Microbes have been used as efficient supporters and stabilizers for palladium nanoparticle (PdNP) synthesis. However, the biomass was regarded inactive and usually discarded to obtain pure PdNPs through centrifugation or pyrolysis. Our study was based on the concept that mature biofilm after being treated with Pd still keeps its metabolic activities and thus may promote some Pd-catalytic reactions through enzymatic processes. In our study, a mature H2-utilizing biofilm dominated by denitrifiers were tested for continuous Pd recovery and PdNP synthesis. Through rapid response to the stress from metal and acid by adapting its community structure and metabolic functions, the biofilm retained &gt;99% of Pd under circumneutral (pH 6.9) and acidic (pH 4.5) conditions, and it accelerated overall Pd immobilization through adsorption and enzymatic reduction. Meanwhile, the biofilm inhibited PdNP agglomeration through rapid encapsulation of Pd monomers at the early stage of nucleation. As a result, PdNPs were embedded in the biofilm as separated 3-4 nm single nanocrystallites dispersedly on cell surfaces and in extracellular polymeric matrix. The intimately coupled PdNP-Biofilm was then tested for short- and long-term nitrate removal. In the short-term test, we reveal that PdNP-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 regulated 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%. In the long-term test that lasted for over 1 year, the PdNP-Biofilm kept high reactivity under various nitrate surface loadings, and the PdNPs remained their nanocrystalline nature with minimal agglomeration or washout. Under higher NO3- loading, compared to the biofilm uncoated with PdNPs that underwent considerable shift of community structure with increased alpha- and beta-diversity and higher abundance of denitrifiers, PdNP-biofilm remained stable; this indicates that PdNPs catalyzed reduction of excess NO3-. From a practical view, our studies open up the door for integrated biofilm system capable of Pd recovery and subsequent water treatment in a sustainable, controllable, and efficient approach.

H2-utilizing biofilm embedded with palladium nanoparticles (PdNP-Biofilm): Assembly, characterization, and application in enhancing denitrification

256th National Meeting (2018)

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