LEE- Çevre Bilimleri Mühendisliği ve Yönetimi-Doktora

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  • Öge
    Optimization of anaerobic membrane bioreactors for sludge treatment
    (Graduate School, 2023-02-01) Abdelrahman, Amr Mustafa ; Erşahin, Mustafa Evren ; Volcke, Eveline ; 501182702 ; Environmental Sciences, Engineering and Management
    Wastewater treatment is an energy intensive process. The energy balance is positively affected by anaerobic sludge digestion, especially primary sludge. The inclusion of a primary clarifier before the biological reactors results in a higher sludge total production compared to the direct treatment of raw wastewater. Conventional anaerobic digesters for sludge treatment are designed as completely mixed reactors operated at long solid retention times (SRTs) for enhanced solids conversion and to maintain the methanogenic activity in the reactor. Consequently, anaerobic digesters are commonly built with large volumes to ensure sufficient reduction of volatile solids (Xu et al., 2011). Anaerobic membrane bioreactor (AnMBR) is a promising alternative to conventional anaerobic digesters for sludge digestion. AnMBRs are operated at long SRTs independent from hydraulic retention time (HRT) by means of physical separation of the membrane. Thus, slow growing methanogenic biomass can be kept longer in the reactor, resulting in enhanced methane production. Moreover, a smaller footprint of the anaerobic reactor can be achieved since the HRT can be controlled by manipulating the flux. To understand the rationale behind the thesis, Chapter 1 presents a brief description about the energy consumption for wastewater treatment and its distribution in the wastewater treatment plant (WWTP). The organic matter removal mechanism in the conventional WWTP is explained. Novel process configurations for organics capture are presented. Anaerobic digestion process and the design parameters of the anaerobic digester are explained as well. The advantages of using AnMBR for sludge treatment are defined. The chapter ends with research gap and an outline of the thesis. The current status and perspectives of the AnMBR technology for sludge treatment are critically reviewed in Chapter 2. It discusses the historical development of the AnMBR for sludge treatment, and factors influencing the AnMBR performance reported in the literature. The operational conditions such as SRT, HRT and temperature have a noticeable effect on the methane production and permeate quality. Volatile fatty acids (VFAs) can be recovered simultaneously during sludge treatment, which can improve the economics of the WWTP. However, there are still problems, such as membrane fouling, which hinder the adoption of AnMBR technology for sludge management, as well as a lack of studies demonstrating the economic benefits of using AnMBRs for sludge treatment. Suggestions for research perspective are given, aiming for overcoming the challenges and for optimization of the AnMBR for sludge treatment. The aim of this thesis was to investigate the applicability of the AnMBR for sludge treatment in the view of energy-positive WWTPs. The objectives of this thesis were met through four different studies. Chapter 3 explains the material used and methods followed during these studies. The results of these studies are explained and disscussed in Chapter 4. In order to maximize organic capture and thus energy recovery from wastewater, novel configurations including an A-stage and CEPT have been proposed as alternatives to primary settling. However, it remains to be investigated to which extent these configurations affect the sludge characteristics, which may affect the economic feasibility of the integrated systems. Therefore, the first study focuses on the effect of these primary treatment methods on sludge characteristics and digestibility, and on plant-wide economics of wastewater treatment. A detailed characterization of sludge obtained from primary settling (primary sludge), A-stage treatment (A-sludge) and CEPT showed significantly different sludge characteristics. The organic compounds in primary sludge consisted mainly of 40% carbohydrates, 23% lipids, and 21% proteins. A-sludge was characterized by a high amount of proteins (40%) and a moderate amount of carbohydrates (23%), and lipids (16%), while in CEPT sludge, organic compounds were mainly 26% proteins, 18% carbohydrates, 18% lignin, and 12% lipids. The biomethane potential test showed that primary sludge and A-sludge had the highest methane yield (347 and 333 mL CH4/g VS, respectively), while methane yield of CEPT sludge was lower(245 mL CH4/g VS). A plant-wide economic evaluation for the three systems, indicated that energy surplus was the highest with CEPT. The inclusion of an A-stage had the lowest positive net energy due to the relatively