Total Organic Carbon Abatement Research Articles

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.

Tannery wastewater treatment using combined electrocoagulation and electro-Fenton processes

Tannery wastewater was performed using electrocoagulation (EC) coupled with an electro-Fenton (EF) process and boron-doped diamond (BDD) anodes to generate hydrogen peroxide (H2O2), and then optimized using the response surface methodology (RSM). Effects of three independent variables (e.g., reaction time, current density and Fe2+ concentration) on the performance of electrochemical processes were analyzed using a statistical experimental design. Current density and reaction time were significant for total organic carbon (TOC) removal when the EC and EF processes were tested. The interaction between initial Fe2+ concentration (0.66 mM L-1, the highest value) and reaction time was significant and achieved 32% TOC removal, but because it was used with the highest current density value tested (70 mA cm-2), the energy consumption was as high as 74.5 kWh m-3. Optimization of the process for TOC removal and energy consumption was accomplished by lowering the current density and treatment time values (40 mA cm-2 and 217 min) during EF treatment. Under these conditions, 25% of TOC removal was achieved. The integrated EC-EF system generated 64% TOC removal using a greater current density (9.7 mA cm-2) during the EC process, and the overall treatment energy consumption was 22.3 kWh m-3. The sludge produced under the tested EC conditions exhibited no hazardous characteristics. The EC treatment was also faster in TOC abatement (sixth-order kinetic), compared to the EF treatment (third-order kinetic).

Performance of TiO2/UV-LED-Based Processes for Degradation of Pharmaceuticals: Effect of Matrix Composition and Process Variables.

Ultra-violet light-emitting diode (UV-LED)-based processes for water treatment have shown the potential to surpass the hurdles that prevent the adoption of photocatalysis at a large scale due to UV-LEDs’ unique features and design flexibility. In this work, the degradation of five EU Watch List 2020/1161 pharmaceutical compounds was comprehensively investigated. Initially, the UV-A and UV-C photolytic and photocatalytic degradation of individual compounds and their mixtures were explored. A design of experiments (DoE) approach was used to quantify the effects of numerous variables on the compounds’ degradation rate constant, total organic carbon abatement, and toxicity. The reaction mechanisms of UV-A photocatalysis were investigated by adding different radical scavengers to the mix. The influence of the initial pH was tested and a second DoE helped evaluate the impact of matrix constituents on degradation rates during UV-A photocatalysis. The results showed that each compound had widely different responses to each treatment/scenario, meaning that the optimized design will depend on matrix composition, target pollutant reactivity, and required effluent standards. Each situation should be analyzed individually with care. The levels of the electrical energy per order are still unfeasible for practical applications, but LEDs of lower wavelengths (UV-C) are now approaching UV-A performance levels.

Electro-Fenton mineralization of diazo dye Black NT2 using a pre-pilot flow plant

This project assessed the mineralization of Black NT2 (BNT2), a diazo dye frequently used in tanneries, using electrochemical technologies based on boron-doped diamond electrodes (BDD). The experimental trials included adding an Fe2+-catalyzed process known as the electro-Fenton (EF) reaction. The process was carried out in a recirculating pre-pilot plant that used a filter-press electrochemical reactor connected to a reservoir. The pre-pilot reactor was equipped with a BDD plate anode coupled with a BDD cathode to electrogenerate hydrogen peroxide (H2O2) in situ. The effects of experimental variables such as current density (j) and initial BNT2 concentration were tested. The best conditions to mineralize an initial BNT2 concentration equivalent to 250 mg L−1 of total organic carbon (TOC) in a 50 mM Na2SO4 solution using the EF process were 0.3 mM Fe2+, pH 3.0, j = 30 mA cm2, and Q = 12 L min−1. After 90 min of treatment, 100% TOC abatement was achieved. In all cases, TOC decreased following a pseudo-first-order kinetics. For the highest initial dye concentration, 100% TOC was achieved after 120 min, with 70% average current efficiency and 0.01088 KWh (g TOC)−1 energy consumption at the end of the process. For experiments without complete mineralization, the evolution of some nontoxic, short-chain carboxylic acids—such as oxalic, maleic, succinic, acetic, and formic—were quantified using high performance liquid chromatography (HPLC) analysis. These findings suggest that the EF reaction is an interesting, feasible alternative for enhanced dye degradation in tannery water treatment processes.

