Halving gypsum dose by Penicillium oxalicum on alkaline neutralization and microbial community reconstruction in bauxite residue

Abstract

Bauxite residue is a high-alkaline solid waste generated during alumina production, which greatly limits the growth of soil microorganisms and plants. Here, we developed a novel integrated approach to stabilize alkalinity and reduce the dose of Ca-contained solid waste by inoculation with alkali-tolerant and acid-producing microorganisms. The integrated application of Penicillium oxalicum (P. oxalicum) and gypsum maintained pH at about 9.0 and reduced the dose of gypsum to 2% compared to 4% (w/w) gypsum. Alkaline mineral transformation and organic components conversion in the solid and liquid phases of residues by XRD, XPS, SEM-EDS, FT-IR, and spectroscopic technology demonstrated that P. oxalicum could alleviate extreme saline-alkaline environment by the secreting of carboxylic acids (e.g., oxalic acid) and continuously neutralizing the alkalinity. The ternary plots obtained by high-throughput sequencing revealed that the excessive exogenous ameliorants enhanced the metabolic burden of microorganisms and changed the community assembly processes. Inoculation with P. oxalicum enriched microbial taxa, including Pseudomonas, Alkalibacterium, P. oxalicum, and Epicoccum nigrum, which may also drive a greater response of opportunistic taxa throughout the biomes during amelioration. Overall, the results of the study provided an eco-friendly strategy for alkaline regulation and secondary risk control by the integrated application of functional microorganisms and solid wastes prior to ecological rehabilitation. This work will enhance the understanding of de-alkalization in bauxite residue and demonstrate the application potential of functional microorganisms in ecological reconstruction at disposal areas.