WO2021212186A1

WO2021212186A1 - Method and system for water treatment

Info

Publication number: WO2021212186A1
Application number: PCT/AU2021/050373
Authority: WO
Inventors: Bartlomiej Piotr KOLODZIEJCZYK; John Andrew Henry FORREST
Original assignee: Fortescue Future Industries Pty Ltd
Priority date: 2020-04-24
Filing date: 2021-04-23
Publication date: 2021-10-28
Also published as: AR121930A1

Abstract

A system for treating water, the system including a water source, and a water treatment plant, wherein the water source is located at an elevated level such that gravitational potential energy of the water at the water source is used for powering the water treatment plant.

Description

METHOD AND SYSTEM FOR WATER TREATMENT

FIELD OF THE INVENTION

The present invention relates generally to the field of water treatment and, more particularly, but not exclusively, to a method and system for using a low or zero carbon emission energy source for powering water treatment by reverse osmosis.

BACKGROUND TO THE INVENTION

Water treatment through reverse osmosis (RO) is well developed and broadly applied globally. Reverse osmosis allows for the removal of the majority of impurities, including the removal of dissolved salts, and as such, it is used in desalination. The applicant has identified that existing reverse osmosis systems require a high applied pressure to overcome osmotic pressure and that this is typically provided by way of a pump which is expensive to provide as well as to power, in addition to generating significant carbon emissions. It would be beneficial for there to be provided a method and apparatus for conducting water treatment through reverse osmosis while providing savings in cost, energy and in carbon emissions.

Prior art document US 2007/0221576 A1 discloses static head reverse osmosis involving locating a reverse osmosis plant in an earth cavity at a depth below ground level. The applicant has identified that locating reverse osmosis in an earth cavity or at a depth is highly impractical, as treated water has to be pumped back to the ground level. In particular, the applicant has determined that the benefits of using static head are neglected by the requirement of using a pump to bring treated water back to the ground level. The document also relies on intensifying static head pressure by using pressure generating means, whereas the present applicant has identified that such an arrangement is sub-optimal.

Publication EP 0764610 A1 discloses a plant for desalting marine water by reverse osmosis, by means of hydrostatic pressure. The document uses marine water which is pumped to an elevated level to be subsequently purified by a reverse osmosis system located at a ground level using means of hydrostatic pressure. The arrangement shown in the document requires a pump and energy to transport water to an elevated tank. The applicant has determined that such an arrangement is inefficient and impractical. Examples of the present invention seek to provide an improved method and apparatus for water treatment which ameliorates or at least alleviates one or more disadvantages of existing water purification systems.

SUMMARY OF THE INVENTION

In accordance with one aspect of the present invention, there is provided a system for treating water, the system including a water source, and a water treatment plant, wherein the water source is located at an elevated level such that gravitational potential energy of the water at the water source is used for powering the water treatment plant.

Preferably, the water source is located at an elevated level relative to the level at which the water treatment plant is located.

Preferably, a reverse osmosis process of the water treatment plant is powered solely by the gravitational potential energy in the water at the water source. More preferably, the water treatment plant is a reverse osmosis plant and pressure from a head of the water from the water source powers the reverse osmosis process of the water treatment plant.

In a preferred form, the system includes a conduit from the water source to the water treatment plant for feeding water from the water source to the water treatment plant. More preferably, said pressure is from the head of water in the conduit. Even more preferably, said pressure from the water is applied to a reverse osmosis membrane unit of the water treatment plant.

Preferably, the system includes a series of water pipes/conduits that connect separate units/devices in the system.

The system may include a pre-filtration unit.

In a preferred form, the system includes an energy recovery device which is powered from gravitational potential energy in the water from the water source and which powers the reverse osmosis unit of the water treatment plant.

Preferably, the system includes a post-filtration unit. Preferably, the system includes a water storage tank.

Preferably, the water source is a naturally elevated water reservoir for water feedstock.

In a preferred form, the water source is an existing elevated water reservoir for water feedstock, being a structure existing prior to construction of the water treatment plant. As such, the site may be chosen to have a water source specifically fitting this criteria prior to location and construction of the water treatment plant.

Preferably, the water source is an artificially elevated water reservoir for water feedstock. More preferably, the water source is a dam. Alternatively, the water source may be in the form of a hydroelectric scheme.

