Water Treatment

Abstract

Provided herein is a method for controlling biocide dosing 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, said difference being a system ΔrH; comparing the system ΔrH to a predefined target ΔrH corresponding to a desired disinfection performance in the water treatment system; and adjusting the amount of biocide administered to the water based on the deviation of the system ΔrH from the target ΔrH.

Description

[Technical Field]

[0001] The present disclosure relates generally to controlling biocide dosing in water treatment systems. The present disclosure particularly, but not exclusively, to methods for controlling biocide dosing in water treatment systems using a determined temperature and pH adjusted oxidation-reduction potential (rH). The present disclosure further relates to water treatment systems capable of controlling biocide dosing using a determined temperature and pH adjusted oxidation-reduction potential (rH). [Background technology]

[0002] Demand for pure water is growing rapidly worldwide. 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. There is also a need to use chemicals that are biodegradable or otherwise have fewer harmful effects on health.

[0003] Chlorine-based compounds (e.g., hypochlorite, chlorine dioxide, and chloramines) have traditionally been used to disinfect water, including wastewater. Chlorine-based disinfectants are highly effective against bacteria, but are less effective against viruses, bacterial spores, and protozoan cysts. Chlorine-based disinfectants also produce potentially toxic and mutagenic by-products, making their use in disinfection processes less desirable.

[0004] Regulations regarding the use of chlorine-based compounds to disinfect wastewater treatment plant effluents have become stricter in recent years, leading to an increase in the popularity of non-chlorine-based disinfectants, particularly organic acids such as peracetic acid and performic acid, which are known to be effective broad-spectrum disinfectants.

[0005] Peracetic acid (PAA or CH3COOOH) is commercially available as an acidic quaternary equilibrium mixture containing acetic acid, hydrogen peroxide (H2O2), and water, as shown in reaction (1) below. [ka]

[0006] PAA has a high redox potential, and its disinfection mechanism may involve the release of highly reactive oxygen species (ROS). ROS can alter the metabolism of microorganisms and damage the structure of microbial cells through chain reactions between ROS and biomolecules such as enzymes, lipids, structural proteins, and DNA. PAA has the advantage of producing almost no toxic / mutagenic by-products after reacting with organic substances and being decomposed into acetic acid, hydrogen peroxide, and water.

[0007] Performic acid (PFA or HCOOOH) is usually applied as an equilibrium mixture of PFA, water, hydrogen peroxide, and formic acid, as shown in reaction (2) below. [ka]

[0008] PFA is highly unstable and typically must be generated on-site immediately before use. The disinfection mechanism of PFA is thought to be similar to that of PAA and may involve the generation of reactive oxygen species (ROS). PFA is believed to be more effective at disinfecting (e.g., requiring lower dosages and / or shorter contact times) than PAA, at least in inactivating microorganisms, including E. coli and enterococci. This is likely due to PFA's higher redox potential and its enhanced ability to oxidize contaminants. Like PAA, PFA produces few toxic / mutagenic by-products after reaction with organic matter. PFA is completely biodegradable, and its degradation products include carbon dioxide and water.

[0009] In water treatment systems, the initial disinfectant dosage is typically determined based on microbial analysis before and after the addition of the biocide. The initial dosage is often maintained in the system unless 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 corresponding changes to the disinfectant dosage. As a result, microbial counts may exceed regulatory limits (if the required level of disinfectant activity is not achieved) or excess unused disinfectant may remain in the effluent, violating regulatory limits and increasing operating costs.

[0010] SUMMARY OF THE INVENTION It is therefore an object of the present invention to more effectively manage the dosing of disinfectants in water treatment systems and overcome the problems mentioned above. Summary of the Invention

[0011] Accordingly, in a first aspect, the present invention provides a method for controlling biocide dosing in a water treatment system, the method comprising: administering a biocide to the water to be treated; determining rH prior to administration of the biocide to obtain a first rH value (rH1); determining rH after the biocide administration to obtain a second rH value (rH2); determining the difference between rH1 and rH2, and designating said difference as system ΔrH; comparing the system ΔrH to a predefined target ΔrH, the predefined target ΔrH corresponding to a desired disinfection performance in the water treatment system; adjusting the amount of biocide administered to the water based on deviation of the system ΔrH from the target ΔrH.

[0012] In a second aspect, the present invention provides a water treatment system for carrying out the above method, the system comprising: at least one chamber having an inlet for receiving water to be treated and an outlet for discharging treated water; a first device configured to administer a biocide to 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; a controller operatively connected to the first device and the second device; The control device receiving output data relating to the determined rH1 and rH2 from the second device; determining the difference between rH1 and rH2, and designating said difference as system ΔrH; comparing the system ΔrH to a predefined target ΔrH, the predefined target ΔrH corresponding to a desired disinfection performance in the water treatment system; The system is constructed and arranged to adjust the amount of biocide administered to the water based on deviation of the system ΔrH from the target ΔrH.

[0013] Preferred features for all aspects of the invention are defined in the dependent claims.

[0014] The methods and systems defined in this disclosure are particularly useful in wastewater treatment and in treating process water in paper mills.

[0015] The inventors have unexpectedly discovered a strong correlation between ΔrH and disinfection performance in a water treatment system, such that biocide dosage can be adjusted based on the system ΔrH to ensure that microbial levels remain within a desired range and avoid overdosing of biocide, which could violate environmental regulations.

