Electrochemical method supports nitrogen circular economy
New approach developed by Feng Jiao converts nitrogen waste into valuable chemical product
By Shawn Ballard
Imagine a world where industrial waste isn’t just reduced, it’s turned into something useful. This kind of circular economy is already in the works for carbon. Now, researchers in energy, environmental & chemical engineering at Washington University in St. Louis have developed a promising pathway to convert harmful nitric oxide, a key component of acid rain, into valuable nitric acid, which is used in everyday applications from fertilizer production to metal processing.
Feng Jiao, the Lauren and Lee Fixel Distinguished Professor in the McKelvey School of Engineering at WashU, and collaborators developed a method to convert nitric oxide (NO) emissions into high-purity, concentrated nitric acid (HNO₃). The new process operates at near-ambient conditions with minimal infrastructure, offering an economically viable solution to industrial nitrogen waste with economic and environmental benefits. The work published April 3, in Nature Catalysis.
“We’ve developed an electrochemical approach to converting NO, a toxic waste gas, into valuable nitric acid,” Jiao said. “Our primary motivation is to address NO waste gases from mining sites, where large amounts of nitric acid are used to dissolve metal ores, leading to significant emissions. Our technology enables on-site NO conversion back into nitric acid for immediate reuse, creating a more sustainable and circular process.”
The innovative electrochemical process uses a low-cost carbon-based catalyst for NO oxidation. When combined with a single-metal oxygen reduction catalyst developed by Gang Wu, professor of energy, environmental & chemical engineering in McKelvey Engineering, the process operates with low energy consumption to convert NO into HNO₃ without the need for chemical additives or extra purification steps.
The electrochemical oxidation system is designed to be “plug and play,” Jiao says, constructed on-site without massive investments in infrastructure or expensive raw materials, such as precious metals. It is flexible and customizable for small- or medium-scale operations, and it works at near room temperature, significantly reducing energy use, cost and environmental impact compared with the most prevalent NO processing method that requires elevated operating temperatures.
The system achieves over 90% faradaic efficiency when using pure NO. Even at lower concentrations of NO, the system retains more than 70% faradaic efficiency, making it adaptable to a variety of industrial waste streams. The direct synthesis of concentrated high-purity HNO3 – up to 32% by weight – from NO and water without electrolyte additives or downstream purification establishes an electrochemical route to valorize NO waste gases, advancing sustainable pollution mitigation and chemical manufacturing.
Beyond mining, Jiao noted that the approach may have broader industrial applications as well as strong commercial potential, which Jiao and his collaborators demonstrated in a detailed techno-economic analysis that showed their process boasts lower energy consumption and reduced costs compared with traditional HNO₃ manufacturing methods. Turning industrial pollutants into valuable chemical products is just good business, as well as being good for the environment, Jiao said.
“The nitric acid output by our system can be directly used in mining applications or other chemical processes,” Jiao said. “We’ve already achieved very impressive efficiency and purity in our output. Going forward, we’ll be working to improve those numbers even further while also scaling up for practical applications. We’re looking at how we can build this technology into a nitrogen circular economy that will open doors to more efficient and sustainable agriculture, manufacturing and many other things.”
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Xia R, Dronsfield S, Lee A, Crandall BS, Liang J, Hasa B, Redder A, Wu G, Goncalves TJ, Siahrostami S, Jiao F. Electrochemical oxidation of nitric oxide to concentrated nitric acid with carbon-based catalysts at near-ambient conditions. Nature Catalysis, online April 3, 2025. DOI: https://www.nature.com/articles/s41929-025-01315-8
This work was supported by Washington University in St. Louis, the University of Calgary’s Canada First Research Excellence Fund Program and the Global Research Initiative in Sustainable Low Carbon Unconventional Resources. It was also enabled in part by support provided by computational resources at the University of Calgary and Compute Canada
Journal
Nature Catalysis
Article Publication Date
3-Apr-2025
Carbon-neutral marine fuel from wastewater
KIT spin-off ICODOS and partners launch “Mannheim 001,” the first facility for carbon-neutral e-methanol production in sewage plants
Karlsruher Institut für Technologie (KIT)
Europe’s approximately 80,000 sewage treatment plants offer considerable potential for an innovative, carbon-neutral process for the production of the universal chemical methanol.. ICODOS, a start-up founded at the Karlsruhe Institute of Technology (KIT), and its partners have built an innovative facility at Mannheim’s sewage treatment plant. The facility purifies the biogas produced by the plant and uses green hydrogen to convert it into carbon-neutral fuel for ships. They opened the facility today, March 24, 2025.
