Kinetics of the Organic Compounds and Ammonium Nitrogen Electrochemical Oxidation in Landfill Leachates at Boron-Doped Diamond Anodes

At a Glance

Metadata	Details
Publication Date	2021-08-31
Journal	Materials
Authors	Barbara Wilk, Małgorzata Szopińska, Aneta Łuczkiewicz, Michał Sobaszek, Ewa Maria Siedlecka
Institutions	Gdańsk University of Technology, University of Gdańsk
Citations	10
Analysis	Full AI Review Included

Technical Documentation & Analysis: Boron-Doped Diamond Anodes for Advanced Oxidation Processes (AOPs)

Executive Summary

This analysis confirms the critical role of Boron-Doped Diamond (BDD) anodes, specifically those manufactured via Microwave Plasma Assisted Chemical Vapor Deposition (MPCVD), in high-efficiency electrochemical oxidation (EO) for complex wastewater treatment.

Material Validation: Boron-Doped Diamond (BDD) electrodes are validated as highly effective, “non-active” anodes for the degradation of refractory organic compounds (COD) and ammonium nitrogen (N-NH₄⁺) in high-salinity Landfill Leachates (LLs).
Optimal Doping Identified: Low boron doping (0.5 k, 500 ppm [B]/[C]) demonstrated superior performance for direct oxidation, achieving a wider electrochemical working window (3.9 V) compared to highly doped samples (2.23 V for 15 k).
High Removal Efficiency: Optimized conditions (0.5 k BDD, j = 100 mA·cm^-2) resulted in near-complete Chemical Oxygen Demand (COD) removal (C_8h/C₀ = 0.09 ± 0.14).
Pre-treatment Efficacy: EO treatment successfully doubled the biodegradability index (BI) from 0.11 to 0.22 (using 0.5 k BDD at j = 50 mA·cm^-2), confirming BDD-based EO as an essential pre-treatment step prior to biological processing.
Kinetic Modeling: COD removal kinetics were accurately modeled as pseudo-first-order reactions, while N-NH₄⁺ removal generally followed second-order kinetics, highlighting distinct degradation pathways (direct vs. chlorine-mediated oxidation).
Energy Optimization: Optimal cost-effective treatment conditions were identified, achieving >70% COD removal after 4 hours with an energy consumption of 200 kW·m^-3.

Technical Specifications

Parameter	Value	Unit	Context
Anode Material	BDD on Silicon (BDD/Si)	N/A	Synthesized via MWPACVD
Boron Doping Levels	500 (0.5 k), 10,000 (10 k), 15,000 (15 k)	ppm ([B]/[C] ratio)	Tested for performance comparison
Optimal Current Density (j)	100	mA·cm^-2	Highest COD removal efficiency
Electrochemical Window (0.5 k BDD)	3.9	V	Widest window, best for direct oxidation
Electrochemical Window (15 k BDD)	2.23	V	Narrowest window, high defect concentration
COD Removal (0.5 k BDD, 100 mA·cm^-2)	0.09 ± 0.14	C_8h/C₀	Near-complete removal after 8 hours
N-NH₄⁺ Removal (0.5 k BDD, 100 mA·cm^-2)	0.39 ± 0.05	C_8h/C₀	Lower removal efficiency (chlorine-mediated)
Maximum Biodegradability Index (BI)	0.22 ± 0.05	BOD₂₀/COD ratio	Achieved using 0.5 k BDD at 50 mA·cm^-2
Optimized Energy Consumption (EC)	200	kW·m^-3	For >70% COD removal after 4 hours (0.5 k BDD)
Initial COD Concentration (LLs)	3608 ± 123	mg O₂·L^-1	Raw Landfill Leachate characteristic
Initial N-NH₄⁺ Concentration (LLs)	2069 ± 103	mg·L^-1	Raw Landfill Leachate characteristic
Electrode Surface Area	10.5	cm²	Geometric area of flat anode/cathode
Interelectrode Distance	2.0	cm	Experimental setup parameter

Key Methodologies

The BDD electrodes were synthesized using the Microwave Plasma Assisted Chemical Vapor Deposition (MWPACVD) process, followed by galvanostatic electrochemical testing.

BDD Synthesis (MWPACVD):
- Substrate: Two-inch Silicon wafers.
- Deposition Time: 12 hours.
- Chamber Pressure: 50 Torr.
- Microwave Power: 1300 W (2.45 GHz).
- Induction Heating Temperature: 700 °C.
- Total Gas Flow Rate: 300 sccm.
- Molar Ratio (Methane): 1%.
- Dopant Precursor: Diborane (B₂H₆).
- Doping Levels Tested: 500, 10,000, and 15,000 ppm [B]/[C] ratio in the gas phase.
Electrochemical Oxidation (EO) Setup:
- Reactor Type: 500-mL single-chambered reactor (400 mL sample volume).
- Anode: BDD/Si electrodes (10.5 cm² area).
- Cathode: Stainless-steel mesh (10.5 cm² area).
- Operating Mode: Galvanostatic (constant current density, j).
- Current Densities Tested (j): 25, 30, 50, 75, and 100 mA·cm^-2.
- Temperature Control: Maintained at 25 ± 1 °C (using a cooling bath).
- Duration: 8 hours, with samples collected every 2 hours.
Characterization:
- Morphology: SEM imaging revealed grain size decreased from approximately 2 µm (0.5 k BDD) to 0.5 µm (15 k BDD) with increasing boron content.
- Structure/Doping Confirmation: Raman spectroscopy confirmed sp³ diamond lines and the Fano effect in highly doped samples, correlating the shift and asymmetry of the diamond peak to boron incorporation.
- Electrochemical Properties: Cyclic voltammetry (CV) measured the electrochemical potential windows in 1 M KCl.

