Filter-press Reactor Research Articles

Solar photoelectro-Fenton flow plant modeling for the degradation of the antibiotic erythromycin in sulfate medium

A solar photoelectro-Fenton (SPEF) plant containing a filter-press FM01-LC flow reactor in series with a compound parabolic collector (CPC) as photoreactor, operating in batch recirculation mode, was simulated using a parametric model. The degradation of 10dm3 of solutions of the heterocyclic antibiotic erythromycin (ERY) in 0.050moldm−3 Na2SO4 at pH 3.0 was used for validation. The filter-press reactor contained a platinized titanium plate anode and a graphite-felt cathode that produced H2O2 from the reduction of dissolved oxygen (0.24mmoldm−3). Trials were performed under potentiostatic and galvanostatic conditions with predominance of H2O2 production, minimizing H2 evolution reaction. The effect of initial catalyst (Fe2+) concentration, current density (j), initial antibiotic concentration as dissolved organic carbon (DOC) and volumetric flow rate on the ERY mineralization was studied. Good agreement between simulations and experimental DOC decays was obtained. Mineralization current efficiencies and specific energy consumptions were also determined. The best performance under galvanostatic conditions was found for 0.225mmoldm−3 ERY (100mgdm−3 DOC), 0.50mmoldm−3 Fe2+, volumetric flow rate of 3.0dm3min−1 and jcath=-0.16mAcm−2, reaching 69% mineralization with current efficiency of 75% and specific energy consumption of 0.059kWh (g DOC)−1. Six organic by-products were identified by gas chromatography-mass spectrometry, whereas final short-chain carboxylic acids like formic and oxalic acid were detected by ion-exclusion high-performance liquid chromatography. The initial N atom of ERY was predominantly converted into NO3− ion, although NH4+ ion was formed as well.

Electrodegradation of the Acid Green 28 dye using Ti/β-PbO2 and Ti-Pt/β-PbO2 anodes

The statistical Response Surface Methodology (RSM) is applied to investigate the effect of different parameters (current density, j, NaCl concentration, [NaCl], pH, and temperature, θ) and their interactions on the electrochemical degradation of the Acid Green (AG) 28 dye using a Ti/β-PbO2 or Ti-Pt/β-PbO2 anode in a filter-press reactor. LC/MS is employed to identify intermediate compounds. For both anodes, the best experimental conditions are j = 50 mA cm−2, [NaCl] = 1.5 g L−1, pH = 5, and θ = 25 °C. After 3 h of electrolysis, a dye solution treated under these conditions presents the following parameters: electric charge per unit volume of the electrolyzed solution required for 90% decolorization (Q90) of 0.34–0.37 A h L−1, %COD removal of ∼100%, specific energy consumption of 18–20 kW h m−3, and %TOC removal of 32–33%. No loss of the β-PbO2 film is observed during all the experiments. The β-PbO2 films present excellent stability for solutions with pH ≥ 5 ([Pb2+] < 0.5 mg L−1). Chloroform is the only volatile organic halo compound present in the treated solution under those optimized conditions. Hydroxylated anthraquinone derivatives, aromatic chloramines, and naphthoquinones are formed during the electrolyses. The Ti/β-PbO2 and Ti-Pt/β-PbO2 anodes show significantly better performance than a commercial DSA anode for the electrochemical degradation of the AG 28 dye. The Ti/β-PbO2 anode, prepared as described in this work, is an excellent option for the treatment of textile effluents because of its low cost of fabrication and good performance.

