Degradation of refractory compounds in industrial wastewaters by advanced technologies based on electrochemical and photochemical oxidation
At a Glance
Section titled âAt a Glanceâ| Metadata | Details |
|---|---|
| Publication Date | 2022-11-21 |
| Journal | Global NEST International Conference on Environmental Science & Technology |
| Authors | Konstantinos V. Plakas, Panagiota Petsi, Vasilios Sarasidis, A.J. Karabelas |
| Institutions | Centre for Research and Technology Hellas |
| Analysis | Full AI Review Included |
Executive Summary
Section titled âExecutive SummaryâThis analysis summarizes the investigation into using Advanced Oxidation Processes (AOPs)âAnodic Oxidation (AO) and H2O2/UV-C photolysisâto treat highly refractory and non-biodegradable wastewater from a pesticides manufacturing plant.
- Core Challenge: Efficient mineralization of high-load industrial effluent (TOC 800-1820 mg/L, COD 1398-7400 mg/L) containing toxic, recalcitrant organics.
- Optimal Performance (Hybrid): The combined AO/H2O2/UV-C process achieved the fastest Total Organic Carbon (TOC) abatement rate of 534 mgC/h, significantly exceeding the individual processes.
- AO Optimization: Boron-Doped Diamond (BDD) AO efficiency was maximized by increasing the recirculation flow rate (up to 1400 mL/min), which lowered ohmic resistance and allowed for higher current densities (up to 100 mA/cm2), leading to near-total mineralization in 12h.
- Photochemical Efficiency: H2O2/UV-C achieved a TOC removal rate of 369 mgC/h and excellent color removal (>98% in 4h). Efficiency was highly dependent on the radiant power per unit volume (PR).
- Industrial Relevance: The hybrid system utilized âon-lineâ H2O2 dosing, simulating continuous industrial operation, and demonstrated high performance (75% TOC removal) after 12h of treatment.
- Material Selection: BDD was confirmed as the optimal anode material due to its high O2-overvoltage, enhancing hydroxyl radical (â˘OH) production for mineralization.
Technical Specifications
Section titled âTechnical Specificationsâ| Parameter | Value | Unit | Context |
|---|---|---|---|
| Initial TOC Range | 800 - 1820 | mg/L | Raw Wastewater Load |
| Initial COD Range | 1398 - 7400 | mg/L | Raw Wastewater Load |
| Optimal Hybrid TOC Abatement Rate | 534 | mgC/h | Combined AO/H2O2/UV-C Process |
| Optimal H2O2/UV-C TOC Removal Rate | 369 | mgC/h | Photochemical Process Alone |
| Optimal AO TOC Removal Rate | 36.4 | mgC/h | Anodic Oxidation Process Alone |
| Optimal AO Current Density (CD) | 100 | mA/cm2 | For AO process (Exp. No 6) |
| Optimal AO Recirculation Flow Rate | 1400 | mL/min | Maximizes mass transfer and reduces ohmic resistance |
| UV-C Irradiation Wavelength | 253.7 | nm | Low-pressure mercury-vapor lamps |
| Highest Tested Radiant Power (PR) | 11.8 | W/L | H2O2/UV-C (4 lamps) |
| Hybrid H2O2 Dosing Rate | 15.7 | g/L | âOn-lineâ dosing for 12h test |
| H2O2/UV-C Color Removal | >98 | % | Achieved after 4h treatment |
| AO Anode Material | Boron-Doped Diamond (BDD) | - | High O2-overvoltage electrode |
| AO Cathode Material | Carbon-PTFE (GDE-Ni) | - | Gas Diffusion Electrode (Nickel mesh reinforced) |
Key Methodologies
Section titled âKey MethodologiesâThe experimental investigation utilized three distinct setups: Anodic Oxidation (AO), H2O2/UV-C photolysis, and a combined hybrid system.
1. Wastewater Preparation and Characterization
Section titled â1. Wastewater Preparation and Characterizationâ- Pre-treatment: Raw wastewater was filtered using a 1.5 Âľm glass fiber filter to remove suspended solids, preventing deposition on electrode surfaces.
- Analysis: TOC, Total Nitrogen (TN), Chemical Oxygen Demand (COD), and Total Phosphate (TP) were measured using standard APHA colorimetric and analyzer methods.
2. Anodic Oxidation (AO) Setup and Operation
Section titled â2. Anodic Oxidation (AO) Setup and Operationâ- Reactor: Bench-scale plate-and-frame electrochemical cell (Micro Flow Cell).
