Water treatment

Abstract

Provided herein are methods of controlling the dosing of a biocide in a water treatment system, comprising dosing a biocide to water to be treated, determining rH before dosing the biocide to obtain a first rH value (rH1), determining rH after dosing the biocide to obtain a second rH value (rH2), determining a difference between rH1 and rH2, where the difference is system [delta] rH, comparing system [delta] rH to a predefined target [delta] rH, wherein the predefined target [Delta] rH corresponds to the biocidal performance required in the water treatment system, and adjusting the amount of biocide administered to the water based on a deviation of the system [Delta] rH from the target [Delta] rH.

Description

Field of the Invention

[0001] The present disclosure generally relates to controlling biocide dosing in a water treatment system. The present disclosure particularly, but not exclusively, relates to a method of controlling biocide dosing in a water treatment system using a determined temperature and pH adjusted redox potential (rH). The present disclosure also relates to a water treatment system capable of controlling biocide dosing using a determined temperature and pH adjusted redox potential (rH). Background of the Invention

[0003] The demand for pure water is increasing rapidly around the world. Efforts are being made to produce pure water from impure water using lower concentrations of chemical biocides (including disinfectants) without significantly increasing the cost of the purification process. In addition, there is a need to use biodegradable or other less hazardous chemicals that have less hazardous health effects.

[0004] Chlorine-based compounds (e.g., hypochlorite, chlorine dioxide, and chloramines) are traditionally used to disinfect water, including wastewater. Chlorine-based disinfectants are very effective against bacteria, but are less effective against viruses, bacterial spores, and protozoan cysts. In addition, chlorine-based disinfectants produce potentially toxic and mutagenic byproducts, making them less desirable for use in disinfection processes.

[0005] Regulations regarding the use of chlorine-based compounds to disinfect wastewater treatment plant effluents have become more stringent in recent years, and as a result other non-chlorine-based disinfectants have become increasingly popular. In particular, organic acids such as peracetic acid and performic acid have been found to be effective broad-spectrum disinfectants.

[0006] Peracetic acid (PAA or CH3COOOH) is commercially available as an acidic quaternary equilibrium mixture with acetic acid, hydrogen peroxide (H2O2) and water as shown in the following reaction (1):

[0007]

[0008] PAA has a high redox potential, and the disinfection mechanism of PAA may include the release of highly reactive oxygen species (ROS). ROS can alter the metabolism of microorganisms and damage the structure of microbial cells due to a chain reaction between ROS and biomolecules (e.g., enzymes, lipids, structural proteins, and DNA). PAA advantageously produces little to no toxic / mutagenic byproducts after reacting with organic materials, and degrades to acetic acid, hydrogen peroxide, and water.

[0009] Performic acid (PFA or HCOOOH) is typically applied as an equilibrium mixture of PFA, water, hydrogen peroxide, and formic acid as shown in the following reaction (2):

[0010]

[0011] PFA is very unstable and typically needs to be generated on site shortly before use. The disinfection mechanism of PFA is believed to be similar to that of PAA and may include the generation of ROS. PFA is considered to be more effective than PAA in disinfection (e.g., requiring lower dosages and / or shorter contact times) for inactivating at least some microorganisms (including E. coli and enterococci). This can be attributed to the higher redox potential of PFA, which provides a greater ability to oxidize pollutants. Similar to PAA, PFA produces little to no toxic / mutagenic byproducts after reacting with organic materials. PFA is completely biodegradable and the degradation products of PFA include carbon dioxide and water.

[0012] In water treatment systems, the initial dosage of disinfectant is typically determined based on microbial analysis before and after the addition of the biocide. This initial dosage is often maintained in the system until there is a significant change or deviation from the desired microbial removal rate. However, this approach does not take into account changes in process conditions, which may require a corresponding change in disinfectant dosage. This can result in microbial counts exceeding regulatory limits (if the required level of disinfectant activity is not achieved) or excess unused disinfectant remaining in the discharged water, resulting in violations of regulatory limits and increased operating costs.

[0013] It is therefore an object of the present invention to more effectively manage the dosing of disinfectants in a water treatment system to overcome the above problems. Summary of the invention

[0014] Thus, in a first aspect, the present invention provides a method of controlling dosing of a biocide in a water treatment system, the method comprising:

[0015] The biocide is dosed into the water to be treated,

[0016] determining rH before dosing the biocide to obtain a first rH value (rH1),

[0017] determining rH after dosing the biocide to obtain a second rH value (rH2),

[0018] Determine the difference between rH1 and rH2, where this difference is the system ΔrH,

[0019] comparing the system ΔrH to a predefined target ΔrH, wherein the predefined target ΔrH corresponds to a desired biocidal performance in the water treatment system, and

[0020] The amount of biocide dosed into the water is adjusted based on the deviation of the system ΔrH from the target ΔrH.

[0021] In a second aspect, the present invention provides a water treatment system for performing the above method, the system comprising:

[0022] at least one chamber comprising an inlet for receiving water to be treated and an outlet for discharging treated water therefrom,

[0023] a first device configured to dose a biocide into the water in the at least one chamber,

[0024] a second device configured to measure pH, ORP, and temperature and determine rH1 and rH2 based on the measured pH, ORP, and temperature;

[0025] and a control device operatively connected to the first device and the second device,

[0026] The control device is constructed and arranged as follows:

[0027] receiving output data related to the determined rH1 and rH2 from the second device,

[0028] Determine the difference between rH1 and rH2, where this difference is the system ΔrH,

[0029] comparing the system ΔrH to a predefined target ΔrH, wherein the predefined target ΔrH corresponds to a desired biocidal performance in the water treatment system, and

[0030] The amount of biocide dosed into the water is adjusted based on the deviation of the system ΔrH from the target ΔrH.

[0031] Preferred features of all aspects of the invention are defined in the dependent claims.

[0032] The method and system as defined herein are particularly useful for wastewater treatment and the treatment of process water in paper mills. The inventors unexpectedly discovered a strong correlation between ΔrH and biocidal performance in water treatment systems. Therefore, the dosing of biocides can be adjusted based on the system ΔrH to ensure that microbial levels remain within desired limits and to avoid overdosing of biocides that may violate environmental regulations.

