Civil and Environmental Engineering

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Deep Learning-Based Probabilistic Hierarchical Reconciliation for Hydrological and Water Resources Forecasting
(University of Waterloo, 2024-09-10) Jahangir, Mohammad Sina
Accurate, probabilistic, and consistent forecasts at different timescales (e.g., daily, weekly, monthly) are important for effective water resources management. Considering the different timescales together as a hierarchical structure, there is no guarantee that when forecast models are developed independently for each timescale in the hierarchy, they will result in consistent forecasts. For example, there is no guarantee that one-seven day(s) ahead forecasts from one model will sum to a weekly forecast from another model. Significant efforts have been made in the time-series forecasting community over the last two decades to solve this problem, resulting in the development of temporal hierarchical reconciliation (THR) methods. Until recently, THR methods had yet to be explored for hydrological and water resources forecasting. The main goal of this research is to introduce THR to the field of hydrological and water resources forecasting and to merge it with the latest advancements in deep learning (DL) to provide researchers and practitioners with a state-of-the-art model that can be used to produce accurate, probabilistic, and consistent multi-timescale forecasts. To achieve this goal, this research follows three interconnected objectives, each including a main contribution to the field of DL-based hydrological forecasting. In the first main contribution of this research, the potential of THR to produce accurate and consistent hydrological forecasts was verified for the first time in hydrology through a large-scale precipitation forecasting experiment using 84 catchments across Canada. Three THR methods were coupled with three popular time-series forecasting models (exponential time-series smoothing, artificial neural network, and seasonal auto-regressive integrated moving average) for annual precipitation forecasting at monthly (12-steps ahead), bi-monthly (6-steps ahead), quarterly (4-steps ahead), 4-monthly (3-steps ahead), semi-annual (2-steps ahead), and annual (1-step ahead) timescales. It was confirmed that not only does utilizing THR guarantee forecast consistency across all timescales, but it can also improve forecast accuracy. DL models are increasingly being used for hydrological modeling, particularly for lumped simulation, due to their ability to capture complex non-linear relationships within hydrological data as well as their efficiency in deployment. Likewise, the application of DL for hydrological forecasting has gained momentum recently. DL models can extract complex patterns from meteorological forcing data (e.g., precipitation) to forecast future streamflow, often leading to forecasts that are more accurate than current conceptual models. However, due to uncertainty in the phenomena affecting hydrological processes, it is necessary to develop accurate probabilistic forecast models to provide insights for informed water management decisions. In the second main contribution of this research, two novel state-of-art sequence-to-sequence probabilistic DL (PDL) models were developed, tested, and applied for short-term (one-seven day(s) ahead) streamflow forecasting in over 75 catchments with varied hydrometeorological properties across both the continental United States (CONUS) and Canada. The two designed models, namely quantile-based encoder-decoder and conditional variational auto-encoder (CVAE) showed superior performance compared to the benchmark long-short-term memory (LSTM) network considering forecast accuracy and reliability. Specifically, CVAE, a generative DL model that can estimate magnitudes of different sources of uncertainty (e.g., aleatoric, epistemic), proved to be effective in producing reliable forecasts for longer forecast lead times (three-seven days ahead). Given the introduction of THR to the field of hydrological forecasting through the first main contribution, there is no guidance on how to couple THR with the latest advancements in DL, especially PDL, to produce accurate, and consistent probabilistic hydrological forecasts. Furthermore, existing methods for combining THR with DL models, particularly PDL models, suffer from several limitations. Firstly, almost all approaches treat THR as a post-processing step. Secondly, existing THR methods often lack adaptability, meaning they are unable to adjust properly to changing data distributions or new information. Finally, there is limited research on implementing probabilistic THR, a crucial aspect for making probabilistic forecasts consistent. As the third main contribution, a hierarchical DL model (HDL) was introduced where THR was integrated directly into the DL model. Specifically, a custom THR layer was developed that can be combined with any DL model, much like a LSTM layer or a linear layer, to produce the proposed HDL. This integrated approach (via the new THR layer) allows any DL model to leverage temporal information across multiple timescales during training, perform probabilistic THR, and be efficient for real-time application. Furthermore, the proposed HDL is based on auto-regressive normalizing flows, a state-of-the-art generative DL model that is more flexible than CVAE in that it can non-parametrically estimate the probability distribution of the target variable (e.g., streamflow). HDL was tested on more than 400 catchments across CONUS for weekly streamflow forecasting at daily (seven-steps ahead) and weekly (one-step ahead) timescales. The performance of HDL was benchmarked against LSTM variants. HDL produced forecasts that had substantially higher accuracy than the LSTM variants and simultaneously generated consistent forecasts at both daily and weekly timescales, without the need for post-processing (as in the vast majority of THR methods). The implementation of THR as a neural network layer allows it to be seamlessly combined with other DL layers. For example, the new THR layer can be coupled with physics-based differentiable routing layers for multi-timescale distributed hydrological forecasting. It is expected that HDL will serve as a benchmark upon which future THR methods will be compared for streamflow forecasting. Furthermore, given the generality of the approach, HDL can be used for forecasting other important variables within hydrology (e.g., soil moisture) and water resources (e.g., urban water demand), as well as other disciplines, such as renewable energy (e.g., solar power).
Fatigue and Fracture Behaviour of Steel Wire-Arc Additively Manufactured Structural Materials
(University of Waterloo, 2024-09-04) Lee, Jun Seo
There is an increasing demand for automation that has influenced many industries to find ways to integrate it into their markets. Within the civil sector, the integration of automation into the various stages of a project unlocks new opportunities that were previously difficult to achieve. If the desires of the architects appeared unachievable due to high planning and manufacturing costs, this can now be resolved with the addition of automation and robotics embedded in the early stages of project development. The wire arc additive manufacturing (WAAM) process is an additive manufacturing (AM) process that allows efficient fabrication of structural elements. This process, also referred to as gas-metal arc additive manufacturing (GMAAM), uses directed energy deposition (DED) to create components. Specific to the WAAM process, a metal wire is fed into an electric arc, and then welded into a designed shape. For structural steel fabricators, this automated technology could allow for the reduction of supply chains, part inventories, and scrap waste, and will help improve the digitalization of the fabrication process. Moreover, the WAAM process allows the fabrication of customized connection nodes and unique structural shapes that are difficult to achieve with conventional subtractive manufacturing. Despite the many potential advantages of the WAAM process, research is needed for WAAM structural steel to be used in the civil engineering sector. Mechanical properties such as the elastic modulus, yield strength (YS), and the ultimate tensile strength (UTS) of WAAM material should be tested and validated. In addition, WAAM steel can have a very rough and wavy surface due to the additive manufacturing process. The rough surface can cause stress concentration zones within the material that may affect its fatigue performance. Although this can be mitigated by post-processing steps such as surface milling, it is important to study its properties in its as-built state as milling is an additional fabrication step, which takes time and cost and may not be necessary for some projects and applications. This thesis aims to explore the material properties, fracture toughness, and fatigue behaviour of WAAM steel components. Through experimental testing, mechanical properties such as the elastic modulus, yield strength, and ultimate tensile strength are determined. Further test results include Charpy v-notch impact tests to determine fracture toughness, as well as tests to determine crack propagation properties. Lastly, the experimental program included testing the fatigue behaviour of WAAM steel for both the smooth and rough (as-fabricated) specimens. The experimental program also examined the effects of weld direction by including tests on specimens oriented both perpendicular and parallel to the weld. The fatigue data collected from the experimental program was used to plot a stress-life (S-N) curve for WAAM steel. The data was then statistically analyzed and compared to current codes such as CSA S6 and S16. It was found that the fatigue behaviour of the WAAM steel was dependent on the weld direction. The specimens oriented parallel to the weld showed behaviour similar to CSA Detail Category B. Specimens oriented perpendicular to the weld showed behaviour similar to CSA Detail Category E. A metallurgical study of the WAAM steel showed that its microstructure showed resemblance to welded steel components. Looking at the microstructure, the grain sizes and boundaries indicated differences in the as-deposited zones and the reheated zones. The reheated zones, where the addition of new layers disturbed the microstructure, consisted of finer grains expected to exhibit greater toughness. Lastly, a linear elastic fracture mechanics (LEFM) model was used to predict the fatigue lives of the WAAM steel fatigue specimens in the perpendicular- and parallel-to-weld orientations. The model was able to predict the fatigue behaviour of the WAAM steel specimens, but the results were greatly dependent on the assumed surface stress concentration factors, Kt. More research is needed to obtain Kt values that will enable greater accuracy in determining the fatigue behaviour of WAAM steel.
