Browsing by Subject "Civil engineering"

Now showing 1 - 20 of 38
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    Accessibility and the allocation of time: changes in travel behavior 1990-2010
    (2014-11) Brosnan, Martin Paul
    Using detailed travel surveys conducted by the Metropolitan Council of the Minneapo- lis/Saint Paul region for 1990, 2000-2001, and 2010-2011, this study analyzes journey- to-work times, activity allocation and accessibility. The analysis shows a decline in the time people spend outside of their homes as well as the time people spend in travel over the past decade. Although distances per trip are increasing, the willingness to make trips is declining, resulting in fewer kilometers traveled and less time allocated to travel. This study finds accessibility to be a significant factor in commute durations. Accessibility and commute duration have large affects on the amount of time spent at work therefore activity patterns are influenced by transportation and the urban environment.
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    Accessibility and the choice of network investments in the London underground
    (2014-08) Giacomin, David J.
    In 1863, the Metropolitan Railway of what came to be known as the London Underground successfully opened as the world's first subway. Its high ridership spawned interest in additional links. Entrepreneurs secured funding and then proposed new lines to Parliament for approval, though only a portion were actually approved. While putative rail barons may have conducted some economic analysis, the final decision lay with Parliament, which did not have available modern transportation economic or geographic analysis tools. How good were the decisions that Parliament made in approving Underground Lines? This paper explores the role accessibility played on the decision to approve or reject proposed early London Tube Schemes.
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    Aerodynamic wake study: oscillating model wind turbine within a turbulent boundary layer
    (2015-03) Feist, Christopher James
    An experimental investigation on the aerodynamic wake behind a pitching and/or heaving model wind turbine was performed. The study was split into two quasi-coupled phases; the first phase characterized the motion of an offshore floating wind turbine subjected to linear wave forcing, the second phase replicated specific motion cases, which were driven by results from phase I, on a model wind turbine within a turbulent boundary layer. Wake measurements were made in an effort to quantify fluctuations in the flow associated with the motion of the turbine. Weak differences were observed in the mean, streamwise velocity and turbulent fluctuations between the static and oscillating turbine cases. These weak differences were a result of opposing trends in the velocity quantities based on turbine motion phases. The wake oscillations created by the turbine motion was characteristic of a 2D wave (with convection in the x plane and amplitude in the z plane) with a relatively small amplitude as compared to u_rms.
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    Analytical and numerical investigation of an air entraining hydraulic jump
    (2014-10) Witt, Adam Matthew
    A significant environmental concern associated with hydropower electricity generation is the effect of operations on water quality. Of particular interest is the need to maintain elevated concentrations of dissolved oxygen (DO) in water passed through or over the dam. The hydraulic jump is commonly employed as a cost-effective mechanism to transfer oxygen into the flow and increase downstream DO through air entrainment and air-bubble mass transfer. However, dam operators currently lack the ability to accurately predict gas transfer at a given structure due to largely unknown initial and boundary conditions. The hydropower industry has a strong desire for improved DO predictive models that can quantify air entrainment under a variety of flow conditions across multiple structures.The purpose of this thesis is to better characterize the air entrainment that occurs at a hydraulic jump. The investigation is carried out in two parts: (1) development of a predictive equation for gas transfer at low-head gated dams, and (2) numerical simulations of an air entraining hydraulic jump. In Part 1, field measurements are analyzed to develop a dimensionless relationship between inflow conditions, dam geometry, and oxygen transfer efficiency. An improved predictive equation for gas transfer efficiency is derived that incorporates bubble physics and hydraulic jump scaling factors. Part 2 will describe the development and investigation of numerical simulations of the hydraulic jump. The numerical method was designed to capture air entrainment in a laboratory scale hydraulic jump and resolve the breakup of large air pockets in the turbulent shear region. Examination of the 3D flow field provides an improved understanding of the flow physics, particularly the behavior of vortical structures and their effect on bubble transport.
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    Arterial travel time distribution estimation and applications.
