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AZERBAIJAN CHEMICAL JOURNAL № 3 2023 ISSN 2522-1841 (Online)
ISSN 0005-2531 (Print)
UDC 541.13
AN OVERVIEW OF ELECTRO-FENTON TECHNOLOGY FOR ORGANIC WASTEWATER TREATMENT: OPTIMAL CONDITIONS AND ELECTRODES
SELECTION
Forat Yasir AlJaberi
Chemical Engineering Department, College of Engineering, Al-Muthanna University,
Al-Muthanna, Iraq
furat_yasir@yahoo.com
Received 11.03.2023 Accepted 19.05.2023
Several conventional methods have been employed to eliminate numerous types of pollutants from domestic and industrial wastewater. Electrochemical techniques are one of these treatment methods used in wastewater treatment. Electro-Fenton technology (EFT) is one type of electrochemical technique. The present review paper aims to provide readers with extensive information about the EFT general definitions, terminologies, mechanisms, fundamental conditions, and statistical analysis based on the published articles for the recent years. The core findings of this work proved that the EFT is more applicable for removing organic contaminants than inorganic ones because of the affinity degree between the adsorbents formed in the reactor and the pollutants. The most important conditions of this technology are the type of anode, the applied current, and the period of the treatment process. The development of the conventional cathode electrode was the most interested field in the literature. The advantages of EFT provide the ability to perform it as a primary or secondary treatment process with other conventional treatment processes. The statistical analysis shows that 68% of the selected cited articles achieved a high performance of EFT when it has performed alone while 32% of these cited articles attained the best performance of EFT in the integrated system with other technologies. The electro-Fenton method is a promising technology to treat wastewater, especially that involving organic pollutants.
Keywords: organic wastewater; electrochemical technologies; optimal conditions; statistical analysis. doi.org/10.32737/0005-2531-2023-3-70-82
Introduction
Huge amounts of wastewater are discharged from various domestic and commercial operations worldwide that are related with population blooms (Avancini et al. 2019, Xu et al. 2019a). A variety of organic pollutants is presented in domestic wastewater that varies in concentration and type depending on human requirements. Various industrial activities, such as textiles, food processing units, and the petroleum and petrochemical industries discharge large amounts of industrial wastewater (AlJaberi 2018a, Ghanbari et al 2020). Contaminated water may contains chemical oxygen demand (COD) and biochemical oxygen demand (BOD), total organic carbon (TOC), high salinity, oils, and toxic metals.
Therefore, wastewater should be treated before discarding into soil or aquatic systems using effective treatment technologies (Ta-laiekhozani et al. 2020, Xu et al. 2019a).
Several works have investigated the ability of different remediation systems to eliminate contaminants from wastewater to strict environmental regulations. Chemical, physical, and biological treatments are the most common treatment techniques employed for this purpose.
Electrochemical technologies are one of the most effective conventional treatment systems for eliminating various pollutants from wastewater discharged from different activities of industrial and domestic operations (AlJaberi 2018b, Meiramkulova et al. 2020). Electro-oxidation, electro-flotation, electro-coagulation, electro-dialysis, and electro-Fenton are the most popular types of electrochemical technique which are used individually or in combination with other conventional methods for removing various contaminants from wastewater and then reusing it according to legal standards (AlJaberi 2022, AlJaberi et al. 2023).
This work aims to analyse recent high-impact articles published in recent years to assess the electro-Fenton technology and its operating conditions, either alone or in integration with other conventional technologies. This review paper performs a new classification strategy that has not been conducted before rather than delving into the mechanism of the electro-Fenton technology (EFT), this investigation supplies an obvious view of the most critical findings.
Electro-Fenton Technology (EFT)
The chemical Fenton process is a conventional wastewater treatment method that produces hydroxyl radicals (OH*) from the reaction of hydrogen peroxide (H2O2) with iron ions (Betruguera et al. 2019), as explained in Eq. (1) to Eq. (7): Fe2+ + H2O2 -Fe3+ + H2O2-
Fe3+ + OH + OH-
Fe2+ + OH^2 + H+ OH + H2O2—+ H2O OH + Fe2+ — Fe3++ OH-
Fe2+ + O2H+
Fe + HO^2
Fe2+ + HO^2 + H+ —Fe3+ + H2O2 2HO 2 — H2O2 + O2
Since the chemical Fenton method is active only in an acidic condition, it was replaced by the electro-Fenton process, which is de-
(1) (2) (3)
(4)
(5)
(6) (7)
pends on the electro-generation of active hydroxyl radicals based on H2O2 catalysed by iron ions throughout an electrochemical cell (Rebecca et al. 2021) as explained in Fig. 1. The hydroxyl radicals can be employed to remediate wastewater by oxidising pollutants under the effect of various operating conditions, such as the configuration and materials of the electrodes, iron concentration, hydrogen peroxide concentration, solution pH, electrolytes, and current applied (Zhao et al. 2018, Nadais et al. 2018, Özcan et al. 2018).