high energy consumption in aeration. Considering the effluent quality of the three systems, CEPT had the highest benefits, followed by A-stage. Overall, integration of CEPT or A-stage, instead of primary clarification in existing wastewater treatment plants, has the potential to improve the effluent quality and energy recovery. AnMBRs have been applied as compact alternatives for anaerobic digesters for sludge treatment in conventional WWTPs. However, there is no information about the impact of integrating an A-stage, instead of primary clarifier, on sludge digestion in an AnMBR. The second study examines the performance of lab-scale AnMBRs, in terms of treatment and filtration performances, for both digestion of primary sludge and A-sludge. The results showed that anaerobic digestion of A-sludge yielded more methane and improved methanogenic activity in the AnMBR compared to primary sludge. The permeate of the AnMBR fed with A-sludge contained higher nitrogen and phosphorous concentrations due to higher nitrogen and dissolved phosphorous concentrations of A-sludge. No coliforms were detected in the permeates, which showed that from the hygienic point of view, the permeate had the potential to be directly used for irrigation purposes. A higher EPS concentration was observed during the digestion of A-sludge compared to the primary sludge, which accumulated on the surface of the membrane and caused an increase in transmembrane pressure (TMP) and filtration resistance. On a plant-wide level, the integration of an A-stage increased the amount of organic matter (COD) recovered from wastewater in the form of methane gas by about 15% compared to a WWTP configuration with a primary clarifier. Anaerobic digesters are operated at either mesophilic (35°C) or thermophilic (55°C) conditions. In general, it is known that higher amounts of biogas are produced from digesters operated at thermophilic conditions because of higher biochemical reaction rates. However, the specific effect of temperature on AnMBR performance for A-sludge digestion has not yet been assessed. Therefore, the third study evaluates the treatment and filtration performances of lab-scale AnMBR under mesophilic and thermophilic conditions. Higher biogas and VFAs were produced under thermophilic conditions, which were 23% and 47% higher than those under mesophilic one, respectively. Besides, the membrane could be operated at lower TMP under thermophilic conditions. However, taking into account the energy consumption and production, operating the AnMBR under mesophilic conditions would result in a more than three-fold higher net energy production than operating under thermophilic conditions, whereas surplus energy recovery under thermophilic conditions was less than the additional energy consumption. Therefore, despite the advantages of thermophilic conditions, operating AnMBR for sludge digestion under mesophilic conditions has a higher potential to improve the energy balance in the WWTPs. As found during the review (Chapter 2), there is a lack of studies demonstrating the economic benefits of using AnMBRs for sludge treatment in the WWTP. Therefore, the feasibility of the AnMBR for sludge (primary and waste activated sludge) treatment in a conventional WWTP is evaluated in the fourth study, through mathematical modeling and simulation, on unit process and plant-wide levels. The impact of HRT and SRT as control handles on the performance of the AnMBR was assessed. The amount of COD converted into methane could be increased by increasing the SRT or lowering the HRT, the former having a higher positive impact. The nitrogen and phosphorous load in the permeate increased by increasing the SRT or lowering the HRT, while the COD concentration in the permeate was hardly affected. As for the energy balance, increasing the SRT was more efficient than lowering the HRT. Indeed, increasing the SRT caused a significant increase in energy production while lowering the HRT only slightly reduced the energy consumption and did not affect the energy production. On a plant-wide level, the integration of an AnMBR instead of the anaerobic digester decreased the operational costs of the WWTP by 27%, but led to a worse effluent quality. The latter could be remedied by post-treatment of the permeate by struvite recovery and nitrogen removal through partial nitritation/anammox, at the same time further decreasing the operational costs - with 35% compared to a conventional WWTP. Overall, applying AnMBR for sludge treatment combined with post-treatment of the permeate provides effluent quality that meets the EU regulations and implies significant operational cost savings for wastewater treatment. Finally, Chapter 5 summarizes the main findings of the previous chapters and gives perspectives for further research inspired from the thesis.