Hydrochars from compost derived from municipal solid waste: Production process optimization and catalytic applications

Catalytic hydrochars were produced by hydrothermal carbonization (HTC) of compost derived from Municipal Solid Waste (MSW). The HTC process was studied through a Design of Experiments to assess the influence of the variables: (i) time (1–5 h), (ii) load of compost (1–4 g in 30 mL) and, (iii) temperature (150–230 °C). Total organic carbon (TOC), conductivity and volume variation of the liquid fraction, as well as the mass and carbon content of the solid fraction (hydrochars), were the evaluated responses. Reliable models (R2 > 0.95 and p-values < 0.05) were fitted to the responses, and the load of compost was found as the most significant variable influencing the process. The Fenton reaction was proposed as an effective treatment of the liquid fraction generated from HTC of compost. A TOC abatement of 73% was obtained after 24 h of reaction under the studied operating conditions (80 °C, initial pH 3.0, 100 mg L−1 Fe+2 and two times the stoichiometric amount of H2O2 needed for the complete mineralization of the TOC present in the liquid fraction). The hydrochars produced show high catalytic activity in the decomposition of H2O2, a reaction of interest in a variety of chemical processes, 100% of H2O2 degradation being obtained after 6 h of reaction.

Slaughterhouse Wastewater Treatment By Anodic Oxidation Using Two Different DSA-Type Anodes

