LEE- Çevre Bilimleri Mühendisliği ve Yönetimi Lisansüstü Programı
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ÖgeNutrient recovery from source separated human urine and the treatment of the residual urine with anaerobic processing and ion exchange/adsorption(Graduate School, 2022-05-11) Akdağ, Yasemin ; Baykal Beler, Bilsen ; 501181734 ; Environmental Sciences Engineering and ManagementGlobal population is continuously increasing with a predicted increase to 9.7 billion by 2050. On the other hand, resources are facing with extinction. Sustainable food production greatly depends upon fertilizer production, which has nitrogen, phosphorus and potassium as key elements. Nitrogen, which is abundant in the air, is fixated by Haber-Bosch process, which consumes enormous amounts of energy, to be used in the fertilizer production. Phosphorus, which is a vital element, has limited resources, which is distributed unevenly around the world. The current domestic wastewater management, which adopts mixed collection of wastewater, is based on "treat" and "discard". Valuable materials in wastewater cannot be recovered with the current management practices. Therefore, an alternative way is needed to be generated. Segregation of domestic wastewater into different streams at the source of generation is suggested to get benefit from each stream. ECOSAN is an alternative sanitation concept that claims wastewater is not waste to be discarded but a source to be revaluated. Within this context, each stream is separately collected at the source and is processed for the recovery/reuse of valuable materials. ECOSAN is based on the separation of different domestic wastewater streams into three streams as yellow water, grey water and brown water. Yellow water, which is mainly source separated human urine, is a valuable waste stream in terms of macro plant nutrients (N, P, K). Yellow water constitutes only 1 % of conventional domestic wastewater by volume; however, it contains over 80% of nitrogen, over 50% of phosphorus and over 50% of potassium. This rich nutrient content makes urine a potential source of fertilizers. There are two routes to use source separated human urine as fertilizer in agriculture; (i) direct application and (ii) indirect application. Direct application of human urine as fertilizer is based on the collection of human urine, followed by transport (if required), storage of human urine to destruct pathogens and direct application of stored urine onto soil as fertilizer. Indirect use of human urine as fertilizer necessitates processing urine before intended use. Urine is frequently processed to produce urine-based fertilizers through struvite precipitation, ammonia stripping/absorption and ion exchange/adsorption. Nutrient removal/recovery from source separated human urine was widely investigated in literature. After nutrient removal, the residual liquid phase needs to be handled in an appropriate way as it still contains appreciable amounts of organic matter and nutrients. However, studies on the handling of residual urine are scarce. This study aims the investigation of nutrient recovery from source separated human urine by ion exchange/adsorption on one hand, while investigating organic matter and nitrogen removal from the residual urine by anaerobic processing and ion exchange/adsorption. The behavior of organic matter was closely monitored during different phases of the investigation. Within the scope, urine was collected from two urine diverting toilets and a urinal, and then it was stored for the conversion of urea to ammonium, which is the desired form of nitrogen for ion exchange. Ion exchange/adsorption was employed for nutrient removal from stored urine. The residual urine was processed with anerobic processing and second stage ion exchange/adsorption. Anaerobic processing was suggested to reduce organic matter content of the residual urine and to investigate possible production of biogas. Second stage ion exchange/adsorption was employed to reduce organic matter content of the residual urine and to maximize nutrient removal from the residue. The results of this study revealed that storage was a crucial step not only for urea hydrolysis but also for organic matter removal as between 25% to 39% of COD in urine was removed during storage. Through ion exchange/adsorption for nutrient removal/recovery with the initial loading of 15 mg NH4+/g clinoptilolite, 82% of ammonium and 28% of COD were removed from stored urine. The residual urine still contained appreciable amounts of COD and ammonium, and a high level of salinity for which a special care should be taken. During nutrient recovery, 99% of ammonium and 94% of phosphorus were recovered from the surface of nutrient enriched clinoptilolite upon contact with tap water with the contact time of 5 min in 16 days. 63% of ammonium and 100% of phosphorus were recovered with the contact time of 300 min in 35 days. The COD release from the surface was not considerable for both contact times, indicating that organic matter is not released appreciably from the surface of the clinoptilolite upon contact with water. This is beneficial from the standpoint of pollution prevention when nutrient enriched clinoptilolite is applied as fertilizer in agriculture. Anaerobic granular sludge from a confectionery industry was adapted to highly saline human urine using synthetic urine as feed in attempt to control adaptation conditions. During adaptation the effect of salinity and COD concentration on the removal of organic matter were investigated. During adaptation to high salinity levels at constant COD, organic matter removal efficiency was decreased from 90% to 85% when electrical conductivity was gradually increased from 14000 to 32000 µs/cm, indicating that organic matter removal was not considerably affected by salinity. For different COD concentrations at constant salinity, organic matter removal efficiency was decreased from 83% to 53% when COD was reduced from 2000 mg/L to 750 mg/L, indicating that organic matter removal efficiency was greatly affected by COD concentration. The results showed that selection of the treatment process for residual urine was case specific. Anaerobic processing seems to be a better option for organic matter removal in case of higher COD in residual urine. However, second stage ion exchange/adsorption seems to be a better choice for the treatment of residual urine in case of lower COD concentrations. Anaerobic processing has a potential of a calculated biogas production between 0.2 to 0.46 L CH4/L urine. However, not all of this could be collected under the conditions of the experiments in this work. Second stage ion exchange/adsorption, on the other hand, was advantageous in terms of complete removal of ammonium from residual urine. This study showed that the suggested processing layout was applicable for simultaneous recovery of nutrients and treatment of residual urine. For residual urine, process selection should be evaluated based on the conditions of specific cases to be handled.
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ÖgeOptimization 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 ManagementWastewater 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.
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ÖgeRecovery of rare earth elements from waste and wastewater(Graduate School, 2021-12-14) Yüksekdağ, Ayşe ; Koyuncu, İsmail ; 501152710 ; Environmental Science Engineering and ManagementREEs 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.