Browsing by Subject "Filtration"

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Block polymer membranes for selective separations.
(2009-06) Phillip, William A.
Polymeric membranes are used for many separations. Some act as selective filters, separating viruses and other undesirable solutes from drinking water. Others perform chemical separations, separating air to make an atmosphere which extends fruit shelf-life. The ability of a membrane to perform a separation is determined by its chemistry and microstructure. Block polymers are macromolecules composed of two or more chemically incompatible polymers (blocks) covalently bonded together. Depending upon the relative amounts of each block, the polymer forms different ordered structures 5-50 nm in scale. This control over the constituent polymers and microstructure will be used to produce membranes with different transport properties. Ammonia selective membranes which retain selectivity in mixed gas systems are made from poly(cycloocetene-b-styrene sulfonate). Using poly(styrene-b-lactide) as a template, ultrafiltration membranes with a monodisperse pore size distribution are formed.
Capturing Stormwater Nitrate and Phosphate with Sorptive Filter Media
(2017-07) Erickson, Andrew
Soluble phosphate and nitrate are more bioavailable than particulate forms. These nutrients result in eutrophication in both freshwater (typically phosphate-limited) and marine (typically nitrate-limited) systems. In addition, nitrate poses a public health risk at elevated concentrations in drinking water. This research shows that sand filters mixed with 5% iron filings captured, on average, 88% of the influent phosphate in laboratory experiments. Neither incorporation of iron filings into a sand filter nor capture of phosphate had a significant effect on the hydraulic conductivity. Pond-perimeter applications of iron enhanced sand filtration (IESF) with up to 10.7% iron by weight achieved between 29% and 91% phosphate reduction for five events within the first year of operation. After five years, however, a different pond perimeter IESF retained on average 26% of the influent phosphate over three rainy seasons. Retention was best for larger filtered volume events, but negative removal was observed for events with smaller filtered volume and low influent phosphate concentration. Non-routine maintenance improved the hydraulic performance of the pond perimeter IESF and, after a rinsing event, also improved phosphate retention rates to an average of 45%. An IESF was installed to treat agricultural tile drainage and found to reduce total phosphorus loads by 42% to 95% with a flow-weighted mean reduction of 66.3% ± 6.7% (a = 0.05) for 20 events in 2016. The phosphate load reduction varied from 9% to 87% with a flow-weighted mean reduction of 63.9% ± 7.7% (a = 0.05) for 31 events in 2015 and 2016. This research also shows that nitrate is captured abiotically by granular activated carbon (GAC) in laboratory experiments designed to mimic urban and agricultural stormwater runoff. The short contact time and inorganic characteristics of the influent synthetic stormwater suggest that the nitrate was captured by ion exchange, but (bi)carbonate may have competed with nitrate for capture by GAC. Abiotic capture of nitrate requires less stormwater storage volume and less residence time to remove nitrate compared to denitrification, and thus GAC could be used to design smaller treatment practices for nitrate removal.
Complex droplet interfaces at the microscale: Surfactant and hydrodynamic effects in the separation of water-in-oil emulsions
(2020-08) Narayan, Shweta
Complex, surfactant-stabilized emulsions are relevant to various technological applications, such as the removal of dispersed water from diesel fuel in engines. Due to chemical stabilization of micrometer-sized dispersed droplets by surfactant molecules, emulsions can be challenging to separate, especially because surfactant transport to the interface is enhanced by the small droplet size and large interfacial curvature. The main goal of this work is to measure fundamental emulsion properties affecting their stability, such as dynamic interfacial tension and interfacial rheological properties, on the microscale, and relate these properties to droplet dynamics and coalescence behavior in water-in-fuel emulsions. First, dynamic interfacial tension (IFT) of water-in-diesel fuel systems containing surface-active additives such as monoolein and poly(isobutyl) succinimide (PIBSI), relevant to fuel filtration, is measured using a microfluidic tensiometer with contraction-expansion geometries. Microfluidic dynamic IFT measurements are compared with pendant drop tensiometry measurements employing millimeter-sized droplets. It is found that the dynamic interfacial tension decreases on orders of magnitude faster timescales on the microscale due to enhanced diffusive flux to curved microscale interfaces. This result has implications for fuel-water separation testing in the filtration industry. Next, a microfluidic hydrodynamic ‘Stokes’ trap is used to trap droplets in a cross-slot geometry. A four-channel hydrodynamic trap is applied towards studying drop shape relaxation as well as binary droplet coalescence of water droplets in mineral oils, stabilized by SPAN 80. It is found that the film drainage time for coalescence increases with droplet radius and surfactant concentration, while it decreases with incoming drop velocity. Critical conditions for flocculation and rebound of droplets are identified in terms of the capillary number. Finally, interfacial dilatational rheological properties of water-in-diesel fuel systems are measured using a capillary pressure microtensiometer. PIBSI and monoolein are added to the diesel fuel, and the dependence of the dilatational modulus on oscillation frequency and surfactant concentration is investigated. The dilatational modulus is found to increase with oscillation frequency and decrease with surfactant concentration. PIBSI-laden interfaces have higher modulus than monoolein-laden interfaces. Collectively, these experiments enhance our understanding of the intricate relationship between surfactant transport on the microscale, and droplet coalescence leading to emulsion separation.
