VTechWorks Repository :: Browsing by Author "Grizzard, Thomas J."

Browsing by Author "Grizzard, Thomas J."

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Abnormal Pattern Recognition in Spatial Data
Kou, Yufeng (Virginia Tech, 2006-11-29)
In the recent years, abnormal spatial pattern recognition has received a great deal of attention from both industry and academia, and has become an important branch of data mining. Abnormal spatial patterns, or spatial outliers, are those observations whose characteristics are markedly different from their spatial neighbors. The identification of spatial outliers can be used to reveal hidden but valuable knowledge in many applications. For example, it can help locate extreme meteorological events such as tornadoes and hurricanes, identify aberrant genes or tumor cells, discover highway traffic congestion points, pinpoint military targets in satellite images, determine possible locations of oil reservoirs, and detect water pollution incidents. Numerous traditional outlier detection methods have been developed, but they cannot be directly applied to spatial data in order to extract abnormal patterns. Traditional outlier detection mainly focuses on "global comparison" and identifies deviations from the remainder of the entire data set. In contrast, spatial outlier detection concentrates on discovering neighborhood instabilities that break the spatial continuity. In recent years, a number of techniques have been proposed for spatial outlier detection. However, they have the following limitations. First, most of them focus primarily on single-attribute outlier detection. Second, they may not accurately locate outliers when multiple outliers exist in a cluster and correlate with each other. Third, the existing algorithms tend to abstract spatial objects as isolated points and do not consider their geometrical and topological properties, which may lead to inexact results. This dissertation reports a study of the problem of abnormal spatial pattern recognition, and proposes a suite of novel algorithms. Contributions include: (1) formal definitions of various spatial outliers, including single-attribute outliers, multi-attribute outliers, and region outliers; (2) a set of algorithms for the accurate detection of single-attribute spatial outliers; (3) a systematic approach to identifying and tracking region outliers in continuous meteorological data sequences; (4) a novel Mahalanobis-distance-based algorithm to detect outliers with multiple attributes; (5) a set of graph-based algorithms to identify point outliers and region outliers; and (6) extensive analysis of experiments on several spatial data sets (e.g., West Nile virus data and NOAA meteorological data) to evaluate the effectiveness and efficiency of the proposed algorithms.
Analysis of an Urban Stormwater Bioretention Management Practice in Prince William County, Virginia
Angelo, Suzanne (Virginia Tech, 2005-11-21)
The performance of an urban stormwater bioretention management practice in the Kingsbrooke Subdivision of Prince William County, Virginia was examined over a one-year period. Bioretention is a relatively new urban stormwater best management practice (BMP) intended to mimic the pollutant-removal characteristics of an upland forest habitat. Typical bioretention areas utilize shallow ponding and highly-infiltrative sandy soils to treat the stormwater runoff from small commercial or residential drainage sites. The Kingsbrooke bioretention area was found to be atypical in several ways, including its relatively large, 14 acre, drainage area and the high clay content of its topsoil. Hydrologic and chemical data were collected by Virginia Tech staff for a total of 8 months in 2003 and 2004. Analysis of pollutant loading data was complicated by the presence of three unmeasured water flows: overland inflow bypassing the inflow gage, and groundwater flows both entering and exiting the bioretention soils. The BMP did reduce peak runoff rates for some storms, but did not significantly reduce total storm volumes because of the combined effects of the large drainage area to BMP area ratio and the poor infiltration capacity of the soil. Pollutant load calculations determined that the site removed about 28% of total suspended solids, 32% of total phosphorus, and about 15% of total nitrogen. Removals of approximately 16% and 7% were observed for lead and zinc, respectively. Although the Kingsbrooke bioretention area did improve water quality, the pollutant removal efficiencies were lower than those reported in the literature from more conventional bioretention areas.
Application of system dynamics modeling techniques to an existing stream water quality model
Finley, Allan Michael (Virginia Tech, 1991-05-05)
From the results of this project and report the following conclusions seem warranted: 1. The actual behavior of any real stream system, subject to a point load, is dependent on an extremely complex and integrated network of events which can occur in series or parallel. 2. The QUAL2E model considers the major events or cycles of a stream system in a fully integrated manner, offers the user many configuration options, and provides for a wealth of essential output data. The documentation provides reasonable explanation as to the means by which the model simulates a stream system. The QUAL2E model can be executed successfully by the first time user with minimal effort. 3. The DYNAMO model can be effectively invoked through the use of differential equations that can be translated into suitable DYNAMO expressions. The model is easy to learn and can be executed by the first time user with minimal effort. 4. Input parameters and initial conditions for the both the QUAL2E and DYNAMO models were reasonable for the purpose intended. That being the comparison of the behavior of the two systems.
