AU2009202672A1

AU2009202672A1 - Apparatus and method for improving the quality of water from an aquifer

Info

Publication number: AU2009202672A1
Application number: AU2009202672A
Authority: AU
Inventors: Christopher Barber
Original assignee: Desaln8 Pty Ltd
Current assignee: Desaln8 Pty Ltd
Priority date: 2009-07-01
Filing date: 2009-07-01
Publication date: 2011-01-20
Anticipated expiration: 2029-07-01
Also published as: AU2009202672B2

Description

AUSTRALIA Patents Act COMPLETE SPECIFICATION (ORIGINAL) Class Int. Class Application Number: Lodged: Complete Specification Lodged: Accepted: Published: Priority Related Art: Name of Applicant: Desaln8 Pty Ltd Actual Inventor(s): Christopher Barber Address for Service and Correspondence: PHILLIPS ORMONDE FITZPATRICK Patent and Trade Mark Attorneys 367 Collins Street Melbourne 3000 AUSTRALIA Invention Title: APPARATUS AND METHOD FOR IMPROVING THE QUALITY OF WATER FROM AN AQUIFER Our Ref : 856881 POF Code: 477898/477898 The following statement is a full description of this invention, including the best method of performing it known to applicant(s): e-01q 2 Apparatus and Method for Improving the Quality of Water from an Aquifer Field 5 The present invention relates to a system for improving the quality of water from a bore hole in an aquifer and Method for Improving the Quality of Water from a borehole in an Aquifer. The invention may be utilized in preparing water for productive use above ground or in improving the general quality of water in the upper, more readily accessible, part of an aquifer. 10 Background Ground water is an important resource for industrial and domestic use. It is particularly important in arid regions where ground water is frequently the most readily available and inexpensive source of water. In many instances, however, 15 the quality of groundwater is poor due to the level of impurities. Impurities in groundwater may take the form of naturally occurring inorganic materials such as common salt which is frequently present at a level which makes the groundwater unsuitable for human or animal consumption or for the 20 desired industrial use. Other inorganic metals and metal salts may contaminate ground water as a consequence of the local geology or through human intervention. For example, by overuse or inappropriate use of groundwater or from discharge of contaminating substances onto soils resulting in poor quality groundwater. 25 Pollution of ground water often results in formation of a plume diffusing gradually from the source of contamination. A groundwater pollution plume may result from a source such as a mine spoil heap or other landfill or from an industrial plant. These "point" sources can be relatively easily recognized and dealt with, but 30 more widely distributed "diffuse" sources of contamination such as from leaching of fertilizers and pesticides in agricultural regions, can give more problematic contamination of groundwater which because of its widespread nature, is more 3 difficult to deal with. Such cases, and those of increased salts in groundwater from natural causes such as aridity, or from human-induced salinisation from overpumping, require treatment of groundwater prior to use, such as desalination using reverse osmosis technologies. 5 The discussion of documents, acts, materials, devices, articles and the like is included in this specification solely for the purpose of providing a context for the present invention. It is not suggested or represented that any or all of these matters formed part of the prior art base or were common general knowledge in 10 the field relevant to the present invention as it existed before the priority date of each claim of this application. Summary There is provided a system for improving the quality of water from a bore hole in 15 an aquifer, the system comprising: a borehole casing comprising at least two portions comprising a relatively larger diameter portion at least part of which is perforated so as to admit water from an aquifer and a relatively smaller diameter portion which is attached to the larger diameter portion which in use extends below the portion 20 of relatively larger diameter; a water treatment apparatus comprising: a seal movable within the portion of relatively larger diameter and of diameter for sealing against the wall below the perforated part of the portion of larger diameter so as to inhibit the mixing of water above and 25 below the seal within the borehole casing; a vessel comprising one or more membrane treatment units for providing a permeate or relatively high quality water and concentrate of relatively low quality water; a submersible pump for passing a stream of water through the vessel from 30 above the seal; an inlet for receiving groundwater above the seal; 4 a permeate outlet for water of improved quality; and an outlet below the seal for returning concentrate from the vessel to the aquifer after treatment. 5 In a particularly preferred embodiment the water treatment apparatus including the vessel, inlet and concentrate outlet are for use in situ within the borehole casing. In one embodiment the permeate outlet delivers water of improved quality to the ground surface and in an alternative embodiment the outlet returns improved quality water to the aquifer to improve the quality of water in the upper 10 part of the aquifer. In one set of embodiments the portion of the borehole casing of relatively smaller diameter comprises a perforated portion. In this embodiment it is generally preferred that the upper part of the portion of the casing of relatively smaller 15 diameter is not perforated, to allow the seal to form an effective seal within the borehole casing. The seal is preferably slidable within the portion of the borehole of relatively larger diameter and is of diameter to engage the wall of the borehole casing 20 below the upper portion of relatively larger diameter. The permeate outlet may be provided with an outlet conduit for delivering filtered water to the surface. Alternatively the filtered water may reinject filtered water into the aquifer so as to improve the quality of the water in the upper part of the 25 aquifer. In one set of embodiments of the invention the relatively smaller diameter portion is attached to the larger diameter portion and comprises a portion which tapers from the larger diameter portion to the portion of smaller diameter. In this 30 embodiment it is preferred that the seal is of diameter to engage the tapered portion or portion of relatively smaller diameter.

