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    Evaluation of reverse electrodialysis (RED) system performance with various compositions of salt solutions for production of salinity gradient energy (SGE)
    (Ege Üniversitesi, Fen Bilimleri Enstitüsü, 2021) Kaya, Tuğçe Zeynep; Güler, Enver
    In this study, the effect of different ions and different types of spacers on salinity gradient power generation by Reverse Electrodialysis (RED) were investigated. The studies were performed in two different sections. The first section includes the studies of co-existing ion effect and the second one contains the studies about spacer effect. In the first section of this paper, the investigation of the effect of different ions in feed solutions was aimed through salinity gradient power generation from concentrate solution of reverse osmosis by RED was performed using different ion-exchange membranes (IEMs). Heterogeneous Ralex AMH-PES, Ralex CMH-PES, homogeneous Neosepta AMX, Neosepta CMX and Fujifilm AEM Type II, Fujifilm CEM Type II and also, custom-made homogeneous CM AESD, CM KESD membranes were used for all studies performed with RED stack, having 3 and 5 membrane pairs. For the preparation of feed solutions, 90wt.% of NaCl salt was mixed with 10wt.% of different salt types of LiCl, KCl, CaCl2, MgCl2 and Na2SO4. The salt ratio of feed solutions was kept constant at 1:30 (g/g). The feed solutions were fed to the RED stack at different flow velocities of 0.208, 0.521 and 0.833 cm/s. So, the effect of monovalent ions (Na+, Li+, K+ and Cl-) and divalent ions (Mg2+, Ca2+ and SO42-) on power generation performance of RED were examined in first section of this report. In the second section of this paper, different spacer types and geometries were tested for eliminating the negative effects such as concentration polarization and shadow effect of inert spacers on the performance of power generation by RED. The studies were performed with homogeneous Neosepta AMX and Neosepta CMX membranes at four different flow velocities (0.208, 0.417, 0.625 and 0.833 cm/s). Firstly, custom-made ion conductive spacers produced by Wroclaw University were used instead of inert spacers. Additionally, Fujifilm AEM Type II and Fujifilm CEM Type II were cut in accordance with spacers and used as spacers in RED stack. And then, the studies performed with different types of spacers were compared with the study carried out with inert spacers. Considering the results obtained in the studies of ion effect, it was observed that the performance of power generation was generally reduced when the divalent ions were added to feed solutions. On the other hand, the effect of monovalent ions on the power generation performance of the RED system was demonstrated differences according to IEMs used in RED stack. In spacer effect studies, the leakage problems were occurred during usage of ion conductive spacers in the RED system. The geometry of ion conductive spacers was changed for the prevention of the leakage. The performance of power generation in the studies performed with ion conductive spacers was obtained lower than that of the studies carried out with inert spacers. As a result of the studies of spacer effect, the maximum power generation was obtained with using the inert spacers. In this context, it was considered that the ion conductive spacers and different spacer geometries should be deeply examined.