Browsing by Author "Venayagamoorthy, S. Karan, advisor"

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Open Access
Assessment and improvement of hydraulic disinfection efficiency of a live small drinking water system in South Africa
(Colorado State University. Libraries, 2018) Baker, Jessica L., author; Venayagamoorthy, S. Karan, advisor; Niemann, Jeffrey, committee member; Leisz, Stephen, committee member
Since the implementation of chlorination, the most common method of water disinfection, diseases such as Cholera, Typhoid Fever, and Dysentery have been essentially eliminated in the U.S. and other industrialized countries (WHO 2017). However, these nations still experience challenges in meeting drinking water standards. In 2009, the Colorado Department of Public Health and Environment contracted Colorado State University (CSU)'s Department of Civil and Environmental Engineering to address the poor hydraulic disinfection efficiency of contact tanks of small-scale drinking water systems. From this research, the Baffling Factor Guidance Manual (2014) was published, which presents innovative modifications proven to increase the hydraulic disinfection efficiency of small-scale contact tanks. The proposed innovative technology has the potential to have a significant positive impact in developing nations since at least 2 billion people worldwide use a drinking water source that is contaminated with feces (WHO 2017). Historical experience suggests that simply transporting a technology does not necessarily equate to long-lasting impact, but how that technology is transferred is critical to its sustainability. A successful solution to the need for disinfected water must be holistic, taking into consideration culture, law, politics, economics, environment, etc. The focus of this thesis is to investigate further the application of the innovative contact tank modifications of an inlet manifold and random packing material (RPM) on live systems. A case study was conducted on a small waterworks in the rural town of Rosetta, KwaZulu-Natal, South Africa, in collaboration with Umgeni Water. Physical tracer tests were conducted on a 10,000L cylindrical tank acting as the contact chamber to assess the hydraulic disinfection efficiency in terms of baffling factor (BF), before and after the installation of a 4-way inlet manifold modification. This modification resulted in a 37% improvement in the BF, increasing the contact time (CT), an important aspect of disinfection, in the cylindrical contact tank from 8.4 min-mg/L to 11.0 min-mg/L. In addition to the international case study, a pilot study was conducted at CSU to address the biofilm formation concerns of the innovative use of random packing material (RPM) in contact tanks. Preliminary results support the hypothesis that the presence of a disinfectant in the contact tank, though in the process of disinfecting the water, would mitigate the growth of a biofilm on the RPM.
Open Access
Computational modeling of wind turbine wake interactions
(Colorado State University. Libraries, 2012) Davis, Cole J., author; Venayagamoorthy, S. Karan, advisor; Heyliger, Paul R., advisor; Maloney, Eric D., committee member
The rapid expansion of the wind energy market necessitates the need for advanced computational modeling and understanding of wind turbine aerodynamics and wake interactions. The following thesis work looks to study turbulence closure methods widely used in computational fluid dynamics (CFD) and their applicability for modeling wind turbine aerodynamics. The first investigation is a parametric study of turbulence models and their performance on geometries of stationary in-line turbines and disks spaced at different intervals. A variety of Reynolds-averaged Navier-Stokes (RANS) closure schemes (Spalart-Allmaras, Standard k-ε, k-ε Realizable, k-ε RNG, Standard k-ω, k-ω SST) were studied as well as a large eddy simulation (LES) with a dynamic Smagorinsky-Lilly sub-grid scale (SGS) model. The simulations showed the grid refinement to be inadequate for LES studies. The RANS closure schemes did not indicate a dominant model. However, relevant literature on separating flows has shown the k-ω SST model to be preeminent. The second investigation uses only the k-ω SST RANS closure scheme to model wake development and resolution for both a single fully resolved rotating turbine as well as two in-line fully resolved rotating turbines. These simulations were successful in predicting wake development and resolution, as well as predicting velocity deficits experienced by the downstream turbine. Vorticity results also showed an accurate wake structure and helical tendencies. In the third investigation, a grid independence study was performed to gain an accurate pressure distribution on the blade surfaces for a separate, collaborative, non-linear, structural study of wind turbine blades. This study showed a strong asymptotic relationship of the maximum pressure on the blades to the predicted Bernoulli pressure on the blade. The results of this research show clear wake development, structure and resolution. The velocity deficits found translate directly in to power deficits for downstream turbines and the vorticity translates directly into increased fatigue experienced by the blades. In contrast to the vast super-computer simulations found in literature, all simulations in this thesis work were calculated using four parallel processors. The accuracy was achieved through assumptions, which were designed to maintain the desired physics while simplifying the complexity of the problem to the capabilities of desktop computing. This research demonstrates the significance of model design and capabilities and accuracy achievable using desktop computing power. This has vast implications of accessibility into academia and the further development of the wind power industry.
