Batch or semi-batch hyperfiltration system and the operation thereof

Abstract

Provided herein is a batch or semi-batch hyperfiltration system comprising a recirculation loop, a storage volume and a control device. The storage volume is suitable to receive, retain and discharge a portion of retentate from the system, and the control device is suitable to provide a response based on the detecting precipitation, for example the precipitation of sparingly soluble salts, in the retentate retained in the storage volume. Further provided is a method of treating water using the batch or semi-batch hyperfiltration system described herein.

Description

[0001] DI83938-WO-PCT PATENT

[0002] Title of the Invention

[0003] Batch or semi-batch hyperfiltration system and the operation thereof

[0004] Cross-references to related applications

[0005] The present application claims priority under 35 U.S.C. § 365(c) to U.S. Provisional Appln. Nos. 63 / 729,763 and 63 / 729,774, both filed on December 9, 2024, each of which is incorporated herein by reference in its entirety.

[0006] Field of the invention

[0007] Provided herein is a batch or semi-batch hyperfiltration system comprising a recirculation loop, a storage volume and a control device. The storage volume is suitable to receive, retain, and discharge a portion of retentate from the system, and the control device is suitable to provide a response based on detecting precipitation, for example the precipitation of sparingly soluble salts, in the retentate retained in the storage volume. Also provided is a method of treating water using the batch or semi-batch hyperfiltration system described herein.

[0008] Background of the Invention

[0009] Several patents, patent applications, and publications are cited in this description in order to more fully describe the state of the art to which this invention pertains. The entire disclosure of each of these patents, patent applications, and publications is incorporated by reference herein.

[0010] This application relates to a system and method for scale avoidance while operating a reverse osmosis or nanofiltration membrane.

[0011] There is a continuum between reverse osmosis (RO) and nanofiltration (NF) membranes, and there is a variety of membranes having different properties within each class. RO membranes are relatively impermeable to dissolved salts and typically reject more than about 95% (frequently substantially more than 95%) of salts having monovalent ions such as sodium chloride. By contrast, NF membranes are more permeable than RO membranes and typically reject less than about 95% of salts having monovalent ions while rejecting more than about 50% (and often more than 90%) of salts having divalent ions, depending upon the specific constituents in the feed (e.g., the species of divalent ion) and the operating conditions of the NF system. The term "hyperfiltration" collectively includes both reverse osmosis (RO) and nanofiltration (NF). In operation, a feed solution passes across the hyperfiltration membrane under pressure. The applied pressure causes "solvent" (e.g., water) to pass through the membrane (i.e., forming a "permeate") while "solutes" (e.g., salts) are unable to pass through the membrane and are concentrated in the remaining feed (i.e., forming a "retentate" or "concentrate" solution). In some cases, the retentate continues to be treated (and further concentrated) by additional membranes in series. In other cases, the retentate is recirculated to be additionally treated (and concentrated) by the same membrane. It is not uncommon that the relative concentration of dissolved salts may increase up to 4 to 10 times in the bulk, increasing the concentration of the sparingly soluble inorganic salts or minerals such as for example those including ions of calcium, magnesium, carbonate, sulphate, phosphate and silica ions. Because species rejected by the membrane need to either diffuse or mix back into the bulk solution, concentrations at the membrane surface are further increased (often substantially) by concentration polarization.

[0012] One inefficiency in RO and NF operation is that when the ion concentrations exceed a solubility limit, sparingly soluble salts may crystallize in the bulk water or on the membrane surface. Retained salts will begin to form scale in solution (homogeneous precipitation) or on the membrane surface (heterogeneous precipitation). Common scale types observed include calcite (CaCO3), gypsum (CaSO4)'2H2O), barite (BaSO4), strontium sulfate (SrSO4), silica (SiO2), and magnesium hydroxide (Mg(OH)2). Attempts may be made to control the concentration of multivalent cations in the feed water by reducing the sparingly soluble inorganic mineral ion concentration, adjusting the pH value, or adding anti-scaling agents. Still, scale formation can adversely impact both flux (or energy consumption) and salt passage. This is particularly the case when scale combines with organics and biofouling on the surface of a membrane.

[0013] Batch and semi-batch operations have potential to reduce scaling within an RO / NF system. The time and location of scale formation depend on several factors, but nucleation theory posits that a solution exceeding its thermodynamic solubility must be supersaturated for a period of time before nucleation of sparingly soluble salts can take place. This is known as the induction time, and some systems are operated in such a manner that concentrated solution is retained within the system for only a short time, refreshing the solution and membrane surface prior to substantial scale formation.

[0014] Closed-Circuit Reverse Osmosis (CCRO) systems which have been demonstrated to achieve higher salt concentrations in the retentate solution without substantial scale formation are commercially available from DuPont de Nemours, Inc., of Wilmington, DE, under the tradename DesaliTec(TM)CCRO High Efficiency Smart Reverse Osmosis Systems. See also U.S. Patent No. 8,025,804. In this semi-batch process, the system operates in many successive cycles and each cycle includes two steps (or modes). In the longer "recirculation" step, a lower-concentration permeate is continually produced and the concentrated retentate stream from hyperfiltration membrane elements is recycled back to the feed. In the "flush" step, the concentrated retentate stream is discharged to an outlet. When the duration of each cycle is approximately less than the induction time, it has been observed that scale formation will be reduced and higher retentate concentrations may be achieved before problems are observed.

[0015] When scale is formed, however, different approaches may be used to remove it. The operating system may be washed as described in U.S. Patent No. 10,407,331 or flow reversed as described in Inti. Patent Appln. Publn. No. W02005 / 053824. Inti. Patent Appln. Publn. No. WO2023 / 215207 describes the detection of the silica concentration in the retentate of a CCRO system and switching between three production phases including concentrate circulation, silica adsorption and concentrate purge.

[0016] Whether in a batch- or semi-batch system, however, the optimization of the many controlled operating parameters in a system that can impact scale formation (e.g., flux, recovery, cross flow rate, periodic cleanings) is a complex task. Beyond these controlled factors, natural variations in feed composition, temperature, and pH can each be very impactful to potential scale formation in hyperfiltration systems. Plainly, additional feedback would be useful to enable the optimization of operating parameters or the addition of cleaning steps within or between cycles.

