Mechanistic insights into bio-stabilization of lead (II) in flue gas by a sulfate-reducing bioreactor

Abstract

This study investigated bio-stabilization of divalent lead (Pb2+) in the simulated flue gas by a sulfate-reducing bioreactor (SRBR). The SRBR achieved Pb2+ bio-removal effectively (95.7–98.7%). Metagenomic and metaproteomic analyses revealed that bacterial heavy metal resistance, sulfate bio-reduction/dephosphorylation-driven Pb2+ bioprecipitation, Pb2+ bio-complexation by extracellular polymeric substances (EPS) and thiols, Pb2+ biosorption by cell wall and cell membrane, as well as Pb2+ bio-expulsion by bacterial efflux and secretion system synergistically actualized flue gas Pb2+ biodetoxification. Lead speciation analysis by sequential extraction processes followed by inductively coupled mass spectrometry and further characterization by a series of spectroscopic and spectrometric techniques comprehensively verified that well-crystalized Galena (PbS) and Pyromorphite (Pb5(PO4)3Cl) cell surface-deposited microparticles in the form of residual lead (Res-Pb, 53.4–73.7%) were the major products in Pb2+ bio-stabilization. Besides, organic matter-bound lead (OM-Pb, 4.1–12.6%) and humic acids-bound lead (HA-Pb, 9.0–23.1%) were the second major products. Flue gas Pb2+ mostly bioprecipitated with biogenic sulfides and phosphates to form PbS and Pb5(PO4)3Cl, partly complexed by humic acids, EPS and thiols to form HA-Pb and OM-Pb, and was partly immobilized by cell wall and cell membrane. The weakly stable OM-Pb and HA-Pb may thermodynamically convert into the less mobile, highly chemically stable and less bioavailable products: PbS and Pb5(PO4)3Cl via long-term equilibration. Therefore, SRBR effectively achieved bio-removal, bio-stabilization and bio-recovery of Pb2+ in flue gas, which may provide a feasible and environment-friendly biotechnique for flue gas Pb2+ decontamination.