Feasibility of Micropollutants Treatment by Coupling Nanofiltration and Electrochemical Oxidation - Case of Hospital Wastewater

At a Glance

Metadata	Details
Publication Date	2015-04-17
Journal	International Journal of Chemical Reactor Engineering
Authors	Yandi Lan, Clémence Coetsier, Christel Causserand, Karine Groenen Serrano
Institutions	Laboratoire de Génie Chimique
Citations	15
Analysis	Full AI Review Included

Technical Documentation & Brief: MPCVD Diamond for Advanced Water Treatment

6CCVD Ref: DOC-EO-HWW-03519067 Application: Electrochemical Oxidation (EO) of Refractory Micropollutants Source Paper: Feasibility of Micropollutants Treatment by Coupling Nanofiltration and Electrochemical Oxidation: Case of Hospital Wastewater

Executive Summary

This research validates the use of coupled Nanofiltration (NF) and highly efficient Electrochemical Oxidation (EO) utilizing Boron-Doped Diamond (BDD) anodes for the tertiary treatment of hospital wastewater, specifically targeting the pharmaceutical pollutant Ciprofloxacin (CIP).

Material Validation: Confirmed that MPCVD Boron-Doped Diamond (BDD) anodes provide the superior electrochemical activity necessary for high-efficiency mineralization of refractory organic compounds.
High Removal Efficiency: Achieved complete (100%) Chemical Oxygen Demand (COD) removal and 97% Total Organic Carbon (TOC) removal in the NF retentate within 300 minutes of electrolysis.
Target Pollutant Destruction: Ciprofloxacin (CIP) was completely eliminated in the retentate within 150 minutes, demonstrating the powerful non-selective oxidation capability of BDD-generated hydroxyl radicals (OH•).
Process Optimization: The NF preconcentration step successfully reduced the required treatment volume (VRF=5), mitigating mass transfer limitations inherent in dilute solutions and making the subsequent EO process economically viable.
Energy Metrics: The total COD removal was achieved with a competitive Specific Energy Consumption (SEC) of 50 kW h kg^-1 COD.
Final Effluent Quality: The global final effluent (NF permeate and EO final tank) contained less than 5 mg L^-1 of organics, meeting stringent discharge limits.

Technical Specifications

The following table extracts critical operating parameters and performance metrics from the electrochemical oxidation (EO) phase of the study, highlighting the requirements for high-performance BDD anodes.

Parameter	Value	Unit	Context
Anode Material Used	Boron-Doped Diamond (BDD)	-	Elaborated by CVD on Silicon (Si) substrate
Reactor Type	Single-compartment flow filterpress	-	Galvanostatic operating conditions
Anode Active Surface Area	63	cm²	Two circular disc electrodes used
Electrode Separation	10	mm	Spacing within the electrochemical cell (3)
Electrolysis Temperature	30	°C	Controlled using a thermoregulated reservoir
Applied Current Density (MBR Effluent)	7.9	mA cm^-2	Operates above the limiting current density
Electrolyte Composition	0.1 M K₂SO₄	-	Used for conductivity enhancement
COD Final Concentration	0	mg L^-1	Achieved after 300 min electrolysis
TOC Final Concentration	1.9	mg L^-1	Achieved after 300 min electrolysis (Initial 62 mg L^-1)
Specific Energy Consumption (SEC)	50	kW h kg^-1 COD	Metric for total COD removal

Key Methodologies

The Electrochemical Oxidation (EO) stage was critically dependent on specific reactor design and operational parameters to maximize the generation of hydroxyl radicals (OH•) and ensure complete mineralization.

Feed Preparation: Nanofiltration (NF) retentate (Volume Reduction Factor, VRF = 5) was collected, resulting in a concentrated stream of micropollutants.
Electrolyte Conditioning: The pH of the retentate was adjusted to 3.0, and 0.1 M K₂SO₄ was added as the supporting electrolyte to increase conductivity.
Electrode Fabrication: The BDD anode was fabricated via Chemical Vapor Deposition (CVD) onto a conductive silicon substrate.
Reactor Setup: A discontinuous, single-compartment flow filterpress reactor was utilized, employing two BDD disc electrodes (63 cm² each) separated by 10 mm.
Galvanostatic Control: Electrolyses were conducted under galvanostatic conditions (constant current density), specifically 7.9 mA cm^-2 for the MBR effluent matrix.
Oxidation Mechanism: The high applied current density ensured the kinetic regime was mass-transfer limited, maximizing the non-selective oxidation mediated by physisorbed hydroxyl radicals generated at the BDD surface.

