WO2012129604A1

WO2012129604A1 - Method and system for treating water

Info

Publication number: WO2012129604A1
Application number: PCT/AU2012/000322
Authority: WO
Inventors: James Patrick HUNTER; David John PONT
Original assignee: The Water & Carbon Group Pty Ltd
Priority date: 2011-03-29
Filing date: 2012-03-29
Publication date: 2012-10-04
Also published as: AU2012101909B4; AU2012101909A4; AU2012234912A1

Abstract

A system for the treatment of water and a corresponding method is disclosed herein. The system comprises a wetland system planted with plants. The system and method for may be used for the treatment of impure water produced by any one of a mining operation, and domestic and/or industrial water consumption.

Description

METHOD AND SYSTEM FOR TREATING WATER Technical Field

The disclosure generally relates to the treatment of water, and specifically but not exclusively to a system and a corresponding method for the treatment of impure water produced by any one of a mining operation, and domestic and/or industrial water consumption.

Background Art

Impure water may be a waste or by-product of mining operations, domestic and industrial water usage. Coal seam water, for example, can contain contaminants; the coal seam water may have concentrations of sodium chloride up to 8 g L, which is about 16 times more than the typical upper limit for drinking and irrigation, may have a high pH, and may have carbonates, magnesium, hydrocarbons, and toxic BTEX which may be used during a coal seam gas extraction process.

Before coal seam water is released into the environment it may be treated to reduce environmental impacts such as soil salinity, and the pollution of surface and ground water. Similarly, the water may be treated before domestic, agricultural and industrial use. Recently, reverse osmosis, a type of membrane filtration, has been used to remove contaminants from coal seam water. The power required to push the coal seam water through the membrane increases as contaminant concentration - especially salt concentration - increases. The lifetime of the membrane decreases with increasing contaminant concentration. Membrane filtration also concentrates the contaminants in a solution which is inconvenient and expensive to dispose of.

In the context of this document, "membrane filtration" encompasses, but is not limited to, nano-filtration, ultra-filtration, micro-filtration, and reverse osmosis.

It is to be understood that a reference to background art herein does not constitute an admission that the art forms a part of the common general knowledge of a person of ordinary skill in the art, in Australia or in any other country. Such a reference is not intended in any way to limit the scope of the system and method as disclosed herein. Summary of the Disclosure

Disclosed herein is a water treatment system comprising a wetland system planted with plants.

In an embodiment, the wetland system comprises an artificial wetland system.

In an embodiment, the system may comprise a water flow moderator that receives water and is configured to moderate a flow of the water therethrough. The wetland system may be in fluid communication with the water flow moderator for receiving the moderated flow of water from the water flow moderator. The water flow moderator may have algae that can at least in part normalise the pH of the water. The moderator may have bacteria.

In an embodiment, the water flow moderator may have fixed carbon, for example dead organic matter or other complex molecules having carbon. The algae and/or bacteria may die and form the fixed carbon.

I In an embodiment, the water flow moderator may be between lm and 2m deep at its deepest point. Greater depths may add more complexity, capital and operational costs.

In an embodiment, the water resides in the water flow moderator for an average ; of 3 days to 6 days. This may provide sufficient time for the bacteria and/or algae to grow and/or act.

In an embodiment, the water flow moderator may be open to the environment. This may allow chemicals, for example carbonates, in the water to equilibrate with the ) atmosphere.

In an embodiment, the water flow moderator may comprise at least one pond.

In an embodiment, the moderated flow of water is distributed across the wetland ; system. The moderated flow of water may be delivered to a plurality of spaced apart regions. The system may comprise at least one conduit connecting the water flow moderator to the spaced apart regions. The at least one conduit may comprise at least one manifold.

In an embodiment, the water treatment system may have parallel water flow pathways through the wetland system.

In an embodiment, the water treatment system may comprise a water flow control system arranged to alternate the flow of the water through the parallel treatment pathways.

In an embodiment, the wetland system may comprise first and second wetland units. The first wetland unit may be in fluid communication with the water flow moderator for receiving at least some of the moderated flow of water. The second wetland unit may be in fluid communication with the first wetland unit for receiving at least some of the water that has flowed through the first wetland unit.