[0017] Within the context of RO or NF membrane systems, scale formation is sometimes considered to be a type of fouling. There have been attempts to detect the presence of membrane fouling in order to avoid or reduce the fouling impact. For instance, the feed, retentate, or permeate may be intermittently sampled and monitored as indicators of potential fouling. Also, a fouling monitor device may be connected in series to the operating system. See, for example, the systems described in U.S. Patent Appln. Publn. No. 20230280266, or in Alexander et al., Desalination (2024), 586: 117817. A side-stream fouling monitor device may be connected in parallel to the operating system to detect the fouling, as for example in the systems described in Japanese Patent No. 5398695; U.S. Patent Appln. Publn. No. 20190151800; U.S. Patent No. 10,407,331; or in Lisdonk et al., Desalination (2000), 132 (1-3): 101-108. When the precipitate or fouling is detected by the fouling monitor device, it may be presumed that the fouling is also likely in the operating system. The systems described in these publications use a detection membrane in the fouling monitor device to simulate the membrane filtration in the operating system and to detect the absence or presence of fouling deposition on the detection membrane. U.S. Patent No. 10,407,331 also describes the further concentration in the fouling detection unit of the sampled retentate to induce precipitation in the fouling detection unit before the precipitation occurs in the larger system.

[0018] In general, change of one or more system parameters (including, without limitation, the flux, flow rate, pressure, concentrate conductivity, or recovery rate) can be detected and used as indicators of membrane fouling. See, for example, the descriptions in the references cited above and in Inti. Patent Appln. Publn. No. WO2019 / 225308. Alejandro et al., Membranes (2017), 7 (4): 62 lists other predictive models for RO membrane fouling including silt density index, modified fouling index, and fouling potential parameter, and others. Victor et al., J. Water Reuse Desai. (2012), 4 (3): 36-48 describes the measurement of the silt density index of a fouling monitor device to simulate RO system fouling. Minseok et al., Desalin. Water Treat. (2020), 183: 81-87 describes the change of vibration signals of RO system to identify fouling. Anurag et al., J. Membrane Sci. (1999), 159 (1-2): 185-196 and T.H. Chong et al., Desalination (2007), 204 (1-3): 148-154 describe the use of ultrasonic timedomain reflectometry. Other methods are also suggested in Farhat et al., Water Research (2015), 83: 10-20, and Supekar et al., J. Membrane Sci. (2020), 596: 117603.

[0019] Nevertheless, the system(s) and operation(s) mentioned above require either complex fouling monitor device(s) or indirect detection based on the system performance. The reverse deduction rather than the direct detection of actual or potential fouling adds to the complexity of the system(s) and the operation(s). Moreover, the result may be influenced by statistical noise or deviation in the monitoring method(s) and data, because those indirect detection parameters are also affected by phenomena other than fouling.

[0020] It is therefore apparent that a need remains for a system with a simple fouling monitor device and with a direct fouling detection operation, and for a system which is easy to operate, which accurately indicates fouling without interfering with the overall operation of the system, and which enables an effective response to optimize successive operation to reduce fouling tendency or to reduce membrane fouling. Moreover, there remains a need to specifically identify scale formation, distinct from other fouling types, as this may be addressed differently. Summary of the Invention

[0021] Accordingly, provided herein is a batch or semi-batch hyperfiltration system comprising a pressure vessel that contains a plurality of filtration elements, said pressure vessel comprising a pressure vessel inlet for receiving an inlet solution, a pressure vessel retentate outlet for discharging retentate, and a pressure vessel permeate outlet for discharging a filtered permeate; a recirculation loop comprising said pressure vessel, a first junction suitable for supplying said inlet solution to said recirculation loop, a second junction suitable for flushing (optionally intermittently) retentate from said recirculation loop, and a recirculation means suitable to pressurize retentate; a retentate line connected to said second junction, suitable for receiving (optionally intermittently) retentate from said recirculation loop; a storage volume suitable for receiving (optionally intermittently) and retaining a portion of retentate from a sample location selected from the recirculation loop or the retentate line; at least one valve suitable for segregating said recirculation loop from said storage volume; a measurement means suitable for detecting (optionally intermittently) a precipitate, for example a precipitate of sparingly soluble salts, or the absence of a precipitate in said portion of retentate retained within said storage volume and further suitable to generate a signal in response to the presence or absence of a precipitate; and a control device suitable for controlling cycles, wherein a cycle comprises one of the following two modes of operation: a first mode of operation wherein retentate from the pressure vessel retentate outlet is mixed with raw feed at the first junction, and wherein the concentrations of solutes within the recirculation loop increase with time as filtered permeate is discharged; and a second mode of operation wherein retentate is discharged to said retentate line; wherein said control device is suitable for initiating a sampling operation within a first cycle, and wherein, in said sampling operation, said storage volume is caused to receive a portion of retentate from the sample location selected from the recirculation loop, or from the retentate line; and wherein said control device is further suitable for causing the measurement means to detect the presence or absence of a precipitate in said portion of retentate and to initiate a response to the signal generated by the measurement means.

[0022] Further provided herein is a batch or semi-batch hyperfiltration system comprising: a pressure vessel assembly comprising at least one pressure vessel that contains a plurality of filtration elements in series, said pressure vessel assembly comprising an assembly inlet for receiving an inlet solution, an assembly retentate outlet for discharging a retentate from the assembly, and an assembly permeate outlet for discharging a filtered permeate from the assembly; a recirculation loop comprising said pressure vessel assembly, a first junction suitable for supplying said inlet solution to said recirculation loop, a second junction suitable for flushing said retentate from said recirculation loop, and a recirculation means suitable to pressurize said retentate; a retentate line connected to said second junction, suitable for receiving said retentate from said recirculation loop; a storage volume suitable for receiving a portion of said retentate from a sample location selected from the recirculation loop or the retentate line, and further suitable for retaining said portion of said retentate within said storage volume; at least one means such as a valve suitable for segregating said recirculation loop from said storage volume; a measurement means suitable for detecting a precipitate in said portion of said retentate retained within said storage volume for generating a signal to indicate the absence or presence of a precipitate; and a control device suitable for implementing successive cycles, wherein each successive cycle comprises two modes of operation: a first mode of operation wherein the retentate from the assembly retentate outlet is mixed with raw feed at the first junction, and the concentrations of solutes within the recirculation loop increase with time as the filtered permeate is discharged from the pressure vessel assembly; and a second mode of operation wherein the retentate is discharged from the system via said retentate line; wherein said control device is suitable for initiating a sampling operation within a first cycle, wherein said storage volume is caused to receive said portion of the retentate from the sample location; and wherein said control device is suitable for causing the measurement means to detect the precipitate within a second cycle in said portion of said retentate.

