This dissertation characterized two forms of TiO2 engineered nanomaterials (ENMs) to determine the role of solution conditions in mediating differences in the environmental impacts of emerging nanomaterials. In general, ENMs designed for specific product matrices are functionalized to impart distinct characteristics capable of altering the environmental fate and transport (i.e. shape and surface composition). Observations of TiO2 ENM release during product life cycles presents a concern as nanoparticles with unique characteristics begin accumulating in environmental systems. TiO2 nanomaterials were introduced to three consecutive, environmental systems with microbial presence to characterize environmental implications of ENM presence, namely: a model human colon, septic tank, and a quartz sand filtration column.

The following critical findings resulted from this dissertation research. Colonic exposure to food (FG) and industrial (IG) grade TiO2 inhibited a natural shift in microbial composition from Proteobacteria to Firmicutes phyla, with FG TiO2 having the greater impact. Colonic pH levels decreased from IG and FG TiO2 exposure where FG TiO2 (pH 4) again had the greatest impact compared to IG TiO2 (pH 5) and the control (pH 6). Therefore, inherent physical and chemical properties of FG and IG TiO2 can produce different microbial responses in the colonic environment. Next, exposure of the septic system to IG TiO2 particles had minimal effect on the composition of the denitrifying-dominant microbial community, while FG exposures resulted in a mixed functionality community less effective at waste treatment. Nano-FG TiO2 exposure in septic systems may facilitate considerable changes in microbial community activity.

Lastly, FG TiO2 exhibited a high degree of stability in septic conditions and both monovalent electrolyte suspensions. Elution of FG and IG TiO2 was greatest in septic effluent at the higher nanoparticle concentration (100 ppm); however, FG TiO2 was well retained at the low (2 ppm) concentration suggesting low elution from the drainage field.

Valuable insight into the role that inherent physical and chemical properties of emerging ENMs play in environmental systems is gained from this dissertation research. Additionally, the significance of the solution environment at mediating differences observed between uniquely, engineered nanomaterials sheds light on potential mechanisms for minimizing detrimental environmental implications of nanomaterials.

The overall goal of this dissertation was to determine the effects of an emerging contaminant, nanomaterials, on microbial communities in engineered systems. Specifically, communities within a simulated human colon and model septic system were studied. Microbial communities in their natural environments represent realistic scenarios for toxicity testing versus assays with enriched growth media and single cell cultures; the two engineered systems used in this work approach “real” scenarios communities would experience.

This dissertation work has allowed for the following observations. The simulation of metal oxide nanomaterials ingestion with the model colon demonstrated these particles do significantly alter the phenotype of the gut microbial community within the model colon reactor. Next, dosing experiments with copper materials in the septic system established that the effluent had pulses of improper waste treatment and that incomplete organic breakdown was likely occurring. However, even with weekly fluctuations in water quality caused by the particles, data suggest that 100% of the time, water quality parameters and microbial composition were recovering towards baseline conditions. This indicates the system could maintain baseline conditions after perturbances, regardless of the particle type.

Finally, effluent containing copper emitted from the septic system was tested in a high throughput toxicity screening assay with zebrafish embryos. While “as-received” nanoscale copper materials caused the greatest embryo hatching interference, all three “processed” copper materials emitted from the model septic system demonstrated a decline in embryo toxicity, regardless of particle composition/size. Thus, the zebrafish screening in combination with the septic system, provide a novel way to study hazard potentials of commercial Cu-based particulates during partitioning, transformation, and speciation.

This collection of studies provides critical insights into the importance of understanding microbial communities more holistically and in realistic environments. These studies demonstrate the need to update toxicity tests such that they more accurately reflect real exposure scenarios simulating environmental conditions. This research also confirms the invalidity of using “as received” nanoparticles; toxicity tests must use particles reflective of those materials transformed in the environment. Future directions for toxicological studies need new useful testing combinations that provide additional information for complex matrices and microbial communities.