5 In one set of embodiments of the invention the portion of the casing of relatively smaller diameter comprises an upper section having an unperforated wall and a lower section having a perforated wall. In this set of embodiments the seal 5 preferably seals against the upper section having an unperforated wall and the fluids from the vessel after treatment, which are delivered below the seal, are allowed to be reintroduced to the aquifer through the lower perforated section of the smaller diameter portion. The portion of relatively smaller diameter may comprise an end cap in this embodiment so that the concentrate re-enters the 10 aquifer via the perforated wall of the portion of the borehole of relatively smaller diameter (13). Throughout the description and the claims of this specification the word "comprise" and variations of the word, such as "comprising" and "comprises" is 15 not intended to exclude other additives, components, integers or steps. Detailed Description The water treatment apparatus may be located entirely within the borehole casing during use or parts of the water treatment apparatus such as the vessel 20 comprising all or a portion of the membrane treatment units, may be located above ground. If part of the water treatment apparatus is located above ground then allowance can be made for pumps and conduits for lifting the water stream to be treated from the inlet for receiving groundwater above the seal. 25 It is generally particularly preferred for the sake of economics that the water treatment apparatus is for use in situ in the borehole casing and the outlet for permeate is provided with a conduit for transferring the permeate above ground or transfers the permeate back into the aquifer. An in situ water treatment apparatus reduces significantly the energy required to operate the system as it 30 takes advantage of the hydrostatic pressure within the aquifer to aid in passing water through the vessel comprising the membrane treatment units.

