Wastewater treatment process produces “greener” ammonia

Removing ammonia from wastewater marks a step towards making polluted water potable.

Access to a safe and steady supply of water is a requirement for all life on the planet. How to manage and sustain this resource is a persistent consideration, and managing ammonia-containing wastewater is a pressing concern. Could nanotechnology provide a way to treat wastewater and produce ammonia with less impact on the environment?

Engineers based at Rice University working on research partially funded by the US National Science Foundation have developed an electrocatalyst of ruthenium atoms on a mesh of copper nanowires to extract ammonia from wastewater.

The electrocatalyst can remove ammonia—commonly used as an industrial fertiliser—from low levels of nitrates in industrial wastewater and polluted groundwater with close to 100% efficiency, claimed the team which published the research in Nature Nanotechnology.

Chen Feng-Yang, lead author of the study, explained: “We fulfilled a complete water denitrification process. With further water treatment of other contaminants, we can potentially turn industrial wastewater back to drinking water.”

The researchers innovated the ruthenium electrocatalyst process with the mesh of copper nanowires, effectively suppressing hydrogen production.

“We knew that ruthenium was a good metal candidate for nitrate reduction, but we also knew there was a big problem, that it could easily have a competing reaction, which is hydrogen evolution,” Chen said. “When we applied current, a lot of the electrons would just go to hydrogen, not the product we want.”

The team borrowed a concept from other fields like carbon dioxide reduction, which uses copper to suppress hydrogen evolution, according to corresponding author Wang Haotian, who elaborated: “Then we had to find a way to originally combine ruthenium and copper. It turns out that dispersing single ruthenium atoms into the copper matrix works best.”

The efficient process is scalable and could significantly reduce carbon dioxide emissions from industrial ammonia production.

Wang concluded: “While we understand that converting nitrate wastes to ammonia may not be able to fully replace the existing ammonia industry in the short term, we believe this process could make significant contributions to decentralised ammonia production, especially in places with high nitrate sources.”