Effects of Varying Sludge Quality on the Permeability of a Membrane Bioreactor

This master thesis firstly includes a theory part describing, the conventional municipal wastewater treatment plant (WWTP) and especially the conventional activated sludge (CAS) process. As Stockholm municipality want to retrofit the current activated sludge system at Henriksdal into a membrane bioreactor (MBR), an extensive description of the MBR and its advantages and disadvantages are included. Fouling is considered a really important issue for the operation of an MBR since it reduces an MBR’s productivity over time. Therefore, description of the fouling mechanisms and the potential foulants is included as well as a description of the membrane cleaning procedures. Sludge composition is considered a very important parameter which contributes to membrane fouling and thus this master thesis aims to identify the effects of varying sludge quality on the membranes operation. Precipitation chemicals used for phosphorus chemical precipitation and especially ferrous sulphate which is examined in this master thesis are also affecting the sludge quality and the membranes operation. The report includes description of Henriksdal reningsverk and line 1 of the pilot MBR at Hammarby Sjöstadsverk where the experimental work was performed. The following chapter describes the experimental work performed in the laboratory including the determination of total suspended solids (TSS), volatile suspended solids (VSS), sludge volume index (SVI) and sludge’s filterability. The filterability was determined by performing the time to filter (TTF) method and the sludge filtration index (SFI) method. Furthermore, the samples were also examined in the optical microscope to determine their bulkiness and their filaments content. The iron content in the sludge was also measured from Eurofins Environment Testing Sweden AB. In the results section, the different parameters measured are illustrated in charts and they are compared to each other in order to define which factors contribute positively or negatively to the sludge’s filterability and thus affect the sludge quality and the membranes operation. The results indicate that SFI is a more reliable method for measuring filterability compared to TTF. Furthermore, the iron content in the sludge is proportional to the permeability as well as the filaments content observed during microscopy is proportional to the SFI or TTF. Finally, this master thesis includes recommendations for future research which basically include more analyses to identify the sludge biology and more samples taken for longer time periods.

Thermal Conductivity of Hygroscopic Foams Based on Cellulose Nanomaterials

Biobased super-insulating materials could mitigate climate change by minimizing the use of petroleum-based materials, creating artificial carbon sinks and minimizing the energy needed to maintain pleasant interior conditions. Cellulose nanomaterials (CNM) produced from abundantly available cellulose sources constitute versatile, highly anisotropic raw materials with tunable surface chemistry and high strength. This thesis includes the evaluation of the thermal conductivity of isotropic and anisotropic CNM-based foams and aerogels and analysis of the dominant heat transfer mechanisms.  We have developed a customized measurement cell for hygroscopic materials in which the humidity and temperature are carefully controlled while the thermal conductivity is measured. Anisotropic cellulose nanofibrils (CNF) foams with varying diameters showed a super-insulating behavior perpendicular (radial) to the nanofibril direction, that depended non-linearly on the relative humidity (RH) and foam density. Molecular simulations revealed that the very low thermal conductivity is related to phonon scattering due to the increase of the inter-fibrillar gap with increasing RH that resulted in a 6-fold decrease of the thermal boundary conductance. The moisture-induced swelling exceeds the thermal conductivity increase due to water uptake at low and intermediate RH and resulted in a minimum thermal conductivity of 14 mW m-1 K-1 at 35% RH and 295 K for the foams based on the thinnest CNF. The density-dependency of the thermal conductivity of cellulose nanocrystal (CNC) foams with densities of 25 to 129 kg m-3 was investigated and a volume-weighted modelling of the solid and gas thermal conductivity contributions suggested that phonon scattering was essential to explain the low radial thermal conductivity, whereas the replacement of air with water and the Knudsen effect related to the nanoporosity in the foam walls had a small effect. Intermediate-density CNC foams (34 kg m-3) exhibited a radial thermal conductivity of 24 mW m-1 K-1 at 295 K and 20% RH, which is below the value for air. The moisture uptake of foams based on CNMs with different degree of crystallinity and surface modifications decreased significantly with increasing crystallinity and temperature. Molecular simulations showed that the narrow pore size distribution of the amorphous cellulose film, and the relatively low water adsorption in the hydration cell around the oxygen of the carboxyl group play an important role for the moisture uptake of amorphous and crystalline CNM-based materials. Isotropic CNF- and polyoxamer based foams as well as CNF-AL-MIL-53 (an aluminum‑based metal-organic framework) foams were both moderately insulating (>40 mW m-1 K-1) and comparable with commercial expanded polystyrene. The thermal conductivity of CNF and polyoxamer foams displayed a very strong RH dependency that was modelled with a modified Künzel’s model. The presence of hydrophobic AL-MIL-53 decreased the moisture uptake of CNF-AL-MIL-53 aerogels by 42% compared to CNF-polyoxamer foams. Solid and gas conduction are the main heat transfer mechanisms in hygroscopic nanofibrillar foams and aerogels that depend on the interfacial phonon scattering, Knudsen effect and water uptake. It is essential that the thermal conductivity measurements of hygroscopic CNM-based foams and aerogels are determined at controlled RH and that parameters such as the temperature, density, nanoporosity, fibril dimensions and alignment are characterized and controlled for systematic development and upscaling of biobased foams for applications in building insulation and packaging

