Patent Description:
Membrane separation is a technology that selectively separates materials via pores and/or minute gaps in the molecular arrangement of a continuous membrane structure. Membrane separations can be classified by pore size and by the separation driving force. Example membrane separation techniques include microfiltration (MF), ultrafiltration (UF), ionexchange (IE), and reverse osmosis (RO). For example, reverse osmosis is widely used in water purification processes to remove ions, bacteria, and other molecules and larger particles from the water. In a reverse osmosis process, an applied pressure is used to overcome an osmotic pressure across the membrane, allowing substantially pure solvent (e.g., water) to pass through the membrane while a residual solute is retained on the pressurized side of the membrane.

In practice, the degree of purification achieved using the membrane separation process is dictated, at least in part, by the quality and integrity of the membrane used in the process. If there are chemical and/or mechanical failures to the membrane structure, impurities can pass through the membrane breach and into the resulting "purified" product stream. In the case of water purification, harmful impurities and pathogens (e.g., waterborne enteric viruses, Cryptosporidium, Giardia cysts, nanoparticles, organic compounds, and so forth), which can be in the nanosize range, can pass through the membrane breach into the clean water stream, potentially creating health risks.

For these and other reasons, techniques have been used to monitor the performance of membrane separation processes. As one example, such as described in <CIT>, a fluorometric monitoring process may be used to monitor the performance of a membrane separation process by introducing a fluorescent tracer into a feed stream and then detecting the fluorescent tracer in one or more streams downstream of the separation membrane. The extent to which the fluorescent tracer passes through the membrane can provide an indication of the integrity of the membrane. In <CIT> relates to a fluorimetric system, apparatus and method are disclosed to measure an analyte concentration in a sample. A sensor reagent housing is also disclosed which comprises a channel and a porous medium having an analysis chemistry reagent, such as a nucleic acid analysis chemistry reagent. The apparatus and system are portable for field use, with an apparatus housing having a size adapted to fit into a user's hand. <CIT> relates to a sensing instrument and method for measuring the concentration of an analyte. The sensing instrument includes: a sensing element including at least a first emissive indicator characterized by a bimolecular quenching rate constant kq, one or more fluorescence lifetimes tau o above a lowest lifetime tau oL, and capable of emitting analyte concentration dependent signals when exposed to an excitation signal in the presence of quencher; an excitation system which provides an amplitude modulated excitation signal at one or more radial modulation frequencies omega ; a detector; and a processor.

Practical challenges arise when attempting to fluorometrically monitor the performance of a membrane separation process. Since a properly-functioning membrane may separate most of the fluorescent tracer from the purified product stream (also referred to as the permeate), the fluorometer may need to detect very small concentrations of tracer. Small changes in the calibration or measurement accuracy of the fluorometer may cause large errors in the measured tracer concentration at these very small concentrations. Moreover, since many membrane separation processes operate continuously, for example supplying critical water needs, there may be little or no opportunity to recalibrate the fluorometer.

In general, this disclosure is directed to systems and techniques for calibrating fluorometers, including systems and techniques for monitoring and/or controlling membrane separation processes utilizing such fluorometers. The invention is defined in the claims. In some examples, the techniques include partial recalibration of a fluorometer in-situ based on control of a fluorescent tracer introduced into a feed stream being separated using a membrane separation process. Prior to or concurrent with startup of a membrane separation process, a fluorometer used to monitor the process may undergo a full, multi-point calibration. The full calibration process may involve fluorometrically analyzing a reference solution that is a blank or zero fluorescence solution in addition to one or more other reference solutions having known concentrations of fluorescent tracer. A single or higher order calibration curve having a slope and an intercept relating the measured fluorometric response of the fluorometer to a fluorescent tracer concentration can then be stored in a computer readable memory associated with the fluorometer.

In subsequent operation, the fluorescent tracer can be introduced into a feed stream before a membrane used in a membrane separation process. The fluorometer can monitor the feed stream and/or one more streams downstream of the membrane, such as a permeate stream. With reference to the calibration information generated during the full calibration, the concentration of fluorescent tracer in the monitored stream can be monitored based on the fluorescent response of the stream by the fluorometer. Over time, however, the fluorometer may lose calibration. The fluorometer may lose calibration for a variety of reasons, such as fouling buildup, changing electrical resistance of a circuit, changing light source strength, and/or other factors. Accordingly, the accuracy of measurements made by the fluorometer may deteriorate over time.

In accordance with some examples of the present disclosure, a zero point recalibration is performed on the fluorometer without performing a full, multipoint recalibration. When performing the zero point recalibration, the intercept of the calibration curve stored for the fluorometer may be reset, e.g., without changing other parameters defining the calibration curve. It has been found that, in some applications, recalibrating the intercept of the recalibration curve of the fluorometer, particularly when detecting very low concentrations of fluorescent tracer, can provide highly beneficial accuracy improvements even though a full recalibration is not performed. As described in greater detail below, such a partial recalibration may be performed without removing the fluorometer from its operating environment, allowing the accuracy of the fluorometer to be enhanced even though a full recalibration may not be feasible.

Without wishing to be bound by any particular theory, it is believed that, in some applications, zero point drift is a more significant contributor to measurement inaccuracies than other calibration inaccuracies. For example, for fluorometers used to measure ultralow concentrations of fluorescent tracer, such as in membrane separation permeate streams, small shifts in zero point calibration have been found to cause large inaccuracies in measured tracer concentration. For instance, a shift in the zero point of the calibration curve may cause a measurement inaccuracy equivalent to <NUM>µg/L or greater. If measuring higher concentrations of fluorescent tracer, such as <NUM> - <NUM>,<NUM>µg/L, the measurement inaccuracy is <NUM>% or less. However, when measuring ultralow concentrations of fluorescent tracer, such as <NUM>µg/L or less, that same measurement inaccuracy causes a measurement error of <NUM>% or greater.

In some examples, a fluorometer zero point recalibration process can be performed by controlling a fluorescent tracer introduced into a feed stream that is undergoing membrane separation. Typically, the fluorescent tracer will be introduced into the feed stream at a substantially constant rate and/or in an amount effective to achieve a substantially constant concentration. During zero point recalibration, the concentration of the fluorescent tracer may be adjusted to provide a fluorescent signal change that can be used to recalibrate the intercept of the calibration curve for the fluorometer. In different examples, introduction of the fluorescent tracer into the feed stream may be stopped, or increased or decreased relative to a baseline introduction rate. The fluorescent signal measured by the fluorometer can be used to adjust the intercept of the calibration curve, allowing one or more adjusted calibration curve parameters to be stored in a memory associated with the fluorometer for subject use.

In one example, a method of calibrating a fluorometer used to monitor a reverse osmosis membrane separation process is described. The method includes introducing a fluorescent tracer into a feed stream to provide a first concentration of fluorescent tracer in the feed stream and contacting a reverse osmosis membrane with the feed stream, thereby generating a permeate stream and a concentrate stream. The method also includes fluorometrically analyzing the permeate stream generated from the feed stream having the first concentration of fluorescent tracer with a fluorometer and determining therefrom a first measured concentration of the fluorescent tracer in the permeate stream based on a stored calibration curve that includes an intercept. The method further includes adjusting a concentration of the fluorescent tracer introduced into the feed stream to provide a second concentration of fluorescent tracer in the feed stream different than the first concentration. Further, the example method includes fluorometrically analyzing the permeate stream generated from the feed stream having the second concentration of fluorescent tracer with the fluorometer and determining therefrom a second measured concentration of the fluorescent tracer in the permeate stream based on the calibration curve. In addition, the method includes determining an intercept shift for the calibration curve based on comparison of the first measured concentration to the second measured concentration and determining an adjusted intercept for the calibration curve based on the intercept shift.

In another example, a system is described that includes a fluorescent tracer pump configured to introduce fluorescent tracer into a feed stream, a membrane configured to separate the feed stream into a permeate stream and a concentrate stream, a fluorometer configured to fluorometrically analyze the permeate stream, and a controller communicatively coupled to the fluorescent tracer pump and the fluorometer. The example specifies that the controller is configured to control the fluorescent tracer pump to introduce the fluorescent tracer into a feed stream to provide a first concentration of fluorescent tracer in the feed stream. In addition, the controller is configured to control the fluorometer to fluorometrically analyze the permeate stream generated from the feed stream having the first concentration of fluorescent tracer and determine therefrom a first measured concentration of the fluorescent tracer in the permeate stream based on a stored calibration curve that includes an intercept. In addition, the example specifies that the controller is configured to control the fluorescent tracer pump to adjust a concentration of the fluorescent tracer introduced into the feed stream to provide a second concentration of fluorescent tracer in the feed stream different than the first concentration. In addition, the controller is configured to control the fluorometer to fluorometrically analyze the permeate stream generated from the feed stream having the second concentration of fluorescent tracer and determine therefrom a second measured concentration of the fluorescent tracer in the permeate stream based on the calibration curve. The example further states that the controller is configured to determine an intercept shift for the calibration curve based on comparison of the first measured concentration to the second measured concentration and determine an adjusted intercept for the calibration curve based on the intercept shift.

