Emerging Contaminants Decontamination of WWTP Effluents by BDD Anodic Oxidation - A Way towards Its Regeneration

At a Glance

Metadata	Details
Publication Date	2023-04-25
Journal	Water
Authors	Joaquín R. Domínguez, T. González, Sergio E. Correia, Maria M. Núñez
Institutions	Universidad de Extremadura
Citations	9
Analysis	Full AI Review Included

Executive Summary

Core Technology Validation: Electrochemical Oxidation using a Boron-Doped Diamond (EO-BDD) anode was successfully validated for regenerating real Wastewater Treatment Plant effluent (WWTPe).
Broad Contaminant Removal: The technique achieved 100% removal of a broad group of priority emerging contaminants, including neonicotinoid pesticides (TMX, ICP, TCP), antibiotics (AMX, SMX), azole pesticides (IMZ, TBZ, PNZ), and the antidepressant DVF.
Mineralization Efficiency: High mineralization capacity was confirmed, with Total Organic Carbon (TOC) removal reaching up to 77.09% in the WWTP effluent matrix.
Operational Optimization: Applied current density (j) was identified as the primary positive factor influencing contaminant removal and reaction kinetics (k₁), while media conductivity (C) had a positive but moderate influence.
Energy Cost Reduction: Increasing media conductivity significantly improved energy efficiency, reducing the Specific Energy Consumption (SEC) associated costs by up to 38%. SEC ranged from 4.60·10^-3 to 1.72·10^-2 kWh·g^-1 of pollutant removed.
Matrix Effects: The complexity of the real aqueous matrix significantly influenced degradation rates, with the reactivity ranking in WWTP effluent established as: Antidepressants > Antibiotics > Azole Pesticides > Neonicotinoids.
Electrolyte Selection: Sodium sulfate (Na₂SO₄) proved to be the optimal supporting electrolyte, yielding the highest pollutant removal percentages compared to NaCl and NaNO₃.

Technical Specifications

Parameter	Value	Unit	Context
Anode Material	Boron-Doped Diamond (BDD)	N/A	Best-known electrode for refractory organic degradation
Cathode Material	Stainless Steel (AISI 304)	N/A	Used in the circular single-cell reactor
Electrode Geometric Area	78	cm²	Area of circular electrodes
Electrode Gap	9	mm	Distance between anode and cathode
Current Density (j) Range	5.6 to 34.14	mA·cm^-2	Range used in the Central Composite Design (CCD)
Conductivity (C) Range	1.4 to 5.6	mS·cm^-1	Adjusted using Na₂SO₄
Maximum Pollutant Removal	100	%	Achieved for most ECs at 120 min
Maximum TOC Removal	77.09	%	Achieved at high current density (EO-3, 120 min)
Specific Energy Consumption (SEC) Range	4.60·10^-3 to 1.72·10^-2	kWh·g^-1	Measured energy cost per mass of pollutant removed
Maximum Kinetic Rate (k_TMX)	0.0920	min^-1	Pseudo-first-order rate constant for Thiamethoxam (EO-3)
Optimal Electrolyte	Na₂SO₄	N/A	Best performance due to persulfate (S₂O₈^2-) generation

Key Methodologies

Electrochemical Setup: Experiments were conducted in a circular single-cell reactor using a BDD anode and an AISI 304 stainless steel cathode.
Electrode Pre-treatment: Electrodes were polarized and cleaned using a 10 mM Na₂SO₄ solution at a current density of 20 mA·cm^-2 for 15 minutes prior to electrolysis.
Aqueous Matrix Preparation: Real water matrices (WWTP effluent, river water, reservoir water) were filtered (0.45 µm) and spiked (doped) with mixtures of emerging contaminants (NCTs, azoles, antibiotics, antidepressants) at a concentration of 1 µM each.
Experimental Design: A randomized Central Composite Orthogonal and Rotatable Design (CCORD) was employed to statistically analyze and model the influence of current density (j) and media conductivity (C).
Target Variable Measurement: Key performance indicators included:
- Pollutant removal percentage (E, %).
- Apparent pseudo-first-order kinetic rate constant (k₁).
- Total Organic Carbon (TOC) removal percentage.
- Specific Energy Consumption (SEC, kWh µM^-1).
Analytical Quantification: Contaminant degradation was monitored using Reverse-Phase High-Performance Liquid Chromatography (HPLC). TOC content was determined using an Analytikjena Multi N/C® 3100 analyzer.

Commercial Applications

The findings directly support the implementation of BDD-based electrochemical systems in advanced water treatment sectors:

Wastewater Treatment and Reuse: Regeneration of municipal WWTP effluents for non-potable, high-quality demanding uses, such as agricultural irrigation (meeting EU Decision 2020/741 standards) and industrial cooling.
Pharmaceutical and Pesticide Effluent Remediation: Targeted removal and mineralization of refractory organic compounds (e.g., neonicotinoids, azoles, antibiotics) from industrial discharge streams.
Advanced Oxidation Processes (AOPs): Integration of BDD anodes into tertiary treatment systems where high hydroxyl radical (•OH) generation is required for complete mineralization.
BDD Electrode Manufacturing and Supply: The results confirm the high performance and viability of BDD material for long-term, high-current density electrochemical applications in complex aqueous matrices.

View Original Abstract

Electrochemical oxidation using a boron-doped diamond anode (EO-BDD) was tested to remove emerging contaminants commonly present in wastewater treatment plant effluents (WWTPe). The main objective of the work was the regeneration of this water for its possible reuse in high-quality demanding uses. In the first part of the work, we investigated the potential of this technique for removing a group of neonicotinoid pesticides (thiamethoxam (TMX), imidacloprid (ICP), acetamiprid (ACP), and thiacloprid (TCP)) in a WWTP effluent. The influence of operating variables, such as current density, the conductivity of media, supporting electrolyte type (Na2SO4, NaCl or NaNO3), or the natural aqueous matrix on target variables were fully established. Selected target variables were: (1) the percentage of pollutant removal, (2) the kinetics (apparent pseudo-first-order kinetic rate constant), (3) total organic carbon (TOC) removal, and (4) the specific energy consumption (SEC). A response surface methodology (RSM) was applied to model the results for all cases. In the paper’s final part, this technology was tested with a more broad group of common emerging pollutants, including some azole pesticides (such as fluconazole (FLZ), imazalil (IMZ), tebuconazole (TBZ), or penconazole (PNZ)), antibiotics (amoxicillin (AMX), trimethoprim (TMP), and sulfamethoxazole (SMX)), and an antidepressant (desvenlafaxine (DVF)). The results confirm the power of this technology to remove this emerging contamination in WWTP effluents which supposes an interesting way towards its regeneration.

Tech Support

Original Source

DOI: https://doi.org/10.3390/w15091668

References

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