Method of monitoring membrane separation processes

Abstract

Methods and systems for monitoring and/or controlling membrane separation systems or processes are provided. The present invention uses measurable amounts of inert fluorescent tracers and tagged fluorescent agents added to a feed stream to evaluate and/or control one or more parameters specific to membrane separation such that performance thereof can be optimized. The methods and systems of the present invention can be used in a variety of different industrial applications including raw water processing and waste water processing.

Description

FIELD OF THE INVENTION

[0002] This invention relates generally to membrane separation and, more particularly, to methods for monitoring and/or controlling membrane separation processes.

BACKGROUND OF THE INVENTION

[0003] Membrane separation, which uses a selective membrane, is a fairly recent addition to the industrial separation technology for processing of liquid streams, such as water purification. In membrane separation, constituents of the influent typically pass through the membrane as a result of a driving force(s) in one effluent stream, thus leaving behind some portion of the original constituents in a second stream. Membrane separations commonly used for water purification or other liquid processing include microfiltration (MF), ultrafiltration (UF), nanofiltration (NF), reverse osmosis (RO), electrodialysis, electrodeionization, pervaporation, membrane extraction, membrane distillation, membrane stripping, membrane aeration, and other processes. The driving force of the separation depends on the type of the membrane separation. Pressure-driven membrane filtration, also known as membrane filtration, includes microfiltration, ultrafiltration, nanofiltration and reverse osmosis, and uses pressure as a driving force, whereas the electrical driving force is used in electrodialysis and electrodeionization. Historically, membrane separation processes or systems were not considered cost effective for water treatment due to the adverse impacts that membrane scaling, membrane fouling, membrane degradation and the like had on the efficiency of removing solutes from aqueous water streams. However, advancements in technology have now made membrane separation a more commercially viable technology for treating aqueous feed streams suitable for use in industrial processes.

[0004] Further, membrane separation processes have also been made more practical for industrial use, particularly for raw and wastewater purification. This has been achieved through the use of improved diagnostic tools or techniques for evaluating membrane separation performance. The performance of membrane separation, such as efficiency (e.g. flux or membrane permeability) and effectiveness (e.g. rejection or selectivity), are typically affected by various parameters concerning the operating conditions of the process. Therefore, it is desirable to monitor these and other types of process parameters specific to membrane separation to assess the performance of the process and/or the operating conditions. In this regard, a variety of different diagnostic techniques for monitoring membrane separation processes have been routinely used and are now understood and accepted as essential to its practicality and viability for industrial use.

[0005] However, monitoring is typically conducted on an intermittent basis, for example, once a work shift or at times less frequently. Known employed monitoring techniques can also be labor and time intensive. Thus, adjustments made to membrane separation processes in order to enhance performance based on typical monitoring may not be made in an expeditious manner. In addition, the presently available monitoring techniques often do not provide optimal sensitivity and selectivity with respect to monitoring a variety of process parameters that are generally relied on as indicators to evaluate and/or control membrane separation processes.

[0006] For example, monitoring techniques typically applied to reverse osmosis and nanofiltration include conductivity measurements and flow measurements. Conductivity measurements are inherently less accurate in order to determine the recovery of solutes which are substantially retained by the membrane. In this regard, conductive salts, typically used as an indicator during conductive measurements, can pass through the membrane. Since salts generally pass through the membrane as a percentage of the total salt concentration, changes in local concentration due to concentration gradients or the like can change the conductivity of the product water without necessarily indicating membrane damage. This is especially true in the last stage of a multi-stage cross flow membrane system where salt concentrations (and, therefore, passage of salts as a percentage of that concentration) reach their highest levels. In this regard, the salt passage/percent rejection parameter is generally determined as an average value based on values measured during all stages of the membrane system.

[0007] Further, flow meters generally employed in such systems are subject to calibration inaccuracies, thus requiring frequent calibration. Moreover, typical monitoring of reverse osmosis and other membrane separations can routinely require the additional and/or combined use of a number of different techniques, thus increasing the complexity and expense of monitoring.

[0008] Accordingly, a need exists to monitor and/or control membrane separation processes which can treat feed streams, such as aqueous feed streams, suitable for use in industrial processes where conventional monitoring techniques are generally complex and/or may lack the sensitivity and selectivity necessary to adequately monitor one or more process parameters specific to membrane separation processes which are important to the evaluation of the performance of membrane separation.

SUMMARY OF THE INVENTION

[0009] The first aspect of the instant claimed invention is a method for monitoring a membrane separation process comprising the steps of:

[0010] (a) providing an industrial process, wherein within said industrial process there are feed streams comprising one or more solutes in an aqueous liquid;

[0011] (b) providing a membrane capable of removing solutes from a feed stream by separating said feed stream into a first stream and a second stream, wherein said first steam is the permeate stream and said second stream is the concentrate stream;

[0012] (c) selecting an inert fluorescent tracer and a tagged fluorescent agent; wherein the selection is made such that it is known in advance whether said inert fluorescent tracer and said tagged fluorescent agent are either

[0013] (i) capable of traveling through the membrane into the permeate stream either separately or together, or

[0014] (ii) not capable of passing through the membrane into the permeate stream either separately or together;

[0015] (d) introducing the inert fluorescent tracer and tagged fluorescent agent into the feed stream;

[0016] (e) providing one or more fluorometers, to enable the detection of the fluorescent signal of the inert fluorescent tracer in the feed stream and the concentrate and optionally the permeate and the detection of the fluorescent signal of the tagged fluorescent agent in the feed stream and the concentrate and optionally the permeate;

[0017] (f) using the one or more fluorometers to detect the fluorescent signal of the inert fluorescent tracer in the feed stream and the concentrate and optionally the permeate and to detect the fluorescent signal of the tagged fluorescent agent in the feed stream and the concentrate and optionally the permeate;

[0018] (g) converting the detected fluorescent signal of the inert fluorescent tracer into the concentration of the inert fluorescent tracer and converting the detected fluorescent signal of the tagged fluorescent agent into the concentration of the tagged fluorescent agent.

[0019] The second aspect of the instant claimed invention is a method for detecting damage to a membrane used in a membrane separation process comprising the steps of:

[0020] (a) providing an industrial process, wherein within said industrial process there are feed streams comprising one or more solutes in an aqueous liquid;

[0021] (b) providing a membrane capable of removing solutes from a feed stream by separating said feed stream into a first stream and a second stream, wherein said first steam is the permeate stream and said second stream is the concentrate stream;

[0022] (c) selecting an inert fluorescent tracer and a tagged fluorescent agent; wherein the selection is made such that it is known in advance that one or both of said inert fluorescent tracer and said tagged fluorescent agent are not capable of passing through the membrane into the permeate stream;

[0023] (d) introducing the inert fluorescent tracer and tagged fluorescent agent into the feed stream;

[0024] (e) providing one or more fluorometers, to enable the detection of the fluorescent signal of the inert fluorescent tracer in the feed stream and in the permeate stream and the detection of the fluorescent signal of the tagged fluorescent agent in the feed stream and in the permeate stream;

[0025] (f) using the one or more fluorometers to detect the fluorescent signal of the inert fluorescent tracer in the feed stream and in the permeate stream and to detect the fluorescent signal of the tagged fluorescent agent in the feed stream and in the permeate stream;

[0026] wherein, if one or both of the fluorescent signals of the inert fluorescent tracer and the tagged fluorescent agent are found in the permeate then this indicates the membrane is damaged in some way.

DETAILED DESCRIPTION OF THE PRESENTLY PREFERRED EMBODIMENTS

[0027] The first aspect of the instant claimed invention is a method for monitoring a membrane separation process comprising the steps of:

[0028] (a) providing an industrial process, wherein within said industrial process there are feed streams comprising one or more solutes in an aqueous liquid;

[0029] (b) providing a membrane capable of removing solutes from a feed stream by separating said feed stream into a first stream and a second stream, wherein said first steam is the permeate stream and said second stream is the concentrate stream;

[0030] (c) selecting an inert fluorescent tracer and a tagged fluorescent agent; wherein the selection is made such that it is known in advance whether said inert fluorescent tracer and said tagged fluorescent agent are either

[0031] (i) capable of traveling through the membrane into the permeate stream either separately or together, or

[0032] (ii) not capable of passing through the membrane into the permeate stream either separately or together;

[0033] (d) introducing the inert fluorescent tracer and tagged fluorescent agent into the feed stream;

[0034] (e) providing one or more fluorometers, to enable the detection of the fluorescent signal of the inert fluorescent tracer in the feed stream and the concentrate and optionally the permeate and the detection of the fluorescent signal of the tagged fluorescent agent in the feed stream and the concentrate and optionally the permeate;

[0035] (f) using the one or more fluorometers to detect the fluorescent signal of the inert fluorescent tracer in the feed stream and the concentrate and optionally the permeate and to detect the fluorescent signal of the tagged fluorescent agent in the feed stream and the concentrate and optionally the permeate;

[0036] converting the detected fluorescent signal of the inert fluorescent tracer into the concentration of the inert fluorescent tracer in the feed stream and the concentrate and optionally the permeate and converting the detected fluorescent signal of the tagged fluorescent agent into the concentration of the tagged fluorescent agent in the feed stream and the concentrate and optionally the permeate.

