Achieving Sustainable Development Goal 6 Electrochemical-Based Solution for Treating Groundwater Polluted by Fuel Station

At a Glance

Metadata	Details
Publication Date	2022-09-17
Journal	Water
Authors	Júlio César Oliveira da Silva, Aline Maria Sales Solano, Inalmar D. Barbosa Segundo, Elisama Vieira dos Santos, Carlos A. Martínez‐Huitle
Institutions	Instituto Federal do Rio Grande do Norte, Universidade Federal do Rio Grande do Norte
Citations	13
Analysis	Full AI Review Included

Executive Summary

This study successfully demonstrated the viability of electrochemical advanced oxidation processes (EAOPs) for treating groundwater contaminated by fuel leaks, aligning with Sustainable Development Goal 6 (SDG 6).

Core Achievement: An 87% Chemical Oxygen Demand (COD) abatement was achieved in a 5 L pre-pilot flow plant using a Ti/RuO₂ double-sided anode under optimized conditions (30 mA cm^-2, 0.5 M Na₂SO₄).
Contaminant Removal: Near-complete removal of Benzene, Toluene, and Ethylbenzene (BTEX) was attained, reducing concentrations to below 1.5 µg L^-1, meeting most Brazilian environmental standards for human consumption.
Electrode Selection: While Boron-Doped Diamond (BDD) showed superior intrinsic mineralization (64.61% TOC removal in batch mode), the Ti/RuO₂ anode was selected for scale-up due to its lower energy consumption and better eco-technological suitability.
Energy Efficiency (Batch): The lowest energy consumption in batch mode was 0.050 kWh (gCOD)^-1 using Ti/RuO₂ with Na₂SO₄, demonstrating the positive effect of the supporting electrolyte on efficiency.
Scale-Up Performance: The pilot plant achieved 68% organic matter degradation and 87% COD removal over 300 minutes, requiring 2.53 kWh kg COD^-1, proving the technology’s potential for industrial application.
Mechanism: The process relies on the reaction of organics with hydroxyl radicals (•OH) generated at the anode surface, favoring direct electrochemical oxidation on the active Ti/RuO₂ surface.

Technical Specifications

Parameter	Value	Unit	Context
Initial COD	230	mg L^-1	Groundwater effluent
Initial TOC	91.5	mg L^-1	Groundwater effluent
Initial Xylene Concentration	5435.5	µg L^-1	Highest initial BTEX component
Anode Material (Pilot)	Ti/RuO₂	N/A	Double-sided plate
Cathode Material (Pilot)	Stainless Steel	N/A	Two plates
Optimal Current Density ($j$)	30	mA cm^-2	Batch and Pilot operation
Electrolyte	0.5	M Na₂SO₄	Supporting electrolyte
Pilot Reactor Volume	5	L	Flow cell capacity
Pilot Anode Area	286	cm²	Geometrical area
Pilot Flow Rate	153	L h^-1	Recirculation rate
Pilot Treatment Time	300	min	Optimized run time
Final COD Abatement (Pilot)	87	%	Achieved 30 mg L^-1 final COD
Final TOC Mineralization (Pilot)	36.7	mg L^-1	Approximately 40% mineralization
BTEX Removal (Pilot)	<1.5	µg L^-1	Benzene, Toluene, Ethylbenzene
Energy Consumption (Pilot)	2.53	kWh kg COD^-1	Optimized conditions
Lowest EC (Batch, Ti/RuO₂)	0.050	kWh (gCOD)^-1	30 mA cm^-2, with Na₂SO₄
Mass Transfer Coefficient ($k_{m}$) (Pilot)	8.8 x 10^-6	m s^-1	Hydrodynamic characterization

Key Methodologies

The study involved a two-stage approach: laboratory batch optimization followed by pre-pilot flow cell scale-up.

