A study of brush seal porous media resistance coefficients

Developments in turbine technologies lead to higher operating temperature and pressure conditions. Parasitic leakage flows around the turbine account for considerable efficiency losses that increase fuel cost dramatically. Brush seal has recently emerged as an improved sealing technology to provide better leakage performance and to replace classical labyrinth seals. In order to optimize efficiency, comprehensive study of the factors causing the leakage is required. The leakage performance of the brush seal is directly related with geometry, operating inlet and outlet boundary conditions, bristle pack configuration. Brush seal flow and pressure profiles with turbine operating conditions become complicated, and analytical formulations remain inadequate to correlate design parameters and leakage performance in operating conditions. Recently brush seals have found ever increasing applications in steam turbines. Literature review indicates that there is very limited studies of brush seal for steam environment. There is also no correlation available for brush seal porosity coefficients in the literature. In an attempt to meet this need, six brush seals have been tested in a rotary test rig up to 100 psi upstream pressure. Analytical correlations and CFD (Computational Fluid Dynamics) simulations have been performed for test seals and results have been correlated with the test data. Axisymmetric CFD models have been designed to reach anisotropic resistance coefficients for the brush seals based on experiments. Porous Medium Approach has been applied for representing bristle pack. Leakage rate of brush seals (steam environment) has been optimized through CFD models. Moreover, velocity and pressure characteristics in the bristle pack have been illustrated for an optimum solutions. Consequently, empirical correlations for brush seal porosity coefficients have been correlated through a systematic methodology

The impact of COVID-19 pandemic in medical waste amounts: a case study from a high-populated city of Turkey

In this study, the amount of medical waste generated in a high-populated city in Turkey between January 2018 and August 2021 was evaluated, and the effect of the COVID-19 pandemic on waste amounts and waste production rate was investigated. While a total of 79,027 kg/month of medical waste was produced in the city before COVID-19, this value reached 116,714 kg/month after COVID-19. The increase in the amount of medical waste due to the COVID-19 pandemic in the province was calculated as 48% on average. It was determined that 75% of this waste amount originates from public hospitals in the city. While the production of medical waste was 0.86 kg/bed day in the pre-COVID-19 period, this value increased to 0.96 kg/bed day in 2020 and to 1.34 kg/bed day in 2021 with the COVID-19 pandemic. According to the results obtained, the amount of medical waste reached in the province due to COVID-19 is the amount of medical waste expected to be generated in the 2040s under normal conditions. It is a very important issue in terms of public health that the capacity of waste disposal in medical waste management in cities is flexible to respond to severe epidemic conditions. Based on the information obtained within the scope of the study, changes in the amount of medical waste in a city with a dense population under pandemic conditions can be obtained based on real data and projections regarding disposal capacity can be made more realistically

Climate change adaptation exertions on the use of alternative water resources in Antalya, Turkiye

This study presents the payback periods of applying rainwater harvesting (RWH) and/or graywater reuse (GWR) systems as alternative water resources in different building typologies, such as a hospital, shopping mall, and hotel. These buildings are under operation in the Antalya Province of Turkiye, which is a large city having the densest tourism activities. The significance of the work performed through the cost-benefit analyses for the selected case studies basically lies on the water savings while serving to four of the sustainable development goals, namely, clean water and sanitation, sustainable cities and communities, responsible consumption and production, and climate action. These efforts may be considered valuable urban-based solutions toward climate change effects. Thorough surveys on the existing selected typologies are conducted regarding their water consumption and probable water savings via reuse activities. As-built plumbing projects and plans are also investigated during the accomplishment of the comprehensive design work leading to the calculation of the total investment and operation costs of the rainwater harvesting and graywater reuse practices. The up-to-date prices are used in monetary terms, and euro currency is used to make the results more meaningful by the interested parties. All the selected typologies undergo cost-benefit analysis for both of the alternative water reuse systems. The payback periods are calculated as 6, 2, and 9 years for RWH and as 5, 6, and 9 years for GWR for the hospital, shopping mall, and the hotel, respectively. The water savings for RWH varied between 20% and 50% whereas for GWR, the range was 48%-99%. Both of the systems are performed for the shopping mall simultaneously, and the resulting payback period is found to be 5 years, and water saving reached 72%. Recent information on the amortization periods in the literature states that less than a decade demonstrates achievable and highly acceptable applications. As such, the design attempts in this study also correlated with these findings. However, feasibility of these practices may be increased by encouraging the public on their utility and benefit of water savings. As is the case in many of the developed countries, incentives like tax reductions and even exemptions may be realized to achieve better applicability of these alternative technologies

