Bioaugmented sulfate reduction using enriched anaerobic microflora in the presence of zero valent iron

Biological sulfate reduction was evaluated in batch and continuous reactors that were inoculated with enriched microflora cultivated from sulfate laden medium. Heterotrophic sulfate-reducing bacteria (SRB) principally reduced the sulphate when the chemical oxygen demand was sufficient. The heterotrophic SRB in the enriched microflora could not efficiently reduce sulphate at T < 33 °C and/or pH < 6.0. However, when 200 mg L−1 of zero valent iron (ZVI) was added to the reactor, the sulphate reduction rate was increased by 15% while the inhibition of the SRB activity occurred at T < 25 °C or pH < 4.5, broader than those noted for non-ZVI systems. In batch tests, the autotrophic SRB reduced 95% of 1500 mg L−1 sulphate in <50 h at 15 °C when the substrate was amended with 8 g L−1 ZVI. In continuous up-flow anaerobic multiple bed reactor tests conducted to evaluate the remediation of sulphate in acid mine runoff, ZVI enhanced the activity of SRB, resulting in a 61% reduction of 20.8 g L−1 sulphate when the reactor was operated at 25 °C and pH 2.6 with a hydraulic remain time of 96 h.