Membrane-based online fouling monitor for performance tracking in reverse osmosis and nanofiltration systems

Abstract

A novel reverse osmosis or nanofiltration (RO / NF) system is developed that utilizes a uniquely configured membrane permeate flow path within the system to detect and respond to the onset of fouling, generating time-sensitive data. Membrane performance data under real-time operating conditions is then used to rapidly detect membrane fouling, fouling rate, and fouling causes. Subsequently, controller-based system-generated actions are employed to stop fouling and recover from or slow it down. Furthermore, operator intervention steps are anticipated, planned, and scheduled, if necessary, to restore optimal system operating conditions. The end result is a novel, energy-efficient, and advanced (machine learning) reverse osmosis system for brackish water desalination and fouling management.

Description

[0001] none.

[0002] Statement on federally funded research

[0003] none.

[0004] Cross-references to related applications

[0005] The priority date is U.S. Patent Application No. 18 / 242,922 and the granted patent #US11938450B1. Technical Field

[0006] This invention relates to the field of desalination, and primarily focuses on the desalination of brackish water (typically in the range of 100 mg / L to 25,000 mg / L based on total dissolved solids (TDS). The concepts disclosed in this application are specific to reverse osmosis (RO) and nanofiltration (NF) systems and related processes utilizing RO and NF membranes within pressure vessels. The novel concepts described in this application allow for online monitoring of membrane fouling in RO and NF systems. Utilizing a uniquely configured membrane permeate flow path within the system, membrane performance data from real-time operating conditions are used to rapidly detect membrane fouling, fouling rate, and fouling causes, followed by remedial actions to stop, recover from, or slow fouling, and to anticipate, plan, and schedule operator intervention steps to restore optimal system operating conditions. The end result is a novel, energy-efficient, and advanced (intelligent) reverse osmosis system for brackish water desalination with robust fouling management. Background of the Invention

[0007] Without limiting the scope of the invention, the background of this invention relates to water purification membranes using RO / NF membrane technology to remove total dissolved solids (TDS). Primary water purification may involve biological or chemical methods, such as bioreactors or clarifiers with coagulation / flocculation processes, followed by the removal of suspended solids using porous media such as bag filters, cartridge filters, multilayer filters, sand filters, and microfiltration or ultrafiltration membranes. Primary treatment processes cannot remove dissolved solids and impurities, focusing only on organic matter and suspended solids. Additionally, secondary treatment processes such as softening, ion exchange (IX), NF, or RO are implemented to remove dissolved solids (desalination), such as sodium, chloride, sulfate, carbonate, silicate, calcium, and magnesium.

[0008] NF and RO membranes have proven to be effective and energy-friendly for desalination applications. They are designed and highly optimized to remove specific materials from the influent, such as total dissolved solids (TDS) in the form of monovalent, divalent, and trivalent ions, including Na+. + Cl - Mg 2+ Ca 2+ SO42- Al 3+ N 3- And other high molecular weight materials, such as sugars, chemicals, organic molecules, and other macromolecules. RO membranes are optimized to reject minimal ions, such as Na+. + Cl - The NF membrane is optimized to retain slightly larger and more charged Ca ions. ++ and Mg ++ ion.

[0009] RO or NF membranes have a polymer matrix with a charged and dense barrier layer (typically a polyamide membrane). Most separation occurs in the barrier layer, which allows water to pass through while rejecting solutes such as salt ions. These membranes can treat water with varying salt concentrations (10 to 40,000 parts per million [ppm]) and can remove 95%–99.8% (50%–90% in the case of NF membranes) of salt from the feed stream. This process requires applying high pressure to the feed side of the membrane, typically 50 psi-300 psi (3 bar-20 bar) for low-salinity brackish water (100 ppm-10000 ppm TDS), 300 psi-600 psi (20 bar-40 bar) for medium-salinity brackish water (10000 ppm-25,000 ppm TDS), and 600 psi-1,000 psi (40 bar-70 bar) for seawater (30,000 ppm-45,000 ppm TDS), to overcome the osmotic pressure corresponding to the salt concentration.

