LEE- Çevre Bilimleri Mühendisliği ve Yönetimi-Doktora

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  • Öge
    Coupling ozone with GAC, AIX and biochar: Removal of pharmaceuticals from the biologically treated wastewater and fate of their transformation products
    (Graduate School, 2024-09-24) Kutlu Fakıoğlu, Malhun ; Öztürk, İzzet ; 501172707 ; Environmental Science, Engineering and Management
    In order to prevent water pollution in the water bodies, there has been a rising interest in improving cost-efficient quaternary treatment technologies to efficiently remove pharmaceuticals from the effluents of wastewater treatment plants. Various methods, including physical, biological, and chemical processes, are being utilized to eliminate organic micropollutants (OMPs) which include pharmaceuticals and persistent pollutants such as per- and polyfluoroalkyl substances (PFAS). Among these advanced techniques, ozonation and activated carbon adsorption are currently suggested as the most feasible options for substantially decreasing pharmaceutical concentrations in the wastewaters. Carbon-based materials such as activated carbon are notably effective adsorbents used for removing pharmaceuticals. Likewise, ozone is a highly potent oxidizing agent capable of oxidizing micropollutants directly via O3 itself or indirectly through the generation of hydroxyl radicals. However, after ozonation, instead of being mineralized, compounds can be converted into other substances known as transformation products, which may pose greater toxicity than the original compound. Additionally, the reaction between bromide and ozone produces bromate which is a toxic and carcinogenic by-product. To mitigate potential adverse effects from ozonation, it is often recommended to implement post-treatments such as biological or adsorptive systems like granular activated carbon (GAC) to eliminate potential transformation products and by-products. When combined with activated carbon adsorption, ozonation acts as an additional method for removing compounds that are resistant to adsorption. Crucially, activated carbon, with its extensive specific surface area and high concentration of functional groups, has demonstrated its ability to eliminate transformation products and by-products that may be generated during ozonation. While the effectiveness of the O3-GAC pairing is well-documented in literature, less attention has been given to combinations like ozonation with anion exchange (AIX) or other potentially more sustainable sorption materials such as biochar. The O3-AIX combination is particularly intriguing for this study, as many wastewater treatment plants, including the WWTP that provided wastewater for this research, are grappling with the challenge of removing PFAS. The treated wastewater from the aforementioned WWTP is released into the Fyrisån River, which flows into Ekoln Lake, Mälaren Lake, and eventually to the Baltic Sea. Fyrisån River also contributes to replenishing a groundwater source used for the city's drinking water. Consequently, the conventionally treated wastewater, containing untreated micropollutants, is discharged into a river that ultimately serves as a drinking water source. Thus, this study aims to simulate a potential combined advanced treatment step for the wastewater treatment plant. This research is particularly noteworthy as it not only provides guidance for implementing advanced techniques to remove micropollutants in full-scale wastewater treatment plants, but also investigates the fate of transformation products within three different combined systems: ozone and granular activated carbon filtration, ozone and ion exchange, and ozone and biochar. The objective of this thesis was both to examine the effectiveness of removing 24 selected pharmaceuticals and to monitor the fate of 7 of their metabolites, including oxidation transformation products. This investigation utilized a combination of processes, namely O3-GAC, O3-biochar (with two different types of biochar), and O3-AIX, in laboratory-scale experiments using actual effluent from a full-scale WWTP. The entire system was operated with three different O3 dosages, each maintained continuously for two weeks. Various sorption filters, including two types of biochar (one derived from forest biomass and the other from sewage sludge), reactivated GAC, and an AIX resin, were assessed. The evaluation of results focused not only on micropollutant removal but also on the generation of transformation products and by-products. 23 out of the 24 pharmaceuticals examined were detected in the effluent wastewater collected from the Kungsängsverket WWTP in total. The findings revealed that concentrations of sertraline, trimethoprim, fluconazole, atenolol, and sulfamethoxazole were below 500 ng/L, whereas the average concentrations of venlafaxine, desvenlafaxine, fexofenadine, bicalutamide, and lamotrigine were above 5,000 ng/L. According to the study findings, the average removal of selected pharmaceuticals varied between 8.8% and 97% with an O3 dosage of 0.28 g O3/g DOC, while it ranged from 86% to 99% for higher O3 dosages (0.96 and 2.17 g O3/g DOC). Pharmaceuticals such as fluconazole, atenolol, metoprolol, and tramadol exhibited relatively lower removal rates (9-15%) with the specific O3 dosage of 0.28 g O3/g DOC compared to furosemide, propranolol, clindamycin, and clarithromycin, which showed high removal