Kinetic Insights and Process Selection for Electrochemical Remediation of Industrial Dye Effluents Using Mixed Electrode Systems
At a Glance
Section titled âAt a Glanceâ| Metadata | Details |
|---|---|
| Publication Date | 2025-09-29 |
| Journal | Preprints.org |
| Authors | Carmen Barcenas-Granjeno, MartĂn PachecoâĂlvarez, Enric Brillas, Miguel A. Sandoval, Juan M. PeraltaâHernĂĄndez |
| Analysis | Full AI Review Included |
Executive Summary
Section titled âExecutive SummaryâThis study systematically compares Anodic Oxidation (AO), Electro-Fenton (EF), and Photoelectro-Fenton (PEF) processes using Boron-Doped Diamond (BDD) and Mixed Metal Oxide (MMO) electrodes for the remediation of complex industrial dye effluents.
- Process Selection Rules: The optimal electrochemical advanced oxidation process (EAOP) depends critically on pollutant load, dye structure, and UV availability, confirming that decolorization alone is an insufficient metric for efficiency.
- Robust Dark Option (EF-BDD): Electro-Fenton using BDD electrodes proved the most robust dark treatment, achieving rapid decolorization (>98% in 23 min) and consistent mineralization (~70% COD removal) for the high-load ternary dye mixture.
- Fastest UV Option (PEF-MMO): Photoelectro-Fenton using MMO electrodes delivered the fastest kinetics and highest mineralization (up to ~90% COD removal), leveraging efficient UVA photolysis of Fe(III)-carboxylate complexes adsorbed on the hydrated MMO surface.
- Anodic Oxidation Limitation: AO processes (AO-BDD and AO-MMO) were significantly slower for complex mixtures, requiring nearly 60 minutes for completion, as competitive adsorption limited the access of multiple chromophores to the anode surface.
- Kinetic Drivers: AO-BDD dominates only at very low pollutant loads due to high surface flux of BDD(âąOH). At medium to high loads, bulk radical generation (H2O2/Fenton) becomes essential, favoring EF and PEF.
- Energy Efficiency: EF-BDD is the most energy-efficient option under dark conditions, while PEF-MMO is superior when UVA irradiation (sunlight or artificial) is available, minimizing treatment time for high mineralization levels.
Technical Specifications
Section titled âTechnical Specificationsâ| Parameter | Value | Unit | Context |
|---|---|---|---|
| Anode Materials Tested | BDD, MMO (Ti/IrO2-SnO2-Sb2O5) | - | Electrochemical advanced oxidation processes (EAOPs) |
| Cathode Materials Tested | Graphite, BDD, MMO | - | Used for H2O2 electrogeneration (EF/PEF) |
| Current Density (j) Range | 20, 40, 60 | mA cm-2 | Applied constant current |
| Supporting Electrolyte | 50 | mM | Na2SO4 |
| Initial pH | 3.0 | - | Optimized for Fenton chemistry |
| Fe2+ Concentration (EF/PEF) | 0.5 | mM | Catalyst concentration |
| Reactor Volume | 250 | mL | Thermostated batch reactor |
| Operating Temperature | 25 ± 1 | °C | Controlled environment |
| UVA Lamp Power | 6 | W | Black-light lamp (PEF process) |
| UVA Wavelength (lambdamax) | ~360 (355-370) | nm | Emission band |
| UVA Irradiance | 7.5 ± 5% | W m-2 | Measured at liquid surface |
| Air Flow Rate | 1.5 | L min-1 | For dissolved O2 supply |
| Decolorization Efficiency | >98 | % | Achieved by EF-BDD and PEF-MMO (Ternary Mix) |
| Time to 90% Decolorization | 22-23 | min | EF-BDD and PEF-MMO (120 mg L-1 mixture) |
| COD Removal (EF-BDD) | ~70 | % | Ternary mixture (200 mg L-1, 60 min) |
| COD Removal (PEF-MMO) | ~90 | % | Ternary mixture (200 mg L-1, 60 min) |
Key Methodologies
Section titled âKey Methodologiesâ- Electrochemical System: Experiments were conducted in a thermostated 250 mL batch reactor under continuous magnetic stirring (500 rpm) at 25 °C.