    (2011-08) Feng, Yiheng
    Travel time estimation on signalized urban arterials has been one of the biggest challenges in transportation engineering. This thesis focuses on the characterization of arterial travel times by estimating the travel time distributions and collecting GPS data from probe vehicles to predict travel times. The main factors that affect travel time patterns on an arterial link roughly fall into four categories: geometric structure, driving behavior, signal control and traffic demand. Four states of travel time for through-through vehicles are defined. State 1 (non-stopped) and State 3 (stopped) can be approximated using mixture normal densities while State 2 (nonstopped with delay) and State 4 (stopped with delay) can be approximated with uniform distributions. When prior travel time data is available, travel time distributions could be estimated by EM algorithm. Otherwise, they can be estimated based on signal control and geometric structure of the arterial. Link travel times are then extended to route travel times. A method based on Markov Chain is proposed to estimate mean route travel time. Results suggest that the proposed method can capture the relationship of link travel times well and provide an accurate estimation of mean route travel time. Combined with travel time data collected from GPS probe vehicles, a real-time traffic condition identification approach based on Bayes theorem is proposed. Numerical examples show a single GPS probe is able to identify real-time traffic condition successfully in most cases. In addition, GPS travel times can also be used to refine the existing travel time distributions using Bayesian update. Finally, a comprehensive case study based on the NGSIM Peachtree Street Dataset is demonstrated. Travel time distributions estimated from signal timing and the geometry iii are considered as prior distributions. Traffic condition identification process is performed and the probability one travel time sequence belongs to each traffic condition is calculated. Data are then classified according to the posterior probabilities. Finally, a Bayesian update is run to calculate posterior distributions under each traffic condition combining with classified data. This update process can be repeated iteratively when new GPS data are available. The results obtained from Bayesian update are also compared to those estimated from EM algorithm. Overall the EM algorithm fits the data better than Bayesian update. However, sometime Bayesian approach could reflect the real world situation when some data is missing while EM does not.
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    Boundedly rational user equilibrium: models and applications
    (2014-08) Di, Xuan
    Efficient transportation management requires good understanding of people's travel behavior. Most transportation planning models assume travelers are perfectly rational in decision-making. However, much of the empirical evidence from psychology, economics, and transportation has shown that perfect rationality is not realistic in modeling travelers' decision-making process. Thus existing transportation planning models may provide inaccurate predictions to transportation planners. Motivated by travelers' route choice changes in response to the reopening of the I-35W Bridge in Minneapolis, this dissertation shows that travelers are boundedly rational (BR) in making route choices. Though the BR travel behavioral model was proposed in the 1980's, empirical validation of such behavioral principle using real-world data along with a theoretical framework was non-existent. This study is dedicated to bridging these gaps from both empirical and theoretical perspectives.The first contribution of this dissertation is the empirical verification and estimation of boundedly rational route choice behavior. By analyzing recorded GPS trajectories from 143 commuters before and after the reopening of the I-35W Bridge in Minneapolis, we employ a probit model to estimate the bounded rationality parameters in Twin Cities. Despite the behavioral appeal of bounded rationality, a rigorous study of boundedly rational user equilibria (BRUE) solution has been lacking, partly due to its mathematical complexity. This research offers a systematic approach of deriving the BRUE solutions analytically on networks with fixed travel demands. Based on the definition of ε-BRUE, where ε is the indifference band for perceived travel times, we formulate the ε-BRUE problem as a nonlinear complementarity problem (NCP). With the increase of the indifference band, the path set that contains equilibrium flows will be augmented and the critical values of the indifference band to augment the path set can be identified by solving a sequence of mathematical programs with equilibrium constraints (MPEC). A novel solution method is provided to obtain the BRUE solution set and numerical examples are given to illustrate this finding. To provide guidelines to policy-makers for congestion mitigation, this research also explores an important phenomenon which should be avoided in transportation network design, i.e., Braess paradox. The classical Braess paradox was built upon the perfectly rational behavioral assumption. Under the framework of bounded rationality, each equilibrium flow pattern leads to a different total system travel time, resulting in non-unique network performance measures. Because of the non-uniqueness of BRUE solutions, which particular equilibrium pattern should be used to compare network performances before and after new roads are built remains a question. This dissertation aims to study the analytical properties of Braess paradox under bounded rationality by exploring the relationships between the occurrence of Braess paradox and the indifference band as well as the demand level. The unveiled relationships offer a guideline for transportation planners to prevent the occurrence of Braess paradox and pave the way for strategic transportation management under the bounded rationality assumption.
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    Calibration of microscopic traffic simulators using travel times and trajectories.
