Aplicação e otimização de métodos eletroquímicos combinados para remoção e determinação de cromo hexavalente em efluentes simulados

Hexavalent chromium is a heavy metal present in various industrial effluents, and depending on its concentration may cause irreparable damage to the environment and to humans. Facing this surrounding context, this study aimed on the application of electrochemical methods to determine and remove the hexavalent chromium (Cr6+) in simulated wastewater. To determine was applied to cathodic stripping voltammetry (CSV) using ultra trace graphite electrodes ultra trace (work), Ag/AgCl (reference) and platinum (counter electrode), the samples were complexed with 1,5- diphenylcarbazide and then subjected to analysis. The removal of Cr6+ was applied electrocoagulation process (EC) using Fe and Al electrodes. The variables that constituted the factorial design 24, applied to optimizing the EC process, were: current density (5 and 10 mA.cm-2), temperature (25 and 60 ºC), concentration (50 and 100 ppm) and agitation rate (400 and 600 RPM). Through the preliminary test it was possible the adequacy of applying the CSV for determining of Cr6+, removed during the EC process. The Fe and Al electrodes as anodes sacrifice showed satisfactory results in the EC process, however Fe favored complete removal in 30 min, whereas with Al occurred at 240 min. In the application of factorial design 24 and analysis of Response Surface Methodology was possible to optimize the EC process for removal of Cr6+ in H2SO4 solution (0.5 mol.L-1), in which the temperature, with positive effect, was the variable that presented higher statistical significance compared with other variables and interactions, while in optimizing the EC process for removal of Cr6+ in NaCl solution (0.1 mol.L-1) the current density, with positive effect, and concentration, with a negative effect were the variables that had greater statistical significance with greater statistical significance compared with other variables and interactions. The utilization of electrolytes supports NaCl and Na2SO4 showed no significant differences, however NaCl resulted in rapid improvement in Cr6+ removal kinetics and increasing the NaCl concentration provided an increase in conductivity of the solution, resulting in lower energy consumption. The wear of the electrodes evaluated in all the process of EC showed that the Al in H2SO4 solution (0.5 mol.L-1), undergoes during the process of anodization CE, then the experimental mass loss is less than the theoretical mass loss, however, the Fe in the same medium showed a loss of mass greater experimental estimated theoretically. This fact is due to a spontaneous reaction of Fe with H2SO4, and when the reaction medium was the NaCl and Na2SO4 loss experimental mass approached the theoretical mass loss. Furthermore, it was observed the energy consumption of all processes involved in this study had a low operating cost, thus enabling the application of the EC process for treating industrial effluents. The results were satisfactory, it was achieved complete removal of Cr6+ in all processes used in this study.

Adição de policloreto de alumínio e remoção de peixes bentívoros como técnicas de restauração de lagos rasos do semiárido brasileiro

Eutrophication is the most common cause of water quality degradation in the world. This process occurs by excessive nutrients inputs, nitrogen and phosphorus, to the aquatic systems resulting in algal and cyanobacterial blooms. In shallow lakes these effects are pronounced due to the higher interaction of the lake with watershed, air and sediment. There are innumerous restoration techniques of eutrophied lakes with a range of successful results but there is only one case of successful lake restoration in Brazil: Paranoá Lake in Brasília city. The Brazilian semiarid region has many artificial lakes, named açudes, which are mostly eutrophic and shallow lakes. The eutrophication in these lakes is reported and the phytoplankton community is dominated by potentially toxic cyanobacteria species, mainly Cylindrospermopsis raciborskii. The aim of this thesis is to test techniques for water quality management which can be easily applied in Brazilian semiarid lakes. Results from a laboratory experiment suggest that the addition of a phosphorus sorbent clay associated with an aluminium based coagulant is an effective technique in removing soluble reactive phosphorus and reducing C. raciborskii growth rate – cyanobacteria potentially toxic dominant in reservoirs of Brazilian semiarid – but this effect is dependent on the biomass in the application moment. Results from a field experiment in mesocosm in a eutrophied lake showed that the addition of aluminium based coagulant and removal of benthivorous fish is more efficient in removing total phosphorus and chlorophyll-a from water column than the isolated application of one of the techniques. Lastly, laboratory tests showed that aluminium based coagulant exhibited good performance in removing turbidity and total phosphorus from water of six reservoirs but the efficiency was reduced by algal biomass and pH. The results of this study showed that the improvement in water quality of eutrophied reservoirs in semiarid region is possible through internal loading control by phosphorus precipitation and inactivation in sediments or inhibition of phosphorus release by benthivorous fishes, and also that these results show are additives in water quality improvement.