According to estimates by the International Maritime Organization, shipping accounts for approximately 3 percent of global greenhouse gas emissions. To reduce those emissions, environmentally friendly alternatives to conventional fossil fuels are urgently needed. Today (March 24, 2025) a consortium consisting of the Institute for Micro Process Engineering and the Institute for Automation and Applied Informatics at KIT, the KIT spin-off ICODOS, and the Waste Water Department of the City of Mannheim began operation of a demonstration plant that uses wastewater as a resource for the production of carbon-neutral methanol, a future marine fuel. Dr. Volker Wissing, Germany’s Federal Minister for Digital and Transport, pressed the start button.
“We need to keep all of our technology options open in order to achieve our climate objectives. In addition to electrification and hydrogen propulsion, we need climate-friendly fuels for marine shipping in particular, and Germany should play a leading role in their research and development. That will be a growth market in the future,” Wissing said. “This is also about making our country independent from energy imports. Mannheim 001 shows how economic efficiency and climate action can go hand in hand. This project can serve as an example for many other locations in Germany and Europe.”
“This new facility is a striking demonstration of how research and entrepreneurship can lead to practical solutions for the successful transformation of our economy,” said Professor Thomas Hirth, KIT’s Vice President for Transfer and International Affairs. "The biogas it produces during wastewater treatment is a valuable resource. This is an innovative approach that shows how available resources can be used in a smart and climate-friendly way.”
“As a lighthouse project, Mannheim 001 is further proof that climate action and industrial growth can go hand in hand with new technologies,” said Mannheim’s mayor, Christian Specht, who was also present. “With support from Mannheim’s climate fund and in close cooperation with our waste water department, it’s showing how a start-up from our Mafinex Technology Center can produce green fuel for the shipping industry. That’s another innovation made in Mannheim that we can be proud of.”
Innovative Process Using Biogas
The Mannheim 001 demonstration plant uses a patented process to convert biogas extracted from wastewater into carbon-neutral methanol. In the first stage, the biogas originating in the sewage treatment plant is purified. The CO₂ it contains then reacts with green hydrogen to produce methanol, a versatile raw material that can be used in the chemical industry or as fuel for ships. “With our technology, we can extract a high-quality energy carrier from an existing source,” said Dr. Vidal Vazquez, a co-founder of ICODOS. “Sewage plants could produce several million tonnes of renewable methanol per year in Germany alone.” With its compact and scalable design, the process is ideal for distributed implementation. “Our current project shows the previously untapped potential of sewage plants as a core element of sustainable fuel production,” Vazquez said. ICODOS is already in discussions with other sewage plant operators about building further production systems.
About ICODOS
ICODOS GmbH, a climate-tech start-up based in Mannheim, originated in a KIT research project. It specializes in the sustainable production of fuels and chemicals using renewable sources such as biogas and CO₂ in combination with green electricity. ICODOS’s goal is to use process engineering and modular facilities to make an economically viable contribution to climate change mitigation.
