The concept of simultaneous microbial-driven and Pd-catalyzed nitrate (NO3 ) reduction was evaluated in terms of NO3 -removal efficiency and reduction-product selectivity. Experiments were conducted in three identical H2-based membrane biofilm reactors (MBfR) operated in parallel: biogenic Pd nanoparticles (PdNPs) associated with biofilm (“Pd-biofilm”), biofilm alone (“Biofilm”), and abiotic PdNPs alone (“Pd-film”). Solid-state characterizations confirmed that the PdNPs in Pd-biofilm were dominated by Pd0 nanocrystallites similar to those in Pd-film, and molecular microbiological analyses confirm that the microbial community in Pd-biofilm were dominated by β-proteobacteria with denitrifying activity similar to Biofilm. Pd-biofilm accelerated NO3 reduction to NO2 mainly through enzymatic activity and accelerated subsequent NO2 reduction mainly through PdNP catalysis. When H2 could be delivered at a rate approximately equal to the total demand to reduce NO3 to N2, active biofilm reduced NO3 /NO2 exclusively to N2, and it also attenuated NH4 + formation; as a result, the overall selectivity towards N2 in Pd-biofilm was nearly 100% and higher than in Pd-film. Thus, coupling PdNP catalysis and microbial denitrification promoted H2-based NO3 reduction and led to greater selectivity towards N2 as long as H2 delivery was controlled. From a practical perspective, delivering H2 by diffusion through bubbleless membranes enabled accurate control of N selectivity.

Original languageEnglish (US)
Pages (from-to)461-470
Number of pages10
JournalApplied Catalysis B: Environmental
StatePublished - Jun 5 2017


  • Membrane biofilm reactor (MBfR)
  • Microbial denitrification
  • N selectivity
  • Nanoparticles
  • Pd-catalyzed nitrate reduction

ASJC Scopus subject areas

  • Catalysis
  • General Environmental Science
  • Process Chemistry and Technology


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