[0033] BRIEF DESCRIPTION OF THE DRAWINGS

[0034] To assist in understanding the present disclosure and to show how the embodiments may be carried into effect, reference is made, by way of example only, to the accompanying drawings, in which:

[0035] Figure 1 is a schematic diagram illustrating a water treatment system according to an example of the present invention.

[0036] Figure 2 is a schematic block diagram illustrating a control device according to an example of the present invention.

[0037] Figure 3 is a graph illustrating the relationship between ΔrH and the killing efficacy affected by PFA in water from a paper mill when using PFA.

[0038] Figure 4 is a graph illustrating the relationship between ΔrH and killing efficacy affected by monochloramine (MCA) in water from a paper mill.

[0039] Figure 5 is a graph illustrating the relationship between ΔrH and the killing efficacy affected by PFA in water from a wastewater treatment plant.

[0040] Fig. 6A is a line graph illustrating the correlation between ORP and the concentration of residual biocide.

[0041] Figure 6B is a line graph illustrating the correlation between rH and the concentration of residual biocide.

[0042] Figure 6C is a line graph illustrating the correlation between ΔrH and the concentration of residual biocide.

[0043] DETAILED DESCRIPTION OF THE INVENTION

[0044] Regardless of the biocidal technology, biocidal performance is mainly controlled by the concentration of residual biocides. As used herein, the term "concentration of residual biocides" refers to the concentration of biocides remaining after contacting (or being exposed to) water to be treated for a period of time. Therefore, if the critical concentration of residual biocides is dynamically maintained during the disinfection process, consistent biocidal performance will be met. However, specifically with respect to the use of percarboxylic acids as biocides in wastewater treatment systems, changes in water quality and quantity, as well as a variety of side reactions between biocides and water pollutants, can reduce the concentration of residual biocides and therefore have an adverse effect on biocidal performance. For example, when added to wastewater, PFA and PAA experience more gradual decay after initial rapid consumption (i.e., instantaneous disinfectant demand). Poor water quality and water pollutants can accelerate initial consumption and subsequent decay. As a result, dosing strategies that do not take into account conditions that affect demand and / or decay can lead to insufficient biocidal performance and may violate regulatory microbial restrictions.

[0045] As mentioned above, the present invention provides a method for controlling biocide dosing in a water treatment system, the method comprising:

[0046] The biocide is dosed into the water to be treated,

[0047] determining rH before dosing the biocide to obtain a first rH value (rH1),

[0048] determining rH after dosing the biocide to obtain a second rH value (rH2),

[0049] Determine the difference between rH1 and rH2, where this difference is the system ΔrH,

[0050] comparing the system ΔrH to a predefined target ΔrH, wherein the predefined target ΔrH corresponds to a desired biocidal performance in the water treatment system, and

[0051] The amount of biocide dosed into the water is adjusted based on the deviation of the system ΔrH from the target ΔrH.

[0052] As used herein, "biocide" refers to any chemical substance capable of destroying, preventing, rendering harmless, or exerting a growth control effect on any harmful organism.

[0053] In some embodiments, the biocide may comprise a disinfectant. As used herein, "disinfectant" refers to a chemical substance that can destroy, prevent, render harmless, or exert a growth control effect on at least one microorganism selected from bacteria, bacterial spores, fungi, viruses, and protozoa.

[0054] The biocide can be any biocide that can increase the redox potential (ORP) of water when added to water. In a preferred embodiment, the biocide comprises an oxidizing biocide. The oxidizing biocide can be selected from one or more of the following: monochloramine (MCA), chlorine dioxide, percarboxylic acids, alkali metal and alkaline earth metal hypochlorites, halogenated hydantoins such as monochlorodimethylhydantoin (MCDMH) and bromochlorodimethylhydantoin (BCDMH), chlorine and ozone. Preferably, the oxidizing biocide comprises percarboxylic acids. Preferably, the percarboxylic acids comprise performic acid (PFA) and / or peracetic acid (PAA). In a preferred embodiment, the oxidizing biocide comprises PFA. In other examples, the biocide comprises a non-oxidizing biocide. The non-oxidizing biocide may comprise 2,2-dibromo-3-nitrilopropionamide (DBNPA).

[0055] The skilled person will understand that rH corresponds to the oxidation-reduction potential (ORP) adjusted for pH and temperature. In one example, rH can be calculated using the following formula:

[0056] rH=2·pH+2·Eh·F / (2.3026·R·T)

[0057] in:

[0058] Eh = Redox potential measured using a standard hydrogen electrode (V)

[0059] F = Faraday constant (96485C·mol -1 )

[0060] R = gas constant 8.314 J·K -1 ·mol -1

[0061] T = Temperature (K)

[0062] A standard pH probe or pH meter can be used to determine the pH of the water. A standard sensor or electrode can be used to measure ORP. A standard thermometer can be used to determine the temperature of the water. Therefore, determining rH in the context of the present invention can include determining pH, temperature, and ORP at relevant times and / or locations, as discussed below. In preferred embodiments, pH, temperature, and ORP are determined simultaneously. In other embodiments, pH, temperature, and ORP are determined sequentially (in any order) within a period of no more than 5 seconds, 10 seconds, 20 seconds, 30 seconds, 1 minute, 5 minutes, or 10 minutes. In other embodiments, the water treatment system is maintained at a constant set temperature so that no further measurement of temperature is required to determine rH. In these embodiments, pH and ORP can be determined simultaneously or sequentially as described above.

[0063] In other examples, one or more of pH, temperature and ORP are determined online. In other examples, one or more of pH, temperature and ORP are determined inline. In other examples, each of pH, temperature and ORP is determined online or inline, and preferably simultaneously. Both online and inline measurements are forms of continuous in-situ measurements. Online measurements are not made directly in the main process line, but in a built-in branch or bypass (e.g., a sampling loop), into which a sample of treated water is automatically fed. Inline measurements are made directly in the main process line, which requires that the relevant probe or sampling interface be placed directly in the process flow or aligned with the process flow.

