electro-Fenton Process Research Articles

Levofloxacin degradation performance and mechanism in the novel electro-Fenton system constructed with vanadium oxide electrodes under neutral pH

• A novel VO-EF system was proposed for levofloxacin degradation under neutral pH. • The redox of VO x on cathode and oxygen vacancies on anode ensured good performance. • Complete mineralization of levofloxacin and low H 2 O 2 residue were achieved. • Degradation pathways and mechanism of levofloxacin were proposed. • Great bioavailability in the effluent was observed. Heterogenous ferrum-based materials usually suffer from large overpotential between the redox of Fe 3+ /Fe 2+ and two-electron oxygen reduction reaction (2e − ORR), leading to less desired performance in electro-Fenton (EF) process. Herein, heterogeneous vanadium oxide EF system (VO-EF) was proposed by electrodepositing VO on carbon paper cathode (VO x @CP) and anode (V 3 O 7 @CP) for levofloxacin degradation. The VO x @CP cathode showed the optimal potential of 2e − ORR at −0.90 V (vs. SCE) with H 2 O 2 generation rate of 1.44 × 10 −4 mmol·L −1 ·cm −2 ·s −1 . Though overpotential disparity of 0.35 V was exhibited between the redox of VO x and 2e − ORR, rapid H 2 O 2 consumption rate was still achieved and facilitated ·OH generation. The oxygen vacancies existed in V 3 O 7 @CP anode reduced oxygen evolution reaction potential, leading to the cell voltage decrease of 0.36 V. Levofloxacin (30 mg·L −1 ) degradation efficiency of 97.67% was achieved in the VO-EF system within 120 min, and 19.19 mg·L −1 TOC was mineralized with energy consumption of 12.3 J·mg·L −1 TOC under neutral pH condition. Complete mineralization and low H 2 O 2 residue allowed good bioavailability in the effluent. Levofloxacin degradation pathways and mechanism were proposed based on identified intermediates and theoretical calculation. This study provides inspiration for developing novel EF systems for efficient pollutants degradation.

A novel NH2-MIL-88B(Fe)-modified ceramic membrane for the integration of electro-Fenton and filtration processes: A case study on naproxen degradation

• Novel NH 2 -MIL-88B(Fe)-decorated ceramic membrane for combined filtration-EF at mild pH. • Almost total degradation of naproxen in Na 2 SO 4 after 90 min at 50 mA and 2 mL min −1 . • Mechanism for heterogeneous EF with catalytic ceramic membrane (EFCCM) treatment. • Identification of 7 primary oxidation byproducts and EFCCM viability in urban wastewater. • Low iron release (<1 mg L −1 at pH ≥ 5) ensured a good CM reusability for at least 5 cycles. Process intensification based on innovative coupling between membrane microfiltration and catalytic oxidation technologies has become a promising strategy for water treatment. Here, a surface-nucleated metal–organic framework (MOF) was grown in situ to obtain an NH 2 -MIL-88B(Fe)-functionalized catalytic ceramic membrane (NH 2 -MIL-88B(Fe)@CM), whose ability to remove naproxen from water matrices via the so-called electro-Fenton with catalytic ceramic membrane (EFCCM) process was systematically investigated. The physicochemical properties of the NH 2 -MIL-88B(Fe) and membranes were characterized by XRD, FTIR, XPS and SEM, revealing the formation of a well-defined NH 2 -MIL-88B(Fe) layer on the porous CM with a thickness of around 13.5 µm, which provides a large amount of active sites for H 2 O 2 activation to generate hydroxyl radical ( OH). The EFCCM treatment of naproxen in Na 2 SO 4 solution under recirculation batch mode yielded almost complete drug removal in 90 min at 50 mA, whereas the stability and catalyst loss tests gave evidence of good membrane reusability for 5 cycles. The treatment of naproxen in urban wastewater confronted severe membrane fouling, but this was effectively mitigated by combining hot water backwash with EF self-cleaning. Finally, the naproxen degradation routes involving 7 byproducts are proposed. This is an effective approach to the fabrication of CCM, which could be used for wastewater treatment in continuous mode as suggested by the minimal NPX content at the membrane outlet.

