Hidden in plain sight – using a scoping review to reveal the neglected sachet economy crisis

Single-portion, multilayer sachets are a popular packaging format for food, home and self-care products in low-income countries. Sachet waste is non-recyclable, and visibly litters land, freshwater and ocean environments, particularly in South East Asian countries described as having a ‘sachet economy’. As annual global sachet sales exceed one trillion units, we ask whether low levels of research on sachets and the sachet economy could contribute to misinformation about environmental and socioeconomic damage and a lack of policy action to reduce sachet use. Based on the PRISMA-ScR method, our scoping review included novel comparative analyses of multiple exclusion screenings and development of a waste hierarchy for literature analysis to reveal how information available to stakeholders changes as criteria are tightened. We found little empirical research, with knowledge gaps often addressed by institutions and NGOs, particularly regarding alternatives to the sachet economy at the top of the waste hierarchy. Policymakers and consumers in the Philippines and Indonesia were the most common target audience and geographical context. A high proportion of grey literature and inconsistent terminology may introduce the potential for bias and reduced impact. Our research highlights the urgency of further research into social and environmental impacts of the sachet lifecycle and alternatives such as refill. As sachet use rises and spreads globally, we assert that without robust research and practical guidance for decision makers, environmental and socioeconomic consequences of sachet use will continue to grow in South East Asia and spread quickly to other low-income economies, hidden in plain sight.The Lead Author is in the Water-WISER (Waste Infrastructure and Services Engineered for Resilience) Centre for Doctoral Training funded by UKRI through the Engineering and Physical Sciences Research Council. Grant number EP/S022066/1.Cleaner and Responsible Consumptio

Sources, characterisation and exposure risk of airborne microplastic emissions from municipal solid waste dumping site in Nigeria

Walton, Christopher - Associate SupervisorAirborne microplastics (AMPs) represent an emerging environmental and public health challenge, with their sources, transport mechanisms, and impacts still poorly understood, particularly in developing regions with inadequate waste management systems. This research addresses three key gaps: the need for cost-effective and efficient AMP sampling tools, the AMP flux estimations under different environmental conditions, and the modelling of AMP dispersion to understand their transport and potential exposure risks downwind. This research tackles these challenges by developing a low-cost sampler for AMP collection. The low-cost sampler was validated against the commercial sampler (SKC Deployable Sampler equipped with a Total Suspended Particulate (TSP) head), with a focus on fibres, fragments, and films across diverse environmental conditions. The emission of AMPs was quantified using a modified Fick’s law, which incorporates sitespecific parameters such as wind speed, temperature, and particle properties. Seasonal variation in AMP emissions was analysed by collecting and processing 226 environmental samples (42 soil and 184 air) from the municipal solid waste disposal site and its environment during dry and wet seasons. Dispersion modelling was conducted using SCREEN3 to simulate the downwind transport of AMPs. A low-cost sampler (LCS) was developed and evaluated against a commercial sampler, demonstrating a strong correlation (ρ = 0.976) and high accuracy (94.12%) compared to a reference sampler. The LCS effectively captured seasonal variations in AMP abundance. Polymer analysis identified five predominant polymers, with nylon (fibres), PVC (fragments), and PE (films) accounting for the majority of microplastics. The cost analysis revealed that the LCS offers 61% savings over second-hand and 98% over new commercial samplers, making it a reliable and affordable tool for AMP research in resource-limited settings. The airborne microplastics measured on-site reveal seasonal variations in concentrations. Notably, the dry season reveals higher concentrations (mean: 14.37 ± 3.87 MP/m³) comparable to the wet season (mean: 11.31 ± 3.00 MP/m³). Upwind concentrations were considerably lower, averaging 4.25 ± 1.17 MP/m³ during the dry season and 2.75 ± 1.43 MP/m³ during the wet season, reflecting contributions from distant fibre-rich sources, likely indoor emissions. On-site, films exhibited the lowest emissions but retained moderate mobility during the wet season. Fibres showed the highest diffusion coefficients, indicating potential for long-range transport. Fragments were the most abundant microplastic type (55% dry, 53% wet), with high emission factors (188 µg/day dry, 170 µg/day wet). Rising velocities were higher during the dry season due to favourable wind conditions, with values of 0.1056 m/s for nylon fibres, 0.0835 m/s for PVC fragments, and 0.0742 m/s for PE films. The rising velocities and flux measurements highlighted the influence of soil porosity and wind speed on resuspension and transport of microplastics. The SCREEN3 dispersion model reveals distinct seasonal variations in the transport of AMP from MSW sites. Peak AMP concentrations occurred at 100–107 m downwind, with wet season levels (fibres: 2.28 × 10⁻² μg/m³, fragments: 6.81 × 10⁻² μg/m³, films: 2.41 × 10⁻³ μg/m³) exceeding dry season concentrations by 2.1–2.2 times. Fragments posed the highest health risks (Level III), particularly during short-term exposures, while fibres and films showed lower risks. SCREEN3 agreed well with ground measurements (R2 = 0.98 to 0.96) and identified key drivers such as stability classes and precipitation, affirming its utility for AMP transport modelling and risk assessment. This study highlights the significant environmental and health implications of airborne microplastic (AMP) emissions from municipal solid waste (MSW) sites. Fragments pose the greatest risks, particularly during the wet season. The development of a lowcost sampler and advanced dispersion modelling provides essential tools for AMP monitoring. To mitigate AMP impacts, improved waste management practices, such as minimising open burning, are necessary. Integrating AMP data into air quality monitoring frameworks and prioritising seasonal mitigation measures are also recommended. Future studies should investigate long-range transport mechanisms, refine emission factor models, and chronic exposure risks to develop comprehensive strategies for mitigating AMP impacts globally.PhD in Energy and Powe