Field-scale evaluation of MN-sourced biochar for comprehensive contaminant removal from parking lot runoff
(2023-03) Weelborg, Karina
The performance of catchment-scale filters containing sand and red-pine biochar, produced at 550oC, were monitored for 2 years. Six events from the 2022 field season showed relative flow equalization between the sand and biochar filters and were used for detailed performance analysis. Both filters provided removal of E. coli, total phosphorus, metals, total organic carbon, and total suspended solids. The sand and biochar filters provided inconsistent removal of orthophosphate. Both filters exported nitrate, though the biochar filter to a lesser degree. The addition of biochar provided greater concentration decreases for zinc and total suspended solids though no statistically significant difference between the sand and biochar was found for any filter performance. Results from this study highlight the importance of adjusting biochar production conditions for development of characteristics needed for contaminant removal and the importance of validating laboratory results in the field.
Gasoline Engine-out Particulate Matter Characterization and Control & Low-Cost Particulate Matter Light-Scattering Sensing
(2023-11) Chen, Weiqi
Particulate matter (PM) consists of minuscule solid or liquid airborne particles. Among these particles, fine particles like PM2.5 (particles with a diameter of 2.5 micrometers or smaller) are particularly concerning due to their ability to deeply penetrate the lungs and even enter the bloodstream and contribute to various adverse health effects, including an increased risk of heart disease, lung cancers, and other health issues. The engine combustion process of fossil fuels is a significant contributor to PM2.5 pollution in many urban areas. Furthermore, recent advancements in low-cost light-scattering PM sensors present a cost-effective solution for real-time spatiotemporal PM monitoring. Despite their benefits, these sensors have limitations in data quality due to relaxed quality control and their sensitivity to environmental conditions affecting light scattering. Therefore, this dissertation is driven by two primary objectives: Part 1 aims to mitigate Engine-out PM emissions by reducing their formation in the combustion chamber and improving filtration within the aftertreatment system. On the other hand, Part 2 is dedicated to evaluating and improving low-cost light-scattering PM sensor technology and exploring its diverse applications.In Part 1 Chapter 2, we investigated how combustion strategy and ethanol content affect particle properties in emissions from a lean burn gasoline direct injection (GDI) engine. GDI engines, increasingly used in light-duty vehicles for higher power and fuel efficiency, tend to produce elevated PM emissions. Different combustion strategies and fuel properties (like volatility and aromaticity) influence PM emission rates and characteristics. We measured particle number, size, mass concentration, effective density, and mass-mobility exponent for a GDI engine fueled with E10, E30, and E50, and operated in three combustion modes: stoichiometric, lean homogeneous, and lean stratified. Key findings include lower particle number and higher effective density with stoichiometric operation using E10, while lean homogeneous operation resulted in the smallest particles and lowest effective density. Lean stratified operation produced the highest particle concentrations and effective densities between lean homogeneous and stoichiometric conditions. Ethanol content changes influenced mass and number concentrations and effective density differently based on the combustion mode. In Part 1 Chapters 3-4, we focus on enhancing PM filtration control in gasoline particulate filters (GPFs) within aftertreatment systems, particularly for gasoline direct injection (GDI) engines that emit higher PM levels. GPFs use deep-bed filtration through ceramic walls in a honeycomb channel structure for effective PM emission control. The increasingly stringent global PM emissions regulations have amplified the demand for GPFs. Chapter 3 