Breakpoint Chlorination as an Alternate means for Ammoia-Nitrogen removal at a Water Reclamation Plant
Brooks, Matthew A. (Virginia Tech, 2004-02-04)
Numerous wastewater treatment processes are currently available for nitrogen removal or ammonia conversion to nitrate. Those that are economically feasible rely mostly on microbiological processes, which are only effective when the microorganisms remain in a healthy state. If a biological process upset was to occur, due to a toxic shock load or cold weather, it may result in a discharge of ammonia or total nitrogen into the receiving water body. The impact of such a discharge could have deleterious effects on aquatic life or human health. The main objective of the breakpoint pilot study was to define optimum breakpoint pilot plant operating conditions which could then be applied to the design of a full scale breakpoint facility and serve as an emergency backup to biological nitrification. A pilot study was built on site at the Upper Occoquan Sewage Authority's Regional Water Reclamation Facility in Centreville Virginia. Testing was conducted in two phases (I and II) over a two year period in order to determine the operating conditions at which the breakpoint reaction performed best. Tests were performed during Phase I to determine the optimum operating pH, Cl₂:NH₃-N dose ratio, S0₂:Cl₂ dose ratio, and the minimum detention time for completion of the breakpoint reaction. Other testing done during Phase I included several special studies; including examination of appropriate analytical methods for monitoring breakpoint reactions, and investigation of the breakpoint reaction by-product nitrogen trichloride. Phase II testing examined how varying breakpoint operating temperatures, varying influent ammonia concentrations, higher influent organic nitrogen concentrations, and higher influent nitrite concentrations influenced the performance of the breakpoint pilot operation. Averages of data from operation at three different rapid mix pHs (7.0, 7.5, and 8.0) showed that pilot performance (i.e., ammonia oxidation) improved and the reaction was more stable at the higher operating pHs 7.5 and 8.0. Examination of dose ratios used during the study showed that the ideal operating ratios for this particular water was around 8:1 Cl₂:NH₃-N for the breakpoint reaction and 1.3:1 S0₂:Cl₂ for the dechlorination reaction. Although detention times for completion of the breakpoint reaction varied with pilot influent temperature, it generally required around 30-35 minutes to reach ammonia concentrations of < 0.2 mg/L NH₃-N at 8-12°C. Completion of the breakpoint reaction was found to be quickest at 20°C (the highest water temperature tested at the pilot). The tests of varying influent ammonia concentrations showed that although higher influent ammonia concentrations (11.0 mg/L) resulted in faster ammonia oxidation rates initially, the pilot operated better and had the same final performance results when the influent ammonia was lowered. Increasing the organic nitrogen concentrations (~ 1.0 mg/L) in the pilot influent resulted in a slightly higher Cl₂:NH₃-N dose ratio needed to reach breakpoint, a higher S0₂:Cl₂ dose needed to dechlorinate, and resulted in the formation of numerous disinfection byproducts. Increasing the nitrite concentration in the pilot influent increased the chlorination dose requirement.
A Complex, Linked Watershed-Reservoir Hydrology and Water Quality Model Application for the Occoquan Watershed, Virginia
Xu, Zhongyan (Virginia Tech, 2005-12-16)
The Occoquan Watershed is a 1515 square kilometer basin located in northern Virginia and contains two principal waterbodies: the Occoquan Reservoir and Lake Manassas. Both waterbodies are principal drinking water supplies for local residents and experience eutrophication and summer algae growth. They are continuously threatened by new development from the rapid expansion of the greater Washington D.C. region. The Occoquan model, consisting of six HSPF and two CE-QUAL-W2 submodels linked in a complex way, has been developed and applied to simulate hydrology and water quality activities in the two major reservoirs and the associated drainage areas. The studied water quality constituents include temperature, dissolved oxygen, ammonium nitrogen, oxidized nitrogen, orthophosphate phosphorus, and algae. The calibration of the linked model is for the years 1993-95, with a validation period of 1996-97. The results show that a successful calibration can be achieved using the linked approach, with moderate additional effort. The spatial and temporal distribution of hydrology processes, nutrient detachment and transport, stream temperature and dissolved oxygen were well reproduced by HSPF submodels. By using the outputs generated by HSPF submodels, the CE-QUAL-W2 submodels adequately captured the water budgets, hydrodynamics, temperature, temporal and spatial distribution of dissolved oxygen, ammonium nitrogen, oxidized nitrogen, orthophosphate phosphorus, and algae in Lake Manassas and Occoquan Reservoir. This demonstrates the validity of linking two types of state of the art water quality models: the watershed model HSPF and the reservoir model CE-QUAL-W2. One of the advantages of the linked model approach is to develop a direct cause and effect relationship between upstream activities and downstream water quality. Therefore, scenarios of various land use proposals, BMP implementation, and point source management can be incorporated into HSPF applications, so that the CE-QUAL-W2 submodels can use the boundary conditions corresponding with these scenarios to predict the water quality variations in the receiving waterbodies. In this research, two land use scenarios were developed. One represented the background condition assuming all the land covered by forest and the other represented the environmental stress posed by future commercial and residential expansion. The results confirm the increases of external nutrient loads due to urbanization and other human activities, which eventually lead to nutrient enrichment and enhanced algae growth in the receiving waterbodies. The increases of external nutrient loads depend on land use patterns and are not evenly spread across the watershed. The future development in the non urban areas will greatly increase the external nutrient production and BMPs should be implemented to reduce the potential environmental degradation. For the existing urban areas, the model results suggest a potential threshold of nutrient production despite future land development. The model results also demonstrate the catchment function of Lake Manassas in reducing nutrient transport downstream.