Electrochemical mineralization of norfloxacin using distinct boron-doped diamond anodes in a filter-press reactor, with investigations of toxicity and oxidation by-products

The contamination of water bodies by antibiotics is a cause of concern due to chronic toxic effects and the possible development of resistance to them by microorganisms, which can lead to serious health problems to humans. Thus, in this work, for the first time the degradation of norfloxacin (100mgL−1 NOR in 0.1molL−1 Na2SO4) is carried out electrochemically, using a filter-press flow reactor with boron-doped diamond (BDD) anodes of distinct characteristics. The investigated variables (and their ranges) were solution pH (3, 7, 10, and without specific control), current density (10, 20, and 30mAcm−2), temperature (10, 25, and 40°C), and boron content–sp2/sp3 carbon ratio of the BDD anode (100ppm – 215, 500ppm – 325, and 2500ppm – 284). The NOR electrodegradation performance of the distinct anodes was assessed by monitoring the degradation by-products (aromatic compounds and carboxylic acids), NOR concentration and total organic carbon concentration of the electrolyzed solutions, as well as their toxicity to Escherichia coli (i.e. growth inhibition). For the complete removal of NOR, the best condition (not pH dependent) was attained at 10mAcm−2 and 40°C, when the system is under mass transfer limitations. Concerning NOR oxidation and mineralization rates, mineralization current efficiency, energy consumption, and degradation products, similar results (including the complete detoxification of the electrolyzed solution) were attained for all tested BDD anodes under mass or charge transfer controlled processes. Clearly, the oxidation power of the tested BDD anodes is not affected by the values of their boron content–sp2/sp3 carbon ratio.

Photoelectrocatalytic hydrogen production from oilfield-produced wastewater in a filter-press reactor using TiO2-based photoanodes

Photoelectrocatalytic hydrogen production and simultaneous oxidation of organic pollutants from oilfield-produced wastewater were evaluated in a continuous filter-press reactor at bench scale using TiO2-based photoanodes under visible-light illumination. TiO2 films were prepared on AISI/SAE 304 stainless steel expanded meshes by sol-gel dip-coating. Nickeled AISI/SAE 304 stainless steel expanded meshes were used as cathode. Initially, the experiments were carried out using synthetic produced wastewater with a salinity equivalent to that of oilfield-produced wastewater and containing phenol at the same concentration as the refractory organic pollutants in this effluent. Cathodic and anodic potential ranges were established by micro-electrolysis studies using voltammetric techniques. Appropriate cathode/anode area ratios for different flow rates were estimated by macro-electrolysis studies using chronoamperometric measurements, in order to establish the cell currents required to obtain the adequate electrode potentials. After 2h, the highest hydrogen production rate (12.36μmol/h) was achieved at a flow rate of 0.76L/min applying a cell current of 32.44mA and the lowest hydrogen production rate (5.98μmol/h) was achieved at a flow rate of 2.00L/min applying a cell current of 17.90mA. Using oilfield-produced wastewater, the hydrogen production rate was 9.11μmol/h at the most appropriate operating conditions (0.76L/min, 32.44mA).

Electrochemical ozone production using electrolyte-free water for environmental applications

Oxide fine-mesh electrodes composed of lead dioxide doped with Fe3+ (OFM-Fe-PbO2) were prepared by electrodeposition onto a stainless-steel fine-mesh support in order to obtain fluid-permeable electrodes for an electrochemical filter-press reactor. These electrodes were used in electrochemical ozone production (EOP) carried out during the electrolysis of electrolyte-free water in order to obtain an environmentally friendly technology for the “in situ” water treatment. SEM images of electrodes prepared using different electrodeposition conditions showed the formation of well-defined crystalline grains, which uniformly covered the metallic wires of the support. X-ray analysis revealed that the formation of a β-PbO2 phase is more pronounced than the α-PbO2 phase. A maximum EOP current efficiency of 10%, obtained at j=1.5Acm−2, corresponding to a rate for the ozone generation of 1.58gh−1 and a specific electric energy consumption of 0.250kWhg−1, was attained for the OFM-Fe-PbO2 electrode formed using the electrodeposition bath containing 1.0mM Fe3+. The performance of the electrochemical reactor was evaluated during long-term galvanostatic electrolysis (t=60 days, j=1.0Acm−2 and 24°C), during which it was verified that the reactor voltage (U) and EOP current efficiency (ΦEOP) were both stable. The robustness of the SPE filter-press electrochemical reactor allied to a moderate EOP current efficiency indicated that the OFM-Fe-PbO2 electrode (1.0mM Fe3+) is promising for in situ ozone production from the electrolysis of electrolyte-free water.