  • Öge
    Recovery of rare earth elements from waste and wastewater
    (Graduate School, 2021-12-14) Yüksekdağ, Ayşe ; Koyuncu, İsmail ; 501152710 ; Environmental Science Engineering and Management
    REEs is a group of elements comprising Lanthanides, Scandium, and Yttrium. These elements are used in many alloys, permanent magnets, wind turbines, defense industry products, magnetic resonance imaging systems, catalytic converters, mobile phones, computers, and so on. Due to their unique physical and chemical properties, these elements contribute to the development of many technological products due to their efficiency, size reduction, energy reduction, and superior chemical and physical stability. REEs are classified as LREEs (La, Ce, Pr, Nd, Pm, Sm) and HREEs (Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Y) according to their arrangement in the periodic table. Another classification method is based on the criticality of these elements and is as follows: Critical REEs (Nd, Eu, Tb, Dy, Er, Y), uncritical REEs (La, Pr, Sm, Gd), and excess REEs (Ce, Ho, Tm, Yb, Lu). These elements are also called "vitamins of modern industry" due to their unique properties. In the first stage of the thesis, a comprehensive literature review was prepared. Recovery of REEs and scandium from secondary sources under a circular economy framework was reviewed with a holistic approach. Moreover, the latest statistical data and studies have been summarized. 46 million tons of red mud was generated in the first four months of 2021 worldwide. In 2018, 750 million tons of thermal power plant fly ash were released in European Union member countries. Globally, over 53 million of e-waste was generated in 2019. These and many other types of waste need appropriate management, as they are large in quantity. On the other hand, they are valuable secondary resources due to their critical element content. Within the scope of the second chapter of the thesis, a total of 32 different samples containing (1) combustion residues, (2) mine wastes, (3) treatment sludges & sediments, (4) e-waste, and (5) various water, wastewater, and geothermal water were investigated. Then, REEs, scandium, and other critical, precious, and base element potentials were exhibited. According to the results obtained, Ce, La, Nd, and Y elements were found the most in the secondary sources obtained from Turkey, respectively. The highest total REEs concentration was found in thermal power plant fly ash and e-waste mixture. The waste with the highest content of critical rare earth elements was e-waste. For this reason, e-waste was chosen for recovery studies. In the third stage of the thesis, e-waste was crushed, ground, and sieved, respectively, and separated into size fractions. The effects of the particle size of the waste, the type of acid used, and the waste:acid ratio on the leaching of REEs were investigated. It was seen that the highest leaching efficiency was obtained from the smallest grain size. However, it was observed that the leaching efficiency decreased as the amount of e-waste used per unit volume of acid increased. The highest yield was obtained with aqua regia and the lowest waste:acid (5 mg/mL acid) ratio. In the fourth step, which is the last experimental part of the thesis, the separation of rare earth elements by membrane applications from e-waste leachate, prepared with nitric acid, was optimized using response surface methodology. In the first stage, e-waste leachate was pre-treated and concentrated in the nanofiltration process. This stage was optimized as a pretreatment pH of 1.5 and an NF operating pressure of 14.5 bar. In the second stage, the pre-treated leachate was fed directly to the supported liquid membrane process, which is a kind of membrane solvent extraction. Finally, the optimization studies were repeated by feeding the NF concentrated phase to the supported liquid membrane. Optimum operating conditions were found to be the same as for direct membrane solvent extraction (pH: 1.5 and D2EHPA concentration: 15%). An increase in the separation efficiency of HREEs and a decrease in the separation of LREEs were observed in the case of MSX with pre-concentration. In sum, HREEs could be separated with higher purity by applying NF concentration before membrane solvent extraction.
