Pilot scale investigation of an advanced photo-electro-chemical oxidation process for treatment of effluents from pesticides manufacturing plants
At a Glance
Section titled âAt a Glanceâ| Metadata | Details |
|---|---|
| Publication Date | 2023-08-28 |
| Journal | Global NEST International Conference on Environmental Science & Technology |
| Authors | Vasilis C. Sarasidis, Panagiota Petsi, Konstantinos V. Plakas, A.J. Karabelas |
| Analysis | Full AI Review Included |
Executive Summary
Section titled âExecutive SummaryâThis study reports on the successful pilot-scale implementation of a hybrid Advanced Oxidation Process (AOP) designed for treating highly recalcitrant wastewater from a pesticides manufacturing plant.
- Core Technology: The system integrates Anodic Oxidation (AO) using Boron-Doped Diamond (BDD) electrodes with Photochemical Oxidation (H2O2/UV-C) to maximize the in-situ generation of powerful hydroxyl radicals (OH).
- Performance Metrics: Under near-optimal conditions (40 mA/cm2 CD, 0.6 W/L UV-C dose, 1140 mg·L-1·h-1 H2O2 dosing), the process achieved 71% Total Organic Carbon (TOC) mineralization and 93% color removal after 27 hours.
- Micropollutant Elimination: The process demonstrated exceptional effectiveness, achieving complete degradation (>99%) of 53 out of 54 identified organic micropollutants, including compounds like Imidacloprid and Acetamiprid.
- Synergistic Efficiency: High utilization of injected H2O2 (approx. 80-90%) confirms the strong synergistic effect between the electrochemical and photochemical components, which is crucial for treating heavy organic loads.
- Process Optimization: The âOn-Line Dosingâ (OLD) mode for H2O2 addition proved superior to âOnce Throughâ addition, and a recirculation flow rate of 8.4 L/min was necessary to prevent ohmic resistance buildup in the electrochemical cell.
- Commercial Viability: The resulting treated effluent meets standards for safe disposal to local biological treatment plants, positioning this hybrid AOP as a sustainable and attractive alternative to conventional, costly methods like chemical coagulation and Granular Activated Carbon (GAC) adsorption.
Technical Specifications
Section titled âTechnical Specificationsâ| Parameter | Value | Unit | Context |
|---|---|---|---|
| Effluent Initial TOC | 891 - 1100 | mg/L | Pesticides wastewater feed |
| Effluent Initial COD | 2860 - 3710 | mg/L | Pesticides wastewater feed |
| Treated Volume (Batch) | 45 | L | Experimental batch size |
| UV-C Dose (Constant) | 0.60 | W/L | Photoreactor operation |
| Optimal Current Density (CD) | 40 | mA/cm2 | Anodic Oxidation (AO) process |
| Optimal Recirculation Flow Rate (Q) | 8.4 | L/min | AO/H2O2/UV-C process |
| Optimal H2O2 Dosing Rate | 1140 | mg·L-1·h-1 | On-Line Dosing (OLD) mode |
| H2O2 Utilization (Max) | 87 | % | Achieved in Exp. No 5 |
| TOC Removal (Max) | 71 | % | After 27h treatment (Exp. No 5) |
| Color Removal (Max) | 93 | % | After 27h treatment (Exp. No 5) |
| Electrode Material (Anode) | Boron Doped Diamond (BDD) | N/A | Electrochemical Cell (EC) |
| Electrode Material (Cathode) | Stainless Steel (SS304) | N/A | Electrochemical Cell (EC) |
| Electrode Active Surface Area | 0.01 | m2 | Per electrode |
| UV-C Wavelength | 253.7 | nm | Germicidal lamps |
Key Methodologies
Section titled âKey MethodologiesâThe pilot unit combined a plate-and-frame electrochemical cell (EC) and a 10 L cylindrical UV photoreactor, operated in batch mode (45 L total volume).
- Feed Preparation: Industrial effluent underwent preliminary coagulation/separation to remove suspended solids (TSS < 112 mg/L). 40 L of this pre-treated wastewater was loaded into the feed tank.
