to capital and operating costs, other parameters such as local incentives or subsidies may also contribute to the large difference in desalted water cost between regions and facilities. The cost of desalinated seawater has fallen below US$0.50/m3 for a large scale seawater reverse osmosis plant at a specific location and conditions while in other locations the cost is 50% higher (US$1.00/m3) for a similar facility. in desalination cost as a result of significant technol. Desalination capacity has rapidly increased in the last decade because of the increase in water demand and a significant redn. This is valuable since it could lead to a reduction of deionization time and subsequently the energy consumption for reaching the required water standards, although quantifying this gain is outside the scope of the current work.Ī review. Generally, it can be noted that picking the best option means that fewer ions need to be removed than if the other operation had been used. Furthermore, if the calcium concentration had been much higher, it would still have been possible to reduce both calcium and fluoride to desirable levels using longer electrosorption periods instead or a combination of long and short electrosorption periods. This suggests that a deionization process using short electrosorption periods would not require Ca 2+ remineralization at all. Here, a simplified calculation indicates that long desalination periods would remove 78% of the Ca 2+ down to 24 mg/L, while short desalination periods would remove 51% down to 53 mg/L (a detailed derivation is provided in the Supplementary S-3).
Pick a priority ion and determine the concentration to be removed.Ĭalculate the removal of the other ions of the same charge sign using eq 10.Ĭalculate the removal of the ions of an opposite charge sign by numerically solving the system of equations defining the total charge removed and by eq 10 for each ion compared to a baseline ion of the same charge sign. Measure the initial concentration of each ion for the solution of interest, if unknown.
To calculate the adsorption of each ion in a multi-ion solution, the following six steps are used: 1. Below, we describe a method for implementing the result in practice for real-world samples that contain multiple ionic species in different concentrations. The previous sections have demonstrated that the relative adsorption between ions can be predicted for shorter and longer ion-adsorption periods, meaning that a degree of ion selectivity can be obtained and predicted. (c) Relative adsorption between Ca 2+ and Na + based on multi-ion competition data from Table 2 in the report by Hou et al. Since no specific Cl – adsorption data is provided for this experiment, the data for Cl – adsorption was taken from the experiment with the corresponding concentrations in Figure 4 in ref (42), using the assumption that changing the concentration of trace ions has a negligible impact on the major-ion adsorption. The data for NO 3 – adsorption was taken from Figure 6 in ref (42). The relative adsorption between NO 3 – and Cl – is shown as a function of their relative initial concentrations. (b) NaNO 3 (300 mg/L) was mixed with 1.5, 2, and 3 g/L NaCl, respectively. The relative adsorption between F – and Cl – is shown as a function of their relative initial concentrations ( eq 7). A fixed concentration of 20 mg/L NaF was mixed with 0.5, 1, 1.5, 2, and 3 g/L NaCl, respectively, and batch-mode desalination was performed at 1.6 V until saturation. In conclusion, the method could be valuable for predicting the impact of improved device operation on capacitive deionization with multi-ion compositions prevalent in natural water sources.įigure 2. Furthermore, we demonstrate an example of how this selectivity could reduce excess removal of ions to avoid remineralization needs.
This is leveraged to directly predict and enhance the selective ion removal in CDI. Crucially, we derive a simple relationship between the adsorption of different ionic species for short and long adsorption periods. A dynamic Langmuir (DL) model has been a starting point for deriving the theory, and the model predictions have been validated using data from reports in the literature. In this work, we have investigated the effect of device operation on the preferential removal of different ionic species. Multiple ionic species can be present in natural water sources in addition to sodium chloride, and capacitive deionization (CDI) is an upcoming technology with the potential to address these challenges because of its efficacy in removing charged species from water by electro-adsorption. Lack of potable water in communities across the globe is a serious humanitarian problem promoting the desalination of saline water (seawater and brackish water) to meet the growing demands of human civilization.
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