Electrolytic Oxidation as a Sustainable Method to Transform Urine into Nutrients

At a Glance

Metadata	Details
Publication Date	2020-04-14
Journal	Processes
Authors	Nasr Bensalah, Sondos Dbira, Ahmed Bedoui, Mohammad I. Ahmad
Institutions	Qatar University, University of Gabès
Citations	6
Analysis	Full AI Review Included

Technical Documentation & Analysis: Electrolytic Oxidation for Nutrient Recovery

Executive Summary

This analysis focuses on the application of thin-film Boron-Doped Diamond (BDD) anodes in the electrolytic oxidation of synthetic urine for nutrient recovery and pollutant degradation. The research confirms BDD’s superior performance in achieving complete organic carbon mineralization compared to Dimensionally Stable Anodes (DSA).

Core Application: Sustainable transformation of urine into a liquid fertilizer rich in inorganic nitrogen (NO₃¯, NH₄⁺) and phosphorus, while simultaneously removing organic pollutants (TOC, COD) and deactivating pathogens.
Material Superiority: BDD anodes demonstrated faster kinetics for Chemical Oxygen Demand (COD) and Total Organic Carbon (TOC) removal, and produced significantly higher concentrations of desirable inorganic nitrogen species (up to 250 mg N/L NH₄⁺).
Mechanism: BDD’s large electrochemical window facilitates the generation of powerful hydroxyl radicals (HO•), leading to more complete mineralization (TOC decay) compared to DSA, which relies more heavily on active chlorine generation.
Critical Process Control: The study highlights that current density is the critical operational parameter. Low current densities (≤20 mA/cm²) are essential to minimize the formation of toxic, regulated chlorine byproducts (chlorates and perchlorates).
6CCVD Relevance: The successful implementation relies entirely on high-quality, thin-film BDD electrodes deposited on silicon substrates, a core specialization of 6CCVD, enabling the scale-up and optimization of this sustainable wastewater treatment technology.

Technical Specifications

The following hard data points were extracted from the study, detailing the synthetic urine composition and critical electrochemical operating parameters.

Parameter	Value	Unit	Context
Anode Material (Tested)	BDD Thin Film	N/A	Deposited on p-type Si(100) substrate (0.1 Ω cm)
Anode Material (Comparison)	DSA (IrO₂-RuO₂)	N/A	Mixed metal oxide on 3 mm thick Ti sheet
Electrode Geometry	100	mm diameter	Geometric Area: 78 cm²
Electrode Separation	9	mm	Single-compartment flow cell
Initial TOC	750	mg C/L	Synthetic urine organic content
Initial COD	825	mg O₂/L	Synthetic urine oxygen demand
Initial Conductivity	6.5	mS/cm	Equivalent to 6500 µS/cm
Initial pH	5.5	N/A	Synthetic urine starting condition
Current Densities Tested	20, 60, 100	mA/cm²	Galvanostatic mode operation
Optimal Current Density	≤20	mA/cm²	Required to meet regulatory limits for chlorates/perchlorates
Max NH₄⁺ (BDD)	250	mg N/L	Measured at the end of treatment
Max NO₃¯ (BDD)	70	mg N/L	Measured at the end of treatment
Chlorate Concentration (BDD)	325.4	mg Cl/L	At 20 mA/cm², 800 mL/min, 17 Ah/L
Perchlorate Concentration (BDD)	20.5	mg Cl/L	At 20 mA/cm², 800 mL/min, 17 Ah/L
Operating Temperature	25, 50	°C	Temperature showed efficiency gains at 50 °C

Key Methodologies

The electrolytic oxidation was conducted using a single-compartment electrochemical flow cell operating in galvanostatic (constant current density) mode.

Anode Fabrication: BDD thin films were fabricated using Hot Filament Chemical Vapor Deposition (HF CVD) onto single-crystal p-type Si(100) substrates. DSA anodes were mixed metal oxide (IrO₂-RuO₂) coated onto titanium sheets.
Electrochemical Cell: A single-compartment flow cell was utilized with circular electrodes (100 mm diameter) and a stainless steel (AISI 304) cathode.
Electrolyte Circulation: Synthetic urine (600 mL volume) was circulated through the cell using a centrifugal pump at variable flow rates (800-1780 mL/min).
Operational Control: Experiments were run under galvanostatic control (constant current density) using a digital DC power supply (0-30 A, 0-20 V). Temperature was maintained using a thermostatic bath (25 °C and 50 °C).
Monitoring Parameters: Key performance indicators monitored included TOC, COD, pH, conductivity, and the speciation of inorganic ions (NO₃¯, NH₄⁺, Cl¯, ClO¯, ClO₃¯, ClO₄¯, and chloramines).

