**4. The proposed system**

**Figure 5** shows the general configuration of the proposed system which simultaneously desalinates brackish water by RO and ED. The system's primary source of energy is wind power which is harnessed by windmills that pump brackish water to a reservoir at a certain height (less than 20 m). A subsystem (the hydraulic power column (HPC)) uses the gravitational potential energy of the stored water to achieve the necessary pressure (about 15 bar for brackish water) to feed the RO module. Notice that the flux of brine (still at high pressure) exiting the RO module is used to activate the Pelton wheel which, in turn, produces electricity to run the ED module.

**Figure 6** shows the block diagram of the model outlining the hydraulic power column (HPC) where the increase in pressure occurs (from less than 2 bar to over 15 bar). As is technically required for RO and ED, before saline water reaches the membrane modules, it should undergo a pretreatment process to avoid premature malfunction. Cautiously, this feature should be integrated in the system both for the RO and the ED modules.

For seawater desalination, one needs to have an operation pressure of around 55 bar, while for brackish water it is around 20 bar. With the proposed system, this magnitude of pressure is given by a special piston working inside the HPC.

**Figure 7** shows the proposed configuration for the HPC. The model is composed of two HPCs which, separately, can be seen as individual special piston pump. The two individual pumps are connected through a hydraulic automation system in

**Figure 5.** *The hydraulic power column renewable system.*

**69**

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

order to send a continuous flux of salted water to the modules of membrane where

With the system here proposed, to recover the brine energy, a Clark pump is used. It is a kind of flow work device. Brine at high pressure enters the Clark pump, leaves it at atmospheric pressure, and delivers work through a double piston pump.

Calculations have shown [2, 3] that it is possible to reach high pressures with a special piston of moderate dimensions. The counterweight gets the necessary volume of water (GPE) from the reservoir R1 to make the special piston go upward. The system of pulleys is designed so that it yields a reasonable force reduction to lift the piston. When the CW empties, the special piston goes downward, exerting pressure on the water in chamber R3. Consequently water is pumped into the reverse osmosis module under the designed and desired pressure, making reverse osmosis happen. Shortly, during the parallel operation of columns A and B, (see **Figure 7**) there

1.When the piston PB of column B reaches its bottom course, two events occur:

• The bottom of the piston rests on the dampers DP, pressing the fluid inside them. Simultaneously the actuators AC of column A retract due to the signal (fluid under pressure) received from DP, and the piston of that column is

Reciprocally, when the piston of column A reaches its bottom course, two identi-

• The counterweight CW is filled up because valve V5 opens.

The system uses this work to pump water to the top reservoir R1.

*Parallel operation of two hydraulic pressure columns. R1 fed with a windmill.*

The pretreatment of seawater, namely, filtering, is designed to occur by gravity in reservoir R1. After the filtering process, chemicals may be added if necessary. Note that if a reverse osmosis desalination system works with a low recovery rate (e.g., 20%), chemicals may not be needed. Recovery rate is the percentage of drinking water obtained from a volume of sea water that passes the membrane module

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

the desalination occurs.

**Figure 7.**

are the following events:

released.

cal events occur:

(the rest is brine at high pressure).

**Figure 6.**

*The hydraulic power column renewable system.*

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

#### **Figure 7.**

*Electrodialysis*

ED module.

RO and the ED modules.

**4. The proposed system**

**Figure 5** shows the general configuration of the proposed system which simultaneously desalinates brackish water by RO and ED. The system's primary source of energy is wind power which is harnessed by windmills that pump brackish water to a reservoir at a certain height (less than 20 m). A subsystem (the hydraulic power column (HPC)) uses the gravitational potential energy of the stored water to achieve the necessary pressure (about 15 bar for brackish water) to feed the RO module. Notice that the flux of brine (still at high pressure) exiting the RO module is used to activate the Pelton wheel which, in turn, produces electricity to run the

**Figure 6** shows the block diagram of the model outlining the hydraulic power column (HPC) where the increase in pressure occurs (from less than 2 bar to over 15 bar). As is technically required for RO and ED, before saline water reaches the membrane modules, it should undergo a pretreatment process to avoid premature malfunction. Cautiously, this feature should be integrated in the system both for the

For seawater desalination, one needs to have an operation pressure of around 55 bar, while for brackish water it is around 20 bar. With the proposed system, this

**Figure 7** shows the proposed configuration for the HPC. The model is composed of two HPCs which, separately, can be seen as individual special piston pump. The two individual pumps are connected through a hydraulic automation system in

magnitude of pressure is given by a special piston working inside the HPC.

**68**

**Figure 6.**

**Figure 5.**

*The hydraulic power column renewable system.*

*The hydraulic power column renewable system.*

*Parallel operation of two hydraulic pressure columns. R1 fed with a windmill.*

order to send a continuous flux of salted water to the modules of membrane where the desalination occurs.

The pretreatment of seawater, namely, filtering, is designed to occur by gravity in reservoir R1. After the filtering process, chemicals may be added if necessary. Note that if a reverse osmosis desalination system works with a low recovery rate (e.g., 20%), chemicals may not be needed. Recovery rate is the percentage of drinking water obtained from a volume of sea water that passes the membrane module (the rest is brine at high pressure).

With the system here proposed, to recover the brine energy, a Clark pump is used. It is a kind of flow work device. Brine at high pressure enters the Clark pump, leaves it at atmospheric pressure, and delivers work through a double piston pump. The system uses this work to pump water to the top reservoir R1.

Calculations have shown [2, 3] that it is possible to reach high pressures with a special piston of moderate dimensions. The counterweight gets the necessary volume of water (GPE) from the reservoir R1 to make the special piston go upward. The system of pulleys is designed so that it yields a reasonable force reduction to lift the piston. When the CW empties, the special piston goes downward, exerting pressure on the water in chamber R3. Consequently water is pumped into the reverse osmosis module under the designed and desired pressure, making reverse osmosis happen.

Shortly, during the parallel operation of columns A and B, (see **Figure 7**) there are the following events:

1.When the piston PB of column B reaches its bottom course, two events occur:


Reciprocally, when the piston of column A reaches its bottom course, two identical events occur:

	- It is braked by the actuators and will remain in that position until, after filled up with water, it receives the signal sent by the actuators of column A.
	- Its CW empties because valve V6 opens.

An identical process takes place when the piston of column A comes to its upper course.

The hydraulic automatism guarantees the continuous function of the system as long as there is enough water in the reservoirs R1. The continuous flux of salted water to the modules of membrane is guaranteed by the two-way valve V7 that connects the two columns.

So far, a small prototype has been constructed at the polytechnic school of the *Universidade de São Paulo-USP in Brazil*. The prototype has proven that the mechanism of the HPC works. Since osmosis reverse is already a solid technique, the focus of the prototype was not to obtain drinking water because it would not be reasonable to reach 55 bar because of the size of the special piston.

Therefore the objective of the prototype was to prove that the HPC pumps water using the gravitational potential energy obtained from the water in R1 and that the necessary increase of pressure is achieved due to the shape of the special piston. The flux under the pressure exerted by the piston was used to drive a small Pelton wheel supported with magnetic levitation. This was done so, also to prove that the system can be used for electricity generation which is to be used to power the ED module.
