Electrochemical Wastewater Treatment Research Articles

Elaboration of Highly Modified Stainless Steel/Lead Dioxide Anodes for Enhanced Electrochemical Degradation of Ampicillin in Water

Lead dioxide-based electrodes have shown a great performance in the electrochemical treatment of organic wastewater. In the present study, modified PbO2 anodes supported on stainless steel (SS) with a titanium oxide interlayer such as SS/TiO2/PbO2 and SS/TiO2/PbO2-10% Boron (B) were prepared by the sol–gel spin-coating technique. The morphological and structural properties of the prepared electrodes were characterized by scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), and X-ray photoelectron spectroscopy (XPS). It was found that the SS/TiO2/PbO2-10% B anode led to a rougher active surface, larger specific surface area, and therefore stronger ability to generate powerful oxidizing agents. The electrochemical impedance spectroscopy (EIS) measurements showed that the modified PbO2 anodes displayed a lower charge transfer resistance Rct. The influence of the introduction of a TiO2 intermediate layer and the boron doping of a PbO2 active surface layer on the electrochemical degradation of ampicillin (AMP) antibiotic have been investigated by chemical oxygen demand measurements and HPLC analysis. Although HPLC analysis showed that the degradation process of AMP with SS/PbO2 was slightly faster than the modified PbO2 anodes, the results revealed that SS/TiO2/PbO2-10%B was the most efficient and economical anode toward the pollutant degradation due to its physico-chemical properties. At the end of the electrolysis, the chemical oxygen demand (COD), the average current efficiency (ACE) and the energy consumption (EC) reached, respectively, 69.23%, 60.30% and 0.056 kWh (g COD)−1, making SS/TiO2/PbO2-10%B a promising anode for the degradation of ampicillin antibiotic in aqueous solutions.

Electrochemical treatment of malachite green dye wastewater by pulse three-dimensional electrode method

ABSTRACT Water pollution is becoming more and more serious nowadays, and water resources are in shortage. As an environmentally friendly wastewater treatment technology without secondary pollution, the three-dimensional electrode method has received more and more attention. However, the conventional direct current (DC) three-dimensional electrode method has the disadvantages of high energy consumption and low current efficiency. Based on this, this work investigated the treatment of malachite green (MG) dye wastewater by pulse three-dimensional electrode method. The influences of pulse duty cycle, pulse period, electrolysis voltage, initial pH, aeration rate and Na2SO4 concentration on MG degradation were investigated. The results showed that under the optimal operating conditions of pulse duty cycle of 0.4, pulse period of 15 s, electrolysis voltage of 15 V, initial pH of 5, aeration rate of 0.5 L/min, Na2SO4 concentration of 0.10 mol/L, the removal rates of MG and COD reached 96.2% and 80.5%, respectively, the current efficiency reached 93.4%, and the energy consumption was 24.2 kWh/kg COD after 150 min. Compared with DC power supply mode, the MG removal rate, COD removal rate and current efficiency were enhanced, and the energy consumption was reduced by 83.9%. Moreover, the generation capacity of ·OH was increased under pulse power supply mode. Finally, a possible degradation pathway of MG in pulse power supply mode was inferred using UV-vis and GC-MS analysis. This study indicates that the pulse three-dimensional electrode method is an efficient and low-energy-consumption wastewater treatment method with stable degradation performance for MG dye wastewater.

Fabrication of high performance Ti/SnO2-Nb2O5 electrodes for electrochemical textile wastewater treatment

