LEE- Çevre Biyoteknolojisi- Doktora
Bu koleksiyon için kalıcı URI
Gözat
Son Başvurular
1 - 5 / 7
-
ÖgeEnvironmental stresses applied to microalgae for high lipid production(Graduate School, 2023-07-17)Natural resources are a major part of global economy, and a number of regulations have been implemented to increase the demand for renewable energy resources. There is a great deal of potential in biomass energy, since it is a low-cost and sustainable form of energy. In recent years, there has been significant research on the use of vegetable oil in the production of biodiesel as a competitive fuel to oil-based diesel, which results in significantly less environmental damage. The use of renewable energy sources such as biomass, water, and solar is becoming increasingly prevalent in an attempt to minimize environmental problems and emissions from fossil fuels. A very attractive solution would be to use microalgae as a fuel source since they can store high levels of lipids and can be fueled by solar energy. Due to their low space requirements and high lipid content, microalgae are preferred by researchers over plants and other types of energy sources. The majority of current studies on microalgae focus on macroalgae that produce high levels of lipids. Accordingly, stress conditions, adaptations, or genetic manipulations are being investigated. Autotrophs and heterotrophs produce a large amount of lipids, making them ideal candidates for biofuel production. In spite of this, fossil fuel production still has a relatively low cost in comparison to the production of fuel from algae. Due to these reasons, using microalgae as biodiesel is not economically feasible. Furthermore, in order for microalgae to be economically competitive, it is necessary to increase lipid production efficiency. It is likely that the increased efficiency of lipid production has been attributed to both an increase in the amount of lipid produced and a concurrently high rate of biomass production. According to previous studies, microalgae under stress induce biomass production, biomass inhibition, or significant changes in the structure of biochemical substances. They produce higher levels of lipids, proteins, carbohydrates, and fatty acids, as well as higher quality methyl ester fatty acids. It has been determined that microalgae that are intended for use as biofuels are required to produce a high level of biomass, a high level of lipid, and a high level of fatty acid methyl ester quality. A major objective of this study is to reduce the cost of producing lipids that can be used in the production of biodiesel, which can be used in place of fossil fuels. Thus, an extremely significant step will be taken to obtain microalgae efficient enough to compete economically with fossil fuels. In this study, the microalgae, mainly Auxenochlorella protothecoides, which have both heterotrophic and phototrophic growth properties, were investigated to obtain microalgae with suitable biomass, lipid, and lipid composition. The thesis is organized into ten chapters. In order to evaluate the sustainability of microalgae biodiesel production under stressful environmental conditions, various nutrient stress factors will be examined in relation to growth parameters, such as growth kinetics, biomass, lipid and fatty acid methyl ester composition, chlorophyll content, and carotene content. Based on the results obtained, it was determined whether or not biodiesel-quality lipids could be obtained. In the next step, multiple effects of different stress factors were examined, and optimum parameter values were derived using the surface response approach. The final section of the study examined the effect of the two-stage growth process on microalgae lipid production. Studying the addition or deprivation of ferrous sulfate at different concentrations revealed that only a concentration of 0.2 mM and 14.4 mM ferrous sulfate maintained the lipid in high-quality biodiesel. Additionally, Auxenochlorella protothecoides displayed growth properties even at a concentration of 21.6 mM iron sulfate. At 1.08 mM ferrous sulfate concentration, the highest biomass was obtained (1520 mg / L), while the highest saturated fatty acids were obtained at 1.44 mM ferrous sulfate concentration. Despite no significant variation in lipid production, iron deprivation led to the greatest amount of lipid (59.6%). When nitrogen starvation, deprivation, and excess addition were applied, only biomass grown under 0.8 mM NH4Cl met the biodiesel standard. In this case, the amount of lipid measured is 53.8%. However, the biomass obtained in this case is 1.7 times lower than that obtained in a nitrogen-containing medium. This study illustrates that biomass decreases under stress in response to an increase in lipid content. Through participation in various cell metabolic pathways via changing some enzyme activities, plant hormones are able to change the metabolism of plants, including acceleration or deceleration of cell growth and stimulation of cell biochemical products. Abscisic acid hormone is an inhibitory growth hormone used in plants. Adding this hormone to the growth environment of Auxenochlorella