    (2011-09) Collins, Michael Bandera
    Traffic network simulation has become the solution for estimating the performance of existing and future projects. It provides this framework through the incorporation of several driver behavior models, which through their interaction create a realistic representation of individual drivers. As such, calibration of these sub-models is necessary to emulate reality. In this work, two methodologies are presented that use trajectories (or derivatives, from the Next-Generation Simulation (NGSIM) data set and a GPS study, respectively) to perform automated calibration. The techniques for the respective calibrations are sampling and optimization. Both methodolgies utilize Latin Hypercube Sampling, but the second methodology is paired with a meta-heuristic optimization, called the Firefly Algorithm for further performance improvement.
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    Catalysts and magnets: built environment effects on bicycle commuting
    (2013-09) Schoner, Jessica Elizabeth
    What effects do bicycle infrastructure and the built environment have on people's decisions to commute by bicycle? While many studies have considered this question, commonly employed methodologies fail to address the unique statistical challenge of modeling such a low mode share. Additionally, self selection effects that are not adequately accounted for may lead to overestimation of built environment impacts. This study addresses these two key issues by using a zero-inflated negative binomial model to jointly estimate participation in and frequency of commuting by bicycle, controlling for demographics, residential preferences, and travel attitudes. The findings suggest a strong self selection effect and modest contributions of bicycle accessibility: that bicycle lanes act as ``magnets" to attract bicyclists to a neighborhood, rather than being the ``catalyst" that encourages non-bikers to shift modes. The results have implications for planners and policymakers attempting to increase bicycling mode share via the strategic infrastructure development.
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    Characterizing the performance of a new iniltrometer and hydraulic properties of roadside swales
    (2014-09) Ahmed, Farzana
    A roadside swale is an infiltration practice that removes water during rainfall-runoff, infiltrate water into the soil and filter the soil and associate pollutant from the water. Infiltration rate is an important factor affecting the performance of a swale. Though roadside swales convey and treat road runoff, data on the performance of swales with regards to infiltration is relatively sparse. Therefore, the objective of this study is to, 1) Modify the optimization technique of the new Modified Philip Dunne (MPD) infiltrometer, 2) Verify the results obtained from this MPD infiltrometer for uniform soil, layered soil and uniform soil with macopores by numerical simulation, 3) Utilize the MPD infiltrometer to characterize the field-saturated hydraulic conductivity (Kfs) of five roadside swales located in Twin-Cities, MN and one swale located in Madison, WI and 4) Analyze the derived results obtained from the measurements taken by the MPD infiltrometer. From numerical simulations it was found that MPD Infiltrometer overestimates Kfs value by 10 to 36% for the uniform soil, 12% to 63% for layered soil and 4% to 29% for uniform soil containing macropores. MPD infiltrometer allows collecting multiple infiltration measurements simultaneously to capture the spatial variation of infiltration rate of an infiltration practice. In this study a total of 720 infiltration measurements were collected in swales located in Twin-Cities, MN and in Madison, WI. Statistical analysis was performed on the Kfs values to analyze the effect of initial soil moisture content, season, soil texture class and distance in downstream direction on the geometric mean Kfs value of a swale. Because of high spatial variation of Kfs value in the same swale no effect of initial soil moisture content, season and soil texture class was observed on the geometric mean Kfs value. But the distance in downstream direction may have positive or negative effect on the Kfs value.