Removal of chemical oxygen demand (COD) from hospital wastewater by electro fenton process using graphite–graphite electrochemical system

Removal of COD from hospital wastewater generated from Al- Diwaniyah hospital located in Iraq was achieved using graphite–graphite electro-Fenton (EF) system. The effect of various operational parameters on the COD removal efficiency was investigated based on response surface methodology (RSM). Optimal conditions were current density of 20mA/cm2, FeSO4 concentration of 0.697 mM and time of 48.687 min. At these conditions COD elimination efficiency of 97.964 % was achieved at a specific energy consumption of 10.78 kWh/kg. The results indicated that time had the least effect on the COD removal efficiency, while the impact of current density had the greatest effect, followed by the FeSO4 concentration. The adequacy of the model equation was confirmed by its high R2 value (99.62%). The present study shows that graphite–graphite EF system was an efficient tool for removing of COD from hospital wastewaters.

Degradation of 2-Naphthol in Aqueous Solution by Electro-Fenton System with Cu-Supported Stainless Steel Electrode

For the treatment of 2-naphthol wastewater, the homogeneous electro-Fenton process was considered as an effective method but some disadvantages greatly restrict its application. The three-dimensional electro-Fenton (3D-EF) system using a nano zero-valent iron-supported biochar (NZVIs-BC) particle electrode and a Cu-supported stainless steel electrode (Cu-SSE) was proposed to avoid the disadvantages of the homogeneous electro-Fenton. In this work, the 3D-EF system was developed, which consisted of a Cu-SSE (cathode), a graphite rod (anode) and a NZVIs-BC particle electrode. The effect of the ratio of ferrous sulfate heptahydrate (FS) to rice straw (RS), CuSO4•5H2O amount, initial pH of 2-naphthol wastewater and current intensity (the output current of the power supply) on the removal rate of 2-naphthol were investigated. It is noteworthy that more than 98.36% of the 2-naphthol in aqueous solution was removed by the 3D-EF system, and only about 60.09% of 2-naphthol was removed by the homogeneous electro-Fenton system. Furthermore, naphthalene, benzoic acid, β-naphthoquinone, 1, 2-naphthalenedione, phenol and aromatic hydrocarbon were the main degradation products of 2-naphthol by the 3D-EF system; the toxicity of 2-naphthol wastewater was also greatly reduced.

A novel Fe/HNT visible light-driven heterogeneous photocatalyst: Development as a semiconductor and photocatalytic application

Fe/HNT (Iron/Halloysite-nanotube) heterogeneous semiconductor catalysts operating effectively under visible light were developed by using FeCl3, FeSO4 and Fe(OH)3 sludge precipitated after electro-Fenton process and named as Fe/HNT-I, Fe/HNT-II and Fe/HNT-III, respectively. Chemical configuration and particle morphology of the catalysts were characterized with XRD, SEM-EDS and UV–vis DRS. Effect of the developed Fe/HNT photocatalysts was investigated for the degradation of Reactive Orange 16 (RO16) textile dye under visible light. The photocatalytic decolorization of RO16 was 95.6%, 99.3% and 96.6%, respectively. It was found that the photocatalytic performance of Fe/HNT-III catalyst under visible light was effective compared to Fe/HNT-I and Fe/HNT-II. The iron ratio in the catalyst's structure (Fe:HNT ratio 0.25, 0.5 and 0.75 (w/w)) and pH value (4, 7 and 9) in production phase were also changed to investigate the photocatalytic effect of Fe/HNT-III. An Fe:HNT ratio of 0.25 and a pH of 4 were determined as the optimum conditions for catalyst production. Optimum H2O2 dosage value was also investigated for photocatalytic oxidation process and determined to be 10 ​mM. Finally, the optimum conditions were further used for the degradation of Terbinafine hydrochloride (TerHCl) active drug and the treatment of wastewater from the textile and pharmaceutical industries.