In a preferred form, the water treatment plant is located at or above a ground level.

The system may be powered solely by gravitational potential energy of the water at the water source such that an external power source is not required.

In accordance with another aspect of the present invention, there is provided a method for treating water, including the steps of: providing a water source; providing a water treatment plant relative to the water source such that the water treatment plant is located at a lower level than a level of the water source; and using potential energy of the water at the water source to power the water treatment plant.

Preferably, the method includes the steps of choosing a site according to the criteria of having an existing water source at an elevated height relative to ground level; and subsequently constructing a water treatment plant at the site, at a level below the existing water source and at or above ground level. The invention generally comprises a water source at the elevated height, a pre filtration unit (optional), a reverse osmosis membrane unit, an energy recovery device (optional), post-filtration unit (optional), water storage tank (optional), and a series of water pipes/conduits that connect separate units/devices in the system.

BRIEF DESCRIPTION OF THE DRAWINGS

Preferred embodiments of the invention will be described, by way of a non-limiting example only, with reference to the accompanying drawings in which:

Figure 1 shows in graph form a relationship between water salinity and osmotic pressure;

Figure 2 shows diagrammatically an example of reverse osmosis desalination plant schematics;

Figure 3 shows one possible configuration of a gravity-driven reverse osmosis desalination plant schematics in accordance with one example of the present invention;

Figure 4 shows rough pressure and elevation range for desalination of brackish and seawater (without an energy recovery device) - the dashed line corresponds to a direct relation between the two parameters. For the purpose of the calculations, water density is assumed to be 1,000 kg/m³, and acceleration of gravity is 9.81 m/s²; and

Figure 5 shows reverse osmosis performance versus operational parameters (generic membrane example).

DETAILED DESCRIPTION

With reference to the drawings and, in particular, Figure 3 of the drawings, there is provided a system 10 for treating water, the system 10 including a water source 12, and a membrane unit 14. The water source 12 is located at an elevated level such that gravitational potential energy of the water at the water source 12 is used for powering the membrane unit 14. The water source 12 at the elevated level may be in the form of a dam situated at an elevated ground level.

More specifically, the water source 12 is located at a level elevated relative to a level at which the membrane unit 14 is located.

The membrane unit 14 may be in the form of a reverse osmosis unit, as shown in Figure 3 of the drawings. In this example, a reverse osmosis process of the membrane unit 14 is powered solely by the gravitational potential energy in the water at the water source 12. Specifically, the membrane unit 14 is a reverse osmosis plant and pressure from a head of the water from the water source 12 powers the reverse osmosis process of the membrane unit 14.

The system 10 includes a conduit 16 from the water source 12 to the membrane unit 14 for feeding water from the water source 12 to the membrane unit 14. More preferably, the pressure is from the hydraulic head 18 of water in the conduit 16. The pressure from the hydraulic head 18 is applied to a reverse osmosis membrane unit of the membrane unit 14 so as to power the reverse osmosis process.

As shown in Figure 3, the system 10 includes a series of water pipes/conduits that connect separate units/devices in the system. In particular, the system 10 includes the conduit 16 from the water source 12 to a pre-filtration unit/device 20, then a waterpipe/conduit 22 from the pre-filtration unit/device 20 to an energy recovery device 24.

The energy recovery device (ERD) 24 may be powered from gravitational potential energy in the water from the water source 12 and powers the reverse osmosis unit of the membrane unit 14.

The system 10 may also include a post-filtration unit, and possibly also a water storage tank. A conduit 26 feeds water from the energy recovery device 24 to the reverse osmosis unit. The reverse osmosis unit has a collection conduit 28, as well as a return conduit 30 which returns high pressure concentrate to the energy recovery device 24.

Optionally, membrane unit 14 can be connected to post-treatment unit 32 (i.e., pH adjustment) through conduit 34 before discharging permeate through a collection conduit 28.