In another example, a method of calibrating a fluorometer used to monitor a reverse osmosis membrane separation process is described. The method includes introducing a fluorescent tracer into a feed stream and contacting a reverse osmosis membrane with the feed stream, thereby generating a permeate stream and a concentrate stream. The method further involves terminating the introduction of fluorescent tracer introduced into the feed stream and fluorometrically analyzing the permeate stream generated from the feed stream following termination of the fluorescent tracer and determining therefrom a measured concentration of the fluorescent tracer in the permeate stream based on a stored calibration curve that includes an intercept. The method further includes determining an adjusted intercept for the calibration curve of the fluorometer by at least using the measured concentration of the fluorescent tracer as an intercept shift.

In another example, a system is described that includes a fluorescent tracer pump configured to introduce fluorescent tracer into a feed stream, a reverse osmosis membrane configured to separate the feed stream into a permeate stream and a concentrate stream, a fluorometer configured to fluorometrically analyze the permeate stream, and a controller communicatively coupled to the fluorescent tracer pump and the fluorometer. The example specifies that the controller is configured to control the fluorescent tracer pump to introduce a fluorescent tracer into the feed stream and subsequently control the fluorescent tracer pump to terminate the introduction of fluorescent tracer introduced into the feed stream. The controller is also configured to control the fluorometer to fluorometrically analyze the permeate stream generated from the feed stream following termination of the fluorescent tracer and determine therefrom a measured concentration of the fluorescent tracer in the permeate stream based on a stored calibration curve that includes an intercept. In addition, the example states that the controller is configured to determine an adjusted intercept for the calibration curve of the fluorometer by at least using the measured concentration of the fluorescent tracer as an intercept shift.

In another example, a method for calibrating a fluorometer is described. The method includes performing a multi-point calibration with a fluorometer, the multi-point calibration comprising fluorometrically analyzing a first fluid substantially devoid of a fluorescent tracer and a second fluid having a known concentration of the fluorescent tracer and determining therefrom a calibration curve for the fluorometer that includes a slope and an intercept. The method includes subsequent to performing the multi-point calibration, fluorometrically analyzing, with the fluorometer, an aqueous stream in which the fluorescent tracer is introduced at a first concentration level and determining a measured concentration of the fluorescent tracer in the aqueous stream based on the calibration curve. The method further includes adjusting the concentration of fluorescent tracer introduced into the aqueous stream by one of terminating an addition of the fluorescent tracer to the aqueous stream, increasing an amount of the fluorescent tracer added to the aqueous stream, or decreasing the amount of the fluorescent tracer added to the aqueous stream. In addition, the method involves fluorometrically analyzing, with the fluorometer, the aqueous stream following adjustment of the concentration of fluorescent tracer and determining an intercept shift for the calibration curve based on fluorometric analysis of the aqueous stream following adjustment of the concentration of fluorescent tracer without determining an adjusted slope for the calibration curve. The method also includes storing an adjusted intercept for the calibration curve compensating for the intercept shift in a non-transitory memory associated with the fluorometer.

In general, this disclosure describes systems and techniques for calibrating fluorometric sensors as well as membrane separation systems and processes utilizing such fluorometric sensors. In some examples, a multi-point calibration is performed with the fluorometer prior to use in the membrane separation process. The multipoint calibration process may involve fluorometrically analyzing a first fluid substantially or entirely devoid of a fluorescent tracer, a second fluid having a known concentration of the fluorescent tracer, and optionally one or more additional fluids having known concentrations of the fluorescent tracer different than the second fluid. A calibration curve for the fluorometer can be determined from the fluorometric analysis of the different fluids. The calibration curve may be in the form of a single or higher order equation having a slope and an intercept.

In subsequent use, the fluorometer can be used to fluorometrically analyze an aqueous stream in which the fluorescent tracer for which the fluorometer was previously calibrated is introduced. For example, the fluorometer may analyze a permeate stream passing through a membrane filter in a reverse osmosis process in which the fluorescent tracer is introduced into the corresponding feed stream. The fluorescent tracer may be introduced at a first concentration level and a measured concentration of the fluorescent tracer in the aqueous stream being monitored determined based on the calibration curve.

To recalibrate the fluorometer, the concentration of fluorescent tracer introduced into the aqueous stream may be adjusted. For example, introduction of the fluorescent tracer may be decreased up to and including being terminated (or, in other cases, may not be terminated) or increased relative to the first concentration level. The fluorometer can then fluorometrically analyze the aqueous stream following adjustment of the concentration of fluorescent tracer. Based on the fluorometric response measured, an intercept shift for the calibration curve can be determined, e.g., without determining an adjusted slope for the calibration curve. This intercept shift can be used to determine an adjusted intercept for the calibration curve that is then stored for subsequent use.

<FIG> is a conceptual diagram illustrating an example membrane separation system <NUM> that can utilize one or more fluorometers that may be calibrated as described herein. System <NUM> includes a separation membrane <NUM>, at least one fluorometer <NUM>, and a controller <NUM>. System <NUM> in <FIG> is also illustrated as including a feed stream pressurization pump <NUM> and a fluorescent tracer pump <NUM>. Feed stream pressurization pump <NUM> is in fluid communication with a source <NUM> of fluid to be purified using membrane <NUM>. Fluorescent tracer pump <NUM> is in fluid communication with a source of fluorescent tracer <NUM> to be introduced into a feed stream contacting membrane <NUM>. In operation, a feed stream <NUM> is supplied to membrane <NUM>, which is capable of treating or purifying the feed stream by dividing the feed stream into at least a first stream and a second stream, such as a permeate stream <NUM> and a concentrate stream <NUM> (which may also be referred to as a reject stream). Fluorometer <NUM> is optically connected to one or more of feed stream <NUM>, permeate stream <NUM>, and/or concentrate stream <NUM> and is configured to fluorometrically analyze the stream.

In the illustrated configuration, a single fluorometer <NUM> is illustrated as being positioned to receive slip streams from each of the feed stream <NUM>, permeate stream <NUM>, and concentrate stream <NUM>. When so configured, valves or other flow control mechanisms may be used to selectively place the fluorometer in fluid communication with each of the respective streams at different times. In other configurations, fluorometer <NUM> may be implemented to only fluorometrically analyze a single stream (e.g., feed stream <NUM> or permeate stream <NUM>), or two of the three stream (e.g., feed stream <NUM> and permeate stream <NUM>). In these alternative configurations, system <NUM> may include more than one fluorometer, such as a separate fluorometer for each stream to be fluorometrically analyzed during operation.

Controller <NUM> is communicatively connected to fluorometer <NUM>, feed stream pressurization pump <NUM>, fluorescent tracer pump <NUM>, and optionally any other controllable components or sensors that may be desirably implemented in system <NUM>. Controller <NUM> includes processor <NUM> and memory <NUM>. Controller <NUM> communicates with controllable components in system <NUM> via connections. For example, signals generated by fluorometer <NUM> may be communicated to controller <NUM> via a wired or wireless connection, which in the example of <FIG> is illustrated as wired connection. Memory <NUM> stores software for running controller <NUM> and may also store data generated or received by processor <NUM>, e.g., from fluorometer <NUM>. Processor <NUM> runs software stored in memory <NUM> to manage the operation of system <NUM>.

As described in greater detail below, fluorometer <NUM> may be used to fluorometrically analyze the separation performance of membrane <NUM>. Fluorometer <NUM> can emit excitation light into a fluid stream / sample under analysis and receive fluorescent emissions generated in response to the excitation light. The amount of fluorescent emission light detected by the fluorometer can be processed with reference to calibration information stored in memory to determine a concentration of a fluorescing tracer in the fluid sample under analysis. This, in turn, can provide an indication of the separation performance of membrane <NUM>. Fluorometer <NUM> can be recalibrated as will be described to help calibration errors that may arise during operation of the fluorometer.

During operation of system <NUM>, membrane <NUM> can be contacted with fluid to be purified from source <NUM> to remove ion, molecules, pathogens, and/or other particulate contaminants. For example, feed stream <NUM> can contain various solutes, such as dissolved organics, dissolved inorganics, dissolved solids, suspended solids, the like or combinations thereof. Upon separation of feed stream <NUM> into permeate stream <NUM> and concentrate stream <NUM>, in membrane <NUM>, the permeate stream can contain a substantially lower concentration of dissolved and/or suspended solutes as compared to the feed stream. On the other hand, the concentrate stream <NUM> can have a higher concentration of dissolved and/or suspended solutes as compared to the feed stream. In this regard, the permeate stream <NUM> represents a purified feed stream, such as a purified aqueous feed stream.

System <NUM> and membrane <NUM> can be configured for any desired type of membrane separation process, including cross flow separation processes, dead-end flow separation processes, reverse osmosis, ultrafiltration, microfiltration, nanofiltration, electrodialysis, electrodeionization, pervaporation, membrane extraction, membrane distillation, membrane stripping, membrane aeration and the like or combinations thereof. Typically, however, system <NUM> and membrane <NUM> may be implemented as a reverse osmosis, ultrafiltration, microfiltration, or nanofiltration membrane separation process.

In reverse osmosis, feed stream <NUM> is typically processed under cross flow conditions. When so configured, feed stream <NUM> may flow 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 typically 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 can reduce 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.

