Hydraulic, Chemical, and Vegetation Characteristics of the Corridor Creek Wetland Filter: Implications for Biopolishing Efficiency

Processing uranium ores into transportable oxide powders produces a stream of wastewaters high in metals, acids, and predominantly nitrogenous nutrients. Conventional water treatment can remove metal ions and buffer acids, but nutrient removal is problematic as it entails both oxidative and reductive steps. Engineered wetlands can achieve nutrient removal by a process of biopolishing, i.e. employing metabolic characteristics of the natural wetland microbiota to carry out the oxidative and reductive steps in series. In this study, we report on the hydraulic characteristics, dissolved oxygen (DO) dynamics, and vegetation of the Corridor Creek Wetland Filter (CCWF) at the Ranger Uranium Mine. Breakthrough curve analysis of dual-tracer test data showed the CCWF to be a highly dispersive wetland system with a dispersion coefficient ≥ ≈ 10,000 m 2 d −1 . The times for 95% of the tracer to pass through the individual wetland cells were 2–3 times the corresponding cell residence times. DO concentration data suggests that anaerobic conditions are unlikely to occur in the water column. Macrophyte cover in the six cells ranged from 15 to 95% of the cell area and contained 47–96 kg of nitrogen: this compares to an anticipated nitrogen load of 60 kg d −1 from the water treatment plant. Our study demonstrated that the CCWF is a complex physical, hydraulic, and biogeochemical system. Operational conditions required consideration of varying, rather than constant, wetland flow conditions in the breakthrough curve analysis used to quantify the dispersivity of the wetland cells. Water column DO dynamics indicated limited scope for denitrification. The high variability of macrophyte and microbial biomass constrained access to parts of the CCWF, largely limiting measurements to the open water regions. Therefore, rather than attempt quantitative biogeochemical modelling of wetland performance, our study focussed on identifying and understanding key processes in the CCWF. Comparable studies of wetland filters may encounter similar challenges in process quantification.