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Introduction. High chloride and nitrate concentrations in groundwater hinders the use of these water resources for drinking water or irrigation purposes [1, 2]. Commercial desalination techniques result often in full desalination leading to the need of remineralisation as post-treatment. Monovalent selective desalination is an emerging technology which reduces mainly monovalent impurities by remaining important polyvalent substances as calcium and magnesium in the water [3].
Experimental/methodology. The monovalent ion selective desalination is performed by using a lab-scale and pilot-scale plant from DEUKUM GmbH and elkoplan staiger GmbH (Figure 1) with synthetic and realistic groundwater from Nienburg with nitrate concentrations >50 mg/L and Langeoog with chloride concentrations >250 mg/L. Within the joint project innovatION [4], we test the influence of process parameters as voltage and flow rate (2-100 L/h) as well as the build-up of the cell with different self-made monovalent selective ion exchange membranes and a nanofiltration membrane supplied by FUMATECH BWT GmbH and Leibniz Institute of Polymer Research Dresden, Germany on the desalination performance and energy efficiency.
Results and discussion. Increasing the voltage (0.8-3.6 V) leads to higher reduction of chloride and nitrate, whereby the reduction of sulphate is depending on the specific characteristics of the build-up of the cell and the used membranes. Monovalent ions can be reduced up to 20-folds more than polyvalent ions. The energy efficiency depends highly on the electrical resistance of the membrane and desorption process of the membrane capacitive desalination resulting in a specific energy consumption of <1 kWh/m³.