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ÖgeAnaerobic digestion of lignocellulosic waste usingphysico-chemical pretreatment methods interms of performance, microbial community, and cost analysis(Graduate School, 2024-09-26)Increasing population and energy demand emphasize the global need to use energy resources more effectively and responsibly. Specifically, reliance on fossil fuels and the repercussions of climate change have hastened the hunt for renewable energy. However, current sustainable energy supplies are insufficient to fulfill rising demand alone. In this context, transforming organic solid waste into a sustainable resource and energy solves the environmental pollution problem while also creating new resource prospects. Although anaerobic treatment is a well-known and widely utilized method, it remains a field for further improvement. However, the lignocellulosic structure of organic solid wastes makes hydrolysis, the first stage in anaerobic digestion, more difficult than with other forms of waste. The use of lignocellulosic wastes in anaerobic digestion systems offers significant waste management potential. However, biodegradation of such wastes is challenging due to their complicated structure, hence several pre-treatment procedures have been devised. Physicochemical pretreatment procedures, particularly microwave and acid treatments, speed up the breakdown of lignin and cellulose structures, allowing microorganisms to operate more efficiently with the waste. As a result, the anaerobic process becomes more efficient, and important chemicals like methane and volatile fatty acids are produced in greater quantities. Sunflower waste is a major raw material source for anaerobic treatment procedures in Turkey and across the world. Turkey is one of the world's largest sunflower producers, with sunflowers growing across vast agricultural regions, particularly in the Thrace region. Stem, head, and other biomass wastes from sunflower cultivation are typically left on agricultural areas or disposed of using inefficient ways. However, these wastes have a significant potential in biogas production thanks to their high cellulose and lignin content. Integrating these wastes into the circular economy makes significant contributions to both environmental sustainability and economic gains. Agricultural wastes have great potential for biomass energy production and can be converted into various products such as biogas, bioethanol, compost. In addition, by utilizing agricultural waste, farmers' income sources diversify and contribute to the strengthening of the rural economy. Products obtained by recycling agricultural wastes both ensure efficient use of resources within the scope of the circular economy model and contribute to meeting Turkey's energy needs with sustainable resources. As a result of these reasons, sunflower was chosen as organic waste in the study. Even though pretreatment methods are basically divided into physical, chemical, biological and combined pretreatment, research has shown that combined pretreatment can be more successful. Combined pretreatments are preferred to ensure more effective breakdown of lignocellulosic wastes, because methods used alone often cannot adequately break down the complex structure of the waste. Combined pretreatments are generally applied by combining physical, chemical or biological methods, whereby the advantages of each method create a synergistic effect, providing more efficient results. For example, the combination of microwave and acid-based pretreatment disrupts the structure of biomass both thermally and chemically, resulting in higher biogas and volatile fatty acid production. While these methods increase energy efficiency, they also provide sustainable solutions in terms of cost effectiveness. In this study, physico-chemical pretreatment was chosen to break down the lignocellulosic structure most successfully. For a physicochemical process, microwave was used for physical pretreatment and hydrochloric acid was used for chemical pretreatment. In this way, a more effective hydrolysis process was achieved with combined pretreatment. The substrate was microwave pretreated in 0.8%, 1.2% and 1.6% HCl solutions for 30 minutes at 120oC and 140oC. After pre-treatment, sCOD values were examined to understand under which condition the efficiency was more successful. Compared to the control sample without pretreatment, it was observed that 47% higher sCOD was obtained in the sample that underwent combined pretreatment in 1.2% HCl solution at 120oC for 30 minutes. The sCOD value measured without pretreatment is 22395 mg/L sCOD, and with 1.2% HCl 120oC pretreatment, the sCOD value is 32908 mg/L. In this way, the most effective pretreatment method was obtained in the study. At the same time, TS and VS values for seed sludge, control sample and the most efficient pretreatment were determined by standard methods. When