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    A comprehensive evaluation of the effects of climate in MEPDG predictions and of MEPDG EICM model using MnROAD data
    (2011-03) Johanneck, Luke Anton
    Although new construction of composite (AC/PCC or PCC/PCC) pavements is not common, a substantial amount of knowledge has been acquired over the past 35 years regarding the materials, design, and construction of composite pavements. The Mechanistic-Empirical Pavement Design Guide (MEPDG) provides useful prediction models, analysis methodologies, and a design procedure that, with further improvements and calibrations, can be made to provide reasonable prediction capabilities for new composite pavements. This thesis investigates the applicability of the MEPDG models for predicting structural responses of composite pavements, with special attention paid to the geographic location of the pavement section, and the temperature distributions predicted by the EICM for a composite pavement. A section of this thesis examines the effects of climate on pavement performance, and the effect of climate file generation using the MEPDG. This section details the effort to design and test an asphalt-over-concrete (AC/PCC) composite pavement for 610 locations across the United States using the MEPDG version 1.0. While results support the general notion of environmental effects on pavement performance, the performance prediction was found to contain inconsistencies in terms of predicted transverse cracking in the PCC layer. These inconsistencies are attributed to climatic data, and they include the use of stations with incomplete data. It was concluded that the climatic database available to the MEPDG should be cleansed of incomplete or questionable climatic data files to ensure accurate transverse cracking prediction in AC/PCC. Otherwise, the presence of this questionable climatic data can only adversely affect performance prediction. The other primary focus of this thesis describes research aimed to evaluate modeling of the thermal behavior of concrete and composite pavements by the Enhanced Integrated Climatic Model (EICM), the climate modeling package used in the MEPDG. The study uses temperature data collected at the Minnesota Road Research facility from PCC and iv AC/PCC pavements to first investigate benefits of AC overlays on the thermal characteristics of PCC slabs. Furthermore, the study validates EICM predictions of thermal gradients through the slabs and investigates the effect of MEPDG user inputs for thermal conductivity of the PCC. This section examines measured data from MnROAD for AC/PCC pavements and their single-layer PCC counterparts and attempts to explain how similar pavement systems and their thermal characteristics are accounted for in the MEPDG. The research concluded that evaluation of the material thermal inputs should be a part of a process of local calibration and adaptation of the MEPDG. Also included in this paper is a sensitivity analysis to a wide range of input parameters that might be expected for composite pavements. This includes AC and PCC layer thickness, PCC joint spacing, PCC slab width, and the coefficient of thermal expansion in the PCC layer. Thermal properties of the materials that can affect the temperature distribution, thermal conductivity and heat capacity, are also included in the sensitivity analysis. This thesis concludes that the environmental and material thermal property inputs should be considered with equal importance as traffic, design features, and non-thermal material properties.
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    Degradation of groundwater contaminants by iron containing systems.
    (2010-09) Moore, Kirsten Marie
    Iron-containing systems are effective at reducing common groundwater contaminants. Zero-valent iron particles are an effective remediation technology for groundwater contaminated with halogenated organic compounds. Iron salts were used to generate iron oxide nanoparticles, which were reduced to zero-valent iron. The reactivity of the resulting zero-valent iron nanoparticles was quantified by monitoring the kinetics of carbon tetrachloride reduction, and significant differences in reactivity were observed. Furthermore, substantial variations in the solid-state products of oxidation were also observed. Fe(II)-iron mineral systems are also an effective method for reducing nitroaromatic compounds, such as pesticides. The objective of this study was to link changes in the mineralogy of goethite particles to changes in the reactivity of an Fe(II)-goethite system. The reactivity of Fe(II)-goethite and Fe(II)-goethite sand systems were quantified by monitoring the kinetics of trifluralin reduction. Changes in the goethite mineralogy were observed by transmission electron microscopy. Differences in goethite reactivity and the solid-state products were observed, as compared to previous work using goethite.
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    Development and estimation of traffic data-based operational measures for effective winter snow management
    (2014-08) Hong, Seong Ah
    Snow storms degenerate safety and traffic mobility by creating adverse driving conditions including visibility impairments, reducing pavement friction, obstructed road facilities. Improving the effectiveness of the snow management requires an efficient assessment of the operational strategies with the data that can be directly measureable from the field. While there have been various types of operational measures used in the state DOTs in the US, the traffic data-based operational measures that can quantify the effects of snow plowing activities are still lacking. To be sure, the existing approaches developed to date employed the variations of traffic speed or travel time during the snow events and those measures cannot fully reflect the road weather conditions when traffic is congested.Developing the operational measures that can objectively and accurately reflect the time-variant road weather conditions is essential in improving the effectiveness of the snow management strategies. In this research, an automatic process is developed for estimating the traffic data-based operational measures for winter snow management. Those measures include the Road Condition Recovery Time (RCR), the estimate of the `bare-lane regain time', which is the major performance measure of the winter snow maintenance operations at the Minnesota Department of Transportation. The automatic process was then applied to a sample snow section in Twin Cities, MN. The results of the example application showed that the operational measures can reasonably measure the performance of snow plowing operations by reflecting the impacts of the traffic flow resulted by the time-variant road weather conditions.
