http://bura.brunel.ac.uk/handle/2438/25431 2026-04-07T12:11:26Z 2026-04-07T12:11:26Z Yousef, Wasef http://bura.brunel.ac.uk/handle/2438/32411 2025-12-13T16:28:40Z 2020-01-01T00:00:00Z

Title: The self-healing mechanisms of bacterial cementitious materials via novel isolated ureolytic bacterium species Authors: Yousef, Wasef Abstract: The self-healing approach used in this study is based on the urease hydrolysing bacterium, namely, Bacillus Sphaericus. The scope of the work is diverse as it combines and brings together both aspects of the bioengineering and civil engineering in order to provide better understanding of the self-healing mechanisms that lie behind the yielding of the calcium carbonate precipitation. The initial stage of this study, comprised of collecting different soil samples from different alkaline sources to extract and isolate urease bacterium species. In addition, a collection of more than 100 different bacterial strains belong to bacillus Sphaericus were screened for the presence of urease enzyme and ability to produce copious amount of calcium carbonate under extreme alkaline conditions. In-vitro calcium carbonate precipitation experiments were performed to stress the selected bacterial strains prior to the application for the self-healing mortar. Parameters such as temperature, pH, shaking conditions, ability to form endospores and the production of copious amount of calcium carbonate were placed under scrutiny. The biochemical properties of the selected bacterial strain were studied and investigated further by monitoring the evolution in pH, the production of ammonium, insoluble and soluble calcium and the colony forming unit. Following the characterisation, three strains were promoted forward for the use of self-healing mortar. In-vitro calcium carbonate perception in broth state showed that the yielding of CaCO3 was maximum in the case of strain 89 and strain 67 at 0.5932g/100ml and 0.8398 g/100ml, respectively. The need for an encapsulating material that provides suitable environment for the bacteria to endure the mechanical and physical forces in addition to the high alkaline environment of the cement matrix, is indeed a key component towards the self-healing applications. As a result, the autoclaved aerated recycled concrete (AAC) aggregates were selected for this study, due to the high porous structure which implies high absorption properties. Three healing systems were proposed for the application of the self-healing mortar. The first approach comprises of bacterial spores impregnated under vacuum into the AARC aggregates along with a suitable nutrient designed specifically for maximum yielding of calcium carbonate precipitation. The second approach comprised of a three-component healing system with the introduction of a mixed culture to enhance the healing capacity in addition to providing reinforcement for the cement matrix. The third approach comprised of direct incorporation of different bacterial cells into cement mortar to test for the capacity of the strain to heal cracks under high alkaline environment. Mortar specimens were cracked at 28 days of curing, ranging from 0.127 to 0.875mm, the introduction of the three-healing system provided promising results in regard to healing cracks of 0.875mm over the period of 289 days of curing. Direct incorporation of bacterial strains at different concentrations 107cells/ml and 108cells/ml showed the tendency to heal cracks of 0.127 and 0.253mm, respectively. Furthermore, direct incorporation of bacterial cells into the cement matrix, supported the analysis that urea hydrolysing bacteria is indeed an enzymatic activity. Two key enzymes were defined and strongly linked to the calcium carbonate precipitation process that is the urease enzyme and the carbonic anhydrase enzyme, where the latter is a zinc enzyme that catalyses the conversion of calcium dioxide into carbonate acid and ultimately promotes further insoluble calcium carbonate precipitation. The introduction of a three-component healing system showed enhanced healing capacity, Direct Incorporation of 107cells/ml with 30% impregnated aggregates showed the capacity to partially heal cracks of 0.791mm by 28.3% over 14 days and 100% over 28 days healing period. Increasing the number of cells showed expected higher healing efficiency, specimens in set 22.1B were able to completely seal cracks of 0.875mm by 99.085 % over the period of 28 days. Description: This thesis was submitted for the award of Doctor of Philosophy and was awarded by Brunel University London

2020-01-01T00:00:00Z Petrovic, Ben A. http://bura.brunel.ac.uk/handle/2438/32339 2025-11-13T03:00:25Z 2024-01-01T00:00:00Z

Title: Engineering biomass combustion fly-ash derived zeolites for post-combustion CO₂ capture Authors: Petrovic, Ben A. Abstract: Mitigation of CO₂ emissions through the use of carbon removal technologies is widely recognised as a pivotal tool on the path to net-zero GHG emissions. Beyond these targets, net-negative emissions will be essential to stabilise global temperatures. Technologies such as bioenergy with carbon capture and storage, considered a net-negative emission technology is therefore poised for a significant share in the power generation mix. However, this is associated with the production of a significant quantity of waste ash residues such as fly ash. Valorisation of this waste stream provides an opportunity to simultaneously mitigate the requirement for waste disposal (i.e. landfilling) and provide a pathway to value-added products, zeolites. In this thesis, industrially produced biomass combustion fly ashes have been comprehensively characterised and subsequently investigated for their potential as zeolite precursors. Suitable design of experiment techniques have been employed to systematically assess the influence of various factors on the alkaline fusion assisted hydrothermal synthesis to maximise the CO₂ equilibrium adsorption capacity. The bulk biomass combustion fly ash has been shown to present a CO₂ adsorption capacity of over 1.8 mmol·g⁻¹ at 50 °C and 1 bar, with a stable capacity of 87% of that after 40 cycles. This adsorbent was then produced at a larger scale to facilitate breakthrough performance assessments in a fixed-bed temperature swing adsorption system designed and built during this research. The process was optimised via Taguchi design of experiment to reveal the influential factors on the bed utilisation efficiency. The results indicate a usable bed capacity of approximately 0.6 mmol·g⁻¹ corresponding to a bed utilisation efficiency of 62% under the optimal factor and level configuration. These findings underscore the feasibility of industrial biomass combustion fly ashes as feedstocks in the preparation of zeolitic adsorbents/catalyst for post-combustion CO₂ capture. Description: This thesis was submitted for the award of Doctor of Philosophy and was awarded by Brunel University London