protothecoides may lead to more lipid production. According to this theory, abscisic acid was added in a different medium than in other studies, which served as a source of carbon for glycerol. Under 2.5 µM to 40 µM abscisic acid concentrations, microalgal lipids met high-quality biodiesel standards. It was also concluded that a concentration of 2.5 µM abscisic acid promotes growth. Additionally, high levels of lipids were found at concentrations of 2.5 µM and 10 µM abscisic acid. This thesis also examines the effects of multiple stress factors on microalgae lipids and biomass by using the surface response method and experimental results were correlated with quadratic equations, and optimum conditions for maximum biomass and maximum lipid were determined. For this purpose, in the first study, the acetate parameters known as the carbon source and pH as an indicator of hydrogen ion concentration were selected as variables. The growth experiments of batch microalgal growth have been conducted in different pH and acetate-containing media, which were modeled in three dimensions using surface response methodology, resulting in situations where high biomass and high lipid conditions were achieved and obtained as a result of this model. A second study concerning multiple stresses examined the effects of magnesium deprivation and sodium chloride salt on chlorophyll, carotene, biomass, lipid, protein, and carbohydrate parameters in growth media. Biomarkers of stress such as reactive oxygen species and malondialdehyde, a product of lipid peroxidation, confirmed these changes. Surface response methodologies were used to obtain three-dimensional graphs of the results, and magnesium and sodium chloride concentrations, which were likely to maximize biomass and lipid production, were calculated. An increase in lipid content while a decrease in biomass is generally insufficient to develop a strain with improved biodiesel properties. A robust strain with high lipid and biomass content may be obtained through chemical mutagenesis such as ethyl methane sulfonate. In this study, suitable mutants have been selected considering a selective environment which is a kind of ACCase inhibitor herbicide. In the final stages of this thesis, this study examined the effect of different forms of nitrogen (nitrate and ammonia) on the growth of mixed microalgal cultures in anaerobic digestate. The Biodiesel properties of lipids obtained from microalgae cultured under salt and iron stress were evaluated for their suitability as biodiesel feedstock. This thesis revealed that it is necessary to develop systems that make biomass available as a source of energy so as to reduce the use of fossil fuels as an alternative energy source. Furthermore, results were obtained to support microalgae-based biodiesel production, which would contribute to the lack of literature on multiple stress and singular stress.
-
ÖgeCarbondioxide capturing from industrial flue gas via calcium carbonate inducing microorganisms(Graduate School, 2025-03-19)The increase in greenhouse gases, primarily caused by human activities in the past century, has led to the effects of global climate change becoming increasingly evident. Legal regulations in Europe and neighboring countries are becoming more stringent, and new taxation systems such as the Carbon Border Adjustment Mechanism are pushing industries with high carbon emissions to seek different solutions. In the near future, where conventional flue gas treatment methods alone will be insufficient, carbon capture technologies have been improved in recent years by scientists and even industry's research and development departments. Solutions involving microorganisms allow for many options with individual benefits, such as atmospheric and closed-loop systems. Carbon capture using microorganisms, especially algae, offers a promising solution. Within the scope of this study, experiments were conducted on two algae species with coccus and filamentous morphological structures obtained from Lake Salda together with Chlorella vulgaris, Spirulina, Chlamydomonas reinhardtii species. Many analyses were conducted on these algae including growth rates, growth periods, pigment contents such as chlorophyll and carotenoid, carbonic anhydrase enzyme activity values, biochemical content, and fatty acid types. The fact that Lake Salda is in the high pH category with a pH value greater than 9 was an effective factor in including the samples obtained from here in the study. In all analyses, the pH at which the relevant algae species showed the most growth between pH 8 and 11 at 0.5 intervals was examined. The two species obtained from Lake Salda, which were subjected to the same growth conditions as other algae species using BG11 medium, were not included in further studies as they grew relatively less. In addition, the measurement of carbonic anhydrase enzyme activity was considered as a parameter at least as important as growth during species selection. The presence of the relevant enzyme that enables the gaseous carbon dioxide to be converted into dissolved gas was evaluated as an factor that needs to be developed for carbon dioxide capture