[0037] The present invention is applicable to all industries that can employ membrane separation processes. For example, the different types of industrial processes in which the method-of the present invention can be applied generally include raw water processes, waste water processes, industrial water processes, municipal water treatment, food and beverage processes, pharmaceutical processes, electronic manufacturing, utility operations, pulp and paper processes, mining and mineral processes, transportation-related processes, textile processes, plating and metal working processes, laundry and cleaning processes, leather and tanning processes, and paint processes.

[0038] In particular, food and beverage processes can include, for example, dairy processes relating to the production of cream, low-fat milk, cheese, specialty milk products, protein isolates, lactose manufacture, whey, casein, fat separation, and brine recovery from salting cheese. Uses relating to the beverage industry including, for example, fruit juice clarification, concentration or deacidification, alcoholic beverage clarification, alcohol removal for low-alcohol content beverages, process water; and uses relating to sugar refining, vegetable protein processing, vegetable oil production/processing, wet milling of grain, animal processing (e.g., red meat, eggs, gelatin, fish and poultry), reclamation of wash waters, food processing waste and the like.

[0039] Examples of industrial water uses as applied to the present invention include, for example, boiler water production, process water purification and recycle/reuse, softening of raw water, treatment of cooling water blow-down, reclamation of water from papermaking processes, desalination of sea and brackish water for industrial and municipal use, drinking/raw/surface water purification including, for example, the use of membranes to exclude harmful micro-organisms from drinking water, polishing of softened water, membrane bio-reactors, mining and mineral process waters.

[0040] Examples of waste water treatment applications with respect to the tracer monitoring of the methods of the present invention include, for example, industrial waste water treatment, biological waste treatment systems, removal of heavy metal contaminants, polishing of tertiary effluent water, oily waste waters, transportation related processes (e.g., tank car wash water), textile waste (e.g., dye, adhesives, size, oils for wool scouring, fabric finishing oils), plating and metal working waste, laundries, printing, leather and tanning, pulp and paper (e.g., color removal, concentration of dilute spent sulfite liquor, lignon recovery, recovery of paper coatings), chemicals (e.g., emulsions, latex, pigments, paints, chemical reaction by-products), and municipal waste water treatment (e.g., sewage, industrial waste).

[0041] Other examples of industrial applications of the present invention include, for example, semiconductor rinse water processes, production of water for injection, pharmaceutical water including water used in enzyme production/recovery and product formulation, and electro-coat paint processing.

[0042] It should be appreciated that the present invention can be used with respect to a number of different types of membrane separation processes including, for example, cross-flow processes, dead-end flow processes, reverse osmosis, ultrafiltration, microfiltration, nanofiltration, electrodialysis, electrodeionization, pervaporation, membrane extraction, membrane distillation, membrane stripping, membrane aeration and the like or combinations thereof. Reverse osmosis, ultrafiltration, microfiltration and nanofiltration are the preferred membrane separation processes.

[0043] In reverse osmosis, the feed stream is typically processed under cross-flow conditions. In this regard, the feed stream flows substantially parallel to the membrane surface such that only a portion of the feed stream diffuses through the membrane as permeate. The cross-flow rate is routinely high in order to provide a scouring action that lessens membrane surface fouling. This can also decrease concentration polarization effects (e.g., concentration of solutes in the reduced-turbulence boundary layer at the membrane surface which can increase the osmotic pressure at the membrane and thus reduces permeate flow). The concentration polarization effects can inhibit the feed stream water from passing through the membrane as permeate, thus decreasing the recovery ratio, e.g., the ratio of permeate to applied feed stream. A recycle loop(s) may be employed to maintain a high flow rate across the membrane surface.

[0044] Reverse osmosis processes can employ a variety of different types of membranes. Such commercial membrane element types include, without limitation, hollow fiber membrane elements, tubular membrane elements, spiral-wound membrane elements, plate and frame membrane elements, and the like, some of which are described in more detail in “The Nalco Water Handbook,” Second Edition, Frank N. Kemmer ed., McGraw-Hill Book Company, New York, N.Y., 1988, particularly Chapter 15 entitled “Membrane Separation”. It should be appreciated that a single membrane element may be used in a given membrane filtration system, but a number of membrane elements can also be used depending on the industrial application.

[0045] A typical reverse osmosis system is described as an example of membrane filtration and more generally membrane separation. Reverse osmosis uses mainly spiral wound elements or modules, which are constructed by winding layers of semi-porous membranes with feed spacers and permeate water carriers around a central perforated permeate collection tube. Typically the modules are sealed with tape and/or fiberglass over-wrap. The resulting construction has one channel which can receive an inlet flow. The inlet stream flows longitudinally along the membrane module and exits the other end as a concentrate stream. Within the module, water passes through the semi-porous membrane and is trapped in a permeate channel which flows to a central collection tube. From this tube it flows out of a designated channel and is collected.

[0046] In practice, membrane modules are stacked together, end to end, with inter-connectors joining the permeate tubes of the first module to the permeate tube of the second module, and so on. These membrane module stacks are housed in pressure vessels. Within the pressure vessel feed water passes into the first module in the stack, which removes a portion of the water as permeate water. The concentrate stream from the first membrane becomes the feed stream of the second membrane and so on down the stack. The permeate streams from all of the membranes in the stack are collected in the joined permeate tubes. Only the feed stream entering the first module, the combined permeate stream and the final concentrate stream from the last module in the stack are commonly monitored.

[0047] Within most reverse osmosis systems, pressure vessels are arranged in either “stages” or “passes.” In a staged membrane system, the combined concentrate streams from a bank of pressure vessels are directed to a second bank of pressure vessels where they become the feed stream for the second stage. Commonly systems have 2 to 3 stages with successively fewer pressure vessels in each stage. For example, a system may contain 4 pressure vessels in a first stage, the concentrate streams of which feed 2 pressure vessels in a second stage, the concentrate streams of which in turn feed 1 pressure vessel in the third stage. This is designated as a “4:2:1” array. In a staged membrane configuration, the combined permeate streams from all pressure vessels in all stages are collected and used without further membrane treatment. Multi-stage systems are used when large volumes of purified water are required, for example for boiler feed water. The permeate streams from the membrane system may be further purified by ion exchange or other means.

[0048] In a multi-pass system, the permeate streams from each bank of pressure vessels are collected and used as the feed to the subsequent banks of pressure vessels. The concentrate streams from all pressure vessels are combined without further membrane treatment of each individual stream. Multi-pass systems are used when very high purity water is required, for example in the microelectronics or pharmaceutical industries.

[0049] It should be clear from the above examples that the concentrate stream of one stage of an RO system can be the feed stream of another stage. Likewise the permeate stream of a single pass of a multi-pass system may be the feed stream of a subsequent pass. A challenge in monitoring systems such as the reverse osmosis examples cited above is that there are a limited number of places where sampling and monitoring can occur, namely the feed, permeate and concentrate streams. In some, but not all, systems “inter-stage” sampling points allow sampling/monitoring of the first stage concentrate/second stage feed stream. Similar inter-pass sample points may be available on multi-pass systems as well.

[0050] In practice it is possible to “probe” the permeate collection tube within a single pressure vessel to sample the quality of the permeate from each of the membrane elements in the stack. It is a time consuming, messy and inexact method and is not routinely applied except in troubleshooting situations. There is no currently accepted method of examining the feed/concentrate stream quality of individual membrane elements within a single pressure vessel.

[0051] In contrast to cross-flow filtration membrane separation processes, conventional filtration of suspended solids can be conducted by passing a feed fluid through a filter media or membrane in a substantially perpendicular direction. This effectively creates one exit stream during the service cycle. Periodically, the filter is backwashed by passing a clean fluid in a direction opposite to the feed, generating a backwash effluent containing species that have been retained by the filter. Thus conventional filtration produces a feed stream, a purified stream and a backwash stream. This type of membrane separation is typically referred to as dead-end flow separation and is typically limited to the separation of suspended particles greater than about one micron in size.

[0052] Cross-flow filtration techniques, on the other hand, can be used for removing smaller particles (generally about one micron in size or less), colloids and dissolved solutes. Such types of cross-flow membrane separation systems can include, for example, reverse osmosis, microfiltration, ultrafiltration, nanofiltration, electrodialysis or the like. Reverse osmosis can remove even low molecular weight dissolved species that are at least about 0.0001 to about 0.001 microns in minimum diameter, including, for example, ionic and nonionic species, low molecular weight molecules, water-soluble macromolecules or polymers, suspended solids, colloids, and such substances as bacteria and viruses.

[0053] In this regard, reverse osmosis is often used commercially to treat water that has a moderate to high (e.g., 500 ppm or greater) total dissolved solids (“TDS”) content. Typically on order of from about 2 percent to about 5 percent of the TDS of a feed stream will pass through the membrane. Thus, in general the permeate may not be entirely free of solutes. In this regard, the TDS of reverse osmosis permeates may be too high for some industrial applications, such as use as makeup water for high pressure boilers. Therefore, reverse osmosis systems and other like membrane separation systems are frequently used prior to and in combination with an ion exchange process or other suitable process to reduce the TDS loading on the resin and to decrease the amount of hazardous material used and stored for resin regeneration, such as acids and sodium hydroxide.