Adição de policloreto de alumínio e remoção de peixes bentívoros como técnicas de restauração de lagos rasos do semiárido brasileiro

Eutrophication is the most common cause of water quality degradation in the world. This process occurs by excessive nutrients inputs, nitrogen and phosphorus, to the aquatic systems resulting in algal and cyanobacterial blooms. In shallow lakes these effects are pronounced due to the higher interaction of the lake with watershed, air and sediment. There are innumerous restoration techniques of eutrophied lakes with a range of successful results but there is only one case of successful lake restoration in Brazil: Paranoá Lake in Brasília city. The Brazilian semiarid region has many artificial lakes, named açudes, which are mostly eutrophic and shallow lakes. The eutrophication in these lakes is reported and the phytoplankton community is dominated by potentially toxic cyanobacteria species, mainly Cylindrospermopsis raciborskii. The aim of this thesis is to test techniques for water quality management which can be easily applied in Brazilian semiarid lakes. Results from a laboratory experiment suggest that the addition of a phosphorus sorbent clay associated with an aluminium based coagulant is an effective technique in removing soluble reactive phosphorus and reducing C. raciborskii growth rate – cyanobacteria potentially toxic dominant in reservoirs of Brazilian semiarid – but this effect is dependent on the biomass in the application moment. Results from a field experiment in mesocosm in a eutrophied lake showed that the addition of aluminium based coagulant and removal of benthivorous fish is more efficient in removing total phosphorus and chlorophyll-a from water column than the isolated application of one of the techniques. Lastly, laboratory tests showed that aluminium based coagulant exhibited good performance in removing turbidity and total phosphorus from water of six reservoirs but the efficiency was reduced by algal biomass and pH. The results of this study showed that the improvement in water quality of eutrophied reservoirs in semiarid region is possible through internal loading control by phosphorus precipitation and inactivation in sediments or inhibition of phosphorus release by benthivorous fishes, and also that these results show are additives in water quality improvement.

Remoção de fenol de efluentes aquosos utilizando floculação iônica

Oil exploration is one of the most important industrial activities of modern society. Despite its derivatives present numerous applications in industrial processes, there are many undesirable by-products during this process, one of them is water separated from oil, called water production, it is constituted by pollutants difficult to degrade. In addition, the high volume of generated water makes its treatment a major problem for oil industries. Among the major contaminants of such effluents are phenol and its derivatives, substances of difficult natural degradation, which due their toxicity must be removed by a treatment process before its final disposal. In order to facilitate the removal of phenol in wastedwater from oil industry, it was developed an extraction system by ionic flocculation with surfactant. The ionic flocculation relies on the reaction of carboxylate surfactant and calcium íons, yielding in an insoluble surfactant that under stirring, aggregates forming floc capable of attracting the organic matter by adsorption. In this work was used base soap as ionic surfactant in the flocculation process and evaluated phenol removal efficiency in relation to the following parameters: surfactant concentration, phenol, calcium and electrolytes, stirring speed, contact time, temperature and pH. The flocculation of the surfactant occurred in the effluent (initial phenol concentration = 100 ppm) reaching 65% of phenol removal to concentrations of 1300 ppm and calcium of 1000 ppm, respectively, at T = 35 °C, pH = 9.7, stirring rate = 100 rpm and contact time of 5 minutes. The permanence of the flocs in an aqueous medium promotes desorption of the phenol from the flake surface to the solution, reaching 90% of desorption at a time of 150 minutes, and the study of desorption kinetics showed that Lagergren model of pseudo-first order was adequate to describe the phenol desorption. These results shows that the process may configure a new alternative of treatment in regard the removal of phenol of aqueous effluent of oil industry.

