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Occurrence and removal of titanium at full scale wastewater treatment plants: Implications for TiO2 nanomaterials
Abstract
Titanium dioxide nanoparticles increasingly will be used in commercial products and have a high likelihood of entering municipal sewage that flows to centralized wastewater treatment plants (WWTPs). Treated water (effluent) from WWTPs flows into rivers and lakes where nanoparticles may pose an ecological risk. To provide exposure data for risk assessment, titanium concentrations in raw sewage and treated effluent were determined for 10 representative WWTPs that use a range of unit processes. Raw sewage titanium concentrations ranged from 181 to 1233 µg L(-1) (median of 26 samples was 321 µg L(-1)). The WWTPs removed more than 96% of the influent titanium, and all WWTPs had effluent titanium concentrations of less than 25 µg L(-1). To characterize the morphology and presence of titanium oxide nanoparticles in the effluent, colloidal materials were isolated via rota-evaporation, dialysis and lyophilization. High resolution transmission electron microscopy and energy dispersive X-ray analysis indicated the presence of spherical titanium oxide nanoparticles (crystalline and amorphous) on the order of 4 to 30 nm in diameter in WWTP effluents. This research provides clear evidence that some nanoscale particles will pass through WWTPs and enter aquatic systems and offers a methodological framework for collecting and analyzing titanium-based nanomaterials in complex wastewater matrices.
... The results showed that WWTPs can remove 96% of influent titanium with 25 µg/L less effluent titanium quantity. The systematic characterization of effluents from WWTPs revealed the existence of 4-30 nm (diameter) spherical TiO2 particles, which can be utilized for other applications [93]. Similarly, Tou et al. (2017) evaluated samples of sewage sludge in China using a sequential extraction approach coupled with single-particle inductive plasma mass spectrometry for the quantification of metallic nanoparticles. ...
... In recent times, nanotechnology has attracted attention among researchers to be utilized in large-scale WWTPs. Westerhoff et al. (2011) demonstrated the existence and elimination of titanium in a full-scale WWTP, with an implication for titanium dioxide (TiO 2 ) nanomaterials. In this study, concentrations of titanium of about 181 to 1233 µg/L in raw sewage and effluent treatment of 10 representative WWTPs were evaluated. ...
... The results showed that WWTPs can remove 96% of influent titanium with 25 µg/L less effluent titanium quantity. The systematic characterization of effluents from WWTPs revealed the existence of 4-30 nm (diameter) spherical TiO 2 particles, which can be utilized for other applications [93]. Similarly, Tou et al. (2017) evaluated samples of sewage sludge in China using a sequential extraction approach coupled with single-particle inductive plasma mass Energies 2024, 17, 3060 15 of 23 spectrometry for the quantification of metallic nanoparticles. ...
This paper explores the significant role of Wastewater Treatment Plants (WWTPs) in achieving environmental sustainability, with a particular focus on enhancing energy efficiency, resource recovery, and water reuse. WWTPs are crucial for removing pollutants and recovering resources from wastewater, thereby protecting public health and biodiversity. However, they are also associated with high operational costs, substantial carbon footprints, and energy-intensive processes. This article delves into various strategies and technologies to overcome these challenges, aiming to transform WWTPs from energy consumers to energy-efficient resource recovery hubs. Techniques such as anaerobic digestion and the use of advanced oxidation processes and microbial fuel cells are investigated for their potential in energy recovery and efficiency enhancement. Success stories from around the globe are highlighted to demonstrate the feasibility of transitioning to energy-positive WWTP operations. The integration of water reuse systems is also discussed, highlighting recent advancements that enable treated wastewater to be repurposed for agricultural, industrial, and potable uses, thereby promoting sustainability and water conservation. This paper emphasizes the importance of integrating cutting-edge energy management practices to minimize environmental impacts, reduce operational costs, and contribute to a more sustainable water sector.
... It is found naturally in granites and meta-sedimentary rocks. In water, uranium exists in U(VI) state, binds with different anions, and forms et al. 2023a, 2023b) have been reported, and in some cases, removal methods are reported to be very simple (Westerhoff et al. 2011;Kurian 2020;Rajeswari and Venckatesh 2021;Li et al. 2021;Mishra and Ahmaruzzaman 2021;Ghosh et al. 2022a, 2022b, Ghosh et al. 2023Sen et al. 2022;Das et al. 2023b). For example, Das et al. (2023a) reported Cinnamomum tamala-coated magnetite nanoparticles for the adsorption of U(VI), and the process is simple and energy efficient; Recillas et al. (2010) have used hexamethylenetetramine-stabilized cerium oxide nanoparticles for the removal of Cr(VI) ions. ...
