The efficacious of AOP-based processes in concert with electrocoagulation in abatement of CECs from water/wastewater
At a Glance
Section titled âAt a Glanceâ| Metadata | Details |
|---|---|
| Publication Date | 2023-04-11 |
| Journal | npj Clean Water |
| Authors | Zeinab Hajalifard, Milad Mousazadeh, Sara Khademi, Nastaran Khademi, Mehdi Hassanvand Jamadi |
| Institutions | University of Johannesburg, Shoolini University |
| Citations | 59 |
| Analysis | Full AI Review Included |
Executive Summary
Section titled âExecutive SummaryâThis review analyzes the integration of Electrocoagulation (EC) with Advanced Oxidation Processes (AOPs) for the efficient abatement of Contaminants of Emerging Concern (CECs) in water and wastewater.
- Core Value Proposition: Hybrid EC-AOP systems significantly improve pollutant removal efficiency, particularly for recalcitrant CECs (e.g., pharmaceuticals, PFASs), compared to standalone EC or AOP methods.
- Mechanism Synergy: EC acts as an effective pretreatment, removing colloidal particles and suspended solids rapidly, which otherwise hinder the slower, mineralization-focused AOPs (Electro-Oxidation, Fenton, Ozone).
- High Performance Systems: Integrated EC-Fenton/Photo-Fenton processes demonstrated near-complete removal of phenolic compounds in oil refinery wastewater. EC-EO using Boron Doped Diamond (BDD) anodes offers the highest oxidation potential for complete organic mineralization.
- PFAS Abatement: EC-EO treatment using zinc and Ti4O7 electrodes proved highly effective, achieving greater than 95% removal of long-chain Per- and polyfluoroalkyl substances (PFASs).
- Cost and Energy Efficiency: EC integration often reduces overall energy consumption and chemical requirements, mitigating the high operational costs typically associated with AOPs.
- Industrial Readiness Gap: Despite promising lab results, there is a critical lack of comprehensive data and systematic approaches for scaling up these integrated processes to industrial scale using real, complex wastewaters.
- Research Focus Needed: Future research must address the removal of specific CECs, including herbicides, pesticides, microplastics, and micropollutants, where current data is insufficient.
Technical Specifications
Section titled âTechnical Specificationsâ| Parameter | Value | Unit | Context |
|---|---|---|---|
| COD Removal (EC-EO) | 97 | % | Textile Wastewater (Fe/Al, BDD electrodes) |
| TOC Removal (EC-EF) | 100 | % | Cyanobacteria/Cyanotoxins (EC(Fe)-EF(Ti/IrO2)) |
| PFAS Removal (EC-EO) | >95 | % | Long-chain PFASs (Zn/SS, Ti4O7 electrodes) |
| Ibuprofen Removal (EC-O3) | >70 | % | Municipal Wastewater (EC-O3 hybrid process) |
| Energy Consumption (EC-EO) | 18.2 | kWh/m3 | Tannery Wastewater (Hybrid process) |
| Energy Consumption (EC-O3) | 8 | kWhr/m3 | Landfill Leachate (EC(Fe)-O3-Sonication process) |
| Optimal pH (EC-Fenton) | ~3 | - | Required for efficient hydroxyl radical generation |
| Anode Material (Highest Oxidation Potential) | BDD | - | Electro-Oxidation (Most suitable for mineralization) |
| Current Density (EC-O3) | 10 | mA/cm2 | Industrial Park Effluent (Al electrodes) |
| Cefixime Removal (Peroxi-EC) | 99.98 | % | Crude Drug Effluent (Fe electrodes) |
Key Methodologies
Section titled âKey MethodologiesâThe efficacy of hybrid EC-AOP systems relies on optimizing the synergy between coagulation (EC) and radical generation (AOP).
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Electrocoagulation (EC) Pretreatment:
- Function: Rapid removal of suspended solids, colloids, and charged species via flocculation using in-situ generated metal hydroxides (Al(OH)3 or Fe(OH)n).
- Electrode Selection: Iron (Fe) or Aluminum (Al) sacrificial anodes are typically used. Fe electrodes are preferred in EC-O3 and EC-Fenton systems due to their catalytic activity (Fe2+/Fe3+ cycle).
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Electro-Oxidation (EO) Integration:
- Anode Type: Non-active anodes, such as Boron Doped Diamond (BDD), are used for direct mineralization via physiosorbed hydroxyl radicals (OH). Active anodes (IrO2, RuO2) are used for indirect oxidation (mediated anodic oxidation).
- Process Flow: EC is often used sequentially before EO to reduce the operating time and energy consumption required for EO to handle high solids loads.