Ammonia partitioning and recovery from industrial wastewater - exploring precipitation, stripping, and sorption technologies

Jefferson, Bruce - Associate SupervisorCircular economy in wastewater management is increasingly applied, with ammonia recovery playing a critical role. Established ammonia partitioning technologies, being precipitation, typically as struvite, stripping and scrubbing, and sorption, have been predominantly applied to manure, anaerobic digestate, urine and municipal wastewater. Industrial effluents also hold potential for ammonia recovery and have been increasingly targeted by research. These effluents comprise a wide category of wastewaters with diverse physicochemical characteristics, generated by different sectors, including food/drink processing, mining, agro-industrial processes, manufacturing, metallurgy, etc. Some of these effluents contain high ammonia loads alongside significant concentrations of ions, metals, and recalcitrant organic compounds, contributing to complex chemical compositions that can pose challenges for conventional recovery technologies. Despite the increasing focus on industrial wastewaters, there remains limited understanding of how to effectively select and operate recovery technologies, based on the effluent composition and desired recovery outcomes. This research aimed to advance the understanding of how several physicochemical factors impact the mechanisms enabling ammonia partitioning into gas, liquid and solid phases, in order to establish optimum transfer pathways. The key knowledge gaps addressed in this research were i) determination of main criteria for ammonia recovery technology selection for a range of industrial wastewaters, ii) understanding the feasibility and recovery performance of struvite precipitation and ammonia stripping at demonstration scale from distillery wastewater, iii) understanding and quantifying the impact of transition metals and acidic organic compounds on ammonia stripping, iv) assessment and comparison of ammonia separation performance via ion and ligand exchange media and influence of operation parameters (e.g. pH, buffer capacity, metal load, N concentration). The findings are utilised to generate an informed decision process for technology/strategy selection and the operational requirements and potential challenges posed by selected factors, with relevance for industry stakeholders, technology providers, and consultants. A specific focus was placed on distillery wastewater as a case study, a sector concerned with ammonia management and potentially suitable for recovery, particularly in Scotland. A review of the literature found that struvite precipitation is the most widely implemented method with industrial effluents, yet stripping and sorption processes may be preferred for their ability to deliver versatile, ammonia-rich solutions. The identified technology-selection criteria included the feed concentration of ammonia and competing cations, and the struvite formation potential. Based on the practical recommendations developed in this study, an ammonia recovery strategy for distillery wastewater was established, integrating anaerobic digestion with chemical precipitation and ammonia stripping coupled with scrubbing. The performance of this treatment train had never been tested before for filtered digestate of distillery effluent, addressing a key gap in understanding for full scale applications. Demonstration scale trials allowed to understand how the expected performance translated with real digested distillery wastewater and to validate its feasibility. The results demonstrated its technical viability, achieving 76% N removal and 80% P removal, while generating high- quality struvite and ammonia sulphate solution. Moreover, the findings highlighted the critical impact of pH and addressed operational challenges, improving readiness for full-scale application. Beyond distillery effluents, this thesis examined broader challenges in industrial wastewaters treatment, addressing gaps identified in the literature review, relevant for a range of industrial wastewaters, including from metallurgy and agro/food processing. Specifically, the impacts of species found in some of these effluents, such as transition metals (as Ni, Cu, Zn) and organic, acidic compounds (as humic acids), on the stripping process were investigated. Results showed that elevated levels of such species can reduce ammonia availability for stripping, via complex formation and electrostatic interactions. This highlighted the need for mitigation strategies to maintain stripping efficiency with these streams. Additionally, the metal-ammonia bond potential was further explored to assess ligand exchange (LEX) sorption mechanism as alternative to ion exchange (IEX), a mechanism often limited by high concentrations of ammonia and competing cations. Although various media have been tested in literature, comparative studies on their performance under different conditions are lacking, along with insights on how factors such as pH, transition metal and cations load can impact their mechanisms and effectiveness. In this study, two zinc-hybridised sorption media were tested and benchmarked against IEX media, in synthetic and real wastewaters (distillery, municipal). The results showed effective removal, although limited by self-inhibiting pH changes, with a zinc-hybridised media matching or exceeding IEX resin’s performance only when pH 9-10 was maintained (75 meq N/g). pH, buffer capacity and Zn/Na loads were demonstrated to be critical factors to enable or limit IEX and LEX mechanisms. The findings established operational requirements for hybridized sorption media and provided research directions for further improvement. Overall, this work advanced knowledge on the impact of key species on ammonia recovery technologies, with implications for industrial effluents treatment in general and distillery wastewater management in particular. The findings contributed to developing recommendations for selection and operation of ammonia partitioning strategies, optimizing metal-hybridized sorption media, and improving process feasibility for full-scale implementationPhD in Wate

