Progress 09/01/07 to 08/31/11
Outputs
OUTPUTS: Miscible-displacement experiments focused on transport behavior of specific engineered nanoparticles common in biosolids and wastewater effluent (e.g., titanium dioxide (TiO2), aluminum oxide (Al2O3), and iron oxide (Fe2O3)) in a model, sandy natural porous medium. Retention and detachment mechanisms were examined through varying hydrodynamic residence times and solution chemistries. The morphology and surface-charge properties of the nanoparticles were monitored during the transport experiments. This allowed examination of potential changes in properties, and their relationship to observed transport behavior. The morphology of TiO2 nanoparticles in the influent and effluent solutions was investigated by Scanning Electron Microscopy (SEM) (Hitachi S-4800 Type II). The morphology of the particles in the influent and effluent solutions was also examined using Nanoparticle Tracking Analysis (NTA) (Nanosight, L10) and laser Doppler electrophoresis (Zetasizer Nano, Malvern, Inc.). Additionally, we have employed advanced imaging methods to characterize the distribution of nanoparticles on specific surface moieities of the natural porous media. Portland State University's Phenom, a high-resolution desktop scanning electron microscope (SEM), was used to image model natural porous media pre- and post-contact with nanoparticles of Al2O3. Similar samples were also imaged using Portland State's Zeiss Sigma variable pressure field emission SEM. This instrument is equipped with Oxford EDS/WDS detectors. This research has allowed us to formulate an advanced, process-based continuum-scale mathematical model to simulate and analyze the results of our experiments. The model incorporates advection, dispersion, straining (physical trapping of particles), rate-limited attachment/detachment, and consideration of surface blocking effects (e.g., "shadow effect"). The continuous-distribution reaction approach has been used to account for the impact of reaction-site heterogeneity on attachment/detachment observed during transport. The results of our research to date on this project have been disseminated to communities of interest at several venues. Two presentations of our findings were delivered at the 2009 Geological Society of America Annual Meeting, Portland, Oregon, October 2009. Additionally, our results have been shared with representatives of Oregon Department of Environmental Quality and Oregon Association of Clean Water Agencies at briefings held November, 2009, and November, 2011, Portland State University. A presentation was made at The University of Arizona's El Dia Del Agua, March 2010, and at The University of Arizona's Water Sustainability Program. We are delivering two presentations at the 2011 American Geophysical Union Annual Meeting, San Francisco, California, December 2011. PARTICIPANTS: Nothing significant to report during this reporting period. TARGET AUDIENCES: Nothing significant to report during this reporting period. PROJECT MODIFICATIONS: Nothing significant to report during this reporting period.
Impacts
Our research has been conducted under conditions representative of natural subsurface systems. Miscible-displacement experiments using metal oxide nanoparticles indicate significant colloidal mobility in model sands. Observed transport behavior is dependent on environmental conditions, such as, hydrodynamic residence time, solution ionic strength and pH. Observed short-term transport behavior can be described by breakthrough at approximately one pore volume followed by evidence of irreversible attachment/adhesion of the metal oxide nanoparticles to sand. The observed long-term transport behavior appears to be influenced by a temporal change in the magnitude of attachment/adhesion of the nanoscale colloids to sand. Additionally, flow-interrupt experiments indicate a significant impact on the transport behavior upon stopping advective flow through the model sands. The detachment behavior of the nanoparticles showed sharply declining relative concentrations from plateau values (i.e., minimal detachment). However, recovery increased as a result of the flow interruption conducted during elution, indicating enhanced detachment. Similar results were observed for the experiments wherein zero ionic strength water was injected during elution. SEM images indicate that individual TiO2 particles in solution are primarily tubular, with average diameters of approximately 50 nm. The images indicate that aggregates may form, comprised of several individual particles. The effective diameters of the TiO2 particles in the influent sample ranged from approximately 30 to 550 nm, with a mean of 180 nm, as measured by Nanoparticle Tracking Analysis (NTA). This range in diameters indicates that most of the particles in solution exist as aggregates. The mean effective particle diameter for the effluent sample (174 nm) was slightly smaller than the mean for the influent sample. In addition, the >400-nm size fraction present for the influent sample is absent for the effluent sample. This change in particle-size distribution was most likely caused by capture of the larger aggregates (400-nm size range) within the column. However, this fraction comprises a very small portion of the particle population, and thus we have concluded that straining is considered to have a minimal impact on overall transport of the nanoparticles for this system. Real-time images of individual nanoparticles within the sample were captured using a digital video camera, processed to characterize the Brownian movement of the particles. Using the Stokes-Einstein equation we determined particle sizes and particle-size distributions for the sample. The zeta potentials of the porous media and of the nanoparticles were measured using laser Doppler electrophoresis. Retention interactions were further examined by conducting AFM measurements to characterize the forces between TiO2 nanoparticles and the porous media surfaces. These results have impacted the scientists involved in this project by providing new fundamental knowledge significant enough to result in several publications. This project has supported several undergraduate Honor's Theses and several Master's Theses.
