Lincoln Agritech is currently working with ESR and AquaLinc Research Ltd on a three year science project in the Hauraki Plains. The project, as part of the larger “Enhanced Mitigation of Nitrate in Groundwater” programme, investigates using a woodchip denitrifying bioreactor to reduce nitrate loads from pastoral lands.
Approximately 40% of dairying land consists of poorly drained soils. In these instances, artificial drainage is essential, but surface and subsurface water drains contribute to fast and non-attenuated nutrient transfers to streams and rivers. This bioreactor project aims to study and reduce the nitrate discharge from a subsurface drain pipe by stimulating denitrification, that is, the microbial conversion of nitrate into gaseous forms of nitrogen (largely N2). To achieve this, the researchers re-routed drainage water from a lateral subsurface drain into a bioreactor filled with untreated pine woodchips. The presence of woodchips (a carbon source) encourages the naturally-occurring microorganisms to facilitate denitrification. Overall, this bioreactor system is designed to reduce nitrate load from a lateral subsurface drain by 50%.
Lincoln Agritech has been involved in the design, construction, monitoring and operation of the denitrifying bioreactor including collection and analysis of data from monitoring flow, temperature, rainfall and taking regular samples of inlet and outlet water for nitrogen and carbon species. The broad aim is to demonstrate that a woodchip denitrifying bioreactor is a practical and cost-effective technology to enhance nitrate removal from agricultural drainage. By assessing the performance of the system, including possible negative side-effects (e.g. odour), this research will inform best-practice methods and optimisation of future installations of bioreactors in New Zealand.