Dual-chamber Cell Research Articles

Simultaneous removal of nitrate nitrogen and orthophosphate by electroreduction and electrochemical precipitation

Electrochemical methods can effectively remove nitrate nitrogen (NO3-N) and orthophosphate phosphorus (PO4-P) from wastewater. This work proposed a process for the simultaneous removal of NO3-N and PO4-P by combining electroreduction with electrochemically-induced calcium phosphate precipitation, and its performance and mechanisms were studied. For the treatment of 100 mg L–1 NO3-N and 5 mg L–1 PO4-P, NO3-N removal of 60–90% (per cathode area: 0.25–0.38 mg h–1 cm–2) and 80–90% (per cathode area: 0.33–0.38 mg h–1 cm–2) could be acquired within 3 h in single-chamber cell (SCC) and dual-chamber cell (DCC), while P removal was 80–98% (per cathode area: 0.10–0.12 mg h–1 cm–2) in SCC after 30 min and 98% (per cathode area: 0.37 mg h–1 cm–2) in DCC within 10 min. The faster P removal in DCC was due to the higher pH and more abundant Ca2+ in the cathode chamber of DCC, which was caused by the cation exchange membrane (CEM). Interestingly, NO3-N reduction enhanced P removal because more OH– can be produced by nitrate reduction than hydrogen evolution for an equal-charge reaction. For 10 mg L–1 PO4-P in SCC, when the initial NO3-N was 0, 20, 100, and 500 mg L–1, the P removal efficiencies after 1 h treatment were < 10%, 45–55%, 86–99%, and above 98% respectively. An increase in Ca2+ concentration also promoted P removal. However, Ca and P inhibited nitrate reduction in SCC at the relatively low initial Ca/P, as CaP on the cathode limited the charge or mass transfer process. The removal efficiency of NO3-N in SCC after 3 h reaction can reduce by about 17%, 40%, and 34% for Co3O4/Ti, Co/Ti, and TiO2/Ti. The degree of inhibition of P on NO3-N removal was related to the content and composition of CaP deposited on the cathode. On the cathode, the lower the deposited Ca and P, and the higher the deposited Ca/P molar ratio, the weaker the inhibition of P on NO3-N removal. Especially, P had little or even no inhibition on nitrate reduction when treated in DCC instead of SCC or under high initial Ca/P. It is speculated that under these conditions, a high local pH and local high concentration Ca2+ layer near the cathode led to a decrease in CaP deposition and an increase in Ca/P molar ratio on the cathode. High initial concentrations of NO3-N might also be beneficial in reducing the inhibition of P on nitrate reduction, as few CaP with high Ca/P molar ratios were deposited on the cathode. The evaluation of the real wastewater treatment was also conducted.

Improved mineralization and total nitrogen reduction by combination of electro-reduction and electro-oxidation for nitrophenol removal

In this work, p-Nitrophenol (p-NP) was electro-chemically removed by using a prepared Co3O4/Ti cathode and a BDD anode to achieve the simultaneous reduction of total organic carbon (TOC), total nitrogen (TN) and toxicity. The prepared Co3O4/Ti cathode showed higher electro-activity than the Ti cathode towards p-NP reduction with the removal rate higher than 90.6% but without mineralization. The electro-oxidation removed 84.3% of TOC but none of TN. To develop an optimized process for mineralization and TN removal during p-NP electrolysis, the combination of electro-oxidation and electro-reduction were evaluated by using a dual-chamber cell and a single-chamber cell, respectively. As a result of the re-oxidation and re-reduction in the single-chamber cell, the typically used mode of the simultaneous redox, showed a lower removal of TOC and TN than the combination processes as well as an increased toxicity. The TN removal for both combined modes (21.0%–32.9%) was all higher than that of the mode of reduction because the produced inorganic nitrogen such as ammonia and nitrate could be partially oxidized or reduced to nitrogen gas. The results suggested that the combination process could significantly improve the mineralization and TN reduction for p-NP removal, accompanied with 60.3% decrease of acute toxicity for the reduction after oxidation mode.

