Browsing by Subject "Turbidity"
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Item Chemical and Hydrodynamic Effects in Polymer-Clay Flocculation: Anisotropic particulate size and surface morphology effects in varied and controlled hydrodynamic fields(2017-12) Wilkinson, NikolasPolymer-driven flocculation of suspended particles is a critical process for many applications, including composite materials synthesis, paper manufacturing, and water treatment. However, the role of solution physicochemical properties on the polymer-particle assembly dynamics is nontrivial, particularly for non-spherical, polydisperse particulates such as natural clays. Properties including ionic strength and pH affect both the individual particulate aggregates themselves, as well as the polymer – particle flocculation event. In this work, we study the effects of ionic strength and aggregate size and structure on the polymer behavior and flocculation performance with anisotropic bentonite clay particles using traditional jar tests. The final floc structure is largely informed by ionic-strength driven changes to the initial clay aggregate size and surface structure. With increasing bentonite aggregate size, a transition from a networked to a patched polymer − aggregate floc structure is observed, independent of ionic strength during flocculation. Additionally, the clay’s aggregate morphology is a more direct control parameter of optimal polymer dose and final turbidity (turbidity after 5 min sedimentation) than zeta potential for aqueous bentonite systems. Flocculation performance is the same when bentonite aggregate morphology is the same, regardless of a change in zeta potential. Likewise, when bentonite aggregate morphology changes, flocculation performance also changes, regardless of the identical zeta potential. Therefore, initial clay aggregate morphology controls the extent of polymer adsorption and optimal polymer dose, while initial clay aggregate size controls the internal floc structure. While traditional jar tests offer the advantages of experimental simplicity, speed, and mimic treatment geometries, there is limited homogeneity and control over hydrodynamics within the system. Taylor-Couette cells offer a much higher degree of hydrodynamic control and have been shown to improve several industrial processes due to the wide variety of hydrodynamic flow states accessible. Traditional designs, however, limit the ability to introduce new fluids into the annulus during device operation due to geometric confinement and complexity. As a key part of this thesis effort, a co- and counter-rotating Taylor-Couette cell with radial fluid injection has been constructed. The new inner cylinder design does not modify the critical Re for flow instabilities and can precisely inject a desired mass at a desired flow rate. Using the newly designed, modified Taylor-Couette cell, axial mass transport behavior is experimentally determined over two orders of magnitude of Reynolds number. Four different flow states, including laminar and turbulent Taylor vortex flows and laminar and turbulent wavy vortex flows, were studied. Using flow visualization techniques, the estimated dispersion coefficient was found to increase with increasing Re, and a single, unified regression is found for all vortices studied. In addition to mass transport, the vortex structures’ stability to radial injection is also quantified. A new dimensionless stability criterion, the ratio of injection to diffusion timescales, was utilized to capture the conditions under which vortex structures are stable to injection. Using the stability criterion, global and transitional stability regions are identified as a function of Reynolds number, Re. Overall, this thesis examines chemical and hydrodynamic effects in polymer flocculation with natural clays, and shows the importance of initial contaminant properties on flocculation performance. The initial contaminant properties affect both flocculation efficiency and resultant floc structure and are often not considered at treatment plants. Consideration of these properties potentially can improve process predictive capabilities, which improves process performance.Item Developing a Diagnostic Tool for Assessing Excessive Sediment Harm to Stream Communities(University of Minnesota Duluth, 2013) Brady, Valerie; Herrera, LarissaExcess sediment is a top cause of impairment in U.S. rivers and streams. A number of streams on the north shore of Lake Superior’s western arm are on the Minnesota Pollution Control Agency’s impaired waters list due to turbidity problems. The underlying geology of the north shore, in addition to the steep slopes of the Lake Superior escarpment, forms a stream base vulnerable to erosion and excessive sediment deposition in streams. This vulnerability is created, at least in part, by an area of clay loam soil that many north shore stream channels intersect as they come down the escarpment to the shore of Lake Superior. The steep slopes cause high stream velocities which, combined with the high erodability of this soil layer, create high erosion potentials, particularly on outside channel bends. The increased fine sediments traveling through and accumulating in stream substrates potentially presents several problems for aquatic biota. Excess sediment deposits reduce habitat space for aquatic macroinvertebrates, which are vital components of the food web. In addition to potentially decreasing food sources for fish, the excess sediment deposits can bury fish spawning habitats. Even if the fish can clean off nesting areas, they will expend extra energy doing so. There are many stream condition indicators using stream fish or macroinvertebrates, but none address excess sediment specifically. In