Filter-press Reactor Research Articles

Additive manufactured metal lattice structures used as flow-through electrodes in a filter-press electrochemical reactor

This study deals with the electrochemical and hydraulic performances of additive manufactured metal periodic lattice structure electrodes. These electrodes are fabricated by Laser Powder Bed Fusion (LPBF) from the titanium alloy TA6V and two structures have been studied: diagonal and octet-truss. They are integrated, as flow-through electrodes, in an electrochemical filter-press reactor. Current–potential curves are experimentally obtained by linear sweep voltammetry when feeding the reactor with a ferricyanide solution. From the measurement of the limiting current of ferricyanide ions reduction, the volumetric mass transfer coefficient kAe is determined for several flow rates. Numerical simulations of fluid flow and mass transfer in these structures are also performed. Results show high values of kAe for these structures (competing with carbon felt electrodes) while maintaining a high permeability (low flow resistance). The surface roughness, inherent to the additive manufacturing process, is found to induce a low (≲10%) enhancement of mass transfer despite the roughness size (Ra in the range 10-20μm) is close to the average thickness of the diffusion layer (for the investigated fluid velocities). As a result, these electrode structures show promising potential to be used in intensified electrochemical reactors by being further optimized to find the optimal internal dimensions that maximize mass transfer while limiting flow resistance.

Tailoring multi-layered BiVO4/WO3 photoanodes for an efficient photoelectrochemical gas-phase solar water splitting

Photoelectrochemical gas-phase solar water splitting represents a promising avenue for sustainable hydrogen production, fulfilling the energy demands of the future. In this work, we present the fabrication and optimization of the functional performance of visible-light active BiVO4/WO3 photoanodes with a tailored multi-layered structure. The photoanodes are manufactured in a reproducible way by an automated spray pyrolysis technique, including BiVO4 (top layer) and WO3 (bottom layer) in a multi-layered structure with different ratios (80:20; 50:50; 20:80). The photoactive surfaces are fully characterized and then evaluated in a divided filter-press reactor operated in continuous mode under visible light irradiation (100 mW cm−2), where a platinized titanium plate is used as dark cathode. The results demonstrate the pivotal role of mass ratio in optimizing charge transfer kinetics and recombination rates in the photoanode. We demonstrate the synergistic effects between BiVO4 and WO3, elucidating their contributions to enhance light absorption, and reduce electron-hole recombination, determining an optimal ratio of 80:20 for both hydrogen production (155.7 μmol m−2 s−1) and on-off current density gap (0.66 mA cm−2). The developed multi-layered BiVO4/WO3 surfaces thus offer a compelling pathway for advancing gas-phase photoelectrochemical water splitting technology, underscoring the significance of electrode design and paving the way for sustainable solar hydrogen production.

Inter-compartment concentration monitoring of key species in a vanadium redox flow cell operating with and without polarization: Experiments and construction of a predictive model

The usually encountered phenomenon of vanadium crossover in Vanadium Redox Flow Batteries (VRFB), leading to energy capacity losses, is specifically studied without (diffusion measurements) and with the application of an electric current (battery operating conditions). The experimental set-up is an electrochemical filter-press reactor integrating a NafionTM 424 membrane and two storage tanks. The electrolytes composition on both sides was determined using potentiometric titration (VO2+ and H+) and UV–Vis analysis (V2+, V3+ and VO2+). First, experiment is conducted without polarization and a model based on mass balance equation incorporating diffusion flux and electrolyte volumes change is derived to predict electrolytes composition on both sides. The effective diffusion coefficient of VO2+ in the membrane is obtained by fitting the model with experimental data. The experiment is then carried out under galvanostatic polarization (10 mA/cm2) and a model embedding, simultaneously, electrolyte volumes variation, diffusion and migration across the membrane and the electrochemical and self-discharge reactions, is proposed to predict electrolytes composition. The partitioning of the applied current between all possible electrochemical reactions is addressed using a specific algorithm based on logical tests on limiting currents. The resulting system of coupled ordinary differential equations is solved numerically using standard python functions. The results indicate a satisfactory agreement between predicted and experimental data and highlight the requirement of considering all phenomena for an accurate prediction of electrolytes composition in VRFB. The interest of applying the developed model to simulate and predict composition evolution in VRFB (State of Charge (SoC) and acidity) is discussed.

