"BRINE SQUEEZER"

FIELD OF THE INVENTION

The present invention relates to membrane based liquid treatment apparatus, in particular reverse osmosis apparatus to be used to increase the recovery or efficiency of a desalination plant.

BACKGROUND OF THE INVENTION

Cross-flow filtration membrane based liquid treatment apparatus include, but are not limited to, apparatus employing reverse osmosis and nano-filtration membrane technology. For the purposes of providing background and describing the present invention, reference to reverse osmosis membranes will be used. For simplicity water will be referred to throughout this document as the process liquid, the most common application of reverse osmosis.

An reverse osmosis apparatus uses a pump to force feed-water into the reverse osmosis membrane assembly. The feed water passes along one side of the membrane until it meets a restriction on the outlet. The driving pressure caused by the pump pressure and the restriction, forces some of the feed water to pass through the membrane. Essentially the membrane characteristics allows mainly water to pass through the membrane, rejecting most of the dissolved solids in the remaining water (referred to as reject water or concentrate). The water allowed to pass through the reverse osmosis membrane is collected (referred to as product water or permeate) and the reject water is usually dumped as waste to drain. The ratio of the permeate flow rate, divided by the feed flow rate stated as a percentage is known as the recovery rate of the apparatus.

The design philosophy of membrane based liquid treatment apparatus, such as reverse osmosis apparatus, is based upon meeting a specified permeate quality and flow rate and selecting a suitable reverse osmosis membrane from one of the reverse osmosis membrane manufacturers. Conventional apparatus are normally

designed, operated and controlled using pre-set inlet feed pressure (a pressure controlled apparatus) or pre-set flow rates and recovery rates (flow controlled apparatus) with feed water and permeate water quality monitored as an adjunct.

Membrane selection, system configuration and operating parameters are based on the membrane manufacturer's data-sheets, application handbooks and/ or selection software. This manufacturer's data includes a factor of safety to ensure the membrane will perform reliably to meet membrane performance guarantees (if any). Furthermore, apparatus designers apply a factor of safety to their apparatus to ensure their end customer (reverse osmosis apparatus user) satisfaction. In particular, the manufacturer's data is intended to ensure that the membrane does not scale during operation. Scaling is the deposition of water- insoluble constituents such as salt deposits which can crystallize and form a layer of scale on the inlet side of the membrane during operation. The end result is that the membrane selection and apparatus design philosophy is conservative, given the objectives of such apparatus and accordingly, the recovery rate of the apparatus is much lower than is actually achievable.

A typical reverse osmosis plant operating with brackish water may have a recovery rate of 85%. This effectively means that there is 15% reject of saltier water. It is one object of this invention to provide a method and apparatus for processing this reject saltier water to maximise the overall recovery rate.

It is a further object of the present invention to provide a method for operating a cross-flow filtration membrane based liquid treatment apparatus which maximises the recovery rate of the apparatus.

SUMMARY OF THE INVENTION

In one form the invention comprises a method for improving the recovery of product liquid from a filter apparatus including the steps of:

(a) passing a liquid including scale forming materials through a filter for separating the materials from the liquid;

(b) altering one or more parameters of the apparatus until the scale forming materials form a scale on a portion of the filter; (c) continually monitoring the apparatus to detect the scale formation, thereby identifying a scaling threshold of the apparatus;

(d) maintaining the apparatus at or above the scaling threshold by altering one or more parameters where necessary; and

(e) recovering the product liquid which passes through the filter.

The parameter of the apparatus which is altered in step (b) includes at least one of:

- the flow rate of product liquid;

- the recovery rate of the product liquid; - the pressure difference between a feed liquid inlet and a product liquid outlet; and

- the feed pressure of the liquid containing scale forming materials.

The step of monitoring the apparatus includes monitoring at least one of the following characteristics:

- a change in the flow of product liquid;

- a change in the recovery rate of the product liquid;

- a change in the pressure difference between a feed liquid inlet and a liquid reject outlet; - a change in the feed pressure of the liquid containing scale forming materials; and

- a change in the conductivity of the product liquid.