Development of Improved Methods to Establish Toughness Requirements for North American Steel Highway Bridges
(University of Waterloo, 2024-09-04) Chien, Michelle
Brittle fracture is a major concern to structural engineers as it can have significant consequences in terms of safety and cost. Although modern day occurrences are rare, it is well known that they can occur without warning and may lead to the sudden closure of a bridge, loss of service, expensive repairs, and/or loss of property or life. In Canada, steel bridge fracture is a more significant concern due to the harsh climate present through much of the country, which, if the toughness properties are improperly specified, is sufficient to put many steels on the lower shelf of the toughness-temperature curve. The provisions for avoidance of brittle fracture in various bridge design codes vary in complexity. The existing Canadian CSA standards take a fairly simplistic approach for design against brittle fracture, using design tables that have two temperature zones. Depending on the minimum mean daily temperature of the location of interest, one can determine the Charpy V-Notch testing requirements for the grade of steel. However, it is known that temperature is not the only factor that plays a role in the fracture behaviour of steels. Other factors influencing fracture, such as plate thickness, crack size, demand-to-capacity ratio, and considerations related to traffic, are currently neglected. It is generally known, for example, that thin plates (e.g., less than 12.5-19.0 mm in bridge applications) are less susceptible to brittle fracture, due to the rolling reduction ratio at the mill. However, for the same steel grade (with a small distinction between base and weld metal), the same CVN requirements are applicable to a wide range of plate thicknesses (i.e., from the minimum allowed for corrosion considerations up to 100 mm). The existing CSA standards also assign responsibility for identifying fracture-critical members (FCMs) to the design engineer, though regulations on how to identify them are limited and vague, leaving much to engineering judgement. A comparison of brittle fracture design provisions around the world reveals that more sophisticated approaches have been developed in terms of modelling and understanding brittle fracture in existing and new bridges than the ones currently in use in North America. One of these more involved methods is the fracture mechanics method in the European EN 1993-1-10 standard, which allows factors such as plate thickness, crack size, and strain rate to be considered. This standard also gives designers the option of using a simplified method or a much more involved, fracture mechanics-based approach. While the current Canadian brittle fracture provisions generally appear to be meeting the needs of the code users, two issues are noteworthy. The first, which has already been alluded to, is that the North American provisions offer less flexibility and guidance for handling unusual situations than the Eurocode methods. The ‘one size fits all’ approach in the Canadian design standards may not be optimal and may result in structures being overdesigned or under-designed, leading to inefficiencies in safety and cost. This highlights the need for answering questions regarding the feasibility of allowing reduced toughness requirements for bridges fabricated with thinner plates or experiencing lower traffic volumes or demand-to-capacity ratios. The second issue is that few studies can be found in the literature around the world attempting to assess the level of reliability against brittle fracture provided by any of the existing design provisions. The lack of a probabilistic assessment of brittle fracture risk in Canada and the few studies globally highlights a gap in the current understanding and implementation of these design standards. This thesis includes a literature review on: 1) factors affecting material toughness, 2) common methods of evaluating toughness, 3) North American and European brittle fracture provisions, and 4) previous work on design code calibration and reliability analysis for steel structures subject to various failure modes, including brittle fracture. A comparison of the North American and European design provisions using the example of a typical steel-concrete composite highway bridge is then presented. For this case study, it was found that North American codes are typically more conservative than the Eurocode for bridge elements made with thinner plates and less conservative for elements made with thicker plates. Following this, the fracture mechanics-based European brittle fracture limit state is then evaluated in a probabilistic framework using Monte Carlo Simulation (MCS). In order to do this, statistical distributions are established for the various input parameters, and – in particular – statistical models for the live traffic load and temperature are established. Prior to application of the model, a calibration step is performed to establish a design crack depth. Sensitivity studies are then performed where key input parameters are varied to examine how the failure probability is affected by variations in each parameter. The work is then cast in a time-dependent reliability framework, using historical temperature and traffic data, to determine the failure probability with temperature and traffic loading fluctuating on a time scale throughout the year. This time-dependent model is then used to assess the reliability level provided by the current Canadian brittle fracture provisions. Given certain plate thickness, crack size, load levels and geographical temperature data, the annual probability of failure and annual reliability index, β, are obtained. The obtained reliability indices are compared with a target reliability index to assess the extent to which the Canadian provisions provide consistent and adequate levels of reliability against brittle fracture. On the basis of the results, the North American brittle fracture design provisions are critically assessed, and new design tools from these probabilistic studies are presented. Opportunities for improvement in the existing Canadian standards and areas warranting further study are lastly highlighted.
Costs and Benefits of Building Airtightness Improvements for Air Pollution Exposure and Human Health
(University of Waterloo, 2024-08-29) Salehi, Amir Reza
Air pollution is the largest global environmental health threat; fine particulate matter (PM₂.₅) alone, as the most harmful air pollutant, is associated with millions of premature deaths each year. Most studies focus on the impacts of changes in outdoor air PM₂.₅ on human health. This overlooks the fact that most exposure to PM₂.₅ of outdoor-origin occurs indoors, as people tend to spend most of their time indoors, and that the pollution infiltrates the building envelope. Specifically, Americans spend almost 70% of their time in their homes, and approximately 50% of outdoor-origin PM₂.₅ health burdens are due to residential exposure. To better understand the effect of this infiltration on human health, and to explore opportunities for improvement, this study examines the health impact of enhancing building airtightness, particularly in single-family homes where approximately 75% of the U.S. population resides. This thesis conducts a historical study on modeled daily average PM₂.₅ levels between the years 1980 to 2010 in the United States to examine the national and spatial costs and benefits associated with improving the airtightness of these homes to mitigate the health effects of air pollution. To achieve this, an integrated modeling framework was developed, which incorporates mass balance modeling, health impact modeling, and economic modeling. This framework was used to establish baseline and alternative levels of exposure to outdoor-origin PM₂.₅ across the historic building stock in the contiguous United States under the current state and post-intervention state. Subsequently, it evaluates the health benefits and retrofit costs associated with improving airtightness levels. The primary scenarios evaluated involve enhancing building air sealing to meet the standards mandated by the International Energy Conservation Code (IECC) 2018. Additionally, secondary scenarios of 20%, 25%, 40%, and 60% air leakage reductions were also considered. This study analyzes the benefits of improving three distinct building age groups. The results reveal that enhancing the airtightness of single-family homes up to IECC 2018 mandates results in interventions costing approximately $105 ($102, $107) billion nationally. However, they could save about 44,611 (29,831, 58,905) lives annually and deliver annual health benefits valued up to $356 ($45, $1,173) billion in 2020 USD. The result is an annual net benefit of approximately $251 (-$62, $1,067) billion in 2020 USD, in the intervention year. This study also indicates that older homes, particularly those constructed before 1940, exhibit the greatest reductions in indoor PM₂.₅ levels from outdoor sources. These homes demonstrate a potential annual benefit of $55 ($7, $193) billion in 2020 USD and 7,104 (4,655, 9,832) lives saved, translating to about $3,066 ($390, $10,759) in 2020 USD in benefits per resident annually. On a per-house basis, the cost of improvements in these older homes averages $1,686 ($1,616, $1,756) in 2020 USD, while the net benefit per resident can reach up to $2,263 (-$442, $9,825) in 2020 USD in the year of intervention. Significant spatial variability in benefits exists, with the greatest impacts observed in the eastern U.S. due to higher regional pollution levels and leakier homes. Further, there is uncertainty associated with model parameters, particularly associated with the health response to exposure. Despite these uncertainties, most interventions studied show large mean net benefits. These findings strongly support that targeted enhancement of building airtightness substantially impacts public health and should be considered by decision-makers when designing building standards or developing retrofit plans.
