Technical and Economical Assessment and Extrapolation of a 200-dm3 Pilot Bioreactor for Reduction of Sulphate and Metals in Acid Mine Waters

Acidity, presence of metals and high-sulphate concentration are typical characteristics found in acid mine waters (AMWs). A 200-dm³ pilot, allowing bacterial conversion of sulphate into sulphide, was designed to treat AMWs. A fixed-bed column was filled with pozzolana, inoculated with a bacterial population containing the sulphate-reducing organism Desulfomicrobium norvegicum and fed with a H₂ and CO₂ gas mixture. The pilot worked in continuous-feeding conditions during 36 days. An actual AMW was sequentially treated by neutralisation of acidity, precipitation of metals using sulphide produced by the bioreactor and bioconversion of sulphate in the bioreactor fed with the sulphide-treated effluent. The residence time in the bioreactor was decreased down to 8.5 h. The sulphate reduction rate, correlated with the temperature between 5 and 17°C, varied between 35 and 95 mg dm^?3 h^?1. On the basis of the technical assessment previously made and after setting up some extrapolation hypotheses and calculations for a 10 m³ h^?1 unit, the treatment cost per cubic meter of AMW was evaluated.