LEE- Çevre Bilimleri Mühendisliği ve Yönetimi Lisansüstü Programı

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http://hdl.handle.net/11527/19235

Gözat

Konu "activated sludge" ile LEE- Çevre Bilimleri Mühendisliği ve Yönetimi Lisansüstü Programı'a göz atma
  • Öge
    Critical evaluation for nitrogen removal performance of a stereotype activated sludge system under dynamic process conditions
    (Graduate School, 2021-12-28) Bodur, Minel ; İnsel, Güçlü Hayrettin ; 501181724 ; Environmental Sciences Engineering and Management
    In recent years, with the increasing population and the effects of global warming, the design, construction, and operation of domestic and urban wastewater treatment plants are carried out considering the treatment steps that provide nutrient removal. The most suitable treatment alternative to remove nutrients from wastewater in terms of applicability and cost are determined to be Biological Nutrient Removal processes. Because of the need for biological nutrient removal, stress caused by the nutrients and organic matter on receiving water environments are reduced and active sludge systems gain more and more attention moving forward. As widely known, highly complex biological reactions occur in activated sludge systems and although stable state conditions are generally used to simplify design calculations, active sludge systems operate under dynamic conditions. This indicates that input wastewater characterization as well as the inlet flow, various environmental factors (temperature, precipitation, etc.) and operating conditions vary depending on time. Therefore, various modeling tools are used to understand the treatment system more efficiently. With the modelling tools, it is possible to comprehend system dynamics and determine the rehabilitation, refurbishment and expansion requirements of existing treatment plants, while for the new plants, plant design can be optimized considering modeling outputs. Additionally, data from pilot-scale reactors can be evaluated through models and used to predict full-scale plant performance. To reflect the actual conditions at wastewater treatment plants, process simulators which provide guidance on determining the design principles of wastewater treatment plants, creating automation scenarios, choosing equipment, and evaluating process performance for both wastewater and sludge units, are used. The main purpose of this thesis is to evaluate the use of oxidation ditch reactors in series in terms of nitrification and denitrification processes and to model the actual behavior of an Oxidation Ditch (OD) system operated by following the pre-denitrification principles using input wastewater data collected from an urban wastewater treatment plant in the Marmara Region (Istanbul, Turkey) under dynamic conditions. Sumo software was used to model and simulate the wastewater treatment plant under dynamic conditions and the treatment efficiency of the plant in terms of nitrogen removal was examined. This thesis mainly focuses on nitrogen removal under dynamic conditions in a municipal wastewater treatment plant that employs four oxidation ditches located upstream of Bio-P tanks and operated in series. Although simultaneous nitriding denitrification principles apply to plant configuration due to oxidation ditches, the treatment plant is operated as a conventional active sludge system and considers pre-denitrification principles, which the first oxidation ditch is operated under anoxic conditions. The second oxidation ditch in the plant is operated under anoxic and aerobic conditions by controlling the diffusers (on/off), while the remaining two oxidation ditches are continuously aerated by the diffusers located at the bottom of the tanks and operated under aerobic conditions. In this context, a dynamic simulation was carried out using Sumo software for the entire oxidation ditch system. Bio-P tanks and final sedimentation tanks were included in the model to ensure system integrity, but only the nitrogen removal efficiency of oxidation ditch reactors was examined within the scope of this thesis. Modeling and simulation results confirmed that the minimum nitrate production rate occurred in the first oxidation ditch due to lack of aerobic environment. It was also examined that the nitrate recirculated from the fourth oxidation ditch to the first oxidation ditch was consumed within this first reactor. Hence, transfer of recirculated nitrate to the second reactor does not occur. Additionally, it was confirmed by the modelling studies that nitrate is consumed within the first reactor only at rates of the recirculated nitrate. Even if the second OD reactor is operated under anoxic conditions to provide denitrification for the recirculated nitrate, the volume of the first oxidation ditch cannot be used efficiently, because the recirculated nitrate from the fourth OD to the first OD is very low due to simultaneous nitrification denitrification occurs in the remaining reactors. In addition, results confirmed that the highest nitrate consumption rate was achieved within the first reactor, while this is followed by the second, third and fourth reactors, respectively. Nitrate production and utilization rates were determined through model outputs, which were very close in the second oxidation ditch due to operating conditions and creating both anoxic and aerobic zones, while in the third and fourth reactors, the difference between these rates increases due to decreased