An Investigation of Factors Affecting the Adsorption of Per- and Polyfluoroalkyl Substances (PFAS) on Colloidal Activated Carbon (CAC): Implications for In-situ Immobilization of PFAS
(University of Waterloo, 2024-08-28) Gilak Hakimabadi, Seyfollah
The immobilization of per- and polyfluoroalkyl substances (PFAS) by colloidal activated carbon (CAC) barriers has been proposed as a potential in-situ method to mitigate the transport of plumes of PFAS in the subsurface. However, if PFAS are continuously released from a source zone, adsorptive sites on CAC will eventually become saturated, upon which point breakthrough of PFAS from a barrier will occur. To predict the long-term effectiveness of CAC barriers, it is important to investigate the factors that may affect the adsorption of PFAS on CAC. The objective of this research is to investigate some of these factors by answering the following questions: (1) How do co-contaminants, aquifer materials, and typical groundwater constituents affect the adsorption of PFAS by CAC?; and (2) How does reducing the particle size of activated carbons (ACs) affect their physico-chemical properties and ability to adsorb PFAS? To address the first research question, the adsorption of seven anionic PFAS on a polymer-stabilized CAC (i.e., PlumeStop®) and a polymer-free CAC was investigated using batch experiments (Chapter 3). The research employed synthetic solutions consisting of one PFAS, 1 mM of sodium bicarbonate (NaHCO3), and inorganic and organic solutes, including Na+, Cl-, Ca2+, dissolved organic carbon (DOC), diethylene glycol butyl ether (DGBE), trichloroethylene (TCE), benzene, 1,4-dioxane, and ethanol. It was observed that the affinity of PFAS to CACs was in the following order: PFOS > 6:2 FTS > PFHxS > PFOA > PFBS > PFPeA > PFBA. This result indicates that hydrophobic interaction was the predominant adsorption mechanism and that hydrophilic compounds such as PFBA and PFPeA will breakthrough CAC barriers first. The partition coefficient Kd for the adsorption of PFAS on the polymer-stabilized CAC was 1.3–3.5 times smaller than the Kd for the adsorption of PFAS on the polymer-free CAC, suggesting that the polymers decreased the adsorption, presumably due to competition. Thus, the PFAS adsorption capacity of PlumeStop CAC barriers could increase once the polymers are biodegraded and/or desorbed. The affinity of PFOS and PFOA to CAC increased when the ionic strength of the solution increased from 1 to 100 mM, or when the concentration of Ca2+ increased from 0 to 2 mM. In contrast, less mass of PFOS and PFOA was adsorbed in the presence of 1–20 mgC/L Suwannee River fulvic acid, which represented dissolved organic carbon, or in the presence of 10–100 mg/L diethylene glycol butyl ether (DGBE), which is a major component in some aqueous film-forming foam (AFFF) formulations. Therefore, information on the occurrence of DGBE and other glycol ethers in AFFF-impacted groundwater is needed to assess if the effect of these species on CAC barrier performance is appreciable. The presence of 0.5–4.8 mg/L benzene or 0.5–8 mg/L TCE, the co-contaminants that may comingle with PFAS at AFFF-impacted sites, diminished PFOS adsorption but had no effect or slightly enhanced PFOA adsorption. When the initial concentration of TCE was 8 mg/L, the Kd (514 ± 240 L/g) for the adsorption of PFOS was approximately 20 times lower than that in the TCE-free system (Kd = 9,579 ± 829 L/g). Therefore, the effect of TCE and benzene may depend on the type of PFAS. To gain insight into the effect of aquifer materials and water chemistry, the adsorption of PFOS, PFOA, and PFBS on CAC was investigated in the presence of six aquifer materials. Further, the removal of five PFAS (PFOS, PFOA, PFHxA, PFHxS, and 6:2 FTS) from six actual groundwater samples was studied (Chapter 4). Under the experimental conditions employed, the mass of PFBS, PFOA, and PFOS removed from the solution in the presence of CAC and aquifer materials was 2 to 4 orders of magnitude greater than the mass removed when only aquifer materials were present. It was also observed that the presence of aquifer materials did not appreciably affect the adsorption of PFBS, PFOA, and PFOS on CAC. In the experiments with six actual groundwater samples, the affinity of the studied PFAS to CAC was in the following order: PFOS > 6:2 FTS > PFOA ~ PFHxS > PFHxA, except for two instances of 6:2 FTS being the compound removed to the greatest extent. The adsorption affinity trend among the studied PFAS is consistent with the adsorption being driven by the hydrophobic effect. Principal component analyses (PCA) of the results obtained from the experiments with aquifer materials demonstrated that the correlation between the partition coefficient Kd for each PFAS and Ca2+ and DOC was the opposite of the correlations observed in Chapter 3. In the groundwater experiments, the correlation between Kd for each PFAS and ionic strength and Ca2+ was also the opposite of the correlations observed in Chapter 3. These opposite effects were hypothesized to be due to a complex interplay among various parameters affecting the adsorption of PFAS on CAC, which may confound the effect of each parameter. The results of this study indicate that laboratory experiments designed to evaluate the retention of PFAS in a CAC barrier should employ site-specific groundwater and aquifer materials. To address the second research question, four commercial ACs (three granular and one powdered) were pulverized by grinding and micromilling to create powdered activated carbons (PACs) and CACs, and the adsorption of PFBS, PFOA, and PFOS on these adsorbents (11 in total) was investigated (Chapter 5). All three PFAS were adsorbed less by CACs (d50 = 1.2–2.5 m) than by their parents PACs (d50 = 12–107 m). A detailed characterization of the properties (surface area, micropore, and mesopore volumes, pHpzc, and surface elemental composition) of these adsorbents suggests that the reduced adsorption capacity of CACs was likely the result of AC oxidation during milling, which decreased surface hydrophobicity. Granular activated carbons (GACs, 425–1,700 m) adsorbed PFAS less than PACs and CACs, partly due to the slow rate of adsorption. Of all ACs, the materials made from wood possessed the greatest surface area and porosity but adsorbed PFAS the least. The repulsion between the negatively charged surface of these wood-based ACs (pHpzc = 5.1) and the negatively charged headgroup of PFBS, PFOA, and PFOS molecules was identified to be the dominant factor that inhibited adsorption. The results of this study suggest that the adsorption kinetic advantage of CACs may be achieved at the expense of reduced adsorption affinity and that the role of electrostatic interaction between PFAS and AC should be considered when selecting AC for PFAS treatment applications.
Self-prestressing Iron-based Shape Memory Alloy (Fe-SMA) Epoxy Composite for Active Reinforced Concrete Shear Strengthening
(University of Waterloo, 2024-08-23) Pinargote Torres, Johanna
In Canada, the rapid deterioration of aging reinforced concrete (RC) structures has become a continuing issue, with more than 40% of bridges being older than 40 years old and 38% being in poor and fair condition, necessitating billions for rehabilitation (Cusson & Isgor, 2004; Lafleur, 2023). The loss of the strength and stiffness in RC bridge structures can be attributed to age and exposure, and it has been exacerbated with the increase of freight weight, traffic, extreme freezing/thawing cycles, and climate change. A concerning RC failure mode is shear due to its brittle and abrupt nature. Hence, various shear-strengthening mechanisms have been developed. Most of these mechanisms involve fiberreinforced polymers (FRP) and are passive, acting after the structure experiences damage. Active (prestressing) mechanisms have gained notoriety due to their ability to act immediately after application, reducing crack widths and propagation. However, implementing shear prestressing is complex, often requiring expensive and impractical large jacking equipment. Smart materials such as iron-based shape memory alloys (Fe-SMAs) have the potential to be implemented in cost-efficient and simple shear strengthening and retrofitting techniques. Fe-SMAs present a thermomechanical property known as shape memory effect (SME) that allows the material to return to its undeformed shape after reaching an activation temperature, which can be done with resistive heating. If the material is restrained, the Fe-SMA has the capacity to self-prestress an element without the need of jacking tools. This project presents an experimental study on the shear strengthening feasibility and capacity of a near-surface bonded (NSB) active Fe-SMA epoxy composite. The composite consists of u-bent strips embedded into grooves filled with epoxy. After the epoxy cures, the Fe-SMA strips are heated to at least 180oC with an electric current to self-prestress the concrete. Three shear-critical RC beams were cast, with one beam being used as control, and the other two beams being shear strengthened. Two FeSMA ratios were assessed 0.05% and 0.1%. The strengthened beams exhibit about a 27% increase in strength, and the reduction of crack widths and stirrup stresses. The NSB Fe-SMA strips interrupt the formation and widening of diagonal cracks; however, increasing their ratio may not mean an increase in shear strength. A dense NSB Fe-SMA - concrete interface weakens the stirrup plane, creating horizontal cracks running along the top face of the beam (ends of the Fe-SMA u-wrapped strips) in the compression region and causing the separation of the side concrete cover. Additional insights on the active shear strengthening have been provided with two FEA parametric studies using Vector2 by evaluating prestress level and Fe-SMA ratio. This project assesses the shear strengthening effect of near-surface bonded (NSB) active Fe-SMA epoxy composites on the load-displacement response, crack widths, and reinforcement stresses on shear-critical RC specimens.