studies. The species selection was made as Spirulina with the help of the Analytical Hierarchy Process method, which takes into account all other effective factors as well as growth and enzyme activity. In the second phase of the experiment, the optimum mixture ratio of algae and bacteria coculture was examined in order to increase enzyme activity. Here, the Bacillus pasteurii species that secretes the relevant enzyme was selected. In addition to 100 ml of algae and bacteria monocultures in individual sterile bottles, 3:1, 1:1, 1:3 ratios were also added to the experimental set as two sets. After 12 days of incubation, the highest enzyme activity value was measured as 1.33 mU/mg for the algae-bacteria mixture ratio of 3:1. In growth values, the same culture stood out as 2.4 g/L. The same set of experiments was run for a third set, this time with only the Zarrouk medium in a different conical flask. Here, just before the 15-day incubation period was started, CaCl2 was added to the medium so that there would be 60 mM calcium ions in the medium. Advanced experiments such as XRD analysis, SEM imaging and qPCR analysis were performed on the precipitate obtained at the end of 15 days. The coculture 3:1 mixing ratio stood out again, especially due to the high impurity in the calcite it formed. In the third phase of the experiment, while moving on to pilot scale studies, the coculture mixture ratio was decided and it was progressed in a way. First, the study was carried out in atmospheric and agitated tanks positioned side by side in 200 L volume. Incubation lasting 35 days was carried out in October and November. 22 days of this was the time spent only for the growth of microorganisms in the aquatic environment, and CaCl2 was added to the medium in the last 13 days and the calcification process was followed. At the end of the total study, the VSS concentration in the coculture increased by 1.7 times, while the VSS concentration in the monoculture increased by only 1.4 times. At the end of the study, the VSS concentration in the monoculture was measured as 1.1 g/L, and the temperature has a great effect on the relatively low result. With bubble type photobioreactor, 4 days of calcification were performed in monoculture after 4 days of growth, and 4 days of calcification were performed in coculture after 8 days of growth. In the results, 2.12 g/L VSS was observed in coculture, while 4 g/L VSS was observed in monoculture. Despite the remarkable growth in monoculture, almost equal amounts of TSS were measured at the end of both studies as 14.64 g/L in monoculture and 14.42 g/L in coculture, respectively. As a result, it was determined that much more calcite was produced with much lower biomass in coculture. This study elucidates the multifaceted potential of microalgae, specifically Spirulina sp., in diverse biotechnological applications. The comprehensive analyses and experiments conducted have provided critical insights into optimizing conditions for enhanced biomass productivity and efficient CO2 utilization. The investigation into the properties of calcium carbonate (CaCO3) and the enzyme activity of carbonic anhydrase (CA) revealed valuable information for optimizing biomass productivity and CO2 utilization. Experiments conducted in closed photobioreactors demonstrated the advantages of regulating environmental parameters to maximize algal growth and productivity. The evaluation of suspended solids and volatile suspended solids yielded critical data on the overall efficiency and sustainability of the cultivation processes. Furthermore, the structural and compositional attributes of CaCO3 were found to be essential for its application in various industrial processes. The enzyme activity studies highlighted the pivotal role of CA in facilitating CO2 capture and conversion, underscoring its potential in mitigating greenhouse gas emissions. Additionally, the extracellular polymeric substances (EPS) analysis illuminated the complex nature of the extracellular matrix, suggesting avenues for further research into biofilm formation and stability. The study also compared carbon capture via algae with conventional carbon capture and storage (CCS) technologies, noting both advantages and challenges. Despite the benefits, scaling up algae-based capture in energy-intensive sectors remains challenging. Absorption and adsorption are considered more economical and advanced methods for substantial CO2 capture. Using the Analytic Hierarchy Process (AHP) method, the study evaluated various CCS technologies based on factors such as CO2 capture capacity, cost, operational difficulties, scalability, and space requirements. Algae-based CCS technologies face significant economic and spatial challenges, with costs ranging from $702 to $1,585 per ton of CO2 captured, compared to $15 to $340 for conventional methods. In conclusion, while microalgae demonstrate significant promise in addressing environmental and energy challenges, further research and development are necessary for industrial-scale applications. Continued collaboration and research will advance the field of microalgal biotechnology, fostering sustainable development.