[0064] In the method of the present invention, rH is determined before dosing the biocide to provide a first rH value (rH1). In the context of the present invention, determining rH1 may require measuring each of pH, temperature and ORP simultaneously at a given time point, or sequentially (in any order) within a given time period. rH1 can be determined at any time before the dosing of the biocide, although it is preferred to minimize the time between rH1 determination and biocide addition to improve the accuracy of the method. In some examples, rH1 is determined 30 seconds, 1 minute, 5 minutes, 10 minutes, 20 minutes, or 30 minutes before the time when the biocide is dosed into the water. In these examples, rH1 can be determined by simultaneously measuring each of pH, temperature and ORP at the above time. Alternatively, pH, temperature and ORP can be measured immediately (in any order) so that the above time corresponds to the average time of three measurements. Thus, for example, if the pH is determined 35 seconds before the biocide is dosed, the temperature is determined 30 seconds before the biocide is dosed, and the ORP is determined 25 seconds before the biocide is dosed, then the rH1 can be considered to be determined 30 seconds before the biocide is dosed ((35+30+25) / 3). If the pH, temperature, and ORP are measured continuously, it is desirable to make three measurements within a period of no more than 5 seconds, 10 seconds, 20 seconds, 30 seconds, 1 minute, 5 minutes, or 10 minutes. If the pH, temperature, and ORP are measured continuously, it is preferred to make three measurements within a period of no more than 10 minutes.

[0065] In other examples, rH1 is determined immediately before the biocide is dosed into the water. In a continuous flow system, rH1 can be determined at a location upstream of the point at which the biocide is dosed into the water. The rH1 can be determined based on the flow rate of the water (e.g., the m of the flowing water). 3 number of times per minute) and the volume of the container through which the water will flow to the point where the biocide is added (e.g., m 3 Thus, for example, if after determining rH1, the water is heated at 2 m / s before adding the biocide, 3 / min flow rate moves through the corresponding 10m 3 A portion of the volume of the container, 5 minutes before the addition of the biocide will determine the rH1. The pH, temperature and OPR probes or sensors can be placed accordingly at appropriate locations in the water treatment system to achieve the required measurement time.

[0066] If the temperature of the water treatment system is maintained at a constant set level, no further measurement of temperature may be required to determine rH1. In these cases, to determine rH1, pH and ORP may be measured simultaneously or continuously as defined above.

[0067] In the methods of the present invention, a second rH is determined after dosing of the biocide to provide a second rH value (rH2). The rH2 may be determined after a predetermined contact time has elapsed (i.e., the time after the biocide is added to the water). In the context of the present invention, determining rH2 at a given time point may require measuring each of pH, temperature, and ORP simultaneously at a given time point, or sequentially (in any order) over a given period of time.

[0068] In some examples, rH2 is determined after a contact time of 10 seconds to 30 minutes, or 1 minute to 5 minutes, or 5 minutes. In other examples, rH2 is determined after a contact time of 1 second, 10 seconds, 20 seconds, 30 seconds, 1 minute, 5 minutes, 10 minutes, 20 minutes, or 30 minutes. In a preferred example, rH2 is determined after a contact time of 1 minute to 5 minutes or 3 to 5 minutes. In these examples, rH2 can be determined at the above time by measuring each of pH, temperature, and ORP simultaneously. Alternatively, pH, temperature, and ORP can be measured immediately (in any order) so that the above time corresponds to the average time of three measurements. Therefore, for example, if pH is determined 5 seconds after biocide dosing, temperature is determined 15 seconds after biocide dosing, and ORP is determined 25 seconds after biocide dosing, then rH2 can be considered to be determined 15 seconds ((5+15+25) / 3) after biocide dosing. If pH, temperature and ORP are measured continuously, it is desirable to make three measurements within a period of no more than 5 seconds, 10 seconds, 20 seconds, 30 seconds, or 1 minute. If pH, temperature and ORP are measured continuously, it is preferred to make three measurements within a period of no more than 10 minutes.

[0069] In a continuous flow system, the flow rate of the water (e.g., m of the flowing water) can be used to calculate the 3 number of times per minute) and the volume of water that has flowed through the vessel downstream of the point at which the biocide is added (e.g., m 3 The contact times corresponding to those provided above are determined by the number of contact times. Thus, for example, if the water is heated at 2 m 3 / min flow rate moves through the corresponding 20m 3 The contact time at the end of the portion of the container can be calculated as 10 minutes. The pH, temperature and OPR probes or sensors can be placed in the water treatment system at appropriate locations to achieve the required measurement time.

[0070] If the temperature of the water treatment system is maintained at a constant set level, no further measurement of temperature may be required to determine rH2. In these cases, pH and ORP may be measured simultaneously or in the order defined above to determine rH2.

[0071] The time periods for determining rH1 and rH2 should be consistent with those used to determine the target ΔrH as discussed above, so that biocide dosing can be effectively controlled.

[0072] Once rH1 and rH2 are determined, the difference between rH1 and rH2 is determined, wherein the difference is represented by ΔrH and is referred to as "system ΔrH". ΔrH can be determined by subtracting rH1 from rH2 (i.e., rH2-rH1) or by subtracting rH2 from rH1 (i.e., rH1-rH2) in a preferred example. The difference between rH1 and rH2 is determined in the same manner for system ΔrH and a predefined target ΔrH, except that only absolute values ​​are considered. In other words, if the predefined target ΔrH is based on rH2-rH1, the system ΔrH is also based on rH2-rH1. Conversely, if the predefined target ΔrH is based on rH1-rH2, the system ΔrH is also based on rH1-rH2.

[0073] Target ΔrH

[0074] In the inventive method, the system ΔrH is compared to a target ΔrH, and based on any deviation of the system ΔrH from the target ΔrH, the dosing of the biocide can be adjusted to provide optimized biocidal performance.Biocidal performance refers to the killing efficacy of the biocide.

[0075] The inventors unexpectedly found a strong consistent positive correlation between ΔrH and residual biocide concentration in a water treatment system. As mentioned above, the term "concentration of residual biocide" as used herein refers to the concentration of biocide in the system after contacting (or being exposed to) water to be treated for a period of time. The concentration of residual biocide indicates the biocidal performance of the system. When the concentration of residual biocide decreases, the risk of microbial growth increases. The concentration of residual biocide itself is often difficult to measure and monitor. For example, this can be due to the need for complex equipment. In addition, residual biocide measurements are often based on color reactions that can be affected by the turbidity of water. Therefore, by eliminating the need to directly measure the residual concentration of biocide, the present invention provides an advantageous method for achieving and maintaining optimized biocidal performance.