2024-01-01T00:00:00Z Smith, Martyn http://bura.brunel.ac.uk/handle/2438/31895 2025-09-03T14:55:19Z 2025-01-01T00:00:00Z

Title: Improving resilience in chemical plant under cyberattack by adversarial reinforcement learning Authors: Smith, Martyn Abstract: With chemical plant contributing $5.4 trillion to the global economy annually, frequently representing a Major Accident Hazard, and their control systems having an average age of 20 years, the prospect of a cyberattack resulting in full or partial breach by threat actors is of great concern to owners, customers and wider stakeholders (the latter frequently including anyone downwind). A great deal of frameworks to deal with this threat exist, including multiple uses of Machine Learning (ML). However, these only go as far as the detection of cyberattacks, leaving a research gap in automated responses or the use of ML agents to both generate novel threat vectors and respond to them. In this thesis, we cover some historical attacks and incidents involving chemical plant and their impacts, and what existing Laws and frameworks already cover how plant safety and cybersecurity should be considered. We then investigate the use of adversarial Reinforcement Learning (RL) for both generating and identifying threat vectors, then detecting and responding to intrusions of chemical plant. To address this gap, we have developed a customised version of the Tennessee Eastman process as example, suitable for use with existing interfaces for training RL agents. We then trialled this with a benchmark suite of test scenarios using different agents, one defending the plant (“Blue Team”) and one attacking the plant (“Red Team”), mimicking a common operational cybersecurity challenge. These agents were implemented with Deep Q learning and Deep Deterministic Policy Gradient algorithms dependent on the scenario, in order to model different Blue Team and Red Team capabilities, with Deep Deterministic Policy Gradient agents having Continuous manipulation of plant variables available. We additionally implemented a variant where the Blue Team was assisted with a digital twin in order to make enhanced predictions of future plant state, and scenarios which varied the Red Team’s goals, with the default being plant shutdown. The Blue Team learnt passive policies during periods of normal plant operation, so that it would not disrupt the plant. The Red Team was primarily effective at achieving its aims, most commonly producing a plant shutdown in slightly under three minutes by inducing an oscillation in reactor pressure, usually by manipulating both setpoints and sensor readings. Deep Q learning variants of the Red Team could also disrupt the plant, sometimes in as little as 25 seconds. This behaviour was, however, independent of the Red Team’s goals. When combined, the Red Team consistently performed well, with the Blue Team only occasionally extending plant uptime. The testbed developed is extensible for further testing against future Blue Team or Red Team agent implementations, however it is likely to require additional theoretical verification in order to be employed on plant. Observed behaviour such as the reactor pressure oscillation observed could be seen as Indicator of Compromise, as could a divergence between the Digtal Twin and physical plant before failure observed in the digital twin assisted version - these indicators would prove of immense value to Security Operations Centre operatives looking to safeguard a real plant. Description: This thesis was submitted for the award of Doctor of Philosophy and was awarded by Brunel University London

2025-01-01T00:00:00Z Taylor, Jessica H. http://bura.brunel.ac.uk/handle/2438/31493 2025-06-25T02:00:34Z 2024-01-01T00:00:00Z

Title: Synthesis and application of recycled carbon fibre-based adsorbents for the removal of antibiotics from freshwater aquaculture environments Authors: Taylor, Jessica H. Abstract: The growing environmental impact of end-of-life carbon fibre composites and the rising use of antibiotics in aquaculture present two critical sustainability challenges. Carbon fibre reinforced polymers, widely used in aerospace and automotive industries, generate significant waste. While aquaculture is a major source of pharmaceutical pollution. Antibiotics such as ciprofloxacin and oxytetracycline are commonly used in fish farming and have been linked to the emergence of antimicrobial resistance in aquatic environments. This research aimed to develop high-performance, sustainable carbon-based adsorbents using recycled carbon fibres recovered from Carbon fibre reinforced polymer waste, and to optimise their use for the removal of ciprofloxacin and oxytetracycline from water. A systematic approach was applied to optimise each stage of the adsorbent development process including chemical activation, surface modification, adsorption, and regeneration. Design of Experiments techniques were used to identify optimum process parameters. Initial testing with sodium hydroxide-activated recycled carbon fibres yielded low adsorption capacities (16.84 mg/g for methylene blue), indicating incomplete activation. Process optimisation employing potassium hydroxide significantly improved adsorbent performance. The optimum conditions were identified as an activation temperature of 670 °C, impregnation ratio of 1:10 (CF:KOH) and hold time of 0.5 h, achieving methylene blue adsorption capacities above 450 mg/g and yields exceeding 70%. Surface-modified samples utilising 10 M nitirc acid, 16 h contact time at 28 °C, resulted in increased acidity and mesoporosity. However, it was found that additional modification was not essential to maintain high antibiotic removal. Optimised adsorption conditions were identified to be an adsorbent dose of 0.8 g/L, pH of 2 and initial concentration of 2 mg/L, which resulted in removal efficiencies above 95% for both CIP and OTC. Regeneration studies using 0.1 M potassium hydroxide demonstrated strong reusability, with regeneration efficiencies remaining above 75% over seven cycles. The results confirm that recycled carbon fibre-derived adsorbents are effective, reusable, and environmentally sustainable materials for removing antibiotic contaminants from aquaculture wastewater. Description: This thesis was submitted for the award of Doctor of Philosophy and was awarded by Brunel University London

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