Preferably, the liquid is water.

Preferably, the scale forming materials are a sparingly soluble salt.

Preferably, the filter is a membrane.

More preferably, the filter is a reverse osmosis membrane.

In another form the invention comprises a filter apparatus comprising a filter unit, an inlet for liquid provided under pressure, a product outlet and a reject outlet, the filter apparatus further including:

(a) means to detect a characteristic of the liquid at a first location in the filter apparatus;

(b) means to detect a characteristic of the liquid at a second location in the filter apparatus; and

(c) means to compare the characteristic of the liquid at the first location and the second location to detect a scaling threshold; and (d) means to adjust a parameter of the apparatus depending upon the compared characteristic to operate the apparatus at or above the scaling threshold.

The parameter of the apparatus which is altered in step (d) includes at least one of:

- the flow rate of product liquid;

- the recovery rate of the product liquid;

- the pressure difference between a feed liquid inlet and a liquid reject outlet; and - the feed pressure of the liquid containing scale forming materials.

The characteristic of the apparatus includes at least one of:

- a change in the flow of product liquid;

- a change in the recovery rate of the product liquid; - a change in the pressure difference between a feed liquid inlet and a liquid reject outlet;

- a change in the feed pressure of the liquid containing scale forming materials; and

- a change in the conductivity of the product liquid.

Preferably, the first location is selected from the group including the inlet, the reject outlet or the product liquid outlet and the second location is selected from the group including the inlet, the reject outlet or the product liquid outlet.

More preferably, the first location is the inlet and the second location is the reject outlet. Alternatively, the first location is the inlet and the second location is the product liquid outlet.

Preferably, the means to detect a characteristic is selected from a conductivity meter, a flow meter and a pressure sensor.

In one embodiment, the means to detect a change, compare and adjust the detected characteristic is a hydro-mechanical feedback control system. In another embodiment the means to detect a change in the detected characteristic is a programmable logic controller.

Preferably there can be further included a recirculation line from the reject outlet to the inlet to recirculate water for recirculation of reject water for a selected period of time.

In an alternative form the invention comprises a reverse osmosis apparatus comprising a first reverse osmosis unit and a second reverse osmosis unit, the first reverse osmosis unit comprising an inlet for water provided under pressure, a product outlet and a reject outlet, the second reverse osmosis unit comprising an inlet connected to the reject outlet of the first reverse osmosis unit, a second product outlet and a second reject outlet, the second reverse osmosis unit further including:

(a) means to detect a characteristic of the water at a first location in the reject outlet of the first reverse osmosis unit;

(b) means to detect a characteristic of the liquid at a second location in the second reverse osmosis unit; (c) means to compare the characteristic of the liquid at the first location and the second location whereby to determine the scaling threshold of the second reverse osmosis unit; and

(d) means to adjust a parameter of the second reverse osmosis unit to operate the second reverse osmosis unit at or above the scaling threshold.

In an alternative form the invention comprises a method for improving the recovery of product liquid from a dual unit filter apparatus operated in duty/ standby configuration, the dual unit filter apparatus comprising a first filter unit and a second filter unit, the process including the steps of: (a) determining a scaling threshold for a filter of each of the first and second filter units;

(b) passing a liquid including scale forming materials through the first filter unit at or above the scaling threshold of the first filter unit until scaling reaches a selected amount; (c) passing the liquid including scale forming materials through the second filter unit at or above the scaling threshold of the second filter unit until scaling reaches a selected amount while cleaning the first filter unit; (d) returning the first filter unit to operation and cleaning the second filter unit; and (e) continuing to operate and clean the first and second filter units alternatively.

Preferably the step of determining the scaling threshold of each filter unit comprises the steps of (a) passing a liquid including scale forming materials through the respective filter unit;

(b) altering one or more parameters of the apparatus until the scale forming materials form a scale on a portion of the filter; and

(c) continually monitoring the apparatus to detect the scale formation, thereby identifying a scaling threshold of the apparatus.

