The release of mine effluents can have a damaging impact on receiving water bodies. Therefore, treatment of mine waters before discharge is imperative. A novel biological SO²⁻₄ removal technology has been developed whereby the degradation/fermentation products of grass cellulose, volatile fatty acids (VFA), function as the electron donors and SO²⁻₄ as the electron acceptor. The aim of the study presented here was to elucidate the interactions between the cellulose degradation rate, the chemical oxygen demand (COD), VFA production and its/utilisation rate as well as the sulphate reduction rate. To this end, two stirred batch reactors were operated: a test and a control reactor. The results showed that high COD and VFA concentrations were achieved after cellulose degradation, which resulted in a rapid decrease in the SO²⁻₄ concentration in the test reactor. The VFA results indicated that propionic and butyric acids were preferentially utilised, producing acetate. In the control reactor, the VFA and the COD production increased initially at the same rate, followed later by a decrease at a similar rate. These results suggest that the degradation products formed were utilised by the methanogenic bacteria to produce methane rather than by the sulphate-reducing bacteria, since the control reactor contained no sulphate (Visser 1995). Furthermore, these results showed a clear relationship between the COD/VFA production and the SO²⁻₄reduction in the test reactor and between the COD and VFA pattern in the control reactor.
Vast volumes of Acid Mine Drainage (AMD) are still being generated in South Africa, due to decant from both active and closed mines. Research to find a cost effective, environmentally friendly treatment system to reduce the salinity and to neutralise the acidity of AMD is ongoing. The study presented here showed that high sulphate removal efficiencies were achieved applying the biological treatment technology, thereby using the degradation products of grass-cellulose as the carbon and energy sources. The process was conducted at 25 degrees C, as opposed to 37 degrees C described previously, using a one-stage hybrid reactor system, treating both sulphate rich synthetic feed water and pre-treated AMD. The results showed that the fermentation microbes, originating from rumen fluid, derived from cattle, could generate the carbon and energy sources for the sulphate reducing bacteria at 25 degrees C. When comparing the results obtained at 25 degrees C with those obtained at 37 degrees C, it was observed that these were similar. However, at the higher temperature a faster flow-rate to the reactor was possible. The findings implied that the biological sulphate removal system described can be operated more economically at 25 degrees C than at 37 degrees C, as heating the reactor system can be omitted.
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