Optimization of nitrogen removal and microbial mechanism of a hydrogen-based membrane biofilm reactor

The hydrogen-based membrane biofilm reactor (H₂-MBfR) is an emerging biological nitrogen removal technology characterized by high efficiency, energy-saving capability, and environmental friendliness. The technology achieves denitrification and denitrogenation of microorganisms by passing hydrogen as an electron donor from inside to outside through the hollow fibre membrane module, and eventually the hydrogen reachs the biofilm attached to the surface of the fibre membrane. H₂-MBfR has obtained favourable outcomes in the treatment of secondary biochemical effluent and low concentration nitrogen polluted water source. The experiment was optimized by s single-factor testing and response surface methodology-based optimization (RSM), and the optimal operational conditions were obtained as follows: an influent flow rate of 2 mL/min, hydrogen pressure of 0.04 MPa, and influent nitrate concentration of 24.29 mg/L. Under these conditions, a high nitrate removal rate of 98.25% was achieved. In addition, Proteobacteria and Bacteroidetes were the dominant bacteria in all stages, and the genus Hydrogenophaga was sufficiently enriched, occurring at 13.0%-49.0% throughout the reactor operation. Furthermore, the Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway for nitrate reduction and inorganic carbon utilization by microorganisms in the H₂-MBfR was explored through comparison with the KEGG database. The results provided a mechanistic explanation for the denitrification and carbon sequestration capacity of the H₂-MBfR.