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Potential Impacts of Nanoparticles on Bacterial Systems Open Access


Other title
Wastewater Treatment
Bacterial Aggregation
Antimicrobial Effects
Activated Sludge
Bacterial Adhesion
Type of item
Degree grantor
University of Alberta
Author or creator
Sun, Xiaohui
Supervisor and department
Yang Liu (Civil and Environmental Engineering)
Examining committee member and department
Aloke Kumar (Mechanical Engineering)
Yaman Boluk (Civil and Environmental Engineering)
Leonidas Perez Estrada (Civil and Environmental Engineering)
Chuanwu Xi (Department of Environmental Health Sciences University of Michigan School of Public Health)
Department of Civil and Environmental Engineering
Environmental Engineering
Date accepted
Graduation date
Doctor of Philosophy
Degree level
With the widespread use of nanoparticles (NPs) in commercial products, it is inevitable that NPs will be released into and accumulated in domestic and industrial waste streams (such as wastewater treatment systems), which might have unknown effects. To determine the effects of Ag NPs on the complex microbial communities present in activated sludge, experiments were performed to determine the effects of 1 mg/L Ag NPs on microbial communities in activated sludge. Activated sludge samples with and without gravity settling were compared to evaluate the impact of activated sludge flocs structure on the response of microbial communities to Ag NPs. The effects of Ag NPs on the entire microbial community in activated sludge were analyzed using 16S rRNA gene based polymerase chain reaction-denaturing gradient gel electrophoresis (PCR-DGGE). The results suggest that certain microbial species in the intact activated sludge were highly sensitive to Ag NPs treatment, although no reduction in cell culturability was detected through heterotrophic plate counts (HPCs) during the 24 hours Ag NPs treatment. Conversely, one log unit reduction in the HPCs with no microbial community structure changes was observed for unsettled activated sludge flocs (intact activated sludge treated by 3 hours gravity-settling) after 24 hours Ag NPs treatment. These results strongly suggest that Ag NPs can impact the activated sludge microbial community and cell culturability depending on the physical structure of the activated sludge flocs, the spatial distribution of microorganisms in activated sludge flocs, and the community structures in the activated sludge. In comparison to metal NPs, cellulose nanocrystals (CNC) is a type of rod-shaped biodegradable NPs. Depletion induced flocculation and phase separation of Pseudomonas aeruginosa PAO1 bacteria due to the presence of CNC particles were observed by using confocal laser scanning microscopy and turbidity measurements. CNC with length of 90 nm, diameter of 8 nm and zeta potential of –51.5 mV (in H2O at neutral pH) was used to investigate the depletion effect of CNC in bacterial systems. Bacterial flocculation was observed at the CNC concentration of less than 0.1% due to the depletion effect. These results indicate that rod-shaped nanosized CNC are effective for the depletion flocculation of colloidal size bacteria and that phase separation of bacteria can occur at very low concentrations of CNC particles. In order to verify the impact of extracellular polymeric substance (EPS) on bacterial aggregation and adhesion in the presence of CNC, deposition on silica surfaces of two Pseudomonas fluorescens strains (CHA0 and CHA19-WS) having different EPS producing capacities, was studied in the absence and presence of CNC. The results demonstrate that bacterial initial adhesion to solid surfaces can be significantly hindered by CNC and this hinderance is related to the mount of EPS. In the presence of CNC, bacteria with more EPS aggregated more significantly compared to bacteria with less EPS, and that bacterial deposition in this condition decreased to a greater extent. The effects of pH and IS on the aggregation and deposition of E. coli K12 on silica surfaces were investigated in the absence and presence of CNC. The results indicate that at pH ranging from 5.2 to 7.2 and IS ranging from 10 mM to 50 mM conditions, depletion attraction is the dominant mechanism for CNC induced bacterial aggregation.
Permission is hereby granted to the University of Alberta Libraries to reproduce single copies of this thesis and to lend or sell such copies for private, scholarly or scientific research purposes only. The author reserves all other publication and other rights in association with the copyright in the thesis and, except as herein before provided, neither the thesis nor any substantial portion thereof may be printed or otherwise reproduced in any material form whatsoever without the author's prior written permission.
Citation for previous publication
Sun X, Danumah C, Liu Y, Boluk Y. Flocculation of bacteria by depletion interactions due to rod-shaped cellulose nanocrystals. Chemical Engineering Journal 2012; 198: 476–481.Sun X, Lu Q, Boluk Y, Liu Y. The impact of cellulose nanocrystals on the aggregation and initial adhesion of Pseudomonas fluorescens bacteria. Soft Matter 2014; 10: 8923–8931.Sun X, Sheng Z, Liu Y. Effects of silver nanoparticles on microbial community structure in activated sludge. Science of the Total Environment 2013; 443: 828–835.

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