Metronidazole Electro-Oxidation Degradation on a Pilot Scale

At a Glance

Metadata	Details
Publication Date	2024-12-31
Journal	Catalysts
Authors	Sandra Maldonado, Carlos Barrera-Díaz, Patricia Balderas‐Hernández, Deysi Amado-Piña, Teresa Torres-Blancas
Institutions	Instituto Tecnológico de Toluca, Tecnológico Nacional de México
Citations	3
Analysis	Full AI Review Included

Executive Summary

This study successfully demonstrated the pilot-scale electro-oxidation of Metronidazole (MTZ) using a Boron-Doped Diamond (BDD) anode and Stainless Steel (SS) cathode in a DiaClean® cell, focusing on optimizing current density for industrial pre-treatment viability.

High Degradation Efficiency: 100% MTZ removal (initial concentration 30 mg L^-1) was achieved at the optimal current density of 100 mA cm^-2 within 180 minutes in the 16 L batch reactor.
Biodegradability Enhancement: The key achievement was the significant increase in the biodegradability index (BOD₅/COD) from 0.67 (low biodegradability) to 0.93 (highly biodegradable) at 100 mA cm^-2, making the effluent suitable for subsequent conventional biological treatment.
Kinetics: The degradation follows pseudo-first order kinetics, yielding a maximum reaction rate constant (k₁) of 0.0258 min^-1 at 100 mA cm^-2.
Mineralization Limitation: Total Organic Carbon (TOC) removal remained low (max 29.9%), confirming the recalcitrant nature of MTZ and the formation of stable, low molecular weight organic acids (formic and acetic acid).
Economic Viability: The process is energetically viable for pre-treatment, with the highest tested condition (100 mA cm^-2 for 3 hours) resulting in a specific energy consumption of 0.049063 kWh m^-3, costing less than $1 USD per batch.

Technical Specifications

Parameter	Value	Unit	Context
Reactor Scale	16	L	Feed tank volume
Anode Material	BDD/Silicon	-	DiaClean® cell 101
Cathode Material	Stainless Steel	-	DiaClean® cell 101
Anode Surface Area	78.53	cm²	Electrode geometry (Disc)
Inner Electrode Gap	5	mm	Cell configuration
Electrolyte Support	0.05	M	Na₂SO₄ concentration
Initial MTZ Concentration	30	mg L^-1	Synthetic wastewater
Recirculation Flow Rate	286.92	L h^-1	Peristaltic pump setting
Optimal Current Density (J)	100	mA cm^-2	Highest degradation rate
Max MTZ Degradation	100	%	Achieved at 100 mA cm^-2 (180 min)
Max TOC Mineralization	29.9	%	Achieved at 100 mA cm^-2 (180 min)
Max Biodegradability Index	0.93	-	BOD₅/COD ratio at 100 mA cm^-2 (180 min)
Highest Reaction Rate (k₁)	0.0258	min^-1	Pseudo-first order constant (100 mA cm^-2)
Specific Energy Consumption (Ec)	0.049063	kWh m^-3	At 100 mA cm^-2 (3 hours)
BDD Boron Content	500	mg dm^-3	Anode specification
BDD Thickness	2.83	µm	Anode specification
BDD sp³/sp² Ratio	217	-	Anode specification

Key Methodologies

The electro-oxidation experiments were conducted at pilot scale in a batch recirculation system under galvanostatic control:

Electrochemical Setup: A DiaClean® cell model 101 (Adamant Technologies) was used, featuring a Boron-Doped Diamond (BDD) anode and a Stainless Steel (SS) cathode, separated by a 5 mm gap.
Solution Preparation: 16 L of synthetic wastewater containing 30 mg L^-1 MTZ was prepared, utilizing 0.05 M Na₂SO₄ as the supporting electrolyte.
Operation Conditions: The system was operated galvanostatically at three distinct current densities: 30 mA cm^-2, 50 mA cm^-2, and 100 mA cm^-2, for a total treatment time of 180 minutes.
Recirculation: The solution was continuously circulated between the tank and the cell at a high flow rate of 286.92 L h^-1, ensuring a short retention time (0.557 h) within the cell.
Pollutant Quantification: MTZ concentration was monitored using Ultra-High-Performance Liquid Chromatography (UHPLC) at 320 nm. Carboxylic acids were quantified using UHPLC with an Aminex HPX-87H column.
Water Quality Assessment: Mineralization was tracked via Total Organic Carbon (TOC) analysis. Biodegradability was determined by measuring the Biochemical Oxygen Demand after five days (BOD₅) and calculating the BOD₅/COD ratio.

Commercial Applications

The successful pilot-scale demonstration of MTZ degradation using BDD electro-oxidation validates this technology for several high-impact industrial and environmental sectors:

Pharmaceutical Wastewater Treatment: Implementation as an efficient pre-treatment step for complex, recalcitrant effluents from pharmaceutical manufacturing, hospitals, and veterinary facilities.
Biodegradability Enhancement: Utilizing the BDD process to convert low-biodegradability wastewater (BOD₅/COD < 0.7) into highly biodegradable streams (BOD₅/COD > 0.8), allowing cost-effective integration with existing municipal biological treatment plants.
Advanced Oxidation Processes (AOPs): Deployment of BDD-based electrochemical reactors for the destruction of various emerging contaminants (e.g., ammonia, cyanide, chlorophenols) in industrial water streams where high hydroxyl radical generation is required.
Resource Recovery (Circular Economy): Optimization of operational parameters (e.g., current density, retention time) to maximize the selective production and subsequent recovery of valuable organic acids (formic acid, acetic acid) generated during partial mineralization.
Industrial Scale-Up: The pilot-scale data provides critical engineering guidelines for scaling BDD technology to full industrial capacity, particularly for high-volume applications in farms and large industrial complexes.

View Original Abstract

In this investigation, metronidazole was degraded in an aqueous solution through electro-oxidation. A DiaClean® cell was used to accommodate a stainless-steel electrode as a cathode and a boron-doped diamond (BDD) electrode as anode. This setup provides several electrochemical advantages, including low currents, a high operational potential, and, frequently, low adsorption compared to conventional carbon materials. The physicochemical parameters were estimated after 180 min of treatment, applying different current densities. The concentration of metronidazole was monitored by HPLC to assess degradation, resulting in 30.67% for 30 mA cm−2, 79.4% for 50 mA cm−2, and 100% for 100 mA cm−2. The TOC mineralization percentages were 12.71% for 30 mA cm−2, 14.8% for 50 mA cm−2, and 29.9% for 100 mA cm−2. Also, biodegradability indices of 0.70 for 30 mA cm−2, 0.81 for 50 mA cm−2, and 0.93 for 100 mA cm−2 were obtained. The byproducts found were formic acid and acetic acid. A pseudo-first order kinetic model was thus obtained due to the quasi-stable concentration achieved through hydroxyl radicals, given that they do not accumulate in the medium, due to their high rate of destruction and short lifespan.

Tech Support

Original Source

DOI: https://doi.org/10.3390/catal15010029

References

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