[0016] To assist in understanding the present disclosure and to show how embodiments may be put into practice, reference will now be made, by way of example only, to the accompanying drawings in which: [Brief explanation of the drawings]

[0017] [Figure 1] 1 is a schematic diagram showing a water treatment system according to an example of the present invention. [Figure 2]1 is a schematic block diagram illustrating a control device according to an example of the present invention. [Figure 3] 1 is a graph showing PFA-mediated killing efficacy versus ΔrH in paper mill water. [Figure 4] 1 is a graph showing monochloramine (MCA)-mediated killing efficacy versus ΔrH in paper mill water. [Figure 5] 1 is a graph showing PFA-mediated killing efficacy versus ΔrH in wastewater treatment plant water. [Figure 6A] 1 is a line graph showing the correlation between ORP and residual biocide concentration. [Figure 6B] 1 is a line graph showing the correlation between rH and residual biocide concentration. [Figure 6C] 1 is a line graph showing the correlation between ΔrH and concentration of residual biocide. DETAILED DESCRIPTION OF THE INVENTION

[0018] Regardless of biocide technology, disinfection performance is primarily determined by the residual biocide concentration. As used in this disclosure, the term "residual biocide concentration" refers to the concentration of biocide remaining after contact (or exposure) with the water being treated. Therefore, consistent disinfection performance can be achieved if a threshold residual biocide concentration is dynamically maintained during the disinfection process. However, with regard to the use of percarboxylic acids as biocides in wastewater treatment systems, fluctuations in water quality and volume, as well as numerous side reactions between the biocide and contaminants in the water, can reduce the residual biocide concentration and, consequently, adversely affect disinfection performance. For example, when added to wastewater, PFA and PAA are initially consumed rapidly (i.e., instantaneous disinfection demand) followed by a more gradual decay. Poor water quality or contaminants in the water can accelerate the initial consumption and subsequent decay. As a result, dosing strategies that do not consider conditions affecting demand and / or decay can result in insufficient disinfection performance and violations of regulated microbial limits.

[0019] As previously mentioned, the present invention provides a method for controlling biocide dosing in a water treatment system, the method comprising: administering a biocide to the water to be treated; determining rH prior to administration of the biocide to obtain a first rH value (rH1); determining rH after the biocide administration to obtain a second rH value (rH2); determining the difference between rH1 and rH2, and designating said difference as system ΔrH; comparing the system ΔrH to a predefined target ΔrH, the predefined target ΔrH corresponding to a desired disinfection performance in the water treatment system; adjusting the amount of biocide administered to the water based on deviation of the system ΔrH from the target ΔrH.

[0020] In this disclosure, a "biocide" is a chemical substance that is effective in destroying, inhibiting, rendering harmless, or controlling the growth of harmful organisms.

[0021] In some embodiments, a biocide may include a disinfectant, which, as used herein, refers to a chemical substance that is effective in destroying, inhibiting, rendering harmless, or controlling the growth of at least one microorganism selected from bacteria, bacterial spores, fungi, viruses, and protozoa.

[0022] The biocide may be any biocide that can increase the oxidation-reduction potential (ORP) of water when added to the water. In a preferred example, the biocide comprises an oxidizing biocide. The oxidizing biocide may be selected from one or more of monochloramine (MCA), chlorine dioxide, percarboxylic acid, alkali and alkaline earth hypochlorites, halogenated hydantoins such as monochlorodimethylhydantoin (MCDMH) and bromochlorodimethylhydantoin (BCDMH), chlorine gas, and ozone. Preferably, the oxidizing biocide comprises a percarboxylic acid. Preferably, the percarboxylic acid comprises performic acid (PFA) and / or peracetic acid (PAA). In a preferred example, the oxidizing biocide comprises a PFA. In another example, the biocide comprises a non-oxidizing biocide. The non-oxidizing biocide may comprise 2,2-dibromo-3-nitrilopropionamide (DBNPA).

[0023] As one skilled in the art will appreciate, rH corresponds to the pH and temperature adjusted oxidation-reduction potential (ORP). In certain instances, rH may be calculated using the following formula: rH=2·pH+2·Eh·F / (2.3026·R·T) During the ceremony: Eh = oxidation-reduction potential (V) measured using a standard hydrogen electrode F = Faraday constant (96485 C mol -1 ) R = gas constant (8.314 J K -1 mol -1 ) T=temperature (K)

[0024] The pH of the water may be determined using a standard pH probe or pH meter. The ORP may be measured using a standard sensor or electrode. The temperature of the water may be measured using a standard thermometer. Thus, as described below, determining rH in the context of the present invention may include measuring pH, temperature, and ORP at relevant times and / or locations. In preferred examples, the pH, temperature, and ORP are determined simultaneously. In other examples, the pH, temperature, and ORP are determined consecutively (in any order) within a time period of 5 seconds, 10 seconds, 20 seconds, 30 seconds, 1 minute, 5 minutes, or 10 minutes. In further examples, the water treatment system is maintained at a constant set temperature, so that an additional temperature measurement may not be necessary to determine rH. In these examples, the pH and ORP may be measured simultaneously or consecutively, as described above.

[0025] In a further example, one or more of pH, temperature, and ORP are measured online. In another example, one or more of pH, temperature, and ORP are measured inline. In a further example, each of pH, temperature, and ORP is determined online or inline, preferably by measurement. Both online and inline measurements are forms of continuous in-situ measurement. Online measurements are not performed directly in the main process line, but rather in a built-in branch or bypass (e.g., sampling loop) that is automatically supplied with a sample of treated water. Inline measurements are performed directly in the main process line, requiring an associated probe or sampling interface to be placed directly in or in line with the process flow.

