Polluted runoff from densely populated and poorly serviced informal settlements is a growing issue in South Africa that leads to various health risks and environmental degradation. Surface waters affected by informal settlements are known to display high nutrient (NH3, NO2 - , NO3 - and PO4 3- ) concentrations. These nutrient concentrations are highly variable due to the fluctuations in the type and frequency of human activities occurring in the informal settlements. A decentralised, non-invasive and easy to maintain surface water rehabilitation system that is capable of handling variable inlet nutrient concentrations is therefore necessary in these areas. Engineered nature-based solutions such as horizontally orientated subsurface flow biofilters are a potential suitable remediation measure, as they are cost-effective, scalable and easy to maintain. However, the variable nutrient levels in surface waters affected by informal settlements pose a challenge to achieving consistent nutrient reduction in a system. The nutrient degradation potential of a microbially colonised horizontally orientated subsurface flow pilot-scale biofilter (length: 2 m; width: 0.44 m; depth: 0.7 m) that was packed with stones of 8-11 mm in diameter was assessed in this study. The purpose of performing controlled experiments on the pilot-scale biofilter was to enable data collection for the design of optimum full scale biofilters. Pulse tracer studies at varying flow rates (0.5 -3 L/min) determined that the flow behaviour in the pilot-scale biofilter approximated plug flow; with the extent of plug flow behaviour and degree of mixing in the radial direction increasing with a decrease in flow rate Surface runoff from the Stiebeuel River, contaminated by an upstream informal settlement called Langrug, was used as the polluted water source for the pilot-scale biofilter. Six nutrient degradation studies were carried out on the microbially colonised pilot biofilter with each study occurring over a 10-day period (228 hours). Three of the nutrient degradation studies were carried out at a flow rate of 0.5 L/min and three were carried out at a flow rate of 1.5 L/min. Water from the Stiebeuel River (200 L) was circulated through the system during the batch nutrient degradation studies with samples being taken every six hours. The inlet concentration varied in each study with an inlet concentration range of 8.41 - 24.2 mg/L NH3, 1.06 - 2.30 mg/L NO3 - and 1.45 - 6.82 mg/L PO4 3- being observed. An NH3 reduction of up to 91.8%, total nitrogen reduction of up to 82.4% and a PO4 3- reduction of up to 88.3% was observed. The main biological processes occurring within the pilot biofilter were nitrification and denitrification. An extent of nitrification of up to 91.7% and an extent of denitrification of up to 95.6% were observed in the nutrient degradation studies. Ammonia degradation and orthophosphate removal in the system was described using the double first-order in parallel reaction kinetic model which expresses the reaction kinetics as the sum of first two order reactions. The results of the nutrient degradation studies show that the microbial community in the pilot-scale biofilter system is able to metabolise moderate pulses of nutrients when fresh contaminated water is introduced to the system at varying inlet concentrations. The microbial community is able to survive under nutrient limited conditions. These findings indicate the effectiveness of stone biofilters at degrading nutrients in polluted runoff from informal settlements in a controlled batch experiment.

Due to the continuous melting of sea ice and rising sea levels, more studies are conducted on sea ice morphology and factors influencing the growth of ice. Sea ice is an integral part of the global climate system. It plays a vital role in the polar ecosystem, providing a habitat for organisms. Sea ice growth and behaviour has been observed to be largely affected by climate change and global warming. However, the consequences thereof, on sea ice extent and seasonal changes are still being studied. Artificial sea ice experiments have been used as they offer an advantage of control and help isolate variables during sea ice growth. Additionally, in-situ experiments are expensive, and can present logistical difficulty for measuring these variables long term. Factors such as growth dynamics, crystal texture and brine inclusions were investigated by variation of ambient temperature, starting artificial ocean salinity, reactor volume and the presence of microorganism' secretions: extracellular polymeric substances (EPS). Salinities of 10 psu, 20 psu, and 30 psu, were used at the following temperatures: -20°C, -10°C and -5°C. The temperature and salinity data showed that the growth rate of ice, increases with the decreasing ambient temperature, decreasing starting artificial sea ice salinity, decreasing reactor volume, as well as in the presence of microorganisms' secretions. The cross-polarisation results revealed a decreasing percentage of granular texture with increasing starting artificial ocean salinity and increasing ambient temperature. Similarly, the same trend was observed for increasing reactor volume. In the presence of microorganisms, however, a blotchy granular and a disordered columnar texture were observed. An increase in artificial sea ice porosity due to brine inclusions was revealed by the micro-ct scanning data for an increasing starting artificial ocean salinity. Furthermore, overall porosity increased with decreasing ambient temperature and in the presence of microorganism secretion.