6 Accordingly, in one set of embodiments there is provided an in situ system adapted for use in a borehole for improving the quality of water from a subterranean aquifer, the system comprising: 5 a borehole casing comprising at least two portions comprising a relatively larger diameter portion at least part of which is perforated so as to admit water from an aquifer and a relatively smaller diameter portion which is attached to the larger diameter portion and in use extends below the portion 10 of relatively larger diameter; a water treatment apparatus for use in situ in the bore hole casing comprising: a seal movable within the portion of relatively larger diameter and of diameter for sealing against the walls of the portion of smaller diameter so as to inhibit the passage of water within the casing; 15 a vessel comprising one or more membrane treatment units for removing contaminants; a submersible pump for passing a stream of water through the vessel; an inlet for receiving groundwater above the seal; a permeate outlet for water of improved quality in fluid communication with the 20 vessel downstream thereof, and an outlet below the sealing means to return fluids from the vessel after treatment to the aquifer. The borehole casing of the system includes a portion of relatively larger diameter 25 and a portion of relatively smaller diameter extending below the portion of relatively larger diameter. The two portions may be joined by a stepped portion of borehole casing or a tapered portion. In one embodiment a stepped portion is used. In this embodiment the stepped portion may provide a seat for the seal. In an alternative and generally more preferred embodiment the portion of 30 relatively larger diameter and the portion of relatively smaller diameter are connected by a tapered portion. A tapered portion is generally preferred as it 7 serves as a guide for smooth passage of the water treatment apparatus into the portion of the borehole casing of relatively smaller diameter. The placement to locate the seal in engagement with one of the narrowing portion and portion of relatively smaller diameter is assisted by introduction of the bottom end of the 5 water treatment apparatus, which generally comprises the concentrate outlet below the seal, to the tapered portion and then to the portion of relatively smaller diameter. The system uses a borehole casing comprising at least two portions comprising a 10 relatively larger diameter portion at least part of which is perforated so as to admit water from an aquifer and a relatively smaller diameter portion which is attached to the larger diameter portion which in use extends below the portion of relatively larger diameter. The bore hole casing of this type provides significant advantages in combination with the seal which divides the borehole into upper 15 and lower parts. The seal is of dimensions so as to slide easily within the upper casing portion but engages the portion of the casing of relatively smaller diameter. This construction facilitates easy placement and removal of the water treatment apparatus. 20 The seal may be of any type such as an inflatable packer or K-packer (also referred to as a tri-seal). The portion of the casing of relatively larger diameter is generally a cylindrical tubular shape. The portion of the casing of relatively smaller diameter extends in use from the lower end of the portion of relatively larger diameter and in preferred embodiments comprises a part which tapers to a 25 cylindrical tubular portion of relatively smaller diameter. The upper part of the casing portion of relatively smaller diameter is generally a continuous or unperforated wall against which the seal is engaged to prevent mixing of water from parts of the borehole above and below the seal. In this way contamination of the inlet water to be treated by outlet water usually referred to as concentrates is 30 avoided and concentrates descend within the aquifer being more dense than 8 groundwater so as to not unduly affect the quality of water in the upper regions of the aquifer which may be used in future. The casing may if desired include additional portions of even smaller or larger diameter although this is not generally required for efficient operation and 5 generally we have found the use of two cylindrical parts joined by a tapered section is significant. The invention is particularly suited to providing desalination of brackish or saline water using one or more membrane treatment units adapted for desalination. 10 The one or more membrane treatment units may, for example, be selected from the group consisting of reverse osmosis membranes, nanofiltration membranes, ultrafiltration membranes electrodialysis reversal systems and/or combinations thereof. Reverse osmosis membranes are particularly preferred. The concentrate remaining following reverse osmosis or other membrane treatment is delivered to 15 the portion of relatively smaller diameter casing below the seal and descends within the aquifer by virtue of the natural density contrast between the relatively high density concentrate and relatively low density water within the aquifer to thereby avoid concentrating the salt in the upper region of the aquifer. 20 The system in one set of embodiments further comprises a conduit for delivering the permeate outlet to the surface for use above ground. This allows a continuous supply of good quality and generally potable water for irrigation, drinking, industrial use or use as a household water supply. 25 In another set of embodiments the permeate is reintroduced to the aquifer to improve the quality of water therein. While the concentrate left over after treatment will descend within the aquifer the purified water which is reintroduced improves the quality of water accessible in the upper part of the aquifer. 30 In another set of embodiments the water in the aquifer comprises contaminants such as nitrates which in passing through the system remain in the concentrate 9 and descend within the aquifer to more anoxic regions of the aquifer. In the more anoxic regions of the aquifer the nitrates more readily undergo denitrification as part of the naturally occurring process in anoxic parts of the aquifer. 5 The system of the invention comprises a seal which divides the bore hole casing into an upper section in which water collects from the aquifer via the perforated wall in the upper portion of the bore hole casing and a lower section in which the concentrate is reintroduced to the aquifer. The seal may be formed of any suitable material which will enable the seal to abut the wall of the lower portion of 10 the bore hole casing so as to inhibit the passage of water about the seal. The seal will generally have a peripheral portion formed of a resiliently deformable material such as a polymeric material. Rubber such as a natural or synthetic rubber is particularly useful in the role. In one embodiment the seal comprises a central portion of a relatively rigid material, when compared with the resiliently 15 deformable material, such as a metal or relatively rigid polymeric material and an annular portion about the central portion formed of a resiliently deformable material such as rubber or other resilient polymeric material comprises one or more annular resiliently deformable ribs adapted to form a seal in the portion of borehole casing of relatively smaller diameter. 20 In this set of embodiments the ribs may be the outer part of a rubber sleeve located about a cylindrical inner portion which in turn is located about a portion of the water treatment apparatus extending below the seal such as part of the vessel and/or the outlet for returning fluids to the aquifer. The cylindrical inner 25 portion is closed off at either end to prevent flow of water. The seal separates the borehole casing into an upper part for receiving water from the aquifer via the perforations in the upper portion of the casing and a lower part into which the concentrate removed in purifying the water is delivered. 30 The seal will thus generally be disposed about and connected to a portion of the water treatment apparatus.

