Overview of Known Alkaliphilic Bacteria from Bauxite Residue

Abstract

Alkaliphilic bacteria usually grow well at pH 9, and the most extremophilic strains can grow up to values as high as pH 12-13. This group of bacteria has the ability to metabolically reduce alkalinity and are tolerant of high concentrations of ions and metals. Interest in extreme alkaliphiles has been shown as they are sources of useful, stable enzymes, and the cells themselves can be used for biotechnological and other applications at high pH values. Many industrial processes produce highly alkaline waste that is contaminated with toxic trace metals/metalloid. Thus, using alkaliphilic microorganisms is considered an attractive alternative method for treating industrial alkaline residues. Bauxite refining is one of the activities that most produces highly alkaline waste. Alumina extraction from bauxite using concentrated sodium hydroxide in the Bayer process generates a slurry and an extremely alkaline (pH of 9 to 13) by-product known as bauxite residue or red mud. For each ton of alumina extracted from bauxite, approximately 1.5-2.0 tons of bauxite residue is generated. Disposal of such a by-product is a serious problem at alumina plants because of environmental risks and financial costs. Thus, it is very important to know bacteria that can survive in such an extreme environment since these bacteria could be used as a method for treating alkaline residues. Firmicutes have been described as one of the most representative bacterial phyla in bauxite residue, and the Bacillus genus as one of the most frequent. Different species of Bacillus have already been isolated from red mud and have shown great potential for the bioremediation process. For this reason, the aim of this article is to carry out a literature review on alkaliphilic bacteria isolated from red mud.


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