Project Status: Complete
Project Participants: Alcoa, Department of Agriculture and Food WA, Southern Gateway Alliance, Main Roads WA, Wallis Water, Peel Harvey Catchment Council, Conservation Council of WA
Project Leader: David Cooling (Alcoa)
The overall aim of the project was to install and monitor a nutrient stripping device to retain nutrients
from agricultural land and to assess the feasibility, effectiveness and potential impact of using bauxite residue (for nutrient attenuation) to improve the quality of runoff water.
The Southern Gateway Alliance planned to capture nutrient runoff from agricultural land through a constructed wetland to reduce the nutrient concentration, particularly that of phosphorus. The strategy was to install a Storm-max system (designed by the Wallis Group) incorporating bauxite residue and place it at the southern end of the constructed wetland. Water would flow through the Storm-max system, stripping the nutrients, and into a constructed settling basin. Bauxite residue has a high phosphorus adsorption capacity and this will enable phosphorus to be captured. Road runoff would be captured and treated separately to remove suspended solids and floating matter including hydrocarbons.
During 2009/10, a filter was constructed in an artificial wetland near Coolup in Western Australia. The filter was was constructed from a mixture of native sand, limestone and bauxite residue (with 10 percent phosphogypsum). This study assessed the effectiveness of the removal of nutrients and measured the impact of the filter by comparing the concentration of any contaminants in the filtered water with established standards, background levels and contaminants in runoff from the highway. The total amount of water that passed over the outlet weir was approximately 20,000 cubic metres.
The filter has been effective in removing phosphorus. It is anticipated that with improved surface water access into the wetland, higher concentrations of phosphorus will enter the wetland in the second half of 2010, saturating the upstream portion with nutrients and water, and enabling a better test of this aspect of the trial as well as determining the lifetime of the filter.
Without the wetland, the nutrients entering the drain downstream of the wetland would have been much higher – as demonstrated by the high concentrations draining from the farmland into the inlet of the wetland.
An important subsidiary aim of this project was to determine the nature of any contaminants that may be leached from the filter in the short and long term. The leaching from the filter of constituents with potential environmental concerns was examined and it is unlikely that release from the filter poses any further risk than what is already occurring in the Mayfield drain and elsewhere.
The ultimate outcomes from this project will:
The project participants will continue the trial beyond the term of CSRP to determine whether the trends in nutrient removal and constituent behaviour continue in the second year.