Preferably the step of cleaning each of the units comprises the step of recirculating a cleaning fluid through the unit from an inlet to a reject outlet for a selected period of time, to remove accumulated scale.

Preferably each of the filter units is a reverse osmosis membrane.

In an alternative form the invention comprises a reverse osmosis apparatus comprising a first reverse osmosis unit and a second reverse osmosis unit in a parallel duty/ standby configuration, the first reverse osmosis unit comprising an inlet for water provided under pressure, a product outlet and a reject outlet, the second reverse osmosis unit comprising an inlet for water provided under pressure, a product outlet and a reject outlet; each reverse osmosis unit further including;

(a) means to detect a characteristic of the water at a first location; (b) means to detect a characteristic of the liquid at a second location;

(c) means to compare the characteristic of the liquid at the first location and the second location whereby to determine the scaling threshold for each of the first and second reverse osmosis units; and

(d) means to adjust a parameter of each reverse osmosis unit to operate each reverse osmosis unit at or above the scaling threshold;

(e) means to select supply of the water provided under pressure to the water provided under pressure and means to supply cleaning fluid to the other of the first and second reverse osmosis units.

Hence it will be seen, that the invention provides a process and apparatus to maximize the recovery of product water from feed water from a cross-flow

filtration membrane based apparatus using a control system to continually drive the membrane at or above the threshold of scaling based on membrane operating conditions rather than a control system based on set-points pre-determined from a membrane manufacturer's design guideline. This enables operation of the apparatus at the membrane scaling threshold to maximize product water recovery. The apparatus provides the advantage that the recovery of product water from the feed stream is controlled relative to the membrane dynamic operating conditions rather than controlled to a set of pre-determined set-points.

Throughout this specification unless the context requires otherwise, the words 'comprise' and 'include' and variations such as 'comprising' and 'including' will be understood to imply the inclusion of a stated integer or group of integers but not the exclusion of any other integer or group of integers.

The reference to any prior art in this specification is not, and should not be taken as, an acknowledgement or any form of suggestion that such prior art forms part of the common general knowledge.

Specific embodiments of the invention will now be described in some further detail with reference to and as illustrated in the accompanying drawings. These embodiments are illustrative, and is not meant to be restrictive of the scope of the invention. Suggestions and descriptions of other embodiments may be included within the scope of the invention but they may not be illustrated in the accompanying figures or alternatively features of the invention may be shown in the figures but not described in the specification.

BRIEF DESCRIPTION OF THE DRAWINGS

Illustrative embodiments of the present invention will be discussed with reference to the accompanying drawings and examples wherein:

Figure 1 shows a schematic flow diagram of a reverse osmosis membrane based filter apparatus incorporating a brine squeezer according to the present invention;

Figure 2 shows schematic of a background art reverse osmosis membrane based filter apparatus using a conventional control system based on pressure control;

Figure 3 is a schematic of a background art reverse osmosis membrane based filter apparatus using a conventional control system based on flow ratio control; Figure 4 is a schematic of a single pass reverse osmosis membrane and reject control valve control using a differential pressure measurement according to a preferred embodiment of the present invention;

Figure 5 show a duty/ standby configuration with two reverse osmosis units according to one embodiment of the present invention; Figure 6 shows an alternative embodiment of reverse osmosis unit according to an embodiment of the present invention;

Figure 7 shows schematically an alternative embodiment of the invention where the scaling threshold is determined and scaling is controlled by the measurement of recovery rate; Figure 8 shows schematically an alternative embodiment of the invention where the scaling threshold is determined and scaling is controlled by the measurement of recovery flow rate only;

Figure 9 shows schematically an alternative embodiment of the invention where the scaling threshold is determined and scaling is controlled by the measurement of feed pressure only;

Figure 10 shows schematically an alternative embodiment of the invention where the scaling threshold is determined and scaling is controlled by the measurement of conductivity.