Investigation of the Interrelationships between Orthophosphate Corrosion Inhibitors, Monochloramine Residual, Biofilm Development, and Nitrification in Chloraminated Drinking Water Distribution Systems
(University of Waterloo, 2024-08-21) Badawy, Mahmoud
Lead contamination in drinking water distribution systems (DWDS) due to pipe corrosion is a human health concern. Orthophosphate, used to control corrosion, creates passive films to eliminate lead release. At the same time, it may enhance biofilm growth, monochloramine decay, and nitrification potential since phosphorus is an essential nutrient for microorganisms. However, there is limited and contradictory information on these effects in the previous studies, which may be attributed to variations in nutrient limitations in the water used across these studies. Specifically, the addition of phosphate may enhance microbiological growth in phosphorus-limited water. However, most previous studies did not examine phosphorus limitations in the water employed in their experiments. Biofilm growth and monochloramine breakdown have not been tracked concurrently in most of the previous studies. This could be the key to understanding how orthophosphate affects monochloramine decay. Furthermore, there is a lack of research on the effect of phosphate on nitrification in real-world DWDS; hence, more research needs to be conducted. The main goal of this thesis was to investigate the effect of orthophosphate on biofilm development by assessing microbiological growth, biofilm formation potential, and metabolic activity, in addition to monitoring the effects of orthophosphate on monochloramine decay and nitrogenous compounds. These parameters were monitored simultaneously in both the presence and absence of orthophosphate to facilitate a more comprehensive understanding of its effects. This objective was achieved primarily through experiments with bench-scale flow through model distribution systems (MDS) and additional laboratory batch tests using treated water from a Great Lakes utility. In the first phase of this study, initial batch tests indicated that the test water used throughout the thesis is phosphorus-limited. Subsequently, in a 3-month experiment with 4 MDS fed with chloraminated water (2 mg Cl2/L) and orthophosphate doses of 0 to 4 mg PO43-/L, it was found that increasing the dose of orthophosphate enhanced the biofilm growth and monochloramine decay (measured as total chlorine) in the MDS, with the highest increases between 1 and 2 mg PO43-/L. A positive relationship between biofilm microbiological growth and the total chlorine decay coefficients indicates that the higher monochloramine decay due to orthophosphate addition are attributed to increased microbial activity. In the second phase, the impacts of monochloramine doses of 2 and 3 mg Cl2/L were explored with and without 2 mg PO43-/L of orthophosphate over 108 days. The presence of orthophosphate enhanced both the growth and development of the biofilm and the rates of monochloramine degradation, as observed in the first phase. Increasing the monochloramine dose from 2 to 3 mg Cl2/L slightly reduced microbiological growth and noticeably decreased first-order monochloramine coefficients (measured as total chlorine). Despite this reduction, free ammonia levels increased with the higher monochloramine dose due to a greater total ammonia presence. A strong correlation was also noted between total chlorine decay coefficients and biofilm microbiological parameters. Additionally, orthophosphate increased the genetic diversity within biofilm communities, whereas increasing the monochloramine dose resulted in a noticeable reduction in genetic diversity. In the third phase, the effect of residence time (6 days and 12 days) on monochloramine decay in the presence and absence of orthophosphate (2 mg PO43-/L) was studied using two MDSs. It was found that the longer residence time of 12 days led to higher microbial activity, monochloramine decay coefficients (measured as total chlorine), and nitrite formation compared to the shorter residence time of 6 days. Additionally, orthophosphate enhanced microbiological growth, monochloramine decomposition, and nitrite formation at the 12-day site, whereas its impact was less pronounced and became only evident after day 62 at the 6-day site. First-order total chlorine decay coefficients and nitrite concentration remained stable throughout the experiment in both MDSs at the 6-day residence time. However, at the 12-day residence time, monochloramine decay progressively increased over time, accompanied by a rise in nitrite formation by the end of the experiment. The links between monochloramine decay and biofilm microbiological parameters were also noted. These correlations suggest that the increase in monochloramine decomposition, which may have resulted from increased residence time and/or the addition of orthophosphate, was largely driven by microbiological growth and activity. In the fourth phase, the results from previous phases were evaluated on another phosphorus-limited water source with different water chemistry. A selected water source from batch-testing of different water sources and reference water from earlier phases were chloraminated at 2 mg Cl2/L and tested in four MDSs, two fed with the reference water (one control and one with 2 mg PO43-/L) and two fed with the selected water source (one control and one with 2 mg PO43-/L). The effects of orthophosphate on the two water sources concerning the growth and development of biofilm and the decomposition of monochloramine were similar. The similar impacts of orthophosphate on both water sources indicate that the results obtained in the previous phases may be valid for other phosphorus-limited water sources, even with different chemical compositions. In the final phase, a batch test study was conducted on full-scale DWDS samples that employ monochloramine and orthophosphate to assess monochloramine decay and nitrification potential. This study was compared to an earlier study conducted before the introduction of orthophosphate, which utilized samples from the same DWDS sampling sites and identical batch-testing procedures. Monochloramine decomposition due to microbiological processes was found to be higher at further points in the DWDS with longer residence time after adding orthophosphate. Also, nitrite formation during batch tests using samples collected from locations far from the distribution system's entrance was greater after adding orthophosphate, indicating a higher potential for nitrification. Monochloramine decay due to chemical processes was similar before and after orthophosphate addition. In conclusion, orthophosphate promoted biofilm formation, genetic diversity, and nitrification potential, which, in turn, increased monochloramine decay. To mitigate these effects, the thesis recommends some strategies that can be adopted, including decreasing orthophosphate dosages, increasing monochloramine dosages, and shortening the residence time while closely monitoring water quality parameters, especially nitrification indicators.
Direct Method of Generating Floor Response Spectra for Structures Considering Soil-Structure Interaction
(University of Waterloo, 2024-08-21) Li, Yue
Floor Response Spectra (FRS) are crucial for the seismic design and safety assessment of structures, systems, and components (SSCs) in nuclear power facilities. Generating accurate FRS requires considering soil-structure interaction (SSI) effects, especially for structures with flexible foundations and spatially varying ground motions. This thesis presents a comprehensive approach to address these challenges in the context of nuclear power plant (NPP) structures, with a specific focus on the applicability of this method to Small Modular Reactors (SMRs). The main contributions are as follows: (1). A novel direct spectra-to-spectra method is extended for efficient FRS generation in multi-supported structures, incorporating SSI effects through a substructure approach. This method converts Foundation Input Response Spectra (FIRS) into Foundation Level Input Response Spectra (FLIRS) using analytically derived transfer matrices based on soil stiffness and structural modal information. It accommodates both flexible and rigid foundations under varying seismic inputs, eliminating intermediate spectrum-compatible time history generations and full system reanalysis when properties change. (2). A numerical example of a 3-DOF structure with two structural nodes and one foundation node supported by a generalized soil spring is presented to verify the proposed method. Both theoretical formulation and numerical simulation verified and solidified the equivalence of seismic responses between the coupled soil-structure system under FIRS excitations and the decoupled structure under FLIRS inputs. This validation confirms the theoretical rigour of replacing FIRS with FLIRS in the analysis. (3). A comprehensive methodology for evaluating dynamic soil stiffness matrices is presented, utilizing the relationship between dynamic flexibility and stiffness matrices. The method applies sinusoidal excitations to calculate steady-state response amplitudes and phase lags, deriving real and imaginary parts of the dynamic response. A progressive validation strategy is employed, systematically validating the method from simple lumped-mass systems to continuous-mass systems, then to complex 3D half-space soil models, ensuring its reliability across various scenarios. This approach provides a robust and versatile tool for characterizing dynamic soil stiffness properties across various structural complexities. The method can significantly reduces dependence on specialized software running in “blackbox”, such as ACS SASSI, thus enhance the accessibility and efficiency of seismic analysis for nuclear facilities. (4). The proposed direct method was applied to the multiple supported structure with SSI taken into account. The FRS from the proposed method shows excellent agreement with “benchmark” time history results, particularly in horizontal directions, with errors consistently below 5%. Two seismic input scenarios, fully correlated and fully independent excitations at multiple supports, are explored, showcasing the method’s versatility. Some discrepancies in vertical direction are attributed to limitations in vertical tRS, indicating areas for future refinement including the need to refine tRS. (5). Parametric studies investigate the influence of site conditions and internal-external structure coupling element stiffness on FRS. Evaluated across various site classes per ASCE 7-10 standard, the method demonstrates robust performance for most site types. The study reveals optimal stiffness ranges affecting FRS peaks. It also identifies energy transfer patterns between structural components as the stiffness in the connecting elements changes, offering insights for nuclear facility design. The methodologies developed in this thesis advance the state-of-the-art in seismic analysis and design of nuclear structures, particularly SMRs. By addressing the complex challenges posed by multi-support excitations and SSI, this research provides a foundation for safer and more economical designs of nuclear facilities.
Leading Pedestrian Intervals at Intersections in Proximity to Schools: An Evaluation of Safety and Effectiveness
(University of Waterloo, 2024-08-21) Kaur, Mavjot
Pedestrians encounter substantial risks on roadways, particularly at signalized intersections where their exposure to traffic is unavoidable. A predominant cause of pedestrian crashes at these intersections is drivers' failure to yield while making turning maneuvers. One effective countermeasure proposed to mitigate this issue is Leading Pedestrian Interval (LPI), which provides pedestrians with a walk signal during the 'all red' phase, preceding the green signal for parallel vehicular traffic. This timing allows pedestrians to establish themselves in the crosswalk, thereby enhancing their visibility to drivers. Despite extensive research demonstrating the effectiveness of LPIs, there is a lack of research regarding their safety effect when implemented at signalized intersections near schools and the factors influencing their effectiveness. Many existing guidelines and safety programs recommend LPI implementation near schools as part of comprehensive pedestrian safety strategies, highlighting the need to evaluate these proposed guidelines. The main goal of this research is to assess the effectiveness of implementing LPIs at signalized intersections near schools. Additionally, the study aims to analyze in detail the factors that influence pedestrian crash risk in this context. The case study was conducted using ten-year crash data from thirty-three signalized intersections in the Region of Waterloo. An Empirical Bayesian (EB) before and-after analysis was utilized to evaluate the impact of LPIs on pedestrian safety. Comprehensive data collection efforts were made to gather the necessary information for developing the Safety Performance Function (SPF) model. The collected data comprised detailed records of traffic volumes, pedestrian counts, roadway and intersection characteristics, and historical crash data. In this study, two SPF models were selected using different traffic exposure variables. One model used Estimated Daily Traffic (EDT), while the other employed surrogate exposure measure - the number of legs with commercial entries/exits or residential driveways within 50 meters of the intersection (NCE). Several key factors were identified that increase pedestrian crash risks at intersections, including residential and commercial areas, the presence of commercial entries/exits or residential driveways, longer crosswalks, non-conventional crosswalk markings, and higher pedestrian and vehicular volumes. In contrast, certain factors were found to decrease pedestrian crashes at intersections, such as the presence of slip lanes and missing sidewalks. The effectiveness of LPIs was evaluated using Crash Modification Factors (CMFs). The results suggest a 26.8% reduction in pedestrian–vehicle crashes at treated intersections. The effectiveness of iv LPIs is significantly improved under certain conditions. LPIs are more effective at intersections with high pedestrian and vehicle volumes and those with complete pedestrian infrastructure, such as all sidewalks and non-conventional crosswalk markings. Conversely, LPIs are less effective at intersections with slip lanes. Calibrating the model significantly enhanced estimate accuracy and further reduced the CMF to 0.65, underscoring the importance of proper calibration to accurately measure the true impact of pedestrian safety measures.