The water may be delivered to a first plurality of spaced apart regions within the first wetland unit. At least some of the water may be delivered to a second plurality of spaced apart regions within the second wetland unit.

Each of the first and second wetland units may comprise at least one of a pipe arrangement, conduits, and manifold that deliver the water at a plurality of spaced apart regions.

The first wetland unit may have a smaller area than the second wetland unit. The first wetland unit may have less than half the area of the second wetland unit. The first wetland unit may be sized for at least one of sedimentation and sediment adsorption.

The first wetland unit may have a sediment substrate to which a metal in the water binds. The sediment substrate may oxidise a chemical in the water. The sediment substrate may be soil, or dead organic matter, for example.

In an embodiment, at least one of the first and second wetland units may slope 0% to 0.5%. Low slopes such as these may prevent short circuiting, that is, water flowing straight through one and/or both of the wetland units. The formation of rivulets may be prevented. In an embodiment, the first wetland unit may have an operating water depth of 50mm to 300mm.

In an embodiment, the water residence time in the first wetland unit may be on average 1 to 2 days. The first wetland unit may be configured as a transition between the water flow moderator and the second wetland unit.

In an embodiment, the first wetland unit may have an application rate of 20mm to 100mm per day.

In an embodiment, at least one of the first and second wetlands units may be open to the environment. This may allow chemicals, for example carbonates, in the water to equilibrate with the atmosphere.

In an embodiment, the second wetland unit may be sized for sedimentation.

In an embodiment, the first and/or second wetland unit may have organic matter to which a bio-film can bind.

In an embodiment, the second wetland unit may have an application rate of 10 mm - 50 mm per day.

In an embodiment, the water residence time in the second wetland unit may be on average between 1 day to 5 days.

In an embodiment, the system comprises a third wetland unit which may comprise a filter cartridge. The filter cartridge may comprise bags of palletised material, for example gravel. The filter cartridge may absorb heavy metals. The third wetland unit may be disposed between the first and second wetland units.

In an embodiment, the water treatment system may comprise means to introduce other water into the system.

In an embodiment, the water treatment system may comprise at least one coal seam gas well head. The coal seam gas well head may be in water communication with one of the water flow moderator and the wetland system. Also disclosed herein is a water treatment arrangement comprising:

a water treatment system in accordance with the first aspect; and

a membrane filter in fluid communication with the water treatment system that filters at least some of the water that has flowed through the wetland system.

In an embodiment, the membrane filter may comprise a reverse osmosis membrane.

Also disclosed herein is a method for treating water, the method comprising the steps of:

moderating a flow of the water;

passing the moderated flow of water through a wetland system.

In an embodiment, the method may comprise the step of extracting the impure water from a coal seam.

In an embodiment, the method may comprise the step of separating the water from coal seam gas.

In an embodiment, the method may comprise the step of passing the water through a membrane filter.

In an embodiment, the method may comprise adding other water before, during, or after any step thereof.

passing the water through a wetland system; and

passing the water through a membrane filter.

In an embodiment, the method may comprise the step of extracting the water from a coal seam.

passing the water through a wetland system; and

diluting the water. The water may be diluted before or after the wetland system, or while it is in the wetland system.

Brief Description of the Drawings

Embodiments of the system and method will now be described, by way of example only, with reference with the accompanying figures in which:

Figure 1 shows a flow diagram of one embodiment of a method for treating in pure water;

Figure 2 shows an embodiment of a water treatment system;

Figure 3 shows another embodiment of a water treatment system; and

Figure 4 shows yet another embodiment of a water treatment system.

Detailed Description of Specific Embodiments

Figure 1 shows a flow diagram of one embodiment of a method for treating impure water, the method generally being indicated by the numeral 10. The impure water may originate, for example, from a mining operation such as a coal mining or coal seam gas extraction, sewage treatment, industrial operations and generally any sources. In the following the use of the system for treating coal seam water - a by-product of coal seam gas extraction - will be described but it is to be understood that the method can be used to treat impure water from a variety of sources. Coal seam gas is also known as coal bed methane.