comparing control samples and pretreated samples, TS degradation increased by 45% and VS by 52%. An increase in the TS and VS values of the solid material is a sign of effective deterioration. Thus, lignocellulosic wastes can be shown to decompose more efficiently, meaning that a more efficient hydrolysis will result in a larger VFA output. In recent years, it has become quite common to suppress the presence of archaea in the anaerobic digestion process and to ensure the formation of volatile fatty acids. The main reason for this is that although methane is used as an energy source, it is an important source of greenhouse gases. At the same time, CO2 is also formed as a byproduct in addition to methane (CH4) in semi-anaerobic digestion. The most important motivation of this study is to obtain volatile fatty acids. In addition to the development of pre-treatment technologies, the production of volatile fatty acids, which have an important place in the circular economy and are used in many different sectors, has become very popular. In this study, sunflower used as lignocellulosic waste was kept at pH 5.5 after being exposed to combined pretreatment. While archaea, that is, microorganisms that provide methane formation, cannot survive in this pH range, only the formation of volatile fatty acids is possible with acidogenesis microorganisms. At this pH value, microorganisms produce volatile fatty acids, but these volatile fatty acids do not turn into methane because the archaea cannot survive. Once the archaea were inhibited and the pH was checked every day, samples were taken on certain days. The formation amount of volatile fatty acid types, which are used in various sectors and have different usage purposes, on determined days was measured in mg/L sCOD. Cumulative VFA formation was determined for acetic acid, propionic acid, butyric acid, isobutyric acid, valeric acid and isovaleric acid. The 1st day sCOD value for the pretreated sample was 32908 mg/L; At the end of the 30th day, it was observed to be 19324 mg/L. It is showed that a success rate of volatile fatty acid formation of approximately 40%. In summary, the acid types, from most produced to least produced, are as follows: Propionic Acid: 3089 mg/L, Isovaleric Acid: 2993 mg/L, Isobutyric Acid: 2700 mg/L, Butyric Acid: 2137 mg/L, Isocaproic Acid: 2421 mg/L, Caproic Acid: 760 mg/L, Acetic Acid: 539 mg/L, Valeric Acid: 245 mg/L. Another important aspect of the study is the generation of genomic sequences of microbial communities for taxonomy categorization. The aim is to fully characterize microbial species using Oxford Nanopore MinION technology in combination with fast and long-read approaches. After DNA isolation, PCR and sequencing were performed under appropriate conditions. 16S, 18S and archaeal microorganism communities were classified and compared as phylum, class and species. Genetic sequencing of microbial communities has revealed a diverse spectrum of microorganisms involved in the anaerobic digestion process, including many species of bacteria and archaea. The most dominant species in microbial communities were observed as follows: Armatimonadota, Caloramator sp. E03, Dysgonomonadaceae:, Stephanoeca, Prototheca ciferrii, Prototheca wickerhamii, Tetramitus dokdoensis, Methanosarcina vacuolata, Methanothrix soehngenii, Methanosarcina barkeri. These findings will provide resources for future studies on understanding the microbial community of the anaerobic digestion process and improving system efficiency. Finally, a cost analysis was performed using all collected data. The economic values according to the types of volatile fatty acids obtained from 1.5 grams of substrate are as follows: Acetic Acid: $17, Propionic Acid: $250, Isobutyric Acid: $476, Butyric Acid: $247, Isovaleric Acid: $673, Valeric Acid: $24, Isocaproic Acid: $385, Caproic Acid: $122. Microbial analysis is very important to check system success efficiency. Archaea were shown to persist in this manner. Anaerobic digestion is an extremely sensitive process. Although successful pretreatment was used and archaea were predicted to be absent, their continued presence indicated that a more precise process application could yield more efficient VFA synthesis. At the end of this entire study, the following conclusions can be made: Increasing population and energy demand increases the need to replace traditional energy sources with sustainable alternatives. In this context, the use of organic solid wastes, especially those with a lignocellulosic structure, in the production of biogas and volatile fatty acids is important. However, the complexity of the lignocellulosic structure makes biodegradation difficult. Therefore, physicochemical pretreatment methods such as microwave and HCl enable waste to be hydrolyzed more easily and increase biogas yield. Studies show that combined pretreatment methods disrupt the structural integrity of wastes, leading to higher methane and volatile fatty acid production. In countries where sunflower production is intense, such as Türkiye, these wastes offer a great energy potential. While volatile fatty acid production in anaerobic treatment stands out as a more environmentally friendly and economical option, effective taxonomic analysis of microbial communities has the potential to further increase process efficiency.