A Route-Choice Model for Predicting Pedestrian Behaviour and Violations
(University of Waterloo, 2024-08-19) Lehmann Skelton, Christopher
Pedestrians exhibit diverse behaviours, including crossing violations. Traditionally, development of behavioural models has been divided into route choice and crossing behaviour. Route choice models are stochastic and focused on crowd dynamics, while crossing behaviour models are probabilistic or deterministic and focused on local-level behaviours. Route choice and crossing behaviour are often addressed separately, but they are inherently related. This research proposes a new pedestrian simulation model where pedestrians navigate through an intersection or mid-block environment, modelled as a grid. Each cell is assigned a cost that varies over time based on the presence of nearby vehicle traffic or changes to signal indications. Each pedestrian perceives the costs in the environment uniquely depending on their own personal preferences, like desired crossing gap or comfort committing a violation and seeks to minimize their total path cost. Pedestrians who are more comfortable committing violations perceive a lower cost for committing a violation. This approach integrates crossing behaviour with route choice and models the trade-offs of engaging in a particular behaviour. The proposed model is calibrated using video data. The model was applied to three case-studies: a stop-controlled intersection, mid-block crossing, and two crosswalks along the minor approach of a signalized intersection. The model simulates the trade-offs between walking on different surfaces, as well as the trade-off between waiting for a gap in traffic to cross, versus diverting to the nearest designated crosswalk. In the third case study, the model successfully reproduced the proportion of pedestrians crossing against the signal for the north leg crosswalk but did not reproduce the proportion of violations for the south leg crosswalk, which is across a private access. Further investigation should be undertaken into the causes of this and other differences.
Development of a Risk Ranking System for Prioritizing Asset Maintenance Decisions
(University of Waterloo, 2024-08-19) Ayyamperumal, Cibi Chakravarthy
This thesis presents a modified approach to prioritize asset maintenance decisions by evaluating the overall risk rating of engineering systems. Traditional methods rely on subjective assessments by experts, which potentially lead to greater subjectivity and inconsistency in risk prioritization, thus requiring improvements. The thesis performs a comparative analysis of existing risk prioritization techniques to understand the challenges in ranking systems. Analytical Hierarchical process (AHP) and fuzzy logic are proposed to develop a risk ranking system. AHP is employed to compute the weights of multiple criteria, providing a structured framework for decision-making and enabling systematic prioritization of system components. The Mamdani Fuzzy Inference System is integrated to manage the inherent uncertainty and imprecision in assigning ranks. The proposed AHP-Fuzzy model is applied to a plant aging management problem in the nuclear industry with various maintenance tasks, demonstrating its effectiveness in decision-making. The risk rating distribution and sensitivity analyses are studied. The results indicate that integrating AHP and Fuzzy Logic improves decision-making by effective risk prioritization. The thesis contributes to the field of engineering management by providing practical, actionable strategies for enhancing risk management practices to ensure the safety of engineering systems.
Traffic Conflict-based Road Safety Analysis: Data Requirements and Evaluation of Safety Countermeasures
(University of Waterloo, 2024-08-16) Keung, Jessica May Ting
Driven by the vision to eliminate road fatalities, Vision Zero initiatives have been widely adopted by many cities around the world, with significant investments of resources in various safety programs and countermeasures. Conflict-based traffic safety analysis is a burgeoning field, but many studies have failed to address the important question of how much data should be collected to make credible safety-related inferences and how the effectiveness of safety countermeasures could be quantified using conflict data. In this thesis research, a comprehensive framework based on power analysis is first proposed to determine the minimum sample size required for a conflict analysis study. Two case studies are investigated to illustrate how power analysis can be conducted for different types of conflict analysis study specifications, using the corresponding statistical tests. Power analysis is a well-established statistical tool used in many different scientific fields for determining an appropriate sample size. The power analysis exploits the significance criterion (α), power (1-β), and effect size (ES) such that the sample size is large enough to protect investigators from Type I and Type II errors to conventional thresholds of 95% and 80%, respectively. The minimum sample size is also the optimal sample size because it minimizes the observation period while maintaining acceptable protection from Type I and Type II errors. A case study is then conducted to assess the safety benefits of three Vision Zero safety countermeasures using data from the City of Toronto. By applying a combination of case-control and cross-sectional studies, the research attempts to quantify the safety effects of three commonly applied Vision Zero countermeasures, namely, Leading Pedestrian Interval (LPI), No Right Turn On Red (NRTOR), and installation of a dedicated Bicycle Lane (BL). The traffic interactions between vehicles and vulnerable road users (VRUs) were extracted using a video data processing platform and two surrogate measures of safety, including post-encroachment time (PET) and conflict speed, were obtained and then used to classify the conflict severity into different levels. A comparative analysis using mixed-effects negative binomial regression was conducted to quantify the impacts of different treatments on the frequency of traffic conflicts under specific road weather and traffic conditions. The results show that these three types of traffic countermeasures can effectively reduce the frequency of high-risk and moderate-risk traffic conflicts, moderated by various, traffic exposure, weather and environmental conditions, and accessible pedestrian signals (APS). These findings could help road safety engineers and decision makers make better informed decisions on their road safety initiatives and projects.
Advancements in the Experimental Study for the Design and Classification of Cured In Place Pipe (CIPP) Liners
(University of Waterloo, 2024-08-16) Ogunbanjo, Babajide
Thermoset Cured In Place Pipe (CIPP) liners have been used extensively in North America to rehabilitate aging buried gravity and watermain pipe networks. The design and performance assessment of CIPP requires a good understanding of its short- and long-term material properties. Unfortunately, the material properties of CIPP have not been studied extensively. This study presents the results of the experimental investigations completed on reinforced and non-reinforced CIPP liners to better understand some of their material properties such as Long-Term Flexural Strengths (LTFS), Strength Retention Factors (SRF), Short-Term Burst Strengths, and Long-Term Hydrostatic Burst properties. Short-term flexural tests and 10,000-hour flexural creep-rupture tests were completed on both reinforced and non-reinforced CIPP flat coupon specimens and the results were plotted and extrapolated to determine their short-term flexural strengths and 50-year (expected service life) LTFS respectively. The LTFS for non-reinforced CIPP liners was determined to be 83.3% - 84.4% of the first break stress. Reinforced CIPP test samples were found to sustain applied stress without failure up to 5% strain limit, and that creep failure will not occur in reinforced CIPP specimens load to 95 percent of the ASTM D790 short-term yield stress. The long-term SRFs of both reinforced and non-reinforced CIPP are greater than the typically applied 50% retention factor. Full-scale reinforced CIPP pressure liners used for the renovation of watermains were tested using a University of Waterloo designed, built, validated, and commissioned burst testing facility. Short-term burst tests were completed on 150mm and 200mm OD CIPP pressure liners and their short-term burst pressures were determined. Long-term hydrostatic tests were completed on the 200mm OD CIPP pressure liners using the Hydrostatic Design Basis (HDB) standard testing methods. This is in line with the industry-recognized design and classification standard used for other watermain renovation products such as PVC, HDPE, and GRP. The long-term material properties of CIPP pressure liners such as Long-term Hydrostatic Strengths (LTHS), Hydrostatic Design Basis (HDB) stress, Hydrostatic Design Stress (HDS), and Pressure Rating (PR) were determined. The long-term hydrostatic properties of CIPP pressure liners compared well with those of other watermain renovation products. This establishes the HDB design and classification approach as appropriate for designing and classifying CIPP pressure liners. HDB testing found that the CIPP liners is approximately 4 times lower than the short-term burst value.
Numerical and Experimental Investigation of Higher Capacity Cold Formed Steel Shear Walls.
(University of Waterloo, 2024-08-12) Ghaith Abdulrahman Alshamsi, Ghaith
In this research project, three unique, higher-capacity cold-formed steel (CFS) shear wall configurations are proposed and tested, with the aim of extending CFS framing applications into mid-to-high rise buildings. The shear wall configurations consist of a concentric-sheathed shear wall with built-up hat section studs, a concentric-sheathed shear wall with an intermediate stud located at mid-span, and a diagonally strapped concentric sheathed shear wall with built-up hat section studs. A preliminary, full-scale testing program was carried out in collaboration with Chongqing University that included monotonic and cyclic tests of the shear wall specimens, cyclic tests of screw connection assemblies in double shear, and coupon material tests. The test results were analyzed using the Equivalent Energy Elastic Plastic (EEEP) method and the analysis results indicate that the shear walls investigated herein attained substantially higher strengths and ductility than code approved shear walls. Numerical non-linear shell finite element models of each specimen was established and calibrated using the experimental results. To overcome convergences issues, the explicit solver was employed. The finite element results demonstrated good correlation with the experimental results for all shear wall configurations, with the exception of the diagonally-strapped specimen. The verified numerical models were then used to conduct an extensive parametric study, where the influence of several parameters such as screw spacing, stud and sheet thickness, and aspect ratio were assessed. An analytical model for predicting the monotonic response of the concentric-sheathed wall and a simplified method for determining the axial force and bending moment demand on the boundary studs are proposed. Both methods consider semi-rigid behaviour in the boundary frame of the shear wall and have showed good agreement with the shell finite element results, suggesting that the methods can be used for preliminary design purposes.