anoxic volume. Considering the information obtained from the modeling studies, it can be stated that the system is divided into two parts as the first oxidation ditch reactor and the remaining tanks (OD-2, OD-3 and OD-4). This is because nitrate can be removed from wastewater in OD-1 reactor only at a rate and an amount of the recirculated nitrate, which is determined to be low due to simultaneous nitrification denitrification occurred within the remaining OD reactors. Hence, the first oxidation ditch reactor volume, operated under anoxic conditions to provide denitrification, is not used effectively, and does not fit for purpose. Therefore, it was recommended that the optimization of the system could be achieved by operating four oxidation ditches in parallel with the principles of simultaneous denitrification nitrification. In addition, it is envisaged that this will also provide flexibility to plant operators in case of maintenance works etc., and the treatment system can be operated without interruption even if one of the tanks is out of operation. It may also be beneficial to select simpler and more efficient treatment systems for the plant configurations to prevent such treatment complications in the future.
  • Öge
    Plant-wide process analysis targeting reliable estimation of biogas production from anaerobic sludge digestion
    (Graduate School, 2024-05-17) Özyıldız, Gökşin ; İnsel, H. Güçlü ; 501172714 ; Environmental Sciences Engineering and Management
    Anaerobic sludge digestion is a critical and widely used technology employed in wastewater treatment plants for the stabilization of solids generated during the treatment process and for the production of biogas as a renewable energy source. This process typically involves the treatment of mixed primary and biological sludge in digesters. Primary sludge comprises inorganic solids and organic matter, whereas biological sludge is rich in active biomass and residues from biochemical reactions. The process faces challenges, such as the lower organic degradation efficiency of waste activated sludge (WAS) under both aerobic and anaerobic conditions, necessitating extended sludge retention times. Hydrolysis, identified as the rate-limiting step in microbial degradation across various environmental conditions, significantly influences the efficiency of the anaerobic digestion process. Therefore, the nature of the degradation of the hydrolysable matter directly influences the efficiency of the anaerobic digestion process. Traditional activated sludge models, which conceptualize COD turnover through a single hydrolysable matter component (XB), do not adequately account for the range of hydrolysis kinetics observed in practice. Despite a plethora of parameter values proposed for anaerobic hydrolysis, research into the kinetic analysis of anaerobic sludge digestion, particularly considering varying mixes of primary and waste activated sludge, remains sparse. The appropriate selection of wastewater treatment and sludge disposal methods depends on specific aspects, including the organic matter components in the influent wastewater and the kinetic parameters specific to the biomass. Therefore, the integration of experimental studies with plant-wide modeling tools is becoming an important strategy for selecting suitable treatment systems and executing reliable process calculations. In this study, seven large-scale wastewater treatment plants were analyzed for operational parameters and dynamic modeling was combined with plant-focused batch experiments to uncover deviations from the calculated data during the design phase. The long-term performance of three full-scale carbon and biological nutrient removal plants with anaerobic sludge digestion systems was rigorously monitored. This approach aimed to improve the understanding of process kinetics for carbon removal, nutrient removal, and anaerobic digestion. It involved COD fractionation, nitrification and denitrification kinetics, and anaerobic batch experiments. Plant-specific kinetic parameters were determined experimentally and integrated with plant-wide SUMO model simulations. The research revealed that anaerobic hydrolysis rates are significantly lower than the available literature values. The study identified this stage as a critical point in optimizing biogas production. Anaerobic digestion batch experiments and plant-wide model calibration showed that anaerobic hydrolysis rate is the critical parameter for biogas production. In parallel, anaerobic digestion performance and modeling studies in full-scale plants showed low biogas production efficiency. The innovative use of plant-wide model calibration, in conjuction with anaerobic digestion tests in the study, illuminated the significant challenges posed by low anaerobic hydrolysis rates for efficient biogas production. This was demonstrated by the poor performance and low biogas yields in full-scale plants. The study also discovered that the degradation rate of primary sludge through anaerobic hydrolysis is significantly higher compared to the hydrolysis rate of biological sludge, shedding light on areas for process improvement. In the second stage of the study, the effect of anaerobic hydrolysis rate on biogas production was investigated with mesophilic digesters in seven large-scale wastewater treatment plants. This phase was critical in understanding how the process parameters underpinning anaerobic digestion could be optimized to enhance biogas production.