... Wang et al. (2019) proposed that the silicacoated cerium oxide microsphere can be used as an efficient adsorbent for the fluoride ions from wastewater. According to Westerhoff et al. (2011), TiO 2 NPs can be an efficient candidate to remove toxic metal ions like titanium from municipal sewage, and they had used the TiO 2 NPs in fullscale wastewater treatment plants. Das et al. (2023b) used cost-effective and non-toxic N. sativa seed extract-modified magnetite nanoparticles toward the elimination of a pharmaceutical waste (hydrocortisone) via simple photocatalytic degradation, and the nanoparticles were magnetic reproducible and recyclable. ...
In this article, the multifunctional behavior of novel, efficient, and cost-effective humic acid–coated nanoceria (HA@CeO2 NPs) was utilized for the sorptive removal of U(VI), Cr(VI), and F⁻ ions at different conditions. The production cost of HA@CeO2 was $19.28/kg and was well characterized by DLS, FESEM, HRTEM, FTIR, XRD, XPS, and TGA. Batch adsorption study for U(VI) (at pH ~ 8), Cr(VI) (at pH ~ 1), and F⁻ (at pH ~ 2) revealed that the maximum percentage of sorption was > 80% for all the cases. From the contact time experiment, it was concluded that pseudo-second-order kinetics followed, and hence, the process should be a chemisorption. The adsorption study revealed that U(VI) and Cr(VI) followed the Freundlich isotherm, whereas F⁻ followed the Langmuir isotherm. Maximum adsorption capacity for F⁻ was 96 mg g⁻¹. Experiments in real water suggest that adsorption is decreased in Kaljani River water (~ 12% for Cr(VI) and ~ 11% for F⁻) and Kochbihar Lake water (25.04% for Cr(VI) and 20.5% for F⁻) because of competing ion effect. Mechanism was well established by the kinetic study as well as XPS analysis. Because of high adsorption efficiency, HA@CeO2 NPs can be used for the removal of other harmful water contaminants to make healthy aquatic life as well as purified drinking water.
Graphical Abstract
... TiO 2 P25 (a powder-form photocatalyst) offers relatively high photocatalytic degradation of organic dyes [10] and pharmaceuticals [10][11][12][13] and a high possibility of practicalscale application. However, TiO 2 P25 use in the form of suspension (slurry) may pose an ecological risk to aquatic organisms [14], which should require an expensive filtration process to separate the suspension catalyst from the treated water. Therefore, many nanostructured TiO 2 films developed on rigid substrates by the anodizing method (e.g., TiO 2 nanotubes [15], TiO 2 nanowires on TiO 2 nanotube arrays [16][17][18]) have been studied for photocatalyst, solar energy conversion, and other applications [15]. ...
The development of nanocomposite photocatalysts with high photocatalytic activity, cost-effectiveness, a simple preparation process, and scalability for practical applications is of great interest. In this study, nanocomposites of TiO2 Degussa P25 nanoparticles/activated carbon (TiO2/AC) were prepared at various mass ratios of (4:1), (3:2), (2:3), and (1:4) by a facile process involving manual mechanical pounding, ultrasonic-assisted mixing in an ethanol solution, paper filtration, and mild thermal annealing. The characterization methods included XRD, SEM-EDS, Raman, FTIR, XPS, and UV-Vis spectroscopies. The effects of TiO2/AC mass ratios on the structural, morphological, and photocatalytic properties were systematically studied in comparison with bare TiO2 and bare AC. TiO2 nanoparticles exhibited dominant anatase and minor rutile phases and a crystallite size of approximately 21 nm, while AC had XRD peaks of graphite and carbon and a crystallite size of 49 nm. The composites exhibited tight decoration of TiO2 nanoparticles on micron-/submicron AC particles, and uniform TiO2/AC composites were obtained, as evidenced by the uniform distribution of Ti, O, and C in an EDS mapping. Moreover, Raman spectra show the typical vibration modes of anatase TiO2 (e.g., E1g(1), B1g(1), Eg(3)) and carbon materials with D and G bands. The TiO2/AC with (4:1), (3:2), and (2:3) possessed higher reaction rate constants (k) in photocatalytic degradation of methylene blue (MB) than that of either TiO2 or AC. Among the investigated materials, TiO2/AC = 4:1 achieved the highest photocatalytic activity with a high k of 55.2 × 10−3 min−1 and an MB removal efficiency of 96.6% after 30 min of treatment under UV-Vis irradiation (120 mW/cm2). The enhanced photocatalytic activity for TiO2/AC is due to the synergistic effect of the high adsorption capability of AC and the high photocatalytic activity of TiO2. Furthermore, TiO2/AC promotes the separation of photoexcited electron/hole (e−/h+) pairs to reduce their recombination rate and thus enhance photocatalytic activity. The optimal TiO2/AC composite with a mass ratio of 4/1 is suggested for treating industrial or household wastewater with organic pollutants.