[0026] In the method of the present invention, rH is determined before the administration of a biocide to obtain a first rH value (rH1). In the context of the present invention, determining rH1 may require simultaneous measurement of pH, temperature, and ORP at a predetermined time point, or sequential measurement (in any order) within a predetermined period. rH1 may be determined at any time before the administration of a biocide, but to improve the accuracy of the method, it is preferable to minimize the time between the determination of rH1 and the addition of the biocide. In some examples, rH1 is determined 30 seconds, 1 minute, 5 minutes, 10 minutes, 20 minutes, or 30 minutes before the biocide is introduced into the water. In these examples, rH1 may be determined by simultaneously measuring pH, temperature, and ORP at the above-mentioned times. Alternatively, pH, temperature, and ORP may be measured sequentially (in any order), with the aforementioned time corresponding to the average time of the three measurements. Thus, for example, if pH is determined 35 seconds before biocide administration, temperature is determined 30 seconds before biocide administration, and ORP is determined 25 seconds before biocide administration, rH1 may be considered to have been determined 30 seconds before biocide administration ((35 + 30 + 25) / 3). When pH, temperature, and ORP are measured sequentially, it is desirable to take three measurements within a time period of 5 seconds, 10 seconds, 20 seconds, 30 seconds, 1 minute, 5 minutes, and 10 minutes. When pH, temperature, and ORP are measured sequentially, the three measurements are preferably taken within a time period of 10 minutes or less.

[0027] In another example, rH1 is determined immediately before the biocide is administered to the water. In a continuous flow system, rH1 may be determined at a location upstream of the point at which the biocide is administered to the water. The time corresponding to the above-specified time is determined based on the water flow rate (e.g., the number of flowing water m 3 / min) and the volume of the vessel through which the water flows to the point of biocide addition (e.g., m 3 Therefore, for example, after determining rH1, the 3 / min flow rate and volume of 10m 3If the water travels through a section of the vessel equivalent to rH1, then rH1 has been determined 5 minutes before biocide addition. pH, temperature, and OPR probes or sensors can be placed accordingly in appropriate locations within the water treatment system to achieve the required measurement time.

[0028] If the temperature of the water treatment system is maintained at a constant set level, it may not be necessary to further measure the temperature to determine rH1. In these cases, pH and ORP, as defined above, may be measured simultaneously or sequentially to determine rH1.

[0029] In the method of the present invention, a second rH is determined after administration of a biocide to obtain a second rH value (rH2). The rH2 may be determined after a predetermined contact time (i.e., the time after adding the biocide to the water). In the context of the present invention, determining rH2 at a given time may require simultaneous measurement of each of pH, temperature, and ORP at a given time, or sequential measurements (in any order) within a given period of time.

[0030] 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 preferred examples, rH2 is determined after a contact time of 1 minute to 5 minutes or 3 minutes to 5 minutes. In these examples, rH2 may be determined by simultaneously measuring pH, temperature, and ORP at the above-mentioned times. Alternatively, pH, temperature, and ORP may be measured sequentially (in any order) such that the aforementioned times correspond to the average time of the three measurements. Thus, for example, if pH is determined 5 seconds after biocide administration, temperature is determined 15 seconds after biocide administration, and ORP is determined 25 seconds after biocide administration, rH2 may be considered to have been determined 15 seconds after biocide administration ((5 + 15 + 25) / 3). When measuring pH, temperature, and ORP consecutively, it is desirable to obtain the three measurements within 5 seconds, 10 seconds, 20 seconds, 30 seconds, and 1 minute.When measuring pH, temperature, and ORP consecutively, it is desirable to obtain the three measurements within 10 minutes.

[0031] In a continuous flow system, the contact time corresponding to the time set forth above is determined by the water flow rate (e.g., the number of flowing water m 3 / min) and the volume of the vessel through which the water has passed downstream of the point of biocide addition (e.g., m 3 Thus, for example, if a biocide is added at 20 ml 3 The container part equivalent to the volume of 2m 3 If the water is moving at a flow rate of 1 / min, the contact time at the end of the vessel section may be calculated to be 10 minutes. pH, temperature, and OPR probes or sensors may be placed accordingly in the water treatment system at appropriate locations to achieve the required measurement time.

[0032] If the temperature of the water treatment system is maintained at a constant set level, it may not be necessary to additionally measure temperature to determine rH2. In these cases, pH and ORP, as defined above, may be measured simultaneously or sequentially to determine rH2.

[0033] The period for determining rH1 and rH2 should coincide with the period for determining the target ΔrH, as described below, allowing for effective control of biocide dosage.

[0034] Once rH1 and rH2 are determined, the difference between rH1 and rH2 is determined, and this difference is represented as ΔrH and referred to as the "system ΔrH." In a preferred example, ΔrH may be determined by subtracting rH1 from rH2 (i.e., rH2-rH1) or by subtracting rH2 from rH1 (i.e., rH1-rH2). With respect to the system ΔrH and the predefined target ΔrH, the difference between rH1 and rH2 is determined in the same manner, except that only absolute values ​​are considered. In other words, if the predefined target ΔrH is based on rH2-rH1, then the system ΔrH will also be based on rH2-rH1. Conversely, if the predefined target ΔrH is based on rH1-rH2, then the system ΔrH will also be based on rH1-rH2.

[0035] Target ΔrH In the methods of the present invention, the system ΔrH is compared to a target ΔrH, and based on deviation of the system ΔrH from the target ΔrH, the dosage of the biocide may be adjusted to allow for optimal biocidal performance, which refers to the killing efficacy of the biocide.

[0036] The inventors unexpectedly discovered a strong, positive, and consistent correlation between ΔrH and residual biocide concentration in a water treatment system. As noted above, the term "residual biocide concentration," as used herein, refers to the concentration of biocide in a system after a period of contact (or exposure) with the water to be treated. The residual biocide concentration indicates the system's disinfection performance. As the residual biocide concentration decreases, the risk of microbial growth increases. Measuring and monitoring residual biocide concentration is often difficult, for example, due to the need for complex equipment. Furthermore, residual biocide measurements are often based on color reactions that can be affected by water turbidity. Therefore, by eliminating the need to directly measure residual biocide concentrations, the present invention provides a valuable method for achieving and maintaining optimal disinfection performance.