Water is an essential resource for life, the environment and the industrial development; hence the treatment of wastewater has become crucial to ensure a good quality effluent before disposal the municipal sewer systems. The slaughterhouse industry produces a large volume of wastewater due to the slaughtering of animals, meat processing and the cleaning of the slaughterhouse facilities [1]. Treatment and adequate disposal of slaughterhouse wastewater (SW) is a worldwide economy and public health necessity which is regulated by International Standard [2]. SW contains elevated amounts of organic matter and salts. Typical parametrical analyses include pH, chemical oxygen demand (COD), biochemical oxygen demand (BOD), total nitrogen (TN), total phosphorous (TP), total organic carbon (TOC) and total suspended solids (TSS) [3]. After preliminary treatment, where most large particles are removed, the coagulation-flocculation technology is the most used primary treatment. However, it produces secondary pollution. Nowadays, electrochemical processes such anodic oxidation (AO) have been considered an alternative technology for the treatment of SW due to its mild operation conditions, quite compact and easy operation and not secondary waste streams among others. AO may oxidize the organic pollutants via two different ways: i) directly oxidized, where electron transfer occurs at the anode surface (M) and/or ii) indirectly oxidized, where the organic pollutants are oxidized through the mediation of some species electro-generated in situ at the anode surface and/or agents in the bulk solution.In this study, a real beef slaughterhouse wastewater presented the following characteristics: TOC (1150 mg L–1), COD (4320 mg L–1), TP (25 mg L–1), TN (72.28 mg L–1), TSS (1433 mg L–1) at pH 7.18 and conductivity of 2.79 mS cm–1. Bright red color was observed at 416 nm (1.24 A.U.) and the presence of coliform bacteria was confirmed (> 1600 MPN). AO tests were carried out in a single open cell compartment in batch operation mode. 0.1 L of SW was introduced into the electrolytic cell with constant stirring to ensure mass transport of the oxidant specie towards/from the anode to the bulk. AO was assessed using two different dimensionally stable anodes (DSA) type anodes: i) Ti/IrO2/Ta2O5 coating (DSA-O2) ii) Ti/Ru0,3Ti0,7O2 (DSA-Cl2). AISI 304 stainless steel plate was used as cathode. The geometrical bare area of both, cathode and anode, was about 5 cm2, having a 1 cm of interelectrode gap. AO experiments were analyzed at different applied current densities (2, 10 and 20 mA cm–2) and supporting electrolyte (0.05 M Na2SO4; 0.05 M NaCl) in order to find the best operating conditions.This study focuses on TOC and COD removal as a function of the current density and the electrolysis time. Minimizing TOC and COD values is the main objective in SW treatment. However, TOC is the most important role to determine the organic compounds in SW. Figure 1 shows the TOC removal during five hours of electrochemical treatment utilizing the two different DSA-type anodes at the higher current density (j = 20 mA cm–2). As can be seen in Figure 1a), EO process using DSA-O2 without supporting electrolyte reached the maximum removal of total organic carbon at the end of the electrolysis time. Residual TOC concentration achieved 232.66 mg L–1 (79.77 % removal efficiency). Figure 1b) displays the TOC abatement from SW using DSA-Cl2 anode. Alike the DSA-O2 the best EO test was the one where not supporting electrolyte was added, the maximum TOC removal efficiency reached 78.62 % (245.89 mg L–1) unlike the other tests using supporting electrolyte.The best operating conditions were found at current density of 20 mA cm–2 without supporting electrolyte. TOC, COD and TP removal efficiency were 79.77% and 78.62 %; 89.22% and 79.4%; 96.0% and 64% using DSA-Cl2 (Ti/Ru0,3Ti0,7O2) and DSA-O2 (Ti/IrO2/Ta2O5), respectively. Moreover, a complete discoloration and disinfection were achieved. Electrochemical oxidation test at best operating conditions gave energy consumption and specific energy consumption values for TOC, COD and TP using DSA-Cl2 and DSA-O2 of 24.5 and 26.5 kW h m–3, 27.1 and 28.9 kW h kgTOC –1, 7.14 and 6.88 kW h kgCOD –1 and, 1531.25 and 1104.17 kW h kgTP –1, respectively.[1] Bustillo-Lecompte C.F., Mehrvar M., 2015. J. Environ. Manag. 161 287–302.[2] US Environmental Protection Agency. Final Rule; Federal Register. 2004;69(173):54476–54555.[3] Bustillo-Lecompte, C.F., Mehrvar, M., 2017. J. Clean. Prod. 141, 278–289. Figure 1

Elimination of pharmaceutical pollutants by solar photoelectro-Fenton process in a pilot plant

In this study, the simultaneous degradation of antibiotics (ampicillin, sulfamethazine, and tetracycline; and non-steroidal anti-inflammatories (diclofenac and salicylic acid)) including the total organic carbon abatement by solar photoelectro-Fenton process was assessed. Eight liters of solution containing the mixture of the five pharmaceuticals in 1mmolL-1 Fe2+, 0.05molL-1 Na2SO4 at pH3 and 35°C were electrolyzed applying different current densities (j = 10, 25, and 50mAcm-2) in a solar-electrochemical pilot plant. The pilot plant was equipped with an electrochemical filter press cell with a dimensionally stable anode (DSA type) and an air-diffusion cathode coupled to a solar photoreactor exposed directly to sunlight radiation. All pharmaceuticals were degraded during the first 10min. A TOC removal efficiency of 99.2% after 100min of treatment with an energy consumption of 534.23kWh (kgTOC)-1 and 7.15kWhm-3 was achieved. The pharmaceutical concentration decay followed a pseudo-first-order kinetics. The specific energy per unit of mass of ampicillin, diclofenac, salicylic acid, sulfamethazine, and tetracycline was obtained at 11.73, 19.56, 35.2, 11.73, and 39.32kWh (kgPD)-1 for ampicillin, diclofenac, salicylic acid, sulfamethazine, and tetracycline, respectively. With our results, we demonstrated that SPEF is an emerging technology for the treatment of this type of pollutants in short time.