Controlling Dissolved Oxygen, Iron and Manganese in Water-Supply Reservoirs using Hypolimnetic Oxygenation
Gantzer, Paul Anthony (Virginia Tech, 2008-03-26)
Hypolimnetic oxygenation systems, such as linear bubble-plume diffusers, are used to improve raw water quality. Linear bubble-plume diffusers were installed in Spring Hollow Reservoir (SHR) and Carvins Cove Reservoir (CCR). Diffusers induce mixing that aids distribution of oxygen throughout the hypolimnion. The induced mixing also creates an undesirable effect by increasing hypolimnetic oxygen demand (HOD). Nevertheless, oxygenation systems are commonly used and long-term oxygenation is hypothesized to actually decrease HOD. Increased oxygen concentrations in combination with the induced mixing affect the location of the oxic/anoxic boundary relative to the sediment water interface. If the oxic/anoxic boundary is pushed beneath the sediment/water interface, the concentrations of soluble iron and manganese in the bulk water are reduced. This work was performed to further validate a recently published bubble-plume model that predicts oxygen addition rates and the elevation in the reservoir where the majority of the oxygen is added. Also, the first field observations of a theoretically expected secondary plume are presented. Model predicted addition rates were compared to observed accumulation rates to evaluate HOD over a wide range of applied gas flow rates. Observations in both reservoirs showed evidence of horizontal spreading that correlated well with plume-model predictions and of vertical spreading below diffuser elevations, showing oxygen penetration into the sediment. Experimental observations of a theoretically expected secondary plume structure also correlated well with model predictions. Plume-induced mixing was shown to be a function of applied gas flow rates, and was observed to increase HOD. HOD was also observed to be independent of bulk hypolimnion oxygen concentration, indicating that the increase in oxygen concentration is not the cause of the increased HOD. Long-term oxygenation resulted in an overall decrease in background HOD as well as a decrease in induced HOD during diffuser operation. Elevated oxygen concentrations and mixing, which occur naturally during destratification and artificially during oxygenation, were observed to coincide with low dissolved metal concentrations in CCR. Movement of the oxic/anoxic boundary out of the sediment, which is also common during stratified periods, appears to facilitate transport of reduced Mn to the overlying waters. Hypolimnetic oxygenation increased oxygen concentrations throughout the hypolimnion, including down to the SWI, and induced mixing, although not to the extent observed during destratification. Subsequently, elevated Mn concentrations were observed to be restricted to the benthic waters located immediately over the sediments, while bulk (hypolimnion) water Mn concentrations remained low. The good agreement between the model and the experimental data show that the model can be used as a predictive tool when designing and operating bubble-plume diffusers. Linear bubble-plume diffusers provide sufficient horizontal and vertical spreading to enable oxygen to reach the sediments. Hypolimnetic oxygenation, despite the increased HOD, is a viable method to manage the negative consequences of hypolimnetic anoxia in water-supply reservoirs.
Design and implementation of a microcomputer based Laboratory and Operations Information System (LOIS) for wastewater treatment plants
Harvey, Glenn B. (Virginia Tech, 1989-10-05)
The requirements for a wastewater treatment plant microcomputer based Laboratory and Operations Information System (LOIS) were considered. Emphasis was placed on combining data generated by the laboratory and the operations divisions of the Alexandria Sanitation Authority. Goals were established to meet the information needs of key decision makers within the Authority and external information consumers such as regulatory authorities and design engineers. Integration of laboratory analysis and plant operational data was of prime importance. A series of related computer programs was developed to manage laboratory and operational data and calculate results derived from both sources. The programs stressed data integrity, flexible report generation, statistical and graphical data analysis, and ease of use. A program was developed to address laboratory quality control data management and the production of quality control charts. The computer programs were written in a generic fashion so as to be applicable to other water or wastewater treatment plants and to provide maximum flexibility for future expansion. Programs were developed in a modular fashion to allow greater ease of maintenance and revision in the future. Common subroutines were employed wherever possible. Some report generation subprograms were written specifically to the requirements of the Alexandria Sanitation Authority.
