OPTIMIZATION AND PRECONDITIONING OF MICROBIAL INOCULA AND ORGANIC CARBON SUBSTRATES FOR THE BIOREMEDIATION OF BAUXITE RESIDUE

Refining bauxite to produce alumina via the Bayer process produces a highly alkaline (pH 12-13), saline byproduct (bauxite residue) that is inhospitable for the majority of plant and microbial life. Fortunately, recent research has identified the viability of microbially driven bioremediation in neutralising the pH of bauxite residue. By augmenting the microbial community within bauxite residue and supplying it with a suitable organic carbon source, microbially driven bioremediation neutralises pH through the production of acidic metabolites via the microbial fermentation of organic substrates. However, both the optimal microbial inoculant and organic carbon substrates to fuel this process have not yet been determined. As such, this experiment aimed to determine the optimal combination of microbial inoculant and carbon substrate to produce the greatest and most rapid neutralization of pH using Western Australian bauxite residue from Alcoa of Australia Limited. The effect of residue preconditioning was also tested by transferring remediated residue to bioreactors with differing inoculants that had not been neutralized. Here, we show that a combination of a mixed inoculum from a geochemically similar environment, and a simple sugar substrate (for example, glucose or fructose) produced the most rapid neutralization of residue. This is mostly attributed to the metabolic efficiency of degrading simpler monosaccharides and a group of key species within the inoculum that drives neutralization. Future research may focus on further exploring metabolite compositions in remediated residue and adding new functionality to the bioremediation process to achieve other remediation goals.