[0054] As discussed above, the performance of membrane separation systems can vary with respect to a number of different operational conditions specific to membrane separation, such as temperature, pH, pressure, permeate flow, activity of treatment and/or cleaning agents, fouling activity and the like. When developing and/or implementing a monitoring and/or control program based on the detection of fluorescent agents (e.g., inert fluorescent tracers and tagged fluorescent agents), the effects of the operational conditions specific to membrane separation must necessarily be taken into consideration. As previously discussed, the operational conditions of water treatment processes can vary greatly from process to process. In this regard, the monitoring techniques as applied to each process can also vary greatly.

[0055] Membrane separation processes and the monitoring thereof are unique because of the following considerations.

[0056] 1. Systems are constructed with limited flexibility in terms of where monitoring may be done and/or where samples may be collected.

[0057] 2. Membrane separation systems include a concentration polarization layer that forms as water is permeated through the barrier. This is not present in other water treatment systems, such as cooling water systems.

[0058] 3. Membrane separation systems operate at significantly lower temperatures than industrial processes where inverse solubility of solutes is a problem. However, in the case of membrane separation systems such as reverse osmosis and nanofiltration, this low temperature leads to scaling from salts that are less likely to be problematic in higher temperature processes (such as silica and silicate salts). In this regard, typical day-to-day membrane separation operations (for example RO and NF) occur at about 75° F.

[0059] 4. Because it is essential that the surface of the membrane remain clean, a relatively small amount of fine precipitate can cause a significant performance loss. The performance loss in a membrane is, thus, more sensitive to precipitate deposition as compared to cooling water treatment. In this regard, performance loss in a membrane can occur at a film thickness appreciably lower than that required for heat transfer loss to occur in a cooling water system.

[0060] 5. Water loss in membrane filtration is due to “permeation” or passage through the membrane barrier. Damaged or otherwise imperfect membranes are susceptible to undesirable leakage of solutes through the membrane. Thus it is critical to monitor leakage through the membrane to keep it operating at maximum efficiency.

[0061] 6. The thin, semi-permeable films (polymeric, organic or inorganic) are sensitive to degradation by chemical species. Products which contact the membrane surface must be compatible with the membrane chemistry to avoid damaging the surface and thereby degrading performance.

[0062] 7. Chemical treatments used in membrane systems must be demonstrated to be compatible with the membrane material prior to use. Damage from incompatible chemicals can result in immediate loss of performance and perhaps degradation of the membrane surface. Such immediate, irreversible damage from a chemical treatment is highly uncommon in cooling water systems.

[0063] Based on these differences, a number of different factors and considerations must necessarily be taken into account when developing and/or implementing monitoring and/or controlling programs with respect to membrane separation systems as compared to other water treatment processes, such as cooling water treatment processes.

[0064] A variety of different and suitable types of compounds can be used as inert fluorescent tracers. The term “inert,” as used herein refers to an inert fluorescent tracer that is not appreciably or significantly affected by any other chemistry in the system, or by the other system parameters such as pH, temperature, ionic strength, redox potential, microbiological activity or biocide concentration. To quantify what is meant by “not appreciably or significantly affected”, this statement means that an inert fluorescent compound has no more than a 10% change in its fluorescent signal, under severe conditions encountered in industrial water systems. Severe conditions normally encountered in industrial water systems are known to people of ordinary skill in the art of industrial water systems.

[0065] In an embodiment, the inert fluorescent compounds can include, for example, the following compounds:

[0066] 3,6-acridinediamine, N,N,N′,N′-tetramethyl-, monohydrochloride, also known as Acridine Orange (CAS Registry No. 65-61-2),

[0067] 2-anthracenesulfonic acid sodium salt (CAS Registry No. 16106-40-4),

[0068] 1,5-anthracenedisulfonic acid (CAS Registry No. 61736-91-2) and salts thereof,

[0069] 2,6-anthracenedisulfonic acid (CAS Registry No. 61736-95-6) and salts thereof,

[0070] 1,8-anthracenedisulfonic acid (CAS Registry No. 61736-92-3) and salts thereof,

[0071] anthra[9,1,2-cde]benzo[rst]pentaphene-5,10-diol, 16,17-dimethoxy-, bis(hydrogen sulfate), disodium salt, also known as Anthrasol Green IBA (CAS Registry No. 2538-84-3, aka Solubilized Vat Dye),

[0072] bathophenanthrolinedisulfonic acid disodium salt (CAS Registry No. 52746-49-3),

[0073] amino 2,5-benzene disulfonic acid (CAS Registry No. 41184-20-7),

[0074] 2-(4-aminophenyl)-6-methylbenzothiazole (CAS Registry No. 92-36-4),

[0075] 1H-benz[de]isoquinoline-5-sulfonic acid, 6-amino-2,3-dihydro-2-(4-methylphenyl)-1,3-dioxo-, monosodium salt, also known as Brilliant Acid Yellow 8G (CAS Registry No. 2391-30-2, aka Lissamine Yellow FF, Acid Yellow 7),

[0076] phenoxazin-5-ium, 1-(aminocarbonyl)-7-(diethylamino)-3,4-dihydroxy-, chloride, also known as Celestine Blue (CAS Registry No. 1562-90-9),

[0077] benzo[a]phenoxazin-7-ium, 5,9-diamino-, acetate, also known as cresyl violet acetate (CAS Registry No. 10510-54-0),

[0078] 4-dibenzofuransulfonic acid (CAS Registry No. 42137-76-8),

[0079] 3-dibenzoftiransulfonic acid (CAS Registry No. 215189-98-3),

[0080] 1-ethylquinaldinium iodide (CAS Registry No. 606-53-3),

[0081] fluorescein (CAS Registry No. 2321-07-5),

[0082] fluorescein, sodium salt (CAS Registry No. 518-47-8, aka Acid Yellow 73, Uranine),

[0083] Keyfluor White ST (CAS Registry No. 144470-48-4, aka Flu. Bright 28),

[0084] benzenesulfonic acid, 2,2′-(1,2-ethenediyl)bis[5-[[4-[bis(2-hydroxyethyl)amino]-6-[(4-sulfophenyl)amino]-1,3,5-triazin-2-yl]amino]-, tetrasodium salt, also known as Keyfluor White CN (CAS Registry No. 16470-24-9),

[0085] C.I. Fluorescent Brightener 230, also known as Leucophor BSB (CAS Registry No. 68444-86-0),

[0086] benzenesulfonic acid, 2,2′-(1,2-ethenediyl)bis[5-[[4-[bis(2-hydroxyethyl)amino]-6-[(4-sulfophenyl)amino]-1,3,5-triazin-2-yl]amino]-, tetrasodium salt, also known as Leucophor BMB (CAS Registry No. 16470-24-9, aka Leucophor U, Flu. Bright. 290),

[0087] 9,9′-biacridinium, 10,10′-dimethyl-, dinitrate, also known as Lucigenin (CAS Registry No. 2315-97-1, aka bis-N-methylacridinium nitrate),

[0088] 1-deoxy-1-(3,4-dihydro-7,8-dimethyl-2,4-dioxobenzo[g]pteridin-10(2H)-yl)-D-ribitol, also known as Riboflavin or Vitamin B2 (CAS Registry No. 83-88-5),

[0089] mono-, di-, or tri-sulfonated napthalenes, including but not limited to

[0090] 1,5-naphthalenedisulfonic acid, disodium salt (hydrate) (CAS Registry No. 1655-29-4, aka 1,5-NDSA hydrate),

[0091] 2-amino-1-naphthalenesulfonic acid (CAS Registry No. 81-16-3),

[0092] 5-amino-2-naphthalenesulfonic acid (CAS Registry No. 119-79-9),

[0093] 4-amino-3-hydroxy-1-naphthalenesulfonic acid (CAS Registry No. 90-51-7),

[0094] 6-amino-4-hydroxy-2-naphthalenesulfonic acid (CAS Registry No. 116-63-2),

[0095] 7-amino-1,3-naphthalenesulfonic acid, potassium salt (CAS Registry No. 79873-35-1),

[0096] 4-amino-5-hydroxy-2,7-naphthalenedisulfonic acid (CAS Registry No. 90-20-0),

[0097] 5-dimethylamino-1-naphthalenesulfonic acid (CAS Registry No. 4272-77-9),

[0098] 1-amino-4-naphthalene sulfonic acid (CAS Registry No. 84-86-6),

[0099] 1-amino-7-naphthalene sulfonic acid (CAS Registry No. 119-28-8), and

[0100] 2,6-naphthalenedicarboxylic acid, dipotassium salt (CAS Registry No. 2666-06-0),

[0101] 3,4,9,10-perylenetetracarboxylic acid (CAS Registry No. 81-32-3),

[0102] C.I. Fluorescent Brightener 191, also known as Phorwite CL (CAS Registry No. 12270-53-0),