[0076] The target ΔrH is defined based on the biocidal performance required by the water treatment system in which the method of controlling the dosing of the biocide is performed. The predefined target ΔrH may include a target ΔrH value or a target range of ΔrH values. In some examples, the target range of ΔrH values ​​is based on the acceptable tolerance limit of the target ΔrH value. In some examples, the acceptable tolerance limit may be + / -1%, 5%, 10%, or 20% of the target ΔrH value. The target ΔrH can be determined by a suitable calibration method, in which the concentration of the relevant biocide is tested, and the resulting killing efficacy and ΔrH are determined. ΔrH can be determined as described above. In determining the target ΔrH, the time period for determining rH1 and rH2 relative to the time of biocide addition at each tested biocide concentration will typically be consistent with the time period to be selected for determining rH1 and rH2 to obtain the system ΔrH. The killing efficacy can be determined by using standard methods such as agar plate culture medium and bacterial counts to perform bacterial counts. The ΔrH value or range of values ​​that provides acceptable or desired killing efficacy can then be used to define a target ΔrH.

[0077] In some examples, a target ΔrH is defined alternatively or additionally based on a correlation between ΔrH and residual biocide concentration. In these examples, the target ΔrH can be determined by a suitable calibration method in which varying concentrations of the biocide of interest are tested and the resulting concentration of the residual biocide and the ΔrH are determined. Thus, the target ΔrH can correspond to an optimized concentration or concentration range of the residual biocide to provide the desired biocidal performance.

[0078] In some examples, the predefined target ΔrH value, based on absolute values, may be 1-15, or 10-15, or 12-15. In other examples, the target ΔrH value, based on absolute values, may be 2-10, or 2-8, or 2-6, or 2-4, or 4-10, or 4-8, or 4-6, or 6-10, or 6-8, or 8-10. In examples where the predefined target ΔrH is a range of ΔrH values, based on absolute values, the lower limit of the range may be 1 or more, and the upper limit of the range may be 15 or less. In other examples, the lower limit may be 10 or more and the upper limit may be 15 or less, or the lower limit may be 12 or more and the upper limit may be 15 or less. In further examples, the lower limit may be 2 or more and the upper limit may be 8, 6, or 4 or less; the lower limit may be 4 or more and the upper limit may be 10, 8, 6 or less; the lower limit may be 6 or more and the upper limit may be 10 or 8 or less; or the lower limit may be 8 or more and the upper limit may be 10 or less.

[0079] The target ΔrH may be relatively high in wastewater treatment systems where significant microbial reduction is typically desired. In wastewater treatment systems, the target ΔrH (either as a single value or as a range of values ​​providing acceptable tolerance limits), based on absolute values, may be 5-15. The target ΔrH may be lower in other systems such as paper production plants (paper mills). For example, in a paper mill, the target ΔrH (either as a single value or as a range of values ​​providing acceptable tolerance limits), based on absolute values, may be 1-5.

[0080] When the system ΔrH (as determined by rH2-rH1) is below a predefined target ΔrH value or below the minimum of a target ΔrH value range, the dosing of the biocide can be increased to restore ΔrH to the target ΔrH value or to a value falling within the target ΔrH value range and provide adequate biocidal performance. When the system ΔrH (as determined by rH2-rH1) is above a predefined target ΔrH value or exceeds the maximum of a target ΔrH value range, the dosing of the biocide can be reduced to restore ΔrH to the target ΔrH value or to a value falling within the target ΔrH value range, and thus prevent the accumulation of unused biocide.

[0081] When the system ΔrH (as determined by rH1-rH2) is below a predefined target ΔrH value or below the minimum of the target ΔrH value range, the dosing of the biocide can be reduced to restore ΔrH to the target ΔrH value or to a value falling within the target ΔrH value range, and thus prevent the accumulation of unused biocide. When the system ΔrH (as determined by rH1-rH2) is above a predefined target ΔrH value or exceeds the maximum of the target ΔrH value range, the dosing of the biocide can be increased to restore ΔrH to the target ΔrH value or to a value falling within the target ΔrH value range and provide sufficient biocidal performance.

[0082] In other examples, when the system ΔrH (as determined by rH2-rH1 or by rH1-rH2) is below a predefined target ΔrH value or below a minimum value of a target ΔrH value range, the dosing of the biocide can be increased to restore ΔrH to the target ΔrH value or to a value falling within the target ΔrH value range and provide adequate biocidal performance. When the system ΔrH (as determined by rH2-rH1 or by rH1-rH2) is above a predefined target ΔrH value or exceeds a maximum value of a target ΔrH value range, the dosing of the biocide can be reduced to restore ΔrH to the target ΔrH value or to a value falling within the target ΔrH value range and thereby prevent the accumulation of unused biocide. In these examples, the value of the system ΔrH, the predefined target ΔrH value, and the predefined target range of ΔrH values ​​are represented by respective absolute values.

[0083] In some instances, monitoring the system ΔrH enables detection of any deviation from a predefined target ΔrH, and adjusting the dosing of the biocide without delay. This prevents an undesired increase in microbial growth (when the system's biocidal performance is below an acceptable level) or an overdose of the biocide (when the need for the biocide is reduced). Therefore, a continuous manner can be used to determine and monitor the system ΔrH. In this context, "continuous" means at regular intervals, without pauses or interruptions. In some instances, the system ΔrH is determined at regular time intervals of 1 to 60 minutes, 1 to 30 minutes, 1 to 20 minutes, 1 to 10 minutes, 1 to 5 minutes, or 1 to 2 minutes. The system ΔrH can be determined every minute, every 2 minutes, every 3 minutes, every 4 minutes, every 5 minutes, every 10 minutes, every 20 minutes, or every 30 minutes.

[0084] The deviation of the system ΔrH from the target ΔrH may be of any magnitude. In some examples, the biocide dosage is adjusted when there is at least 5%, or at least 10%, or at least 20% deviation from a predefined target ΔrH value, or at least 1%, 2%, 5%, or 10% deviation from the minimum or maximum value of a predefined range of target ΔrH values. This may prevent the adjustment of the biocide dosage when there are negligible fluctuations in the system ΔrH due to experimental error or due to insignificant changes in process conditions. In other examples, when the system ΔrH does not deviate from the target ΔrH, or there is less than 5%, 10%, or 20% deviation from a predefined target ΔrH value, or there is less than 1%, 2%, 5%, or 10% deviation from the minimum or maximum value of a predefined range of target ΔrH values, no adjustment of the biocide dosage is made.