Open Access
Effects of inlet/outlet locations and influent temperature on hydraulic disinfection efficiency in contact tanks
(Colorado State University. Libraries, 2017) Zhang, Yishu, author; Venayagamoorthy, S. Karan, advisor; Ramirez, Jorge A., committee member; Prasad, Ashok, committee member
This study focuses on understanding the effect of inlet/outlet locations and influent temperature on hydraulic disinfection efficiency of drinking water contact tanks for small systems. Computational fluid dynamics (CFD) simulations of flow and scalar transport in a concrete rectangular tank with three inlet/outlet location configurations were performed. The temperature of the influent into the system was varied in the second part of this study in order explore the effects of temperature gradients on the flow and scalar transport. Hydraulic disinfection efficiencies were computed through the use of residence time distribution (RTD) curves obtained from the CFD simulations and the baffling factor (BF). The physical tank that was used for all tracer tests is located at the Hydraulics Lab at Colorado State University's Engineering Research Center (ERC) in Fort Collins. The rectangular concrete tank was initially constructed with a bottom inlet and top outlet configuration and has a total volume of 1500 gallons. After the CFD simulation results were validated using tracer tests, two principle objectives were investigated using CFD simulations. First, the effect of inlet/outlet locations and their respective sizes were investigated. For a given constant temperature for both the inflow and ambient water in the tank, three inlet/outlet location combinations (i.e. bottom inlet-bottom outlet, bottom inlet-top outlet, and top inlet-bottom outlet) with two different outlet sizes (i.e. 2-in.-diameter and 4-in.-diameter) were modeled using 15 CFD simulations. Both baffled and un-baffled tanks were modeled. The resultsshow that a small modification of the outlet pipe diameter results in minor changes in the baffling factor and hydraulic disinfection efficiency. All adjusted un-baffled tanks (i.e. with the three different inlet/outlet configurations) did not yield any satisfactory disinfection performance due to the severe short circuiting that occurs in the tank. The main finding is that for baffled tanks, the top inlet-bottom outlet configuration performed the best and increased baffling factor by over 30% relative to the bottom inlet-bottom outlet configuration for the baffled tank which is commonly found in praxis. Second, the effect of buoyancy that can occur in disinfection tanks due to drastic temperature differences between the inflow and the ambient water in the contact tank was investigated. Only negatively buoyant conditions were studied in this research. Temperature differences of 0°C, 5°C, 10°C, and 15°C were created by injecting cold inflow to the baffled tanks under two conditions namely: (i) no heat flux condition and (ii) constant wall condition. For the first condition, it was assumed that no heat exchange between tank (and baffle) walls and fluid occurs; while for the second condition, the wall temperature was held constant at 20°C. Both conditions were simulated at different flow rates to capture flow regimes ranging from laminar to turbulent. It was found that the baffling factor varied significantly between laminar, transitional, and turbulent flows. The best hydraulic disinfection efficiency was achieved when the flow was laminar. For no heat flux condition, the effects of the buoyancy increased baffling factor by 57% compared to the base case with no temperature difference. On the other hand, for turbulent flow conditions with a strong temperature difference, the baffling factor reduced by 49% compared to the base case. The constant wall temperature condition produced similar results, but with a smaller change in baffling factor. From a hydrodynamic analysis of the flow fields obtained from CFD simulations, it was concluded that buoyancy could either increase hydraulic disinfection efficiency or decrease it, depending on the flow regime. Hence, care should be exercised to avoid flows in transitional to turbulent regimes because the negative buoyancy could decrease the baffling factor and lead to inadequate microbial deactivation.
