title: Microbial community response of nitrifying sequencing batch reactors to silver, zero-valent iron, titanium dioxide and cerium dioxide nanomaterials.
abstract: As nanomaterials in consumer products increasingly enter wastewater treatment plants, there is concern that they may have adverse effects on biological wastewater treatment. Effects of silver (nanoAg), zero-valent iron (NZVI), titanium dioxide (nanoTiO₂) and cerium dioxide (nanoCeO₂) nanomaterials on nitrification and microbial community structure were examined in duplicate lab-scale nitrifying sequencing batch reactors (SBRs) relative to control SBRs that received no nanomaterials or ionic/bulk analogs. Nitrification function was not measurably inhibited in the SBRs by any of the materials as dosing was initiated at 0.1 mg/L and sequentially increased every 14 days to 1, 10, and 20 mg/L. However, SBRs rapidly lost nitrification function when the Ag⁺ experiment was repeated at a continuous high load of 20 mg/L. Shifts in microbial community structure and decreased microbial diversity were associated with both sequential and high loading of nanoAg and Ag⁺, with more pronounced effects for Ag⁺. Bacteroidetes became more dominant in SBRs dosed with Ag⁺, while Proteobacteria became more dominant in SBRs dosed with nanoAg. The two forms of silver also had distinct effects on specific bacterial genera. A decrease in nitrification gene markers (amoA) was observed in SBRs dosed with nanoAg and Ag⁺. In contrast, impacts of NZVI, nanoTiO₂, nanoCeO₂ and their analogs on microbial community structure and nitrification gene markers were limited. TEM-EDS analysis indicated that a large portion of nanoAg remained dispersed in the activated sludge and formed Ag–S complexes, while NZVI, nanoTiO₂ and nanoCeO₂ were mostly aggregated and chemically unmodified. Overall, this study suggests a high threshold of the four nanomaterials in terms of exerting adverse effects on nitrification function. However, distinct microbial community responses to nanoAg indicate potential long-term effects.
authors.affiliation: Via Department of Civil and Environmental Engineering, 418 Durham Hall, Virginia Tech, Blacksburg, VA 24061, USA. yanjunm6@vt.edu
authors.forename: Yanjun
authors.initials: Y
authors.lastname: Ma
authors.forename: Jacob W
authors.initials: JW
authors.lastname: Metch
authors.forename: Eric P
authors.initials: EP
authors.lastname: Vejerano
authors.forename: Ian J
authors.initials: IJ
authors.lastname: Miller
authors.forename: Elena C
authors.initials: EC
authors.lastname: Leon
authors.forename: Linsey C
authors.initials: LC
authors.lastname: Marr
authors.forename: Peter J
authors.initials: PJ
authors.lastname: Vikesland
authors.forename: Amy
authors.initials: A
authors.lastname: Pruden
mesh_terms: D001419:Bacteria / Q000187:drug effects*; D019149:Bioreactors / Q000382:microbiology; D053768:Metal Nanoparticles / Q000633:toxicity*; D046529:Microscopy, Electron, Transmission; D058465:Nitrification; D012722:Sewage / Q000032:analysis*; D013052:Spectrometry, X-Ray Emission; D014865:Waste Disposal, Fluid; D062065:Wastewater / Q000633:toxicity*; D014874:Water Pollutants, Chemical / Q000633:toxicity*
chemical_list: D012722:Sewage; D062065:Wastewater; D014874:Water Pollutants, Chemical