rates (>90%). Tertiary amines like cetirizine and fexofenadine, known for their high reactivity with ozone, achieved removal rates of 79% and 89%, respectively, via 0.28 g O3/g DOC in this study. Furthermore, highly reactive compounds such as carbamazepine, diclofenac, sulfamethoxazole, and trimethoprim were removed by 70%, 85%, 70%, and 88%, respectively, with 0.28 g O3/g DOC, consistent with existing literature. Conversely, fluconazole exhibited a removal rate of 9% with an O3 dosage of 0.28 g O3/g DOC, while atenolol had an average removal rate of 15%. Among all materials tested, GAC emerged as the top-performing sorbent, effectively removing nearly all compounds below the limit of quantification (LOQ) even after continuous operation for two weeks (BV=864). The potential efficacy of biochar 2 for pharmaceutical removal, which was derived from sewage sludge, was particularly significant for the overall sustainability of the WWTP. Although biochar 1 exhibited better performance than biochar 2, both sorption materials showed decreased sorption capacity over the two-week period (BV=864) for most target compounds, including carbamazepine, fexofenadine, tramadol, fluconazole, sulfamethoxazole, and erythromycin. By the end of the continuous two-week operation, biochar 1 achieved removal rates ranging between 30% and 89% (mean 68%), while biochar 2 removed selected compounds at rates of 8.5% to 82% (mean 38%). Conversely, AIX that has been included for PFAS removal, demonstrated lower removal rates as expected after two weeks compared to biochars 1 and 2, ranging between 2% and 55% (average: 20%) for positive removal rates (BV= 3,264). Based on the findings, GAC exhibited the highest performance when paired with ozone (>99%), followed by biochar 1. Generally, the combination of ozone with biochar 1 proved to be more effective (mean=91%, range: 42-99%) than with biochar 2 (mean=79%, range: 29-99%). As anticipated, the combination of ozone with AIX yielded the lowest removal rates for pharmaceuticals (mean=58%, range: 6-98%). Based on the findings, six out of seven metabolites were identified in samples both pre- and post-ozonation. The results suggested that while the concentrations of certain metabolites decreased during ozonation, some metabolites, including oxidation transformation products like citalopram N-oxide, exhibited an increase over the two weeks of continuous operation. On average, citalopram concentration decreased by 81%, whereas the concentration of citalopram N-oxide increased by 19% with an O3 dosage of 0.28 g O3/g DOC. With the system operating at 2.17 g O3/g DOC, citalopram's average removal reached the LOQ, while the increase in citalopram N-oxide exceeded to 33%. Furthermore, all detected metabolites were eliminated to below the LOQ using GAC after two weeks of operation. Concentrations of most metabolites exhibited a linear decrease over time for biochar 1 and biochar 2, while for AIX, concentrations of certain metabolites increased over time. During all three O3 dosages (0.28, 0.96, and 2.17 g O3/g DOC), bromate concentrations remained below 5 µg/L. At the lower O3 dosage of 0.28 g O3/g DOC, the bromide concentration in the utilized WWTP effluent was 1.03 mg/L, whereas at the higher O3 dosages of 0.96 and 2.17 g O3/g DOC, the bromide concentrations were 0.52 and <0.50 mg/L, respectively. This variation resulted in an inability to assess the potential formation of bromate. Removal of DOC via different O3 dosages ranged from 19% to 26%, while GAC removed over 90% of DOC under all operational conditions. Conversely, AIX only removed less than 10% of initial DOC across all operational conditions, while in all cases, biochar 1 and biochar 2 removed within the range of 18-23% and 5-10%, respectively. In summary, ozonation exhibited high removal efficiency of pharmaceuticals and their metabolites at higher O3 dosages (>0.96 g O3/g DOC), while at lower O3 dosages (0.28 g O3/g DOC), a post-treatment became necessary for effective pharmaceutical removal. However, higher O3 dosages entail increased operational costs and pose a risk of transformation product formation. Therefore, employing combined systems for pharmaceutical and metabolites elimination is suggested as a preferable alternative to sole reliance on ozonation as the advanced treatment method. Comparative analysis of different post-treatment filter sorbents indicated that GAC yielded the most favorable results for pharmaceutical and metabolite removal. Conversely, the adsorption capacities of two distinct biochar types diminished over the continuous two-week operation, whereas GAC's performance remained consistent throughout. Biochar 1 outperformed biochar 2 in terms of pharmaceutical removal. AIX exhibited the lowest removal efficiencies, suggesting it may not suffice as a polishing step for ozonation when simultaneous removal of pharmaceuticals and PFAS is targeted. Overall, the combination of O3 with GAC demonstrated the most effective performance for pharmaceutical removal. Biochar holds promise as a more sustainable substitute for GAC, as it can be sourced from renewable materials like wood. However, there is a need for ongoing development to better understand the efficacy of combined O3-filter systems, with a focus on considering long-term operation. Before scaling up to a full-scale WWTP, conducting a life cycle assessment and feasibility analysis would be prudent steps to take.
