Treatment of cheese whey wastewater by electrochemical oxidation using BDD, Ti/RuO2-TiO2, and Ti/RuO2-IrO2-Pt anodes - ecotoxicological and energetic evaluation
At a Glance
Section titled âAt a Glanceâ| Metadata | Details |
|---|---|
| Publication Date | 2025-03-04 |
| Journal | Environmental Science and Pollution Research |
| Authors | Imen Souli, Annabel Fernandes, Ana Lopes, InĂȘs B. Gomes, Alexandra Afonso |
| Institutions | University of Beira Interior, University of GabĂšs |
| Citations | 3 |
| Analysis | Full AI Review Included |
Executive Summary
Section titled âExecutive SummaryâThis study evaluated Boron-Doped Diamond (BDD) and Titanium Mixed Metal Oxide (Ti/MMO) anodes for the electrochemical oxidation (EO) of raw Cheese Whey Wastewater (CWW), focusing on organic removal, energy efficiency, and ecotoxicity.
- Superior Organic Removal: BDD anodes achieved the highest removal rates for organic compounds (up to 86% COD removal at 500 A m-2) and demonstrated the highest degree of mineralization.
- Toxicity Mitigation (BDD): BDD treatment successfully reduced CWW ecotoxicity towards Daphnia magna from âvery toxicâ (21.7 TU) to âtoxicâ (1.87 TU), nearly reaching the ânon-toxicâ level.
- Biodegradability Enhancement: EO with BDD significantly improved the biodegradability index (BOD5/COD) from 0.55 to 0.81, making the effluent highly suitable for subsequent biological treatment.
- Nitrogen Removal and Energy Efficiency (Ti/MMO): Ti/MMO anodes exhibited higher Total Dissolved Nitrogen (TDN) removal (up to 55%) and achieved the lowest Electric Energy per Order (EEO) consumption (117 kWh m-3 order-1) at low current densities (50 A m-2).
- Toxicity Escalation (Ti/MMO): A critical drawback of Ti/MMO anodes was the increase in effluent ecotoxicity (up to 38.8 TU), attributed to the indirect oxidation mechanism forming toxic organochlorinated compounds and chloramines in the chloride-rich CWW.
- Anode Comparison: Ti/RuO2-IrO2-Pt generally outperformed Ti/RuO2-TiO2, showing slightly higher COD removal and lower EEO values, especially at low current densities.
Technical Specifications
Section titled âTechnical Specificationsâ| Parameter | Value | Unit | Context |
|---|---|---|---|
| Raw CWW COD | 3.9 ± 0.1 | g L-1 | Initial concentration |
| Raw CWW BOD5/COD | 0.55 | Ratio | Initial biodegradability index |
| Raw CWW Ecotoxicity (TU) | 21.7 | TU | Initial classification: âvery toxicâ |
| Raw CWW Chloride | 800 ± 9 | mg L-1 | High salinity content |
| Anode Materials Tested | BDD, Ti/RuO2-TiO2, Ti/RuO2-IrO2-Pt | N/A | Anode types |
| Cathode Material | Stainless Steel | N/A | Counter electrode |
| Applied Current Density (j) Range | 50 to 500 | A m-2 | Experimental range |
| Electrolysis Duration | 8 | h | Treatment time |
| Highest COD Removal (BDD) | 86 | % | At 500 A m-2 |
| Highest TDN Removal (Ti/MMO) | 55 | % | Ti/RuO2-IrO2-Pt at 500 A m-2 |
| Lowest EEO (Ti/RuO2-IrO2-Pt) | 117 | kWh m-3 order-1 | At 50 A m-2 |
| Final BOD5/COD (BDD) | 0.81 | Ratio | At 500 A m-2 (Classification: âfairly biodegradableâ) |
| Final Ecotoxicity (BDD) | 1.87 | TU | At 500 A m-2 (Classification: âtoxicâ) |
| Final Ecotoxicity (Ti/MMO) | 38.8 | TU | Ti/RuO2-IrO2-Pt at 500 A m-2 (Classification: âvery toxicâ) |
Key Methodologies
Section titled âKey MethodologiesâThe electrochemical oxidation (EO) experiments were conducted in batch mode using an undivided cylindrical glass cell.
