Mining activities require large volumes of water during ore processing, often resulting in its contamination. A common contaminant associated with the gold mining industry is thiocyanate; forming through the reaction between cyanide, added as a gold lixivant, and sulfide present in the ore. Large volumes of the resulting thiocyanate contaminated wastewater are typically stored in open air tailings storage facilities (TSF’s). The potential for accidental environmental release of the thiocyanate contaminated water, through groundwater seepage and dam failure, drives the need for developing an effective thiocyanate treatment technique. Enzymatic thiocyanate degradation by a diversity of microorganisms is well known; the ability to harness this metabolic trait, therefore, offers the potential for an effective remediation strategy. Although much work is being done to understand these processes in engineered biotechnological systems, relatively little is known about the potential for in situ thiocyanate biodegradation in contaminated environmental systems, such as TSF’s. This project, therefore, sought to assess the potential for in situ thiocyanate biodegradation in the surface waters of a TSF at an operating gold mine.
Through lab and field tests, phosphate was found to be the limiting nutrient in the TSF water and upon its sole addition biostimulation of extant thiocyanate degrading microorganisms was achieved. In addition, environmental factors, such as air supply and light exposure, were found to significantly impact thiocyanate degradation and the subsequent cycling of its sulfur and nitrogen containing degradation products. High-throughput sequencing of the 16S and 18S rRNA genes revealed a complex microbial community inhabiting the TSF water, consisting primarily of phototrophic and oligotrophic taxa. Upon phosphate addition and onset of thiocyanate degradation, it was noted that bacteria of the sulfur-oxidising, chemolithotrophic, Thiobacillus genus, known to contain thiocyanate degrading strains, proliferated. These findings form a proof of concept for in situ biostimulation of thiocyanate degradation, which was later confirmed under field conditions. Valuable insights were also obtained on the microbial ecology of gold mine tailings and how the community structure changes over the bioremediation process.