Electrochemical Oxidation Approach towards the Treatment of Acetamiprid Pesticide from Polluted Water

Introduction: Acetamiprid (AP) is one of the most widely used pesticides in the neonicotinoid class. AP residues in the environment have received considerable due to their potential toxicity to humans. Therefore, it is important to remove AP from the aqueous solution.&#x0D; Materials and Methods: In the current study, response surface methodology (RSM) was used as an efficient approach to optimize the removal of AP using the electro-Fenton (EF) process. The effects of the main variables, including reaction time, AP concentration, current density, and H2O2 dosage were investigated and optimized. ANOVA technique was also used to identify the Fisher’s value (F-value) and P-value of the model.&#x0D; Results: The predicted AP removal efficiency by the model was in good agreement with the obtained experimental results with correlation regression of 0.9885. The ANOVA test proved that the developed quadratic model was significant with very low P-values less than 0.05, the high F-value of 240.1, and regression coefficients close to 1 at a 95% confidence level. The optimum condition for AP removal efficiency of 99.02% was attained at the reaction time of 12 min, AP concentration of 3.5 mg L-1, the current density of 12 mA cm-2, and H2O2 dosage of 86 µL.&#x0D; Conclusion: RSM was employed as a suitable method to optimize the operating condition and maximize the AP removal. Herein, the EF process as an eco-friendly electrochemical advanced oxidation process (EAOP) successfully applied to remove AP from the water and wastewater.

Friction and wear mechanisms for single crystal GaN based on an electro-Fenton enhanced chemical reaction

Electro-Fenton polishing is a chemical mechanical polishing (CMP) technology with enhanced chemical reaction, which hydroxyl radicals (•OH) can be efficiently and controllably generated by using an electric Fenton method. The oxidation and corrosion of single crystal gallium nitride (GaN), and the synergistic mechanism of chemical and mechanical effects in the electro-Fenton polishing process are key to the electro-Fenton polishing of GaN. This article evaluated the effects of different media (electrolyte, H2O2, Fenton, and electro-Fenton) and different conditions (H2O2 mass fraction, means of H2O2 addition, cathode potential, Fe–C catalyst mass fraction, and pH) through ball-disk friction and wear tests. The results showed that electro-Fenton media demonstrated the best oxidation and corrosion effects on the GaN surface among the four media. In the electro-Fenton slurries, the oxidation was very sensitive to the H2O2 mass fraction which showed that 5 wt % H2O2 was the optimal mass fraction; the oxidation efficiency was greatly improved by regularly supplementing H2O2. The friction and wear behavior of GaN exhibited a good response to the cathode potential with the optimal cathode potential being −0.5 V. Meanwhile, the best Fe–C catalyst mass fraction was 3 wt % and the optimal pH was 2. In addition, the friction and wear behavior were investigated, and the energy spectrum tests was carried out to verify the effect of the chemical reaction. The synergistic mechanism of chemical action and mechanical removal in the friction and wear process was revealed. This research provides theoretical support for on-line electro-Fenton polishing technology.

Fe3O4/Mn3O4/ZnO-rGO hybrid quaternary nano-catalyst for effective treatment of tannery wastewater with the heterogeneous electro-Fenton process: Process optimization

This study investigated chemical oxygen demand (COD) removal from tannery wastewater (TWW) with a novel Fe3O4/Mn3O4/ZnO-rGO heterogeneous electro Fenton (HEF) hybrid magnetically-separable nano-catalyst. The graphite cathode and Ti/IrO2/RuO2 anode were used in the HEF process. With aeration (2 L/min), in-situ H2O2 generation occurred. The nano-catalyst was characterized by XRD, XPS, DLS, FT-IR, ζ potential, SEM, TEM, and BET techniques in detail. The system was modelled with a central composite design and optimized numerically. The established model was adequate, valid, reliable, and reproducible to predict the COD removal efficiency. OH and O2− were the oxidative species responsible for organic matter degradation. The effect of different processes was investigated, and efficiency was ranked from high to low as; HEF > anodic oxidation-H2O2 > anodic oxidation > adsorption. Under the optimum conditions; pH: 3.5, current density: 7.37 mA/cm2, reaction time: 79.43 min, and catalyst dose: 0.06 g/L, COD removal efficiency reached a maximum of 97.08%. The energy consumption and cost to remove 1 kg COD were 10.87 kWh and $1.41. The degradation of COD fitted the pseudo-first-order model. The nano-catalyst was stable and reusable with a minimum yield of 78.12% after 5 cycles.