Accordingly, there is also provided a method for treating water, including the steps of providing a water source 12, providing a membrane unit 14 relative to the water source 12 such that the membrane unit 14 is located at a lower level than a level of the water source 12, and using potential energy of the water at the water source 12 to power the membrane unit 14. The applicant has identified that the pressure used to force the fluid movement through reverse osmosis membranes can be significant and is a function of impurities and/or salts dissolved in treated water. High pressure must be exerted on the high-concentration side of the membrane pressure required for fresh and brackish water treatment is, generally, in the range of 4 to 17 bar, whereas seawater usually requires 40 to 82 bar to overcome a natural osmotic pressure of around 27 to 32 bar. Hypersaline water treatment requires even higher pressures. This high-pressure requirement makes the process both energy and capital intensive (requiring capital expenditure for the high-pressure pump).

Advantageously, the invention described herein relates to the use of natural hydraulic pressure created by the column of water that the applicant has determined is sufficient to perform the reverse osmosis process. The invention can be applied in any setting where water is available at an elevated height - predominantly, but not limited to, hydraulic dams or hydropower schemes, where the invention can be integrated as part of the system allowing for energy and capital savings.

With the emerging hydrogen industry, this energy and capital trade-off can play a major role in reducing the overall cost of generated hydrogen. The continuity of pressure gradient provided by the river run or a dam allows for continuous and uninterrupted operation for the reverse osmosis process. However, a degree of intermittency can also be accommodated by appropriately sizing the treated (reverse osmosis) water storage tank. This invention is not solely limited to the hydrogen industry and can be applied in any setting where elevated water is available. This includes providing clean water for hydropower personnel in remote areas, or various industrial processes attached to and powered by hydroelectric schemes.

Growing water scarcity and threats posed by water security have become a serious issue worldwide and a challenge of great priority. In 2019, the World Economic Forum listed water scarcity as one of the largest global risks in terms of potential impact over the next decade. Ongoing research and development across the globe focus on various attempts to solve this issue by proposing novel approaches and alternatives to purify or desalinate seawater. Water scarcity becomes especially pronounced in arid and semi-arid countries, like Australia. Along with wastewater reclamation and reuse, desalination and reverse osmosis have been adopted as non-conventional water supply methods in water-scarce regions. While both technologies, desalination and reverse osmosis, are mature and commercially available, they require significant energy inputs to treat water. Given growing energy demand, energy security, and costs of energy supply, these energy hungry solutions address the issue of water scarcity but in its place create an energy supply challenge.

Conventionally, reverse osmosis plants use a high-pressure pump, powered by electricity or derived from fossil fuels. More recently, a myriad of approaches have been proposed that replace fossil fuel energy supply with renewable energy sources to generate clean energy to power the high-pressure pump in the reverse osmosis system. While these solutions are more environmentally friendly, they tend to be significantly more expensive and highly intermittent.

The function of the high-pressure pump is to create enough pressure to overcome the natural osmotic pressure of treated water and to send a flux of saline water to a group of semi-permeable membrane modules, where the dissolved salts are separated from the water.

The average salt concentration in seawater is 3.5 %w/w, which corresponds to the osmotic pressure of roughly 27 to 32 bar, see Figure 1.

The reverse osmosis-based system needs to provide enough pressure to overcome the natural osmotic pressure of treated water and enable the flux through the membrane. Because the energy intensity of the process is highly dependent on input water quality, the mean pump energy consumption can vary between 2.5 to 10 kWh/m³.

A traditional reverse osmosis water treatment system 32 equipped with a high- pressure pump 34 powered by an alternating current (AC) source of electricity 36 is shown in Figure 2.

The osmotic pressure of average seawater of 27 to 32 bar corresponds to the hydraulic head of roughly 275 and 327 metres. Generally, supplied pressure must be higher in order to enable the flux through the membrane. This very high elevation gradient has been a limiting factor for gravity-driven reverse osmosis of seawater. While saltwater is abundant, it rarely occurs at an elevated height. Brackish water, however, like that found in river estuaries, has much lower salt concentration, and lower osmotic pressure is required. It is assumed that the osmotic pressure of brackish water in rivers ranges on average between 4 and 17 bar, which corresponds to hydraulic heads of 41 and 174 metres, respectively. This makes gravity-driven reverse osmosis more attainable because natural and artificial rivers and water flows are common throughout the globe.

The use of the energy recovery device 24 recycles the pressure available in the concentrate flow to intensify the feed pressure and significantly reduces the required pressure, and as such, the required elevation can be significantly reduced. The schematics of the gravity-driven reverse osmosis system is shown in Figure 3 and illustrates one possible configuration of a gravity-driven reverse osmosis desalination plant.