Open Access
Evaluation of flow and scalar transport characteristics of small public drinking water disinfection systems using computational fluid dynamics
(Colorado State University. Libraries, 2011) Wilson, Jordan M., author; Venayagamoorthy, S. Karan, advisor; Gates, Timothy K., committee member; Wickramasinghe, S. Ranil, committee member
This study focuses on the evaluation of flow and scalar transport characteristics of small disinfection systems, primarily through computational fluid dynamics (CFD) as well as physical conservative tracer studies. Original research was performed on a pipe loop, series of pressurized tanks, and two separate open surface tank contact systems and a case study was performed on a baffled tank system. The flow dynamics for each of these respective disinfection systems were evaluated using CFD. The flow dynamics govern the transport of any quantity (e.g., a passive scalar, conservative tracer, or chlorine-containing species) through the system visualized through plotting the effluent concentration (e.g., passive scalar for computational models and conservative tracer for physical experiments) through time forming what is commonly referred to as a residence time distribution (RTD), or flow-through, curve. Physical experiments provided validation for the CFD models that give a more complete view of hydraulic efficiency thus overcoming the common "black-box" approach to contact tank design using only the theoretical detention time (TDT) (defined as the system volume V divided by the volumetric flow rate Q). The differing geometries of contact tank systems yield significantly different flow paths with varying degrees of separation, recirculation, inlet and outlet effects, and wall effects prompting the need for the evaluation of hydraulic efficiency to be unique to the system. Yet current practice evaluates the hydraulic efficiency of disinfection contact tank systems based on the TDT and the rising limb of the RTD curve, designated by the United States Environmental Protection Agency (USEPA) as baffle factor (BF). Research presented in this study using CFD models and physical tracer studies shows that evaluation methods based upon TDT tend to overestimate, severely in some instances, the actual hydraulic efficiency as obtained from the systems' flow and scalar transport dynamics and subsequent RTD curves. The main objectives of this study were to determine the systems' respective hydraulic efficiencies and to analyze an alternative measure of hydraulic efficiency, the ratio t10/t90, where t10 and t90 are the time taken for 10 and 90 percent of the input concentration to be observed at the outlet of a system. The pipe loop system was dominated by advection and thus showed little variance in the values of BF and t10/t90. Analysis of the series of pressurized tank systems showed significant regions of turbulent mixing and recirculation corresponding to a system that was much less efficient than the pipe loop system. BF values for the pressurized tank systems were nearly 100 percent greater than t10/t90 values as a result of a system behavior further from plug flow. The open surface tank systems exhibited the most uneven flow paths and lowest efficiencies seen in this study with BF and t10/t90 values differing by at least 100 percent. These systems exhibited significant degrees of short-circuiting and recirculation largely due to their inlet and outlet configurations. Finally, the baffled tank system showed an increase in system efficiency with the number of baffles (e.g., increase in advective forces) and a corresponding decrease in the variance between BF and t10/t90 values. Overall, the research presented in this thesis provides an extensive evaluation for the flow and scalar characteristics of the described small public drinking water disinfection systems allowing for the development of t10/t90 as a more representative evaluation of hydraulic efficiency.
