Optimisation of Nitrogen Removal Capacity for ‘Best Practice’ Stormwater Biofiltration Systems
(2005 – current)
In an era of global climate change, increasing urbanisation and nutrient enrichment, ecosystems are struggling to cope. While events such as iceberg melting and shifting in weather patterns have become a reality, almost half of the Earth’s water bodies are experiencing a gradual process of dying called eutrophication. This eutrophication of water bodies is triggered by the discharge of urban runoff (or stormwater) which is the primary carrier of nutrient-rich sediments.
Excess of nitrogen in stormwater is a principal cause for eutrophication of many water bodies in the world. Biofilters, which use a vegetated soil media, have the potential to reduce nitrogen concentrations in stormwater. In this multi-stage study the effectiveness of novel biofilter technology in removing pollutants from urban runoff was investigated. A large scale baseline study showed that whilst biofilters could readily remove high levels of sediment (averaging 98% removal), phosphorus (85%) and heavy metals (greater than 90% removal for most metals), nitrogen removal was often poor.
As a result the biofilter configuration was redesigned and optimised to maximise total nitrogen removal and facilitate NOx (oxidised nitrogen) reduction. The optimised design was tested through a range of different climate conditions. Of the Australian plants investigated, Carex appressa was found to be superior in removing nitrogen and phosphorous relative to other plants. Additionally, the combination of creating a saturated anoxic zone (SAZ) at the bottom of the filter and adding a carbon source as an electron donor in the filter media increased biofilter efficiency in removing total nitrogen from urban runoff. Moreover, this new design proved to be able to withstand the harsh climatic conditions that are typical to Australia. This novel technology is now adopted by industry in Australia with current implementation trials/pilots in Israel and Singapore (refer to project Piloting Biofiltration in Israel: the Kvar-Sava Biofilter). It has the potential to protect Australian waterways from polluted urban runoff, and to provide a treatment technology which will allow stormwater to be harvested as an alternative water supply.