The effects of temperature and pH on the kinetics of an acidophilic sulfidogenic bioreactor and indigenous microbial communities

Biosulfidogenesis (the microbial generation of H2S by reduction of more oxidized sulfur species) is a very useful technology for remediating acidic, metal-rich waste-waters, such as acid mine drainage. Many transition metals form highly insoluble sulfide phases when contacted with H2S, and bacterial reduction of sulfate to sulfide is, in acidic liquors, a proton-consuming reaction. Commercial-scale sulfidogenic bioreactors use neutrophilic species of sulfate- (or sulfur-) reducing bacteria that need to be shielded from direct contact with acidic waste waters, which is not the case with acidophilic and acid-tolerant species (aSRB). Here we report the kinetics and microbial dynamics of a low pH, laboratory-scale sulfidogenic bioreactor, operated as a continuous flow system for 462 days, at pH values between 4.0 and 5.0, and temperatures between 30 and 45 °C. While changing an operating parameter caused minor perturbations in the performance of the bioreactor, these were transient, and the system performed consistently well throughout the entire test period, with pH 4.0 and 35 °C being marginally the optimum operating conditions. Two species of aSRB mediated sulfide formation: Desulfosporosinus acididurans, preferentially at higher pH and lower temperatures, and Peptococcaceae CEB3, at lower pH and higher temperatures. The relative abundances of these two bacteria changed in response to an operational (pH, temperature) change. The results highlighted the robustness and adaptability of the low pH microbial consortium used to generate sulfide, and to precipitate transition metals both in situ and ex situ.