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Process integration and electrification with digital twins
(The University of Waikato, 2026-05-14) Lincoln, Benjamin James; Walmsley, Timothy Gordon; Atkins, Martin John; Walmsley, Michael R.W.; Young, Brent R.
The decarbonisation of industrial process heat is one of the most pressing challenges in the global energy transition. In New Zealand, fossil fuels remain the dominant source of process heat, despite having over 80% renewable electricity generation. Milk powder production is a major consumer of process heat, with evaporation and drying processes relying on large amounts of coal- and gas-fired steam. Electrification technologies such as industrial heat pumps and mechanical vapour recompression (MVR) have the potential to significantly reduce emissions, yet widespread adoption has been limited because of the complex interactions between heat and power, in addition to uncertainties around practicality. Conventional process integration (PI) techniques were designed for fossil-fuelled utilities and are poorly aligned with the work requirements and integration constraints of electrification. Meanwhile, legacy simulation tools are ill-suited to the complex fluids and system interactions of food and dairy processes. This thesis addresses these gaps by developing a generalisable Process Integration and Electrification (PI&E) methodology that combines exergy-based targeting, retrofit strategies, and techno-economic evaluation coupled with an iterative design-centric digital twin framework. The thesis is structured in two parts. Part A develops the digitalisation foundations, including the preparation of a milk evaporation case study, the creation of advanced thermophysical property packages for complex fluids (milk, refrigerants, humid air), and the construction of a design digital twin using both commercial and open-source platforms. Part B applies the digital twin to PI&E, integrating operational optimisation, Exergy Pinch Analysis, and systematic evaluation of electrification technologies in both greenfield and retrofit contexts. For greenfield design, the research extends Pinch Analysis principles to heat pump integration by utilising heat pockets to create multiple Pinch points, enabling systematic minimisation of temperature lift and improved integration opportunities. Building on this, an iterative PI&E design workflow was developed to guide technology placement and evaluate electrification pathways. This culminated in the design of a novel fully electric milk evaporator system that achieved a specific electricity consumption of 120 kWh per tonne of milk powder, compared with 159 kWh/tp for a simpler single heat pump design, demonstrating higher efficiency. For retrofit applications, the thesis advances PI&E by extending heat pump bridge analysis to explicitly include process unit heat flows, allowing process modifications to be considered alongside heat exchanger reconfiguration. This innovation addresses a key gap identified in previous literature, enabling more retrofit strategies. The method was demonstrated through multiple related case studies of milk evaporator plants, producing a set of common retrofit solutions. These include replacing thermal vapour recompression (TVR) and/or direct steam injection with MVR systems, which were shown to deliver lower levelised costs of heat compared with reference boiler-based designs. The culmination of the research is a unified PI&E methodology that combines digital twins, rigorous thermodynamic analysis, and practical integration strategies. The results show that electrification of milk evaporation systems can be achieved in both new and existing plants with significant efficiency gains and competitive economics. PI&E has been tested across multiple platforms: Aspen HYSYS, DWSIM and the Ahuora Digital Twin Platform, powered by IDAES – proving to be a platform-agnostic, yet digitalisation-centred, methodology. Although developed and applied in the context of New Zealand’s dairy sector, the methods and insights are broadly transferable to other low- to medium-temperature process industries, offering a robust and scalable pathway to accelerate industrial decarbonisation.
Valorisation of waste mussel shells and harakeke fibres for enhanced performance in polypropylene composites
(The University of Waikato, 2026) Xu, Jing; Mucalo, Michael R.; Pickering, Kim L.