[0023] Further provided herein is a method of operating the batch or semi-batch hyperfiltration system, comprising the steps of running one or more successive cycles after a first cycle, wherein each successive cycle comprises one of the following two modes of operation: a first mode of operation where retentate from the pressure vessel retentate outlet is mixed with raw feed at the first junction, and wherein the concentrations of solutes within the recirculation loop increase with time as filtered permeate is discharged; and a second mode of operation where retentate is discharged to said retentate line; wherein the method comprises the steps of within the first cycle, initiating a sampling operation wherein said storage volume receives a portion of retentate from the sample location ; retaining said portion of retentate within said storage volume; initiating a precipitate detection operation wherein said measurement means detects the presence or absence of a precipitate in said portion of retentate to generate a signal; and sending said signal to said control device to determine whether to initiate a response and, if so, to determine the response based on the signal.

[0024] The advantages and features of novelty that characterize the invention are pointed out with particularity in the claims annexed hereto and forming a part hereof. For a better understanding of the invention, its advantages, and the objects obtained by its use, however, reference should be made to the drawings which form a further part hereof, and to the accompanying descriptive matter, in which there is illustrated and described one or more preferred embodiments of the invention. Brief Description of the Drawings

[0025] Figure 1 is a schematic diagram illustrating a system as described herein.

[0026] Figure 2 is a schematic diagram illustrating a second system as described herein.

[0027] Figure 3 is a schematic diagram illustrating a third system as described herein.

[0028] Figure 4 is a schematic diagram illustrating a fourth system as described herein.

[0029] Figure 5 is a block diagram of a control device as described herein.

[0030] Figures 6(a) and 6(b) are cross-sectional views illustrating two embodiments of pressure vessel assemblies.

[0031] Figure 7 is a flow chart illustrating the successive cycles of one operation timeframe as described herein.

[0032] Figure 8 is a flow chart illustrating the successive cycles of another operation timeframe as described herein.

[0033] Detailed Description of the Invention

[0034] Unless expressly stated to the contrary in limited circumstances, the conjunction "or" refers to an inclusive or and not to an exclusive or. For example, the condition "A or B" is satisfied by any one of the following: A is true (or present) and B is false (or not 30 present), A is false (or not present) and B is true (or present), and both A and B are true (or present). Exclusive "or" is designated herein by terms such as "either A or B" and "one of A or B", for example.

[0035] Osmosis is a natural process in which solvent is drawn through a semi-permeable membrane, from a solution of low solute concentration to one of high solute concentration. In reverse osmosis (RO), pressure is applied to the high solute concentration side of the membrane and the chemical potential gradient that drives osmosis is reversed. The result is permeation of solvent through the membrane, from a higher solute concentration side to a lower solute concentration side. The reverse osmosis feed is separated into a purified solvent solution (permeate) and a more concentrated (retentate) solution.

[0036] Nanofiltration (NF) is similar to reverse osmosis in that pressure applied to the membrane overcomes an osmotic pressure difference and forces water through a membrane. Nanofiltration membranes are typically distinguished by the fact that some salts are substantially passed, while other salts are selectively retained. NF membranes are sometimes referred to as "loose RO", and these may more readily pass larger neutral molecules. An advantage of NF membranes is that they often operate at lower energy due to both increased water permeability and reduced osmotic pressure across the membrane. RO and NF membranes can be made in both flat sheet and hollow fiber forms, both of which may be employed in elements. Flat sheet membranes may also be used in a plate- and-frame configuration. However, most commonly today, RO and NF membranes are configured in a series of spiral wound elements because such elements allow a large amount of membrane area to be packed into a small volume. The construction of spiral wound elements used in water purification has been described in the art. See, e.g., U.S. Pat. Nos. 5,538,642 and 5,681,467.

[0037] Because the feed stream must be under pressure in order for elements to function for reverse osmosis or nanofiltration, the elements are arranged to operate within a pressure vessel. Pressure vessels are known in the art and are described in U.S. Pat. No. 6,074,595 and U.S. Pat. No. 6,165,303, inter alia. A pressure vessel assembly may vary in size from a single pressure vessel to multiple pressure vessels combined in series or parallel. Typically, each pressure vessel contains several elements connected in series. In commercial RO applications, a large filtration system may be composed of more than 10,000 elements, usually distributed in pressure vessels containing 4 to 8 elements each.

[0038] In filtration systems configured for once-through operation,, high recovery is frequently obtained by employing a pressure vessel assembly that has multiple stages of parallel pressure vessels in series, each successive stage containing a smaller number of parallel pressure vessels. (See, for example, the tapered design in Fig. 1 of U.S. Patent Appln. Publn. No. 2005 / 00067341 Al.) An alternative configuration to operate continuously and obtain high recovery is illustrated in Fig. 13 of U.S. Patent . No. US 5,503,734 A, wherein a portion of the retentate is recirculated to mix with raw feed for re-treatment. The pressure vessel assembly within such a recirculating system may employ one pressure vessel or a stage of parallel pressure vessels. Less commonly, the recirculating system may employ multiple stages of pressure vessels in series. A disadvantage of operating these filtration systems continuously is that localized regions of the membrane surface may become substantially higher in the concentration of rejected species, resulting in fouling or scaling. Particularly, scale formation will happen most readily in regions that continuously operate with higher concentrations of scale-forming species than exist in the raw feed. For example, scaling frequently occurs in elements at the tail-end of a vessel.

[0039] In batch and semi-batch operations, high concentrations of species rejected and retained on the feed-side of a membrane are concentrated over time, and then the concentrated feed is periodically flushed from the system. In a semi-batch process, permeate may be continuously produced during both the concentrating and flushing modes. Batch-wise operation of a system designed for continuous operation is possible, such as by periodically stopping and flushing the systems with water or a lower concentration feed. However, while this may periodically reduce the high concentrations on membrane surfaces that are most likely to form scale, this approach is generally less economical than the use of a system designed for batch or semi-batch operation.

[0040] Referring now to the drawings, wherein like reference numerals designate corresponding structure throughout the views, and referring in particular to Fig. 1, a preferred filtration system that facilitates batch and semi-batch operations is illustrated. As with previously mentioned configurations, the filtration system 1 comprises a pressure vessel assembly 100. The pressure vessel assembly 100 comprises at least one pressure vessel 2 which itself preferably contains a plurality of filtration elements 3. Suitable pressure vessel assemblies and filtration elements are known in the art. Two examples are depicted in Figs. 6a and 6b; these and other suitable pressure vessel assemblies and filtration elements are further illustrated and described in Inti. Patent Appln. Publn.

