A comparison of electrooxidation of phenol on boron doped diamond and mixed metal oxide anodes
At a Glance
Section titled âAt a Glanceâ| Metadata | Details |
|---|---|
| Publication Date | 2022-11-21 |
| Journal | Global NEST International Conference on Environmental Science & Technology |
| Authors | Borislav N. MalinoviÄ, Tijana DjuriÄiÄ, Helena Prosen, Aleksander Kravos, SaĹĄa MiÄin |
| Analysis | Full AI Review Included |
Executive Summary
Section titled âExecutive SummaryâThis study compares Boron Doped Diamond (BDD) and Mixed Metal Oxide (MMO) anodes for the electrooxidation (EO) of phenol in synthetic wastewater, focusing on efficiency, energy consumption, and by-product formation.
- Superior Anode Performance: BDD anodes consistently outperformed MMO (Ti/IrO2-RuO2) anodes under identical operating conditions (j=20 mA/cm2, 50 mg/L initial phenol).
- Highest Efficiency/Lowest EC: BDD achieved the maximum phenol removal (99.9% Ef) in the shortest time (60 min) when using NaCl as the supporting electrolyte, resulting in the lowest energy consumption (116.62 kWh/kgphenol).
- Electrolyte Dependence: MMO efficiency was extremely low (max 48.23% Ef) unless chlorine species were generated (via NaCl), confirming MMO relies heavily on indirect oxidation mechanisms.
- Toxicity Mitigation Recommendation: While NaCl provided the fastest removal, BDD with Na2SO4 (99.3% Ef) or H2SO4 (94.8% Ef) is recommended for industrial application due to the absence of toxic organochlorinated by-products.
- By-product Analysis: Treatment with NaCl (both BDD and MMO) generated chlorinated products (e.g., 2,4-dichlorophenol, chloroform). Non-chlorinated electrolytes primarily yielded less toxic organic acids (oxalic, acetic, formic acid) and quinone derivatives.
Technical Specifications
Section titled âTechnical Specificationsâ| Parameter | Value | Unit | Context |
|---|---|---|---|
| Initial Phenol Concentration (C0) | 50 | mg/L | Model wastewater |
| Current Density (j) | 20 | mA/cm2 | Constant applied current |
| Anode Material 1 | BDD on Nb | N/A | Inactive electrode |
| Anode Material 2 | MMO (IrO2/RuO2) on Ti | N/A | Active electrode |
| Cathode Material | Stainless Steel (SS) | N/A | EN 1.4301/AISI 304 |
| Anode Useful Area | 28.26 | cm2 | Both BDD and MMO |
| Reactor Volume | 400 | cm3 | Batch electrochemical reactor |
| Electrode Gap | 2 | cm | Distance between anode and cathode |
| Target Conductivity | ~3 | mS/cm | Achieved by electrolyte dosing |
| BDD (NaCl) Removal Ef | 99.9 | % | Achieved in 60 min |
| BDD (NaCl) Energy Consumption (EC) | 116.62 | kWh/kgphenol | Lowest recorded EC |
| BDD (Na2SO4) Removal Ef | 99.3 | % | Achieved in 160 min |
| MMO (NaCl) Removal Ef | 48.23 | % | Achieved in 120 min (Maximum for MMO) |
Key Methodologies
Section titled âKey MethodologiesâThe electrooxidation (EO) process was conducted in a batch reactor under controlled ambient conditions to compare the performance of BDD and MMO anodes.
- Wastewater Preparation: Synthetic wastewater was prepared by dissolving 99.5% phenol in distilled water to achieve an initial concentration of 50 mg/L.
- Electrolyte Selection and Dosing: Three supporting electrolytes were tested: NaCl (2 g/L), Na2SO4 (2 g/L), and H2SO4 (2.5 mL/L of 2 M solution). Concentrations were adjusted to maintain a consistent wastewater conductivity of approximately 3 mS/cm.
- Electrochemical Setup: A polyester batch reactor (400 cm3 volume) was used. The anode was either BDD on Nb or MMO (IrO2/RuO2) on Ti (28.26 cm2 area). The cathode was Stainless Steel (SS). The electrode distance was fixed at 2 cm.
- Process Operation: Electrolysis was performed at ambient temperature, stirred at 300 rpm, and controlled by a constant current density of 20 mA/cm2.
- Phenol Quantification: Phenol concentration before and after treatment was determined using the standard spectrophotometric method with 4-aminoantipyrine, verified by High-Performance Liquid Chromatography with Diode-Array Detection (HPLC-DAD).
- By-product Identification: Transformation products were analyzed using multiple chromatographic techniques:
- HPLC-DAD and Liquid Chromatography-Tandem Mass Spectrometry (LC-MS/MS) for non-volatile products.
- Solid-Phase Microextraction Gas Chromatography-Mass Spectrometry (SPME GC-MS) for volatile products (e.g., chloroform).
- Ion Chromatography (IC) for organic acids (e.g., oxalic, maleic, acetic).
Commercial Applications
Section titled âCommercial ApplicationsâThis research directly supports the engineering and optimization of electrochemical systems for industrial wastewater treatment, particularly focusing on recalcitrant organic pollutants.
- Industrial Wastewater Treatment: Direct application in treating effluents from industries known for high phenol content, including petroleum refining, petrochemicals, dyes, pesticides, and pharmaceuticals.
- Advanced Oxidation Processes (AOPs): Implementation of EO as a primary or polishing step in AOP trains, leveraging the high oxidizing power of BDD (direct hydroxyl radical generation).
- Electrode Material Selection: Provides critical data for selecting the optimal anode/electrolyte pair based on cost, desired treatment speed, and regulatory limits on chlorinated by-products. BDD is confirmed as the high-performance, low-toxicity option for direct oxidation.
- Process Design Engineering: Data on energy consumption (EC) and treatment time (t) allows engineers to size power supplies and estimate operational costs for full-scale EO reactors.
- Chlorine/Hypochlorite Production: The MMO anode (IrO2-RuO2) performance confirms its traditional role in chlorine generation, highlighting its utility when indirect oxidation via active chlorine species is desired (e.g., in disinfection or specific industrial processes).
View Original Abstract
Phenolic compounds are widespread in wastewater from various industries. Since the phenols are potentially carcinogenic for humans and hazardous for the environment, their presence in wastewater raises concerns. In this paper electrooxidation process was used for treatment of synthetical prepared wastewater containing phenol. Initial phenol concentration in wastewater was 50 mg/L with addition of different supporting electrolytes (NaCl, Na2SO4, H2SO4). The treatment was performed in a batch electrochemical reactor at constant current density of 20 mA/cm2. Boron doped diamond (BDD) and mixed metal oxide (MMO) anode materials were examined, and stainless steel was used as cathode. Phenol concentration before and after treatment was determined by standard spectrophotometric method with 4-aminoantipyrine, while transformation products were identified by different chromatographic methods. Experiments have shown that the treatment is very efficient and with low energy consumption, wherein the phenol removal efficiency mostly depends on the duration of treatment and the type of supporting electrolyte.