There is a rising concern on the sustainability of Zero Liquid Discharge (ZLD) desalination. In this study, Multi-criteria Decision-making (MCDM) is applied to compare the sustainability performance of various ZLD scenarios, which is part of a Strong Sustainability (SS) assessment of desalination. ZLD desalination systems are considered to be complex and have intricate interdependence among various factors, which were seldom recognized in previous research. The purpose of this study is to explore the impact of interdependence among criteria on the MCDM process, with a desalination case study from Water Mining project used for demonstration. A transparent MCDM methodology is proposed in this study, which consists of Best Worst Method – Decision Making Trial and Evaluation Laboratory (BWM-DEMATEL), hierarchical clustering, and Preference Ranking Organization Method for Enrichment Evaluations (PROMETHEE).
In the desalination case study, the use of hierarchical clustering allows for the identification and preservation of both majority and minority opinions, based on which, the same ranking of desalination scenarios is produced through PROMETHEE. Concerning the interdependence among criteria, the results reveal that it can help identify the crucial factors for improvement of sustainability performance of the alternatives. In addition, by considering it, the understanding of criteria is enhanced, which leads to more concentrated opinions of stakeholders in the desalination case. However, the findings indicate that the influence of incorporating the criteria independency on the final decisions is restricted in cases insensitive to weight variation.
The application of BWM-DEMATEL method is a complex and time-consuming activity. Considering the effectiveness and the cost of implementation, BWM-DEMATEL might be not as worthy of application in this case study. Inspired by this, it is meaningful to develop an approach to estimate the impact of the interdependence among criteria on the alternatives ranking in a certain decision problem in the future.
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The brine generated from desalination is a threat to the environment, and its disposal has been a great challenge. A new concept Zero liquid discharge (ZLD) can minimize the environmental impact of brine. However, the high costs for construction and running of a ZLD plant limits its growth in desalination market. Therefore, a new strategy integrating brine mining with desalination is proposed to improve its economic performance due to the valuable minerals in brine. A cost-effectiveness analysis (CEA) is carried out to assess its economic performance and compare this strategy with other ZLD strategies. The results present that the cost-effectiveness of the studied strategy is lower than ZLD systems which only maximize water recovery. The cost-effectiveness ratio of the studied strategy is 0.056€/kg of freshwater, higher than ZLD maximizing water recovery (0.032€/kg of freshwater). However, its profitability is higher than other ZLD schemes. This study shows that the integrated desalination and brine mining strategy has a great economic potential. Its cost-benefit of is 1.12, far lower than that of ZLD only maximizing water recovery (26.08). In addition, it can be indicated that CEA is not comprehensive enough to assess the economic performance of a multi-product desalination system. It doesn’t include the revenues from by-products, which are an important part of the studied strategy. For further research, a more integrated approach of economic analysis is needed to make a decision on the different alternatives of desalination. ... Read more