Canine Intestinal Organoids in a Dual-Chamber Permeable Support System

The permeable support system is typically used in conjunction with traditional two-dimensional (2D) cell lines as an in vitro tool for evaluating the oral permeability of new therapeutic drug candidates. However, the use of these conventional cell lines has limitations, such as altered expression of tight junctions, partial cell differentiation, and the absence of key nuclear receptors. Despite these shortcomings, the Caco-2 and MDCK models are widely accepted and validated for the prediction of human in vivo oral permeability. Dogs are a relevant translational model for biomedical research due to their similarities in gastrointestinal anatomy and intestinal microflora with humans. Accordingly, and in support of parallel drug development, the elaboration of an efficient and accurate in vitro tool for predicting in vivo drug permeability characteristics both in dogs and humans is highly desirable. Such a tool could be the canine intestinal organoid system, characterized by three-dimensional (3D), self-assembled epithelial structures derived from adult stem cells. The (1) Permeable Support Seeding Protocol describes the experimental methods for dissociating and seeding canine organoids in the inserts. Canine organoid isolation, culture, and harvest have been previously described in a separate set of protocols in this special issue. Methods for general upkeep of the canine intestinal organoid monolayer are discussed thoroughly in the (2) Monolayer Maintenance Protocol. Additionally, this protocol describes methods to assess the structural integrity of the monolayer via transepithelial electrical resistance (TEER) measurements and light microscopy. Finally, the (3) Permeability Experimental Protocol describes the tasks directly preceding an experiment, including in vitro validation of experimental results. Overall, the canine organoid model, combined with a dual-chamber cell culture technology, overcomes limitations associated with 2D experimental models, thereby improving the reliability of predictions of the apparent oral permeability of therapeutic drug candidates both in the canine and human patient.

Canine Intestinal Organoids in a Dual-Chamber Permeable Support System.

The permeable support system is typically used in conjunction with traditional two-dimensional (2D) cell lines as an in vitro tool for evaluating the oral permeability of new therapeutic drug candidates. However, the use of these conventional cell lines has limitations, such as altered expression of tight junctions, partial cell differentiation, and the absence of key nuclear receptors. Despite these shortcomings, the Caco-2 and MDCK models are widely accepted and validated for the prediction of human in vivo oral permeability. Dogs are a relevant translational model for biomedical research due to their similarities in gastrointestinal anatomy and intestinal microflora with humans. Accordingly, and in support of parallel drug development, the elaboration of an efficient and accurate in vitro tool for predicting in vivo drug permeability characteristics both in dogs and humans is highly desirable. Such a tool could be the canine intestinal organoid system, characterized by three-dimensional (3D), self-assembled epithelial structures derived from adult stem cells. The (1) Permeable Support Seeding Protocol describes the experimental methods for dissociating and seeding canine organoids in the inserts. Canine organoid isolation, culture, and harvest have been previously described in a separate set of protocols in this special issue. Methods for general upkeep of the canine intestinal organoid monolayer are discussed thoroughly in the (2) Monolayer Maintenance Protocol. Additionally, this protocol describes methods to assess the structural integrity of the monolayer via transepithelial electrical resistance (TEER) measurements and light microscopy. Finally, the (3) Permeability Experimental Protocoldescribes the tasks directly preceding an experiment, including in vitro validation of experimental results. Overall, the canine organoid model, combined with a dual-chamber cell culture technology, overcomes limitations associated with 2D experimental models, thereby improving the reliability of predictions of the apparent oral permeability of therapeutic drug candidates both in the canine and human patient.

Nitrate reduction by electrochemical processes using copper electrode: evaluating operational parameters aiming low nitrite formation.