Foodborne illnesses lead to 400,000 deaths annually worldwide, and microbial contamination of fresh produce continues to pose a risk to human health in even the most developed countries. In the United States, 1 in 6 Americans are impacted by foodborne illness every year as the large number of steps that food goes through from farm to fork makes effectively tracing the source of a foodborne outbreak all the more difficult. Modern food production and distribution systems create complex and dynamic environments in which bacteria may attach and proliferate on produce surfaces, which has created a challenge for developing scientifically rigorous food safety regulations. Therefore, this doctoral research aimed to investigate the effects of various environmental conditions on bacterial adhesion, detachment, and disinfection on leafy greens using colloidal transport theory and fundamental research models. Overall, the results of this dissertation work indicate that the likelihood of bacterial attachment onto produce surfaces will vary throughout the watering, washing, and rinsing processes that take place between harvest and consumption. Employing a suite of environmentally relevant bacteria, the kinetics of bacterial attachment and removal from spinach epicuticle surfaces was investigated using a parallel-plate flow cell that allows for simulated gentle rinsing and real-time observation and enumeration of cells. Environmental factors like restricted nutrient availability and complex water chemistry increased attachment rates of foodborne bacteria to the leaf surface, which was attributed to decreases in cell surface charge and changes in extracellular polymers in favor of proteins. The introduction of copper oxide nanoparticles enhanced adhesion and minimized detachment of bacteria from spinach leaf surfaces, while nano-titanium dioxide had the opposite effect, highlighting potential unintended consequences of their application as pesticides or fertilizers in agricultural waters. By modeling standard chlorine disinfection rinses, leaf surface roughness was found to reduce the effectiveness of bleach in removing and inactivating pathogens adhered to spinach leaves. An alternative, enzyme-based disinfectant was produced and shown to increase bacterial detachment from the spinach surface and prevent biofilm formation on polycarbonate. Further, this doctoral research addresses the gap between scientists and policymakers through two projects that identify and explore mechanisms for translating scientific data into public policy change for promoting sustainable diets in the developing world and managing diverse, statewide water data in California. As a whole, this work has elucidated technical and political challenges and opportunities in ensuring food safety and security that warrant further research to inform scientifically rigorous policy and regulations.

The overall aim of this PhD research was to identify mechanisms involved in the removal of nanomaterials in conventional water treatment. This project was developed based upon the need for assessing current water treatment infrastructure, and its capacity of effectiveness in removing nanomaterials. The bulk of this dissertation investigated "primary treatment" steps of coagulation, flocculation, and sedimentation, simulated by full-scale and micro-scale jar tests. The remainder of the dissertation has been the development of a 2D micromodel flow cell to simulate the filtration stage. The model nanoparticles used in this research were primarily Degussa P25 titanium dioxide (TiO2), with select experiments using meso-2,3-dimercaptosuccinic acid coated TiO2, and fluorescently-labeled polystyrene latex microspheres.

Overall, >one-log removal was seen for the model groundwater for all coagulants at a constant dose of 50 mg/L, and across the range of particle concentrations tested (10, 25, 50, and 100 mg/L). In surface water, >90% removal was observed with FeSO4 and Al2(SO4)3, but <60% when using FeCl3. Additionally, removal was most effective at higher nanoparticle concentrations (50 and 100 mg/L) in AGW when compared to ASW. In the presence of more complex scenarios, results showed that removal was most efficient in the presence of divalent cations (Ca2+), and in the absence of NOM and nanoparticle coating, achieving >1 log removal. However, with the presence of nanoparticle coating and NOM, removal decreased to a maximum of ~80%.

Finally, a 2D micromodel flow cell was designed and fabricated to demonstrate a new tool for the investigation of nanoparticle filtration. Specifically, the micromodel allows for direct visualization of pore-scale physico-chemical processes by using an array of 2D silica cylinders through which a model nanoparticle (i.e. fluorescent nanoparticles) can be transported. Through the development of this 2D system, future studies can compare filtration phenomena to a 3D macro-scale column experiment. Thus far, this study accomplished the following 1) fabrication of micromodels and construction of the experimental set-up, 2) development of a robust cleaning protocol for micromodel re-use, 3) demonstration of technique and confirmation that filtration trends (i.e. attachment efficiency) between our micromodel and published data from column experiments can be compared.

Bacteria transport in aqueous environments is heavily influenced by nanoscale forces that govern deposition on and detachment from environmental surfaces. Surface interaction can prevent these species from being carried long distances by fluid flow. Nuances in deposition and detachment properties of waterborne pathogenic bacteria can xii mean the difference between life and death or serious economic losses. In this dissertation, deposition and detachment properties of the human pathogen Escherichia coli O157:H7 and the plant pathogen Xylella fastidiosa are analyzed using a variety of engineering tools. Sand column experiments, parallel plate experiments, and thermodynamic surface interaction predictions are used to study how nanoparticles could affect the transport of E. coli O157:H7 in agricultural soils. Results indicate that the presence of titanium dioxide (TiO2) nanoparticles in agricultural waters could increase E. coli O157:H7 soil transport, especially during rain events. However, the presence of copper oxide (CuO) nanoparticles may decrease E. coli O157:H7 transport. Xylella fastidiosa transport in an insect-plant system was studied in silico. Fluid flow fields in this system were simulated and integrated with custom-made MATLAB code to predict bacteria detachment under relevant environmental conditions. Results support a model of key fluid dynamic mechanisms involved in X. fastidiosa spread within plants and between plants. The model can be used to investigate potential targets for fighting costly crop diseases caused by X. fastidiosa. The application of computational and experimental tools in this dissertation demonstrate how engineering methods can enhance analyses of bacterial transport in diverse environmental systems.

