pH and Organic Carbon Dose Rates Control Microbially Driven Bioremediation Efficacy in Alkaline Bauxite Residue

Abstract

Bioremediation of alkaline tailings, based on fermentative microbial metabolisms, is a novel strategy for achieving rapid pH neutralization and thus improving environmental outcomes associated with mining and refining activities. Laboratory-scale bioreactors containing bauxite residue (an alkaline, saline tailings material generated as a byproduct of alumina refining), to which a diverse microbial inoculum was added, were used in this study to identify key factors (pH, salinity, organic carbon supply) controlling the rates and extent of microbially driven pH neutralization (bioremediation) in alkaline tailings. Initial tailings pH and organic carbon dose rates both significantly affected bioremediation extent and efficiency with lower minimum pHs and higher extents of pH neutralization occurring under low initial pH or high organic carbon conditions. Rates of pH neutralization (up to 0.13 mM H produced per day with pH decreasing from 9.5 to ≤6.5 in three days) were significantly higher in low initial pH treatments. Representatives of the Bacillaceae and Enterobacteriaceae, which contain many known facultative anaerobes and fermenters, were identified as key contributors to 2,3-butanediol and/or mixed acid fermentation as the major mechanism(s) of pH neutralization. Initial pH and salinity significantly influenced microbial community successional trajectories, and microbial community structure was significantly related to markers of fermentation activity. This study provides the first experimental demonstration of bioremediation in bauxite residue, identifying pH and organic carbon dose rates as key controls on bioremediation efficacy, and will enable future development of bioreactor technologies at full field scale.

Extreme Geochemical Conditions and Dispersal Limitation Retard Primary Succession of Microbial Communities in Gold Tailings

“…Microbial DNA was extracted from frozen samples (0.60 g tailings or soil) with a MoBio PowerSoil DNA Isolation kit, amplified by PCR with the universal Bacteria/Archaea 16S rRNA primers 926F/1392R (V6–V8 region) and sequenced with the Illumina MiSeq platform according to the procedure outlined in Santini et al (2016) . Sequence data were processed using QIIME according to Santini et al (2015b) for quality control through to taxonomy assignment.…”

“…Most studies to date have focused on the role of vegetation in driving in situ rehabilitation and the establishment of a stable, self-sustaining ecosystem in tailings ( Young et al, 2012 , 2015 ; Ni et al, 2014 , 2015 ), neglecting the role of microbial communities in in situ rehabilitation. Microbial communities can make important contributions to key aspects of tailings rehabilitation including pH neutralization ( Santini et al, 2015a , 2016 ), nutrient accumulation ( Banning et al, 2010 ; Zhan and Sun, 2011 ; Nelson et al, 2015 ; Santini et al, 2015a ; Li et al, 2016 ), degradation of tailings-specific contaminants such as cyanide and thiocyanate ( Skowronski and Strobel, 1969 ; Akcil, 2003 ; Vu et al, 2013 ), and plant-microbe symbioses ( Grandlic et al, 2008 ; Banning et al, 2010 ; Solis-Dominguez et al, 2011 ; Young et al, 2012 ). Enhancing these beneficial contributions is predicated on an improved understanding of the early stages of microbial community assembly and succession in tailings; in particular, the key geochemical and physical controls on microbial recruitment, growth, and community succession.…”

Effect of Acid Production by Penicillium oxalicum on Physicochemical Properties of Bauxite Residue

“…residue and found that microorganisms can secrete organic acids through glucose metabolism, thereby reducing the pH from 9.5 to 6.5 (Santini et al, 2016). Bulk storage of bauxite residue provides an anaerobic environment for microorganisms, enabling them to metabolize organic acid.…”

The Microbiology of Metal Mine Waste: Bioremediation Applications and Implications for Planetary Health

“…In one study the best results were obtained by adding both a source of organic carbon and a soil inoculum containing microorganisms, and as well as decreasing the pH, the concentrations of As, Mo, V, and Al in solution also decreased, likely via sorption and precipitation (Santini & Peng, 2017). Solid bauxite tailings amended with glucose and microorganisms again demonstrated that stimulating the development of anaerobic and fermentative conditions was an effective remediation strategy (Santini et al, 2016). These results were replicated in scaled up 30 L experiments (Santini et al, 2019).…”