Bioaugmentation coupled with activated carbon for the treatment of petroleum hydrocarbons in groundwater systems
(University of Waterloo, 2024-07-26) Schneider, Adam
The contamination of groundwater by petroleum hydrocarbons (PHCs) is a global concern with negative human health and environmental impacts. The injection of an activated carbon (AC) particulate amendment to create a permeable reactive barrier (PRB) to prevent additional downgradient migration of a dissolved PHC plume from a source area has gained popularity. In this remedial application the selected AC amendment is strategically injected across a dissolved PHC plume and provides sufficient adsorption capacity to remove dissolved PHCs from the groundwater that flows through the PRB. This concentrated mass of PHCs is considered to serve as a haven for indigenous microorganisms to thrive and results in biodegradation of the PHCs and regeneration of the adsorption capacity of the AC. Often anaerobic conditions develop within the PRB which leads to depleted concentrations of electron acceptors. To overcome this limitation, bacterial cultures are co-injected with the AC to increase the rate of biodegradation since some indigenous microorganisms are perhaps not capable, in low abundance or not present to operate effectivity under anaerobic conditions. The overarching objective of this research was to investigate if an AC particulate amendment coupled with bioaugmentation (culture injection) can synergistically enhance the biodegradation of PHCs. The hypothesis postulated was that the combination of powdered AC (PAC) and enriched methanogenic cultures will enhance the biodegradation of benzene, toluene and o-xylene (BTX) under anaerobic conditions. To evaluate this hypothesis, data was collected from microcosm experiments representing static conditions, and from continuous flow column experiments mimicking in situ conditions. Both the microcosm and column experiments were conducted in anaerobic environments and included controls and active treatment systems involving combinations of BTX, PAC, and/or bioaugmentation (BA). The PAC utilized was a virgin coconut-based thermally activated product with a mean particle size of 13.1 μm. The methanogenic cultures were enriched from nature and have been shown to completely degrade benzene (DGG™-B), toluene (DGG™-T), and o-xylene (DGG™-X). The aquifer material used in the experiments was collected from the University of Waterloo Groundwater Research Facility at Canadian Forces Base (CFB) Borden. Five different microcosm systems were constructed using artificial groundwater, aquifer material, methanogenic cultures and PAC. A single-compound experiment used toluene only while a multicompound experiment used BTX. The active systems included microcosms with and without BA and with (A-PAC-BA and A-PAC) and without (A-BA and A) PAC. Control microcosm systems included killed control (autoclaved with biocide), positive control (BA without aquifer material), and starved control (no addition of toluene or BTX). A total of 300 microcosms bottles were assembled and stored on their side in an anerobic glove chamber undistributed except during sampling. Microcosms were sampled at selected timepoints over a period of nearly one year using a repetitive and sacrificial strategy. Dissolved phase samples were used to determine pH, oxidative reductive potential (ORP), dissolved oxygen (DO), BTX concentrations, dissolved inorganic carbon (DIC) content, and sulfate and sulfide concentrations. Gas phase samples collected from the microcosm headspace were analyzed for methane (CH4) and carbon dioxide (CO2). Solid phase samples were also collected to determine bulk BTX concentrations, and deoxyribonucleic acid (DNA) extractions were assayed by quantitative polymerase chain reaction (qPCR). Toluene or BTX mass was replenished as needed in the active systems. There was no evidence of biodegradation in either the killed or starved controls. Depletion of toluene and o-xylene in conjunction with consumption of sulfate and production of methane and carbon dioxide indicated biodegradation occurred in the positive control and all active bioaugmented microcosm systems. In all microcosm systems the depletion of benzene was not observed. As expected, the presence of PAC in the active microcosm systems considerably reduced the aqueous concentrations of toluene or BTX. Bulk toluene or BTX concentration data provided evidence for the regeneration of PAC sorption capacity because of biodegradation. qPCR results support the depletion of toluene and o-xylene in the active bioaugmented systems with elevated populations of key degraders (Desulfosporosinus (DSP) and Peptococcaceae (PEP)). During the final ~30 days, a higher temporal resolution sampling strategy was implemented to collect data to estimate compartmental mass distributions and system biodegradation rates. The estimated biodegradation rate for A and A-PAC microcosms (no BA) were not statistically different at the 5% LOS, as well as the estimated biodegradation rate for A-BA and A-PAC-BA microcosms. Based on the data set assembled from the microcosm experiments, there is no evidence that supports the stated hypothesis. Specifically, the presence of PAC by itself or in combination with BA did not increase the mass of toluene and o-xylene biodegraded or the rate of biodegradation. Five different columns systems were used to examine BTX biodegradation under anaerobic conditions. The active systems included columns with and without BA and with (A-PAC-BA and A-PAC) and without (A-BA and A) PAC. A control column (killed control) containing PAC was constructed from autoclaved materials. The columns were packed with aquifer material and a 6-cm long PAC zone (0.5% by wt) was emplaced in the central part of the column to mimic a PRB for some systems. An access port was used to inject cultures into the PAC zone. Anerobic artificial groundwater augmented with BTX was used as the feed solution. Biocide was added to the feed solution for the killed control column. The columns were run for a one-year acclimation period followed by 9 months of a comprehensive sampling. Dissolved phase samples collected from the influent and effluent were used to determine pH, ORP, DO, DIC content, and BTX, sulfate, CH4, and CO2 concentrations. At the termination of the experiment, solid phase subsamples were collected from each active column and used to determine bulk BTX concentrations, and DNA extractions were assayed by qPCR. There was no evidence of biodegradation in the killed control column. In the absence of BA (A vs A-PAC columns), the PAC zone improved the biodegradation of toluene as supported by the production of CH4 and CO2, and increased population of toluene degraders within the PAC zone. While in both BA systems (A-BA and A-PAC-BA) toluene biodegradation was near complete (>95% mass reduction), suggesting that the PAC zone did not enhance the biodegradation capacity of toluene when combined with BA. Biodegradation of benzene (~25% mass reduction) occurred in the A-PAC-BA system, despite a larger population of benzene degrading microbes in the A-BA system. O-xylene biodegradation was the highest in the A-BA system (~90% mass reduction), which was supported by the DNA results (>107 copies/g o-xylene degraders), along with production of CH4 and CO2. Based on the data set assembled, there is evidence that supports the stated hypothesis. Specifically, the presence of a PAC zone in the column by itself improved the biodegradation of toluene (~95% versus ~70% mass reduction) and o-xylene (~25% versus <20 % mass reduction) compared to the column with no PAC zone. The combination of PAC and BA increased benzene biodegradation (~25% versus <20 % mass reduction) but decreased o-xylene biodegradation (~90% versus ~80% mass reduction) compared to BA but without a PAC zone. Taken together, experimental findings were not able to prove that PAC and BA work synergistically to enhance the biodegradation of BTX. Nevertheless, PAC did not reduce the biodegradation ability of the systems and can therefore still provide benefits when used for groundwater remediation applications. Specifically, the use of PAC in combination with bioaugmentation in field applications may provide benefits by containing the BTX mass in a more spatially confined area for longer durations (> 20 years), which would provide more time for biodegradation to occur.