  • Öge
    Application of different strategies to improve aerobic granular sludge process performance for treatment of municipal wastewater
    (Graduate School, 2022-09-29) Koşar, Şadiye ; Erşahin, Mustafa Evren ; 501162714 ; Environmental Sciences, Engineering and Management
    Aerobic granular sludge (AGS) process is an energy-efficient alternative biological wastewater treatment process to the conventional activated sludge (CAS) process which requires high energy and big space. In CAS systems, flocs sized above 0.2 mm are referred as granule. So far flocs and granules could be easily differentiated by size clustering as well as their capabilities of removal for organic matter and nutrients. Surface of the granule has porous morphology, and this allows the substrate penetration and as well as oxygen diffusion into the inner layers of the granule. The diffusion of oxygen is somehow can be a limiting factor for the simultaneous carbon and nutrient removal due to structure of the granule. In many cases, granule has a compact and dense structure that limits the oxygen transfer to the inner core layers of the granule which improves the denitrification and allows better phosphorus (P) removal within the granule. Whereas in some situations, granules have amorphous structure which do not improve any core inside the granule so affects the removal of substrate. Aerobic granules are heavier than flocs formed in waste sludge, so they settle faster, and this improves the settleability of the sludge which further allows to operate in one reactor. For this reason, large sedimentation tanks are not required in AGS systems. Since aerobic, anoxic and anaerobic biological activities take place inside the granule, AGS process offers 25-75% less space and consumes 20-50% less energy compared to conventional activated sludge plants. Nitrification takes place on the surface of the granule during aeration phase and denitrification occurs in the inner layers of the granule under anoxic conditions. P removal is maintained by polyphosphate accumulating organisms (PAOs) that are located in the core part of the granule. PAOs and denitrifiers which are responsible for the denitrification are both heterotrophic organisms and compete for the carbon sources as substrate. For this reason, it is important to have sufficient amount of organic matter for nitrogen (N) and P removal. Since PAOs are located in the inner layer of the granule they are only capable of using organic that are in dissolved form. In municipal wastewater, organic matter is particulate and dissolved forms. Particulate matter reduces N and P removal up to 40% and 46% respectively. Particulate organic matter is turned into dissolved form in the presence of extracellular polymeric substances (EPS) which are hydrolyzing them further. Hydrolysis ends up in anaerobic phase when the attached particulate matter on the surface of the granules hydrolyzed and it is uptaken by PAOs and denitrifiers. If dissolved organic matter cannot be consumed by these species, then it would be consumed by the aerobic heterotrophic bacteria on the surface of the granule which further causes filamentous microorganisms' overgrowth. This leads to amorphous structure and disintegration of the granule. In this thesis, the treatability municipal wastewater by AGS process was investigated under different circumstances. Four separate studies were conducted within the scope of this study. In the first study, two different sludge were comparatively investigated as inoculum: (a) waste activated sludge (WAS) taken from the return activated sludge line of an advanced biological wastewater treatment plant (WWTP), (b) WAS taken from the return activated sludge line of a pilot scale high-rate activated sludge (HRAS) system. This study was conducted in two stages: AGS system was seeded with the WAS taken from the return activated sludge line of an advanced biological wastewater treatment plant in the first stage; in the second stage, AGS system was seeded with the mixture of WAS taken from the return activated sludge line of an advanced biological WWTP and WAS of pilot scale HRAS process as volume in proportion of 1:1. This study was performed to reveal the contribution of microorganisms found in the flocculent sludge to the granulation process. Since HRAS process sludge has high settleability and the mixture of WAS with HRAS process as inoculum was expected to enhance the settling properties of granular sludge as well as achieving good treatment