Inhibition of staphylococci and S. aureus in wastewater by ferrates and electrochemical methods
At a Glance
Section titled âAt a Glanceâ| Metadata | Details |
|---|---|
| Publication Date | 2020-10-01 |
| Journal | Acta Chimica Slovaca |
| Authors | AlĹžbeta MedveÄÂovĂĄ, Stanislava KecskĂŠsovĂĄ, Anna KrivjanskĂĄ, MariĂĄn Vojs, MariĂĄn Marton |
| Institutions | PalackĂ˝ University Olomouc, Slovak University of Technology in Bratislava |
| Analysis | Full AI Review Included |
Executive Summary
Section titled âExecutive SummaryâThis study evaluates the effectiveness of Boron-Doped Diamond (BDD) electrodes and ferrates for disinfecting municipal wastewater, focusing on the elimination of coagulase-positive Staphylococci and S. aureus.
- Core Technology: Advanced oxidation using BDD thin films grown via Hot Filament Chemical Vapor Deposition (HFCVD) was compared against chemical oxidation using powdered ferrates.
- Optimal Performance (BDD): The anodic connection of the BDD electrode achieved the highest efficiency, resulting in complete (100%) inhibition of target bacteria in effluent wastewater within 40 minutes.
- Mechanism: High disinfection efficiency in the anodic configuration is attributed to the generation of potent oxidizing agents, primarily hydroxide radicals (HOË).
- Energy Constraint: Complete disinfection using the BDD anode required 3.96 kWh/m3, which is approximately ten times higher than the energy consumption of standard biological WWTP treatment (approx. 0.4 kWh/m3).
- Ferrate Performance: The highest ferrate dose (100 mg) achieved significant inhibition (up to 98.8% for S. aureus in influent). However, lower doses (10 mg, 50 mg) sometimes resulted in an increase in bacterial counts in effluent, suggesting complex interactions influenced by the resulting high pH (up to 9.55).
- Recommendation: BDD electrochemical treatment is recommended for tertiary treatment stages in WWTPs due to its high efficacy, provided the high energy cost can be mitigated or justified.
Technical Specifications
Section titled âTechnical Specificationsâ| Parameter | Value | Unit | Context |
|---|---|---|---|
| BDD Film Thickness | ~500 | nm | Grown via HFCVD |
| B/C Doping Ratio | 10,000 | ppm | Achieved using trimethylboron (TMB) |
| Substrate Temperature | 650 | °C | HFCVD deposition temperature |
| Filament Temperature | 2100 | °C | Tungsten filament activation temperature |
| Deposition Pressure | 3 | kPa | HFCVD process pressure |
| Anode Area (Total) | 16 | cm2 | Composed of 10 BDD substrates |
| Applied Voltage (DC) | 30 | V | Used for electrochemical disinfection |
| Electrode Gap | 1 | cm | Distance between BDD and graphite counter electrode |
| Optimal Disinfection Time (Effluent) | 40 | min | Time for 100% inhibition using BDD anode |
| Energy Consumption (BDD Anode) | 3.96 | kWh/m3 | Required for complete effluent disinfection |
| Standard WWTP Energy Consumption | ~0.4 | kWh/m3 | Baseline for biological treatment |
| Optimal Ferrate Dose | 100 | mg | Added to 300 ml wastewater sample |
| Maximum pH Change (Ferrates) | 7.5 to 9.55 | - | Initial pH vs. pH after 100 mg ferrate addition |
| Ferrate Inhibition (S. aureus Influent) | 97-99 | % | Achieved with 100 mg dose |
Key Methodologies
Section titled âKey MethodologiesâThe study employed two primary disinfection methods: electrochemical oxidation using BDD electrodes and chemical oxidation using ferrates.
1. BDD Thin Film Production (HFCVD)
Section titled â1. BDD Thin Film Production (HFCVD)â- Substrate: Silicon (Si) wafers (10 x 10 mm).
- Growth Technique: Hot Filament Chemical Vapor Deposition (HFCVD).