More about the KIT Energy Center
Being “The Research University in the Helmholtz Association”, KIT creates and imparts knowledge for the society and the environment. It is the objective to make significant contributions to the global challenges in the fields of energy, mobility, and information. For this, about 10,000 employees cooperate in a broad range of disciplines in natural sciences, engineering sciences, economics, and the humanities and social sciences. KIT prepares its 22,800 students for responsible tasks in society, industry, and science by offering research-based study programs. Innovation efforts at KIT build a bridge between important scientific findings and their application for the benefit of society, economic prosperity, and the preservation of our natural basis of life. KIT is one of the German universities of excellence.
Exploring sustainable energy solutions through hydrothermal carbonization of sewage sludge
Higher Education Press
image:
Sewage Sludge to Hydrochar-Coal Slurry Process and Analysis
view moreCredit: Asma Leghari, Yao Xiao, Lu Ding, Hammad Sadiq, Abdul Raheem, Guangsuo Yu
In an era where sustainable energy solutions are more critical than ever, a team of researchers from East China University of Science and Technology and Aston University has made significant strides in blending coal with sewage sludge-derived hydrochar (HC) to create a more environmentally friendly energy source. Their study, published on January 15, 2025 in Frontiers of Chemical Science and Engineering, investigates the potential of hydrothermal carbonization (HTC) to transform sewage sludge into a valuable component of coal-water slurry (CWS), offering a promising pathway for waste-to-energy conversion.
Sewage sludge, a byproduct of wastewater treatment, poses significant environmental challenges due to its high volume and complex composition. However, this study demonstrates that through HTC, sewage sludge can be converted into hydrochar, a carbon-rich material that can be effectively blended with coal to enhance the performance of CWS. This innovative approach not only addresses waste management issues but also contributes to the sustainable utilization of coal, one of the world's major energy sources.
The research highlights several groundbreaking findings. Firstly, the study identifies optimal conditions for the preparation of hydrochar from sewage sludge. The results show that hydrochar prepared at 180°C with a 30% ratio in CWS exhibits the best performance in terms of viscosity and ash content. This optimal ratio ensures that the slurry remains stable and fluid, making it suitable for industrial applications.
Moreover, the study explores the gasification reactivity of hydrochar, revealing that a 30% HC ratio in CWS achieves higher reactivity compared to higher ratios. This finding is crucial as it suggests that blending hydrochar with coal can enhance the overall energy efficiency of the slurry. However, increasing the HC ratio to 50% reduces reactivity, indicating a delicate balance between HC content and energy output.
Another notable innovation lies in the detailed characterization of hydrochar. The study employs advanced techniques such as scanning electron microscopy (SEM) and Fourier-transform infrared spectroscopy (FTIR) to analyze the structural changes in sewage sludge during HTC. The results show that HTC significantly alters the surface morphology of sludge, creating a porous structure that enhances water drainage and improves the overall performance of CWS.
The social and environmental implications of this research are profound. By converting sewage sludge into a valuable energy resource, the study offers a sustainable solution to the growing problem of waste management. Additionally, the optimized blending of hydrochar with coal reduces the reliance on traditional fossil fuels, contributing to a more sustainable energy landscape.
Dr. Lu Ding, one of the lead researchers, emphasized the importance of this work: "Our study demonstrates that sewage sludge, often seen as a waste product, can be transformed into a valuable resource through hydrothermal carbonization. This not only addresses environmental concerns but also enhances the efficiency of coal utilization, making it a win-win solution."
Looking ahead, the researchers suggest that further studies should focus on optimizing the HTC process to achieve even higher energy yields and exploring the potential of other waste materials for similar applications. The findings of this study pave the way for more comprehensive research into waste-to-energy conversion, offering hope for a more sustainable and efficient energy future.
In conclusion, this pioneering research not only highlights the potential of sewage sludge-derived hydrochar in enhancing the performance of coal-water slurry but also underscores the importance of innovative solutions in addressing global energy and environmental challenges.
DOI: 10.1007/s11705-024-2508-z
Journal
Frontiers of Chemical Science and Engineering
Method of Research
Experimental study
Subject of Research
Not applicable
Article Title
Influence of hydrothermal carbonized sewage sludge on coal water slurry performance
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