This work aims to present different electroreduction and electrocatalytic processes configurations to treat nitrate contaminated water. The parameters tested were: current density, cell potential, electrode potential, pH values, cell type and catalyst use. It was found that the nitrite ion is present in all process variations used, being the resulting nitrite concentration higher in an alkaline pH. The increase in current density on galvanostatic operation mode provides a greater reduction of nitrate (64%, 1.4 mA cm-2) if compared to the potentiostatic (20%) and constant cell potential (37%) configurations. In a dual-chamber cell the nitrate reduction with current density of 1.4 mA cm-2 was tested and obtained as a NO3- reduction of 85%. The use of single chamber cell presented 32 ± 3% of nitrate reduction, indicating that in this cell type the nitrate reduction is smaller than in dual-chamber cell (64%). The presence of a Pd catalyst with 3.1% wt. decreased the nitrite (1.0 N-mg L-1) and increased the gaseous compounds (9.4 N-mg L-1) formation. The best configuration showed that, by fixing the current density, the highest nitrate reduction is obtained and the pH presents a significant influence during the tests. The use of the catalyst decreased the nitrite and enhanced the gaseous compounds formation.

Cu, Ni and multi-walled carbon-nanotube-modified graphite felt electrode for nitrate electroreduction in water

A three-dimensional bimetal carbon-based electrode, CuNi/multi-walled carbon nanotube/graphite felt (CuNi/M/GF), was designed for the electrochemical reduction of nitrate. Multi-walled carbon nanotubes (MWCNTs) served as the interlayer and skeleton, which increased the electrochemical reduction activity of GF to nitrate. CuNi/M/GF with different atomic ratios of copper and nickel was prepared by adjusting the electrodeposition potential. The performance of the CuNi/M/GF, Cu foam, Ni foam, M/GF and GF in a dual-chamber cell and single-chamber cell was evaluated for different concentrations of chlorine, current density, energy consumption and degradation. In a solution of 100 mg/L NO3−-N, the removal of NO3−-N and total nitrogen (TN) by the optimal electrode in a single-chamber cell (SCC) can reach 99%. Aeration in the dual-chamber cell cathode can blow out more than 99% of the ammonia nitrogen that is converted from NO3−-N. More than 95% of the TN in a 100 ml, 700 mg/L NO3−-N solution was removed within 6 h. CuNi/M/GF showed excellent corrosion resistance and stability in the cyclic tests. CuNi–1.3/M/GF is more resistant to corrosion in the DCC than in the SCC which may be attributed to contact of the cathode with the oxidizing substance in the SCC. The application of CuNi/M/GF in practical wastewater that contained a high concentration of NaCl and nitrate-N shows that the electrode has considerable application prospects in TN removal.

Comparison of different electrode materials for the nitrate electrocatalytic reduction in a dual-chamber cell

Nitrogen compounds in water are mainly associated to the use of fertilizers and to the discharge of industrial wastewater from tanneries, food and textile industry. The presence of high nitrate concentration in water can be dangerous to human health and the nitrate reduction through the electrocatalytic process is a promising treatment technology to minimize the presence of this ion in water resources. In this work, different sponge electrodes (Ni, Ni-Cu, Ni-Pd, Ni-Cu-Pd and Ni-Pd-Cu) were tested for the treatment of solutions containing high nitrate concentrations (600 mg L−1 of nitrate, that corresponds to 135.5 N-mg L-1). The electrodes are comprised of nickel (Ni) sponges that are chemically coated with copper (Cu) and/or palladium (Pd). A dual-chamber cell (DCC), separated by a cation-exchange membrane, was used for the nitrate reduction experiments. The obtained results indicated that it is possible to treat the nitrate solution by using nickel sponges coated with Pd and Cu as electrodes. The highest nitrate reduction (44 %) was obtained with a Ni-Cu electrode, being nitrite the main product generated. With the Ni-Pd-Cu electrode the highest ammonium formation (28 N-mg L-1) was obtained. The pH adjustment to 6−6,5 increased the gaseous compounds formation (33 N-mg L-1). The results show that the process studied here can be used either as a first step treatment, to reduce nitrate to other chemical compounds, or as a final treatment, producing ammonium or nitrogen, when solutions of high nitrate concentration are being treated.