Electro-Fenton alone for pollutants removal
Organic pollutants presented in waste-water was eliminated employing the EFT by Zhao et al. (2018). They attained high removal of COD with 6.38 kWh/kg energy consumption using Fluorine to the electrochemical cell to control the carbon structure and speeding up the recovery of iron ions within a solution pH range of (2-6) and 60 min of the contact time of 60 min. Nadais et al. (2018) conducted a biological electro-Fenton method to eliminate 97% of NSAID drugs from municipal wastewater at optimal variables values of applied voltage of 0.3 V, solution pH 2, 7.5 mM Fe (II), reaction time of 5 h, and airflow rate of 8 mL/min.
Fig. 1. Schematic of the Electro-Fenton process.
They proved that the acidic medium was more effective to remove drugs compared to the basic medium. Such conclusion was attained when a higher removal of TOC from dye wastewater containing naphthol blue-black and diazo dyes was investigated by Zcan et al. (2018) performing electro-Fenton technology. The highest removal of contaminants was attained after one hour of contact time and 300 mA of applied current and acidic medium. Liu et al. (2018) achieved 97% of ibuprofen removal from wastewater after 2 hours of reaction time, 7 mA/cm of current density, and pH 6.8 using a heterogeneous electro-Fenton process consuming 2.65 kWh/m of electrical energy. They verified that the supported ferric citrate cathode was effective for drugs removal from pharmaceutical wastewater.
Kaur et al. (2018) performed Ti/RuÜ2 electrode in a continuous electro-Fenton reactor to remove COD and colour from wastewater under the impact of the applied current (0.25-3 A) and the reaction time (15-175 min). They obtained 81% COD removal and 99% colour elimination at an applied current of 0.75 A within 137 min of the reaction time and 142 min of the retention time, consuming 15 kWh/kg COD of electrical energy. The core findings of this study proved the non-toxic nature of the remediated wastewater produced when EFT was employed. In contrast, Divyapriya et al. (2018) investigated the performance of EFT using a ferrocene-functionalized graphene oxide-based electrode for ciprofloxacin removal under the effect of applied voltage (-0.75 - -2.5 V) and solution pH (3-9). The highest removal efficiency of 99% was obtained at pH 7 and 2 hours of contact time. They found that there was no notable increase in pollutants elimination after the 5th-cycle of electrode reusability at any conditions of solution pH. He et al. (2018) used a (g-C3N4/ACF) electrode in an electro-Fenton reactor to remove TÜC from wastewater under the influence of the reaction time of (0-240 min), current density of (1-4 mA/cm ), and solution pH (2-7). They attained 91% of TÜC removal after 4 hours, 3 mA/cm2, and pH 3.
This study concluded that the supported electrode enabled the electro-generation of hydrogen peroxide and the regeneration of Fe(II) ions from surface-adsorbed Fe ions. While Zhao et al. (2019) have improved the formation of H2O2 to remove COD from cooking wastewater performing the fabrication of fluorinated activated carbon. The highest COD removal of 71% was achieved after 2 h and acidic medium. The main finding of this study is that the electro- generation of H2O2 is extremely influenced by the oxygen-involving groups of fluorinated activated carbon.