Coal seam water may be produced during the drilling of a coal seam gas well and/or extraction of coal seam gas from a coal seam. The water can be separated from the gas using techniques such as down hole water separation, mechanical blocking devices in the well or the bore, and generally any other suitable process control and optimisation technique. Water may flow from the well head via a well head off-take. Impure water from more than one coal seam gas well may be combined to produce a flow of impure water. The water may optionally be diluted with other relatively pure water, for example rain water, as indicated by numeral 11 for example. In a step indicated by the numeral 12 of the method 10, the flow of impure water is moderated. Sometimes there may be a sudden surge of water from operations which if not moderated may exceed the capacity of the corresponding system to treat. At other times, the water flow through the system may drop below acceptable limits if not moderated. Insufficient impure water inflows into the system may be compensated by adding other water. In the step indicated by numeral 14 of the method 10 the moderated flow of water is passed through a wetland system. The wetland system may be planted with plants, such as salt tolerant aquatic plants for example. The wetland system, in this but not all embodiments, is artificially created. In other embodiments, the wetland system may be paitly or entirely natural. The step of passing the moderated flow of water through the wetland system at least in part improves the quality of the water. In many cases, the water can then be used. In an optional step indicate by the numeral 16 of the method 10, the water that has passed through the wetland system is then passed through a membrane filter such as a reverse osmosis membrane. The water can then be used for irrigation, industry, domestic applications or released to the environment or any other use as suitable.

Figure 2 shows an embodiment of a water treatment system generally indicated by the numeral 20. Water from a plurality of gas wells, such as that indicated by numeral 22, is collected in a series of connecting pipes such as 24. The water is then delivered to a water flow regulator, which in this embodiment is actually two regulation units indicated by 26 and 28. In other embodiments, there may be more or less than two regulation units. The regulator - as is each regulation unit - is configured to receive the water from the gas wells, such as 22, and moderate a flow of the water therethrough.

In the embodiment of Figure 2, the water flow regulation units each comprise a pond. The ponds are in this embodiment, but not necessarily in all embodiments, configured to promote sediment deposition therein. The ponds have, in this but not necessarily in all embodiments, algae that can at least in part normalise the pH of the water that flows through them. They also may have fixed carbon which can remove certain contaminates from the water. Examples of such contaminants include phosphorus, which is absorbed and metabolised by an algae/bacterial symbiosis. The phosphorous is sedimented when the organisms die. The ponds of the embodiment of Figure 1 are, at their deepest point, between 1 metre and 2 metres although it would be appreciated that values outside of this range may be acceptable in certain

circumstances. The volume of the pond may depend on the operational parameters of the gas wells and the water treatment system, however, it is desirable in some circumstances that they be configured such that it takes on average 3-6 days for the water to flow through the ponds. This gives the fixed carbon and the algae enough time to act on the water to improve its water quality. Typically, the ponds are open to the environment which may aid in the treatment of the water, although in other

embodiments the pond may be closed.

In some embodiments, the water flow moderator in the form of a pond, for example, is not required. This function may be performed by the wetland system.

The water from the ponds then flows into a wetland system comprising wetland units 30, 32, 34 and 36. Water from pond 26 flows into wetland unit 30, and the water from wetland unit 30 flows into wetland unit 32. Similarly, water from pond 28 flows into wetland unit 34, and the water from wetland unit 34 flows into wetland unit 36. That is, water flowing from 26 to 30 to 32 is a first water flow pathway and water flowing through 28, 34 and 36 is a second parallel water flow pathway. There may be optional conduits between 30 and 34, and between 32 and 36, for example, in some other embodiments. A valve before each of ponds 26 and 28, indicated by numerals 38 and 40 respectively, can close and open respective conduits connecting the gas wells to the respective pond. These valves can be independently opened and closed. In normal use, only one of the valves is open and the other is closed. In this way, at any particular time only one of the flow paths is opened and the other one is closed. For example, at a particular time a valve 40 may be opened and valve 38 may be closed and consequently the water flows through 28, 34 and 36 but no water flows through 26, 30 and 32. The water flow control system comprising the valves may allow periodic alternative flows through the parallel pathways. This allows for one of the flow pathways to be rested while the other is active. Also, this alternation allows maintenance on one of the flow pathways while the other is in use or remediation of one of the flow pathways when the other is in use. In some circumstances where greater than normal flow is experienced both valves may be opened so that the two pathways are in simultaneous use.