6CCVD Solutions & Capabilities

6CCVD is an expert provider of MPCVD diamond, specializing in the custom materials required to replicate, scale, and advance high-performance electrochemical oxidation systems like the one described. Our integrated material science and engineering support ensures seamless integration of BDD into industrial or research reactors.

Applicable Materials

To replicate the high removal efficiencies demonstrated in this study, the primary material requirement is a robust, high-performance anode capable of maximizing the production of non-selective oxidants.

Material Grade	Description	Connection to Research Requirements
Heavy Boron-Doped Diamond (BDD)	Polycrystalline (PCD) or Single Crystal (SCD) diamond heavily doped for conductivity and electrochemical stability.	Essential for generating high concentrations of hydroxyl radicals (OH•) required for 100% COD mineralization and low SEC.
BDD on Conductive Substrates	BDD films grown directly on conductive Silicon (Si) or Tantalum (Ta) supports.	Directly meets the study’s requirement for BDD deposited on a conductive silicium substrate for optimal electrode function.
High Purity Single Crystal Diamond (SCD)	SCD (Grade IIa or Optical) plates (0.1 µm to 500 µm thick).	While BDD is the primary electrode material, high purity SCD can be utilized for advanced sensor applications or specific optical monitoring elements within the reactor environment.

Customization Potential

The experimental setup relied on specific electrode dimensions (63 cm² discs) and configurations. 6CCVD’s advanced MPCVD capabilities are perfectly suited to supply materials for scaling this technology.

Requirement	6CCVD Capability	Direct Relevance
Custom Electrode Dimensions	Production of plates and wafers up to 125 mm (PCD/BDD).	Allows immediate scale-up from the 63 cm² lab discs to larger circular or rectangular flow-cell geometries.
Thickness Control	BDD layers available from 0.1 µm to 500 µm on insulating or conductive substrates.	Enables optimization of BDD film thickness for longevity, mechanical strength, and electrical resistance requirements of the reactor.
Substrate Integration	In-house laser cutting and machining services for complex geometries.	Provides custom BDD electrode shapes ready for integration into proprietary filterpress or plate-and-frame reactor designs.
Advanced Metalization	Standard and custom metalization (Au, Pt, Pd, Ti, W, Cu) for contact layers.	Necessary for creating durable, low-resistance electrical connections required for high-current galvanostatic operation.

Engineering Support

Our team of in-house PhD material scientists specializes in the electrochemistry of diamond and advanced water treatment applications.

Application Expertise: We offer consultation on optimizing BDD doping levels and surface termination to maximize hydroxyl radical generation rates for similar Electrochemical Water Treatment projects.
Scale-Up Guidance: Our experts provide technical guidance on selecting the optimal BDD substrate (e.g., Si vs. Ta) and dimensions for moving from lab-scale (1 L reservoir used in the paper) to pilot-scale reactors, focusing on minimizing SEC.
Electrochemical Design: We assist in material selection to ensure chemical compatibility with various aggressive media (high acidity, sulfate, chloride, etc.) encountered during industrial EO processes.

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

View Original Abstract

Abstract In spite of good performances of the membrane bioreactor (MBR) process, permeate from it can still contain refractory pollutants that have to be removed before water reuse or discharge. The present study is an attempt to combine the advantages of two well-known technologies, which are nanofiltration (NF) and electrochemical oxidation (EO) to treat MBR effluent from hospital wastewater. The concept is based on a preconcentration of micropollutants with a reduction of the wastewater volume by NF and treatment of the NF retentate by oxidation. During filtration process the rejection of ciprofloxacin, as a target molecule, reached beyond 97%. Then the NF retentate was treated by EO using a boron-doped diamond anode (BDD). Galvanostatic electrolyses showed that this anode is efficient to mineralize not only ciprofloxacin but also all the micropollutants and organics contained in MBR effluent. The results demonstrated that rapid mineralization occurred: the removal of total organic carbon and chemical oxygen demand (COD) reached 97% and 100%, respectively, in our conditions in 300 min maximum. The speciﬁc energy consumption for the total removal of COD was calculated to be 50 kW h kg ˗1 COD.

Tech Support

Original Source

DOI: https://doi.org/10.1515/ijcre-2014-0136

References

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