Development and Evaluation of Infilling Methods for Missing Hydrologic and Chemical Watershed Monitoring Data
Johnston, Carey Andrew (Virginia Tech, 1999-08-24)
Watershed monitoring programs generally do not have perfect data collection success rates due to a variety of field and laboratory factors. A major source of error in many stream-gaging records is lost or missing data caused by malfunctioning stream-side equipment. Studies estimate that between 5 and 20 percent of stream-gaging data may be marked as missing for one reason or another. Reconstructing or infilling missing data methods generate larger sets of data. These larger data sets generally generate better estimates of the sampled parameter and permit practical applications of the data in hydrologic or water quality calculations. This study utilizes data from a watershed monitoring program operating in the Northern Virginia area to: (1) identify and summarize the major reasons for the occurrence of missing data; (2) provide recommendations for reducing the occurrence of missing data; (3) describe methods for infilling missing chemical data; (4) develop and evaluate methods for infilling values to replace missing chemical data; and (5) recommend different infilling methods for various conditions. An evaluation of different infilling methods for chemical data over a variety of factors (e.g., amount of annual rainfall, whether the missing chemical parameter is strongly correlated with flow, amount of missing data) is performed using Monte Carlo modeling. Using the results of the Monte Carlo modeling, a Decision Support System (DSS) is developed for easy application of the most appropriate infilling method.
Development of a Design-Based Computational Model of Bioretention Systems
Liu, Jia (Virginia Tech, 2013-12-03)
Multiple problems caused by urban runoff have emerged as a consequence to the continuing development of urban areas in recent decades. The increase of impervious land areas can significantly alter watershed hydrology and water quality. Typical impacts to downstream hydrologic regimes include higher peak flows and runoff volumes, shorter concentration times, and reduced infiltration. Urban runoff increases the transport of pollutants and nutrients and thus degrades water bodies adjacent to urban areas. One of the most frequently used practices to restore the hydrology and water quality of urban watersheds is bioretention (also known as a rain garden). Despite its wide applicability, an understanding of its multiple physiochemical and biological treatment processes remains an active research area. To provide a wide ability to evaluate the hydrologic input to bioretention systems, spatial and temporal distribution of storm events in Virginia were studied. Results generated from long-term frequency analysis of 60-year precipitation data demonstrate that the 90 percentile, or 10-year return period rainfall depth and dry duration in Virginia are between 22.9 – 35.6 mm and 15.3 – 25.8 days, respectively. Monte-Carlo simulations demonstrated that sampling programs applied in different regions would likely encounter more than 30% of precipitation events less than 2.54 mm, and 10% over 25.4 mm. Further experimental research was conducted to evaluate bioretention recipes for retaining stormwater nitrogen (N) and phosphorus (P). A mesocosm experiment was performed to simulate bioretention facilities with 3 different bioretention blends as media layers with underdrain pipes for leachate collection. A control group with 3 duplicates for each media was compared with a replicated vegetated group. Field measurement of dissolved oxygen (DO), oxidation-reduction potential (ORP), pH, and total dissolved solids (TDS) was combined with laboratory analyses of total suspended solids (TSS), nitrate (NO3), ammonium (NH4), phosphate (PO4), total Kjeldahl nitrogen (TKN) and total phosphorus (TP) to evaluate the nutrient removal efficacies of these blends. Physicochemical measurements for property parameters were performed to determine characteristics of blends. Isotherm experiments to examine P adsorption were also conducted to provide supplementary data for evaluation of bioretention media blends. The results show that the blend with water treatment residuals (WTR) removed >90% P from influent, and its effluent had the least TDS / TSS. Another blend with mulch-free compost retained the most (50 – 75%) total nitrogen (TN), and had the smallest DO / ORP values, which appears to promote denitrification under anaerobic conditions. Increase of hydraulic retention time (HRT) to 6 h could influence DO, ORP, TKN, and TN positively. Plant health should also be considered as part of a compromise mix that sustains vegetation. Two-way analysis of variance (ANOVA) found that single and interaction effects of HRT and plants existed, and could affect water quality parameters of mesocosm leachate. Based upon the understanding of the physiochemical and hydrologic conditions mentioned previously, a design model of a bioretention system became the next logical step. The computational model was developed within the Matlab® programming environment to describe the hydraulic performance and nutrient removal of a bioretention system. The model comprises a main function and multiple subroutines for hydraulics and treatment computations. Evapotranspiration (ET), inflow, infiltration, and outflow were calculated for hydrologic quantitation. Biomass accumulation, nitrogen cycle and phosphorus fate within bioretention systems were also computed on basis of the hydrologic outputs. The model was calibrated with the observed flow and water quality data from a field-scale bioretention in Blacksburg, VA. The calibrated model is capable of providing quantitative estimates on flow pattern and nutrient removal that agree with the observed data. Sensitivity analyses determined the major factors affecting discharge were: watershed width and roughness for inflow; pipe head and diameter for outflow. Nutrient concentrations in inflow are very influential to outflow quality. A long-term simulation demonstrates that the model can be used to estimate bioretention performance and evaluate its impact on the surrounding environment. This research advances the current understanding of bioretention systems in a systematic way, from hydrologic behavior, monitoring, design criteria, physiochemical performance, and computational modeling. The computational model, combined with the results from precipitation frequency analysis and evaluation of bioretention blends, can be used to improve the operation, maintenance, and design of bioretention facilities in practical applications.