Remoção de fenol de efluentes aquosos utilizando floculação iônica

Oil exploration is one of the most important industrial activities of modern society. Despite its derivatives present numerous applications in industrial processes, there are many undesirable by-products during this process, one of them is water separated from oil, called water production, it is constituted by pollutants difficult to degrade. In addition, the high volume of generated water makes its treatment a major problem for oil industries. Among the major contaminants of such effluents are phenol and its derivatives, substances of difficult natural degradation, which due their toxicity must be removed by a treatment process before its final disposal. In order to facilitate the removal of phenol in wastedwater from oil industry, it was developed an extraction system by ionic flocculation with surfactant. The ionic flocculation relies on the reaction of carboxylate surfactant and calcium íons, yielding in an insoluble surfactant that under stirring, aggregates forming floc capable of attracting the organic matter by adsorption. In this work was used base soap as ionic surfactant in the flocculation process and evaluated phenol removal efficiency in relation to the following parameters: surfactant concentration, phenol, calcium and electrolytes, stirring speed, contact time, temperature and pH. The flocculation of the surfactant occurred in the effluent (initial phenol concentration = 100 ppm) reaching 65% of phenol removal to concentrations of 1300 ppm and calcium of 1000 ppm, respectively, at T = 35 °C, pH = 9.7, stirring rate = 100 rpm and contact time of 5 minutes. The permanence of the flocs in an aqueous medium promotes desorption of the phenol from the flake surface to the solution, reaching 90% of desorption at a time of 150 minutes, and the study of desorption kinetics showed that Lagergren model of pseudo-first order was adequate to describe the phenol desorption. These results shows that the process may configure a new alternative of treatment in regard the removal of phenol of aqueous effluent of oil industry.

Remoção de carbonatos para otimizar a biolixiviação de rejeito calcopirítico empregando consórcio de microrganismos

The bioleaching of chalcopyrite has not been applied on a commercial scale due to the low process efficiency, so this process has been extensively studied in recent years. The bioleaching of chalcopyrite tailings becomes even more difficult by the presence of higher amounts of impurities, among them are the carbonates. The presence of carbonates in the ore promotes the increase in pH of the solution and may inhibit the development of bioleaching. Therefore, this research aims to apply the acid treatment for optimization of bioleaching process, in order to recover the lost copper throughout the process besides reducing the content of this toxic metal in the tailings pond. The removal and recovery of toxic metals is very important in protecting the environment and human health. The bioleaching experiments were performed in two stages, the first made up using the pre-treated tailing with sulfuric acid in bioleaching, and the second was made using the tailing without treatment with sulfuric acid addition at the beginning of bioleaching. The acid treatment was carried out in bioreactors with three different volumes of H2SO4 96% and a control experiment. All bioleaching experiments were performed in triplicate over a control, without addition of inoculum. The results showed that acid treatment was effective in removal of carbonates and managed to promote a good performance in the bioleaching of chalcopyrite in both steps studied, it is demonstrated that circa 47% copper recovery can be achieved.

Remoção de carbonatos para otimizar a biolixiviação de rejeito calcopirítico empregando consórcio de microrganismos

The bioleaching of chalcopyrite has not been applied on a commercial scale due to the low process efficiency, so this process has been extensively studied in recent years. The bioleaching of chalcopyrite tailings becomes even more difficult by the presence of higher amounts of impurities, among them are the carbonates. The presence of carbonates in the ore promotes the increase in pH of the solution and may inhibit the development of bioleaching. Therefore, this research aims to apply the acid treatment for optimization of bioleaching process, in order to recover the lost copper throughout the process besides reducing the content of this toxic metal in the tailings pond. The removal and recovery of toxic metals is very important in protecting the environment and human health. The bioleaching experiments were performed in two stages, the first made up using the pre-treated tailing with sulfuric acid in bioleaching, and the second was made using the tailing without treatment with sulfuric acid addition at the beginning of bioleaching. The acid treatment was carried out in bioreactors with three different volumes of H2SO4 96% and a control experiment. All bioleaching experiments were performed in triplicate over a control, without addition of inoculum. The results showed that acid treatment was effective in removal of carbonates and managed to promote a good performance in the bioleaching of chalcopyrite in both steps studied, it is demonstrated that circa 47% copper recovery can be achieved.

