Denitrifying bioreactors are a passive, on-farm technology, for removing excess dissolved inorganic nitrogen (mainly nitrate) from agricultural drainage water prior to its discharge to surface water bodies. As such, they may have a role in reducing excess nutrients running to the Great Barrier Reef lagoon.
Bioreactors are made by routing drainage water through a buried trench filled with a high carbon substrate (normally woodchips). Under anaerobic (e.g. flooded) conditions, naturally occurring bacteria convert dissolved nitrate (NO3-) in the drainage water to inert nitrogen (N2) gas, which is released to the atmosphere. Two basic configurations have been employed extensively in other parts of the world; a bioreactor “wall” (Fig 1a) in which the woodchips are installed in a trench perpendicular to ground water flow, and bioreactor “bed” in which drainage water is diverted from existing drainage networks to an offline and lined trench aligned with the direction of flow (Fig 1b). In both, temperature and solute retention time are key determinants of bioreactor efficacy, with working lifespan determined by the type and volume of carbon substrate used in relation to DIN loads. Given the unique hydrologic and geomorphic conditions prevalent in much of the Australian Wet Tropics we have developed a number of novel bioreactor designs, however questions remain as to their efficacy, and potential as a management option here in the Wet Tropics.
This research project will establish the effectiveness of denitrifying bioreactors as component of an integrated treatment train, including sediment traps and a constructed wetland, being established to manage dissolved inorganic nitrogen in waters flowing from the Babinda Swamp Drainage Area, an area of (mostly) sugar cane production within the Russell River catchment, in the Australian Wet Tropics. In addition to evaluating the potential efficacy of bioreactors to reduce dissolved inorganic nitrogen loads, we will be integrating this knowledge with landscape drainage models and an understanding of likely landowner participation to develop plausible scenarios of how bioreactors may offer an additional nutrient management strategy here in the Australian Wet Tropics.
The project is a partnership between Jaragun Pty Ltd, James Cook University, Australian Wetland Consulting, the Queensland Department of Agriculture and Fisheries, and Terrain NRM. It is funded by the Queensland Department of Environment and Heritage Protection and will run from 2017-2020. For further information please contact Liz Owen (liz@jaragun.com.au) or Dr Alex Cheesman (alex.cheesman@jcu.edu.au).
Bioreactors are made by routing drainage water through a buried trench filled with a high carbon substrate (normally woodchips). Under anaerobic (e.g. flooded) conditions, naturally occurring bacteria convert dissolved nitrate (NO3-) in the drainage water to inert nitrogen (N2) gas, which is released to the atmosphere. Two basic configurations have been employed extensively in other parts of the world; a bioreactor “wall” (Fig 1a) in which the woodchips are installed in a trench perpendicular to ground water flow, and bioreactor “bed” in which drainage water is diverted from existing drainage networks to an offline and lined trench aligned with the direction of flow (Fig 1b). In both, temperature and solute retention time are key determinants of bioreactor efficacy, with working lifespan determined by the type and volume of carbon substrate used in relation to DIN loads. Given the unique hydrologic and geomorphic conditions prevalent in much of the Australian Wet Tropics we have developed a number of novel bioreactor designs, however questions remain as to their efficacy, and potential as a management option here in the Wet Tropics.
This research project will establish the effectiveness of denitrifying bioreactors as component of an integrated treatment train, including sediment traps and a constructed wetland, being established to manage dissolved inorganic nitrogen in waters flowing from the Babinda Swamp Drainage Area, an area of (mostly) sugar cane production within the Russell River catchment, in the Australian Wet Tropics. In addition to evaluating the potential efficacy of bioreactors to reduce dissolved inorganic nitrogen loads, we will be integrating this knowledge with landscape drainage models and an understanding of likely landowner participation to develop plausible scenarios of how bioreactors may offer an additional nutrient management strategy here in the Australian Wet Tropics.
The project is a partnership between Jaragun Pty Ltd, James Cook University, Australian Wetland Consulting, the Queensland Department of Agriculture and Fisheries, and Terrain NRM. It is funded by the Queensland Department of Environment and Heritage Protection and will run from 2017-2020. For further information please contact Liz Owen (liz@jaragun.com.au) or Dr Alex Cheesman (alex.cheesman@jcu.edu.au).
Fig. 1. Schematic of standard denitrifying bioreactors. (a) Side view of wall installed to impervious layer forcing shallow groundwater through the wall. (b) Side view of a bed treating concentrated discharges of effluent or drainage water. From Addy et al. (2016). J. Environ. Qual. 45, 873-81.