[0103] C.I. Fluorescent Brightener 200, also known as Phorwite BKL (CAS Registry No. 61968-72-7),

[0104] benzenesulfonic acid, 2,2′-(1,2-ethenediyl)bis[5-(4-phenyl-2H-1,2,3-triazol-2-yl)-, dipotassium salt, also known as Phorwite BHC 766 (CAS Registry No. 52237-03-3),

[0105] benzenesulfonic acid, 5-(2H-naphtho[1,2-d]triazol-2-yl)-2-(2-phenylethenyl)-, sodium salt, also known as Pylaklor White S-15A (CAS Registry No. 6416-68-8),

[0106] 1,3,6,8-pyrenetetrasulfonic acid, tetrasodium salt (CAS Registry No. 59572-10-0), pyranine, (CAS Registry No. 6358-69-6, aka 8-hydroxy-1,3,6-pyrenetrisulfonic acid, trisodium salt),

[0107] quinoline (CAS Registry No. 91-22-5),

[0108] 3H-phenoxazin-3-one, 7-hydroxy-, 10-oxide, also known as Rhodalux (CAS Registry No. 550-82-3),

[0109] xanthylium, 9-(2,4-dicarboxyphenyl)-3,6-bis(diethylamino)-, chloride, disodium salt, also known as Rhodamine WT (CAS Registry No. 37299-86-8),

[0110] phenazinium, 3,7-diamino-2,8-dimethyl-5-phenyl-, chloride, also known as Safranine 0 (CAS Registry No. 477-73-6),

[0111] C.I. Fluorescent Brightener 235, also known as Sandoz CW (CAS Registry No. 56509-06-9),

[0112] benzenesulfonic acid, 2,2′-(1,2-ethenediyl)bis[5-[[4-[bis(2-hydroxyethyl)amino]-6-[(4-sulfophenyl)amino]-1,3,5-triazin-2-yl]amino]-, tetrasodium salt, also known as Sandoz CD (CAS Registry No. 16470-24-9, aka Flu. Bright. 220),

[0113] benzenesulfonic acid, 2,2′-(1,2-ethenediyl)bis[5-[[4-[(2-hydroxypropyl)amino]-6-(phenylamino)-1,3,5-triazin-2-yl]amino]-, disodium salt, also known as Sandoz TH-40 (CAS Registry No. 32694-95-4),

[0114] xanthylium, 3,6-bis(diethylamino)-9-(2,4-disulfophenyl)-, inner salt, sodium salt, also known as Sulforhodamine B (CAS Registry No. 3520-42-1, aka Acid Red 52),

[0115] benzenesulfonic acid, 2,2′-(1,2-ethenediyl)bis[5-[[4-[(aminomethyl)(2-hydroxyethyl)amino]-6-(phenylamino)-1,3,5-triazin-2-yl]amino]-, disodium salt, also known as Tinopal 5BM-GX (CAS Registry No. 169762-28-1),

[0116] Tinopol DCS (CAS Registry No. 205265-33-4),

[0117] benzenesulfonic acid, 2,2′-([1,1′-biphenyl]-4,4′-diyldi-2,1-ethenediyl)bis-, disodium salt also known as Tinopal CBS-X (CAS Registry No. 27344-41-8),

[0118] benzenesulfonic acid, 5-(2H-naphtho[1,2-d]triazol-2-yl)-2-(2-phenylethenyl)-, sodium salt, also known as Tinopal RBS 200, (CAS Registry No. 6416-68-8),

[0119] 7-benzothiazolesulfonic acid, 2,2′-(1-triazene-1,3-diyldi-4,1-phenylene)bis[6-methyl-, disodium salt, also known as Titan Yellow (CAS Registry No. 1829-00-1, aka Thiazole Yellow G), and all ammonium, potassium and sodium salts thereof, and all like agents and suitable mixtures thereof.

[0120] Preferred inert fluorescent tracers include:

[0121] 1-deoxy-1-(3,4-dihydro-7,8-dimethyl-2,4-dioxobenzo[g]pteridin-10(2H)-yl)-D-ribitol, also known as Riboflavin or Vitamin B2 (CAS Registry No. 83-88-5),

[0122] fluorescein (CAS Registry No. 2321-07-5),

[0123] fluorescein, sodium salt (CAS Registry No. 518-47-8, aka Acid Yellow 73, Uranine),

[0124] 2-anthracenesulfonic acid sodium salt (CAS Registry No. 16106-40-4),

[0125] 1,5-anthracenedisulfonic acid (CAS Registry No. 61736-91-2) and salts thereof,

[0126] 2,6-anthracenedisulfonic acid (CAS Registry No. 61736-95-6) and salts thereof,

[0127] 1,8-anthracenedisulfonic acid (CAS Registry No. 61736-92-3) and salts thereof,

[0128] mono-, di-, or tri-sulfonated napthalenes, including but not limited to

[0129] 1,5-naphthalenedisulfonic acid, disodium salt (hydrate) (CAS Registry No. 1655-29-4, aka 1,5-NDSA hydrate),

[0130] 2-amino-1-naphthalenesulfonic acid (CAS Registry No. 81-16-3),

[0131] 5-amino-2-naphthalenesulfonic acid (CAS Registry No. 119-79-9),

[0132] 4-amino-3-hydroxy-1-naphthalenesulfonic acid (CAS Registry No. 90-51-7),

[0133] 6-amino-4-hydroxy-2-naphthalenesulfonic acid (CAS Registry No. 116-63-2),

[0134] 7-amino-1,3-naphthalenesulfonic acid, potassium salt (CAS Registry No. 79873-35-1),

[0135] 4-amino-5-hydroxy-2,7-naphthalenedisulfonic acid (CAS Registry No. 90-20-0),

[0136] 5-dimethylamino-1-naphthalenesulfonic acid (CAS Registry No. 4272-77-9),

[0137] 1-amino-4-naphthalene sulfonic acid (CAS Registry No. 84-86-6),

[0138] 1-amino-7-naphthalene sulfonic acid (CAS Registry No. 119-28-8), and

[0139] 2,6-naphthalenedicarboxylic acid, dipotassium salt (CAS Registry No. 2666-06-0),

[0140] 3,4,9,10-perylenetetracarboxylic acid (CAS Registry No. 81-32-3),

[0141] C.I. Fluorescent Brightener 191, also known as, Phorwite CL (CAS Registry No. 12270-53-0),

[0142] C.I. Fluorescent Brightener 200, also known as Phorwite BKL (CAS Registry No. 61968-72-7),

[0143] benzenesulfonic acid, 2,2′-(1,2-ethenediyl)bis[5-(4-phenyl-2H-1,2,3-triazol-2-yl)-, dipotassium salt, also known as Phorwite BHC 766 (CAS Registry No. 52237-03-3),

[0144] benzenesulfonic acid, 5-(2H-naphtho[1,2-d]triazol-2-yl)-2-(2-phenylethenyl)-, sodium salt, also known as Pylaklor White S-1SA (CAS Registry No. 6416-68-8),

[0145] 1,3,6,8-pyrenetetrasulfonic acid, tetrasodium salt (CAS Registry No. 59572-10-0),

[0146] pyranine, (CAS Registry No. 6358-69-6, aka 8-hydroxy-1,3,6-pyrenetrisulfonic acid, trisodium salt),

[0147] quinoline (CAS Registry No. 91-22-5),

[0148] 3H-phenoxazin-3-one, 7-hydroxy-, 10-oxide, also known as Rhodalux (CAS Registry No. 550-82-3),

[0149] xanthylium, 9-(2,4-dicarboxyphenyl)-3,6-bis(diethylamino)-, chloride, disodium salt, also known as Rhodamine WT (CAS Registry No. 37299-86-8),

[0150] phenazinium, 3,7-diamino-2,8-dimethyl-5-phenyl-, chloride, also known as Safranine O (CAS Registry No. 477-73-6),

[0151] C.I. Fluorescent Brightener 235, also known as Sandoz CW (CAS Registry No. 56509-06-9),

[0152] benzenesulfonic acid, 2,2′-(1,2-ethenediyl)bis[5-[[4-[bis(2-hydroxyethyl)amino]-6-[(4-sulfophenyl)amino]-1,3,5-triazin-2-yl]amino]-, tetrasodium salt, also known as Sandoz CD (CAS Registry No. 16470-24-9, aka Flu. Bright. 220),

[0153] benzenesulfonic acid, 2,2′-(1,2-ethenediyl)bis[5-[[4-[(2-hydroxypropyl)amino]-6-(phenylamino)-1,3,5-triazin-2-yl]amino]-, disodium salt, also known as Sandoz TH-40 (CAS Registry No. 32694-95-4),

[0154] xanthylium, 3,6-bis(diethylamino)-9-(2,4-disulfophenyl)-, inner salt, sodium salt, also known as Sulforhodamine B (CAS Registry No. 3520-42-1, aka Acid Red 52),

[0155] benzenesulfonic acid, 2,2′-(1,2-ethenediyl)bis[5-[[4-[(aminomethyl)(2-hydroxyethyl)amino]-6-(phenylamino)-1,3,5-triazin-2-yl]amino]-, disodium salt, also known as Tinopal 5BM-GX (CAS Registry No. 169762-28-1),

[0156] Tinopol DCS (CAS Registry No. 205265-33-4),

[0157] benzenesulfonic acid, 2,2′-([1,1′-biphenyl]-4,4′-diyldi-2,1-ethenediyl)bis-, disodium salt, also known as Tinopal CBS-X (CAS Registry No. 27344-41-8),

[0158] benzenesulfonic acid, 5-(2H-naphtho[1,2-d]triazol-2-yl)-2-(2-phenylethenyl)-, sodium salt, also known as Tinopal RBS 200, (CAS Registry No. 6416-68-8),

[0159] 7-benzothiazolesulfonic acid, 2,2′-(1-triazene-1,3-diyldi-4,1-phenylene)bis[6-methyl-, disodium salt, also known as Titan Yellow (CAS Registry No. 1829-00-1, aka Thiazole Yellow G), and all ammonium, potassium and sodium salts thereof, and all like agents and suitable mixtures thereof.