Development of a Guide to Lake and Reservoir Zone Determination
Saji, Niffy (Virginia Tech, 2008-03-17)
Reservoirs are generally created by damming rivers. The upper reaches of any reservoir is generally narrow and winding like the parent river. This is the riverine zone of the reservoir. The reservoir is deepest and widest near the dam. Here, lake-like conditions exist and the water is quiescent. This is the lacustrine zone. The transitional zone separates the lacustrine and riverine zone. It has intermediate characteristics. There are many characteristics, both physical and chemical, that differentiate between these three zones. Based on the differences in characteristics between the three zones, a method has been developed to successfully divide any reservoir into three zones. The method developed was applied to Lake Manassas and the Occoquan Reservoir located in the Occoquan watershed in Virginia. Both are man-made impoundments. Analysis of data, based on the method developed, was successfully in dividing both reservoirs into the three zones. This method may therefore be successfully applied to obtain zonation in reservoirs.
Development of a Web-Based System for Water Quality Data Management and Visualization
Yang, Wei (Virginia Tech, 2010-05-03)
With increasing urbanization and population growth, humankind faces multiple environmental challenges. Stresses on limited resources, especially water resources, are now greater than ever before. Watershed monitoring and management are important components of programs to abate water resource stresses. The increasing water quantity and quality monitoring has produced a need for better data management techniques to manage the vast amount of watershed monitoring data being observed. These data must be stored, error checked, manipulated, retrieved and shared with the watershed management community. The web-based data visualization and analysis technology has played a critical role in all aspects of watershed management. Especially in recent years, computer-assisted data analysis has matured enormously. This maturing technology makes web-based visualization and analysis technology change its role to become an integrated system which combines applications of databases, and internet technology. The main objective of this study is to develop a prototype system which has ability of data visualization and analysis. Microsoft SQL Server is used to build a comprehensive database, which includes all datasets collected by OWML. A Web-Based Data Visualization and Analysis System which provides an integrated interface for permitted users to explore, analyze and download data has been developed.
Development of Design Guidelines for In-Stream Flow Control Structures
Radspinner, Robert Ryan (Virginia Tech, 2009-05-06)
The use of in-stream flow control structures for channel stabilization has become increasingly popular due to its potential cost-effectiveness and ecological benefits. These structures help to protect the bank from erosion and lateral migration. However, a large number of these projects fail due to inadequate design guidelines. This study aims to create authoritative design guidelines which are based on hydraulic and physical criteria attributed to the channel reach. In this report, some of the most common types of in-stream structures have been reviewed and results from a practitioner experience survey have been analyzed. This research has allowed for the selection of the most promising structures which will be studied later in the project.
Development of Transitional Settling Regimen Parameters to Characterize and Optimize Solids-liquid Separation Performance
Mancell-Egala, Abdul Salim (Virginia Tech, 2016-09-20)
Novel settling characteristic metrics were developed based on the fundamental mechanisms of coagulation, flocculation, and settling. The settling metrics determined parameters that are essential in monitoring and optimizing the activated sludge process without the need for expensive or specialized equipment. Current settling characteristic measurements that don't require specialized instruments such as sludge volume index (SVI) or initial settling velocity (ISV), have no fundamental basis in solid-liquid separation and only indicate whether settling is good or bad without providing information as to limitations present in a sludge matrix. Furthermore, the emergence of aerobic granulation as a potential pathway to mitigate solid-separation issues further stresses the need for new settling characteristic metrics to enable integration of the new technology with the current infrastructure. The granule or intrinsic aggregate fraction in different types was of sludge was quantified by simulating different surface overflow rates (SOR). The technique named Intrinsic Settling Classes (ISC) was able to separate granules and floc by simulating high SOR values due to the lack of a flocculation time needed for granules. The method had to be performed in a discrete settling environment to characterize a range of flocculation behavior and was able to classify the granular portion of five different types of sludge. ISC was proven to accurately (±2%) determine the granule fraction and discrete particle distribution. The major significance of the test is its ability to show if a system is producing particles that will eventually grow to become granules. This methodology proved to be very valuable in obtaining information as to the granular fraction of sludge and the granular production of a system. Flocculent settling (stokesian) was found to be predominant within ideally operating clarifiers, and the shift to 'slower' hindered settling (non-stokesian) causes both failure and poor effluent quality. Therefore, a new metric for settling characteristics was developed and classified as Limit of Stokesian Settling (LOSS). The technique consisted of determining the total suspended solids (TSS) concentration at which mixed liquor settling characteristics transition from stokesian to non–stokesian settling. An image analytical technique was developed with the aid of MATLAB to identify this transition. The MATLAB tool analyzed RGB images from video, and identified the presence of an interface by a dramatic shift in the Red indices. LOSS data for Secondary activated-sludge systems were analyzed for a period of 60 