Accelerating bauxite residue remediation with microbial biotechnology

Biological neutralisation of pH, driven by the microbial fermentation of added organic carbon substrates such as glucose, has recently emerged as a promising technique for remediation of bauxite residue, dropping pH from >11 to <8 in five days. Here, we report on a glasshouse experiment combining this novel microbially-driven pH neutralisation technology with other existing (abiotic) remediation approaches, including addition of gypsum, sewage sludge, and irrigation. Scaling up the bioremediation treatment by three orders of magnitude from previous laboratory trials to these glasshouse trials was successful. Adding bioremediated residue (5 cm thick) at the residue surface significantly enhanced pH neutralisation to depth, decreasing pH from 13 to ~10 as far as 25 cm below the residue surface. Increasing irrigation and tillage frequency accelerated salt removal. Combining our microbial bioneutralisation treatment with fortnightly tillage and daily irrigation provided the best opportunity to rapidly decrease pH and salinity, and is currently being trialled at field scale.