[0010] During filtration, NF / RO membranes allow water to permeate while trapping dissolved solids, leading to an increased concentration of dissolved ions and the formation of a concentration polarization (CP) layer near the membrane surface. As concentration polarization develops near the membrane surface, the concentrations of foulants, scaling ions (such as sulfates, carbonates, silicates, colloidal silica), and biological elements (such as bacteria, biofilms, bacterial food (nitrates), etc.) increase, typically accelerating fouling and scaling on the membrane surface. Furthermore, the CP layer increases osmotic pressure, resulting in a higher net driving force required for the same permeability. Therefore, the membrane requires additional pressure (electrical energy) to maintain its target productivity. Subsequently, once their flux decreases by more than 20%, they require chemical in-situ cleaning (CIP), resulting in downtime and additional chemical and labor costs. Over time, irreversible fouling may occur, necessitating membrane replacement. Moreover, each CIP degrades membrane performance due to heating and exposure to corrosive acids and caustic environments. Typically, membranes may degrade beyond their usable lifespan after approximately 20–25 CIP cycles. Managing membrane fouling by using a uniquely configured membrane permeate flow path and analysis leading to real-time performance measurements via a “membrane element monitor” can extend the duration between CIP cycles and reduce irreversible fouling, thus significantly extending membrane life. Furthermore, fouling management operations result in reduced downtime, reduced chemicals and energy consumption (lower operating pressure), and reduced wastewater discharge (higher recovery rates), thereby achieving optimal operation and lower maintenance costs.

[0011] A typical brackish water RO / NF treatment system consumes approximately 1.0 kWh–2.5 kWh / 1000 gallons (3800 liters) of treated product water. Membrane fouling in these systems, which typically experience 10%–20% flux losses, can lead to high energy usage of 20%–40%. With real-time fouling detection, mechanisms using membrane element monitors and controller-based remedial responses will manage flux declines and achieve energy savings of up to 30% over their operational life.

[0012] Increased concentrations of CP layers and contaminants on membrane surfaces, particularly in low-mixing regions and areas with high concentrations leading to ion precipitation, create favorable conditions for the formation of seed sites for accelerated fouling and biofouling. Several strategies have been employed in existing NF / RO systems to mitigate the formation of CP layers near the membrane surface and to reduce membrane adhesion. These strategies include: a) spacer design and geometry that promote mixing [Shewei et al. - 1], b) using unique spacers to increase crossflow velocities [Geraldes et al. - 2], c) membranes with surface modifications – such as hydrophilic, less charged, or smoother surfaces – to reduce contaminant adhesion [Freeman et al. - 3], and d) operating systems with critical flux limits for a given type of water. Critical flux is defined as the membrane productivity per unit area that allows the flux to remain stable over an extended period of time. In addition, for membrane hydraulic design and surface modification, chemicals (scale inhibitors, oxidants, and biocides) are typically injected into the feed stream of the NF / RO system – a) to delay the precipitation or expansion of scale-forming ionic substances such as CaCO3, CaSO4, CaPO4, BaSO4, MgSO4 solubility limitations, b) to chelate oxidizing metal substances such as Fe, Mn, and Al, and c) to decompose biofilm and reduce biofouling.

[0013] During membrane fouling, depending on the nature of the contaminants, in a multi-stage, multi-membrane system, the first-stage lead-membrane may become fouled from particulate loads, biofouling, or organic matter more rapidly than any other membrane in the system. This is because the lead-membrane's peak flux rate treats >20% more water than intermediate membranes and >50% more than tail-membrane. Similarly, the tail-membrane in the final stage typically becomes fouled from scale deposits and oxidants generated by the continuous concentration of the feed stream as it passes through the system. Tail-membranes generally do not experience significant biofouling or particulate fouling because their flux is significantly lower than that of the lead-membrane, and the higher salinity environment is less conducive to biological growth.