Data-driven primary sedimentation (or settling) tank (DDPST) model was recently developed to improve the existing primary sedimentation (or settling) tank (PST) models which are largely total suspended solids (TSS) based. The purpose of the DDPST model is to realistically simulate the full-scale PST (FS-PST) underflow and overflow outputs in terms of biodegradable particulate organics (BPO), unbiodegradable particulate organics (UPO), and inorganic suspended solids (ISS) compositions. This characterization is fundamental to the planning of the downstream resource recovery systems such as anaerobic digestion (AD) and activated sludge (AS) systems through accurate process predictions. The DDPST model was previously subjected to rigorous mass balance verifications and has undergone a general sensitivity analysis (GSA) to identify the most important parameters required to allow the accurate predictions. The settling velocities and settling proportions of the five particle settling velocity groups (SVGs) were identified as significant. These five SVGs are characterized by different proportions of settleable BPO (BPOset), settleable UPO (UPOset) and settleable ISS (ISetS). Due to variability in wastewater (WW) characteristics from plant to plant, the DDPST model requires settleability data that is specific to a plant to make correct predictions. A five-column settleometer (5C-settleometer) has been proposed as a tool that can provide this necessary data. Essentially, the 5C-settleometer is regarded a labscale PST that allows detailed study of the FS-PST critical parameters through segregation of settleable TSS into five different SVGs. Along with the Augment Biomethane Potential (AugBMP) test procedure and parameter estimation tools, the particles from the SVGs can be fractionated into BPOset, UPOset, and ISetS. To this date, however, the accurateness of the 5C-settleometer to provide accurate FS-PST settleability characteristics has not been confirmed. This implies that the 5C-settleometer, as a suggested tool to provide the necessary data, cannot be used with confidence, and so is the DDPST model. The purpose of this study was to evaluate the DDPST model through comprehensive characterization of the primary sewage sludge (PSS). To achieve this, the ability of the 5Csettleometer to accurately characterize the PSS in terms of settling velocities and settling proportions was verified. This was done by collecting the FS-PST influent, underflow, and overflow diurnal data in parallel with the 5C-settleometer test runs at the Bellville Wastewater Treatment Works (WWTWs). Using the FS-PST diurnal data, the related percentage removals for settleable solids (in terms of BPOset, UPOset, and ISetS) were determined. Using the 5Csettleometer characterized PSS outputs, the parameters required to run the DDPST model (i.e., five settling velocity groups and their corresponding BPOset, UPOset, and ISetS settling proportions) were determined to allow the PST underflow and overflow model predictions. Following this, the PST percentage removals (underflow) and overflow characteristics from (i) the DDPST model, and (ii) the FS-PST, were compared to confirm whether the model predictions fully replicate the FS-PST. Important to note is that both the FS-PST and the 5Csettleometer received the same influent characteristics to ensure that the settleometer overflow and underflow are reasonably compared with the FS-PST to check the representativeness. While the 5C-settleometer has proven (i) the ability to segregate the particles into distinguishable particle sizes, and (ii) the ability to somewhat account for the overall removal proportions that are comparable to the FS-PST at a flow rate fluctuating between 0.6 and 0.8 l/min, its relationship with the DDPST model needs to be reassessed. The settleometer upflow velocities appeared to be too high to allow accurate model predictions. Unfortunately, it is impossible to achieve very low velocities to fulfil the DDPST model requirements with the current settleometer design. This shortfall on the model to represent the 5C-settleometer makes it impossible to yield reasonable predictions. This gap requires to be addressed to ensure that the 5C-settleometer, as a lab-scale version of the FS-PST, is correctly translated into the DDPST model, not only in terms of the upflow velocities which govern the particle settling, but also, the accompanying settleometer features which affects the particle or flow movements, i.e., (i) the occurrence of sharp bends or curvatures in a 5C-settleometer, or (ii) the increased probability of inter-particle forces especially when operating the settleometer at low flow rates. While it may be a challenge to model these interfering instances, it is essential that they are accounted for in the model to ensure accurate DDPST model predictions. It is further recommended to explore ways to improve the operation of the current settleometer. For instance, investing in a higher capacity pump and a settleometer flow meter will, with no doubt, add a benefit to the quality of the settleometer output data. In addition, the use of multiple settleometer runs with a combination of high and low flow rates can be explored, to achieve exceptionally representative FS-PST data. In terms of the elemental compositions (EMs), the five SVGs showed a marginally varied BPOset and UPOset compositions. This could be the result of particulate material differences between the SVGs. Nonetheless, the average BPO and UPO compositions recorded in terms of CXHYOZNAPB are C1H5.99O1.13N0.05P0.00 and C1H1.79O0.45N0.22P0.02, respectively. The subscript “Y” (i.e., 5.99) of the BPO composition marginally differs from what has already been reported on literature. This difference could be linked to (i) the discrepancies related to the carbon measurements experimentally (carbon is calculated from biogas measurement and alkalinity), and (ii) the source of Bellville WW, i.e., Bellville WWTWs receives both domestic and industrial WW. Overall, the ISetS (76.7%) and UPOset (78.1%) were found to be removed in greater proportions than BPOset (37.7%) in the FS-PST.

