Lead removal by its precipitation with biogenic sulfide in a membrane biofilm reactor.

We evaluated the feasibility of using hydrogen (H)-based membrane biofilm reactors (MBfRs) to promote the growth of hydrogenotrophic sulfate-reducing bacteria (SRB) to remove lead (Pb) through its precipitation as lead sulfide (PbS) via biogenic sulfide (HS) production. Two MBfRs (R1 and R2) were set-up to treat synthetic water rich in sulfate (SO) (585 mg/L) and Pb (50, 100, or 250 mg/L). R1 had one influent that had the Pb and synthetic media mixed together; R2 received the Pb solution and synthetic medium through separate influent lines. Oxygen (O) and nitrate (NO) were secondary electron acceptors in R1 and R2, respectively. R1 and R2 produced enough HS (> 73 mg/L) to precipitate Pb, and Pb removal reached >97 %. Chemical equilibrium calculations identified which solids were possible in each stage of operation. Precipitation of Pb with phosphate (PO) occurred in the feed solution in R1, but phosphate precipitation was avoided in the R2 influent. The predominant Pb precipitate inside R2 was PbS, which was confirmed by SEM-EDX analysis. The microbial communities of R1 and R2 were dominated by two SRB - Desulfomicrobium and Fusibacter - along with sulfur oxidizer Thiovirga and denitrifier Thauera. Although the presence of electron acceptors other than SO enabled other respiratory metabolisms, they did not prevent SO reduction to HS or the precipitation of PbS.