performance. Although at the start-up period sludge wash-out occurred and mainly fluffy waste sludge wasted, HRAS process sludge settles faster, and it remained in the reactor. So, in this case especially denitrifiers were mostly washed out of the system which deteriorated system performance compared to the AGS system operated solely with WAS. At the end of this study, WAS waste sludge was chosen as seed sludge for the further studies to obtain aerobic granulation based upon AGS system treatment performance. In the second study, WAS taken from the return activated sludge line of an advanced biological WWTP was used as seed sludge. Study was conducted in two stages: (a) AGS system was fed directly with the synthetic municipal wastewater, (b) AGS system was fed with the pre-settled synthetic municipal wastewater (30 min of settling) to simulate pre-sedimentation tanks in the full-scale wastewater treatment plants (WWTPs). With pre-settling application, it was proposed that particulate matter would settle so mainly dissolved organic matter could be introduced to the AGS system. Since AGS system is anaerobically fed, this would improve the nutrient removal by allowing the uptake of organic matter easily by PAOs and denitrifiers. It was shown that up to 60% of particulate matter was removed by settling and as a result carbon/nitrogen (C/N) ratio decreased 20% lead deterioration of the AGS system treatment performance. It was apparent that a combination of pre-sedimentation in AGS process didn't improve the system. In the third study, AGS system was operated in three different stages continuously following each other without having different start-up periods: (a) AGS system was fed directly with raw municipal wastewater, (b) AGS system was fed with the pilot scale HRAS system's effluent (treated wastewater), (c) AGS system was fed with the mixture these two flows: raw municipal wastewater (20%) and HRAS process effluent (80%). Waste sludge taken from the return activated sludge line of an advanced biological wastewater treatment plant was used as inoculum. Firstly, aerobic granulation was maintained by introducing municipal wastewater than HRAS process effluent fed to the system and AGS system performance was followed thoroughly. It was shown that the granule stability remained somehow same, but AGS system performance was affected by decreased C/N ratio. AGS system was fed with the mixture the raw municipal wastewater and HRAS process effluent to improve the system performance. As a result, AGS system performance was improved with the increase in C/N ratio (20% increase compared to feeding with only HRAS process effluent). Thus, HRAS process integration with AGS process was found to be energy efficient configuration. Both systems comparably occupy less space than conventional treatment systems and their integration will definitely improve the effluent quality. In the fourth study, digestibility of AGS which was obtained from the third study was compared to the WAS taken from the return activated sludge line of an advanced biological wastewater treatment plant. It is known that AGS process sludge has low digestibility than WAS. Thus, ultrasonication was applied to improve the solubilization of organic matter for increasing sludge digestibility. Since aerobic granules are clusters of microorganisms that are attached together, they are bigger in size and more compact than WAS flocs. Therefore, relying on their physical differences, it was assumed that ultrasonication would enhance digestibility of the AGS. It was shown that ultrasonication as pre-treatment method led to solubilization for both sludge sources in terms of volatile fatty acids (VFAs), protein and carbohydrates besides causing decrease in particle size. A direct relation found between the release of organic compounds, ammonium, phosphorus and heavy metals with the increase in ultrasonication intensity. Overall results obtained from this thesis showed a comprehensive approach to treat municipal wastewater by AGS process while improving the treatment performance by focusing on inoculum source as well as feeding strategy. Besides, sludge from AGS process was evaluated in terms of soluble products release by applying ultrasonication process compared to the WAS. This thesis would enhance the knowledge on AGS technology in terms of seeding and feeding regimes beneath giving clues for full-scale AGS process applications.
  • Öge
    Tarım kaynaklı pestisitlerin SWAT ile havza ölçeğinde modellenmesi