[0014] In another published U.S. patent [Agnihotri et al.-4] (incorporated herein), the applicant teaches a technique to reduce flux distribution differences between the lead and tail segments in a multi-stage RO / NF system by mixing the feed stream with interstage concentrate before supplying it as a feed stream to subsequent stages. This technique also teaches how to increase periodic mixing in the final stage by supplying an additional feed stream to the final stage and temporarily reducing the recovery rate to agitate and flush settled particles in the low-rate zone during operation. Such a strategy allows for a flatter flux distribution in the RO / NF system and disperses particle loading and reduces scale buildup, ultimately allowing for high recovery rate operation.

[0015] When an RO / NF system begins to foul, whether due to an unknown system failure, a change in feed water chemistry, or other factors, the membrane begins to lose production (flux), and depending on its particulate or biological load or scale, either the lead element or the tail element will foul first. Since the system operates at a fixed output, once any membrane element fouls and causes flux loss, the production load shifts to other membranes. Today, most NF / RO systems operate at a set production point (product demand) and automatically compensate for flux losses due to fouling or scaling by increasing operating pressure. Apart from observing the increase in operating pressure, operators are unaware of how the system fouls over time. The pressure increase can be caused by more than one factor – a) a decrease in feed water temperature, b) membrane fouling (surface area loss due to cake or scale buildup), c) an increase in salinity, and d) membrane compaction during high-temperature CIP. Once the feed pump reaches its pressure limit, the system is no longer able to produce the required product. At this point, the operator has no choice but to subject the entire system to CIP treatment, which can take 8–12 hours and may require cleaning steps using low-pH or high-pH chemicals or combinations thereof. Of the four causes of increased operating pressure, changes in temperature and salinity can be observed via probes; however, fouling information is not directly visible in current probes. Experts in this subject use normalized temperature and salinity data to track whether the membrane is fouled or scaled. However, normalized flux data is not helpful for multi-stage systems because yields are inversely correlated between stages with temperature and pressure loss. As temperatures rise, higher salinity concentrations occur in later stages due to increased overall permeability, and increased pressure loss results in significantly reduced yields from tail-stage elements, leading to higher yields from upstream elements. These correlations are difficult to normalize and can only measure and interpret average behavior across the entire system. In most practical implementations, NF / RO systems often foul or scale and reach points of inoperability without the option of pre-intervention. Finally, offline CIP must be performed when the system is taken out of service. Repeated CIP cycles result in decreased membrane retention performance with each cycle, eventually requiring replacement.

[0016] Ideally, if an NF / RO system can detect the onset of fouling early, remedial steps can be taken to stop or slow it down. These steps may include: a) reducing total throughput (the system's average flux), b) reducing total recovery (a decrease in the concentration factor), c) improving flux distribution, d) more frequently disrupting the CP layer, and e) adding a biocide (in the case of biofouling) or a low-pH scale-dissolving solution, or a high-pH organic matter-dissolving solution, or a specific chemical selected for a specific contaminant during a shutdown flush. However, in typical multistage systems with 12-18 membranes in a cascaded series [DOW RO Technical Handbook-5], fouling and scaling progress slowly, and on average, the entire system may lose 10% of flux or experience a 20% increase in pressure. Such small decreases or increases in pressure occur over long periods – worst-case scenario 2-3 days, and best-case scenario 2-3 months. An example of a multistage 3:2:1 / 4M configuration is shown in […]. Figure 1 The diagram is shown for reference, highlighting the staged design of brackish water desalination and the use of a common header to collect permeate from all membranes within the pressure vessel.

[0017] For monitoring RO and NF systems, existing techniques have focused on visualized, stand-alone, ex-situ monitors [Cohen et al., Rahardianto et al., and Echizen et al. – 6, 7, 8]. These techniques are poorly representative of online membrane behavior in terms of surface velocities, fluxes, and concentrations. They are based on monitoring units with flat sheet membranes and transparent windows with side conduits for liquid flow. This arrangement results in velocities, pressure losses, and fluxes that are not representative of their corresponding in-line spiral wound membranes. These techniques have a narrow range of concentrations and velocities for simulating the real membrane surface and changing dynamics of systems several orders of magnitude larger. The visual nature of these techniques is quite expensive to implement and maintain, and requires operators or computer systems trained for image analysis and decision-making.

