Abstract
M.Sc.
Water is essential to life on our planet (Miller, 1999) because no living organism can survive without it (Kupchella & Hyland, 1993). Thus there is a demand for clean, unpolluted water to be in substantial supply. There is growing awareness worldwide of the environmental legacy of coal mining activities that have been undertaken with little concern for the environment (EMCBC, 2001). Coal mining by its nature consumes, diverts and can seriously pollute water resources (Miller, 1999).
Acid mine drainage is a major problem on coalmines throughout the world (Kupchella & Hyland, 1993), and South Witbank Colliery, the main focus of this study, is no exception. Various studies that have been undertaken at South Witbank Colliery have shown that the water decanting from the mine is highly acidic (pH 2 – pH 4), and as such cannot be released into the natural watercourse (streams). Some form of water treatment to nullify or neutralise the acid levels of the mine water is necessary. Currently a temporary liming plant is being utilised to treat the water and to reduce its acidity levels to between pH 5.0 – pH 9.5, however, this plant is seen as a limited treatment option as it does not guarantee that the acidic nature of the water will be sufficiently nullified.
This study endeavours to identify and analyse a variety of permanent, long-term water treatment methods relevant to acid mine water mitigation at South Witbank Colliery. Four long-term water treatment methods, namely artificial wetlands, anoxic limestone drains, transfer of water to a water treatment plant, and construction of a permanent liming facility at South Witbank Colliery, were identified and discussed.
Artificial wetland technology has not been proven for treatment on such variable pollutant loads as present in the South Witbank Colliery mine water decant. A constraint to this technology also lies in its necessity for large surface area requirements, which is restricted due to site subsidence and sinkhole formation (as a result of shallow mining). This technology is also known to increase water evaporation rates, which may result in additional water removal from an already stressed resource.
The anoxic limestone drain water treatment technology is considered unsuitable for the study area, ultimately due to it having more a pre-treatment functionality than a total treatment one. It is also limited due to its ability to address only certain water quality variables. If considered for use in a partnership with other acid mine drainage water treatment technologies, its use might be more viable than when considered as a stand-alone treatment technology.
Transferring of the acid mine drainage water decant from South Witbank Colliery to a water treatment plant is a feasible option. The Brugspruit Water Pollution Control Works, operated by the Department of Water Affairs and Forestry, is the most likely option. The water treatment would become the responsibility of DWAF, thereby ensuring that the treated water is compliant with specified water quality standards and requirements. The attractiveness of this option is that it minimizes the short and long term water management requirements for South Witbank Colliery, but is ultimately dependant on a formal contract being negotiated between the relevant parties.
Construction of a permanent liming facility at South Witbank Colliery is possible and, in comparison to the current temporary liming plant, is likely to treat the water adequately so as to comply with specified water quality standards and requirements. A permanent facility would allow for more water to be treated than is currently possible at the temporary liming plant. Due to this option being based on proven technology increases its feasibility in terms of use at South Witbank Colliery.
Given that water is a scarce resource in South Africa, the implementation of these water treatment options is dependent on the acceptability of each option by the Department of Water Affairs and Forestry. Of the four treatment options identified the latter two, namely transfer of water to a water treatment facility and construction of a permanent liming plant, are considered to be the most suitable solutions for the treatment of acid mine drainage at South Witbank Colliery.