1,721,013 research outputs found
A methodological approach for dynamic modelling of membrane integrated biosorption: a case study on Sphaerotilus natans as biosorbent
No full textThis work is a review of the study performed on heavy metals biosorption by Sphaerotilus natans confined in an ultrafiltration membrane module. A methodological approach has been applied aiming at the dynamic modelling of the process: i) firstly, biosorbent was characterised according to acid-base properties of binding sites; ii) then, equilibrium studies were performed both in single metal and multimetal systems in order to evidence any competition for binding sites and to find mechanicistic models that are able to describe biosorption equilibrium; iii) finally, biosorption in membrane processes was investigated in laboratory scale, in the case of both single- metal and two- metal systems, and a dynamic model was developed accounting for binding site competition and for binding ability of cell's fragments generated by tangential flow shear stress
Equilibrium biosorption studies in single and multi-metal systems
No full textDifferent models were used in order to describe equilibrium data obtained by heavy metal biosorption tests. Arthrobacter sp. biomass was suspended in aqueous solution and tested as biosorbent material for copper and cadmium ions. The effects of pH on biosorption in single metal systems (copper and cadmium) and on the selectivity of biomass in two metal systems (copper-cadmium) was studied. Biosorption trials performed for each single metal (in the range 0-2 mmol/l) at different equilibrium pHs (3-6 units) showed a general positive effect of pH increase on metal specific uptake. Experimental data obtained for each metal were fitted using adsorption models including Langmuir, Freundlich and Redlich-Peterson isotherms. Biosorption tests were also carried out using binary solutions of copper and cadmium at different equilibrium pH to evaluate biomass selectivity. Modified Langmuir and Freundlich models were used to fit these equilibrium data. The biomass tested was more selective for copper ions and this selectivity changes with equilibrium PH. In both single and two metal systems, a simple procedure of model discrimination was performed to establish which of the tested models better represents the experimental behaviour. (C) 2001 Elsevier Science Ltd. All rights reserved
The gametogenetic cycle of two syntopic populations of moles: Talpa romana and Talpa europaea (Mammalia, Insectivora, Talpidae)
No full textThe gametogenetic activity of two syntopic populations of moles, Talpa romana and T europaea (Mammalia, Insectivora, Talpidae), was compared. The testes and the ovaries of 42 specimens of T romana and of 41 specimens of T europaea were histologically characterised. Male gametogenetic activity was shown by the presence of spermatozoa in the epididymis. The diameter of seminiferous tubules was also measured. Female gametogenetic activity was evaluated on the basis of the number of secondary and pluristratified primary follicles in the ovary. Though not identical, the gametogenetic cycle of T romana largely overlaps that of T europaea. Moreover, for the two populations of moles a relationship between the duration of the reproductive activity and climatic and latitude-dependent parameters is suggested
Valorisation of whey through continuous fermentation coupled with MF and RO membrane processes: biomass production and water reuse
No full textUltrastructure of the spermatozoon of Talpa romana (Mammalia, Lipotyphla)
No full textIn this study, we used SEM and TEM to investigate the ultrastructure of spermatozoa from the cauda epididymis of Talpa romana. For comparison, we also analysed spermatozoa from the cauda epididymis of T. europaea captured in the same area. The male gamete of T. romana has a flattened head with an elliptic profile, consisting of a large acrosome and a nuclear region separated by a thin subacrosomal space. At the tip of the nucleus, the subacrosomal space ends in a finger-shaped projection. The tail includes a connecting piece, middle piece, principal piece and end piece. The male gametes of T. romana are substantially similar to those of T. europaea. A comparison with other species of insectivores permits extension of the similarity of sperm features to Scalopus aquaticus and Condylura cristata. Many spermatozoa from the cauda epididymis of T. romana and T. europaea have the tail bent at the annulus, and this is always associated with remnants of cytoplasmic droplets. This morphology is considered to be a common phenomenon
Biosorption of copper in Sphaerotilus natans immobilsed in polysulfone matrix: equilibrium and kinetic analysis
No full textTreatment of concentrated arsenic(V) solutions by micellar enhanced ultrafiltration with high molecular weight cut-off membrane
