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Access status: Open Access ,
Analysis of promising cosmologies in addressing cosmological tensions
(Graduate School, 2026-06-29) Gökçen, Mine; Akarsu, Özgür; 509231114; Physics Engineering
The concordance model of cosmology, $\Lambda$CDM, has been subjected to increasingly rigorous scrutiny following the emergence of cosmological tensions over the past decade. Simultaneously, studies exploring the nature of dark energy, the unknown driver of the accelerated expansion of the Universe, have gained renewed importance because of their potential relevance to cosmological tensions. Recent observational results have also brought renewed attention to the ``$\Lambda$'' pillar of the standard $\Lambda$CDM model, giving new urgency to dark energy studies. Latest DESI DR2 baryon acoustic oscillations (BAO) measurements, when combined with cosmic microwave background (CMB) and Type Ia supernovae (SNeIa) data, exhibit a $3.2\sigma$--$3.4\sigma$ preference for dynamical dark energy described by the Chevallier--Polarski--Linder (CPL)-parametrized equation of state. A particularly striking feature of these reconstructions is an apparent transition from an early-time phantom-like regime to a late-time quintessence-like behavior, whose theoretical realization is highly nontrivial. For positive-definite dark energy densities, this transition is often phrased as a crossing of the phantom divide line (PDL) at $w_{\rm DE}(a)=-1$. Allowing the dark energy density to become negative, however, renders the PDL (in the sense of $w_{\rm DE}(a)=-1$) non-diagnostic as a global separator: the physically meaningful criterion is instead the null energy condition boundary (NECB) for dark energy, $\rho_{\rm DE}+p_{\rm DE}=0$. We therefore test whether the data-driven preference for NECB-crossing in CPL reconstructions persists once alternative realizations of phantom behavior are admitted, specifically through sign-switching dark energy densities. To this end, we introduce and constrain two controlled phenomenological extensions of the CPL framework featuring a negative dark energy phase in the past. In the CPL$\to-\Lambda$ model, the switching epoch is tied to the CPL-inferred NECB-crossing scale factor, yielding an early-time negative cosmological-constant phase, while the post-switch evolution follows the CPL branch. In the sCPL model, the CPL equation of state is maintained at all times, while the sign switch in the energy density occurs at an independent transition redshift. We find that late-time BAO and SNeIa data drive the negative-density phase beyond their effective redshift coverage, and that this requirement is the primary driver of the inferred parameter behavior. While both models are statistically disfavored relative to the baseline CPL, admitting a negative dark energy phase generally reduces the significance of deviations from a cosmological constant. Overall, this thesis exemplifies the process by which a scientific paradigm may evolve when an established standard model becomes increasingly challenged by observational tensions. We first identify shortcomings of existing models and isolate the features that exacerbate or alleviate the tensions. Building on these insights, we construct novel phenomenological models inspired by promising contenders in the literature. We then confront these models with observational data and assess their statistical performance relative to reference scenarios. When no decisive statistical evidence favors a proposed model, we identify the features that lead to improved performance and use these insights to guide subsequent model development. This process can then be iterated with an increasingly refined understanding of the underlying physics.
