title: Bacterial response to a continuous long-term exposure of silver nanoparticles at sub-ppm silver concentrations in a membrane bioreactor activated sludge system.
abstract: Silver nanoparticles (nanosilver or AgNPs) have excellent antimicrobial properties. Because of their increasing use, there is a concern about the potential impact of AgNPs in wastewater treatment systems. This study investigated the long-term effects of AgNPs (continuous loading for more than 60 days) on membrane bioreactor (MBR) activated sludge performance. At the influent AgNP concentration of 0.10 mg Ag/L, there was no significant difference in effluent water quality or bacterial activities before and after AgNP exposure. Nitrifying bacterial community structure was relatively stable before and after the long-term AgNP loading. Both ammonia-oxidizing bacteria (AOB) Nitrosomonas spp. and Nitrosospira spp. were present while Nitrospira spp. was the dominant nitrite-oxidizing bacterial species throughout this study. Abundance of silver resistance gene silE in the MBR, however, increased by 50-fold 41 days after the AgNP exposure, and then decreased with continuous AgNP exposure. The long-term nanosilver exposure did not change the membrane fouling rate although extracellular polymeric substances (EPS) concentration increased significantly after nanosilver dosing. The results suggest that AgNPs at the influent concentrations of 0.10 mg/L and below have almost no impact on activated sludge wastewater treatment performance, as activated sludge can effectively reduce nanosilver toxicity by adsorbing or precipitating AgNPs and silver ions (Ag(+)) released from the dissolution of AgNPs.
authors.affiliation: Department of Civil and Environmental Engineering, University of Missouri - Columbia, Columbia, MO 65211, USA.
authors.forename: Chiqian
authors.initials: C
authors.lastname: Zhang
authors.affiliation: Department of Civil and Environmental Engineering, University of Missouri - Columbia, Columbia, MO 65211, USA; Department of Civil and Environmental Engineering, Prairie View A&M University, Prairie View, TX 77446, USA.
authors.forename: Zhihua
authors.initials: Z
authors.lastname: Liang
authors.affiliation: Department of Civil and Environmental Engineering, University of Missouri - Columbia, Columbia, MO 65211, USA. Electronic address: huzh@missouri.edu.
authors.forename: Zhiqiang
authors.initials: Z
authors.lastname: Hu
mesh_terms: D000332:Aerobiosis / Q000187:drug effects; D000641:Ammonia / Q000378:metabolism; D052818:Autotrophic Processes / Q000187:drug effects; D001419:Bacteria / Q000187:drug effects* / Q000378:metabolism; D001704:Biopolymers / Q000032:analysis; D019149:Bioreactors / Q000382:microbiology*; D052836:Heterotrophic Processes / Q000187:drug effects; D008567:Membranes, Artificial; D053768:Metal Nanoparticles / Q000737:chemistry*; D058465:Nitrification / Q000187:drug effects; D009584:Nitrogen / Q000032:analysis; D010084:Oxidation-Reduction / Q000187:drug effects; D012150:Polymorphism, Restriction Fragment Length; D011312:Pressure; D012722:Sewage / Q000382:microbiology*; D012834:Silver / Q000032:analysis / Q000494:pharmacology*; D013997:Time Factors; D014865:Waste Disposal, Fluid; D060753:Water Quality
chemical_list: D001704:Biopolymers; D008567:Membranes, Artificial; D012722:Sewage; D012834:Silver; D000641:Ammonia; D009584:Nitrogen
keywords: Membrane bioreactor (MBR); Nitrifying bacterial community structure; Nitrogen removal; Quantitative polymerase chain reaction; Silver nanoparticles; Wastewater treatment