Avaliação de processo de lodos ativos por batelada seguido de tratamento terciário com ênfase na remoção de matéria orgânica e na sedimentabilidade do lodo

This paper evaluate the performance of a Wastewater Treatment Plant (WWTP) in sequential batch activated sludge modality with tertiary treatment step, located in high temperature region. It also presents the analysis of organic matter’s removal and the evaluation of sludge sedimentation conditions through reactors in bench scale, fed with different substrate’s and biomass’ concentrations, from the WWTP in study. The results showed high efficiency and stability of the treatment process using Sequential Batch Reactors for domestic sewage, even with sudden changes of organic and hydraulic load, reaching more than 90% of efficiency in the removal of biodegradable organic matter. The removal of organic matter and sedimentation tests in bench reactors showed the good performance in respect of the organic matter’s removal, however, the high concentration of micro-organism results in a lower sludge sedimentation rate, which can compromise the quality of the final effluent. The relation Food/Microorganism in the conditions of the WWTP’s current operation showed a value of 0.06 gCOD/gVSS.d. and zonal sedimentation velocity of 0.59 m/h, the great ratio of the concentration of the substrate by biomass concentration, which obtained the maximum operational efficiency, showed a value of 0.09 gCOD/gVSS.d. and zonal sedimentation velocity of 1.4 m/h.

Avaliação de processo de lodos ativos por batelada seguido de tratamento terciário com ênfase na remoção de matéria orgânica e na sedimentabilidade do lodo

This paper evaluate the performance of a Wastewater Treatment Plant (WWTP) in sequential batch activated sludge modality with tertiary treatment step, located in high temperature region. It also presents the analysis of organic matter’s removal and the evaluation of sludge sedimentation conditions through reactors in bench scale, fed with different substrate’s and biomass’ concentrations, from the WWTP in study. The results showed high efficiency and stability of the treatment process using Sequential Batch Reactors for domestic sewage, even with sudden changes of organic and hydraulic load, reaching more than 90% of efficiency in the removal of biodegradable organic matter. The removal of organic matter and sedimentation tests in bench reactors showed the good performance in respect of the organic matter’s removal, however, the high concentration of micro-organism results in a lower sludge sedimentation rate, which can compromise the quality of the final effluent. The relation Food/Microorganism in the conditions of the WWTP’s current operation showed a value of 0.06 gCOD/gVSS.d. and zonal sedimentation velocity of 0.59 m/h, the great ratio of the concentration of the substrate by biomass concentration, which obtained the maximum operational efficiency, showed a value of 0.09 gCOD/gVSS.d. and zonal sedimentation velocity of 1.4 m/h.

The song of humpback whale and the potential effects of whale-watching in the abrolhos bank, BA, Brazil

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

The song of humpback whale and the potential effects of whale-watching in the abrolhos bank, BA, Brazil

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Estudo da eficiência dos adsorventes de Al2O3 e Fe/Al2O3 para remoção de BTX presente em água contaminada com gasolina

Contamination of groundwater by BTX has been featured in recent decades. This type of contamination is due to small and continuous leaks at gas stations, causing serious problems to public health and the environment. Based on these antecedents, the search for new alternatives for treating contaminated water is shown to be essential. Therefore, this study aimed to evaluate the efficiency of removal of BTX by adsorption processes employing commercial alumina (Al2O3) and alumina supported with iron (Fe/Al2O3) as adsorbents. It was prepared by a in a synthetic gasoline solution and distilled water to simulate an actual sample. Initially, the adsorbents were characterized by techniques XRD, TG / DTG, XRF, FTIR and SEM/EDS, several trials, where he was placed synthetic solution to react in the presence of Al2O3 and Fe/Al2O3 in a closed, mechanical stirring system were performed varying the catalyst concentration 2, 4 and 6 g.L-1 every 0, 10, 30 60, 90 and 120 min, aliquots were taken and brought to analysis by gas chromatography flame ionization with headspace extraction. The results indicated that the absorbent which has higher BTX removal capacity was the Fe/Al2O3 at a concentration of 6 g.L-1, pH = 4 and time of 90 minutes reaction, resulting in an efficiency, resulting in a 86,5% efficiency for benzene removal, for the 95,4% toluene, 90,8% for ɱ,ρ- xylene and 93.7% for the θ-xylenes. Subsequently, we performed a kinetic study of the reactions, the values of experimental adsorption capacity (qe) showed agreement with the values of the theoretical adsorption capacity (qc) to the pseudo-second-order model in the adsorption tests using 2 and 6 gL-1 of Al2O3 and assays using 2, 4 and 6 g.L-1 of Fe/Al2O3. A fact corroborated by the R2 values, thus indicating that the chemical interactions are present in the adsorption mechanisms of BTX.