... A recent study reported the estimated releases of ENPs into environment such as landfills, soils, waters and atmosphere and they demonstrated 63-91% of ENPs end up in landfills [2]. As a result, it is an inevitable situation that ENPs will be discarded into landfill sites or wastewater treatment plants (WWTPs) and previous studies has reported the occurrence of NPs in WWTPs [3][4][5] and landfill leachate [6,7]. ...
This study developed multi-linear regression (MLR) quantitative structure-activity relationships (QSARs) to predict n-TiO2 aggregation in the presence of high concentrations of representative emerging organic contaminants (EOCs), which presented favorable conditions to interaction with n-TiO2. The largest diameter change (Δ 517 nm at 0 h and Δ 1164 nm at 12 h) of n-TiO2 was observed by estrone, while the smallest diameter change (Δ −114 nm at 0 h and – 4 nm at 12 h) was observed by lincomycin during experimental periods. In addition, the zeta potential changes of n-TiO2 were observed that the biggest changes were observed by 17β-estradiol (−1.3 mV) and alachlor (−10.02 mV) at 0 h, while 17β-estradiol (−1.31 mV) and pendimethalin (−11.4 mV) showed the biggest changes at 12 h comparing to control. These changes of n-TiO2 diameter and zeta potential may implicate the effects of unique physico-chemical properties of each EOC on the surface modification of n-TiO2. Based on the interaction results, this study investigated the QSARs between n-TiO2 aggregation and physico-chemical descriptors of EOCs with 7 representative descriptors (pKa, Cw, log Kow, M.W., P.S.A., M.V., # of HBD) for predicting n-TiO2 aggregation rate kinetics at 0 h and 12 h by applying MATLAB statistical methods (model 1 - fitlm and model 2 - stepwiselm). In a model 1, QSARs showed the good coefficients of determination (R² = 0.92) at 0 h and (R² = 0.87) at 12 h with 7 descriptors. In a model 2, QSARs showed the goodness of fit of a model (R² = 0.9998) with 8 descriptors (pKa, Cw, log Kow, M.W., P.S.A., M.V., #HBD, pKa⋅#H bond donors) at 0 h, while QSARs showed the coefficients of determination (R² = 0.68) with 2 descriptors (pKa, M.V.) at 12 h. Particularly, we observed that some descriptors of EOCs such as pKa and # of HBD having polarity have more influenced on the n-TiO2 aggregation rate kinetics. Our developed QSARs demonstrated that the 7 descriptors of EOCs were significantly effective descriptors for predicting n-TiO2 aggregation rate kinetics in favorable conditions, which may implicate the complexity interactions between heterogeneous surfaces of n-TiO2 and physico-chemical properties of EOCs.
... https://inter-publishing.com/index.php/AJSLD/index are essential factors in determining whether the membrane is appropriate for a given filtering job and how long it will last [18]. These qualities determine the membrane's resistance to physical wear and tear over time, its capacity to tolerate severe chemical conditions, and how it interacts with various substances [19] (See Figure 3). Another critical aspect affecting the pace of filtration and the process's overall efficiency is the operating pressure used to force the fluid through the membrane. ...