[0041] No. WO2024 / 220488. The pressure vessel assembly 100 also comprises a pressure vessel assembly inlet 4 for receiving an inlet solution, a pressure vessel assembly retentate outlet 5 for discharging retentate, and a pressure vessel assembly permeate outlet 6 for discharging a filtered permeate.

[0042] Still referring to Fig. 1, the pressure vessel assembly 100 is within a recirculation loop 10. That recirculation loop 10 also contains a first junction 12 suitable for supplying said inlet solution to said recirculation loop 10, a second junction 14 suitable for intermittently flushing retentate from said recirculation loop 10, and a recirculation means 20 suitable to pressurize retentate. A retentate line 15 connected to the second junction 14 is suitable for receiving retentate from said recirculation loop 10 and intermittently discharging it from the system 1.

[0043] Still referring to Fig. 1, a control device 18 is suitable for controlling successive cycles, wherein each cycle comprises one of the following two modes of operation of the filtration system: a first mode of operation wherein retentate from the pressure vessel assembly retentate outlet 5 (also referred to herein as the "assembly retentate outlet 5") is mixed with raw feed 40 at the first junction 12, and wherein the concentrations of solutes within the recirculation loop 10 increase with time as filtered permeate is discharged; and a second mode of operation wherein the retentate is discharged to said retentate line 15.

[0044] Preferably, the recirculation means 20 within the recirculation loop 10 is separate and distinct from a high-pressure pump that supplies a pressurized inlet solution to the recirculation loop. In preferred embodiments, the recirculation means 20 is a pump. Those of skill in the art are capable of selecting a suitable pump for pressurizing the fluid within the recirculation loop 10. In an alternative embodiment (not shown), the recirculation loop includes the high-pressure pump, and retentate from the recirculation loop is mixed with the raw feed and re-pressurized by the high-pressure pump.

[0045] The filtration systems 1 shown in Figs. 1, 2 and 3 also include features suitable to detect scale formation. A storage volume 16 is suitable to intermittently receive a portion of retentate from a sample location 19 selected from either the recirculation loop 10 (Figs. 1 and 2) or the retentate line 15 (Fig. 3). This portion of retentate is subsequently held within the storage volume 16 for a period of time.

[0046] Referring once more to Fig. 1, the filtration system 1 further comprises: optionally at least one valve 21 suitable for segregating said recirculation loop 10 from said storage volume 16; a measurement means 17 suitable for detecting (optionally intermittently) precipitate in said portion of retentate retained within said storage volume 16 and also suitable for generating a signal based on the amount of precipitate present in the portion of retentate or the absence of a precipitate; and a control device 18 that is suitable for initiating a sampling operation, wherein said storage volume 16 is caused to receive a portion of retentate from the sample location 19 selected from the recirculation loop 10 or the retentate line 15.

[0047] Further provided herein are methods for operating RO or NF processes. Each cycle in the methods described herein comprises at least two modes of operation: a first mode of operation wherein retentate from the pressure vessel assembly retentate outlet 5 is mixed with feed solution at the first junction 12, and the concentrations of solutes within the recirculation loop 10 increase with time as filtered permeate is discharged; and a second mode of operation where retentate is discharged to said retentate line 15.

[0048] In an optional third mode of operation in any cycle, a scaling mitigation operation is performed to reduce membrane scaling. The scaling mitigation operation may be selected from any methods that are known in the art, preferably one or more of osmotic backwash, chemical cleaning, permeate flush, and feed water flush with or without permeation.

[0049] In operation, a small pressure drop occurs in the recirculation loop 10 as the inlet solution (feed solution) flows through a pressure vessel assembly 100. The recirculation means 20 is for the purpose of re-pressurizing retentate leaving the pressure vessel assembly 100 through the pressure vessel assembly retentate outlet 5, so that it can be mixed with the raw feed 40 at the first junction 12 to create an inlet solution. The recirculation means 20 can include a recirculation pump such as those described in, e.g., U.S. Patent No. 8,025,804 and employed in the DesaliTec™ CCRO system described above. The recirculation means 20 might also be a pressure recovery unit such as that sold by ERI (Energy Recovery of San Leandro, California). The recirculation means 20 might also be a jet pump.

[0050] Still referring to Figure 1, when the sample location 19 is in the recirculation loop 10, the retentate can be sampled to the storage volume 16 during the first mode of operation, during the second mode of operation, or during both modes of operation. Preferably, the retentate is sampled to the storage volume 16 during the first mode of operation. When the sample location 19 is in the retentate line 15, the retentate is preferably sampled to the storage volume 16 during the second mode of operation.

[0051] The storage volume 16 provides a location for controlled scaling for a time period that extends beyond the cycle in which a sample is collected. However, the storage volume 16 is not used to simulate the running situation of the membranes in the pressure vessel 2. There is no need or desire to install a substantially functioning membrane in the storage volume 16. Preferably, there is no substantially functioning membrane in the storage volume 16. More preferably, there is no membrane whatsoever installed in the storage volume 16. "Substantially functioning membrane" implies that at least a part of the membrane functions to filter solution within the storage volume. The storage volume 16 is a space mainly for receiving a portion of retentate and retaining the portion of retentate for a period of time for the measurement operation to detect precipitate in the portion of retentate. There is no limitation in the type, shape, or dimension of the storage volume 16.

[0052] Initiated by the control device 18, a portion of retentate can be dispensed to the storage volume 16 and retained in the storage volume 16. Precipitate may be present in the sampled portion of retentate. Alternatively, the sample may be held in the storage volume 16 for a period of time sufficient to cause a precipitate to form. While the precipitation of sparingly soluble salts may be favored in equilibrium conditions, the kinetics of scaling may prevent its formation or detection within a short time period. Accordingly, additional means may be employed to induce or accelerate the precipitation of sparingly soluble salts in the sampled portion of retentate.

[0053] For example, referring to Fig. 2, one or more temperature adjustment means 30 may be used to modify the temperature of the liquid retained within the storage volume 16. The temperature adjustment means 30 may include one or more of a heater, a cooler, or a heat exchanger. Alternatively, another fluid that is at a temperature different from the average temperature of the liquid in the recirculation loop 10 may be introduced into the storage volume 16 through a line or lines that are not depicted to modify the temperature of the liquid therein. The system 1 also preferably includes a temperature measurement means (not shown), such as a thermocouple, thermistor, or IR sensor to use in conjunction with the temperature adjustment means 30. Preferably, the fluid within the storage volume 16 is set to a prescribed temperature that encourages more rapid precipitation of the solute(s) in the retentate. Preferably, the temperature adjustment means 30 and the temperature measurement means, if present, are in communication with the controlling device 18, and the controlling device 18 communicates with the temperature adjustment means 30 to produce the heating or cooling necessary to effect precipitation in the retentate that resides in the storage volume 16.