many areas of the country there are any number of human‐caused stressors affecting stream condition, including agricultural runoff, high stormwater discharges, loss of stream shoreline habitat, deforestation, development, and industrial discharges. When there are many stressors impacting streams, it is hard to differentiate among them to determine which stressors are creating which problems for stream biota. While some north shore streams have non‐turbidity impairments, there are considerably fewer than in other parts of the country. The dominance of erosion‐based impairments provided the opportunity to develop an indicator diagnostic of excessive sediment deposition in stream substrate as the cause of biotic impairment in north shore streams. We selected stream macroinvertebrates for indicator development for several reasons. They are less mobile than fish, meaning that they have limited ability to escape from disturbance, and even more limited ability to return after a disturbance ceases (at least until the next generation begins). Macroinvertebrates are easy to collect, are present in relatively high abundances, and have high morphological diversity. For all of these reasons, macroinvertebrates are commonly used in stream condition assessments, and their use is ubiquitous across the US and across agencies. Because most agencies collect stream macroinvertebrate information already, their use to create a diagnostic indicator could allow agencies and managers to get more information out of data they already have, without the need for additional sampling. The goal of this project was to develop a suite of stream macroinvertebrate metrics diagnostic of invertebrate community impairment caused by excessive fine sediment deposition in stream substrate; in other words, burial or partial burial of streambed rocks by sand, silt, and clay. Such a diagnostic tool would aid managers in their stream assessment work. While similar projects have been previously attempted (and failed) in other parts of the country, most have been in areas suffering from a number of stressors, making development of an indicator diagnostic of just sediment impairment more difficult. Our hope in attempting such work using north shore streams was that the relative lack of other stressors in northeastern Minnesota would make the development of such an indicator more possible. Having such an indicator should help agencies make a stronger connection between the Total Maximum Daily Load (TMDL) turbidity measurements and sediment deposition presumed to be causing harm to stream biota.Item Development and Evaluation of Effective Turbidity Monitoring Methods for Construction Projects(Minnesota Department of Transportation Research Services & Library, 2014-07) Perkins, Rebekah Lynn; Hansen, Brad; Wilson, Bruce N.; Gulliver, John S.Various agencies have discussed the possibility of using turbidity as an effluent standard for construction site. Turbidity monitoring can be difficult for dynamic construction sites. This project investigated turbidity relationships for conditions of Minnesota and developed protocols for the design and installation of cost-effective monitoring systems. Turbidity characteristics of fourteen different soils in Minnesota were investigated using the laboratory protocols. Trends in turbidity with sediment concentrations were well represented by power functions. The exponent of these power functions was relatively constant between soils and the log-intercept, or scaling parameter varied substantially among the different soils. A regression analysis for the scaling parameter was a function of percent silt, interrill erodibility, and maximum abstraction. A power value of 7/5 was chosen to represent all soils. The field studies were also used to develop turbidity monitoring systems that would be adaptable to construction sites and to collect turbidity data on construction site runoff. Construction site turbidities often exceeded 1000 NTUs and sometimes surpassed 3000 NTUs.Item Estimating sediment, nutrient and mercury loads from four western Lake superior watersheds using continuous in-stream turbidity monitoring.(2010-12) Ruzycki, Elaine M.Many streams along the Minnesota coast of Lake Superior have been listed as impaired from high turbidity, suspended sediment, or high fish mercury concentrations. Both total suspended sediment (TSS) and total mercury have been shown to be strongly correlated to turbidity in many disturbed watersheds. Total suspended sediments, phosphorus, and total mercury loads were estimated in four western Lake Superior watersheds from 2005-2006 using automated in-stream turbidity measurements. Regression models were developed relating this near-continuous turbidity data to grab sample measures of mercury, suspended sediments and nutrients during differing flow regimes. Suspended sediment and phosphorus loads estimated using the turbidity surrogate were compared to those made using FLUX software, a standard assessment technique based on discharge and grab sampling for TSS. Stream specific turbidity vs. TSS measures were strongly correlated (r2 = 0.6 to 0.95; p < 0.05) and total mercury also showed a close relationship with TSS (r2 = 0.82, n = 23; p < 0.05) for all four streams. Continuous turbidity monitoring appears to be a reasonable surrogate for both suspended sediment and total mercury concentration, providing information when manual sample collection is cost-prohibitive or logistically difficult, and across a wide range of flows.Item Identifying Erosional Hotspots in Streams along the North Shore of Lake Superior, Minnesota using High-Resolution Elevation and Soils Data(2013) Wick, Molly JaneThis is a University of Minnesota Water Resources Science master’s thesis describing original