Methiocarb Degradation by Electro-Fenton - Ecotoxicological Evaluation

At a Glance

Metadata	Details
Publication Date	2020-12-12
Journal	Molecules
Authors	Faléstine Souiad, Ana Sofia Rodrigues, Ana Lopes, Lurdes Ciríaco, Maria José Pacheco
Institutions	Université Constantine 2, University of Beira Interior
Citations	11
Analysis	Full AI Review Included

Executive Summary

This study investigates the efficacy of the Electro-Fenton (EF) process, utilizing a Boron-Doped Diamond (BDD) anode and a carbon felt cathode, for the degradation and detoxification of the highly hazardous pesticide Methiocarb (MC).

High Degradation Efficiency: Total MC removal (>99%) was achieved rapidly across all tested conditions, requiring only 40 minutes of treatment or an applied electric charge of 120 C.
Significant Detoxification: The EF process resulted in a drastic reduction in acute toxicity towards the model organism Daphnia magna, achieving an average reduction factor of 450x (from approximately 900 Toxic Units (TU) to ~2 TU).
Optimal Mineralization Conditions: The highest Total Organic Carbon (TOC) removal (>90%) was obtained at the lowest tested parameters: 10 mg L^-1 iron concentration and 12.5 A m^-2 applied current density.
Mechanism Insight: Higher TOC removal at low current densities suggests that organic oxidation via hydroxyl radicals adsorbed on the BDD anode surface (BDD(OH)) is highly effective for mineralization.
Catalyst Flexibility: No significant differences in MC removal rates were observed between the two iron sources tested (ferric sulfate vs. ferric chloride).
Process Comparison: The EF process is confirmed as a feasible alternative to Anodic Oxidation (AO) for remediation, achieving similar final detoxification levels despite the initial increased toxicity caused by the added iron salts.

Technical Specifications

Parameter	Value	Unit	Context
Anode Material	Boron-Doped Diamond (BDD)	N/A	High O₂-overpotential
Cathode Material	Carbon Felt	N/A	H₂O₂ electrogeneration
Anode Immersed Area	20	cm²	Geometric area
Cathode Immersed Area	130	cm²	Geometric area
Initial Methiocarb Concentration	20.0 ± 0.6	mg L^-1	Model aqueous solution
Initial pH	2.81 to 3.34	N/A	Optimum range for EF
Applied Current Density (j)	12.5, 25, 50	A m^-2	Experimental variables
Iron Concentration ([Fe³⁺])	10, 30	mg L^-1	Experimental variables
Total MC Removal Charge	120	C	Required for >99% removal
Maximum TOC Removal	>90	%	Achieved at 12.5 A m^-2, 10 mg L^-1 Fe
Initial Acute Toxicity (TU)	883.1 to 929.4	TU	Highly Toxic classification
Final Acute Toxicity (TU)	1.96 to 2.02	TU	Toxic/Non-Toxic classification (after 720 C)
Toxicity Reduction Factor	450	x	Average reduction achieved

Key Methodologies

The Electro-Fenton (EF) experiments were conducted in a batch reactor setup using controlled electrochemical and chemical parameters:

Solution Preparation: Methiocarb (MC) solutions (20 mg L^-1) were prepared using ultrapure water. Iron catalyst was introduced as either Iron(III) sulfate pentahydrate (Fe₂(SO₄)₃·5H₂O) or ferric chloride hexahydrate (FeCl₃·6H₂O) to achieve concentrations of 10 or 30 mg L^-1 Fe.
Reactor Configuration: A 200 mL undivided cylindrical glass cell was used, maintained under continuous magnetic stirring to enhance mass transport.
Electrode Placement: A Boron-Doped Diamond (BDD) electrode (20 cm² immersed area) served as the anode, centered within the cell. A carbon felt piece (130 cm² immersed area) served as the cathode, covering the inner wall.
Oxygen Supply: Compressed air was continuously bubbled into the solution at 1 L min^-1, starting 10 minutes before the assay, to ensure continuous in situ electrogeneration of H₂O₂ at the cathode.
Electrochemical Operation: A DC power supply was used to maintain constant anodic current densities (j) of 12.5, 25, or 50 A m^-2. Experiments were run until an applied electric charge of 720 C was reached for final analysis.
Analytical Monitoring: MC decay was tracked using High-Performance Liquid Chromatography (HPLC). Mineralization was assessed by measuring Total Organic Carbon (TOC). Dissolved Fe²⁺ and H₂O₂ concentrations were determined spectrophotometrically.
Ecotoxicity Assessment: Acute toxicity was evaluated using the Daphtoxkit F microbiotest, measuring the 48 h EC₅₀ (concentration causing 50% immobilization) of Daphnia magna neonates.