[0018] Another approach has been used, in which a non-in-situ independent monitoring unit has been implemented using chemical tracking to track membrane fouling [Kemira Oyj-009]. This method requires tracking consumables, making it more difficult to implement. Again, it also requires side guides and cannot replicate actual in-line membrane elements, as in-line membrane elements operate within a pressure vessel. The proposed technique teaches a simple, elegant, and cost-effective method that eliminates the need for expensive monitoring units, cameras, image analysis, chemical analysis, etc., and utilizes the performance of an in-line membrane (monitor) operating under 100% real operating conditions within a pressure vessel.

[0019] During fouling in an RO system, either the lead or tail membrane may lose >70% of flux or exhibit significant retention losses within a short period (hours to days, depending on the application). The sensitivity of a single lead or tail membrane element to tracking fouling and scaling is directly proportional to the loss of its surface area, the increased mass resistance from sludge membranes, or the retention losses due to oxidative damage. Since lead or tail elements typically foul first, real-time monitoring of this small portion of the RO's flux or retention loss provides early detection of fouling across the entire system. In contrast, monitoring the flux or retention loss of the entire system is slow and highly silent because, in constant production operation, the loss of a small portion of the RO is averaged across all membranes. For example, at a flux of 15-gfd and 24 membrane elements (each with 400 ft... 2 In a 100 gpm RO operation (area), the first element or the last element in a 100 ft RO operation. 2A partial area loss will result in a 25% flux loss for that specific element; however, across the entire system, the relative loss is only about 1% of the total area, leading to a pressure increase of only 1%. If monitoring the behavior of the pressure vessel rather than the entire system, a similar area loss would account for ~6% in a 4-element long pressure vessel and ~4% in a 6-element long pressure vessel. A 10-25x increase in sensitivity is achieved relative to the entire system when tracking the performance of a single element (depending on array design and length). However, a 4-6x increase in sensitivity is achieved relative to a single pressure vessel with 4-6 elements when tracking the performance of a single element. This first-order sensitivity increase comes directly from the change in the surface area of ​​a single membrane relative to the surface area of ​​all membranes in the system, and as discussed, depends on the number of elements and the RO configuration, ranging from 4-25x. However, second-order sensitivity increases are also caused by the relative and strategic positions of the monitoring membrane elements, such as the leading or trailing elements, where an additional 1-3x increase in sensitivity is achieved. Lead-up membrane elements tend to foul first, primarily from particles, bioburden, or organic matter, because these membranes operate at 20%–40% higher flux relative to the rest. Tail-up membrane elements tend to foul and lose surface area, mainly due to precipitation caused by the maximum concentration factor, while other membranes are not affected by this.

[0020] This application discloses a system in which the performance of the pre- and post-contamination elements of any stage of an RO / NF membrane can be directly measured online without the insertion of parallel and external monitoring devices. This method offers greater sensitivity and earlier identification of fault initiation in RO / NF systems. While the novel approach disclosed herein can be implemented in any stage of an RO / NF system, the most valuable locations are the pre- and post-contamination elements of the first stage and the last stage, allowing for early detection and sensitivity at the onset of fouling and scaling with a five- to six-fold reduction in timescale.

[0021] Once the direct membrane performance signal confirms the onset of fouling in the leading elements of the RO / NF, mitigation actions can be taken. Such responses include alerting the operator to verify any malfunctions in the pretreatment system (such as a damaged cartridge filter), taking corrective actions to improve the pretreatment, and bypassing the feed supply to subsequent stages to reduce over-flux, as described in the design by Agnihotri et al. [4]. Similarly, once the direct membrane performance signal confirms the onset of fouling / scaling or retention loss in the tail elements of the RO / NF, mitigation actions can be taken by reducing the concentration factor and alerting the operator to verify the presence of oxidizing contaminants (such as free chlorine and metals). In addition, further actions can be triggered, such as compositional analysis of the chemical composition of the feed water, calculation of specific scale that causes ion concentrations, saturation index, adjustment of the feed supply pH, and planning for future CIP events. These mitigation and remedial actions can be a combination of actions taken by an automated pre-programmed controller using a decision matrix, an algorithm with a self-learning correlation matrix for action and response patterns (i.e., machine learning), or operator-assisted changes to operating conditions, resulting in more resilient and intelligent RO / NF systems. The key criterion for such actions to be effective depends strictly on the system's response time relative to the onset of contamination and the system's response time after mitigation steps are taken, thus providing a feedback loop for corrective actions and responses to these actions.