Decentralized electro-sanitation system as proof of concept to treat urine produced in long-distance bus

Long-distance transportation provides in-vehicle access to essential sanitation to the passengers. However, generated yellow and black waters may not be correctly managed prior sanitary effluent discharge. Processes that can handle decentralized effluent treatment can be considered alternatives to traditional chemical treatment systems. In this study, decentralized electrochemically-driven treatment is presented as a proof of concept. A compact electrochemical reactor design considering the boundary conditions and requirements for decentralized sanitary treatment for long-distance bus transportation has been accomplished. Treatment of synthetic urine effluents was conducted under filter-press reactor with continuous flow in a closed upward recirculation reactor containing a carbon felt (CF) cathode and a dimensionally stable anode (DSA: Ti/Ru0.36Ti0.64O2). The experimental design allowed the assessment of operational variable impacts on reduction of urea concentration, and consequent estimate of the total organic carbon abatement. The results revealed that synthetic urine solution diluted from toilet water flushing (TOC = 402 mg L−1) can be effectively treated under application of low current densities of 18 mA cm−2 in 300 min (average time of on-road service). Real-time monitoring of parameters revealed a decrease in pH from 6.98 to 3.49, and a gradual increase in temperature from 25.3 °C to 32.0 °C at the end of the process. Those physico-chemical changes can be useful to inhibit urea hydrolysis. Thus, the results encourage the application of electrochemical technology in decentralized effluent treatment systems to enhance and enable ecologically correct sanitation actions in portable urinary collectors, such as those used in bus road transport.

Continuous Electrolysis of Carbon Dioxide for the Production of Formate with High Efficiency

Carbon dioxide capture, storage, and utilization is nowadays considered one of the most interesting approaches to reduce emissions to the atmosphere and, therefore, to mitigate climate change. In this sense, the electrochemical reduction of carbon dioxide to value-added products is gaining attention, since it permits storing excess of energy from renewable and intermittent sources (e.g. solar or wind), in the form of chemicals [1]. Among the reaction products, both formic acid and formate are products of great interest that could be obtained by this process, due to its use as raw materials in several industries and its promising use as a reactant in low-temperature fuel cells and as a renewable hydrogen carrier molecule. Although there is a large number of studies published in literature focusing on the electrocatalytic reduction of carbon dioxide to formic acid and formate[2], few of them achieve relevant trade-offs among the figures of merit typically used to analyze the performance of the process, like (i) the concentration of formate, (ii) the Faradaic Efficiency towards the reaction products, (iii) the energy consumption per kmol of formate and (iv) the current density supplied to the electrochemical reactor.In this context, this communication aims at studying the continuous electrolysis of carbon dioxide, operating with a single pass of the reactants through the electrochemical reactor and using Bi-carbon supported electrocatalysts, to obtain formate with high energy efficiency. In this sense, the electrocatalysts are deposited by air-brushing techniques in the form of a membrane electrode assembly in the cathodic compartment of the electrochemical reactor. This configuration permits direct contact between the Gas Diffusion Electrode and the Nafion cationic exchange membrane which acts as a separator between both compartments of the electrochemical filter press reactor [3].The influence of some key variables is rigorously studied, such as (i) the amount of water in the carbon dioxide input stream, (ii) the current density and (iii) the Bi catalyst loading deposited over the cathode. Firstly, the performance of the electrocatalytic reduction of carbon dioxide to formate employing a Bi catalyst loading of 0.75 mg·cm-2 in terms of i) formate concentration, ii) Faradaic Efficiency towards formate and iii) energy consumption per kmol of formate are assessed as a function of the current density and the water flow in the carbon dioxide input stream. In this point, it is important to remark that, working with an industrially-relevant current density of 200 mA·cm-2 and with a water flow of 0.5 g·h-1, high formateconcentrations of up to 312 g·L-1 were obtained with Faradaic Efficiency towards formateof 25 %, respectively. Consequently, additional tests are performed with a Bi loading in the cathode of the electrochemical filter press of 1.5 mg·cm-2. Combinations of relevant values of concentrations, Faradaic Efficiency for formate and energy consumption of 337 g·L-1, 89 %, and 180 kWh·kmol-1, respectively, are achieved with a current density of 45 mA·cm-2 and with a water flow of 2 g·h-1. These results are one of the best trade-offs reported in the field of carbon dioxide electroreduction to formic acid or formate among these figures of merit, thus achieving a significant advance in this field. However, there are many challenges to be addressed for the implementation of the process at an industrial scale, and therefore, more research focused on the advanced electrocatalytic materials, innovative electrode configuration, and improved electrochemical reactors are still required.