DESCRIPTION OF PRIOR ART AND PREFERRED EMBODIMENTS Figure 2 is background art illustrating a basic pressure controlled apparatus using prior art design and control system methodology. Feed water is provided to the apparatus 1, and fed to the high pressure feed pump 2, which in turn feeds the reverse osmosis membrane 3. Reject control valve (RCV) 4, of fixed setting, provides the restriction to drive a percentage of the water in the feed stream through the reverse osmosis membrane to produce product water (or permeate) at product water outlet 6. The remaining reject water (or concentrate) is dumped to drain 5. Pressure sensor 7, measures the feed water pressure at the inlet to the reverse osmosis membrane. Pressure information is sent via signal line 8 to a controller 9. The controller maintains the pre-determined feed pressure set-point by adjusting pump speed (in the case of a frequency controlled centrifugal pump) via motor 10 and output signal line 11. Variations include throttling the pump using a control valve on the pump discharge in lieu of pump speed. Feed conductivity sensor 12, and product water conductivity sensor 13 provide water quality information to the operator only and do not take part in the process control.

The feed pressure set-point is pre-determined during apparatus design according to the membrane flux required (the rate of permeate flow across a membrane area) required; the membrane manufacture's technical data and recommendations based on membrane feed pressure; flux limit; and scaling limits. The recovery rate of product water is dependent upon these features, however, it is possible that more product water could have been recovered from the feed water rather than dumped to drain as reject.

Figure 3 is background art illustrating a basic filter apparatus using prior art design and control system methodology based on flow ratios. Feed water is provided to the apparatus 15, and fed to the high pressure feed pump 16, which in turn feeds the reverse osmosis membrane 17. Reject control valve (RCV) 18,

provides the restriction to drive a percentage of the water in the feed stream through the reverse osmosis membrane to produce product water at product water outlet 19. The remaining reject water is dumped to drain 20. Flow sensor 21, measures the feed water flow rate and flow sensor 22, measures the reject water flow rate. Flow rate information is sent via signal lines 23 and 24 to a controller 25. Flow rate and recovery set-points pre-determined during apparatus design according to the membrane manufacturer's design guidelines are programmed into controller. Controller 25, sends output control signal via signal line 26, to reject control valve 18, and output control signal via signal line 30 to pump motor 29. The reject control valve and pump speed will be adjusted to maintain the predetermined flow rate and recovery set points. Feed conductivity sensor 27, and product water conductivity sensor 28 provide water quality information to the operator only and do not take part in the process control. Again, since the process works at pre-determined values, some additional reject water could have been recovered as product water if the apparatus were optimized.

In these two background art processes, the apparatus is not designed or operated at the limit of the membranes capability. Prior art control philosophy does not use sensors to find and control to a limit but rather controls to a pre-determined set point. However, in some applications there is a need to optimize the amount of product water produced from the feed water. An example of this is where the feed water may be a scarce resource or where it is difficult to dispose of the reject water. The present invention can be used, for example, to produce additional product water from the reject of a prior art reverse osmosis apparatus to reduce the amount of waste water to be disposed of.

Figure 1 shows a schematic flow diagram of a reverse osmosis membrane based filter apparatus incorporating a brine squeezer according to the present invention. In a usual reverse osmosis unit a brackish feed water 40, for instance, is supplied to a reverse osmosis apparatus 42 and a product water 44 of improved quality is produced and a reject water 46 of increased salinity is produced. The reverse

osmosis apparatus 42 may have multiple reverse osmosis units operated in series or in parallel. At highest efficiency the recovery (product as a proportion of feed) may typically be up to 85% . This means that there is at least 15% waste which must be disposed of. This disposal may require, for instance, evaporation pans.

5 By the addition of a brine squeezer stage for the reject or waste according to the present invention the amount of saline water to be sent to evaporation can be i considerably reduced.