[0054] Precipitation rates may also be affected by changing the composition of the solution retained within the storage volume 16. In one suitable process, a chemical dosing means is suitable to adjust pH value of the liquid retained within the storage volume 16, such as by introducing an acid, base or buffer solution. The chemical dosing means may also supply a salt solution. For example, when it is expected that a metal salt may precipitate from the retentate, the liquid retained within the storage volume 16 may be dosed with a soluble salt containing the same anion as the metal salt to drive the precipitation of the metal salt. Also preferably, the chemical dosing means is controlled by the control device 18. For example, the storage volume 16 may comprise a pH measuring means (not shown) that is in communication with the controlling device 18, and the controlling device 18 communicates with the chemical dosing means to add one or more of an acid, a base, a salt solution, or a buffer solution in an amount that will affect precipitation in the retentate that resides in the storage volume 16 through a line or lines that are not depicted. Any suitable pH measuring means may be used, for example, one that is selected from among the pH measuring devices that are well-known in the art. When the thermal adjustment means 30 includes introducing the other fluid into the storage volume 16, the chemical dosing means may also be used to effect this addition.

[0055] Still referring to Fig. 1, the storage volume 16 further comprises at least one measurement means 17 suitable for detecting precipitate or the absence of precipitate. Within the storage volume 16 at a prescribed time, there may be no precipitate detected or there may be particles (including crystals of sparingly soluble salts that may be present or suspended in the portion of retentate) retained within the storage volume 16. When the precipitate must be suspended in order for the measurement means 17 to function properly, the storage volume 16 is preferably equipped with an agitator or other means of maintaining the suspension, such as for example, stirring the retentate sample, shaking the storage volume 16, or passing bubbles of gas through the retentate sample. The measurement means 17 is preferably installed within the storage volume 16. Non-limiting examples of the measurement means 17 include analytical equipment capable of detecting, measuring, or both detecting and measuring light scattering or turbidity, light absorption, sound wave conductivity (acoustic sensing), specific ion concentration, or electrical conductivity or resistance. Suitable detection and measurement devices for use as measurement means 17 are well known in the art.

[0056] The control device 18 is further suitable to control operating cycles. Figure 5 illustrates units of a preferred control device 18, wherein each unit represents functions associated with a control device 18 that can be enacted through hardware or software. A sample unit 181 is suitable to initiate a sampling operation wherein said storage volume 16 is caused to receive a portion of retentate from the sample location 19 selected from one or both of the recirculation loop 10 and the retentate line 15. A measurement unit 182 is suitable to cause the measurement means 17 to detect, to quantify, or to detect and quantify a precipitate or the absence of precipitate in said portion of retentate retained within said storage volume 16. An input unit 183 is suitable to receive signals from the measurement means 17. An adjustment unit 184 is suitable to adjust the operation modes and operation parameters. The adjustment unit 184 is also suitable to enable the open and close operation of the valves 21, 21', 22, and 23, which are illustrated in Figs. 1 through 4). Valves 22 and 23 may be separate, as depicted in Figures 1 through 4, for example, and these valves may be operated independently of each other. Alternatively, fluid flow within the recirculation loop 10 and the retentate line 15 may be directed by a three-way valve (not shown) at the second junction 14, the open and close operation of which is also enabled by the adjustment unit 184. A notification unit 185 is suitable to transmit or display a notification message that may be generated by the adjustment unit 184 or received by the input unit 183, for example. A storage unit 187 is suitable to store historical information including one or more of the signals, parameters, operation modes, adjustment, and learning history, etc.

[0057] Still referring to Fig. 5, a learning unit 186 is suitable to enable a machine learning algorithm to conduct one or more of the following operations:

[0058] 1) evaluate the relative effectiveness of the operation parameters or operation modes in reducing scaling tendency,

[0059] 2) determine the most effective operation parameter or operation mode, and

[0060] 3) communicate with the adjustment unit 184 to cause it to initiate the most effective operation parameter or operation mode.

[0061] In addition, the learning unit 186 is suitable to enable a machine learning algorithm to conduct one or more of the following operations:

[0062] 1) evaluate the relative effectiveness of the multiple different scaling mitigation operations in reducing membrane scaling,

[0063] 2) determine the most effective operation from the multiple different scaling mitigation operations, and

[0064] 3) communicate with the adjustment unit 184 to cause it to initiate said most effective operation of the multiple different scaling operations.

[0065] The method of operating the batch or semi-batch hyperfiltration system described herein comprises the steps of running successive cycles, for example, a first cycle and a second cycle. Each cycle comprises at least two modes of operation, as is set forth in detail above. Accordingly, the method comprises the steps of within the first cycle, initiating a sampling operation where the storage volume 16 is caused by the control device 18 to receive a portion of retentate from the sample location 19 selected from the recirculation loop 10, or the retentate line 15; retaining the portion of retentate within the storage volume 16, controlled by the control device 18, and initiating a precipitate detection operation wherein the measurement means 17 detects precipitation in the portion of retentate retained within the storage volume 16 to generate a signal.

[0066] The detection of the precipitate may be conducted during the first cycle or the second cycle. The terms "first cycle", as used herein does not refer to the initial cycle or the physically first cycle counted from the very beginning of the system operation. Rather, the term "first cycle" may be used to refer to any cycle in which a sampling operation is initiated by transferring fluid to the storage volume 16 . It follows that when the sampling operation is conducted intermittently or in multiple cycles, there are multiple "first cycles." A "second cycle" closely follows a first cycle in this order, although one or more cycles may take place between the "first cycle" and the "second cycle". Additional sets of "first cycle" and "second cycle" which are closely neighboring cycles in this order are referred as "another first cycle" and "another second cycle". There could be two or more cycles for one sampling operation. Besides a first cycle within which a sampling operation and optionally a detection operation are initiated, there could be a third cycle after the second cycle, a fourth cycle after the third cycle, and so on till another first cycle is initiated by another sampling operation. In some embodiments, the storage volume 16 may be cleaned before each sampling operation, to remove residual precipitate or reagent(s) that may cause a false detection of precipitation in the succeeding sample.