Hybrid water treatment flow plant using hydrogen peroxide-based electro-activated persulfate and photoelectro-Fenton processes: The combustion of Reactive Orange 16 dye

This paper implements an innovative hybrid water treatment process in a flow plant using hydrogen peroxide-based electro-activated persulfate (EPS-H2O2) combined with photoelectro-Fenton (PEF) method. The Reactive Orange 16 (RO16) azo dye was used as a persistent organic pollutant (POP) model. A filter-press reactor utilized a Ti|RuO2 plate and a gas diffusion electrode (GDE) as the anode and cathode. In EPS-H2O2, persulfate (PS) reacts with H2O2 yielding hydroxyl (•OH) and sulfate (SO4·-) radicals. In PEF, H2O2 reacts with Fe2+ producing more •OH, completing the TOC removal in the presence of UVA light. The influence of pH (3–9), initial PS concentration (0.5–1.5 mM), initial RO16 dye content (30–50 mg L-1 TOC), applied current density (j, 5–30 mA cm−2), and mean linear flow velocity (u, 7.3–29.1 cm s−1) on the EPS-H2O2 process efficiency was examined. The best trial for EPS-H2O2 achieved 37% TOC removal in 360 min electrolysis at j = 10 mA cm−1, u = 14.6 cm s−1, and PGDE = 3 psi. Subsequently, at t ≥ 360 min, the synergistic effect between the EPS-H2O2 and PEF processes was carried out by adding 0.5 mM Fe2+ and UVA light. The best hybrid (EPS-H2O2 + PEF) process test reached 98% mineralization with 30% current efficiency and 0.060 kWh (g TOC)-1 electrolytic energy consumption. Six carboxylic acids were determined as the main intermediaries, whereas ammonium was the main nitrogen compound throughout the EPS-H2O2 and PEF processes.

Coupling continuous CO2 electroreduction to formate with efficient Ni-based anodes

CO2 electroreduction to formic acid and formate has been focus of great research attention in the last years. Thus, considerable and relevant efforts have been accomplished in this field, mainly by operating with different types of catalysts and electrode configurations in the cathodic compartment. Still, Pt-based anodes, which are expensive and scarce, are typically the preferred materials to carry out the oxygen evolution reaction in alkaline medium. However, it is crucial to search for new materials of lower prices, with high stability, and good performances able to be competitive with traditional Pt-based electrodes. Hence, we study hand-made NiO-based anodes for the continuous CO2 electroreduction for formate in a filter press reactor with a single pass of the reactants through the electrochemical reactor. The use of the NiO-based anodes enhances the results obtained in previous studies with DSA/O2 anodes, combining excellent values of Faradaic Efficiency for formate of 100 %, and energy consumptions values close to only 200 kWh·kmol−1. In addition, employing Sustainion® as a binder in the fabrication of the anode results in a significant improvement in the durability, maintaining similar performance in terms of key metrics.