-
ÖgeFate, environmental impact and treatability of favipiravir and surveillance of sars-cov-2 RNA: Comparison with Covid-19 cases(Graduate School, 2024-10-18)Pharmaceutical substances, such as antiviral drugs, antibiotics, antidepressants, anti-inflammatory drugs, antipyretics, beta-blockers and lipid regulators have become more common in both human and animal healthcare to enhance quality of life and prolong lifespan. This increase in pharmaceutical usage has become a significant global environmental concern in recent years. Therefore, the extensive use of these substances worldwide requires attentive monitoring to manage their contamination and environmental impact of water sources. In the second and third chapter, two reviews aimed to provide a comprehensive discussion of the physicochemical properties, analytical detection methods, removal techniques, and ecotoxicological impacts of antiviral drugs. Also, combined assessment of antiviral drugs and virus discharged in the environment were reviewed. These reviews address the challenges faced and explores future opportunities in this field of study. Special emphasis was placed on the occurrence of antiviral drugs employed in the treatment of COVID-19 in water and wastewater. In the fourth chapter, the long-term presence of favipiravir in influent, effluent wastewater, and sludge samples from two WWTPs in Istanbul were investigated. Additionally, the potential environmental risks of favipiravir were assessed using two model organisms. The study determined the mass balance, removal efficiency, and seasonal variations in favipiravir concentrations. The correlation between the number of confirmed COVID-19 cases and favipiravir concentrations in influent wastewater was also analyzed. Furthermore, the impact of drug concentration on the microbial community in sludge from various WWTPs during the pandemic was compared with post-pandemic sludge. The results demonstrate that favipiravir is partially removed (<50%) in WWTPs, with the majority of its removal mechanism being attributed to biodegradation. Additionally, a significant statistical correlation was observed between the concentration of favipiravir and the incidence of COVID-19 in Istanbul, with p-values of 0.025 and 0.039 for WWTP-1 and WWTP-2, respectively. The microbiological distribution was found to vary significantly between sludge samples taken during the COVID-19 pandemic and those from the post-pandemic period. The fifth chapter presents that the presence and quantification of SARS-CoV-2 RNA in raw wastewater, treated effluents, and secondary sludge samples were monitored between June 2021 and January 2022 at two different WWTPs in Istanbul, Turkey. The obtained data were compared with the number of COVID-19 cases and deaths in Istanbul. Additionally, the seasonal variations of SARS-CoV-2 and its relationship with TN, TP, and COD parameters were analyzed using PCA. The results indicated that secondary treatment effectively reduces SARS-CoV-2 levels, thereby mitigating the associated risks from wastewater. This study highlights a moderate correlation between the concentration of SARS-CoV-2 genes and the number of reported COVID-19 cases and deaths in Istanbul. Furthermore, a correlation was observed between the amounts of gene copies and the levels of TP and COD for both the N1 and N2 genes at the two wastewater treatment plants. In the sixth chapter, degradation kinetics of favipiravir under UV, UV/H₂O₂, and UV/Co-doped ZnS processes was investigated. The influence of initial favipiravir concentration, pH, and water matrices (distilled water, tap water, and WWTP effluent) on the degradation kinetics of favipiravir in these processes were assessed. The ecotoxicity risks of favipiravir using algae with treated solutions containing various initial FAV concentrations were evaluated. The degradation of favipiravir after 45 min was observed to be 77.3%, 100%, 89.8%, and 100% for the UV, UV/H₂O₂, UV/Co-doped ZnS, and UV/H₂O₂/Co-doped ZnS processes, respectively. In the seventh chapter was to examine how initial concentrations of antiviral drugs and sludge retention time (SRT) affect favipiravir removal efficiency in membrane bioreactor (MBR) systems. The biotransformation kinetics of favipiravir were also investigated to understand the relationship between biokinetic coefficients, initial drug concentration and SRT. Additionally, an environmental risk assessment was carried out to assess the potential risks associated with favipiravir. Favipiravir was eliminated >99% regardless of its initial concentration in MBR systems. The removal efficiency of favipiravir improved from 48.9% to 86.4% as the sludge retention time (SRT) increased from 15 days to 45 days.