Commercial Applications

The BDD-based Electro-Fenton technology demonstrated in this research is highly relevant for advanced environmental engineering applications, particularly in the treatment of persistent organic pollutants (POPs).

Pesticide and Herbicide Remediation: Direct application in treating agricultural runoff and industrial wastewater streams contaminated with carbamate pesticides (like Methiocarb) and other recalcitrant organic compounds.
Advanced Oxidation Processes (AOPs): Integration of the EF system as a high-efficiency tertiary treatment stage in municipal or industrial wastewater treatment plants to achieve final detoxification and high mineralization indexes.
BDD Electrode Technology: Increased demand for high-performance BDD anodes in electrochemical reactors, valued for their stability, high oxygen overpotential, and ability to generate powerful hydroxyl radicals for bulk and surface oxidation.
Water Reuse and Recycling: Enabling the safe reuse of contaminated water sources by effectively reducing acute toxicity to aquatic life, a critical step for environmental discharge compliance.
In Situ Reagent Generation: Utilization of the EF process eliminates the logistical and safety challenges associated with storing and handling bulk chemical oxidants (H₂O₂), promoting safer and more sustainable water treatment operations.

View Original Abstract

This paper studies the degradation of methiocarb, a highly hazardous pesticide found in waters and wastewaters, through an electro-Fenton process, using a boron-doped diamond anode and a carbon felt cathode; and evaluates its potential to reduce toxicity towards the model organism Daphnia magna. The influence of applied current density and type and concentration of added iron source, Fe2(SO4)3·5H2O or FeCl3·6H2O, is assessed in the degradation experiments of methiocarb aqueous solutions. The experimental results show that electro-Fenton can be successfully used to degrade methiocarb and to reduce its high toxicity towards D. magna. Total methiocarb removal is achieved at the applied electric charge of 90 C, and a 450× reduction in the acute toxicity towards D. magna, on average, from approximately 900 toxic units to 2 toxic units, is observed at the end of the experiments. No significant differences are found between the two iron sources studied. At the lowest applied anodic current density, 12.5 A m−2, an increase in iron concentration led to lower methiocarb removal rates, but the opposite is found at the highest applied current densities. The highest organic carbon removal is obtained at the lowest applied current density and added iron concentration.

Tech Support

Original Source

DOI: https://doi.org/10.3390/molecules25245893

References

2017 - Investigation of the presence and endocrine activities of pesticides found in wastewater effluent using yeast-based bioassays [Crossref]
2016 - Effect of Fe2+ on the degradation of the pesticide profenofos by electrogenerated H2O2 [Crossref]
2014 - Electrochemically assisted remediation of pesticides in soils and water: A review [Crossref]
2018 - Electrochemical oxidation of organic pollutants for wastewater treatment [Crossref]
2017 - Electrochemical advanced oxidation processes: A review on their application to synthetic and real wastewaters [Crossref]
2013 - Removal of residual anti-inflammatory and analgesic pharmaceuticals from aqueous systems by electrochemical advanced oxidation processes. A review [Crossref]
2017 - Anodic oxidation of the insecticide imidacloprid on mixed metal oxide (RuO2-TiO2 and IrO2-RuO2-TiO2) anodes [Crossref]