6CCVD Solutions & Capabilities

The successful replication and optimization of this advanced electrochemical process for sustainable nutrient recovery require high-quality, customized Boron-Doped Diamond (BDD) anodes. 6CCVD is uniquely positioned to supply the necessary materials and engineering support.

Applicable Materials

To replicate or extend the high-efficiency mineralization achieved in this research, the following 6CCVD material is required:

Heavy Boron-Doped Diamond (BDD) on Silicon Substrate: The research utilized BDD thin films on p-type Si(100). 6CCVD specializes in producing high-quality, heavily doped BDD films via MPCVD, ensuring the high oxygen evolution over-potential necessary for efficient hydroxyl radical (HO•) generation and complete organic mineralization.
Custom Doping Levels: Precise control over boron doping (achieved via MPCVD) is critical for maximizing HO• production while maintaining electrode stability, crucial for long-term industrial applications.

Customization Potential

The experimental setup utilized 100 mm diameter circular electrodes. 6CCVD’s manufacturing capabilities directly address these specific dimensional and structural requirements, facilitating seamless transition from lab-scale research to pilot-scale implementation.

Research Requirement	6CCVD Capability	Benefit to Client
Electrode Dimensions	Custom plates/wafers up to 125 mm (PCD/SCD/BDD)	Easily accommodate the 100 mm diameter required for scale-up or larger flow cells.
Anode Thickness	SCD/PCD/BDD layers from 0.1 µm up to 500 µm	Supply thin-film BDD layers optimized for electrochemical activity and cost efficiency.
Substrate Integration	BDD on Si, Ti, or other custom substrates	Provide BDD films on the specified p-type Si substrate or transition to robust, conductive substrates like Ti for industrial reactor designs.
Metalization/Contacts	Internal capability for Au, Pt, Ti, W, Cu metalization	Offer custom metal contacts or current collector layers necessary for robust electrical connection in flow cell reactors.
Surface Finish	Polishing available (Ra < 1nm SCD, < 5nm PCD)	Ensure optimal surface morphology for consistent electrochemical performance and longevity.

Engineering Support

The study emphasizes that controlling toxic byproduct formation (chlorates/perchlorates) requires precise control of current density and, implicitly, high material quality.

Process Optimization: 6CCVD’s in-house PhD team can assist engineers and scientists in selecting the optimal BDD material specifications (doping concentration, film thickness, and substrate resistivity) to maximize nutrient recovery efficiency while adhering to strict regulatory limits (e.g., controlling ClO₃¯ and ClO₄¯ formation) for similar Electrochemical Advanced Oxidation Processes (EAOPs) projects.
Electrode Longevity: We provide comprehensive material characterization to ensure the BDD anodes maintain electrochemical stability and resist deterioration or passivation, crucial for the long-term sustainability of urine treatment systems.
Global Supply Chain: 6CCVD offers reliable global shipping (DDU default, DDP available) to ensure timely delivery of custom BDD electrodes worldwide, supporting rapid deployment of research and pilot projects.

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

View Original Abstract

In this work, the transformation of urine into nutrients using electrolytic oxidation in a single-compartment electrochemical cell in galvanostatic mode was investigated. The electrolytic oxidation was performed using thin film anode materials: boron-doped diamond (BDD) and dimensionally stable anodes (DSA). The transformation of urine into nutrients was confirmed by the release of nitrate (NO3−) and ammonium (NH4+) ions during electrolytic treatment of synthetic urine aqueous solutions. The removal of chemical oxygen demand (COD) and total organic carbon (TOC) during electrolytic treatment confirmed the conversion of organic pollutants into biocompatible substances. Higher amounts of NO3− and NH4+ were released by electrolytic oxidation using BDD compared to DSA anodes. The removal of COD and TOC was faster using BDD anodes at different current densities. Active chlorine and chloramines were formed during electrolytic treatment, which is advantageous to deactivate any pathogenic microorganisms. Larger quantities of active chlorine and chloramines were measured with DSA anodes. The control of chlorine by-products to concentrations lower than the regulations require can be possible by lowering the current density to values smaller than 20 mA/cm2. Electrolytic oxidation using BDD or DSA thin film anodes seems to be a sustainable method capable of transforming urine into nutrients, removing organic pollution, and deactivating pathogens.

Tech Support

Original Source

DOI: https://doi.org/10.3390/pr8040460