Chemical and Biomolecular Engineering - Theses
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ItemNitrogen Removal from Wastewater Treatment Using Filamentous Algae( 2023-09)Nitrogen removal from wastewater using freshwater filamentous algae has advantages over conventional bacterially-dominant systems, especially for reducing greenhouse gas emissions. Further, filamentous algae provide easier harvesting compared to microalgal processes. However, there are large research gaps that must be addressed before this technology can be implemented at large scale. This thesis aims to understand how filamentous algae can be utilised in wastewater treatment for nitrogen removal alongside traditional treatment processes, with key research objectives being to understand the ammonia tolerance and organic carbon uptake of filamentous algae, and physical design parameters and practical considerations needed for implementation in outdoor conditions. Key experimental methods specific to the study of filamentous algae were also developed in the thesis. The ammonia tolerance of four filamentous algae species from the Oedogonium, Tribonema, Spirogyra and Cladophora genera was investigated, by cultivation under different combinations of pH, temperature and ammonia concentrations. At 60 mg-N/L initial TAN, the critical pH range was found to be approximately 8.0–8.6, 7.5–8.3 and 7.5–8.0 for Tribonema, Oedogonium and Spirogyra respectively. The critical threshold calculated based on the initial amount of free NH3 was 1.5–3 mg-N/L for Tribonema and Oedogonium and approximately 1 mg-N/L for Spirogyra. Although Oedogonium cultivated with TAN at pH 7.5 and 15 degree Celsius showed stable growth and capability to utilise TAN under controlled conditions, it was concluded that the use of filamentous algae for downstream wastewater treatment rather than direct TAN removal may be a more practical option. In terms of organic carbon utilisation, the filamentous alga Tribonema was found to have increased productivity and enhanced photosynthesis by direct utilisation of glucose. In contrast, acetate could only be indirectly utilised in the presence of bacteria, whereas ethanol could not be utilised under any conditions. Despite the positive results with respect to glucose utilisation, it was also found that bacteria can easily outcompete Tribonema in terms of organic carbon utilisation, implying that the algae-bacteria interactions require further understanding and optimisation especially for the complex outdoor environments. It was therefore concluded that Tribonema is more suitable for treatment of wastewater with low organic carbon concentrations, such as secondary-treated wastewater effluent. The performance of filamentous algae in real wastewater was also investigated during a series of outdoor trials. The effects of key parameters that require consideration for scale-up were investigated, including aeration, wastewater strength, weather, tank setup and operations, and the filamentous algae’s adaptability to strong wastewater. Overall, Tribonema was found to be able to remove nitrogen from diluted anaerobically treated wastewater at the Western Treatment Plant (Melbourne) under outdoor conditions, with the use of undiluted wastewater also possible following a lengthy adaptation period for the algae. However, the nitrogen recovery rate into the algal biomass was relatively low compared to the overall nitrogen removal rate required. Therefore, it was concluded that applying filamentous algal systems to remove nitrogen from partially treated wastewater containing reduced nitrogen levels is a more practical option, since the operation under low wastewater toxicity improves the robustness of the system without compromising nitrogen recovery and CO2 capture by filamentous algae. Combining the findings from all chapters, it was concluded that filamentous algae can be used for nitrogen recovery and CO2 capture in partially-treated, low-strength wastewater, with Tribonema identified to be the most suitable algal genera among the four isolated candidates. Despite the promising results presented in this thesis, more future studies focusing on the variations and complexity of large industrial scale operations need to be performed before the process can be implemented.