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    Development and estimation of traffic data-based operational measures for effective winter snow management
    (2014-08) Hong, Seong Ah
    Snow storms degenerate safety and traffic mobility by creating adverse driving conditions including visibility impairments, reducing pavement friction, obstructed road facilities. Improving the effectiveness of the snow management requires an efficient assessment of the operational strategies with the data that can be directly measureable from the field. While there have been various types of operational measures used in the state DOTs in the US, the traffic data-based operational measures that can quantify the effects of snow plowing activities are still lacking. To be sure, the existing approaches developed to date employed the variations of traffic speed or travel time during the snow events and those measures cannot fully reflect the road weather conditions when traffic is congested.Developing the operational measures that can objectively and accurately reflect the time-variant road weather conditions is essential in improving the effectiveness of the snow management strategies. In this research, an automatic process is developed for estimating the traffic data-based operational measures for winter snow management. Those measures include the Road Condition Recovery Time (RCR), the estimate of the `bare-lane regain time', which is the major performance measure of the winter snow maintenance operations at the Minnesota Department of Transportation. The automatic process was then applied to a sample snow section in Twin Cities, MN. The results of the example application showed that the operational measures can reasonably measure the performance of snow plowing operations by reflecting the impacts of the traffic flow resulted by the time-variant road weather conditions.
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    Development of a longitudinal cracking fatigue damage model for jointed plain concrete pavements using the principles of similarity
    (2014-07) Lederle, Rita Elizabeth
    Mechanistic-empirical (M-E) pavement design computes stresses induced in a concrete slab due to applied traffic and environmental loads, and correlates these stresses to distress levels using empirical correlations. Currently, the Mechanistic-Empirical Pavement Design Guide (MEPDG) is one of the most advanced and prevalent methods of M-E pavement design. While the MEPDG predicts transverse cracking, longitudinal cracking is not predicted, even though longitudinal cracking is commonly observed in jointed plain concrete pavements (JPCPs). In this research, an MEPDG compatible model was developed to predict longitudinal cracking fatigue damage in JPCPs. This modeled adapts the framework of the MEPDG specifically for longitudinal cracking. In order to develop an M-E longitudinal cracking fatigue damage model, it is necessary to compute stresses at the critical location for longitudinal cracking due to the various traffic and environmental loads to which a pavement could be exposed. The principles of similarity were used to map the original problem into similar space, which drastically reduces the complexity of the problem without introducing any error. To avoid the computational inefficiency associated with embedding a finite element program within the program, neural networks are used for rapid stress solutions. Stresses determined in similar space are converted back into real space for damage computation. Modifications were made to the MEPDG fatigue damage computation process to eliminate simplifying assumptions and to make the procedure applicable to longitudinal cracking. A study was also conducted to determine characteristics of pavement susceptible to longitudinal cracking based on various parameters. This study made use of the principles of similarity to examine almost all pavements which could be considered in M-E design. By identifying the characteristics of pavements susceptible to longitudinal cracking, engineers can identify pavements for which longitudinal cracking analysis should be conducted. The model and design procedure developed in this research provides the tools needed to conduct such an analysis.
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    Development of best practices for inspection of PT bridges in Minnesota
    (2012-05) Berg, Kyle Matthew
    Post-tensioned (PT) concrete bridges can be very durable if properly constructed with high performance materials. Problems were found in grouted post-tensioned ducts in Florida during the late 1990s and early 2000s that indicated a change in grouting materials and construction practices were necessary. Since that time, materials and practices have been significantly improved. States that have investigated older PT bridges have found widely varying levels of deterioration depending on climate, construction practices, structure type and other variables. In the case of bridges built prior to approximately 2003, voided areas in the grouted tendons are fairly common (after 2003 specifications governing materials use and construction practices were in place). This thesis focuses on PT bridges built in Minnesota prior to 2003. The scope is limited to providing a targeted check of bridges that are most likely to have grouting related corrosion problems based on a review of plans and inspection notes. The project consisted of three phases: 1) review of plans and inspection reports of 40 post-tensioned bridges constructed prior to 2003; 2) selection of 10 bridges for a limited on site inspection of the exterior of the bridge; 3) invasive inspection of 3 select bridges. The bridges selected were chosen to represent different bridge construction types and to provide a spot check of the PT bridge inventory in Minnesota. One of the three bridges has corrosion and voids due to poor grouting, one has a major corrosion problem related to construction issues (but appears to have good grout), and one showed no tendon corrosion or grouting problems during the invasive spot checks.