Türkiye'de optimum maliyete dayalı atıksu arıtma tesisi tasarımı

Besides the civilization process, the economic conditions of Turkey make realization of the most of the investment necessary for urbanization, impossible.  One of the strongest examples of this is the inadequacy of the wastewater collection and treatment systems in our cities. It is an absolute necessity of the life in a city that the discharged water shall be collected, treated and disposed to the receiving bodies afterwards, without any damage. Therefore; determination of the treatment method for each population range, based on optimum cost and application, provides most convenient use of the already limited financial resources of our country, considering the variable populations of around 3,000 municipalities, which do not have a wastewater treatment plant. In this study, a standard method for the design and establishment of a wastewater treatment plant process, base on optimum cost for the settlement populations ranging between 5,000 people up to 2,000,000, will be proposed. In the determination of this method the most convenient processes of the available treatment processes have been studied based upon the analyses, carried in all population ranges in the consideration of the laws and regulations currently in force, unit wastewater formation with respect to population and wastewater characterization. The investment amounts obtained, and main operational costs have been analyzed and the most convenient treatment technology has been proposed for each of population range. Keywords: Wastewater, finance and optimization of wastewater treatment plant, unit treatment cost.   Türkiye’de atıksu arıtma tesisi olmayan yaklaşık 3 000 belediyenin değişken nüfus değerleri dikkate alındığında her biri için optimum maliyete dayalı arıtma yönteminin belirlenmesi ve uygulanması kısıtlı finansman kaynaklarının uygun biçimde kullanılmasını sağlar. Bu çalışmada nüfusu 5 000 ile 2 000 000 arasında değişen yerleşim birimleri için optimum maliyete dayalı atıksu artıma tesisi prosesinin belirlenmesine çalışılmış ve tasarımı için bir standart yöntem önerilmiştir. Bu yöntemin belirlenmesinde mevcut kanun ve yönetmelikler, nüfusa bağlı birim atıksu oluşumu ve atıksu karakterizasyonu, bütün nüfus değerleri için hesaplara temel alınmıştır. Mevcut arıtma proseslerinin uygun olanları denenmiş, elde edilen yatırım maliyetleri ve ana işletme giderleri, finansman hesaplarından değerlendirilerek, her nüfus aralığı için birim atıksu miktarı başına en düşük maliyeti getiren arıtma teknolojisi optimum yöntem olarak önerilmiştir.  Anahtar Kelimeler: Atıksu, atıksu arıtma tesisi finansmanı ve optimizasyonu, birim arıtma maliyeti. &nbsp

Setting Measures for Tackling Agricultural Diffuse Pollution of Küçük Menderes Basin

We explained the methodology used in setting the basic and supplementary measures for diffuse pollutants at Küçük Menderes Basin. As the majority of diffuse pollutants arise from livestock breeding and agricultural activities, we focused to propose measures regarded with tackling the pollution from agricultural activities. The types and distribution of diffuse loads were expressed by total nitrogen and phosphorous parameters. We used the results of a yearlong surface water quality monitoring involving physico-chemical, chemical and biological parameters with specific pollutants and priority substances, set in the European Union Water Framework Directive as the AquaTool input data. The AquaTool model was run for attaining the outcomes of a series of measures determined according to the ecological sensitivity of each water body. The removal efficiency of pollution loads provided by the best management practices in agricultural activities and livestock breeding were compiled from literature, and typical removal rates were further determined for the basin. We produced nine alternative scenarios at first cycle for determining compliance measures for mitigating point and diffuse sources of pollution in surface water bodies, and water quality improvements observed in the Model were reported. A number of exemptions were defined for some of the water bodies that could not achieve the environmental objectives at the end of first implementation cycle. 759 proposed measures for tackling diffuse pollution were 81% of the total measures considered. Additionally, the measures for mitigating diffuse agricultural pollution were almost equal to half of the diffuse pollutant measures, and 40% of the overall measures liste

