Many technologies for the treatment of arsenic-containing drinking water are available, but most of them are more effective on arsenic oxidized forms. Therefore, the pre-oxidation of As3+ is ...necessary. The electrochemical processes represent a very promising method due to the simultaneous oxidation of compounds using electrochemical conditions and the reactive radicals produced. In this work, As3+ oxidation was experimentally studied at a pilot scale using an electrochemical oxidation cell (voltage: 10 V; current: 1.7 A). The effect of the initial arsenite concentration, pH, and conductivity of drinking water on the oxidation of As3+ into As5+ was investigated. The results showed that the initial As3+ concentration strongly directly influences the oxidation process. Increasing the initial arsenite concentration from 500 to 5000 µg L−1, the pseudo-first order kinetic constant (k) strongly decreased from 0.521 to 0.038 min−1, and after 10 min, only 21.3% of As3+ was oxidized (vs. 99.9% in the case of As3+ equal to 500 µg L−1). Slightly alkaline conditions (pH = 8) favored the electrochemical oxidation into As5+, while the process was partially inhibited in the presence of a more alkaline or acidic pH. The increase in conductivity up to 2000 µS cm−1 enhanced the kinetic of the oxidation, despite remaining on the same order of magnitude as in the case of conductivity equal to 700 µS cm−1. After 10 min, 99.9 and 95% of As3+ was oxidized, respectively. It is the opinion of the authors that the influence of other operational factors, such as voltage and current density, and the impact of the high concentration of other pollutants should be deeply studied in order to optimize the process, especially in the case of an application at full scale. However, these results provide helpful indications to future research having highlighted the influence of initial As3+ concentration, pH, and conductivity on the electrochemical oxidation of arsenic.
Reversed micelle solvents represent nanometer-sized aqueous droplets stabilized by surfactants inside the bulk organic solvents. The aqueous cores can host various hydrophilic solutes, including ...bioactive substances thus revealing a challenge to the biotechnology's needs of the safe media for bioseparations and bioconversions. This review discusses the structure and the properties of reversed micelle solvents in view of the parameters that can be easily operated in technology to achieve safe liquid–liquid extraction of proteins/enzymes or bioconversion of hydrophobic substrates. The paper highlights the importance of how the reversed micelle microenvironment should be arranged with respect to the preservation of the activity of the enzyme as target product or biocatalyst. The main aspects are demonstrated with own experimental results on α-amylase purification and lipase-catalyzed esterification using cationic reversed micelle solvents. The trials of performing continuous processes involving reversed micellar separation and reaction media are also reviewed and the current problems are addressed.
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Membrane processes are of crucial importance for downstream processing in biotechnology. This is due to their selectivity and the mild operating conditions, enabling to extract target products ...without damages caused by overheating and chemical agents. Besides the most spread membrane processes like ultrafiltration and reverse osmosis, electrodialysis is very important for removal and extraction of electrically charged products, i. e. anions of organic acids, some antibiotics, etc. The electrodialysis process can be organized in batch or continuous mode. On the other hand, in the electro-crossflow filtration, the transport of target solutes across the membrane is guided by two main driving forces, the transmembrane pressure and the electric potential. This combination enables various possibilities for more selective and efficient downstream processing in biotechnology. This chapter provides a brief overview of recent achievements of electrodialysis in selected bioproducts separations and recovery. A special focus, including original experimental data, is then given to electro-filtration, which is a powerful tool creating new opportunities for performing separations on the basis of both electric charge and particle size differences.