System <NUM> can employ a variety of different types of membranes as membrane <NUM>. 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. For example, reverse osmosis typically uses 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 may have one channel that 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 can pass through the semi-porous membrane and is trapped in a permeate channel, which flows to a central collection tube. From this tube it can flow out of a designated channel and is collected.

In different applications, membrane <NUM> can be implemented using a single membrane element or multiple membrane elements depending on the application. For example, multiple membrane elements may be used forming membrane modules that 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 can be housed in pressure vessels. Within the pressure vessel, feed stream <NUM> can pass into the first module in the stack, which removes a portion of the water as permeate water. The concentrate stream from the first membrane can then become the feed stream of the second membrane and so on down the stack. The permeate streams from all of the membranes in the stack can be collected in the joined permeate tubes. In these applications, the feed stream entering the first module and/or the combined permeate stream and/or the final concentrate stream from the last module in the stack may be monitored using one or more fluorometers <NUM>.

Within most reverse osmosis systems, pressure vessels may be arranged in either "stages" or "passes. " In a staged membrane system, the combined concentrate streams from a bank of pressure vessels can be directed to a second bank of pressure vessels where they become the feed stream for the second stage. Commonly, systems have two to three stages with successively fewer pressure vessels in each stage. For example, a system may contain four pressure vessels in a first stage, the concentrate streams of which feed two pressure vessels in a second stage, the concentrate streams of which in turn feeds one pressure vessel in the third stage. This is designated as a "<NUM>:<NUM>: <NUM>" array. In a staged membrane configuration, the combined permeate streams from all pressure vessels in all stages may be collected and used without further membrane treatment. Multi-stage systems are commonly 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. 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 can be combined without further membrane treatment of each individual stream. Multi-pass systems are typically used when very high purity water is required, for example in the microelectronics or pharmaceutical industries. When system <NUM> is implemented as a reverse osmosis process, one or more membranes <NUM> may be configured as a multi-stage and/or multi-pass system.

While system <NUM> and membrane <NUM> may be implemented as cross-flow filtration process, in other configurations, the system may be arranged for conventional filtration of suspended solids by passing feed stream <NUM> through a filter media or membrane in a substantially perpendicular direction. This arrangement can create one exit stream (e.g., purified stream <NUM>) during the service cycle. Periodically, the filter may be 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. In this arrangement, system <NUM> may have a feed stream <NUM>, a purified stream <NUM>, and a backwash stream <NUM>. 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.

To monitor the performance of membrane <NUM>, a fluorescent tracer from fluorescent tracer source <NUM> can be introduced into feed stream <NUM>. Operating under the control of controller <NUM>, fluorescent tracer pump <NUM> can inject fluorescent tracer into feed stream <NUM> upstream of membrane <NUM>. In the illustrated example, fluorescent tracer is shown as being introduced upstream of feed stream pump <NUM>, although in other configurations, may be introduced downstream of the feed stream pump. In either case, the feed stream <NUM> containing an amount of fluorescent tracer can contact membrane <NUM> to undergo a separation or purification process.

As with other molecules or particulates being separated out of the feed stream, a majority of the fluorescent tracer may be concentrated in concentrate stream <NUM>. Only a small minority of the fluorescent tracer introduced into feed stream <NUM> may carry through to permeate stream <NUM>, e.g., when membrane <NUM> is functioning as intended. The amount of fluorescent tracer passing through membrane <NUM> from feed stream <NUM> and into permeate stream <NUM> may be indicative of the quality and/or operational efficiency of the membrane. For example, if membrane <NUM> has an integrity breach affecting the separation efficiency of the membrane, a higher concentration of fluorescent tracer introduced into feed stream <NUM> via fluorescent tracer pump <NUM> may carry through to permeate stream <NUM> than if the membrane does not have such a breach.

Operating on a periodic or continuous monitoring basis, one or more fluorometers <NUM> can monitor the concentration of fluorescent tracer in one or more corresponding streams of system <NUM> to evaluate the performance of the system. For example, fluorometer <NUM> may measure feed stream <NUM> to determine a measured concentration of the fluorescent tracer introduced into the stream by fluorescent tracer pump <NUM>. Fluorometer <NUM> may also measure permeate stream <NUM> to determine a measured concentration of the fluorescent tracer passing through membrane <NUM> and present in permeate stream <NUM>.

Various performance metrics can be determined based on the measured fluorescent properties of the monitored streams. As one example, controller <NUM> may calculate a dye rejection efficiency factor Rt based on the following equation: <MAT>.

In the equation above, Rt is the dye rejection efficiency, CF is the fluorescent dye concentration of the feed stream, Cp is the fluorescent dye concentration of the permeate stream, CF, BKG is the background fluorescence of the feed stream, and CP,BKG is the background fluorescence of the permeate stream. Additional performance parameters that may be calculated by controller <NUM> with reference to information stored in memory <NUM> and data from fluorometer <NUM> are described in <CIT>.

In normal operation, the dye rejection efficiency of membrane <NUM> may be greater than <NUM> percent, such as greater than <NUM> percent, greater than <NUM> percent, or greater than <NUM> percent. For example, controller <NUM> may control fluorescent tracer pump <NUM> to introduce an amount of fluorescent tracer into feed stream <NUM> effective to achieve a concentration ranging from <NUM> parts per billion (ppb) to <NUM>,<NUM> ppb, such as from <NUM> ppb to <NUM> ppb, or from <NUM> ppb to <NUM>,<NUM> ppb. By comparison, the amount of fluorescent tracer passing through membrane <NUM> and present in permeate stream <NUM> at these feed stream concentrations may be less than <NUM> ppb, such as less than <NUM> ppb, or less than <NUM> ppb, or less than <NUM> parts per trillion (ppt). Controller <NUM> can control fluorescent tracer pump <NUM> to introduce the tracer at a substantially constant rate and/or to achieve a substantially constant concentration in feed stream <NUM> (e.g., adjusting the rate of introduction based on flow rate changes to feed stream <NUM>). Alternatively, the rate and/or concentration of the fluorescent tracer may vary over time.

In general, the fluorescent tracer introduced into feed stream <NUM> is an inert tracer. The term "inert" refers to a 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. The fluorescent tracer should be transportable with the water of the membrane separation system and thus substantially, if not wholly, water-soluble therein at the concentration it is used, under the temperature and pressure conditions specific and unique to the membrane separation system. In other words, the fluorescent tracer may display properties similar to a solute of the membrane separation process in which it is used.

In some examples, the fluorescent tracer added to feed stream <NUM> is a component of a formulation, rather than as a separate component, such as a dry solid or neat liquid. For example, the fluorescent tracer may be contained in (e.g., intermixed with) treatment chemicals injected into feed stream <NUM> to enhance the membrane separation process, e.g., antiscalants that retard/prevent membrane scale deposition, antifoulants that retard/prevent membrane fouling, biodispersants, microbial-growth inhibiting agents, such as biocides and cleaning chemicals that remove membrane deposits. The composition containing the fluorescent tracer may include an aqueous or other water-soluble solution or other substantially homogeneous mixture that disperses with reasonable rapidity in the membrane separation system to which it is added. In applications where the fluorescent tracer composition (or product containing the fluorescent tracer) is in solid form, fluorescent tracer pump <NUM> may be replaced with a solid metering device.