The water from pond 26, for example, leaves via conduit 42 and is distributed across the wetland unit 30. This is achieved, in this but not necessarily in all embodiments, by delivering the water into wetland unit 30 to a plurality of spaced apart regions within wetland unit 30. Spaced apart regions are indicated by numerals 44, 46, 48 and 50. Because the water is delivered into spaced apart regions, each of the regions is the head of a respective water path within the wetland system. This is preferable to delivering the water to a single point within the wetland system. When water is delivered to a single point, the water may form a single (or a few) rivulet and the water does not distribute across the wetland system sufficiently for better treatment. The distribution of the water is, in this example, achieved through the use of a manifold 52 however any system that achieve the same or similar effect is generally satisfactory. For example conduits, pipes, sprinklers, drippers, fountains, moving hoses etc may each be used to distribute the water. Each of the other wetland units also have a manifold indicated by the numerals 54, 56 and 60.

The upstream wetland units 30, 34 generally have a smaller surface area than the downstream wetland units 36, 32. In some embodiments, the deposition of hazardous or undesirable materials or chemicals or sediments will be deposited more in the upstream wetland units than the downstream units. The upstream unit may have a particular mineralogy or of a chemical nature that favours adsorption, absorption or sedimentation, flocculation or coagulation processes. This may concentrate the materials in a more manageable manner. Having a smaller area minimises the area of land that requires remediation after the conclusion of the treatment system's life.

In the embodiment of Figure 2, the first wetland unit is sized for sedimentation and/or sediment adsorption. There is, at least in this embodiment, a sediment substrate such as an iron- or aluminium- or calcium-rich material, in a favourable pH and/or Eh condition in the upstream wetland units to which a metal, such a heavy metal as cadmium or zinc, in the water binds. For example, the sediments substrate may oxidize a chemical in the water when the flow of water is slowed and more time is available for the chemical to react with the sediment substrate.

In the embodiment of Figure 1, the wetland units are configured for horizontal flow and slope between 0% and 0.5% although it would be appreciated that other slopes may be used as appropriate. In some alternative embodiments, other types of wetlands, such as vertical wetlands, may be used.

The first wetland unit may have a varying water depth of 50mm to 300mm which can be adjusted by devices such as pipes and valves according to the

requirements of the specific plants, water contamination, climate and materials passing through the system. Every water body in each well is likely to be different in some way, and treatment objectives vary. The average water residence time the first wetland unit is, in this embodiment, one to two days although other values are possible. The application rate (volume applied divided by area) in the upstream wetland units may be between 20mm and 100mm per day according to the requirements of the plants, water, climate and materials passing through the system, although other values are possible. All the wetland units may be open to the environment and this may assist water treatment.

All the wetlands are generally heavily vegetated, and may be vegetated with native plants.

The downstream wetland units such as 36 and 32 are generally sized for sedimentation such that the area is sufficient to produce flow velocities slow enough to encourage settling of solids. These can also have organic matter such as plant stems and dead leaves to which a bio film, an organic microbial matrix encased in a gel-like film can bind. The downstream wetland units may generally have an application rate, i.e. a depth of water calculated as volume applied divided by area, of between 50mm and 500mm a day according to the requirements of the plants, water, climate and materials passing through the system, although other values are possible where appropriate. The water residence time of the downstream wetland units is on average between 1 to 5 days depending on the specific nature of the project objectives, the flows and materials contained in the flows, although other residence times are possible.

After the water has flown from the wetland system, the purity of the water may have improved. Many solids may have been deposited in one or more of the wetland units, the salinity may have dropped, the pH may have normalised, some heavy metals and other contaminates may be removed.

Optionally, the water may then be delivered from the downstream wetland units 36, 32 to a membrane filtration unit 68 to further purify the water. The pre-treatment by the wetland system reduces the work that needs to be done by the membrane, increasing energy efficiency, reducing the impurity load on the membrane which further increases the efficiency of the system, and preventing premature clogging of the membrane.