Access status: Open Access ,
The effect of water treatment plant sludge addition to the performance of a pilot-scale high-rate activated sludge system
(Graduate School, 2026-07-13) Dizaji Faraji, Reza; Güven, Hüseyin; 501231727; Environmental Sciences, Engineering and Management
The rising energy demand driven by rapid population growth has encouraged the adoption of energy-efficient technologies in wastewater treatment, as in many other sectors. While the primary goal of wastewater treatment is removing pollutants, certain processes also enable greater recovery of energy from the organic matter present in wastewater, therby contributing to sustainability. Among the range of biological wastewater treatment methods, the activated sludge process is highly favored. In the conventional activated sludge (CAS) process, most of the organic material in wastewater is converted into carbon dioxide under intensive aeration. This process serves as an energy source for microorganisms and also contributes to their growth. Excess microorganisms are removed from the system as waste sludge based on the predetermined sludge age. The organic material in this excess sludge can then be converted into biogas containing approxiamtely 60-70% methane through anaerobic digestion. Biogas is subsequently utilized for power generation in gas motors, enabling energy recovery from wastewater. From an energy management perspective in wastewater treatment, the conversion of organic matter to carbon dioxide by aerobic microorganisms in CAS systems represents an energy loss, as this carbon can no longer be converted to methane in anaerobic digestion. To maximize energy recovery from wastewater, organic matter should be concentrated in excess sludge as rapidly as possible while minimizing its oxidation to carbon dioxide. The high rate activated sludge (HRAS) process can provide these conditions, as the design of the HRAS process relies on adsorbing and storing organic matter from wastewater while minimizing mineralization. Unlike CAS systems, which typically operate with a sludge age exceeding 5 days, dissolved oxygen (DO) levels above 2 mg/L, and a hydraulic retention time (HRT) of around 8 hours, HRAS systems keep organic matter mineralization to a minimum. In HRAS systems, the sludge age is kept below 2 days, the DO concentration below 1 mg/L, and the HRT under 2 hours, all to minimize the conversion of organic matter to carbon dioxide. Due to the presence of coagulants in it, water treatment plant (WTP) sludge holds potential as a valuable resource. Reduced access to landfill sites due to rising landfill disposal costs, including taxes, together with the growing emphasis on zero-waste targets, are driving the adoption of more sustainable and resource-oriented approaches to sludge management, such as the reuse and recycling of WTP sludge. Due to its low combustibility and organic content, incineration and anaerobic digestion are generally considered as unsuitable methods for WTP sludge management. Consequently, the exploration of options for recycling and reusing WTP sludge has gained substantial attention. For instance, one viable approach involves transforming it into cement, ceramics, or lightweight aggregates. Additionally, alternative approaches include using WTP sludge as a bed layer material in constructed wetlands or as a coagulant in wastewater treatment plants (WWTPs) to enhance solids removal, improve sludge settling, and facilitate dewatering processes. The primary aim of this thesis was to comprehensively investigate the feasibility of reusing WTP sludge as a low-dose coagulant in the HRAS process. To achieve this goal, a pilot-scale HRAS system was continuously operated with and without WTP sludge addition to treat preliminary treated municipal wastewater received from a full-scale WWTP in Istanbul, Türkiye. Samples of alum and iron sludges were collected from the dewatering units of full-scale water treatment plants, and subsequent jar tests were conducted in the laboratory to determine the appropriate WTP sludge dose for addition to the bioreactor of the HRAS plant. Based on the jar tests conducted using seed sludge mixed with iron and alum WTP sludges diluted to 3% solids and applied at a dosage of 0.3 mL/L HRAS sludge, the amount of WTP sludge added to the HRAS system was limited to a level that would increase excess sludge generation by no more than approximately 10%. Iron sludge increased total suspended solids (TSS), chemical oxygen demand (COD), and total phosphorus (TP) removal by 1.3±0.1%, 2.6±1.4%, and 3.0±1.7%, respectively, compared to the without WTP sludge addition case. In contrast, alum sludge resulted in smaller improvements of 1.0±0.1% for TSS, 0.4±1.0% for COD, and 0.6±0.9% for TP. Iron sludge was selected because it demonstrated overall higher removal efficiencies compared to alum sludge. Accordingly, the iron sludge dose was restricted to 20.1±1.6 mg dry matter per liter of wastewater to avoid increasing the inorganic matter content of HRAS sludge and not to deteriorate its methane potential. Since the average solids content of the WTP sludge was around 30%, it was diluted with tap water to approximately 3% solids to facilitate pumping. This diluted mixture was then fed to the bioreactor of the HRAS system via a peristaltic pump. Following the addition of WTP sludge, modest improvements were observed in the removal efficiencies of TSS, particulate chemical oxygen demand (pCOD), and TP, increasing from 78.0±0.4%, 75.2±2.3%, and 60.1±4.1% to 80.0±3.2%, 81.3±0.9%, and 63.8±2.3%, respectively. Moreover, the addition of WTP sludge significantly influenced some sludge characteristics, particularly by increasing the median particle size (D50) in the