This dissertation discusses how the receiver and the LNA contained within the receiver are the major contributors to the sensitivity. Furthermore, a method for testing and determining the equivalent noise temperature of a cryogenic LNA operating at a physical temperature of 20 K is selected and presented. This method was tested at the Klerefontein support base and the measurements allowed conclusions to be drawn that show that the uncertainty was unacceptable due to a few factors. One of the factors is the thermal gradient across the attenuator. This was investigated via a limited thermal study and a solution was proposed and implemented.

The analysis of a three-stage cascaded thermal energy storage is presented in this dissertation. Cascaded thermal energy storage systems has many advantages over conventional thermal energy storages, majorly it allows for maintaining of a nigh-constant temperature between the HTF and PCM during the charging and discharging cycles leading to improved performance of the system. This dissertation investigates the performance and transient response of a packed bed operating under high-temperature conditions with phase change materials in varying encapsulations (cascaded in a three-stage format) during charging and discharging cycle by employing computational numerical techniques via commercially available ANSYS Fluent software. The analysis was performed for nine different encapsulation geometries with increased surface area and constant volume in comparison to the base geometry (sphere) to determine the effects of each new encapsulation on the performance of the thermal energy storage (TES). The computational model used in the development of this work compares well with the experimental results by Raul [1]. Additionally, the effect of packing scheme/PCM layout is also investigated in this work. Comparative data analysis was performed on the TES with the various PCM encapsulation designs and the standard spherical PCM encapsulation to determine which geometry provides better performance during charging and discharging cycles. The results of this study show that the thermal performance of the cascaded thermal energy storage improves with each new encapsulation as evidenced by the decreases in charging and discharging times in comparison to the base encapsulation. This study also highlights which capsule design is most practical when considering the bed dimension increases/ decreases with in increasing thermal performance. This study's findings can serve as a benchmark for future optimization of cascaded thermal energy storage systems.

Capillary evaporation from nanoporous membranes is defined as an evaporation process where liquid water is drawn passively by capillary force from the membrane inlet to the evaporating meniscus. It has been considered as one of the most effective methods for phase-change heat and mass transfer as both the heat and mass transport resistance are minimized, finding promising applications in electronic cooling, solar-powered desalination, and membrane-based water treatment. This thesis aims to explore novel methods to tune capillary evaporation from nanoporous membranes and new applications that can utilize such effective phase-change heat/mass transfer. First of all, the effect of nanopore surface charge on evaporation area and evaporation flux per pore area is investigated numerically. Our results show that the evaporation flux increases as the nanopore surface charge density increases, being 81.1% higher when the surface charge density reaches -80 mC/m2. Secondly, hybrid nanochannel-nanopore devices with varied hydraulic resistance are fabricated to tune capillary evaporation by changing the meniscus area during evaporation. We find that the mass flux is actually the highest when the meniscus is flat and attribute it to the change of hydrogen bond network due to meniscus extension-induced negative pressure and/or interfacial surface charge density. Next, a parylene C membrane and a laser-reduced graphite oxide membrane are tested for capillary evaporation based surface heating membrane distillation. For the parylene C membrane, a 1D analysis is conducted to model the vapor transport and temperature distribution within the system. The optimized mass flux and HUE is 152.63% and 28% higher than the state-of-the-art device, respectively. On the other hand, the laser-reduced graphite oxide membrane serves as an attempt for large scale manufacturing. Finally, a suspended thermal island design is proposed to address the challenges that the current hybrid nanochannel-nanopore device encountered.