Textile wastewater contains many organic compounds and colors that affect aquatic life and human health when discharged into the environment. High coloration due to excess dyes entering the wastewater causes coloration to the receiving water stream, affects the photosynthesis process of aquatic species, and adversely affects the landscape. SnO2-based electrodes have been extensively used in electrochemical water treatment, but their low durability decreases the pollutant treatment ability. Therefore, it is necessary to add another stable oxide to improve the performance and stability of SnO2 electrodes. This study aims to fabricate Ti/SnO2-Nb2O5 electrodes for the textile wastewater treatment using the electrochemical oxidation method. Different molar ratios of SnO2:Nb2O5 coating were prepared using the sol-gel method and then coated on the Ti substrates for calcination in 60 min at 500 °C. Scanning electron microscopy (SEM), X-ray diffraction (XRD), Brunauer Emmett Teller (BET), and cyclic voltammetry (CV) were used to determine the surface and electrochemical properties of Ti/SnO2-Nb2O5 electrodes. The SEM images show that SnO2-Nb2O5 electrode surfaces have the appearance of typical cracking structures of mixed metal oxides electrodes. The XRD spectrum show the SnO2 peaks of facet (110), (101), (200), (301), (321) and Nb2O5 peaks of facet (001), (002), (100), (101), (102) on Ti substrates. Furthermore, the specific surface area of the Ti/SnO2-Nb2O5 electrode ranges from 37.354 m2/g (SnO2:Nb2O5 = 9:1) to 71.885 m2/g (SnO2:Nb2O5 = 1:9). The electrochemical properties of SnO2:Nb2O5 electrodes showed high oxygen, chlorine evolution potential and high organic pollutant degradation in textile wastewater with COD removal at 83 %, decolorization at 74 % and the generation of many free radicals such as HO•, H2O2, O3, Cl2. The results demonstrate that the Ti/SnO2-Nb2O5 electrode with the mole ratio of 3:7 is the best in textile wastewater treatment with the longest service life (39 h).

Electrochemical treatment of hemodialysis wastewater including pharmaceutical products

Hemodialysis is an extracorporeal kidney replacement procedure to remove impurities or waste products from the blood that is used in the treatment of kidney failure. During this process, large amounts of water are used, which, lacking control, end up in sewage systems, potentially flushing high levels of organic and inorganic contaminants into the receiver's aqua biota. This research considered the treatment of synthetic hemodialysis water under acid and basic conditions. To better simulate the presence of organic compounds, 10 mg L−1 of amoxicillin, an antibiotic commonly present in wastewater from clinics and hospitals, was added. Laboratory and pilot tests were performed using coupled electrocoagulation and electro-oxidation. During electrocoagulation, the use of stainless steel and aluminum, as sacrificial anodes, were compared in acidic and basic pH. The stainless steel rod anode and a titanium mesh cathode were used during electrocoagulation in acidic conditions at a field strength of 3.0 V which was applied for 60 min. After electrocoagulation, the solution obtained was filtered to separate precipitates. The supernatant was then treated with electro-oxidation using an IrO2-Ta2O5|Ti anode and the titanium mesh cathode while applying 10 mA for 120 min. Wear of the stainless steel anode was identified by scanning electron microscopy and microanalysis. Removal of organic compounds including amoxicillin was significant. These results were confirmed by decreased contaminant concentration found by diode coupled chromatography detection. In the final analysis this coupled treatment system completely eliminated amoxicillin and significantly reduced entrained salts.

Environmental application of a cost-effective smartphone-based method for COD analysis: Applicability in the electrochemical treatment of real wastewater

This study aims to develop a cheap method for the evaluation of quality of water or the assessment of the treatment of water by chemical oxygen demand (COD) measurements throughout the use of the HSV color model in digital devices. A free application installed on a smartphone was used for analyzing the images in which the colors were acquired before to be quantified. The proposed method was also validated by the standard and spectrophotometric methods, demonstrating that no significant statistical differences were attained (average accuracy of 97 %). With these results, the utilization of this smartphone-based method for COD analysis was used/evaluated, for first time, by treating electrochemically a real water matrix with substantial organic and salts content using BDD and Pt/Ti anodes. Aiming to understand the performance of both anodes, bulk experiments were performed under real pH by applying current densities (j) of 15, 30, and 60 mA cm−2. COD abatement results (which were achieved with this novel smart water security solution) clearly showed that different organic matter removal efficiencies were achieved, depending on the electrocatalytic material used as well as the applied current density (42 %, 45 %, and 85 % for Ti/Pt while 93 %, 97 % and total degradation for BDD by applying 15, 30, and 60 mA cm−2, respectively). However, when the persulfate-mediated oxidation approach was used, with the addition of 2 or 4 g Na2SO4 L−1, COD removal efficiencies were enhanced, obtaining total degradation with 4 g Na2SO4 L−1 and by applying 15 mA cm−2. Finally, this smartphone imaging-based method provides a simple and rapid method for the evaluation of COD during the use of electrochemical remediation technology, developing and decentralizing analytics technologies for smart water solutions which play a key role in achieving the Sustainable Development Goal 6 (SDG6).