6CCVD Solutions & Capabilities

6CCVD is uniquely positioned to support and advance research in electrochemical oxidation using BDD anodes, offering custom materials and engineering support that directly addresses the requirements and future scalability of this technology.

Applicable Materials

The research confirms that Boron-Doped Diamond (BDD) is the optimal material for high-efficiency EO of complex leachates. 6CCVD offers BDD materials tailored for this application:

Heavy Boron Doped PCD (Polycrystalline Diamond): Ideal for large-scale industrial anodes. We offer plates/wafers up to 125 mm in diameter, significantly exceeding the 2-inch wafers used in the study, enabling scale-up.
Custom Doping Control: The study highlights the critical importance of precise boron concentration (e.g., the superior performance of the 0.5 k BDD). 6CCVD provides custom BDD doping levels to optimize the electrochemical window and maximize direct oxidation efficiency for specific wastewater matrices.
BDD Thin Films on Silicon Substrates: We supply BDD films on Si substrates, replicating the exact material configuration used in this research, suitable for R&D and pilot studies.

Customization Potential

To replicate or extend the findings of this study, 6CCVD offers comprehensive customization services:

Research Requirement	6CCVD Customization Capability	Technical Advantage
Custom Doping Levels	Precise control over [B]/[C] ratio (e.g., 500 ppm, 10k ppm, 15k ppm)	Enables fine-tuning of the electrochemical window for maximum hydroxyl radical generation.
Large Area Anodes	PCD plates/wafers up to 125 mm diameter.	Facilitates immediate scale-up from laboratory (10.5 cm²) to industrial reactor sizes.
Custom Thickness	SCD/PCD films from 0.1 µm to 500 µm.	Allows optimization of diamond layer thickness for cost-efficiency and long-term stability.
Electrode Geometry	Laser cutting and shaping services.	Provides custom geometric surface areas (e.g., 10.5 cm² flat plates) and complex 3D structures for enhanced mass transfer.
Current Collection/Contacts	In-house metalization (Au, Pt, Pd, Ti, W, Cu).	Essential for robust electrical contacts and integration into flow reactors, addressing the need for stable, low-resistance connections.

Engineering Support

The complexity of LL treatment kinetics (pseudo-first-order for COD, second-order for N-NH₄⁺) necessitates expert material selection. 6CCVD’s in-house PhD team specializes in diamond electrochemistry and can assist clients with:

Material Selection for AOPs: Consulting on the optimal BDD doping level and substrate choice (PCD vs. SCD) to maximize direct oxidation pathways and minimize energy consumption (EC) for specific Landfill Leachate Treatment projects.
Electrode Lifetime and Stability: Providing guidance on maximizing electrode stability and minimizing defect formation, crucial for long-term economic viability, especially when operating at high current densities (up to 100 mA·cm^-2).
Reactor Design Integration: Supporting the integration of custom BDD anodes into compact and modular reactor designs, a key factor cited in the paper for wider industrial implementation.

For custom specifications or material consultation, visit 6ccvd.com or contact our engineering team directly.

View Original Abstract

Electrochemical oxidation (EO) of organic compounds and ammonium in the complex matrix of landfill leachates (LLs) was investigated using three different boron-doped diamond electrodes produced on silicon substrate (BDD/Si)(levels of boron doping [B]/[C] = 500, 10,000, and 15,000 ppm—0.5 k; 10 k, and 15 k, respectively) during 8-h tests. The LLs were collected from an old landfill in the Pomerania region (Northern Poland) and were characterized by a high concentration of N-NH4+ (2069 ± 103 mg·L−1), chemical oxygen demand (COD) (3608 ± 123 mg·L−1), high salinity (2690 ± 70 mg Cl−·L−1, 1353 ± 70 mg SO42−·L−1), and poor biodegradability. The experiments revealed that electrochemical oxidation of LLs using BDD 0.5 k and current density (j) = 100 mA·cm−2 was the most effective amongst those tested (C8h/C0: COD = 0.09 ± 0.14 mg·L−1, N-NH4+ = 0.39 ± 0.05 mg·L−1). COD removal fits the model of pseudo-first-order reactions and N-NH4+ removal in most cases follows second-order kinetics. The double increase in biodegradability index—to 0.22 ± 0.05 (BDD 0.5 k, j = 50 mA·cm−2) shows the potential application of EO prior biological treatment. Despite EO still being an energy consuming process, optimum conditions (COD removal > 70%) might be achieved after 4 h of treatment with an energy consumption of 200 kW·m−3 (BDD 0.5 k, j = 100 mA·cm−2).

Tech Support

Original Source

DOI: https://doi.org/10.3390/ma14174971

References

2020 - Determining the effects of Class I landfill leachate on biological nutrient removal in wastewater treatment [Crossref]
2020 - Effective treatment of high-salinity landfill leachate using ultraviolet/ultrasonication/ peroxymonosulfate system [Crossref]
2019 - Landfill leachates and wastewater of maritime origin as possible sources of endocrine disruptors in municipal wastewater [Crossref]
2021 - Optimization of the process variables for landfill leachate treatment using Fenton based advanced oxidation technique
2006 - Combined biological and chemical degradation for treating a mature municipal landfill leachate [Crossref]
2021 - Performance of coupling electrocoagulation and biofiltration processes for the treatment of leachate from the largest landfill in Hanoi, Vietnam: Impact of operating conditions [Crossref]