Technologies Within Our Scope

Salinity Gradient Technologies

Last updated: September 2020

Authors: Jesús N. Hernández – Pérez1, Mateo Roldan – Carvajal2, Eduardo Joel López – Torres3

Organizations: ESIQIE – Instituto Politécnico Nacional1, Mexico; Universidad Nacional de Colombia – Sede Medellín2, Colombia; Centro Mexicano de Innovación en Energía del Océano3, Mexico

Salinity gradient energy (SGE) is available in the mixing of two water streams whit different salinity [1,2,3,4]. In general, their concentration gradient is proportional to the available energy [1,2,3]. This form of energy is widely distributed throughout the planet in natural systems as deltas, estuaries, and coastal lagoons [1,5]. Figure 1 shows the ocean surface salinity recorded by NASA. In the American continent, the highest levels of salinity are found in tropical areas; the higher salinity gradients are found in the region of the Gulf of Mexico and the Caribbean Sea, as well as the western coast of Brazil.

Figure 1. Surface salinity of the oceans throughout the world as of April 2019. The colors of the ocean represent the relative salinity (the bar indicates the salinity level in UPS).
Recovered from https://salinity.oceansciences.org/data-maps.htm

To take advantage of saline gradients, different ways of converting part of the released energy into a practical form of energy have been studied. The most developed are the membrane-based technologies: Pressure Retarded Osmosis (PRO) and Reverse Electrodialysis (RED, analogous to the widely known desalination technologies: Reverse Osmosis and Electrodialysis, respectively.

To convert part of the mixing Gibbs free energy (∆𝐺𝑚𝑖𝑥) into electricity, PRO key components are an osmotic membrane, a pressure exchanger, and a turbine (Figure 2).

Figure 2. Schematic representation of the pressure retarded osmosis processes.

 Conversely, RED is an electrochemical technique composed of an arrangement of ion exchange membranes in which the generated ionic flux is converted to electricity through redox reactions at the electrodes [1,2,3,4,6,7,8,9]. Figure 3 shows a diagram of the basic operation of a reverse electrodialysis stack.

Figure 3. Schematic representation of the reverse electrodialysis unit.

In the operation stage, SGE technologies are non-GHG emitting processes that follow the water cycle of ecosystems, naturally levelling salinity levels.

Research Institutes in Pan-America

  • Universidad Nacional de Colombia, Colombia
  • Universidad del Norte, Colombia
  • Universidad de Antioquia, Colombia
  • Universidad Nacional Autónoma de México, México
  • Instituto Politécnico Nacional, México
  • Centro Mexicano de Innovación en Energía del Océano (CEMIE-Oceáno), México

Note: If you would like to see your research in this list, please let us know by contacting us via emaill to tattiana@pamec.energy.


[1]  Anderson, T. R., Hawkins, E., Jones, P. D. (2016). CO2, the greenhouse effect and global warming: from the pioneering work of Arrhenius and Callendar to today’s Earth System Models. Endeavour, 40 (3). http://dx.doi.org/10.1016/j.endeavour.2016.07.002 

[2]  Reyes-Mendoza, O., Alvarez-Silva, O., Chiappa-Carrara, X., Enriquez, C., (2020).  Variability of the thermohaline structure of a coastal hypersaline lagoon and the implications for salinity gradient energy harvesting. Sustainable Energy Technologies and Assessments, 38 (100645). https://doi.org/10.1016/j.seta.2020.100645 

[3]  Post, J. W., Veerman, J., Hamelers, H. V. M., Euverink, G. J. W., Metz, S. J., Nijmeijer, K., Buisman, C. J. N., (2007). Salinity-gradient power: Evaluation of pressure-retarded osmosis and reverse electrodialysis. Journal of Membrane Science, 288, 218 – 230. 10.1016/j.memsci.2006.11.018 

[4]  Pawlowski, S., Crespo, J., Velizarov, S., (2016).  Sustainable Power Generation from Salinity Gradient Energy by Reverse Electrodialysis. In: Ribeiro A., Mateus E., Couto N. (eds) Electrokinetics Across Disciplines and Continents. Springer, Cham. https://doi.org/10.1007/978-3-319-20179-5_4 

[5]  Pattle, R. E., (1954). Production of Electric Power by Mixing Fresh and Salt Water in the Hydroelectric Pile. Nature, 174, 660. 

[6]  Veerman, J., Saakes, M., Metz, S. J., (2010). Reverse electrodialysis: evaluation of suitable electrode systems. Journal of Applied Electrochemistry, 40, 1461 – 1474. 10.1007/s10800-010-0124-8

[7]  Tedesco, M., Brauns, E., Cipollina, A., Micale, G., Modica, P., Russo, G., Helsen, J., (2015).   Reverse Electrodialysis with saline waters and concentrated brines: a laboratory investigation towards technology scale-up. Journal of Membrane Science, 492, 09 – 20. https://doi.org/10.1016/j.memsci.2015.05.020 

[8]  Ortiz-Imedio, R., Gomez-Coma, L., Fallanza, M., Ortiz, A., Ibañez, R., Ortiz, I., (2019). Comparative performance of Salinity Gradient Power-Reverse Electrodialysis under different operating conditions. Desalination, 457, 8 – 21. https://doi.org/10.1016/j.desal.2019.01.005 

[9]  Scialdone, O., Albanese, A., D’Angelo, A., Galia, A., Guarisco, C., (2013). Investigation of electrode material – redox couple systems for reverse electrodyalisis processes. Part II: experiments in a stack with 10-50 cell pairs. Journal of Electroanalytical Chemistry, 704, 1 – 9. http://dx.doi.org/10.1016/j.jelechem.2013.06.001

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