[0037] The target ΔrH is defined based on the desired disinfection performance of the water treatment system in which the disinfectant injection control method is implemented. 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 acceptable tolerance limits for the target ΔrH value. In some examples, the acceptable tolerance limits may be ±1%, 5%, 10%, or 20% of the target ΔrH value. The target ΔrH may be determined by a suitable calibration method, in which varying concentrations of the relevant biocide are tested and the resulting kill efficacy and ΔrH are determined. ΔrH may be determined as described above. When setting the target ΔrH, the time periods for determining rH1 and rH2 for the biocide addition time points at each tested biocide concentration are typically aligned with the time periods selected for determining rH1 and rH2 to obtain the system ΔrH. Kill efficacy may be determined by enumerating bacteria using standard methods, such as agar plate or colony counting. A ΔrH value or range of values ​​that results in acceptable or desired killing efficacy may be used to define a target rH.

[0038] In some examples, the target ΔrH may alternatively or additionally be defined based on a correlation between ΔrH and residual biocide concentration. In these examples, the target ΔrH may be determined by a suitable calibration method, in which varying concentrations of the relevant biocide are tested and the resulting residual biocide concentration and ΔrH are determined. Thus, the target ΔrH may correspond to an optimal concentration or concentration range of residual biocide that provides the required biocidal performance.

[0039] In some examples, the predefined target ΔrH value may be, based on absolute value, 1 to 15, or 10 to 15, or 12 to 15. In other examples, the target ΔrH value may be, based on absolute value, 2 to 10, or 2 to 8, or 2 to 6, or 2 to 4, or 4 to 10, or 4 to 8, or 4 to 6, or 6 to 10, or 6 to 8, or 8 to 10. In examples where the predefined target ΔrH is a range of ΔrH values, based on absolute value, the lower limit of the range may be 1 or greater and the upper limit of the range may be 15 or less. In other examples, the lower limit may be 10 or greater and the upper limit may be 15 or less, or the lower limit may be 12 or greater 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, or 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.

[0040] In wastewater treatment systems, where significant microbial reduction is typically required, the target ΔrH may be set relatively high. In wastewater treatment systems, the target ΔrH (either a single value or a range of values ​​defining acceptable tolerance limits) may be based on an absolute value, between 5 and 15. In other systems, such as paper production plants (paper mills), the target ΔrH may be lower. For example, in a paper mill, the target ΔrH (either a single value or a range of values ​​defining acceptable tolerance limits) may be based on an absolute value, between 1 and 5.

[0041] If the system ΔrH (determined by rH2-rH1) is lower than a predefined target ΔrH value or is lower than the minimum value of the range of target ΔrH values, the dosage of biocide may be increased to return ΔrH to the target ΔrH value or to a value within the target ΔrH value range so that sufficient disinfection performance is achieved. If the system ΔrH (determined by rH2-rH1) is higher than a predefined target ΔrH value or exceeds the maximum value of the range of target ΔrH values, the dosage of biocide may be decreased to return ΔrH to the target ΔrH value or to a value within the target ΔrH value range so as to prevent the accumulation of unused biocide.

[0042] If the system ΔrH (determined by rH1-rH2) is lower than a predefined target ΔrH value or is lower than the minimum value of the range of target ΔrH values, the dosage of biocide may be reduced to return ΔrH to the target ΔrH value or to a value within the target ΔrH value range, thereby preventing the accumulation of unused biocide. If the system ΔrH (determined by rH1-rH2) is higher than a predefined target ΔrH value or exceeds the maximum value of the range of target ΔrH values, the dosage of biocide may be increased to return ΔrH to the target ΔrH value or to a value within the target ΔrH value range, thereby achieving sufficient disinfection performance.

[0043] In other examples, if the system ΔrH (determined by rH2-rH1 or rH1-rH2) is lower than a predefined target ΔrH value or falls below the minimum value of a range of target ΔrH values, the dosage of biocide may be increased to return ΔrH to the target ΔrH value or to a value within the target ΔrH value range so that sufficient disinfection performance is achieved. If the system ΔrH (determined by rH2-rH1 or rH1-rH2) is higher than a predefined target ΔrH value or exceeds the maximum value of a range of target ΔrH values, the dosage of biocide may be decreased to return ΔrH to the target ΔrH value or to a value within the target ΔrH value range, thereby preventing the accumulation of unused biocide. In these examples, the system ΔrH value, the predefined target ΔH value, and the predefined target range of ΔrH values ​​are expressed as corresponding absolute values.

[0044] In some examples, the system ΔrH is monitored to detect deviations from a predefined target ΔrH, and biocide dosage is adjusted without delay. This prevents undesirable increases in microbial growth (when the system's disinfection performance falls below acceptable levels) or excessive biocide use (when biocide demand decreases). Therefore, the system ΔrH may be determined and monitored continuously. "Continuously" in this context means at regular intervals without pauses or interruptions. In some examples, 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 may be determined every 1 minute, 2 minutes, 3 minutes, 4 minutes, 5 minutes, 10 minutes, 20 minutes, or 30 minutes.

[0045] The deviation between the system ΔrH and the target ΔrH may be any magnitude. In some examples, biocide dosage is adjusted when there is at least a 5%, at least a 10%, or at least a 20% deviation from a predefined target ΔrH value, or when there is at least a 1%, 2%, 5%, or 10% deviation from the minimum or maximum of a range of predefined target ΔrH values. This may prevent biocide dosage adjustments when there is negligible variation in the system ΔrH due to experimental error or minor changes in process conditions. In other examples, biocide dosage adjustments are not performed when the system ΔrH does not deviate from the target ΔrH value, or when there is less than a 5%, 10%, or 20% deviation from a predefined target ΔrH value, or when there is less than a 1%, 2%, 5%, or 10% deviation from the minimum or maximum of a range of predefined target ΔrH values.

