title: Palladium Recovery in a H2-Based Membrane Biofilm Reactor: Formation of Pd(0) Nanoparticles through Enzymatic and Autocatalytic Reductions.
abstract: Recovering 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.
authors.affiliation: Swette Center for Environmental Biotechnology, Biodesign Institute, Arizona State University , Tempe, Arizona 85287, United States.
authors.forename: Chen
authors.initials: C
authors.lastname: Zhou
authors.affiliation: Swette Center for Environmental Biotechnology, Biodesign Institute, Arizona State University , Tempe, Arizona 85287, United States.
authors.forename: Aura
authors.initials: A
authors.lastname: Ontiveros-Valencia
authors.affiliation: Swette Center for Environmental Biotechnology, Biodesign Institute, Arizona State University , Tempe, Arizona 85287, United States.|Department of Water Engineering and Science, College of Civil Engineering, Hunan University , Changsha, China.
authors.forename: Zhaocheng
authors.initials: Z
authors.lastname: Wang
authors.affiliation: Swette Center for Environmental Biotechnology, Biodesign Institute, Arizona State University , Tempe, Arizona 85287, United States.
authors.forename: Juan
authors.initials: J
authors.lastname: Maldonado
authors.affiliation: Department of Environmental Engineering, College of Environmental and Resource Sciences, Zhejiang University , Hangzhou, China.
authors.forename: He-Ping
authors.initials: HP
authors.lastname: Zhao
authors.affiliation: Swette Center for Environmental Biotechnology, Biodesign Institute, Arizona State University , Tempe, Arizona 85287, United States.
authors.forename: Rosa
authors.initials: R
authors.lastname: Krajmalnik-Brown
authors.affiliation: Swette Center for Environmental Biotechnology, Biodesign Institute, Arizona State University , Tempe, Arizona 85287, United States.
authors.forename: Bruce E
authors.initials: BE
authors.lastname: Rittmann
mesh_terms: D020562:Betaproteobacteria / Q000378:metabolism; D018441:Biofilms; D019149:Bioreactors / Q000382:microbiology*; D058440:Denitrification; D004867:Equipment Design; D006863:Hydrogen-Ion Concentration; D059013:Microbial Consortia / Q000502:physiology; D053758:Nanoparticles / Q000737:chemistry*; D010084:Oxidation-Reduction; D010165:Palladium / Q000737:chemistry / Q000302:isolation & purification*; D043362:Rhodocyclaceae / Q000378:metabolism; D018505:Waste Management / Q000295:instrumentation / Q000379:methods*
chemical_list: D010165:Palladium