This doctoral research develops high-performance, environmentally sustainable polypropylene (PP) composites by valorising low-value biogenic waste. Within a Circular Economy framework, it addresses challenges in plastic sustainability and the need for bio-based alternatives by utilising mussel shells (MS), an aquaculture by-product, and harakeke fibres (HF, Phormium tenax), derived from agricultural waste, as reinforcing materials. Through systematic characterisation, surface modification, filler hybridisation, and multi-scale evaluation, this study demonstrates the successful transformation of these biogenic low-value resources into functional reinforcements for PP. The structural and surface properties of MS-derived fillers were first investigated, focusing on functionalization with a mussel-inspired polydopamine (PDA) coating. Solid-state nuclear magnetic resonance (SS-NMR) and Fourier-transform infrared spectroscopy (FTIR) confirmed PDA formation, revealing its indole/indoline units and quinonoid groups. X-ray diffraction (XRD), SS-NMR, and FTIR showed that MS contains calcite and aragonite phases, which remain intact after coating. Thermogravimetric analysis (TGA) confirmed the thermal stability of MS, slightly improved by PDA, while X-ray photoelectron spectroscopy (XPS) verified successful coating deposition on MS fillers via nitrogen-containing groups. Surface energy analysis revealed that PDA coating increased MS filler hydrophilicity, whereas maleic anhydridegrafted polypropylene (MAPP) treatment particularly when combined with PDA enhanced filler hydrophobicity, establishing PDA/MAPP co-modification as an effective strategy to improve filler interaction with the hydrophobic PP matrix. Polypropylene (PP) composites reinforced with pristine, maleic anhydride-grafted polypropylene (MAPP)-modified, and PDA/MAPP co-modified mussel shell (MS) fillers were systematically compared with neat PP to assess thermal and mechanical performance. Thermogravimetric analysis (TGA) revealed improved thermal stability across all composites, most notably with PDA/MAPP-MS. X-ray diffraction (XRD) and differential scanning calorimetry (DSC) confirmed that MAPP and PDA/MAPP surface treatments enhanced nucleation and crystallinity, promoting -crystal formation in the PP matrix. Mechanical testing showed that unmodified MS reduced tensile and flexural strength, an effect mitigated by MAPP modification. PDA/MAPP co-modification yielded the greatest improvements, with tensile strength, flexural strength, and modulus all significantly enhanced at 40 wt.% loading. Dynamic mechanical analysis (DMA), creep recovery, and melt rheology further supported the advantages of PDA/MAPP comodification, consistent with scanning electron microscopy (SEM) observations of improved interfacial bonding. The study further explored hybrid reinforcements combining MS with HF. Crystalline structure analysis showed both fillers acted as nucleating agents, with hybrid systems producing higher crystallinity than neat PP. XRD confirmed the co-existence of - and -crystals. Composites with 10% MAPP-MS/30% HF and 10% PDA/MAPP-MS/30% HF showed the highest -phase content (17.32% and 16.71%, respectively), enhancing toughness and elongation while retaining strength and stiffness. SEM backscattered electron (BSE) analysis confirmed improved fibre matrix adhesion and polymer bridging, while energy-dispersive X-ray spectroscopy (EDS) mapping showed uniform filler distribution. These hybrid systems outperformed single-filler composites, with 10% MAPP-MS/30% HF achieving a 48% increase in tensile strength over neat PP. DMA confirmed a higher storage modulus, improved energy dissipation, and better adhesion. Creep-recovery tests demonstrated greater dimensional stability, particularly for the 10% PDA/MAPP-MS/30% HF system. Melt rheology behaviour suggested the formation of a hybrid filler network that further restricts chain mobility. Finally, composites with 5% PDA/MAPP-MS fillers demonstrated superior UV stability. After 1,000 hours of accelerated weathering, neat PP exhibited cracking, roughening, and discolouration, while PDA/MAPP-MS composites retained smooth, intact surfaces. FTIR confirmed their lowest carbonyl index increase, reflecting suppressed photo-oxidative degradation. XRD and DSC showed a stable crystalline structure, and mechanical testing revealed only a 15.6% tensile strength loss, compared to 62% for neat PP. DMA further confirmed superior viscoelastic stability. These results indicate dual protection: MS act as UV shield, while PDA scavenges free radicals to delay degradation. Overall, this research establishes mussel shell and harakeke fibre as sustainable, high-performance reinforcements for PP. PDA/MAPP co-modification and hybridisation strategies optimise filler matrix interactions, yielding composites with enhanced thermal, mechanical, rheological, and weathering properties. These findings highlight the potential of low-value biogenic fillers for sustainable, durable, and environmentally resilient composites.
The investigation of military style academies as an intervention for young people with serious and persistent criminality
(The University of Waikato, 2025) Kazadi, Mujinga Deborah; Roen, Katrina
A developmental perspective asserts that criminal trajectories arise due to the complex interactions between environmental factors and individual factors increasing vulnerabilities towards persistent criminality. These criminal trajectories are identifiable during early childhood and represent unaddressed vulnerabilities across social, cognitive and familial contexts. The presence of serious and persistent offending amongst young people is significant because it highlights the accumulative effects of risk factors present in childhood and places them at increased risk of transitioning into persistent criminality in adulthood. It is therefore advantageous to design interventions targeting serious and persistent offending in young people. Aotearoa’s National government proposed military style academies (MSAs) as an intervention to reduce the amount of young people involved in serious and persistent offending. The combination of physical activity and rehabilitative components is proposed to alter criminal trajectories and encourage desistance from crime. This thesis investigates youth practitioner’s perceptions of MSAs, an intervention for youth with serious and persistent criminality to conceptualize how youth rehabilitation can be shaped to positively contribute to the wellbeing of Aotearoa’s most vulnerable young people. Reflexive thematic analysis was used to analyse 11 interviews with youth practitioners with at least one year’s experience working with vulnerable youth. Four main themes and nine sub-themes were identified. The four main themes included addressing the root causes of crime, reducing re-offending, cultural considerations and the juvenile justice system. Serious and persistent offending amongst young people was viewed to be the result of a lack of early interventions targeting those at the highest risk of developing enduring criminal identities. The whānau unit was highlighted as a key target for early interventions and rehabilitative programmes. Participants raised concerns about the incongruence between MSAs and a Te Ao Māori world view. Participants suggested that MSAs failed to recognise the extent to which young people who offend are often victims first. Further, they argued that MSAs did not facilitate reintegration into the community. These factors were associated with increasing the likelihood that young people will go on to offend. These findings support the need for interventions to embrace a therapeutic model emphasizing the reconciliation and redemption of the young person. As such, the re-structure of youth rehabilitation and the juvenile justice system to more closely align with Mātauranga Māori and desistance theories can be considered a robust strategy to disrupt the care to custody pipeline so prevalent in young people who offend.
