| Metadata | Details |
|---|
| Publication Date | 2021-08-24 |
| Journal | Processes |
| Authors | Thorben Muddemann, Rieke Neuber, Dennis Haupt, Tobias GraĂl, Mohammad Issa |
| Institutions | Deutsches Zentrum fĂŒr Luft- und Raumfahrt e. V. (DLR), Clausthal University of Technology |
| Citations | 28 |
| Analysis | Full AI Review Included |
- Core Value Proposition: Development and validation of novel Electrochemical Advanced Oxidation Processes (EAOPÂź) reactors utilizing next-generation Tantalum-based Boron-Doped Diamond (Ta-BDD) anodes and Gas Diffusion Electrodes (GDEs) to significantly reduce operational costs (OPEX) and improve treatment efficiency.
- Anode Durability: The Ta-BDD anode demonstrated exceptional long-term stability, exhibiting only 4.8% thickness loss over 12,222 hours of operation, projecting an estimated service life of up to 18 years.
- Cost Reduction: This extended BDD lifetime reduces the OPEX for electrode replacement by up to a factor of 5 compared to previous Niobium-based BDD standards.
- System Efficiency (BDD-GDE): The BDD anode combined with a H2O2-generating GDE cathode achieved a degradation efficiency up to 135% greater than the BDD-stainless steel system.
- Energy Savings: The BDD-GDE system required substantially less energy for COD removal, consuming only 75% of the energy of the BDD-stainless steel system, 14% of the ozonation system, and 8% of the peroxonation system.
- Treatment Performance: Both novel electrolysis systems achieved near-complete mineralization (>99.5% COD removal) of high-strength phenolic wastewater (2000 mg L-1 initial COD).
| Parameter | Value | Unit | Context |
|---|
| Anode Material | Boron-Doped Diamond (BDD) | - | DIACHEMÂź on Tantalum (Ta) substrate |
| BDD Coating Thickness | 15 | ”m | Multi-layer coating |
| BDD Lifetime (Projected) | Up to 18 | years | Based on 4.8% loss over 12,222 h |
| Cathode Type (Cell A) | Stainless Steel | - | Hydrogen Evolution Reaction (HER) |
| Cathode Type (Cell B) | Gas Diffusion Electrode (GDE) | - | H2O2 generation (Printex L6 catalyst) |
| Initial COD Concentration | 2000 | mg L-1 | Artificial Phenolic Wastewater |
| Target COD Discharge Limit | 99 | mg L-1 | German regulatory standard |
| Electrolyte | 9 g L-1 Na2SO4 | - | Conductive salt |
| Current Density Range (j) | 0.5 to 0.1 | kA m-2 | Adapted operation |
| Electrode Gap Distance | 2 | mm | Maintained by PTFE frame |
| BDD-GDE Specific Energy (COD Discharge) | 29.42 ± 0.59 | kWh kgCOD-1 | Energy to reach 99 mg L-1 COD |
| BDD-SS Specific Energy (COD Discharge) | 39.45 ± 1.92 | kWh kgCOD-1 | Energy to reach 99 mg L-1 COD |
| GDE Air Stoichiometric Excess | 3 | Factor | O2 in synthetic air |
| GDE Air Compartment Pressure | Approx. 40 | mbar | - |
| OPEX Reduction (Electrode) | Up to 80 | % | Ta-BDD vs. Nb-BDD |
- Wastewater Simulation: Artificial wastewater containing 0.85 g L-1 phenol and 9 g L-1 Na2SO4 was used to simulate pharmaceutical effluent. Sulfate was chosen as the conductive salt to avoid the generation of hazardous chlorine species.
- Anode Manufacturing (DIACHEMŸ): BDD anodes were produced using Hot-Filament Chemical Vapor Deposition (HF-CVD) on a Tantalum (Ta) substrate, featuring a 15 ”m triple multi-layer coating optimized for durability.
- Reactor Design: Filter-press cells (SSZ100/ES and SSZ100/GDE) were constructed from stainless steel, incorporating a flat gasket design to protect the BDD anode edges from corrosive reactions and electric fields.
- Cathode Comparison:
- Cell (a) utilized a standard stainless steel cathode (H2 evolution).
- Cell (b) integrated a carbon-based GDE (Printex L6 on Ag-plated Ni mesh) into the endplate for in situ H2O2 generation, eliminating H2 evolution and lowering cathodic potential.
- Operational Strategy: Current density (j) was dynamically adjusted (from 0.5 kA m-2 down to 0.1 kA m-2) based on the decreasing COD concentration to prevent mass transfer limitations and optimize energy consumption throughout the batch treatment.
- Durability Assessment: The Ta-BDD anode was subjected to 12,222 hours of operation. Diamond coating thickness loss was measured using beta backscattering methodology, and surface morphology changes were analyzed using color 3D laser scanning microscopy (LSM).
- Process Comparison: Electrolysis results were compared against ozonation and peroxonation processes, using varied O3 generator power inputs and continuous H2O2 dosing for the peroxone tests.
- Decentralized Wastewater Treatment: Highly efficient and autonomous treatment of high-strength industrial effluents, particularly from pharmaceutical manufacturing (phenolic wastewater).
- Circular Economy Integration: Enables sustainable water reuse and ecological discharge by achieving >99.5% mineralization, minimizing toxic byproducts.
- Low OPEX EAOPÂź Systems: The 18-year projected lifetime of the Ta-BDD anode drastically lowers the long-term cost of ownership for industrial EAOPÂź installations.
- Renewable Energy Coupling: Optimized energy consumption (especially BDD-GDE) makes the system highly suitable for efficient coupling with intermittent renewable energy sources (e.g., Photovoltaic or Wind Turbine systems).
- In Situ Oxidant Generation: The GDE technology provides a clean, cost-effective method for generating H2O2 in situ, avoiding the complexities and costs associated with storing and dosing bulk chemical oxidants.
View Original Abstract
Electrochemical advanced oxidation processes (EAOPÂź) are promising technologies for the decentralized treatment of water and will be important elements in achieving a circular economy. To overcome the drawback of the high operational expenses of EAOPÂź systems, two novel reactors based on a next-generation boron-doped diamond (BDD) anode and a stainless steel cathode or a hydrogen-peroxide-generating gas diffusion electrode (GDE) are presented. This reactor design ensures the long-term stability of BDD anodes. The application potential of the novel reactors is evaluated with artificial wastewater containing phenol (COD of 2000 mg Lâ1); the reactors are compared to each other and to ozone and peroxone systems. The investigations show that the BDD anode can be optimized for a service life of up to 18 years, reducing the costs for EAOPÂź significantly. The process comparison shows a degradation efficiency for the BDD-GDE system of up to 135% in comparison to the BDD-stainless steel electrode combination, showing only 75%, 14%, and 8% of the energy consumption of the BDD-stainless steel, ozonation, and peroxonation systems, respectively. Treatment efficiencies of nearly 100% are achieved with both novel electrolysis reactors. Due to the current density adaptation and the GDE integration, which result in energy savings as well as the improvements that significantly extend the lifetime of the BDD electrode, less resources and raw materials are consumed for the power generation and electrode manufacturing processes.
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