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.
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).
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.
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
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