10 The seal may support the water treatment apparatus within the borehole casing. The seal may be the only means of support but generally the apparatus will also be supported from the ground surface. 5 The borehole casing is generally placed in use so that perforations in the portion of relatively larger diameter admit water from the aquifer. Accordingly at least part of the perforated section in the upper portion of relatively larger diameter will generally be placed below the upper surface of the water in the aquifer. 10 The submersible pump is located above the seal and disposed within the borehole so as to be located below the surface of the water. The submersible pump delivers water to be purified under pressure to the vessel comprising one or more membrane treatment units. 15 In one set of embodiments the system further comprises pressure lines linking the vessel with the surface for measuring treatment pressures and for sampling of feed and concentrate, and allowing fluid communication between the surface and the treatment vessel for delivery of membrane cleaning fluids. This 20 embodiment allows the system to remain in situ in a bore hole for extended periods without the need to remove the apparatus for servicing or replacement of the membranes. In this set of embodiments a gate valve may be used with a non return valve in the submersible pump when the pump is not operational to hydraulically isolate the treatment vessel during operation of the membrane 25 cleaning process. Further, in this set of embodiments the system may be provided with a source of cleaning fluids which comprise at least one cleaning fluid selected from the group consisting of an alkaline (pHl10) solution of permeate, acidic *(pH 2) solution of 30 permeate, a sterilising solution of sodium metabisulphite in permeate and permeate itself.

