Electrochemical Oxidation of Landfill Leachate after Biological Treatment by Electro-Fenton System with Corroding Electrode of Iron

At a Glance

Metadata	Details
Publication Date	2022-06-24
Journal	International Journal of Environmental Research and Public Health
Authors	Juan Tang, Shuo Yao, Fei Xiao, Jianxin Xia, Xing Xuan
Institutions	Energy Foundation, Minzu University of China
Citations	7
Analysis	Full AI Review Included

Executive Summary

The research investigates the advanced treatment of biologically pre-treated landfill leachate using a novel, highly efficient electrochemical system.

Core Technology: A BDD-Fec-CF system, integrating a Boron-Doped Diamond (BDD) anode, a corroding iron (Fe_c) electrode, and a Carbon Felt (CF) cathode, was developed to combine electrochemical oxidation and electro-Fenton processes.
Optimization: Response Surface Methodology (RSM) with Box-Behnken Design (BBD) was used to optimize key variables: current density, electrolytic time, and pH.
Peak Performance: Under optimal conditions (25 mA·cm^-2, 9 h, pH 11), the system achieved exceptional pollutant removal efficiencies.
Key Achievements: Chemical Oxygen Demand (COD) removal reached 81.3%, and Ammonia Nitrogen (NH₃-N) removal reached 99.8%.
Mechanism Versatility: The system operates effectively across a wide pH range (3-11). Acidic conditions favor Fenton oxidation (·OH production), while alkaline conditions utilize coagulation (Fe(OH)₃), Fe(VI) oxidation, and NH₃ volatilization.
Mineralization Success: GC-MS analysis confirmed significant degradation of refractory organics, reducing the number of detected organic compounds from 56 types to only 16 types after treatment.

Technical Specifications

Parameter	Value	Unit	Context
Optimal Current Density (X₁)	25	mA·cm^-2	RSM optimized condition
Optimal Electrolytic Time (X₂)	9	h	RSM optimized condition
Optimal pH Value (X₃)	11	-	RSM optimized condition (Alkaline)
Actual COD Removal Efficiency	81.3	%	Under optimal conditions
Actual NH₃-N Removal Efficiency	99.8	%	Under optimal conditions
Initial COD Concentration (Average)	2464	mg·L^-1	Biologically treated leachate sample
Initial NH₃-N Concentration (Average)	154.4	mg·L^-1	Biologically treated leachate sample
BDD Anode Dimensions	20 x 20 x 1	mm	Electrode size
Electrode Surface Area (BDD/CF)	4	cm²	Active area in reactor
Anode-Cathode Gap	15	mm	Reactor setup
Initial Organic Compounds (GC-MS)	56	types	Before treatment
Final Organic Compounds (GC-MS)	16	types	After treatment
COD Model R² (Determination Coeff.)	0.9941	-	Statistical fit of RSM model
NH₃-N Model R² (Determination Coeff.)	0.9768	-	Statistical fit of RSM model
Adequate Precision (AP) COD Model	42.000	-	Model predictor indicator (AP > 4 required)

Key Methodologies

The treatment utilized a custom BDD-Fec-CF electrochemical reactor optimized via statistical design.

Reactor Setup: A one-compartment cell (400 mL) was used, operating under galvanostatic conditions (constant direct current). The BDD anode and CF cathode were separated by 15 mm.
Corroding Electrode: A sheet of iron (Fe_c) was inserted between the BDD and CF electrodes. The Fe_c was pre-treated by sanding and soaking in 0.5 M HCl for 10 min.
Electrode Pretreatment: The CF cathode was pre-soaked sequentially in 4.5 M NaOH and 5 M HCl to ensure optimal performance for H₂O₂ generation.
Optimization Design: Response Surface Methodology (RSM) using a three-factor, three-level Box-Behnken Design (BBD) was implemented to determine the synergistic effects of:
- Current Density (15 to 25 mA·cm^-2)
- Electrolytic Time (3 to 9 h)
- pH Value (3 to 11)
Pollutant Analysis: COD was measured using the standard titrimetric method (dichromate digestion at 150 °C). NH₃-N was measured via Nessler’s reagent colorimetry.
Organic Compound Identification: GC-MS (Agilent 6890/5973) was used. Samples were extracted sequentially under neutral, alkaline (pH 12), and acidic (pH 2) conditions using CH₂Cl₂, followed by concentration via rotary evaporator.

Commercial Applications

The BDD-Fec-CF system offers a robust and versatile solution for treating complex, bio-refractory liquid waste streams.

Landfill Leachate Treatment: Provides an effective tertiary treatment step for biologically pre-treated leachate, ensuring compliance with strict environmental discharge limits for COD and NH₃-N.
Industrial Wastewater Remediation: Applicable to high-strength industrial effluents containing persistent organic pollutants (POPs), such as those from chemical, pharmaceutical, and textile industries.
Electrochemical AOPs (Advanced Oxidation Processes): The BDD anode, known for its high stability and ability to generate powerful oxidants (e.g., ·OH), is critical for developing next-generation AOP reactors.
Cost-Effective Fenton Chemistry: The use of a sacrificial iron electrode (Fe_c) eliminates the need for continuous external dosing of ferrous salts (FeSO₄), significantly lowering operational costs associated with traditional Fenton processes.
Wide-Range pH Systems: The system’s ability to maintain high efficiency across pH 3-11 allows for flexible operation without the intensive pH control required by conventional electro-Fenton (which typically requires pH ~3).
Nitrogen Removal Technologies: Highly efficient removal of ammonia nitrogen, combining electrochemical conversion with pH-driven volatilization, suitable for facilities facing strict nutrient discharge regulations.

View Original Abstract

Electrochemical oxidation of landfill leachate after biological treatment by a novel electrochemical system, which was constructed by introducing a corroding electrode of iron (Fec) between a boron-doped diamond (BDD) anode and carbon felt (CF) cathode (named as BDD-Fec-CF), was investigated in the present study. Response surface methodology (RSM) with Box-Behnken (BBD) statistical experiment design was applied to optimize the experimental conditions. Effects of variables including current density, electrolytic time and pH on chemical oxygen demand (COD) and ammonia nitrogen (NH3-N) removal efficiency were analyzed. Results showed that electrolytic time was more important than current density and pH for both COD and NH3-N degradation. Based on analysis of variance (ANOVA) under the optimum conditions (current density of 25 mA·cm−2, electrolytic time of 9 h and pH of 11), the removal efficiencies for COD and NH3-N were 81.3% and 99.8%, respectively. In the BDD-Fec-CF system, organic pollutants were oxidized by electrochemical and Fenton oxidation under acidic conditions. Under alkaline conditions, coagulation by Fe(OH)3 and oxidation by Fe(VI) have great contribution on organic compounds degradation. What is more, species of organic compounds before and after electrochemical treatment were analyzed by GC-MS, with 56 kinds components detected before treatment and only 16 kinds left after treatment. These results demonstrated that electrochemical oxidation by the BDD-Fec-CF system has great potential for the advanced treatment of landfill leachate.

Tech Support

Original Source

DOI: https://doi.org/10.3390/ijerph19137745

References

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