Passive Treatment of Acid Mine Drainage from a Sulphidic Coalfield

Abstract

An ongoing concern is acid mine drainage (AMD) from abandoned sulphidic mines in the Sydney coalfield, which threatens local water bodies and fishing industries if left untreated. This work focuses on evaluating the performance of two semi-passive treatment systems at the Neville Street facility that treat this AMD, which is acidic and contains heavy metals such as iron, manganese, and aluminum. These treatment systems include caustic soda addition, aeration cascades, settling ponds, and constructed wetlands. Current monthly sampling by a local government agency may or may not represent worst-case scenarios as sampling may not coincide with conditions that could impact performance, such as peak loading. This work was divided into three research objectives: (1) characterize system performance during peak loading, (2) statistically evaluate treatment performance, and (3) develop a treatment performance model of the constructed wetlands. Analysis of sampling data during peak loading events indicates that both systems are effectively removing iron from the mine water with effluent readings meeting federal and provincial guidelines. However, inlet iron concentrations have been increasing over time for both systems; thus, exceedances of guideline limits could become a concern in the future. Due to newly adopted federal and provincial guidelines for manganese and sulphate, exceedances of these guideline limits have been or are likely to become a concern in the near future. Modeling of wetland treatment performance using a modified tanks-in-series (TIS) model revealed the necessity for site-specific calibration of model constants. Areal rate constants at 20 °C for iron were developed for both systems based on design and average operating conditions. The design areal rate constants at 20 °C for the two systems were 2,325 m/year and 1,380 m/year; the average areal rate constants at 20 °C were 1,930 m/year and 560 m/year.