Ramato Ashu Tufa

Potential of brackish water and brine for energy generation by salinity gradient power-reverse electrodialysis (SGP-RE)

In the present work, a salinity gradient power-reverse electrodialysis (SGP-RE) unit was tested for the production of electrical energy by exploiting the chemical potential of real brackish water and exhaust brine from a solar pond. A cross-flow SGP-RE module (REDstack B.V.), equipped with AEM-80045 and CEM-80050 membranes specifically developed by Fujifilm Manufacturing Europe B.V. within the EU-funded project REAPOWER (“Reverse Electrodialysis Alternative Power Production”), was able to generate a maximum power density (expressed in W m−2 membrane pair – MP) of 3.04 W m−2 MP when operated with pure NaCl aqueous solutions (0.1 M in low concentration compartment – LCC, 5 M in high concentration compartment – HCC) at 20 °C and at a recirculation rate of 20 L h−1. However, a drastic reduction to 1.13 W m−2 (−63%) was observed when feeding the SGP-RE unit with artificial multi-ion solutions mimicking real brackish water and exhaust brine. Further experimental activity allowed to identify Mg2+ ion as responsible for the significant increase in stack resistance and consequent depletion in SGP-RE performance. Therefore, specific softening treatments of the real solutions should be considered in order to maintain the process efficiency at practical level.

3.8 Membrane-Based Processes for Sustainable Power Generation Using Water: Pressure-Retarded Osmosis (PRO), Reverse Electrodialysis (RED), and Capacitive Mixing (CAPMIX)

Salinity gradient energy, a clean and renewable energy, is generated by mixing two solutions of different salinities. Membrane-based systems allow the capture of salinity gradient energy from natural and wastewaters. Emerging processes as sustainable methods for capturing salinity gradient energy involve pressure-retarded osmosis, reverse electrodialysis, and capacitive mixing. The theoretical principles, research developments, and applications of each system are presented together with the challenges and technology outlook.