[0160] The most preferred inert fluorescent tracers of the present invention include 1,3,6,8-pyrenetetrasulfonic acid tetrasodium salt (CAS Registry No. 59572-10-0); 1,5-naphthalenedisulfonic acid disodium salt (hydrate) (CAS Registry No. 1655-29-4, aka 1,5-NDSA hydrate); xanthylium, 9-(2,4-dicarboxyphenyl)-3,6-bis(diethylamino)-, chloride, disodium salt, also known as Rhodamine WT (CAS Registry No. 37299-86-8); 1-deoxy-1-(3,4-dihydro-7,8-dimethyl-2,4-dioxobenzo[g]pteridin-10(2H)-yl)-D-ribitol, also known as Riboflavin or Vitamin B2 (CAS Registry No. 83-88-5); fluorescein (CAS Registry No. 2321-07-5); fluorescein, sodium salt (CAS Registry No. 518-47-8, aka Acid Yellow 73, Uranine); 2-anthracenesulfonic acid sodium salt (CAS Registry No. 16106-40-4); 1,5-anthracenedisulfonic acid (CAS Registry No. 61736-91-2) and salts thereof; 2,6-anthracenedisulfonic acid (CAS Registry No. 61736-95-6) and salts thereof; 1,8-anthracenedisulfonic acid (CAS Registry No. 61736-92-3) and salts thereof; and mixtures thereof. The fluorescent tracers listed above are commercially available from a variety of different chemical supply companies.

[0161] In addition to the tracers listed above, those skilled in the art will recognize that salts using alternate counter ions may also be used. Thus, for example, anionic tracers which have Na+ as a counter ion could also be used in forms where the counter ion is chosen from the list of: K+, Li+, NH4+, Ca+2, Mg+2 or other appropriate counter ions. In the same way, cationic tracers may have a variety of counter ions, for example: Cl−, So4−2, PO4−3, HPO4−2; H2PO4−; CO3−2; HCO3−; or other appropriate counter ions.

[0162] Modifications of these tracers to control molecular weight or physical size within a desirable size range by, for example, affixing them to an inert polymeric molecule, incorporating them into a fluorescent microsphere or adding additional chemical moieties in the side chains of the molecules should be obvious to those skilled in the art. Such modifications are included herein.

[0163] The inert fluorescent tracer is used in combination with the tagged fluorescent agent to enhance monitoring of membrane separation, particularly with respect to the monitoring and effect of treatment agents added to membrane separation in order to treat scaling and/or fouling.

[0164] In this regard, the inert fluorescent tracer and the tagged fluorescent agent can each be measured such that fluctuations in the ratio of the inert fluorescent tracer to the tagged fluorescent agent can be monitored. Such fluctuations can be used to signal consumption of a chemical treatment agent, the onset of scaling and/or fouling, or the like. Adjustments to membrane separation can then be made controllably and responsively to correct for fluctuations with respect to the ratio. Thus, membrane separation performance can be enhanced by, for example, adjusting the amount of treatment agents added to optimize the treatment of scale, foulants and other like deposits which can adversely impact membrane separation.

[0165] The fluorescent compounds of the present invention (i.e. the inert fluorescent tracer, the tagged fluorescent agent, or combinations thereof) can be added to the membrane separation process in any suitable form. For example, the present invention uses a combination of inert fluorescent tracers and tagged fluorescent agents. In this regard, the inert fluorescent tracers can be used to monitor the dosage of treatment agents (e.g., anti-scalants and/or biocides) that are added to the process. The tagged fluorescent agents can be used to monitor the active chemical ingredient of such treatment. Thus, the loss of treatment due to, for example, adsorption of a treatment agent on a growing crystal, can be detected based on fluctuations in the ratio of inert fluorescent tracer(s) to tagged fluorescent agents during membrane separating. The diagnostic capabilities of the present invention can be performed with a high degree of sensitivity, selectivity and accuracy with respect to the monitoring of process parameters specific to a membrane separation. In this regard, the method and system of the present invention can be effectively used to optimize the performance of membrane separation processes.

[0166] The tagged fluorescent agent can include a variety of different and suitable materials. In an embodiment, the tagged fluorescent agent includes a polymeric compound that has one or more fluorescent groups attached or incorporated to its polymeric structure. In an embodiment, the polymeric compound has a molecular weight that ranges from about 2000 atomic mass units (“amu”) to about 20,000 amu. The polymeric compound is water-soluble and has one or more monomer components in any suitable amount including, for example, acrylamide, acrylic acid, methacrylamide, vinyl acetate, dimethylaminoethyl acrylate methyl chloride quaternary salt, dimethylaminoethyl acrylate benzyl chloride quaternary salt, diallyldimethyl ammonium chloride, N-vinyl formamide, dimethylaminoethyl methacrylate methyl chloride quaternary salt, dimethylaminoethyl methacrylate benzyl chloride quaternary salt, methacrylamino propyl trimethyl ammonium chloride, acrylamidopropyl trimethyl ammonium chloride, and combinations thereof. Different combinations of these polymeric compounds may be chosen for their ability to target specific scales.

[0167] The fluorescent group of the tagged fluorescent agent can include a variety of different and suitable materials including, hydroxy allyloxypropyl napthalimide quat, 4-methoxy-N-(3-N′N′-dimethylaminopropyl)napthalimide, 2-hydroxy-3-allyloxypropyl quat, 8-(3-vinylbenzyloxy)-1,3,6-pyrene trisulfonic acid, 8-(4-vinylbenzyloxy)-1,3,6-pyrene trisulfonic acid, 8-(allyloxy)-1,3,6-pyrene trisulfonic acid, 1-(substituted)naphthalene, 9-(substituted) anthracene, 2-(substituted) quinoline monohydrochloride, 2-(substituted) benzimidazole, 5-(substituted) fluorescein, 4-(substituted)coumarin, coumarin derivatives, 3-(substituted)-6,7-dimethoxy-1-methyl-2(1H)-quinoxazolinone, mixtures thereof and derivatives thereof.

[0168] In an embodiment, the tagged fluorescent agent of the present invention includes a hydroxy allyloxy propyl naphthalimide quat, such as 4-methoxy-N-(3-N′,N′-dimethylaminopropyl)napthalimide, 2-hydroxy-3-allyloxy propyl quat, tagged onto a 35% aqueous solution of a sulfomethylated copolymer of acrylate and acrylamide wherein the fluorescent group is an amount of about 2% or less by weight of the polymeric compound. A variety of different and suitable tagged fluorescent agents are disclosed in the U.S. Pat. Nos. 5,128,419; 5,171,450; 5,216,086; 5,260,386 and 5,986,030 which are each herein incorporated by reference. In an embodiment, the tagged fluorescent agent or moiety is stable at a pH ranging from about 2 to about 10.

[0169] It should be appreciated that a variety of different and suitable modifications, variations and/or derivatives thereof of the above-described tagged fluorescent agents and/or fluorescent groups can be used. For example, the hydrogen of the sulfonic acid groups of the substituted pyrene trisulfonic acids discussed above can be replaced with a suitable metal ion including, for example, sodium, potassium, cesium, rubidium, lithium and ammonium. Further, the allyloxy group of the substituted pyrene sulfonic acid can include any suitable number of carbon atoms including, for example, three, four, five, six, eight, eleven and the like.

[0170] The selection of inert fluorescent tracer and tagged fluorescent agent is made based on the membrane system being monitored and the purpose of the monitoring. Factors influencing the permeability of a material through a membrane include the following:

[0171] a) Size of the material and size of the holes in the membrane;

[0172] b) Charge of the material and charge (or lack thereof) of the membrane;

[0173] c) Tendency of the material to adsorb on the surface of the membrane, rather than pass through the membrane;

[0174] d) Concentration Differentials between the material on one side of the membrane and the material on the other side of the membrane; and

[0175] e) Residence times of the feed stream containing the material being in contact with the membrane.