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ÖgeAnaerobic digestion of lignocellulosic waste using alkali pretreatment method interms of performance, microbial community, and cost analysis(Graduate School, 2024-09-26)Agricultural residues with lignocellulosic structures play a crucial role among renewable bioenergy sources and are abundantly available in nature. Anaerobic digestion (AD) is considered an ideal technology for agricultural waste stabilization/treatment and the production of renewable energy carriers. However, the overall economic value of the produced methane remains low, especially when compared to the potential value of waste streams. In this project, the aim is to facilitate the transition to anaerobic fermentation using agricultural waste, specifically sunflower stalks and heads with lignocellulosic structures, to increase the production of volatile fatty acids (VFA). An alkali pretreatment method will be employed as a chemical pretreatment process to investigate the yield from the selected agricultural waste and assess its impact on acidification efficiency. The purpose of using a pretreatment process is to make lignocellulosic material which is difficult to biologically degrade, more easily digestible thereby enhancing process efficiency. Wastes subjected to pretreatment with Potassium Hydroxide (KOH) at various dosages will be thoroughly examined for VFA yield. During the research process, the taxonomic classification of the microbial community active throughout the process will be conducted using the third-generation sequencing technology provided by Oxford Nanopore MinION, targeting the 16S and 18S rRNA gene regions. Finally, a cost analysis will be developed based on the obtained data. This analysis aims to contribute significantly to research in this field by providing practical guidelines to enhance the effectiveness of anaerobic treatment systems and transform organic waste into a sustainable energy source
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ÖgeRelating microbiome profiles to removal of non-steroidal anti-inflammatory drugs in sequencing batch reactors along a sludge retention time(Graduate School, 2023)Non-Steroidal Anti-Inflammatory Drugs (NSAIDs) are medications commonly used for pain and inflammation treatment. The residues generated from their use can contaminate water sources. The primary concern regarding these pollutants is their insufficient removal in wastewater treatment plants, leading to their release into the environment. In recent years, studies investigating the presence of NSAIDs in aquatic environments at critical levels and their long term effects have increased. The environmental impacts of these pollutants are not yet fully understood, raising concerns. In March 2015, the Water Framework Directive initiated by the European Commission listed some NSAIDs on the Watch List under Decision 2015/495/EU. The concept of harnessing the activities of adaptable microorganisms in low-cost and conventional systems, instead of expensive advanced wastewater treatment plants, is important for the treatment of micropollutants. Activated sludge based treatment processes have the potential to partially remove micropollutants; however, there is insufficient knowledge regarding which microorganisms play an active role. Furthermore, there have been limited studies on determining the appropriate sludge retention time for the biological treatment of micropollutants. The microbial communities in activated sludge can vary depending on the different chemicals present in the wastewater, which can adversely affect the system's performance. In this study, the impact of a mixture of six NSAIDs (diclofenac, ibuprofen, ketoprofen, naproxen, indomethacin, and mefenamic acid) on microbial population and composition in activated sludge systems was investigated using advanced molecular biotechnology and bioinformatics tools. This study mainly focused on (i) the impact of sludge age (SRT) on the treatability of the selected mixture of NSAIDs in activated sludge systems, (ii) a comparison of the microbiome analysis of samples collected from an advanced wastewater treatment plants in Istanbul and three lab scale sequential batch reactors operated at sludge retention times (SRTs) of 5, 10, and 20 days, (iii) the impact of reference database selection on the analysis of the activated sludge microbiome, (iv) the analysis of the impact of the selected NSAIDs on the microbial population and composition using bioinformatics