aeration tank from 96±3 µm to 163 ±14 µm while reducing sludge volume index (SVI30) from 38±6 mL/g to 32±4 mL/g. These changes enhanced sludge settleability and dewaterability, potentially reducing sludge treatment costs. However, biomethane potential (BMP) tests showed that WTP sludge addition reduced BMP by 8.9%, decreasing the average BMP from 330 NmL CH₄/g volatile solids (VS) to 301 NmL CH₄/g VS. The environmental impact of the investigated system, assessed using the effluent quality index (EQI) calculated from the average effluent concentrations of TSS, COD, total nitrogen (TN), and TP from both stages with literature-based weighting factors, showed a 2% improvement in case of WTP addition. When different sludge management scenarios, namely adding and not adding WTP sludge to the HRAS pilot-scale system, were analyzed to compare the costs of using WTP sludge in a hypothetical HRAS plant considering sludge transportation, sludge landfilling, and treatment costs, along with energy recovery from biogas production, the results indicated a total cost reduction of approximately 11% compared to the not adding case. This analysis included the transportation and landfilling of both WTP and HRAS sludge, as well as the energy and chemical use in the HRAS plant. This result underscores the benefits of reusing WTP sludge as a coagulant in wastewater treatment. This approach promotes a symbiotic relationship between WTPs and WWTPs, contributing to the development of a circular economy and enhancing resource circularity. This thesis found that integrating WTP sludge into the HRAS process resulted in limited improvements in treatment performance; however, future research could explore ways to investigate the impact of WTP sludge addition on treatment efficiency and biogas production. Moreover, advanced options for coagulant recovery, such as acidification, could also be investigated in this context. Then, long-term performance assessments would be beneficial for evaluating the operational stability, economic feasibility, and environmental sustainability of WWTPs with different configurations utilizing WTP sludge. Key areas for future research also include detailed process optimization, investigation of the effects of WTP sludge characteristics (e.g., iron vs. alum sludge) on anaerobic digestibility, and comprehensive cost-benefit analyses that consider both expenses and energy recovery potential. Additionally, examining relevant regulatory frameworks for wastewater management and aligning sludge reuse practices with broader waste management policies could help identify institutional barriers and opportunities. Collectively, these future directions provide valuable insights into the circular integration of water, wastewater and waste management systems and support the transition toward more sustainable and resource-efficient practices.
Access status: Metadata only ,
A New High-Resolution Black Sea Physics Reanalysis
(Copernicus GmbH, 2025-03-18) Leonardo Lima; Diana Azevedo; Mehmet Ilicak; Filipe Costa; Adil Sözer; Sergio Cretì; Salvatore Causio; Pietro Miraglio; Eric Jansen; Emanuela Clementi; Avrasya Yer Bilimleri Enstitüsü; Ilıcak, Mehmet
Ocean reanalyses utilize state-of-the-art models that are constrained by atmospheric forcing and incorporate the best available observations through data assimilation techniques to reconstruct historical conditions. The Black Sea Physics Reanalysis (BLK-REA) product delivered within the Copernicus Marine Service provides a comprehensive dataset of oceanographic fields for the Black Sea basin, starting from January 1993. This high-resolution reanalysis is built using the NEMOv4.0 general circulation ocean model, implemented at a horizontal resolution of 1/40 #176; and 121 vertical levels, delivering a detailed and accurate representation of ocean dynamics in the region. The BLK-REA is driven by atmospheric fluxes derived from ECMWF ERA5 fields with spatial and temporal resolutions of 1/4 #176; and 1 hour, respectively. Sea surface temperature (SST) relaxation, based on the ESA-CCI SST-L4 product, is applied for heat flux corrections. A key advancement in this version is the incorporation of lateral open boundary conditions (LOBCs), enabling more accurate inflow and outflow dynamics at the Bosphorus Strait. The data assimilation system, OceanVar, utilizes a three-dimensional variational (3D-Var) assimilation algorithm. It integrates model outputs with along-track sea level anomaly (SLA) observations from Copernicus Marine, as well as in-situ temperature and salinity profiles sourced from SeaDataNet and Copernicus Marine datasets. Enhancements in the data assimilation include the adoption of an improved background error covariance matrix and an observation-based mean dynamic topography for SLA assimilation. The results of the reanalysis demonstrate a significant improvement in accuracy compared to previous versions, with better alignment to observed data. BLK-REA has proven to be an invaluable tool for generating Ocean Monitoring Indicators, essential for assessing climate change impacts in the Black Sea. For example, the analysis reveals ongoing warming within the 25 #8211;150 m depth range, corresponding to the Cold Intermediate Layer.Looking ahead, future iterations of BLK-REA aim to expand the domain to include the Azov Sea and introduce enhanced Bosphorus LOBCs. Planned upgrades to the data assimilation system include the integration of a barotropic model for SLA assimilation and the first-guess-at-the-appropriate-time approach. Starting from 1980, the next reanalysis will provide a more comprehensive temporal scope, further enhancing the monitoring and assessment of climate-related changes in the Black Sea region.