A three-dimensional iron foam was conducted by Zheng et al. (2019) as an electrode in an electro-Fenton reactor to eliminate COD and total nitrogen under the effect of the operating conditions of the initial COD concentration (5000-15000 ppm), applied current (100-400 mA), contact time (0-350 min), and solution pH (3-9). Within 6 h of electrolysis, they obtained 44% and 70% reduction in COD and total nitrogen content, respectively, using at solution pH 3 and 300 mA of applied current. They revealed that the electro-Fenton process with iron-foam particle cathode was a practicable method for folic acid wastewater treatment. The complete removal of pollutants was attained after 22 hours of the reaction time. In contrast, Yang et al. (2019) performed a gra-phene-based cathode to maximize H2O2 yield at current density of (4.16-58.33 mA/cm ) and solution pH 3 to obtain full removal of Imatinib drug from wastewater after 8 h of treatment time, consuming 14.3 kWh/g of electrical energy. Wang et al. (2018) compared the performance between a conventional cathode (CF) and modified cathode (MF) to eliminate sulfamethoxazole from wastewater using electro-Fenton technology. The TOC removal was 90% at neutral pH using the MF cathode in comparison to 61% achieved using the CF cathode by applying 50-500 mA of current for 300 min of reaction time. A tweaked graphite felt cathode was investigated by Ou et al. (2019) in electro-Fenton cell to eliminate aniline from wastewater under the influence of oxygen flow rate of 360 mL/min, solution pH 3, and (6-12
2
mA/cm ) of current density. They attained 97% of removal efficiency after 60 min and 10 mA/cm of current density. While Li et al. (2020) performed a graphite felt electrode in an electro-Fenton cell but with aeration assistant to remove TOC and dimethyl phthalate under the effects of solution pH and current density. They proved that for an increase of solution pH, the removal efficiency of pollutants will decrease. Therefore, the highest removal efficiency of 50% was achieved at solution pH 3 at 17.6 mA/cm2 of current density and 60 min of the reaction time. Another investigation of the EFT performance was done by Cao et al. (2020) using FeOx/CuNxHPC to remove phenol from wastewater attaining 82% of pollutants removal after 1.5 hour, -0.6 V of applied potential, and solution pH 6. They concluded that the present type of iron-oxide nanoparticles was suggested as the appropriate cathodic material for the applicable heterogeneous EFT. Ren et al. (2020) studied the performance of using updated graphite felt cathodes and DSA mesh anodes in an electro-Fenton cell. They obtained more than 90% of COD, NH3-N, TSS, and TP removal at flow rate of 30 mL/min and an applied voltage of 2.5 V. They demonstrated that the proposed electro-Fenton reactor could be employed as an energy-effective system for domestic wastewater treatment and reuse. However, Luo et al. (2020) tested another cathode composite of Cu-doped Fe@Fe2O3 core-shell nanoparticles as a catalyst on nickel foam to eliminate tetracycline from wastewater. The highest removal of tetracycline (98%) was achieved at acidic medium, 40 mA/cm of current density, and 120 min of treatment period. As found by this work that the doping of copper improved the producing paths of the reactive oxygen-species.
An efficient carbon felt cathode was developed by Zhu et al. (2020) to be used in electro-Fenton treatment of wastewater containing RhB dye. They achieved a complete removal efficiency of 20 mM RhB within 60 min of the treatment, -0.4 V of the applied cathode potential, solution pH 3, 50 mM N2SO4, 0.1 mM Fe2SO4, and 1.5 L/min of
the gas flow rate. This study found that any increment of the applied cathode potential above the optimal value will decrease the electro-generated of H2O2. While Wei et al. (2022) have performed a three-dimensional (3D) porous electrode in electro-Fenton system to eliminate COD from real acid wastewater. The electrode used in this study was made-up in-situ on a Ni foam substrate combined with nitrogen-doped carbon nano-tubes. The highest COD removal efficiency was attained at -0.7 V of the cathode potential, and 25 min of the contact time consuming 6.52 kWh/kg of energy. Dung et al. (2022) applied cobalt ferrite coated carbon felt as cathode in an electro-Fenton cell to remove tartrazine from wastewater under the effect of cobalt and iron contents and solvothermal temperature for synthesis conditions, as well as solution pH, current density, electrolytes, and tartrazine concentration. The highest removal efficiency of 97.05% was attained at 4 mM of Fe and 2 mM of Co precursors, 220°C of sol-vothermal temperature, solution pH 3, 8.33 mA cm-2 of current density, 50 mM of sodium sulfate, and 50 mg of tartrazine consuming electrical energy of 8.24 kWh/kg tartrazine after 40 min of the reaction time. They proved that the elimination of pollutants decreases as the solvothermal temperature and initial concentration of pollutants increased.
The performance of heterogeneous EFT using three-dimensional graphene was investigated Hajiahmadi et al. (2022) to eliminate antineoplastic medicine from wastewater. They attained 99.13% of 3 ppm of pollutants removal at pH 7, Pyrite 4.5 g/L, 300 mA of current efficiency after 2 hours of the reaction time. This study proved that the recyclable iron minerals derived from Pyrite was more better than Siderite, Magnetite, Limonite, and Hematite. A 98.8% of RhB dye from wastewater was obtained within 60 min by Gao et al. (2022) when they employed EFT containing a modified carbon felt cathode (AQS/PANI@CF) to increase the electro-
generation of hydrogen peroxide at 0.1 M N2SO4, 0.1 mM Fe(II) ions, solution pH 2, and - 0.5 V of the cathode potential. This study proved that the further addition of Fe(II) ions or more decrease of pH will reduce the RhB elimination due to precipitation of the ferric hydroxide and the occurring of side reactions at the more acidic medium.