  • Öge
    Optimization of anaerobic membrane bioreactors for sludge treatment
    (Graduate School, 2023-02-01) Abdelrahman, Amr Mustafa ; Erşahin, Mustafa Evren ; Volcke, Eveline ; 501182702 ; Environmental Sciences, Engineering and Management
    Wastewater treatment is an energy intensive process. The energy balance is positively affected by anaerobic sludge digestion, especially primary sludge. The inclusion of a primary clarifier before the biological reactors results in a higher sludge total production compared to the direct treatment of raw wastewater. Conventional anaerobic digesters for sludge treatment are designed as completely mixed reactors operated at long solid retention times (SRTs) for enhanced solids conversion and to maintain the methanogenic activity in the reactor. Consequently, anaerobic digesters are commonly built with large volumes to ensure sufficient reduction of volatile solids (Xu et al., 2011). Anaerobic membrane bioreactor (AnMBR) is a promising alternative to conventional anaerobic digesters for sludge digestion. AnMBRs are operated at long SRTs independent from hydraulic retention time (HRT) by means of physical separation of the membrane. Thus, slow growing methanogenic biomass can be kept longer in the reactor, resulting in enhanced methane production. Moreover, a smaller footprint of the anaerobic reactor can be achieved since the HRT can be controlled by manipulating the flux. To understand the rationale behind the thesis, Chapter 1 presents a brief description about the energy consumption for wastewater treatment and its distribution in the wastewater treatment plant (WWTP). The organic matter removal mechanism in the conventional WWTP is explained. Novel process configurations for organics capture are presented. Anaerobic digestion process and the design parameters of the anaerobic digester are explained as well. The advantages of using AnMBR for sludge treatment are defined. The chapter ends with research gap and an outline of the thesis. The current status and perspectives of the AnMBR technology for sludge treatment are critically reviewed in Chapter 2. It discusses the historical development of the AnMBR for sludge treatment, and factors influencing the AnMBR performance reported in the literature. The operational conditions such as SRT, HRT and temperature have a noticeable effect on the methane production and permeate quality. Volatile fatty acids (VFAs) can be recovered simultaneously during sludge treatment, which can improve the economics of the WWTP. However, there are still problems, such as membrane fouling, which hinder the adoption of AnMBR technology for sludge management, as well as a lack of studies demonstrating the economic benefits of using AnMBRs for sludge treatment. Suggestions for research perspective are given, aiming for overcoming the challenges and for optimization of the AnMBR for sludge treatment. The aim of this thesis was to investigate the applicability of the AnMBR for sludge treatment in the view of energy-positive WWTPs. The objectives of this thesis were met through four different studies. Chapter 3 explains the material used and methods followed during these studies. The results of these studies are explained and disscussed in Chapter 4. In order to maximize organic capture and thus energy recovery from wastewater, novel configurations including an A-stage and CEPT have been proposed as alternatives to primary settling. However, it remains to be investigated to which extent these configurations affect the sludge characteristics, which may affect the economic feasibility of the integrated systems. Therefore, the first study focuses on the effect of these primary treatment methods on sludge characteristics and digestibility, and on plant-wide economics of wastewater treatment. A detailed characterization of sludge obtained from primary settling (primary sludge), A-stage treatment (A-sludge) and CEPT showed significantly different sludge characteristics. The organic compounds in primary sludge consisted mainly of 40% carbohydrates, 23% lipids, and 21% proteins. A-sludge was characterized by a high amount of proteins (40%) and a moderate amount of carbohydrates (23%), and lipids (16%), while in CEPT sludge, organic compounds were mainly 26% proteins, 18% carbohydrates, 18% lignin, and 12% lipids. The biomethane potential test showed that primary sludge and A-sludge had the highest methane yield (347 and 333 mL CH4/g VS, respectively), while methane yield of CEPT sludge was lower(245 mL CH4/g VS). A plant-wide economic evaluation for the three systems, indicated that energy surplus was the highest with CEPT. The inclusion of an A-stage had the lowest positive net energy due to the relatively high energy consumption in aeration. Considering