Granular filters and membrane filters, two essential filtration methods in environmental engineering, are thoroughly examined in this study. These techniques greatly aid air pollution control problems and water and wastewater treatment. The first section of the study outlines the basic ideas that underpin each filtration technique. The mechanical particle trapping mechanisms of granular filters, their wide range of applications in water treatment, and design factors, including media kinds and layers, are all examined. On the other hand, membrane filters are closely scrutinised because of their size exclusion principles, variety of types (from microfiltration to ultrafiltration), and vital function in industrial waste treatment and desalination processes. The study goes into additional detail about the maintenance, clogging, and financial ramifications that different filtering techniques must deal with. A comparison analysis provides insights into each method's applicability for various environmental engineering applications by illuminating its efficacy, affordability, and application specificity. The study's conclusion considers the potential for growth and current and upcoming technical developments in the filtration industry. This study lays the groundwork for forthcoming advancements and uses in the field of environmental engineering while also highlighting the significance of these filtering methods in modern ecological engineering.
A 2-year (2017 and 2018) field lysimeter study was carried out to examine the effect of titanium dioxide nanoparticles (TiO2 NPs) in irrigation wastewater on soil characteristics and potato (Solanum tuberosum L.) yield. Potatoes were planted in lysimeters (1.00 m × 0.45 m) in sandy soil and subjected to four treatments: freshwater (FW), wastewater (WW), freshwater + TiO2 NPs (FW + NP) and wastewater + TiO2 NPs (WW + NP), in triplicate. Potato tubers were harvested at maturity (120 days after planting). Both the TiO2 NPs (with/without 1 mg L−1 TiO2 NPs) and irrigation treatments (FW vs. WW) had a significant effect (p ≤ 0.05) on chlorophyll content; however, they had little or no effect on soil physicochemical parameters (cation exchange capacity (CEC), pH and soil organic matter (SOM)), plant growth parameters (plant height, above-ground and root fresh weight) or yield (tuber weight, number of tubers and tuber grading). For both years, the total nitrogen content of the leaves increased consistently together with leaf chlorophyll content. Furthermore, tuber yield under FW, WW and WW + NP treatments were higher in the first year than in the second, likely due to higher growing season temperatures in the second year. This study furthers the knowledge on the impact of TiO2 NPs on plant growth by showing that at 1 mg L−1, irrigation water can increase greenness without inhibiting plant growth and yield. In addition, the potato plants, irrigated with water containing TiO2 NPs, did not become infected with early and late blight diseases either year.
This review article addresses the increasing environmental concerns posed by synthetic dyes in water, exploring innovative approaches for their removal with a focus on zero-valent iron nanoparticles (nZVIs) synthesized through environmentally friendly methods. The article begins by highlighting the persistent nature of synthetic dyes and the limitations of conventional degradation processes. The role of nanoparticles in environmental applications is then discussed, covering diverse methods for metallic nanoparticle production aligned with green chemistry principles. Various methods, including the incorporation of secondary metals, surface coating, emulsification, fixed support, encapsulation, and electrostatic stabilization, are detailed in relation to the stabilization of nZVIs. A novel aspect is introduced in the use of plant extract or biomimetic approaches for chemical reduction during nZVI synthesis. The review investigates the specific challenges posed by dye pollution in wastewater from industrial sources, particularly in the context of garment coloring. Current approaches for dye removal in aqueous environments are discussed, with an emphasis on the effectiveness of green-synthesized nZVIs. The article concludes by offering insights into future perspectives and challenges in the field. The intricate landscape of environmentally friendly nZVI synthesis has been presented, showcasing its potential as a sustainable solution for addressing dye pollution in water.
Selectively and efficiently capturing trace titanium dioxide nanoparticles (TiO 2 NPs) in environmental waters is a prerequisite for their determination to understand their occurrence, behavior and effects in the environment.
Low-pressure membranes suffer from particulate, organic and biological fouling during operation. In order to elucidate the impact of nanoparticles on membrane fouling, experiments were carried out with a small membrane test unit operated with artifi cial and natural waters. Both microfi ltration (MF) and ultrafi ltration (UF) membranes were used. Artifi cial waters were made from ultra pure water spiked with polystyrene or magnetite nanoparticles with sizes between 20 and 250 nm in varying particle concentrations. During the fi ltration tests the permeability decreased with time indicating a blocking of the membrane pores by nanoparticles. During the fi ltration of small particles (20–30 nm) the permeability dropped to a signifi cantly lower level than during fi ltration of larger particles (100–250 nm). Under the tested conditions the nanoparticle concentration seemed to have no infl uence. In natural waters particulate fouling tended to be overlapped by other fouling processes such as organic fouling. With the test unit the fouling potential of raw waters could be characterized within a short period of time whereas the nanoparticles in the feed waters were characterized by a special analysis based on Laser-induced Breakdown Detection (LIBD). With this highly sensitive quantifi cation method it was possible to determine both nanoparticle size (down to 10 nm in diameter) and concentration (down to a few ng/L) in the feed and the fi ltrate. In the fi ltrates of the MF membrane operated with spiked feed waters, nanoparticles were detected indicating their breakthrough. Comparatively, under similar conditions the UF membrane showed a very high retention of such nanoparticles.