- Electrodes: BDD served as the anode; Carbon-PTFE reinforced with Nickel mesh (GDE-Ni) served as the cathode.
- Operation Mode: Batch experiments conducted under galvanostatic conditions (constant current applied).
- Optimization Variables: Current density (20 to 150 mA/cm2), recirculation flow rate (60 to 1400 mL/min), and electrolyte concentration (Na2SO4).
- Key Finding: Increasing flow rate to 1400 mL/min was crucial for enhancing mass transfer and reducing ohmic resistance, enabling higher current densities and faster mineralization.
3. Photochemical Oxidation (H2O2/UV-C) Setup and Operation
Section titled â3. Photochemical Oxidation (H2O2/UV-C) Setup and Operationâ- Reactor: Double-wall cylindrical stainless steel photoreactor (4 L working volume).
- Irradiation Source: Four low-pressure mercury-vapor lamps (24W, 253.7 nm) housed in quartz sleeves.
- H2O2 Dosing: Hydrogen peroxide was added in a single batch dose (e.g., 6 g/L or 12 g/L) at the start of the experiment (t=0).
- Optimization Variables: Radiant power per unit volume (PR) (5.9 W/L up to 11.8 W/L) and H2O2 concentration.
4. Hybrid AO/H2O2/UV-C Operation
Section titled â4. Hybrid AO/H2O2/UV-C Operationâ- Configuration: The electrochemical cell outlet was driven directly into the photoreactor, creating a continuous recirculation loop between the two units.
- H2O2 Dosing: H2O2 was added via a dosing pump at a constant rate (âon-lineâ dosing) throughout the treatment time (6h or 12h) to simulate industrial conditions.
- Synergy: The combination proved highly effective, suggesting synergistic action between the heterogeneously generated â˘OH (from BDD) and the homogeneously generated â˘OH (from H2O2 photolysis).
Commercial Applications
Section titled âCommercial ApplicationsâThe developed hybrid electrochemical and photochemical AOP system is highly relevant for industries generating toxic, high-load, and non-biodegradable liquid waste streams.
- Pesticide and Agrochemical Manufacturing: Direct application for treating concentrated, refractory effluents, enabling compliance with stringent discharge limits.
- Pharmaceutical and Fine Chemical Production: Effective mineralization of complex organic molecules and drug residues that resist conventional biological treatment.
- Textile and Dyeing Industries: High efficiency in color removal (>98%), addressing a major aesthetic and regulatory challenge in textile wastewater.
- Industrial Water Reuse and Recycling: Achieving near-total mineralization (conversion to CO2, water, and inorganic ions) allows treated water to be safely reused in production processes.
- Electrochemical Reactor Engineering: Validation of BDD electrode performance under high current density and high flow rate conditions, informing the design of scalable industrial EAOP reactors.
- Hazardous Waste Management: Treatment of concentrated waste streams where conventional methods (e.g., activated carbon) face issues related to saturation and costly disposal of spent sorbents.
View Original Abstract
Results are presented of a systematic experimental investigation aiming to eliminate refractory organics from industrial effluents, of high and non-biodegradable organic load, by two Advanced Oxidation Processes (AOPs). Bench scale experiments were performed with real wastewater samples collected from a pesticides manufacturing plant, of varying TOC content (800-1820 mg/L), to investigate the effectiveness of boron-doped diamond (BDD) anodic oxidation (AO), of H2O2 photolysis with UV-C irradiation (H2O2/UV-C), and their combination (i.e. AO/H2O2/UV-C) on the total organic carbon (TOC) removal. The effect of main operating conditions was investigated for both processes, separately and in combination. In the case of AO, TOC and COD were removed at a rate of 36.4 mgC/h and 89.5 mgO2/L, by applying a current density of 100 mA/cm2 and a recirculation flow rate of 1400 mL/min. The H2O2/UV-C process achieved a TOC removal rate of 369 mgC/h and over 98% color removal after 4 h of treatment, when a single dose of 6 g/L H2O2 and 11.8 W/L of UVC irradiation dose were applied. Finally, the combined process (AO/H2O2/UV-C) led to a faster TOC abatement (534 mgC/h) and a higher color removal, after treating the wastewater with 77 mA/cm2 current density, 5.9 W/L UVC irradiation dose and âon-lineâ dosing 15.7 g/L H2O2.