[0085] The regulation of the dosing of the biocide in response to the system ΔrH can be achieved by different arrangements. In some instances, the biocide is fed to the water to be treated via a biocide line. The biocide line may include one or more pumps. When an increase in the dosing of the biocide is required, as determined by the system ΔrH, the speed of one or more pumps may be increased. Conversely, when a decrease in the dosing of the biocide is required, as determined by the system ΔrH, the speed of one or more pumps may be reduced. Other ways of controlling the dosing of the biocide are also envisioned, such as valves that can be opened and closed to increase and decrease the dosing of the biocide, respectively.

[0086] The inventors unexpectedly discovered that ΔrH is a more effective parameter for determining the concentration of residual biocides and the resulting biocidal performance of a water system than rH or oxidation-reduction potential (ORP). The correlation between ΔrH and the concentration of residual biocides is significantly more robust and consistent than the correlation between rH and the concentration of residual biocides, or between ORP and the concentration of residual biocides. As mentioned above, low concentrations of residual biocides increase the risk of microbial growth. An increase in water temperature may also increase microbial growth, resulting in increased consumption of biocides and reduced ΔrH. An increase in organic load may also consume biocides and thus reduce ΔrH. Therefore, ΔrH is sensitive to any factor that affects the concentration of residual biocides, which in turn will affect the biocidal performance of the system.

[0087] rH and ORP can vary independently of residual biocide concentration, depending on water quality and process conditions. Thus, within a given system, rH and ORP can vary over time, and therefore a target based on rH or ORP that was determined to provide an acceptable level of biocidal performance under a first set of conditions may need to be periodically reset due to changing conditions. In contrast, ΔrH is a more robust indicator and tolerates changes in water quality, such that once a target ΔrH value or range of values ​​that provides an acceptable level of biocidal performance is set for a given system, the target can be maintained and used as a reference point for a relatively long period of time without further calibration.

[0088] The inventors have additionally discovered that when rH2 is determined five minutes or less after the addition of the biocide (or in a continuous system, at a distance corresponding to 5 minutes or less after the addition of the biocide), there is an improved resolution between effective and inadequate biocidal performance, and thus control of biocide dosing becomes more effective when this time frame is used. In particular, as described in the Examples below, when rH2 is determined after a contact time of five minutes or less after the addition of the biocide, a greater increase in ΔrH is observed with an increase in biocide dosing than when rH2 is determined after a longer contact time.

[0089] Water to be treated

[0090] The water to be treated in the method of the present invention is not particularly limited and is any water or aqueous solution that requires biocidal treatment. The water to be treated may comprise raw water (e.g., surface water of a lake, ocean, or river), drainage, industrial water, and / or wastewater.

[0091] Wastewater can comprise municipal wastewater, industrial wastewater or their mixture. In some instances, wastewater can comprise sewage. Industrial wastewater can comprise process water used in industrial processes and facilities such as those related to pulp and paper industry, oil industry, gas industry, mining industry, food industry or any other applicable industry. In some instances, process water can comprise circulating water from papermaking or board mill. Water to be treated typically comprises one or more pollutants such as bacteria, viruses and other non-living organisms.

[0092] Water that has been treated by the method of the invention can be discharged to the environment, undergo further purification steps, or, in the case of process water, can be reused in the same process from which it originates or in a different process. In one example, recycled water originating from a paper or board manufacturing process that has been treated with a biocide according to the method of the invention is reused in paper or board manufacturing. In another example, wastewater treated with a biocide according to the method of the invention is reused in agriculture.

[0093] Wastewater treatment

[0094] In a preferred embodiment, the method for controlling the dosing of biocides according to the present invention can be carried out in a wastewater treatment system or a factory. The wastewater to be treated may include municipal wastewater, sewage and / or industrial wastewater.

[0095] Municipal wastewater or sewage treatment generally includes the following sequential processes: preparatory, primary, secondary and tertiary treatment. These are well known to those skilled in the art of wastewater treatment and water purification and are discussed further below.

[0096] Preparatory treatment may remove coarse suspended materials that may be readily collected from raw sewage or wastewater, such as by screening and / or shredding, before the coarse suspended materials damage or clog any pumps and sewage lines of the primary treatment facility.

[0097] Primary treatment is designed to remove gross solids, suspended solids, and floating solids from raw sewage or wastewater. Primary treatment may include screening to capture solid objects and gravity settling to remove suspended solids (removed and collected as sludge).

[0098] After primary treatment, the wastewater may be directed to secondary treatment, which typically includes a biological treatment step and sedimentation. In particular, the primary effluent may undergo an activated sludge technique, in which the effluent is aerated and aerobic microorganisms metabolize the organic matter into carbon dioxide and water and multiply to form a microbial community. Organic nitrogen compounds may be converted to ammonia and subsequently to nitrates. A secondary sedimentation tank may aggregate and settle microorganisms and solid waste into sludge. At least some of the collected sludge (activated sludge) may then be recycled to serve as an inoculum for biological treatment of further incoming wastewater.

[0099] Primary and secondary treatment are often sufficient for many purposes, and not all wastewater treatment plants use tertiary treatment. Those that use tertiary treatment achieve more stringent cleanliness levels to meet strict standards governing water reuse, especially in public water supplies. Tertiary treatment is also beneficial when a facility must discharge water into sensitive or fragile ecosystems (e.g., estuaries, low-flow rivers, coral reefs, etc.). Tertiary treatment can include filtration, disinfection, and removal of nitrogen and phosphorus.

[0100] In a preferred embodiment, the biocide is dosed into the wastewater after the secondary treatment. The dosing of the biocide can be considered as a tertiary treatment. Therefore, rH1 and rH2 are determined before and after the dosing of the biocide. Alternatively or additionally, the biocide can be dosed into the water in the influent or effluent of the primary treatment, or in the influent or effluent of the secondary treatment (if additional disinfection is required at these stages).

[0101] Biocide Dosing

[0102] In a continuous water system, the biocide may be fed to the water continuously (i.e. without pauses) or at regular predetermined time intervals. The dosing of the biocide may also be automatic. By way of example, a biocide comprising a percarboxylic acid such as PFA may be dosed to water such as wastewater at a basic dosing concentration of 1 to 2 mg / l (i.e. the concentration of active biocide in the water to be treated at the feed point). The basic dosing concentration of chlorine-based biocides based on total active chlorine may be 1-4 mg / l in wastewater, 1 to 4 mg / l in fresh water and 5 to 10 mg / l in paper mill process water. The basic dosing concentration may be subsequently adjusted based on changes in disinfection needs, such as determined by changes in the system ΔrH.

