Developments in the desalination technologies have been driven not only to meet the increasing demands for freshwater, but also to reduce the energy demand and cost of the process and to make desalination more sustainable. Challenges facing the desalination industry include the salinity limits of commercial processes such as reverse osmosis (RO) and brine management issues. The membrane distillation process is positioned as an emerging zero liquid discharge (ZLD) technology, yet its large-scale implementation is hindered by the low water fluxes, poor long-term stability, and high production costs of membrane materials along with the low thermal energy efficiency of the process.

The aim of this thesis was to develop and assess membrane materials with high permeability, long-term stability and scalability prospects to reduce the energy and costs associated with desalination. To fulfil this aim, the integration of experimental evaluation of novel membrane materials with numerical modelling was conducted to improve understanding of factors hindering the widespread implementation of desalination technologies, including vacuum membrane distillation (VMD) and pervaporation (PV), and to gain insights for guiding future material design strategies.

Ceramic membrane materials, which exhibit favorable thermal and mechanical properties for VMD applications yet are sparsely represented in the literature, were evaluated for their feasibility for large-scale deployment. Selected alumina-based membranes with different characteristic properties were evaluated and benchmarked against a commercial polymeric membrane. A silane-based grafting method was developed and implemented for the hydrophobization of the selected ceramic membranes. Among the studied membranes were asymmetric α-alumina membranes that differ in thickness, along with symmetric anodic alumina membranes that exhibited superhydrophobic characteristics. For the short-term VMD evaluation, the developed anodic alumina membranes exhibited superior permeation properties, with fluxes as high as 316 kg/(m²·h) along with NaCl rejection above 99.9%. The water flux of symmetric membranes was successfully modelled, along with model extension to describe the performance of the asymmetric membranes. These evaluations also revealed the effect of the support used in reducing the effective transport area used for flux calculations of symmetric membranes.

The long-term stability of the silane-grafted membranes was assessed through500 hours of VMD operation using a feed with different NaCl concentrations at 80°C. Independent of the feed NaCl concentration, the asymmetric alumina membranes exhibited superior stability maintaining a water flux of 50 kg/(m²·h) and NaCl rejection as high as 99.9% over 500 hours of VMD operation. These membranes also exhibited superior wetting resistance in the presence of iron oxide particulate scalants. Thinner asymmetric α-alumina membranes and the symmetric membranes displayed higher water fluxes yet were prone to scaling and eventual wetting during their long-term operation.

Towards enabling the wider implementation of the VMD process, novel multi-stage VMD plant layouts with integrated energy recovery were simulated using the tubular form of the asymmetric α-alumina membranes that exhibited superior long-term stability. A techno-economic analysis of the plant layouts indicated that specific thermal energy consumptions as low as 180 kWh/m³ were feasible, along with a water recovery ratio as high as 85%. For simulations based on a prospective cost for the membranes, the levelized cost of water production was within a reasonable range of 3-8 $/m³. Furthermore, it was found that choice preference between the multi-stage VMD plant layouts is influenced by the type of waste heat source available (latent versus sensible heat sources). Furthermore, the potential of PV alongside nanofiltration as candidate processes for recovering water from a thermoresponsive draw solution in a hybrid desalination process was demonstrated. The experimental evaluation together with the simulation studies indicate the high potential of the α-alumina membranes developed in this thesis.

This mixed-method dissertation explores the barriers, drivers, and antecedents of pro-environmental behavior in tourism, with a focus on Generations Y and Z. Based on interviews with Generation Z consumers, the first study identifies primarily low motivation, but also limited knowledge, and restricted opportunities as key barriers to pro-environmental travel engagement. It proposes structural and informational interventions to make eco-friendly options more appealing and accessible. The second study delves into Reddit discussions, uncovering that while users recognize the link between tourism and climate change, low self-efficacy and ten perceived barriers hinder important behaviors. The findings provide insights into which tourism choices are important for consumers when striving to minimize their climate impact. The third study draws on survey data to compare Generations Y and Z on psychological constructs influencing their pro-environmental behavior. The results show that Generation Y reports higher levels of psychological empowerment and perceived social norms. Perceived behavioral control is identified as the strongest predictor of personal norms, followed by psychological empowerment and awareness of consequences. The study also reveals a striking gap: while 65% of respondents report strong personal norms to protect the environment, less than 3% of the total sample chose to learn more about eco-friendly travel when given the opportunity in the online setting. The fourth study, also survey-based, examines how subjective knowledge, awareness of consequences, environmental concern, and psychological empowerment influence personal norms and behavioral intentions. A moderation analysis finds that environmental concern has a stronger impact among individuals with higher objective environmental knowledge. The dissertation presents key lessons learned during the PhD journey, offering a discussion of strengths, areas for improvement, and integrated insights from all studies.