[0046] Adjusting the biocide dosage in response to the system ΔrH may be accomplished in a variety of ways. In some examples, the biocide is supplied to the water being treated via a biocide line. The biocide line may include one or more pumps. When an increased biocide dosage is required as determined by the system ΔrH, the speed of one or more pumps may be increased. Conversely, when a decreased biocide dosage is required as determined by the system ΔrH, the speed of one or more pumps may be decreased. Other means of controlling the biocide dosage are also contemplated, such as a valve that can be opened or closed to increase or decrease the biocide dosage.

[0047] The inventors unexpectedly discovered that system ΔrH is a more effective parameter for determining the residual biocide concentration and resulting biocidal performance of an aqueous system than either rH or oxidation-reduction potential (ORP). The correlation between ΔrH and residual biocide concentration is much stronger and more consistent than the correlation between rH and residual biocide concentration or the correlation between ORP and residual biocide concentration. As previously discussed, low residual biocide concentrations increase the risk of microbial growth. Increased water temperature can also promote microbial growth, increasing biocide consumption and decreasing ΔrH. Increased organic loads can also consume biocide, thereby decreasing ΔrH. Thus, ΔrH is highly dependent on factors that affect residual biocide concentration, which in turn can affect the disinfection performance of a system.

[0048] rH and ORP may vary with water quality and process conditions, independent of residual biocide concentration. Thus, within a given system, rH and ORP may vary over time, and accordingly, rH- or ORP-based targets determined to provide an acceptable level of biocidal performance under an initial set of conditions may need to be periodically reset as conditions change. In contrast, ΔrH is a more robust indicator and is more resistant to changes in water quality, so once a target ΔrH value or range of values ​​that provides an acceptable level of biocidal performance for a given system is established, that target value can be maintained and used as a reference point for a relatively long period of time without further calibration.

[0049] Furthermore, the inventors have found that measuring rH2 within 5 minutes after biocide addition (or, for continuous systems, the equivalent distance within 5 minutes after biocide addition) improves discrimination between effective and poor biocide performance, thereby allowing for more effective biocide dosing control in this time frame. In particular, as shown in the Examples below, the increase in ΔrH observed with increasing biocide dosing is greater when rH2 is determined after 5 minutes or less of contact time from biocide addition compared to when rH2 is determined after longer contact times.

[0050] Untreated water The water to be treated in the method of the present invention is not particularly limited and may be any water or aqueous solution that requires sterilization treatment. The water to be treated may be raw water (e.g., surface water from a lake, sea, or river), wastewater, industrial water, and / or wastewater.

[0051] Wastewater may include municipal wastewater, industrial wastewater, or a mixture thereof. In some examples, wastewater may include sewage. Industrial water may include process water used in industrial processes or facilities associated with, for example, the pulp and paper industry, oil industry, gas industry, mining industry, food industry, or other applicable industries. In some examples, industrial water may include recycled water from a paper or paperboard mill. The water to be treated typically contains one or more contaminants, such as bacteria, viruses, or other non-living organic matter.

[0052] Water treated by the method of the present invention may be discharged to the environment, subjected to further purification steps, or, in the case of process water, reused in a process similar to or different from the original process. In one example, recycled water from a paper or paperboard manufacturing process that has been treated with a biocide according to the method of the present invention is reused in paper or paperboard manufacturing. In another example, wastewater treated with a biocide according to the method of the present invention is reused in agriculture.

[0053] wastewater treatment In a preferred example, the method for controlling biocide dosage according to the present invention may be implemented in a wastewater treatment system or plant. The wastewater to be treated may include municipal wastewater, sewage, and / or industrial wastewater.

[0054] Generally, municipal wastewater or sewage treatment involves a series of steps: preliminary, primary, secondary, and tertiary treatment, which are well known to those skilled in the art of wastewater treatment and water purification, and are further described below.

[0055] Preliminary treatment may involve removing coarse, large suspended solids from raw sewage or wastewater, for example by screening and / or grinding, that can be easily collected before they damage or block the pumps and sewer lines of the primary treatment equipment.

[0056] Primary treatment is designed to remove coarse, suspended, and suspended solids from raw sewage or wastewater. Primary treatment may involve screening to capture solids and gravity settling to remove suspended solids, which are removed and collected as sludge.

[0057] After primary treatment, wastewater may proceed to secondary treatment, which typically involves biological treatment steps and sedimentation. Specifically, primary effluent may be subjected to activated sludge treatment technology, in which the wastewater is aerated and aerobic microorganisms metabolize organic matter to carbon dioxide and water, multiplying to form a microbial community. Organic nitrogen compounds may be converted to ammonia and then to nitrates. A secondary settling tank can flocculate the microorganisms and solid waste and settle them as sludge. At least a portion of the recovered sludge (activated sludge) can then be reused as inoculum for further biological treatment of influent wastewater.

[0058] In many cases, primary and secondary treatment are sufficient; not all wastewater treatment plants employ tertiary treatment. Those that do achieve more stringent cleanliness levels to meet the strict standards governing water reuse, especially in public water supplies. Tertiary treatment is also beneficial when facilities must discharge water into sensitive or fragile ecosystems (e.g., estuaries, low-flow rivers, coral reefs, etc.). Tertiary treatment may include filtration, disinfection, and nitrogen and phosphorus removal.

[0059] In a preferred example, the biocide is administered to the wastewater after secondary treatment. The administration of the biocide is considered tertiary treatment. Therefore, rH1 and rH2 are determined before and after the administration of the biocide. Alternatively or additionally, the biocide may be injected into the influent or effluent of primary treatment. It may also be injected into the influent or effluent of secondary treatment, but only if additional disinfection is required at these stages.

[0060] Biocide administration In continuous water systems, biocides may be fed to the water continuously (i.e., without pauses) or at regular, predetermined intervals. The dosing of biocides may also be automated. For example, a biocide containing a percarboxylic acid, such as PFA, may be dosed to water, e.g., wastewater, at a basal dosing concentration (i.e., the active biocide concentration in the water being treated at the point of delivery) of 1-2 mg / L. For chlorine-based biocides, the basal dosing concentration based on total active chlorine may be 1 mg / L to 4 mg / L for wastewater, 1 mg / L to 4 mg / L for freshwater, and 5 mg / L to 10 mg / L for paper mill process water. The basal dosing concentration may then be adjusted based on changes in disinfection demand, as determined by changes in system ΔrH.