Influence of anode material and chlorides in the new-gen solid polymer electrolyte cell for electrochemical oxidation – Optimization of Chloroxylenol degradation with response surface methodology

• Efficient removal of Chloroxylenol with BDD/SPE in low conductive solutions. • First application of Ti/RuO 2 (DSA) as anode coupled with solid polymer electrolyte. • Application of response surface methodology for process optimization. • Optimization allows decreasing the energy consumption preserving COD removal. • Promising results for DSA/SPE application in chlorinated environments. In this study the solid polymer electrolyte – based (SPE-based) system recently developed for electrochemical wastewater treatment is used for the degradation of Chloroxylenol (CXL). To the best of authors knowledge, this is the first study that deals the investigation of the effect of anode material in such electrochemical cell configuration. The most used BDD/SPE cell is compared with DSA/SPE (Ti/RuO 2 anode) system considering the effect of chlorides concentration to activate the process mediated by active chlorine. The preliminary tests to evaluate the feasibility of the process show that BDD/SPE is able to completely degrade the CXL reaching a COD removal close to 90 % also in absence of supporting electrolyte and in a low conductive solution (0.025 mS cm −1 ). The DSA anode suffers the lack of chlorides in solution but became more competitive when NaCl is added, with a maximum COD removal equal to 71.6 % with 50 mM NaCl. The response surface methodology based on three-factors Doehlert matrix is applied to optimize the operating conditions for both systems. The selected factors are the current density (2–20 mA cm −2 ), the NaCl concentration (0–20 mM), and CXL concentration (10–100 mg L −1 ). The optimization analysis allows identifying the operating conditions needed to maximize COD removal and to minimize energy consumptions for BDD/SPE and DSA/SPE setups. In particular, the RSM analysis shows that under peculiar conditions (i = 15.5 mA cm −2 ; NaCl > 13 mM) DSA/SPE can reach a COD removal analogous to those obtained with BDD electrode over 90%, suggesting the possibility to exploit this electrode material in solid polymer electrolyte electrochemical cells.

Electrodegradation of Acid Mixture Dye through the Employment Electrooxidation and Lemnoideae in Na2SO4 Synthetic Wastewater

In this study, we report on the effectiveness of electrochemical and biological wastewater treatment for artificially prepared industrial wastewater, comprising small amounts of technologically important dyes, namely Acid Mixture composed of Acid Violet 90 (AV90) and Acid Red 357 (AR357) in Na2SO4 (ESS—electrolyte supporting solution), as well as their impact on the environment, using Lemna minor as a bioindicator. Our study revealed that among the tested dyes, the raw ones (AM in ESS+OM) and those subjected to electrooxidation with the use of an iron anode and a copper cathode [AMFe/Cuox in ESS+OM (OECD medium is a medium recommended by the Organization for Economic Co-operation and Development for Lemna sp. Growth Inhibition Test)] were the most phytotoxic for L. minor. No phytotoxicity was detected for the tested plants in solution after electrooxidation with graphite anode and cathode (AMCox in ESS+OM). Quantitative identification of acid mixture removal was carried out by supplementary UPLC/MS-MS (Ultra-Performance Liquid Chromatography/tandem Mass Spectrometry) and UV-VIS (UltraViolet-Visible spectroscopy) instrumental analysis. The final removal after electrochemical and biological treatment of AV90 and AR357 dye components was 98 and over 99%, respectively. The results suggest that it may be a suitable replacement/addition for the generally used wastewater treatment methods.

