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Woodchip bioreactor, denitrifying bioreactor, denitrifying wall, bioreactor wall, denitrifying bed, bioreactor bed
Bioreactors convert nitrate in groundwater or surface water to nitrogen gas using microbes and a carbon source (typically woodchip) under anoxic* conditions.
Bioreactor walls consist of a trench filled with woodchips or another carbon source, located perpendicular to the groundwater flow. Denitrification (the conversion of nitrates to nitrogen gas) is enhanced in the presence of carbon and anoxic conditions and occurs as the groundwater passes through the wall.
Bioreactor beds consist of a bed of woodchips or other carbon source through which water from subsurface pipes (e.g. tile drains, mole drains) or an open drain is passed. They are either inline (within a drain) or offline (water is diverted into the bioreactor via an offtake). An inlet and outlet structure is required in either instance. Excess flow is bypassed. A sediment trap is required upstream to prevent clogging of the bioreactor bed.
Bioreactors work by passing irrigation tailwater, stormwater runoff, deep drainage, or shallow groundwater containing nitrates through the carbon source (e.g. woodchips). As water passes through the bioreactor, denitrification occurs, thereby removing nitrates from the water.
Bioreactors can be used to treat nitrate in groundwater or surface waters. They are a relatively inexpensive technology for the removal of nitrate provided the site conditions are suitable (i.e. shallow groundwater, subsurface drainage network etc.).
The main services that bioreactors provide include:
*Anoxic refers to a metabolic state where there is no free oxygen but molecularly bound oxygen (such as in nitrate (NO3)) is still available (often measuring less than 2mg/L dissolved oxygen).
Anaerobic relates to a metabolic state where there is no free oxygen available and no molecularly bound oxygen (such as in nitrate (NO3)) . In soil science it is when free oxygen is deficient and reducing processes are dominant (i.e. reducing nitrates to nitrogen gas), such as in waterlogged soil.
In addition to the standard disclaimer located at the bottom of the page, please note the content presented is based on published knowledge of treatment systems. Many of the treatment systems described have not been trialled in different regions or land uses in Queensland. The information will be updated as new trials are conducted and monitored. If you have any additional information on treatment systems or suggestions for additional technologies please contact us using the feedback link at the bottom of this page.
Last updated: 5 October 2018
This page should be cited as:
Department of Environment and Science, Queensland (2018) Bioreactors, WetlandInfo website, accessed 24 September 2020. Available at: https://wetlandinfo.des.qld.gov.au/wetlands/management/treatment-systems/for-agriculture/treatment-sys-nav-page/bioreactors/