Open Access
Experimental investigations for improving the accuracy of flow measurement in irrigation canals
(Colorado State University. Libraries, 2021) Pugh, Joseph E., author; Venayagamoorthy, S. Karan, advisor; Gates, TImothy K., advisor; Windom, Bret C., committee member
Flow measurement in open-channels refers to the process by which a volume amount of water passing through a channel cross section is quantified per unit time. In the irrigation water management context, this is done to account for available water resources so that water distribution systems can be properly managed to achieve adequate and efficient allocation. Today, irrigation water use remains the largest consumptive draw on our collective water budget, while the availability of this resource is becoming increasingly scarce. Additionally, access to reliable irrigation water acts as a major factor in maintaining strong crop production and healthy rural livelihoods. Improvement in the accuracy of flow measurement methodologies is then motivated by a need for implementing more conservative practices to limit unnecessary waste and to promote effective and equitable allocation. The two principal means by which flow is quantified in open-channels are the velocity-area method and the use of stage-discharge relationships associated with hydraulic structures placed within the channels. The present study investigates improvements to the accuracy of flow measurement for each of these methodologies. The velocity-area method involves the integration of several point measurements of velocity multiplied by sub-components of the channel cross-sectional area to achieve an estimate of flow rate via the principle of continuity. Traditionally, these methods have been time-consuming and subject to inaccuracy due to the large number of measurements needed. In recent decades, the development of Acoustic Doppler Current Profilers (ADCPs) has offered a means for measuring flow using the velocity-area method with time-efficiency and less intrusiveness into the flow. However, opportunity still exists for refining the operational protocols for this device to quantify and reduce measurement uncertainty, especially within the irrigation water management context. With this motivation, a StreamPro ADCP manufactured by Teledyne RD Instruments was used to quantify flow rates in man-made irrigation canals with the aim of determining best practices for: the method of deployment of an ADCP using a moving boat, the duration of the measurement transect per unit width of canal, and the number of transects to use in computing mean steady discharge. The purpose of these refinements is to better resolve a mean representation of the fluctuating turbulent velocity flow field by lessening user-induced uncertainty and estimating the point of diminishing returns for additional data collection. Suggested protocols developed from this experimentation indicate that a reduction of 30 to 70% in the values of uncertainty metrics can be accomplished utilizing a remotely operated tagline deployment method with a minimum transect duration relative to the canal top width of 24 s/m (7.3 s/ft), equivalent to 24 vertical pings per meter of an ADCP measuring at 1 Hz; and at least six total transects taken in reciprocal directions included in measurements of mean steady discharge. These findings provide further specificity beyond current guidelines to enhance the likelihood of practical implementation by ADCP users. Refinement of ADCP measurement protocols also serve as a chief aid in the accuracy of hydraulic structure calibration. As permanent fixtures within an open-channel, these structures rep- resent a means of obtaining continuous flow measurement without the time cost of velocity-area methods. The fundamental principle upon which hydraulic structures operate is the stage-discharge relationship. This equation relates an upstream measurement of the water surface elevation to the flow rate passing through the channel. However, the theoretical derivation of stage-discharge equations require several simplifying assumptions that must be corrected for using empirical calibration. In the present study, the nature of the stage-discharge relationship for a particular hydraulic structure known as the Obermeyer pivot weir is investigated. This device was primarily designed as a control for upstream water levels, and the current effort to establish a means by which the weir can be used for flow measurement purposes represents a novel contribution to the literature. In general, research on pivot weirs remains sparse, and no consensus has been reached concerning the correct theoretical approach for establishing the stage-discharge equation for this type of structure. Here, using a set of field observations, four alternative approaches are investigated to elucidate the optimal method for the use of pivot weirs for flow measurement. Specifically, a hypothesis concerning the effect of the changing angle of a pivot weir on the flow dynamics is tested. A recommended approach is given and informed by knowledge of practical implementation limitations. Finally, preliminary investigations using a laboratory model of the Obermeyer pivot weir are discussed, which offer insight into the complex nature of the dynamics for flow over this type of structure. The results of the present study offer important refinements to the current body of knowledge found within the literature and identify promising avenues for future research.