Solar photoelectro-Fenton-like process with anodically-generated HClO in a flow reactor: Norfloxacin as a pollutant with a particular structure

The degradation and mineralization of the drug norfloxacin (NFX) has been assessed in a model solution, containing 15 mM NaCl +45 mM Na2SO4 at pH 3.0, using a flow plant with an FM01-LC filter-press reactor equipped with a Ti|Ir-Sn-Ru oxides anode to electrogenerate HClO from Cl− oxidation and a stainless-steel cathode. Unexpectedly, anodic oxidation with active chlorine (AO-HClO) outperformed electro-Fenton (EF-HClO), photoelectro-Fenton (PEF-HClO) and solar photoelectro-Fenton (SPEF-HClO) due to: (i) the formation of refractory complexes between iron ions and carboxyl group of NFX, and (ii) the conversion of HClO into less effective •OH upon its Fenton-like reaction with added Fe2+ catalyst. SPEF-HClO was superior among Fenton-based treatments because the •OH concentration was largely increased by the photolysis of Fe(III) species. At an initial NFX concentration in the range 0.103–0.146 mM, the optimum conditions for SPEF-HClO were 0.40 mM Fe2+ and 15 mA cm−2. A BDD anode allowed a higher production of •OH, accelerating the degradation and mineralization, with similar energy requirements as compared to trials with Ti|Ir-Sn-Ru oxides anode. The SPEF-HClO process in urban wastewater was less powerful because of the parallel oxidation of natural organic matter. HClO, Fe2+ and Fetotal were quantified in both water matrices. The initial degradation sequence for NFX, proposed from 10 primary by-products identified by LC-MS/MS, revealed the occurrence of hydroxylation, chlorination and defluorination steps. Additionally, 5 stable by-products were detected by GC–MS.

An alternative approach to the kinetic modeling of pharmaceuticals degradation in high saline water by electrogenerated active chlorine species

A semiempirical approach considering the rate of reactive chlorine species-RCS- production (ΦE) as a function of current and Cl− concentration for the modeling of acetaminophen (ACE) degradation is presented. A filter-press reactor having a Ti/RuO2–ZrO2 (Sb2O3 doped) anode, NaCl (0.04–0.1 mol L−1) as supporting electrolyte, and operated in continuous mode, was considered. A current of 100 mA and a flow of 11 mL min−1 favored the electrogeneration of RCS and ACE degradation. Hydraulic retention time and ΦE were the most relevant parameters for the RCS production. These two parameters, plus the pollutant concentration, were very determinant for the ACE degradation. The model successfully reproduced the ACE removal in distilled water at different concentrations (10, 20, 40, and 60 mg L−1). The electrochemical system achieved removals between 80 and 100% of ACE in distilled water. The ACE treatment in actual seawater (a chloride-rich matrix, 0.539 mol L−1 of Cl−) was assessed, and the degradation was simulated using the developed model. The competing role toward electrogenerated RCS by intrinsic organic matter (3.2 mg L−1) in the seawater was a critical point, and the simulated values fitted well with the experimental data. Finally, the action of the electrochemical system on ciprofloxacin (CIP) in real seawater and its antimicrobial activity was tested. CIP removal (100% at 120 s) was faster than that observed for ACE (100% of degradation after 180 s) due to CIP has amine groups that are more reactive toward RCS than phenol moiety on ACE. Moreover, the system removed 100% of the antimicrobial activity associated with CIP, indicating a positive environmental effect of the treatment.

Use of a turbulence promoter in an electrochemical filter-press reactor: Consolidated evidence of significant enhancement of organics mass transport and degradation rates

