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Potential implication of silver nanoparticles on biological wastewater treatment

  • Author / Creator
    Sheng, Zhiya
  • Nano-silver is the most popular nanomaterial in commercial products. However, its wide use also becomes a concern because Ag-NPs can have potential adverse effects on biological wastewater treatment processes due to its strong antibacterial property. Considerable efforts have been made to study the effects of Ag-NPs on biological wastewater treatment, but great controversy still exists. The research in this dissertation focused on engineered ecosystems including biofilm and activated sludge used in biological wastewater treatment processes. Ag-NPs were applied to isolated single strains from biological wastewater treatment plants, laboratory mixed cultures with isolated strains, and activated sludge and biofilms, to gain insights on the rules governing the effects of Ag-NPs on microbial communities in complicated ecosystems in biological wastewater treatment. To assess the protective effects of extracellular polymeric substances (EPS), biofilms without loosely bound EPS were also tested. Doses of Ag-NP applied ranged from 1 to 200 mg Ag/L. 1% PBS buffer was used to mimic wastewater environment; real and synthetic wastewater was also tested. 16s rRNA gene based polymerase chain reaction — denaturing gradient gel electrophoresis (PCR-DGGE) was used to analyze the microbial community shift after Ag-NP treatment. Transmission electron microscopy (TEM) was used to examine the biofilm uptake of Ag-NPs. qPCR was used to quantify changes in total bacteria and the abundance of selected bacteria group. GeoChip analysis was done to investigate the effects of Ag-NPs on the functional structure of the microbial community. 16s rRNA gene based pyrosequencing was used to monitor the compositional change in the bacterial community. The properties of the sludge, accumulation of silver species inside the sludge, and characteristics of the Ag-NPs were examined to explain observed the phenomena. Results were compared and the tolerance from the lowest to the highest followed the order: single strain < laboratory mixed culture < activated sludge in laboratory reactor < biofilm without loosely bound EPS < original biofilm. Higher tolerance corresponds with higher community diversity and more compact EPS structure. Stimulatory effects of Ag-NPs under low dose were detected under certain conditions, indicating that the effects of Ag-NPs may conform to the hormetic model. Considering the high robustness of full-scale biological wastewater treatment processes, they may be able to stand a relatively high concentration of Ag-NPs and a potentially wider stimulatory dose range can even be observed compared with laboratory systems. However, the higher biomass concentration and community diversity caused by Ag-NPs does not correspond with improved reactor performance and can potentially trigger the appearance of “superbugs” that would pose a significant danger to the health of the public and environment.

  • Subjects / Keywords
  • Graduation date
    2016-06
  • Type of Item
    Thesis
  • Degree
    Doctor of Philosophy
  • DOI
    https://doi.org/10.7939/R3FQ9QH99
  • License
    This thesis is made available by the University of Alberta Libraries with permission of the copyright owner solely for non-commercial purposes. This thesis, or any portion thereof, may not otherwise be copied or reproduced without the written consent of the copyright owner, except to the extent permitted by Canadian copyright law.
  • Language
    English
  • Institution
    University of Alberta
  • Degree level
    Doctoral
  • Department
    • Department of Civil and Environmental Engineering
  • Specialization
    • Environmental Engineering
  • Supervisor / co-supervisor and their department(s)
    • Yang Liu (Civil and Environmental Engineering)
  • Examining committee members and their departments
    • Nicholas Ashbolt (School of Public Health)
    • Ian Buchanan (Civil and Environmental Engineering)
    • Joo-Hwa Tay (Civil Engineering, University of Calgary)
    • James Bolton (Civil and Environmental Engineering)