tools and software, and (v) the correlation of the changing microbial population and composition with the treatment efficiency of the wastewater and selected NSAIDs. In the laboratory scale study, a total of six parallel sequential batch activated sludge reactors were operated with three different SRT: 5, 10, and 20 days. Among these reactors, three served as control reactors, while the remaining three were designated as micropollutant added reactors. Each SRT had a corresponding pair of control and micropollutant added reactors. The control reactors were operated under normal conditions without the addition of micropollutants, while the micropollutant added reactors were operated with the addition of a specific mixture of selected NSAIDs in predetermined proportions. The operating performance of the reactors was monitored regularly by measuring various parameters including suspended solids (SS), volatile suspended solids (VSS), pH in the reactor and chemical oxygen demans (COD), ammonia (NH4+), nitrite (NO2-) and nitrate (NO3-) in the effluent. The result of these analysis showed that these chemicals did not have a long term inhibitory effect on biological degradation in all six reactors. There was no significant change in COD removal efficiency in reactors where NSAIDs were added. The nitrification efficiencies were found to be better in the micropollutant added reactors with sludge retention times of 5 and 20 days compared to the control reactors. The removal efficiencies of the six NSAIDs were individually determined in all sludge retention time reactors. Ibuprofen exhibited removal efficiencies exceeding 99% in all micropollutant added reactors operated for 5, 10, and 20 days. Ketoprofen showed average removal efficiencies above 75% in reactors operated for 5 and 20 days. Naproxen had removal efficiency above 90%, with the highest removal efficiency observed in the reactor operated for 20 days. Indomethacin exhibited removal efficiencies above 90% in all micropollutant added reactors. Mefenamic acid had the highest removal efficiency observed in the reactor operated for 5 days, but its removal efficiency decreased in reactors with longer sludge retention times. Diclofenac removal efficiency was adversely affected in reactors with longer sludge retention times. This study aimed to understand the impact of micropollutants on the diversity and activity of microbial communities within activated sludge, which play a crucial role in wastewater treatment. Using next generation sequencing technology, the microbial communities involved in the degradation of six NSAIDs were investigated in laboratory scale activated sludge reactors, along with the potential adverse effects of these drugs on the communities. The sequenced data obtained from the Illumina MiSeq platform were analyzed using the QIIME2 software package to assess microbial diversity. A comparison between the NCBI and SILVA databases revealed that the NCBI database provided more taxonomic information at the species level. The addition of NSAIDs was found to affect microbial diversity in the 5 and 10 day sludge retention time systems, reducing species richness at the taxonomic level. However, in the micropollutant added 20 day sludge retention time system, an increase in diversity was observed. The observed operational taxonomic unit (OTU) numbers in the clone libraries for the sludge samples collected from the control and micropollutant added reactors were 203 and 145 for 5 day sludge retention time, 171 and 106 for 10 days sludge retention time, and 100 and 182 for 20 days sludge retention time, respectively. In this study, it was determined that Proteobacteria, Actinobacteria, and Bacteroidetes phyla were dominant in raw sludge, control, and micropollutant added reactors. The presence of NSAIDs at a sludge retention time of 5 days increased the abundance of the Verrucomicrobia phylum, while it decreased at a sludge retention time of 10 days. In the control reactor, Verrucomicrobia was not detected at a sludge retention time of 20 days, but its abundance increased with the addition of NSAIDs. In the micropollutant added reactors, different species became dominant at different sludge retention times. Prosthecobacter and Paracoccus species were dominant at a sludge retention time of 5 days, Chryseobacterium and Niabella species at a sludge retention time of 10 days, and Niabella and Parafilimonas species at a sludge retention time of 20 days. The presence of these species can be associated with their capacity to degrade NSAIDs in the micropollutant added reactors. In contrast, the presence of NSAIDs led to the disappearance of more than 80% of species such as Frigidibacter albus and Prosthecobacter vanneervenii in the reactor with a sludge retention time of 5 days, Thauera terpenica in the reactor with a sludge retention time of 10 days, and Intrasporangium oryzae in the reactor with a sludge retention time of 20 days. These species were unable to adapt to the new conditions created by the addition of NSAIDs. Changes in bacterial abundance in functional groups were also observed in the presence of NSAIDs. Specifically, an increase in the abundance of species involved in the nitrification process was observed in the reactor with a sludge retention time of 20 days with NSAID addition.