days at the Blue Plains Advanced Wastewater Treatment Plant. LOSS numbers collected experimentally were validated with the Takacs et al. (1991) settling model. When compared to flux curves with small changes in the sludge concentration matrix, LOSS was found to be faster at characterizing the hindered settling velocity and was less erratic. Simple batch experiments based on the critical settling velocity (CSV) selection were used as the basis for the development of two novel parameters: threshold of flocculation/flocculation limitation (TOF/a), and floc strength. TOF quantified the minimum solids concentration needed to form large flocs and was directly linked to collision efficiency. In hybrid systems, an exponential fitting on a CSV matrix was proposed to quantify the collision efficiency of flocs (a). Shear studies were conducted to quantify floc strength. The methods were applied to a wide spectrum of sludge types to show the broad applicability and sensitivity of the novel methods. Three different activated sludge systems from the Blue Plains AWWTP were monitored for a 1 year period to explore the relationship between effluent suspended solids (ESS) and activated sludge settling and flocculation behavior. Novel metrics based on the transitional solids concentration (TOF, and LOSS) were also collected weekly. A pilot clarifier and settling column were run and filmed to determine floc morphological properties. SVI was found to lose sensitivity (r < 0.20) when characterizing ISV above a hindered settling rate of 3 m h-1. ISV and LOSS had a strong correlation (r = 0.71), but ISV was subject to change, depending on the solids concentration. Two sludge matrix limitations influencing ESS were characterized by transition concentrations; pinpoint floc formation, and loose floc formation. Pinpoint flocs had TOF values above 400 mg TSS L-1; loose floc formation sludge had TOF and LOSS values below 400 mg TSS L-1 and 900 mg TSS L-1, respectively. TOF was found to correlate with the particle size distribution while LOSS correlated to the settling velocity distribution. The use of both TOF and LOSS is a quick and effective way to characterize limitations affecting ESS.
Dominance Based Measurement of Environmental Performance and Productive Efficiency of Manufacturing
Otis, Paul T. (Virginia Tech, 1999-01-29)
The concept of efficiency measurement is based on the definition of a frontier that envelopes observed production plans. The effect of pollution on productive efficiency is typically studied by considering pollution as not freely disposable (i.e., there is a cost incurred to dispose of pollution) or by assigning shadow prices to pollution outputs. However, the frontier along with the required technological assumptions (such as convexity) needed for a definition of a frontier may be replaced with the concept of pair-wise dominance. With data from a manufacturing facility, the use of pair-wise dominance allows one to consider a wide spectrum of inputs and outputs. Pair-wise dominance can also be applied to segregate production plans into sets according to their relative environmental performance and productive efficiency. These sets are used to identify reference production plans upon which distance-based measures of performance are defined. This research applies pair-wise dominance to time series data from a printed circuit board manufacturing facility to illustrate the approach. The proposed approach is compared to the Data Envelopment Analysis (DEA) approach. It was observed that for detailed production data the proposed approach was more informative concerning the measurement of productive efficiency than the standard methods.
The effect of anoxic selectors on the control of activated sludge bulking and foaming
Mangrum, Carl Robert Lawrence II (Virginia Tech, 1998-10-26)
Laboratory scale activated sludge experiments were conducted on primary effluent municipal wastewater to evaluate the effects of anoxic selectors on controlling activated sludge bulking and foaming. These experiments were conducted with two pilot plants; a three stage anoxic selector preceding a complete mix system (experimental unit) and a complete mix system (control unit). Successful selector operation requires balancing two conflicting requirements; obtain a high substrate concentration in the selector while achieving a high substrate removal efficiency in the selector. The high substrate concentration enables rapid substrate uptake to occur predominately by floc forming microorganisms while the high substrate removal efficiency ensures that a feed-starve cycle is created whereby filamentous microorganisms are selected against. The reported metabolic mechanisms responsible for substrate uptake in the selector are the formation of internal storage products and high rate metabolism. As presented by Jenkins et al., (1993) small amounts of substrate are oxidized in the selector during the formation of internal storage products. Hence, large quantities of substrate can be removed while reducing only small amounts of the terminal electron acceptor. The internal stores are metabolized in the main biological reactor only after the exogenous substrate has been exhausted. High rate metabolism in the selector results in larger amounts of substrate oxidation. Consequently, for successful selector operation large quantities of the terminal electron acceptor must be reduced. The anoxic selector pilot unit successfully reduced activated sludge settleability and biological foams relative to the control unit. Results from this study indicate that the mode of substrate removal was influenced by the initial selector floc load. This is in general agreement with the findings by Goel and Gaudy (1968) and Gaudy and Gaudy (1988) on oxidative assimilation in activated sludge treatment. The floc load depicts the instantaneous organic loading in the selector irrespective of hydraulic retention time. Results from this study further indicate that for lower floc loadings substrate storage is predominate. Alternatively, at higher floc loadings high rate substrate metabolism is predominate. Therefore, it is hypothesized that for selector zones with high enough F/M ratios to promote rapid substrate uptake, the mechanism predominately responsible for substrate removal is influenced by the floc loading.
