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.
- Membrane biofilm reactor (MBfR)
- Microbial denitrification
- N selectivity
- Pd-catalyzed nitrate reduction
ASJC Scopus subject areas
- Environmental Science(all)
- Process Chemistry and Technology