A variety of different and suitable types of compounds can be utilized as fluorescent tracers. Example fluorescent compounds that can be used in system <NUM> include, but are not limited to: <NUM>,<NUM>-acridinediamine, N,N,N',N'-tetramethyl-, monohydrochloride, also known as Acridine Orange (<NPL>); <NUM>-anthracenesulfonic acid sodium salt (<NPL>); <NUM>,<NUM>-anthracenedisulfonic acid (<NPL>) and salts thereof; <NUM>,<NUM>-anthracenedisulfonic acid (<NPL>) and salts thereof; <NUM>,<NUM>-anthracenedisulfonic acid (<NPL>) and salts thereof; anthra[<NUM>,<NUM>,<NUM>-cde]benzo[rst]pentaphene-<NUM>, <NUM>-diol, <NUM>,<NUM>-dimethoxy-, bis(hydrogen sulfate), disodium salt, also known as Anthrasol Green IBA (<NPL>, aka Solubilized Vat Dye); bathophenanthrolinedisulfonic acid disodium salt (<NPL>); amino <NUM>,<NUM>-benzene disulfonic acid (<NPL>); <NUM>-(<NUM>-aminophenyl)-<NUM>-methylbenzothiazole (<NPL>); <NUM>-benz[de]isoquinoline-<NUM>-sulfonic acid, <NUM>-amino-<NUM>,<NUM>-dihydro-<NUM>-(<NUM>-methylphenyl)<NUM>,<NUM>-dioxo-, monosodium salt, also known as Brilliant Acid Yellow <NUM> (<NPL>, aka Lissamine Yellow FF, Acid Yellow <NUM>); phenoxazin-<NUM>-ium, <NUM>-(aminocarbonyl)-<NUM>-(diethylamino)-<NUM>,<NUM>-dihydroxy-, chloride, also known as Celestine Blue (<NPL>); benzo[a]phenoxazin-<NUM>-ium, <NUM>,<NUM>-diamino-, acetate, also known as cresyl violet acetate (<NPL>); <NUM>-dibenzofuransulfonic acid (<NPL>); <NUM>-dibenzofuransulfonic acid (<NPL>); <NUM>-ethylquinaldinium iodide (<NPL>); fluorescein (<NPL>); fluorescein, sodium salt (<NPL>, aka Acid Yellow <NUM>, Uranine); Keyfluor White ST (<NPL>, aka Flu. Bright <NUM>); benzenesulfonic acid, <NUM>,<NUM>'-(<NUM>,<NUM>-ethenediyl)bis[<NUM>-[[<NUM>-[bis(<NUM>-hydroxyethyl)amino]-<NUM>-[(<NUM>-sulfophenyl)amino]-<NUM>,<NUM>,<NUM>-triazin-<NUM>-yl]amino]-, tetrasodium salt, also known as Keyfluor White CN (<NPL>); C. Fluorescent Brightener <NUM>, also known as Leucophor BSB (<NPL>); benzenesulfonic acid, <NUM>,<NUM>'-(<NUM>,<NUM>-ethenediyl)bis[<NUM>-[[<NUM>-[bis(<NUM>-hydroxyethyl)amino]-<NUM>-[(<NUM>-sulfophenyl)amino]-<NUM>,<NUM>,<NUM>-triazin-<NUM>-yl]amino]-, tetrasodium salt, also known as Leucophor BMB (<NPL>, aka Leucophor U, Flu. <NUM>); <NUM>,<NUM>'-biacridinium, <NUM>,<NUM>'-dimethyl-, dinitrate, also known as Lucigenin (<NPL>, aka bis-N-methylacridinium nitrate); <NUM>-deoxy-<NUM>-(<NUM>,<NUM>-dihydro-<NUM>,<NUM>-dimethyl-<NUM>,<NUM>-dioxobenzo[g]pteridin-<NUM>(<NUM>)-yl)-D-ribitol, also known as Riboflavin or Vitamin B2 (<NPL>); mono-, di-, or tri-sulfonated napthalenes, including but not limited to <NUM>,<NUM>-naphthalenedisulfonic acid, disodium salt (hydrate) (<NPL>, aka <NUM>,<NUM>-NDSA hydrate); <NUM>-amino-<NUM>-naphthalenesulfonic acid (<NPL>); <NUM>-amino-<NUM>-naphthalenesulfonic acid (<NPL>); <NUM>-amino-<NUM>-hydroxy-<NUM>-aphthalenesulfonic acid (<NPL>); <NUM>-amino-<NUM>-hydroxy-<NUM>-naphthalenesulfonic acid (<NPL>); <NUM>-amino-<NUM>,<NUM>-naphthalenesulfonic acid, potassium salt (<NPL>); <NUM>-amino-<NUM>-hydroxy-<NUM>,<NUM>-naphthalenedisulfonic acid (<NPL>); <NUM>-dimethylamino-<NUM>-naphthalenesulfonic acid (<NPL>); <NUM>-amino-<NUM>-naphthalene sulfonic acid (<NPL>); <NUM>-amino-<NUM>-naphthalene sulfonic acid (<NPL>); <NUM>,<NUM>-naphthalenedicarboxylic acid, dipotassium salt (<NPL>); <NUM>,<NUM>,<NUM>,<NUM>-perylenetetracarboxylic acid (<NPL>); C. Fluorescent Brightener <NUM>, also known as Phorwite CL (<NPL>); C. Fluorescent Brightener <NUM>, also known as Phorwite BKL (<NPL>); benzenesulfonic acid, <NUM>,<NUM>'-(<NUM>,<NUM>-ethenediyl)bis[<NUM>-(<NUM>-phenyl-<NUM>-<NUM>,<NUM>,<NUM>-triazol-<NUM>-yl)-, dipotassium salt, also known as Phorwite BHC <NUM> (<NPL>); benzenesulfonic acid, <NUM>-(<NUM>-naphtho[<NUM>,<NUM>-d]triazol-<NUM>-yl)-<NUM>-(<NUM>-phenylethenyl)-, sodium salt, also known as Pylaklor White S-ISA (<NPL>); <NUM>,<NUM>,<NUM>,<NUM>-pyrenetetrasulfonic acid, tetrasodium salt (<NPL>); pyranine (<NPL>, aka <NUM>-hydroxy-<NUM>, <NUM>, <NUM>-pyrenetrisulfonic acid, trisodium salt),quinoline (<NPL>); <NUM>-phenoxazin-<NUM>-one, <NUM>-hydroxy-, <NUM>-oxide, also known as Rhodalux (<NPL>); xanthylium, <NUM>-(<NUM>,<NUM>-dicarboxyphenyl)-<NUM>,<NUM>-bis(diethylamino)-, chloride, disodium salt, also known as Rhodamine WT (<NPL>); phenazinium, <NUM>,<NUM>-diamino-<NUM>,<NUM>-dimethyl-<NUM>-phenyl-, chloride, also known as Safranine <NUM> (<NPL>); C. Fluorescent Brightener <NUM>, also known as Sandoz CW (<NPL>); benzenesulfonic acid, <NUM>,<NUM>'-(<NUM>,<NUM>- thenediyl)bis[<NUM>-[[<NUM>-[bis(<NUM>-hydroxyethyl)amino]-<NUM>-[(<NUM>-sulfophenyl)amino]-<NUM>,<NUM>,<NUM>-triazin-<NUM>-yl]amino]-, tetrasodium salt, also known as Sandoz CD (<NPL>, aka Flu. <NUM>); benzenesulfonic acid, <NUM>,<NUM>'-(<NUM>,<NUM>-ethenediyl)bis[<NUM>-[[<NUM>-[(<NUM>-hydroxypropyl)amino]-<NUM>-(phenylamino)-<NUM>,<NUM>,<NUM>-triazin-<NUM>-yl]amino]-, disodium salt, also known as Sandoz TH-<NUM> (<NPL>); xanthylium, <NUM>,<NUM>-bis(diethylamino)-<NUM>-(<NUM>,<NUM>-disulfophenyl)-, inner salt, sodium salt, also known as Sulforhodamine B (<NPL>, aka Acid Red <NUM>); benzenesulfonic acid, <NUM>,<NUM>'-(<NUM>,<NUM>-ethenediyl)bis[<NUM>-[[<NUM>-[(aminomethyl)(<NUM>-hydroxyethyl)amino]-<NUM>-(phenylamino)-<NUM>,<NUM>,<NUM>-triazin-<NUM>-yl]amino]-, disodium salt, also known as Tinopal 5BM-GX (<NPL>); Tinopol DCS (<NPL>); benzenesulfonic acid, <NUM>,<NUM>'-([<NUM>,<NUM>'-biphenyl]-<NUM>,<NUM>'-diyldi-<NUM>,<NUM>-ethenediyl)bis-, disodium salt also known as Tinopal CBS-X (<NPL>); benzenesulfonic acid, <NUM>-(<NUM>-naphtho[<NUM>,<NUM>-d]triazol-<NUM>-yl)<NUM>-(<NUM>-phenylethenyl)-, sodium salt, also known as Tinopal RBS <NUM>, (<NPL>); <NUM>-benzothiazolesulfonic acid, <NUM>,<NUM>'-(<NUM>-triazene-<NUM>,<NUM>-diyldi-<NUM>,<NUM>-phenylene)bis[<NUM>-methyl-, disodium salt, also known as Titan Yellow (<NPL>, aka Thiazole Yellow G), and all ammonium, potassium and sodium salts thereof, and all like agents and suitable mixtures thereof.

In some examples, the fluorescent tracer is not a visible dye, e.g., such that the fluorescent tracer is a chemical species that does not have a strong absorption of electromagnetic radiation in the visible region, which extends from about <NUM> Angstroms to about <NUM> Angstroms (from about <NUM> nanometers ("nm") to about <NUM>). For example, the fluorescent tracer may be chosen from a class of materials which are excited by absorption of light and produce fluorescent light emission, where the excitation and emission light occurs at any point within the far ultraviolet to near infrared spectral regions (e.g., wavelengths from <NUM>-<NUM>).

System <NUM> can be used to purify any desired type of fluid. Example aqueous (water-based) liquid feed sources <NUM> that may be purified using system <NUM> include raw water streams (e.g., extracted from a fresh water source), waste water and recycle water streams (e.g., from municipal and/or industrial sources), streams in food and beverage processes, streams in pharmaceutical processes, streams in electronic manufacturing, streams in utility operations, streams in pulp and paper processes, streams in mining and mineral processes, streams in transportation-related processes, streams in textile processes, streams in plating and metal working processes, streams in laundry and cleaning processes, streams in leather and tanning processes, streams in paint processes, and combinations thereof.

