Elemental sulfur biorecovery from phosphogypsum using oxygen-membrane biofilm reactor: Bioreactor parameters optimization, metagenomic analysis and metabolic prediction of the biofilm activity.

This work investigated elemental sulfur (S) biorecovery from Phosphogypsum (PG) using sulfur-oxidizing bacteria in an O-based membrane biofilm reactor (MBfR). The system was first optimized using synthetic sulfide medium (SSM) as influent, then switched to biogenic sulfide medium (BSM) generated by biological reduction of PG alkaline leachate. The results using SSM had high sulfide-oxidation efficiency (98 %), sulfide to S conversion (∼90 %), and S production rate up to 2.7 g S/(m.d), when the O/S ratio was ∼0.5 g O/g S. With the BSM influent, the system maintained high sulfide-to-S conversion rate (97 %), and S-production rate of 1.6 g S/(m.d). Metagenomic analysis revealed that Thauera was the dominant genus in SSM and BSM biofilms. Furthermore, influent composition affected the bacterial community structure and abundances of functional microbial sulfur genes, modifying the sulfur-transformation pathways in the biofilms. Overall, this work shows promise for O-MBfR usage in S biorecovery from PG-leachate and other sulfidogenic effluents.