Characterisation of the complex microbial community associated with the ASTER™ thiocyanate biodegradation system

•The ASTER™ reactor contains distinct biofilm-associated and planktonic microbial communities.•The ASTER™ biofilm ensures biomass retention even at low hydraulic retention times.•The ASTER™ biofilm is made up of morphologically diverse bacterial species and eukaryotes.•ASTER™ associated microbial community is far more diverse than previously reported.•The significant microbial diversity may ensure robustness for treating a dynamic effluent stream.

The ASTER™ process is used to bioremediate cyanide- (CN−) and thiocyanate- (SCN−) containing waste water. This aerobic process is able to reduce the CN− and SCN− concentrations to below 1 mg/L efficiently in a continuous system, facilitating reuse of process water or safe discharge. Such remediation systems, which completely eliminate risk associated with the pollutants, are essential for sustainable mineral processing and the long term minimisation of environmental burden through both pollutant destruction and exploiting opportunities for nutrient recycle. Process robustness of these bioremediation options can be enhanced by good understanding of the microbial community involved in the process. To date, the microbial consortia associated with the ASTER™ bioprocess have been poorly characterised using isolation approaches only. As a result, the relative abundance and diversity of the community has been significantly under-represented. In this study, both planktonic and biofilm-associated biomass have been observed. Microscopy has revealed the diversity of these communities, including bacteria, motile eukaryotes, filamentous fungi and algae, with the biofilm densely packed with microorganisms. The results of the molecular characterisation study reported here, using a clone library approach, demonstrate that the microbial community associated with the ASTER™ bioprocess system is far more complex than previously suggested, with over 30 bacterial species identified thus far. On-going investigations focus on identification of key microbial community members associated with SCN− biodegradation and other critical metabolic functions, as well as the expected dynamic response of this complex microbial community to shifts in the operating window of the process.