Effects of Varying Sludge Quality on the Permeability of a Membrane Bioreactor

This master thesis firstly includes a theory part describing, the conventional municipal wastewater treatment plant (WWTP) and especially the conventional activated sludge (CAS) process. As Stockholm municipality want to retrofit the current activated sludge system at Henriksdal into a membrane bioreactor (MBR), an extensive description of the MBR and its advantages and disadvantages are included. Fouling is considered a really important issue for the operation of an MBR since it reduces an MBR’s productivity over time. Therefore, description of the fouling mechanisms and the potential foulants is included as well as a description of the membrane cleaning procedures. Sludge composition is considered a very important parameter which contributes to membrane fouling and thus this master thesis aims to identify the effects of varying sludge quality on the membranes operation. Precipitation chemicals used for phosphorus chemical precipitation and especially ferrous sulphate which is examined in this master thesis are also affecting the sludge quality and the membranes operation. The report includes description of Henriksdal reningsverk and line 1 of the pilot MBR at Hammarby Sjöstadsverk where the experimental work was performed. The following chapter describes the experimental work performed in the laboratory including the determination of total suspended solids (TSS), volatile suspended solids (VSS), sludge volume index (SVI) and sludge’s filterability. The filterability was determined by performing the time to filter (TTF) method and the sludge filtration index (SFI) method. Furthermore, the samples were also examined in the optical microscope to determine their bulkiness and their filaments content. The iron content in the sludge was also measured from Eurofins Environment Testing Sweden AB. In the results section, the different parameters measured are illustrated in charts and they are compared to each other in order to define which factors contribute positively or negatively to the sludge’s filterability and thus affect the sludge quality and the membranes operation. The results indicate that SFI is a more reliable method for measuring filterability compared to TTF. Furthermore, the iron content in the sludge is proportional to the permeability as well as the filaments content observed during microscopy is proportional to the SFI or TTF. Finally, this master thesis includes recommendations for future research which basically include more analyses to identify the sludge biology and more samples taken for longer time periods.

Synthesis of Poly(methyl methacrylate) and Polystyrene with Nanometer-scale Hematite Powder and their Characterization

