WTMIP trials help inform new bioreactor guidelines

In a world first, denitrifying bioreactors – woodchip filled trenches that intercept and treat nitrate in surface run-off and shallow ground water – now have comprehensive guidelines for their use in improving water quality leaving farms.

The Wet Tropics Major Integrated Project (WTMIP) has been a key player in agricultural bioreactor trials, with seven installed as proof-of-concept systems on cane and banana farms across the Tully and Johnstone basins.

The WTMIP’s place-based approach has modified conventional wall and bed bioreactor designs to trial three other designs (in-drain, ag pipe and partial in-drain bioreactors), developed with help from local growers and machinery operators to suit the unique nature of Wet Tropics landscapes.

WTMIP Catchment Repair Coordinator Chris Algar said the input received from participating landholders had been a crucial part of the process.

“They’ve not only provided us with sites to implement trials, but invaluable knowledge on the lay of their land.”

“The WTMIP is the first project to trial a range of different bioreactors, each designed to suit the landscape where they’re positioned.”

“There’s no ‘one size fits all’ solution. The variability of soil, land and water flow led us to tailor each bioreactor to the conditions,” Mr Algar said.

A denitrifying bioreactor works by intercepting surface run-off or shallow ground water. The carbon in the woodchip and low oxygen environment provides the right conditions for microbes to convert nitrate in the water into harmless nitrogen gas through the process of denitrification.

One advantage of bioreactors is the minimal impact they have on productive land.

“Bioreactors come in various shapes and sizes depending on their purpose.”

“The WTMIP trials required only a small area of land for construction, site selection was dependent on finding the right location in the landscape as not all locations were suitable for the trials.”

“The ideal condition for a bioreactor site is an area that’s freely draining, where leaching is occurring through the soil,” Mr Algar said.

The WTMIP bioreactor trials have enabled considerable research and understanding into how the water treatment systems work in Wet Tropics landscapes and conditions.

Carla Wegscheidl from the Department of Agriculture and Fisheries has managed the bioreactor guidelines project and said it was truly a collaborative effort.

“We couldn’t have completed these trials and research without the help of the Bioreactor Network, whose members include Jaragun EcoServices, Terrain NRM (the lead organisation delivering the WTMIP), James Cook University, Queensland University of Technology, Australian Wetlands Consulting and the Department of Environment and Science,” Ms Wegscheidl said.

The guidelines were developed as part of the Bioreactors for Great Barrier Reef and the Agricultural Water Treatment projects, with funding from the Queensland Government’s Reef Water Quality Program. These guidelines provide another tool for land managers looking for ways to reduce nitrate leaving Queensland farms.

Guidelines and fact sheets to assist with planning, design, installation and management of treatment systems in agriculture and aquaculture, to improve water quality can be found here.