Abstract
This paper describes a novel system for the biological sulphate reduction (BSR) of acid mine drainage (AMD) using primary sewage sludge (PSS) as carbon source in an upflow anaerobic sludge bed (UASB) reactor configuration. A UASB reactor was operated at a temperature of 35oC and it received PSS (1 875 mgCOD/.) augmented with sulphate (1 500 mgSO4 2-/.). The experimental results indicate that high treatment efficiency was achieved at more than 90% sulphate reduction at a liquid hydraulic retention time (HRT) of 13.5 h. In this study, the effects of various operational parameters were also investigated. The effect of a biomass recycle stream from the top to the bottom of the sludge bed was found to initiate rapid BSR from the bottom of the bed. Profile tests showed that effective and immediate sulphate reduction was achieved as soon as theinfluent entered the reactor. From these results, it can be concluded that the UASB configuration using PSS as energy source would be a viable method for the BSR of AMD.
Highlights
Acid mine drainage (AMD) poses a significant environmental threat
Though upflow anaerobic sludge bed (UASB) R1 was inoculated with 6 l of stored sulphatereducing sludge, the start-up of the biological sulphate reduction (BSR) system was slow
Steady state conditions were allowed to last for about 4 to 7 days before the hydraulic retention time (HRT) was reduced stepwise from 30 h down to 12 h, usually in 1 h steps
Summary
The AMD waters emanate from both surface and underground mine workings, intentionally through pumping to prevent mine flooding or unintentionally through seepages, and are characterised by low pH (2 to 3), high iron (10 to 6 700 mg/l) and sulphate (3 000 to 30 000 mgSO42-/l) and variable non-ferrous (usually heavy) metals and TDS (1 800 to 45 000 mg/l) (Christensen et al, 1996). These characteristics occur as a result of sulphide oxidation in rock exposed to air and water (Thomas and Jonathan, 1994). These metals stay dissolved in solution until the pH rises to a level where precipitation occurs
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