The membrane filter may be one of, for example, a nano-filtration filter, an ultra filtration filter, a micro filtration filter, and a reverse osmosis filter. The filter may, for example, be made of cellulose acetate. Generally, the membrane filter is a

semi-permeable membranes.

Figure 3 shows another embodiment of a water treatment system generally indicated by the numeral 69. In his embodiment, a flow of water 70 from a gas well is combined from a water flow 72 from a reservoir 74 of fresh water. A managed mixing of fresh and salt water may be able to produce a target salt concentration according to project objectives for the reuse or discharge application. The water from the gas well 70 and the fresh water flow 72 are combined and delivered to ponds 76 and 78. A series of wetland units such 80, 82, 84, 86, 88 and 90 then pre-treat the combined water flows. The water may be then delivered 92 for use in agriculture, for example, with the same or lower salt concentrations, or alternatively sent to a membrane filter 94 for membrane filtration. The fresh water may be rain water, for example. If sufficient quantities of fresh water are available the water from the wetland system may be discharged into the environment without further treatment by membrane filtration, for example. The embodiment of figure 1 indicates that the fresh water, or other water, may, in fact, be introduced at any point in the process.

Figure 4 shows another embodiment of a water treatment system generally indicated by the numeral 100. In this embodiment, water from a gas well 104 is delivered to a water flow moderator in the form of a pond 106. The water from the pond 106 is then delivered to a wetland system 108. Also delivered to the wetland system is fresh water 102 that has been stored in a fresh water storage reservoir 1 10. The water flowing from the fresh water reservoir 102 is delivered to the wetland system 108 independently from the pond 106. The water 112 flowing from the wetland system is suitable for most agriculture and may have similar or lower salt concentrations than that from the coal seam water, and may be, but not necessarily, membrane 114 filtered. The water may then be discharged for reuse into the environment, for example, or any other suitable use.

Now that embodiments have been described it will be appreciated that some embodiments may have some of the following advantages:

« The wetlands prepare the water for purification using a membrane filtration technique such as reverse osmosis.

• The wetlands reduce the energy needed to drive the purification using a

membrane technique such as reverse osmosis.

• The wetlands reduce the cost of the purification using a membrane technique such as reverse osmosis.

« The wetlands extend the life of membrane filters.

• Contaminants such as heavy metals, dissolved solids, and hydrocarbons are removed from the coal seam water by: organisms in the wetlands; assimilation in plants; sorption; sedimentation; and oxidation. It will be understood to persons skilled in the art that many modifications may be made without departing from the spirit and scope of the disclosure. For example, the pond may be replaced by a tank, dam, vessel or any suitable structure. The flow moderator may be integral with the wetland system.

In the claims which follow and in the preceding description, except where the context requires otherwise due to express language or necessary implication, the word "comprise" or variations such as "comprises" or "comprising" is used in an inclusive sense, i.e. to specify the presence of the stated features but not to preclude the presence or addition of further features in various embodiments of the system and method.

Claims

1. A water treatment system comprising:

a wetland system planted with plants.

2. A water treatment system defined by claim 1 comprising a water flow moderator that receives water and is configured to moderate a flow of the water therethrough, the wetland system being in fluid communication with the water flow moderator for receiving the moderated flow of water from the water flow moderator.

3. A water treatment system defined by claim 2 wherein the water flow moderator has algae that can at least in part normalises the pH of the water, and has fixed carbon.

4. A water treatment system defined by either one of the claims 2 and 3 wherein the water flow moderator is between lm and 2m deep at its deepest point.

5. A water treatment system defined by any one of the claims 2 to 4 wherein the water resides in the water flow moderator for an average of 3 days to 6 days.

6. A water treatment system defined by any one of the claims 2 to 5 wherein the water flow moderator is open to the environment.

7. A water treatment system defined by any one of the claims 2 to 6 wherein the water flow moderator comprises at least one pond.

8. A water treatment system defined by any one of the claims 2 to 7 wherein the moderated flow of water is distributed across the wetland system.

9. A water treatment system defined by claim 8 wherein the moderated flow of water is delivered to a plurality of spaced apart regions, the system comprising at least one conduit connecting the water flow moderator to the spaced apart regions.