[0022] References such as the Dow Reverse Osmosis Membrane Technical Manual[5] and the Veolia report by Erickson et al.

[10] can also be consulted to understand how the flux through the RO membrane can be calculated and its dependence on the chemical properties of the feed water, such as ion concentration (osmotic pressure), temperature and pressure loss due to velocity and osmosis. Invention Overview

[0023] The novel concept described in this application allows for real-time online monitoring of membrane fouling in RO and NF systems. Utilizing a uniquely configured membrane permeate flow path within the system, membrane performance data from real-time in-situ operating conditions is used to rapidly detect membrane fouling, fouling rate, and fouling causes. This detection is followed by remedial actions to stop and recover from or slow down fouling, and anticipates, plans, and schedules operator intervention steps to restore optimal system operating conditions. The end result is a novel, energy-efficient, and advanced (machine learning) reverse osmosis system for brackish water desalination and fouling management.

[0024] Invention Description

[0025] While the various embodiments of the invention and their uses are discussed in detail below, it should be understood that the invention provides many applicable inventive concepts that can be embodied in a variety of environments. The descriptions herein merely exemplify different ways of making and using the invention and do not limit the scope of the invention.

[0026] To facilitate understanding of the present invention, several terms are defined below. The terms defined herein have meanings as commonly understood by one of ordinary skill in the art related to the present invention. Terms such as “a,” “an,” and “the” are not intended to refer to a singular entity, but rather to encompass general categories that can be illustrated using specific examples. The terms are used herein to describe specific embodiments of the invention, but their use does not limit the invention, except as outlined in the claims.

[0027] By including Figure 1 The prior art, challenges, and limitations disclosed in the background section are provided in this section, which outlines the above-mentioned and... Figure 2 , Figure 3 and Figure 4 The descriptive details and various embodiments of the invention cited herein.

[0028] In one embodiment of the invention, a blanked-off permeate interconnector is used to isolate and redirect the permeate of a first membrane element (lead-edge membrane) within at least one pressure vessel of the first stage from and divert the permeate of the remaining membrane elements within the pressure vessel. The in-line permeate of the lead-edge membrane element (hereinafter referred to as the "lead-edge monitor") is collected through its pressure vessel end, while the permeate of all other remaining membrane elements is collected from the opposite end of the pressure vessel using a pass-through permeate interconnector.

[0029] In one embodiment of the invention, a closed permeate interconnect is used to isolate and redirect the permeate from the permeate of at least one tail-edge membrane element (tail-edge membrane) within the last stage of the pressure vessel to the permeate of the remaining membrane elements within the pressure vessel. The in-line permeate of the tail-edge membrane element (hereinafter referred to as the "tail-edge monitor") is collected through its pressure vessel end, while the permeate of all other remaining membrane elements is collected from the opposite end of the pressure vessel using a straight-through permeate interconnect.

[0030] In one embodiment of the invention, a closed permeate interconnect is used to isolate and redirect the permeate from and from the permeate of any other leading or trailing element within the pressure vessel of any stage of the RO / NF system, within the pressure vessel. The in-line permeate of this leading or trailing membrane element (hereinafter referred to as “Stage #-Leading Monitor” or “Stage #-Tail Monitor”, respectively, where # represents any stage between the first and last stages) is isolated and collected through its pressure vessel end, while the permeate of all other remaining membrane elements is combined and collected from the opposite end of the pressure vessel using a straight-through permeate interconnect.

[0031] In one embodiment of the invention, the permeate from the leading-edge monitor, trailing-edge monitor, or any other stage-leader or stage-tailer monitor passes through a flow channel equipped with online flow and / or conductivity meters. The performance of any stage membrane element (leader or tail) is measured by its productivity (flux) and separation performance (retention rate), and is a direct online measurement of system performance in real time. Any fouling or scaling begins to be reflected in real-time trends as flux loss and retention behavior loss, at least four times faster than measurements based on the entire stage itself, and at least ten times faster than measurements based on the entire system itself.

