Abstract
Thiocyanate is a toxic compound produced by the mining and metallurgy industries that needs to be remediated prior to its release into the environment. If the industry is situated at high altitudes or near the poles, economic factors require a low temperature treatment process. Microbial fuel cells are a developing technology that have the benefits of both removing such toxic compounds while recovering electrical energy. In this study, simultaneous thiocyanate degradation and electrical current generation was demonstrated and it was suggested that extracellular electron transfer to the anode occurred. Investigation of the microbial community by 16S rRNA metatranscriptome reads supported that the anode attached and planktonic anolyte consortia were dominated by a Thiobacillus-like population. Metatranscriptomic sequencing also suggested thiocyanate degradation primarily occurred via the ‘cyanate’ degradation pathway. The generated sulfide was metabolized via sulfite and ultimately to sulfate mediated by reverse dissimilatory sulfite reductase, APS reductase, and sulfate adenylyltransferase and the released electrons were potentially transferred to the anode via soluble electron shuttles. Finally, the ammonium from thiocyanate degradation was assimilated to glutamate as nitrogen source and carbon dioxide was fixed as carbon source. This study is one of the first to demonstrate a low temperature inorganic sulfur utilizing microbial fuel cell and the first to provide evidence for pathways of thiocyanate degradation coupled to electron transfer.
Highlights
The toxic compound thiocyanate (SCN−) is generated by the mining and metallurgy industries during gold recovery [up to 4000 mg/L (Kantor et al, 2017)] with cyanide and it should be removed from wastewaters before being released to recipient water bodies (Zagury et al, 2004; Van Zyl et al, 2011)
We report the first endeavor of a such approach to investigate a novel low temperature SCN− degrading microbial consortium able to facilitate electrical current generation in microbial fuel cells (MFCs, a type of Bioelectrochemical Systems (BESs))
Metatranscriptomic analysis suggested that the anodic microbial consortium could degrade thiocyanate while the resultant sulfide was oxidized for energy conservation; ammonium was assimilated; and carbon dioxide was fixed via various pathways
Summary
The toxic compound thiocyanate (SCN−) is generated by the mining and metallurgy industries during gold recovery [up to 4000 mg/L (Kantor et al, 2017)] with cyanide and it should be removed from wastewaters before being released to recipient water bodies (Zagury et al, 2004; Van Zyl et al, 2011). Chemical removal of SCN− is both inefficient and costly (Van Zyl et al, 2011). Biodegradation is relatively inexpensive and can completely remove SCN− and other contaminants such as cyanide (Kantor et al, 2015). In the ‘COS pathway’ (Eqs. 2, 3), SCN− is initially hydrolyzed into ammonia and carbonyl sulfide (COS), and the carbonyl sulfide is subsequently oxidized into carbon dioxide and sulfate in an energy yielding reaction with a key enzyme in this pathway being the cobalt-coordinating thiocyanate hydrolase (Scn) (Katayama et al, 1992, 1993; Kim and Katayama, 2000)
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