This thesis investigates optical monitoring of laser-based additive manufacturing processes. The main focus is on spectral and Schlieren-based process monitoring for real-time defect detection and process optimization.

The research involves two new monitoring strategies for powder bed fusion - laser beam/metal, analysing energy absorption and process emissions in the first three papers. In paper A, the spectral signal of the laser-material interaction zone in powder bed fusion – laser beam/metal is analyzed using a coaxial and quasi-coaxial measurement setup. The study demonstrates that the detected spectral intensity distribution strongly depends on the angle of incidence between the measuring beam and the process zone. High-speed recordings and optical simulations enabled the development of a correction model for solid materials, which accounts for the numerical aperture of the measuring optics and laser intensity distribution across the working field. However, when measuring powders, strong signal fluctuations were observed, preventing a direct transfer of the correction model. This variation was attributed to differences in powder absorbance, which is further explored in paper B. This paper systematically investigates the absorbance behaviour of metal powders used in laser-based additive manufacturing. A high-precision spectrometer was used to measure 39 powders over a broad spectral range, examining the influence of aging, grain size, contamination and usage conditions. The study derives 20 technically relevant laser wavelengths, identifying those with improved process efficiency and stability. The resulting dataset provides a valuable foundation for laser parameter optimization by estimating the energy coupling efficiency for different materials. To enable in-situ absorbance determination in powder bed fusion - laser beam/metal, paper C introduces a method for high-resolution coaxial imaging of the powder bed at multiple wavelengths. This technique enables spatially resolved absorbance mapping across the entire processing plane, allowing for the detection of impurities, oxidation and foreign particles. The concept was experimentally validated using 20 different powders and further confirmed through optical simulations, ray tracing and comparative spectrometer measurements.

In three further papers, the laser material interaction and its effect on the refractive index variation of the gaseous process media is investigated for laser directed energy deposition. In paper D, a Schlieren imaging setup was applied to real-time monitoring of laser directed energy deposition, classifying different Schlieren phenomena and linking them to process instabilities and parameter deviations. A previously unknown recurring Schlieren structure was identified and its influence on coaxial imaging accuracy was analyzed using optical simulations that assigned a precise refractive index distribution to the observed Schlieren object. Paper E expands on these findings by implementing a background-oriented Schlieren system alongside shadowgraphy to analyze gas flow and refractive index variations from multiple orientations. A quantitative image processing method was developed to extract Schlieren intensity gradients and directional vectors, allowing for the correlation of Schlieren activity with process parameters. This approach enables the derivation of process boundaries based on optical flow measurements, offering a novel method for assessing process stability. Finally, paper F explores whether Schlieren-induced refractive index variations can be inferred from coaxial imaging data using an artificial-intelligence-based approach. A machine learning model was trained on background-oriented Schlieren data and coaxial imaging artifacts, demonstrating the feasibility of an indirect Schlieren analysis without requiring a dedicated Schlieren setup. By linking Schlieren structures to melt pool behaviour and process instabilities, the study contributes to real-time process monitoring and adaptive control strategies in laser directed energy deposition.

Overall, this thesis provides new insights into laser-material interactions, spectral absorbance properties and advanced optical process monitoring techniques. By combining spectroscopy, Schlieren imaging and artificial-intelligence driven analysis, this research advances the digitalization of laser-based additive manufacturing processes, improving process control, defect detection and manufacturing efficiency in powder bed fusion - laser beam/metal and laser directed energy deposition applications.

Greywater (GW) originates from the kitchen sinks, dishwashers, handbasins, showers, and laundry. GW can account for 70–90% of domestic wastewater volume and contains organics, nutrients, microorganisms, micropollutants, and microplastics. Effective treatment can unlock the potential of GW for non-potable reuse purposes like urban landscaping or irrigation. The overall aim of this thesis was to investigate on-site GW treatment systems which included package-plants, two green walls and a constructed wetland and assess the treatment performance in terms of organic matter, nitrogen (N), phosphorus (P), microorganisms and microplastics (MPs), including the potential resource recovery and safe reuse of GW.