A brine squeezer stage 47 according to the present invention takes the 15% reject 0 from line 46 from the first reverse osmosis apparatus 42 and processes it as discussed below. At the brine squeezer stage 47 a reverse osmosis unit 48 there may give a recovery of typically 50% of product water with respect to feed which will give 7 ¹ A ⁰ Zo additional recovery at the brine squeezer product outlet 50 with respect to the original brackish feed water 40 and a reject of 7Vi ⁰ Zo at the brine 5 squeezer waste outlet 52 with respect to the brackish feed water 40. This means that the overall efficiency has increased to 92 ¹ Zz ⁰ Zo and only half the water needs be transferred to the evaporation pans, for instance. It will be realized that these figures can vary considerably depending a number of factors including water quality, type of salts, membrane type and the like. Savings in the necessary size of 0 an evaporation pan, for instance, could pay for the brine squeezer stage 47.

Figure 4 shows a brine squeezer according to one embodiment of the present invention. A feed liquid is provided at the inlet 29 of a filter apparatus. The liquid can be reject water from for instance a conventional reverse osmosis plant as 5 discussed above. A high pressure feed pump 30, provides the inlet feed water flow to the reverse osmosis membrane 31. The feed water passes along one side of the membrane until it meets a restriction provided by a reject control valve (RCV) 32. Reject control valve 32, provides the restriction to drive a percentage of the water in the feed stream through the reverse osmosis membrane 31, to produce 0 product water at product water outlet 50. The reject water in line 34 is dumped to drain 34a.

The membrane performance is dictated by the solubility limit of materials dissolved in the feed water (i.e. salts). Once a solubility limit is exceeded the dissolved salts begin to precipitate and deposit or scale on the membrane surface. This is known as membrane scaling. The scale is formed by scale forming materials in the liquid. The scale forming materials are dissolved solids such as salts or any other materials which can form a scale or crystallize out onto the membrane.

Scaling commences at the tail end of the membrane where the concentration of the dissolved solids is highest and the cross flow velocity is lowest due to the fact that a percentage of product water has been produced from the feed water at the leading end of the membrane area leaving less water at lower flow rate at the tail end on the reject water side. However, the remaining water at the tail end on the reject water side largely contains the original mass of dissolved salts.

As the membrane scales the membrane surface becomes blocked preventing the passage of water and forcing the leading (unblocked) membrane area to carry the load. Subject to the extent of membrane scaling and whether or not scaling has occurred to such an extent to cause membrane damage, it is possible to remove scale from a membrane by using membrane cleaning chemicals and cleaning processes to extend the service life of the membrane.

Manufacturers usually conservatively recommend solubility limits of the scaling salts and a minimum cross-flow velocity to minimize scaling of the membrane surface. These characteristics therefore dictate the recovery and flow rates allowed by the membrane manufacturer for a given membrane. In the present invention, however, a control system is used to measure the membrane operating parameters at or above a scaling threshold (i.e. as the membrane scales) and adjusts the apparatus to so that the actual membrane performance is at its limit based on these measurements.

Scaling of the membrane can be detected by any or a combination of the following characteristics:

- a decrease in the flow rate of product water; - a decrease in recovery rate of the product water;

- an increase in the pressure difference between the feed liquid inlet and the reject liquid outlet;

- an increase in the feed pressure; and

- an increase in the conductivity of the product liquid.

Different dissolved materials have different behaviors and solubility limits so that the monitoring of all, or different combinations of the above characteristics may be required to detect membrane scaling for different feed water types. The first two characteristics are directly related and typically observed in a pressure controlled apparatus whilst the third and fourth are typically observed in a flow controlled apparatus. The pressure difference across the feed/ reject side of the membrane to the product water is termed the trans membrane pressure (TMP). The pressure difference between the feed inlet and reject outlet on the concentrate side is termed the membrane differential pressure (DP). An increase in differential pressure (DP) is a common indication of membrane scaling.