[0103] In some instances, and with reference to Figure 1 , the method for controlling the dosing of a biocide is carried out in a water treatment system 1, the water treatment system 1 comprising at least one chamber 2 comprising an inlet for receiving water to be treated and an outlet for discharging treated water therefrom, a first device 16 configured to dose a biocide into the water in the at least one chamber 2 via a pipeline 17, a second device 19 configured to measure pH, ORP and temperature and determine rH1 and rH2 based on the measured pH, ORP and temperature, and a control device 18 operably connected to the first device 16 and the second device 19. As used herein, "device" refers to any device capable of performing a specified function, including mechanical or electronic equipment, and may include multiple devices. Thus, for example, the second device 19 in the system of the present invention may include a probe for measuring pH, a probe for measuring OPR, and a thermometer.

[0104] In a preferred example, the control device 18 is constructed and arranged to: receive output data related to the determined rH1 and rH2 from the second device 19, calculate the difference between rH1 and rH2, wherein the difference is the system ΔrH, compare the system ΔrH with a predefined target ΔrH, wherein the predefined target ΔrH corresponds to the desired biocidal performance in the water treatment system, and adjust the amount of biocide dosed into the water based on the deviation of the system ΔrH from the target ΔrH.

[0105] In the water treatment system, biocide may be fed into the water in the chamber via biocide line 17. One or more pumps or valves 17a may be present in the biocide line to control the flow of biocide into the water. When the system ΔrH deviates from the target ΔrH, the control device 19 may cause an increase or decrease in the speed of one or more pumps or cause one or more valves to open or close in order to adjust the dosing of biocide into the water.

[0106] Thus, the control device may comprise a computing device. In one example, a control device is provided, comprising at least one processor and at least one memory, the memory including computer program code, the at least one memory and the computer code together with the at least one processor being configured to cause the device to perform any of the methods described herein.

[0107] Figure 2 1 is a block diagram of a control device 18 according to an example of the present invention. The control device 18 is suitable for implementing at least some of the operations described herein. Figure 2 , the control device 18 may include at least one processor 28, at least one memory 29, a communication interface 32, and a user interface 31. The control device may further include other internal circuits and components necessary to perform the tasks described herein. The control device 18 may be constructed and arranged to receive output data including system ΔrH measurements from the second device 19 and adjust the feed of biocide from the first device 16. In some examples, the control device 18 may be constructed and arranged to monitor the system ΔrH and adjust the dosing of the biocide based on the monitored ΔrH.

[0108] The control device 18 may include a communication interface 32 for connecting the control device to a data communication system and enabling data communication with the device. The communication interface 32 may include wired and / or wireless communication circuits, such as Ethernet, wireless LAN, Bluetooth, GSM, CDMA, WCDMA, LTE, 5G circuits and / or analog circuits. The communication interface may be integrated into the control device 18, or provided as part of an adapter, card, etc., which can be attached to the control device 20. The communication interface 32 may support one or more different communication technologies. The control device 18 may also or alternatively include more than one communication interface 32.

[0109] User interface 31 may include circuitry for receiving input from a user of control device 18, e.g., via a keyboard, a graphical user interface displayed on a display of the device, voice recognition circuitry, or an accessory device such as headphones, and for providing output to the user, e.g., via a graphical user interface or a speaker. The control device may be remotely operated.

[0110] At least one processor 28 may be coupled to at least one memory 29. At least one processor 28 may be configured to execute appropriate computer program code to implement one or more aspects described herein. At least one processor 28 may be a central processing unit (CPU), a microprocessor, a digital signal processor (DSP), a graphics processing unit, an application specific integrated circuit (ASIC), a field programmable gate array, a microcontroller, or a combination of such elements.

[0111] The at least one memory 29 may include working memory 30 and persistent (non-volatile, N / V) memory 33, which is configured to store computer program code 34 and data 35. The memory 33 may include any one or more of the following: read-only memory (ROM), programmable read-only memory (PROM), erasable programmable read-only memory (EPROM), random access memory (RAM), flash memory, data disk, optical storage, magnetic storage, smart card, solid state drive (SSD), etc. The control device 18 may include other possible components for use in the execution of the software and hardware-assisted tasks (which it is designed to perform).

[0112] The control device 18 may include a plurality of memories 33. The memories 33 may be constructed as part of the control device 18, or may be an attachment that is inserted into a slot, port, etc. of the device 18 by a user or by another person or by a robot. The memories 33 may serve the sole purpose of storing data, or may be constructed as part of the device 18 (which serves other purposes, such as processing data).

[0113] The skilled person will understand that in addition to Figure 2 In addition to the components shown in FIG. 1 , the control device 18 may include other components, such as a microphone, a display, and additional circuits, such as input / output (I / O) circuits, memory chips, application-specific integrated circuits (ASICs), processing circuits for specific purposes, such as source encoding / decoding circuits, channel encoding / decoding circuits, encryption / decryption circuits, etc. In addition, the control device 18 may include a disposable or rechargeable battery (not shown) for powering the device 18 if an external power source is not available. In addition, note that Figure 1 Only one device 18 is shown, but some embodiments may also be implemented in a group of the shown devices.

[0114] In some examples, the control device 18 may be configured to receive input of a particular parameter (e.g., a predefined target ΔrH, which as discussed above may be a single value of ΔrH or a range of ΔrH values). The particular parameter may be input via the user interface 31. In these embodiments, based on the output data received from the second device 19, the control device 18 may detect a deviation of the system ΔrH from the predefined target ΔrH.

[0115] If the system ΔrH drops below a predefined target ΔrH value or below the minimum of a range of target ΔrH values ​​(where ΔrH is determined by rH2-rH1), as may occur when the disinfection demand increases, the control device 18 may therefore cause the first device 16 to increase the amount of biocide fed to the water to be treated within a given time period to restore the concentration of residual biocide and thus restore the system ΔrH to the predefined target. This may be achieved by increasing the speed of one or more pumps 17a in the biocide feed line 17, or by opening one or more valves 17a in the biocide feed line 17, as described above.