- Wastewater Preparation: Raw CWW (initial pH 11.8 ± 0.1, COD 3.9 g L-1) was collected from a cheese factory in Portugal and stored at -20 °C prior to use.
- Electrochemical Setup: A 150 mL sample of CWW was treated in the cell with continuous stirring (200 rpm).
- Electrode Configuration: Anodes (BDD, Ti/RuO2-TiO2, or Ti/RuO2-IrO2-Pt) and the stainless-steel cathode were placed in parallel with an immersed area of 10 cm2 each. The inter-electrode gap was maintained at 0.5 cm.
- Power Application: A GW, Lab DC power supply (GPS-3030D) was used to maintain constant current densities (j) of 50, 100, 300, and 500 A m-2.
- Duration and Replication: All assays were run for 8 hours (h) and performed in duplicate to ensure reproducibility.
- Analytical Monitoring: COD, BOD5, TDC, DOC, DIC, and TDN were measured. Chloride was analyzed via ionic chromatography.
- Ecotoxicity Testing: Acute toxicity was determined using the Daphnia magna model organism following OECD guideline 202 (2004), calculating the EC50 and Toxicity Units (TU).
Commercial Applications
Section titled âCommercial ApplicationsâThe findings provide critical data for selecting appropriate anode materials for industrial wastewater treatment systems, balancing mineralization efficiency, energy cost, and effluent toxicity.
- High-Strength Industrial Wastewater Treatment: Direct application for treating high-load effluents from the dairy, agrofood, and fermentation industries, where high COD and salinity are common challenges.
- Tertiary Treatment for Mineralization: BDD anodes are ideal for use as a final polishing step (tertiary treatment) to achieve complete mineralization of recalcitrant organics and ensure the effluent meets strict non-toxic discharge standards.
- Pre-treatment for Biological Systems: BDD EO is highly effective in increasing the BOD5/COD ratio, making previously refractory CWW suitable for subsequent, cost-effective biological treatment processes.
- Energy-Optimized Nitrogen Removal: Ti/MMO anodes (specifically Ti/RuO2-IrO2-Pt) are commercially viable for applications prioritizing low energy consumption (EEO) and efficient nitrogen (TDN) removal, especially when operating at current densities < 100 A m-2.
- Electrode Selection Strategy: Engineers must select BDD when toxicity reduction and mineralization are paramount, or select Ti/MMO when nitrogen removal and low energy cost at low current density are the primary objectives, provided the formation of organochlorides can be managed or mitigated.
View Original Abstract
Abstract The effectiveness of boron-doped diamond (BDD) and titanium metal-mixed oxides (Ti/MMO: Ti/RuO 2 -TiO 2 and Ti/RuO 2 -IrO 2 -Pt) anodes to treat cheese whey wastewater (CWW) by electrochemical oxidation (EO) was evaluated. The results show that EO with BDD is effective in the removal of organic compounds. Conversely, Ti/MMO anodes exhibit higher removals of nitrogenated compounds. After 8 h of EO treatment at an applied current density of 500 A m â2 , the biodegradability index increased from 0.55 to 0.81 with the BDD anode, while with Ti/MMO only reached 0.64. The acute toxicity of the CWW, before and after treatment, was assessed with the model organism Daphnia magna . The use of BDD showed favorable outcomes, leading to a reduction in ecotoxicity, which changed the CWW classification from âvery toxicâ to âtoxic,â very close to the ânon-toxicâ level. Contrarywise, the use of Ti/MMO anodes led to an escalation of potentially harmful substances in the treated effluent. Still, Ti/MMO anodes provide the most favorable energy consumption when operating at current densities equal to or below 100 A m â2 . While both Ti/RuO 2 -TiO 2 and Ti/RuO 2 -IrO 2 -Pt exhibit similar performance, the effectiveness of Ti/RuO 2 -TiO 2 is somewhat lower.