Advantageously, the present invention relates to the use of natural or artificial elevation gradient, which results in hydraulic head sufficient to provide a pressure to overcome osmotic pressure and perform reverse osmosis without the need for energy and capital-intensive pump(s). Examples of the invention can be integrated into existing hydropower or artificial dam schemes or used in a setting where the natural landscape provides an elevation gradient between water intake and the reverse osmosis cell. It is estimated that energy costs account for 40% to 47% of the total operating expenses, the majority of which is used by a high-pressure pump to provide enough pressure for reverse osmosis flux. The pump is also a major capital expense component of the reverse osmosis system, and due to its moving parts requires ongoing maintenance. Examples of the present invention are able to operate without the need for an expensive pump, providing cost-savings and significantly reduced requirements for system maintenance.

The invention generally comprises of a water source at the elevated height, a pre filtration unit (optional), a reverse osmosis membrane unit, an energy recovery device (optional), post-filtration unit (optional), water storage tank (optional), and a series of water pipes/conduits that connect separate units/devices in the system.

The invention uses a natural or artificial elevation gradient (hydraulic head) to create sufficient static pressure to desalinate water through a reverse osmosis membrane unit. Water at elevated height is allowed to flow through the specially designed system to a reverse osmosis membrane unit placed at an elevation lower than the water intake. Depending on the system arrangement and available elevation, this can allow for zero energy use for desalination. Optionally, the feed pressure can be intensified by using an energy recovery device (ERD) 24. The energy recovery device 24 allows the use of the pressure in the concentrate stream to intensify the feed pressure and significantly reduce the required elevation.

The provided system operates continuously because it is given continuous water feedstock. The system is also autonomous, self-regulating, and in the majority of instances does not require an external power source. The major drawback of the system is that it relies on elevated water reservoirs, and as such, it can be deployed only if conditions (hydraulic head, elevated water availability, etc.) are correct. The reverse osmosis membrane units are designed for continuous operation. The reverse osmosis unit can be used at full capacity to provide continuous pure water supply. Continuity of the operation also extends the system lifetime and prevents biofouling. The simplicity of the design allows for its installation in remote and off-grid areas, making it advantageous over traditional reverse osmosis systems that rely on a high-pressure pump and external power supply.

Elevated water reservoir

The water treatment system relies on the availability of natural elevation or man made structures of feedstock water reservoirs. Natural elevation examples may include but are not limited to hills, cliffs, and waterfalls, whereas man-made structures may include dams, water towers, aqueducts. In one example, the system is integrated with the existing hydropower dam, and in another example, the small-scale unit is integrated with a water tower.

The elevation of the feedstock reservoir is directly correlated with feedstock water quality and its osmotic pressure. In one instance for brackish water, the elevated water reservoir may be placed at the elevation of 200 metres above the reverse osmosis membrane unit. However, generally, for brackish water, this elevation would be significantly lower. For example, desalination of brackish water with lower salinity than that of seawater may be sufficiently achieved utilising elevations as low as 50 metres between the feedstock inlet and the reverse osmosis membrane unit. The use of an energy recovery device 24 may further reduce this elevation requirement.

Desalination of seawater will often require a feedstock reservoir to be placed at a much higher elevation, in the range of 400 to 600 metres or higher. As such, gravity-driven desalination of the seawater poses significant challenges. Pre-filtration unit

The optional pre-filtration unit/step serves to remove any solid matter, micro- and macro-suspended impurities, and/or impurities of a biological origin. Pre-filtration units are broadly accessible and often incorporated in various water purification and desalination systems. The pre-filtration step extends the life of the reverse osmosis membrane unit and the decision whether or not to incorporate a pre-filtration step is based on the initial water quality evaluation.

Reverse osmosis membrane unit

The reverse osmosis membrane unit is known in the art. The unit contains a specially designed membrane that allows to separate salts (and often other impurities) in feedwater to desalinate this water. The membrane used in such reverse osmosis device is semi -permeable. The desalination process requires application of pressure at least equal, if not higher, to overcome osmotic pressure of the treated water and enable flux through the membrane.

