Competition between lactate oxidisers and fermenters under biosulphidogenic conditions: implications in the biological treatment of AMD

Abstract

This study investigated the influence of culture conditions on the dominant metabolic pathways and resultant reaction stoichiometry, using chemostat cultures. The kinetic properties (μmax and Ks) under conditions dominated by either lactate oxidation or lactate fermentation were determined. These properties were used to simulate the competition between lactate fermentation and oxidation. Sulphate reduction and lactate utilisation were determined across residence times of 1 to 5 d and feed sulphate concentrations of 1.0 to 10.0 g l-1. Assuming lactate limitation, results revealed a lower maximal growth rate ?μmax of 0.2 h -1 and a higher affinity for lactate characterised by Ks of 0.6 g l-1 for the lactate oxidisers (SRB) than the lactate fermenters. The latter were characterised by a μmax of 0.3 h -1 and Ks of 3.3 g l-1. Modelling of the competition between lactate fermenters and lactate oxidisers illustrated that lactate oxidisers compete more effectively for lactate under conditions of low lactate concentration (≤5 g l-1) and high sulphide concentration (0.5 g l-1). On the other hand lactate fermenters outcompete the oxidisers under conditions of higher lactate concentration (>5 g l -1). Findings from this study show that in order to optimise BSR system, an understanding of the impact of physicochemical conditions on the metabolic dominance is critical.