Among the eight package-plants investigated, commercial systems included three type A, two type B and C systems. Type D was a conventional sand filter. After the pre-treatment septic tanks, the treatment unit of type A consisted of a geotextile-fitted trickling filter over a sand bed, type B consisted of a mineral wool filter, and type C had fine plastic mesh filters. The two green wall studies were conducted at a testbed facility, RecoLab, which received GW from a newly developed urban city district (800 P.E.). The treatment efficiency of a pilot-scale indoor green wall with five filter media (pumice, biochar, hemp fiber, spent coffee grounds (SCG), and composted fiber soil (CFS, a paper industry byproduct)) was investigated with vertical flow rates (FRs) of 4.5, 9, and 18 L/d. The real-scale outdoor green wall with four levels filled with biochar and LECA as filter media was investigated for one year, using a subsurface horizontal FR of 430 L/d. A long-term performance evaluation of a constructed wetland for treating GW from a residential building (100 P.E.) in Norway was conducted using GW quality data from 2001–2024. The constructed wetland consisted of a biofilter with Filtralite® media and a horizontal subsurface filter with FiltraliteP® media for enhanced phosphorus removal.

The treatment efficiency of the systems was highly influenced by the filter media and FRs while seasonal temperature changes had a low effect. All the systems demonstrated effective treatment of GW and met the local discharge guideline of 80% BOD reduction and <3mg/L of P in the effluent. However, only the pilot-scale green wall and constructed wetland could produce an effluent with <1 mg P/L, a limit for sensitive regions. Among the filter media, sand, biochar and Filtralite® were the most efficient, up to 4 log10, in removing the microorganisms Escherichia coli, enterococci, Clostridium perfringens, Legionella spp, Pseudomonas aeruginosa and met the European Commission’s guideline for reuse of reclaimed water in agriculture. The quantitative microbial risk assessment (QMRA) on effluent GW from the constructed wetland, for multiple exposure scenario (16 exposures/year) of accidental ingestion of 1 mL, indicated safe reuse in a water cascade during summer season with regards to E. coli and C. perfringens. In addition, using TED-/Pyro-GC/MS, high variability of MPs was observed in GW from different sources of generation while all the filter media of the respective systems effectively retained the MPs, except for mineral wool and hemp fiber. 

The findings of this thesis could contribute to the resource-efficient wastewater management and Water-Food-Energy nexus by demonstrating the potential of decentralized GW treatment systems.

This thesis deals with the transition to fossil-free (fuel) passenger transport in rural areas, highlighting the rural inhabitants’ perspective. More specifically, it focuses on how preconditions for rural inhabitants can be met, and what support is needed for rural inhabitants to make the transition from a bottom-up perspective. The environment for transition in rural areas is challenging, with significant accessibility issues. There is a lack of public alternatives, and car dependency is high. There are also challenges in terms of ensuring a transition that is socially sustainable and ensures sustainable accessibility. Alternatives to the fossil-fuel car are essential but, in the context of low populations, it has proven hard to make these alternatives viable. The electric car also stand out as a socio-economic privilege, as only some perceive they can afford it.

The thesis focuses on the two northernmost regions in Sweden, Norrbotten and Västerbotten, where both limiting factors and enablers are identified. Västerbotten and Norrbotten do not represent the ‘ordinary countryside’ but rather an extreme environment, at least from a European perspective. Belonging to Europe’s northernmost region, with the lowest population density, the area presents a very challenging context. Extreme conditions need to be addressed to respond to challenges in these areas, and it is not enough that a transition occurs in more ‘ordinary’ rural areas: change is needed even within the toughest locations.

In general, the transition from using fossil-based fuels to fossil-free fuels is not the only issue involved in the process. For inhabitants in rural areas, the transition involves change in several ways. It encompasses adjusting from mainly personal responsibility and private transport to more sharing and dependency on others. The transition also involves a change in planning strategies, sometimes requiring more planning for travel. This means a change in terms of technology but also behaviour, from one to several modes of transport. It also requires changes in risk planning and how safety measures should be handled. All of these issues need to be addressed to bring about a transition that ensures accessibility for rural inhabitants.

