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Palladium Recovery in a H2‑Based Membrane Biofilm Reactor: Formation of Pd(0) Nanoparticles through Enzymatic and Autocatalytic Reductions
journal contribution
posted on 2016-02-17, 00:00 authored by Chen Zhou, Aura Ontiveros-Valencia, Zhaocheng Wang, Juan Maldonado, He-Ping Zhao, Rosa Krajmalnik-Brown, Bruce E. RittmannRecovering
palladium (Pd) from waste streams opens up the possibility
of augmenting the supply of this important catalyst. We evaluated
Pd reduction and recovery as a novel application of a H2-based membrane biofilm reactor (MBfR). At steady states, over 99%
of the input soluble Pd(II) was reduced through concomitant enzymatic
and autocatalytic processes at acidic or near neutral pHs. Nanoparticulate
Pd(0), at an average crystallite size of 10 nm, was recovered with
minimal leaching and heterogeneously associated with microbial cells
and extracellular polymeric substances in the biofilm. The dominant
phylotypes potentially responsible for Pd(II) reduction at circumneutral
pH were denitrifying β-proteobacteria mainly consisting of the
family Rhodocyclaceae. Though greatly shifted by
acidic pH, the biofilm microbial community largely bounced back when
the pH was returned to 7 within 2 weeks. These discoveries infer that
the biofilm was capable of rapid adaptive evolution to stressed environmental
change, and facilitated Pd recovery in versatile ways. This study
demonstrates the promise of effective microbially driven Pd recovery
in a single MBfR system that could be applied for the treatment of
the waste streams, and it documents the role of biofilms in this reduction
and recovery process.