Reverse osmosis process allows only a fraction of the saline water to pass through the membrane and salt being removed. The remainder of the feedstock containing high salt concentration, dubbed “concentrate”, is flushed away. The percentage of saline (concentrate) water to desalinated water is dependent on many parameters, including salinity of the feedstock water, type of the membrane used, the pressure applied, and temperature, among other factors. This ratio is called the recovery ratio. The pressure of the concentrate flow typically is only a couple of bar (typically up to 5 bar) lower than the feed pressure. As such, concentrate flow carries a significant amount of energy that can be reused.

Traditionally, high-pressure at the inlet to reverse osmosis membrane unit is generated by high-pressure pumps that consume significant amounts of energy and are costly. In the present invention, high-pressure comes in the form of hydrostatic pressure produced by the elevated water column. In addition, valuable pressure stored in the concentrate can be reused with the help of the energy recovery device 24. This significantly reduces the inlet pressure and elevation requirement.

Reverse osmosis is the most widely commoditised, cost effective, and lowest energy desalination technology. Reverse osmosis membranes have their limits which can include sensitivity to organics, oxidants, scaling ions, and declining productivity with increasing feedstock water salinity. As the brine concentration increases, flux through the membrane and permeate quality decrease (Figure 5). Using less saline water, i.e., brackish river water poses less limitations, allows for higher flux, higher recovery ratio and extended membrane life.

Energy recovery device

Energy recovery devices are known in the art. The purpose of this device is to harness the high-pressure of the concentrate flow from the reverse osmosis unit. The high-pressure concentrate is high-pressure refuse from the desalination process. Energy recovery devices are generally mechanical systems that, in most of the cases, do not require external energy supply. The energy recovery device is capable of reusing high-pressure from waste concentrate to provide additional pressure for feedstock water and at the same time reducing the power/pressure/height requirement for the desalination process. In one instance, a certain type of commercially available energy recovery device (energy recovery turbine) allows for 30% to 40% energy decrease. In another instance, other types of more costly energy recovery devices (pressure exchanger) may allow for 50% to 60% energy decrease. Energy decrease corresponds to pressure and hydraulic head decrease for water desalination. In one particular case, energy recovery devices using isobaric technology (also called pressure or work exchangers) developed for the desalination industry can recover 98% of the energy in the brine waste stream. This recovered energy is then used to pressurise raw feedstock water, while at the same time reducing the energy input required for the high-pressure feed pumps by up to 60%. For the present invention, such energy recovery device 24 can reduce the pressure and corresponding hydraulic head. Post-filtration treatment

After desalination in the reverse osmosis membrane unit, resulting water may optionally undergo further treatment. The treatment may include but is not limited to the addition of minerals or nutrients to make water suitable for human consumption or further treatment, i.e., deionization to produce ultrapure water for industrial and other uses, i.e., hydrogen generation by proton exchange membrane electrolysis.

Water storage unit

The water desalination system may include an optional water storage unit located at the lower, same or similar elevation to the reverse osmosis membrane unit. The purpose of this storage unit is to store treated water for later use. Alternatively, the treated water may be supplied continuously for direct use.

EXAMPLE - WATER TREATMENT APPLICATION IN HYDROPOWER SCHEME

In one example, the invention can be integrated with a hydropower dam. The dam was built to stop the river flow and create a reservoir for continuous and uninterrupted power generation using hydropower turbines. Calculations have been performed that evaluated water quality and osmotic pressure. It was evaluated that the dam provided sufficient hydraulic head to create static pressure sufficient to overcome the osmotic pressure of available water and enable a flux to perform reverse osmosis. The osmotic pressure of the brackish water in the river and reservoir was estimated to be in the range of 0.8 to 1.4 %w/w, whereas corresponding osmotic pressure was evaluated to be in the range of 4.7 to 8.2 bar, which corresponds to the hydraulic head of 48 to 86 metres (9.81 bar). Given the hydropower scheme had a hydraulic head of 100 metres, the intake of innovative gravity-driven reverse osmosis was installed to have a hydraulic head of 100 metres in order to overcome the osmotic pressure of the water and surplus to enable water flux through the membrane. For the purpose of calculations, water density is assumed to be 1,000 kg/m³, and acceleration of gravity 9.81 m/s².