The present invention monitors one or more of the above characteristics and adjusts or alters the parameters of the apparatus in accord with these characteristics so as to operate the membrane at its scaling limit to optimize (or at least improve) the recovery of product liquid. Differential pressure (DP) will be used to illustrate the fundamentals of the invention, however, it will be understood that any of the apparatus' parameters could be altered in order to identify a scaling threshold. The parameters of the apparatus which can be altered include at least one of: - the flow rate of product water;

- the recovery rate of the product water;

- the pressure difference between the inlet and the reject; and

- the feed pressure of the water.

Once the parameters of the apparatus at the scaling threshold have been identified, the apparatus is maintained at or above the scaling threshold by altering the parameters as necessary.

For illustration of this, referring back to Figure 4, a pressure sensor 35 (the means for detecting a characteristic of the liquid), is located on the inlet feed line to the reverse osmosis membrane (a first location) and another pressure sensor 36, is located on the reverse osmosis membrane reject outlet line (a second location). The signals from the pressure sensors are sent to a controller 37, via signal lines 38 and 39. In the preferred embodiment, the controller is a hydro-mechanical feedback control system. Alternatively, the parameters of the filter apparatus are controllable (altered by) a programmable logic controller (PLC). The controller calculates the differential pressure (DP) by subtracting the reject outlet line pressure from the inlet feed line pressure. The controller therefore acts as a means for comparing the characteristics of the liquid. It should be understood that other means for detecting a characteristic could be used, for example a conductivity meter could be used to detect a change in conductivity. Furthermore, the locations of the pressure sensors or conductivity meters can be varied, e.g. it is an option that pressure sensors are located at the inlet and the product water outlet so the TMP rather than the DP is measured

The apparatus is initially set to run at the maximum DP according to the membrane manufacturer's recommendations. As described above the manufacturer's recommendation usually include a factor of safety. The DP will be monitored over a period of time and the DP trend analyzed. A very slow increase in DP over time will indicate that the membrane is not being operated at a high recovery rate for the feed water being supplied (i.e. more product water could be obtained). The apparatus recovery will be increased by adjusting the parameters

for example by adjusting the reject control valve (RCV) 32, to restrict the reject stream further and increase recovery. The DP and DP rate of change will continue to be measured to determine the DP threshold for membrane scaling. The membrane scaling threshold DP is then used as the apparatus set-point.

As at least a portion of the membrane scales, which will be inevitable when operating at or above the membrane scaling threshold, the DP will increase. Upon sensing the measured DP is greater than the threshold DP the controller sends a signal via signal line 40, to the RCV 32, to reduce the restriction on the reject outlet to reduce the measured DP back to the DP threshold set-point. This means for controlling the supply of liquid to the apparatus improves the output of the filter since it runs to a threshold rather than to manufacturer's data. Product water 50 which passes through the filter is recovered and mixed with the product water or permeate 44 (see Figure 1) to boost the overall efficiency or recovery of the reverse osmosis plant.

As the membrane scales and this process of operating at the membrane scaling threshold continues, the recovery of the apparatus may fall. Based on trend analysis and possible pilot plant studies a low recovery value can be identified that provides a point at which the membrane can be cleaned to remove scale before it reaches an unrecoverable stage.

In other forms of the invention the other aforementioned phenomena associated with membrane scaling indications can be used in conjunction with, or separately to, each other as a means to operate the membrane at the membrane scaling threshold by adjusting the apparatus according to measured parameters. However, the control philosophy of measurement and adjustment of the apparatus to operate the membrane at the scaling threshold remains consistent.

Another embodiment of the invention is shown in Figure 5. In this embodiment there is used two reverse osmosis units in a parallel duty/ standby configuration

where one of the apparatuses can undergo chemical cleaning (due to forced scaling) while the other apparatus is in service thereby allowing continuous product water production without interruption.