Open Access
Impact of geometric design of hydraulic contact tanks on residence time distributions
(Colorado State University. Libraries, 2015) Carlston, Jeremy S., author; Venayagamoorthy, S. Karan, advisor; Ramirez, Jorge A., committee member; Sakurai, Hiroshi, committee member
The research outlined in this thesis investigates how geometric design affects the mixing efficiency of contact tanks used for drinking water disinfection. In particular the configuration of baffles and inlets are assessed in depth using both physical tracer studies and computational fluid dynamics (CFD) simulations. Two rectangular contact tanks were used, both of which are assumed to be representative of disinfection tanks for small municipalities throughout the United States. System performance is analyzed by means of residence time distributions from which the baffling factor (BF) and Morrill index (MI) performance indicators can be calculated. First, a parametric study of a 300 gallon tank used for previous research was undertaken. After model validation, 30 CFD simulations were conducted in order to determine optimal baffle configuration by altering channel width, baffle length, and flow orientation. It was found that the baffle lengths should be prescribed such that their openings are roughly equal to the width of the tank's channels. In this manner excessive constrictions or expansions, which lead to undesirable flow separation, can be prevented. It was also confirmed that high length-to-width ratios in the flow lead to a better emulation of ideal plug flow by promoting advective transport of both the water and disinfectant. Second, a 1,500 gallon, two-baffled tank housed at Colorado State University's hydraulic laboratory in the Engineering Research Center was used to investigate "sharp" inlets, which lead to poor mixing conditions. Unfortunately operating budgets prohibit many small disinfection facilities from upgrading these preexisting sharp inlets. In an attempt to provide an inexpensive solution, seven attachments to the inlet were tested for potential improvements to contact tank performance. Physical tracer studies were conducted on the prototype in order to obtain RTD curves resulting from each modification. The horizontal T-shaped attachment performed best, attaining a BF of 0.59 at a flow rate of 40 gallons per minute (gpm). This is a 74% gain over the unmodified inlet's BF of 0.34. From a hydrodynamic analysis of the flow fields obtained from CFD simulations, it was concluded that any inlet configuration leading to a quicker homogenization of longitudinal velocities (especially in the first channel of the tank) and hence better approximation of plug flow will improve system performance. Finally, seven different inlet modifications to the un-baffled counterpart of the 1,500 gallon tank were investigated. Without any alterations the un-baffled sharp inlet tank provides extremely poor disinfection as evidenced by its baffling factor of 0.05. Due to good agreement between physical and numerical tests for the baffled tank, the un-baffled system was only researched with CFD. Four equally-spaced orifices deflecting flow to the back wall of the tank resulted in the largest gain in performance with an estimated BF of 0.27. A hydrodynamic analysis again confirmed that despite lower length-to-width ratios leading to a lower ceiling of mixing performance, better imitation of plug flow results in larger baffling factors and lower Morrill indices.
Open Access
Investigating overturning high sided vehicles through modeling high Reynolds number incompressible flow around a rectangular cylinder near a plane wall boundary
(Colorado State University. Libraries, 2023) Sanchez, Daniel K., author; Venayagamoorthy, S. Karan, advisor; Chen, Suren, advisor; Olsen, Daniel, committee member
Safety on public roadways is of paramount importance to road users, road authorities, the local economy, and the general wellbeing of society. High sided vehicles (commonly known as semitrucks in the United States (US) or lorries in the European Union (EU)) are used throughout the world for transporting freight, but they are susceptible to roll-over accidents due to high crosswind. The overturning of high sided vehicles is of concern during extreme wind events. In Boulder, Colorado, it is estimated that eight high wind events (with gusts greater than 75 mph) occur every year. The research field of overturning high sided vehicles is young compared to other areas of knowledge since CJ Baker of the United Kingdom (UK) opened the research field in 1986. The traditional method applied for evaluating the likelihood of a high sided vehicle to overturn is to use the predetermined rolling moment coefficient (Crolling) and translate the wind speed into a rolling moment. The resulting rolling moment can be compared to the restoring moment to determine the force required to overturn the high sided vehicle. This methodology requires that Crolling be accurate with respect to the high sided vehicle being analyzed. A recent study conglomerated many papers that have investigated Crolling, showing wide variation in the expected Crolling for yaw angles between 45° and 90° (a direct crosswind). Through this thesis, it was discovered that some of the variation is due to the fact that Crolling is Reynolds number dependent. In this thesis a comprehensive verification analysis and validation of a computational fluid dynamics (CFD) model was completed. Verification and validation are key components to performing a quality CFD analysis. When referring to verification, this traditionally implies a grid independence study to ensure the CFD results are accurate with respect to the mesh sizing. However, this study explores why a comprehensive verification study is necessary to evaluate the influence of the flow domain size for high Reynolds number incompressible flow around a bluff body. Additionally, it was found for flow around a rectangular cylinder near a plane wall boundary with a gap ratio of 0.407, that the drag coefficient (Cdrag) is dependent on Reynolds number. This fundamental field was connected to the application of overturning high sided vehicles, with the assumption that a 2D rectangular cylinder could represent the trailer section of a high sided vehicle. It was found that traditional studies on overturning high sided vehicles assume the aerodynamic coefficients are Reynolds number independent, whereas the fundamental field shows that there is a Reynolds number dependence. It is apparent that additional work on determining Crolling is needed due to the Reynolds number dependency.