Energy from hydropower can be calculated as W = p Vg h-m , where W corresponds to energy in Jules, p is a water density in kilograms per cubic meters, Fis a volume of water in cubic metres, g corresponds to acceleration of gravity (9.81) expressed in metres per second square, h is a hydraulic head in metres, and m is dimensionless efficiency factor and generally ranges between 0.75 to 0.95. For our calculations efficiency (m ) was selected to be 0.92. In 1 cubic metre of brackish river water, it is expected to have around 30% rejection, meaning that roughly 30% of feedstock is a concentrate, which is discarded. The remaining 70% permeate is a pure end product. As such, the total water that enters the reverse osmosis membrane unit is 1.43 cubic metres. Energy from 1.43 cubic metres of water at the hydraulic head of 100 metres and efficiency of 0.92 equals 1,289.3 kJ or 0.36 kWh.

To purify the same amount of water (1.43 m³) in a traditional reverse osmosis system expected energy would be 1.43 to 3.14 kWh (1.0 to 2.2 kWh/m³). Running the same amount of water through the turbine would result in generating enough energy to purify only 11.4 to 25.1 % of this water volume. Running water through a gravity-driven osmosis scheme instead of the hydropower turbine allows for significant energy reduction. A high-pressure pump present in the traditional reverse osmosis system is made redundant, and as such, capital and operational expenditure related to the pump is not required.

The optional use of energy recovery device 24 can significantly reduce the head requirement of this system.

The applicant has identified that the present invention may be of benefit in optimising the value chain for hydrogen production. While single components and systems that collectively form the hydrogen generation value chain have been designed and perfected to run separately at the most optimal conditions, the effort to optimise the value chain has not previously been performed. Examples may include reusing heat energy from the Haber- Bosch process to increase the performance of the electrolyser.

The present invention focusses on the optimisation of water treatment, where pure water is an important feedstock for hydrogen generation via electrolysis. Water treatment via reverse osmosis is well-developed, but it requires high pressure and, as such, is energy- intensive. High pressure pumps are also capital-intensive. The pressure of the water column at sufficient hydraulic head (elevation gradient) overcomes osmotic pressure of the treated water and enables low cost, scalable water purification. The invention is not limited purely to hydropower schemes or hydrogen generation but can be applied in any setting where water treatment is required and elevation gradient available.

Advantageously, the present invention uses natural or artificial (e.g. a dam) elevation gradient for water purification. Previous attempts focused on pumping water directly through the membrane or pumping water to an elevated level to achieve desired hydraulic head and pressure. The present invention also allows optimal energy use with lack of expensive and energy-intensive pump. Advantageously, there is provided the potential to integrate the invention with existing hydropower plants or dams, using a design methodology based on input and desired output water quality and available hydraulic head. Optionally, an energy recovery device 24 may be used for settings with lower elevated water levels.

The present invention may be used as part of a system for generating the lowest cost hydrogen from renewable energy resources, including hydropower.

Examples of the invention may enable a significant cost saving in water treatment. In comparison, if a given volume of water was firstly converted in the hydropower turbine to be later used to power a traditional reverse osmosis system, it would be sufficient to purify only between 17 and 41% of the water (depending on feedstock water quality) otherwise purified using the gravity-based approach.

Advantageously, examples of the present invention provide significant advantages over existing technologies. In particular, examples of the present invention do not use any additional pressure generating means other than hydraulic head (static pressure). Examples of the invention do not require storage of treated water below ground level - rather, water may be stored at or above ground level. In this way, the applicant has found that the present invention provides significant advantages as it does not require the consumption of energy to supplement the process and ought to pump water to ground level.

Examples of the present invention provide feedstock water located at an elevated height, with a reverse osmosis plant located at or above ground level. This approach uses existing dams or hydropower schemes by integrating, in an intelligent and inventive manner, water treatment with dam/hydropower facilities. This approach does not require use of a pump to recover purified water and to bring it to a surface or ground level. Furthermore, the applicant has identified that some existing technologies require drilling of a cavity to accommodate a reverse osmosis system. Drilling deep wells is costly and is obviated by examples of the present invention.