Biofiltration for Manganese Removal from Groundwater: Mechanistic Insights and Operational Strategies
(University of Waterloo, 2024-06-17) Arora, Hemant
Groundwater is an essential source of drinking water worldwide. Among various contaminants that are present in groundwater, manganese (Mn) is one of them. Manganese in drinking water can cause aesthetic and operational problems and has been associated with cognitive and neurobehavioral effects in children. In response, Health Canada has established as guidelines a maximum acceptable concentration (MAC) of 120 µg/L and an aesthetic objective (AO) of 20 µg/L for Mn in drinking water. Biofiltration provides an environmentally friendly and effective method for removing Mn from water, as it does not require chemicals and does not produce harmful by-products. However, limitations include a prolonged start-up period with virgin media and diminished efficacy at lower water temperatures (< 15°C) due to reduced microbial activity, particularly when iron (Fe) is present as a co-contaminant in groundwater. Additionally, while biofilters are typically operated continuously (24 h/d), intermittent operation (6-12 h/d) in small-scale or remote communities, depending on local demand, may affect the performance of biofilters. Despite research on Mn removal mechanisms by biofiltration, the evolution of these processes as biofilters mature requires further investigation. Consequently, this research aims to deepen the understanding of Mn removal mechanisms in biofilters from startup to maturity and to investigate the influence of filter media characteristics and operational modes (intermittent vs. continuous) on the performance of biofilters for Mn and Fe removal. The research was conducted in three phases, utilizing a combination of pilot-scale biofilters and bench-scale batch experiments. Pilot-scale biofilters were designed and constructed at a drinking water facility in Southern Ontario, Canada and were operated under various configurations for approximately 400 days with raw groundwater containing Mn and Fe. Concurrent bench-scale batch experiments with and without inhibitors were conducted to elucidate different Mn removal mechanisms. This study employed multiple analytical techniques such as scanning electron microscopy (SEM), energy dispersive X-ray (EDX), Raman spectroscopy, adenosine triphosphate (ATP) measurements, extracellular polymeric substance (EPS) analysis, cultural plating techniques, and 16S rRNA gene sequencing. Phase one evaluated the impact of different filter media, including granular activated carbon (GAC), sand, and anthracite, on startup, Mn removal mechanisms, and microbial community dynamics. Findings indicated that filter media characteristics influence the startup period of Mn removal; GAC biofilters primarily initiated Mn removal through adsorption, transitioning to biological and physicochemical processes, while sand and anthracite predominantly engaged in biological processes. The batch tests confirmed these findings, with sand and anthracite media showing biological dominance at the top layer and GAC media exhibiting physicochemical dominance throughout. The presence of manganese-oxidizing bacteria (MnOB) genera varied across biofilter media types and depths, highlighting the complex interplay between biofilter media and microbial colonization patterns. Phase two focused on the evolution of Mn removal mechanisms in a sand biofilter from startup to maturity, utilizing a combination of pilot-scale biofilter and bench-scale batch experiments. The study revealed an initial dominance of biologically generated manganese oxides (Bio-MnOx), which gradually transitioned to physicochemical forms of MnOx. This shift is likely due to the competitive dynamics between MnOx and MnOB, with the influence of MnOB diminishing over time. Other contributing factors include changes in the nutrient consumption patterns of MnOB and shifts in microbial community composition. Several MnOB genera, including Sphingopyxis, Sphingomonas, Hyphomicrobium, Hydrogenophaga, and Variovorax, were present in the biofilter from startup to maturity. Genes associated with direct and indirect biological Mn oxidation pathways were also predicted, highlighting the complex, multi-pathway nature of biological Mn oxidation. Phase three evaluated the performance of intermittently (6 h/d, 12 h/d) and continuously operated biofilters (24 h/d), in addition to the effects of a 10-day shutdown. The findings demonstrated that intermittently operated biofilters maintain Mn and Fe removal efficiency comparable to continuously operated biofilters, although continuous biofilters exhibited higher ATP and EPS levels. Biofilters quickly recovered after a 10-day shutdown, highlighting their robustness. The overall microbial community composition was not significantly different between continuously and intermittently operated biofilters. Overall, the study successfully demonstrated that pilot-scale biofilters could reduce Mn levels below the Health Canada recommended AO of 20 μg/L, achieving over 90% removal efficiency in the presence of Fe at low water temperatures (15°C). The findings highlight the potential of GAC media to shorten start-up times and the feasibility of operating biofilters intermittently without compromising Mn and Fe removal efficiency.
Investigating the impacts of upgrading a full-scale conventional activated sludge process with a hybrid membrane aerated biofilm reactor
(University of Waterloo, 2024-06-06) Lakshminarasimman Meanakshi Sekar, Narasimman
Membrane aerated biofilm reactors (MABR) are an emerging wastewater treatment technology that offer several process advantages such as higher aeration efficiency, simultaneous nitrification and denitrification, and reduced nitrous oxide (N₂O) emission. However, the current knowledge on MABR operations is largely based on bench- and pilot-scale systems that differ in mixing conditions, biofilm thickness control strategies, and cassette arrangement from those employed in full-scale. This study bridged this critical knowledge gap by investigating the long-term performance (20 months) of one of the largest MABR installations in North America and reported the findings on a wide range of responses related to effluent quality, electricity consumption, N₂O emissions, and biofilm characteristics. The key performance metrics related to nitrogen removal, aeration tank operations, and electricity consumption were monitored in a full-scale conventional activated sludge (CAS) before and after upgrading with a hybrid MABR. The inclusion of the hybrid MABR process improved the seasonal nitrification observed in the CAS process before the upgrade to year-round ammonia removal. Denitrification in the hybrid MABR doubled the TN removal in the plant from 30-40% before upgrade to 70-80% afterwards. Operation at reduced MABR airflow (4.5 NL m⁻² hr⁻¹) resulted in lower nitrification rates due to insufficient biofilm thickness control that led to diffusional limitations. Temperature was found to impact nitrification in the MABR with a 22% decrease in nitrification rate from 1.8 ± 0.2 g-N m⁻² d⁻¹ during warm weather to 1.4 ± 0.2 g-N m⁻² d⁻¹ during cold weather conditions. Operation at higher MABR airflow (6 NL m⁻² hr⁻¹) increased the NH₄-N removal efficiency in the aeration tank during cold weather conditions suggesting increased nitrifier seeding due to enhanced sloughing of biofilm into the suspended sludge. The hybrid MABR process achieved high denitrification efficiency (80-97%) throughout the study and was not substantially impacted by ammonia loading, process airflow, or wastewater temperature. Aeration related electricity consumption, as described by volumetric energy intensity (kWh m⁻³), decreased by 50% after the upgrade due to the efficiency of oxygen supply by the MABR and the reduction of aeration requirements downstream aeration basin. Overall, the improved N removal under reduced electricity consumption at full scale demonstrated the potential of MABR as a suitable process intensification technology. Pollutant removal in biofilm processes such as membrane aerated biofilm reactors (MABR) is directly influenced by the biofilm thickness and microbial community functions. However, these biofilm characteristics have not been studied in full-scale MABR systems before. This study addressed this knowledge gap by characterizing the spatial and operational dynamics of key biofilm properties such as thickness, and microbial community structure and functionalities in a full-scale MABR facility. The arrangement of the MABR cassettes in an array along the length of the plug flow MABR train resulted in a longitudinal biofilm thickness gradient. The biofilms on the front cassettes were more than twice as thick as those on cassettes at the back. Examination of biofilm thickness as a function of MABR process airflow indicated that a lower airflow (4.5 NL m⁻² hr⁻¹) resulted in a thicker biofilm (> 1000 µm) throughout the tank. Consistent with the trends in thickness, analysis of Bray-Curtis dissimilarity index showed that there were differences in the biofilm microbial community composition along the length of the MABR tank and between operating phases. Thicker biofilms in the front cassettes of the full-scale tank were predicted to have a higher relative abundance of organisms with anaerobic functions such as fermentation and sulfur reduction and lower relative abundance of organisms with aerobic functions such as aerobic heterotrophy and nitrification. Nitrosomonas was identified to be the main ammonia oxidizer and Nitrospira and Nitrotoga were the main nitrite oxidizers in the biofilm samples. The 16s RNA gene profiles were strongly correlated with biofilm thickness (R² = 0.8) and MABR nitrification rate (R² = 0.4). Phases with thinner biofilm showed higher relative abundance of nitrifiers which corresponded to higher nitrification rates. Thus, optimizing the process airflow to provide adequate biofilm thickness control is key to maximizing nitrification rate in full-scale MABR. Biological nitrogen removal often results in emission of nitrous oxide (N₂O) which is a highly potent greenhouse gas. Current published models for N₂O emissions in MABR have several simplifications that are not representative of full-scale systems. This study developed an improved MABR N₂O model that captured commonly overlooked phenomena such as back diffusion of generated N₂O into MABR lumen gas and the recirculation of the N₂O laden lumen gas for tank mixing and biofilm thickness control. The improved model was validated with measured N₂O concentrations in the lumen gas phase and bulk mixed liquor in a full-scale hybrid MABR facility. The validated model was used to obtain insights into N₂O bioconversion pathways. Model predictions revealed that all N₂O generated in the inner layers of the biofilm, which back diffused into the lumen gas, was via ammonium oxidizing organism activity. The N₂O transported to the outer biofilm layers was reduced via the heterotrophic denitrification pathway. The N₂O gas model predicted that up to 70% of the N₂O carried by the recirculated lumen gas was scrubbed into the mixed liquor which was further denitrified. An N₂O emission factor of 0.18 ± 0.01% N₂O-N/N load was estimated for the full-scale MABR process which removed up to 50% of the influent N load, highlighting the potential of this technology to mitigate N₂O emissions when compared to conventional activated sludge. Release of organic micropollutants (OMP) such as pharmaceuticals and personal care product ingredients in the treated wastewater effluents is concerning as these compounds could have harmful effects in the aquatic ecosystem. This study monitored the removal of 16 OMPs over multiple seasons in a full-scale CAS before and after an upgrade with a hybrid MABR process. A comparison of OMP concentrations in the plant effluent showed that 12 out of 16 target compounds were present at lower concentrations after the upgrade. An examination of plantwide removal efficiencies revealed that highly removable compounds (> 75%) such as acetaminophen, ibuprofen, naproxen, triclosan, triclocarban, and norfluoxetine and the recalcitrant carbamazepine were not impacted by the addition of the MABR process. However, six compounds namely gemfibrozil, sulfamethoxazole, trimethoprim, atorvastatin and its ortho- and para- hydroxy metabolites, that were poorly removed (< 25%) by the CAS configuration had moderate removals (25 to 75%) with the hybrid MABR/CAS configuration. After the MABR upgrade it was found that six OMPs showed higher removal under warm weather conditions (19.3 ± 1.6℃) when compared to cold weather conditions (13 ± 1.2℃). Mass balance analyses on the MABR tank revealed a broad range of compound specific responses such as complete biotransformation (acetaminophen), partial removal (naproxen), and compound formation from unmeasured precursors (sulfamethoxazole, carbamazepine). Overall, long-term monitoring of the full-scale facility before and after the upgrade revealed that upgrading of CAS to a hybrid MABR configuration can enhance the removal of some OMPs that are poorly removed by the CAS process alone.