This paper provides an overview of current knowledge regarding the aquatic effects of nanomaterials. Aquatic receptors can potentially be exposed to nanoparticles through ingestion, movement across gills, passive transport, and cellular absorption. Our review indicates that the toxicological research on nanomaterials is still relatively narrow. The present research has been targeted primarily at understanding potential effects to humans, and relatively few ecotoxicity studies have been conducted; however, new research is evolving rapidly. The studies that are currently available focus on metal oxide particles, carbon nanotubes, and fullerenes. Aquatic tests have examined the uptake of these nanoparticles by fish and filter feeders, and have provided evidence of toxicity or behavioral changes. Some of these studies conclude that nanoparticles can be taken up by or produce effects in biota, and that dose-response relationships and patterns of relative toxicity among types of particles are emerging. Caution should be used in designing and interpreting studies on nanoparticles, because factors such as the particle medium preparation method, the presence of other chemicals, and particle behavior such as agglomeration can influence exposure and aquatic toxicity. Ultimately, the objectives of this review are to expand our knowledge of the effects of nanomaterials on ecological processes and aquatic receptor populations, as well as help guide future research.
Membrane bioreactors (MBRs) have been widely used as advanced wastewater treatment process in recent years. However, MBR system has a membrane fouling problem, which makes the system less competitive. Thus there have been great efforts for fouling mitigation. In this study, two types of TiO 2 immobilized ultrafiltration membranes (TiO 2 entrapped and deposited membranes) were prepared and applied to activated sludge filtration in order to evaluate their fouling mitigation effect. Membrane performances were changed by addition of TiO 2 nanoparticles to the casting solution. TiO 2 entrapped membrane showed lower flux decline compared to that of neat polymeric membrane. Fouling mitigation effect increased with nanoparticle content, but it reached limit content above which fouling mitigation did not increase. Regardless of polymeric materials, membrane fouling was mitigated by TiO 2 immobilization. TiO 2 deposited membrane showed greater fouling mitigation effect compared to that of TiO 2 entrapped membrane, since larger amount of nanoparticle was located on membrane surface. It can be concluded that TiO 2 immobilized membranes are simple and powerful alternative for fouling mitigation in MBR application.
The white pigment market is served almost exclusively by titanium dioxide pigments. The objective of this overview is to familiarize readers with the one ingredient that may take the lion share of costs in a coating - titanium dioxide. Issues specific to TiO2 are discussed, including commerce, manufacture, characteristics, performance and commercial grades.
The solubility of rutile was measured in H2O, H2O–SiO2 and H2O–NaAlSi3O8 fluids at 700–1000 °C, 0.7–2.0 GPa, in a piston-cylinder apparatus. Solubility was determined by weight loss using a double-capsule method. Rutile solubility in pure H2O shows isothermal increase with pressure (P), isobaric increase with temperature (T), and is low at all conditions investigated (6–118 ppm Ti). Rutile solubility in H2O is given by logcTi° = 6.173 − 5425/T + 178.4P/T, where cTi° is Ti concentration in ppm, T is in K, and P in GPa. This leads to thermodynamic properties of the reaction rutile = TiO2,aq of ΔSr° = 28.6 J/mol K, ΔHr° = 104 kJ/mol, and ΔVr° = − 3.4 cm³/mol. At 800 °C and 1 GPa, addition of SiO2 (up to quartz saturation) did not change rutile solubility relative to that in pure H2O. Determination of rutile solubility in H2O–NaAlSi3O8 fluids was complicated by incongruent dissolution of albite to paragonite or corundum + fluid; however, fluid compositions could be estimated within narrow limits using a mass-balance scheme. The solubility of rutile increases linearly with dissolved Na–Al silicate at fixed P and T, as described by cTi = cTi° + Bws where cTi is ppm Ti, ws is wt.% dissolved silicate and B is given by log B 6.512 − 1.665P − 6224/T + 2215P/T, with T and P again in K and GPa.