    (Lisansüstü Eğitim Enstitüsü, 2022-06-28) Doğan, Fatma Nihan ; Karpuzcu, Mahmut Ekrem ; 501152702 ; Çevre Bilimleri Mühendisliği ve Yönetimi
    Tarımsal kaynaklı yayılı kirleticiler özellikle tarım ilaçları, kontrolsüz ve aşırı kullanımlarından ötürü su kaynakları, doğa, insan ve diğer canlılar için tehlike oluşturmaktadır. Nüfus artışları ile birlikte tarım alanlarından maksimum verim alabilmek amacıyla gübre ve pestisitlerin kullanımı kaçınılmaz olmuştur. Piyasada farklı etken maddeli birçok pestisit çeşidinin olması ve bu pestisitlerin herhangi bir sınırlama olmaksızın satın alınıp kullanılabiliyor olması çevre için en büyük riski oluşturmaktadır. Bu çalışmada, İstanbul'da tarımsal faaliyetlerin yoğun yapıldığı Terkos Havzası ve drenaj alanındaki pestisit kirliliği karar destek sistemleri ile değerlendirilmiş, bu kirliliğin kontrolü ve giderimi için uygulanacak yöntemler belirlenmiştir. Terkos Havzası, İstanbul için en önemli ve görece en temiz içme suyu kaynaklarındandır. Diğer İstanbul havzalarına göre Terkos Havzası, yoğun orman alanları ve az şehirleşmesi ile daha bakir alanlara sahiptir. Fakat havzadaki Terkos Gölü rezervuarı ve gölü besleyen nehir ağlarının çok yakınında tarımsal faaliyetlerin yapılması, tarım alanlarından nehre ve dolayısıyla rezervuara pestisit taşınımına yol açmaktadır. Pestisit endüstrisinin gelişmesiyle, bitki zararlılarına karşı çok çeşitli yeni ilaçların üretilip kullanıması su kaynaklarındaki pestisit kirliliğinin kontrolünü zorlaştırmaktadır. Ayrıca şu an kullanımı yasak fakat geçmişte kullanılmış, tarım alanlarında depolanan bozunmaya karşı dirençli pestisitler de su kaynakları için büyük risk oluşturmaktadır. Tarımsal sürdürülebilirliği sağlayacak şekilde tarım ilaçlarının kullanımın kontrol altına alınması sadece su kaynaklarını korumak için değil gıdalardaki kalıntı pestisit miktarını azaltarak gıda güvenliğini sağlamak, sucul ekosistemin iyileştirmek ve insan sağlığına yönelik tehditlerin azaltmak için de gereklidir. Türkiye, Bütünleşik Havza Yönetimi anlayışını benimsemiş olup bu anlayış tarımsal kaynaklı kirleticilerin kontrolünü ve yönetimini içermektedir. Bu amaçla havza bazlı pestisit kullanımının ilk aşamasından su kaynaklarına ulaşana kadar tüm aşamalarında pestisit kirliliğinin yönetimine dair stratejiler geliştirilmelidir. Tarım ilaçlarının aşırı ve gereksiz kullanımını engelleyecek Entegre Pestisit Yönetimi, Zararlılarla Entegre Mücadele, Entegre Ürün Yönetimi, İyi Tarım Uygulamaları gibi yöntemlerin uygulanması pestisit kirliliğini kaynağında önlemeye yönelik faaliyetlerdir. Kullanılması muhtemel pestisitlerin izleme çalışmaları ile tespitinin yapılması ve bu kirleticilerin su ortamına ulaşana kadar uğradıkları dönüşümler ve izledikleri yolların karar destek sistemleri ile belirlenmesi ve En İyi Yönetim Uygulamaları (EİYU) olarak adlandırılan doğal arıtma yöntemleri ile pestisit kirliliğinin su kaynaklarına ulaşmadan kontrolünde önemli adımlardır. Bu çalışmanın amacı, Terkos Havzası'nda tarımsal kaynaklı pestisitlerin su kaynaklarına etkisini tespit edebilmek, mevcut arazi kullanım şartlarında nasıl bir yol izlediklerini ve çevreye etkilerini bir karar destek sistemi olan SWAT (Soil Water Assessment Tool) modeli ile değerlendirmektir. Bu amaçla, öncelikle SWAT modeli yardımı ile havzanın su dengesi oluşturulmuş, hidrolojik modellemesi yapılmıştır. Hidrolojik modellemede havzaya ait topografik, arazi kullanımı ve iklimsel verilerin kullanılmasıyla havzanın su bütçesini çıkarılmış ve suyun havzadaki çevrimi tespit edilmiştir Hidrolojik modelleme, daha sonraki taşınım ve su kalitesi modellemesi için bir altlık görevi görmektedir. Hidrolojik modelin kalibrasyonu ve validasyonu sonunda, sediment ve pestisit taşınım ve akıbeti modellemesi gerçekleştirilmiştir. Pestisit taşınım ve akıbeti modelinin kalibrasyonu için havzadaki çeltik ve kuru tarımın yoğun olarak yapıldığı Karamandere'den numuneler alınmıştır. Pestisit modellemesi sonucunda, havzadaki kritik alanlar belirlenerek, bu bölgelere pestisit yükünü azaltmak amacıyla EİYU'lar eklenmiştir. EİYU'lar ile birlikte havzadaki pestisit kirliliğinin yönetimine dair yapılması gerekenler belirlenmiştir. Havzaya yapılan saha gezilerinde uzun yıllardır havzada tarım yapan çiftçiler, ziraii bayiler ve kalkınma kooperatifleri ile görüşülmüş, çeltik ve kuru tarım hakkında bilgiler edinilmiştir. Havzadaki durum su kaynakları, tarımsal faaliyet, orman habitatı, toprak korunumu, sosyal-ekonomik boyutuyla birlikte ele alınarak havzanın geleceğine dair görüş ve önerilerde bulunulmuştur.