Mathematical modeling of rapid mixing unit in pilot scale drinking water treatment plant

Konvansiyonel arıtma üniteleri suda bulunan partiküler ve kolloidal maddelerin uzaklaştırılmasında yaygın olarak kullanılmaktadır. Ham sudaki organik maddenin karakteri ve konsantrasyonu, bulanıklık, pH, alkalinite ve sıcaklık gibi parametreler arıtma verimini önemli ölçüde etkilemektedir. Arıtma ünitelerinin verimini artırmak amacıyla genellikle inorganik pıhtılaştırıcılara ihtiyaç duyulmaktadır. İnorganik pıhtılaştırıcılar hızlı karıştırma ünitesine ilave edilmektedir ve suda çözündüğünde pH ile diğer parametrelere etki edebilmektedir. Konvansiyonel arıtma ünitelerinden biri olan hızlı karıştırma ünitesi, partiküler ve kolloidal maddelerin destabilize edilmesinde önemli rol oynamaktadır. Hızlı karıştırma ünitesinin verimli olması sonraki ünitelerin de verimlerini etkilemektedir. Bu çalışma kapsamında Büyükçekmece İçme Suyu Arıtma Tesisi ham suyu ile pilot ölçekli tesis işletilerek hızlı karıştırma ünitesi modellenmiştir. Ham su parametreleri kullanılarak hızlı karıştırma ünitesinin çıkış pH değerini tahmin edebilmek için korelasyon ve regresyon analizleri gerçekleştirilmiştir. İstatistiksel analiz ve modellemede Excel veri çözümleme araçları kullanılmıştır. %1,90 hata sınırı içerisinde pH değeri tahmin edilmiştir. Böylece, Türkiye’de ilk defa hızlı karıştırma ünitesi için bir matematiksel model oluşturulmuştur. Bu sonuçlar, oluşturulan modelin içme suyu arıtma tesislerinde kullanılabilir olacağını göstermektedir.Conventional treatment units are widely used for the removal of particulate and colloidal substances in water. Parameters such as character and concentration of organic matter in raw water, turbidity, pH, alkalinity and temperature significantly affect the treatment efficiency. Inorganic coagulants are usually needed to increase the efficiency of treatment units. They are added to the rapid mixing unit and can affect pH and other parameters when dissolved in water. The rapid mixing unit, one of the conventional treatment units, plays an important role in destabilizing particulate and colloidal substances. The efficiency of the rapid mixing unit also affects the efficiency of the subsequent units. Within the scope of this study, a pilot plant was operated with the raw waters of Buyukcekmece Drinking Water Treatment Plant and a rapid mixing unit was modeled in terms of pH. Correlation and regression analyses were carried out to estimate the outlet pH of the rapid mixing unit by using the raw water parameters. Excel data analysis tools were used in statistical analysis and modeling. The pH value was estimated within the 1.90% error limit. Thus, a mathematical model has been developed for the rapid mixing unit for the first time in Turkey. These results indicate that the model created will be usable in drinking water treatment plants

