abstract
- © 2017 Elsevier B.V.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 Pd0nanocrystallites similar to those in Pd-film, and molecular microbiological analyses confirm that the microbial community in Pd-biofilm were dominated by ß-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 H2could 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 N2in 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 N2as long as H2delivery was controlled. From a practical perspective, delivering H2by diffusion through bubbleless membranes enabled accurate control of N selectivity.