Variable activity and selectivity for electrochemical oxidation wastewater treatment using a magnetically assembled electrode based on Ti/PbO2 and carbon nanotubes

Magnetic multi-walled carbon nanotubes (CNTs) were loaded on Ti/PbO2 electrode by a magnet in this study to improve the efficiency of electrochemical oxidation wastewater treatment (EOWT). These physically attached carbonaceous small granules worked as additional modules, giving the newly created electrode unique characteristics. Series of electrodes’ electrochemical properties, as well as their electrochemical oxidation performances against the azo dye acid red G, phenol, and real petrochemical wastewater, were studied. These carbonaceous granules improved the electrode's electroactivity as well as the affinity between the organics and the electrode. More importantly, the amount of CNTs loaded had a strong influence on the degrading efficiency and selectivity towards various target contaminants as well as their intermediate products in treating synthetic or real wastewaters. Lower CNTs loading resulted in heterogeneous electrode properties, whereas higher CNTs loading resulted in the new electrode acting as a porous carbonaceous electrode. The deeper operating mechanism of the new magnetically assembled electrode were discussed based on both the experiment results and multiphysics simulation.

Cu-mediated optimization of PbO2 anodes for electrochemical treatment of electroless nickel plating wastewater

Effective removal of Ni(Ⅱ)-organic complexes from electroless nickel plating wastewater remains a challenge by conventional industrial effluent treatment processes. In this study, electrochemical oxidation using a PbO2 anode is proposed for effective decomplexation of Ni-organic complexes. The electrode quality and electrocatalytic capability of the PbO2 anode is shown to be greatly affected by the nature of the PbO2 active layer that is formed during the electrodeposition process with the current density, cathode material and electrolyte constitutions all exerting an influence on the Pb deposition behavior. Our investigations reveal that the presence of Cu2+ in the electrolyte can precisely control the amount of elemental Pb formed with Pb cathodic reduction and deposition prevented as a result of preferential Cu0 deposition. The doping of PbO2 with Cu significantly improved the morphology and electrocatalytic performance of the PbO2 deposit. Ni-citrate and TOC removal percentages of 83 % and 55 % respectively were achieved with the optimal Cu-doped PbO2 anode with 73 % of the Ni recovered at the cathode at a relatively low specific energy consumption of 12.7 kWh m−3. A possible mineralization pathway of Ni-citrate by the PbO2 anodic oxidation process is proposed.

Optimization and assessment of an electrochemical advanced oxidation system for synthetic stormwater treatment.

Electrochemical advanced oxidation processes (eAOPs) such as the current advanced oxidation system (AOS) are a type of electrochemical wastewater treatment that creates oxidative species, such as iodide species, chloride species, and hydroxyl radicals, that can treat even the most recalcitrant contaminants. It is important to determine the concentrations and locations of oxidative species in eAOPs for optimization of the wastewater treatment process. In this study, a spectrophotometric methodology was used to determine concentrations of iodide and chloride oxidative species (starting at 10, 25, and 50ppm) within an AOS under various input voltages (6, 12, and 24V). Overall, it was found that iodate and chlorite were the dominant species created in their respective treatments. Additionally, the concentration of iodide oxidative species increased with increasing voltage, whereas the chloride species decreased with increasing voltage. The optimal conditions for the efficient creation of AOS oxidative species were 12V and 10ppm potassium iodide and 6V and 10ppm sodium chloride, respectively. In addition, the use of iodide is recommended for wastewater treatment using the AOS to effectively create oxidative species. Following optimization, the AOS performance was tested for synthetic stormwater. Results indicated that the AOS performed well for reduction of Escherichia coli; however, reduction of other contaminants was inconsistent as would be expected given the AOS was optimized for disinfection, not decontamination. Further AOS optimization for decontamination would be expected to result in improved decontamination performance.

Chlorate induced false reduction in chemical oxygen demand (COD) based on standard dichromate method: Countermeasure and mechanism

Deliberate addition of mildly oxidative chlorate (ClO3−), so-called “chemical oxygen demand (COD) remover”, into wastewater in China or electrochemical production of ClO3− from Cl− induces the false COD reduction, which would bring about false appearance of effluents meeting the COD discharge standards. In this study, an easy sulfite-based reduction method was developed for the first time to remove ClO3− from the water samples before COD determination to eliminate this interference of ClO3−. In this reaction system, keeping the reaction temperature of sulfite reducing ClO3− at 60 °C was crucial for fast ClO3− removal rate, fixed molar [sulfite]ini/[chlorate]ini ratio value and the synchronous exhaustion of sulfite and ClO3−, which were of great significance for the real application of this improved COD determination method. The ClO3− interference on COD determination could be successfully eliminated after 20 min reduction of ClO3− by sulfite at pHini 4.0∼6.0 with the molar [sulfite]ini/[chlorate]ini ratio value in the range of 5∼6 when concentration of ClO3− was below 5 mM. Despite of the involvement of SO4·− in the sulfite reducing ClO3− system, the degradation of organic matters by SO4·− could be greatly impeded due to the lessened dissolved oxygen for SO4·− production at high reaction temperature and the scavenging of SO4·− by sulfite. In this reaction system, ClO2, ClO2− and ClO− were also generated and could be further reduced by sulfite stoichiometrically via oxygen transfer process with Cl− as the final product. In general, this study pioneered an effective, fast and convenient method for COD determination of the ClO3−-laden wastewaters and evaluating the real electrochemical wastewater treatment performance in terms of COD removal.

