Technology solutions to change…

The Energy of change

Technology solutions to change…

Basic Principle of Reverse Osmosis


We have often heard people talk about reverse osmosis and its importance in the water desalination process, but what is this process and what is its origin?

Osmosis is a natural phenomenon that consists of a solvent (for example, water) passing through a membrane, that is, a barrier that only allows the solvent to pass through and not solutes or salts that this might contain (figure a and b).

Osmosis inversaFigure 1. Diagram of different osmotic processes.

Osmotic pressure takes place naturally and spontaneously.

Let’s take for example a container. We divide it with a membrane or semipermeable barrier so that there’s no type of contact between the two parts of the container. Now we put distilled water on one side of the membrane and, on the other, water with some kind of dissolved solute (salt, sugar, etc.) so that both are at the same level. As time passes, we will note that the level of the container with distilled water has dropped by the same amount that the level in the container with salt (figure b) has gone up, owing to the passage of water, and only water, through the membrane. This height difference generates a pressure difference that is known as osmotic pressure , which takes place naturally and spontaneously.

Currently, reverse osmosis technology desalinates at a lower energy cost per cubic meter of water.

If, however, you want to facilitate the flow in the opposite direction (from the more concentrated solution to the most diluted), it is necessary to apply hydraulic pressure (Force P) which has to overcome the osmotic pressure and the natural flow of the water through the membrane (figure c and d). Specifically, this is the phenomenon that takes place, for example, in a desalination plant where salt-free water is obtained by applying pressure to it, causing it to pass through the semipermeable membrane.

In broad strokes, this is the basic principle of reverse osmosis, which is a mature technology that currently desalinates at a lower energy cost per cubic meter of water, and which only needs electrical energy to work.

Juan Pablo Pocostales, Abengoa Water.

Juan Pablo Pocostales,
Abengoa Water.

Leave a comment

Leave a Reply

Your email address will not be published. Required fields are marked *


Abengoa ensures the confidentiality of the information provided by you through this form and with the purpose solely and exclusively of answering your questions or suggestions. Abengoa guarantees that this information will not be provided to third parties in any case. Pursuant to the provisions set forth in Spanish Organic Law 15/1999 of 13 December on the Protection of Personal Data and in the European Data Protection Regulation (2016/679), we hereby inform you that you may exercise your rights of access, rectification, cancellation, opposition, portability and limitation by sending a letter with the reference "Protection of Data" stating your request, along with a copy of your National Identity Document, to or

Likewise, you may contact the Company's DPO “Data Protection Officer” to clarify any question you may have concerning the treatment of your personal data.

Abengoa S.A. is the company responsible for the treatment of your personal data with address in Campus Palmas Altas, Calle Energía Solar 1, 41014 Seville, Spain.

Most read posts