Differential pulse voltammetry as a powerful tool to monitor the electro-Fenton process

This study presents the applicability of differential pulse voltammetry (DPV) technique to carry out in-depth research of electro-Fenton process. To this end, the degradation of the ionic liquid p-xylene-bis(n-pyridinium bromide) was performed, and the main parameters that influence this process were also evaluated. DPV allowed monitoring the evolution of Fe(III) reduction as redox probe, enabling to examine the degradation of ionic liquid and the effect of the potential as well as main intermediates formed throughout the process. By using DPV tool, application of sequential current intensities along the electro-Fenton process was evaluated as alternative to reduce the energy consumption keeping the same efficiency. Based on the profile of the voltammetric curves and the determination of hydroxyl radicals, currents of 50 and 600 mA were chosen for testing a bi-electrical current system. Thus, a current of 600 mA was applied for 30 min followed by 50 mA for 60 min (600, 50), and vice versa (50, 600). Both trials achieved a total organic carbon (TOC) abatement around 60%, being the system (600, 50) less energy consuming (0.24 kWh g−1 TOC) than the other system (50, 600) (5.90 kWh g−1 TOC). Furthermore, chromatographic analyses of inorganic ions allowed validating the attained results. Finally, the feasibility of this bi-electrical current process to a real matrix was successfully carried out, achieving the same TOC abatement when working with synthetic solution. This fact demonstrated the potential of the bi-electrical current electro-Fenton system and its suitability for more complex matrix, as well as the potential of DPV technique to deeply study the electro-Fenton process.

Foam separation for effective removal of disperse and reactive dyes from aqueous solutions

In this study, the effectiveness of the foam separation process for removal of color and total organic carbon (TOC) from the dye solution was assessed. The optimum experimental conditions for the selected parameters such as pH, air flowrate, concentration of surfactant etc. were determined for RR 241 and DB 60, and the performance difference of the foam separation process for water-soluble and insoluble dyes has been demonstrated. The optimum conditions were determined as pH 5 and pH 3 with surfactant concentration of 100 mg⋅L−1 and at air flowrate of 0.5 and 0.2 L⋅min−1 for the treatment of 500 mL of 100 mg⋅L−1 RR 241 and DB 60 solutions, respectively. At these optimum conditions, 99.6 – 92.4% color and 92.5 – 85.6% TOC removals were reached for RR 241 and DB 60, respectively. In the case of nitrogen gas bubbled into the column instead of air under the same optimum conditions, color and TOC abatements were 99.1 – 99.4% and 91.1 – 84.8% for RR 241 and DB 60, respectively. In the nitrogen gas assays, the experiments were performed under the same conditions with air as pH 5 and pH 3 with surfactant concentration of 100 mg⋅L−1 and at gas flowrate of 0.5 and 0.2 L⋅min−1 for the treatment of 500 mL of 100 mg⋅L−1 RR 241 and DB 60 solutions, respectively. According to the results, the treatment performance of foam separation process depends strongly on the structure of pollutant and type of the carrier gas used in the column.

Coupling electro-Fenton process to a biological treatment, a new methodology for the removal of ionic liquids?

This work proposes a hybrid system for the remediation of toxic and/or refractory pollutants, such as the ionic liquid 1-butyl-1-methylpyrrolidinium chloride, which cannot be degraded by conventional methods such as biological oxidation. Therefore, the electro-Fenton process was evaluated as a pre-treatment stage, since it is a powerful technology capable of degrading complex organic pollutants. First, the key operating parameters (anodic material, iron dosage, current applied and initial pollutant concentration) were evaluated to reach complete ionic liquid degradation (98% total organic carbon abatement). The electro-Fenton treatment target pollutant was accompanied by an increase of its biodegradability, tested from average oxidation state and carbon oxidation state parameters. Based on these values, 30 min of pre-treatment by electron-Fenton process was selected and then the solution thus treated was subjected to biological treatment using bacteria and fungi consortiums. The evolution of TOC and carboxylic acids were followed during assays, attaining an overall abatement of 78% and 67% for bacteria and fungi cultures, respectively. Conversely, a control test of ionic liquid performed without pre-treatment was showed no variation in TOC and no formation of carboxylic acids. Therefore, the feasibility at laboratory scale of the coupling between electro-Fenton and biological treatment has been demonstrated.