Progress in Preparation and Application of Titanium Sub-Oxides Electrode in Electrocatalytic Degradation for Wastewater Treatment

To achieve low-carbon and sustainable development it is imperative to explore water treatment technologies in a carbon-neutral model. Because of its advantages of high efficiency, low consumption, and no secondary pollution, electrocatalytic oxidation technology has attracted increasing attention in tackling the challenges of organic wastewater treatment. The performance of an electrocatalytic oxidation system depends mainly on the properties of electrodes materials. Compared with the instability of graphite electrodes, the high expenditure of noble metal electrodes and boron-doped diamond electrodes, and the hidden dangers of titanium-based metal oxide electrodes, a titanium sub-oxide material has been characterized as an ideal choice of anode material due to its unique crystal and electronic structure, including high conductivity, decent catalytic activity, intense physical and chemical stability, corrosion resistance, low cost, and long service life, etc. This paper systematically reviews the electrode preparation technology of Magnéli phase titanium sub-oxide and its research progress in the electrochemical advanced oxidation treatment of organic wastewater in recent years, with technical difficulties highlighted. Future research directions are further proposed in process optimization, material modification, and application expansion. It is worth noting that Magnéli phase titanium sub-oxides have played very important roles in organic degradation. There is no doubt that titanium sub-oxides will become indispensable materials in the future.

Oxygen-vacancy-enriched substrate-less SnOx/La-Sb anode for high-performance electrocatalytic oxidation of antibiotics in wastewater

Electrocatalytic oxidation is a promising technology for treating toxic organic pollutants in water and wastewater, but conventional Ti-based anodes often exhibit a short service life and low efficiency in application. Oxygen vacancy (OV)-based defect engineering is an effective activation method for enhancing the electrocatalytic activity of electrodes. Herein, the controllable formation of OV on the surface of a freestanding SnO2-Sb anode was achieved by the quantitative doping of La3+ into the SnO2 crystal structure of the anode for high-performance electrochemical wastewater treatment. The resultant SnOx/La-Sb anode degraded nearly 100% moxifloxacin (MOX, 10 mg L−1) in 30 min, with a low energy consumption of 0.09 kWh m−3. The SnOx/La-Sb anode with an OV density of 1.09% had the highest degradation rate constant (0.226 min−1), 8 times higher than that of the SnO2-Sb anode and 16 times higher than that of the state-of-the-art boron-doped diamond anode. La3+ doping-induced OV activated the anode surface for electrochemical reactions by boosting the interfacial electron transfer and •OH generation (103% increase). The novel 3D permeable SnOx/La-Sb anode also exhibited remarkable stability (predicted service life of 59 years) and high-rate performance (>98%) in a continuous flow-through treatment system (<1 min through the anode).

Removal of Phenol from Water in the Presence of NaCl in Undivided Cells Equipped with Carbon Felt or Ni Cathodes: Effect of Air Pressure

AbstractRecently, the electrochemical treatment of wastewater polluted by recalcitrant organics and containing chlorides was shown to be significantly improved adopting proper operative conditions such as suitable anodes and cathodes and low current density. In particular, the use of suitable cathodes such as carbon felt or silver could increase the removal of TOC and reduce the formation of chlorinated by‐products. In this study, attention was focused on the utilization of carbon felt cathodes with the main aim to evaluate the effect of air pressure on the process using phenol as model organic pollutant. It was shown that, in the presence of carbon felt cathode, the use of pressurized air allows both to increase the removal of TOC and to reduce the formation of chlorate. Moreover, the effect of the nature of the anode and of the presence of FeSO4, in order to study the involvement of electro‐Fenton process, was evaluated.

