**2. Reverse osmosis (RO)**

Reverse osmosis is the reversal of a process that occurs naturally named osmosis. Osmosis occurs when two solutions with different concentrations are separated by a semipermeable membrane (**Figure 2**).

In such circumstances, there is a natural tendency to achieve the chemical equilibrium. Thus, the solvent crosses the membrane from the side of less concentration to the other side until the concentrations on both sides are the same. To reverse this natural tendency, a pressure (higher than the osmotic pressure) must be exerted on the side originally with higher concentration. This is what is done to achieve

**67**

**Figure 4.**

*Electrodialysis membrane configuration. Source [1].*

*A Reverse Osmosis and Electrodialysis System Simultaneously Powered by Gravitational…*

desalination by reverse osmosis and why, generally, there is a high specific energy

In this chapter, an alternative RO system powered by wind and gravitational potential energy (GPE) is proposed. The proposed system would basically replace the high-pressure circulation pump shown in the configuration of **Figure 3**.

The scientific principle that sustains electrodialysis (ED) is the electrical attractions between ions and electrodes of opposite electric charge. This phenomenon suits desalination since the dissolved particles in salted water are electrically charged (positive and negative ions). In ED desalination selective membranes are used to "sift" the ions. Some retain the positive ions and allow the negative ones to pass through, while others perform with the inverse characteristic. Membranes with inverse characteristic are placed alternately between the positive and negative electrodes. This configuration yields two separate outlet fluxes, drinking water, and brine. **Figure 4** depicts a conventional ED desalination module. ED is mostly used

consumption. **Figure 3** shows a schematic of a RO desalination plant.

*DOI: http://dx.doi.org/10.5772/intechopen.91135*

*Scheme of a reverse osmosis desalination plant.*

**3. Electrodialysis**

**Figure 3.**

to desalinate brackish water.

**Figure 2.** *Fluxes by osmosis and by reverse osmosis.*

*A Reverse Osmosis and Electrodialysis System Simultaneously Powered by Gravitational… DOI: http://dx.doi.org/10.5772/intechopen.91135*

#### **Figure 3.**

*Electrodialysis*

in kWh/m3

**Figure 1.**

**2. Reverse osmosis (RO)**

*Simplified scheme of a desalination unit.*

semipermeable membrane (**Figure 2**).

. Among all desalination processes, we will briefly describe the reverse

Reverse osmosis is the reversal of a process that occurs naturally named osmosis. Osmosis occurs when two solutions with different concentrations are separated by a

In such circumstances, there is a natural tendency to achieve the chemical equilibrium. Thus, the solvent crosses the membrane from the side of less concentration to the other side until the concentrations on both sides are the same. To reverse this natural tendency, a pressure (higher than the osmotic pressure) must be exerted on the side originally with higher concentration. This is what is done to achieve

osmosis process for it is the one used with the system proposed in this chapter.

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**Figure 2.**

*Fluxes by osmosis and by reverse osmosis.*

*Scheme of a reverse osmosis desalination plant.*

desalination by reverse osmosis and why, generally, there is a high specific energy consumption. **Figure 3** shows a schematic of a RO desalination plant.

In this chapter, an alternative RO system powered by wind and gravitational potential energy (GPE) is proposed. The proposed system would basically replace the high-pressure circulation pump shown in the configuration of **Figure 3**.