Effluent Characterization:
- Groundwater samples were collected 10 m below the water level at fuel recovery stations.
- Contaminants (BTEX, Phenol) were identified and quantified using Gas Chromatography-Mass Spectroscopy (GC-MS) coupled with Solid-Phase Micro-Extraction (SPME).
- Bulk parameters (COD, TOC, BOD₅, pH, Conductivity, SUVA₂₅₄) were measured using standard methods and photometers.
Batch Electrochemical Optimization (0.5 L Cell):
- Anodes Tested: Ti/RuO₂, Ti/Pt, and Nb/BDD (13.5 cm² area).
- Conditions: Galvanostatic control at 10, 30, and 60 mA cm^-2, 25 °C, 240 min.
- Electrolyte Effect: A second set of experiments was run at the optimal current density (30 mA cm^-2) with the addition of 0.5 M Na₂SO₄ to increase conductivity and promote sulfate-based oxidant generation.
- Evaluation: COD decay and Energy Consumption (EC) in kWh (gCOD)^-1 were the primary metrics for comparison.
Electrochemical Flow Reactor Scale-Up (5 L Cell):
- Reactor Design: Flow cell with a double-sided Ti/RuO₂ anode and two stainless steel cathodes (286 cm² area).
- Hydrodynamic Characterization: Mass-transfer coefficient ($k_{m}$) was determined using the limiting diffusion current technique with potassium ferricyanide solutions (20-80 mol m^-3 in 0.5 M NaOH).
- Pilot Operation: The system was run at the optimized batch conditions: 30 mA cm^-2, 0.5 M Na₂SO₄, 25 °C, with recirculation at 153 L h^-1 for 300 minutes.
Performance Monitoring:
- COD and TOC reduction were tracked to assess organic matter degradation and mineralization.
- Specific Ultraviolet Absorbance (SUVA₂₅₄) was used as an indicator of aromaticity changes.
- Discoloration was calculated using the DFZy method (DIN EN 7884:2012) based on UV-Vis absorbance reduction.

Commercial Applications

This electrochemical oxidation technology, particularly utilizing advanced dimensionally stable anodes (DSAs) like Ti/RuO₂ and high-performance materials like BDD, is highly relevant for several environmental and industrial sectors.

Wastewater Treatment and Remediation:
- Groundwater Remediation: Direct application for cleaning aquifers contaminated by petroleum hydrocarbons (BTEX, TPHs) from fuel stations or industrial spills.
- Industrial Effluent Treatment: Effective for degrading recalcitrant organic pollutants in complex industrial matrices, including textile dyes and pharmaceutical waste.
Electrode Manufacturing and Supply:
- Dimensionally Stable Anodes (DSAs): Production and supply of Ti/RuO₂ and Ti/Pt electrodes for large-scale electrochemical reactors.
- Advanced Electrode Materials: Manufacturing of high-performance Boron-Doped Diamond (BDD) electrodes, which offer superior mineralization capabilities via physisorbed •OH generation, suitable for highly toxic or concentrated waste streams.
Water Security and Sanitation (SDG 6):
- Water Disinfection: Electrochemical generation of oxidizing species (e.g., chlorine, sulfate radicals) for microbial inactivation in water systems.
- Decentralized Water Treatment: Development of robust, modular electrochemical flow reactors suitable for remote or decentralized water purification powered potentially by renewable energy sources.

View Original Abstract

Oil leakage occurs at fuel service stations due to improper storage, which pollutes soil and, subsequently, can reach the groundwater. Many compounds of petroleum-derived fuels pose hazards to aquatic systems, and so must be treated to guarantee clean and safe consumption, which is a right proposed by the United Nations in their Sustainable Development Goal 6 (SDG 6: Clean Water and Sanitation). In this study, contaminated groundwater with emerging pollutants by petroleum-derived fuel was electrochemically treated in constantly mixed 0.5 L samples using three different anodes: Ni/BDD, Ti/Pt, Ti/RuO2. Parameters were investigated according to chemical oxygen demand (COD), energy consumption analysis, by applying different electrodes, current densities (j), time, and the use of Na2SO4 as an electrolyte. Despite a similar COD decrease, better degradation was achieved after 240 min of electrochemical treatment at Ti/RuO2 system (almost 70%) by applying 30 mA cm−2, even without electrolyte. Furthermore, energy consumption was lower with the RuO2 anode, and greater when 0.5 M of Na2SO4 was added; while the order, when compared with the other electrocatalytic materials, was Ti/RuO2 > Ti/Pt > Ni/BDD. Thereafter, aiming to verify the viability of treatment at a large scale, a pilot flow plant with a capacity of 5 L was used, with a double-sided Ti/RuO2 as the anode, and two stainless steel cathodes. The optimal conditions for the effective treatment of the polluted water were a j of 30 mA cm−2, and 0.5 M of Na2SO4, resulting in 68% degradation after 300 min, with almost complete removal of BTEX compounds (benzene, toluene, ethyl-benzene, and xylene, which are found in emerging pollutants) from the water and other toxic compounds. These significant results proved that the technology used here could be an effective SDG 6 electrochemical-based solution for the treatment of groundwater, seeking to improve the quality of water, removing contaminants, and focusing on Brazilian environmental legislations and, consequently, converting pollutants into effluent that can be returned to the water cycle.

Tech Support

Original Source

DOI: https://doi.org/10.3390/w14182911

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