[0061] 1, in some examples, a method for controlling biocide administration is performed in a water treatment system 1 that includes at least one chamber 2 having an inlet for receiving water to be treated and an outlet for discharging treated water, a first device 16 configured to administer a biocide to the water in at least one chamber 2 via line 17, a second device 19 configured to measure pH, ORP, and temperature and to determine rH1 and rH2 based on the measured pH, ORP, and temperature, and a controller 18 operably connected to first device 16 and second device 19. As used herein, a "device" refers to any device, including a mechanical or electrical device, capable of performing a specified function and may include multiple devices. Thus, for example, second device 19 in a system of the present invention may include a probe for measuring pH, a probe for measuring ORP, and a thermometer.

[0062] In a preferred example, the controller 18 is constructed and arranged to receive output data from the second device 19 regarding the determined rH1 and rH2, calculate the difference between rH1 and rH2, which is the system ΔrH, compare the system ΔrH to a predefined target ΔrH corresponding to the disinfection performance desired in the water treatment system, and adjust the amount of biocide administered to the water based on the deviation of the system ΔrH from the target ΔrH.

[0063] In a water treatment system, a biocide may be supplied to the water in the chamber via a biocide line 17. The biocide line may have one or more pumps or valves 17a to control the flow of biocide into the water. When the system ΔrH deviates from the target ΔrH, a controller 19 can increase or decrease the flow rate of one or more pumps or open or close one or more valves to adjust the dosage of biocide into the water.

[0064] Thus, the controller may comprise a computer device. In one example, a controller is provided that includes at least one processor and at least one memory containing computer program code, the at least one memory and the computer code, together with the at least one processor, configured to cause the device to perform any of the methods described herein.

[0065] FIG. 2 is a block diagram of a controller 18 according to one example of the present invention. The controller 18 is suitable for implementing at least a portion of the operations described herein. With particular reference to FIG. 2, the controller 18 may include at least one processor 28, at least one memory 29, a communications interface 32, and a user interface 31. The controller may further include other internal circuitry and components necessary to perform the tasks described herein. The controller 18 may be constructed and arranged to receive output data including a system ΔrH measurement from the second device 19 and adjust the delivery of biocide from the first device 16. In some examples, the controller 18 may be constructed and arranged to monitor the system ΔrH and adjust the dosing of biocide based on the monitored ΔrH.

[0066] The controller 18 may include a communications interface 32 for connecting the controller to a data communications system and enabling data communications with the device. The communications interface 32 may include wired and / or wireless communications circuitry, such as Ethernet, WLAN, Bluetooth, GSM, CDMA, WCDMA, LTE, 5G circuitry, and / or analog. The communications interface may be integrated into the controller 18 or may be provided as part of an adapter, card, or the like that can be attached to the controller 20. The communications interface 32 may support one or more different communications technologies. The controller 18 may also include multiple communications interfaces 32.

[0067] The user interface 31 may include circuitry for receiving input from a user of the controller 18, for example, via a keyboard, a graphical user interface displayed on a display of the device, voice recognition circuitry, or an accessory device such as a headset, and for providing output to the user, for example, via a graphical user interface and a speaker. The controller may also be operated remotely.

[0068] The at least one processor 28 may be coupled to at least one memory 29. The at least one processor 28 may be configured to execute appropriate computer program code for implementing one or more aspects described herein. The 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.

[0069] The at least one memory 29 may comprise a working memory 30 and a persistent (non-volatile, N / V) memory 33 configured to store program code 34 and data 35. The memory 33 may comprise any one or more of read-only memory (ROM), programmable read-only memory (PROM), erasable programmable read-only memory (EPROM), random access memory (RAM), flash memory, data disks, optical storage, magnetic storage, smart cards, solid-state drives (SSD), etc. The controller 18 may be configured with other possible components for use in software- and hardware-assisted execution of the tasks it is designed to perform.

[0070] The controller 18 may include multiple memories 33. The memories 33 may be constructed as part of the controller 18 or as attachments that are inserted into slots, ports, or the like of the controller 18 by a user, another person, or a robot. The memories 33 may serve the sole purpose of storing data, or may be constructed as part of the controller 18 that serves other purposes, such as data processing.

[0071] Those skilled in the art will appreciate that, in addition to the elements shown in Figure 2, controller 18 may include other elements such as a microphone and a display, as well as additional circuitry including input / output (I / O) circuitry, memory chips, application-specific integrated circuits (ASICs), and application-specific processing circuitry (e.g., source encoding / decoding circuitry, channel encoding / decoding circuitry, encryption / decryption circuitry, etc.). Additionally, controller 18 may include a disposable or rechargeable battery (not shown) for powering device 18 when an external power source is unavailable. Furthermore, while only one device 18 is shown in Figure 1, it should be noted that in some embodiments, the illustrated devices may similarly be implemented in a cluster.

[0072] In some examples, the controller 18 may be configured to receive input of a particular parameter, e.g., a predefined target ΔrH, which may be a single ΔrH value or a range of ΔrH values, as described above. 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 controller 18 may detect that the system ΔrH deviates from the predefined target ΔrH.

[0073] If the system ΔrH falls below a predefined target ΔrH value or below the minimum value of a range of target ΔrH values ​​(where ΔrH is determined by rH2-rH1), as may occur during periods of increased disinfection demand, the controller 18 may in response cause the first device 16 to increase the supply of biocide to the water to be treated for a specified period of time to restore the residual biocide concentration and thus restore the system ΔrH to the predefined target value. This may be accomplished by increasing the flow rate of one or more pumps 17a in the biocide supply line 17 or by opening one or more valves 17a in the biocide supply line 17, as described above.

