Impacts of different nanoparticles on functional bacterial community in activated sludge

Rapidly developing industry raises concerns about the environmental impacts of nanoparticles, but the effects of inorganic nanoparticles on functional bacterial community in wastewater treatment remain unclear. The discriminated effects of silver nanoparticles (Ag-NP) and zinc oxide nanoparticles (ZnO-NP) in a simulated sequencing batch reactor (SBR) system were therefore evaluated by the RNA-based terminal restricted fragment length polymorphism (T-RFLP), 16S rcDNA gene clone library and real-time reverse transcription-PCR (RT-PCR) analyses. Although the COD and NH4-N removal efficiencies were not or slightly reduced by the addition of ZnO-NP and Ag-NP, the functional bacterial community changed remarkably. The denitrification related species were inhibited by high dosage of ZnO-NP and Ag-NP, including Diaphorobacter species, Thauera species and those in the Sphaerotilus-Leptothrix group. However, the bacteria related to sludge bulking, heavy metal resistant and biosorption were increased, especially by ZnO-NPs treatment, including those closely related to Haliscomenobacter hydrossis, Zoogloea ramigera and Methyloversatilis universalis. In addition, Ag-NP and ZnO-NP treatments influenced the functional bacterial community differently. Increasing of bulking related bacteria may help to compensate the COD removal efficiency and to maintain functional redundancy, but could lead to operation failure of activated sludge system when expose to ZnO-NPs.