- Electrochemical Setup: The EC utilized a BDD anode and a Stainless Steel (SS304) cathode (0.01 m2 active area each). Three PVDF spacers were used to ensure optimal fluid distribution and flow conditions within the cell.
- Photochemical Setup: The UV photoreactor housed two 40W germicidal lamps, providing a constant UV-C dose of 0.60 W/L.
- H2O2 Dosing Strategy: Hydrogen peroxide (50% w/w stock) was diluted and added using two primary modes:
- Once Through (OT): Total H2O2 volume added directly to the feed tank at the start.
- On-Line Dosing (OLD): H2O2 injected at a constant rate (e.g., 1140 mg·L-1·h-1) throughout the experiment via a dosing pump.
- Process Operation: Wastewater was continuously recirculated (optimal Q = 8.4 L/min) between the EC and the photoreactor for up to 27 hours. Key parameters (Current Density, H2O2 concentration, and time) were varied to assess performance.
- Performance Monitoring: Samples were collected at specific time intervals to measure TOC (mineralization), color (discoloration), H2O2 concentration, and the concentration of 54 specific organic micropollutants (via LC-MS).
Commercial Applications
Section titled âCommercial ApplicationsâThis hybrid AO/H2O2/UV-C technology is highly relevant for industries generating complex, non-biodegradable liquid waste streams.
- Pesticides and Agrochemical Manufacturing: Direct application for treating high-load, colored effluents containing persistent organic pollutants (POPs) and micropollutants.
- Specialty Chemical and Pharmaceutical Production: Effective pre-treatment or tertiary treatment for wastewater streams characterized by high Chemical Oxygen Demand (COD) and recalcitrant compounds that inhibit biological activity.
- Industrial Water Reuse: Implementation as a final polishing step to mineralize trace organics, enabling the recycling of industrial process water back into manufacturing operations.
- Environmental Remediation: Utilization of BDD-based electrochemical systems for generating powerful oxidants in situ, offering a robust alternative to conventional chemical oxidation methods for complex matrices.
View Original Abstract
This paper reports on the effectiveness of an innovative hybrid advanced oxidation process-scheme aiming to degrade recalcitrant organic compounds in industrial effluents. Following targeted experimental work, a pilot unit was developed/built combining two advanced oxidation processes, based on in-situ production of powerful hydroxyl radicals (HOï); i.e., electrochemical anodic oxidation (AO) employing boron-doped diamond (BDD) electrodes and photochemical oxidation via H2O2 photolysis under UV-C irradiation (H2O2/UV-C). The pilot-unit was operated, in batch mode for six months in a pesticides manufacturing plant, treating colored effluents characterized by high, recalcitrant organic load (typically ~3300 mg/L COD, ~1000 mg/L TOC). The effect was examined of key process parameters, including current density, UV-C dose, H2O2 concentration, recirculation flow rate and processing time, on system performance, mainly regarding organic-matter mineralization and discoloration rate. For the aforementioned effluent organic load, applying a near-optimal set of process-parameter values (i.e. 40 mA/cm2 current density, 0.65 W/L UV-C dose, âon-lineâ dosing of approx. 1140 mgïL-1ïh-1 H2O2 and 8.4 L/min recirculation flow rate), TOC and color removal reached 71% and 93%, respectively. The effectiveness of the combined AO/H2O2/UV-C process, mainly due to high utilization of injected H2O2 (approx. 80-90%), is judged as remarkable, considering that complete degradation (>99%) was observed of the 53 out of the total 54 organic compounds identified in the wastewater. Furthermore, the treated effluents by the hybrid AO/H2O2/UV-C process meet the standards (i.e. COD<1000 mg/L and TSS<350 mg/L) for safe disposal to local/regional biological effluent-treatment plant. Therefore, the demonstrated technology is an attractive, sustainable alternative to the currently employed special treatment, which involves chemical coagulation/granular activated carbon adsorption and necessitates costly extra-treatment of the resulting secondary wastes. Steps are currently in progress towards implementation at large scale, of the hybrid AO/H2O2/UV-C technology, for treatment of similar heavily polluted industrial effluents.