Publications
- Cox, H., Zhong, H., Miao, Z., Johnson, G.R., Brusseau, M.L. (2011). Transport of TiO2 Nanoparticles in Porous Media: Characterizing Changes in Particle Morphology and Surface Charge. Chemosphere, Submitted for Publication, 14 November 2011.
- Cox, H., Johnson, G.R., Brusseau, M.L. (2011) Retention and Detachment Interactions of Titanium Dioxide Nanoparticles in Porous Media. Electronic conference proceedings (abstract), American Geophysical Union, San Francisco, California, December 2011.
- Norwood, S., Reynolds, M., Miao, Z., Heimbucher, C., Brusseau, M.L., Johnson, G.R. (2011) Nano-scale Aluminum Oxide Transport through Porous Media: Favorable versus Unfavorable Attachment Conditions. Chemosphere, In preparation.
- Norwood, S., Reynolds, M., Miao, Z., Brusseau, M.L., Johnson, G.R. (2011) Characterization of Nano-scale Aluminum Oxide Transport through Porous Media. Electronic conference proceedings (abstract), American Geophysical Union, San Francisco, California, December 2011.
- Cox, H., Johnson, G.R., Brusseau, M.L. (2011) Measuring Attachment Energy using AFM Nanoparticle-specific Probing Technique. In preparation.
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Progress 09/01/09 to 08/31/10
Outputs
OUTPUTS: Many scientists have investigated the mechanisms mediating nanoparticle transport in porous media primarily using relatively inert nanoparticles such as polystyrene latex beads. Conversely, fewer studies have focused on specific engineered nanoparticles common in biosolids and wastewater effluent. Of these, TiO2 nanoparticles have been a primary focus of attention, with studies examining transport under a variety of conditions. The results of these studies have provided insight into the influence of factors such as aqueous geochemistry (pH, ionic strength) and flow rate on TiO2 transport. However, essentially all of these studies have focused primarily on attachment behavior, with minimal examination of potential detachment. In addition, most studies of nanoparticle transport are conducted using small input functions, and thus do not evaluate the impacts of longer-term input such as associated with primary environmental sources (e.g., land application of biosolids and wastewater). The objective of our research during this reporting period included an examination of the retention and transport behavior of TiO2 nanoparticles, with a particular focus on conditions representative of longer-term source input and examination of TiO2 detachment behavior. The impact of residence time and ionic strength on attachment as well as detachment are examined. Furthermore, we employed methods to specifically characterize potential nanoparticle suspension population heterogeneities (e.g., particle aggregation effects) during transport. Specifically, the morphology of the TiO2 nanoparticles in the influent and effluent solutions was investigated by Scanning Electron Microscopy (SEM) (Hitachi S-4800 Type II). The morphology of the particles in the influent and effluent solutions was also examined using Nanoparticle Tracking Analysis (NTA) (Nanosight, L10). An advantage of this method is the ability to characterize morphology under natural, aqueous-environment conditions. That same solution morphology for nanoparticles of Al2O3 is being characterized on Portland's State's Zeiss Sigma variable pressure field emission SEM. This reporting period also included the use of advanced imaging methods to begin characterization of the distribution of nanoparticles on the surface of model natural porous media. Portland State University's Phenom, a high-resolution desktop scanning electron microscope (SEM), was used to image model natural porous media pre- and post-contact with nanoparticles of Al2O3. Similar samples were also imaged using Portland State's Zeiss Sigma variable pressure field emission SEM. This instrument is equipped with Oxford EDS/WDS detectors and ultimately, we expect to resolve the mechanisms responsible for attachment of nanoparticles on the surfaces of these sands. Results during this reporting period were shared at The University of Arizona's El Dia Del Agua, held March 2010 and at The University of Arizona's Water Sustainability Program. PARTICIPANTS: Nothing significant to report during this reporting period. TARGET AUDIENCES: Nothing significant to report during this reporting period. PROJECT MODIFICATIONS: Nothing significant to report during this reporting period.
