Fate of Diclofenac and Its Transformation and Inorganic By-Products in Different Water Matrices during Electrochemical Advanced Oxidation Process Using a Boron-Doped Diamond Electrode

At a Glance

Metadata	Details
Publication Date	2020-06-12
Journal	Water
Authors	Carolin Heim, Mohamad Rajab, Giorgia Greco, Sylvia Grosse, Jörg E. Drewes
Institutions	Technical University of Munich
Citations	17
Analysis	Full AI Review Included

Technical Documentation & Analysis: Electrochemical Advanced Oxidation using Boron-Doped Diamond (BDD)

This document analyzes the research paper “Fate of Diclofenac and Its Transformation and Inorganic By-Products in Different Water Matrices during Electrochemical Advanced Oxidation Process Using a Boron-Doped Diamond Electrode” to provide technical specifications and highlight how 6CCVD’s advanced MPCVD diamond solutions can support and scale this critical water treatment technology.

Executive Summary

The study successfully validates the use of Boron-Doped Diamond (BDD) electrodes in electrochemical Advanced Oxidation Processes (AOP) for the removal of persistent micropollutants.

Material Validation: Confirmed the high efficacy of BDD electrodes for generating powerful oxidants (hydroxyl radicals and ozone) necessary for water treatment.
Target Removal: Achieved complete removal of Diclofenac (DCF), a challenging pharmaceutical pollutant, across three complex water matrices (deionized, drinking water, and wastewater effluent).
Kinetic Dependence: DCF degradation kinetics were highly dependent on the water matrix complexity and the applied current density ($j$), requiring higher cumulative charge input (Q/V) in wastewater effluent (~670 mAh/L) compared to deionized water (~350 mAh/L).
By-Product Risk: Higher current densities (292 mA/cm²) accelerated DCF removal but significantly increased the formation of hazardous inorganic by-products, specifically oxohalogenides like chlorate (ClO₃^-) and perchlorate (ClO₄^-).
Mineralization Potential: Identified highly oxidized transformation products (TPs), including oxalic acid (TP_46), indicating near-complete mineralization of the parent compound.
Optimization Strategy: Recommended operating the BDD electrode at a moderate current density (e.g., 167 mA/cm²) to achieve an optimal balance between high DCF removal efficiency, minimized energy expenditure, and reduced formation of toxic inorganic by-products.

Technical Specifications

The following hard data points were extracted from the experimental setup and results:

Parameter	Value	Unit	Context
Electrode Material	Boron-Doped Diamond (BDD)	N/A	Anode layer on Niobium substrate
BDD Layer Thickness	5 to 7	µm	Used in DIACHEM® electrode stack
Electrode Surface Area	24 x 50	mm²	Per electrode pair
Initial DCF Concentration	50	µM	Spiked into all water matrices
Applied Current Densities ($j$)	42, 167, 292	mA/cm²	Operational range investigated
Complete DCF Removal Charge (DI Water, 167 mA/cm²)	~350	mAh/L	Required cumulative charge input
Complete DCF Removal Charge (WW Effluent, 292 mA/cm²)	~670	mAh/L	Highest charge required due to matrix complexity
Maximum Dissolved Ozone (Drinking Water, 292 mA/cm²)	1.07	mg/L	Measured oxidant concentration
Maximum Perchlorate (DI Water, 644 mAh/L)	0.921	mg/L	Highest measured inorganic by-product (IC data)
Recommended Operating $j$	167	mA/cm²	Optimized for economic and toxicological balance

Key Methodologies

The electrochemical advanced oxidation process relied on precise material fabrication and sophisticated analytical techniques:

Electrode Fabrication: A DIACHEM® electrode stack was utilized, consisting of a single anode/cathode pair of Niobium coated with a 5- to 7-µm-thick Boron-Doped Diamond (BDD) layer.
Reactor Setup: Experiments were conducted using a CONDIAPURE® test system. A Nafion cation exchange membrane was placed in direct contact with the electrodes to create a gap-free sandwich structure, promoting localized high current density and ozone formation.
Water Matrices: Three matrices were tested: deionized water, synthetic hard drinking water (high inorganic ion content), and real municipal wastewater effluent (high organic content). All were spiked with 50 µM DCF.
Electrolysis Conditions: Treatment was performed using constant current densities ($j$) of 42, 167, and 292 mA/cm². Treatment times were 30 min (DI water) or 60 min (DW/WW effluent).
Organic Analysis: DCF and Transformation Products (TPs) were analyzed using a serial two-dimensional Liquid Chromatography system (RPLC-HILIC) coupled with Electrospray Ionization Time-of-Flight Mass Spectrometry (ESI-TOF-MS).
Inorganic Analysis: Quantitative analysis of critical inorganic by-products (chloride, bromide, chlorate, and perchlorate) was performed using Ion Chromatography (IC). Semi-quantitative analysis of bromate and perbromate was performed using RPLC-HILIC-MS.