Estudo da evolução das tensões residuais através da difratometria de raios x em aço rolamento submetido a esforços cíclicos

The micro-deformations caused by cyclic loading origins the variation of the distances between atoms of the crystal lattice producing the irreversible component. In order to study and understand the microstructural behavior of the material this paper investigated the influence suffered by residual stresses in thrust rolling bearing races fabricated in AISI 52100 steel, after tests by cyclic rolling contact in a tribometer at 1m/s under two contact pressures (500 MPa and 1400 MPa) in dry and boundary lubrication conditions. Procedures of tests thermo-acustically isolated were developed for monitoring the contact temperature and sound pressure level signals to establish a comparison between the residual stress measurements, micro-hardness Vickers and micrographic registers searching an indication of wear evolution. The sin²ψ method by X-ray diffraction technique was used to quantify the residual stresses. Three raceway zones were selected for the evaluation of wear and surface morphology after predetermined cycling, comparing with their new condition ("as received"). Micro-hardness and residual stress measurements showed significant changes after the tests and it was possible to observe the relationship between the increase of sound pressure level and the residual stress for dry and lubricated conditions.

Estudo da evolução das tensões residuais através da difratometria de raios x em aço rolamento submetido a esforços cíclicos

The micro-deformations caused by cyclic loading origins the variation of the distances between atoms of the crystal lattice producing the irreversible component. In order to study and understand the microstructural behavior of the material this paper investigated the influence suffered by residual stresses in thrust rolling bearing races fabricated in AISI 52100 steel, after tests by cyclic rolling contact in a tribometer at 1m/s under two contact pressures (500 MPa and 1400 MPa) in dry and boundary lubrication conditions. Procedures of tests thermo-acustically isolated were developed for monitoring the contact temperature and sound pressure level signals to establish a comparison between the residual stress measurements, micro-hardness Vickers and micrographic registers searching an indication of wear evolution. The sin²ψ method by X-ray diffraction technique was used to quantify the residual stresses. Three raceway zones were selected for the evaluation of wear and surface morphology after predetermined cycling, comparing with their new condition ("as received"). Micro-hardness and residual stress measurements showed significant changes after the tests and it was possible to observe the relationship between the increase of sound pressure level and the residual stress for dry and lubricated conditions.

Rugosidade superficial e adesão bacteriana em compósitos com nanopartículas após acabamento e polimento

Objective: To evaluate in vitro the surface roughness and bacterial adhesion of nanoparticle composites, after being subjected to different finishing and polishing systems. Materials and Methods: 66 specimens were prepared, and 30 with Filtek Z350 XT (3M ESPE, USA) and 30 with the resin IPS Empress Direct (Ivoclar Vivadent, USA), divided into 6 groups (n = 10 ). Six specimens were prepared for analysis in scanning electron microscopy (SEM) .Each kind of resin was subjected to finishing and polishing systems: Sof-Lex Pop-On discs (3M ESPE, USA) and AstropolTM system (Ivoclar Vivadent , USA), featuring the experimental group. The control group did not undergo any kind of finishing and polishing technique. The average roughness (Ra) in both groups was measured using a roughness in the setting of 0.25 mm (cut off) and surface images obtained with photomicrographs taken with a scanning electron microscope (SEM) magnified 500 times. Bacterial adherence was evaluated by determining the absorbance (OD) of the suspension of adhered cells by spectrophotometer at 570 nm. The results were submitted for analyzed with 2-way ANOVA at α=.05 and Tukey multiple comparison tests. Results: Statistically significant differences were found between the groups in terms of roughness and bacterial adhesion. Filtek Z350 XT for resin were no differences between the tested finishing and polishing systems, where the system of lowest surface roughness was the Sof-Lex Pop-On. To the resin IPS Empress Direct, the finishing and polishing system Astropol, had lower results of surface roughness. As for bacterial adhesion, the lowest optical density value for Filtek Z350 XT was for the group that used the finishing and polishing system Sof-Lex Pop-On and the resin IPS Empress Direct the group that used the Astropol system. In addition, there was a positive correlation between surface roughness and bacterial adhesion on polished surfaces (r = 0.612) Conclusions: surface roughness and bacterial adhesion are closely related. The finishing and polishing Sof-Lex Pop-On system is more suitable for nanoparticulate Filtek Z350 XT and the finishing and polishing system Astropol for resin nanohíbrida IPS Empress Direct.