Hydrodynamic design of electrochemical reactors based on computational fluid dynamics

The design of electrochemical reactors using computational fluid dynamics (CFD), was investigated. A numerical methodology which considers a complete solution of transport governing equations of fluid dynamics linked together to the electrochemistry was developed. Emphasis was put on the boundary layer region, where most of the reactions between electrolyte and cathode take place, as well as mass transport, km. Properties of cupric sulfur (CuSO4 + 5H2O) compound were considered in the mass transport simulating as part of an electrodeposit process in a parallel plate channel filter-press cell. The proposed design method does not make use of correlations where km is proportional to bulk dimensionless parameters like the Reynolds (Re), Sherwood (Sh), and Schmidt (Sc) numbers. Electrochemical reactor′s design based on these bulk parameters requires a fully developed flow condition that warranties the accuracy of the km calculation. Instead, many designs of reactors can be evaluated in terms of their effective electrochemical reactions if the km and other variables are calculated at the electrolyte dynamic condition in the region of electroactivity, despite it is part of a fully developed flow or not. The Reynolds equations were solved using the commercial code ANSYS Fluent, and turbulence was modeled using the RNG k-ε model. The method was validated by comparing the predicted results against velocity measurements, conducted in a laboratory model of filter-press reactor using particle image velocimetry, PIV. Measured data and predictions showed a channel flow of strong velocity gradients and a recirculation zone. Calculated profiles of km along the reactor were compared using both the measured and predicted velocity. A comparison of reported results for the FM01-LC electrolyser against the present method demonstrates that the use of CFD allows accurate designs. This is because the electroactivity and dynamics are both taken into account in the viscous sub-layer. The method can be useful for the design of electrochemical parallel plate reactors involving mass transport and chemical reactions near the cathode operating under laminar or turbulent flow conditions.

Arsenic and fluoride removal from groundwater by electrocoagulation using a continuous filter-press reactor.

We investigated simultaneous arsenic and fluoride removal from ground water by electrocoagulation (EC) using aluminum as the sacrificial anode in a continuous filter-press reactor. The groundwater was collected at a depth of 320 m in the Bajío region in Guanajuato Mexico (arsenic 43 µg L(-1), fluoride 2.5 mg L(-1), sulfate 89.6 mg L(-1), phosphate 1.8 mg L(-1), hydrated silica 112.4 mg L(-1), hardness 9.8 mg L(-1), alkalinity 31.3 mg L(-1), pH 7.6 and conductivity 993 µS cm(-1)). EC was performed after arsenite was oxidized to arsenate by addition of 1 mg L(-1) hypochlorite. The EC tests revealed that at current densities of 4, 5 and 6 mA cm(-2) and flow velocities of 0.91 and 1.82 cm s(-1), arsenate was abated and residual fluoride concentration satisfies the WHO standard (CF < 1.5 mg L(-1)). Spectrometric analyses performed on aluminum flocs indicated that these are mainly composed of aluminum-silicates of calcium and magnesium. Arsenate removal by EC involves adsorption on aluminum flocs, while fluoride replaces a hydroxyl group from aluminum aggregates. The best EC was obtained at 4 mA cm(-2) and 1.82 cm s(-1) with electrolytic energy consumption of 0.34 KWh m(-3).

