The Relationships Between Sulphate Reduction and COD/VFA Utilisation Using Grass Cellulose as Carbon and Energy Sources

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 SO₄^{2 -} {\hbox{SO}}_4^{2 - } removal technology has been developed whereby the degradation/fermentation products of grass cellulose, volatile fatty acids (VFA), function as the electron donors and SO₄^{2 -} {\hbox{SO}}_4^{2 - } 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 SO₄^{2 -} {\hbox{SO}}_4^{2 - } 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 SO₄^{2 -} {\hbox{SO}}_4^{2 - } reduction in the test reactor and between the COD and VFA pattern in the control reactor.