92 σ.Στην παρούσα διπλωματική εργασία μελετήθηκε η σύνθεση πολυ(μεθακρυλικού μεθυλίου) και πολυστυρενίου με πρόσθετο νανοσκόνη αιματίτη (α – Fe2O3) ακολουθώντας την τεχνική του πολυμερισμού αιωρήματος για δύο ποσοστά ενσωμάτωσης του αιματίτη στη μήτρα. Κατά την τεχνική του πολυμερισμού αιωρήματος (suspension polymerisation) τα απαραίτητα αντιδραστήρια ήταν το μονομερές (μεθακρυλικό μεθύλιο ή στυρένιο), ο αιματίτης, ο σταθεροποιητής (CMC), ο διεγέρτης (BPO), το απιονισμένο νερό και η μεθανόλη. Οι τεχνικές που χρησιμοποιήθηκαν για τον χαρακτηρισμό των καθαρών πολυμερών και των σύνθετων μικροσφαιρών ήταν η ιξωδομετρία Ubbelohde, η ηλεκτρονική μικροσκοπία σάρωσης (SEM), η οπτική μικροσκοπία ανάκλασης, η περίθλαση ακτίνων – Χ (XRD) και η υπέρυθρη φασματοσκοπία μετασχηματισμού Fourier (FTIR). Η ιξωδομετρία Ubbelohde, χρησιμοποιήθηκε για την μέτρηση του μοριακού βάρους των καθαρών πολυμερών. Η χρήση της ηλεκτρονικής μικροσκοπίας σάρωσης και της οπτικής μικροσκοπίας ανάκλασης, πραγματοποιήθηκαν με σκοπό την απόκτηση φωτογραφιών των δειγμάτων για εξέταση της μορφολογίας της επιφάνειας των δειγμάτων καθώς και για την εξαγωγή συμπερασμάτων για τα διαφορετικά ποσοστά ενσωμάτωσης του αιματίτη στην πολυμερική μήτρα. Επιπρόσθετα, η περίθλαση ακτίνων-Χ και η υπέρυθρη φασματοσκοπία μετασχηματισμού Fourier χρησιμοποιήθηκαν για τον χαρακτηρισμό των συνθέτων με σκοπό την επιβεβαίωση των ιδιοτήτων της μήτρας και του προσθέτου στο σύνθετο υλικό. Τέλος, παρουσιάζονται τα γενικά συμπεράσματα της μελέτης καθώς και οι προτάσεις.In this degree project, it was examined the synthesis of poly(methyl methacrylate) and polystyrene with nanometer – scale hematite powder (α – Fe2O3) as additive via suspension polymerization. In suspension polymerization, the essential materials are, the monomer (MMA or Sty), the nanometer – scale hematite powder, the stabilizer (CMC), the stimulator (BPO), deionized water and methanol. These microspheres were prepared for two different contents (wt%) of hematite in the polymer matrix. The techniques, we used, in order to characterize our samples, are the Ubbelohde viscometry, the scanning electron microscopy (SEM), the optical microscopy, the X-ray Diffraction (XRD) and the Fourier transform infrared spectroscopy (FTIR). The Ubbelohde viscometry, was used in order to count the molecular weight of the pure polymers. The scanning electron microscopy and the optical microscopy techniques, were not only used in order to examine the morphology of the sample’s surface, but also in order to realize the differences between the two different contents of hematite in the polymer matrix. Furthermore, the X-ray Diffraction and the Fourier transform infrared spectroscopy were used in order to prove the properties of the polymer matrix and of the hematite powder in the composite material. Finally, we enclose our general conclusions and our suggestions for the future.Βαρβάρα Φ. Αποστολοπούλου-Καλκαβούρ

Strong silica-nanocellulose anisotropic composite foams combine low thermal conductivity and low moisture uptake

We report the fabrication of anisotropic lightweight composite foams based on commercial colloidal silica particles and TEMPO-oxidized cellulose nanofibrils (TOCNF). The unidirectional ice-templating of silica-TOCNF dispersions resulted in anisotropic foams with columnar porous structures in which the inorganic and organic components were homogeneously distributed. The facile addition of silica particles yielded a significant enhancement in mechanical strength, compared to TOCNF-only foams, and a 3.5-fold increase in toughness at a density of 20 kg m−3. The shape of the silica particles had a large effect on the mechanical properties; anisotropic silica particles were found to strengthen the foams more efficiently than spherical particles. The water uptake of the foams and the axial thermal conductivity in humid air were reduced by the addition of silica. The composite foams were super-insulating at dry conditions at room temperature, with a radial thermal conductivity value as low as 24 mW m−1 K−1, and remained lower than 35 mW m−1 K−1 up to 80% relative humidity. The combination of high strength, low thermal conductivity and manageable moisture sensitivity suggests that silica-TOCNF composite foams could be an attractive alternative to the oil-based thermal insulating materials

Analysis of the Porous Architecture and Properties of Anisotropic Nanocellulose Foams: A Novel Approach to Assess the Quality of Cellulose Nanofibrils (CNFs)

Cellulose nanofibrils (CNFs) are a unique nanomaterial because of their abundant, renewable, and biocompatible origin. Compared with synthetic nanoparticles, CNFs are commonly produced from cellulose fibers (e.g., wood pulp) by repetitive high-shear mechanical disintegration. Yet, this process is still highly demanding in energy and costly, slowing down the large-scale production and commercialization of CNFs. Reducing the energy consumption during fibers fibrillation without using any chemical or enzymatic pretreatments while sustaining the CNF quality is challenging. Here, we show that the anisotropic properties of the CNF foams are directly connected to the degree of nanofibrillation of the cellulose fibers. CNFs were produced from wood pulps using a grinder at increasing specific energy consumptions. The anisotropic CNF foams were made by directional ice templating. The porous architecture, the compressive behavior of the foams, and the CNF alignment in the foam cell walls were correlated to the degree of fibrillation. A particular value of specific energy consumption was identified with respect to the highest obtained foam properties and CNF alignment. This value indicated that the optimal degree of fibrillation, and thus CNF quality, was achieved for the studied cellulose pulp. Our approach is a straightforward tool to evaluate the CNF quality and a promising method for the benchmarking of different CNF grades

