Model of simultaneous denitrification and methanogenesis in an upflow packed-bed biofilm reactor: Nitrogen compounds' inhibition and pseudo two-dimensional biofilm model

Background: The modelling of simultaneous denitrification and methanogenesis (DM) in upflow packed-bed biofilm reactors (UPBR) and the effect of inhibition by nitrogen compounds on methanogenesis has received little attention. This study evaluated the effect using amodel that incorporates a pseudo-two-dimensional biofilm model. Results: The model was validated through comparison with experimental data, and achieved deviations below 5% for the liquid and gas phases. The model indicated that biomass stratification exists throughout the reactor and within the biofilm interior. At C/N ratios close to the stoichiometric C/N ratio, the process achieves efficiencies greater than 70% for nitrogen load rate (NLR) < 270 mg NO₃ ^--N dm^-3 h^-1. At high C/N ratios (50 mg total organic carbon (TOC) mg^-1 NO₃ ^--N), the process achieves efficiencies greater than 70% for organic load rate (OLR) < 83 mg TOC dm^-3 h^-1. Conclusion: The inclusion of the inhibition of methanogenesis by nitrogen compounds did not improve the predictions. Indeed, mass transfer in the biofilm was the phenomenon that most influenced the process. At C/N ratios close to the stoichiometric C/N ratio, process efficiency depends on the NLR; while at high C/N ratios, process efficiency depends on the OLR.