[0074] Conversely, if the system ΔrH exceeds a predefined target ΔrH value or exceeds the maximum value of a range of target ΔrH values ​​(where ΔrH is determined by rH2-rH1), as may occur, for example, when disinfection demand decreases, the controller 18 may in response cause the first device 16 to reduce the supply of biocide to the water to be treated for a specified period of time to restore the residual biocide concentration and thus restore the system ΔrH to the predefined target value. This may be accomplished by reducing the flow rate of one or more pumps 17a in the biocide supply line 17 or by closing one or more valves 17a in the biocide supply line 17, as described above.

[0075] Corresponding control measures would also apply if ΔrH is determined by rH1-rH2.

[0076] As previously mentioned, suitable computer program code 34, when executed by processor 28 and stored in memory 29, may determine, based on output measurement data received from second device 19, whether the system ΔrH deviates from a predefined target ΔrH and the necessary adjustments to the amount of biocide supplied to the water to restore ΔrH to the predefined target ΔrH. Accordingly, controller 18 may be constructed and arranged to compare the system ΔrH with the predefined target ΔrH, and may also be constructed and arranged to adjust the performance of first device 16.

[0077] In an example of the present invention, the at least one processor 28 may comprise a proportional-integral-derivative (PID) controller. A PID controller is a feedback-based control loop mechanism widely used in industrial control systems and various other applications requiring continuous modulation control. The PID controller may continuously calculate an error value as the difference between a predefined ΔrH and the system ΔrH, and then apply a correction based on proportional, integral, and derivative terms. The controller may attempt to minimize the error over time by adjusting the output (e.g., by adjusting the flow rate of one or more pumps 17a) to maintain a predefined target ΔrH. In another example, a PI (proportional, integral)-based controller is used.

[0078] In systems that specifically use biocides containing PFA, the instability and rapid decomposition time of PFA may require that the PFA be generated immediately before use. Preferably, the PFA may be generated on-site (i.e., within the water treatment system itself) by a first device. Thus, the first device of the water treatment system may comprise a reaction vessel in which the PFA is produced. In other embodiments, the PFA may be produced outside the water treatment system and transferred directly and rapidly to the first device for delivery to the water. A preferred method for preparing PFA involves combining formic acid with hydrogen peroxide, optionally in the presence of an acid catalyst such as sulfuric acid, ascorbic acid, or boric acid, according to reaction (2): The equilibrium in reaction (2) may be shifted in favor of PFA formation by increasing the molar ratio of formic acid to hydrogen peroxide or by removing water from the reaction. [ka]

[0079] A commercially available device for the generation and delivery of PFA is the KemConnect™ DEX.

[0080] In systems that synthesize PFA (or other biocides) in situ, an additional level of control may be provided. For example, if the system ΔrH is found to deviate from a predefined target ΔrH and a biocide dosage adjustment is required, this adjustment may be achieved by increasing or decreasing the feed rate of the reagents formic acid and hydrogen peroxide to the reaction vessel, thereby increasing or decreasing the rate of PFA production.

[0081] While at least some aspects of the embodiments described herein with reference to the drawings involve computer processes executed on a processing system or processor, the present invention is not limited thereto and extends to a computer program on or in a medium, particularly adapted for carrying out the present invention. The program may be in the form of non-transitory source code, object code, an intermediate form between source code and object code (e.g., a partially compiled form), or any other non-transitory form suitable for carrying out the processes of the present invention. The medium may be any object or device capable of carrying a program. For example, the medium may include a storage medium such as a solid-state drive (SSD) or other semiconductor-based RAM; a ROM, e.g., a CD-ROM or semiconductor ROM; a magnetic recording medium, e.g., a floppy disk or hard disk; optical memory devices in general, etc.

[0082] The following are examples only and are not intended to limit the present disclosure. [Example]

[0083] Example 1 - Paper Mill (PFA) Process water from a paper mill producing board from recycled fibers was used in this study. 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 the rH was measured 5 minutes and 30 minutes after dosing for each PFA concentration during the test. Accordingly, the ΔrH was determined. The total aerobic bacterial count (using a standard agar plate method) was also measured 30 minutes after dosing. The tests were performed at a room temperature of +22°C.

[0084] Table 1 and Figure 3 show that when ΔrH is 1.0 or greater in PFA-treated samples, the killing efficacy is greater than 2 log units, sufficient for this application. When ΔrH is 0.7 units, the killing efficacy is lower (less than 1 log unit). Therefore, a ΔrH of approximately 1 is optimal for PFA dosage. The data also demonstrate that measuring rH 5 minutes after administration improves discrimination between the doses of PFA tested.

[0085] [Table 1]

[0086] Example 2 - Paper Mill (MCA) Example 1 was repeated using various doses of MCA, and the results are shown in Table 2 and Figure 4.

[0087] [Table 2]

[0088] Table 2 and Figure 4 show that when ΔrH is approximately 2.0 for MCA-treated samples, the killing efficacy is greater than 2 log units, sufficient for this application. Thus, a ΔrH of approximately 2 provides optimal dosage for MCA. The data also demonstrate that measuring rH at 5 minutes post-dose improves discrimination between the doses of PFA tested.

[0089] Example 3 - Wastewater Treatment Plant Biocidal efficacy testing using PFA was conducted at a wastewater treatment plant treating both municipal and industrial wastewater. Sieved but otherwise untreated wastewater was treated with PFA online. The first sample was taken before PFA dosing began. Five ppm of PFA (active) was then added, and 10 minutes after addition, OPR, pH, and temperature were measured and rH determined. The PFA dose was then increased to 10 ppm before another rH determination was performed. The PFA was rapidly cooled at the 10-minute sampling point to prevent further biocidal activity and changes to rH. The following day, each sample was counted on agar plates for total coliforms, E. coli, enterococci, and total aerobic bacteria. Testing was performed at room temperature (22°C). Table 4 and Figure 5 show the results.