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    Effects of compressive and tensile fields on the load carrying capacity of headed anchors.
    (2011-02) Piccinin, Roberto
    The results of research initiated in the early 1980s led to the replacement of plasticity-based design guidelines for the load-carrying capacity (concrete breakout) of headed anchors embedded in concrete with those developed using fracture mechanics. While provisions are available in the design codes that account for the presence of tensile fields causing concrete cracking, no provisions are available for anchors embedded in prestressed concrete. This thesis presents the results of linear and nonlinear elastic fracture mechanics analyses of the progressive failure of headed anchors embedded in a concrete matrix under compressive or tensile prestress. In addition, and because of the complete lack of experimental evidence, the results of a relatively large experimental investigation of the behavior of headed anchors embedded in compressively prestressed concrete are presented. Discrete crack finite element models and experiments predict an increase (decrease) in load-carrying capacity and post-peak dissipated energy with increasing compressive (tensile) prestress for all the embedment depths investigated. For extremely shallow cases, in which the embedment depth is less than the (typical) maximum aggregate size of concrete, it is shown that deterministic continuum-based models are not applicable. Overall, the results show that there is very little difference between the linear elastic and nonlinear elastic fracture mechanics approaches, this implying that the concrete breakout strength is governed by the strongest possible size effect. In addition to providing analytical support to the existing design approaches for the capacity of headed anchors embedded in cracked concrete (under tension), the present work provides an experimentally and analytically based preliminary easy-to-use design formula for the concrete breakout capacity of headed anchors in compressively prestressed concrete.
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    An Engineering Perspective on Invasive Fish Control: A Study of Bubble Curtain Deterrent Systems to Control Carp Movement
    (2013-07) Zielinski, Daniel Patrick
    The objective of this research was to investigate the ability of bubble curtain deterrent systems to inhibit the movement of invasive fish. Bubble curtains, which consist of a wall of bubbles (e.g. produced by forcing air through perforated pipes), fall into the category of behavioral deterrent systems that rely on aversive stimuli (e.g. sound and light) to guide fish in taxon specific manners. These systems provide advantages over physical/mechanical screens because they do not restrict fluid flow or negatively impact navigation. Bubble curtains are particularly appealing, because they are less expensive than other electrical or sonic barriers, are easily maintained, safe, and produce complex acoustic and hydrodynamic stimuli which may be optimized to deter fish movement. However, few studies have examined whether or how bubble curtains might work. In three studies, the common carp (Cyprinus carpio), a cyprinid responsible for water quality degradation in shallow water ecosystems, was used to investigate how bubble curtains influence fish behavior and might be optimized. First, through a laboratory experiment, two different bubble curtains were shown to reduce passage of common carp by 75-80% in both up- and down-stream directions. These findings also suggested that avoidance behaviors were attributed to fluid motion and sound stimuli. Second, a field test demonstrated that the performance of a bubble curtain under natural conditions was consistent with laboratory results, blocking 57±12% of downstream swimming carp, versus 75-80% in the laboratory. Third, a fish movement model based on diffusion theory and phonotaxic response was derived. In a novel application, a stability analysis of the fish movement model demonstrated that acoustic stimuli produced by the bubble curtains can be sufficient to disrupt movement (i.e. deter passage) of common carp. Overall, I have shown through rigorous experimental and holistic quantitative analysis that bubble curtains can indeed deter common carp movement, but improvements must be identified in order for bubble curtains to remain a viable management tool in the future.
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    Experimental studies of fluid turbulence during the entrainment of an individual gravel particle.
    (2011-06) Templin, Kirby E.
    Experiments were performed in a laboratory flume to investigate the relative importance of different turbulence mechanisms for the entrainment of an individual gravel particle into bed-load transport. The bed conditions tested in these experiments were a mobile gravel bed with a rough-to-smooth (R-S) transition, a fixed gravel bed with a R-S transition, and a fixed gravel bed with a smooth-to-rough (S-R) transition. One location of interest was in a region of steady uniform flow located away from the transition (SS location), and the other location of interest was in a region of steady non-uniform flow located near the roughness transition (T location). Fluid velocity measurements were taken directly above a tracer particle during entrainment into bed-load. Turbulence statistics of interest in this investigation included the downstream velocity (u), vertical velocity (w), downstream normal Reynolds stress (u’u’), vertical normal Reynolds stress (w’w’), and the Reynolds shear stress (u’w’). Conditionally averaged results show a strong correlation of particle entrainment with increases in u and decreases in w for all SS and T locations over the bed conditions tested. The fixed bed R-S transition results also show a correlation between initial motion and increases in u’u’, and u’w’ for the SS location but not the T location. The peaks seen in the trends of the conditionally averaged u results primarily occur prior to initial motion, and the time difference increases with distance above the bed. This suggests that inclined coherent structures are responsible for the entrainment of individual gravel particles.
