Sustainability Assessment of Desalination Technologies

Water scarcity is a major issue for socioeconomic development and sustainable resource management. To ensure long-term freshwater availability, desalination has emerged as a solution. Existing desalination technologies are generally classified into thermal processes and membrane-based processes. Despite significant technological advances, desalination remains associated with environmental concerns, particularly brine discharge and high energy consumption. Consequently, the development of sustainable desalination solutions, including the integration of renewable energy (RE) and minimum- or zero-liquid-discharge (MLD/ZLD) systems, has become increasingly important. Selecting the most sustainable desalination technology is complex because of the multidimensional nature of sustainability, which requires simultaneous consideration of environmental, economic, technical, and social factors. Multi-Criteria Decision-Making (MCDM) methods have therefore emerged as valuable tools for evaluating and ranking desalination alternatives. In this context, this thesis aims to assess the sustainability of desalination configurations using an MCDM framework. Specifically, it aims: i) to conduct a comprehensive review of existing research on the application of MCDM methods in the desalination field, with the aim of identifying commonly used evaluation criteria and methods, ii) to assess different Minimum and zero liquid discharge (MLD/ZLD) system, and iii) to compare renewable energy-powered desalination configurations in a specific desalination plant, namely the one located in the Mar de Alborán (Andalusia, Spain). The comprehensive review indicates that the AHP is the most frequently used MCDM method for criteria weighting, while TOPSIS is most commonly employed for ranking desalination alternatives. The results reveal strong heterogeneity in the selection and weighting of criteria, reflecting differences in study objectives, data availability, and expert judgment. Consequently, identifying a single optimal desalination technology or plant location remains challenging, as rankings are highly context-dependent and sensitive to subjective assumptions in decision-making. Furthermore, the evaluation of MLD/ZLD configurations, which employs the AHP to weight the criteria and TOPSIS to rank the alternatives, reveals that technical and environmental criteria dominate the decision-making process, with specific energy consumption and CO2 emissions as the most influential factors. In addition, nanofiltration (NF) + Multi-effect Distillation (MED) + Evaporation ponds (EPs), Reverse Osmosis (RO) + multistage NF + EPs, and RO + membrane distillation (MD) + EPs are identified as the top-performing MLD/ZLD configurations. Sensitivity analysis indicates generally robust rankings, although land availability can become a decisive factor depending on local spatial constraints. Finally, applying the non-compensatory C-K-Y-L ranking method to assess eight RE-powered desalination configurations reveals that configurations relying on conventional energy sources consistently rank higher across scenarios that prioritize techno-economic and social criteria, due to their commercial maturity, reliability, flexibility, and limited land requirements. Conversely, fully renewable configurations are preferred when environmental criteria have a higher importance weight in the decision-making process. The sensitivity analysis confirms that the overall ranking remains robust to variations in the preferences threshold.