Zero Liquid Discharge - Cold process for Desalination of saline waters with Salt Repellent Technique

The world is facing a water crisis. Desalination of seawater is essential, but current methods, like distillation and reverse osmosis, create pollution in the form of leftover salty water.  Super saline wastewaters from industries pose an additional problem. The Salt Repellent Technique offers a revolutionary solution.

(For simplicity, the term ‘seawater’ denotes all types of saline waters including RO, nano and super saline wastewaters).

When seawater freezes, ice forms, but salt gets trapped inside. Traditional methods to wash away this salt are not cost-effective. We use special substances called repellents. In small amounts These repellents force the salts away from water molecules, creating pure ice.

The process is explained in these steps:

1. Water is the solvent for all the salts in seawater.
2. In ethanol, the Repellent, most of the salts are sparingly soluble. 
3. Water and ethanol are easily miscible and give a clear solution. 
4. Due to the presence of ethanol in water, all the salts are repelled away from water molecules.    
5. By cooling water to between -4°C to -10°C, the water alone is solidified as pure solid ice, leaving behind all salts in the remaining water, as concentrated brine.

The ice- brine slurry is centrifuged to get desalted ice which on warming, gives desalted water.

Seawater is filtered under vacuum   to remove air and impurities, mixed with repellents, cooled to -10°C, to get salt-free ice slurry. From this, the ice crystals are separated by centrifuging and the ice is warmed to get pure potable water. The desalting step is repeated on the leftover salty water to get more clean water and a higher yield of 70% of desalted water. A flowsheet of the above operations is furnished below