[0116] Conversely, if the system ΔrH exceeds a predefined target ΔrH value or a maximum value of a range of target ΔrH values ​​(where ΔrH is determined by rH2-rH1), as may occur when the disinfection demand decreases, the control device 18 may therefore cause the first device 16 to reduce the amount of biocide fed to the water to be treated within a given time period to restore the concentration of residual biocide and thus restore the system ΔrH to the predefined target. This may be achieved by reducing the speed of one or more pumps 17a in the biocide feed line 17, or by closing one or more valves 17a in the biocide feed line 17, as described above.

[0117] When ΔrH is determined by rH1-rH2, corresponding control measures will be applied.

[0118] As described herein, suitable computer program code 34 (e.g., executed by processor 28 and stored in memory 29) may determine whether the system ΔrH deviates from a predefined target ΔrH based on the output measurement data received from the second device 19, and determine the adjustment required in the amount of biocide fed to the water in order to restore the ΔrH to the predefined target ΔrH. Thus, the control apparatus 18 may be constructed and arranged to compare the system ΔrH to the predefined target ΔrH, and may be constructed and arranged to adjust the performance of the first device 16.

[0119] In an example of the present invention, at least one processor 28 may include a proportional-integral-derivative (PID) controller. A PID controller is a control loop mechanism that employs feedback and is widely used in industrial control systems and various other applications that require continuous modulation control. A PID controller may continuously calculate an error value as the difference between a predefined ΔrH and a system ΔrH, and may then be corrected based on proportional, integral, and derivative terms. The controller may attempt to minimize the error over time by adjusting its output (e.g., by adjusting the speed of one or more pumps 17a) so that a predefined target ΔrH may be maintained. In another example, a PI (proportional-integral) based controller is used.

[0120] In systems where biocides comprising PFA are particularly used, due to the instability and fast degradation time of PFA, it may be necessary to generate PFA immediately before use. Preferably, PFA can be generated in situ (i.e., in the water treatment system itself) by a first device. In this way, the first device of the water treatment system may include a reaction vessel in which PFA is produced. In other embodiments, PFA can be produced outside the water treatment system and directly and quickly transferred to the first device for feeding to water. A preferred method for preparing PFA comprises mixing formic acid with hydrogen peroxide according to the following reaction (2), optionally in the presence of an acid catalyst such as sulfuric acid, ascorbic acid or boric acid. If the molar ratio of formic acid to hydrogen peroxide is increased, or by removing water from the reaction, the balance of reaction (2) may be offset, favoring the formation of PFA.

[0121]

[0122] A commercially available device for generating and delivering PFA is the KemConnect TM DEX.

[0123] Additional levels of control can be provided in systems that synthesize PFA (or any other biocide) in situ. For example, when the system ΔrH is found to deviate from a predefined target ΔrH, and therefore adjustment of the biocide dosing is required, the adjustment can be achieved by increasing or decreasing the delivery rate of the reagents formic acid and hydrogen peroxide to the reaction vessel to increase or decrease the PFA production rate, respectively.

[0124] Although at least some aspects of the embodiments described herein with reference to the accompanying drawings comprise computer processes carried out in a processing system or processor, the invention also extends to computer programs suitable for practicing the invention, in particular computer programs on or in a carrier. The program may be in the form of a non-transient source code, an object code, a code intermediate source and object code, such as a partially compiled form, or any other non-transient form suitable for use in implementing the process according to the invention. The carrier may be any entity or device capable of carrying the program. For example, the carrier may include a storage medium, such as a solid state drive (SSD) or other semiconductor-based RAM; a ROM, such as a CD ROM or a semiconductor ROM; a magnetic recording medium, such as a floppy disk or a hard disk; a typical optical storage device, etc.

[0125] The following is intended to be exemplary only and not limiting of the present disclosure. Example

[0126] Example 1 - Paper Mill (PFA)

[0127] Process water from a paper mill producing boards from recycled fibers was used in this test. Tests 1a and 1b were performed on the same water but at different times. Different concentrations of biocide (PFA) were dosed into the water and rH was determined at each concentration of the tested PFA 5 minutes after dosing and 30 minutes after dosing. ΔrH was thus determined. Total aerobic bacteria counts (by standard agar plate culture medium method) were also determined 30 minutes after dosing. The test was completed at room temperature (+22°C).

[0128] Table 1 and Figure 3 It is illustrated that in the sample processed by PFA, when ΔrH is 1.0 or greater, the killing efficacy is>2 logarithmic units, which is sufficient for this application. When ΔrH is 0.7 units, the killing efficacy is lower (<1 logarithmic unit). Therefore, ΔrH is approximately 1 and provides the optimized dosing of PFA. The data also show that measuring rH after dosing for 5 minutes provides an improved solution between the tested dosings of PFA.

[0129]

[0130] Example 2 - Paper Mill (MCA)

[0131] Example 1 was repeated using different doses of MCA. Figure 4 The results are described in .

[0132]

[0133] Table 2 and Figure 4This shows that when ΔrH is about 2.0 in the sample treated with MCA, the killing efficacy is>2 log units, which is sufficient for this application. Therefore, ΔrH of about 2 provides an optimized dosing of MCA. The data also show that measuring rH 5 minutes after dosing provides an improved solution between the tested dosings of PFA.

[0134] Example 3 - Wastewater Treatment Plant

[0135] The killing efficacy test using PFA was carried out at a wastewater treatment plant that treats both municipal and industrial wastewater. Screened but otherwise untreated wastewater was treated online with PFA. The first sample was collected before the start of PFA dosing. Then 5ppm PFA (active) was added, and OPR, pH and temperature were measured, and rH was determined 10 minutes after the addition. Before rH was determined again, PFA dosing was subsequently increased to 10ppm. PFA was quenched at the 10-minute sampling point to prevent further biocidal activity and changes in rH. The next day, total coliforms, Escherichia coli, enterococci and total aerobic bacteria in each sample were counted on agar plates. The test was carried out at room temperature (+22°C). Table 4 and Figure 5 Describe the results.

[0136] Table 4

[0137]

[0138] It can be seen that a ΔrH value of 12.6 corresponding to 10 ppm PFA resulted in adequate killing efficacy of the measured bacterial species and reduced pathogenic bacteria (coliforms, E. coli, enterococci) to very low levels. The untreated wastewater had a very high initial bacterial concentration (data not shown), and therefore in this system, 5 ppm active PFA, which resulted in ΔrH values ​​of 5.71-7.29, was insufficient to provide the required biocidal performance.