[0067] As illustrated in Figure 7 and Figure 8, for example, a method of operating the batch or semi-batch hyperfiltration system described herein comprises the steps of running successive cycles comprising a first cycle, a second cycle and a third cycle in this order. While not illustrated in Figures 7 and 8, intermediate cycles may also be located between the first and second cycles to allow for increased precipitation time or between the second and third cycles, such as to enable increased data for decisions.

[0068] Each cycle comprises at least two modes of operation: a first mode of operation where retentate from the pressure vessel assembly retentate outlet 5 is mixed with raw feed 40 at the first junction 12, and the concentrations of solutes within the recirculation loop 10 increase with time as filtered permeate is discharged; and a second mode of operation where retentate is discharged to said retentate line 15;

[0069] The first mode of operation is generally at least twice as long as the second mode of operation in a cycle.

[0070] In an optional third mode of operation that may occur after precipitation is detected in the first mode or second mode of operation, a scaling mitigation operation suitable to reduce membrane scaling, as described above, is applied. The scaling mitigation operation may be controlled by the control device 18 and operated by a scaling mitigation means 31, as illustrated in Fig. 4. Referring once more to Figs. 7 and 8, a solid round dot indicates the point at which an operation is initiated, a dashed line indicates the time period within which at any point an operation can be initiated, and the solid line indicates the time period during which an operation lasts. As illustrated in Figure 7, at any point during the second mode of operation within the first cycle of some preferred methods, a sampling operation can be initiated wherein the storage volume 16 is caused to receive a portion of retentate from the sample location 19 selected from the recirculation loop 10, or the retentate line 15. Preferably the sample location 19 is in the retentate line 15 to simplify the process without impact on the system recovery rate. As illustrated in Figure 8, at any point during the first mode of operation and the second mode of operation within the first cycle of other preferred methods, a sampling operation can be initiated wherein the storage volume 16 is caused to receive a portion of retentate from the sample location 19 from the recirculation loop 10.

[0071] The concentrations of solutes within the recirculation loop 10 increase with time as filtered permeate is discharged in the first mode of operation. The concentration at the second junction 14 continues to increase during early stages of the second mode of operation. The maximum concentration at the second junction 14 during a cycle is defined as the "highest concentration" in the cycle. Preferably the retentate is sampled when its solute concentration is within 20% of the highest concentration in this cycle, more preferably within 10% of the highest concentration in this cycle, even more preferably within 5% of its highest concentration in this cycle. The highest concentration may be different in different cycles.

[0072] In any one of the first cycles, the sampling operation is initiated and may continue for as long a time as is necessary to acquire a sample that is of sufficient volume or for detection of a precipitate or for treatment to cause or enhance precipitation. Preferably the sampling operation ends within the second mode of operation within the first cycle.

[0073] In general, after the second mode of operation within a first cycle, there comes a second cycle. The sampled retentate in the storage volume 16 is preferably retained during at least a part of the first mode of operation within the second cycle till the measurement means 17 begins a precipitate detection operation in the retained retentate within the storage volume 16 and generates a signal. There may be multiple precipitate detection operations in the retained retentate within the storage volume 16, generating multiple signals. The precipitate detection operation ends and preferably the storage volume 16 is emptied via line 41 and cleaned of precipitate or reagent(s), as described above, before the next sampling operation begins. Also preferably, the precipitate detection operation ends before the end of the second mode of operation within the second cycle. More preferably, the precipitate detection operation ends before the second mode of operation within the second cycle, as depicted in Figures 7 and 8. The measurement means 17 is preferably recalibrated or cleaned after each precipitate detection operation.

[0074] The signal generated by the measurement means 17 is sent to the control device 18 and, based on the signal, the control device 18 determines whether to provide a response, as described in greater detail below. That is, the retentate is sampled in a first cycle and retained until the precipitate detection is conducted in the next cycle, for example, the second cycle. The signal from the precipitate detection is received by the control device 18 and leads to a corresponding response that may include the modification of one or more operation parameters such as pump pressure, recovery, flux, cross flow rate, duration, pH, other chemical dosing, and flow direction. The control device 18 may also be used to alternate between the first and second modes of operation. Each mode of operation has a respective duration in time that may be varied by the control device 18.

[0075] Referring once more to Figs 1 through 4, the control device 18 also operates at least one valve 21, 21', 22, 23 to cause the storage volume 16 to receive a portion of retentate from the recirculation loop 10 or from the retentate line 15. For example, as illustrated in Figure 1, the valve 22 may be closed while the valve 21 is open, to cause a portion of retentate to be routed to the storage volume 16. As illustrated in Figure 2, the valves 22 may be closed while the valve 21' is open to cause a portion of retentate to be routed to the storage volume 16. As illustrated in Figure 3, the valve 22 may be closed while the valves 21' and 23 are open to cause a portion of retentate to be routed to the storage volume 16.

[0076] Still referring to Figs. 1 through 4, the control device 18 also operates at least one valve 21, 21' to cause the liquid within the storage volume 16 to be segregated from the recirculation loop 10. As shown in Fig. 1, a valve 21 could be positioned between the storage volume 16 and the recirculation loop 10. Alternatively, as shown in Fig. 2, a valve 21' could be positioned downstream of the storage volume 16. In another acceptable implementation, a conduit (also shown in Fig. 2) extends between the recirculation loop 10 and the storage volume 16, and a valve 21' located downstream of the storage volume 16 prevents flow through the conduit. In this way, although the recirculation loop 10 and the storage volume 16 are fluidly connected, they are effectively segregated from mixing over the time period of a cycle. Preferably, as shown in Figure 1, a valve 21 is located between the recirculation loop 10 and the inlet of the storage volume 16. An exit line 41 from the storage volume 16 connects to the retentate line 15 or to a point 42 downstream of the retentate line 15. When the valve 21, 21' is closed, the liquid in the recirculation loop 10 does not mix with the liquid within the storage volume 16 and does not influence the solute concentrations in the storage volume 16. Alternatively, as illustrated in Figure 3, the storage volume 16 may be connected to the retentate line 15, such that a reject valve 23 intermittently isolates both the retentate line 15 and the storage volume 16 from recirculation loop 10.

[0077] The control device 18 also operates to retain the liquid within the storage volume 16. The measurement means 17 may be equipped with a precipitate detection operation or multiple precipitate detection operations. The period of time during which the retentate sample is held in the storage volume 16 is long enough to identify precipitation or potential precipitation in the portion of retentate. In addition, the retaining time is long enough to accomplish at least one task selected from the group consisting of: identifying any change of potential precipitation in the portion of retentate; or identifying a change in the rate of change of precipitation; or completing the precipitate detection operation or multiple precipitate detection operations in the cycle. Preferably, the portion of retentate within said storage volume 16 is retained during at least a part of the second mode of operation within the first cycle and at least a part of the first mode of operation within the second cycle. Within the second cycle, the retaining time should exceed 25%, more preferably 50%, even more preferably 75%, of the duration of the first mode of operation.

