Oxidation of biologically-produced sulphur in a continuous mixed-suspension reactor

Microbial oxidation of biologically produced elemental sulphur was studied in a continuous bubble-column reactor. This sulphur was supplied from a sulphide oxidizing bioreactor as a suspension or as a suspended sulphur powder. The work focused on two aspects: (1) investigation of the bio-chemical stability of a biologically-produced sulphur suspension when exposed to aeration at pH 8 in a bioreactor, and (2) sulphuric acid production resulting from oxidation of biologically produced sulphur by acidophillic thiobacilli. At pH 8, biomass growth showed an apparent Monod kinetics. At dilution rates of 0.1 up to 0.35 h−1, 35–40% of easily available sulphur was oxidized. At D <0.1 h−1, the sulphur conversion at pH=8 steeply increased, reaching ultimately values of 80–90%. In acidophillic conditions in the bioreactor, the maximum sulfuric acid production rate was searched for. The lowest pH value reached in the bioreactor was 1.7, whilst a maximum sulphuric acid production rate of 1 mmol H2SO4•L−1 h−1 was found. The possible application of the acidification process for bioleaching is discussed.