Simple Organic Carbon Sources and High Diversity Inocula Enhance Microbial Bioneutralization of Alkaline Bauxite Residues

Bioneutralization
of pH by microbial fermentation of added carbon
substrates is a promising new method for remediation of the 1.7 GT/yr
of alkaline mining tailings produced globally. Here, we present the
first study to systematically compare and optimize the efficacy of
microbial inocula of varying diversities, structures, and provenance
and organic carbon substrates of varying complexities on the rate
and extent of pH bioneutralization in alkaline bauxite residue tailings.
Laboratory-scale bioreactors inoculated with soda lake sediments or
with monosaccharide substrates added had a significantly lower minimum
pH (<8) and a significantly higher maximum rate of pH neutralization
(>0.02 μmol H+ day–1) and achieved
these in significantly less time (<26 days) compared to bioreactors
with other inocula or substrates. The soda lake sediment introduced
a significantly higher-diversity microbial community with a distinct
structure (dominated by Euryarchaeota and Bacteroidetes, rather than Acidobacteria and Actinobacteria), supporting higher acetate
and formate-yielding fermentation pathways compared to other inocula.
The strong performance of monosaccharides is attributed to widespread
microbial capacity for efficient fermentation. Using either monosaccharide
carbon substrates or soda lake sediments is recommended to maximize
bioneutralization efficiency at the industrial scale.