Browsing by Author "Sen, Dipankar"

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    Cod removal, nitrification and denitrification kinetics and mathematical modeling of an integrated fixed film activated sludge (IFAS) system
    Sen, Dipankar (Virginia Tech, 1995)
    Biological nitrogen and phosphorus removal are being recommended at several wastewater treatment facilities in the U.S. to control eutrophication in water bodies receiving their effluent. In several instances, nitrogen removal is being recommended on a year round basis at plants located in the temperate climates. Concerns have been raised regarding the cost of additional reactors and clarifiers required for nitrogen removal in winter using activated sludge systems. Several facilities do not have the space to construct additional units. This research was undertaken to evaluate the potential for reducing reactor and clarifier requirements, maximize use of existing facilities, and economize costs for year round nitrification and nitrogen removal. The purpose was to develop Integrated Fixed Film Activated Sludge Systems in which biofilm support media was installed in the activated sludge basins to enhance nitrogen removal. The objectives were to evaluate the COD removal, nitrification and denitrification kinetics, which would help develop design and mathematical models for the process, and optimize the layout in terms of costs and media required for nitrogen removal. A bench scale pilot study was undertaken in conjunction with two full scale studies with two types of media: (i) free floating media and (ii) media fixed in frames. Amongst biofilm support media in the first category, sponge cuboids (Captor) were selected. For the second category, rope type Ringlace media was selected. Following preliminary screening for satisfactorily simulation of full scale conditions in a bench scale system, the IFAS-Sponge system was selected for kinetic coefficient evaluation and IF AS system model development.
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    A Decision Support System for Indirect Potable Reuse Based on Integrated Modeling
    Lodhi, Adnan Ghaffar (Virginia Tech, 2019-07-01)
    Optimal operation of water reclamation facilities (WRFs) is critical for an indirect potable reuse (IPR) system, especially when the reclaimed water constitutes a major portion of the reservoir's safe yield. It requires timely and informed decision-making in response to the fluctuating operational conditions, e.g., weather patterns, plant performance, water demand, etc. Advanced integrated modeling techniques can be used to develop reliable operational strategies to mitigate future risks associated with water quality without needing high levels of financial investment. The Upper Occoquan Service Authority (UOSA) WRF, located in northern Virginia, discharges nitrified reclaimed water directly into a tributary of the Occoquan Reservoir, one of the major water supply sources for Fairfax County. Among the many operational challenges at UOSA, one is to regulate the nitrate concentration in its reclaimed water based on the denitrifying capacity of the reservoir. This study presents an integrated model that is used to predict future reservoir conditions based on the weather and streamflow forecasts obtained from the Climate Forecast System and the National Water Model. The application captures the dynamic transformations of the pollutant loadings in the streams, withdrawals by the water treatment plant, WRF effluent flows, and plant operations to manage the WRF performance. It provides plant operators with useful feedback for correctly targeting the effluent nitrates using an intelligent process simulator called IViewOps. The platform is powered by URUNME, a new software that fully automates the operation of the reservoir and process models integrating forecasting products, and data sources. URUNME was developed in C#.NET to provide out-of-the-box functionality for model coupling, data storage, analysis, visualization, scenario management, and decision support systems. The software automatically runs the entire integrated model and outputs data on user-friendly dashboards, displaying historical and forecasting trends, on a periodic basis. This decision support system can provide stakeholders with a holistic view for the design, planning, risk assessments, and potential improvements in various components of the water supply chain, not just for the Occoquan but for any reservoir augmentation type IPR system.
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    Kinetics of the release and precipitation of phosphorus in anaerobic digesters sequencing biological phosphorus removal systems
    Sen, Dipankar (Virginia Polytechnic Institute and State University, 1986)
    The extent of release and precipitation of phosphorus stored in the poly-phosphate granules of microorganisms present in anaerobic digesters sequencing a biological phosphorus removal (BPR) activated sludge system was examined. The research was conducted at the York River Wastewaster Treatment plant which was converted from a conventional system to a A/O process for biological phosphorus removal. The primary and secondary anaerobic digesters each had a solids retention time of approximately 120 days. The results indicated that at least 60 percent of the phosphorus in the poly-phosphate granules would be solubilized during endogenous decay and digestion under anaerobic conditions. This is accompanied by the release of potassium, magnesium and limited amounts of calcium. The release of magnesium and phosphorus in the high ammonium containing environment of the primary digester results in the precipitation of about 1000 mg/L of struvite (MgNH₄PQ₄H₂O), a relatively adhesive and kinetically fast precipitate. Struvite can form on floes of biomass inside the primary digester, on walls, inside pipes, and in areas affected by lower temperatures and higher pH. The phosphorus level in the secondary digester effluent is controlled by the kinetics of formation of competitive precipitates like struvite, calcium-phosphorus compounds and vivianite (Fe₃(PO₄)₂). The formation of vivianite is limited by the competitive precipitation of siderite (FeCO₃ ). The extent to which the compounds are precipitated depends on the solids retention times, ionic strengths, size and amorphous nature of the precipitates and the substitution of foreign ions in the crystal lattice. The effective solubility products of these precipitates, as applicable to anaerobic digesters, were determined.