Moisture uptake in nanocellulose : the effects of relative humidity, temperature and degree of crystallinity

Foams made from cellulose nanomaterials are highly porous and possess excellent mechanical and thermal insulation properties. However, the moisture uptake and hygroscopic properties of these materials need to be better understood for their use in biomedical and bioelectronics applications, in humidity sensing and thermal insulation. In this work, we present a combination of hybrid Grand Canonical Monte Carlo and Molecular Dynamics simulations and experimental measurements to investigate the moisture uptake within nanocellulose foams. To explore the effect of surface modification on moisture uptake we used two types of celluloses, namely TEMPO-oxidized cellulose nanofibrils and carboxymethylated cellulose nanofibrils. We find that the moisture uptake in both the cellulose nanomaterials increases with increasing relative humidity (RH) and decreases with increasing temperature, which is explained using the basic thermodynamic principles. The measured and calculated moisture uptake in amorphous cellulose (for a given RH or temperature) is higher as compared to crystalline cellulose with TEMPO- and CM-modified surfaces. The high water uptake of amorphous cellulose films is related to the formation of water-filled pores with increasing RH. The microscopic insight of water uptake in nanocellulose provided in this study can assist the design and fabrication of high-performance cellulose materials with improved properties for thermal insulation in humid climates or packaging of water sensitive goods.Funding Agencies|Linkoping University</p

Elastic Aerogels of Cellulose Nanofibers@Metal–Organic Frameworks for Thermal Insulation and Fire Retardancy

Metal–organic frameworks (MOFs) with high microporosity and relatively high thermal stability are potential thermal insulation and flame-retardant materials. However, the difficulties in processing and shaping MOFs have largely hampered their applications in these areas. This study outlines the fabrication of hybrid CNF@MOF aerogels by a stepwise assembly approach involving the coating and cross-linking of cellulose nanofibers (CNFs) with continuous nanolayers of MOFs. The cross-linking gives the aerogels high mechanical strength but superelasticity (80% maximum recoverable strain, high specific compression modulus of ~ 200 MPa cm3 g−1, and specific stress of ~ 100 MPa cm3 g−1).The resultant lightweight aerogels have a cellular network structure and hierarchical porosity, which render the aerogels with relatively low thermal conductivity of ~ 40 mW m−1 K−1. The hydrophobic, thermally stable MOF nanolayers wrapped around the CNFs result in good moisture resistance and fire retardancy. This study demonstrates that MOFs can be used as efficient thermal insulation and flame-retardant materials. It presents a pathway for the design of thermally insulating, superelastic fire-retardant nanocomposites based on MOFs and nanocellulose

Humidity-Dependent Thermal Boundary Conductance Controls Heat Transport of Super-Insulating Nanofibrillar Foams

Cellulose nanomaterial (CNM)-based foams and aerogels with thermal conductivities substantially below the value for air attract significant interest as super-insulating materials in energy-efficient green buildings. However, the moisture dependence of the thermal conductivity of hygroscopic CNM-based materials is poorly understood, and the importance of phonon scattering in nanofibrillar foams remains unexplored. Here, we show that the thermal conductivity perpendicular to the aligned nanofibrils in super-insulating icetemplated nanocellulose foams is lower for thinner fibrils and depends strongly on relative humidity (RH), with the lowest thermal conductivity (14 mW m(-1) K-1) attained at 35% RH. Molecular simulations show that the thermal boundary conductance is reduced by the moisture-uptake-controlled increase of the fibril-fibril separation distance and increased by the replacement of air with water in the foam walls. Controlling the heat transport of hygroscopic super-insulating nanofibrillar foams by moisture uptake and release is of potential interest in packaging and building applications.Funding Agencies|Swedish EnergyAgency (Energimyndigheten)Swedish Energy Agency [2019-006749]; FormasSwedish Research Council Formas [2015-2032]; Wallenberg Wood Science Center (WWSC); Swedish Research CouncilSwedish Research Council [201605990]; Swedish e-Research Centre (SeRC); Aforsk</p