Developing the through-transmission technique in pulsed thermography for material characterisation

Zhao, Yifan - Associate SupervisorPulsed Thermography (PT) is a reliable, non-contact, and non-intrusive non- destructive testing (NDT) technique for assessing the structural health of materials. Based on the relative positioning of the thermal excitation source and the infrared radiometer, measurements can be conducted in either reflection or transmission mode. While reflection mode is widely adopted due to its single- sided accessibility, transmission mode offers superior lateral resolution but remains limited in use due to the lack of reliable depth quantification methods. In the context of thermal diffusivity evaluation, the transmission mode has demonstrated greater reliability; however, the existing literature lacks a deterministic approach to systematically assess this in laboratory settings. This research investigates the current state-of-the-art in through-transmission thermography and identifies key knowledge gaps. A transparent and repeatable methodology is developed to evaluate thermal diffusivity using both finite element models (FEM) and controlled laboratory experiments. The FEM is also used to assess the temporal behaviour of a sample containing subsurface defects, and a physical sample is fabricated to validate the simulation results. A novel method for defect depth quantification is then proposed by establishing a relationship with the Fourier number. This approach demonstrated a 63% improvement in depth estimation accuracy (from a 29.3% measurement error to 10.75%) compared to the Log Second Derivative (LSD) method derived from thermographic signal reconstruction (TSR) in the simulation environment across all defect sizes and depths. Additionally, the technique shows potential for estimating impact damage in carbon fibre-reinforced polymer (CFRP) samples subjected to varying impact energy levels. By addressing the challenges of thermal property measurement and depth quantification within the transmission mode, this thesis provides a foundation for improved material characterisation and supports renewed research interest in through-transmission pulsed thermography.PhD in Manufacturin

Investigation of procurement risk management strategies in the post-contract award phase