[0032] In one embodiment of the invention, permeate from one or more of these direct membrane element monitors is added to a common permeate manifold that collects permeate from all other unmonitored membrane elements and delivers it to a storage tank.

[0033] In one embodiment of the invention, the measured flux, rejection rate, and composition (such as silica, hardness, or total organic carbon (TOC)) of the feed water and concentrate water samples are analyzed by a control program for mitigation and remedial actions. These actions are a combination of automatically pre-programmed rule-based logic or data-driven algorithms with pre-programmed correlation matrices for "action and response patterns" (i.e., machine learning), or operator warnings and assistance regarding changes in operating conditions, resulting in an advanced (machine learning) RO / NF system.

[0034] In one embodiment of the present invention, the various membrane performance monitors described in paragraphs [024-028] are collectively referred to as “membrane element monitors”.

[0035] In one embodiment of the invention, as disclosed in paragraphs [016, 017], permeate quality (rejection rate) and quantity (flux) measurements are direct membrane performance signals for detecting the onset and progression of fouling, compared to any other fouling techniques used in the past, because fouling is driven by the hydrodynamics of the flow within the feed channel, and flux, and the rate of change of flux, are directly related to fouling. Any deviation from typical conditions in terms of membrane permeability and rejection rate is detected directly in our invention without requiring any external parallel visual monitors or large-volume overall system performance monitors, which are too slow, too expensive, or difficult to maintain.

[0036] In one embodiment of the invention, an additional pressure vessel is included upstream of at least one pressure vessel in a first-stage pressure vessel having a monitor membrane element, serving as a possible leading-edge monitor for a large-scale system.

[0037] In one embodiment of the invention, all pressure vessels in the RO / NF system have the same size and a uniformly distributed number of elements. For example, in a 3-stage, 4-membrane-length system, the system configuration can be represented as 3:2:1 / 4M with 4” or 8” membrane elements. In such a system, there are 12 membrane length series (24 membranes in total), and the fouling monitor locations can be elements #1 (leading edge), #5 (stage 2-leading edge), #8 (stage 2-tailing edge), #9 (stage 3-leading edge), and #12 (tailing edge) in this series. In another example, in a 3-stage, 6-membrane-length system, the system configuration can be represented as 6:4:2 / 6M with 4” or 8” membrane elements. In such a system, there are 18 membrane length series (72 membranes in total), and the fouling monitor locations can be elements #1 (leading edge), #7 (stage 2-leading edge), #12 (stage 2-tailing edge), #13 (stage 3-leading edge), and #18 (tailing edge) in the series. In one example, the membrane element monitor can be housed separately in a single-element pressure vessel, either before the first stage or after the last stage. A leading edge (particle load, TOC, organic matter, etc.) and a trailing edge (scale, solids, and oxidant concentrate) are practical for most needs.

[0038] like Figure 2As shown, in one embodiment of the invention, a closed permeate tube is used to isolate the permeate from a single membrane element and redirects it from one end of the pressure vessel via a flow meter and conductivity meter before connecting it to a common permeate manifold for all permeates. Permeates from all other membranes are collected from the opposite end of the pressure vessel using hollow permeate interconnectors and sent to the common permeate manifold. One example (“First Stage Example A”) illustrates a leading-edge membrane element monitor for a first stage that isolates and redirects the permeate from a first element in one of several pressure vessels. Another example (“Last Stage Example A”) illustrates a trailing-edge membrane monitor for a last stage that isolates and redirects the permeate from a last element in a single pressure vessel.

[0039] like Figure 3 As shown, in one embodiment of the invention, we disclose the isolation, redirection, and measurement of permeate (mass and quantity) from a first-stage leading-edge monitor, a first element from more than one pressure vessel (two pressure vessels are shown).

[0040] like Figure 3 As further shown, in one embodiment of the invention, an example of a trailing edge membrane element monitor (“Last Stage Example B”) is located in a separate pressure vessel downstream of at least one pressure vessel in a pressure vessel having at least one membrane element in the last stage. In addition to permeate flux and rejection rate, this arrangement also allows for the measurement of the pressure differential across the contamination monitor.