Open Access
Mixing of scalars in turbulent flows using direct numerical simulations
(Colorado State University. Libraries, 2015) Nithianantham, Ajithshanthar, author; Venayagamoorthy, S. Karan, advisor; Julien, Pierre, committee member; Sakurai, Hiroshi, committee member
The research presented in this thesis focuses on scalar mixing in unstratified (neutral) flows and stably stratified flows using Direct Numerical Simulations (DNS). Such flows are ubiquitous in natural flows such as rivers, estuaries, oceans and the atmosphere. First, a detailed study was performed to investigate the effect of varying Schmidt numbers (Sc) on turbulent mixing of a passive scalar in a stationary homogeneous unstratified flow using forced DNS. A total of 6 simulations were performed for 0.1 ≤ Sc < 3. Qualitative and quantitative results of the flow field and the passive scalar fields are presented and discussed. The effect of the Schmidt number on the turbulent mixing was found to be negligible and becomes important (as it should) only when mixing occurs under laminar flow conditions. Using a model proposed by Venayagamoorthy and Stretch in 2006 for the turbulent diascalar diffusivity as a basis, a practical (and new) model for quantifying the turbulent diascalar diffusivity is proposed asKS = 1.1 γ' LT k1/2, where LT is defined as the Thorpe length scale, k is the turbulent kinetic energy and γ' is one-half of the mechanical to scalar time scale ratio, which was shown by previous researchers to be approximately 0.7. The novelty of the proposed model lies in the use of LT, which is a widely used length scale in stably stratified flows (almost exclusively used in oceanography), for quantifying turbulent mixing in unstratified flows. LT can be readily obtained in the field using a Conductivity, Temperature and Depth (CTD) profiler or obtained from density fields in a numerical model. The turbulent kinetic energy is mostly contained in the large scales of the flow field and hence can be measured in the field using devices such as an Acoustic Doppler Current Profiler (ADCP) or modeled in numerical simulations. Comparisons using DNS data show remarkably good agreement between the predicted and exact diffusivities. Finally, the suitability of the proposed model for stably stratified flows was explored for varying degrees of stratification ranging from mildly stable flow conditions to strongly stable conditions. In stably stratified flows, density variations of the fluid dynamically affect the flow field and hence the density acts as what is widely known as an active scalar. Under strongly stable conditions, the DNS results indicate an inverse relationship between the Thorpe scale LT and kinetic energy length scale Lkε, which is different to the direct (almost one to one correspondence) relationship that was found for unstratified flows. Hence, in order to account for this difference, a modified turbulent diascalar diffusivity model was proposed as Kd = 13 γ' LT3 k1/2. It must be noted that this modified model while dimensionally inconsistent (due to the inverse relationship between the length scales), provides reasonable quantitative estimates of the diffusivity under stably stratified flow conditions. The models proposed in this study require further (extensive) testing under higher Reynolds number flow conditions. If shown to be valid, they would be widely useful for quantifying turbulent mixing using field measurements of large scale quantities (i.e. LT and k) as well as a simple and improved turbulence closure scheme.
