UC Berkeley

During the processing of refractory gold ores, cyanide (CN-) and residual sulphur species react to form an effluent stream containing thiocyanate (SCN-) and residual CN-. The release of SCN- and CN- containing effluent water to the environment is prohibited, necessitating effective treatment prior to discharge and/or reuse of contaminated plant water. Biologically mediated effluent remediation processes have been developed for commercial use, to remediate SCN-containing effluents, with the aim of enabling recycling of process water and improving the quality of effluent water prior to disposal. Bioremediation processes to treat these effluents rely on a complex consortium of microorganisms to metabolise the SCN- resulting in the production of ammonium that is in turn removed by conversion to nitrite and subsequent denitrification. Increasingly, genomic methods are being used to investigate processes in wastewater treatment to identify key microbial species and, thereby, inform the rationale design and operation of these bioremediation systems. The microbial ecology of laboratory-based SCN- degrading bioprocesses have been investigated, using genome resolved metagenomics, to provide detailed information on the community composition and metabolic profile of abundant microbial community members. Three Thiobacillus strains and an Afipia strain capable of SCN- degradation were shown to be highly abundant within a reactor system enabling biofilm formation. In contrast the inclusion of suspended mineral tailings within an alternative reactor system, led to the selection of an active planktonic microbial community with reduced microbial diversity containing only a single SCN-degrading Thiobacillus sp. This information is being used to inform further rational development of SCN- degradation processes for treatment of contaminated industrial wastewater effluents.