Emerging organic contaminants in wastewater - Understanding electrochemical reactors for triclosan and its by-products degradation

At a Glance

Metadata	Details
Publication Date	2019-12-30
Journal	Chemosphere
Authors	Cátia Magro, Eduardo P. Mateus, Juan Manuel Paz-García, Alexandra B. Ribeiro
Institutions	Universidad de Málaga, Universidade Nova de Lisboa
Citations	59
Analysis	Full AI Review Included

MPCVD Boron-Doped Diamond (BDD) for High-Efficiency Electrochemical Degradation of Emerging Organic Contaminants (EOCs)

This technical documentation analyzes the use of Boron-Doped Diamond (BDD) electrodes in electrochemical reactors for the advanced oxidation and degradation of Triclosan and its hazardous by-products in real wastewater matrices.

Executive Summary

This study validates the critical role of Boron-Doped Diamond (BDD) anodes in Advanced Oxidation Processes (AOPs) for environmental remediation, demonstrating superior performance for specific contaminants compared to Mixed Metal Oxide (MMO) electrodes.

Application: Electrochemical degradation of Emerging Organic Contaminants (EOCs)—specifically Triclosan (TCS), Methyl-Triclosan (MTCS), and chlorophenols—in secondary wastewater effluent.
Material Comparison: Niobium/Boron-Doped Diamond (Nb/BDD) plates were tested against Titanium/Mixed Metal Oxide (Ti/MMO) wires in both Batch (EBR) and Flow (EFR) reactors.
Key Performance Metrics (EBR): Ti/MMO achieved degradation below the detection limit for TCS and 2,4,6-trichlorophenol (TCP) in 4 h. However, BDD was clearly more efficient at degrading MTCS (47% to 84% removal).
Mechanism: BDD demonstrated a stronger tendency for water oxidation, promoting media acidification (pH 8 to 3.8) and enhancing the generation of highly potent hydroxyl radicals (•OH), crucial for mineralization.
Scale-Up Potential: The Electrochemical Flow Reactor (EFR) design, mimicking secondary settling tanks, achieved high degradation efficiencies (41% to 87% for all four contaminants in approximately 1 hour), suggesting BDD/MMO-based reactors are viable for operational implementation.
6CCVD Advantage: 6CCVD provides the high-quality, heavily Boron-doped SCD and PCD materials required for commercial BDD anode fabrication, offering custom dimensions (up to 125mm) and integrated metallic substrates (Nb, Ti).

Technical Specifications

The following table summarizes the critical material specifications and performance data extracted from the electrochemical reactor experiments.

Parameter	Value	Unit	Context
Anode Material (BDD)	Nb/BDD Plate	N/A	High-oxidation potential material
BDD Plate Dimensions (H x L x T)	50 x 80 x 1	mm	Geometry tested in the study
Substrate Material	Niobium (Nb)	N/A	Used for BDD deposition
Current Density (Ti/MMO Optimum)	7	mA/cm²	Chosen for faster kinetics, less intermediates
Current Density (Nb/BDD Optimum)	10	mA/cm²	Chosen for higher MTCS degradation
Max EFR Retention Time	55	min	Equivalent treatment time in flow reactor
Max TCS Degradation (EBR, 4h)	< Detection Limit	N/A	Achieved using Ti/MMO (7 mA/cm²)
Max DCP Degradation (EBR, 4h)	94	%	2,4-dichlorophenol removal (Ti/MMO)
MTCS Degradation (BDD EFR, 1h)	49	%	Methyl-Triclosan removal (Nb/BDD)
MTCS Degradation (BDD EBR, 4h)	84	%	Methyl-Triclosan removal (Nb/BDD)
TOC Decay (EBR, Ti/MMO)	36	%	Measure of total mineralization potential

Key Methodologies

The degradation of EOCs was performed using two reactor setups comparing Nb/BDD and Ti/MMO anodes under controlled electrochemical conditions.

Reactor Design: Experiments used an Electrochemical Batch Reactor (EBR) and an Electrochemical Flow Reactor (EFR), the latter mimicking a secondary settling tank with a 9 mL/min flow rate (55 min retention time).
Electrode Specifications:
- Nb/BDD: Plate, H=50 mm, L=80 mm, T=1 mm. Used as anode or cathode.
- Ti/MMO: Permaskand wire, Ø = 3 mm, L = 80 mm. Used as anode or cathode.
Electrolyte Matrix: Secondary effluent collected from a wastewater treatment plant (Lisbon, Portugal), spiked with 0.8 mg/L of each target compound (TCS, MTCS, DCP, TCP).
Operational Control: Constant current was maintained by a power supply, monitoring voltage. Experiments were run in duplicate, in dark conditions, at a controlled room temperature of 22 °C.
Kinetic Analysis: EBR samples were collected every 15 minutes for 4 hours. EOC removal followed pseudo first-order kinetics (R² ≥ 0.9).
Analytical Techniques: EOCs were quantified using Solid-Phase Extraction (SPE) followed by High-Performance Liquid Chromatography (HPLC) with DAD/Fluorescence detection. Mineralization potential was assessed via Total Organic Carbon (TOC) decay using a Vario TOC select analyzer.

