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DairyNZ and the Institute of Environmental Science and Research (ESR) won the Research and Science category at the 2024 Primary Industries NZ Summit Awards.
The win recognized the work carried out by DairyNZ's chief scientist, Dr. Lee Burbery, has worked with ESR for the past 10 years. Together they researched and developed bioreactors to denitrify wood chips as a marginal practice to reduce nitrogen pollution in New Zealand's waterways.
“I was inspired by the forestry transitions that were taking place in Canterbury around 2014,” says Lee.
“I noticed one occasion where we were dumping a significant amount of timber in Canterbury and farming intensively on porous soils that were susceptible to nitrate leaching.
“By adopting a circular economy approach, we could use some of the deforestation waste to build a water treatment plant for nitrate filtration.”
The bioreactors are pits filled with wood chips that function like a water filter. The carbon in wood helps bacteria convert harmful nitrate in water into harmless nitrogen gas during their natural respiration process.
Lee holds a PhD from the Faculty of Environmental Sciences at Lancaster University in the United Kingdom. He used his hydrological knowledge to overcome the challenge of setting up wood chip filters in this environment.
“Water follows the path of least resistance, so the wood chip bioreactor had to be as permeable as the gravel found in Canterbury,” explains Lee.
“We added gravel to the wood chips to strengthen the bioreactor and increase its performance. Various wood chip and gravel combinations were tested.”
He knew that there were deposits of very coarse gravel material in Canterbury and in much of the South and some North Islands. It was crucial to design something that served its purpose in these environments, which had not been done before.
Working with ESR, Lee oversaw the construction of two wood chip denitrification test sites. One was a wall to treat nitrate in shallow groundwater at a site near Kaiapoi, the other was a bed to treat agricultural drainage at a dairy farm near Geraldine.
DairyNZ and ESR have been working together to monitor the wood chip bioreactor near Geraldine for two years, carrying out some innovative experiments. The concept was successful, but Lee points out that there is a caveat.
“We have shown that wood chip bioreactors are extremely effective at removing nitrate. However, due to hydrological challenges, construction costs and compliance issues, it is a niche solution with limited applicability.”
He explains that there is currently no design standard in New Zealand. So if a farmer were interested in installing one of their own, they would have to do a little homework to put it together.
“What we do on land – to reduce nitrogen inputs and better manage nitrogen losses from the soil – is where we get the most benefit from reducing our nitrate footprint.”
Lee spent most of his 25-year academic career working on issues relating to New Zealand's groundwater resource management. Since joining DairyNZ in 2021, he has enjoyed learning about dairy farming systems and working with farming communities.
This story first appeared in Inside Dairy, the official publication of DairyNZ.
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