The applicant has also identified that other existing processes use sailing ground or seawater which is pumped to an elevated level to be subsequently purified by a reverse osmosis system located at ground level using means of hydraulic pressure of an elevated water column. Such existing processes require a pump and energy to transport water to an elevated tank. The applicant has identified that this is impractical as the gain of using hydraulic pressure for desalination is outweighed by the energy spent on pumping water to an elevated level. Advantageously, with examples of the present invention, a pump or external energy source is not required as water is not pumped to an elevated level (an externally powered pumping system is not needed). In accordance with examples of the present invention, water starts from an elevated level of a natural or artificial reservoir, dam or hydroelectric scheme making the system significantly different and more practical. Integration of a desalination system/water treatment with a hydroelectric plant is new and has not been disclosed or suggested by the prior art.

While various embodiments of the present invention have been described above, it should be understood that they have been presented by way of example only, and not by way of limitation. It will be apparent to a person skilled in the relevant art that various changes in form and detail can be made therein without departing from the spirit and scope of the invention. Thus, the present invention should not be limited by any of the above described exemplary embodiments.

The reference in this specification to any prior publication (or information derived from it), or to any matter which is known, is not, and should not be taken as an acknowledgment or admission or any form of suggestion that that prior publication (or information derived from it) or known matter forms part of the common general knowledge in the field of endeavour to which this specification relates.

Claims

THE CLAIMS DEFINING THE INVENTION ARE AS FOLLOWS:

1. A system for treating water, the system including a water source, and a water treatment plant, wherein the water source is located at an elevated level such that gravitational potential energy of the water at the water source is used for powering the water treatment plant.

2. A system for treating water as claimed in claim 1 , wherein the water source is located at an elevated level relative to a level at which the water treatment plant is located.

3. A system for treating water as claimed in claim 1 or claim 2, wherein a reverse osmosis process of the water treatment plant is powered solely by the potential energy in the water at the water source.

4. A system for treating water as claimed in claim 3, wherein the water treatment plant is a reverse osmosis plant and pressure from a head of the water from the water source powers the reverse osmosis process of the water treatment plant.

5. A system for treating water as claimed in any one of claims 1 to 4, wherein the system includes a conduit from the water source to the water treatment plant for feeding water from the water source to the water treatment plant.

6. A system for treating water as claimed in claim 5 when dependent on claim 4, wherein said pressure is from the water in the conduit.

7. A system for treating water as claimed in claim 6, wherein said pressure from the water is applied to a reverse osmosis membrane unit of the water treatment plant.

8. A system for treating water as claimed in any one of claims 1 to 7, wherein the system includes a series of water pipes/conduits that connect separate units/devices in the system.

9. A system for treating water as claimed in any one of claims 1 to 8, wherein the system includes a pre-filtration unit.

10. A system for treating water as claimed in any one of claims 1 to 9, wherein the system includes an energy recovery device which is powered from potential energy in the water from the water source and which powers the reverse osmosis unit of the water treatment plant.

11. A system for treating water as claimed in any one of claims 1 to 10, wherein the system includes a post-filtration unit.

12. A system for treating water as claimed in any one of claims 1 to 11, wherein the system includes a water storage tank which stores treated water.

13. A system for treating water as claimed in any one of claims 1 to 12, wherein the water source is a naturally elevated water reservoir for water feedstock.

14. A system for treating water as claimed in any one of claims 1 to 12, wherein the water source is an existing elevated water reservoir for water feedstock, being a structure existing prior to construction of the water treatment plant.

15. A system for treating water as claimed in any one of claims 1 to 12, wherein the water source is an artificially elevated water reservoir for water feedstock.

16. A system for treating water as claimed in claim 14 or claim 15, wherein the water source is a dam.

17. A system for treating water as claimed in claim 14 or claim 15, wherein the water source is a hydroelectric scheme.

18. A system for treating water as claimed in any one of claims 1 to 17, wherein the water treatment plant is located at or above a ground level.

19. A system for treating water as claimed in any one of claims 1 to 18, wherein the system is powered solely by gravitational potential energy of the water at the water source such that an external power source is not required.

20. A method for treating water, including the steps of: providing a water source; providing a water treatment plant relative to the water source such that the water treatment plant is located at a lower level than a level of the water source; and using potential energy of the water at the water source to power the water treatment plant.

21. A method for treating water as claimed in claim 20, including the steps of choosing a site according to the criteria of having an existing water source at an elevated height relative to ground level; and subsequently constructing a water treatment plant at the site, at a level below the existing water source and at or above ground level.