Impacts
Inspection of the SEM images indicates that the individual (singular) TiO2 particles in solution are primarily tubular, with average diameters of approximately 50 nm. The images indicate that aggregates may form, comprised of several individual particles. The effective diameters of the TiO2 particles in the influent sample ranged from approximately 30 to 550 nm, with a mean of 180 nm, as measured by NTA. This range in diameters indicates that most of the particles in solution exist as aggregates. The mean effective particle diameter for the effluent sample (174 nm) was slightly smaller than the mean for the influent sample. In addition, the >400-nm size fraction present for the influent sample is absent for the effluent sample. This change in particle-size distribution was most likely caused by capture of the larger aggregates (400-nm size range) within the column. However, this fraction comprises a very small portion of the particle population, and thus straining is considered to have a minimal impact on overall transport of the nanoparticles for this system. Additionally, images of attached Al2O3 nanoparticles on model natural sands using the Phenom and Zeiss SEMs showed well-resolved nanoparticles of effective diameters approximately equal to 100 nm in size. The transport behavior of the TiO2 nanoparticles comprised initial breakthrough at approximately one pore volume, followed by a steady-state stage wherein effluent concentrations remained below the influent concentration for an extended time. Comparing recoveries for experiments conducted at different ionic strengths and similar pore-water velocities reveals that recovery varied inversely with ionic strength. The detachment behavior of the nanoparticles showed sharply declining relative concentrations from plateau values, indicating relatively minimal detachment. However, recovery increased as a result of the flow interruption conducted during elution, indicating enhanced detachment. Similar results were observed for the experiments wherein zero ionic strength water was injected during elution. It is assumed for standard colloid transport theory that attachment is irreversible. However, the results of the experiments presented herein indicate that detachment occurred. The rebound in concentration observed herein corresponded to approximately 20% of the previously retained particles being released. The detachment also appeared to be rate-limited, as shown by an increase in relative concentration observed for a flow-interruption test conducted during elution.
Publications
- H. Cox, G. R. Johnson, M. L. Brusseau, 2010. Transport of TiO2 Nanoparticles in Porous Media. Chemosphere, Submitted for Publication, 30 November 2010.
- H. Cox, G. R. Johnson, M. L. Brusseau, 2010. Transport of Titanium Dioxide Nanoparticles in Sand. Electronic conference proceedings (abstract), The University of Arizona's El Dia del Agua, 31 March 2010.
- H. Cox, G. R. Johnson, M. L. Brusseau, 2010. Transport of TiO2 Nanoparticles in Porous Media. Electronic conference proceedings (abstract), The University of Arizona's Water Sustainability Program, 22 November 2010. Winner: 1st Price, Outstanding Student Presentation.
