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Sousa W.T.Z.,Tiradentes University | Thomaz S.M.,State University of Maringá | Murphy K.J.,University of Glasgow
Acta Oecologica | Year: 2011

We explored the hypothesis that flood events and connectivity interact with local factors (biotic and abiotic) to drive changes in aquatic vegetation in a typical backwater lake connected to the River Paraná, Brazil. Over three years, we conducted quarterly surveys to analyse macrophyte composition and abundance, and environmental variables. In total 34 macrophyte species were recorded, with strong dominance of Eichhornia azurea. During periods of low water level, the lake vegetation was primarily structured by distance from the river. Total community abundance and emergent species diversity increased from the outer to the inner lake, while the opposite occurred for submersed and floating species. These changes were strongly associated with gradients of depth, slope, water transparency, oxygen and phosphorus. Two summer flood periods had different effects upon plants depending on flood features (e.g. intensity, duration) and location. Flood-pulses tended to reset the community, both in terms of species abundance and richness, and disrupt competitive processes. Flood disturbances likely governed interactions among facilitation and competition processes. While recovering from the major flood disturbance, E. azurea invested strongly in stem horizontal growth, but less so in leaf production. In this situation the physical structure of E. azurea facilitated colonization by several other macrophyte species, resulting in substantial and rapid increase in species richness. Under a more stable hydrology E. azurea displaced less competitive species by forming dense stands. Connectivity and flood-pulses were the main factors responsible for sustaining high diversity of aquatic macrophytes in the lake, but these drivers interact, in both time and space, with local environmental and biotic drivers to structure the temporally and spatially shifting mosaic of lake vegetation. Our results show the fundamental importance of natural variability of hydrological connectivity and flood disturbances for biodiversity conservation in tropical riverine floodplains. © 2011 Elsevier Masson SAS.


Freitas S.V.D.,University of Aveiro | Freitas S.V.D.,Tiradentes University | Paredes M.L.L.,State University of Rio de Janeiro | Daridon J.-L.,University of Pau and Pays de l'Adour | And 2 more authors.
Fuel | Year: 2013

Speed of sound is an important fuel thermophysical property that directly characterizes the fuel injection and the NOx emissions in diesel engines especially for injectors activated with pressure. Nevertheless, the experimental data of speed of sound for biodiesel fuels are very scarce in the literature. Thereby, this work aims at measuring the speed of sound for biodiesels fuels and evaluating some predictive models to estimate the speed of sound from the composition of fatty acid methyl esters in the biodiesel. For that purpose the measurement of speeds of sound for three fatty acid methyl esters and ten biodiesel fuels at atmospheric pressure and temperatures from 288.15 to 343.15 K was done. The ability of two versions of Auerbach's relation, and the ideal mixture mixing rule to describe the speed of sound of biodiesels was evaluated. The results evinced that, with the exception to the original version of Auerbach's relation, the other models studied provide a good estimate of the experimental data. The modified Auerbach's relation displays an overall average relative deviation of 1.64%, and the ideal mixture mixing rules predict the biodiesel speed of sound with only 0.37% of overall deviation. Moreover, the dependency of speed of sound on pressure was also correlated with a linear equation, presenting only an overall deviation of 0.56%. These models can thus be a good tool to estimate the speeds of sound using only information about the biodiesel composition. © 2012 Elsevier Ltd. All rights reserved.


Garcia-Segura S.,University of Barcelona | Cavalcanti E.B.,Tiradentes University | Brillas E.,University of Barcelona
Applied Catalysis B: Environmental | Year: 2013

Chloramphenicol is a widely used broad-spectrum antibiotic, which has been detected as emerging pollutant in natural waters. The mineralization of this drug in a synthetic sulfate solution of pH 3.0 has been studied by anodic oxidation with electrogenerated H2O2 (AO-H2O2), electro-Fenton (EF), UVA photoelectro-Fenton (PEF) and solar photoelectro-Fenton (SPEF). Comparative electrolyses carried out with 100mL stirred tank reactors equipped with a boron-doped diamond (BDD) or Pt anode and an air-diffusion cathode at constant current density showed the superiority of the processes with BDD because of the higher oxidation ability of ™OH formed from water oxidation at the BDD surface. Total mineralization was rapidly reached for the most potent treatment of SPEF with BDD due to the additional oxidation by ™OH produced from Fenton's reaction between added Fe2+ (0.5mM) and H2O2 generated at the cathode, together the synergistic photolytic action of sunlight, much more intense than the 6W UVA lamp used in PEF. Chloramphenicol decay always followed a pseudo-first-order kinetics. The influence of current density and substrate concentration on SPEF with BDD was examined. Nine aromatic products, thirteen hydroxylated derivatives and seven carboxylic acids were identified by different chromatographic techniques. While the initial Cl of the drug was released as chloride ion, its initial N was lost as nitrate ion and, in smaller proportion, as ammonium ion. From the detected products, a general reaction pathway for chloramphenicol mineralization is proposed. The viability of SPEF was confirmed in a 10L pre-pilot plant with a Pt/air-diffusion filter-press reactor coupled to a solar CPCs photoreactor. After 180min of electrolysis at 100mAcm-2, a 245mgL-1 chloramphenicol solution in 0.05M Na2SO4 with 0.5mM Fe2+ at pH 3.0 underwent 89% mineralization with 36% current efficiency and 30.8kWhm-3 energy cost. © 2013 Elsevier B.V.


