Dr Anna Garden's alternative experimentation process may just be the answer to New Zealand's nitrate problem.

Converting nitrates: science’s alternative solution for clean drinking water

Concern about nitrates in Canterbury municipal water supplies emphasises the need for new ways to solve the nitrate problem, and Dr Anna Garden might be the scientist to do it.

Dr Anna Garden is not your typical chemist. You won’t find her in a laboratory. She sits at a computer imitating experimental conditions unachievable in a lab. This theoretical approach allows her to fast-track chemical research without expensive and time-consuming lab experimentation – and allows her to solve problems fast.

Last week concerns were raised about the links between nitrate levels in Canterbury’s drinking water and an increased risk of bowel cancer. Garden, together with Ph.D. student Caitlin Casey-Stevens, are working on research to address the nitrate problem in New Zealand’s drinking water, and her alternative approach to experimentation means results can happen much sooner.

“Cleaning up a municipal water supply is a different problem to cleaning up a river, and does give us the opportunity to address it in a different way. It’s actually potentially a simpler problem to solve than removing nitrates in groundwater.”

The MacDiarmid Institute and University of Otago researcher is designing new catalysts that could selectively convert the nitrate pollutants in water into harmless nitrogen gas. Using theoretical modelling, she can ‘try out’ different elements and shapes for the catalysts, working to reduce the toxicity of potential additives.

“We don’t want to put more hazardous material into the environment in order to ‘clean it up’”, she says. “So experimenting theoretically can help us rule out toxic ones and helps lab researchers to focus on those that will be both most effective and least polluting.”

Garden experiments theoretically with nanoparticle sized catalysts, which she says are important because they use far less material than bulk catalysts, but they also come in many different shapes, which can lead to really interesting reactivity.

“The edges and corners on nanoparticle catalysts are often highly reactive. These different sites can drive reactions in different ways, either towards desired products, such as nitrogen gas, or undesired byproducts.”

Modelling these on a computer can reveal what types of nanoparticles lead to the desired products while minimising harmful products. This would take months or years of an experimental-lab scientist’s time.

“The computational approach gives a level of control over conditions that would be really hard to get experimentally. So you can investigate precise shapes and compositions of likely catalysts, and carefully understand all the variables, which can be challenging in the lab.”

This type of computational modelling could help solve New Zealand’s nitrate problem.

“We have horrible nitrate issues in New Zealand. We’ve known for years about the run-offs into rivers, and now we’re seeing concern about contamination in municipal water supplies.”

This research isn’t going to mean that we can keep putting nitrates into our waterways. Alongside her work, we also need to address the level of nitrates in the environment in the first place, she says.

“But we do also need a solution for nitrate conversion in groundwater and in municipal water supplies, particularly now with the concerns in Canterbury. And materials science offers a potential solution. Moreover, we have a good e-science infrastructure in this country making us well-placed to conduct this research.”

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Garden was awarded a Marsden grant in 2018. With the Marsden grant, she is looking to identify computationally, bimetallic nanoparticle catalysts that will most effectively convert nitrates to nitrogen gas.

As she watched young people take to the streets in the climate marches across the country, Garden could see the potential her field offers the next generation of students who want to work in this area. And those students are coming from unexpected places.

“A lot of students who come to university and study chemistry come from rural backgrounds – they’ve seen the nitrate problem, experiencing it directly in their home environments, and they are very motivated to find solutions.”

The MacDiarmid Institute is the sponsor of The Spinoff’s science section. 


The Spinoff’s science content is made possible thanks to the support of The MacDiarmid Institute for Advanced Materials and Nanotechnology, a national institute devoted to scientific research.


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