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From the sea to your house: post-treatment of desalinated water

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Even after water has passed through reverse osmosis membranes, it still requires treatment before it can be sent to your tap. We provide a brief explanation of these processes below.

Desalinating water is a difficult process that requires a great deal of elements and details to be controlled. Although a large part of the work revolves around converting sea water (or another source of saltwater) into fresh water, this isn’t the final step in the desalination process. For desalinated water to be apt for human consumption, it still needs to pass through the post-treatment phase, which aims to give the water the chemical characteristics required for it to be drinkable.

Desalinated water is so pure that it is lacking in minerals that are good for your health, meaning it needs further processing to add these minerals in.

Desalinated water is very pure water, which is almost completely devoid of any dissolved salts or micro-organisms. This is a result of having passed through a meticulous pre-treatment process, which generally includes physico-chemical processes followed by filtration (through sand filters or micro-filtration/ultra-filtration membranes), prior to a reverse osmosis process, where the water is passed through a semi-permeable membrane that essentially permits the passage of water molecules while blocking compounds with a larger molecular size and dissolved ions.

post-treatment of desalinated water

However, many of the mineral components that are removed during reverse osmosis are actually good and even necessary for drinking water. In addition, this desalinated water is corrosive because of its low pH and the absence of the absorption potential of carbon-based molecules that are usually found in natural water. As such, all desalinated water must go through a post-treatment process to resolve its mineral deficiencies and slightly adjust its pH to make it more alkaline.

The post-treatment phase generally includes two processes: first, remineralisation together with reducing its corrosive properties, and then disinfection.

The techniques used for remineralisation aim to increase the calcium hardness and alkalinity of the desalinated water to make the remineralised water stable when it is released into nature or water distribution networks. There are various ways to remineralise desalinated water. However, those used most often in practice are remineralisation with calcium carbonate and carbon dioxide, and with calcium hydroxide and carbon dioxide.

Next, disinfection consists of adding chlorine, sulphuric acid or other chemical agents that can help to eliminate micro-biological material that managed to pass through the membranes or could have found their way into the stored desalinated water, ensuring that it meets with drinking water standards required for public distribution.

Every Abengoa dealination plant follows the same rigorous advanced post-treatment processes, ensuring the release of quality water that complies with the most demanding standards in the sector.

Catie Romero Finger, Marketing and communication manager for Abengoa Water.

Catie Romero Finger,
Marketing and communication manager for Abengoa Water.

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