Double benefit of electrochemical techniques: Treatment and electroanalysis for remediation of water polluted with organic compounds

Concern about the current pollution of water environments and the inefficacy of conventional water treatments for the elimination of refractory contaminants has placed electrochemistry in the spotlight. With the objective of demonstrating the diverse applications that electrochemical techniques can have in the area of water remediation, this study is focused on the use of three different methods: (i) electro-Fenton process with heterogeneous catalyst as the treatment for the degradation of the target compounds; (ii) cyclic voltammetry for the characterization of the electrochemical system, and (iii) differential pulse voltammetry for the monitoring of the evolution of the degradation process. Four organic compounds were selected as target pollutants: the ionic liquid 1,3-Bis(2,4,6-trimethylphenyl)imidazolinium chloride, Mesitol, Mesidine and 2,5-Xylidine. Results were corroborated and complemented with chromatographic and total organic carbon (TOC) measurements. After 420 min of heterogeneous electro-Fenton treatment, almost 80% of TOC abatement was achieved for the ionic liquid and more than 90% for Mesitol, Mesidine and 2,5-Xylidine. Cyclic voltammetry studies for Mesitol and Mesidine suggested the formation of a polymeric film which remains adsorbed on the electrode surface. Finally, it was possible to conclude that the coupling of differential pulse voltammetry with the heterogeneous electro-Fenton process provides useful information about the evolution of the degradation process of pollutants in just a couple of minutes.

Enhanced performance of cobalt ferrite encapsulated in graphitic shell by means of AC magnetically activated catalytic wet peroxide oxidation of 4-nitrophenol

Here we report preliminary catalytic wet peroxide oxidation (CWPO) experiments performed in the presence of an alternating current (AC) magnetic field. One ferromagnetic graphitic nanocomposite – composed by a cobalt ferrite core and a graphitic shell (CoFe2O4/MGNC), was employed in the process, here named magnetically activated catalytic wet peroxide oxidation (MA-CWPO). An aqueous solution containing 5.0 g L−1 of 4-nitrophenol (4-NP) to simulate a high strength polluted stream was used as model system. The experiments were performed at room temperature and atmospheric pressure, with stoichiometric amount of hydrogen peroxide (H2O2), pH = 3 and CoFe2O4/MGNC catalyst load = 5.0 g L−1 (corresponding to a 4-NP/CoFe2O4 mass ratio of 6.9, as CoFe2O4 accounts for 14.4 wt% of CoFe2O4/MGNC). It was shown that the performance of CWPO is enhanced upon application of an AC magnetic field (frequency of 533.9 kHz and magnitude of 240 G). As a result, high 4-NP mineralization was obtained by MA-CWPO (as reflected by a total organic carbon abatement of 79% after 4 h of reaction, instead of 39% in the absence of a magnetic field). This positive effect was ascribed to the localised increase of CoFe2O4/MGNC surface temperature resulting from heat release upon exposure of the nanoparticulated catalyst to an AC magnetic field, which accelerates the catalytic decomposition of H2O2 via hydroxyl radicals (HO) formation.