Electrochemical degradation of estrone using a boron-doped diamond anode in a filter-press reactor

Estrone (E1), an endocrine-disrupting chemical (EDC) with health and environmental consequences, is commonly found in wastewater worldwide; thus, effective ways to degrade this EDC are welcome. For the first time, a one-compartment filter-press reactor with a boron-doped diamond (BDD) anode is used in the electrochemical degradation of E1. The effect of the following variables on E1 degradation (monitored through LC/UV–vis) is investigated: flow rate (qV), current density (j), concentration [E1], pH, and absence or presence of Cl– ions in solution. The best degradation performance was attained under the following conditions, with total degradation of E1 (initial concentration, [E1]0=500μgL−1, in 0.1molL−1 Na2SO4; 0.5L) in about 25min: qV=2.0Lmin−1 (kapp=2.1×10−3s−1), j=10mAcm−2, and pH≤7. The addition of Cl– ions (0.36mmolL−1) to the E1 solution significantly enhances the rate of E1 degradation (independently of pH), to such an extent that only 10min were needed to attain total degradation of E1. On the other hand, in the absence of Cl– ions in solution and at j=10mAcm−2, the decay of the relative concentration of E1 ([E1]rel) does not depend on [E1]0, as would be expected for processes limited by mass transport; this means that OH radicals are present in excess. Under optimized conditions, the performance attained with the BDD anode was compared with that with a β-PbO2 anode; then, the higher oxidation power of the BDD anode became evident through its significantly better performance: a decay of [E1]rel of about 98 % was attained in just 30min, compared to only 35 % for the β-PbO2 anode after 60min of electrolysis.

The abatement of indigo carmine using active chlorine electrogenerated on ternary Sb2O5-doped Ti/RuO2-ZrO2 anodes in a filter-press FM01-LC reactor

Dimensionally Stable Anodes (DSA) of Sb2O5-doped Ti/RuO2-ZrO2 are prepared by the Pechini method to perform the degradation of indigo carmine (IC) under conditions similar to textile wastewater effluents. XRD results along with Rietveld refinement reveal that the co-deposited phases on the DSA exhibit a tetragonal crystal structure (P4/mmm) for RuO2 and monoclinic structure (P2/m) for ZrO2. Degradation tests conducted in solutions containing 0.64mM IC and 0.05M NaCl using a filter-press reactor (FM01-LC) show that the degradation rate is faster and more efficient at 200Am−2 with a flow rate of 5Lmin−1, although the energy consumption is moderately higher. Under this condition, the pollutant is efficiently removed, and converted to aliphatic acid compounds of low molecular weight, as indicated by 90 % Chemical Oxygen Demand (COD), 22 % Total Organic Carbon (TOC) elimination, along with an Average Oxidation State (AOS) value equal to 3.0. The energy consumptions revealed that it is feasible to carry out the IC degradation under reasonable operating costs. Topological and Natural Bond Orbital (NBO) analyses are computed using density functional theory (DFT), and combined with experimental results to propose a reaction pathway for IC abatement.

Electrochemical degradation of the herbicide picloram using a filter-press flow reactor with a boron-doped diamond or β-PbO2 anode

Galvanostatic electrolyses are performed in a filter-press reactor to investigate the electrochemical degradation of picloram (100mgL−1, from a commercial herbicide formulation) using a boron-doped diamond (BDD) or β-PbO2 anode. The effect of pH (3, 6, or 10), applied current density (japl=10, 30, or 50mAcm−2), and absence or presence of Cl– ions (25mM) in the supporting electrolyte (aqueous 0.10M Na2SO4) is investigated, while the picloram concentration, solution chemical oxygen demand (COD) and total organic carbon content (TOC), and energy consumption are monitored as a function of electrolysis time. From the obtained results, it is clear that the electrochemical degradation of picloram is possible using either of the anodes, but with different overall performances. In general, the presence of Cl– ions in the supporting electrolyte (leading to electrogenerated active chlorine) has a positive effect on the performance of both anodes, except for TOC abatement using the BDD anode; the best electrodegradation performances are attained at pH values around 6, when HClO is the predominant active-chlorine species. Faster rates of initial electrodegradation of picloram and of solution TOC abatement are obtained as japl is increased, but, as expected, lower energy consumptions are always attained at the lowest value of japl. The performances of the two anodes are virtually the same in the initial degradation of picloram; however, the BDD anode greatly surpasses the β-PbO2 anode in the abatement of solution COD or TOC. This confirms the importance of the oxidation power of the anode, even when indirect oxidation by active chlorine plays a concomitant role.