[0176] Persons of ordinary skill in the art of membranes know how to set up and run the routine tests necessary to determine whether a particular inert tracer in combination with a particular tagged fluorescent agent is capable of passing through the holes in a membrane.

[0177] It should be appreciated that the amount of inert fluorescent tracer and tagged fluorescent agent to be added to the membrane separation process that is effective without being grossly excessive will vary with a respect to a variety of factors including, without limitation, the monitoring method selected, the extent of background interference associated with the selected monitoring method, the magnitude of the expected tracer(s) concentration in the feedwater and/or concentrate, the monitoring mode (such as an on-line continuous monitoring mode), and other similar factors. In an embodiment, the dosage of each of an inert fluorescent tracer(s) and tagged fluorescent agent to the feed water of the membrane separation system includes an amount that is at least sufficient to provide a measurable concentration of the fluorescent agents (i.e., inert fluorescent tracer and tagged fluorescent agent) in the concentrate at steady state of at least about 5 ppt, and preferably at least about 1 part per billion (“ppb”) or about 5 ppb or higher, such as, up to about 100 ppm or about 200 ppm, or even as high as about 1000 ppm in the concentrate or other effluent stream. In an embodiment, the amount of fluorescent agents ranges from about 5 ppt to about 1000 ppm, preferably from about 1 ppb to about 50 ppm, and more preferably from about 5 ppb to about 50 ppb.

[0178] It should be appreciated that the concentration of tagged fluorescent agent can be modified by varying the number of fluorescent groups on the polymeric compound and/or varying the concentration of the polymeric compound.

[0179] The inert fluorescent tracers and tagged fluorescent agents of the present invention can be detected by using a variety of different and suitable fluorometers. For example, fluorescence emission spectroscopy on a substantially continuous basis, at least over a given time period, is one of the preferred analytical techniques according to an embodiment of the present invention. One method for the continuous on-stream measuring of chemical species by fluorescence emission spectroscopy and other analysis methods is described in U.S. Pat. No. 4,992,380, B. E. Moriarty, J. J. Hickey, W. H. Hoy, J. E. Hoots and D. A. Johnson, issued Feb. 12, 1991, incorporated hereinto by reference.

[0180] In general, for most fluorescence emission spectroscopy methods having a reasonable degree of practicality, it is preferable to perform the analysis without isolating in any manner the fluorescent species. Thus, there may be some degree of background fluorescence in the influent/feedwater and/or concentrate on which the fluorescence analysis is conducted. This background fluorescence may come from chemical compounds in the membrane separation system (including the influent/feedwater system thereof) that are unrelated to the membrane separation process of the present invention.

[0181] In instances where the background fluorescence is low, the relative measurable intensities (measured against a standard fluorescent compound at a standard concentration and assigned a relative intensity, for instance 100) of the fluorescence of each of the tracer and the tagged fluorophore versus the background can be very high, for instance a ratio of 100/10 or 500/10, when certain combinations of excitation and emission wavelengths are employed even at low fluorescent compound concentrations. Such ratios would be representative of a “relative fluorescence” (under like conditions) of respectively 10 and 50. In an embodiment, the excitation/emission wavelengths and/or the amount of each of the tracer and tagged fluorophore employed are selected to provide a relative fluorescence of at least about 5 or 10 for the given background fluorescence anticipated.

[0182] Examples of fluorometers that may be used in the practice of this invention include the TRASAR® 3000 and TRASAR® 8000 fluorometers (available from Ondeo Nalco Company of Naperville, Ill.); the Hitachi F-4500 fluorometer (available from Hitachi through Hitachi Instruments Inc. of San Jose, Calif.); the JOBIN YVON FluoroMax-3 “SPEX” fluorometer (available from JOBIN YVON Inc. of Edison, N.J.); and the Gilford Fluoro-IV spectrophotometer or the SFM 25 (available from Bio-tech Kontron through Research Instruments International of San Diego, Calif.). It should be appreciated that the fluorometer list is not comprehensive and is intended only to show examples of fluorometers. Other commercially available fluorometers and modifications thereof can also be used in this invention.

[0183] After the fluorometers have been selected the locations for monitoring are selected. As previously indicated, the fluorescent signals of the inert fluorescent tracer and tagged fluorescent agent may be detected in the feed stream, the condensate and optionally the permeate. The detection in the permeate is optional, simply because it is known that not all the inert tracers and tagged fluorescent agents listed herein are capable of traveling through the holes in all the membrane separation systems listed herein. It is the selection of the inert fluorescent tracer and the tagged fluorescent agent and the membrane system they are being used in that determines whether both or either of the inert fluorescent tracer and the tagged fluorescent agent are capable of being detected in the permeate.

[0184] It should be appreciated that locations for monitoring should not be positioned across a flow-through site that has a high concentration of solids, for instance a solids concentration of at least about 5 or about 10 weight percent per unit volume based on a measured volume unit of about one cubic inch. Such high solids concentration flow-through sites are found at the site of filter cakes and the like. In this regard, these sites may absorb, or selectively absorb, at least some amount of the tracer. This can distort the significance of monitoring comparison. When a tracer is added upstream of, for instance, a cartridge filter, in an embodiment, the monitoring location should preferably be downstream of such sites.

[0185] After the fluorometer has been used to detect the fluorescent signal of the inert fluorescent tracer and the tagged fluorescent agent, then it is possible, using techniques known to people in the art of fluorometry to convert the detected fluorescent signal of the inert fluorescent tracer into the concentration of the inert fluorescent tracer in each of the streams it was detected in and to convert the detected fluorescent signal of the tagged fluorescent agent into the concentration of the tagged fluorescent agent in each of the streams it was measured in.

[0186] After the concentrations of the inert fluorescent tracer and tagged fluorescent agent are known in each of the streams, then it is possible to calculate a ratio of the concentrations. In continuous monitoring of the system, this ratio calculation can be used to determine useful information regarding permeation and consumption rates in each of the streams so monitored.

[0187] The second aspect of the instant claimed invention involves deliberately selecting an inert tracer and a tagged fluorescent agent that are known to not be capable of traveling through the membrane into the permeate. Upon beginning this method, one or more fluorometers, previously described, is(are) set up to look for the fluorescent signals of both the inert fluorescent tracer and the tagged fluorescent agent in the permeate. Should those fluorescent signals be detected, then it is an indication that the membrane is damaged in some way, indicating the need for inspection and maintenance.

[0188] As previously discussed, the present invention can provide highly selective and/or sensitive monitoring of a variety of process parameters unique and specific to the membrane separation process. The monitoring is based on the measurable amounts of an inert fluorescent tracer in combination with a tagged fluorescent agent analyzed during the membrane separation process. In this regard, the fluorescent species (i.e., inert fluorescent tracer and tagged fluorescent agent) can be detected at any suitable location or locations within the membrane separation process, such as any suitable position in a membrane filtration process along the feedwater stream, the concentrate stream and optionally in the permeate stream, the like or combinations thereof. This effectively corresponds to a concentration of the fluorescent species in each stream.

[0189] In this regard, monitoring of an amount of the inert fluorescent tracer and tagged fluorescent agent as it may vary during membrane filtration can be used to evaluate a number of process parameters specific to membrane filtration such as the ratio of the inert fluorescent tracer to the tagged fluorescent agent or the like, with a high degree of sensitivity, selectivity and accuracy, as previously discussed. The ability to evaluate these types of membrane separation process parameters with such level of certainty, sensitivity and selectivity and on a continual basis in accordance with the present invention can provide a better understanding, in real time, of the performance of the membrane. Thus, adjustments to the membrane separation process can be made more responsively and effectively based on the measured amount of the inert fluorescent tracer and/or the tagged fluorescent agent, if needed, to optimize membrane performance. For example, adjustments can be made to increase the recovery ratio or percent recovery of the membrane separation system. In this regard, increasing the recovery ratio or percent recovery, for unit product, will reduce the feedwater required and thus reduce feedwater costs, lower influent fluid pretreatment costs and chemical treatment requirements. It should be appreciated that the optimal percent rejection value can vary with respect to the type of membrane separation system.

[0190] Applicants have uniquely discovered that the monitoring and/or controlling techniques of membrane separation processes in accordance with the present invention are faster, more sensitive, more comprehensive and/or more reliable than conventional techniques presently available, particularly where the monitoring methods of the present invention are employed on a substantially continuous basis. The present invention has enhanced diagnostic capabilities such that, for example, lack of chemical treatment, scaling and/or fouling problems unique to membrane separation and consumption of active chemical treatment can be detected with reasonable certainty, with far greater sensitivity, under a far less elapsed time than the presently available methods. In this regard, temporary system upsets or other short-lived variations can be detected during continuous monitoring as the transient conditions that they are, rather than as incorrect warning signs as detected by sporadic monitoring.

[0191] The following example is presented to be illustrative of the present invention and to teach one of ordinary skill how to make and use the invention. This example is not intended to limit the invention or its protection in any way.