Green hydrogen has gathered increasing interest as a medium in the transition to a carbonneutral economy, with several large, export-focused projects currently under development in Southern Africa. However, the environmental implications of hydrogen production and utilisation are not well understood. To address this challenge, a comprehensive literature review for hydrogen production and utilisation lifecycle assessment studies was conducted, and two prospective comparative lifecycle assessments are presented for green and grey hydrogen production and utilisation in the South African context. The first LCA aims to quantify the environmental impacts of producing green hydrogen, relative to grey hydrogen, and determine the production route with the least environmental impacts. The scenarios investigated for hydrogen production are water electrolysis powered by wind, solar PV or concentrated solar power, steam methane reforming, and water electrolysis powered by a 2040 grid electricity mix. Furthermore, the impacts of three available electrolysis technologies; viz. polymer electrolytic membrane (PEM), alkaline, and solid oxide electrolysis were compared. The second LCA aims to compare two systems of utilisation for the green hydrogen that would be produced in South Africa to determine the option where the highest level of decarbonisation could be achieved. The application considered for the assessment is the fuelling of heavy-duty truck transportation. The systems considered are local utilisation for fuelling heavy-duty trucks and hydrogen exportation to Germany also to fuel heavy-duty trucks. These two systems were expanded to include conventional fuel utilisation, making the functional units of the systems equal and thus the systems comparable. SimaPro was used to conduct the two LCAs, and the ReCiPe 2016 midpoint method was used for the lifecycle impact assessments. Grid-powered water electrolysis is found to have the highest potential impacts across most impact categories, even for the case of the significantly decarbonised 2040 grid mix, with SMR second. Solar PV-powered electrolysis leads to the highest potential human non-carcinogenic toxicity impact caused, by the supply chains of PV panels. Wind-powered water electrolysis is the least impactful option across most categories. However, it has the highest potential human carcinogenic toxicity impact among the renewable production options, though it is less than half compared to the value for non-renewable hydrogen production. This toxicity is caused by the supply chains of wind turbines. Considering optimal electrolyser utilisation, combined wind and solar PV-powered electrolysis is the best option. When comparing the water electrolysis technologies, PEM electrolysis leads to the highest environmental impacts. The energy input for production dominates all the impacts. In terms of utilisation, the environmental impact reductions achievable by the export case outweigh the environmental impact reductions achievable by using the green hydrogen locally, across all impact categories. The highest level of decarbonisation is achieved by replacing the most environmentally harmful fuel; South African coal-based diesel used to fuel heavy-duty trucks. The results of the first LCA confirm that green hydrogen is indeed significantly less environmentally impactful compared to grey hydrogen, but with one hotspot for each of the PV and wind-powered electrolysis, which require attention by project developers. The environmental impacts of all the production scenarios are dominated by the energy required for the production processes. The main finding for the second LCA is that local hydrogen utilisation for heavy-duty truck transportation leads to a larger environmental benefit compared to hydrogen exportation in the case of usage for heavy-duty truck transportation in another country. The highest level of decarbonisation is achieved by displacing South African coal-based diesel first.

Tissue engineering aims to develop viable tissue constructs that mimic native tissues by seeding cells onto a biodegradable scaffold. In this study, it was hypothesized that dynamic fluid flow coupled with FGF-2 treatment would enhance in vitro recellularization of porcine aortic valves. Decellularized aortic valve leaflets were seeded with porcine valvular interstitial cells in a rotating wall bioreactor, a rocker plate and static conditions. To determine the optimal condition for recellularization, the scaffolds were recellularized with and without the addition of FGF-2 (n=3). Follow-up experiments were performed to analyze the molecular mechanisms involved in the FGF-2 activation pathway. The results demonstrated high cell density and high protein levels and gene expression under dynamic conditions especially in the rotating wall bioreactor recellularized scaffolds. In conclusion,the rotating wall bioreactor conditions might have stimulated the interstitial cells to produce more FGF-2 and increase FGFR-2 expression and TGF-Beta/SMAD signaling pathway plays a vital role in this.

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