Effective Modeling of Nutrient Losses and Nutrient Management Practices in an Agricultural and Urbanizing Watershed
Liu, Yingmei (Virginia Tech, 2011-12-05)
The Lake Manassas Watershed is a 189 km2 basin located in the Northern Virginia suburbs of Washington, DC. Lake Manassas is a major waterbody in the watershed and serves as a drinking water source for the City of Manassas. Lake Manassas is experiencing eutrophication due to nutrient loads associated with agricultural activities and urban development in its drainage areas. Two watershed model applications using HSPF, and one receiving water quality model application using CE-QUAL-W2, were linked to simulate Lake Manassas as well as its drainage areas: the Upper Broad Run (126.21 km2) and Middle Broad Run (62.79 km2) subbasins. The calibration of the linked model was for the years 2002-05, with a validation period of 2006-07. The aspects of effective modeling of nutrient losses and nutrient management practices in the Lake Manassas watershed were investigated. The study was mainly conducted in the Upper Broad Run subbasin, which was simulated with an HSPF model. For nutrient simulation, HSPF provides two algorithms: PQUAL (simple, empirically based) and AGCHEM (detailed, process-based). This study evaluated and compared the modeling capabilities and performance of PQUAL and AGCHEM, and investigated significant inputs and parameters for their application. Integral to the study was to develop, calibrate and validate HSPF/PQUAL and HSPF/AGCHEM models in the Upper Broad Run subbasin. "One-variable-at-a-time" sensitivity analysis was conducted on the calibrated Upper Broad Run HSPF/PQUAL and HSPF/AGCHEM models to identify significant inputs and parameters for nutrient load generation. The sensitivity analysis results confirmed the importance of accurate meteorological inputs and flow simulation for effective nutrient modeling. OP (orthophosphate phosphorus) and NH4-N (ammonium nitrogen) loads were sensitive to PQUAL parameters describing pollutant buildup and washoff at land surface. The significant PQUAL parameter for Ox-N (oxidized nitrogen) load was groundwater nitrate concentration. For the HSPF/AGCHEM model, fertilizer application rate and time were very important for nutrient load generation. NH4-N and OP loads were sensitive to the AGCHEM parameters describing pollutant adsorption and desorption in the soil. On the other hand, plant uptake of nitrogen played an important role for Ox-N load generation. A side by side comparison was conducted on the Upper Broad Run HSPF/PQUAL and HSPF/AGCHEM models. Both PQUAL and AGCHEM provided good-to-reasonable nutrient simulation. The comparison results showed that AGCHEM performed better than PQUAL for OP simulation, but PQUAL captured temporal variations in the NH4-N and Ox-N loads better than AGCHEM. Compared to PQUAL, AGCHEM is less user-friendly, requires a lot more model input parameters and takes much more time in model development and calibration. On the other hand, use of AGCHEM affords more model capabilities, such as tracking nutrient balances and evaluating alternative nutrient management practices. This study also demonstrated the application of HSPF/AGCHEM within a linked watershed-reservoir model system in the Lake Manassas watershed. By using the outputs generated by the HSPF/AGCHEM models in the Upper Broad Run and Middle Broad Run subbasins, the Lake Manassas CE-QUAL-W2 model adequately captured water budget, temporal and spatial distribution of water quality constituents associated with summer stratification in the lake. The linked model was used to evaluate water quality benefits of implementing nutrient management plan in the watershed. The results confirmed that without the nutrient management plan OP loads would be much higher, which would lead to OP enrichment and enhanced algae growth in Lake Manassas.