Open Access
To treat or not to treat: the evolution of wastewater treatment management approaches
(Colorado State University. Libraries, 2018) Turner, Sydney S., author; Venayagamoorthy, S. Karan, advisor; Grigg, Neil, committee member; Kent, Suzanne, committee member
The research presented in this thesis focuses on wastewater management practices to further the understanding of the evolution of wastewater treatment approaches. Within this thesis, wastewater treatment technologies and processes are categorized into four groups: dilution dependent, conventional, alternative, and emerging. The evolution of wastewater treatment technologies is initiated with initial investment by a society to self-organize; transformed when there are alterations in the way the society lives, primarily considering the urbanization and industrialization of societies; and satisfied when the society has incorporated sustainable practices that can ensure water security for future generations. The motivation of this research is to interpret how the concept of conventional wastewater treatment can be driven to encompass more sustainable approaches in both the developed and developing world. In order to facilitate understanding of this, we aim to address the following: what wastewater technologies are available and how practical are they?, what are some significant drivers that have driven the evolution of wastewater treatment up till now?, how do institutional arrangements affect implementation of technologies?, and how does public perception play a role in the adoption or repudiation of wastewater treatment technologies? To investigate these questions, South Africa and the United States were used as primary case studies. There is an abundance of technologies used in the field of wastewater treatment; however, the resources (natural, financial, and technical) of a society will determine the practicality of implementing certain technologies. The major drivers that lead to the transformation of treatment technologies include the following: population growth and urbanization, public health initiatives, actions to prevent the degradation of the natural environment, capacity building within institutional arrangements such as societal organization and regulation, concerns of climate change, objectives to minimize conflict, the demand on water from energy and food sectors, and social perception of science. In the United States, "conventional" technologies have been pushed to encompass secondary treatment standards for point source wastewater through policy measures. South Africa, due to its historical Apartheid era, has an additional layer of water management methods that pertains to the access to sanitation services as a human right. In both countries, development of industry has been clashing with preserving the environment and protecting public health. Sustainable, emerging technologies are trying to harmonize economic growth and environmental conservation by treating wastewater as a feed of resources to be recovered. In the exploratory Wastewater Treatment Survey presented in this thesis, responses from 655 U.S. participants were analyzed to demonstrate the effectiveness of surveys to produce social perception data for water managers. From the survey, it was observed that over 35% of U.S. participants were not at all likely or not so likely able to explain what happens to their wastewater. Even within the STEM field respondents, 30% were unsure what happens to their wastewater. This exemplifies a wide gap in the link between humans and their waste disposal. Of the 655 U.S. respondents, over 90% were moderately to extremely concerned about water pollution. A higher level of concern for wastewater pollution was also correlated with people who believed they had a better understanding of wastewater treatment. Those who were more concerned about water pollution were also more likely to get involved in water resources management activities. The respondents chose protecting public health and the integrity of the environment as the two main reasons why wastewater treatment is necessary. Of the U.S. respondents, around three-quarters of the participants believe that no longer can dilution be treated as the solution to pollution with the majority of the other participants believing that it may only be conditionally sufficient. Many alternative and emerging technologies are being heavily scrutinized by the public. Public buy-in is necessary to transform the wastewater field and will only be accomplished when societal perception and wastewater treatment technologies are linked. From the survey data, almost 60% of the U.S. participants were willing to increase a utility bill by at least 3 additional USD to pay for improvements in their wastewater treatment plant's treatment capabilities whereas only 46% were willing to pay at least 3 additional USD for improvements in their wastewater treatment plant's energy efficiency. In the real world, these improvements for a treatment plant may not be mutually exclusive; however, this type of information may help a water manager build public buy-in for the project. Only 14.35% of U.S. respondents were completely willing to drink direct potable reuse water, with an additional 22.29% very willing to drink it.
Open Access
Towards improved understanding and optimization of the internal hydraulics of chlorine contact tanks
(Colorado State University. Libraries, 2012) Taylor, Zachary H., author; Venayagamoorthy, S. Karan, advisor; Bledsoe, Brian, committee member; Wohl, Ellen, committee member