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Progress 09/01/08 to 08/31/09
Outputs
OUTPUTS: A series of miscible-displacement experiments have been conducted to characterize the retention and transport of representative biosolid nano-colloids in model porous media. These experiments were conducted with both small and large input pulses to evaluate the impact of short-term and long-term transport behavior of the nanoscale colloids. Additionally, many of these studies included flow-interrupt (i.e., stop-flow) experiments to assess the degree of nonequilibrium transport and fate behavior. Miscible-displacement experiments using aluminum oxide nanoparticles were conducted to characterize the impact of (1) aqueous-phase concentration; (2) pore-water velocity; and (3) solution ionic strength on transport behavior through model sands. Similar miscible-displacement experiments using titanium dioxide nanoparticles were conducted to characterize the effects of (1) pore-water velocity and (2) solution ionic strength on transport. In addition, column experiments using an aqueous solution of aluminum oxide were conducted to estimate the possible facilitated transport of cadmium in model sands. Batch experiments to determine the degree of cadmium uptake to nanoparticles of aluminum oxide were conducted. A series of large input pulse column experiments using iron oxide nanoparticles have been completed. An advanced, process-based continuum-scale mathematical model has been formulated to simulate and analyze the results of the experiments. The model incorporates advection, dispersion, straining (physical trapping of particles), rate-limited attachment/detachment, and consideration of surface blocking effects (e.g., "shadow effect") to describe the potential processes responsible for the observed transport behavior. The continuous-distribution reaction approach has been used to account for the impact of reaction-site heterogeneity on attachment/detachment. This phase of the project has included the teaching and mentoring of three doctoral students (one at Portland State University and two at The University of Arizona), two masters-level students (Portland State University), and three undergraduate students each working towards an Honor's Thesis at Portland State University. The results of our research to date on this project have been disseminated to communities of interest at several recent venues. Specifically, two presentations of these findings were delivered at the 2009 Geological Society of America Annual Meeting held in Portland, Oregon, October 2009. Additionally, these results have been shared with representatives of Oregon Department of Environmental Quality at a brief, informal meeting held in November, 2009, at Portland State University. PARTICIPANTS: Nothing significant to report during this reporting period. TARGET AUDIENCES: Nothing significant to report during this reporting period. PROJECT MODIFICATIONS: Nothing significant to report during this reporting period.
Impacts
It may be of interest to note, our research has been conducted at pore-water velocities and nanoparticle aqueous-phase concentrations representative of natural subsurface systems. Results of column experiments using nanoparticles of aluminum oxide and titanium dioxide indicate significant colloidal mobility in model sands. The transport behavior of these nanoscale colloids is strongly dependent on environmental conditions, such as, solution ionic strength, aqueous-phase concentration, and pore-water velocity. The observed short-term transport behavior can be described by breakthrough at approximately one pore volume followed by evidence of irreversible attachment/adhesion of the metal oxide nanoparticles to sand. The observed long-term transport behavior appears to be influenced by a temporal change in the magnitude of attachment/adhesion of the nanoscale colloids to sand. Additionally, flow-interrupt experiments conducted on column experiments using aluminum oxide and iron oxide indicate a significant impact on the transport behavior of these nanoparticles upon stopping advective flow through the model sands. Finally, the association of cadmium with nanoparticles of aluminum oxide is significant and additional experiments to further investigate the potential facilitated transport of this heavy metal are needed. These results have impacted the scientists involved in this project by providing new fundamental knowledge. The resulting change in knowledge is significant enough to result in several publications, the first of which will be submitted for review in December, 2009. Furthermore, this project has supported several undergraduate Honor's Theses and as a result has encouraged two of those students to pursue a graduate program of study.
Publications
- Cox, H., Johnson, G.R., and Brusseau, M.L., 2009. Transport of titanium oxide nanoparticles in sand. Electronic conference proceedings (abstract), 2009 Geological Society of America Annual Meeting, Portland, Oregon. October, 2009.
- Johnson, G.R., Reynolds, M.S., Miao, Z., and Brusseau, M.L. 2009. On the transport and fate of biosolid colloids in porous media. Electronic conference proceedings (abstract), 2009 Geological Society of America Annual Meeting, Portland, Oregon. October, 2009.
