Acidophilic sulphate-reducing bacteria: candidates for bioremediation of acid mine drainage

Abstract

Acid mine drainage (AMD) is currently one of the most widespread forms of pollution worldwide. It is mainly anthropogenic in nature, resulting from mining activities. AMD occurs as an end result of the oxidation of sulphide minerals, producing high concentrations of sulphate.These oxidation processes are acceleratedbyactivityof iron-oxidising chemolithotrophic microorganisms. Acidophilic sulphate-reducing bacteria (aSRB) exist in anaerobic sediments in acid mine drainage environments, and can reduce sulphate to sulphide. This results in the precipitation of metal sulphides and the release of hydrogen sulphide. Current biotechnological processes employ neutrophilic SRB to remove metals and sulphate from acidic wastewaters; however, a pre-treatment step is necessary in order to produce the circumneutral pH required by the bacteria, aSRB therefore have a potentially important role in bioremediation of AMD, in view of their ability to withstand low pH. The culture and potential use of aSRB for this purpose is examined. Acidophilic sulphate-reducing bacteria were sampled from acid mine drainage environments in Wales, UK, and the Caribbean island of Montserrat. These were used as inocula for bench- scale bioreactors, where enrichments for aSRB and investigations into alkalinity generation by the mixed cultures following acidification were carried out. This was demonstrated using one mixed culture at a pH as low as 1.73. Sulphate reduction by two immobilised mixed cultures in batch systems was determined in order to identify the optimum pH for bioremediation using the aSRB. Samples taken from the bioreactors were used to inoculate overlay plates at pH 3 and 3.6.