Efficient treatment for tannery wastewater through sequential electro-Fenton and electrocoagulation processes

This work aims to study the ability of using single and sequential electro-Fenton (EF) and electrocoagulation (EC) processes in order to treat tannery wastewater. The first method (EF) was run with an air diffusion cathode for H2O2 generation and boron–doped diamond (BDD) as an anode. The second method (EC) was conducted with mild steel electrodes. The applied processes' performance was monitored by the removals of chemical oxygen demand (COD) along with the total Cr in addition to the electric energy consumption (EEC). To achieve the allowable discharge limits in aquatic media, a hybrid 2 h EF-5 h EC process was applied to treat tannery wastewater, based on the optimization results of every single method, achieving (88.1 ± 4.8)% COD removal rate with total elimination of Cr. In addition, the results of other parameters evolution such as pH, turbidity and the concentration of ions were discussed. As a result, the global EEC of the hybrid treatment was reduced to about 1.7 times. Finally, precipitate and sludge generated at the end of each treatment were examined by X-Ray Diffraction (XRD) analysis to determine their crystalline structure for valorization or reuse possibilities.

Heterogeneous degradation of amoxicillin in the presence of synthesized alginate-Fe beads catalyst by the electro-Fenton process using a graphite cathode recovered from used batteries.

Iron alginate beads (Fe-Alg) were prepared, characterized and implemented for the degradation of amoxicillin (AMX) by the heterogeneous electro-Fenton process using a graphite cathode recovered from used batteries. Scanning electron microscopy (SEM) showed that (Fe-Alg) beads have a spherical shape and the results of energy dispersive spectrometric (EDS) revealed the presence of iron in (Fe-Alg). Optimization of the operating parameters showed that a complete degradation of AMX was achieved within 90 min of heterogeneous electro-Fenton treatment by operating under these conditions: initial AMX concentration: 0.0136 mM, I = 600 mA, [Na2SO4] = 50 mM, pH = 3, T = 25 °C, ω = 360 rpm. The corresponding chemical oxygen demand (COD) abatement was 50%. Increasing the contact time increased the COD abatement to 85.71%, after 150 min of heterogeneous electro-Fenton treatment. The results of the kinetic study by using nonlinear methods demonstrated that the reaction of AMX degradation obeyed to a pseudo-second-order kinetic. Iron content of 4.63% w/w was determined by the acid digestion method. After 5 cycles of use, the Alg-Fe catalyst depletion was only 8%. Biodegradability was remarkably improved after electro-Fenton pretreatment, since it increased from 0.07 initially to 0.36. The heterogeneous electro-Fenton process had efficiently eliminated AMX and it increased the biodegradability of the treated solution.

Cu/Fe oxide integrated on graphite felt for degradation of sulfamethoxazole in the heterogeneous electro-Fenton process under near-neutral conditions

In the heterogeneous electro-Fenton (EF) system, high-efficiency and durable materials have attracted widespread attention as cathodes for degradation of refractory organic pollutants. In this study, a stable Cu/Fe oxide modified graphite felt electrode (Cu0.33Fe0.67NBDC-300/GF) was fabricated via a one-step hydrothermal method and subsequent thermal treatment, which used a bimetallic metal–organic framework (MOF) with 2-aminoterephthalic acid (NH2BDC) ligand as the precursor. The Cu0.33Fe0.67NBDC-300/GF electrode was used as the cathode for sulfamethoxazole (SMX) degradation in the heterogeneous EF process. The coexistence of the FeII/FeIII and CuI/CuII redox couples significantly accelerates the regeneration of FeII and promotes the generation of active free radicals (•OH and •O2−). FeIV was detected during the process, which indicates that the high-valent iron-oxo species was produced in near-neutral pH conditions. The removal efficiency of SMX (10 mg L−1) can reach 100.0% within 75 min over a wide pH range (4.0–9.0). After five cycles, the electrode retained a high stability and an outstanding catalytic capacity. Furthermore, the mechanisms and pathways for SMX degradation were proposed, the products and intermediates of SMX were analyzed, and the toxicity was evaluated. It was found that the toxicity decreased after degradation. This study displays a novel strategy for building an efficient and stable self-supporting electrode for treating antibiotic wastewater.