A modified cathode of nitrogen-doped sludge-derived biochar (NSBC) was made-up by Xing et al. (2022) for electro-Fenton removal of sulfamethoxazole (95.72%) and TOC (85.11%) from wastewater consuming 12.03 kWh/kg of energy consumption at 50 mM Na2SO4, pH 3, 15 mA of current intensity, 4 mM of Fe(II), 500 mL/min of the aeration rate, and 120 min of the reaction time. The main conclusion of this study is the promising application of the optimum cathode (NSBC*@Ni-F). Gamarra-Guere et al. (2022) proved that the electro-Fenton TOC treatment was more efficient than Fenton, photo-Fenton, and electro-oxidation. The highest removal efficiency of TOC (35%) was attained at current density of 25 mA/cm2, 4 ppm of FE(II), 50 mM N2SO4, pH 3, and 20 min of the reaction time. This study found that the hydrogen peroxide/Fe(II) ratio is the most essential condition affecting the elimination of pollutants in Fenton-based methods.
Electro-Fenton in hybrid systems for pollutants removal
Several studies have conducted electro-Fenton process to eliminate organic pollutants in combination systems from wastewater released from various domestic and industrial activities. Zhang et al. (2018) integrated electro-Fenton and adsorption methods using in situ regenerating active-carbon to remove tetracycline from wastewater under the influences of flow rate (1.75-10.5 ml/min), solution pH (3-9), initial concentration of tetracycline (20-150 ppm), and applied current (20-110 mA). The maximum removal of 90% was attained at optimum conditions of 7 ml/min flow rate, 80 mA applied current after 2 hours of the reaction time, consuming 48.6 kWh/kg tetracycline of electrical energy. A hybrid system involving cathodic electro-Fenton and anodic photocatalysis was investiga-
ted by Xu et al. (2019) to eliminate phenol, BOD, COD, and TOC from coal gasification wastewater. The operating conditions were solution pH (1-7), airflow rate (0-0.6 L/min), initial COD concentration (100-400 ppm), and current density (5-20 mA/cm2). They achieving 84% COD removal at flow rate of 0.4 L/min, solution pH 3, current density of 10 mA/cm after 2 hours.
Casamada et al. (2019) proved the cost-effectiveness of the combination systems through the integration of electrocoagulation method involving iron electrodes and electro-Fenton method involving RuO2 or BDD anodes to remediate lactic acid bacteria (LAB) from wastewater under the effect of applied current (100 and 200 mA). The highest removal of pollutants was obtained at solution pH 5.7, RuO2 anode, and 2 hours of the contact time consuming total electrical energy of 8.2 kWh/m . The concept of integrating EFT with other technologies was performed by Arellano et al. (2020) to eliminate carboxylic acids and TOC from ionic oil under the effect of initial pollutant concentration (0.075-2.5 mM), catalyst dosage (0.1 and 0.2 mM), applied current (400-100 mA), anode materials BDD and Ti4O7, and 250 min of the contact time. They attained removal efficiencies of 67% and 78% of carboxylic acids and TOC, respectively, with 0.1 mM of catalyst dose and 0.4 kWh/g of energy consumption. Thor et al.
(2020) obtained 84% of colour removal at 0.012 mA/cm2 and solution pH of 3 when they employed a combination system involving EFT and photocatalytic fuel cell to remove colour under the influence of solution pH (3-10) and aeration. They evidenced that the in-situ production of OH radicals was the key parameter for dye wastewater remediation in the hybrid system.
A combined electro-Fenton and nanofil-tration process was used by Keller et al.
(2021) to convert cellobiose into glucose as a prior stage before transferred to another elec-tro-Fenton wastewater treatment process. The best degradation of 8 mM cellobiose was achieved at pH 3, 250C of the solution temperature, 500 mA of current applied, 5 mM FeSO4, 100 mM Na2SO4, and 20 mL/min O2. While Zheng et al. (2021) solved the reversible fouling of the nano-membrane filtration that was caused by the extracellular organic
pollutants (EOP) in microalgae harvesting through the combination with EFT. The optimal conditions that provide 100% of pollutants removal were -1.0 V of the applied voltage, solution pH 7, 0.05 M N2SO4 within 30 min of the treatment. They concluded that the membrane resistance increased without the combination of electro-Fenton process. An integrated system involves heterogeneous EFT and membrane microfiltration (NH2-MIL-88B(Fe)@CM) was invented by Ye et al. (2022) to eliminate naproxen drug from urban wastewater. They proved that the present combination was more significant for complete elimination of drug at 50 mA of applied current, 250C of solution temperature, pH 6.2, and 1.5 hour of the treatment compared to that obtained by the individual usage of these two technologies.