Batch Electrochemical Treatment of Raw Pulp and Paper Mill Wastewater Using Electrode Combinations

SS and Cu electrodes were used in the electrochemical coagulation to treat pulp and paper mill wastewater using 4SS and 3SS 1Cu electrodes by applying cell voltages 12 – 24 V. Optimal cell voltage 18V showed COD removal of 89.64% for 4SS electrode and 84.74% for 3SS 1Cu electrode with simultaneous color removal of 99% and 90%. Other control factors used for optimal operation are sludge volume index (SVI), filterability, etc. SVI values were &lt;100 mL/g for 4SS electrodes. The filtration characteristics of the ECC-treated sludge were established to determine the specific cake resistance (α) and the resistance of the filter medium (Rm). Lower α and Rm values for 4SS and 3SS-1Cu electrodes were found at 60 min ET. Proximate and ultimate analyses showed that 4SS and 3SS-1Cu sludge could be used as additive as well as adsorbent material for treating low strength wastewater.

The Investigation of COD Treatment and Energy Consumption of Urban Wastewater by a Continuous Electrocoagulation System

In this study, electrochemical treatment of urban wastewater with electrical conductivity of 1000 μS cm−1 and chemical oxygen demand of 250 mg L−1 was investigated using the variables of initial pH value, current density and flow rate. Electrocoagulation was used, in which aluminum and stainless steel were selected, as the electrochemical treatment process. The electrocoagulation process was operated in continuous mode. The data obtained in experimental studies show that the best COD removal efficiency occurred in experiments where the initial pH value was 6. The increase in current density from 5 A to 15 A decreased the removal efficiency from 79 to 67%. The increase in flow rate under constant current density also reduced the efficiency of removal as expected. In experiments in which current density and flow rate were examined together, the increase in flow rate allowed the application of higher current densities. This situation led to considerable reductions in energy consumption values, even if the COD removal efficiency did not significantly increase. The high COD removal obtained with the use of high flow rate and high current density indicates that the electrocoagulation process can be used for high flow rate municipal wastewater treatment.

Non-traditional power supply mode: Investigation of electrodeposition towards a better understanding of PbO2 electrode for electrochemical wastewater treatment

The power supply mode is a non-negligible character in electrochemical process. Constant current mode is used in the traditional electrodeposition preparation process of PbO2 electrode, and there are very few studies on its electrodeposition power supply mode. In this paper, two non-traditional power supply modes (linear increase power supply mode and linear decrease power supply mode) were used to fabricate PbO2 electrodes, and the properties of prepared electrodes were compared with those of the traditional constant current power supply mode. On the premise of improving the electrode properties, the non-traditional power supply mode also significantly reduced the energy consumption of the electrodeposition process of PbO2. After material characterization (Scanning electron microscope, X-ray diffraction), electrochemical characterization (Electrochemical impedance spectroscopy, linear sweep voltammetry etc.) and stability test, it can be seen that the electrode surface prepared by the non-traditional power supply mode was spherical particles and its average grain size was smaller than that of the traditional one. The PbO2 electrode prepared by linear increase power supply mode had higher oxygen evolution overpotential (1.962 V), more active sites, smaller membrane impedance (33.15 Ω) and better stability (accelerated life up to 125.1 h). In the electrocatalytic oxidation tests of the three electrodes, the PbO2 electrode prepared by linear increase mode had the best performance in decolorization rate, Chemical oxygen demand removal rate, average current efficiency and energy consumption. Owing to favorable effects obtained, non-traditional power supply mode could be considered a promising alternative for PbO2 electrode preparation and applied electrochemical process for wastewater treatment.