Yates, Nicky - Associate SupervisorThis research empirically investigated how procurement risk management (PRM) strategies are used to manage risks in the post-contract award phase. Through three sequential papers, this study adopted multiple methods to gain insights into the procurement risks, risk management strategies, and risk management tools and techniques used in the post-contract award phase in manufacturing sector. Paper 1 is a literature review of the risk management strategies used in the three procurement phases: pre-contract, selection and contracting, and post-contract award. The author conducted an SLR of 100 peer-reviewed articles published between 2000 and 2025. The key findings of this study are twofold. First, it synthesized four main themes: procurement risks, procurement risk management tools and techniques, procurement risk mitigation strategies, and factors that influence the selection of risk mitigation strategies across the three procurement phases. Second, the findings highlighted that procurement risk management tools and techniques in the post-contract award phase have been neglected in the literature compared to the pre-contract, and selection and contracting phases. Paper 2, an empirical study, adopted a qualitative approach to gain insights into procurement risk management in the post-contract award phase. The author interviewed Procurement professionals (23) from 7 manufacturing industries in the United Kingdom (UK) and highlighted three key findings based on the interview insights. First, the results identified five risk categories: supplier performance, contract design, supplier relationship, ethical, and disruption risks. Second, procurement professionals combined technological tools, such as data analytics and machine learning, with human engagement techniques, including site visits and review meetings, to identify and assess risks and plan mitigation strategies. Third, a combination of preventive and reactive PRM strategies were implemented in the post-contract award phase. Paper 3, an empirical study, examined how sociological mechanisms affect procurement risks and procurement risk management performance during the post-contract award phase. A quantitative survey was conducted among 313 procurement professionals from the US automotive manufacturing industry. This study has four key findings. First, combining trust with information sharing, commitment, and flexibility mitigates the negative effects of switching costs on procurement risk management performance than using trust alone. Second, combining trust with information sharing, commitment, and flexibility mitigates the negative effects of switching costs and negotiation costs on procurement risk management performance than using trust alone. Third, sociological constructs are insufficient as PRM mechanisms to mitigate the negative impact of environmental uncertainties on procurement risk management performance. Fourth, sociological constructs are insufficient as PRM mechanisms to mitigate the negative influence of supplier opportunistic behaviours on procurement risk management performance. Overall, this thesis makes several key contributions and extends the literature in the following ways. This SLR study contributes to the existing literature by aligning the fragmented strands of risk management literature and systematically synthesizing the procurement risks, the tools and techniques for identifying, assessing, and mitigating risks, and the risk mitigation strategies in each procurement phase. Second, it provides a new, empirically based procurement risk management model that integrates procurement risk identification, assessment, and mitigation strategies into the post-contract award phase. Third, it provides new empirical evidence that combining trust with information sharing, commitment, and flexibility mitigates the negative effects of switching costs and negotiation costs on procurement risk management performance more effectively than using trust alone. Fourth, it provides new empirical evidence that combining trust with information sharing, commitment, and flexibility mitigates the negative effects of switching costs and negotiation costs on procurement risk management performance than using trust alone.PhD in Leadership and Managemen

Analysis of active aerodynamics for high-performance vehicles

The pursuit of greater efficiency and performance drives advancements in the automotive and motorsport industries, with active aerodynamics emerging as a promising approach due to their ability to dynamically adapt aerodynamic characteristics to specific operating conditions. However, their development presents challenges, including the need for practical yet accurate simulation methodologies, a deeper understanding of vehicle aerodynamics in dynamic conditions, and a comprehensive assessment of their performance potential. This research addresses these challenges through interdependent studies. A cost-effective Computational Fluid Dynamics (CFD) workflow is developed and validated against experimental and high-fidelity simulation data, complemented by a structured wind tunnel correlation process to ensure reliable aerodynamic predictions. Yaw and cornering effects on flow field characteristics and aerodynamic performance are analysed using wind tunnel experiments and CFD simulations. Finally, active aerodynamic configurations, including 2D systems capable of modulating aerodynamic balance longitudinally and laterally, are designed and examined using minimum lap time simulations to assess performance gains, optimal control strategies, and dependencies on vehicle setup. The CFD workflow demonstrates high predictive accuracy across various aerodynamic conditions, with the structured correlation process improving experimental data interpretation and validation. However, conditions critically dominated by highly unsteady flow phenomena require higher-fidelity simulations. Yaw and cornering conditions induce significant flow field alterations, including underbody interference, enhanced upper surface flow acceleration, and asymmetric wake structures, leading to substantial downforce and drag penalties. Active aerodynamic systems provide significant performance benefits across diverse scenarios, with 2D systems consistently outperforming conventional designs by prioritising aerodynamic loads on underloaded tyres to improve total grip. Overall, this research advances numerical methodologies, deepens understanding of vehicle aerodynamics in dynamic conditions, and demonstrates the performance potential of various active aerodynamic designs. The work establishes a foundation for optimising vehicle performance with active aerodynamic systems, supporting future research and industry innovations in automotive and high-performance vehicle engineering.PhD in Transport System