Other studies combined biological method with electro-Fenton technology, such as Li et al. (2019) to remove phenolic compounds from wastewater using a biological EFT based on a composite cathode of Fe-Mn/graphite under the effect of initial concentration of pollutants (20100 ppm), current density (10-1700 mA/m2), and solution pH. Baiju et al. (2018) integrated EFT with a biological method to enhance the biodeg-radability of leachate attaining COD removal efficiency of 97% after 90 min of the reaction time, 5 V of applied voltage, and solution pH 2. As well, Gholizadeh et al (2020) investigated the performance of integrating EFT with the biological system to remove contaminants from wastewater under the effect of initial concentration of phena-zopyridine drug (5-30 ppm), applied current (0.10.4 A), plant amount (5-25 g), treatment time (048 h), and solution pH (5-11). They found that 99% of drug removal could be obtained within 120 min at pH 7 and 0.2 A of applied current using 20 g of plant amount. Sathe et al. (2021) investigated the performance of bio-EFT- microbial fuel cell to degrade sodium dodecyl sulphate from contaminated water using catalytic cathode fabricated from iron oxide and activated carbon. The 87.4% removal efficiency of pollutants was obtained at natural
pH within 4 hours which was 1.5 times higher than that was obtained by the conventional method. They proved that power density (mW/m2) and polarization (mV) for the bioEFT- microbial fuel cell was higher than the conventional microbial fuel cell. Another study combined EFT and biological process was done by Aboudalle et al. (2021) to remove 100 ppm of metronidazole from wastewater using 50 mM Na2SO4 and 0.1 mM FeSO4-7H2O as supporting electrolyte. They attained 97% of antibiotic removal efficiency after 16 days of the reaction time, 200C of solution temperature, pH 3, and 100 mA of current intensity. This work verified that the integration system was more efficient compared to the conventional biological methods that required 120 h to achieve 58% of antibiotic elimination.
Statistical analysis of the EFT
Table 1 lists the operating parameters for the EFT process in the cited studies, which involves the type of pollutants, type of configuration, whether it is individual or hybrid, and the operating variables investigated. As observed that the employment of individual electro-Fenton system was the most operation configuration used by the cited works. The applied current, reaction time, type of anodes, and solution pH were the most investigated variables to achieve significant elimination while the studied responses by the cited works and their optimal conditions are listed in Table 2. Moreover, the type of anodes and cathodes performed by the cited works is clearly documented in Table 3 which reveals that the most developed electrode is the cathode. The statistical analysis of cited works is clearly presented in Figure 2 which shows that the electro-Fenton method is almost performed alone, rather than in combination systems, as explained in this study. Most integrated systems that use EFT have been revealed to be capable to eliminate small amounts of biological pollutants without releasing sludge emissions.
Table 1. Summary of the operational conditions for electro-Fenton studies
References Pollutants Alone or Hybrid Operational variables
He et al. (2018) TOC Alone pH, reaction time, and current density
Zcan et al. (2018) dyes Alone Applied current and reaction time
Zhao et al. (2018) COD Alone pH and reaction time
Baiju et al. (2018) COD Hybrid pH, reaction time, and applied voltage
Zhang et al. (2018) Tetracycline Hybrid pH, reaction time, applied current, and flow rate
Nadais et al. (2018) NSAIDs Alone pH, air flow, Fe (II) amount, applied voltage, and reaction time
Divyapriya et al. (2018) Ciprofloxacin Alone pH and reaction time
Liu et al. (2018) Ibuprofen Alone pH, reaction time, and current density
Kaur et al. (2018) COD Alone Applied current and reaction time
Li et al. (2019) Phenolic comp. Hybrid pH, reaction time, and current density
Yang et al. (2019) Imatinib Alone pH, reaction time, and current density
Zhao et al. (2019) COD Alone pH, reaction time, and applied voltage
Zheng et al. (2019) COD Alone pH, reaction time, and applied current
Ou et al. (2019) Aniline Alone pH, reaction time, current density, and oxygen flow rate
Wang et al. (2019) TOC Alone pH, reaction time, and applied current
Casamada et al. (2019) Lactic acid Hybrid pH, reaction time, and applied current
Xu et al. (2019b) COD Hybrid pH, reaction time, current density, and flow rate
Li et al. (2020) TOC Alone pH, reaction time, and current density
Cao et al. (2020) Phenol Alone pH, reaction time, and applied voltage
Ren et al. (2020) COD Alone Applied voltage and flow rate
Luo et al. (2020) Tetracycline Alone pH, reaction time, and current density
Gholizadeh et al. (2020) PhP Hybrid pH, reaction time, and applied current
Arellano et al. (2020) TOC Hybrid Reaction time and applied current
Thor et al. (2020) Color Hybrid pH and current density
Zhu et al. (2020) RhB dye Alone time of the treatment, the applied cathode potential, solution pH, amount of Na2SO4, amount Fe2SO4, and the gas flow rate
Keller et al. (2021) Cellobiose Hybrid pH, solution temperature, current applied, amount of FeSO4, amount of Na2SO4, flow rate of O2
Sathe el al. (2021) sodium dodecyl sulphate Hybrid pH, reaction time, cathode potential
Aboudalle et al. (2021) Metronidazole Hybrid reaction time, solution temperature, pH, and current intensity
Zheng et al. (2021) EOP Hybrid Applied voltage, solution pH, 0.05 M Na2SO4, the treatment time
Wei et al. (2022) COD Alone The cathode potential and reaction time.