Feed water 62, which may come from a first reverse osmosis stage as discussed in Figure 1, is supplied to a duty/ standby parallel circuit which has reverse osmosis units 60 and 70. In the first circuit pump 64 pressurizes the feed water and supplies it under high pressure to the reverse osmosis unit 60. Permeate is extracted in line 66 and waste is extracted in line 68. Use of the first circuit continues until the reverse osmosis unit 60 has scaled up to such an extent that it is very inefficient. This stage can be determined by pressure differential, etc, as discussed above. Water supply is then diverted to the second circuit and pump 74 pressurizes the feed water and supplies it under high pressure to the reverse osmosis unit 70. Permeate is extracted in line 76 and waste is extracted in line 78. The first reverse osmosis unit 60 is then cleaned by re-circulating cleaning liquid from tank 80 via pump 82 into the first reverse osmosis unit 60 and extracting it via the waste line 68 and back to the tank 84. Alternatively cleaning can be by reverse flow. Similarly when the second circuit is scaled up the cleaning of the first circuit is stopped and that circuit put back into service and the second circuit cleaned in a similar manner to that of the first circuit. The circuits can be designed so that a single high pressure pump supplies both reverse osmosis units 60 and 70. The scaling thresholds for each of the first and second reverse osmosis units 60 and 70 can be determined as explained in relation to any one of Figures 4, 7, 8, 9 or 10.

The times for scaling up and cleaning can vary enormously depending upon the nature and quantity of the scaling materials in the supply water and recovery attained but in one embodiment the circuits may be in service for an hour and cleaned for an hour.

Figure 6 shows an alternative embodiment of brine squeezer according to the present invention. In this embodiment the reverse osmosis unit 90 is supplied with feed water 92 via high pressure pump 94. Recirculation line 98 returns a proportion of the water passing through the reverse osmosis unit back to the feed line to be re-pressurised by the high pressure pump 94 and recirculated through the reverse osmosis unit 90. The amount of recirculation can be set by setting of the reject recirculation valve 96 on the recirculation line 98. The amount of product 97 can be set by the reject control valve 99. This gives high flow recirculation of feed through the reverse osmosis unit 90. The high flow will tend to discourage scaling and therefore increase the time between cleaning cycles. The scaling thresholds for the reverse osmosis unit 90 can be determined as explained in relation to any one of Figures 4, 7, 8, 9 or 10.

The embodiment of reverse osmosis unit shown in Figure 6 can be used for each of the reverse osmosis units shown in Figure 5.

For this embodiment of the invention it is advantageous to use a larger than standard channel spacer membranes to enable higher flow rates through the reverse osmosis unit and more efficient chemical cleaning after scaling has occurred. The use of larger than standard channel spacer membranes can be applied to all embodiments of the invention.

Figure 7 shows schematically an alternative embodiment of the invention where the scaling threshold is determined and scaling is controlled by the measurement of recovery rate. This embodiment is similar to the embodiment shown in Figure 4 and the same reference numerals are used for corresponding items.

Figure 7 shows a feed liquid provided at the inlet 29 of a filter apparatus. The liquid can be reject water from for instance a conventional reverse osmosis plant as discussed above. A high pressure feed pump 30, provides the inlet feed water flow to the reverse osmosis unit 31. The feed water passes along one side of the

reverse osmosis membrane 31a until it meets a restriction provided by a reject control valve (RCV) 32. Reject control valve 32, provides the restriction to drive a percentage of the water in the feed stream through the reverse osmosis membrane 31a, to produce product water at product water outlet 50. The reject water is dumped to drain 34.

Flow measuring device 102 measures the flow (Fi) in the input line and flow measuring device 104 measures the flow (F2) in the output line. A change in recovery is used to determine the scaling threshold and the controller 37 adjusts the reject control valve 32 via line 105 to adjust the recovery rate or flow rate of product liquid.

As an alternative, the controller 37 can control, via line 107, a variable speed motor 30a driving the centrifugal pump 30 to maintain optimum recovery between cleaning cycles by adjusting the feed pressure of the liquid containing scale forming materials.