The one or more fluorometers <NUM> used in system <NUM> may be implemented in a number of different ways in system <NUM>. In the example shown in <FIG>, a pipe, tube, or other conduit is connected between a main fluid pathway and a flow chamber of fluorometer <NUM>, e.g., providing a slip stream or sample stream from the bulk of flowing liquid. In such examples, the conduit can fluidly connect the flow chamber (e.g., an inlet of the flow chamber) of fluorometer <NUM> to the main fluid pathway. As fluid moves through the main fluid pathway, a portion of the fluid may enter the conduit and pass adjacent a sensor head positioned within a fluid chamber, thereby allowing fluorometer <NUM> to determine one or more characteristics of fluid flowing through the fluid pathway. After passing through the flow chamber, analyzed fluid may or may not be returned to the main fluid pathway, e.g., via another conduit connecting an outlet of the flow chamber to the fluid pathway. In alternative configurations, fluorometer <NUM> positioned in-line with a main fluid pathway, e.g., allowing the fluorometer to directly sample and/or fluorometrically analyze the primary flowing fluid stream without drawing a slip stream.

In either case, when implemented to receive fluid directly from a main fluid pathway or stream without user intervention, fluorometer <NUM> may be characterized as an online optical sensor. Controller <NUM> may control fluorometer <NUM> to continuously fluorometrically analyze a fluid stream over a period of time or intermittently fluorometrically analyze the fluid stream at periodic intervals. When fluorometer <NUM> is implemented as an online fluorometer, it may be difficult to remove the fluorometer from service for calibration if such removal may require shutting down system <NUM> or causing undesirable monitoring gaps in the performance of the system.

In other applications, fluorometer <NUM> may be used to fluorometrically analyze a stationary volume of fluid that does not flow through a flow chamber of the optical sensor. For example, in these alternative configurations, fluorometer <NUM> may be implemented as an offline monitoring tool (e.g., as a handheld sensor), that requires filling the optical sensor with a fluid sample manually extracted from system <NUM>.

<FIG> is a block diagram illustrating an example of fluorometer <NUM> that may be used in the fluid separation system of <FIG>. Fluorometer <NUM> includes controller <NUM>, one or more optical emitters <NUM> (referred to herein as "optical emitter <NUM>"), and one or more optical detectors <NUM> (referred to herein as "optical detector <NUM>"). Controller <NUM> includes previously-described processor <NUM> and a memory <NUM>. Optical emitter <NUM> directs light into fluid pathway <NUM> and optical detector <NUM> receives transmitted light on the opposite side of the fluid pathway. The components of fluorometer <NUM> may be implemented on a single printed circuit board (PCB) or may be implemented using two or more PCB boards. Further, in some examples, fluorometer <NUM> communicates with an external device, such as a system controller controlling system <NUM>, remote server, cloud-computing environment, or other physically remote computing device.

For purposes of discussion, controller <NUM> described with respect to <FIG> as controlling system <NUM> is also illustrated as the controller controlling fluorometer <NUM>. In practice, fluorometer <NUM> may have a separate controller from one or more system controller controlling the overall operation of system <NUM>. Accordingly, it should be appreciated that the computing functionality attributed to controller <NUM> in system <NUM> and fluorometer <NUM> may be performed on any one or more controllers associated with the system, be it physically onsite or remotely located, and the functionalities described herein are not limited to being performed on any specific hardware device.

Memory <NUM> stores software and data used or generated by controller <NUM>. For example, memory <NUM> may store data representative of one or more calibration curves <NUM> used by controller <NUM> to determine a concentration of a fluorescent tracer in fluid medium passing through fluid pathway <NUM>. Calibration curve data <NUM> may relate fluorescent emission light detected by optical detector <NUM> to a concentration of a fluorescent tracer in the fluid under analysis. In some examples, calibration curve data <NUM> is in the form of an equation that relates light measurements taken by optical detector <NUM> to fluorescent tracer concentration information. For example, the equation may be a single or higher-order equation having one or more slope coefficients and an intercept, each of which are stored in memory and referenced by controller <NUM> to convert light information measured by optical detector <NUM> to fluorescent tracer concentration information.

For ease of description, calibration curve data <NUM> is generally described below as being calibration information that is determined by fluorometer <NUM> and stored in memory <NUM> of the fluorometer. In other examples, calibration curve data <NUM> may be determined separately from fluorometer <NUM> (e.g., using a laboratory spectrophotometer and computing device) and stored in memory <NUM> and/or a separate computing device communicatively coupled to fluorometer <NUM>. Therefore, although fluorometer <NUM> is described below as being configured to determine calibration curve data <NUM> and further being configured to determine a measured concentration of fluorescent tracer, it should be appreciated that the disclosure is not limited to such an example sensor. In different examples, hardware and/or software operating outside of fluorometer <NUM> may be utilized to implement functions attributed to fluorometer <NUM> in this disclosure.

In examples in which fluorometer <NUM> determines calibration curve data <NUM>, the calibration curve data may be based on an analysis of baseline detection values produced by optical detector <NUM> and processed by controller <NUM>. The baseline detection values may be detected by optical detector <NUM> when one or more fluid solutions having a known concentration of fluorescent tracer are passed through fluid pathway <NUM>. These fluid solutions having a known concentration of fluorescent tracer may be referred to as reference solutions. For example, controller <NUM> may determine calibration curve data by fluorometrically analyzing a first fluid substantially or entirely devoid of a fluorescent tracer, a second fluid having a known concentration of the fluorescent tracer, and optionally one or more additional fluids having known concentrations of the fluorescent tracer different than the second fluid (e.g., covering the range of fluorescent tracer concentrations expected to be measured by fluorometer <NUM> in subsequent operation).

Upon receiving detection values from the reference fluids, processor <NUM> of controller <NUM> (or a processor of another computing device) can analyze the detection values to establish a relationship between the known characteristic and the detection values. For example, processor <NUM> may perform a curve fitting process such as linear regression to determine a relationship between the known concentration of fluorescent tracer and the detected fluorescent emissions. The determined relationship (or coefficients associated therewith) can then be stored as calibration curve data <NUM>.

In the example of a single order calibration curve, for example, controller <NUM> may fit a curve representing known fluorescent tracer concentration values plotted on a y-axis of a graph with corresponding measured fluorescent emissions plotted on the x-axis of the graph. A first order curve having the form y=m*x+b, where y is the fluorescent tracer concentration, x is the measured fluorescent emissions, and m is the slope of the curve, and b is the intercept of the curve, may be fit to the data to determine slope and intercept calibration values. The slope and intercept values can be stored as calibration curve data <NUM> in memory <NUM>. In the case of a higher order curve (e.g., second order, third order, or higher), additional coefficients corresponding to the higher order curve may be stored in memory (e.g., in addition to the intercept). Controller <NUM> may employ any suitable statistical software package such as, e.g., Minitab, Excel, or the like, to generate calibration curve data <NUM>.

Processor <NUM> runs software stored in memory <NUM> to perform functions attributed to fluorometer <NUM> and controller <NUM> in this disclosure. Components described as processors within controller <NUM>, controller <NUM>, or any other device described in this disclosure may each include one or more processors, such as one or more microprocessors, digital signal processors (DSPs), application specific integrated circuits (ASICs), field programmable gate arrays (FPGAs), programmable logic circuitry, or the like, either alone or in any suitable combination.

Optical emitter <NUM> includes at least one optical emitter that emits radiation having a specified wavelength or wavelength range. In different examples, optical emitter <NUM> can emit radiation continuously or intermittently. In some examples, optical emitter <NUM> emits radiation at a plurality of discrete wavelengths. For example, optical emitter <NUM> may emit at two, three, four or more discrete wavelengths.

Optical emitter <NUM> can emit light at any suitable wavelength, as described in greater detail below. In some examples, optical emitter <NUM> emits light within a spectrum ranging from <NUM> to <NUM>. Light emitted by optical emitter <NUM> propagates through fluid pathway <NUM> of fluorometer <NUM> and may be detected by optical detector <NUM>. In response to receiving the optical energy, fluorescing molecules within the fluid may excite, causing the molecules to produce fluorescent emissions. The fluorescent emissions, which may or may not be at a different frequency than the energy emitted by optical emitter <NUM>, may be generated as excited electrons within fluorescing molecules change energy states. The energy emitted by the fluorescing molecules may be detected by optical detector <NUM>. For example, optical detector <NUM> may detect fluorescent emissions emitted in a frequency range from <NUM> to <NUM>.

Optical detector <NUM> includes at least one optical detector that detects radiation within associated wavelength ranges within the UV light spectrum. Optical detector <NUM> detects radiation that is emitted by optical emitter <NUM> and that has propagated through fluid pathway <NUM> and any fluid solution in the fluid pathway. Optical detector <NUM> may be implemented using multiple detectors, one for each wavelength or wavelength range, or may be implemented using a single detector such as, e.g., a detector that is programmable to detect multiple wavelength ranges.

Controller <NUM> controls the operation of optical emitter <NUM> and receives signals concerning the amount of light detected by optical detector <NUM>. In some examples, controller <NUM> further processes signals, e.g., to develop calibration curve data <NUM> and/or to determine a concentration of fluorescent tracer in a fluid solution passing through fluid pathway <NUM> using calibration curve data <NUM>. While controller <NUM> may perform various signal processing functionalities, as described herein, controller <NUM> need not be configured to perform any or all of the described functionalities. In different examples, signal processing, e.g., to develop calibration curve data <NUM> and/or to determine a characteristic of a fluid solution based on calibration curve data <NUM> may be performed outside of fluorometer <NUM>. For example, controller <NUM> (<FIG>) or another controller may perform one or more functions generally attributed to controller <NUM> in this disclosure. Accordingly, it should be appreciated that functions attributed to controller <NUM> herein are for ease of description, and the described functions may, in fact, be implemented within fluorometer <NUM> or within one or more separate devices, which may or may not be communicatively coupled to fluorometer <NUM>.