Microbial and colloidal particle transport and deposition onto solid surfaces are of great significance to many environmental and technological processes. Initial attachment of particles is governed by the interactions between particles and surfaces. Classic Derjaguin-Landau-Verwey-Overbeek (DLVO) theory is utilized to predict interactions between particles and surfaces. However, discrepancies between experimental observations and theoretical predictions exist and the failure of the predictive model is often attributed to particle and solid collector physical and chemical heterogeneities.

This work sought to elucidate the contribution of heterogeneity to the initial particle deposition behavior in a radial stagnation point flow system or a parallel plate flow chamber system by systematically adjusting particle type and size, as well as collector surface chemical and/or physical properties. In Chapter 2 and 3, the role of particle heterogeneity (type and size) was examined. Comparable deposition trends were observed between particles, in this case groundwater and marine bacteria, Burkholderia cepacia G4g and Halomonas pacifica g, respectively. However, the deposition kinetics of H. pacifica g appeared to be more sensitive to solution chemistry than that of B. cepacia G4g. Experimental results also demonstrated that particle size (colloidal and bacterial) had a considerable impact on the transport and interaction with surfaces. In Chapter 4, a method to influence collector surface charge and subsequent colloid deposition was described. Experimental results suggest colloids respond to local variations in surface potential through electrostatic interactions, altering particle streamlines flowing along the surface, and ultimately the extent of deposition. In Chapter 5, cell deposition onto bare and zeolite coated aluminum alloy and stainless steel surfaces was investigated using bacterium H. pacifica g. Collector surface properties found to have the most notable effect on cell attachment were the electrokinetic and hydrophobic nature of the bare metal and zeolite coated surfaces. In Chapter 6, the relative impact of physical roughness on antifouling nature of zeolite surfaces, as compared to these other chemical mechanisms was investigated.

This comprehensive dissertation project established both particle and collector surface heterogeneity has a significant effect on particle deposition, which was clearly identified by altering various physical and chemical interaction parameters between particles and surfaces.

The overarching goal of this study was to systematically investigate how engineered particles behave in engineered filters under a range of relevant solution chemistry conditions. Specifically, the approach was to conduct a combination of fundamental and applied experiments, looking at engineered particles transport in idealized conditions, followed by those simulating actual scenarios in the filtration stage of drinking water treatment. It was confirmed that the leading factors in engineered particles destabilization which leads to their removal include the type and concentrations of salts in solution, and the process operating conditions (ionic strength and coagulant residual). Ultimately, through the systematic variation of these parameters in the proposed micromodel experiments described below, the conditions for optimal engineered particles destabilization and removal was determined.

This dissertation work has allowed for the following observations. In the 2D micromodel, the removal efficiency of latex nanoparticles and food grade TiO2 in filtration is sensitive to the particle aggregate size, surface charge, and surface composition. The model was built to show single collector removal efficiency as a function of particle size and ionic strength, as well as predict the behavior or deposition location on collector of any nanoparticles entering the filtration system in order to improve the field of environmental nanotechnology. Furthermore, the predictions generated from the present work parallel those of the constricted 3D model, for instance, the collector size and average velocity. Ultimately, this research could be applied in place of 3D columns when designing filters for water and wastewater treatment.

Finally, the role of coagulant residual, TiO2 structure, and solution chemistry on the removal efficiency were studied as well in simulated water (AGW and ASW). Results from this study indicate that for all TiO2 suspensions, the greater coagulant residual concentrations increased the removal efficiency up until 0.5 mg/L alum, above that threshold the effect of coagulant residual were negligible. This collection of studies provides critical insights into the importance of understanding particles size and coagulant residual concentrations more impactful and in realistic environments. These studies demonstrate the need to update more tests such that they more

accurately reflect real exposure scenarios simulating environmental conditions.

The overall goal of this research was to identify the mechanisms involved in the fate, transport, and removal of nanomaterials in both natural and engineered systems. The project was developed based upon the hypothesis that nanomaterial properties (type, size, shape) and environmental parameters including solution chemistry (pH, ionic strength, and ion valence), as well as the presence of natural organic matter (NOM) and bacteria will control the transport and removal of nanomaterials. Nine different nanomaterials were used including three metal oxides, three sizes of TiO₂ and three types of single walled carbon nanotubes(SWNTs). Wide variation in physicochemical properties among these nanomaterials allowed the comparison with respect to size, shape, type, and synthesis method. Complementary transport studies were conducted in both macroscopic (column) and microscopic (flow cells) systems.