Figure 8 shows schematically an alternative embodiment of the invention where the scaling threshold is determined and scaling is controlled by the measurement of recovery flow rate only. This embodiment is similar to the embodiment shown in Figure 4 and the same reference numerals are used for corresponding items.

Figure 8 shows a feed liquid provided at the inlet 29 of a filter apparatus. The liquid can be reject water from for instance a conventional reverse osmosis plant as discussed above. A high pressure feed pump 30, provides the inlet feed water flow to the reverse osmosis unit 31. The feed water passes along one side of the reverse osmosis membrane 31a until it meets a restriction provided by a reject control valve (RCV) 32. Reject control valve 32, provides the restriction to drive a percentage of the water in the feed stream through the reverse osmosis membrane 31a, to produce product water at product water outlet 50. The reject water is dumped to drain 34.

Flow measuring device 106 measures the flow (F2) in the output line. A change in output flow is used to determine the scaling threshold and the controller 37 adjusts the reject control valve 32 via line 108 to adjust the recovery rate or flow rate of product liquid.

Figure 9 shows schematically an alternative embodiment of the invention where the scaling threshold is determined and scaling is controlled by the measurement of feed pressure only. This embodiment is similar to the embodiment shown in Figure 4 and the same reference numerals are used for corresponding items.

Figure 9 shows a feed liquid provided at the inlet 29 of a filter apparatus. The liquid can be reject water from for instance a conventional reverse osmosis plant as discussed above. A high pressure feed pump 30, provides the inlet feed water flow to the reverse osmosis unit 31. The feed water passes along one side of the reverse osmosis membrane 31a until it meets a restriction provided by a reject control valve (RCV) 32. Reject control valve 32, provides the restriction to drive a percentage of the water in the feed stream through the reverse osmosis membrane 31a, to produce product water at product water outlet 50. The reject water is dumped to drain 34.

Feed pressure measuring device 112 measures the pressure (P) in the input line and supplies the signal to the controller 37. The rate of pressure increase is used to determine the scaling threshold and is then used to control the setting on the reject control valve 32 via line 109 to maintain optimum recovery before cleaning. Alternatively there can be a fixed reject control valve 32 and the pump 30 can be a variable speed pump and its speed can be controlled to maintain optimum recovery before cleaning.

Figure 10 shows schematically an alternative embodiment of the invention where the scaling threshold is determined and scaling is controlled by the measurement

of conductivity. This embodiment is similar to the embodiment shown in Figure 4 and the same reference numerals are used for corresponding items.

Figure 10 shows a feed liquid provided at the inlet 29 of a filter apparatus. The liquid can be reject water from for instance a conventional reverse osmosis plant as discussed above. A high pressure feed pump 30, provides the inlet feed water flow to the reverse osmosis unit 31. The feed water passes along one side of the reverse osmosis membrane 31a until it meets a restriction provided by a reject control valve (RCV) 32. Reject control valve 32, provides the restriction to drive a percentage of the water in the feed stream through the reverse osmosis membrane 31a, to produce product water at product water outlet 50. The reject water is dumped to drain 34.

Conductivity measuring device 114 measures the conductivity (C ₁ ) of the water in the input line and conductivity measuring device 116 measures the conductivity (C ₂ ) of the water in the output line. Conductivity difference across the reverse osmosis unit is used to determine the scaling threshold and the controller 37 adjusts the reject control valve 32 via line 111 to adjust the recovery rate or flow rate of product liquid.

Any of the different methods of determining scaling threshold and maintaining recovery at or above the scaling threshold as discussed in relation to Figures 4 and 7 to 10 can be used on relation to the embodiments of brine squeezer shown in Figures 5 and 6.

Although preferred embodiments of the apparatus of the present invention has been described in the foregoing detailed description, it will be understood that the invention is not limited to the embodiment disclosed, but is capable of numerous rearrangements, modifications and substitutions without departing from the scope of the invention. Modifications and variations such as would be apparent to a skilled addressee are deemed to be within the scope of the present invention.