- Electrode Configurations: Six configurations were evaluated, encompassing AO, EF, and PEF processes using BDD and MMO (Ti/IrO2-SnO2-Sb2O5) anodes, paired with graphite, BDD, or MMO cathodes. All electrodes had a 4 cm2 surface area.
- Chemical Preparation: Solutions were prepared using 50 mM Na2SO4 electrolyte and adjusted to pH 3.0. EF and PEF assays included 0.5 mM FeSO4·7H2O as the Fenton catalyst.
- H2O2 Generation: Continuous air bubbling (1.5 L min-1) was maintained to supply dissolved oxygen for the two-electron reduction of O2 at the cathode, generating H2O2 in situ for Fenton reactions.
- Photo-Assistance (PEF): PEF processes utilized a 6 W UVA black-light lamp (360 nm) positioned 2.5 cm above the solution, delivering 7.5 W m-2 irradiance to promote the photoreduction of Fe3+ complexes and enhance radical flux.
- Kinetic Analysis: Decolorization was monitored via UV-Vis spectrophotometry and fitted to pseudo-first-order kinetics (Ln(A0/A) = kat).
- Mineralization and Efficiency Assessment: Mineralization was quantified by Chemical Oxygen Demand (COD) decay. Energy consumption was normalized against COD removal (ECCOD, kWh·(g COD)-1) to compare true process sustainability.
Commercial Applications
Section titled âCommercial ApplicationsâThe findings provide actionable guidelines for optimizing electrochemical treatment systems in industrial settings dealing with complex organic pollutants.
- Textile and Dyeing Wastewater Treatment: Directly applicable to treating real industrial effluents characterized by high color, chemical recalcitrance, and complex mixtures of azo and anthraquinone dyes.
- Optimized EAOP Selection: Enables engineers to select the most efficient and cost-effective EAOP configuration based on site-specific conditions:
- Dark Operation: EF-BDD is recommended for robust, consistent performance where UV light is unavailable (e.g., indoor facilities or night operation).
- UV/Solar Integration: PEF-MMO is the preferred choice when solar energy or artificial UVA can be integrated, maximizing mineralization speed and minimizing energy demand per unit of COD removed.
- Electrode Material Specification: Provides clear evidence that BDD is superior for surface-driven oxidation (low loads/simple matrices), while MMO surfaces, when coupled with UV, excel in bulk photo-Fenton chemistry for complex, high-load effluents.
- Sustainable Water Reuse: Achieving high COD removal (up to 90%) facilitates the potential reuse of treated water in industrial processes, significantly reducing freshwater consumption and aligning with Sustainable Development Goals (SDGs 6 and 12).
- Decentralized Systems: The operational simplicity and ambient conditions of EAOPs support the deployment of modular, decentralized treatment units at manufacturing sites.
View Original Abstract
The discharge of dye-laden effluents remains an environmental challenge since conventional treatments remove color but not the organic load. This study systematically compared anodic oxidation (AO), electro-Fenton (EF), and photoelectro-Fenton (PEF) processes for three representative industrial dyes, such as Coriasol Red CB, Brown RBH, and Blue VT, and their ternary mixture, using boron-doped diamond (BDD) and Ti/IrOâ-SnOâ-SbâOâ (MMO) anodes. Experiments were conducted in a batch reactor with 50 mM NaâSOâ at pH =3.0 and current densities of 20-60 mA cmâ»ÂČ. Kinetic analysis showed that AO-BDD was most effective at low pollutant loads, EF-BDD became superior at medium loads due to efficient HâOâ electrogeneration, and PEF-MMO dominated at higher loads by fast UVA photolysis of surface Fe(OH)ÂČâș complexes. In a ternary mixture of 120 mg Lâ»Âč of dyes, EF-BDD and PEF-MMO achieved >98 % decolorization in 22-23 min with pseudo-first order rate constants of 0.111-0.136 minâ»Âč, whereas AO processes remained slower. COD assays revealed partial mineralization of 60-80 %, with EF-BDD providing the most consistent reduction and PEF-MMO minimizing treatment time. These findings confirm that decolorization overestimates efficiency, and electrode selection must be tailored to dye structure and effluent composition. Process-selection rules allow concluding that EF-BDD is the best robust dark option, and PEF-MMO, when UVA is available, offers practical guidelines for cost-effective electrochemical treatment of textile wastewater.