The research presented in this thesis focuses on utilizing computational fluid dynamics (CFD) to further the understanding of the internal flow dynamics in chlorine contact tanks. In particular, we aim to address the following two critical questions: (1) for a given footprint of a serpentine chlorine contact tank with a fixed inlet configuration, how does the hydraulic efficiency of the tank depend on the configuration of internal baffles?, and (2) for water storage tanks modified for use as chlorine contact tanks, can inlet conditions be modified such that near plug flow conditions are induced close to the inlet and throughout the rest of the tank? Key design parameters were identified and parametrically tested for each of these design problems. For the serpentine baffle tanks, a benchmark contact tank geometry based on a scaled model of the Embsay chlorine contact tank in Yorkshire, England was used for validation and then subsequently modified by varying both the number and length of baffles. In order to define guidelines for hydraulically efficient baffle tanks, a parametric study consisting of forty high-resolution 3-D simulations of different tank configurations were performed to quantify the efficiency of the scaled contact tank as a function of the dimensional relationships between the inlet width, channel width, tank width, tank length, and baffle opening lengths. The simulations tested the hydraulic efficiencies of the different tank configurations. Hydraulic efficiency was quantified by the baffle factor (BF). We found that the most efficient tank had a BF of 0.71, and that hydraulic efficiency was optimized in this tank by maximizing the length to width ratio in baffle chambers and by minimizing flow separation through the tank, which was achieved by setting equal dimensions to the inlet width, channel width, and baffle opening length. A new contact tank geometry was then developed by applying the dimensional relationships that were shown by the parametric study to optimize BF, and by modifying the baffle geometries to minimize flow separation around baffle tips. The new contact tank design had a BF of 0.78, which represents a 10 percent improvement in hydraulic efficiency compared to the Embsay contact tank. In the study of inlet modifications for cylindrical storage tanks, inlet diffusers and inlet manifolds were developed and modeled. Experimental flow through curves (FTCs) of a benchmark storage tank used as a contact tank were used to validate the CFD model that was utilized in the study. Thirty-seven modified inlet configurations using two representative flow rates were modeled. The inlet manifolds improved BF significantly, whereas the inlet diffuser had insignificant effects. The key design parameters identified for the inlet manifold were the number of inlets and the height of the inlet(s) in the tank. The inlet manifold designed with 16 inlets with the inlet height set at 10 percent of the tank height improved the BF of the storage tank from 0.16 to 0.51. This 220 percent increase in BF represents a major improvement in hydraulic efficiency for such cylindrical contact tanks that are widely used by small water treatment systems.
Open Access
Use of innovative techniques to optimize the residence time distribution of drinking water contact tanks
(Colorado State University. Libraries, 2014) Kattnig, Justin J., author; Venayagamoorthy, S. Karan, advisor; Gates, Timothy K., committee member; Sakurai, Hiroshi, committee member
The focus of this study is to understand the complex nature of flow dynamics within water disinfection contact tanks and to use this understanding in the development of beneficial tank modifications. In particular this study focuses on systems classified as small by the United States Environmental Protection Agency (USEPA). Methods involved in this process included the use of computational fluid dynamics (CFD), physical tracer studies, and acoustic doppler velocimetry (ADV). Attempted tank alterations included the installation of baffles, inlet modification, and the use of industrial packing material. Tested modifications aimed at altering existing velocity fields in order to increase the hydraulic disinfection efficiency of a given system. Hydraulic disinfection efficiency was measured through the use of residence time distribution (RTD) curves and the well-known baffling factor (BF) (as defined by the USEPA). The principal system that was investigated was a 1500 gallon rectangular concrete tank with a sharp circular inlet. A physical prototype of this system currently resides at Colorado State University's (CSU) Engineering Research Center (ERC) and was used for all physical testing. CFD models were used to compute the average velocity fields within the tank and to produce modeled RTD curves. This was done for the empty tank and for 37 different baffled configurations. Baffles were placed parallel to the longest axis of the tank and varied in number and length. Optimal configurations yielded baffling factors between 0.70 and 0.8, which is more than thirteen times as efficient as the original system. Several configurations were selected and physically constructed in the existing tank in order to validate the applied numerical methodology. After CFD models were experimentally validated, random packing material was placed within the tank at areas of high velocity and flow separation (at the inlet and at baffle turns). An extensive parametric study was conducted in order to determine the effects of using packing material as an inlet modifier within the open tank. Packing material was placed in box-like structures and fastened over the inlet. Dimensions of these packing boxes were systematically varied and tested at different flow rates. Observed baffling factors were as high as 0.36, which represents an improvement over the basic system by a factor of six. Resulting findings from the inlet modification study were then used to design and test internal modifications for a baffled system. In addition to material being placed over the inlet, structures were placed over channel openings at baffle turns. Configurations were tested at a number of flow rates in order to determine relative effects on gains in efficiency. The most effective system obtained a baffling factor of 0.72, representing an increase from the base system by a factor of 13. ADV measurements were conducted within the baffled system in order to assess changes in the velocity field and explain observed increases in baffling factor. Packing material was not modeled due to complexity and high computational cost. Results from this study show that the innovative use of industrial packing material and other modifications can significantly increase the hydraulic disinfection efficiency of simple systems. It also shows that the use of CFD is an invaluable guide in this endeavor. The work summarized in this thesis aids in an ongoing effort to understand the hydraulic characteristics of small scale drinking water systems. The findings summarized here will help to shape the designs of the future.