[0041] like Figure 4 As shown, in one embodiment of the invention, an example of a system with only two stages, featuring multiple membrane leading-edge and trailing-edge monitors, is designed to further improve sensitivity and accuracy through larger volume measurements. This example illustrates a monitor with three (3) first-stage leading-edge permeates (“First-Stage Example C”), which are isolated using a closed permeate tube and redirected and combined before quality and quantity measurements. A second example illustrates a monitor with two (2) last-stage trailing-edge permeates (“Last-Stage Example C”), which are isolated using a closed permeate tube and redirected and combined before quality and quantity measurements. The final monitor permeate is combined with the permeates from all other unmonitored membranes in a common manifold.

[0042] In one embodiment of the invention, the pollution monitoring pressure vessel can be isolated from the system to remove internal membrane elements for cleaning or replacement without interrupting the operation of the rest of the system and permeate production.

[0043] It is worth noting that the length, diameter, and number of components within an RO / NF system can vary in different implementations of the techniques taught herein.

[0044] Although the inventive methods described in paragraphs 19-39 above are taught in relation to a 3-stage RO system design, similar functionality can be implemented in single-stage or multi-stage systems, and monitors can be implemented at leading-edge membrane elements, trailing-edge membrane elements, or interstage leading-edge or trailing-edge membrane elements. In most applications, the most useful location for direct online monitoring is likely the leading edge of the first stage or the trailing edge of the last stage. In some applications, data from specific leading-edge or trailing-edge monitors in other stages can provide additional control points. By referencing the disclosure of examples of 3-stage implementations, as demonstrated herein, those skilled in the art (PHOSITA) can likely implement the concept and inventive steps in any RO / NF system, even if it is a single-stage system, such as seawater desalination RO applications or 2-stage or 4-stage systems for medium and low salinity levels respectively. Attached Figure Description

[0045] A more complete and thorough understanding of this embodiment and its advantages can be obtained by referring to the following description taken in conjunction with the accompanying drawings, wherein:

[0046] Figure 1 An exemplary multi-stage (shown as a 3-stage 3:2:1) RO or NF brackish water system with parallel CIP loops for cleaning all stages of the combination. Inter-stage isolation valves (V2, V3) open during normal operation and close during offline CIP cleaning to provide parallel CIP loops. A single high-pressure pump Pl drives the RO or NF system operation. Instruments and valves such as flow meters [FM 1-FM 2], conductivity meters [CM 1-CM 3], flow control valves [FCV 1-FCV 3], and valves [V1-V10] provide process control for system operation. The pressure vessel for all stages shows feed channels (shaded) and permeate channels (unshaded) for multiple spiral wound membrane elements (shown as a 4M configuration with 4 membranes). The membrane permeate channels are connected via straight-through interconnects to allow permeate collection at one or both ends of the pressure vessel.

[0047] Figure 2 : Figure 1This extension features a novel process design for online membrane performance monitoring, using a solid-plugged permeate interconnector for either the leading or trailing membrane of any stage to isolate and redirect its permeate through one end of the pressure vessel, and then through flow meters [FM M1-FM M2] and conductivity meters [CM M1-CM M2]. This permeate is then added to a common permeate header. Permeate from all other (non-isolated) membranes is collected from the opposite end of the pressure vessel using a straight-through interconnect and sent to the common permeate header. The quality and quantity of the combined final permeate are measured using FM2 and CM2 flow and conductivity sensors. "First Stage Example A" illustrates a leading-edge membrane element monitor for the first stage by isolating and redirecting the first membrane permeate from one of many pressure vessels. Similarly, "Last Stage Example A" illustrates a trailing-edge membrane element monitor for the last stage by isolating and redirecting the last membrane permeate from a single pressure vessel in a 3:2:1 / 4M system configuration. In this example, intermediate stages are not monitored.