introduces a rapid screening method using wafer-based nanoscale membranes to improve GPF performance. It explores the use of artificial aerosols to synthesize nano-scale membranes resembling soot cake in diesel particulate filters (DPFs), enhancing GPF performance. The experiments show that membranes with larger aggregate sizes or under lower face velocity yield significantly improved performance. Chapter 4 delves into a theoretical study, while Chapter 3 focuses on experimental investigation. In Chapter 4, an analytical filter model is developed to understand efficiency and pressure drop under engine conditions, aiming to reduce development costs for meeting emission regulations and engine performance targets. The study treats the deep bed regime as two co-existing filters with different geometries based on natural morphologies, dynamically considering changes in pore size distribution and soot dendrite growth during loading. Model validation using 12 sets of experimental filter loading data demonstrates reasonable predictions for filter efficiency and pressure drop during deep-bed loading for various GPF wall-flow filters and operating conditions. The model was also used to examine the impact of porosity, mean pore size, and pore size distribution on filter loading performance, suggesting strategies for future filter optimization. Part 2 addresses the second objective of the dissertation, focusing on low-cost light-scattering PM sensors. In Chapter 6, the study describes the development of sensor test systems, including a lab-simulated environmental chamber, a field test sensor chamber, and a sensor data acquisition platform. The lab environmental chamber can simulate various environmental conditions for sensor performance assessment, including RH, temperature, aerosol types, and concentrations. Conversely, the field sensor chamber is designed to protect sensors in outdoor environments while ensuring precise sampling. The data acquisition platform involves the development of a custom printed circuit board (PCB) design and a dedicated sensor website, essential for extensive data collection, wireless transmission, and online storage capabilities. Chapter 7 begins by presenting a thorough assessment of sensor performance by conducting side-by-side experiments with gravimetric filter method (Federal Reference Methods (FRMs)) as reference to examine the dynamic response of more than 10 different popular low-cost light-scattering core sensors under diverse conditions in both controlled laboratory settings and the real-world outdoor environment. When measuring atmospheric salt particles, it was found that the low-cost sensors generally provide accurate readings within the 30% to 70% RH range but exhibit a significant spike after surpassing the deliquescence relative humidity (DRH). When environment shifts from wet to dry conditions, it was observed that sensor bias is more pronounced compared to the increasing RH conditions. Moreover, the behavior of the sensor was observed to demonstrate a strong dependency on both concentrations and particle composition. Based on the analysis, the performance ranking for all the tested sensors is provided. Following the performance assessment, Chapter 7 demonstrated various methods for improving sensor performance, including 1) Utilizing calibrations employing a multi-variable nonlinear model that incorporates RH level and differentiate the models for different concentration levels and RH hysteresis; 2) implementing sensor accessory/add-on, specifically, a silica dryer was affixed to the sensor inlet to mitigate the RH impact; 3) and exploring different sensing theories to enhance sensor lower detectable size limit. Moving to Chapter 8, the dissertation delved into exploring the various potential applications of low-cost light-scattering PM sensors. These applications included spatiotemporal measurements and filtration applications. By exploring these applications, the advantages of low-cost sensors compared to traditional reference instruments were highlighted, and the insights into the opportunities associated with the deployment of these sensors were provided.
