Use of Electrooxidation as a Polishing Step for the Residual Water Obtained in a Solar Wastewater Treatment
At a Glance
Section titled âAt a Glanceâ| Metadata | Details |
|---|---|
| Publication Date | 2023-09-19 |
| Journal | Journal of the Mexican Chemical Society |
| Authors | Eva Carina Tarango-Brito, Anabel Ramos-GarcĂa, Liliana Ivette Ăvila CĂłrdoba, Carlos Barrera-DĂaz |
| Institutions | Universidad AutĂłnoma del Estado de MĂ©xico |
| Analysis | Full AI Review Included |
Executive Summary
Section titled âExecutive SummaryâThis research details a highly efficient, two-stage hybrid process combining solar distillation/photocatalysis with Boron-Doped Diamond (BDD) electrooxidation (EO) for treating synthetic wastewater containing Carmine Red dye.
- Hybrid System Efficiency: The initial solar process successfully recovers 66% of the input volume as high-quality distilled water, concentrating the remaining contaminants (dye and intermediates) into a 33% residual volume.
- Polishing Step Success: BDD electrooxidation was applied as a polishing step to the concentrated residue, achieving rapid and significant contaminant removal.
- Rapid COD Reduction: Under optimal acidic conditions (pH 2.7) and high current density (22.2 mA cm-2), the EO process reduced the Chemical Oxygen Demand (COD) of the solar residue to less than 1 mg/L in only 5 minutes.
- High Degradation Rate: The combined system effectively eliminates the characteristic Carmine Red peak (503 nm) from the UV-Vis spectrum of the treated water.
- Energy Efficiency: The overall process is deemed environmentally friendly due to low energy consumption for the residual treatment, calculated at 5 kWh L-1.
- Mechanism: The high efficiency is attributed to the formation of powerful hydroxyl radicals (OH) on the BDD surface, favored by the low pH conditions.
Technical Specifications
Section titled âTechnical Specificationsâ| Parameter | Value | Unit | Context |
|---|---|---|---|
| Initial Dye Concentration | 25 | ppm | Carmine Red synthetic wastewater |
| Solar Preheating Temperature | Up to 80 | °C | Parabolic solar concentrator output |
| Solar Distillate Yield | 66 | % | Volume recovered |
| Residual Water Volume | 33 | % | Volume requiring polishing treatment |
| Solar Degradation Efficiency | 70 | % | Dye removal in residual water (120 min exposure) |
| Optimal EO pH | 2.7 | - | Acidic conditions for BDD electrooxidation |
| Optimal Current Density (j) | 22.2 | mA cm-2 | Applied to BDD electrodes |
| BDD Electrode Surface Area | 45 | cm2 | Anode/Cathode area in EO reactor |
| Initial COD (Synthetic Water) | 37 | mg/L | Before any treatment |
| EO Time to COD <1 mg/L (Solar Residue) | 5 | min | Polishing step at optimal conditions |
| EO Time to COD <1 mg/L (Initial Water) | 45 | min | Direct EO treatment at pH 6.2, 22.2 mA cm-2 |
| Energy Consumption (ECv) | 5 | kWh L-1 | For treating the residual water |
| Estimated Treatment Cost | 0.355 | US$ L-1 | Based on average industrial electricity price |
| Hydroxyl Radical Oxidation Potential | 2.80 | V | Potential of OH radical |
| Characteristic Dye Peak (UV-Vis) | 503 | nm | Carmine Red absorbance peak |
Key Methodologies
Section titled âKey MethodologiesâThe treatment involves a sequential two-step process: solar distillation/photocatalysis followed by BDD electrooxidation.
- Synthetic Wastewater Preparation: A 25 ppm solution of Carmine Red dye was prepared in distilled water for testing.
- Solar Preheating: The wastewater was introduced into a parabolic solar concentrator designed to preheat the solution up to 80 °C.
- Solar Distillation/Photocatalysis: Preheated water was transferred to a single-slope solar distiller (20° inclination) containing a Zinc Oxide (ZnO) plate, which functioned as a photocatalyst under direct sunlight exposure.