[0048] Figure 3 : A multi-stage (3:2:1 / 4M configuration) RO or NF process flow with monitors. The figure shows a “First Stage Example B” where the isolation and redirection of permeate from more than one pressure vessel (shown as 2) is combined for leading-edge membrane monitoring in the first stage. The figure also shows a “Last Stage Example B” where a separate unit pressure vessel is added as an additional stage to collect and monitor trailing-edge membrane performance using individual element permeate before combining individual element permeate in a common permeate header.

[0049] Figure 4 This diagram illustrates an example of a two-stage (3:2 / 4M configuration) RO or NF process flow. "Example C, First Stage" shows the isolation and redirection of permeate from the first membrane combination of all three pressure vessels, subsequently used for monitoring the leading edge membrane elements of the first stage. Additionally, "Example C, Last Stage" is shown, where monitoring of the trailing edge membrane elements of the last stage is accomplished by isolating and redirecting the final membrane permeate from the combination of two pressure vessels.

[0050] References

[0051]

Claims

1. A desalination system having a spiral wound membrane element housed in a pressure vessel, the desalination system comprising: The main feed stream used for processing; Main permeate stream, in which permeates from the entire system are collected for use; and final concentrated logistics; One or more stages, wherein each stage has one or more pressure vessels and a common feed inlet manifold, a common concentrate outlet manifold and one or more permeate outlet manifolds, the one or more permeate outlet manifolds being ultimately combined to form the main permeate stream; The inlet stream of the first stage includes the main feed stream, and the inlet stream of subsequent stages includes the pre-concentrated stream, or a blend of the pre-concentrated stream and a portion of the main feed stream. Each pressure vessel has one or more spiral wound membrane elements and a central permeate channel with hollow interconnectors to collect and transfer membrane permeate through one or both ends of the pressure vessel to form the main permeate stream; In any stage, one or more pressure vessels have a closed interconnect for isolating and redirecting the permeate from the leading or trailing membrane element to the remaining membrane elements within the pressure vessel, thereby allowing measurement of the quality and quantity of permeate from a particular membrane element. In this process, the permeate from one or more isolated membrane elements of the leading or trailing membrane elements within the stage is collected and combined into "redirected permeate" through their own pressure vessel ends, while the permeate from all other membrane elements is collected through the opposite ends of the isolated membrane elements. In order to obtain real-time data on the diverted permeate for online monitoring, a certain mass and quantity of the "diverted permeate" flows through one or more measuring devices for temperature, pressure, conductivity, composition, flow rate, pH or oxidation potential, and the diverted permeate is subsequently combined with the main permeate stream. The permeate data, referred to as the "membrane element monitor," is used for real-time membrane performance measurement at the front or rear end of a stage within the system. The tracking and analysis of the quality, quantity, rate of change, limits, lookup tables, and correlation with feed water composition of membrane element monitor data enable rapid detection of membrane fouling and execution of automated or operator-assisted actions, resulting in: a) slowing down fouling, b) stopping fouling, c) recovering from fouling, and d) anticipating, planning, and arranging steps for system recovery and performance improvement.

2. The desalination system according to claim 1, wherein, At least one leading edge membrane element monitor is included in the first stage to track and analyze contamination from particulate and organic loads caused by the overflux of the leading membrane element.

3. The desalination system according to claim 1, wherein, At least one trailing edge membrane element monitor is included in the final stage to track and analyze the damage to the membrane caused by fouling and concentrated oxidants.

4. The desalination system according to claim 1, wherein, The membrane element monitor is implemented in a separate, independent pressure vessel, similar to a single membrane level, to obtain additional measurements of the transmembrane pressure across the membrane element monitor, which is not possible when implemented in a conventional pressure vessel.

5. The desalination system according to claim 1, wherein, "Membrane element monitors" and other measuring devices for temperature, pressure, conductivity, flow rate, composition, pH, or oxidation potential are used simultaneously to construct a correlation matrix of action and response patterns for improved overall system operation.

6. The desalination system according to claim 1, wherein the spiral wound membrane is a reverse osmosis membrane or a nanofiltration membrane.

7. The desalination system according to claim 1, wherein, The existing system has been retrofitted with one or more "membrane element monitors" and programmed to predict and control fouling to improve overall system performance.

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