[0078] In summary, the control device 18 receives a signal from said measurement means 17. Based on the signal(s) from a single cycle or from multiple cycles, the control device 18 determines whether to provide a response selected from

[0079] 1) initiating a third mode of operation,

[0080] 2) modifying one or more operation parameters, or

[0081] 3) providing a notification of a recommended response.

[0082] Optionally, based on the signal(s) from a single cycle or from multiple cycles, the control device 18 determines whether to provide a response selected from:

[0083] 1) initiating a third mode of operation within a second cycle or a third cycle,

[0084] 2) modifying one or more operation parameters within a third cycle, or

[0085] 3) providing a notification of a recommended response.

[0086] To improve efficiency or shorten the retaining time, additional means may be used for precipitation inducing operations to induce precipitation in the sampled portion of retentate. For example, temperature adjustment means 30 are described in detail above. The temperature of the liquid retained within the storage volume 16 may be adjusted by the temperature adjustment means 30 to deviate by more than 2°C, more than 5°C, more than 7°C, or more than 10°C in a direction that promotes scale formation, from the temperature of retentate from the recirculation loop 10. Chemical dosing means (not shown) to adjust pH value of the liquid retained within the storage volume 16 are also discussed above. The pH of the liquid retained within the storage volume 16 to is adjusted to deviate by more than 0.1 pH units, more than 0.5 pH units, more than one pH unit, or more than two pH units, in a direction that promotes scale formation, from the pH of retentate from the recirculation loop 10.

[0087] The measurement means 17 detects precipitate in the portion of retentate retained within the storage volume 16. The measurement means 17 is preferably installed within the storage volume 16. Temperature and pH value of the retained retentate can be adjusted, or vibration and centrifugation can be used to induce or fasten the precipitation. Preferably light scattering is used. Light scattering detects the suspended particles or crystals directly. Light scattering also tracks the change of suspended particles or crystals directly. The measurement means 17 quantifies light scattering from the portion of retentate retained within the storage volume 16 during at least a part of the first mode of operation within the second cycle, preferably, during at least a part of the second mode of operation within the first cycle and at least a part of the first mode of operation within the second cycle. When electrical resistance is measured by the measurement means 17, at least one electrode (not shown) preferably further comprises a heating element (not shown).

[0088] The measurement means 17 preferably also detects any change of the measured parameters, and the rate of change of the measured parameters in the portion of retentate retained within the storage volume 16. Different rates of change may lead to different responses. A rapid rate of change may require an immediate discharge of the retentate from the recirculation loop 10. If the retained retentate is stable for a reasonable time without precipitation, it may be inferred or predicted that precipitation will not occur in the system. If the retained retentate is stable for a longer time than the reasonable time without precipitation, which is defined as a "safe time", the system recovery, that is, the volume of permeate relative to the volume of supplied feed, can be increased. "Reasonable time" and "safe time" depend on the composition of the inlet solution, the operation parameters, and the precipitation inducing operations. With sufficient experience of the filtration system's operation, the reasonable time and the safe time may be pre-set based on the inlet solution and operation parameters. During the reasonable time, there could be a "quick-check time." The control device 18, optionally using a timer, may initiate one precipitation detection operation when the sampled retentate has been retained for the length of the quick-check time period, another when the sampled retentate has been retained for the reasonable time period, and a third when the sampled retentate has been retained for the safe time period. If precipitate is detected before or at the quick-check time, the retentate in the recirculation loop 10 may be discharged immediately, and the operation parameters may be adjusted to reduce the scaling tendency. The system may also be cleaned by a third mode of operation. If precipitate is not detected before or at the quick-check time but is detected before or at the reasonable time, the retentate in the recirculation loop 10 may be discharged, and the operation parameters may be optimized to reduce the scaling tendency. The system may also be cleaned by a third mode of operation. If precipitate is not detected at or after the reasonable time, there is no need to adjust operation parameters since precipitation is not occurring in the system at this point. Optionally, the operation parameters may be optimized to reduce the scaling tendency. The quick-check time is preferably 30 seconds or one minute or more. The reasonable time is preferably two minutes or more. The safe time is preferably five minutes or more. Each of the quick-check time, the reasonable time, and the safe time is preferably determined with the concurrent deployment of any precipitationinducing operations that are deemed appropriate.

[0089] In addition, the rate of change in the amount of precipitation over time may be determined. This gradient may be less sensitive to common changes in the environment or in the system operation, compared to a single measurement of the amount of precipitation. Therefore, multiple precipitate detection operations may also be initiated in a single cycle or over multiple cycles, preferably based on one or more pre-set time interval(s) to determine the rate of change of the amount of precipitation.

[0090] While certain of the preferred embodiments of the present invention have been described and specifically exemplified above, it is not intended that the invention be limited to such embodiments. Rather, it is to be understood that even though numerous characteristics and advantages of the present invention have been set forth in the foregoing description, together with details of the structure and function of the invention, the disclosure is illustrative only, and changes may be made in detail, especially in matters of shape, size and arrangement of parts within the principles of the invention to the full extent indicated by the broad general meaning of the terms in which the appended claims are expressed.

Claims

Claims1. A batch or semi-batch hyperfiltration system 1 comprising: a pressure vessel assembly 100 comprising at least one pressure vessel 2 that contains a plurality of filtration elements 3 in series, said pressure vessel assembly 100 comprising an assembly inlet 4 for receiving an inlet solution, an assembly retentate outlet 5 for discharging a retentate from the assembly, and an assembly permeate outlet 6 for discharging a filtered permeate from the assembly; a recirculation loop 10 comprising said pressure vessel assembly 100, a first junction 12 suitable for supplying said inlet solution to said recirculation loop 10, a second junction 14 suitable for flushing said retentate from said recirculation loop 10, and a recirculation means 20 suitable to pressurize said retentate; a retentate line 15 connected to said second junction 14, suitable for receiving said retentate from said recirculation loop 10; a storage volume 16 suitable for receiving a portion of said retentate from a sample location 19 selected from the recirculation loop 10 or the retentate line 15, and further suitable for retaining said portion of said retentate within said storage volume 16; at least one means such as a valve suitable for segregating said recirculation loop 10 from said storage volume 16; a measurement means 17 suitable for detecting a precipitate in said portion of said retentate retained within said storage volume 16 for generating a signal to indicate the absence or presence of a precipitate; and a control device 18 suitable for implementing successive cycles, wherein each successive cycle comprises two modes of operation: a first mode of operation wherein the retentate from the assembly retentate outlet 5 is mixed with raw feed 40 at the first junction 12, and the concentrations of solutes within the recirculation loop 10 increase with time as the filtered permeate is discharged from the pressure vessel assembly 100; and a second mode of operation wherein the retentate is discharged from the system 1 via said retentate line 15;wherein said control device 18 is suitable for initiating a sampling operation within a first cycle, wherein said storage volume 16 is caused to receive said portion of the retentate from the sample location 19; and wherein said control device 18 is suitable for causing the measurement means 17 to detect the precipitate within a second cycle in said portion of said retentate.