-
ÖgeValorization of lignocellulosic waste by oleaginous yeast(Graduate School, 2023-09-15)In this study, biomass and lipid production capacity of oleaginous yeast Yarrowia lipolytica grown on wood hydrolysate was invesitgated. The demand in biofuel market prompted the third generation of bio-oil production via oleaginous species. Being noncompetitive with food resources unlike other second generation oil plants, microbial oil production provides a chance for the valorization of a variety of nutrient sources abundant in the environment such as waste and waste streams, industrial, agricultural, and forest residues. Among these resources, the potential of woody biomass as a feedstock for biotechnological species has recently increased efforts for its utilization to produce valuable microbial products due to the high content of lignocellulosic (LC) sugars for their bioconversion.
-
ÖgeInvestigation of treatment performances and energy recoveries from a real textile wastewater in conventional and high-rate MBR processes(Graduate School, 2024-01-11)Textile industry wastewater, which is among the most water-consuming sectors worldwide, is extremely hazardous for receiving water bodies due to its toxic and complex structure. Many studies have been conducted involving physical, chemical, biological and combined processes for the textile wastewater treatment, but none of them alone is sufficient to meet discharge standards, and each process requires higher investment and operating costs. Additionally, energy-neutral plants should be expanded to ensure circular economy during the textile wastewater treatment, and the treated wastewater should be appropriate to be used for further reuse processes. Aerobic membrane bioreactors (MBRs) have been widely preferred in the textile wastewater treatment due to their ease of operation, lower volume requirement, and providing higher quality effluent compared to traditional biological methods. However, aerobic MBRs require higher energy input to both supply the oxygen requirement of microorganisms and minimize membrane fouling. In the treatment of textile industry wastewater, a single aerobic process is not sufficient to remove organic matters, azo and reactive dyes (anaerobic/aerobic combined system are needed) and nitrogen-based pollutants (nitrification and denitrification processes are needed). In addition, processes selected should be less-energy consuming due to high volume of textile industry wastewater. Considering that water resources are decreasing globally today, it is not enough to treat textile industry wastewater and their recycling is also extremely important. Therefore, sustainable and practical treatment strategies should be developed for textile industry. This thesis aims to investigate the treatment potential of two different biological processes with different advantages for real textile wastewater. First of all, the treatment performance of the real textile wastewater and the recovery of organic matter that can be preferred as a raw material source for biomethane generation were investigated in an aerobic high-rate MBR including a hollow fiber (HF) ultrafiltration membrane (UF) with a pore size of 0.04 µm. In the high-rate MBR process, it was aimed to recover organic matters rather than oxidation at short (0.5-5 days) sludge retention times (SRTs) and hydraulic retention times (HRTs). Additionally, the effects of SRT/HRT ratios on membrane filtration performance, sludge characterization, sludge production, and the energy requirements for aeration were examined, and all parameters were compared with a conventional long SRT aerobic MBR system operated in parallel. In another MBR process equipped with an HF-UF membrane, the feasibility of intermittent aeration strategy for simultaneous nitrification and denitrification to remove nitrogen-based pollutants and for energy minimization were investigated. Additionally, the effects of different aeration patterns on membrane filtration performance, sludge characterization, sludge production and energy requirements for aeration, and specific removal rates were studied. Within the scope of this thesis, all studies were carried out in four stages. In the first stage, textile wastewater treatment performances of conventional MBRs were investigated at SRTs of 30, 20 and 10 d. During this stage, two identical MBR systems were run, one at SRT for 30 days (MBR-1), and the other at SRT for 20 and 10 days (MBR-2), respectively. The average total chemical oxygen demand (COD), color and total dissolved nitrogen concentrations of textile wastewater used in the study averaged 927±277 mg/L, 910±287 Pt–Co and 39±10 mg/L, respectively. While COD removal performance was above 90% in all SRTs, color removal reached its lowest value at SRT of 10 d and did not show any correlation with SRT. In both MBRs, transmembrane pressure (TMP) was below 10 mbar throughout the study and no membrane fouling was observed. Supernatant filterability (SF) and