Liquid-borne nanoparticle characterization and its application to nanometer-rated liquid filter evaluation
(2013-08) Ling, Tsz Yan
Nanoparticles are often found in liquid-borne dispersed phases, in addition to the airborne and surface-borne phases. Characterization techniques for nanoparticles are needed for the environmental, health and safety studies of nanomaterials. On the other hand, membrane filtration has been demonstrated to be effective for the removal of liquid-borne nanoparticles. Such technique has found many applications, including: 1) contamination control in liquids used in industries which require high level of cleanliness, 2) control of the release of engineered nanoparticles for environmental health and safety and 3) drinking water purification and disinfection. For evaluating filtration performance of nanometer-rated filters, reliable techniques for counting and sizing liquid-borne nanoparticles are desirable. The objectives of this thesis are to 1) explore methods for characterizing liquid-borne nanoparticles and 2) apply these methods to study nanoparticle filtration problems. In Chapter 2, calibration results of the Nanoparticle Tracking Analysis (NTA) technique in our lab are reported. The concentration measurements agree well with that estimated by suspension mass concentration within the range of 108-1010 particles/ml. To ensure the concentration measurements are made within the linear valid range, a single sample should be diluted and the NTA concentration measurements for the original and diluted samples should agree. Applying the NTA technique, the size distribution and concentration of nanoparticles in the water used in Abrasive Waterjet Machining (AWM) and Electrical Discharge Machining (EDM) processes were measured. The particles generally have a most probable size of 100-200 nm. The filtration systems of the AWM and EDM processes were found to remove of 70 and 90 % the nanoparticles present, respectively. However, the particle concentration of the filtered water from the AWM was still four times higher than that found in regular tap water. These nanoparticles are mostly agglomerated, according to the microscopy analysis. Since AWM and EDM are widely used, the handling and disposal of used filters collected with nanoparticles, release of nanoparticles to the sewer and potential use of higher performance filters for these processes will deserve further considerations. The development of an aerosolization technique to measure liquid-borne nanoparticles down to 30 nm and its application to filter evaluation is discussed in Chapter 3. This technique involves dispersing nanoparticle suspensions into airborne form with an atomizer or electrospray aerosol generator, and measuring the size and concentration by a differential mobility analyzer coupled to a condensation particle counter. With the electrospray aerosol generator, residue particles can be controlled to be less than 10 nm, allowing particles as small as 30 nm to be clearly distinguished from the size distribution measurements. Calibrations with 30, 50, 125 and 200 nm polystyrene latex particles showed that liquid-borne and airborne particle concentrations are proportionally related. This provides an effective way to quantify liquid-borne particles as small as 30 nm, which cannot be analyzed by state-of-the-art liquid particle counters. Comparing to NTA, the aerosolization technique gives more accurate representation for polydisperse size distribution. The aim of Chapter 4 is to study the filtration process of a model membrane filter, the nuclepore filter. Initial filtration efficiency experimentally measured using the aerosolization and NTA techniques are comparable with each other. The capillary tube model modified from that developed for aerosol filtration was found to be useful to represent the experimental results, when a sticking coefficient of 0.15 is incorporated. This suggests that for the polystyrene latex (PSL) particles-nuclepore filter-water system, only 15% of the particle collisions with the filter results in successful attachment. The small sticking coefficient found can be explained by the unfavorable surface interactions between the particles and the filter medium. The sieving mechanism, in which particles are removed when they are larger than the filter pore size, is primarily used to describe the filtration process. The capture of particles smaller than the pore size, by adsorption via diffusion and interception, becomes effective when the combined electrostatic and van der Waals interactions between particle and filter surface are favorable. In Chapter 5, retention efficiency of a 50 nm- rated Polytetrafluoroethylene (PTFE) filter against nanoparticles of different materials (gold, PSL and silica), sizes (80, 50 and 30 nm), concentrations (2×109 to 4×1011 particles/ml) and size distributions (monodisperse and polydisperse) was measured. The decreasing trend of retention efficiency as a function of particle loading can be readily explained by the sieving mechanism. Among different particle materials, silica shows much lower retention efficiency compared to PSL and gold particles of the same size. This observation can be explained with the DLVO theory, which suggests that higher ionic strength of PSL and gold suspensions causes a decrease in the magnitude of energy barrier and favors their adsorption to the filter surface. In addition, this study observed higher retention efficiency for mixed particles compared to monodisperse ones and there is less than 10% of re-entrainment of particles collected by adsorption. In Chapter 6, numerical simulations for change in membrane filter's retention efficiency in the presence of a particle previously captured within the filter are reported. Because of the complex porous structure of the membrane, the filter model is simplified into two cases: 1) capillary tube model and 2) single fiber model. Simulations for the capillary tube model show that a particle captured near the pore opening can increase the collection efficiency of 30 nm particles due to impaction and interception by about two times, depending on the relative size of the particles to the pore. From the single fiber model, a particle attached on the fiber can increase the combined impaction-interception single fiber efficiency by 10 times, depending on the location of the particle attached. The capillary tube simulation results can be incorporated into pore blockage model which considers filters as multiple layers of parallel pores. The single fiber simulations can explain the higher collection efficiency due to a previously captured particle. However, the single fiber theory alone cannot account for the observed decreasing trend with particle loading.
