Mercury removal from flue gas using nitrate as an electron acceptor in a membrane biofilm reactor

Membrane bioreactor achieved mercury removal using nitrate as an electron acceptor. The biological mercury oxidation increased with the increase of oxygen concentration. Ferrous sulfide could make both Hg²⁺ and MeHg transform into HgS-like substances. Nitrate drives mercury oxidation through katE, katG, nar, nir, nor, and nos. Mercury (Hg⁰) is a hazardous air pollutant for its toxicity, and bioaccumulation. This study reported that membrane biofilm reactor achieved mercury removal from flue gas using nitrate as the electron acceptor. Hg⁰ removal efficiency was up to 88.7% in 280 days of operation. Oxygen content in flue gas affected mercury redox reactions, mercury biooxidation and microbial methylation. The biological mercury oxidation increased with the increase of oxygen concentration (2%?17%), methylation of mercury reduced with the increase of oxygen concentration. The dominant bacteria at oxygen concentration of 2%, 6%, 17%, 21% were Halomonas, Anaerobacillus, Halomonas and Pseudomonas, respectively. The addition of ferrous sulfide could immobilize Hg²⁺ effectively, and make both Hg²⁺ and MeHg transform into HgS-like substances, which could achieve the inhibition effect of methylation, and promote conversion of mercury. The dominant bacteria changed from Halomonas to Planctopirus after FeS addition. Nitrate drives mercury oxidation through katE, katG, nar, nir, nor, and nos for Hg⁰ removal in flue gas.