• Turbulence promotion enables a remarkable enhancement of the electrolysis performance. • The mass transfer coefficient is thus increased by approximately threefold. • The electrolysis time to attain 98% removal of bisphenol S is reduced by about 62%. • The organic load removal (mineralization) rate is almost doubled. • Significant energy savings are achieved for organics degradation by anodic oxidation. In this communication, consolidated evidence of the significant effect of turbulence promotion on organics anodic oxidation is presented. Thus, the performance of a filter-press reactor fitted or not with a turbulence promoter (three randomly superposed plastic meshes) is assessed using a recirculating flow system. For a given volumetric flow rate ( q V ), the mass transfer coefficient ( k m ) for the oxidation of the [Fe(CN) 6 ] 4− species at the surface of the boron-doped diamond anode (geometric area = 24.2 cm 2 ) is increased approximately threefold (e.g. to 9.44 × 10 −5 m s −1 at q V = 7.0 L min −1 ), indicating that mass transport is significantly enhanced by the presence of the turbulence promoter in the filter-press reactor. In fact, a given value of k m can be attained using a q V value that is only about one fifth that needed in the absence of the turbulence promoter. Using bisphenol S (BPS) as a model organic compound, an approximately threefold increase in its degradation rate is also brought on by the use of the turbulence promoter, which e.g. means a reduction of ~ 62% in the electrolysis time to attain 98% BPS removal. Additionally, the mineralization rate is doubled, which e.g. means a reduction of ~ 45% in the electrolysis time needed to remove 84% of the solution organic load. These results confirm that turbulence promoters in filter-press reactors indeed enable significant savings in the energy expenses associated to the electrochemical degradation of organics, greatly increasing the efficiency of the process.

Continuous electroreduction of CO2 towards formate in gas-phase operation at high current densities with an anion exchange membrane

The carbon dioxide (CO2) electroreduction to formate is nowadays considered as a promising approach to convert CO2 into a value-added product and simultaneously, in the context of strategies for mitigating climate change. However, there is a scarce number of studies published in the literature operating with a current density higher than 200 mA cm−2, and there is the need of operating at higher current densities, with acceptable performance and low penalty in terms of energy consumption, for future implementation at industrial scale. Thus, in this work, a novel configuration is studied using a filter press reactor in a continuous mode, with a single pass of the reactants through the cell, employing a Sustainion anion exchange membrane and working with a current density up to 600 mA cm−2. Using the same electrocatalysts, the configuration shows a similar performance to the GDE configuration with liquid electrolyte, but with the advantage of operating only with a vapour input to the cathode and avoiding the need for a liquid catholyte. Although at the expense of obtaining a more diluted product, excellent combinations of Faradaic Efficiency for formate (73.7 %), energy consumptions (342 kWh·kmol-1), and product rates (22.9 mmol m−2·s-1) can be achieved at high current densities. Therefore, the configuration with Sustainion membranes reported in this manuscript can be particularly interesting for future applications that do not involve a very concentrated formate product.

Study of the atenolol degradation using a Nb/BDD electrode in a filter-press reactor

The present paper deals with the atenolol (ATL) degradation by advanced anodic oxidation using a boron-doped diamond anode supported on niobium (Nb/BDD). Cyclic voltammetry performed on this electrode revealed that it presents a high quality (diamond-sp3/sp2-carbon ratio), high potential for OER and that ATL can be oxidized directly and/or indirectly by the electrogenerated oxidants, such as hydroxyl radicals, persulfate ions and sulfate radicals.Electrolysis experiments demonstrated that ATL degradation and mineralization follow a mixed (first and zero) order kinetics depending on the applied current density. At high applied current densities, the amount of OH radicals is very high and the overall reaction is limited by the transport of ATL (pseudo first-order kinetics) whereas for low applied current densities, the rate of OH radicals generation at the anode is slower than the rate of arrival of ATL molecules (pseudo-zero order kinetics). Estimated values of kzero and kfirst based on the assumption of pseudo-zero or pseudo-first order kinetics were carried oud as a function of the supporting electrolyte concentration, indicating that both parameters increased with its concentration due the higher production of sulfate reactive species that play an important role in degradation.Finally, MCE increased with the decrease of current density, due to the lower amount of OH present in solution, since this species could be rapidly wasted in parasitic reactions; and the increase of sulfate concentration due to the more efficient production of persulfate.