Measurement and filtration of virus aerosols
(2014-06) Zuo, Zhili
The potential involvement of virus aerosols (i.e., airborne virus-carrying particles) in the transmission of human respiratory diseases has led to increased public concern. This dissertation focuses on 1) measurement of laboratory generated virus aerosols as a function of particle size, virus type, and composition of nebulizer suspensions (Chapter 2 and 3) and 2) performance evaluation of filtering facepiece respirators against virus aerosols (Chapter 4 and 5) with the long term goal to better understand and better control the airborne transmission of viral diseases.
Monitoring an Iron-Enhanced Sand Filter Trench for the Capture of Phosphate from Stormwater Runoff
(2015-09) Erickson, Andrew J.; Gulliver, John S.; Weiss, Peter T.
This monitoring project was performed on an iron enhanced sand filtration (IESF) trench in the City of Prior Lake. Water from the pond and IESF trench discharges into a wetland that ultimately drains into Upper Prior Lake. In 2002, Upper Prior Lake was listed on Minnesota’s 303(d) List of Impaired Waters for nutrient/eutrophication biological indicators with aquatic recreation being impaired. Water quality has been reduced due to excessive phosphorus loading. According to the TMDL implementation plan developed for Spring Lake and Upper Prior Lake, the total phosphorus load must be reduced by 83% and 41%, respectively, to meet water quality goals. Overall, for 28 monitored natural rainfall/runoff events from 2013-2015, the IESF trench removed 26% of the phosphate mass load it received, though after non-routine maintenance in August 2014 the performance improved to 45% phosphate mass load reduction. These results indicate the importance of maintenance. A newer installation was previously monitored, and found to retain 71% of the phosphate (Erickson and Gulliver 2010). Most of the overall phosphate load reduction was achieved during larger events that had comparatively high influent phosphate concentrations (32.3 – 125.2 μg/L) and mass loads. Many small events in this investigation with low influent phosphate concentrations (3.8 – 38.4 μg/L) or mass loads exhibited negative removal (i.e., effluent mass load > influent mass load). The high effluent phosphate concentrations are suspected to be caused by the degradation of floating plants (primarily duckweed) that were deposited on the surface of the filter trench. As mentioned above, nonroutine maintenance to remove this material resulted in substantial performance improvement. After this maintenance, positive removal was observed for influent concentrations ranging from 6.3 – 44.1 μg/L. Detailed results, maintenance activities, design and operating & maintenance recommendations, and lessons learned are given within this report.
Nanoporous materials from ABAC tetrablock terpolymers
(2013-07) Jackson, Elizabeth
This dissertation describes efforts towards the preparation of tough nanoporous membranes from ABAC tetrablock terpolymers. This architecture was strategically chosen to combine an etchable C block, PLA, with a mechanically tough ABA triblock into one ABAC terpolymer. Multiple series of poly(styrene-b-isoprene-bstyrene-lactide) (PS-PI-PS-PLA) tetrablock terpolymers were synthesized. Morphological behavior was characterized for terpolymers containing both a 50:50 and 30:70 PS:PI ratio with between 0 and ~20% PLA by volume. Observed bulk morphologies include hexagonally packed cylinders (HEX), core(PLA)-shell(PS) cylinders (CSC), and a PLA sphere in cylinder morphology. Mechanical properties of PS-PEEP-PS-PLA tetrablocks were also investigated. All materials exhibited mechanical properties characteristic of tough thermoplastic elastomers. Composite membranes were prepared from a thin film of PS-PI-PS-PLA terpolymer and a macroporous polyethersulfone support. Described within are the efforts related to the fabrication and filtration performance of these nanoporous PSPI-PS composite membranes. As part of this process, solvent casting and annealing conditions were varied to investigate effects on tetrablock thin film morphology. Optimum conditions were determined to achieve PS-PI-PS-PLA films with perpendicular PLA cylinder orientation. These conditions included use of a mixed solvent system and the addition of a small amount of homopolymer PLA. Highly ordered films with vertically oriented nanopores were obtained.

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