[0090] [Table 4]

[0091] It can be seen that a ΔrH value of 12.6 corresponding to 10 ppm PFA provided sufficient killing efficacy against the bacterial species measured, reducing pathogenic bacteria (coliforms, E. coli, and enterococci) to very low levels. The untreated wastewater had very high initial bacterial concentrations (data not shown), and therefore, in this system, 5 ppm of active PFA, resulting in ΔrH values ​​of 5.71-7.29, was not sufficient to provide the required disinfection performance.

[0092] Example 4 - Correlation of ΔrH and biocide residue Online testing was conducted in a raw water treatment plant to evaluate the correlations between ΔrH, rH, ORP, and residual biocide concentrations. Hypochlorite (15–25 mg / L, 15% active) and dimethylhydantoin (10–20 mg / L, 15% active) were premixed to form halogenated hydantoins, which were continuously added to the water. rH was measured at regular time intervals corresponding to 1 minute before and 5 minutes after biocide addition, and the system ΔrH was established at these times. Residual biocide concentrations and ORP were also measured at the same time points after biocide addition.

[0093] FIG. 6A shows that there is a poor and inconsistent correlation between ORP and the concentration of residual biocide.

[0094] Figure 6B similarly shows a poor and inconsistent correlation between rH and residual biocide concentration.

[0095] Figure 6C shows a strong and consistent correlation between ΔrH and residual biocide concentration.

Claims

1. 1. A method for controlling biocide dosage in a treatment system, comprising: administering a biocide to the water to be treated; The rH of the water to be treated is determined prior to administration of the biocide to obtain a first rH value (rH １ ) and The rH of the water is determined after the biocide administration to obtain a second rH value (rH ２ ) and rH １ and rH ２ Determine the difference between the two, and call the difference the system ΔrH. comparing the system ΔrH to a predefined target ΔrH, the predefined target ΔrH corresponding to a desired disinfection performance in the water treatment system; A method for adjusting the amount of biocide administered to the water based on deviation of the system ΔrH from the target ΔrH.

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

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

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

5. 5. The method of 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. 10. The method of any preceding claim, wherein the predefined target ΔrH is a predefined target ΔrH value or a predefined target range of ΔrH values.

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

8. 8. The method of claim 6 or 7, wherein if the system ΔrH is lower than the predefined target ΔrH value or lower than a minimum value of the predefined range of ΔrH values, then increasing the amount of biocide administered to the water to increase the system ΔrH to the predefined target ΔrH value or to a value within the predefined range of ΔrH values; or if the system ΔrH is higher than the predefined target ΔrH value or exceeds the maximum value of the predefined range of ΔrH values, reduce the amount of biocide administered to the water to reduce the system ΔrH to the predefined target ΔrH value or to a value within the predefined range of ΔrH values; The method wherein the system ΔrH value, the predefined target ΔrH value, and the predefined target range of ΔrH values ​​are expressed in corresponding absolute values.

9. 10. The method of any of the preceding claims, comprising: ２ is determined when the contact time between the biocide and water is 10 seconds or more and 30 minutes or less.

10. 10. The method of claim 9, wherein rH ２ is determined when the contact time between the biocide and water is 1 minute or more and 5 minutes or less, or 3 minutes or more and 5 minutes or less, or 5 minutes.

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

12. 10. A method according to any preceding claim, comprising determining the pH, oxidation-reduction potential (ORP) and optionally the temperature of the water before and after administration of the biocide, and determining an rH based on the respective measurements of pH, temperature and ORP. １ and rH ２ How to determine.

13. 13. The method of claim 12, wherein rH １ and rH ２ is determined from the pH, the ORP, and the temperature using the following formula (1): rH=2・pH+2・Eh・F / (2.3026・R・T) During the ceremony: Eh = oxidation-reduction potential (V) measured using a standard hydrogen electrode F = Faraday's constant (96485 C mol －１ ) R = gas constant (8.314 J·K －１ ・mol －１ ) T=temperature (K)

14. 10. The method of any of the preceding claims, comprising: １ and rH ２ is determined from in-line or online measurements.

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

16. 10. The method according to any of the preceding claims, wherein the water to be treated comprises raw water, industrial water, and / or wastewater.

17. 17. The method of claim 16, wherein the wastewater comprises municipal wastewater, wastewater from pulp, paper or paperboard production, and / or wastewater from oil or gas production.

18. 18. A water treatment system for carrying out the method of any one of claims 1 to 17, comprising: at least one chamber having an inlet for receiving water to be treated and an outlet for discharging treated water; a first device configured to administer a biocide to the water in the at least one chamber; The pH, ORP, and temperature are measured, and the rH is calculated based on the measured pH, ORP, and temperature. １ and rH ２ a second device configured to determine a controller operatively connected to the first device and the second device; The control device the determined rH from the second device １ and rH ２ receiving output data relating to rH １ and rH ２ Determine the difference between the two, and call the difference the system ΔrH. comparing the system ΔrH to a predefined target ΔrH, the predefined target ΔrH corresponding to a desired disinfection performance in the water treatment system; 10. A water treatment system constructed and arranged to adjust the amount of biocide administered to said water based on deviation of said system ΔrH from said target ΔrH.

19. 19. The system of claim 18, wherein the controller comprises at least one processor and at least one memory containing computer program code, the at least one memory and the computer program code, together with the at least one processor, for transmitting the determined rH １ and rH ２ receiving the output data from the second device relating to rH １ and rH ２ to obtain the system ΔrH, comparing the system ΔrH to a predefined target ΔrH, and adjusting an amount of biocide administered to the water based on a deviation of the system ΔrH from the target ΔrH.

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