Reduction of alkalinity and establishment of vegetation on bauxite residue using Aspergillus tubingensis and different amendments.

Abstract

Bauxite residue (red mud) is a by-product generated in huge quantities from alumina industries with serious environmental issues due to its strong alkalinity, sodicity and salinity. In the present study, an attempt has been made to establish the growth of Bermuda grass (Cynodon dactylon) using Aspergillus tubingensis and various soil amendments such as 10% (w/w) fly ash, sewage sludge, garden soil and 2% of gypsum (CaSO₄) in bauxite residue. Aspergillus tubingensis is able to produce different organic acids in response to bauxite residue. Inoculation of A. tubingensis significantly increased the growth of Bermuda grass in the bauxite residue amended with different ameliorants. The pH was significantly reduced from 11 to 8 in gypsum amended bauxite residue, while EC reduced in all the treatments. Organic carbon, available P, total nitrogen levels were significantly increased in sewage sludge amended bauxite residue inoculated with A. tubingensis followed by fly ash amendment. Soil enzyme activities such as acid phosphatase (484 µM/g/h), alkaline phosphatase (1193 µM/g/h), urease (47.3 µM/g/h) and invertase (778 µM/g/h) were increased due to A. tubingensis inoculation compared to their respective controls where the activities of acid phosphatase, alkaline phosphatase urase and invertase were 123, 90, 50 and 160.6 µM/g/h, respectively. Uptake of elements like Mg, K and Ca increased, while Al, Fe and Na decreased in the biomass due to A. tubingensis inoculation. This study demonstrated that the inoculation of A. tubingensis along with sewage sludge or fly ash as amendments is a sustainable technology for the establishment of green vegetation on bauxite residue.