Structure-based synergistic mechanism for the degradation of typical antibiotics in electro-Fenton process using Pd–Fe3O4 model catalyst: Theoretical and experimental study

The electro-Fenton process with a dimensionally stable anode and a graphite felt cathode was applied to the oxidative degradation of the antibiotics levofloxacin and trimethoprim. The comparison of electron spin resonance spectra for the catalysts Pd-Fe3O4 and Fe3O4 verified that Pd loading contributed to the coexistence of OH and atomic H∗ in the electro-Fenton process. The use of Pd-Fe3O4 instead of Fe3O4 showed evident superiority for the degradation of levofloxacin according to the increased apparent rate constant value from 0.156 to 0.243 min−1, whereas it was almost unchanged (0.041 min−1) for trimethoprim. Moreover, the total organic carbon abatement after 8 h treatment confirmed the superiority of Pd-Fe3O4 attaining the almost complete mineralization of levofloxacin, and the mineralization current efficiency suggested that atomic H∗ weaken the recalcitrant intermediate of levofloxacin more efficiently compared to trimethoprim. The modelling study indicated that the dispersion of Pd particles on the surface of Fe3O4 promoted the d-band center due to more exposure active sites. The structure calculation of antibiotic and typical intermediates is in agreement with the comparison of experimental results, proposing a theoretical approach to evaluate antibiotic wastewater. The calculation of antibiotic structure and modelling study of catalyst were firstly combined to clarify the structure-based synergistic mechanism between the nucleophilic and electrophilic radicals.

Enhanced treatment of pharmaceutical wastewater by combining three-dimensional electrochemical process with ozonation to in situ regenerate granular activated carbon particle electrodes

Abstract The treatment of a real pharmaceutical production wastewater by electrolysis using three-dimensional electrodes (3D electrolysis), ozonation, and their combined process (3D/O3) was investigated in this study. The pharmaceutical wastewater was characterized by a high organic concentration (total organic carbon (TOC) of 13,475 mg/L) and high acute toxicity (100% inhibition of the luminescent bacterial Vibrio fischeri). After 6 h treatment, ∼23% and 43% of TOC could be removed from the pharmaceutical wastewater by individual ozonation and the 3D electrolysis process using granular activated carbon (GAC) as the particle electrodes, respectively. However, the acute toxicity of the wastewater was hardly reduced by the two individual processes. In comparison, by sparging the ozone generator effluent (oxygen and ozone gas mixture) in the three-dimensional electrode reactor, the 3D/O3 process considerably enhanced TOC abatement to ∼71% and reduced the inhibition of the luminescent bacterial to OH) production in the 3D/O3 process via several reaction mechanisms, e.g., the reaction of sparged O3 with in situ generated H2O2, the electrochemical reduction of O3, and GAC catalyzed O3 decomposition, which in turn enhanced the oxidation of organics in the bulk and those adsorbed onto the GAC particle electrodes. The results of this study indicate that there exists a synergistic effect between 3D electrochemical process and ozonation for the degradation of toxic organics in the pharmaceutical wastewater. Compared with the two individual processes, the 3D/O3 process can thus provide a more effective option for the treatment of high-strength pharmaceutical wastewater.

Treatment of olive oil mill wastewater by single electrocoagulation with different electrodes and sequential electrocoagulation/electrochemical Fenton-based processes

The treatment of olive oil mill wastewater (OOMW) by novel sequential processes involving electrocoagulation (EC) followed by electro-Fenton (EF) or photoelectro-Fenton (PEF) under UVA irradiation has been studied using a boron-doped diamond anode and an air-diffusion cathode for H2O2 electrogeneration. Their performance was monitored from the removal of total organic carbon (TOC), chemical oxygen demand, turbidity, total solids and total nitrogen, as well as from the energy consumption. Preliminary EC assays were performed with one pair of electrodes made of Al, Fe, AISI 304 or AISI 316L. The Fe/Fe cell showed the best performance, yielding 40% TOC decay in 20 min. Subsequent EF or PEF at natural pH 7.2 performed similarly, whereas PEF became superior at pH 3.0 due to the action of UVA photons. Comparison between EC/PEF and single EF or PEF at pH 3.0 and 25 mA cm−2 with 0.50 mM Fe2+ revealed the positive outcome of the sequential process, attaining 97.1% TOC abatement after 600 min. GC–MS analysis of the raw wastewater allowed identifying 18 cyclic and 27 aliphatic compounds, most of which could not be removed by EC. The final solutions in EC/EF and EC/PEF contained a large plethora of persistent long-chain aliphatic acids and alkanes.