6CCVD Solutions & Capabilities

This research confirms BDD as the superior material for electrochemical AOP in complex water treatment scenarios. 6CCVD is uniquely positioned to supply the high-quality, customized BDD materials required to replicate, optimize, and scale this technology.

Research Requirement	6CCVD Solution & Value Proposition
Applicable Materials	High-Performance Boron-Doped Diamond (BDD): 6CCVD provides MPCVD BDD films with precise and uniform boron doping levels, critical for maximizing the oxygen evolution overpotential and ensuring efficient hydroxyl radical (OH•) generation, which drives the AOP. Our BDD is available in both Single Crystal (SCD) and Polycrystalline (PCD) formats.
Custom Thickness Control	SCD/PCD Thickness Precision: The study utilized 5-7 µm BDD films. 6CCVD offers SCD and PCD layers with thickness control ranging from 0.1 µm up to 500 µm, allowing researchers and engineers to precisely match the optimal film thickness for longevity and current density requirements.
Customization Potential	Scalable Electrode Dimensions: The experiment used 24 x 50 mm² electrodes. 6CCVD specializes in custom dimensions, supplying plates and wafers up to 125mm (PCD) in diameter. We offer precision laser cutting services to meet specific reactor geometries and enable seamless transition from lab-scale (like the CONDIAPURE® system) to industrial-scale electrochemical cells.
Substrate Integration & Contacts	Advanced Metalization Services: To ensure robust electrical contact and integration onto conductive substrates (such as the Niobium used in this study), 6CCVD offers in-house metalization capabilities, including deposition of Ti, Pt, Au, Pd, W, and Cu.
Engineering Support	AOP Optimization Consultation: The paper emphasizes the need to balance current density (e.g., 167 mA/cm²) to minimize toxic oxohalogenide formation (ClO₄^-, BrO₃^-). 6CCVD’s in-house PhD team provides expert material consultation to assist clients in selecting the optimal BDD specifications (doping level, thickness, surface finish) for similar Electrochemical Water Treatment projects, ensuring regulatory compliance and economic viability.
Surface Quality	Ultra-Low Roughness Polishing: For applications requiring minimal fouling or specific flow dynamics, 6CCVD offers superior polishing services, achieving roughness values of Ra < 1nm (SCD) and Ra < 5nm (Inch-size PCD).

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

View Original Abstract

The focus of this study was to investigate the efficacy of applying boron-doped diamond (BDD) electrodes in an electrochemical advanced oxidation process, for the removal of the target compound diclofenac (DCF) in different water matrices. The reduction of DCF, and at the same time the formation of transformation products (TPs) and inorganic by-products, was investigated as a function of electrode settings and the duration of treatment. Kinetic assessments of DCF and possible TPs derived from data from the literature were performed, based on a serial chromatographic separation with reversed-phase liquid chromatographyfollowed by hydophilic interaction liquid chromatography (RPLC-HILIC system) coupled to ESI-TOF mass spectrometry. The application of the BDD electrode resulted in the complete removal of DCF in deionized water, drinking water and wastewater effluents spiked with DCF. As a function of the applied current density, a variety of TPs appeared, including early stage products, structures after ring opening and highly oxidized small molecules. Both the complexity of the water matrix and the electrode settings had a noticeable influence on the treatment process’s efficacy. In order to achieve effective removal of the target compound under economic conditions, and at the same time minimize by-product formation, it is recommended to operate the electrode at a moderate current density and reduce the extent of the treatment.

Tech Support

Original Source

DOI: https://doi.org/10.3390/w12061686

References

2002 - Removal of pharmaceuticals during drinking water treatment [Crossref]
2005 - Oxidation of pharmaceuticals during ozonation of municipal wastewater effluents: A pilot study [Crossref]
2013 - Removal of diclofenac by conventional drinking water treatment processes and granular activated carbon filtration [Crossref]
2016 - Status of hormones and pain killers in wastewater effluents across several European states—Consideration for the EU watch list considering estradiol and diclofenac
2016 - Diclofenac and its transformation products: Environmental occurence and toxicity—A review [Crossref]
2015 - Biotransformation of trace organic chemical attenuation during groundwater recharge: How useful are first-order rate constants? [Crossref]
2008 - Oxidation of diclofenac with ozone in aqueous solution [Crossref]
2016 - Emerging pollutants and plants—Metabolic activation of diclofenac by peroxidases [Crossref]
2008 - Occurrence of diclofenac and selected metabolites in sewage effluents [Crossref]