Electrochemical degradation of the antibiotic ciprofloxacin in a flow reactor using distinct BDD anodes: Reaction kinetics, identification and toxicity of the degradation products

The performances of distinct BDD anodes (boron doping of 100, 500 and 2500 ppm, with sp3/sp2 carbon ratios of 215, 325, and 284, respectively) in the electrochemical degradation of ciprofloxacin – CIP (0.5 L of 50 mg L−1 in 0.10 M Na2SO4, at 25 °C) were comparatively assessed using a recirculating flow system with a filter-press reactor. Performance was assessed by monitoring the CIP and total organic carbon (TOC) concentrations, oxidation intermediates, and antimicrobial activity against Escherichia coli as a function of electrolysis time. CIP removal was strongly affected by the solution pH (kept fixed), flow conditions, and current density; similar trends were obtained independently of the BDD anode used, but the BDD100 anode yielded the best results. Enhanced mass transport was achieved at a low flow rate by promoting the solution turbulence within the reactor. The fastest complete CIP removal (within 20 min) was attained at j = 30 mA cm−2, pH = 10.0, and qV = 2.5 L min−1 + bypass turbulence promotion. TOC removal was practically accomplished only after 10 h of electrolysis, with quite similar performances by the distinct BDD anodes. Five initial oxidation intermediates were identified (263 ≤ m/z ≤ 348), whereas only two terminal oxidation intermediates were detected (oxamic and formic acids). The antimicrobial activity of the electrolyzed CIP solution was almost completely removed within 10 h of electrolysis. The characteristics of the BDD anodes only had a marked effect on the CIP removal rate (best performance by the least-doped anode), contrasting with other data in the literature.

CO2 electroreduction to formate: Continuous single-pass operation in a filter-press reactor at high current densities using Bi gas diffusion electrodes

Electrocatalytic reduction of CO2 has been taken into consideration as a fascinating option to store energy from intermittent renewable sources in the form of chemical value-added products. Among the different value-added products, formic acid or formate is particularly attractive since it can be used as a fuel for low-temperature fuel-cells and as a renewable hydrogen carrier. Very recently, a rapidly increasing number of studies have revealed Bi as a promising electrocatalytic material for the CO2 electroreduction to formate, but the performance of Bi electrodes operating in a continuous mode and high current density (j) has been hardly investigated yet. Thus, this work aims at studying the CO2 electroreduction to formate working in a continuous mode in a filter-press-reactor at a j up to 300 mA·cm−2 using Bi electrodes. Bismuth Gas Diffusion Electrodes (Bi-GDEs) were fabricated from carbon-supported Bismuth-nanoparticles. The influence of j and the electrolyte flow/area ratio in the performance of the Bi-GDEs towards formate were evaluated. Working at j of 300 mA·cm−2, a concentration of 5.2 g formate·L−1 with a faradaic efficiency (FE) and rate of 70% and 11 mmol·m−2·s−1, respectively were achieved. Lowering the j to 90 mA·cm−2, formate concentrations of up to 7.5 g·L−1 could be obtained with an excellent FE of 90%. Interestingly, the highest concentration of formate obtained was 18 g·L−1, but at expenses of an important decrease in FE. Although the results of this study are interesting and promising, further research is required to increase formate concentration for a future implementation at industrial scale.

Electrochemical water softening: Influence of water composition on the precipitation behaviour

Hardness in membrane concentrates implies lower water recoveries in desalination. Electrochemical water softening is considered as a possible solution to control this hardness. This technique is based on the electrochemically forced precipitation of insoluble compounds of hardness ions onto the cathode surface. In this work we studied, in practical conditions, the effect of water composition on the technique efficiency and on the properties of the electroprecipitates. Experiments were conducted with a filter-press reactor and a 3D stainless steel wool cathode and for waters of a fixed hardness but varying the following composition parameters between them: alkalinity, Mg/Ca relationship and presence of an anti-scalant compound. Precipitates were fully characterised by SEM, XRD, TG-DTA and N2 adsorption. Efficiency was measured in terms of hardness removal, demonstrating that the technique removes Ca more efficiently than Mg and that the presence of an anti-scalant does not alter the results. The properties of the electroprecipitates (morphology, texture, porosity and components) were related to water composition, evidencing its relevant effect. Geochemical modeling was realised to explain the electroprecipitation behaviour and why calcite, aragonite, vaterite and brucite are the only phases detected. This information contributes to the technique development, necessary for a future application in desalination practice.

