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2 Ways of How to Decrease The Salinity and The Explanations

by Rezha Ariffianta

salinityThe planet of earth that we live on now consists more water territory or we may say that the number of seas on the earth are more than the mainland. The water territory especially the seas are not only unlimited resources, but also as the places to live for some creatures on the earth. It is important to know that not all creatures can survive in the deepest sea. Only certain animals and plants can be found in the bottom of the sea.

Until now, the seas still keep a lot of mysteries in it. One of the mysteries is that the sea is always salty. Do you know that each seas has different salinity? It surely depends on the geographical and topographical condition. There are a lot of factors that affect salinity in each areas. One of it is evaporation. That’s why the seas in the equator region mostly have higher salinity than the one in the subtropical region.The sea which has the highest salinity in the world is Te Red Sea. While the seas with the lowest salinity in the world is the one in the north side of Bothnia Gulf the one in the east side of Finlandia Gulf.

As mentioned above that not all creatures can adapt the sea water. This is because of high salinity which can’t be consumed especially for human. However, as the time goes on, people start thinking to find another way so that the sea water can be consumed and to substitute the water that has been consumed so far. Then, how to decrease or even remove the salt of the sea water? And the next, how the sea water can be consumed by human?

The process of removing the salt from the sea water then finally it can be consumed, called as desalination. The outcome of desalination process is the water with salinity less than 500 mg/i which is appropriate domestic, agriculture and industry. The other outcome of desalination process called as brine. Brine is high concentrated salt solvent up to 35.000 mg/i protracted salt. We will explain how to decrease the salinity of the sea water.

1. Distillation

One of the ways to decrease the sea salinity is distillation. This is the most used and the first. Distillation method is done by boiling the sea water till evaporating. The fumes will have condensation and becomes clean water. There are some distillation processes, those are multistage flash, multiple effect distillation, and vapor compression that commonly use principle of decreasing the steam pressure of water so that the boiling can happen in a low temperature without any additional burning. In this case, there is a substance separation based on the evaporation differences and speed.

2. Using membrane

The other way to do it is by using membrane. At least, there are 2 kinds of membrane those are used for distillation process, those are Reverse Osmosis (RO) and Electrodialysis (ED). Desalination process using RO membrane is a technology from osmosis. Scientifically, osmosis is a process of a solvent molecule that will flow from low solute area to high solute passing by a semipermeable membrane. Semipermeable membrane is cell membrane. The solvent movement will go on till getting balance in the 2 sides of membrane. While Reverse Osmosis, we can say it as a coercion of a solvent in a high concentrated area to passing by membrane to a low solute area using a coercion which is more than osmotik coercion.

Reverse osmosis is encouraging solution to get through the filter that trap solute from one side while the other side is pure solvent. Water that contains salt will be filtered from the salt when passing by water – permeable membrane. Next, the result of the filtration will flow by the side of pressurized reactor as brine.

Desalination with Reverse Osmosis (RO)

RO is commonly divided into 4 processes:

  1. Pretreatment: the water is adjusted with membrane by separating the suspended solid, adding inhibitor to control the scaling affected by certain compounds and adjusting the pH.
  2. Pressurization: in this process, the pump will help to increase the pressure to the decoy that had pretreatment process till reaches the pressure as the membrane and water decoy salinity.
  3. Membrane Separation: the water that contains salt or the decoy will pass by the permeable membrane, so that it is only salt which is left in this membrane and allow only desalinated products passing by. This process will make 2 flows, those are fresh water and concentrated brine. However, there will be still a few salt filtered and flow along the membrane of water.
  4. Post Treatment Stabilization: in this last process, the water which was filtered by the membrane should have pH adjustment before being streamed to distribution system especially the one that will be used for consumption. The water will be streamed through aeration column. At this time, pH or the water acidity will be increased from 5 to 7 or neutral pH.

Shortly, reverse osmosis method is encouraging solution which is water of the sea to pass by the filter and trap solute in one side and get the pure solvent in the other side. This method actually has been done since 1970 to process sea water to be fresh water.

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