Woodchip bioreactors will help farmers reduce fertiliser pollution in waterways

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Prototype woodchip bioreactors may reduce nitrogen pollution entering nearby waterways by as much as 85% in the right conditions, according to recent studies

PhD researchers Shane White (left) and Praktan Wadnerkar at a blueberry farm where they investigated water run-off

Woodchip bioreactors are used around the world, primarily to treat subsurface water drainage.

More current designs developed by North Coast Local Land Services can help reduce surface run-off from farms and have shown the highest ever nitrate removal rate recorded in a field bioreactor trial.

The Southern Cross University team collaborated with Coffs Harbour City Council and North Coast Local Land Services to test the new approach to minimise the problem.

The bioreactors were trialled in the Coffs Coast region where water quality is being affected by nitrogen pollution from expanding agricultural intensification like protected cropping (hothouse) and blueberry farm run-off. 

Drainage from these practices can enter streams without any treatment.

The two studies were led by the University’s PhD researchers Shane White and Praktan Wadnerkar, who are based at the National Marine Science Centre in Coffs Harbour.

“Our bioreactors stimulate bacteria to consume the nitrate as a food source by using woodchips as a substrate,” said Mr White, lead author of one of the reports.

This partially installed woodchip pipe bioreactor is able to convert nitrate to a harmless di-nitrogen gas

“The woodchip bioreactors are designed to convert nitrate to the harmless di-nitrogen gas. Both bioreactors capture farm run-off, releasing lower nitrogen-laden water to the creek that would otherwise enter nearby waterways during rain events.

Mr Wadnerkar, who authored the second report, said releasing untreated hothouse drainage creates a significant risk to local waterways.

“Drainage from the hothouses growing cucumbers can be up to 28,000 times higher than water quality guidelines,” said Mr Wadnerkar.

“We cannot allow those polluted waters to reach our creeks. While these are still prototype bioreactors, this collaboration has identified ways to improve the design to remove even more pollution. 

“The bioreactors are another tool to improve nutrient management and environmental sustainability of farms if applied at scale.”

Mr White and Mr Wadnerkar emphasised that pollution prevention is still the best option and recommend the industry continue to reduce on-farm nitrogen use to prevent ongoing environmental losses.

This crop of Blueberries has benefited from smart irrigation but it is the run-off that concerns water quality authorities 

“It is more preferable that land managers actively reduce their fertiliser use. Bioreactors can be effective but represent an additional cost to reduce pollution,” Mr White said.

Shaun Morris, a report co-author, is the Senior Land Services Officer at North Coast Local Land Services.

“Farmers have been very willing to cooperate and give us access to their farms to perform these trials,” said Mr Morris.

“Our partnership with Southern Cross, Coffs Harbour City Council and farmers will continue to improve on-farm practices and provide options to protect our valuable waterways while maintaining agricultural productivity.”