- Residue Isolation: The solar process yielded 66% distilled water and 33% concentrated residual wastewater, which exhibited 70% dye degradation.
- Electrooxidation (EO) Setup: The residual water (400 mL volume) was placed in an electrochemical reactor utilizing a Boron-Doped Diamond (BDD) anode and a stainless steel cathode (45 cm2 surface area each).
- pH Adjustment: The pH of the residual water was adjusted to 2.7 to favor the electrochemical generation of highly oxidative OH radicals on the BDD surface.
- Current Application: A direct current power source was used to apply the optimal current density of 22.2 mA cm-2.
- Polishing Treatment: The EO process was run for 5 minutes, achieving satisfactory water quality (COD <1 mg/L) in the concentrated residue.
- Quality Assessment: Water quality was monitored using COD (HACH DR/4000 U), UV-Vis spectrophotometry (VELAB VE-5100UV), and IR-ATR spectrometry (Bruker TENSOR 27) to confirm dye and intermediate removal.
Commercial Applications
Section titled âCommercial ApplicationsâThis hybrid solar-electrochemical system is highly relevant for industries requiring efficient water recovery and treatment of recalcitrant organic pollutants.
- Textile and Dye Manufacturing: Primary application for treating high-volume, high-COD wastewater containing complex, non-biodegradable synthetic dyes (like Carmine Red).
- Industrial Water Recycling: Implementation in facilities aiming for zero liquid discharge (ZLD) by recovering high-quality distilled water (66% yield) and efficiently treating the concentrated brine/residue.
- Advanced Oxidation Processes (AOP): Integration of BDD electrooxidation technology for polishing effluent streams where conventional biological or chemical treatments fail to achieve mineralization.
- Decentralized Water Treatment: Suitable for remote or solar-rich regions, leveraging solar energy for bulk separation and low-energy electrochemical methods for final purification.
- Pharmaceutical and Food Processing: Used for treating specific waste streams containing colorants or complex organic intermediates, ensuring compliance with strict discharge regulations.
View Original Abstract
Abstract. Dyes are widely used in many industrial operations for a variety of products; however, when wastewater is discharged without a treatment in rivers and lakes, severe environmental impacts are observed. In this work, the results of a solar wastewater treatment are presented. The solar treatment consists in parabolic heater coupled with a solar distiller which contains a ZnO plate that works as photocatalyst. Distilled water presents good characteristics; nevertheless, a residue that contains dye and intermediate products is also obtained. An electrooxidation treatment using boron-doped diamond electrodes (BDD), is applied at the residue as a polishing step. It was observed that wastewater quality improves when using an aqueous solution of pH 2.7 and a current density of 22.2 mA cm-2. Physicochemical test such as COD, and UV-Vis were used to evaluate the wastewater quality. It was found that 40 minutes are required to attain the improvement. This technology is environmental friendly since low energy is required (5 kW h L-1). Resumen. Los colorantes son ampliamente utilizados en la industria para una gran variedad de productos; cuando se descargan aguas residuales con dichos compuestos en rĂos o lagos, ocasionan severas afectaciones al medio ambiente. Este trabajo presenta los resultados obtenidos al someter agua sintĂ©tica a un proceso consistente en un calentador acoplado a un destilador solar que contiene un fotocatalizador. En dicho procedimiento se obtiene agua destilada de buena calidad, sin embargo, tambiĂ©n se genera un agua residual concentrada con presencia de colorante y productos intermediarios. A manera de pulimento se aplica la electrooxidaciĂłn empleando electrodos de diamante dopados con boro. Con las mejores condiciones: pH 2.7 y densidad de corriente de 22.2 mA cm-2, se encuentra que el agua residual presenta una notable mejorĂa en caracterĂsticas fisicoquĂmicas de DQO y espectroscopia UV-Vis. Se encontrĂł que es necesario un periodo de tiempo de 40 minutos para mejorar las caracterĂsticas del agua concentrada, lo cual hace que este proceso sea ambientalmente amigable, ya que requiere la aplicaciĂłn de poca energĂa (5kW h L-1).