Ferrate(VI) pre-treatment and subsequent electrochemical advanced oxidation processes: Recycling iron for enhancing oxidation of organic pollutants

Pharmaceutical residues as emerging pollutants constitute an issue of growing concern owing to their continuous accumulation in the aquatic environment. The removal of such compounds from water requires the development of efficient technologies as well as a better understanding of degradation mechanisms since expensive treatment strategies are necessary for the total mineralization of these compounds. This paper focuses on the potential of combining ferrate (FeVI) oxidation with either anodic oxidation (AO) or electro-Fenton (EF) processes, in comparison with standalone processes, for the degradation of a model pharmaceutical compound (paracetamol). Particularly, recycling iron from FeVI oxidation as catalyst for the EF process is reported for the first time. A particular emphasis is done on identification/quantification of by-products, comparison of degradation pathways and evolution of acute toxicity during the treatment in order to provide novel insights on the possibility to use selective or non-selective oxidation processes for the removal of emerging organic pollutants in a cost-effective way. The most promising treatment strategy appeared to be the use of ferrate as a pre-oxidation step and further as iron source for the electro-Fenton process. Fast degradation kinetics, low aromatic by-products formation and strong decrease of the acute toxicity of the treated solutions highlighted a promising potential of this combined process for transformation of the persistent organic pollutant into harmless/biodegradable by-products.

Exploring the pressurized heterogeneous electro-Fenton process and modelling the system

• Hydrogen peroxide electrogeneration was boosted with the application of pressure. • Clofibric acid abatement was significantly enhanced with pressurized electro-Fenton. • Specific energy consumption was reduced when working above atmospheric pressure. • Pressure did not affect leaching nor damaged the heterogeneous catalyst. • Mathematical modelling based on experimental data represented the system behavior. In this research, a bench-scale installation was tested for the heterogeneous electro-Fenton treatment of clofibric acid. The setup consists of a pressurized flow-through electrochemical cell equipped with a catalyst fluidized-bed and aerated with a jet mixer. The novelty of the research is two-fold: the use of the pressurized-jet aerator on an electro-Fenton treatment is tested and it is one of the first studies combining pressure with heterogeneous catalysis in electro-Fenton. Moderate relative pressures, up to 2 bar, were analyzed. Initially, the electrogeneration of hydrogen peroxide was tested, showing that it is remarkably boosted by the application of pressure. Then, the elimination of clofibric acid by means of an electro-Fenton treatment was carried out at 0.12 and 0.25 A, using iron-containing alginate beads as the catalyst. Regardless of the current intensity, the increase from atmospheric pressure to 1 gauge bar boosted the elimination of the pollutant and reduced the specific energy consumption of the electrochemical cell. Specifically, at 0.25 A an abatement higher than 98% was achieved in 8 h at atmospheric pressure while only 1 h was required at 1 bar of gauge pressure. However, a further increase of the pressure to 2 bar did not report a major improvement. Moreover, the effect of pressure on the catalyst was analyzed, concluding that the integrity of the alginate beads was not compromised by pressure. In fact, the iron leaching was very similar at 0, 1 and 2 bar: around 30% after 8 h of treatment. Finally, a mathematical model was developed, using the experimental data to obtain the necessary fitting parameters, which allowed to understand better the behavior of the bench-scale reaction system.

Electro-oxidation combined with electro-Fenton for decolorization of caramel colorant aqueous solution using BDD electrodes

This study focused on the effects of the electro-oxidation combined with electro-Fenton process using boron-doped diamond (BDD) electrodes on the degradation of biorefractory food colorant caramel. Aqueous solutions containing Caramel Class IV, Caramel Class III and Acid Orange 7 were comparatively treated by electrochemical advanced oxidation processes, including electro-oxidation (EO), electro-Fenton (EF) and electro-oxidation combined with electro-Fenton (EO + EF). The experiments were performed in a stirred flask reactor using an inflator pump coupled with an undivided cell with BDD and Ti/Pt electrodes. In EF and EO + EF process, Fe2+ was added as catalyst. The independent parameters of air flow rate, Fe2+ concentration and current intensity in the range of 0.5–1.5 L/min, 0.05–0.2 mM and 0.4–1.5 A, respectively, were studied. The effect of electrode material on decolorization was also examined. The decolorization of pigment was enhanced with increasing air flow rate and current intensity due to the greater production of active species. The color decay was fitted to a pseudo-first-order kinetics. Complete decolorization of caramel colorant was realized with BDD electrodes under all experimental conditions and the highest kinetic constant of 2.3*10−2 min−1 was found under these conditions. This study highlighted the potential of EO + EF process with BDD electrodes for efficient degradation of caramel colorant.

