Rice’s ‘revolutionary’ reactor turns wastewater into green ammonia, drinking water

Ammonia is crucial for global food production, yet its manufacture consumes about 2% of the world’s energy and contributes 1.4% of carbon dioxide emissions.

A groundbreaking study from Rice University engineers presents a potential game-changer in the quest for sustainable ammonia production and water purification.

This innovative reactor system promises to decarbonize ammonia production while addressing water pollution concerns.

Transforming wastewater into a resource

Ammonia production accounts for approximately 2% of global energy use and 1.4% of carbon dioxide emissions. Traditionally, ammonia is synthesized using the Haber-Bosch process, which involves high-temperature, high-pressure reactions between hydrogen and nitrogen.

This method relies on centralized infrastructure and is energy-intensive. In contrast, a new reactor developed by Rice University’s team offers a more sustainable approach by converting nitrates—common pollutants in industrial and agricultural runoff—into ammonia.

The team was led by Haotian Wang, associate professor of Chemical and Biomolecular Engineering at Rice University. The new system uses electrochemical synthesis, which can occur at room temperature and be powered by decentralized renewable energy sources.

“Electrochemistry can occur at room temperature, is more amenable to scalable formats for different infrastructure systems, and has the capacity to be powered by decentralized renewable energy,” explained Feng-Yang Chen, lead author and Rice graduate student, in the press release.

The breakthrough lies in the reactor’s use of a porous solid electrolyte, which significantly improves efficiency by eliminating the need for high concentrations of supporting electrolytes. This challenge has previously hindered sustainable nitrate-to-ammonia conversion. This design not only enhances the reaction’s efficiency but also has the potential to make ammonia production carbon neutral when powered by renewable energy.

Efficient water treatment and ammonia production

The Rice team conducted experiments by flowing nitrate-contaminated water through their reactor. They measured the produced ammonia and the purity of the treated water.

“We discovered that our novel reactor system could turn nitrate-contaminated water into pure ammonia and clean water very efficiently, without the need for extra chemicals. In simple terms, you put wastewater in, and you get pure ammonia and purified water out,” Chen stated in the press release.

This new reactor eliminates the need for traditional denitrification processes used in wastewater treatment plants, which generate nitrogen to be fed into the Haber-Bosch process. By bypassing both denitrification and Haber-Bosch routes, the reactor provides an effective method for water decontamination while producing ammonia.

“Nitrate is one of the priority pollutants that most frequently violates drinking water standards, and it is a significant concern in growing cities as farmland with nitrate-contaminated groundwater supplies is converted to urban development,” noted Pedro Alvarez, the George R. Brown Professor of Civil and Environmental Engineering at Rice.

He added that conventional nitrate removal methods, such as ion exchange or reverse osmosis, often create brines and transfer the pollution problem from one phase to another.

Alvarez praised Wang’s innovation, stating, “Professor Wang’s innovation is very timely and important, as it offers a solution that eliminates nitrate toxicity and associated liability without the need to add treatment chemicals.”

Implications and future directions

The implications of this reactor design extend beyond ammonia production. The study’s techno-economic assessment and reactor design could guide future research into other environmentally friendly chemical processes.

“Our findings suggest a new, greener method of addressing both water pollution and ammonia production, which could influence how industries and communities handle these challenges,” Wang said.

The research highlights an urgent need for sustainable ammonia production methods to meet decarbonization goals.

“If we want to decarbonize the grid and reach net-zero goals by 2050, there is an urgent need to develop alternative ways to produce ammonia sustainably,” Wang emphasized.

This study, supported by Rice University and the National Science Foundation through the Nanosystems Engineering Research Center for Nanotechnology-Enabled Water Treatment (NEWT), represents a significant step towards sustainable chemical processing.

The study was published in the journal Nature Catalysis .