In one example in which controller <NUM> processes signals, controller <NUM> controls optical emitter <NUM> and optical detector <NUM> to create calibration curve data <NUM>. When fluorometer <NUM> is informed of one or more known characteristics of a reference solution flowing through fluid pathway <NUM>, controller <NUM> controls optical emitter <NUM> to emit radiation at one or more wavelengths and further controls optical detector <NUM> to detect the radiation at one or more wavelengths. Fluorometer <NUM> may be so informed, for example, via manual input from a user. Controller <NUM> processes signals concerning the amount of light detected by optical detector <NUM> to determine fluorescent emission characteristics of the reference solution. For example, controller <NUM> may process signals concerning the magnitude and/or wavelength(s) of light detected by optical detector <NUM> for different reference solutions having different known concentrations of fluorescent tracer. Controller <NUM> may store the data in memory <NUM>.

After determining the amount of light detected by optical detector <NUM> through the reference solutions, controller <NUM> can process the light detection information to develop a relationship between the known concentration of fluorescent tracer in the reference solutions and the light detection information. Controller <NUM> can store the relationship as calibration curve data <NUM> in memory <NUM>. In subsequent operation, controller <NUM> can determine a measured concentration of the fluorescent tracer based on the magnitude of fluorescent emissions detected by <NUM> from a fluid having an unknown concentration of the fluorescent tracer (e.g., feed stream <NUM> and/or permeate stream <NUM>) using calibration curve data <NUM>, which relates measured fluorescent emissions to fluorescent tracer concentrations.

As briefly discussed above, fluorometer <NUM> may be calibrated prior to being implemented in system <NUM> or initially being installed in the system, e.g., prior to use in ongoing operation and/or during periodic full recalibration. During full calibration, calibration curve data <NUM> that includes a calibration curve intercept value may be determined and stored in memory <NUM>. As fluorometer is used during subsequent operation of system <NUM> to determine measured concentrations of fluorescent tracer (e.g., in feed stream <NUM> and/or permeate stream <NUM>), the accuracy of the measured concentrations may decrease. That is, the difference between the actual or real value of the fluorescent tracer in the stream being measured and the measured concentration determined by fluorometer <NUM> may increase over time, increasing the inaccuracy of the measured concentration determined by the fluorometer. The fluorometer may lose calibration for a variety of reasons, such as fouling buildup, changing electrical resistance of a circuit, changing light source strength, and/or other factors. To help increase the accuracy of the measured fluorescent concentrations determined by fluorometer <NUM>, the fluorometer may undergo a partial recalibration. The partial calibration may recalibrate the intercept for the calibration curve data <NUM>, e.g., without recalibrating the slope. For example, calibration curve data <NUM> stored in memory <NUM> and used by controller <NUM> to convert measured fluorescent emission data to measured fluorescent tracer concentration data may include a stored calibration curve intercept and stored calibration curve slope coefficients. During partial recalibration, the stored calibration curve intercept may be changed without changing the stored calibration curve slope coefficients. While full recalibration may lead to even further accuracy improvements over a partial recalibration, full recalibration may require removing fluorometer <NUM> from service or otherwise exposing the fluorometer to multiple reference solutions. Partial recalibration as described in some applications herein may be achieved by controlling the introduction of fluorescent tracer into feed stream <NUM>. The partial recalibration may provide meaningful accuracy improvements for fluorometer <NUM> and, optionally, may be performed while the fluorometer remains online (e.g., without disconnecting or removing the fluorometer from a housing or fluid conduit to which it is connected or otherwise removing the fluorometer from its operating environment). <FIG> is an example technique for recalibrating fluorometer <NUM>. The technique of <FIG> is described with reference to system <NUM> in <FIG> and fluorometer <NUM> in <FIG>, although can be performed in other systems and with other fluorometer configurations, e.g., as described herein.

With reference to <FIG>, the technique includes introducing a fluorescent tracer into feed stream <NUM> to provide a first concentration of fluorescent tracer in the feed stream. (<NUM>) Operating under the control of controller <NUM> in system <NUM>, fluorescent tracer pump <NUM> may be controlled to introduce fluorescent tracer into feed stream <NUM> from fluorescent tracer source <NUM>. The amount of fluorescent tracer introduced into feed stream <NUM> may be effective to provide a concentration of fluorescent tracer in feed stream <NUM> within any of the concentration ranges discussed herein, or even concentration ranges outside of those discussed herein in suitable applications.

Feed stream <NUM> contacts membrane <NUM>, separating the feed stream into permeate stream <NUM> and concentrate stream <NUM>. (<NUM>) Membrane <NUM> may be configured as a cross flow membrane, dead-end flow membrane, or have yet other configuration. In one example, system <NUM> is a reverse osmosis system. Feed stream pressure pump <NUM> can pressurize a source of liquid to be purified, overcoming the osmotic pressure of membrane <NUM> to drive the reverse osmosis process and generate the permeate stream <NUM>.

During operation, fluorometer <NUM> can fluorometrically analyze permeate stream <NUM> generated from the feed stream <NUM> in which the fluorescent tracer was introduced, e.g., in an amount effective to achieve the first concentration of fluorescent tracer in the feed stream. (<NUM>) For example, fluorometer <NUM> may be installed online in system <NUM> to measure permeate <NUM> flowing from membrane <NUM> (e.g., either in the main fluid conveyance line carrying the bulk of the permeate stream or via a slipstream connecting fluorometer <NUM> to the main conveyance line). Permeate stream <NUM> or a sample thereof can flow through fluid pathway <NUM> for measurement by fluorometer <NUM>. Controller <NUM> executing instructions stored in memory <NUM> can control optical emitter <NUM> to direct light selected to be at an excitation wavelength for the fluorescent tracer introduced into feed stream <NUM> into the permeate fluid under analysis. Fluorescent tracer molecules within permeate under analysis may fluoresce at a wavelength different than the excitation wavelength in response to the energy emitted at the excitation wavelength. Optical detector <NUM> can detect the fluorescent emissions emitted by the tracer molecules present within the permeate. The magnitude of the fluorescent emissions detected by optical detector <NUM> may vary based on the concentration of the fluorescent tracer molecules present in the permeate under analysis. Processor <NUM> of controller <NUM> can determine a first measured concentration of the fluorescent tracer in permeate stream <NUM> based on the fluorescent emissions detected by optical detector <NUM> and calibration curve data <NUM> stored in memory <NUM>. For example, processor <NUM> of controller <NUM> may use one or more stored slope coefficients and a stored intercept of a calibration curve relating to a magnitude of light detected by optical detector <NUM> (e.g., within one or more wavelengths corresponding to fluorescent emissions of the fluorescent tracer) to a measured concentration of the fluorescent tracer. The first measured concentration of fluorescent tracer determined by processor <NUM> can be stored in memory <NUM> for subsequent use during the calibration procedure.

The example technique of <FIG> also includes adjusting the concentration of fluorescent tracer introduced into feed stream <NUM> to provide a second concentration of fluorescent tracer in the feed stream different than the first concentration. (<NUM>) Under the control of controller <NUM> in system <NUM>, the rate at which fluorescent tracer pump <NUM> introduces fluorescent tracer into feed stream <NUM> from fluorescent tracer source <NUM> and/or the rate at which feed stream <NUM> is delivered to membrane <NUM> may be adjusted to adjust the concentration of fluorescent tracer in the feed stream contacting member <NUM>. In one example, the concentration of fluorescent tracer is increased such that the second concentration of fluorescent tracer in feed stream <NUM> is greater than the first concentration of fluorescent tracer. In another example, the concentration of fluorescent tracer is decreased such that the second concentration of fluorescent tracer in feed stream <NUM> is less than the first concentration of fluorescent tracer. For example, as discussed with respect to <FIG>, fluorescent tracer pump <NUM> may be stopped, terminating the introduction of fluorescent tracer into feed stream <NUM>.

In general, the concentration of fluorescent tracer in feed stream <NUM> may be adjusted an amount effective to cause the second concentration of fluorescent tracer to be measurably different than the first concentration of fluorescent tracer, e.g., taking into account noise and other system fluctuations that may typically be present. For example, the second concentration may be at least <NUM>% different (positive or negative) than the first concentration, such as at least <NUM>% different, at least <NUM>% different, or at least <NUM>% different. When the concentration of fluorescent tracer is adjusted to reduce the concentration of fluorescent tracer relative to the first concentration, the concentration may be reduced until the second concentration ranges from <NUM> to <NUM> times the first concentration, such as from <NUM> to <NUM> times the first concentration, or from <NUM> to <NUM> times the first concentration. When the concentration of fluorescent tracer is adjusted to increase the concentration of fluorescent tracer relative to the first concentration, the concentration may be increased until the second concentration ranges from <NUM> to <NUM> times the first concentration, such as from <NUM> to <NUM> times the first concentration. Accordingly, in some applications, the concentration of fluorescent tracer may be adjusted until the second concentration of fluorescent tracer is at least an order of magnitude greater than the first concentration of fluorescent tracer, or less than an order of magnitude difference. The ratio by which controller <NUM> has increased or decreased the concentration of fluorescent tracer in feed stream <NUM> (e.g., the rate at which the fluorescent tracer is introduced into the feed stream) may be stored in memory <NUM> for subsequent use during a calibration procedure. It should be appreciated that the foregoing ranges of adjusted concentrations are examples and the disclosure is not necessarily limited in this effect.