Evaluation of aerobic stabilization of biological treatment sludges

Ülkemizde uygulanan çevre mevzuatı gerekleri, atıksu arıtma tesislerinde oluşan çamurun arıtımını ve nihai uzaklaştırılmasını zorunlu kılmaktadır. Evsel ve endüstriyel atıksu arıtma tesislerinden kaynaklanan arıtma çamurları üzerinde yapılan analizler sonucu, bu çamurların özellikle toplam ve çözünmüş organik karbon değerlerinin yönetmelikteki değerleri sağlamadığı ve çamurların bu parametreler bakımından tehlikeli atık sınıfında değerlendirmesi gerektiğini ortaya koymaktadır. Bu çalışma kapsamında Marmara Bölgesi’nde yer alan çeşitli evsel ve endüstriyel arıtma tesisinden kaynaklanan çamurların organik madde içerikleri değerlendirilmiş ve bu çamurların stabil hale getirilmesi için aerobik stabilizasyon işlemi uygulanmıştır. Aerobik stabilizasyon reaktörlerinde, 15 gün süreyle organik madde içeriklerinin değişimi UAKM, TOK ve ÇOK parametreleri esas alınarak ve evsel çamur numuneleri için zehirlilik parametresi de dikkate alınarak incelenmiştir. Elde edilen sonuçlara göre aerobik stabilizasyon sonunda genel olarak TOK değerleri azalırken, ÇOK değerlerinde çamur numunelerine bağlı olarak artış ya da azalmalar gözlenmiştir. İncelenen evsel çamurların ikisinde de TOK konsantrasyonu %50’den daha fazla azalırken ÇOK değerlerinde artış tespit edilmiştir. Endüstriyel atıksu arıtma çamurları arasında en yüksek TOK giderimi %62 ile Nevresim Endüstrisi çamurunda gözlenmiş olup, bu endüstri ÇOK giderimde de en yüksek verimi sağlamıştır. Elde edilen bu sonuçlar ışığında, aerobik stabilizasyon işleminin uygulanma aşamasından önce her tesis için ayrıca değerlendirme yapılması gerekliliğini ortaya koymuştur. Her çamur örneği için standartların sağlanması aerobik stabilizasyon ile mümkün olamamasına rağmen, bu işlemin bazı organik maddelerin giderilmesini sağladığı aerobik stabilizasyon sonrasında evsel numunelerdeki zehirliliğin tamamen giderilmesi ile ortaya konmuştur. Anahtar Kelimeler: Çamur, stabilizasyon, aerobik, evsel- endüstriyel-tehlikeli atık.The main waste-product of the biological wastewater treatment processes is the excess sludge which needs to be disposed properly to prevent the entry of the pollutants back into the water cycle, especially after the disposal of the wasted sludge cakes into the landfill area. During the adaptation period of European Union membership of Turkey, the increase in the number of both municipal and industrial Wastewater Treatment Plant (WWTP) due to the stringent new regulations for wastewater treatment will pose more significant sludge disposal and sanitation problems in the future for Turkey. Treatment and ultimate disposal of domestic and industrial wastewater treatment plant sludges is obligated according to the regulations in Turkey. Treatment sludges categorized in three different groups namely: inert sludge, non-hazardous sludge and hazardous sludge according to the characteristics of the sludge. The total organic carbon (TOC) concentration of the sludge itself and dissolved organic carbon (DOC) concentration in the eluent of the sludge are mainly used for this classification. The higher levels of TOC and DOC values qualifies the domestic and industrial wastewater treatment sludges as hazardous sludge. The principal objective of sludge treatment is its stabilization, that is a controlled decomposition of easily degradable organic matter resulting in a significant reduction of volatile suspended solids (VSS) content, a change of an unpleasant smell into an earthy one, and an elimination of sludge putrescibility. Aerobic biological stabilization at ambient conditions has traditionally been undertaken for the stabilization of treatment sludges originated from both domestic and industrial wastewater treatment plants. In this study the characterization of the different treatment sludges originated from domestic and industrial wastewater treatment plants in Turkey was investigated and the stabilization level of these sludges was evaluated by using aerobic stabilization process. The stabilization level of sludges was evaluated by monitoring the VSS, TOC and DOC content of the sludge. Moreover, ecotoxicological assays were conducted on domestic wastewater treatment plant sludges to observe the effect of stabilization on the toxicity. Respirometric and modeling studies were also performed to assess the decrease in the organic content of the domestic wastewater treatment plant sludge during aerobic stabilization. The results of analysis conducted on the sludge itself and sludge eluent indicated that the sludges are in hazardous nature. These results suggest that the treatment sludge generated from both domestic and industrial treatment plants have to stabilized before ultimate disposal. During the course of the aerobic stabilization experiments, VSS, TOC and DOC measurements were performed at the beginning and 15 days after the beginning (at the end of the stabilization experiment) in order to monitor the extent of VSS, TOC and DOC removal. Measured TOC and DOC concentrations during the stabilization experiments of studied treatment sludges did not show a consistent trend during the 15 days of stabilization. However, the stabilization of the industrial wastewater treatment plants sludges showed a paralel stabilization to the domestic sludge. However, it is important to conduct laboratory studies prior to the application of aerobic stabilization to a treatment plant on the case basis. The acute toxicity as EC20 (%) and EC50 (%) shows the toxic value in terms of effective concentrations (%) of tested solutions that result in 20 and 50% of bioluminescence decrease. The EC20 and EC50 values were found between 0.3 and 7.3% for the studied raw domestic sludges which is in accordance with the literature data. Significant decrease in the toxicity of domestic wastewater treatment plant sludges were observed at the end of the 15 days of aerobic stabilization. The evaluation of the results obtained in this study showed that aerobic stabilization could be an alternative for stabilization of sludges originated from domestic and industrial wastewater treatment plants. However, the organic content of the sludges mainly depend on the influent wastewater characterization of wastewater treatment plant which affects the stabilization performance. Sludge stabilization results indicate higher VSS, TOC and DOC removal efficiencies for domestic wastewaters compared to the industrial sludges. Although aerobic stabilization was not successful for the compliance with the standards in each case, the removal of toxicity exerted by sludges after 15 day-stabilization suggest that at least some toxic organic material has been succesfully biodegraded during the stabilization. In order to provide appropriate municipal and industrial sludge management in Turkey, more elaborate research and engineering experience should be gained. Keywords: Sludge, stabilization, aerobic, domestic- industrial-hazardous waste

