Electrolytic Oxidation as a Sustainable Method to Transform Urine into Nutrients
At a Glance
Section titled âAt a Glanceâ| 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 |
Executive Summary
Section titled âExecutive Summaryâ- Core Value Proposition: Electrolytic oxidation using thin film anodes (BDD and DSA) provides a sustainable, single-step method to transform synthetic human urine into a safe, nutrient-rich liquid fertilizer, simultaneously achieving high organic pollutant removal and pathogen deactivation.
- Performance Metrics: Near-complete mineralization of organic carbon (TOC and COD removal >90%) was achieved across tested current densities (20-100 mA/cm2).
- Anode Comparison: Boron-Doped Diamond (BDD) anodes exhibited faster kinetics for TOC and COD removal and produced higher concentrations of inorganic nitrogen (NO3- and NH4+) due to the resulting acidic medium.
- Nutrient Recovery: The process successfully converted organic nitrogen (urea, creatinine) into plant-assimilable forms (NO3- and NH4+). Final phosphate concentrations were sufficient for irrigation needs.
- Safety and Control: Pathogen deactivation is facilitated by the formation of active chlorine and chloramines. However, high current densities (60-100 mA/cm2) lead to massive production of toxic chlorates and perchlorates.
- Optimal Operating Condition: To ensure the treated effluent meets safety regulations for fertilizer use, the current density must be controlled to values less than or equal to 20 mA/cm2, especially when using DSA anodes, which resulted in the lowest hazardous byproduct formation.
Technical Specifications
Section titled âTechnical Specificationsâ| Parameter | Value | Unit | Context |
|---|---|---|---|
| Initial TOC | 750 | mg C/L | Synthetic Urine Composition |
| Initial COD | 825 | mg O2/L | Synthetic Urine Composition |
| Initial Total Nitrogen | ~1650 | mg N/L | Calculated from organic and inorganic components |
| Initial Conductivity | 6.5 | mS/cm | Synthetic Urine at 25 °C |
| Anode Geometric Area | 78 | cm2 | Electrochemical cell setup |
| Electrode Gap | 9 | mm | Separation between anode and cathode |
| Current Density Range Tested | 20 to 100 | mA/cm2 | Galvanostatic operation mode |
| Optimal Current Density (Safety) | â¤20 | mA/cm2 | Required to minimize toxic chlorine species |
| Flow Rate Range Tested | 800 to 1780 | mL/min | Batch-operation flow cell |
| Optimal Temperature (TOC removal) | 50 | °C | Enhanced efficiency in the final stages of treatment |
| Maximum Final NO3- (BDD) | 70 | mg N/L | Measured after 20 Ah/L charge consumption |
| Maximum Final NH4+ (BDD) | 250 | mg N/L | Measured after 20 Ah/L charge consumption |
| Chlorate Concentration (DSA, 20 mA/cm2, 1780 mL/min) | 5.2 | mg Cl/L | Lowest measured hazardous byproduct concentration |
| Perchlorate Concentration (DSA, 20 mA/cm2, 1780 mL/min) | ND | - | Not Detected |
Key Methodologies
Section titled âKey Methodologiesâ- Electrochemical Cell Setup: Experiments were conducted in a single-compartment electrochemical flow cell operating in batch mode, circulating 600 mL of synthetic urine electrolyte.
- Anode Materials:
- BDD (Boron-Doped Diamond): Fabricated via Hot Filament Chemical Vapor Deposition (HF CVD) on p-type Si(100) substrates.
- DSA (Dimensionally Stable Anodes): IrO2-RuO2 mixed metal oxide coating (5-10 Âľm thickness) deposited on titanium sheet (3 mm thickness).
- Cathode Material: Stainless Steel (AISI 304) was used as the counter electrode for all tests.
- Operation Mode: Galvanostatic mode (constant current density) was maintained using a digital DC power supply.
- Parameter Variation: The effects of current density (20, 60, and 100 mA/cm2), flow rate (800-1780 mL/min), and temperature (25 °C and 50 °C) on treatment kinetics were evaluated.
- Analytical Monitoring:
- Organic Content: Chemical Oxygen Demand (COD) and Total Organic Carbon (TOC) were monitored to track mineralization.
- Nutrients: Ion Chromatography (IC) was used for nitrate (NO3-) and phosphate (PO43-). Ammonium (NH4+) was measured using an ion-selective electrode.
- Byproducts/Disinfectants: IC was used for chlorine speciation (Cl-, ClO-, ClO2-, ClO3-, and ClO4-). Chloramines were measured using the DPD colorimetric method.
Commercial Applications
Section titled âCommercial ApplicationsâThe electrolytic oxidation process using thin film anodes is highly relevant for sustainable resource management and decentralized sanitation systems:
- Decentralized Wastewater Treatment: Implementation in source-separated sanitation systems (e.g., toilets designed for urine diversion) to treat high-strength urine effluent locally.
- Sustainable Agriculture and Landscaping: Production of a safe, liquid fertilizer rich in essential macronutrients (Nitrogen, Phosphorus, Potassium) and micronutrients, suitable for direct use or dilution in irrigation.
- Pathogen Control: The electrogeneration of active chlorine and chloramines provides inherent disinfection capabilities, ensuring the treated effluent is safe for agricultural reuse and minimizing the risk of disease transmission.
- Advanced Oxidation Processes (EAOPs): Utilizes robust electrode technology (BDD and DSA) for the efficient mineralization of recalcitrant organic micro-pollutants (hormones, pharmaceuticals) often found in urine.
- Electrochemical Reactor Design: Provides engineering data supporting the design and optimization of flow-through electrochemical reactors for continuous or batch processing of high-concentration waste streams.
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 (NO3â) 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 NO3â 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.