  • Öge
    Profile of priority substances and toxicity assessments of wastewater treatment plants in Istanbul
    (Graduate School, 2023-05-31) Birtek, Rahime İclal ; Öztürk, İzzet ; 501122704 ; Environmental Sciences, Engineering and Management
    Wastewaters formed due to anthropogenic activities around urban areas pose a threat to aquatic environments. The growth in industrial activity along with the worldwide urban migration, as well as the threat posed by climate change, increase the extent of pollution. The discharge of the treated or untreated wastewaters is reported to cause a threat to their receiving water environments. Conventional wastewater treatment plants (WWTPs) are constructed to minimize the nutrient loads of macropollutants (C, N, and P) entering the receiving water bodies. As, removal of some of the emerging contaminants (ECs) or micropollutants present in wastewaters is found to be incomplete in conventional wastewater treatment processes, traces of those non-biodegradable ECs were reported to be found in the receiving environments. The presence of ECs, even in very low concentrations (pg/L - ng/L) in the water environments could cause adverse effects on humans and the ecosystem. In addition to industrial emissions, domestic discharges along with urban runoffs are main contributors of ECs in WWTPs. Understanding the presence, sources and transport of the micropollutants and ECs in wastewaters is important for assessing their impacts, and hence can help their reduction and management in the receiving environment. Micropollutants that have shown toxic, persistent, bioaccumulative, and ubiquitous properties and have been identified in aquatic environments, are designated as priority substances (PSs) by the EU Water Framework Directive (WFD). EU Member States are required to identify the presence of PSs in surface waters, in order not to exceed threshold levels specified by the Environmental Quality Standards (EQS) dictated by WFD. The Turkish Ministry of Forestry and Water Affairs adopted the aforementioned quality standards for the PSs in surface waters in 2012, and updated them in 2016. Since WWTPs are known to be main point sources of ECs entering the receiving water bodies, investigating the occurrence of PSs in wastewaters of Istanbul has generated valuable information. This thesis aims at understanding the occurrences of PSs in the wastewaters of the megacity of Istanbul as well as assessing WWTP effluents as sources of PSs in receiving environments. The thesis also includes the acute toxicity assessment of the same wastewaters. The scope of the study includes the wastewaters of the seven largest WWTPs, a hospital wastewater and leachate of a landfill treatment plant in Istanbul. The results of the PSs analyses allowed estimation of risks posed by the PSs in the WWTP effluents. Lists were formed to PSs showing sufficient risk (RQ>1), and their inclusions are recommended in the surveillance monitoring programs for the effluents of advanced treatment, as well as mechanical treatment. The regulators undertaking environmental risk assessments in the initiation of monitoring programs for the protection of the Sea of Marmara, Bosphorus and the Black Sea may utilize the findings of this study. Chapter 2 provides general information on the background of the study that is related to the aim and objective of the study. Chapter 3 comprises of information regarding the study area as well as methods on the description of all the experiments conducted through this study, namely analyses of PSs, toxicity analyses and physiochemical analyses. Chapter 4 Results and Discussion, provides information on the results of the experiments conducted through this study (PSs analyses, toxicity analyses and physiochemical analyses), as well as discussion of those results. Chapter 5 provides a summary of the whole thesis. The References section includes the complete bibliography. The Appendix includes tables, figures and pictures.