Use of copper plate electrode and Pd catalyst to the nitrate reduction in an electrochemical dual-chamber cell

Nitrate is a chemical species usually present in water, lakes and rivers and in high concentration can be dangerous to the human health. In this work, palladium-coated alumina pellets associated to a copper plate electrode were tested, in an electrochemical dual-chamber cell (DCC), for the treatment of solutions containing high nitrate concentration. The tests evaluated how Pd catalyst, current density and pH have an effect on the reduction reaction and on the formation of nitrite, ammonium and gaseous compounds. It was possible to observe that the Pd catalyst has an influence on the products formed, with an increase on the gaseous compounds production. The current density plays also an important role on the treatment, considering that, by applying 1.1 mA cm−2, 59 % of nitrate reduction was observed, while with 1.5 mA cm−2 the reduction was 64 %. The highest selectivity to gaseous compounds and lower selectivity to nitrite were obtained using alumina pellets coated with 2.5 % wt. of Pd, a current density of 1.5 mA cm−2 and with pH adjustment (6.0–6.5). In these conditions, a nitrate reduction of 49 % was obtained, with a selectivity of 64 % to gaseous compounds, 1% to nitrite and 35 % to ammonium. The main novelty of this work is the reduction cell design, by the use of a dual chamber cell and with the catalyst in pellets form. This cell would be suitable for scaling-up the process.

Technology for the Purification of Electroplating Washwater from Cadmium Ions by Membrane and Membraneless Electrolysis

A technology for removing toxic Cd2+ from electroplating process electrolytes and washwater containing $${\text{SO}}_{4}^{{2 - }}$$ or Cl– is proposed. This technology makes it possible to decrease the concentration of Cd2+ in treated solutions to 0.1–0.07 g/L and the Cd2+ ingress into plant waste waters by 288–366 times and attain a Cd2+ recovery of 99.7%. Electrolysis in a dual-chamber cell with an anion-exchange membrane makes it possible to return Cd and a H2SO4 solution back into the process. The removal of Cd2+ from Cl– containing solutions is recommended to be performed by membrane electrolysis, separating the insoluble anode with a chemically stable cation-exchange membrane to prevent the migration of Cl– from the catholyte into the anolyte and, correspondingly, their oxidation on the insoluble anode with the liberation of toxic Cl2.

Use of a two-step process to denitrification of synthetic brines: electroreduction in a dual-chamber cell and catalytic reduction.

Membrane separation processes are being currently applied to produce drinking water from water contaminated with nitrate. The overall process generates a brine with high nitrate/nitrite concentration that is usually send back to a conventional wastewater treatment plant. Catalytic processes to nitrate reduction are being studied, but the main goal of achieving a high selectivity to nitrogen production is still a matter of research. In this work, a two-step process was evaluated, aiming to verify the best combination of operational parameters to efficiently reduce nitrate to nitrogen. In the first step, the nitrate was reduced to nitrite by electroreduction, applying a copper electrode and different cell potentials. A second step of the process was carried out by reducing the generated nitrite with a catalytic process by hydrogenation. The results showed that the highest nitrate reduction (89%) occurred when a cell potential of 11 V was applied. In this condition, the nitrite ion was generated with all experimental conditions evaluated. Then, to reduce the nitrite ion formed by catalytic reduction, activated carbon fibers (ACF) and powder γ-alumina (γ-Al2O3) were tested as supports for palladium (Pd). With both catalysts, the total nitrite conversion was obtained, being the selectivity to gaseous compounds 94% and 97% for Pd/Al2O3 and Pd/ACF, respectively. Considering the results obtained, a two-stage treatment setup to brine denitrification may be proposed. With electrochemistry, an operating condition was achieved in which ammonium production can be controlled to very low values, but the reduction is predominant to nitrite. With the second step, all nitrite is converted to nitrogen gas and just 3% of ammonium is produced with the most selective catalyst. The main novelty of this work is associated to the use of a two-stage process enabling 89% of nitrate reduction and 100% of nitrite reduction.