Degradation of pesticide mixture by electro-Fenton in filter-press reactor

The efficiency of a prototype equipped with a dimensionally stable anode (DSA) and a carbon felt cathode was analysed by means of H2O2 production and removal of the herbicides diuron (DIU) and glyphosate (GLY) from 0.05 M Na2SO4 solutions, pH 3.0, by electrochemical oxidation (EO), EO with H2O2 electrogeneration and electro-Fenton (EF). Mineralisation current efficiencies and specific energy consumption were also determined. The best performance under galvanostatic conditions was found to be that of the EF, with 1 mM of Fe2+, compressed air flux of 1 L min–1 and current intensity of 1.00 A, for 180 min of treatment, 34% of mineralisation, with 5% current efficiency and specific energy consumption of 0.85 kW h g–1 of total organic carbon was found. A maximal accumulated concentration of 78 mg L–1 of electrolysed H2O2 was achieved in 60 min, and the concentrations of DIU and GLY were reduced by 8% and 94%, respectively. There is a good correlation between the studied flux dispersion in the residence time distribution and the conversion rate verified on degradation, with 100% for GLY and 66.2% for DIU. Two organic by-products as well as short chain carboxylic acids, namely formic, citric and oxalic acid, were detected by LC–MS, and therefore, DIU and GLY degradation mechanisms were proposed.

Combined use of coagulation (M. oleifera) and electrochemical techniques in the treatment of industrial paint wastewater for reuse and/or disposal

In this work, water-based paint (WBP) wastewater was treated using a natural coagulant, Moringa oleifera aqueous extract (MOAE), fortified with Ca2+ (from nitrate and chloride salts). In order to improve the quality of the treated wastewater and render it suitable for disposal, an electrolytic flow process was associated with the wastewater treatment using a filter-press reactor with a boron doped diamond (BDD) electrode. The feasibility of the treatment was evidenced by the reuse of the treated wastewater in the production of a new paint (manufactured by the company supplying the raw wastewater), whose quality was compatible with the water used by the manufacturer. The best conditions for the coagulation-flocculation process involved the use of 80 mL of MOAE (50 g/L of MO and 0.125 mol/L of Ca2+) for every 1.0 L of wastewater at pH 6.5. The limiting current density (35 mA/cm2) and an electrolysis time of 90 min (charge passed of 3.68 A h/L) were used in the electrochemical treatment. Biotoxicity assays using the brine shrimp Artemia salina revealed that the mortality (in %) of microcrustaceans was reduced from 100% (raw wastewater) to only 11% at the end of the electrolysis process, in addition to eliminating the strong odor and 85% of the organic load. Moreover, microbiological tests showed that the number of mesophiles decreased by more than six orders of magnitude and there was no growth of thermotolerant coliforms (TC).

Simulations of H2-H2o Flow during the Electrolysis of Water in a Continuous Reactor Equipped with a Six-Cell Stack

Nowadays the electrochemical reactors in specific the filter-press type in parallel plates configuration are commonly used in industrial and laboratory applications and as multipurpose flow cells utilized in a widely range of electrochemical processes [1]. The characterization of the reaction environment inside of any filter-press reactor must be considered in the design to obtain effective flow dispersion, plus a uniform current and potential distribution. The hydrodynamics is so important inside the reaction environment, because the uniformity and magnitude of mass transport and therefore the current distribution depend on the flow pattern inside the cell, specifically near the electrodes. In many electrochemical processes such as chlorine production, water electrolysis, alumina reduction, electrocoagulation, and many other electrochemical processes appears gas release on the electrodes, H2 or O2 [2]. The hydrodynamic properties and the gas-flow motion in electrochemical cells is of great interest in practice, because the dispersed phase (gas) modifies the electrical properties of the electrolyte (as well as mass and heat transfers), and therefore the macroscopic cell performance. Therefore, this works deals with the H2O-H2 flow simulations inside of a pre-pilot-scale continuous reactor with a stack of six cells in a serpentine array by solving the Reynolds-averaged Navier-Stokes (RANS) equations with κ-ε turbulence model (Euler-Euler approach). The hydrogen evolution reaction comes from the electrolysis of water. The electrodes were plates of aluminum, typically used in electrocoagulation processes. In order to perform a more complete flow pattern characterization, residence time distribution (RTD) studies were carried out to validate the CFD simulations. The RTD simulations were calculated solving the averaged diffusion-convection equation. Close agreement between experimental and theoretical RTD simulations were attained. Finally, comparisons between H2O-H2 and single-phase flow (H2O) simulations were also performed, highlighting that the dispersed phase improves the dispersion of the continuous phase.