11 Brief Description of the Drawings Figure 1 is a schematic drawing showing a borehole casing (Figure 1a) and Water treatment apparatus (Figure 1b) relative to the depth of placement within 5 the borehole casing. Figure 2 is a schematic cross section of a water treatment system comprising a water treatment apparatus in situ in a bore hole casing in which the apparatus is in operational mode 10 Figure 3 is a schematic cross section showing the water treatment apparatus of Figure 2 in the cleaning mode. Figure 4 is a schematic drawing showing a borehole casing (Figure 4a) which is 15 the same as Figure 1a and a further embodiment of water treatment apparatus (Figure 4b) relative to the depth of placement within the borehole casing. Referring the drawings there is shown a system (1) for improving the quality of water comprising a borehole casing (2) below the ground (3) and extending into 20 an aquifer (4). The system further comprises a water treatment apparatus (5). The borehole casing (2) comprises a portion of relatively larger diameter (6) having a cylindrical wall (7) which has a perforated section (8) for allowing water from the aquifer (4) to flow into the borehole casing (2) through the perforated wall section (8). 25 The borehole casing (2) further comprises a cylindrical portion (9) of relatively smaller diameter than the portion of relatively larger diameter (6), which portions (6,9) are joined by a portion (10) which tapers. The tapered portion (10) and upper part (11) of the portion (9) of the borehole casing of relatively smaller diameter are generally not perforated. The lower end (12) of the borehole casing 30 of relatively smaller diameter is closed and the lower part (13) of the portion of smaller diameter is perforated to allow water toward the lower end (12) to be 12 redistributed into the aquifer via the lower perforated wall part (13) of the portion of borehole casing of relatively smaller diameter (9). The water treatment apparatus (5) is supported on an elongated support (14) such as a rod which can be used to guide the apparatus into the borehole from above ground (3). The 5 Water treatment apparatus has a seal (15) which locates the water treatment apparatus in the borehole casing (2) by engaging the wall of the borehole casing in the upper unperforated part (11) of the portion relatively smaller diameter (9). The seal may comprise a cylindrical inner portion (16) which prevents the passage of water and one or more circumferentially extending ribs (17) for 10 engaging the wall of the borehole casing (2). Such seals may be adapted from K packer type seals. The apparatus comprises a submersible pump (18) located with an inlet (19) below the surface of the water level of the aquifer (4) which collects in the 15 borehole casing (2) via the perforated wall (8) of the portion of relatively larger diameter (6). The submersible pump (19) transfers water under pressure via vessel inlet conduit (19a) to a vessel (20) which has a rigid casing (21) and contains a plurality of treatment membrane elements (22) which may comprise reverse osmosis membranes, nanofiltration membranes, ultrafiltration 20 membranes electrodialysis reversal membranes and/or combinations thereof. The elements (22) may comprise cylindrical spiral-wound membranes (23) which are aligned to provide a central passage (24) inboard of the membranes and an annular passage (25) outboard of the aligned membranes (23). The aquifer water from the pump inlet may pass into the annular passage (25) and result in 25 collection of permeate in the central passage (24) after passage through the membrane (23). The permeate is in one embodiment forced to the ground surface (3) from the central passage via a conduit (26) where it may be used for domestic, industrial or agricultural purposed and will generally be potable. The concentrate (in figure 2 shown in the annular passage (25)) passes under 30 pressure into the outlet conduit (27) which passes through the seal (the seal disposed about the outlet conduit) to provide an outlet (28) for concentrate 13 toward the lower end (12). The concentrate is reintroduced to the aquifer via the perforated casing wall of smaller diameter (13). In one set of embodiments of the invention the water treatment apparatus 5 comprised adapted for cleaning the apparatus while in situ in the borehole casing within an aquifer. Referring to Figure 2 and Figure 3 the apparatus further comprises a cleaning system comprising a pressure line (29) connecting the vessel inlet line (19a) to a pressure gauge at the surface via pressure line (29) The pressure line (29) may be used during operation to monitor the pressure in 10 the inlet line as an indication of system performance. The outlet conduit typically comprises a flow control valve (30) above which is located a gate valve which may be operated by gas pressure or by a valve which opens above a specified pressure. The control valve (30) is open during operation and closed to isolate the vessel (20) during cleaning. 15 The pressure lines (29 and 31) provide cleaning liquid conduits, with 29 connecting the concentrate outlet conduit (27) at a point above the flow control valve (30) to the surface and 31 extending from the feed line 19a, forming a closed system when the control valve (30) is closed to allow flushing of the 20 vessel (20) and membrane elements (22) with cleaning fluid. The lines (29, 30) may be used to provide flushing concurrent and countercurrent with the normal water flow. The control valve (30) is used to hydraulically isolate the treatment vessel (20). The control valve may be an activated gate valve on the lower end of the pressure vessel (20), and a one-way valve on the pump may also be 25 provided. The cleaning operation may involve "backwash" of fluids through the concentrate pressure line (27) at the base of the vessel and out of the feed pressure line (29a) back to the surface. The back wash fluids can be either a sterilant such as sodium metabisulphite which limits biofouling, or alkaline (pH 10) or acid (pH 2) fluids for removal of organic and inorganic foulants. The back 30 wash fluids are pumped from the surface through the concentrate pressure line. This can be carried out at suitable intervals (e.g. daily) for -1 hour. We have 14 automated this and provide a recycle loop which filters the fluid and returns it to the backwash fluid reservoir (not shown). Some of the fluids are discarded (those which flush groundwater from the vessel). 5 Referring to Figure 4 there is shown an alternative system which is generally less preferred than the embodiments of Figures 1 to 3. In the embodiment of figure 4 the system (32) comprises a borehole casing identical to the casing shown in Figure 1a and a water treatment apparatus comprising a water treatment vessel (35) located above the ground surface (36). A submersible pump (37) having an 10 inlet (38) below the aquifer surface (39) delivers water from the upper part of the borehole to the vessel (35) at the surface via transfer line (40). The vessel may be in accordance with the vessel (20) shown in Figure 2. The concentrate from the vessel (20) is returned to the aquifer via outlet line (41) to the outlet (42) which reintroduces the concentrate at a point below the seal (43). In accordance 15 with the embodiment shown in Figures 1 to 3 the seal (43) engages the portion of the borehole of relatively smaller diameter (see (9) in Figures 1 to 3) and the concentrate exiting the outlet (42) becomes dispersed ad descends within the aquifer via the perforated lower part of the portion of the screen of relatively smaller diameter (see (13) of Figures 1 to 3).the seal may be the same as the 20 seal in Figures 1 to 3 (see 15 to 17 and accompanying description). The vessel also has a permeate outlet (44) which may be at the surface as shown in Figure 4 or may be provided with a conduit to reintroduce permeate to the aquifer. The dimensions of the borehole casing and water treatment apparatus are not 25 narrowly critical and can be readily determined based of the above disclosure of the proportions and interrelated functions thereof. The borehole casing may be of a range of dimensions having regard to the nature of aquifer, the hydrology and terrain in the area of the borehole and the 30 treatment system dimensions. In some cases the aquifer will be relatively near the ground surface and the relative length of the borehole casing and portions 15 thereof can be short for example at least several metres such as at least about 10 meters whilst in other locations the hydrology and terrain may dictate a relatively long borehole casing for example up to of 250 meters. The main limitation of the system as proposed is the depth to groundwater within the 5 borehole as additional pressure above that required for desalination is required to move permeate from the groundwater level to the surface, also taking account of natural hydrostatic pressure within the desalination vessel below groundwater level. The diameter of the borehole portions of relatively larger diameter and relatively smaller diameter are not critical and convenient diameters can be 10 determined by the skilled worker having regard to the function and operation described herein. Typically the difference in diameter between the smaller and larger diameter portions is at least 5 mm, more preferably at least 10 mm and most preferably at least 20mm. The length of the tapered portion may be readily determined having regard to the differences in the diameter of the portions of 15 borehole casing and the preference to allow the tapered portion to act as a guide for the outlet line to aid in location of the seal in the portion of relatively smaller diameter. The tapered portion may for example be at least 5mm such as at least 10mm, at least 20mm or at least 50mm in length and may, for example be up to 1m in length such as up to 700cm, up to 500cm or up to 250cm. We have found 20 tapered portions of about 5cm to be useful but up to 20cm lengths may be convenient for operation and construction of the system. The diameter of the portion of the borehole of relatively larger diameter may be any of a range of diameters within the constraints of construction provided by the components and relation ship of components described herein. The portion of the borehole casing 25 of relatively larger diameter may for example be up to 1m such as up to 500cm diameter or such as up to 400cm diameter. The diameter will often be at least 10cm diameter such as at least 20cm, at least 50cm at least 75cm or at least 100cm diameter.