- Film Characteristics: BDD thin films grown for 120 minutes, resulting in a thickness of approximately 500 nm.
- Doping: Boron doping achieved by adding trimethylboron (TMB) to the gas mixture, resulting in a Boron/Carbon (B/C) ratio of 10,000 ppm.
- Gas Mixture: 2% CH4 in H2 gas.
- Process Parameters: Substrate temperature maintained at 650 °C; deposition pressure at 3 kPa.
- Activation: Five tungsten filaments (0.7 mm diameter) heated to 2100 °C.
2. Electrochemical Disinfection Setup
Section titled â2. Electrochemical Disinfection Setupâ- Electrode System: Prototype system consisting of 10 BDD substrates (16 cm2 total anode area) and a graphite rod cathode (10 cm2 area).
- Power Supply: Stabilized DC power supply set to 30 V.
- Configurations Tested:
- BDD as Anode (Graphite as Cathode).
- BDD as Cathode (Graphite as Anode).
- BDD serving concurrently as Anode and Cathode (Anode+Cathode).
- Sample Volume: 300 ml wastewater (influent and effluent).
- Monitoring: Treatment efficiency analyzed by sampling at intervals up to 60 minutes, measuring bacterial counts (log CFU/ml), and calculating energy consumption (kWh/m3).
3. Ferrate Disinfection
Section titled â3. Ferrate Disinfectionâ- Agent: Powdered potassium ferrate (K2FeO4).
- Doses: 10 mg, 50 mg, and 100 mg added to 300 ml wastewater samples.
- Procedure: Solution was intensively mixed for one hour at laboratory temperature.
- Monitoring: pH change was tracked over time (up to 180 minutes) due to the release of OH- ions during ferrate decomposition (4FeO42- + 10H2O â 4Fe3+ + 10OH- + 3O2).
Commercial Applications
Section titled âCommercial ApplicationsâThe technologies and materials investigated are highly relevant for advanced environmental engineering and water management sectors.
- Wastewater Treatment (Tertiary Disinfection):
- High-efficiency elimination of antibiotic-resistant organisms (e.g., MRSA, VISA) and other pathogens from hospital and municipal wastewater effluent, ensuring compliance with strict environmental discharge limits.
- Application in decentralized or point-source treatment systems (e.g., health care institutions) where high microbial load reduction is critical.
- Advanced Oxidation Processes (AOPs):
- BDD electrodes are essential components for AOPs targeting the degradation of persistent organic micropollutants (pharmaceuticals, X-ray substances, illicit drugs) that are recalcitrant to biological treatment.
- Water Reclamation and Reuse:
- Providing a robust disinfection barrier necessary for treating wastewater intended for non-potable reuse (e.g., irrigation, industrial cooling).
- Electrochemical Reactor Design:
- Development of compact, modular electrochemical reactors utilizing BDD for industrial water purification requiring high chemical stability and efficient radical generation.
View Original Abstract
Abstract Increasing concentration of antibiotics in environment and their subinhibitory concentrations in wastewater may result in increased antibiotic resistance of present bacteria. Therefore, this study was aimed to analyze the efficiency of coagulase-positive staphylococci and Staphylococcus aureus inhibition in wastewater by electrochemical methods and addition of ferrates. Advanced electrochemical oxidation by boron doped diamond electrodes in anode; cathode and anode-cathode connection were used for wastewater disinfection. Results showed that the most effective connection was the anodic one, as complete inhibition of coagulase-positive staphylococci as well as of S. aureus was observed after 40 min. Energy consumption was 3.69 kWh/m 3 for effluent wastewater disinfection. The second studied method of wastewater disinfection was the application of powdered ferrates. Addition of 100 mg of ferrates resulted in the inhibition of 84â96 % of coagulase-positive staphylococci and 97â99 % of S. aureus in influent water, while the inhibition of coagulase-positive staphylococci and S. aureus was 61â83 % and 83â86 %, respectively, in effluent wastewater.