[0139] Example 4 - Correlation between ΔrH and residual biocide

[0140] Online testing was performed in a raw water treatment plant to evaluate the correlation between ΔrH, rH, ORP and the concentration of residual biocide. Hypochlorite (15-25 mg / l, 15% active) and dimethylhydantoin (10-20 mg / l, 15% active) were premixed to form a halogenated hydantoin. The halogenated hydantoin was continuously fed into the water. The rH was determined at regular time intervals at positions corresponding to 1 minute before and 5 minutes after the addition of the biocide in order to determine the system ΔrH at these time points. The concentration of residual biocide and ORP were also determined after the addition of the biocide at the same time points.

[0141] Fig. 6AThis indicates that there is a poor and inconsistent correlation between ORP and residual biocide concentrations.

[0142] Figure 6B A poor and inconsistent correlation was similarly demonstrated between rH and residual biocide concentrations.

[0143] Figure 6C This indicates that there is a robust and consistent correlation between ΔrH and the concentration of residual biocide.

Claims

1. A method for controlling the dosing of a biocide in a water treatment system, the method comprising: The biocide is dosed into the water to be treated, determining the rH of the water to be treated before dosing the biocide to obtain a first rH value (rH1), determining the rH of the water after dosing with the biocide to obtain a second rH value (rH2), Determine the difference between rH1 and rH2, where this difference is the system ΔrH, comparing the system ΔrH to a predefined target ΔrH, wherein the predefined target ΔrH corresponds to a desired biocidal performance in the water treatment system, and The amount of biocide dosed into the water is adjusted based on the deviation of the system ΔrH from the target ΔrH.

2. The method of claim 1, wherein the biocide comprises an oxidizing biocide.

3. The method of claim 2, wherein the oxidizing biocide is selected from the group consisting of monochloramine (MCA), chlorine dioxide, percarboxylic acids, halogenated hydantoins, alkali metal and alkaline earth metal hypochlorites, chlorine and ozone.

4. The method of claim 3, wherein the halogenated hydantoin comprises monochlorodimethylhydantoin (MCDMH) and bromochlorodimethylhydantoin (BCDMH).

5. The method according to any one of claims 2 to 4, wherein the oxidizing biocide comprises a percarboxylic acid selected from performic acid (PFA) and peracetic acid (PAA).

6. A method according to any preceding claim, wherein the predefined target ΔrH comprises a predefined target ΔrH value or a predefined target range of ΔrH values.

7. The method according to claim 6, wherein the predefined target ΔrH value is 1-15, or the lower limit of the predefined target range of ΔrH values ​​is 1 or greater, and the upper limit of the predefined target range of ΔrH values ​​is 15 or less, and wherein the predefined target ΔrH value or the predefined target range of ΔrH values ​​is represented by corresponding absolute values.

8. A method according to claim 6 or claim 7, wherein the method comprises: If the system ΔrH is below a predefined target ΔrH value or below a minimum value of a predefined range of ΔrH values, increasing the amount of biocide dosed into the water so as to increase the system ΔrH to the predefined target ΔrH value or to a value falling within the predefined range of ΔrH values, or if the system ΔrH is above a predefined target ΔrH value or exceeds a maximum value of a predefined range of ΔrH values, reducing the amount of biocide dosed into the water so as to reduce the system ΔrH to the predefined target ΔrH value or to a value falling within a predefined target range of ΔrH values, Therein the system ΔrH value, the predefined target ΔrH value and the predefined target range of ΔrH values ​​are represented by corresponding absolute values.

9. A method according to any preceding claim, wherein rH2 is determined when the contact time of the biocide with the water is between 10 seconds and 30 minutes.

10. The method of claim 9, wherein rH2 is determined when the contact time of the biocide with the water is 1 minute to 5 minutes, or 3 to 5 minutes, or 5 minutes.

11. A method according to any preceding claim, wherein a target ΔrH is defined based on a correlation between the system ΔrH and the residual concentration of the biocide and / or based on a correlation between the system ΔrH and the killing efficacy within the water treatment system.

12. A method according to any preceding claim, wherein the method comprises determining the pH, oxidation reduction potential (ORP) and optionally temperature of the water before and after dosing the biocide, and determining rH1 and rH2 based on the respective pH, temperature and ORP measurements.

13. The method of claim 12, wherein rH1 and rH2 are determined from pH, ORP and temperature using the following equation (1): rH=2·pH+2·Eh·F / (2.3026·R·T) in: Eh = Redox potential measured using a standard hydrogen electrode (V) F = Faraday constant (96485C·mol -1 ) R = gas constant 8.314 J·K -1 ·mol -1 T = Temperature (K) 14. A method according to any preceding claim, wherein rH1 and rH2 are determined from in-line or on-line measurements.

15. A method according to any preceding claim, wherein the water treatment system is a continuous system and the biocide is dosed continuously into the water to be treated.

16. A method according to any preceding claim, wherein the water to be treated comprises raw water, industrial water and / or waste water.

17. The method according to claim 16, wherein the wastewater comprises municipal wastewater, wastewater originating from pulp, paper or board production and / or wastewater originating from oil or gas production.

18. A water treatment system for carrying out the method according to any one of claims 1 to 17, comprising: at least one chamber comprising an inlet for receiving water to be treated and an outlet for discharging treated water therefrom, a first device configured to dose a biocide into the water in the at least one chamber, a second device configured to measure pH, ORP, and temperature and determine rH1 and rH2 based on the measured pH, ORP, and temperature; and a control device operatively connected to the first device and the second device, The control device is constructed and arranged as follows: receiving output data related to the determined rH1 and rH2 from the second device, Determine the difference between rH1 and rH2, where this difference is the system ΔrH, comparing the system ΔrH to a predefined target ΔrH, wherein the predefined target ΔrH corresponds to a desired biocidal performance in the water treatment system, and The amount of biocide dosed into the water is adjusted based on the deviation of the system ΔrH from the target ΔrH.

19. The system of claim 18, wherein the control device comprises at least one processor and at least one memory including computer program code, the at least one memory and the computer program code being configured to cause the control device, with the at least one processor, to receive output data related to the determined rH1 and rH2 from the second device, determine a difference between rH1 and rH2 to provide a system ΔrH, compare the system ΔrH with a predefined target ΔrH, and adjust the amount of biocide dosed into the water based on the deviation of the system ΔrH from the target ΔrH.

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