Application of oxide fine-mesh electrodes composed of Sb-SnO2 for the electrochemical oxidation of Cibacron Marine FG using an SPE filter-press reactor

Oxide fine-mesh electrodes composed of tin dioxide doped with antimony (OFM-Sb-SnO2), which had different percentages of Sb, were prepared using the thermal decomposition method on a stainless steel fine-mesh support for application in a solid polymer electrolyte (SPE) filter-press reactor. The electrochemical oxidation of Cibacron® Marine FG (CMFG) was carried out during recirculation through a plug-flow reactor, using electrolyte-free dye solutions. An influence of the Sb content on the electrochemical oxidation of CMFG was verified. The highest combustion rate of CMFG was obtained using an electrode containing 6.57 mol% Sb. Studies were carried out as a function of the initial dye concentration (IDC) and the applied current density (j) for this particular electrode composition. It was verified that the decolourisation and mineralisation reactions were affected considerably by IDC and j. In trying to interpret the experimental findings, an electrode mechanism was proposed for the irreversible parallel reactions comprising the oxygen evolution reaction (OER) and the advanced oxidation process (EAOP). The instantaneous current efficiency (ICE) for the mineralisation reaction was calculated for the different cases using the average mass-transport coefficient (〈kL〉) and the initial limiting current (jL0) values. The energy consumption (EC) was also calculated for the mineralisation reaction. It was confirmed that ICE and EC are strongly affected by IDC and j. Analysis of the reactor voltage (U) under galvanostatic conditions revealed that the OFM-Sb-SnO2 electrode (6.57 mol% Sb) is more stable when the OER is partially suppressed during the electrochemical oxidation of CMFG.

Fluoride removal from drinking water by electrocoagulation in a continuous filter press reactor coupled to a flocculator and clarifier

This investigation is about fluoride removal from synthetic drinking water (10mgL−1 F− in 0.5gL−1 Na2SO4 and 1.5mgL−1 ClO− at pH 7.7 and conductivity 410μScm−1), by electrocoagulation (EC) using aluminum as the sacrificial anode in a continuous filter press reactor coupled to a flocculator and clarifier (sludge settler). The influence of current density (j) and linear flow velocity in the EC reactor (ur) on the fluoride removal efficiency was analyzed. The EC tests that satisfy the WHO norm for fluoride (CF⩽1.5mgL−1) were obtained at 0.91⩽ur⩽1.82cms−1 and 5⩽j⩽7mAcm−2, giving aluminum doses between 19.28⩽CAl(III)⩽52.67mgL−1. Scanning Electron Microscopy (SEM), Energy Dispersive Analysis of X-rays (EDA-X) and Fourier Transform Infrared Spectroscopy (FTIR) analyses were performed to confirm the presence of fluoride in the flocs. The best EC tests in terms of energy consumption was obtained at 5mAcm−2, with a mean linear flow velocity in the EC reactor of 1.82cms−1, which gives an energy consumption of 0.37kWhm−3, during the removal of fluoride from 10 to 1mgL−1. EC at j>7mAcm−2 did not improve the EC process any further owing to massive generation of electrolytic gases which promote the breaking of the flocs.

Application of electrochemical advanced oxidation processes to the mineralization of the herbicide diuron

