Simultaneous mercury oxidation and NO reduction in a membrane biofilm reactor.

ABSTRACT

This work demonstrates bacterial oxidation of mercury (Hg0) coupled to nitric oxide (NO) reduction in a denitrifying membrane biofilm reactor (MBfR). In 93 days' operation, Hg0 and NO removal efficiency attained 90.7% and 74.1%, respectively. Thauera, Pseudomonas, Paracoccus and Pannonibacter played dual roles as Hg0 oxidizers and denitrifiers simultaneously. Denitrifying bacteria and the potential mercury resistant bacteria dominated the bacterial community. Denitrification-related genes (norB, norC, norD, norE, norQ and norV) and enzymatic Hg0 oxidation-related genes (katG, katE) were responsible for bacterial oxidation of Hg0 and NO reduction, as shown by metagenomic sequencing. XPS, HPLC-ICP-MS and SEM-EDS indicated the formation of a stable mercuric species (Hg2+) reasulting from Hg0 oxidation in the biofilm. Bacterial oxidation of Hg0 was coupled to NO reduction in which Hg0 served as the initial electron donor while NO served as the terminal electron acceptor and thereby redox between Hg0 and NO was formed. MBfR was capable of both Hg0 bio-oxidation and denitrifying NO reduction. This research opens up new possibilities for application of MBfR to simultaneous flue gas demercuration and denitration.