Dung et al. (2022) Tartrazine Alone Fe and Co precursors, solvothermal temperature, solution pH, current density, electrolytes, initial concentration of tartrazine.
Hajiahmadi et al. (2022) Paclitaxel Alone pH, Pyrite 4.5 g/L, current efficiency, and reaction time after 2 hours
Ye et al. (2022) Naproxen Hybrid applied current, solution temperature, pH, and the treatment time
Gao et al. (2022) RhB dye Alone Reaction time, amount of Na2SO4, amount of Fe(II) ions, solution pH, and cathode potential
Xing et al. (2022) Sulfamethoxazole and TOC Alone Amount of Na2SO4, solution pH, current intensity, amount of Fe(II), the aeration rate, and the reaction time
Gamarra-Guere et al. (2022) TOC Alone current density, amount of FE(II), amount of Na2SO4, pH, and the reaction time
Table 2. Summary of the core results and optimal conditions for electro-Fenton studies
References Pollutants Optimal conditions Removal Efficiency (%) Energy consumption kWh/m3 or (kWh/kg)*
Zhao et al. (2018) COD 2-6 pH and 60 min 93 6.38*
Nadais et al. (2018) NSAIDs pH 2, 8 mL/min, 7.5 mM Fe (II), 0.3 V, and 5 h 97 2.4
Liu et al. (2018) Ibuprofen pH 6.8, 120 min, 7 mA/cm2 97 2.65*
Zcan et al. (2018) dyes pH 3, 300 mA, and 60 min
Divyapriya et al. (2018) Ciprofloxacin pH 7 and 120 min 99 NL
Kaur et al. (2018) COD 0.75 A and 175 min 81 15*
He et al. (2018) TOC pH 3, 240 min, and 3 mA/cm2 91 NL
Baiju et al. (2018) COD pH 2, 90 min, and 5 V 97 NL
Zhang et al. (2018) Tetracycline 120 min, 80 mA, and 7 mL/min 90 48.6*
Zhao et al. (2019) COD 2 h 71 29.7*
Zheng et al. (2019) COD pH 3, 350 min, and 300 mA 44 26*
Li et al. (2019) Phenolic comp. pH 3 and 22 h 100 NL
Yang et al. (2019) Imatinib pH 3 and 8h 100 0.014*
Wang et al. (2019) TOC pH 7 and 300 min 90 NL
Ou et al. (2019) Aniline pH 3, 60 min, and 360 mL/min 97 NL
Xu et al. (2019b) COD pH 3, 120 min, 10 mA/cm2, and 0.4 L/min 84 NL
Casamada et al. (2019) Lactic acid pH 5.7, and 120 min - 8.2
Li et al. (2020) TOC pH 3 and 60 min 55 130*
Cao et al. (2020) Phenol pH 6, 90 min, and (-0.6 V) 82 NL
Ren et al. (2020) COD 2.5 V and 30 mL/min 90 0.97
Luo et al. (2020) Tetracycline 2 h, and 40 mA/cm2 98 NL
Gholizadeh et al. (2020) PhP pH 7, 2 h, and 0.2 A 99 25*
Arellano et al. (2020) TOC 250 min 78 50*
Thor et al. (2020) Color pH 3 and 0.012 mA/cm2 84 NL
Keller et al. (2021) cellobiose pH 3, 250C, 500 mA, 5 mM FeSO4, 100 mM Na2SO4, and 20 mL/min O2 — —
Zhu et al. (2020) RhB dye 60 min, -0.4 V, pH 3, 50 mM Na2SO4, 0.1 mM Fe2SO4, and 1.5 L/min of the gas flow rate 100
Sathe el al. (2021) sodium do-decyl sulphate natural pH, 4 hours, and 600 mV 87 —
Aboudalle et al. (2021) Metronidazole 16 days, 200C, pH 3, and 100 mA 97 —
Zheng et al. (2021) EOP -1.0 V, pH 7, 0.05 M Na2SO4, 30 min of the treatment 100 —
Ye et al. (2022) Naproxen 50 mA, 250C, pH 6.2, and 1.5 hour 100 —
Wei et al. (2022) COD -0.7 V and 25 min 64 6.52*
Dung et al. (2022) Tartrazine 4 mM of Fe and 2 mM of Co precursors, 220 °C, pH 3, 8.33 mA/cm2, 50 mM of Sodium sulfate, and 50 mg of tartrazine 97 8.24*
Hajiahmadi et al. (2022) Paclitaxel pH 7, Pyrite 4.5 g/L, 300 mA, 2 hours 99 59.23*
Gao et al. (2022) RhB dye 60 min, 0.1 M Na2SO4, 0.1 mM Fe(II) ions, - 0.5 V, and pH 2 98.8 —
Xing et al. (2022) Sulfamethoxazole and TOC 50 mM Na2SO4, pH 3, 15 mA of current intensity, 4 mM of Fe(II), 500 mL/min of the aeration rate, and 120 min of the reaction time Sulfamethoxazole: 95.7 TOC: 85 12.03*
Gamarra-Guere et al. (2022) TOC 25 mA/cm2, 4 ppm of FE(II), 50 mM Na2SO4, pH 3, and 20 min of the reaction time 35 1.24
NL: Not listed by the cited study mentioned.
