AQUAbibe Watermakers

Basics of
Seawater Desalination

Basics of Seawater
Desalination

The development of reverse osmosis (RO) lasts back into the 1950th and was initially applied to the desalination of seawater and brackish water.
Over the years the RO technology became more and more attractive because of increasing demands on the industry to safe fresh water.

Over the years the RO technologies became more and more robust and with the introduction of the even today still available RO filter systems in the late 1970th, the seawater desalination with reverse osmosis and nanofiltration became more and more popular.

AQUAbibe Technology

What is reverse osmosis?

Osmosis is natural process in biological systems, where the biological membranes are semipermeable. This means, that these membranes are impermeable to larger and polar molecules (ions or proteins) and at the same time these membranes are permeable to non-polar or hydrophobic molecules loke oxygen.

Water molecules are transported into or out of cells, i.e. Osmosis is responsible for the ability of plant roots to draw water from the soil.

In Figure 1 the principle of Osmosis is shown. When you have a container, which is separated into two compartments by a semipermeable membrane, and you fill in both parts fresh water, then the water molecules pass through the membrane in both direction and nothing will happen. If you have in one compartment a higher concentrated solution (i.e. seawater), then the molecules from the fresh water side (diluted solution) will pass through the membrane only. Therefore, the water level will drop and the water level on the concentrated solution side will rise until there is an equilibrium by the osmotic pressure (by the increased water level) on the concentrated side and the tendency of the molecules on the diluted side to move through the semipermeable membrane.

Figure 1 Schematic Physics of Osmosis

Figure 2 Schematic Physics of Reverse Osmosis (RO)

The mentioned osmotic pressure is the key parameter, which is used during the reverse osmosis process. As soon as the pressure on the concentrated solution compared to the pressure on the diluted solution side is increased by an external pressure, the pure solvent is pressed through the semipermeable membrane from the high concentration to the low concentration side (Figure 2).

This Reverse Osmosis process is used in all currently available seawater desalination plants. It is independent of the size of the system.

Watermaker Set Up

All watermakers in the market are using the RO process as described previously. In Figure 3 a standard set up of your AQUAbibe watermaker in your boat is shown.

There is a high-pressure pump, which is creating the pressure of the Feed Flow (Seawater), which goes directly into the RO membranes. On the other side of the membranes a high-pressure valve is located, which is used to adjust the pressure in the membrane. The standard operating pressure is 55 bar (800PSI).

With this setup a small percentage (up to 15%) of the pumped Seawater flow passes through the membranes as fresh drinking water. The remaining volume of app. 85% of the seawater is called Brine and is discharged back to the sea.

With several valves you can operate the flow and divert the fresh water to your boat tank. You can also use other valves to pickle your system, so you can make sure, that you can store your boat for several months without harming your watermaker.

Figure 3 Schematic process of Reverse Osmosis Seawater Desalination