After adjusting the concentration of fluorescent tracer, fluorometer <NUM> can fluorometrically analyze permeate stream <NUM> generated from the feed stream <NUM> in which the fluorescent tracer at the adjusted concentration level, e.g., in an amount effective to achieve the second concentration of fluorescent tracer in the feed stream. (<NUM>) As discussed with respect to step <NUM> in the example technique of <FIG>, controller <NUM> executing instructions stored in memory <NUM> can control optical emitter <NUM> to direct light selected to be at an excitation wavelength for the fluorescent tracer introduced into feed stream <NUM> into the permeate fluid under analysis. Fluorescent tracer molecules within permeate under analysis may fluoresce at a wavelength different than the excitation wavelength in response to the energy emitted at the excitation wavelength. Optical detector <NUM> can detect the fluorescent emissions emitted by the tracer molecules present within the permeate. The magnitude of the fluorescent emissions detected by optical detector <NUM> may vary based on the concentration of the fluorescent tracer molecules present in the permeate under analysis.

Processor <NUM> of controller <NUM> can determine a second measured concentration of the fluorescent tracer in permeate stream <NUM> based on the fluorescent emissions detected by optical detector <NUM> and calibration curve data <NUM> stored in memory <NUM>. For example, processor <NUM> of controller <NUM> may use one or more stored slope coefficients and a stored intercept of a calibration curve relating a magnitude of light detected by optical detector <NUM> (e.g., within one or more wavelengths corresponding to fluorescent emissions of the fluorescent tracer) to a measured concentration of the fluorescent tracer. The second measured concentration of fluorescent tracer determined by processor <NUM> can be stored in memory <NUM> for subsequent use during the calibration procedure.

In practice, changes to the concentration of fluorescent tracer introduced into feed stream <NUM> may take a period of time to show up in permeate stream <NUM>. For example, when controller <NUM> controls fluorescent tracer pump <NUM> to change a dosing rate of fluorescent tracer into feed stream <NUM>, an equilibrating period of time may need to elapse before a new equilibrium concentration is achieved in both the feed stream and permeate stream. Accordingly, controller <NUM> may control fluorometer <NUM> to determine the second measured concentration of tracer in the permeate stream a period of time after adjusting the concentration of the fluorescent tracer introduced into the feed stream effective to achieve equilibrium concentrations of the fluorescent tracer in the feed stream and in the permeate stream. Depending on the operational parameters of system <NUM>, the period of time needed to achieve equilibrium may be greater than <NUM> minutes, such as greater than <NUM> minutes, or greater than <NUM> minutes. For example, the period of time needed to achieve equilibrium may range from <NUM> minutes to <NUM> minutes, such as from <NUM> minutes to <NUM> minutes.

Controller <NUM> may control fluorometer <NUM> to continuously fluorometrically analyze permeate stream <NUM>, e.g., as frequently as the sampling frequency of the fluorometer will allow. When so configured, controller <NUM> may receive fluorometric data corresponding to feed stream <NUM> having the first concentration of fluorescent tracer, the second concentration of fluorescent tracer, and intermediate concentrations of fluorescent tracer as the system is undergoing equilibration. Controller <NUM> may or may not omit use of the fluorometric data generated from permeate stream <NUM> when the concentration of fluorescent tracer in the stream is not at an equilibrium level during the recalibration process. In other configurations, controller <NUM> may control fluorometer <NUM> to intermittently fluorometrically analyze permeate stream <NUM> rather than continuously analyze the stream.

To recalibrate fluorometer <NUM>, controller <NUM> may determine an intercept shift for the calibration curve stored as calibration curve data <NUM> based on first and second measured concentrations of fluorescent tracer made by fluorometer <NUM> and, e.g., the ratio by which the concentration of fluorescent tracer was adjusted. (<NUM>) The intercept shift may be an error that has developed in the calibration information, e.g., such that the measured fluorescent tracer concentration determined by controller <NUM> is offset or deviated from the true concentration of fluorescent tracer actually present in the permeate stream. <FIG> is a graph illustrating an example intercept shift γ for an example calibration curve showing how the calibration curve may drift over time from its original position due to changing conditions. In this example, the intercept shift is shown as a negative, or downward shift, although the intercept shift may be positive or an upward shift.

To determine the extent to which the intercept of the calibration curve stored in calibration curve data <NUM> has shifted, controller <NUM> may compare the first measured concentration of fluorescent tracer in permeate stream <NUM> to the second measured concentration of fluorescent tracer in the permeate stream. (<NUM>) <FIG> is a graph illustrating an example intercept shift γ for an example calibration curve showing how measured fluorescent tracer concentration data can be used along with information concerning the extent to which the concentration of fluorescent tracer dye has been adjusted. In this example, the concentration of fluorescent tracer in feed stream <NUM> is adjusted (increased in the illustrated example) from a first concentration D to a second concentration xD. In other words, the concentration is adjusted by a factor "x. " This is expected to cause the concentration of fluorescent tracer in permeate stream <NUM> to change from a first concentration "a" to a second concentration "b". Since the rejection efficiency of the fluorescent tracer by membrane <NUM> is expected to be constant over the range of fluorescent tracer used and during the time span of recalibration (e.g., less than <NUM> ppm difference), the ratio of the second concentration of fluorescent tracer in the permeate stream "b" divided by the first concentration of the fluorescent tracer in the permeate stream "a" should be "x" if there is no intercept shift. However, where the ratio of "b" divided by "a" is different than "x," the difference can be considered an intercept shift. Accordingly, in some examples, controller <NUM> may determine an intercept shift with reference to memory <NUM> using the following equation: <MAT>.

In Equation <NUM> above, γ is the intercept shift, a is the first measured concentration of the fluorescent tracer, b is the second measured concentration of the fluorescent tracer, and x is the second concentration of fluorescent tracer divided by the first concentration of fluorescent tracer. Controller <NUM> may store the determined intercept shift in memory <NUM> and/or use the determined intercept shift to establish a new intercept for a recalibrated calibration curve stored as calibration curve data <NUM>.

In the example of <FIG>, controller <NUM> determines an adjusted intercept for the calibration curve based on the determined intercept shift (<NUM>). In some examples, controller <NUM> references calibration curve data <NUM> stored in memory <NUM> and increments or decrements the stored calibration curve intercept by an amount corresponding to the intercept shift. For example, controller <NUM> may add the intercept shift determined in step <NUM> to the stored calibration curve intercept, thereby establishing an adjusted intercept. Controller <NUM> may store the adjusted intercept as calibration curve data <NUM> for use in subsequent fluorometric measurements, e.g., replacing the intercept previously stored.

As previously noted, the calibration curve stored as calibration curve data <NUM> may include one or more slope constants in addition to an intercept value. In performing the recalibration technique of <FIG>, the intercept value for the calibration curve may be adjusted without changing the one or more slope constants stored. That is, the one or more slope constants generated during a full, multipoint calibration process may remain in calibration curve data <NUM> and be used during subsequent fluorometric measurements with only the intercept parameter changing due to recalibration. Accordingly, during partial recalibration, and adjusted intercept parameter for calibration curve data <NUM> may be determined without determining an adjusted slope parameter.

<FIG> is another example technique for recalibrating fluorometer <NUM>. As with the technique of <FIG>, the technique of <FIG> is described with reference to system <NUM> in <FIG> and fluorometer <NUM> in <FIG>, although can be performed in other systems and with other fluorometer configurations, e.g., as described herein.

With reference to <FIG>, the technique includes introducing a fluorescent tracer into feed stream <NUM> to provide a first concentration of fluorescent tracer in the feed stream. (<NUM>) Operating under the control of controller <NUM> in system <NUM>, fluorescent tracer pump <NUM> may be controlled to introduce fluorescent tracer into feed stream <NUM> from fluorescent tracer source <NUM>. The amount of fluorescent tracer introduced into feed stream <NUM> may be effective to provide a concentration of fluorescent tracer in feed stream <NUM> within any of the concentration ranges discussed herein, or even concentration ranges outside of those discussed herein in suitable applications. The fluorescent tracer may be introduced into feed stream <NUM> as part of an ongoing monitoring process to evaluate the rejection efficiency of membrane <NUM>.

