Abstract
decanting of flooded gold mines threatens water supply on the Witwatersrand, South Africa, one of the most intensively mined areas in the world. Large volumes of acid mine drainage wastewaters will require treatment here for decades and possibly centuries. Appropriate treatment technology needs to meet technical, financial, environmental and social sustainable development criteria, with the costs of long-term treatment providing the initial decision gateway. This review details a bioprocess development in which the use of sewage sludge as the electron donor/carbon source for microbial sulphate reduction, and the wastewater treatment public utility as the operator, was investigated in meeting these requirements. A programme is reviewed that led from fundamental studies in microbial ecology, enzymology and mathematical process modelling, through pilot plant studies, to the construction and operation of a full-scale plant treating 10 M. mine water/day. It was shown, in what became known as the Rhodes BioSURE Process, that with careful regulation of the mine water and the sewage sludge dosing flow rates, sulphate levels could be reliably reduced to below 100 mg/., at hydraulic retention times as low as 12 h. Ancillary metal and sulphide removal unit operations are described, as well as investigations into socially sustainable use of treated mine waters.Keywords: acid mine drainage, mine wastewater treatment, sewage sludge, sulphate removal, metal removal
Highlights
The environmental impacts of acid mine drainage (AMD) wastewaters have been the subject of intensive investigation over many years (Lottermoser, 2010), and the processes giving rise to its formation are well-described (Blowes et al, 2003; Johnson, 2003)
Molepane (1999) and Molwantwa (2002) reported investigations into the use of primary sewage sludge (PSS) as an electron donor/carbon source in sulphate reduction reactions and Whittington-Jones (2000) developed the Recycling Sludge Bed Reactor (RSBR) as an experimental system for investigating PSS breakdown in a configuration comparable to the process of sedimentation and upwelling in which complex organic substrates were observed to be degraded in tannery ponds (Fig. 2)
Neba (2006) investigated factors influencing technology decision making relating to sustainable development needs in AMD management, and developed a decision support tool for assisting this process
Summary
The environmental impacts of acid mine drainage (AMD) wastewaters have been the subject of intensive investigation over many years (Lottermoser, 2010), and the processes giving rise to its formation are well-described (Blowes et al, 2003; Johnson, 2003). Settlements in the Southern Hemisphere not located on a river (Turton, 2004) It has been one of the most intensively mined areas in the world, with 37 million kg fine gold extracted (and 6 billion tons of ore milled) since the 1880s. With the termination of mine dewatering and pump-andtreat operations, as functions of the active mining enterprise, groundwater levels have been rising in the East, Central and West Rand Basins along the Witwatersrand (McCarthy, 2011) Hydrogeological modelling of this situation since the mid1990s has predicted the time to reach decant status, the quantity and quality of waters that would decant once the filling of the mines was completed, and total volumes of AMD requiring treatment in this region, which may exceed several hundred Ml/day (Scott, 1995; Tutu et al, 2008; McCarthy, 2010).
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