Cavalcanti E.B.,Tiradentes University | Garcia-Segura S.,University of Barcelona | Centellas F.,University of Barcelona | Brillas E.,University of Barcelona
Water Research | Year: 2013

The electrochemical incineration of omeprazole, a widely prescribed gastrointestinal drug which is detected in natural waters, has been studied in a phosphate buffer of pH 7.0 by anodic oxidation with electrogenerated H2O2 (AO-H2O2) operating at constant current density (j). The experiments were carried out in a cell equipped with either a Pt or a boron-doped diamond (BDD) anode and an air-diffusion cathode to continuously produce H2O2. In these systems, organics are mainly oxidized by hydroxyl radicals formed at the Pt or BDD surface from water oxidation. A partial total organic carbon (TOC) abatement close to 78% for omeprazole was achieved by AO-H2O2 with a BDD anode after consumption of 18 Ah L-1 at 100 mA cm-2, whereas the alternative use of Pt did not allow mineralizing the drug. However, the drug was totally removed using both anodes, although it decayed more rapidly using BDD. In this latter system, increasing j accelerated the degradation process, but lowering the mineralization current efficiency. Greater drug content also enhanced the degradation rate with higher mineralization degree and current efficiency. The kinetics for omeprazole decay always followed a pseudo-first-order reaction and its rate constant increased with increasing j and with decreasing its concentration. Seven heteroaromatic intermediates and four hydroxylated derivatives were detected by LC-MS, while nine short-linear carboxylic acids were identified and quantified by ion-exclusion HPLC. These acids were largely accumulated using Pt and rapidly removed using BDD, thus explaining the partial mineralization of omeprazole achieved by AO-H2O2 with the latter anode. The release of inorganic ions such as NO3-, NH4+ and SO42- was followed by ionic chromatography. A plausible reaction sequence for omeprazole mineralization involving all intermediates detected is proposed. © 2013 Elsevier Ltd.


Ventura S.P.M.,University of Aveiro | De Barros R.L.F.,Tiradentes University | De Pinho Barbosa J.M.,Tiradentes University | Soares C.M.F.,Tiradentes University | And 2 more authors.
Green Chemistry | Year: 2012

The ability of ionic liquid-based aqueous two-phase systems (ATPS) to purify lipase produced by fermentation is here evaluated and compared against conventional PEG-based ATPS systems. Four ionic liquids, chosen after screening of a larger number of ionic liquids are evaluated, with the maximum purification and higher recovery being obtained for the systems based on [C 8mim]Cl. It is shown that IL-based ATPS have a performance superior to PEG-based ATPS for the purification of this enzyme. © The Royal Society of Chemistry 2012.


Pereira J.F.B.,University of Aveiro | Lima A.S.,Tiradentes University | Freire M.G.,University of Aveiro | Coutinho J.A.P.,University of Aveiro
Green Chemistry | Year: 2010

The potential use of ionic liquids (ILs) as adjuvants in typical polymer-salt aqueous systems for the separation and purification of vital biomolecules is investigated. An innovative study involving the addition of various imidazolium-based ILs to conventional PEG/inorganic salt aqueous biphasic systems (ABS), aiming at controlling their phase behaviour and extraction capability for l-tryptophan, is carried out here. For this purpose, phase diagrams and respective tie-lines for PEG 600/Na2SO4 ABS with the addition of small quantities of IL were established. In addition, the partition coefficients of l-tryptophan were determined in those systems. The results obtained indicate that the addition of small amounts of IL to the typical PEG/inorganic salt aqueous systems could largely control the extraction efficiency for l-tryptophan, and that efficiency depends on the IL employed. Salting-in inducing ILs enhance the partition coefficient of l-tryptophan for the PEG-rich phase while salting-out inducing ILs decrease the partitioning of the amino acid. These results are an interesting advance in biotechnological separation processes regarding the extraction of biomolecules that could be used instead of the common approach of PEG functionalization. © 2010 The Royal Society of Chemistry.