This dissertation work has allowed for the following critical observations to be made. Sonication, nanoparticle concentration and solution chemistry can significantly alter physicochemical properties of metal oxide nanoparticles to ensure reproducible dispersion of metal oxide nanoparticles for transport and toxicity studies. Transport of TiO₂ nanoparticles (TNPs) through macroscopic porous media showed that a combination of mechanisms including straining, blocking, DLVO and hydrodynamic forces were involved. Additionally experiments in the parallel plate chamber indicated that deposition of TNPs was controlled by a combination of DLVO and non-DLVO-type forces, aggregation, shear and gravitational forces. Also, the presence of both NOM and bacteria resulted in much less deposition than NOM or bacteria alone, indicating a combination of factors involved in deposition including electrosteric, electrostatic effects, and aggregation state of TNPs and TNP-bacteria. Another study with three distinctly sized TNPs revealed that heterogeneity in the nanoparticle aggregate - due to its composition of primary nanoparticles - plays a significant role in the transport and aggregate breakup. Finally, SWNTs synthesized by different methods resulted in distinctive breakthrough curves due to catalysts used in synthesis, whereas metal content of SWNTs affects the relative elution of SWNTs through column. This collection of studies suggests that consideration of these mechanisms is necessary to improve our ability to predict fate, transport and removal nanomaterials in the aquatic environments as well as set-up environmental regulations.

The primary goals of this doctoral research were to investigate aqueous solution parameters that may affect the aggregation behavior of engineered nanomaterials (ENMs), increase the analytical capacity of the colloidal research community, and explore ways in which scientists and engineers can collaborate across disciplines in ways that make individual efforts more robust and more amenable to positive societal contributions. Studies with ENMs were conducted with materials ranging from established, widespread titanium dioxide, to unique, niche graphene oxide and molybdenum disulfide, to emerging, nascent few-layered black phosphorus. The effects of environmentally relevant parameters (i.e., pH, ionic strength, cation valence, extracellular polymeric substances, surfactants, and coagulant) on the electrokinetic properties, aggregation rates, and/or aggregation morphology of the ENMs were investigated.

The following valuable insights were obtained from this dissertation research. The 2D black phosphorus ENMs investigated were found to be colloidally stable in environmental conditions. This insight could be used to further develop BP towards future biomedical and environmental applications. In addition, this investigation demonstrated the validity of using traditional colloidal characterization techniques on non-spherical, two-dimensional ENMs. Results from this work could lead to further research into the stability of other 2D ENMs, improving the collective scientific knowledge, and leading to further, novel applications of these versatile ENMs. A further aim of this research was to identify effects of specific environmental parameters on titanium dioxide nanoparticles. The resultant information can be used to better predict the fate and transport of this common ENM in complex environments. The final objective of this doctoral research, to lessen the divide between the academic research community and policymakers, was achieved by applying technical expertise and scientific principles to two distinct challenges; the correlation of personality to drinking water preferences and the synthesis of best practices for state-level water data management. This dissertation provides critical understanding of fundamental aggregation behavior of various ENMs and demonstrates the value of extending the tools of the scientific enterprise across disciplinary boundaries and beyond the ivory tower of academia.

The overall goal of this investigation was to elucidate the effects the environment had on pathogenic bacteria in natural and engineered systems. Pathogens are generally studied by growing a single strain in nutrient rich media (ideal conditions), which do not accurately simulate the environments in which these bacteria are found. Thus, this project was developed to show the variations in bacterial phenotype based upon growth phase, to compare the fate and transport of 11 Escherichia coli isolates in an idealized media versus a more environmentally representative bovine manure extract, and to move away from the ideal to the real, by simulating representative environments in which pathogen proliferation can occur.

This dissertation work has allowed for the following critical observations to be made. The conditions in which bacteria are grown in the laboratory can significantly alter the cells' physical-chemical and transport properties. Specifically, the growth phase of Pseudomonas aeruginosa (PAO1) was the main influence on the relative cell surface hydrophobicity. This in turn changed the mechanism by which the cells adhered to a quart crystal microbalance with dissipation (QCM-D) sensor surface. Additionally, experiments investigating 11 E. coli isolates showed that the solution in which the cells are grown (ideal media vs. real manure extract) has a significant influence on their physical-chemical and transport properties of the bacteria. This work demonstrated the need to study pathogens in conditions that better approximate the complexity of natural systems. Thus, three in vitro systems were built to model environments (human colon, septic tank, and groundwater) in which pathogens may be found. A human fecal microbial community was inoculated in the model colon and subsequently into the septic tank and groundwater systems, which led to a change in the microbial community's structure and function. A model pathogen, E. coli O157:H7, was added to the systems and was found to significantly impact the microbes present and their resulting fate and transport. This collection of studies confirms the need to study pathogens in simulated systems that more closely represent the real environments in which the cells may proliferate.