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Progress 09/01/07 to 08/31/08
Outputs
OUTPUTS: Progress on Task 1: Aqueous suspensions of representative biosolid nano-colloids have been created in several ionic strength solutions (e.g., nanopure water, calcium chloride, and potassium chloride) thereby assessing the impact of ionic strength and divalent versus monovalent cations on the aqueous stability of nano-colloids. The effect of aqueous solutions of several surrogates for dissolved organic matter on the aqueous stability of nano-colloids have been measured. Dissolved organic matter has been extracted from natural porous media collected at an agricultural field site in Oregon. Representative biosolid nano-colloids have been contacted with air-dried model porous media. Batch experiments were conducted at a constant ionic strength, fixed pH, and zero-concentration organic-matter coatings. Batch reactors were created in triplicate, equilibrated on a mixing plate for six days, and analyzed for the attachment/adhesion of the metal oxide nanoparticles to the model sands. This phase of the research project included mentoring 3 graduate students. Progress on Task 2: Miscible-displacement experiments have been conducted using representative biosolid nano-colloids and model sands. These experiments, conducted at fixed pH, fixed ionic strength, and zero-concentration organic-matter coatings, included the use of a nonreactive tracer thereby characterizing the contributions of advective-dispersive transport. Additionally, dye tracer experiments have also been conducted to further qualify the contributions of advective-dispersive transport. Effluent samples have been collected to determine the breakthrough curves of the tracers and the representative colloids. Following the completion of one such column experiment, the column was imaged by synchrotron X-ray microtomography providing a 3-D characterization of the entire column. This phase of the project included mentoring 1 graduate student. Progress on Task 3: Biosolid materials were collected from (1) a biosolid land application field site in Oregon and (2) from a wastewater treatment plant in Oregon. These biosolid materials were subjected to a constant source of ultraviolet light for 30 days to make them safe for handling and stored for future use. An intact soil core has been collected from a biosolid land application field site in Oregon. PARTICIPANTS: Significant training opportunities have been discovered and developed through funding made available from this project. Specifically, Mr. Anjan Parajuli has gained experience and knowledge toward the theories behind nano-scale colloidal transport processes while conducting research toward his doctoral degree at Portland State University. Mr. Parajuli has assisted on the project providing analytical assistance for procedure and techniques, literature searches for nano-scale colloidal theory, and experimentation on the transport and fate behavior of nano-scale particle in model sands. Mr. Michael Reynolds has conducted batch experiments and miscible-displacement experiments thereby gaining research experience and knowledge while completing research toward his Master's degree at Portland State University. As Project Director, Gwynn R. Johnson (Portland State University) has supervised and directed the research experiences for these graduate students. Additionally, Dr. Johnson has incorporated some of the results of the research conducted to date in her course curriculum for Subsurface Hydrology and Chemistry of Environmental Toxins classes. As collaborators on the project, Gwynn R. Johnson and Mark L. Brusseau (The University of Arizona) hold regular research meetings to discuss project results, goals, and associated time-lines. Dr. Brusseau has supervised and directed research on the 3-D imaging of soil columns via synchrotron X-ray microtomography. Ms. Hazel Cox is conducting research on the project toward her doctoral degree under the advisement of Dr. Brusseau. TARGET AUDIENCES: Nothing significant to report during this reporting period. PROJECT MODIFICATIONS: Nothing significant to report during this reporting period.
Impacts
Results of attachment/adhesion experiments have indicated significant interaction of nano-colloids with glass and negligible interaction with HDPE plastics. Aqueous suspensions of representative biosolid nano-colloids are stable, while stability is nearly independent of ionic strength. Further experimentation to qualify the effects of divalent versus monovalent cations in solution are necessary. The presence of dissolved organic matter surrogates, expected to create an organic-matter coating on the nano-colloids, decreased aqueous-phase stability of the nano-colloids. Further experimentation using natural dissolved organic matter as an organic-matter coating for the representative nano-colloids is pending. Results from batch experiments of representative biosolid nano-colloids contacted with model porous media have indicated significant agglomeration of nano-colloids following mixing for six days. Additional batch reactors have been created without mixing (results pending analysis) as the kinetic energies associated with the mixing process is suspect in contributing to agglomeration of the nanoparticles. Results of the miscible-displacement experiments have indicated approximately 30% breakthrough of the representative biosolid nano-colloids. Further experimentation to assess the impact of organic-matter coatings on the transport behavior of nano-colloids is pending. Image data collected via synchrotron X-ray microtomography is being analyzed to characterize pore network topology and the pore-scale distribution of the nano-colloids.
Publications
- No publications reported this period
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