In order to bring about such change successfully, the transition has to be seen from the perspective of already existing accessibility challenges. Key to addressing overall accessibility is making sure there is sufficient accessibility alongside the transition, and search for functional and attractive alternatives. Making the transition possible necessitates a diverse series of solutions, both transport-related but also beyond the mode of transportation, including reduced travel, digital services and enhanced local services. This project has also identified several other key factors that are important considerations in the development and implementation of a diverse set of transport solutions and other accessibility-related measures: enhancing the motivation for fossil-free travel, strengthening collaboration within local and personal communities, working to improve perceived opportunities and adaptability to fossil-free alternatives, supporting and nurturing positive expectations and anticipations regarding the transition, and improving physical proximity to essential services.

The global construction sector has witnessed exponential growth in concrete utilization over the past seven decades, with annual consumption over 9.42 billion m³ in 2021. This surge, driven by rapid urbanization, has positioned concrete as the dominant construction material while creating critical environmental burden. In response to these challenges, the Swedish concrete industry has committed to making all concrete climate-neutral by 2045, with market-ready climate-neutral concrete available by 2030. To reduce the negative environmental impact of the concrete, transitioning from linear to circular economic models presents a viable approach, particularly through integrating wastes and industrial by-products (e.g., fly ash, slag) as supplementary cementitious materials (SCM) into concrete formulations. However, this ecofriendly construction practice faces severe challenges at establishing and executing SCM concrete configurations (including concrete mixes and site construction methods). During plan establishment, the systemic environmental and economic impacts of SCM concrete—spanning cradle-to-practicalcompletion phases—remain insufficiently examined. The complex interactions between SCM concrete’s mechanical properties (e.g., prolonged hydration and decreased early strength) and site construction methods (e.g., formwork duration, occupancy of labour and equipment) increase the difficulty in quantification. For example, while SCM concrete reduces embodied carbon in production, its delayed strength gain may necessitate prolonged formwork use or require energy-intensive methods (e.g., thermal treatment) to meet project timelines. To mitigate this, engineers might opt for a higher concrete grade to accelerate early strength development—though this risks offsetting sustainability gains of SCM concrete. Such adaptations often erode projected emission reductions and inflate costs, shifting burdens across stages. These cross-stage trade-offs underscore the need for integrated, cradle-to-practical-completion evaluations of the environmental and economic impacts of SCM concrete to avoid suboptimal overall performance. Furthermore, optimising SCM concrete configurations based on quantified performance metrics presents a significant computational challenge. This is due to the exponentially growing solution space resulting from the numerous combinations of SCM concrete mix designs and site-specific construction methods. As a result, exhaustive exploration of the solution space becomes computationally intensive, often leading to incomplete identification of optimal trade-offs between environmental benefits (e.g., reduced GHG emissions) and economic constraints (e.g., labour costs, construction time). Even after obtaining optimal SCM concrete configurations, real-world variability—such as fluctuating temperatures affecting curing rates —introduces uncertainty into project outcomes during site execution. For example, warmer weather than predicted will make former planed thermal curing measures become overprotection, leading to unnecessary expenses and energy consumption. To address this, robust optimisation frameworks are needed to simultaneously account for cross-stage interdependencies and operational uncertainties. Despite the critical need for integrated solutions, existing research on SCM concrete construction has largely remained discipline-specific—a divide rooted in the fragmented nature of the construction industry and its supply chain. Studies on SCM material properties are primarily limited to construction materials research, while on-site optimisation is explored within construction management. This fragmentation has prevented the integration of these two critical dimensions into a unified framework, limiting a comprehensive understanding of their collective impacts on a project’s economic and environmental performance. Based on gaps in previous studies, three research questions are formulated: RQ1: What systemic interdependencies exist between SCM concrete’s mechanical properties and site construction methods, and how do these interactions influence the cradle-to-practical-completion performance of SCM concrete? RQ2: What critical trade-offs arise when optimizing SCM concrete configurations across environmental benefits and economic constraints, and how can these trade-offs be systematically prioritized to avoid sub-optimisation? RQ3: What influence do weather-induced uncertainties have on the trade-offs between environmental benefits and economic constraints of SCM concrete construction practice across cradle to practical completion, and how should site construction methods be dynamically adapted to optimize these objectives under variable conditions? To address the formulated research questions, the research underlying this thesis was conducted in three following procedures: (1) Problem identification, which investigated both the operational demands of SCM concrete construction practice and existing theoretical limitations hindering the realization of full ecofriendly potentials of SCM concrete; (2) Method development, which constructed a holistic approach to overcome the identified theoretical gaps; (3) Method validation, which built three according prototypes as practical solutions to the identified problems and applied them to actual construction case projects to examine the effectiveness of the proposed methods. Each research question is addressed by a purpose-built model tailored to the specific technical and decision-making challenges associated with the use of SCM concrete. These models offer targeted solutions across life cycle analysis, optimisation, and uncertainty management: CSCD (Collection–Simulation–Calculation–Decision) for RQ1: This model integrates Discrete Event Simulation (DES), environmental impact assessment, and concrete maturity analysis to evaluate the environmental and economic performance of SCM concrete across the cradle-to-practical-completion span. It explicitly captures the interdependencies between SCM concrete’s mechanical properties (e.g., strength development) and construction practices (e.g., formwork duration), supporting holistic performance quantification. ESO (Ensemble learning–Simulation–Optimisation) for RQ2: This model combines ensemble machine learning techniques with simulation-based optimisation to efficiently navigate the expanded solution space of SCM concrete mixes and site construction methods. It enables comprehensive multiobjective trade-off analysis between environmental benefits (e.g., GHG emissions reduction) and economic constraints (e.g., cost, time), while minimising computational demand and the risk of sub-optimal outcomes. MADS (Modelling–Automation–Decision Support) for RQ3: This model integrates dynamic weather data, concrete maturity modelling, and automated decision rules to support the dynamic adaptation of construction practices—such as curing duration and protection measures—in response to temperature fluctuations. It enhances the reliability and responsiveness of SCM concrete implementation under weather-related uncertainties.