6CCVD Solutions & Capabilities

This research confirms Boron-Doped Diamond (BDD) as an essential material for developing highly effective electrochemical AOPs for complex wastewater treatment. 6CCVD is uniquely positioned to supply the advanced diamond materials and integrated electrode structures necessary for replicating and scaling this technology.

Applicable Materials

The study requires a highly conductive diamond material deposited onto a metallic substrate (Nb/BDD). 6CCVD recommends:

6CCVD Material	Application Relevance	Customization & Advantage
Heavy Boron-Doped Diamond (BDD) SCD/PCD	High oxidizing power and radical generation (crucial for MTCS degradation and acidification).	Custom doping levels for tailored conductivity. Thickness control (0.1µm to 500µm BDD layer).
Custom Substrate Integration	The paper used Niobium (Nb) substrates.	We provide BDD deposited directly onto engineer-specified refractory metals (Nb, Ta, Mo, Ti) for robust, high-performance anodes.
Polycrystalline Diamond (PCD) Wafers	Cost-effective and scalable platform for large-area anodes.	Plates available up to 125 mm diameter. Superior uniformity and adhesion compared to third-party BDD providers.

Customization Potential

The success of electrochemical degradation is highly dependent on anode geometry and connectivity. 6CCVD offers full customization tailored to specific reactor geometries (batch, flow, microfluidic).

Custom Dimensions and Shapes: We provide plates and wafers in custom sizes beyond the 50 mm x 80 mm tested, enabling scale-up from R&D (EBR/EFR) to industrial pilot projects.
Precision Machining: In-house laser cutting services allow for intricate electrode patterns, necessary for optimizing mass transport and current density distribution within advanced flow reactors (like the EFR tested).
Advanced Metalization: We offer internal metalization capabilities (Au, Pt, Pd, Ti, W, Cu) to create robust electrical contacts on the BDD surface or substrate, critical for maintaining stability at high current densities (e.g., 7-10 mA/cm²).

Engineering Support

The paper noted that while Ti/MMO was cheaper, it produced detectable by-products, whereas the Nb/BDD system, despite cost, offers higher performance for certain recalcitrant compounds and supports superior water oxidation. Material selection is paramount.

6CCVD’s in-house PhD team specializes in CVD diamond material science and electrochemical applications. We provide consultation on optimizing the BDD material properties—including thickness, doping concentration, and substrate choice (e.g., maximizing sp³/sp² ratio) validated to improve Emergent Organic Contaminant (EOC) degradation projects.
We assist engineers in selecting the optimal balance between cost-effectiveness (PCD) and absolute performance (SCD) for BDD anodes in wastewater treatment systems.

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

Tech Support

Original Source

DOI: https://doi.org/10.1016/j.chemosphere.2019.125758

References

2006 - Boron doped diamond electrode for the wastewater treatment [Crossref]
2019 - Insights into the kinetics of intermediate formation during electrochemical oxidation of the organic model pollutant salicylic acid in chloride electrolyte
2009 - Pilot Scale scale performance of the electro-oxidation of landfill leachate at boron-doped diamond anodes [Crossref]
2004 - Occurrence of methyl triclosan, a transformation product of the bactericide triclosan, in fish from various lakes in Switzerland [Crossref]
2018 - Effects of triclosan in breast milk on the infant fecal microbiome [Crossref]
2015 - Decontamination of wastewaters containing synthetic organic dyes by electrochemical methods. An updated review [Crossref]
2019 - A reduction in triclosan and triclocarban in water resource recovery facilities’ influent, effluent, and biosolids following the U.S. Food and Drug Administration’s 2013 proposed rulemaking on antibacterial products [Crossref]
1988 - Critical review of rate constants for reactions of hydrated electrons, hydrogen atoms and hydroxyl radicals (⋅OH/⋅O− in aqueous solution [Crossref]
2005 - Aquatic degradation of triclosan and formation of toxic chlorophenols in presence of low concentrations of free chlorine [Crossref]
2019 - Nationwide reconnaissance of five parabens, triclosan, triclocarban and its transformation products in sewage sludge from China [Crossref]