Here, solutions with 0.185mM of the herbicide diuron of pH 3.0 have been treated by electrochemical advanced oxidation processes (EAOPs) like electrochemical oxidation with electrogenerated H2O2 (EO-H2O2), electro-Fenton (EF) and UVA photoelectro-Fenton (PEF) or solar PEF (SPEF). Trials were performed in stirred tank reactors of 100mL and in a recirculation flow plant of 2.5L using a filter-press reactor with a Pt or boron-doped diamond (BDD) anode and an air-diffusion cathode for H2O2 electrogeneration. Oxidant hydroxyl radicals were formed from water oxidation at the anode and/or in the bulk from Fenton’s reaction between added Fe2+ and generated H2O2. In both systems, the relative oxidation ability of the EAOPs increased in the sequence EO-H2O2<EF<PEF or SPEF. The two latter processes were more powerful due to the photolysis of intermediates by UV radiation. In the stirred tank reactor, the PEF treatment with BDD was the most potent method, yielding 93% mineralization after 360min at 100mAcm−2. In the flow plant, the SPEF process attained a maximum mineralization of 70% at 100mAcm−2. Lower current densities slightly reduced the mineralization degree in SPEF, enhancing the current efficiency and dropping the energy consumption. The diuron decay always obeyed a pseudo-first-order kinetics, with a much greater apparent rate constant in EF and SPEF compared to EO-H2O2. Oxalic and oxamic acids were detected as final carboxylic acids. Ammonium and chloride ions were also released, the latter ion being partially converted into chlorate and perchlorate ions at the BDD surface.

Electrochemical degradation of the dimethyl phthalate ester on a fluoride-doped Ti/β-PbO2 anode

The electrooxidation of the dimethyl phthalate (DMP) ester was galvanostatically carried out in a filter-press reactor using a fluoride-doped lead dioxide (β-PbO2,F) film electrodeposited on a Ti substrate. The variables investigated were the nature of the supporting electrolyte (NaCl and Na2SO4), pH (3, 7, and 10), current density (10, 20, 40, 60, and 80mAcm−2), and temperature (10, 20, 30, 40, and 50°C). The removal of DMP was monitored through high performance liquid chromatography (HPLC) and total organic carbon (TOC) analysis. The best conditions were obtained using Na2SO4 and at low current densities, independent of the solution pH or temperature. These conditions led to the highest levels of current efficiencies and complete combustion. However, the TOC removal levels were low, due to the generation of highly oxidized intermediates, which was confirmed by the intermediates detected by HPLC.

Performance and Kinetic-Mechanistic Aspects in the Electrochemical Degradation of Sulfadiazine on Boron-Doped Diamond Electrode

The electrochemical performance of boron-doped diamond (BDD) electrode in the electrochemical degradation of wastewaters containing sulfadiazine (SDZ) using a filter-press reactor is presented and discussed. The electrooxidation of the SDZ (volume of 0.5 L, with a SDZ initial concentration of 250 mg L-1) obtained at optimized conditions (current density of 36 mA cm-2, pH 7.0 and volume flow rate of 5.0 L min-1) showed that at the end of only 2 h of electrolysis (corresponding to a charge passed through the cell per unit volume of the wastewater of 5.2 Ah L-1) SDZ was totally eliminated. The reduction of the wastewater organic load, monitored by its chemical oxygen demand (COD) showed that the antibiotic was virtually all mineralized. Under optimized conditions the intermediate compounds were properly identified by gas chromatography-mass spectrometry (GC-MS) and a SDZ oxidation pathway was elucidated. Clearly the BDD electrode proved to be quite efficient for both degradation and mineralization of SDZ.

NADH regenerated using immobilized FDH in a continuously supplied reactor – Application to l-lactate synthesis

The present study deals with the design and optimization of a reduced-scale filter press reactor, containing an immobilized layer of formate dehydrogenase between two layers of chitosan, dedicated to the enzymatic synthesis of chiral molecules. Elaboration and optimization of the overall system was carried out to demonstrate the feasibility of the immobilization of formate dehydrogenase in a continuous synthesis process. The results demonstrate that the immobilized FDH keeps half of its enzymatic activity for practically two weeks. In addition, the polymeric matrix allows transfer of NAD+ with relatively high diffusion coefficients (2.1×10−11m2s−1). Experimental validation of NADH regeneration was achieved for pyruvate reduction to l-lactate. Simulation demonstrated that it is possible to achieve practically quantitative conversion of the NAD+ if the reaction channel reaches a length of half a meter.