EXAMPLE

[0192] A product is made by combining an inert tracer with a tagged fluorescent agent as follows:

Soft water                 about 8.6 weight %
Inert Tracer =             about 2.0 weight %
1, 3, 6, 8 Pyrene tetrasulfonic
acid, tetra sodium salt
Poly Succinic Oligomer     about 32.3 weight %
Tagged fluorescent Agent = About 57.1 weight %
Tagged High Stress Polymer

[0193] All of these ingredients are available from Ondeo Nalco Company, 1601 W. Diehl Road, Naperville, Ill. 60563, (630) 305-1000.

[0194] The above product is put into an operating Reverse Osmosis unit as part of a chemical treatment. The material is placed in the feed stream, then two fluorometers are used to detect the fluorescent signal of the material in the feed stream and in the concentrate stream feed stream).

[0195] The polymeric component (the tagged HSP “high stress polymer” a member of the PRISM polymer family available from Ondeo Nalco Company) is expected to be consumed as it attaches to scale which is forming in the system. By detecting the fluorescent signal of both the inert tracer, which should reflect concentration effects of the RO but not consumption of the active ingredient, and the tagged polymer, functioning as an active scale control ingredient, it is possible to determine the consumption of the active dispersant polymer.

[0196] In Reverse Osmosis membranes, based on knowledge of the size of the tagged polymer and size of the holes in the membrane; the charge of the tagged polymer and charge (or lack thereof) of the membrane; the tendency of the tagged polymer to adsorb on the surface of the membrane, rather than pass through the membrane; the concentration differentials between the tagged polymer on one side of the membrane and the tagged polymer on the other side of the membrane; and the residence times of the feed stream containing the tagged polymer being in contact with the membrane, the tagged polymer is not expected to pass through the system into the permeate unless there is a catastrophic membrane failure. An example of catastrophic failure would be a glue line tearing or opening which allows all components in the feed/concentrate stream to pass into the permeate stream. Therefore, as time passes, periodically fluorometers are used to detect the fluorescent signals of the inert tracer and the tagged polymer in the permeate. If either the inert fluorescent tracer or the tagged polymer is detected in the permeate, then a catastrophic failure of the membrane is indicated.

[0197] While the present invention is described above in connection with preferred or illustrative embodiments, these embodiments are not intended to be exhaustive or limiting of the invention. Rather, the invention is intended to cover all alternatives, modifications and equivalents included within its spirit and scope, as defined by the appended claims.

Claims

1. A method for monitoring a membrane separation process comprising the steps of: (a) providing an industrial process, wherein within said industrial process there are feed streams comprising one or more solutes in an aqueous liquid; (b) providing a membrane capable of removing solutes from a feed stream by separating said feed stream into a first stream and a second stream, wherein said first steam is the permeate stream and said second stream is the concentrate stream; (c) selecting an inert fluorescent tracer and a tagged fluorescent agent; wherein the selection is made such that it is known in advance whether said inert fluorescent tracer and said tagged fluorescent agent are either (i) capable of traveling through the membrane into the permeate stream either separately or together, or (iii) not capable of passing through the membrane into the permeate stream either separately or together; (d) introducing the inert fluorescent tracer and tagged fluorescent agent into the feed stream; (e) providing one or more fluorometers, to enable the detection of the fluorescent signal of the inert fluorescent tracer in the feed stream and the concentrate and optionally the permeate and the detection of the fluorescent signal of the tagged fluorescent agent in the feed stream and the concentrate and optionally the permeate; (f) using the one or more fluorometers to detect the fluorescent signal of the inert fluorescent tracer in the feed stream and the concentrate and optionally the permeate and to detect the fluorescent signal of the tagged fluorescent agent in the feed stream and the concentrate and optionally the permeate; (g) converting the detected fluorescent signal of the inert fluorescent tracer into the concentration of the inert fluorescent tracer in the feed stream and the concentrate and optionally the permeate and converting the detected fluorescent signal of the tagged fluorescent agent into the concentration of the tagged fluorescent agent in the feed stream and the concentrate and optionally the permeate.

2. The method of claim 1 further comprising the step of (h) evaluating at least one process parameter specific to the membrane separation process based on the amount of the inert fluorescent tracer and the tagged fluorescent agent that are measured.

3. The method of claim 1 wherein the membrane separation process is selected from the group consisting of a cross-flow membrane separation process and a dead-end flow membrane separation process.

4. The method of claim 3 wherein the membrane separation process is selected from the group consisting of reverse osmosis, ultrafiltration, microfiltration, nanofiltration, electrodialysis, electrodeionization, pervaporation, membrane extraction, membrane distillation, membrane stripping and combinations thereof.

5. The method of claim 3 wherein the membrane separation process is selected from the group consisting of reverse osmosis, ultrafiltration, microfiltration and nanofiltration.

6. The method of claim 1 wherein the inert fluorescent tracer is selected from the group consisting of 3,6-acridinediamine, N,N,N′,N′-tetramethyl-,monohydrochloride; 2-anthracenesulfonic acid sodium salt; 1,5-anthracenedisulfonic acid; 2,6-anthracenedisulfonic acid; 1,8-anthracenedisulfonic acid; anthra[9,1,2-cde]benzo[rst]pentaphene-5,10-diol, 16,17-dimethoxy-, bis(hydrogen sulfate), disodium salt; bathophenanthrolinedisulfonic acid disodium salt; amino 2,5-benzene disulfonic acid; 2-(4-aminophenyl)-6-methylbenzothiazole; 1H-benz[de]isoquinoline-5-sulfonic acid, 6-amino-2,3-dihydro-2-(4-methylphenyl)-1,3-dioxo-, monosodium salt; phenoxazin-5-ium, 1-(aminocarbonyl)-7-(diethylamino)-3,4-dihydroxy-, chloride; benzo[a]phenoxazin-7-ium, 5,9-diamino-,acetate; 4-dibenzofuransulfonic acid; 3-dibenzofuransulfonic acid; 1-ethylquinaldinium iodide; fluorescein; fluorescein, sodium salt; Keyfluor White ST; benzenesulfonic acid, 2,2′-(1,2-ethenediyl)bis[5-[[4-[bis(2-hydroxyethyl)amino]-6-[(4-sulfophenyl)amino]-1,3 ,5-triazin-2-yl]amino]-,tetrasodium salt; C.I. Florescent Brightener 230; benzenesulfonic acid, 2,2′-(1,2-ethenediyl)bis[5-[[4-[bis(2-hydroxyethyl)amino]-6-[(4-sulfophenyl)amino]-1,3,5-triazin-2-yl]amino]-,tetasodium salt; 9,9′-biacridinium, 10,10′-dimethyl-, dinitrate; 1-deoxy-1-(3,4-dihydro-7,8-dimethyl-2,4-dioxobenzo[g]pteridin-10(2H)-yl)-ribitol; mono-, di-, or tri-sulfonated napthalenes selected from the group consisting of 1,5-naphthalenedisulfonic acid, disodium salt (hydrate); 2-amino-1-naphthalenesulfonic acid; 5-amino-2-naphthalenesulfonic acid; 4-amino-3-hydroxy-1-naphthalenesulfonic acid; 6-amino-4-hydroxy-2-naphthalenesulfonic acid; 7-amino-1,3-naphthalenesulfonic acid, potassium salt; 4-amino-5-hydroxy-2,7-naphthalenedisulfonic acid; 5-dimethylamino-1-naphthalenesulfonic acid; 1-amino-4-naphthalene sulfonic acid; 1-amino-7-naphthalene sulfonic acid; and 2,6-naphthalenedicarboxylic acid, dipotassium salt; 3,4,9,10-perylenetetracarboxylic acid; C.I. Fluorescent Brightener 191; C.I. Fluorescent Brightener 200; benzenesulfonic acid, 2,2′-(1,2-ethenediyl)bis[5-(4-phenyl-2H-1,2,3-triazol-2-yl)-, dipotassium salt; benzenesulfonic acid, 5-(2H-naphtho[1,2-d]triazol-2-yl)-2(2-phenylethenyl)-, sodium salt; 1,3,6,8-pyrenetetrasulfonic acid, tetrasodium salt; pyranine; quinoline; 3H-phenoxazin-3-one, 7-hydroxy-, 10-oxide; xanthylium, 9-(2,4-dicarboxyphenyl)-3,6-bis(diethylamino)-, chloride, disodium salt; phenazinium, 3,7-diamino-2,8-dimethyl-5-phenyl-, chloride; C.I. Fluorescent Brightener 235; benzenesulfonic acid, 2,2′-(1,2-ethenediyl)bis[5-[[4-[bis(2-hydroxyethyl)amino]-6-[(4-sulfophenyl)amino]-1,3,5-triazin-2-yl]amino]-, tetrasodium salt; benzenesulfonic acid, 2,2′-(1,2-ethenediyl)bis[5-[[4-[(2-hydroxypropyl)amino]-6-(phenylamino)-1,3,5-triazin-2-yl]amino]-, disodium salt; xanthylium, 3,6-bis(diethylamino)-9-(2,4-disulfophenyl)-, inner salt, sodium salt; benzenesulfonic acid, 2,2′-(1,2-ethenediyl)bis[5-[[4-[(aminomethyl)(2-hydroxyethyl)amino]-6-(phenylamino)-1,3,5-triazin-2-yl]amino]-, disodium salt; Tinopol DCS; benzenesulfonic acid, 2,2′-([1,1′-biphenyl]-4,4′-diyldi-2,1-ethenediyl)bis, disodium salt; benzenesulfonic acid, 5-(2H-naphtho[1,2-d]triazol-2-yl)-2-(2-phenylethenyl)-, sodium salt; 7-benzothiazolesulfonic acid, 2,2′-(1-triazene-1,3-diyldi-4,1-phenylene)bis[6-methyl-, disodium salt; and all ammonium, potassium and sodium salts thereof; and all mixtures thereof.