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    The fate of antibiotic resistance genes during treatment and disposal of residual municipal wastewater solids
    (2013-12) Burch, Tucker Ramsey
    The development of resistance to antibiotics among pathogens is a global public health dilemma with significant consequences for the length and quality of human life. As a result, the bacterial antibiotic resistance genes (ARGs) that confer resistance are increasingly regarded as environmental contaminants. A significant body of knowledge has been generated that catalogues the occurrence of ARGs in numerous environmental reservoirs, among which residual municipal wastewater solids are one of the largest. Only a handful of studies, however, make the critical paradigm shift to considering treatment technologies and management strategies intended to reduce the quantities of ARGs in those reservoirs. The objective of the work presented here was to evaluate various treatment technologies and management strategies for reducing the quantity of ARGs discharged from the municipal wastewater treatment process during treatment and disposal of residual solids. Aerobic digestion, air drying, and hyperthermophilic (¡Ý 60¡ãC) anaerobic digestion were evaluated for their abilities to reduce ARG quantities in residual municipal wastewater solids using laboratory-scale treatment units. The technologies were compared among each other and to mesophilic (40¡ãC) and thermophilic (56¡ãC) anaerobic digestion on the basis of the kinetics of ARG removal from residual solids. While all technologies were effective, hyperthermophilic anaerobic digestion tended to exhibit the fastest kinetics. In addition, class 1 integrons were identified as a candidate design gene, and batch or semi-batch flow configurations were demonstrated to be a potential means of optimizing the removal of ARGs from residual solids during aerobic digestion, thermophilic anaerobic digestion, and hyperthermophilic anaerobic digestion. The fate of ARGs in soil following simulated disposal was also investigated by applying treated residual solids from full-scale treatment facilities and from numerous laboratory-scale treatment units to soil microcosms. ARGs from residual solids treated at typical full-scale treatment facilities persisted in soil at high concentrations for relatively long periods of time, with half-lives on the order of months. Alkali stabilization, thermophilic anaerobic digestion, hyperthermophilic anaerobic digestion, and pasteurization, however, caused drastic decreases in ARG quantities in soil within one month. The results presented here can be used to optimize and design the residual municipal wastewater solids treatment and disposal process to remove ARGs.
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    The fate of polycyclic aromatic hydrocarbons bound to stormwater pond sediment during composting.
    (2011-03) Kyser, Scott James
    Recently, concentrations of polycyclc aromatic hydrocarbons (PAHs) that are above the Minnesota Pollution Control Agency‘s recommended limits for unrestricted use have been detected in stormwater pond sediments. Effective treatment methods are needed to remediate these PAH contaminated sediments to allow for unrestricted use and cost-effective disposal options. Based on the idea that PAHs in contaminated soil can be biodegraded when mixed with compost, this research sought to evaluate the effectiveness of using compost to biodegrade PAHs in contaminated sediment. Two benchtop experiments were performed that allowed for the simulation of the conditions in a compost pile that would favor biodegradation of PAHs bound to sediment. These experiments were able to effectively simulate the conditions of a compost pile and demonstrated that composting occurred as measured by carbon dioxide respiration, volatile solids content changes and temperature changes. Despite significant microbiological activity, only the three ring PAH phenanthrene, was found to be significantly degraded in all experiments. No PAH with four or more rings was found to be significantly degraded during the extent of composting. An assay that estimated bioavailability by measuring the desorption of PAHs from the contaminated sediment into the aqueous phase indicated that all but one PAH had a potentially bioavailable fraction. Since each PAH had a potentially bioavailable fraction, PAH biodegradation was likely limited both by a microbial community with only a small potential to degrade four to six ring PAHs and low aqueous PAH partitioning from the sediment.