Bacterial inoculation along with different amendments accelerates the remediation of bauxite residue for vegetation establishment

Bauxite residue (red mud) is a by-product generated in huge quantities from the alumina industries with serious environmental issues due to its strong alkalinity, sodicity, and salinity. An attempt has been made to establish vegetation by using bacteria isolated from the bauxite residue along with various amendments. A field study was conducted by inoculating the bacterial consortia (∼350 log cfu/plot) consisting of 10 different bacteria to the bauxite residue mixed with 10% (w/w) of fly ash, sewage sludge, garden soil, and 2% of gypsum. After 6 months of the field experiment, the grass was harvested and determined the growth and mineral uptake. Inoculation of bacterial consortia significantly increased the vegetation in the bauxite residue amended with different ameliorants, and twofold increase in biomass was observed in sewage sludge- and fly ash-amended bauxite residue with bacterial inoculation. Addition of gypsum with bacterial inoculation significantly reduced pH of the bauxite residue from 11.0 to 7.9. Organic carbon, available P, and nitrogen levels were significantly increased in sewage sludge-amended bauxite residue inoculated with bacteria followed by fly ash amendment. Alkaline and acid phosphatases, urease, and invertase enzyme activities also increased due to inoculation of bacterial consortia with all amendments. Uptake of elements such as Mg, K, and Ca increased, while Al, Fe, and Na decreased in the Bermuda grass due to bacterial inoculation. This study demonstrated that inoculation of bacteria along with sewage sludge or fly ash as amendments is a sustainable technology for establishment of green vegetation on bauxite residue.