Hollow fiber layout matters the denitrification performance and mechanism of H2-based membrane biofilm reactor: A comprehensive study of hydrodynamics, bioecology and biokinetics

As a promising technology for water treatment, the decontamination performance of membrane-biofilm reactor (MBfR) is largely affected by its flow distribution, which regulates the biofilm structure and activity. Herein, we firstly optimized the hydraulic conditions to ameliorate the denitrification performance of H₂-based MBfR through a rational design of hollow fiber membrane (HFM) layout. Two MBfRs, assembled by bundled and dispersed modules (termed as B-MBfR and D-MBfR, respectively), were constructed to investigate their process performance and mechanism, from a multi-perspective analysis of flow characteristics, biofilm ecology and microbial kinetics. The results indicated that as the HFM spacing was enlarged from 0 to 4 mm, the shift of flow distribution from bias flow to homogeneous flow occured, leading to the development of annular biofilm and individual biofilms in B-MBfR and D-MBfR, respectively. The superior denitrification flux was attained by D-MBfR instead of B-MBfR (1.1 vs. 0.58 g N/m²·d) in long-term experiments, and so were the denitrification kinetics rates of the former in short-term tests. The biofilms in D-MBfR exhibited the stronger anti-shear capacity over annular biofilm, due to their more uniform distribution of proteins and polysaccharides. Benefiting from the thinner thicknesses of biofilms and narrowed hydrodynamic boundary layer, D-MBfR enabled the greater abundance and metabolic activity of hydrogenotrophic denitrifying bacteria than B-MBfR, which then resulted in the almost full exploitation of H₂ and NO₃^-. The findings of this research can provide important scientific foundation for future design and management of MBfRs.