Researchers from the Centre of Excellence for Carbon Science and Innovation at UNSW Sydney have developed a catalyst that uses single atoms of silver embedded in a carbon and nitrogen matrix to efficiently convert nitrogenous waste pollutants in industrial wastewater into valuable ammonia-based liquid fertiliser.
This innovative technology addresses the long-standing challenge of transforming low concentrations of nitrate and nitrite — common nitrogenous wastes from agriculture and mining — into high-value fertiliser products instead of inert nitrogen gas that has no economic use.
Traditionally, remediation methods focus on high concentrations of nitrogenous wastes and convert them mainly to nitrogen gas, which lacks utility.
The new catalyst overcomes this by precisely integrating silver atoms into a carbon-nitrogen support matrix.
This atomic-level engineering choreographs a complex catalytic process that converts nitrate pollutants into ammonium, a form readily usable in fertilisers.
“Our work showcases how carbon-based materials can be engineered at the atomic level to turn waste nitrate into valuable ammonia using extremely low amounts of silver atoms,” said Dr Thanh Son Bui, lead author and chemical engineering researcher at UNSW.
Dr Rahman Daiyan, Centre Chief Investigator, emphasised the environmental and economic importance of this technology, stating: “Because we are creating that circular economy, this technology is not just about the valued fertiliser end product.
“We are abating the nitrate and nitrite for which there is also a market value.
“That is, there is an environmental penalty and cost associated with not abating these waste forms of nitrogen.”
He further explained the scale of the problem: nitrate and nitrite contamination from mining tailings dams can cover thousands of square kilometres.
Untreated, these can escape into waterways or convert into potent greenhouse gases like nitrous oxide, which is 290 times more potent than CO₂.
“Abating the nitrogen and nitrite and solving the environmental issue is a today problem. It is not a tomorrow problem and that is where the economics of our technology start making sense,” Dr Daiyan added.
The catalyst is engineered to use only 0.1 per cent silver, balanced perfectly to avoid forming silver clumps that reduce efficiency.
“The unique aspect of our research is the atomic design of our catalyst that enables us to target the low concentrations of nitrate in wastewater,” explained Dr Emma Lovell, Centre Chief Investigator.
“We start with a carbon-nitrogen support structure that we tune by removing some of the nitrogen and replacing them with single silver atoms.”
She highlighted the cost-effectiveness of using carbon, a cheap and abundant material, in synergy with trace silver to achieve selective and complete nitrate conversion that would otherwise pollute runoff from fertilisers, urban waste, and mining.
This development not only contributes to closing the nitrogen waste loop by converting pollutants into economically valuable fertiliser but also helps prevent the environmental impacts of nitrogen oxides on aquatic life and human health.