| Summary: | The H<sub>2</sub>-based membrane biofilm reactor (H<sub>2</sub>-MBfR) has been acknowledged as a cost-effective microbial reduction technology for oxyanion removal from drinking water sources, but it remains unknown how the evolution of biofilm characteristics responds to the changing critical operating parameters of the H<sub>2</sub>-MBfR for simultaneous bromate (BrO<sub>3</sub><sup>−</sup>) and nitrate (NO<sub>3</sub><sup>−</sup>) elimination. Therefore, an expanded multispecies model, applicable to mechanistically interpret the bromate-reducing bacteria (BRB)- and denitrifying bacteria (DNB)-dominated metabolic processes in the biofilm of the H<sub>2</sub>-MBfR, was developed in this study. The model outputs indicate that (1) increased BrO<sub>3</sub><sup>−</sup> loading facilitated the metabolism of BRB by increasing BRB fraction and BrO<sub>3</sub><sup>−</sup> gradients in the biofilm, but had a marginal influence on NO<sub>3</sub><sup>−</sup> reduction; (2) H<sub>2</sub> pressure of 0.04 MPa enabled the minimal loss of H<sub>2</sub> and the extension of the active region of BRB and DNB in the biofilm; (3) once the influent NO<sub>3</sub><sup>−</sup> concentration was beyond 10 mg N/L, the fraction and activity of BRB significantly declined; (4) BRB was more tolerant than DNB for the acidic aquatic environment incurred by the CO<sub>2</sub> pressure over 0.02 MPa. The results corroborate that the degree of microbial competition for substrates and space in the biofilm was dependent on system operating parameters.
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