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Potential implication of silver nanoparticles on biological wastewater treatment Open Access


Other title
biological wastewater treatment
silver nanoparticles
Type of item
Degree grantor
University of Alberta
Author or creator
Sheng, Zhiya
Supervisor and department
Yang Liu (Civil and Environmental Engineering)
Examining committee member and department
Joo-Hwa Tay (Civil Engineering, University of Calgary)
Ian Buchanan (Civil and Environmental Engineering)
James Bolton (Civil and Environmental Engineering)
Nicholas Ashbolt (School of Public Health)
Department of Civil and Environmental Engineering
Environmental Engineering
Date accepted
Graduation date
Doctor of Philosophy
Degree level
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.
This thesis is made available by the University of Alberta Libraries with permission of the copyright owner solely for the purpose of private, scholarly or scientific research. 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.
Citation for previous publication
Sheng, Z. and Y. Liu (2011). "Effects of silver nanoparticles on wastewater biofilms." Water Research 45 (18): 6039-6050.Sheng, Z. .; J. D. Van Nostrand; Zhou J.; Liu Y (2015). "The effects of silver nanoparticles on intact wastewater biofilms." Frontiers in Microbiology 6: 680.Sheng, Z.; Mohammed, A.; Liu, Y. (2016). "Stability of full-scale engineered ecosystem under disturbance: Response of an activated sludge biological nutrient removal reactor to high flow rate condition." International Biodeterioration & Biodegradation 109: 88-95.Ikehata, K., Sun, R.N., Sheng, Z., Stuart, D. and Liu, Y. Biochemical investigation on the antibacterial activity of aqueous nano-C60 against Escherichia coli, IWA World Water Congress and Exhibition, Montréal, QC, Canada, 2010, manuscript number: IWA- 3141R1.

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