Many technologies for the treatment of arsenic-containing drinking water are available, but most of them are more effective on arsenic oxidized forms. Therefore, the pre-oxidation of Assup.3+ is ...necessary. The electrochemical processes represent a very promising method due to the simultaneous oxidation of compounds using electrochemical conditions and the reactive radicals produced. In this work, Assup.3+ oxidation was experimentally studied at a pilot scale using an electrochemical oxidation cell (voltage: 10 V; current: 1.7 A). The effect of the initial arsenite concentration, pH, and conductivity of drinking water on the oxidation of Assup.3+ into Assup.5+ was investigated. The results showed that the initial Assup.3+ concentration strongly directly influences the oxidation process. Increasing the initial arsenite concentration from 500 to 5000 µg Lsup.−1, the pseudo-first order kinetic constant (k) strongly decreased from 0.521 to 0.038 minsup.−1, and after 10 min, only 21.3% of Assup.3+ was oxidized (vs. 99.9% in the case of Assup.3+ equal to 500 µg Lsup.−1). Slightly alkaline conditions (pH = 8) favored the electrochemical oxidation into Assup.5+, while the process was partially inhibited in the presence of a more alkaline or acidic pH. The increase in conductivity up to 2000 µS cmsup.−1 enhanced the kinetic of the oxidation, despite remaining on the same order of magnitude as in the case of conductivity equal to 700 µS cmsup.−1. After 10 min, 99.9 and 95% of Assup.3+ was oxidized, respectively. It is the opinion of the authors that the influence of other operational factors, such as voltage and current density, and the impact of the high concentration of other pollutants should be deeply studied in order to optimize the process, especially in the case of an application at full scale. However, these results provide helpful indications to future research having highlighted the influence of initial Assup.3+ concentration, pH, and conductivity on the electrochemical oxidation of arsenic.
Extraction of copper from nitrate/nitric acid aqueous solutions was studied using a HF Membrane Module and four LIX reagents (LIX® 860N-I, LIX® 984N, LIX® 84-I, and LIX® 65N) containing different ...active compounds (ketoximes and/or salicylaldoximes). Kinetic experiments varying the flow rates of both phases, aqueous and organic, and the extractant concentration were carried out to compare the extraction rate and efficiency from nitrate-aqueous media. A mathematical model based on the "aqueous extraction mechanism" in which the chemical reaction takes place in an aqueous-reaction zone was applied to determine the individual resistances of the copper mass-transfer process. It was found that the fractional resistance due to chemical reaction in the aqueous reaction zone, which varied from 92.5% to 95.8% in the order LIX® 860N-I < LIX® 984N < LIX® 84-I < LIX® 65N, controlled the total rate of the hollow-fiber copper extraction from nitrate aqueous media.
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A comparative kinetic study of the extraction of copper from nitrate/nitric acid aqueous solutions by different classes of LIX
®
reagents (LIX 984N, LIX 860N-I, LIX 84-I, LIX 65N) was performed. ...Using a Rotating Diffusion Cell, the rate constants of the chemical reactions (forward and reverse) were estimated and compared. In the case of the mixed extractant LIX 984N, a synergistic effect was observed. The values of the forward reaction constants of all the extractants were found to be an order of magnitude higher than those of the reverse reaction. The relatively low E
a
-values prove the substantial influence of the diffusion on the extraction kinetics under the experimental conditions studied.
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Comparative experimental studies were carried out on extraction of copper(II) cations from aqueous acid nitrate media using four LIX-reagents, representatives of different extractant classes: LIX ...984N-I, LIX 860N, LIX 84-I and LIX 65N. As a diluent, liquid hydrocarbon undecane was used. The extraction behavior of the LIX-reagents was compared based on an analysis of the influence of the main factors on the two-phase mass transfer process: aqueous pH-value, initial copper and extractant concentrations, and temperature. The experimental data received were used in the calculation of important parameters characterizing the efficiency of copper extraction from nitrate media with different LIX reagents: distribution ratios D, concentration extraction constants K
ex
, pH
0.5
-values, and thermodynamic parameters such as enthalpy, entropy, and free energy changes (ΔH
0
, ΔS
0
, ΔG
0
-values).
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In this work, the complex enzyme purification process by means of RME (reversed micelle extraction) was examined using the system α-amylase/CTAB/KBr. The research was focussed on the enzyme aqueous ...source composition. The influence of different inorganic salts present in the source (NaCl, NaBr, and NH
4Cl) as well as salt and protein concentrations on the purification efficiency of the system was investigated. The RME-based enzyme purification was analyzed considering the protein and activity yield changes during the two-step procedure—solubilization and stripping (recovery). The results show that relatively high purification factors could be achieved at relatively low salt concentrations in the source providing the formation of RMs with an appropriate water capacity. A part of the activity lost in the sources containing NaBr, and NH
4Cl was recovered through RM-solubilization and stripping into an aqueous solution containing a small amount of KBr. The RM-system proposed preserves the enzyme stability and biological activity for a long time.
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