7. The method of claim 1 wherein the inert fluorescent tracer is selected from the group consisting of 1-deoxy-1-(3,4-dihydro-7,8-dimethyl-2,4-dioxobenzo[g]pteridin-10(2H)-yl)-D ribitol; fluorescein; fluorescein, sodium salt; 2-anthracenesulfonic acid sodium salt; 1,5-anthracenedisulfonic acid; 2,6-anthracenedisulfonic acid; 1,8-anthracenedisulfonic acid; mono-, di-, or tri-sulfonated napthalenes selected from the group consisting of 1,5-naphthalenedisulfonic acid, disodium salt (hydrate); 2-amino-1-naphthalenesulfonic acid; 5-amino-2-naphthalenesulfonic acid; 4-amino-3-hydroxy-1-naphthalenesulfonic acid; 6-amino-4-hydroxy-2-naphthalenesulfonic acid; 7-amino-1,3-naphthalenesulfonic acid, potassium salt; 4-amino-5-hydroxy-2,7-naphthalenedisulfonic acid; 5-dimethylamino-1-naphthalenesulfonic acid; 1-amino-4-naphthalene sulfonic acid; 1-amino-7-naphthalene sulfonic acid; and 2,6-naphthalenedicarboxylic acid, dipotassium salt; 3,4,9,10-perylenetetracarboxylic acid; C.I. Fluorescent Brightener 191; C.I. Fluorescent Brightener 200; benzenesulfonic acid, 2,2′-(1,2-ethenediyl)bis[5-(4-phenyl-2H-1,2,3-triazol-2-yl)-, dipotassium salt; benzenesulfonic acid, 5-(2H-naphtho[1,2-d]triazol-2-yl)-2-(2-phenylethenyl)-, sodium salt; 1,3,6,8-pyrenetetrasulfonic acid, tetrasodium salt; pyranine; quinoline; 3H-phenoxazin-3-one, 7-hydroxy-, 10-oxide; xanthylium, 9-(2,4-dicarboxyphenyl)-3,6-bis(diethylamino)-, chloride, disodium salt; phenazinium, 3,7-diamino-2,8-dimethyl-5-phenyl-, chloride; C.I. Fluorescent Brightener 235; benzenesulfonic acid, 2,2′-(1,2-ethenediyl)bis[5-[[4-[bis(2-hydroxyethyl)amino]-6-[(4-sulfophenyl)amino]-1,3,5-triazin-2-yl]amino]-, tetrasodium salt; benzenesulfonic acid, 2,2′-(1,2-ethenediyl)bis[5-[[4-[4-[2-hydroxypropyl)amino]-6-(p henylamino)-1,3,5-triazin-2-yl]amino]-, disodium salt; xanthylium, 3,6-bis(diethylamino)-9-(2-4-disulfophenyl)-, inner salt, sodium salt; benzenesulfonic acid, 2,2′-(1,2-ethenediyl)bis[5-[[4-[(aminomethyl)(2-hydroxyethyl)amino]-6-(phenylamino)-1,3,5-triazin-2-yl]amino]-,disodium salt; Tinopol DCS; benzenesulfonic acid, 2,2′-([1,1′-biphenyl]-4,4′-diyldi-2,1-ethenediyl)bis-,disodium salt; benzenesulfonic acid, 5-(2H-naphtho[1,2-d]triazol-2-yl)-2-(2-phenylethenyl)-, sodium salt; 7-benzothiazolesulfonic acid, 2,2′-(1-triazene-1,3-diyldi-4,1-phenylene)bis[6-methyl-, disodium salt; and all ammonium, potassium and sodium salts thereof; and all mixtures thereof.

8. The method of claim 1 wherein the inert fluorescent tracer is selected from the group consisting of 1,3,6,8-pyrenetetrasulfonic acid tetrasodium salt; 1,5-naphthalenedisulfonic acid disodium salt (hydrate); xanthylium, 9-(2,4-dicarboxyphenyl)-3,6-bis(diethylamino)-, chloride, disodium salt; 1-deoxy-1-(3,4-dihydro-7,8-dimethyl-2,4-dioxobenzo[g]pteridin-10(2H)-yl) - D-ribitol; fluorescein; flurorescein, sodium salt; 2-anthracenesulfonic acid sodium salt; 1,5-anthracenedisulfonic acid; 2,6-anthracenedisulfonic acid; 1,8-anthracenedisulfonic acid; and mixtures thereof.

9. The method of claim 1 wherein the tagged fluorescent agent comprises a water-soluble polymer tagged with at least one fluorescent group.

10. The method of claim 9 wherein the fluorescent group is selected from the group consisting of hydroxy allyloxypropyl napthalimide quat, 4-methoxy-N-(3-N′N′-dimethylaminopropyl)napthalimide, 2 hydroxy-3-allyloxypropyl quat, 8-(3-vinylbenzyloxy)-1,3,6-pyrene trisulfonic acid; 8-(4-vinylbenzyloxy)-1,3,6-pyrene trisulfonic acid, 8-(allyloxy)-1,3,6-pyrene trisulfonic acid, 1-(substituted) naphthalene, 9-(substituted)anthracene, 2-(substituted) quinoline monohydrochloride, 2-(substituted) benzimidazole, 5-(substituted) fluorescein, 4-(substituted) coumarin, coumarin derivatives, 3-(substituted)-6,7-dimethoxy-1-methyl-2(1H)-quinoxazolinone, mixtures thereof and derivatives thereof.

11. The method of claim 9 wherein the water-soluble polymer comprises a monomer selected from the group consisting of acrylamide, acrylic acid, methacrylamide, vinyl acetate, dimethylaminoethyl acrylate methyl chloride quaternary salt, dimethylaminoethyl acrylate benzyl chloride quaternary salt, diallyldimethyl ammonium chloride, N-vinyl formamide; dimethylaminoethyl methacrylate methyl chloride quaternary salt, dimethylaminoethyl methacrylate benzyl chloride quaternary salt, methacrylamino propyl trimethyl ammonium chloride, acrylamidopropyl trimethyl ammonium chloride, and combinations thereof.

12. The method of claim 1 wherein the tagged fluorescent agent comprises a copolymer of acrylate and acrylamide tagged with a hydroxy allyloxypropyl napthalimide quat in an amount of about 2% or less by weight of the copolymer.

13. The method of claim 1 wherein the inert fluorescent tracer and the tagged fluorescent agent are each introduced into the feed stream in an amount from about 5 ppt to about 1000 ppm.

14. The method of claim 1 wherein the inert fluorescent tracer and the tagged fluorescent agent are each introduced into the feed stream in an amount from about 1 ppb to about 50 ppm.

15. The method of claim 1 wherein the inert fluorescent tracer and the tagged fluorescent agent are each introduced into the feed stream in an amount from about 5 ppb to about 50 ppb.

16. The method of claim 1 wherein the inert fluorescent tracer and tagged fluorescent agent are added to a formulation capable of treating scaling and/or fouling prior to addition to the feed stream.

17. The method of claim 1 further comprising the step of: (h) determining the ratio of the amount of inert fluorescent tracer to the tagged fluorescent agent based on the concentration of the inert fluorescent tracer and the concentration of the tagged fluorescent agent in each of the streams where the concentrations were measured.

18. A method for detecting damage to a membrane used in a membrane separation process comprising the steps of: (a) providing an industrial process, wherein within said industrial process there are feed streams comprising one or more solutes in an aqueous liquid; (b) providing a membrane capable of removing solutes from a feed stream by separating said feed stream into a first stream and a second stream, wherein said first steam is the permeate stream and said second stream is the concentrate stream; (c) selecting an inert fluorescent tracer and a tagged fluorescent agent; wherein the selection is made such that it is known in advance that one or both of said inert fluorescent tracer and said tagged fluorescent agent are not capable of passing through the membrane into the permeate stream; (d) introducing the inert fluorescent tracer and tagged fluorescent agent into the feed stream; (e) providing one or more fluorometers, to enable the detection of the fluorescent signal of the inert fluorescent tracer in the feed stream and in the permeate stream and the detection of the fluorescent signal of the tagged fluorescent agent in the feed stream and in the permeate stream; (f) using the one or more fluorometers to detect the fluorescent signal of the inert fluorescent tracer in the feed stream and in the permeate stream and to detect the fluorescent signal of the tagged fluorescent agent in the feed stream and in the permeate stream; wherein, if one or both of the fluorescent signals of the inert fluorescent tracer and the tagged fluorescent agent are found in the permeate then this indicates the membrane is damaged in some way.