Psychological Capital and its support to students while they combine work and study
(The University of Waikato, 2026) Bovill, Kimberly; Sutton, Anna
One in every two students in Aotearoa/New Zealand now works approximately 16 hours per week alongside studying, which is driven by the current increasing living costs and decreased access to governmental financial support seen in Aotearoa/New Zealand. This financial strain and need to self-support is a reality for students that requires more attention, due to the potential negative impacts of financial strain on students’ stress, well-being and academic success, altering the students’ time at university and academic outcomes. However, there is variance in students’ experiences and the way they balance these working and student roles, suggesting that individual psychological resources may play a significant role in shaping outcomes. The present study examined whether Psychological Capital (PsyCap), a positive psychological resource comprising hope, self-efficacy, resilience, and optimism (HERO), mediates the negative impacts of combining work and study by buffering the relationship between hours worked and student outcomes. An online survey was administered to 214 undergraduate students currently studying at the University of Waikato, Aotearoa, New Zealand. Data were analysed using correlation and mediation analyses to identify relationships between variables, and explain any relationship found between PsyCap involving the components of HERO and hours worked, stress, well-being and academic success. The results showed that higher levels of PsyCap were associated with lower stress, along with higher levels of well-being and academic performance, giving an insight into the importance of psychological resources. Hours worked showed weak associations with student outcomes and were significantly related only to general university stress, indicating that employment hours can add stress but do not inherently impact a student's outcomes. Mediation analyses showed that PsyCap did not mediate the relationship between hours worked and student outcomes, primarily because hours worked were not significantly related to PsyCap. These findings suggest that psychological resources may play a more substantial role in shaping a student's experience in the ability to juggle these roles, rather than employment intensity alone. The findings highlighted the importance of internal coping resources, especially for students who are juggling multiple roles. Future research recommendations include interventions aimed at strengthening PsyCap, known as Psychological Capital Interventions (PCI), which focus on steps such as goal setting and identifying paths to reach these goals, providing a more practical and realistic approach to promoting student well-being, academic success and commitment to higher education. If these practical interventions are put in place to support students’ academic success, this can positively impact the workforce and the new generation of workers.
Using genetic techniques to improve understanding of source-sink dynamics of the invasive mosquitofish, Gambusia affinis
(The University of Waikato, 2026) Hale, Phoenix; McGaughran, Angela
Biodiversity loss is more prominent in freshwater versus terrestrial or marine ecosystems, with temperate estuaries believed to be the most degraded of all ecosystems globally. This is due, in part, to the proliferation of invasive non-native species and the inadequacies of current biomonitoring practices for monitoring population trends over sufficient spatiotemporal scales to inform management decisions. Environmental DNA (eDNA; genetic material shed to the surrounding environment by organisms) is an increasingly popular, non-invasive biomonitoring method that provides the opportunity to increase the scale at which population trends can be monitored, while also having the potential as a sampling method for population genetic studies. My thesis aimed to use a variety of methods to understand source-sink population dynamics at varying spatial and temporal scales and explore the value genetic techniques can provide to species management, using the invasive pest fish, Gambuis affinis, as a test case. Chapter 2 used traditional netting techniques to survey occupancy patterns of G. affinis to understand the species’ physical dispersal drivers within a large coastal ecosystem in the South Island of New Zealand. I demonstrated a decrease in abundance and likelihood of G. affinis presence as tide height increased, and a decrease in abundance of G. affinis at a specific site as rainfall increased. These findings show that monitoring of occupancy patterns of freshwater fish is often done at too small a spatiotemporal scale and that future work should incorporate additional methods to increase the scale at which monitoring is performed. Chapter 3 analysed mitochondrial DNA collected across New Zealand from both tissue and water samples to explore the efficacy of eDNA as a sampling tool for determining mitochondrial variation at large spatiotemporal scales. I showed that >99% of the G. affinis mitochondrial assemblage was shared by both tissue and water samples, but the remaining detected genetic variation was unique to either tissue or water only. These findings show that, while that eDNA holds great promise for biomonitoring in freshwater environments, careful consideration of study design is required for its use in assessing the drivers of biodiversity differentiation. Together, my thesis demonstrates the utility of eDNA metabarcoding techniques as a complement to traditional survey methods to increase the spatiotemporal scale at which biomonitoring is undertaken. Continued application of a combination of these methods will facilitate improved knowledge of occupancy and dispersal patterns for G. affinis and, as such, greater protection of our native ecosystems and species.