Kademeli beslemeli biyolojik azot giderim sistemlerinin bilgisayar destekli tasarımı

Tez (Doktora) -- İstanbul Teknik Üniversitesi, Fen Bilimleri Enstitüsü, 1996Thesis (Ph.D.) -- İstanbul Technical University, Institute of Science and Technology, 1996 Gelişmiş ülkelerde azot-fosfor gibi besi maddelerine ilişkin deşarj standartları giderek sıküaştınlmaktadır. Avrupa BirliğTne üye olma hazırlığı içindeki Türkiye'nin de "Su Kalite Yönetimi" konusundaki bu gelişmelere karşı gerekli önlemleri şimdiden alma zorunluluğu vardır. Buradan hareketle, bu çalışmada, aüksulardan azot parametresinin giderilmesi amacıyla kademeli olarak beslenen nitrifikasyon-denitrifikasyon sistemlerine yönelik bir tasarım modeli ve bu modelin tam karışımlı, sürekli sistemler için çözümünü yapan bir bilgisayar programı geliştirilmiştir. Biyolojik azot gideriminin temellerine değinilerek kademeli beslemeli sistemlerle ilgili dünya literatürünün bir özeti çalışmanın basma eklenmiştir. Kademeli beslemeli sistemleri temsil etmek üzere seçilen dört reaktörlü - iki beslemeli ve ara reaktörlü - üç beslemeli nitrifikasyon-denitrifikasyon sistemlerinde herbir reaktör etrafinda, kolay ayrışabilir substrat, Ss, yavaş ayrışabilir substrat, Xs, amonyak, Snh ve nitrat, Sno parametreleri için kütle denge denklemleri içsel solunum modeli kullanılarak çıkartılmış ve daha sonra çıkışta istenen nitrat konsantrasyonuna göre sistemin temel tasarım parametreleri olan, çamur yaşı, 6x; debi fraksiyonu, i; hacimsel fraksiyonlar, a ve b; toplam hacim, V v.b. değerleri iteratif bir yaklaşımla elde edilmiştir. Model sonuçlan değerlendirildiğinde, kademeli beslemeli sistemlerle, diğer klasik biyolojik azot giderim sistemlerinde elde edilemeyecek düşük çıkış nitrat değerlerine ulaşılabildiği görülmüştür. Atıksu karakterizasyonuna ve istenen çıkış koşullarına bağlı olarak altı reaktörlü-üç beslemeli sistemlerin de kullanılmasıyla çıkışta çok daha düşük değerler elde edilebilir. Ayrıca kademeli beslemeli sistemlerde içsel nitrat geri devrine gerek kalmaması nedeniyle anoksik hacime verilen çözünmüş oksijen konsantrasyonu sadece çamur geri devri ile sınırlı kalacağından denitrifikasyon verimi artacaktır. Yine bu özellik öndenitrifikasyon sistemlerindeki yüksek geri devir pompaj maliyetlerinden kaçınılacağı için sisteme daha ekonomik olma özelliği kazandıracaktır. Kademeli beslemeli sistemlerin bir başka avantajı ise diğer sistemlere kıyasla daha düşük hacimlerde istenen çıkış verimine ulaşabilmeleridir. Konuyla ilgili gelecekte yapılması gerekli çalışmalar ise, evsel auksularda önemli konsantrasyonlara ulaşabilen yavaş ayrışan substrat, Xs'in hidroliz olma mekanizması üzerine yoğunlaşmak olmalıdır. Bunun dışında, ülkemiz için bir eksiklik olan pilot, tam ve laboratuar ölçekli çalışmalar modelin deneyim kazanarak güçlenmesini sağlayacaktır. The growing demand for water resources has generated an equivalent need for effective water and wastewater management strategies. In all over the world, these driving forces have found support in the regulations that mandate the proper handling and treatment of wastewaters discharged to the aquatic environment. Application of processes to control wastewater discharges to the aquatic environment began around the turn of the century, generally addressing the removal of particulates and oxygen-demanding carbonaceous materials. The removal of other constituents did not receive substantive attention until the latter part of this century. The control of nitrogen has subsequently been identified as an important environmental activity, demonstrated by the adverse effects that excess levels of different forms of nitrogen have had on aquatic systems. Recently several biological nitrogen removal methods with a number of different reactor configurations have been used. Every day, the developed countries make the discharge standards of nitrogen and phosphorus more strict. Turkey as preparing herself to be a member of European Union has to seriously consider the concept of nutrient removal from wastewaters. In this context, this study defines a step feeding biological nitrogen removal system by using endogenous decay type of activated sludge model and develops a computer aided design approach. The step feeding configuration as defined in Figure 1., is basically a single sludge system and its kinetic evaluation should involve all the basic components and processes describing carbon oxidation, nitrification and denitrification. Its design relies on the selection of an appropriate sludge age for the autotrophic and the heterotrophic sludge biomass. The aerobic sludge age, 0xa is particularly important because complete nitrification is a prerequisite for an effective nitrogen removal which takes place within the total anoxic volume, Vd. Appropriate selection of the ratio of the anoxic volume to the total reactor volume, Vd/V and 0xa yields the total sludge age of the system: a °XA !