Volatile fatty acid formation and utilization in anaerobic sulphidogenic batch reactors

Abstract

Acid Mine Drainage (AMD) needs to be treated, before it is recharged in rivers and dams. The biological treatment of AMD can be applied using degradation products of cellulose, for example Volatile Fatty Acids as carbon sources. The aim of this study was to demonstrate that microbes originating from compost and rumen are able to ferment grass cuttings to produce Volatile Fatty Acids which are utilized during the biological sulphate removal process. Two studies were conducted in the first study four stirred batch-test reactors (2 l) were operated, fed with artificial SO4 rich (1700 mg/l) feed water and tap water (controls). The reactors received sulphate reducing bacteria, compost bacteria and grass cuttings. The experimental period was 25 days; the operating temperature was 20 to 22 °C. In the second study two anaerobic reactors (2.5 l) were operated at 37-39 °C and at pH of 6.7 - 6.9 to accommodate the rumen organisms. The test reactor contained SO4 rich water and the control reactor tap water, as well as SRB, rumen bacteria and grass cuttings. The duration of the second study was 32 days. In both studies SO4 reduction could be observed (from ˜ 2000 to 0 mg/l over 8 days). The Volatile Fatty Acids results showed that both butyrate and propionate were produced and subsequently utilised for the sulphate reduction and that a clear relationship existed between the organic acids concentration and sulphate reduction. It was concluded that the compost and rumen microorganisms could degrade grass to high concentrations of Volatile Fatty Acids resulting in continuous SO4 removal