Access status: Metadata only ,
Geochemical Features of Miocene Carbonatite/Carbothermalite-Fenite Complex in Western Anatolia: Evidences from Arıklı and Nusratlı Villages
(Copernicus GmbH, 2025-03-18) Emirhan Kaplan; Özge Yabacı; Alp Ünal; Zeynep Döner; Ali Tuğcan Ünlüer; Jeoloji Mühendisliği Bölümü; Jeoloji Mühendisliği Bölümü; Döner, Zeynep; Ünlüer, Ali Tuğcan
Carbonatite-fenite complexes, associated with alkaline or ultra-alkaline magmatism, typically have high concentrations of rare earth elements (REE), niobium (Nb), thorium (Th) and uranium (U). Although most of these complexes form in intra-continental tectonic settings, in contrast to the majority, they can also develop in post-collisional settings. A few examples of such carbonatite intrusions were identified in China, Turkey, Italy and Spain. In Turkey, a few notable carbonatitic intrusions were identified in Central and Western Anatolia. These complexes are relatively young and some of them are covered by volcanic or volcano-sedimentary rocks. The recently identified carbonatite/carbothermalite (late stage metasomatic halo) intrusion is located at Ar #305;kl #305; and Nusratl #305; Villages in #199;anakkale, NW Anatolia within Miocene volcanics. In Ar #305;kl #305;, a 10-meters-thick carbonatite dyke with stockwork veinlets and potassic fenite zone are clearly visible and cross-cutting relationships can be observed between the carbonatite and the host rocks. Two kilometers east of Ar #305;kl #305;, at the entrance of Nusratl #305; village, also a metasomatic aureole zone can be observed that consists of thin carbonatite veinlets. These veinlets predominantly constituted by #160;subhedral calcite, dolomite, and magnesite, forming a Mg-carbonatite composition and they contain small amounts of uranium (~4 ppm) and thorium (
Access status: Metadata only ,
Preliminary Results from Petrography and Crystal Size Distribution (CSD) Analysis of Lavas from Nelson Island, South Shetland Islands (Antarctica)
(Copernicus GmbH, 2025-03-18) Gökçenur Bayram; Alp Ünal; Şafak Altunkaynak; Jeoloji Mühendisliği Bölümü; Altunkaynak, Şafak
Geological fieldwork was conducted on Nelson Island (South Shetland Islands, West Antarctica) during January and February 2023, with logistical support provided by the Czech Antarctic Research Center and in-kind assistance from T #220;B #304;TAK MAM Polar Research Institute. This study presents the petrography and preliminary crystal size distribution (CSD) results of the volcanic rocks from the Nelson Island-Stansburry Peninsula.Nelson Island is situated in the northwestern region of the Antarctic Peninsula, within the South Shetland Islands. The dominant lithologies in the study area are volcanic and intrusive rocks, with a minor presence of sedimentary rocks distributed throughout the ice-free areas. The volcanic rocks are primarily basalt/basaltic andesite lavas, accompanied by associated pyroclastic rocks. Petrographic analyses reveal that the lavas are predominantly composed of plagioclase and orthopyroxene crystals, with occasional olivine. Plagioclases occur as phenocrysts and microlites, with phenocrysts exhibiting labradorite composition (An50 #8211;70). The basaltic lavas display phaneritic to hemicrystalline-porphyritic textures, with pilotaxitic to intersertal groundmass. Disequilibrium textures, such as sieve-textured plagioclase, multiple generations of plagioclase, and embayed pyroxenes and plagioclases, are prominent.To understand magma chamber processes, the crystal size distributions (CSD) of two basalt samples from Nelson Island were analyzed. A total of 400 crystals were measured, yielding average results indicating a relatively short magma residence time of #160;10.6 years and a population density ( #8203;n0) of 19.7 mm #8315; #8308;. These results produce a concave-up trend in the population density versus size diagram. Petrographic and CSD data collectively highlight dynamic disequilibrium crystallization conditions, likely influenced by variations in temperature and pressure within the magmatic system. Future petrological and geothermobarometric analyses will refine these interpretations, providing deeper insights into the evolution and magma chamber processes of Eocene magmatism in the South Shetland Islands.