--£ xui QRs Qw Figure 1. Schematic diagram of step feeding mtrification-denhrification system The total reactor volume should ensure complete removal of the biodegradable COD, C». Then the heterotrophic biomass, V Xh may be computed as follows: MXH=VXH = YHQ(CS0-CS) i+bHex 0, The amount of autotrophic biomass, Mxa, is a function of nitrification capacity, (Nox) and aerobic sludge age, (9xa ). MXA=VXA = It is postulated that all growth processes consume ammonia nitrogen, Snh as nitrogen source. In the aerated zones, this component is converted into nitrate nitrogen, Sno by means of nitrification. Furthermore, the total biodegradable organic nitrogen concentration in the influent, Cndo may be considered as a potential ammonia nitrogen source assuming that the ammonification of organic nitrogen is not rate limiting. In this context, the following expression defines the mass balance for nitrogen: Nox - Cmo + "Swo - Snh - Nx Nx may be defined on the basis of related kinetic expressions with the assumption that the heterotrophic activity is reduced in the anoxic zones by a correction factor. Different correction factors tig, tjh, t|E may be commonly defined to characterize respectively xiv growth, hydrolysis and decay under anoxic conditions. As no substantial proof has so far been provided in the literature to show that they are significantly different, a single correction factor, r| has been adopted in this study as shown in the following equations: Va+t,Vd=cV and H \ SO S ) Xx = OxB +*XE f*X K C0X) 1+cb Q The unit amount of nitrogen incorporated into biomass, Nx is set for selected values of Vd/V and 6x. For a desired effluent nitrate nitrogen concentration, Sno, Nox and the autotrophic biomass, V XA can be computed from expressions 3 and 5. Similarly, the following kinetic expressions may be derived for the particulate inert COD fractions, Xp andXj: ^xp=v^p=fEx^HexVXH Mn=VX^QXI(iex Slowly biodegradable particulate substrate, Xs accumulates in the system depending on 0x and hydrolysis rate ( KH ). Consequently amount of Xs can be calculated as follows: s \+KHex and, VXT = VX" + VXA + VXS + VXj + VXP An appropriate XT value, selected as the average total particulate COD in the system enables the calculation of the total and the anoxic reactor volumes, V and VD. The procedure so far described applies to all single sludge systems designed for nitrogen removal. Step feed reactor configuration, additionally involves three significant design parameters: the fraction of the influent flow rate fed to the first anoxic reactor, i; the xv volume ratio of the first anoxic reactor, a; and the volume ratio of the first aerobic reactor, b. The volume ratios, a and b are defined as follows: V V ' PI, r A\ a~v ~ V ¥D ' A The selection of the appropriate value for i, is most important for the optimum design of step feeding flow configuration, because the ammonia content of the wastewater fraction, 1-i, diverted to the 2nd aerobic reactor, aside from the relatively small portion incorporated into biomass, will be converted into nitrate and will leave the system as nitrate nitrogen. The latter may be considered as the effluent nitrate nitrogen concentration, Sno, provided that the 2nd anoxic reactor secures complete denitrification, virtually eliminating all nitrate When this balance is satisfied, the kinetic considerations, the following expressions may be derived to define Noxi and Ndk nitrogen (Sncs = 0). In this respect, the 2nd anoxic reactor is the key part of the whole system and should be designed to maintain the delicate balance between its denitrification potential, Ndr and tile nitrate nitrogen generated in the first aerobic reactor, Noxi: When this balance is satisfied, the amount of ammonia nitrogen nitrified in the second aerobic reactor, N0x2 