Table 3. Types of electrodes in the cited papers used Electro-Fenton technology
References Pollutants Anodes Cathodes
Zhao et al. (2018) COD Pt sheet F-doped porous carbon
Nadais et al. (2018) NSAID drugs Carbon brush Graphite plate
Zcan et al. (2018) TOC Boron doped diamond BBD Carbon felt
Liu et al. (2018) Ibuprofen RuO2/Ti Activated carbon fibers (ACFs) supported ferric citrate (Cit-Fe/ACFs)
Kaur et al. (2018) COD Ti/RuO2 Al sheet
Divyapriya et al. (2018) Ciprofloxacin Pt sheet Ferrocene-functionalized graphene ox-ide(Fc-ErGO-GF)
He et al. (2018) TOC Pt sheet Activated carbon fiber-supported graphite carbon nitride (g-C3NVACF)
Wang et al. (2018) TOC Graphene polyacrylamide carbonized aerogel/carbon felt (GPCA/CF) y-FeOOH graphene polyacrylamide carbonized aerogel (y-FeOOH GPCA)
Baiju et al. (2018) COD TiO2/Ti Graphite
Zhang et al. (2018) Tetracycline Round perforated DSA Graphite felt modified with carbon black and polytetrafluoroethylene (PTFE)
Xu et al. (2019) COD TiO2 Fe@Fe2O3/Carbon Felt
Casamada et al. Lactic acid bacteria Boron-doped diamond (BDD) air-diffusion cathode
(2019) (LAB) or RuO2-anode
Zhao et al. (2019) COD Pt sheet Fluorinated AC catalysts
Zheng et al. (2019) COD Graphitic rod Carbon felt
Yang et al. (2019) Imatinib drug DSA (dimensionally stable anode) Caibon felt modified with this electrochem-ically exfoliated graphene (EEGr-CF)
Ou et al. (2019) Aniline IrO2/Ti sheet Modified graphite felt
Li et al. (2019) COD Graphite felt Fe-Mn/graphite
Gholizadeh et al. (2020) Phenazopyridine drug Graphite sheet Graphite sheet
Li et al. (2020) TOC Ti/IrO2/RuO2 mesh Graphite felt
Cao et al. (2020) Phenol Pt sheet Glassy carbon (GC)
Ren et al. (2020) COD DSA mesh Modified graphite felt
Luo et al. (2020) Tetracycline Ti/IrO2-RuO2 Cu-doped Fe@Fe2O3 /Carbone Nano-Tubes composite
Zhu et al. (2020) RhB dye Pt sheet Carbone felt
Arellano et al. (2020) TOC BDD and Ti4O7 3D carbon felt
Thor et al. (2020) Color ZnO/C photoanode Carbon plate
Keller et al. (2021) Cellobiose Iridium-coated titanium felt Carbon paper
Zheng et al. (2021) Extracellular organic pollutants (EOP) Ti-mesh Fe-PC-CNT hollow fiber membranes
Sathe et al. (2021) Sodium dodecyl sulphate (SDS) Carbon felt anode Carbon felt anode
Aboudalle et al. (2021) Metronidazole Pt Three-dimensional graphite felt
Wei et al. (2022) COD Pt sheet Nitrogen-doped carbon nanotubes
Dung et al. (2022) Tartrazine Pt/Ti plate CoFe2O4/carbon felt
Hajiahmadi et al. (2022) Antineoplastic medicine Pt sheet Three-dimensional graphene-gas diffusion electrode (3DG-GDE)
Gao et al. (2022) RhB dye Pt sheet Modified carbon felt cathode (AQS/PANI@CF)
Xing et al. (2022) TOC Pt sheet Nitrogen-doped sludge-derived biochar (NSBC)
Gamarra-Guere et al. TOC Pt sheet Ti/Ruo,3Tio,7O2
(2022)
Ye et al. (2022) Naproxen drug IrO2-based plate Carbon cloth coated with carbon-PTFE
Fig. 2. A statistical analysis of cited studies that used EFT for wastewater treatment.