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EC-Ozone (EC-O3) Hybridization:
- Mechanism: Ozone (O3) is bubbled into the EC reactor. Fe2+ ions released from the anode catalyze the decomposition of O3 into highly reactive hydroxyl radicals (OH), enhancing oxidation (catalytic O3/Fe2+).
- Reactor Design: Novel reactors are employed to minimize floc breakage caused by O3-induced turbulence, ensuring efficient coagulation and oxidation occur simultaneously or sequentially.
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Electro-Fenton (EF) and Peroxi-Coagulation (Peroxi-EC):
- EF Process: Fe2+ ions are generated in situ from the sacrificial Fe anode, and hydrogen peroxide (H2O2) is generated electrochemically at the cathode (O2 reduction). These react to form OH radicals (Fenton reaction).
- Peroxi-EC Process: H2O2 or persulfate (S2O82-) is added externally to the EC system, reacting with the electrochemically generated Fe2+ ions to produce OH or sulfate radicals (SO4-).
- Condition Requirement: Both processes require highly acidic conditions (pH less than or equal to 3) for optimal OH radical generation.
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EC-UV/Photo-Fenton Integration:
- Mechanism: UV light (or solar irradiation) is introduced to enhance radical generation by photoreduction of Fe3+ complexes back to Fe2+, or by photolysis of H2O2, thereby accelerating the Fenton or EC process.
- Sustainability: Solar photo-Fenton is highlighted as the most environmentally sound option due to reduced energy demand for the light source.
Commercial Applications
Section titled âCommercial ApplicationsâThe integrated EC-AOP technologies are highly effective for treating complex, recalcitrant industrial effluents and municipal wastewater containing CECs.
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Industrial Wastewater Treatment:
- Textile Industry: Decolorization and COD/TOC removal from dye-bath effluents (EC-O3, EC-EF).
- Oil Refinery: Near-complete removal of phenolic compounds (EC-Fenton/Photo-Fenton).
- Tannery Effluent: High COD and color removal (EC-EO, EC-UV).
- Distillery Effluent: Effective COD and color reduction (EC-O3, EC-UV).
- Steel Industry: Cyanide and phenol removal (EC-O3, EC-Photo-Fenton).
- Food Processing: Treatment of olive oil mill, pasta, and cookie processing wastewater.
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Environmental Remediation:
- Landfill Leachate: Degradation of highly toxic and complex organic matter (EC-EO, EC-O3-Sonication).
- Groundwater/Drinking Water: Mitigation of viruses, bacteria, and CECs like Metribuzin (EC-EO, EC-UV).
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Contaminants of Emerging Concern (CECs) Abatement:
- PFASs: Highly effective removal of perfluorooctanoic acid (PFOA) and related compounds (EC-EO with Ti4O7).
- Pharmaceuticals: Degradation of antibiotics (Ciprofloxacin, Cefixime), anti-inflammatories (Ibuprofen), and endocrine disruptors (Bisphenol A, Estrone) using EC-EF and Peroxi-EC.
- Pesticides/Herbicides: Successful treatment of effluents containing Malathion and Pentachlorophenol (EC-Peroxomonosulfate).
View Original Abstract
Abstract Combining electrocoagulation with another process is a potential strategy for increasing the efficiency of water and wastewater pollutant removal. The integration of advanced oxidation processes (AOPs) and electrocoagulation (EC) demonstrates improved performance. The mechanism of the EC combined with ozone (O 3 ), hydrogen peroxide (H 2 O 2 ), sulfate radicals, electrooxidation (EO), Fenton/electro-Fenton, and UV is discussed. This review sheds light on EC-AOP hybrid processes in terms of their mechanisms, development, challenges, and their potential application for the removal of contaminants of emerging concern (CECs). The majority of the articles claimed improved performance of the EC process when combined with AOP as a pre-treatment, especially in terms of removing recalcitrant contaminants. For instance, the integrated EC-Fenton/photo-Fenton processes have been shown to be a promising treatment to virtually complete removal of the phenolic compounds in oil refinery wastewater. In EC-EO process, boron doped diamond (BDD) anode, despite being costly electrode, has the highest oxidation potential and is therefore the most suitable type for the mineralization of organic pollutants. PFASs are more effective at being removed from water through zinc and Ti 4 O 7 electrodes in EC-EO treatment. Furthermore, the peroxone and synergistic effects between O 3 and coagulants played almost equal dominant role to removal of ibuprofen using hybrid EC-O 3 . However, enough data for conducting these integrated processes at industrial scale or with real wastewaters do not exist, and so there is a lack for comprehensive and systematic approaches to address complexity of such systems. Although a great number of papers were focused on the degradation of effluents from different industries, viruses, and pharmaceuticals, there is not sufficient research in terms of the removal of herbicides, pesticides, microplastics, and micropollutants.