Electrochemical oxidation of anesthetic tetracaine in aqueous medium. Influence of the anode and matrix composition

The degradation of 150mL of 0.561mM tetracaine hydrochloride at pH 3.0 by electrochemical oxidation with electrogenerated H2O2 (EO-H2O2) has been studied at a low current density of 33.3mAcm−2 in three different matrices: 0.050MNa2SO4, real urban wastewater and a simulated matrix mimicking its electrolyte composition. Comparative trials were performed in an undivided cell with a 3cm2 boron-doped diamond (BDD), Pt, IrO2-based or RuO2-based anode and a 3cm2 air-diffusion cathode that allowed continuous H2O2 electrogeneration. In 0.050MNa2SO4, much faster and overall removal of tetracaine occurred using BDD because of the large oxidation ability of BDD(OH) formed from anodic water oxidation. In either simulated matrix or real wastewater, the RuO2-based anode yielded the quickest tetracaine decay due to a large production of active chlorine from anodic oxidation of Cl−. For the mineralization of the organic matter content, the BDD/air-diffusion cell was the best choice in all aqueous matrices, always reaching more than 50% of total organic carbon abatement after 360min of electrolysis, as expected if BDD(OH) mineralizes more easily the chloroderivatives formed from tetracaine oxidation in the presence of active chlorine. The initial N of tetracaine was partly transformed into NO3−, although the total nitrogen of all solutions always decayed by the release of volatile by-products. In the Cl−-containing matrices, significant amounts of ClO3− and ClO4− were obtained using BDD, whereas active chlorine was much largely produced using the RuO2-based anode. Five aromatic by-products, one of them being chlorinated, along with low concentrations of oxalic acid were identified. The change in toxicity during EO-H2O2 with BDD in the sulfate and simulated matrices was also assessed.

Removal of 4-hydroxyphenylacetic acid from aqueous medium by electrochemical oxidation with a BDD anode: Mineralization, kinetics and oxidation products

The degradation of 100mL of solutions containing 4-hydroxyphenylacetic acid in 0.050M Na2SO4 at pH3.0 has been performed by anodic oxidation with electrogenerated H2O2 (AO-H2O2) using a stirred tank reactor equipped with a boron-doped diamond (BDD) anode and an air-diffusion cathode. An almost total mineralization with 95.5% total organic carbon (TOC) removal was achieved for a 1.03mM substrate solution at 100mAcm−2. The effect of current density between 16.7 and 100mAcm−2 and 4-hydroxyphenylacetic acid content between 0.21 and 2.06mM was examined. Greater current efficiency with lower specific energy consumption and smaller mineralization was found at low current density and high substrate concentration. The TOC abatement as well as the 4-hydroxyphenylacetic acid concentration decay obeyed a pseudo-first-order kinetics. The oxidation role of hydroxyl radical formed from water discharge at the BDD anode is explained on the basis of its electrogeneration rate and competitive wasting reactions. 4-Hydroxybenzenemethanol and its derivative 4-hydroxybenzenealdehyde were identified as primary aromatic by-products by gas chromatography-mass spectrometry. Ion-exclusion HPLC allowed the detection of low amounts of the persistent oxalic acid during the AO-H2O2 process. The remaining TOC in final electrolyzed solutions is related to the presence of a large proportion of unidentified by-products that are even more recalcitrant than common short-chain aliphatic carboxylic acids.

Elimination of radiocontrast agent diatrizoic acid by photo-Fenton process and enhanced treatment by coupling with electro-Fenton process.