16 The invention will now be described with reference to the following examples. It is to be understood that the examples are provided by way of illustration of the invention and that they are in no way limiting to the scope of the invention. 5 Example An in situ desalination borehole casing with a 300mm diameter screen and casing. As an example one aquifer which may be suitable in accordance with the invention may be a gravel aquifer having an upper zone between 20-27m below surface and a lower zone 30-33m, separated by a consistent clay layer, although 10 the invention does not rely on the clay layer being present. In accordance with Figures 1 and 2 the in situ desalination bore is typically configured with 250mm diameter screen within the upper aquifer as a feed zone, and the lower part of the bore below 27m was fitted with a 175mm diameter casing (within the clay) and below this to 125mm diameter screen within the lower gravel aquifer. A tapered 15 portion reducing the diameter from 250mm to the diameter of the smaller casing of 175mm as described above and from 175mm diameter for the smaller casing to 125mm diameter of the lower screened section is used to connect the upper portion of relatively larger diameter and the lower portion of relatively smaller diameter And the lower screen section. The former screened section formed the 20 "groundwater feed" zone and the lower screened section provided the concentrate return zone. The two zones were separated by a seal in the form of a K- packer situated within the 175mm casing. The in situ desalination (ISD) system was equipped with a Grundfos SP8A-37 submersible pump. 25 Given the results of the earlier field trial, a system for in situ washing and sterilizing of membrane elements is incorporated within the unit in accordance with Figures 1 and 2, and cleaning is carried out daily for 40 minutes using sodium metabisulphite solution (500ppm) as a biostat or sterilizer solution. The biostat solution is recycled and recovered at the surface. An automatic PLC 30 controller and monitor are also included in the system to allow remote monitoring 17 and control, and some manual monitoring is carried out. The following are monitored: * Permeate flow using flow meter and manual timed volume measurement * Permeate, feed and concentrate total dissolved solids (TDS) (manual daily 5 measurements) * Feed and concentrate system pressures (automatically logged and manual pressure measurements) The results of the testing are summarised in Table 1, and compared with modeled system performance using the DOW ROSA 6.1 model of the reverse 10 osmosis process (DOW Filmtec, 2007). Table 1. Summary of performance of the ISD system Modelled* After 60 days operation Feed groundwater TDS 3200mg/L 3200mg/L Feed groundwater flow 9.75KL/h 1 OKL/h Permeate TDS 89mg/L 1 00mg/L Permeate flow 3.6KL/h 3.8-4.2KL/h Concentrate TDS 5000mg/L 4800-5040mg/L *DOW ROSA v 6.1 model (DOW Filmtec, 2007) The results indicate that an average of 4 KL/h of permeate is extracted from the 15 aquifer using the ISD system, under the conditions of the test, although there is considerable variability in the flow data (± 5 %) caused by taking measurements at different times of the day in relation to a constant backwash time. The quality of the permeate is very high (TDS 100mg/L). The feed groundwater concentration remains constant over the course of the trial (on average 20 3200mg/L) indicating no dipole flow (return of concentrate flow into the feed stream) was taking place because of limited vertical upflow through the intervening clay and because of the density contrast between natural groundwater and concentrates being discharged into the lower aquifer.. The TDS 18 concentration of concentrates has also remained steady at an average of 5000mg/L (Table 2). In addition, drawdown during pumping is negligible within the ISD bore (2-3cms), and impacts on TDS of groundwater and groundwater levels at the monitoring bore 50m from the ISD bore and within the lower aquifer 5 to which concentrate is returned are negligible, but expected to rise later in the trial. Numerical groundwater modelling using the computer software FEFLOW with input parameters (K, hydraulic gradient, porosity) as determined during site testing, suggests that any increased salt concentrations in groundwater would extend only 200m from the ISD bore after 10 years continuous pumping, with the 10 highest concentrations being close to the ISD bore.