No full textIn this work arsenic removal by micellar enhanced ultrafiltration (MEUF) was investigated using cetylpyridinium chloride (CPC) and a cross-flow polyethersulphone (PES) membrane apparatus. The effects of some operating factors on permeate flux, arsenic and CPC rejections were investigated and, in particular, transmembrane pressure, pH, CPC concentration, As concentration and ionic strength. The novel aim of this work is evaluating the possible advantages of using large molecular weight cut-off membrane (100 kDa) and reduced surfactant concentrations (1-3 mM) for treating high fluxes of concentrated arsenic-bearing solutions (6-10 ppm). The experimental results reported in this paper show that PES membrane apparatus with high molecular weight cut-off allowed to treat large fluxes of concentrated arsenic-bearing solutions (6-10 ppm) even by using low surfactant concentration (1-3 mM). In particular arsenic removal ranged from 93-98% to 70-74% depending on initial As concentration (6 and 10 ppm, respectively). In addition surfactant leakage in the permeate was always below CMC due to presieving of concentration polarisation layer. The favourable combination of high MWCO membranes and low surfactant concentration can benefit to overall process economics for the lower membrane area requirement (due to greater flux) and the reduced surfactant consumption. © 2007 Elsevier B.V. All rights reserved
Biosorption of copper by Sphaerotilus natans immobilised in polysulfone matrix: equilibrium and kinetic analysis
No full textCopper biosorption by Sphaerotilus natans immobilised in polysulfone matrices has been studied. Firstly, a rough characterisation of biosorbent beads has been performed, and operating conditions for beads preparation aimed at biosorption have been optimised. Then, the equilibrium of the process was studied in order to determine the effect of pH and biomass concentration inside beads; experimental data were successfully fitted by the Langrnuir equation, and the highest value for loading was 5.4 mg/g estimated at pH 5.5 and 0.18 g of lyophilised biomass per gram of beads. Biosorption kinetics has also been studied, and an original kinetic model was developed which is able to correlate experimental data. This model was developed from the Shrinking Core Model, considering a variable copper diffusion coefficient dependent on the process conversion. The estimated values for copper diffusion coefficient were obviously lower than copper diffusivity in water, and they depend on biomass concentration inside beads. Beads regeneration was studied using EDTA, HCl and CaCl2. Satisfactory biosorption performances were observed also after 10 sorption/desorption cycles, with CaCl2 as regeneration solution, All the results confirmed the technical feasibility of the biosorption process by a polysulfone-entrapped biomass even though biosorption efficiency should be improved. (C) 2003 Elsevier Science B.V. All rights reserved
Female gonad of moles, genus Talpa (Insectivora, Mammalia): Ovary or ovotestis?
No full textThe female gonads of moles (genus Talpa) are composed of a cortex, functioning as an ovary, and a medulla, which is structurally similar to that of the testis. In the female reproductive apparatus there are masculine glandular annexes, such as a bilobate prostate, two Cowper glands, and a penis-like clitoris. All these features have recently led to the hypothesis of the presence of hermaphroditism due to sex-reversal in Talpa. The purpose of this study is to understand the functional significance of the structural organization of the female gonads in order to verify this hypothesis. Histological, histochemical and ultrastructural analyses have been carried out on several gonads of both sexes of two species: T. europaea and T. romana, including three fetuses. In both species, the cortical region of the female gonad shows a regular oogenetic activity. While the medulla is composed of interstitial cells that are partly organized in cord-like structures, no spermatogenetic activity has been ever observed inside of them. A histochemical analysis shows that in both sexes the interstitial cells secrete steroids, presumably estrogens as well as androgens. The presence of androgens in the female gonads would therefore explain the persistence of male glandular annexes in the female reproductive apparatus and both the sexual and behavioral monomorphism typical of the genus Talpa. Nonetheless, the female gonad of moles is a real ovary and a well-defined gonochorism exists. Therefore, there is no reason to assert the presence of hermaphroditism due to sex reversal. J. Exp. Zool. 286:745-754, 2000
Copper biosorption onto Rhizopus oligosporus: pH-edge tests and related kinetic and equilibrium modelling
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