Mercury oxidation coupled to autotrophic denitrifying branched sulfur oxidation and sulfur disproportionation for simultaneous removal of Hg and NO.

Coupling elemental mercury (Hg) oxidation, autotrophic denitrifying sulfur oxidation, and sulfur disproportionation offers technological potential for simultaneous Hg and nitric oxide (NO) removal. This study shed light on simultaneous demercuration and denitration of flue gas by a sulfur-oxidizing membrane biofilm reactor (MBfR). Removal efficiency of Hg and NO attained 92% and 83%, respectively in long-term operation. Taxonomic and metagenomic study revealed that a tremendous variety of Hg-oxidizing bacteria (MOB) (Thiobacillus, Truepera, etc.), denitrifying/sulfur-oxidizing bacteria (DSOB) (Thioalkalivibrio, Thauera, etc.), sulfur-disproportionating bacteria (SDB) (Desulfobulbus, Desulfomicrobium, etc.), and multi-functional bacteria (Halothiobacillus, Thiobacillus, etc.) significantly increased in abundance during growth under feeding of Hg and NO in simulated flue gas. The comprehensive employment of sequential chemical extraction processes, inductive coupled mass spectrometry, X-ray diffraction, X-ray photoelectron spectroscopy, and scanning electron microscopy coupled to energy disperse spectroscopy confirmed that Hg was finally biologically oxidized to crystallized metacinnabar (β-HgS) extracellular micromolecular particles. Our findings provided mechanistic insights that MOB, DSOB, and multi-functional bacteria synergistically bio-oxidized Hg as the initial electron donor to Hg and denitrified NO as the terminal electron acceptor to N. SDB disproportionated S branched from SO into S and SO, and β-HgS formation from Hg and disproportionation-derived S, thermodynamically favored Hg bio-oxidation. This novel biotechnique can be a cost-effective and environmentally friendly alternative to flue gas Hg and NO treatment. KEY POINTS: • Combination of Hg bio-oxidation and autotrophic denitrifying sulfur oxidation achieved simultaneous Hg and NO removal. • Thiosulfate disproportionation reinforced Hg bio-oxidation for Hg removal. • Mercury-oxidizing bacteria, denitrifying/sulfur-oxidizing bacteria, and sulfur-disproportionating bacteria synergistically accomplished Hg and NO removal.