Freitas S.V.D.,University of Aveiro | Pratas M.J.,University of Aveiro | Ceriani R.,University of Campinas | Lima A.S.,Tiradentes University | Coutinho J.A.P.,University of Aveiro
Energy and Fuels | Year: 2011

Viscosity is an important biodiesel parameter, subject to specifications and with an impact on the fuel quality. A model that could predict the value of viscosity of a biodiesel based on the knowledge of its composition would be useful in the optimization of biodiesel production processes and the planning of blending of raw materials and refined products. This work aims at evaluating the predictive capability of several models previously proposed in the literature for the description of the viscosities of biodiesels and their blend with other fuels. The models evaluated here are Ceriani's, Krisnangkura's, and Yuan's models, along with a revised version of Yuan's model proposed here. The results for several biodiesel systems show that revised Yuan's model proposed provides the best description of the experimental data with an average deviation of 4.65%, as compared to 5.34% for Yuan's model, 8.07% for Ceriani's model, and 7.25% for Krisnangkura's model. The same conclusions were obtained when applying these models to predict the viscosity of blends of biodiesel with petrodiesel. © 2010 American Chemical Society.


Freitas S.V.D.,University of Aveiro | Oliveira M.B.,University of Aveiro | Lima A.S.,Tiradentes University | Coutinho J.A.P.,University of Aveiro
Energy and Fuels | Year: 2012

Vapor pressure directly affects the quality of ignition, atomization, and combustion of a fuel. Lower values lead to delayed ignition, poor atomization, and problematic combustion. Biodiesel fuels might present these problems because they have lower vapor pressure compared to that of petrodiesel. Similar to other properties, however, the magnitude of this property depends upon the composition of fatty acid alkyl esters in biodiesel; therefore, the knowledge of the relationship between these two variables is of great importance. This work reports the vapor pressures of 3 pure methyl esters and 10 biodiesel fuels. The experimental data were used to evaluate the predictive ability of Yuan's, Ceriani's, and cubic-plus-association equation of state (CPA EoS) models for its description. The results underline the good capacity of Yuan's and CPA models for describing the experimental data for all biodiesel fuels studied here, presenting an overall average temperature difference (OΔT m) of 1.12 and 1.25 K, while the overall average deviations (OARDs) in vapor pressure are 3.41 and 0.80%, respectively. © 2012 American Chemical Society.


Lopez-Suarez F.E.,Tiradentes University | Bueno-Lopez A.,University of Alicante | Eguiluz K.I.B.,Tiradentes University | Salazar-Banda G.R.,Tiradentes University
Journal of Power Sources | Year: 2014

A series of Pt-Sn/C catalysts used as anodes during ethanol oxidation are synthesized by a deposition process using NaBH4 as the reducing agent. The order in which the precursors are added affects the electrocatalytic activity and physical-chemical characteristics of the bimetallic catalysts, where the Pt-Sn catalyst prepared by co-precipitation of both metals functions best below a potential of 0.5 V and the catalyst prepared by sequential deposition of Sn and Pt (drying after Sn addition) is most active above a potential of 0.5 V. The electrochemical behavior of catalysts during ethanol oxidation in an acidic medium are characterized and monitored in a half-cell test at room temperature by cyclic voltammetry, chronoamperometry and anode potentiostatic polarization. Catalyst structure and chemical composition are investigated by transmission electron microscopy (TEM), X-ray powder diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). This behavior presented for best Pt-Sn catalyst can be attributed to the so-called bifunctional mechanism and to the electronic interaction between Pt and Sn. © 2014 Elsevier B.V. All rights reserved.


Hydrilla verticillata (Hydrocharitaceae) is a highly prolific, rooted submerged macrophyte native to Asia that has invaded aquatic systems worldwide, causing many ecological and human-related problems. Hydrilla recently invaded the Paraná River basin in Brazil, making other ecologically and socially important Brazilian watersheds more susceptible to invasion by this plant. Here, I summarize the relevant information about Hydrilla, focusing on its biotic attributes, abiotic tolerance and effects on ecosystems. The aim of this review is to provide background information to assist with planning for the potential impacts of this species in the Neotropical region (particularly in Brazil) and the development of research, monitoring and management strategies. A wide ecological amplitude, resistance organs, and high growth rates and dispersion ability provide Hydrilla with great potential to invade and infest a variety of habitats, often resulting in important physico-chemical and biotic effects on the environment. Hydrilla is similar in its morphological and ecological aspects to Egeria najas and Egeria densa (South American Hydrocharitaceae), but this non-native species is a superior competitor and can be expected to exert significant pressure in habitats colonized by these native Hydrocharitaceae. Socially important rivers (such as the São Francisco River) have a high risk of being infested with Hydrilla, especially in stretches affected by dams, which could prejudice important human activities like hydropower generation. Important wetlands for biodiversity conservation (such as the Pantanal) may also be invaded, but they seem to be more resistant to infestations as long as their natural hydrologies are preserved. Before investing substantial effort to control Hydrilla, managers should weigh the potential costs and benefits of available techniques and consider the potential benefits of Hydrilla in providing ecosystem services. © 2011 Springer Science+Business Media B.V.

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