the effluent quality of the three systems, CEPT had the highest benefits, followed by A-stage. Overall, integration of CEPT or A-stage, instead of primary clarification in existing wastewater treatment plants, has the potential to improve the effluent quality and energy recovery. AnMBRs have been applied as compact alternatives for anaerobic digesters for sludge treatment in conventional WWTPs. However, there is no information about the impact of integrating an A-stage, instead of primary clarifier, on sludge digestion in an AnMBR. The second study examines the performance of lab-scale AnMBRs, in terms of treatment and filtration performances, for both digestion of primary sludge and A-sludge. The results showed that anaerobic digestion of A-sludge yielded more methane and improved methanogenic activity in the AnMBR compared to primary sludge. The permeate of the AnMBR fed with A-sludge contained higher nitrogen and phosphorous concentrations due to higher nitrogen and dissolved phosphorous concentrations of A-sludge. No coliforms were detected in the permeates, which showed that from the hygienic point of view, the permeate had the potential to be directly used for irrigation purposes. A higher EPS concentration was observed during the digestion of A-sludge compared to the primary sludge, which accumulated on the surface of the membrane and caused an increase in transmembrane pressure (TMP) and filtration resistance. On a plant-wide level, the integration of an A-stage increased the amount of organic matter (COD) recovered from wastewater in the form of methane gas by about 15% compared to a WWTP configuration with a primary clarifier. Anaerobic digesters are operated at either mesophilic (35°C) or thermophilic (55°C) conditions. In general, it is known that higher amounts of biogas are produced from digesters operated at thermophilic conditions because of higher biochemical reaction rates. However, the specific effect of temperature on AnMBR performance for A-sludge digestion has not yet been assessed. Therefore, the third study evaluates the treatment and filtration performances of lab-scale AnMBR under mesophilic and thermophilic conditions. Higher biogas and VFAs were produced under thermophilic conditions, which were 23% and 47% higher than those under mesophilic one, respectively. Besides, the membrane could be operated at lower TMP under thermophilic conditions. However, taking into account the energy consumption and production, operating the AnMBR under mesophilic conditions would result in a more than three-fold higher net energy production than operating under thermophilic conditions, whereas surplus energy recovery under thermophilic conditions was less than the additional energy consumption. Therefore, despite the advantages of thermophilic conditions, operating AnMBR for sludge digestion under mesophilic conditions has a higher potential to improve the energy balance in the WWTPs. As found during the review (Chapter 2), there is a lack of studies demonstrating the economic benefits of using AnMBRs for sludge treatment in the WWTP. Therefore, the feasibility of the AnMBR for sludge (primary and waste activated sludge) treatment in a conventional WWTP is evaluated in the fourth study, through mathematical modeling and simulation, on unit process and plant-wide levels. The impact of HRT and SRT as control handles on the performance of the AnMBR was assessed. The amount of COD converted into methane could be increased by increasing the SRT or lowering the HRT, the former having a higher positive impact. The nitrogen and phosphorous load in the permeate increased by increasing the SRT or lowering the HRT, while the COD concentration in the permeate was hardly affected. As for the energy balance, increasing the SRT was more efficient than lowering the HRT. Indeed, increasing the SRT caused a significant increase in energy production while lowering the HRT only slightly reduced the energy consumption and did not affect the energy production. On a plant-wide level, the integration of an AnMBR instead of the anaerobic digester decreased the operational costs of the WWTP by 27%, but led to a worse effluent quality. The latter could be remedied by post-treatment of the permeate by struvite recovery and nitrogen removal through partial nitritation/anammox, at the same time further decreasing the operational costs - with 35% compared to a conventional WWTP. Overall, applying AnMBR for sludge treatment combined with post-treatment of the permeate provides effluent quality that meets the EU regulations and implies significant operational cost savings for wastewater treatment. Finally, Chapter 5 summarizes the main findings of the previous chapters and gives perspectives for further research inspired from the thesis.
