Wastewater
Americas
Thursday, 23 January 2020

RESEARCH: Agricultural water pollutants converted back into fertilisers

Relying on an energy-intensive process

Researchers in the US claim to have found a new way to convert ground and surface water contaminants from agricultural fertiliser runoff back into a useful fertiliser.

The Rice University team discovered a new catalyst that can turn nitrite pollutant waste into ammonia, a compound mostly used as fertiliser and household cleaner.

Ammonia-based fertilisers are critical for global food supplies, yet producers still rely heavily on the energy-intensive Haber-Bosch process.

By making ammonia from nitrite waste, it could instead provide a green alternative, according to the university.

The study challenges the idea that only palladium-based catalysts are effective for nitrite reduction and expands the frontiers of the reduction process.

Impact of agricultural runoff

Michael Wong, professor and chair of the Department of Chemical and Biomolecular Engineering in Rice’s Brown School of Engineering, led the study.

Published in the journal ACS Catalysis, the research was partially supported by the National Science Foundation’s Nanosystems Engineering Research Center for Nanotechnology Enabled Water Treatment (NEWT).

“Agricultural fertiliser runoff is contaminating ground, and surface water, which causes ecological effects such as algae blooms as well as significant adverse effects for humans, including cancer, hypertension and developmental issues in babies,” he said.

Following the breadcrumbs to palladium alternatives

One of the key drivers for the project was to find a cheaper alternative to palladium, regarded as the most effective metal for nitrate and nitrite elimination.

Wong’s team of students and collaborators tested how well a rhodium catalyst could remove nitrite compared to palladium.

The team concluded that at higher pH values, palladium created mostly dinitrogen while rhodium created significant quantities of ammonium and smaller amounts of hydrazine.

It was the observation of hydrazine that gave the team ideas on making useful chemicals from nitrite wastewaters.

Cleaning water in a simpler way

According to the university, the findings open up new avenues for designing “robust nitrite reduction catalysts”.

Furthermore, Wong added that catalytic converter technology based on the new rhodium catalyst could be “most useful as a filter installed at sites prone to runoff, such as farms”.

He added: “I’m excited about removing nitrite, forming ammonia and hydrazine, as well as the chemistry that we figured out about how all this happens.”

“The most important takeaway is that we learned how to clean water in a simpler way and created chemicals that are more valuable than the waste stream.”

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