Key Takeaways & Executive Findings
- •• • N-RuO2 achieved 81.4% NH4+-N removal in 3 h, surpassing RuO2 (66.4%), DSA (60.3%), and Com-RuO2 (55.7%), with energy savings of 9.5, 13.1, and 17.7 Wh·g−1, respectively—critical for reducing operational costs in industrial wastewater treatment. • • COD removal reached 91.8% in 100 min with N-RuO2, outperforming RuO2 (90.9%), DSA (88.4%), and Com-RuO2 (83.2%), while cutting energy consumption by 0.5, 0.8, and 1.5 Wh·g−1, demonstrating superior oxidation efficiency. • • N-RuO2 exhibited a 25.6% higher Faradaic efficiency for chlorine evolution and a 2.9-fold longer accelerated lifetime compared to Com-RuO2, ensuring stable and efficient operation under harsh conditions. • • The nanorod morphology increased electrochemical active surface area by 7.3 times and reduced charge transfer resistance by 6.86 Ω, directly enhancing catalytic activity and durability—key for scaling up to industrial electrodes.
Abstract
This study addresses the removal of ammonia nitrogen (NH4+-N) and chemical oxygen demand (COD) from real coal chemical wastewater via electrochemical chlorine evolution. A nanorod-structured ruthenium dioxide catalyst (N-RuO2) was synthesized by modifying ruthenium trichloride precursor with ammonium chloride. Compared with unmodified RuO2, commercial DSA, and commercial RuO2 (Com-RuO2), N-RuO2 exhibited significantly enhanced electrochemical performance: Faradaic efficiency for chlorine evolution increased by 12.9%, 18.5%, and 25.6%, respectively; accelerated lifetime improved by 1.7, 1.9, and 2.9 times, respectively. In treating real coal chemical wastewater, N-RuO2 reduced NH4+-N to 86.4 mg·L−1 and COD to 72 mg·L−1, with degradation rate constants approximately 2.08 and 1.46 times higher than Com-RuO2, while energy consumption decreased by 17.7 Wh·g−1 and 1.5 Wh·g−1, respectively. Further studies showed that increasing chloride ion concentration enhanced removal rates and reduced energy consumption; higher current density accelerated removal but increased energy use; alkaline conditions favored NH4+-N removal, while neutral conditions favored COD removal. The excellent electrochemical performance of RuO2 nanorods indicates broad application prospects in practical water treatment.
1. Introduction
Industrial wastewater containing high concentrations of ammonia nitrogen (NH4+-N) and chemical oxygen demand (COD) represents a complex pollution challenge. Traditional breakpoint chlorination, while effective for NH4+-N removal, relies on external chlorine sources, posing safety risks and high costs. Electrochemical chlorine evolution (CER) offers on-site, on-demand generation of free chlorine, eliminating storage and transport hazards. However, the performance of CER hinges on anode materials; ruthenium dioxide (RuO2) is promising due to its metallic conductivity and catalytic activity, but its efficiency is limited by morphology and valence states. Conventional doping methods, such as Pt-RuO2, often neglect morphological control, while nanorod structures, known for abundant active sites, typically require energy-intensive hydrothermal synthesis, hindering scalability.
This study introduces a simple synthesis route for nanorod-structured RuO2 (N-RuO2) via ammonium chloride modification of ruthenium trichloride precursor. This approach simultaneously achieves doping and morphological control, enhancing catalytic activity and stability. The N-RuO2 anode demonstrates superior performance in treating real coal chemical wastewater, with higher removal rates and lower energy consumption compared to commercial alternatives. The findings address the bottleneck of scalable, high-performance CER anodes, offering a practical solution for industrial wastewater treatment.
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SONG Xiaoyang, WANG Yan, REN Xiaohua, ZHAO Xu (2026). RuO2 Nanorods for Electrochemical Chlorine Evolution and Simultaneous Removal of Ammonia Nitrogen and COD from Wastewater. Chinese Journal of Environmental Engineering. https://doi.org/10.12030/j.cjee.202512066
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Frequently Asked Questions
What is the failure mechanism of N-RuO2 under accelerated lifetime testing, and how does it compare to commercial anodes?
Under accelerated lifetime testing (1 A·cm−2 in 1 mol·L−1 H2SO4), N-RuO2 exhibited a 2.9-fold longer lifetime than Com-RuO2, indicating superior resistance to deactivation. The nanorod structure likely mitigates mechanical stress and promotes bubble detachment, reducing coating delamination and corrosion.
How does the initial chloride ion concentration affect the energy consumption and removal efficiency for NH4+-N and COD?
Increasing chloride ion concentration enhances the generation of active chlorine, thereby improving removal rates of both NH4+-N and COD while reducing energy consumption. For instance, in the presence of Cl−, removal rates increased and energy consumption decreased compared to Cl−-free conditions, where only direct electro-oxidation occurred.
What is the cost parity of N-RuO2 compared to commercial DSA or RuO2 electrodes for industrial-scale application?
Although the synthesis of N-RuO2 involves a simple calcination method using RuCl3·3H2O and NH4Cl, the raw material cost is comparable to commercial RuO2. The enhanced performance—higher Faradaic efficiency (25.6% improvement) and lower energy consumption (17.7 Wh·g−1 savings for NH4+-N)—can offset initial costs over time, making it economically viable for large-scale wastewater treatment.
How does pH influence the selectivity between NH4+-N and COD removal, and what are the optimal conditions?
Alkaline conditions (pH > 7) favor NH4+-N removal because free chlorine exists predominantly as ClO−, which reacts faster with NH4+-N. Neutral conditions (pH ~7) are optimal for COD removal, likely due to the presence of HClO, a stronger oxidant for organic compounds. This pH-dependent selectivity allows process optimization based on target pollutant.
What is the scalability of the N-RuO2 electrode fabrication method for industrial production?
The fabrication method is simple and scalable: it involves dissolving RuCl3·3H2O and NH4Cl in ethanol, drying, calcining at 500°C, and coating onto titanium substrates. This avoids high-pressure hydrothermal steps, reducing energy and equipment costs, and can be easily adapted to large-area electrodes for industrial reactors.
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