Improving the Treatment Efficiency and Lowering the Operating Costs of Electrochemical Advanced Oxidation Processes

At a Glance

Metadata	Details
Publication Date	2021-08-24
Journal	Processes
Authors	Thorben Muddemann, Rieke Neuber, Dennis Haupt, Tobias Graßl, Mohammad Issa
Institutions	Clausthal University of Technology, Deutsches Zentrum für Luft- und Raumfahrt e. V. (DLR)
Citations	28
Analysis	Full AI Review Included

Technical Documentation & Analysis: High-Stability BDD Anodes for Advanced Electrochemical Oxidation Processes (EAOP®)

Executive Summary

This research validates the use of next-generation, Tantalum (Ta)-based Boron-Doped Diamond (BDD) anodes for significantly improving the efficiency and reducing the Operational Expenses (OPEX) of Electrochemical Advanced Oxidation Processes (EAOP®) in wastewater treatment.

Extreme Longevity: The novel Ta-based BDD anode demonstrated a wear rate resulting in an extrapolated service life of approximately 18 years (based on linear wear from 15 µm to 6 µm thickness).
OPEX Reduction: This extended lifetime reduces electrode replacement OPEX by up to a factor of 5 compared to previous Niobium (Nb)-based BDD standards, making EAOP® economically viable for industrial applications.
High Mineralization Efficiency: Both tested reactor configurations (BDD-Stainless Steel Cathode and BDD-Gas Diffusion Electrode) achieved a mineralization rate of >99.5% for high-strength phenolic wastewater (initial COD 2000 mg L⁻¹).
Energy Optimization: The BDD-GDE system, which generates H₂O₂ in situ, showed superior energy performance, requiring only 29.42 kWh kgCOD⁻¹ to reach the target discharge concentration (99 mg L⁻¹).
System Performance: The BDD-GDE configuration achieved up to 135% higher degradation efficiency compared to the BDD-stainless steel system, confirming the synergistic effect of combined ·OH and H₂O₂ oxidation.
Material Innovation: The success is attributed to the optimized multi-layer BDD coating structure and the use of a Ta substrate, coupled with an adapted current density operation strategy.

Technical Specifications

The following hard data points were extracted from the investigation into the Ta-based BDD anodes and reactor performance:

Parameter	Value	Unit	Context
Anode Substrate Material	Tantalum (Ta)	N/A	Thickness: 2 mm
BDD Coating Thickness (Initial)	15	µm	Triple multi-layer coating
BDD Coating Thickness Loss	4.8	%	Measured over 12,222 h of operation
Estimated BDD Service Life	~18	years	Extrapolated lifetime (15 µm down to 6 µm)
Initial Wastewater COD	2000	mg L⁻¹	Artificial phenolic wastewater
Target Discharge COD	99	mg L⁻¹	German legal discharge limit
Mineralization Rate Achieved	>99.5	%	Achieved in 6 days
Current Density (j) Range	0.5 to 0.1	kA m⁻²	Adapted to prevailing COD concentration
Specific Energy Consumption (BDD-GDE)	29.42	kWh kgCOD⁻¹	Energy demand to reach discharge limit
Specific Energy Consumption (BDD-StSteelC)	39.45	kWh kgCOD⁻¹	Energy demand to reach discharge limit
Electrode Replacement OPEX Reduction	Up to 5	Factor	Ta-BDD vs. standard Nb-BDD
Electrode Distance	2	mm	Maintained by PTFE frame

Key Methodologies

The experimental success relied on precise material engineering and controlled electrochemical parameters:

BDD Anode Fabrication: The DIACHEM® BDD anode was manufactured using the Hot-Filament Activated Chemical Vapor Deposition (HF-CVD) process.
Coating Structure: A specialized triple multi-layer coating (15 µm thickness) was deposited onto a 2 mm Tantalum (Ta) substrate.
Cell Design: Filter press reactors (SSZ100/ES and SSZ100/GDE) were constructed from stainless steel, featuring a flat gasket design to protect anode edges and ensure a consistent 2 mm electrode distance.
Electrolyte Flow: Wastewater (WW) was fed upwards at a constant velocity of 0.298 ± 0.019 m s⁻¹ to ensure homogeneous flow and high turbulence.
Current Density Adaptation: Current density (j) was dynamically adjusted based on the prevailing COD concentration, starting at 0.5 kA m⁻² and reducing to 0.1 kA m⁻² to optimize energy usage and minimize mass transfer limitations.
GDE Operation: The Gas Diffusion Electrode (GDE) was supplied with synthetic air (3 × stoichiometric excess O₂) at an air compartment pressure of approximately 40 mbar to maximize in situ H₂O₂ generation.
Lifetime Assessment: BDD coating thickness was monitored using beta backscattering and 3D laser scanning microscopy over 12,222 h of operation to determine the wear rate and estimate long-term stability.

6CCVD Solutions & Capabilities

The findings of this research—particularly the emphasis on BDD longevity, custom substrate integration (Ta), and optimized thickness (15 µm)—align perfectly with 6CCVD’s core manufacturing expertise. We provide the high-performance BDD materials necessary to replicate and advance this critical EAOP® technology.

Applicable Materials for EAOP®

To achieve the 18-year projected lifetime and high efficiency demonstrated in this study, researchers require highly stable, low-defect BDD material.

6CCVD Material Recommendation	Specification	Application Relevance
Heavy Boron-Doped PCD	High conductivity, high oxygen overpotential, robust structure.	Ideal for high-yield ·OH generation and complete organic mineralization (EAOP®).
Custom Substrates (Ta/Nb)	Substrates up to 10 mm thickness.	Direct replacement for the Ta substrate used in the study, ensuring chemical and electrochemical stability.
Custom BDD Thickness	SCD or PCD layers from 0.1 µm up to 500 µm.	Allows precise tuning of coating thickness (e.g., 15 µm used here) for specific lifetime and cost targets.

Customization Potential

The success of the DIACHEM® electrode relies on specific dimensions and integration features. 6CCVD offers full customization to meet these engineering requirements:

Custom Dimensions: We provide plates and wafers up to 125 mm (PCD) and offer precision laser cutting services to match the exact flow channel geometries (e.g., 82.6 cm² or 41.3 cm² active areas) required for filter press cell designs (Figure 2).
Substrate Flexibility: While the paper focused on Ta, 6CCVD can supply BDD coatings on various refractory metals (Ta, Nb, Ti, W) up to 10 mm thick, allowing engineers to optimize cost and performance based on specific chemical environments.
Advanced Metalization: The GDE utilized Ag-plated Ni mesh. For robust electrical contacts and integration layers on the BDD anode, 6CCVD offers internal metalization capabilities, including Ti, Pt, Au, Pd, W, and Cu, ensuring long-term contact stability in aggressive electrochemical media.
Polishing: For applications requiring ultra-low surface roughness (e.g., specific flow dynamics or thin-film deposition), 6CCVD provides polishing services down to Ra < 1 nm (SCD) or Ra < 5 nm (Inch-size PCD).

Engineering Support

The significant finding regarding the 18-year lifetime is a direct result of optimizing the BDD material and operational parameters (current density adaptation). 6CCVD’s in-house team of PhD material scientists and electrochemists specializes in:

Material Selection: Assisting clients in selecting the optimal BDD grade (PCD vs. SCD) and substrate material (Ta vs. Nb) to maximize longevity and minimize OPEX for similar Wastewater Treatment (EAOP®) projects.
Process Integration: Providing consultation on BDD integration into complex reactor designs, including thermal management and electrical contact strategies, crucial for high-current density operation.
Global Supply Chain: Ensuring reliable, DDU or DDP global shipping of custom BDD electrodes, eliminating supply chain bottlenecks for industrial scale-up.

For custom specifications or material consultation, visit 6ccvd.com or contact our engineering team directly.

View Original Abstract

Electrochemical advanced oxidation processes (EAOP®) 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 EAOP® 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 L−1); 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 EAOP® 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.

Tech Support

Original Source

DOI: https://doi.org/10.3390/pr9091482

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