will determine the effluent nitrate nitrogen concentration. On the basis of kinetic considerations, the following expressions may be derived to define Noxi andNcre: V 1 Xoxı=l>-ğXA(Y+ixB)MAi "^»-"'t^ 1- K, l rB Here it is shown that Noxi is a function of b and Sure in the first aerobic reactor. The level of Snh2 is set by the selected 0xa- Since b is computed to reach this level of Sum, the ammonia load entering the reactor determines the magnitude of nitrification. Therefore, Noxi basically relates to and increases with the flow fraction, i. The same way, Ndr varies with the heterotrophic specific growth rate at the third tank, Un3 and consequently with the (1-i) fraction. When the variation of Noxi, Ndr and Sno as a function of the wastewater flow fraction entering the system, i, for selected constant values of 6x and Vd/V is investigated in the second anoxic reactor, it is observed that, for low i values, the amount of available organic carbon in the 2nd anoxic reactor stays beyond the required level to remove the existing nitrate and consequently, Nik > Noxi, indicating an excess of wasted denitrification potential. Conversely, as the value of i increases, the amount of available organic carbon drops and becomes insufficient in removing the steadily increasing amount of nitrate entering the reactor. Therefore the lowest effluent nitrate concentration, Sno is obtained xvi when the denitrification potential is balanced with the amount of available nitrate nitrogen. This balance also yields the optimum value of i for a constant sludge age selected for the operation of the system. Sno cannot be reduced below a limit dictated by the selected 9x or VxJV. To lower this level is only possible by increasing the VdW ratio. It should be noted that the amount of nitrate recycled to the first anoxic tank by means of sludge return, Rs Q Sno determines the volume of this reactor or a. One of the attractive features of the step feeding configuration is the elimination of internal recycling and the sludge return is practically constant. Therefore a higher Vd/V ratio basically affects the volume of the 2nd anoxic reactor and increases Ndk. This lowers the achievable effluent nitrate nitrogen concentration, Sno and increases the optimum value of the flow fraction, i, or in other words, reduces the wastewater flow to be diverted as a step feed. The variation of Sno with i shows the previously explained trend, decreasing to a minimum value as the amount of nitrogen entering to the 2nd anoxic tank drops for higher i values, then increasing for insufficient Ndp2 levels. Finally, kinetic evaluations indicate that the selection of the volume ratio of the first aerobic reactor, b should best be in proportion to the ammonia nitrogen loads; thus b may be given the same value as i. It is concluded that, depending on the wastewater characterization and required effluent limits two fed-four reactor configuration may not be able to give the desired results. In this case, by using three fed-six reactor configuration, better effluent conditions can be obtained. Design procedure of such configuration has been also developed as similar to the previously mentioned two fed-four reactor configuration. There are a lot of advantages of step feeding systems. It is possible to reach very low effluent nitrate values that can never be obtained by predenitrification systems. Since the optimum carbon-nitrogen balance can be set by changing the flow and volume distributions, very important volumetric savings are possible. As the need of internal recirculation gets disappearing, because of the low oxygen transfer to the first anoxic reactor, the denitrification efficiency increases, moreover, the amount of pumping costs due to recirculation decreases. The multi-component activated sludge models - such as endogenous decay - emphasize the importance of wastewater characterization. In this study, the slowly biodegradable substrate, Xs has been assumed to be hydrolyzed with a first order reaction. There is a big gap at the literature about this topic. The hydrolysis mechanism of Xs still needs to be investigated to reach more realistic modeling approaches. Finally, especially in Turkey, more lab-scale, pilot-scale and full-scale experimental investigations have to be run as future works for step feeding systems.DoktoraPh.D

