Caustic Soda by Sea Water Desalination


Caustic Soda by Sea Water Desalination

10 Sep 2018

Caustic Recovery Plant – Water crisis around the world has given rise to different wastewater recycling treatment – be it obtaining fresh water from industrial waste or seawater or brackish water. One of the most popular methods is the seawater desalination. There is a lot of confusion around the word desalination – such as whether it’s a method to separate freshwater from seawater or a method to remove salt from seawater. Well, the main goal of desalination (also knowns as desalting) is both to recover freshwater from seawater or salt water and also the separation of salt from seawater. The reason behind this confusion because the increasing demand for water and people here are only concerned about the byproduct and not about the process. The demand for fresh water is increasing day by day all because of the rising population, use of the fresh water at a large scale, usage and pollution of fresh water by domestic and industrial sector, increasing climate fluctuation, etc. are some of the major aspects that are influencing the water scarcity across the globe. Not only this even the agriculture industry has added to the increasing demand for fresh water for agriculture. Many countries are using both groundwater and seawater for irrigation. In fact, water scarcity is said to be one of the biggest issues the world is facing today.

When it comes to seawater, the proportion of salt to fresh water is 3.5% to 96.5%. And the salt which is separated from the seawater is used in chemical industries for producing caustic soda and soda ash. Not only this, the chemical plants develop brine (feed water) by combining salt and demineralized water. And hence, it can be said that the chemical industries are the largest consumer of the sea as well as fresh water. As industry plants are generally situated on the banks of rivers or seas, they use desalinated and demineralized water for boilers and cooling towers. The increase in the usage of seawater is due to the scarcity of groundwater or drinking water where the industrial sector consumes the largest amount.  Sodium chloride or salt what we eat is a byproduct of solar evaporation of seawater and today there are systems that can produce caustic soda by giving out both the freshwater and sodium chloride. The new systems can produce brine as well as fresh drinking water directly from seawater. The brine is further processed to be used for membrane filtration systems (be it ultrafiltration, nanofiltration,reverse osmosis, etc.) and can be used for the production of caustic soda. Before few years, solar salt was used to produce brine for membrane filtration systems. But as the production of solar salt is a very slow process and even when brine is obtained as a byproduct it does need a thorough purification for the production of caustic soda. This kind of purification system produces large amounts of waste and to overcome this a new system called Zero Liquid Discharge – a desalination process which produces the least amount of waste thereby producing fresh water.

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