induce exopolysaccharide expression and biofilm formation, and enable the long-term colonization of both an artificial soil environment and the intestinal tract of the invertebrate redworm, Eisenia fetida. All of the B. anthracis lysogens existed in a pseudolysogenic-like state in both the soil and worm gut, shedding phages that could in turn infect non-lysogenic B. anthracis recipients and confer survival phenotypes in those environments. Finally, the mechanism behind several phenotypic changes was found to require phage-encoded bacterial sigma factors and the expression of at least one host-encoded protein predicted to be involved in the colonization of invertebrate intestines. The results here demonstrate that during its environmental phase, bacteriophages provide B. anthracis with alternatives to sporulation that involve the activation of soil-survival and endosymbiotic capabilities

Critical Behavior in the La0.6Ca0.4MnO3 Perovskite Manganite

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X-ray diffraction, magnetic and magnetocaloric properties of La0.6Ca0.4Mn1−xFexO3 (0 ≤ x ≤ 0.3) manganites prepared by the sol-gel method

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