Conclusions
The present study has reviewed recent publications to provide an ease overview of the advances in electro-Fenton wastewater treatment whether it is employed alone or in combination systems with conventional methods, a statistical analysis was calculated. The core results proved that the EFT is more applicable to eliminate organic contaminants than inorganic ones without releasing sludge emissions, such as COD, BOD, TOC, oils, dyes, etc. due to the affinity degree between the adsorbents formed in the reactor and the contaminants. The type of anode used, the applied current, and the period of the treatment process are the most critical parameters of the electro-Fenton process. Moreover, integrating systems have concerned new re-
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ÜZVi CiRKAB SULARININ TOMiZLONMOSi Ü£ÜN ELEKTROFENTON TEXNOLOGiYASI iCMALI:
OPTiMAL §ORTLOR VO ELEKTRODLARIN SE0Mi
Forat Yasir Ol-Caberi
Mai§9t va sanaye girkab sularindan goxsayli girklandiricibrin gixarilmasi ügün bir nega ananavi üsuldan istifada olunur. Cirkab sularin tamizlanmasi ügün istifada olunan bela üsullardan biri da elektrokimyavi üsullardir. Elektro-fenton texnologiyasi (EFT) elektrokimyavi üsullarin növbrindan biridir. Bu icmalin maqsadi oxuculara son illarda darc olunmu§ maqabbr asasinda EFT-nin ümumi tarifbri, terminologiyasi, mexanizmbri, fundamental §artbri уэ statistik tahlili haqqinda geni§ malumat vermakdir. Bu i§in asas mticalari sübut etdi ki, EFT reaktorda amala galan adsorbentbrb girkbndiricibr arasinda yaxinliq daracasina göra qeyri-üzvi girkbndiricibrdan daha gox üzvi girkbndiricibrin gixanlmasinda tatbiq edilir. Bu texnologiyanin an vacib ¡jartbri anodun növü, tatbiq olunan carayan уэ tamizbma prosesinin müddatidir. Onanavi katod elektrodunun inki§afi adabiyyatda an maraqli saha olmu§dur. EFT-nin üstünlüyü onu digar ananavi emallarla birlikda ilkin уэ ya ikincil emal kimi hayata kegirmak qabiliyyatindadir. Statistik tahlil gösbrir ki, segilmi§ istinad edilan maqabbrin 68%-i tak tatbiq edildikda EFT-nin yüksak effektivliyina nail olub, bu istinad edilan maqabbrin 32%-i isa digar texnologiyalarla inteqrasiya olunmu§ sistemda EFT-nin an yax§i effektivliyim nail olub. Elektrofenton üsulu tullanti sularinin, xüsusan da tarkibinda üzvi girkbndiricibr olanlarin tamizlanmasi ügün perspektivli texnologiyadir.
Agar sözlar: üzvi tullanti sulari; elektrokimyavi texnologiyalar; optimal §arait; statistik tahlil.
ОБЗОР ЭЛЕКТРОФЕНТОННОЙ ТЕХНОЛОГИИ ДЛЯ ОЧИСТКИ ОРГАНИЧЕСКИХ СТОЧНЫХ ВОД:
ОПТИМАЛЬНЫЕ УСЛОВИЯ И ВЫБОР ЭЛЕКТРОДОВ
Форат Ясир Аль-Джабери
Для удаления многочисленных видов загрязняющих веществ из бытовых и промышленных сточных вод используется несколько традиционных методов. Электрохимические методы являются одним из таких методов, используемых для очистки сточных вод. Электро-фентонная технология (ЭФТ) является одним из видов электрохимических методов. Цель настоящего обзора - предоставить читателям обширную информацию об общих определениях, терминологии, механизмах, фундаментальных условиях и статистическом анализе ЭФТ на основе опубликованных статей за последние годы. Основные выводы данной работы доказали, что EFT более применима для удаления органических загрязнений, чем неорганических, из-за степени сродства между адсорбентами, образующимися в реакторе, и загрязняющими веществами. Наиболее важными условиями этой технологии являются тип анода, приложенный ток и период процесса очистки. Разработка традиционного катодного электрода была наиболее интересной областью в литературе. Преимущества EFT заключаются в возможности проводить ее в качестве первичного или вторичного процесса обработки вместе с другими традиционными процессами обработки. Статистический анализ показывает, что 68% отобранных цитируемых статей достигли высокой эффективности ЭФТ при его самостоятельном применении, в то время как 32% этих цитируемых статей достигли наилучшей эффективности ЭФТ в интегрированной системе с другими технологиями. Метод электрофентона является перспективной технологией для очистки сточных вод, особенно тех, которые содержат органические загрязнители.
Ключевые слова: органические сточные воды; электрохимические технологии; оптимальные условия; статистический анализ.