specific filtration resistance (SRF) values increased at 10 d of SRT. A decrease in viscosity values was also observed due to the decrease in suspended solids (SS) concentration as SRT decreased. While SMP concentrations were similar at all tested SRT values, an increase in EPS concentration was observed at 10 d SRT. Additionally, reducing SRT resulted in an increase in waste sludge generation and observed biomass yield (Yobs), and a decrease in the energy requirement for aeration. According to gel permeation chromatography (GPC) results, as SRT decreased, organic compounds with low molecular weight had higher signals. In the second stage, aim was to investigate textile wastewater treatment performance and organic matter recovery efficiency at short SRTs, and a laboratory-scale high-rate aerobic MBR was run at SRTs of 0.5 – 5 d and HRTs of 1.2 – 24 h, corresponding to predetermined different SRT/HRT ratios of 5, 10 and 20. The average total COD, color, and soluble nitrogen concentrations in the wastewater were 834±143 mg/L and 1037±407 Pt-Co and 51±11 mg/L, respectively. While COD removal performances ranged between 86 and 92% at SRT of 5, 3, and 2 d (in all SRT/HRT ratios), it decreased to 82 and 77% at SRT 1 and 0.5 d (at SRT/HRT ratio of 10), respectively. There was no correlation between decolourization performance and SRT or HRT as it varied between 26% and 70%. The nitrification performance in the system stopped completely at SRTs ≤ 2 d. In particular, when SRT decreased from 5 days to 1 day, the amount of sludge produced and Yobs values increased. The SRT/HRT ratio played an important role in the energy requirement for aeration. In addition, reducing the SRT in the system resulted in higher SRF values, lower SF values, and rapid membrane fouling. SMP in the supernatant increased especially at SRTs ≤ 2 d. The total EPS concentration increased as SRT decreased, but the it decreased as the SRT/HRT ratio increased at each SRT value. No significant change occurred in the molecular weight distributions of the organic substances in the supernatant and filtrate at SRT of 3, 2, and 1 d. Throughout the study, in the cake layer deposited on membrane, Al, Si, and Fe were detected below 2%. In the third stage, the aim was to investigate optimum operating conditions for the simultaneous nitrification and denitrification processes to remove organic matter, color and nitrogen-based pollutants in the real textile wastewater using an MBR with an intermittent aeration strategy. The system was first operated at different dissolved oxygen values (DO of 6 and 3 mg/L) and then aeration-on/off durations varying between 2 min/2 min and 90 min/360 min. The average total COD, color, and TN concentrations of the wastewater were measured as 793±173 mg/L, 1171±458 Pt–Co and 65±15 mg/L, respectively. COD removal performance ranged from 84 to 91%. In all tested conditions, color removal performance was highly variable and independent of operating conditions, ranging from 40 to 68%. While ≥89% nitrification performance was achieved in the MBR at a minimum aeration-on durations of 30 min, the highest denitrification efficiency was achieved in the cycle with an aeration-off durations of 360 min. With the intermittent aeration process, higher TN removal, less sludge production and less energy requirement for aeration were achieved. However, membrane fouling profiles occurred more quickly at the aeration-off durations of 60 min and longer. Additionally, while SS, VSS, SF and viscosity values decreased under intermittent aeration conditions, SRF values increased. Although SMP concentrations decreased with intermittent aeration, EPS concentrations were quite similar. While no change was observed in the molecular weights of the supernatant and filtrate samples of the MBR, the average particle sizes in the supernatant increased as the aeration-off time increased. Finally, according to SEM-EDS results, inorganic substances such as Ca, Mg, Si, and Na were detected in the cake-deposited membrane surfaces. In the fourth stage, the impacts of different aeration patterns on the specific ammonium oxidation, denitritation and denitrification rates were investigated in batch assays. The batch experiments were conducted using the sludge taken from the MBR operated at various DO concentrations and aeration on/off times. While the specific ammonium oxidation rate was determined by batch tests and respirometric studies, specific denitritation and denitrification rates were determined by parallel batch reactors containing different nitrite and nitrate concentrations. The highest specific ammonium oxidation, denitritation, and denitrification rates were obtained as 5.4, 3.8, and 5.3 mg N/(g VSS.h), respectively, at the aeration-on/off durations of 90/360 min. Specific ammonium oxidation rates increased by 1.8 and 2.1 times in the last period (the aeration-on/off time of 90/360 min), compared to continuous aeration conditions with DO of 6 and 3 mg/L, respectively.