Ultrasonic Formation of Fe3O4-Reduced Graphene Oxide-Salicylic Acid Nanoparticles with Switchable Antioxidant Function.

We demonstrate a single-step ultrasonic in situ complexation of salicylic acid during the growth of Fe3O4-reduced graphene oxide nanoparticles (∼10 nm) to improve the antioxidant and antiproliferative effects of pristine drug molecules. These nanoparticles have a precisely defined electronic molecular structure with salicylic acid ligands specifically complexed to Fe(III)/Fe(II) sites, four orders of magnitude larger electric surface potential, and enzymatic activity modulated by ascorbic acid molecules. The diminishing efficiency of hydroxyl radicals by Fe3O4-rGO-SA nanoparticles is tenfold higher than that by pristine salicylic acid in the electro-Fenton process. The H+ production of these nanoparticles can be switched by the interaction with ascorbic acid ligands and cause the redox deactivation of iron or enhanced antioxidation, where rGO plays an important role in enhanced charge transfer catalysis. Fe3O4-rGO-SA nanoparticles are nontoxic to erythrocytes, i.e., human peripheral blood mononuclear cells, but surpassingly inhibit the growth of three cancer cell lines, HeLa, HepG2, and HT29, with respect to pristine salicylic acid molecules.

Microbial fuel cells as an electrical energy source for degradation followed by decolorization of Reactive Black 5 azo dye

The problem of wastewater has long been ubiquitous and has great consequences for the environment and its inhabitants. Microbial fuel cells (MFCs) have enormous potential for the treatment of wastewaters polluted with azo dyes. The amount of energy that can be produced from a single-chamber MFC is sufficient to perform decolorization and degradation of such dyes, which are widely used in the textile industry. This study on the azo dye, reactive black 5 (RB5), provides an alternative method through three parallel-connected MFCs to obtain electricity that directly serves for the dye’s electrochemical degradation. We examined degradation followed by decolorization of RB5 using Fe and Pt electrodes, together with H2O2, to achieve the electro-Fenton process. The amount of voltage produced (295 mV), the current density (276 mA m−3) and the power density (50 mW m−3) were sufficient to degrade 25 mg L-1 RB5 dye with 0.5 mM H2O2 in just 2 h. The dye degradation mechanism was investigated using UV–VIS, FT-IR and HPLC-MS/MS. The ecotoxicity of the degradation products was assessed using a bacterial model, Aliivibrio fischeri. These tests showed that there was successful degradation of the dye to products whose toxicity is less than that of RB5.

Fabrication of FeOCl nanoparticles modified microchannel carbon cathode for flow-through electro-Fenton degradation of refractory organic pollutants

This study described an electro-Fenton filter installing a FeOCl nanoparticles loaded microchannel carbon (MC) cathode for rapid removal of refractory organic pollutants. In 120 s of residence time, more than 1.4 mmol/L of H2O2 was produced via oxygen reduction reaction and the active sites were mesoporous carbon in microchannels with the average diameter of 28 μm. FeOCl nanoparticles was the active sites for efficiently activating H2O2 to generate OH and electric field accelerates the cycle of Fe(III)/Fe(II). For the electro-Fenton process taking the phenol solution with initial concentration of 20 mg/L as a target, 98% of phenol and 51% of total organic carbon were removed at a residence time of 450 s. Similar performances were observed for the degradation of atrazine or sulfamethoxazole. The good performance was ascribed to the micrometer-level diffusion distance for O2 and organics and the effective conversion of H2O2 to OH over FeOCl nanoparticles. And it is high-proportioned for OH in microchannels to contact with and oxidize organics. The study demonstrated that the electro-Fenton filter on basis of catalysts loaded microchannel carbon cathodes was a new approach to generate and utilize OH efficiently.