Leakage performance evaluation of cloth seal

Turbomachinery sealing technology is concerned with the crucial tasks of maintaining pressurized regions, leakage control, cooling control, purge flow, and axial force balance. Thus, advances in sealing technology have considerable impact on overall turbomachinery performance, decreasing operational costs, fuel consumption, and NOx emmisions. Cloth seals as a new stationary seal have been used as an alternative to thick metal shim seals to reduce leakage rate and increase wear life. The cloth seal includes one or more metallic-cloth fibers (cloth weave) and a thin metal shim. Measuring actual cloth seal leakage proves difficult with challenging turbine operating conditions. Modeling the flow through the complex weave voids among each warp and shute fiber involves a very complex flow structure, extensive effort, and high CPU time. Therefore, a bulk porous medium flow model with flow resistance coefficients is applied to the model cloth seal weave fibers. CFD analyses need leakage data depending on the pressure load to calibrate flow resistance coefficients. A test rig is built to measure leakage of cloth weave with respect to the pressure load and weave orientation in four directions. The Sutherland-ideal gas approach is utilized to determine the flow resistance coefficients for Dutch twill metallic-cloth fibers as a function of pressure load. Moreover, equations to calculate the porosity of plain and twill weave are developed and compared with available data. Literature reviews indicate that available published data about cloth seal leakage performance are not adequately detailed to derive a closed-form equation defining the relationship between seal design parameters and cloth seal leakage performance. In an effort to fill this gap, the effect of geometric parameters under varying pressure load on the cloth seal leakage performance has been investigated in this study. In order to reduce the number of parameters to a manageable size, some of the parameters are fixed and excluded from the experimental design based on the studies in the literature. The remaining eight parameters are included in the screening experiments. Their levels are determined to cover typical application ranges. Parameters, which have a major impact on leakage rate, are determined in the screening experiments, and analyzed in the main experiments. A closed-form equation is derived based on the data and presented in this study. Leakage rate trends with respect to levels of each parameter are examined. In order to conduct leakage tests of screening and main experiment designs, several cloth seal designs are manufactured, and another custom test rig has been designed