Optimizing Autotrophic Sulfide Oxidation in the Oxygen-Based Membrane Biofilm Reactor to Recover Elemental Sulfur.

Biological sulfide oxidation is an efficient means to recover elemental sulfur (S 0 ) as a valuable resource from sulfide-bearing wastewater. This work evaluated the autotrophic sulfide oxidation to S 0 in the O 2 -based membrane biofilm reactor (O 2 -MBfR). High recovery of S 0 (80-90% of influent S) and high sulfide oxidation (∼100%) were simultaneously achieved when the ratio of O 2 -delivery capacity to sulfide-to S 0 surface loading (SL) (O 2 /S 2- → S 0 ratio) was around 1.5 (g O 2 /m 2 -day/g O 2 /m 2 -day). On average, most of the produced S 0 was recovered in the MBfR effluent, although the biofilm could be a source or sink for S 0 . Shallow metagenomic analysis of the biofilm showed that the top sulfide-oxidizing genera present in all stages were Thauera , Thiomonas , Thauera_A , and Pseudomonas . Thiomonas or Pseudomonas was the most important genus in stages that produced almost only S 0 (i.e., the O 2 /S 2- → S 0 ratio around 1.5 g of the O 2 /m 2 -day/g O 2 /m 2 -day). With a lower sulfide SL, the S 0 -producing genes were sqr and fccAB in Thiomonas . With a higher sulfide SL, the S 0 -producing genes were in the soxABDXYZ system in Pseudomonas . Thus, the biofilm community of the O 2 -MBfR adapted to different sulfide-to-S 0 SLs and corresponding O 2 -delivery capacities. The results illustrate the potential for S 0 recovery using the O 2 -MBfR.