Removal of arsenic from a deep well by electrocoagulation in a continuous filter press reactor

We investigated arsenic removal from groundwater by electrocoagulation (EC) using aluminum as the sacrificial anode in a continuous filter press reactor. The groundwater was collected at a depth of 200 m in the plateau region, in Central Mexico, (As 134 μg L−1, Fe 0.3 mg L−1, Cd 0.7 mg L−1, Na 58 mg L−1, pH 6.8). The influence of current density (J) and mean linear flow rate (u) on As removal was analyzed. EC revealed that u of 0.91 cm s−1 (which gives a retention time of 53.4 s) at J of 6 and 8 mA cm−2 yielded samples that met the Mexican standard for arsenic (≤25 μg L−1). EC at 10 mA cm−2 did not improve results any further owing to massive generation of gases and anode passivation. The partial EC removal of arsenic can be attributed to the mixture of HAsO2, H3AsO3 and HAsO42−. HAsO42− is more susceptible to removal by adsorption on Al(OH)3 and Al2O3 flocs. The best EC result was obtained at 6 mA cm−2 and 0.91 cm s−1, with energy consumption of 0.89 kWh m−3, which decreased arsenic from 134 to 14 μg L−1.

Mineralization of the antibiotic chloramphenicol by solar photoelectro-Fenton: From stirred tank reactor to solar pre-pilot plant

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

Arsenic removal from groundwater by electrocoagulation in a pre-pilot-scale continuous filter press reactor

We investigated arsenic removal from groundwater by electrocoagulation (EC) using aluminum as the sacrificial anode in a pre-pilot-scale continuous filter press reactor. The groundwater was collected at a depth of 320m in the Bajío region in central Mexico (arsenic 50μgL–1, carbonates 40mgL–1, hardness 80mgL–1, pH 7.5 and conductivity 150μScm–1). The influence of current density, mean linear flow and hypochlorite addition on the As removal efficiency was analyzed. Poor removal of total arsenic (<60%) in the absence of hypochlorite is due to a mixture of arsenite (HAsO2(aq) and H3AsO3(aq)) and arsenate (HAsO42−). Arsenic removal is more efficient when arsenite is oxidized to arsenate by addition of hypochlorite at a concentration typically used for disinfection (1mgL–1). Arsenate removal by EC might involve adsorption on aluminum hydroxides generated in the process. Complete arsenate removal by EC was satisfactory at a current density of 5mAcm–2 and mean linear flow of 0.91cms–1, with electrolytic energy consumption of 3.9kWhm3.

Electrochemical oxidation of bio-refractory dye in a simulated textile industry effluent using DSA electrodes in a filter-press type FM01-LC reactor

This work presents a study on degradation of indigo carmine dye in a filter-press type FM01-LC reactor using Sb2O5-doped Ti/IrO2-SnO2 dimensionally stable anode (DSA) electrodes. Micro- and macroelectrolysis studies were carried out using solutions of 0.8 mM indigo carmine in 0.05 M NaCl, which resemble blue denim laundry industrial wastewater. Microelectrolysis results show the behaviour of DSA electrodes in comparison with the behaviour of boron-doped diamond (BDD) electrodes. In general, dye degradation reactions are carried out indirectly through active chlorine generated on DSA, whereas in the case of BDD electrodes more oxidizing species are formed, mainly OH radicals, on the electrode surface. The well-characterized geometry, flow pattern and mass transport of the FM01-LC reactor used in macroelectrolysis experiments allowed the evaluation of the effect of hydrodynamic conditions on the chlorine-mediated degradation rate. Four values of Reynolds number (Re) (93, 371, 464 and 557) at four current densities (50, 100, 150 and 200 A/m2) were tested. The results show that the degradation rate is independent of Re at low current density (50 A/m2) but becomes dependent on the Re at high current density (200 A/m2). This behaviour shows the central role of mass transport and the reactor parameters and design. The low energy consumption (2.02 and 9.04 kWh/m3 for complete discolouration and chemical oxygen demand elimination at 50 A/m2, respectively) and the low cost of DSA electrodes compared to BDD make DSA electrodes promising for practical application in treating industrial textile effluents. In the present study, chlorinated organic compounds were not detected.