Polar dissolved organic matter (DOM) was isolated from a surface-water sample from the Great Salt Lake by separating it from colloidal organic matter by membrane dialysis, from less-polar DOM fractions by resin sorbents, and from inorganic salts by a combination of sodium cation exchange followed by precipitation of sodium salts by acetic acid during evaporative concentration. Polar DOM was the most abundant DOM fraction, accounting for 56% of the isolated DOM. Colloidal organic matter was 14C-age dated to be about 100% modern carbon and all of the DOM fractions were 14C-age dated to be between 94 and 95% modern carbon. Average structural models of each DOM fraction were derived that incorporated quantitative elemental and infrared, 13C-NMR, and electrospray/mass spectrometric data. The polar DOM model consisted of open-chain N-acetyl hydroxy carboxylic acids likely derived from N-acetyl heteropolysaccharides that constituted the colloidal organic matter. The less polar DOM fraction models consisted of aliphatic alicyclic ring structures substituted with carboxyl, hydroxyl, ether, ester, and methyl groups. These ring structures had characteristics similar to terpenoid precursors. All DOM fractions in the Great Salt Lake are derived from algae and bacteria that dominate DOM inputs in this lake.
An alternative ultrafiltration membrane integrity test is presented and evaluated, based on the use of magnetic nanoparticles (Fe3O4) and measurement of magnetic susceptibility. The mean size of nanoparticles used is around 35 nm and they show a good disparity between 20 and 100 nm. A series of integrity tests were carried out on a Norit membrane module containing 100 fibers under a low transmembrane pressure of 0.25 bar. The results showed that no magnetic susceptibility was detected in permeate when the tests were performed on the intact module in both cross-flow and dead-end filtration, indicating the complete nanoparticle retention by the intact module. However, when even one fiber was broken in the module (1% breakage rate), magnetic susceptibility of permeate could be detected instantaneously even at feed concentrations as low as 1.2 ppm with Bartington magnetic susceptibility meter. This detection is valid during all the filtration process. The results also showed that the membrane permeability could be completely recovered after a backwash. This membrane integrity test, with the advantages of simplicity, on-line operation, high detection specificity and sensitivity, quick detection and very low influence on membrane fouling, seems to be suitable for large-scale drinking water plants.
An elementary step towards a quantitative assessment of the risks of new compounds or pollutants (chemicals, materials) to the environment is to estimate their environmental concentrations. Thus, the calculation of predicted environmental concentrations (PECs) builds the basis of a first exposure assessment. This paper presents a probabilistic method to compute distributions of PECs by means of a stochastic stationary substance/material flow modeling. The evolved model is basically applicable to any substance with a distinct lack of data concerning environmental fate, exposure, emission and transmission characteristics. The model input parameters and variables consider production, application quantities and fate of the compounds in natural and technical environments. To cope with uncertainties concerning the estimation of the model parameters (e.g. transfer and partitioning coefficients, emission factors) as well as uncertainties about the exposure causal mechanisms (e.g. level of compound production and application) themselves, we utilized and combined sensitivity and uncertainty analysis, Monte Carlo simulation and Markov Chain Monte Carlo modeling. The combination of these methods is appropriate to calculate realistic PECs when facing a lack of data. The proposed model is programmed and carried out with the computational tool R and implemented and validated with data for an exemplary case study of flows of the engineered nanoparticle nano-TiO2 in Switzerland.
Quantum dots (QDs) of two different surface chemistries (carboxyl [COOH] and polyethylene glycol [PEG] modified) were utilized to determine the impact of surface functionality on QD mobility and distribution in Pseudomonas aeruginosa PAO1 biofilms. Confocal laser scanning microscopy was utilized to evaluate QD association with biofilm components (proteins, cells, and polysaccharides). Quantum dots did not preferentially associate with cell surfaces compared but did colocalize with extracellular proteins in the biofilm matrix. Neither PEG nor COOH QDs were found to be internalized by individual bacterial cells. Neither QD functionality nor flow rate of QD application (0.3 mL min(-1) or 3.0 mL min(-1)) resulted in a marked difference in QD association with P. aeruginosa biofilms. However, center of density determinations indicated COOH QDs could more easily penetrate the biofilm matrix by diffusion than PEG QDs. Biofilms with PEG QDs associated had rougher polysaccharide layers and rougher cell distribution than biofilms with COOH QDs. This work suggests natural biofilms may serve as deposition locations in natural and engineered environmental systems, and biofilm structural parameters may change based on exposure to nanomaterials of varied physical characteristics.