  • Öge
    Recovery of rare earth elements from waste and wastewater
    (Graduate School, 2021-12-14) Yüksekdağ, Ayşe ; Koyuncu, İsmail ; 501152710 ; Environmental Science Engineering and Management
    REEs is a group of elements comprising Lanthanides, Scandium, and Yttrium. These elements are used in many alloys, permanent magnets, wind turbines, defense industry products, magnetic resonance imaging systems, catalytic converters, mobile phones, computers, and so on. Due to their unique physical and chemical properties, these elements contribute to the development of many technological products due to their efficiency, size reduction, energy reduction, and superior chemical and physical stability. REEs are classified as LREEs (La, Ce, Pr, Nd, Pm, Sm) and HREEs (Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Y) according to their arrangement in the periodic table. Another classification method is based on the criticality of these elements and is as follows: Critical REEs (Nd, Eu, Tb, Dy, Er, Y), uncritical REEs (La, Pr, Sm, Gd), and excess REEs (Ce, Ho, Tm, Yb, Lu). These elements are also called "vitamins of modern industry" due to their unique properties. In the first stage of the thesis, a comprehensive literature review was prepared. Recovery of REEs and scandium from secondary sources under a circular economy framework was reviewed with a holistic approach. Moreover, the latest statistical data and studies have been summarized. 46 million tons of red mud was generated in the first four months of 2021 worldwide. In 2018, 750 million tons of thermal power plant fly ash were released in European Union member countries. Globally, over 53 million of e-waste was generated in 2019. These and many other types of waste need appropriate management, as they are large in quantity. On the other hand, they are valuable secondary resources due to their critical element content. Within the scope of the second chapter of the thesis, a total of 32 different samples containing (1) combustion residues, (2) mine wastes, (3) treatment sludges & sediments, (4) e-waste, and (5) various water, wastewater, and geothermal water were investigated. Then, REEs, scandium, and other critical, precious, and base element potentials were exhibited. According to the results obtained, Ce, La, Nd, and Y elements were found the most in the secondary sources obtained from Turkey, respectively. The highest total REEs concentration was found in thermal power plant fly ash and e-waste mixture. The waste with the highest content of critical rare earth elements was e-waste. For this reason, e-waste was chosen for recovery studies. In the third stage of the thesis, e-waste was crushed, ground, and sieved, respectively, and separated into size fractions. The effects of the particle size of the waste, the type of acid used, and the waste:acid ratio on the leaching of REEs were investigated. It was seen that the highest leaching efficiency was obtained from the smallest grain size. However, it was observed that the leaching efficiency decreased as the amount of e-waste used per unit volume of acid increased. The highest yield was obtained with aqua regia and the lowest waste:acid (5 mg/mL acid) ratio. In the fourth step, which is the last experimental part of the thesis, the separation of rare earth elements by membrane applications from e-waste leachate, prepared with nitric acid, was optimized using response surface methodology. In the first stage, e-waste leachate was pre-treated and concentrated in the nanofiltration process. This stage was optimized as a pretreatment pH of 1.5 and an NF operating pressure of 14.5 bar. In the second stage, the pre-treated leachate was fed directly to the supported liquid membrane process, which is a kind of membrane solvent extraction. Finally, the optimization studies were repeated by feeding the NF concentrated phase to the supported liquid membrane. Optimum operating conditions were found to be the same as for direct membrane solvent extraction (pH: 1.5 and D2EHPA concentration: 15%). An increase in the separation efficiency of HREEs and a decrease in the separation of LREEs were observed in the case of MSX with pre-concentration. In sum, HREEs could be separated with higher purity by applying NF concentration before membrane solvent extraction.