Optimization of the electrochemical degradation process of the antibiotic ciprofloxacin using a double-sided β-PbO2 anode in a flow reactor: kinetics, identification of oxidation intermediates and toxicity evaluation

The electrochemical degradation of ciprofloxacin-CIP (50mgL-1 in 0.10molL-1 Na2SO4) was investigated using a double-sided Ti-Pt/β-PbO2 anode in a filter-press flow reactor, with identification of oxidation intermediates and follow-up of antimicrobial activity against Escherichia coli. The effect of solution pH, flow rate, current density, and temperature on the CIP removal rate was evaluated. All of these parameters did affect the CIP removal performance; thus, optimized electrolysis conditions were further explored: pH = 10, qV = 6.5Lmin-1, j = 30mAcm-2, and θ = 25°C. Therefore, CIP was removed within 2h, whereas ~75% of the total organic carbon concentration (TOC) was removed after 5h and then, the solution no longer presented antimicrobial activity. When the electrochemical degradation of CIP was investigated using a single-sided boron-doped diamond (BDD) anode, its performance in TOC removal was similar to that of the Ti-Pt/β-PbO2 anode; considering the higher oxidation power of BDD, the surprisingly good comparative performance of the Ti-Pt/β-PbO2 anode was ascribed to significantly better hydrodynamic conditions attained in the filter-press reactor used with this electrode. Five initial oxidation intermediates were identified by LC-MS/MS and completely removed after 4h of electrolysis; since they have also been determined in other degradation processes, there must be similarities in the involved oxidation mechanisms. Five terminal oxidation intermediates (acetic, formic, oxamic, propionic, and succinic acids) were identified by LC-UV and all of them (except acetic acid) were removed after 10h of electrolysis.

Degradation of paracetamol in a bubble column reactor with ozone generated in electrolyte-free water using a solid polymer electrolyte filter-press electrochemical reactor

A porous anode composed of β-PbO2 was electrochemically deposited onto a carbon cloth substrate (e.g., CC/β-PbO2) aiming for the electrochemical ozone production (EOP) in electrolyte-free water using a solid polymer electrolyte (SPE) filter-press reactor. Scanning electron microscopy (SEM) images revealed the presence of a three-dimensional oxide structure necessary to obtain a fluid-permeable anode. X-ray analysis showed the predominance of the β-PbO2 phase. The maximum current efficiency for the EOP was 9.5% with an ozone production rate of 1.40 g h−1. Using a constant ozone production rate of 0.5 g h−1, the oxidative degradation of paracetamol (PCT) dissolved in water was accomplished as a function of the PCT concentration (20, 30, and 50 mg L−1) and the pH (acid, natural (without adjustment), and alkaline). The UV-Vis spectrophotometric analysis showed that the degradation process is more pronounced in alkaline media with a strong reduction in the electrical energy per order (E EO). A reduction of the chemical oxygen demand (COD) of up to 80% was observed. A linear correlation between data referring to COD and HPLC measurements with the UV absorbance measured at 243 nm (UV243) was verified indicating that these different techniques can be complementary to each other. The nuclear magnetic resonance (NMR) study of the ozonation by-products revealed that the oxidation of PCT occurred through the rupture of the aromatic ring. The major part of phenol’s ring was oxidized to CO3 2− while no reaction occurs in the acetamide group of paracetamol during the ozonation reaction.