Nitrate is a problem for our waterways. Photo: Lynn Grieveson

Nitrate pollution is a serious problem in New Zealand, with excess nitrate in the water causing algae bloom and didymo, which smother our marine life and poison the fish we eat. But nitrate is a key ingredient in most fertilisers – so what to do?

Victoria University of Wellington’s Dr Putri Fraser, Research Fellow in the School of Chemical and Physical Sciences, has a solution.

“Using iron and microsilicate, we’ve created a chemical that can remove nitrate from soil before it reaches the waterways,” Fraser says. “Our tests so far show it is easy to work with and safe for marine life.”

The road to this chemical has been a long one. Fraser first started work on the project as an Honours student in 2012, testing different materials that might help remove nitrate from soil.

“We already knew iron could help remove nitrate from soil before the nitrate got into the waterways,” Fraser says. “But iron is magnetic, so it clumps together and won’t spread throughout soil, and if it gets in the waterways it is so small that marine life might absorb it, which might affect their health. So it’s far from a perfect solution.”

During a Summer Research Scholarship with Callaghan Innovation in 2012, Fraser discovered a microsilicate product produced as waste during thermal power generation. As a PhD student at Victoria University, she tested the combination of iron and microsilicate on nitrate pollution. The experiments were a success.

“We can coat the iron with this microsilicate waste product. This combination spreads through soil and absorbs much better than plain iron.

“Any product that isn’t absorbed by the soil is safe in the waterways: the individual particles are too big to be absorbed by marine life, the microsilicate is similar to sand and therefore safe for waterways, and the small amounts of iron that could end up in the waterways will have little effect. Although there is still more testing to be done, so far we haven’t found anything to suggest our product will be harmful to the environment.”

Both Fraser and her PhD supervisor, Dr Robin Fulton, “thought it was fitting to use one waste product to deal with another”, she adds.

Using iron, meanwhile, has another major benefit – when iron and nitrate combine, they make ammonium. Ammonium is, among other things, an effective fertiliser for plants.

“Ammonium fertilises plants, and is also absorbed well by the soil, so the chances of fertiliser getting in the waterways is much lower,” Fraser says. “We can both improve the water quality and reduce the amount of fertiliser needed for soil in the first place.”

Fraser hopes to test her methods for other types of pollution, as well as continuing tests and refining the product to help with nitrate pollution.

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