Fe2+, Fe3+, Co2+ as highly efficient cocatalysts in the homogeneous electro-Fenton process for enhanced treatment of real pharmaceutical wastewater

The electro-Fenton process (EFP) has been known as an effective process with highly outstanding oxidation power. In this study, the real pharmaceutical wastewater was successfully mineralized via EFP by using boron-doped diamond (BDD) anode and carbon-fiber brush cathode (CFB) with Fe2+/Fe3+/Co2+ cocatalysts. The effect of various parameters, including the electrode, ratio of cocatalysts, current density, pH, and O2 flow rate, was investigated. The TOC and COD removal efficiencies of 92% and 93%, respectively, were achieved. For the increase in biodegradability, BOD5/COD ratio increased from 0.1 to 0.69 after 2 h in the presence of Fe2+/Fe3+/Co2+ cocatalysts under optimal conditions in a batch experiment (current density of 17 mA cm−2, initial pH of 3, a Fe2+/Fe3+/Co2+ ratio of 1:1:2, O2 flow rate of 0.5 L min−1). In comparison, TOC and COD removal efficiencies were reached 81% and 85% after 10 h of reaction in a continuous-flow condition, respectively. The oxidation of pharmaceutical organic pollutants was mainly found by the electrochemically produced hydroxyl (OH) and sulfate (SO4−) radicals, followed by pseudo-first-order kinetics. Hence, EFP demonstrated the feasibility of potential technology for the treatment of real pharmaceutical wastewater.

Coupling electrode aeration and hydroxylamine for the enhanced Electro-Fenton degradation of organic contaminant: Improving H2O2 generation, Fe3+/Fe2+ cycle and N2 selectivity

To improve H2O2 generation and Fe3+/Fe2+ cycle simultaneously for enhancing Electro-Fenton performance, the electrode aeration (EA) and hydroxylamine sulfate (HA) were coupled. With dimethyl phthalate (DMP) as main target contaminant, combination of HA and EA greatly accelerated the degradation of DMP and exhibited a synergy in the pH of 2.0–6.9 through promoting the key reactions, including electrochemical two-electron reduction of O2 into H2O2 and redox cycles of Fe3+/Fe2+, which then improved the generation of hydroxyl radicals (·OH). The coupling EA and HA reduced the use of HA and converted most of HA into environment-friendly N2 (60.1–62.1% of HA products), while HA/solution aeration(SA) system consumed HA rapidly and the generated N2 only accounted for 5.8–6.7% of HA products. Furthermore, compared with HA/SA and EA Electro-Fenton systems, enhancement degree of DMP degradation in HA/EA Electro-Fenton process was higher in actual waterbody than in ultrapure water. The coupling EA and HA in the Electro-Fenton process could solve the low Fe3+/Fe2+ cycle efficiency and low H2O2 production simultaneously, and improve the N2 selectivity of HA transformation, which advanced its application in practical environmental remediation.

Valorization of UWWTP effluents for ammonium recovery and MC elimination by advanced AOPs

The main objective of this study was to generate ready-to-use revalorized irrigation water for fertilization from urban wastewater treatment plant (UWWTP) effluents. The focus was on controlled retention of NH4+ and microcontaminants (MC), using nanofiltration. Retentates generated were treated by solar photo-Fenton at circumneutral pH using Ethylenediamine-N, N′-disuccinic acid (EDDS) iron complexing agent. Solar photo-Fenton degradation efficacy was compared with electrooxidation processes as anodic oxidation, solar-assisted anodic oxidation, electro-Fenton and solar photoelectro Fenton. Finally, phytotoxicity and acute toxicity tests were performed to demonstrate the potentially safe reuse of treated wastewater for crop irrigation. Nanofiltration was able to produce a ready-to-use permeate stream containing recovered NH4+. (valuable nutrient). Solar photo-Fenton treatment at circumneutral pH would only be of interest for rapid degradation of contaminants at less than 1 mg/L in nanofiltration retentates. Other alternative tertiary treatments, such as electrooxidation processes, are a promising alternative when a high concentration of MC requires longer process times. Anodic oxidation was demonstrated to be able to eliminate >80% of microcontaminants and solar-assisted anodic oxidation significantly reduced the electricity consumption. Electro-Fenton processes were the least efficient of the processes tested. Phytotoxicity results showed that irrigation with the permeates reduced germination, root development was mainly promoted and shoot development was positive only at low retention rate (concentration factor = 2). Acute and chronic Daphnia magna toxicity studies demonstrated that the permeate volumes should be diluted at least 50% before direct reuse for crop irrigation.