Electrochemical Reduction of High-Concentrated Nitrate Using Ti/TiO2 Nanotube Array Anode and Fe Cathode in Dual-Chamber Cell

Electrochemical reduction of nitrate using Fe cathode and Ti/TiO2 nanotube array anode in dual-chamber cell was investigated. The performance of different cathodes for nitrate removal were in the order of Fe>Al>Cu>Ni. The nitrate removal in dual-chamber cell (99.8%) was much higher than that in single-chamber cell (84.3%) with Fe cathode in 2.5 h. In dual-chamber cell, the highest nitrate removal was obtained at the current density of 15 mA/cm2. The nitrate reduction followed first-order kinetics. With increasing initial nitrate concentration, the reduction rate constant slightly decreased from 2.2 h−1 (100.0 mg/L) to 0.9 h−1 (1000.0 mg/L), of which a remarkable nitrate removal of 88.3% could still be achieved with 1000.0 mg/L nitrate. In the presence of 0.5 g/L NaCl, simultaneous reduction of nitrate and oxidation of by-products of ammonia and nitrite were achieved in dual-chamber cell with Fe cathode, of which the nitrate removal rate was 94.3% and no by-products were detected in the solution.

Electroreduction of nitrate in water: Role of cathode and cell configuration

The performance of direct electroreduction of nitrate was studied to investigate the role of different cathodes (graphite felt, GF; Cu–Ni alloy, Cu90Ni10; titanium, Ti) and cell configurations (single-chamber cell, SCC; dual-chamber cell, DCC). Experimental results indicated the performances of these electrodes for nitrate removal rate and cathodic current in linear sweep voltammograms were in the order of GF>Cu90Ni10>Ti. The GF cathode, with the highest nitrate removal of 70%, also exhibited higher corrosion resistance than the Cu90Ni10 cathode. Nitrate removal in DCC was much higher than in SCC with GF as cathode. The cation membrane equipped in the reactor significantly improved the nitrate electroreduction. The nitrate reduction efficiency was the highest at an applied cathodic potential of −1.8V, over which it decreased because of the impediment of hydrogen evolution at higher potential. The nitrate removal rate increased slightly with the presence of chloride ion, however, decreased with sulfate ion in the solution. Nitrate removal in DCC with GF as cathode showed broad application prospect.

Single Chamber Solid Oxide Fuel Cells (SC-SOFCs) based on a Proton Conducting Electrolyte

Single chamber solid oxide fuel cells (SC-SOFCs) are promising for portable power applications because they are simpler than the conventional dual-chamber cells. SC-SOFCs based on the cell Ni/BaCe0.3Zr0.5Y0.2O3-δ (BCZY)/Ba0.5Sr0.5Co0.8Fe0.2O3-δ (BSCF) were investigated under gas mixtures of propane (C3H8), oxygen (O2), and helium (He) with different compositions. To enhance the fuel partial oxidation at low temperatures, a porous layer of Ru was added onto the anode surface. Two configurations, finger (with parallel electrodes) and sandwich (with electrodes on opposite sides of the pellets), were analyzed

Water transport in liquid and vapour equilibrated Nafion™ membranes

Water transport across Nafion membranes was investigated under activity gradients at atmospheric pressure. The activity gradients across the membrane were controlled by exposing one side of the membrane to dry gas under laminar flow, while maintaining liquid or vapour equilibrium with water on the other side of the membrane. The measurements were made under steady state conditions. A dual chamber cell was designed with a gated valve to control boundary and initial conditions for the membrane measurements. The experimental results presented here were used in a vaporization-exchange model reported previously [C.W. Monroe, T. Romero, W. Mérida, M. Eikerling. A vaporization-exchange model for water sorption and flux in Nafion, J. Membr. Sci. 324 (2008)], which showed that sorption across the gas–membrane interface is the limiting transport process for thickness below 300 μm. We hypothesize that the water transport can be represented as the sum of series resistances across the membrane bulk and interfaces. The experimental implementation required new hardware and techniques with precise control over the membrane–gas boundary conditions. Under isothermal conditions, the water transport across liquid-equilibrated (LE) membranes was larger than the corresponding transport under vapour-equilibrated (VE) conditions. Non-isothermal experiments showed that the dehydration at the membrane surface increases the resistance to water transport. These results were interpreted under the assumption that regions of distinct water content will experience diffusion rate variations. Our analysis included consideration of the sorption across the interfaces, and the diffusivity dependency on water content.