Claims

1. A system for improving the quality of water from a bore hole in an aquifer, the system comprising: a borehole casing comprising at least two portions comprising a relatively 5 larger diameter portion at least part of which is perforated so as to admit water from an aquifer and a relatively smaller diameter portion which is attached to the larger diameter portion which in use extends below the portion of relatively larger diameter; a water treatment apparatus comprising: 10 a seal movable within the portion of relatively larger diameter and of diameter for sealing against the wall below the perforated part of the portion of larger diameter so as to inhibit the mixing of water above and below the seal within the borehole casing; a vessel comprising one or more membrane treatment units for providing a 15 permeate or relatively high quality water and concentrate of relatively low quality water; a submersible pump for passing a stream of water through the vessel from above the seal; an inlet for receiving groundwater above the seal; 20 a permeate outlet for water of improved quality; and an outlet below the seal for returning concentrate from the vessel to the aquifer after treatment.

2. A system according to claim 1 wherein the apparatus is in use is located in 25 situ in the borehole casing.

3. A system according to claim 1 or claim 2 wherein the seal engages the portion of the borehole casing of relatively smaller diameter. 20

4. A system according to claim I wherein the relatively smaller diameter portion is attached by a portion which tapers from the larger diameter portion to the portion of smaller diameter.

5 5. A system according to any one of the previous claims wherein the portion of smaller diameter comprises a upper section having an unperforated wall and a lower section having a perforated wall wherein the seal seals against the upper section having an unperforated wall and the fluids from the vessel after treatment, which are delivered below the seal, are 10 reintroduced to the aquifer through the lower perforated section of the smaller diameter portion.

6. A system according to any one of the previous claims wherein the one or more membrane treatment units are adapted for desalination. 15

7. A system according to any one of the previous claims wherein the one or more membrane treatment units are selected from the group consisting of reverse osmosis membranes, nanofiltration membranes, ultrafiltration membranes, electrodialysis reversal membranes and/or combinations 20 thereof.

8. A system according to any one of the previous claims wherein the one or more membrane treatment units comprise reverse osmosis membranes and the system further comprises a concentrate outlet for delivering 25 contaminants removed by reverse osmosis below the seal.

9. A system according to any one of the previous claims wherein the system further comprises a conduit for delivering the permeate outlet to the surface for use above ground. 30 21

10.A system according to any one of the previous claims wherein the permeate is reintroduced to the aquifer to improve the quality of water therein. 5

11.A system according to any one of the previous claims wherein the seal comprises one or more annular resiliently deformable ribs adapted to form a seal in the portion of borehole casing of relatively smaller diameter.

12. A system according to claim 11 wherein the ribs are the outer part of a 10 rubber sleeve attached to a cylindrical steel base which is blanked-off either end, and the concentrate line extends through the steel cylinder to allow concentrate fluids to move to below the seal from the vessel.

13.A system according to any one of the previous claims further comprising 15 pressure lines linking the vessel with the surface for measuring treatment pressures and for sampling of feed and concentrate, and allowing fluid communication between the surface and the treatment vessel for delivery of membrane cleaning fluids. 20

14.A system according claim 13 wherein a gate valve is used with a non return valve in the submersible pump when the pump is not operational to hydraulically isolate the treatment vessel during operation of the membrane cleaning process. 25

15. A system according to claiml3 or claim 14 wherein the system is provided with a source of cleaning fluids which comprise at least one cleaning fluid selected from the group consisting of an alkaline (pH1O) solution of permeate, acidic *(pH 2) solution of permeate, a sterilising solution of sodium metabisulphite in permeate and permeate itself.