Effectiveness of Disinfectant Residuals in Distribution Systems
Warn, Elin Ann (Virginia Tech, 2004-06-07)
In many drinking water systems in the United States, disinfectant is added to water as it leaves the plant to maintain a residual concentration in the distribution system. The disinfectant residual is maintained to inactivate contamination that enters the distribution system, to control biofilms, and to act as a sentinel for contamination in the distribution system. A model was developed to evaluate the potential effectiveness of the disinfectant residual at inactivating contamination. The model was used to examine contamination of a hypothetical distribution system through backpressure at a cross-connection under different operating conditions. The dilution and pathway of the hypothetical contaminant were examined as the contaminant moved through the system. Disinfection and inactivation kinetic relationships were used to model the inactivation of the contaminant in the system by the amount of disinfectant present. The model showed that both chlorine and chloramines in each decay and inactivation condition considered provided some benefit over no disinfectant at all when examining susceptible organisms. Chlorine, under medium and low decay conditions, provided the best inactivation. Where 29.8% of total node time steps received a contamination of concern in the absence of disinfectant residual, as low as 4.8% of total node time steps received a contamination of concern in the presence of disinfectant residual. Chloramines was found to persist longer in the distribution system, but resulted in much lower inactivation compared to chlorine. Disinfectant doses typical of common distribution system operation were able to reduce the impact of contamination once it entered the distribution system but, except for four cases, were unable to prevent contamination from spreading within the distribution system. Therefore, it was concluded that presence of a disinfectant residual will reduce the total number of exposure opportunities from a contamination event, but cannot be relied upon to eliminate the chance of exposure resulting from contamination.
Effectiveness of Porous Pavement and an Infiltration Trench as Urban Best Management Practices
Lathrop, Mitchell Currie (Virginia Tech, 1999-02-12)
The following study is a demonstration of the effectiveness of porous pavement and an infiltration trench as Best Management Practices (BMPs) in the reduction of stormwater and its constituents. The field work of the study was conducted from 1986 through 1988 and the report was written in 1990 and finalized in 1996. Results of the study show that porous pavement and the infiltration trench significantly reduced the volume of stormwater runoff as well as its constituents from an urban parking lot area. In addition, wetfall and dryfall were found to be the major contributors to the runoff loading and yet were not comparable to associated studies. Peak and total flow runoff volumes were reduced significantly thereby reducing the overall pollutant loading. Antecedent dry period was found to be related to pollutant loading but only up to about 5 days total.
Effects of a surface circulator on temperature, dissolved oxygen, water velocity, and photosynthetic yield in Falling Creek Reservoir
Elam, Kevin Patrick (Virginia Tech, 2008-12-02)
Cyanobacteria are a naturally occurring component of reservoir aquatic ecosystems. Given that some species possess the ability to control their depth within the water column, they have a competitive advantage over other species of photosynthetic organisms. This leads to the potential for cyanobacteria blooms, and because of taste and odor problems, as well as possible toxin production associated with certain species of cyanobacteria, these organisms can cause major problems in drinking water production. The Western Virginia Water Authority installed a solar-powered circulator in Falling Creek Reservoir, located in Bedford County, Virginia, in an attempt to limit the growth of these organisms through limiting light exposure by circulating them deeper within the reservoir. Experiments were performed during the summer of 2008 to quantify the effect of the circulator on the reservoir. Temperature, dissolved oxygen, water velocity, and photosynthetic yield were monitored before and during operation of the unit. The overall effect of the mixer was limited to the first 10 m immediately adjacent to the unit during the afternoon. The effect was stronger during the morning when the difference in density between the intake water and the surface of the reservoir was smaller, allowing the water to travel up to 80 m away from the unit. Although the circulator was only intended to mix and possibly deepen the epilimnion, the entire reservoir became mixed about two weeks after the circulator was put into operation. The reservoir is quite shallow, leading to a weak stratification that is easily disrupted by the operation of the circulator.
The effects of seasonal change, impoundment, and stratification on trihalomethane precursors
Aiken, Anne M. (Virginia Tech, 1990-04-05)
The major objectives of this study were to investigate the effects of seasonal changes in Lake Manassas and its watershed (late winter to late summer), the impoundment of Broad Run, and the stratification of Lake Manassas on trihalomethane (THM)-precursors in Broad Run, upstream and downstream of the reservoir, and in Lake Manassas. An additional objective was to determine the molecular-size distributions of the dissolved organic carbon, and the THM precursors of the organic carbon pool in Lake Manassas during stratification. Raw water samples were collected from March through August on Broad Run immediately upstream of the reservoir, at two sites in the reservoir-- one approximately 0.27 miles from the dam and the second, at a more central location, 0.73 miles from the dam, and on Broad Run 2.81 miles below the dam. During stratification two samples were collected from each lake site-- one from the epilimnion, and the second from the hypolimnion. All of the samples were size fractionated by ultrafiltration and chlorinated for determination ofTHMFP. The differences in THMprecursor characteristics were determined by assessing the differences in the total organic carbon (TOC) concentrations and THM-formation potentials (THMFPs) of the various size fractions. The TOe and THM concentrations generally increased from late winter to late summer at all stations. The concentrations in Lake Manassas and in Broad Run below the dam were consistently higher than those observed in Broad Run upstream of the lake, indicating that impoundment causes an increase in levels of THM precursors. In addition, during stratification higher THM yields were produced by the predominantly low-molecular-weight precursors Â« 5,000) in the epilimnion of Lake Manassas, while the predominantly high-molecular-weight precursors (> 5,000 daltons) were low-yielding-THM precursors.

Browsing by Author "Grizzard, Thomas J."

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