This research directly supports the strategic goals of the Swedish roadmap for climate-neutral concrete through a systematic and holistic approach to the use of SCMs. The roadmap emphasizes several key strategies, including: optimising the composition of concrete, replacing parts of the cement with alternative binders; contributing towards ensuring that the right concrete is used in the right place, i.e. avoiding higher concrete quality than necessary for the bearing capacity and durability of the building. The proposed research approach contributes to each of these areas in the following ways: (1) Optimizing Concrete Composition. In alignment with the roadmap’s focus on reducing cement content, this research provides a structured method for evaluating and selecting SCMs as partial cement replacements. The CSCD model, developed in response to RQ1, enables a comprehensive environmental and economic assessment of different SCM concrete mixes, considering their mechanical behavior and performance during construction. (2) Ensuring the Right Concrete is Used in the Right Place. Overdesign of concrete—using unnecessarily high-grade concrete mixes—leads to avoidable emissions and costs. The research supports decision-makers in selecting concrete grades that match structural needs without overdesign. The CSCD model quantifies performance relative to functional demand, minimizing unnecessary environmental burdens and ensuring practical suitability on-site. (3) Lifecycle-Based Environmental and Economic Assessment. Avoiding impact shifting across project stages requires integrated evaluation from material selection to project delivery. This research embeds a cradle-to-practicalcompletion perspective throughout all phases of assessment. While the CSCD model forms the backbone of this life cycle analysis (per RQ1), the ESO and MADS models (developed under RQ2 and RQ3) extend this thinking into planning and execution, capturing downstream impacts and variability. (4) Multi-Objective Optimization for SCM Usage Planning. Identifying optimal SCM configurations under multiple, often conflicting objectives—such as reducing emissions while controlling costs and timelines—is critical. This research introduces the ESO model, developed for RQ2, which combines simulation with ensemble learning to explore a vast solution space efficiently. It reveals optimal trade-offs while managing computational complexity. (5) Managing Construction Uncertainties and Climate Variability. Realworld variability, especially weather-induced fluctuations, can disrupt curing rates and lead to mismatches between planned and actual outcomes. To address this, the MADS model, developed for RQ3, enables dynamic adaptation of construction measures such as curing protocols. It enhances the reliability and environmental performance of SCM concrete application under uncertain site conditions.