In the technique of <FIG>, controller <NUM> controls fluorescent tracer pump <NUM> to terminate the introduction of fluorescent tracer into feed stream <NUM>. (<NUM>) After terminating the introduction of fluorescent tracer, fluorometer <NUM> can fluorometrically analyze permeate stream <NUM> generated from the feed stream <NUM> following termination of the introduction of fluorescent tracer. (<NUM>) As discussed with respect to <FIG>, controller <NUM> executing instructions stored in memory <NUM> can control optical emitter <NUM> to direct light selected to be at an excitation wavelength for the fluorescent tracer introduced into feed stream <NUM> into the permeate fluid under analysis. Fluorescent tracer molecules within permeate under analysis may fluoresce at a wavelength different than the excitation wavelength in response to the energy emitted at the excitation wavelength. Optical detector <NUM> can detect the fluorescent emissions emitted by the tracer molecules present within the permeate. The magnitude of the fluorescent emissions detected by optical detector <NUM> may vary based on the concentration of the fluorescent tracer molecules present in the permeate under analysis.

Processor <NUM> of controller <NUM> can determine a measured concentration of the fluorescent tracer in permeate stream <NUM> based on the fluorescent emissions detected by optical detector <NUM> and calibration curve data <NUM> stored in memory <NUM>. As discussed above with respect to <FIG>, controller <NUM> may control fluorometer <NUM> to determine the measured concentration of tracer in the permeate stream a period of time after terminating the introduction of fluorescent tracer into the feed stream effective to achieve equilibrium conditions in the feed stream and in the permeate stream. Equilibrium conditions may occur when the feed stream and permeate stream are devoid of any added fluorescent tracer molecules. Accordingly, when controller <NUM> determines a "measured concentration" of fluorescent tracer in permeate stream <NUM>-and, in fact, no fluorescent tracer is present-the "measured concentration" may represent a calibration error or offset for calibration curve data <NUM> in memory <NUM>.

To recalibrate fluorometer <NUM>, controller <NUM> may use the "measured concentration" of fluorescent tracer that is measured in the absence of any added fluorescent tracer being present in permeate stream as an intercept shift. For example, controller <NUM> may store and/or use the magnitude of fluorescent tracer measured in the absence of any added fluorescent tracer being present in permeate stream as an intercept shift.

Controller <NUM> can determine an adjusted intercept using the intercept shift. For example, controller <NUM> may reference calibration curve data <NUM> stored in memory <NUM> and increment or decrement the stored calibration curve intercept by an amount corresponding to the intercept shift. For example, if the magnitude of fluorescent tracer measured in the absence of any added fluorescent tracer being present in permeate stream is negative, controller may add to the stored calibration curve intercept an amount effective to adjust the measured concentration to zero, thereby establishing an adjusted intercept. Likewise, if the magnitude of fluorescent tracer measured in the absence of any added fluorescent tracer being present in permeate stream is positive, controller may subtract from the stored calibration curve intercept an amount effective to adjust the measured concentration to zero, thereby establishing an adjusted intercept. Thus, controller <NUM> may determine a difference between the measured or reported concentration of the fluorescent tracer by fluorometer <NUM> in the permeate stream and the intercept to determine an amount by which the stored intercept should be shifted. In either case, controller <NUM> may store the adjusted intercept as calibration curve data <NUM> for use in subsequent fluorometric measurements, e.g., replacing the intercept previously stored.

The calibration curve stored as calibration curve data <NUM> may include one or more slope constants in addition to an intercept value. In performing the recalibration technique of <FIG>, the intercept value for the calibration curve may be adjusted without changing the one or more slope constants stored. That is, the one or more slope constants generated during a full, multipoint calibration process may remain in calibration curve data <NUM> and be used during subsequent fluorometric measurements with only the intercept parameter changing due to recalibration. Accordingly, during partial recalibration, and adjusted intercept parameter for calibration curve data <NUM> may be determined without determining an adjusted slope parameter.

The term "processor" may generally refer to any of the foregoing logic circuitry, alone or in combination with other logic circuitry, or any other equivalent circuitry.

The techniques described in this disclosure may also be embodied or encoded in a computer-readable medium, such as a non-transitory computer-readable storage medium, containing instructions. Instructions embedded or encoded in a computer-readable storage medium may cause a programmable processor, or other processor, to perform the method, e.g., when the instructions are executed. Non-transitory computer readable storage media may include volatile and/or non-volatile memory forms including, e.g., random access memory (RAM), read only memory (ROM), programmable read only memory (PROM), erasable programmable read only memory (EPROM), electronically erasable programmable read only memory (EEPROM), flash memory, a hard disk, a CD-ROM, a floppy disk, a cassette, magnetic media, optical media, or other computer readable media.

The following examples may provide additional details about membrane separation systems and fluorometer calibration techniques according to the disclosure.

An experiment was conducted to determine the effect, if any, changing the concentration of fluorescent tracer introduced into a membrane separation system has on the measured rejection efficiency of the membrane. One <NUM>" spiral wound membrane element (DOW FILMTEC BW30-<NUM>) was used to filter NaCl solution (<NUM>,<NUM>/L) with various fluorescent tracer concentrations. All concentrate from the membrane system was recycled back to a feed tank. Water temperature was controlled at <NUM> degrees Celsius by circulating cooling water through a coil immersed in the feed tank. Feed pressure was set at <NUM> bar or <NUM> psi. Feed and permeate fluorescence were monitored continuously by directing feed and permeate sample through feed and fluorometers, respectively. After adding a small amount of fluorescent tracer into the feed tank, rejection efficiency was estimated based on feed and permeate fluorescence. Then, additional fluorescent tracer was added and rejection efficiency was measured after fluorescence readings became stable, and so on. The results of the experiment are shown in <FIG>, which is a plot of fluorescent tracer concentration in the feed stream versus fluorescent tracer concentration in the permeate and membrane rejection efficiency. As shown, the membrane rejection efficiency was nearly constant regardless of fluorescent tracer concentration in the feed stream.

Using the same experimental system described in Example <NUM> above, an experiment was conducted to evaluate an example calibration curve intercept adjustment according to the present disclosure. A feed fluorometer was calibrated for a fluorescent tracer range between <NUM> and <NUM>µg/L and an ultralow range permeate fluorometer was calibrated for a fluorescent tracer range between <NUM> and <NUM>µg/L. The fluorometers were calibrated using multi-point calibration solutions, including a zero point calibration solution devoid of fluorescent tracer and at least one calibration solution having a known concentration of fluorescent tracer. The intercept or zero point of the ultralow range fluorometer was deliberately moved by -<NUM>µg/L (or -<NUM> ng/L), thereby read -<NUM> ng/L with DI water, artificially create a calibration error. While filtering <NUM>,<NUM>/L NaCl solution using a DOW FILMTEC BW30 membrane, fluorescent tracer was added to the feed tank. After reaching a steady state, fluorescent tracer concentrations in the feed stream and permeate stream were measured at <NUM>µg/L and <NUM> ng/L, respectively, as shown in <FIG>. If the intercept or zero point of the ultralow range permeate fluorometer was not moved by -<NUM> ng/L, the fluorescent tracer concentration in the permeate would have measured at <NUM> ng/L. Additional fluorescent tracer was added to the feed tank to raise the tracer concentration by approximately <NUM>%. After reaching a steady state, the fluorescent tracer concentrations in the feed stream and permeate stream were stabilized at approximately <NUM>µg/L and approximately <NUM> ng/L, respectively.

Using Equation <NUM> above, the intercept shift (γ) for the calibration curve data stored for the ultralow range fluorometer was calculated. The multiplication factor (x) of fluorescent tracer concentration in the feed was calculated at <NUM> (=<NUM>/<NUM>). The average fluorescent tracer concentrations in the permeate before and after raising the fluorescent tracer concentration in feed were <NUM> ng/L (a) and <NUM> ng/L (b), respectively. The intercept shift (γ) was calculated at +<NUM> ng/L, which was sufficient (within +/- <NUM>%) to compensate most of the artificial zero point movement (-<NUM> ng/L) made earlier in the study.

Claim 1:
A method of calibrating a fluorometer (<NUM>) used to monitor a reverse osmosis membrane separation process comprising:
introducing a fluorescent tracer into a feed stream (<NUM>) to provide a first concentration of fluorescent tracer in the feed stream (<NUM>);
contacting a membrane (<NUM>) with the feed stream (<NUM>), thereby generating a permeate stream (<NUM>) and a concentrate stream (<NUM>);
fluorometrically analyzing the permeate stream (<NUM>) generated from the feed stream (<NUM>) having the first concentration of fluorescent tracer with a fluorometer (<NUM>) and determining therefrom a first measured concentration of the fluorescent tracer in the permeate stream (<NUM>) based on a stored calibration curve that includes an intercept;
adjusting a concentration of the fluorescent tracer in the feed stream (<NUM>) to provide a second concentration of fluorescent tracer in the feed stream (<NUM>) different than the first concentration;
fluorometrically analyzing the permeate stream (<NUM>) generated from the feed stream (<NUM>) having the second concentration of fluorescent tracer with the fluorometer (<NUM>) and determining therefrom a second measured concentration of the fluorescent tracer in the permeate stream (<NUM>) based on the calibration curve;
determining an intercept shift for the calibration curve based on comparison of the first measured concentration to the second measured concentration; and
determining an adjusted intercept for the calibration curve based on the intercept shift.