Biodegradation of potassium amyl xanthate from mining flotation wastewater with minimal CS₂ emission

The mining industry produces significant volumes of flotation wastewater that contains xanthates, such as potassium amyl xanthate (PAX, C₆H₁₁OS₂K), that pose toxicity risks to ecosystems and humans. In this study, an oxygen-based membrane biofilm reactor (O₂-MBfR) was applied to biodegrade high concentrations (75∼200 mg/L) of PAX; the MBfR achieved > 99% removal of PAX with minimal carbon disulfide (CS₂) emission at a PAX surface loading rate of 770 mg/m2-d. The microbial community adapted to changing PAX loading and O₂ pressure, and it consistently gave efficient removals of PAX and soluble COD, as well as negligible CS₂ emission. Metagenomic sequencing revealed that Mesorhizobium, Zoogloea, Sediminibacterium, Afipia, and Devosia were important genera that contributed in different ways to oxidation of PAX, PAX metabolites, and CS₂. PAX degradation began with cleavage of C-O or C-S bonds, which was followed by oxidation of sulfur-containing intermediates. Also, the efficient biodegradation of xanthates offers a potential strategy to avoid flotation tailings caused by flotation wastewater reuse.