Evaluation and improvement of robustness in drinking water treatment systems to manage turbidity- and natural organic matter (NOM)-related water quality upsets during extreme weather events
(University of Waterloo, 2024-05-17) Nemani, Kirti Srimani
Climate change poses significant challenges for drinking water treatment plants (DWTPs), with extreme weather events increasingly impacting water quality. While various aspects of climate adaptation, such as source water protection and demand management, are crucial, managing water quality is paramount for consumer safety. Understanding the effects of climate-driven water quality exacerbations on DWTPs is essential, including identifying watershed risk factors and their impact on treatment processes. Quantifying and substantiating a treatment system's capability and vulnerability to different raw water quality scenarios, especially for turbidity and Natural Organic Matter (NOM) is crucial for performance assessment and preparing for future extreme weather events. In this context, enhancing robustness, which is the ability of a DWTP to maintain desired drinking water quality even during raw water quality disturbances, is key to safeguarding treatment processes against sudden and long-term changes in surface water quality. However, existing tools for assessing vulnerabilities and improving resilience in critical infrastructure lack a focus on water quality management and specifically on evaluating and enhancing treatment process robustness. A comprehensive framework is needed to guide utilities in determining the robustness of their systems and devising strategies to address deficiencies. There is also a need for robustness metrics specifically addressing NOM reduction/removal which is still an unexplored area. This thesis contributes to understanding climate impacts on drinking water treatment processes, focusing on two critical water quality parameters (WQPs) - turbidity and NOM. It explores the implications of turbidity and NOM variations on treatment processes within the context of watershed changes due to climate change. Additionally, this thesis examines the robustness of DWTPs as a vital climate adaptation strategy, synthesizing related concepts like resilience, reliability, risk, and vulnerability to present a comprehensive understanding within the context of DWTPs. The most significant contribution of this research is the development and introduction of three robustness frameworks tailored to DWTPs. The general framework outlines systematic steps for assessing and improving overall robustness, while the parameter-specific framework applies this methodology to specific water quality parameters (WQPs). A plant-specific framework then tailors the parameter-specific approach to individual DWTPs. The thesis proposes a parameter-specific framework for turbidity, utilizing the turbidity robustness index (TRI) for evaluation of individual treatment processes and the overall robustness index (ORI) for the overall assessment of the plant. This framework is applied to two full-scale DWTPs, Plants A and B in Ontario, Canada, using historical plant data and bench-scale experimental data simulating extreme high-turbidity scenarios. The application identifies less robust processes vulnerable to climate extremes, operational responses for short-term robustness, and critical WQP thresholds necessitating capital improvements. This framework serves as a valuable tool for assessing and enhancing the robustness of DWTPs, offering insights into their current state, and aiding in climate adaptation planning. Another notable contribution of this research lies in the comparative analysis of outcomes from four DWTPs where the turbidity robustness framework was implemented. This comparison not only underscores the versatility of the framework, but also offers valuable insights into the performance of four distinct plants using standardized metrics. It also introduces a decision-tree for charting out the next steps for utilities based on the robustness assessment and shows examples tailored to each plant, enhancing the practical applicability of the framework. This thesis also addresses the lack of NOM-related robustness metrics and introduces a novel index, Organic Matter Robustness Index (OMRI) to quantify the robustness of critical treatment processes. This index aims to incorporate the complexity of NOM in natural waters and the variety of surrogate parameters used for measurement at DWTPs in the NOM robustness quantification. Apart from the OMRI, this research also proposes another quantitative method for evaluating NOM robustness by extending the use of TRI to appropriate NOM surrogate parameters. This index was incorporated in the NOM robustness framework, which was applied to plant B, with a focus on historical plant data as well as experimental data simulating extremely high NOM scenarios. Short-term adaptation options in the form of operational changes were identified to improve the removal of NOM in such adverse source water situations. The results from this study show the applicability and ease of use of the OMRI to a full-scale DWTP and offer insights into the current operational robustness with respect to NOM of plant B.
Enhancing Real-Time Data Acquisition from Embedded Road Structural Health Monitoring Systems
(University of Waterloo, 2024-04-23) Ceric, Matea
Canada's economy heavily relies on its roadways, yet managing pavement assets faces challenges due to past infrastructure spending cuts. Addressing this, a pavement management system (PMS) is essential for efficient resource allocation. Traditional surface condition monitoring within PMS is time-consuming and costly. In response, in situ condition monitoring, integrating AI and ML, emerges as a viable alternative, aligning with the development of "smart" pavements. This thesis, part of the Smart Pavements project at the University of Waterloo, assesses an instrumented pavement section on Courtland Avenue, Kitchener. It provides a comprehensive assessment of the implementation, data collection, data analysis and database concept development processes of an instrumented test section. It integrates advanced monitoring technologies and predictive modeling, yielding promising results. Identified gaps in the literature are addressed, with scalability and cost-benefit analysis highlighted for future research. Challenges in instrumentation and testing, including weather delays, are discussed, with recommendations provided. Material testing procedures and truck testing results are outlined, emphasizing seasonal variations and the impact of vehicle wander on pavement behavior. Software comparisons and detailed trend analysis reveal insights into pavement performance. Additionally, a basic database framework is proposed for efficient data management. This study contributes to understanding pavement instrumentation, long-term behavior, and the efficacy of simulation methods. Recommendations for future work include AI/ML integration, long-term data collection, database development, and standardized guidelines for sensor implementation, aiming to enhance pavement management practices nationwide.
Effects of Prolonged Shutdown on the Performance and Microbial Activity of Intermittently Operated Biofilters for Manganese Removal from Groundwater: Pilot Scale Study
(University of Waterloo, 2024-04-18) Zore, Ujwal
Apart from aesthetic concerns, manganese (Mn) in drinking water has been associated with cognitive and neurobehavioral effects in children. Recently Health Canada has changed its drinking water guidelines for Mn from an aesthetic parameter to a regulated parameter with a maximum acceptable concentration (MAC) of 120 μg/L, an aesthetic objective (AO) of 20 μg/L, and a treatment objective limit of 15 μg/L. While biofiltration has proved to be an effective treatment option for Mn and iron (Fe), it is not widely used in North America. Also, in small-scale communities, treatment plants often adopt intermittent operation schemes, wherein, water treatment occurs for a few hours per day, based on demand. Among the various operational aspects that could potentially affect the performance of intermittently operated biofilters, prolonged filter shutdown remains a critical concern. However, limited insights exist regarding both the intermittent operation for Mn and Fe removal from groundwater and the impact of a prolonged shutdown. This study aimed to fill these knowledge gaps by comparing the performance of intermittently and continuously operated biofilters for Mn and Fe removal from groundwater, and by investigating the impact or a prolonged shutdown of these filters. To achieve these objectives, three pilot-scale biofilters were located at a drinking water treatment facility in Southern Ontario, Canada, out of which two biofilters were operated continuously and one intermittently (6 h per day). The biofilters were initially operated for a couple of months, then underwent a six-month shutdown period, and then resumed active operation for three months. Sand was used as the biofilter media providing an empty bed contact time (EBCT) of 15.6 minutes. Raw groundwater containing Mn (31 μg/L) and Fe (96 μg/L) was fed to the biofilters and the effluent flow rate was maintained at 5 m/h. Mn and Fe removal was assessed before and after the extended shutdown in order to gauge its impact on biofilter performance. In addition, turbidity, pH, DO, oxidation-reduction potential (ORP) and total organic carbon (TOC), were periodically monitored. Microbiological changes were analyzed using AxP (adenosine triphosphate (ATP), adenosine diphosphate (ADP), adenosine monophosphate (AMP)) and other microbiological analyses. Lastly, the storage strategy (SS) utilized during an extended shutdown period might play a crucial role, therefore four different storage strategies were investigated. To briefly summarize the results, during the start-up phase, after 56 days, all biofilters achieved Mn removal to below 15 μg/L, with the intermittently operated biofilter exhibiting lower removal rates and not reaching a steady state, while Fe removal reached a steady state within a week for all biofilters. Next, during the six-month extended shutdown, a notable reduction in ATP occurred, but all biofilters seemed to have remained viable for 4 months, potentially due to the SS utilized. Also, it was found that manganese oxidizing bacteria (MnOB) were able to persist and actively oxidize Mn even after the six-month-long shutdown. Lastly, post-extended shutdown all biofilters approached the previous Mn removal rates within 20 days of restart and then reached a steady state within a month of operation. Notably, intermittently operated biofilter performed equally well as continuously operated biofilters. Also, Fe removal was not found to be affected by the extended shutdown. This suggests that the biofilters were able to quickly regain their performance even after a six-month extended shutdown highlighting the resilient nature of these biofilter systems. Overall, this study enhances the understanding of Mn removal in intermittently operated biofilters, and suggests ways to mitigate the effects of prolonged shutdowns, thereby expanding the applicability of these biofilters, especially to smaller communities.

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