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ItemCompatibility of Plastic Piping with Future Fuels( 2023-10)The future fuels, methanol, ammonia (NH3) and dimethyl ether (DME), have gained significant attention as a substitute for conventional fossil fuels, owing to their high volumetric energy density and the ability to be synthesised from hydrogen. Utilising existing natural gas infrastructure to transport these future fuels would offer notable advantages from both economic and operational standpoints. However, these future fuels are highly condensable, and have strong interactions with HDPE (high-density polyethylene) pipelines and associated elastomers that may lead to high leakage and material failure. Hence, this thesis investigated the compatibility of commercial HDPE piping samples and common elastomers used in natural gas distribution pipelines with methanol, NH3 and DME. Methanol compatibility was investigated for HDPE, as well as poly(styrene-co-butadiene) (SBR) and poly(acrylonitrile-co-butadiene) (NBR) as the base elastomer material, with the inert polytetrafluoroethylene (PTFE) as the comparison gasket material. Commercial elastomers that incorporated additives were also studied to evaluate the interaction and impact of methanol when additives were present. Methanol solubility and diffusion in those polymeric materials, as well as changes to the mechanical properties, were determined through sorption measurements. Methanol exhibited higher solubility and diffusivity in HDPE than methane, thereby raising concerns about potential inventory losses in practice. Only minor changes in mechanical properties were observed upon exposure of HDPE to methanol, indicating that HDPE pipelines can safely transport methanol. In contrast, the two base elastomers -SBR and especially the more polar NBR- showed orders of magnitude higher solubility of methanol than methane, attributed to methanol’s high condensability and its similar polarity with these elastomers. In comparison, the inert gasket material PTFE was unaffected by exposure to methanol. Commercial elastomers demonstrated significant leaching of additives and mass change after methanol exposure. Subsequent mechanical testing revealed that the methanol significantly impacted the performance of the elastomers by reducing yield strain and therefore lowering flexibility, a key characteristic of elastomers. The compatibility of HDPE and associated elastomers -SBR and NBR- were investigated with gas phase NH3 and DME. A constant volume variable pressure (CVVP) method was employed for measuring transport properties. Both future fuel penetrants exhibited much higher solubility in these materials than methane, especially in the elastomers, due to the similar polar nature between these fuels and elastomers. The permeability of NH3 in HDPE was independent of pressure, while DME permeability displayed significant pressure dependence, which was also associated with a notable loss of structural integrity. DME caused swelling within HDPE, leading to a significantly higher permeability than methane. Over time, the strong interactions reduced the permeability to 52% of its initial value through a process known as anti-plasticisation. This outcome revealed that NH3 can be safely transported within HDPE pipes, but DME cannot be safely transported. DME significantly affected the elastomers, with an almost 70% decline in permeability observed for NBR systems, attributed to the combination of densification of the polymer structure and anti-plasticisation by the penetrant fuel. This indicated that elastomers undergo significant morphology change as a result of exposure to DME and therefore have a higher likelihood of failure when exposed to this fuel. Ammonia-resistant elastomers with low permeance already exist but are based on expensive fluorinated polymers, such as PTFE, which have several health and environmental impacts associated with their fabrication. Hence, methodologies to decrease the NH3 permeance in a common and cost-effective elastomer were developed here. Three kinds of additives were incorporated into the elastomer NBR, deploying three different approaches: increasing the basicity of the elastomer environment; chemically reacting with NH3 to limit transport; and incorporating barrier additives to prevent diffusion. Additives utilised included organic molecules, polymers, metal oxide, metal hydrides, metal organic frames and nanocomposites. The mechanical properties were also assessed, as these are fundamental to an elastomer’s role. The creation of a basic environment through amines, especially putrescine, resulted in NH3 permeability losses of 50%. Chemical additives lowered the permeability from 10% to 20% with limited impact on the tensile properties. The most significant decrease was observed for the addition of 3% graphene oxide to NBR, with NH3 permeability decreasing by 80%, but a negative consequence was the production of a more rigid material. As a result of this investigation, NH3 permeability can be significantly reduced in inexpensive NBR elastomers through tailored additives. This represents a relatively straightforward approach to future-proof natural gas infrastructure for NH3 transportation. This thesis has demonstrated the compatibility of transporting the future fuels methanol and NH3 through pipeline material HDPE, as well as the lack of compatibility for DME transportation. Importantly, the polar nature between elastomers and future fuels results in strong interactions and high sorption, leading to higher permeability than observed for methane, which places a greater safety risk on using these materials with these future fuels.
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ItemSynthetic peptides and polymers for self assembly and the control of surface forces(University of Melbourne, 2009)
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ItemLiving and conventional polymerizations for the development of precision polymers and functional materials(University of Melbourne, 2009)
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ItemNanoengineered capsules for the delivery of nucleic acids(University of Melbourne, 2009)
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ItemCore cross-linked star polymers and their multistar analogues : advancements in their versatility and commercial viability(University of Melbourne, 2009)
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ItemNo Preview AvailableFluorescence investigation of polymer physics and light emitting polymers(University of Melbourne, 2009)
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ItemDairy sludge dewatering(University of Melbourne, 2008)
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ItemNo Preview AvailableSimulating agglomeration in the flash smelting reaction shaft to reduce dust production(University of Melbourne, 2008)
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ItemCo2 separation using a modified polypropylene gas absorption membrane(University of Melbourne, 2007)