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ÖgeInvestigation of toxicity of antiviral drugs in the presence of microplastics and their removal through ozonation and LDH-based catalytic ozonation(Graduate School, 2024-06-28)Following global outbreaks such as SARS-CoV-2 and influenza, the heightened use of pharmaceuticals to treat infected individuals has led to the presence of antiviral drugs and their metabolites in wastewater at significant levels. Since wastewater treatment plants (WWTPs) are not designed to remove antiviral drugs, these contaminants are discharged into receiving environments without treatment. If these substances are not adequately degraded during wastewater treatment, they could potentially harm human and ecosystem health when released into aquatic systems. To address this concern, tertiary treatment applications have to be employed. In this study, in order to assess the treatability of two commonly used antivirals, Oseltamivir (OSE) and Favipiravir (FAV), advanced oxidation processes, involving ozonation and catalytic ozonation were applied. Additionally, the potential ecotoxicological impacts of treated wastewater effluent were investigated on soil and aquatic environments. Moreover, the efficiency of the applied processes was also explored in the presence of microplastics (MPs). In this study, the concentrations of OSE and FAV were selected based on the occurrence of these antivirals in environment ranging from low (500 ng/L) to high (50 µg/L). A biologically treated synthetic wastewater sample, mirroring a typical domestic effluent, was exposed to ozonation with three different ozone dosages: 0.2, 0.6, and 1 mg O3/mg DOC (dissolved organic carbon) at pH values of pH: 7±0.1 and pH: 10±0.1. The degradation of these compounds was also assessed in the presence of catalyst 0.1 g/L of ZnFe LDH (layered double hydroxide), which is a nanocomposite catalyst. The widely found polyethylene (PE) microplastic (0.1 mg/L) was introduced into samples during the ozonation and catalytic ozonation applications. Antiviral compounds and their corresponding removal rates were assessed using liquid chromatography tandem mass spectroscopy (LC-MS/MS), employing the isotope dilution method. Solid phase extraction was employed to facilitate accurate quantification of antivirals in samples. Finally, to assess the potential reusability of treated wastewater, soil organisms Enchytraeus crypticus and acute organisms Vibrio fischeri were exposed to ozonated and catalytic ozonated samples according to OECD and ISO 11348-3 methods. According to the findings, by evaluating conventional parameters in ozonated and catalytic ozonated effluent samples, it was concluded that both ozonation and catalytic ozonation can effectively decrease the amount of organic matter in wastewater, while MPs had a negligible effect on the wastewater characterization. In this regard, the maximum removal rates in chemical oxygen demand (COD), dissolved organic carbon (DOC), and ultraviolet absorbance at 254 nm (UV254) parameters were achieved by catalytic ozonation at pH 10 with 1 mg O3/mg DOC, reaching approximately 27.2%, 17.7%, and 71%, respectively. Additionally, particle size distribution (PSD) analysis was conducted for non-ozonated and ozonated samples revealed an 11% decrease in the COD fraction within the particle size interval of <2nm, contributing to an overall removal efficiency of 21%. This finding underscores the significance of the soluble fraction (<2nm) in COD removal, constituting 54% of the total COD removed. In the case of antiviral removal, it was observed that in single ozonation and without the presence of MPs, both OSE and FAV showed a removal efficiency of 85% at high antiviral concentrations, regardless of the specific ozone dose. However, at low antiviral concentrations, while FAV was completely removed with 100% efficiency, OSE only exhibited a 26% removal under the same conditions. At high concentrations of antiviral compounds, catalytic ozonation did not perform as effectively as single ozonation. When considering the presence of MPs, it can be concluded that they negatively impact the removal efficiency of antiviral compounds. To assess the effectiveness of the treatment process and the potential reusability of ozonated and catalytic ozonated effluent samples, ecotoxicological analysis was conducted on Enchytraeus crypticus and Vibrio fischeri. The soil experiments carried out on high antiviral concentrations did not indicate any toxic effect on E. crypticus organisms; instead, the