The evolution of fixed wing aircraft handling qualities during the first fifty years

Alam, Mushfiqul - Associate SupervisorThe study investigates the evolution of the handling qualities of British aircraft between 1910 and 1950. In this era, before the implementation of rigorous airworthiness requirements, many aircraft were deficient in some form or another by modern standards. Such deficiencies may not be anticipated or understood by today’s pilots who wish to fly old aircraft and this can result in mishandling, loss of control and ultimately accidents. This study uses a combination of quantitative analysis and qualitative judgements from historical sources to investigate vintage aircraft flying qualities. It includes analysis which makes a novel contribution to this area of aeronautics. Contemporaneous pilot accounts reveal that the understanding of the ‘mechanics of flight’ was generally poor. Legacy flight instructor handbooks show that early flying ‘folklore’ tends to outlive its usefulness and also reveal deficiencies in stability and control in the contemporary training aircraft. An analysis was conducted using a group of 41 aircraft, which formed a representative example of British aircraft of the era. The longitudinal, directional and lateral, stability and control parameters were estimated using generic equations and known aircraft geometry. Today’s certification specifications are used as a benchmark against which the vintage aircraft1 in this study are assessed for non-compliances. This analysis shows an inverse near-linear relationship between the year of design of an aircraft and the number of deficiencies it exhibits. Other factors that can affect handling qualities including the cockpit interface, and the aircraft environment are discussed. An analysis of these factors is made to highlight the higher risk areas when flying the vintage aircraft of the era. 1 In this thesis the expression ‘vintage aircraft’ refers to aircraft which were originally designed during the period 1900-1950. The findings are used to develop guidance for a modern pilot2 , planning to fly a strange vintage aircraft for the first time. 2 For the purposes of this study a ‘modern pilot’ is one who has been trained using aircraft certificated to modern certification standards or their military equivalent.MSc by Research in Aerospac

Development of a novel and effective postharvest decision support system (DSS) for stored cereals to minimise mould spoilage and mycotoxins in food

Cereal grains are widely consumed for their nutritional value as food and feed, and are essential in the food supply chain. However, changing climatic conditions have made these crops increasingly susceptible to fungal attacks, elevating the risk of contamination by mycotoxins—often referred to as "invisible mould poison." This can threaten grain safety and quality, posing health risks to humans and animals, and contributing to food insecurity and economic instability. This thesis examines the effects of different abiotic factors (water activity- aw and temperature) on the ratios of regulated and conjugated mycotoxin concentrations in naturally contaminated and irradiated wheat grains inoculated with Fusarium graminearum. Contaminated samples were analysed with Liquid Chromatography Tandem Mass Spectrometry. Deoxynivalenol-3-glucoside concentrations were significantly different from its precursor deoxynivalenol at 0.93 aw (22% moisture content- MC) at 25 °C in the naturally contaminated wheat with a ratio proportion of 56:44, respectively. This research further investigates the effects of different aw and temperature on CO2 production, fungal growth, and mycotoxin contamination in mini-silos of grains. It hypothesizes an integrated sensing approach (combining CO₂, temperature, and relative humidity measurements) as a decision support system (DSS) tool in real-time monitoring of CO₂ produced in stored grains would predict risks of mycotoxin contamination exceeding legislative limits. Findings show that in naturally contaminated and inoculated (Penicillium verrucosum and Fusarium langsethiae) wheat and oat grains, respectively, an increase in aw significantly increased the respiration rates (RR) and mycotoxin (ochratoxins, type A trichothecenes and their conjugate concentrations. Their legislative limits were exceeded at ≥ 0.80 aw (16% MC) with RR ≥ 15 µg CO₂ kg¯¹ h¯¹ . This research provides novel preliminary data for stored wheat and oats that can combine with other pre-harvest modules to develop a cost-effective DSS tool to improve grain storage management.Biotechnology and Biological Sciences Research Council (BBSRC)PhD in Environment and Agrifoo

Examining the relationship between job characteristics and work engagement in mission-oriented and non-mission-oriented roles within the public sector