Template-made tailored mesoporous Ti/SnO2-Sb2O5-IrO2 anodes with enhanced activity towards dye removal

• Ti/SnO 2 –Sb 2 O 5 –IrO 2 are made using micelle templates of amphiphilic block-copolymers. • Template method produces anodes with mesoporous surfaces and enhanced active area. • The template-made anode is highly active towards the removal of reactive black 5-dye. • The template-made anode is 3-fold more stable than the Pechini-made anode. The mixed metal-oxide anode Ti/SnO 2 –Sb 2 O 5 –IrO 2 is a prominent candidate for the electro-oxidation of organic compounds in wastewater treatment systems. The catalytic activity of this material depends on its surface morphology, which strongly depends on the synthesis method used. Hence, here we manufactured innovative Ti/SnO 2 –Sb 2 O 5 –IrO 2 anodes using micelle templates made of amphiphilic block-copolymers and compared them with anodes made of the same composition using the Pechini method. Scanning electron microscopy, X-ray dispersive energy analysis, X-ray diffraction, cyclic voltammetry, and electrochemical impedance spectroscopy were used to characterise the morphology, composition, and electrochemical properties of the developed anodes. The “template method” produces anodes with mesoporous surfaces (11.0 ± 4 nm of pore diameter), which enhanced the electroactive area compared with the anodes made through the Pechini method. The templated anodes are more conductive than the Pechini-made ones and are more active for removing the reactive black 5-dye from 0.1 mol dm −3 Na 2 SO 4 aqueous solutions. The enhanced catalytic activity of the templated anode strongly increases with the addition of low concentrations of NaCl. The rate constants increase 3.9 and 4.7-fold when adding 200 ppm and 1168.8-ppm chloride, respectively. The templated anode removes 100% of the dye after only 15 min of electrolysis applying 20 mA cm −2 and leads to ∼50% mineralization after 60 min of oxidation. Notably, the template anode is 3-fold more stable in accelerated service lifetime tests than the Pechini-made anode. Therefore, our study shows that Ti/SnO 2 –Sb 2 O 5 –IrO 2 anodes made using the template method are highly promising for the electrochemical treatment of wastewater polluted with organic compounds.

Electrochemical Treatment of Synthetic Wastewaters Contaminated by Organic Pollutants at Ti4O7 Anode. Study of the Role of Operative Parameters by Experimental Results and Theoretical Modelling

AbstractIn the last years, an increasing attention has been devoted to the utilization of anodic oxidation (AO) technologies for the treatment of wastewater polluted by recalcitrant organics. Recently, Ti4O7 was proposed as a promising anode for AO for the treatment of various organics. Here the potential utilization of commercial Ti4O7 anodes has been evaluated considering the electrochemical treatment of synthetic wastewater contaminated by three very different organic molecules (namely, oxalic acid, phenol and Acid Orange 7), all characterized by a very high resistance to AO. The performances of Ti4O7 were compared with that of two largely investigated anodes: Boron‐doped diamond (BDD), which is probably the most effective electrode for AO, and an Ir‐based anode which presents a relatively low cost. Moreover, the effect of various operative conditions (current density, mixing rate and initial concentration of the organic) was evaluated by both experimental studies and the adoption of a theoretical model previously developed for BDD anodes. It was shown that the performances of the process can be improved by a proper selection of operative conditions. Moreover, it was found that the proposed model can be effectively used to predict the effect of operative parameters at Ti4O7 anodes, thus helping the process optimization.

Variation of current density with time as a novel method for efficient electrochemical treatment of real dyeing wastewater with energy savings.

Electro-oxidation is a promising technology for wastewater treatment with biorefractory organic and nitrogen pollutants; however, the high energy demand hinders its wide application. In this study, a novel method by regulating significant parameter during the electro-oxidation process in a timely manner for real dyeing wastewater treatment with energy savings was studied. Operating factors (i.e., flow rate, initial pH value, electrode distance, and current density) were investigated for chemical oxygen demand (COD) and ammonia removal, and the results indicated that current density was the key factor that obviously influenced the electrochemical performance. Indirect oxidation by active chlorine was then confirmed as the main reaction pathway for pollutant oxidation, and the relationship between the current density and the generation of active chlorine was established, suggesting that a large part of the generated active chlorine was not utilized effectively. Subsequently, a novel method of varying the current density in a timely manner based on the reaction mechanism was proposed; the results indicated that, with similar pollutant removal efficiencies, energy consumption could be reduced from 31.6 to 20.5 kWh/m3. Additionally, the novel system was further optimized by Box-Behnken design: The COD removal efficiency could reach 71.8%, and the energy demand could be reduced by 45.6%.