10. A water treatment system defined by claim 9 wherein the at least one conduit comprises at least one manifold.

11. A water treatment system defined by any one of the preceding claims having parallel water flow pathways through the wetland system.

12. A water treatment system defined by claim 10 comprising a water flow control system arranged to alternate the flow of the water through the parallel treatment pathways.

13. A water treatment system defined by any one of the claims 2 to 12 wherein the wetland system comprises first and second wetland units, the first wetland unit being in fluid communication with the water flow moderator for receiving at least some of the moderated flow of water, and the second wetland unit being in fluid communication with the first wetland unit for receiving at least some of the water that has flowed through the first wetland unit.

14. A water treatment system defined by claim 13 wherein the water is delivered to a first plurality of spaced apart regions within the first wetland unit.

15. A water treatment plant defined by claim 14 wherein at least some of the

moderated flow of the water is delivered to a second plurality of spaced apart regions within the second wetland unit.

16. A water treatment system defined by claim 15 wherein each of the first and second wetland units comprise at least one of a pipe arrangement, conduits, and manifold that deliver the water at a plurality of spaced apart regions.

17. A water treatment system defined by any one of the claims 13 to 16 wherein the first wetland unit has a smaller area than the second wetland unit.

18. A water treatment system defined by claim 17 wherein the first wetland unit has less than half the area of the second wetland unit.

19. A water treatment system defined by any one of the claims 13 to 18 wherein the first wetland unit is sized for at least one of sedimentation and sediment adsorption.

20. A water treatment system defined by any one of the claims 13 to 19 wherein the first wetland unit has a sediment substrate to which a metal in the water binds.

21. A water treatment system defined by any one of the claims 13 to 20 wherein the sediment substrate oxidises a chemical in the water.

22. A water treatment system defined by any one of the claims 13 to 21 wherein at least one of the first and second wetland units slope 0% to 0.5%.

23. A water treatment system defined by any one of the claims 13 to 22 wherein the first wetland unit has an operating water depth of 50mm to 300mm.

24. A water treatment system defined by any one of the claims 13 to 23 wherein water residence time in the first wetland unit is on average 1 to 2 days.

25. A water treatment system defined by any one of the claims 13 to 24 wherein the first wetland unit has an application rate of 20mm to 100mm per day.

26. A water treatment system defined by any one of the claims 13 to 25 wherein at least one of the first and second wetlands units are open to the environment.

27. A water treatment system defined by any one of the claims 13 to 26 wherein the second wetland unit is sized for sedimentation.

28. A water treatment system defined by any one of the claims 13 to 27 wherein the second wetland unit has organic matter to which a bio-film can bind.

29. A water treatment system defined by any one of the claims 13 to 28 wherein the second wetland unit has an application rate of 10 mm - 50 mm per day.

30. A water treatment system defined by any one of the claims 13 to 29 wherein the water residence time in the second wetland unit is on average between 1 day to 5 days.

31. A water treatment system defined by any one of the claims 13 to 30 comprisin; means to introduce other water into the system.

32. A water treatment system defined by any one of the claims 2 to 31 comprising at least one coal seam gas well head in communication with the water flow moderator for communication of impure water between the coal seam and the water flow moderator.

33. A water treatment arrangement comprising:

a water treatment system defined by any one of the preceding claims; and

34. A method for treating water, the method comprising the steps of:

moderating a flow of the water;

passing the moderated flow of water through a wetland system.

35. A method of treating water defined by claim 34 comprising the step of

extracting the impure water from a coal seam.

36. A method defined by claim 35 comprising the step of separating the water from coal seam gas.

37. A method defined by any one of the claims 34 to 36 comprising the step of passing the water through a membrane filter.

38. A method defined by any one of the claims 34 to 37 comprising the step of adding other water at any point thereof.

39. A method for treating water, the method comprising the steps of:

passing the water through a wetland system; and

passing the water through a membrane filter.

40. A method defined by claim 39 wherein the method comprises the step of

extracting the water from a coal seam.

41. A method for treating water, the method comprising the steps of:

passing the water through a wetland system; and

diluting the water.

42. A method defined by claim 41 wherein the water may be diluted before or after the wetland system, or while it is in the wetland system.