2. The batch or semi-batch hyperfiltration system of claim 1, wherein said control device 18 is suitable to cause said storage volume 16 to receive said portion of retentate from the sample location 19 during the second mode of operation within said first cycle.

3. The batch or semi-batch hyperfiltration system of claim 1 or claim 2, further comprising a temperature adjustment means 30 suitable for adjusting the temperature of the liquid retained within storage volume 16, wherein said control device 18 is optionally further suitable to operate the temperature adjustment means 30, or wherein the system 1 optionally comprises a second control device 18' that is suitable to operate the temperature adjustment means 30.

4. The batch or semi-batch hyperfiltration system of any preceding claim, wherein said storage volume 16 is free of any substantially functioning membrane.

5. The batch or semi-batch hyperfiltration system of any preceding claim, wherein the measurement conducted by the measurement means 17 comprises one or more methods selected from the group consisting of light scattering, turbidity, specific ion concentration, electrical conductivity, and electrical resistance; and preferably wherein the measurement means 17 comprises a light scattering detector.

6. A method of operating the batch or semi-batch hyperfiltration system 1 of any preceding claim, comprising the steps of running a first cycle, a second cycle, and multiple successive cycles, wherein each cycle comprises two modes of operation: a first mode of operation in which retentate from the assembly retentate outlet 5 is mixed with raw feed 40 at the first junction 12, and the concentrations of solutes within the recirculation loop 10 increase with time as filtered permeate is discharged; anda second mode of operation in which retentate is discharged to said retentate line 15; and further comprising the steps of: a) within said first cycle, initiating a sampling operation wherein said storage volume 16 receives a portion of the retentate from the sample location 19; b) retaining said portion of the retentate within said storage volume 16 for a period of time; c) during said second cycle, causing the control device 18 to initiate a precipitate detection operation wherein said measurement means 17 detects an amount of precipitation or the absence of precipitation in said portion of the retentate, and wherein said measurement means 17 generates a signal corresponding to the amount of precipitation or to the absence of precipitation; d) transmitting said signal to said control device 18; and e) causing the control device 18 to determine whether to provide a response based on said signal.

7. The method of claim 6 wherein said sampling operation is initiated during the second mode of operation in said first cycle.

8. The method of claim 6, wherein said method comprises a third cycle subsequent to said second cycle, and wherein said control device 18 determines whether to provide a response selected from the set consisting of1) initiating a third mode of operation within said second cycle or third cycle,2) modifying one or more operation parameters within said third cycle, or3) providing a notification of a recommended response.

9. The method of claim 6, wherein said control device 18 determines said response based upon the rate of change of said signal.

10. The method of claim 6, wherein said control device 18 determines said response based on signals from multiple cycles.

11. The method of claim 6, wherein said portion of retentate is retained within said storage volume 16 during at least a part of the second mode of operation within the first cycle and at least a part of the first mode of operation within the second cycle.

12. The method of claim 11, wherein within said second cycle, said portion of retentate within said storage volume 16 is retained for a time exceeding 25% of the duration of the first mode of operation.

13. The method of claim 12, wherein within said second cycle, said portion of retentate within said storage volume 16 is retained for a time exceeding 75% of the duration of the first mode of operation.

14. The method of claim 6, wherein the control device 18: determines the alternation between said first and second modes of operation, each mode of operation having a respective duration in time that may be varied by the control device 18; operates at least one valve 21, 22, 23 to cause: the storage volume 16 to receive a portion of retentate from the recirculation loop 10 when the solute concentration of the retentate in the recirculation loop 10 is within 20% of its highest concentration in the cycle; or the liquid within the storage volume 16 to be retained for a time period that exceeds 25% of the duration of the first mode of operation; receives a signal from said measurement means 17, and determines whether to provide a response based on said signal, wherein said response is selected from the set consisting of:1) initiating a third mode of operation within said second cycle or said third cycle,2) modifying one or more operation parameters within said third cycle, or3) providing a notification of a recommended response.

15. The method of claim 6, wherein said measurement means 17 is selected from the group consisting of analytical equipment to determine light scattering or turbidity, ion concentration, sound wave conductivity, or electrical conductivity or resistance; and preferably wherein the measurement means 17 quantifies light scattering from said portion of retentate retained within said storage volume 16.

16. The method of claim 15, wherein said measurement means 17 quantifies a change in light scattering of said portion of retentate during the period of time.

17. The method of claim 6, further comprising a step of adjusting the temperature of liquid retained within the storage volume 16 to deviate by more than 10°C or more than 2°C, in a direction that promotes scale formation, from the temperature of retentate in the recirculation loop 10.

18. The method of claim 6, further comprising a step of adjusting the pH of the liquid retained within the storage volume 16 to deviate by more than two pH units, in a direction that promotes scale formation, from the pH of retentate in the recirculation loop 10.

19. The method of claim 6, further comprising a step wherein the control device 18 uses a machine learning algorithm to:1) evaluate the relative effectiveness of the parameters and / or operation modes,2) determine the most effective parameter and / or operation mode, and3) initiate the most effective parameter and / or operation mode.

20. The method of claim 6, further comprising a step wherein the control device 18 initiates multiple different scaling mitigation operations separated by at least one cycle comprising said first and said second modes, and uses a machine learning algorithm to:1) evaluate the relative effectiveness of said multiple different scaling mitigation operations in reducing membrane scaling;2) determine the most effective of said multiple different scaling mitigation operations; and3) initiate said most effective of said multiple different scaling operations.

21. The method of claim 6, wherein said measurement means 17 comprises at least one electrode to measure electrical resistance, and wherein the at least one electrode optionally further comprises a heating element.

Images