The removal of radiocontrast agent diatrizoic acid (DIA) from water was performed using photo-Fenton (PF) process. First, the effect of H2O2 dosage on mineralization efficiency was determined using ultraviolet (UV) irradiation. The system reached a maximum mineralization degree of 60% total organic carbon (TOC) removal at 4h with 20mM initial H2O2 concentration while further concentration values led to a decrease in TOC abatement efficiency. Then, the effect of different concentrations of Fenton's reagents was studied for homogeneous Fenton process. Obtained results revealed that 0.25mM Fe(3+) and 20mM H2O2 were the best conditions, achieving 80% TOC removal efficiency at 4h treatment. Furthermore, heterogeneous PF treatment was developed using iron-activated carbon as catalyst. It was demonstrated that this catalyst is a promising option, reaching 67% of TOC removal within 4h treatment without formation of iron leachate in the medium. In addition, two strategies of enhancement for process efficiency are proposed: coupling of PF with electro-Fenton (EF) process in two ways: photoelectro-Fenton (PEF) or PF followed by EF (PF-EF) treatments, achieving in both cases the complete mineralization of DIA solution within only 2h. Finally, the Microtox tests revealed the formation of more toxic compounds than the initial DIA during PF process, while, it was possible to reach total mineralization by both proposed alternatives (PEF or PF-EF) and thus to remove the toxicity of DIA solution.

Treatment of real wastewater with TiO2-films sensitized by a natural-dye obtained from Picramnia sellowii

A natural dye extracted from Picramnia sellowii (Chokanari) was used to prepare sensitized TiO2 films. Dyes and heterotrophic microorganisms present in wastewater were treated by photocatalysis using visible light. A factorial design 23 was employed to select the operational conditions to sensitize TiO2 films. The combined treatment using a concentration of 0.03% w/v of sensitizer (natural dye), 700rpm (spin-coating) and 300 color units of wastewater showed interesting results, removing close to 60% of the color and 60% of Chemical Oxygen Demand. Kinetic experiments using the best coated films showed that Total Organic Carbon abatement was higher using sensitized films, conversely, no statistical differences were found in color removal when comparing sensitized and non-sensitized films. Heterotrophic microorganisms were completely inactivated following 12h of treatment with sensitized films. Films can be used up to 5 operational cycles with loss of catalytic activity close to 10%.

Effect of RVC porosity on the performance of PbO2 composite coatings with titanate nanotubes for the electrochemical oxidation of azo dyes

Reticulated vitreous carbon (RVC) of different porosities (20, 45, 60, 80, and 100ppi—pores per inch) has been used as a large surface area substrate for preparing 3D-like PbO2 coatings (RVC/PbO2) as well as composite coatings with hydrothermally synthesized titanate nanotubes (RVC/PbO2/TiNT) by galvanostatic electrodeposition from baths containing lead(II) methanesulfonate and methanesulfonic acid. The effect of the RVC porosity on the coating thickness, the electrocatalytic behaviour and the ability to remove the colour and total organic carbon (TOC) from solutions containing the azo dye Methyl Orange has been systematically assessed. As shown from scanning electron micrographs, the greatest thickness (up to 120μm) was obtained using>60ppi, but the β-PbO2 nanocrystallytes mainly grew on the external surface, leaving mostly uncoated inner RVC stripes and ending in planar-like PbO2-based electrodes. In contrast, thinner but perfectly adherent and homogeneous coating of the inner and outer surface was achieved with 20-60 ppi, showing electrodes with an optimal three-dimensionallity. This was especially confirmed by cyclic voltammograms for the composite coatings, as deduced from their highest electroactivity that can be related to enhanced adsorption onto the TiNT clusters and the larger ability to produce active PbO2(OH). The comparative electro-oxidation of 0.25×10−3moldm−3 Methyl Orange acidic solutions in 0.05moldm−3 Na2SO4 at 0.6A demonstrated that RVC (45 ppi)/PbO2/TiNT was the optimum material. It allowed the quickest decolourisation, reaching 60% in 2.5min and>98% at 45min, and>55% TOC abatement at 240min. The anode presented a perfect surface coverage, with no evidence of RVC degradation. The effect of dye concentration and supporting electrolyte nature was studied, revealing a very positive effect of NaCl.