Kelliher, Clare - Associate SupervisorIn recent years, there has been growing academic interest in understanding how contextual features shape employee work engagement, particularly within the public sector where job roles and motivations are highly heterogeneous. While substantial literature has explored engagement through the Job Demands-Resources (JDR) theory, the influence of contextual variation across occupational roles remains under-theorised. This thesis focuses on the heterogeneity of public sector work and examines how differences between mission-oriented and non-mission-oriented roles influence the relationship between job characteristics and employee engagement. Building on longstanding criticisms that engagement research has often neglected context or reduced it to a statistical control, this study draws on Johns’ (2006) framework to conceptualise context as an integral theoretical element. The research empirically investigates how contextual variation interacts with job demands and resources to shape engagement and exhaustion. Using data from the 2021 European Working Conditions Telephone Survey (EWCTS), this study applies Multigroup Structural Equation Modelling (MG-SEM) and Moderated Structural Equation Modelling (MSEM) to a stratified sample of public sector employees across Europe. The analysis tests the differential salience of job characteristics and the buffering role of resources in mitigating the negative effects of job demands. This study finds that employees in mission-oriented public sector roles experience both higher work engagement and higher exhaustion than their non-mission-oriented counterparts, showing the importance of context in shaping psychological experiences at work. Emotional demands function as challenge demand but primarily as hindrance demands in mission roles, being strongly associated with exhaustion but not significantly with engagement. Contrary to expectations, work intensity and work-life interference showed similar effects across both role types. Among job resources, social support had greater significance for engagement in mission-oriented roles, while autonomy and voice were beneficial across roles. Only autonomy demonstrated a significant buffering effect, mitigating the impact of work intensity on exhaustion, but only in mission-oriented roles. Theoretically, the study advances JDR theory by integrating role context as a central explanatory mechanism, using Johns’ (2006) contextual framework. It challenges assumptions of motivational homogeneity in public sector work and illustrates that the effect of job demands and resources is contingent on role type. Methodologically, it employs Multigroup Structural Equation Modelling (MG-SEM) to test the moderating role of context, positioning it as a central variable rather than a control variable. Practically, the study provides a foundation for more tailored, role-sensitive engagement strategies in public sector human resource management.PhD in Leadership and Managemen

Investigation of wire-based laser directed energy deposition (DED) process for high-resolution submillimetre features

Rodrigues Pardal, Goncalo - Associate SupervisorIn this thesis, the feasibility of manufacturing submillimetre-scale wall features using 250 W to 500 W and 1.00 kW to 2.79 kW laser power, from a 1.0 mm small beam to 1.5 mm – 3.0 mm large beams was investigated. The D-ratio correlates the beam diameter with wire diameter was introduced for deposition performance and wire position sensitivity discussion. The study firstly reveals the possibility of fabricating defect-free, smooth surface appearance and submillimetre-scale wall features using 500 W of laser power with large laser beam diameters of 1.50 mm to 2.00 mm (D-ratio of 2.50 to 3.33) without the plume interference. It was found that using a larger beam size can enhance the chance of deposition success due to enough specific point energy applied, a relatively lower but even distribution of the power density, and less energy discrepancy projected on wire and substrate, as a result, increase in the possibility of deposition success. This study also successfully applied 2.79 kW of high-level laser power and a large beam size of 3.00 mm (D-ratio of 5.00) to build the millimetre-scale wall features at a fast processing speed. It was found that fast processing speed, large laser beam size, and high-level laser power enable the chance of feeding more material into the melt pool, meanwhile, a larger D-ratio is needed for preventing the wire position sensitivity introduced back. A deposition rate of 400 g/h was achieved by using a 0.6 mm diameter wire and still exhibits the potential of fabricating submillimetre-scale wall features with the deposition rate potentially reaching 750 g/h, which is comparable to the conventional power-based laser DED process of 600 g/h. Finally, the possibility of applying FLMIPs in the wire-based laser directed energy deposition regime was revealed, but the comprehensive feasibility of applying these parameters in the wire-based laser directed energy deposition regime needs to be further investigated. These imply that wire-based laser DED process is capable of manufacturing submillimetre-scale features with good performance at relatively large beam sizes and has the potential to achieve competitively high deposition rates in submillimetre-scale features to satisfy the rapid manufacturing requirements in the additive manufacturing regime.PhD in Manufacturin