reproduction rate of organisms increased. Moreover, when these organisms were exposed to the samples containing MPs, their reproduction rate increased significantly. The toxicity evaluation using Vibrio fischeri bacteria indicated that biologically treated synthetic wastewater exhibited higher toxicity compared to ozonated wastewater. Furthermore, ozonated wastewater demonstrated slightly higher toxicity than catalytic ozonated wastewater. The leaset toxicity was observed in distilled water. The presence of individual antivirals in the wastewater resulted in lower toxicity compared to their combined presence, revealing the synergistic effect of FAV and OSE. Since antivirals were not completely removed during ozonation and catalytic ozonation at the high initial concentration (50 µg/L), they contributed considerably to the observed toxicity. The experimental results indicated that ozonation and catalytic ozonation could serve as favorable options to upgrade existing wastewater treatment plants. These processes not only contributed to the reduction in the release of antivirals from domestic effluents, but also significantly enhanced the suitability of treated wastewater for irrigation of agricultural areas.
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ÖgeUncertainty analysis in the measurement of nitrification kinetics in urban wastewater treatment plants in Türkiye(Graduate School, 2024-06-28)In this study, relation between the maximum growth rate of nitrifiers and the initial amount of active biomass placed at the beginning of the nitrification experiment was investigated by using parameter estimation and uncertainity analysis for four different wastewater treatment plants, taking into account local conditions. By focusing on these parameters, critical importance of the effects of initial conditions on the nitfication experiment is investigated. To designing and optimising the performance of wastewater treatment plants, nitrification kinetics play a decisive role. Nitrification directly affects aerobic sludge age, which is one of the most important parameters to obtain volume calculations. Understanding of nitrification kinetics will enable predict and control the rates of these biochemical transformations with greater sensitivity and, in turn, increase the effectiveness of future nitrogen removal processes. Nitrification is important for the alleviation of aquatic eutrophication and the minimization of the toxic ammonia concentration to meet the ever-increasing stringent environmental discharge regulations. In addition, it has significant impacts on designed advanced treatment technologies and sustainable practices along the pathways to ensure minimal anthropogenic impact on the natural ecosystems. Four different advanced biological wastewater treatment plants across the Marmara Region of Türkiye are taken into account to highlight the importance of the local conditions. From these plants daily samples were taken and nitrification experiment was carried on, and with the results of the experiments and the data generated by the model are used in this study. Some assumptions such as assuming the respiration and growth as constant are made in order to reduce the complexity of the initial conditions and to improve practical identifiability and lesser uncertainity between the focused parameters. The nitrification experiment results of the plants, that were modeled using Microsoft Excel program, used and with the help of sum of squared method, parameter estimations are performed, and the effect of the initial conditions of the experiment, and uncertainties are investigated. According to the results, approximate confidence intervals were visualized as contour plots based on critical values calculated at a 95% confidence level for each plant. The effects of local conditions on nitrification kinetics experiments were discussed based on observed similar trends in approximate confidence intervals. Nitrifiers growth rates in Türkiye found to be lower than that of standard values, and errors in maximum growth rate of nitrifiers are calculated to be in the order of 5-10%, which is acceptable according to the general design margins which is typically range between 20% to 25%. Also, for the practical applications overdesign is very general approach for construction of wastewater treathment plant design and oftenly varies between 10-30%. Thus, the importance of factors that may arise from the initial conditions of the experiment was emphasized, and the most suitable experimental conditions were examined. In many studies, the significance test of the data can be overlooked; however, this study focuses on the uncertainty analysis between the maximum growth rate of nitrifiers and the initial active biomass placed at the beginning of the experiment. Meanwhile, it is important to acknowledge that this study may be one of the first investigations to explore this specific aspect.