Why bioreactors?
Increased loading of nitrates to estuarine and marine environments through the inefficient and/or improper use of nitrogen fertilisers is a major constraint to the improved and sustained health of Qld’s tropical waters and reef environments.
Agronomic strategies to increase nitrogen use efficiency in cropping and dairy systems rarely achieve greater than 40% uptake of added nitrogen by the plant even with the implementation of Best Management Practices.
Lessons from high rainfall intensive livestock and cropping systems in both New Zealand and Mid-West USA have conclusively shown that in situ denitrification bioreactors are a viable, low cost farmer friendly solution to this problem.
What is a bioreactor?
Bioreactors are flooded trenches that convert sub-surface nitrate loads to gaseous nitrogen. The microbial denitrification process is temperature dependent, requires a saturated environment and a relatively small amount of reactive carbon to effectively complete the conversion of nitrate to nitrogen gases. The conversion process is amplified using porous denitrification walls or beds filled with a renewable organic carbon source (e.g. wood chips), effectively intercepting nitrates, forming a zone of prolonged saturation to complete the denitrification process.
This novel mitigation/abatement solution requires no changes to farm layout or practices and is ideally suited to the warmer temperatures in tropical and sub-tropical environments.
Shallow 2-3 m trenches can be backfilled with organic materials to form porous saturated walls to intercept lateral sub-surface flows prior to discharge to water ways thus removing nitrates through the denitrification process.
Bioreactor configurations
Bioreactor “walls” are a low cost on-farm solution to reducing nitrate pollution which can be easily constructed by growers on any farm using existing equipment.
Shallow 2-3m trenches can be backfilled with organic materials to form porous saturated walls to intercept lateral sub-surface flows prior to discharge to water ways thus removing nitrates through the denitrification process. These walls normally be constructed directly adjacent and parallel to the waterway or drain.
Alternatively, denitrification “beds” can be constructed within existing drainage lines and trenches.