research to determine fluvial erosion in three coastal streams (Amity, Talmadge and French) of Minnesota’s Lake Superior shoreline. All three streams have elevated levels of turbidity, with potential for damage to fisheries. The goal of this project was to develop a GIS-based model using new, openly-available, high-resolution LiDAR datasets to predict erosional hotspots at a reach scale. The abstract summarizing the study’s key findings is extracted and reproduced below. Abstract: “Many streams on the North Shore of Lake Superior, Minnesota, USA, are impaired for turbidity driven by excess fine sediment loading. The goal of this project was to develop a GIS-based model using new, openly-available, high-resolution remote datasets to predict erosional hotspots at a reach scale, based on three study watersheds: Amity Creek, the Talmadge River, and the French River. The ability to identify erosional hotspots, or locations that are highly susceptible to erosion, using remote data would be helpful for watershed managers in implementing practices to reduce turbidity in these streams. “Erosion in streams is a balance between driving forces, largely controlled by topography; and resisting forces, controlled by the materials that make up a channel’s bed and banks. New high-resolution topography and soils datasets for the North Shore provide the opportunity to extract these driving and resisting forces from remote datasets and possibly predict erosion potential and identify erosional hotspots. We used 3-meter LiDAR-derived DEMs to calculate a stream power-based erosion index, to identify stream reaches with high radius of curvature, and to identify stream reaches proximal to high bluffs. We used the Soil Survey Geographic (SSURGO) Database to investigate changes in erodibility along the channel. Because bedrock exposure significantly limits erodibility, we investigated bedrock exposure using bedrock outcrop maps made available by the Minnesota Geological Survey (MGS, Hobbs, 2002; Hobbs, 2009), and by using a feature extraction tool to remotely map bedrock exposure using high-resolution air photos and LiDAR data. “Predictions based on remote data were compared with two datasets. Bank Erosion Hazard Index surveys, which are surveys designed to evaluate erosion susceptibility of banks, were collected along the three streams. In addition, a 500-year flood event during our field season gave us the opportunity to collect erosion data after a major event and validate our erosion hotspot predictions. Regressions between predictors and field datasets indicate that the most significant variables are bedrock exposure, the stream power-based erosion index, and bluff proximity. A logistic model developed using the three successful predictors for Amity Creek watershed was largely unsuccessful. A threshold-based model including the three successful predictors (stream power-based erosion index, bluff proximity, and bedrock exposure) was 70% accurate for predicting erosion hotspots along Amity Creek. The limited predictive power of the models stemmed in part from differences in locations of erosion hotspots in a single large-scale flood event and long-term erosion hotspots. The inability to predict site-specific characteristics like large woody debris or vegetation patterns makes predicting erosion hotspots in a given event very difficult. A field dataset including long-term erosion data may improve the model significantly. This model also requires high resolution bedrock exposure data which may limit its application to other North Shore streams.”Item Turbidity monitoring on construction sites: insight into the factors influencing the turbidity and TSS relationship(2013-05) Perkins, Rebekah LynnStormwater runoff from construction sites can transport eroded sediment to nearby water bodies degrading water quality and impairing biotic communities. The United States Environmental Protection Agency (EPA) is considering a turbidity limit for effluent stormwater on construction and demolition sites and is requesting data to support that limit (EPA, 2011). Laboratory protocols have been developed herein for studying the factors that impact turbidity from construction site soils. Experimental procedures include the use of a rainfall simulator to generate runoff and turbidity values from soils carefully packed in appropriate test boxes. Turbidity characteristics of fourteen different soils in Minnesota were investigated using the laboratory protocols. Trends in turbidity with sediment concentrations were well represented by power functions. The exponent of these power functions was relatively constant between soils and the log-intercept, or scaling parameter varied substantially among the different soils. Multiple soil properties were evaluated for each soil. An extensive regression analysis resulted in a model using percent silt, interrill erodibility, and maximum abstraction that best represented the intercept term. A power value of 7/5 was chosen to represent all soils. A second laboratory experiment was performed to determine how particle settling affects the coefficients of the turbidity -TSS relationship. The scaling parameter increased with sediment deposition and the power value decreased. Field studies on two construction sites in the Twin Cities of metropolitan area of Minnesota were performed for this project. Grab samples and continuously monitored turbidity were collected for each site. The grab samples also exhibited a strong power relationship between turbidity and TSS with similar coefficients as the laboratory samples. The laboratory relationships were also applied to the observed field conditions to demonstrate their usefulness in estimating turbidity, concentration, sediment load, and load reduction.