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Established desalination processes, such as reverse osmosis or thermal processes, do not work selectively and require large amounts of energy. In the case of reverse osmosis, sufficient energy must be applied to overcome the osmotic pressure and, in the case of thermal processes, the energy required for evaporation. An alternative technology for treating slightly saline groundwater (TDS < 5 g/L) is membrane-assisted capacitive deionisation (MCDI), in which ions adsorb on opposing electrodes by applying an electric field. By reversing the electric field, the ions are desorbed again and retained in the flow channel by the respective ion exchange membrane. One advantage of MCDI is the low energy requirement, which depends on the quantity of ions removed.
The joint project innovatION (BMBF 02WV1572A) has set the goal of developing a monovalent selective MCDI (mMCDI) using selective materials and testing it on a laboratory and pilot scale. The monoselectivity means that energy only has to be applied to the ions that are actually removed and the product water does not have to be re-enriched for further use, e.g. for drinking water production or groundwater recharge.
The development of the system is accompanied by flow and process modelling. The flow model is used to analyse the cells and stacks from several cells in the laboratory and pilot plant in terms of flow loss and flow rate.