Water quality testing methods

Abstract

To provide a water quality measuring method capable of measuring an acid combustion amount or alkali consumption amount of a sample until a pH corresponding to the sample is reached, and capable of measuring a concentration of a component contained in the sample in addition to measuring an acidity or alkalinity.SOLUTION: A water quality measuring method for measuring an acid consumption amount or alkali consumption amount of a sample and a concentration of a component contained in the sample by titration comprises the steps of: setting a target pH corresponding to the sample; setting a pH range corresponding to the component contained in the sample; supplying a titrant to the sample after both the step of setting the target pH and the step of setting the pH range; calculating an acid consumption amount or alkali consumption amount of the sample based on an amount of titrant supplied to the sample after starting the supply of titrant to the sample until the pH of the sample reaches the target pH; and calculating a concentration of the component contained in the sample based on the amount of titrant supplied to the sample after starting the supply of titrant to the sample until the pH of the sample changes from an upper limit to a lower limit, or from the lower limit to the upper limit, of the pH range.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present disclosure relates to a water quality measurement method for measuring the acid consumption or alkali consumption of a sample and the concentration of components contained in the sample by titration.

Background Art

[0002] Patent Document 1 discloses a water quality measurement method for measuring the total alkalinity and total carbonate concentration in water, particularly in seawater. In this water quality measurement method, acid titration is performed on the test water (seawater) sealed in a sample bottle until a predetermined pH is reached, and the total alkalinity and total carbonate concentration are measured from the acid titration amount obtained from the result of this acid titration and the displacement of the pH electrode.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] When measuring the acid consumption or alkali consumption of a sample, a titrant may be supplied until the pH corresponding to this sample is reached. Also, when measuring the concentration of components contained in a sample from the amount of titrant supplied to the sample, the pH range for obtaining the amount of titrant varies depending on the component. However, with the technique described in Patent Document 1, it is not possible to obtain the acid consumption or alkali consumption of the sample until the pH corresponding to the sample is reached. Furthermore, if the pH range for concentration measurement deviates from the pH for measuring the acid consumption or alkali consumption, there is a risk that the concentration measurement cannot be performed together with the measurement of the acid consumption or alkali consumption.

[0005] This disclosure has been made in view of the above-mentioned problems, and aims to provide a water quality measurement method that can measure the amount of acid or alkali consumed by a sample until it reaches a pH corresponding to the sample, and that can measure the concentration of components contained in the sample along with the measurement of this acid or alkali consumption. [Means for solving the problem]

[0006] To achieve the above objectives, the water quality measurement method relating to this disclosure provides, by titration, the acid consumption or alkali consumption of a sample, and the components contained in the sample. These are volatile fatty acids and ammonia nitrogen. A water quality measurement method for measuring the concentration of, The aforementioned sample is the contents of a methane fermentation tank that produces methane gas by hydrolyzing waste materials and then breaking them down into smaller molecules using microorganisms. Based on the influence function that affects the rate of methane gas production in the methane fermentation tank, The method comprises the steps of: setting a target pH corresponding to the sample; setting a pH range corresponding to the components contained in the sample; supplying a titrator to the sample after both the step of setting the target pH and the step of setting the pH range; calculating the acid consumption or alkali consumption of the sample based on the amount of titrator supplied to the sample until the pH of the sample reaches the target pH, after the supply of the titrator to the sample has begun; and calculating the concentration of the components contained in the sample based on the amount of titrator supplied to the sample until the pH of the sample moves from the upper limit to the lower limit, or from the lower limit to the upper limit, after the supply of the titrator to the sample has begun. The target pH is pH 7, and the step of calculating the acid consumption or alkali consumption of the sample involves calculating the acid consumption of the sample based on the amount of titration supplied to the sample from the start of supplying the titration to the sample until the pH of the sample reaches pH 7, and the pH range includes a first pH range of pH 2.8 to 6.8, which corresponds to the volatile fatty acid. . [Effects of the Invention]

[0007] According to the water quality measurement method disclosed herein, it is possible to measure the amount of acid or alkali consumed by the sample until it reaches a pH corresponding to the sample, and it is possible to measure the concentration of components contained in the sample along with this acidity or alkalinity measurement. [Brief explanation of the drawing]

[0008] [Figure 1] This diagram schematically shows the configuration of a waste treatment system according to several embodiments. [Figure 2] This is a flowchart of the water quality measurement method according to the first embodiment. [Figure 3] This graph shows the relationship between the amount of sodium hydroxide aqueous solution supplied and the pH of the sample in the first embodiment. [Figure 4] This is a flowchart of the water quality measurement method according to the third embodiment. [Figure 5] This is a flowchart showing how to set up the first calibration curve. [Figure 6] This graph shows the relationship between the supply amount of aqueous sodium hydroxide solution and the concentration of volatile fatty acids in the third embodiment. [Figure 7] This is a flowchart showing how to set up the second calibration curve. [Figure 8] This graph shows the relationship between the supply amount of sodium hydroxide aqueous solution and the concentration of ammonia nitrogen in the third embodiment. [Figure 9] This graph shows the relationship between the acid dissociation constant and temperature. [Modes for carrying out the invention]

[0009] The water quality measurement method according to the embodiments of this disclosure will be described below with reference to the drawings. Such embodiments represent one aspect of this disclosure and are not limiting, and can be modified at will within the scope of the technical idea of ​​this disclosure.

[0010] The water quality measurement method described herein is a method for measuring the acid consumption or alkali consumption of a sample, and the concentration of components contained in the sample, by titration. In this disclosure, the acid consumption is a value calculated from the amount of acidic titrant supplied to the sample until a predetermined pH is reached. The alkali consumption is a value calculated from the amount of alkaline titrant supplied to the sample until a predetermined pH is reached. In this disclosure, the case in which the contents of a methane fermenter in a waste treatment system for purifying methane gas from waste are the sample measured by the water quality measurement method described herein is explained as an example. The sample is not particularly limited as long as it is a solution containing a solvent and a solute.

[0011] (Waste disposal system) FIG. 1 is a diagram schematically showing the configuration of a waste treatment system 1 according to some embodiments. As illustrated in FIG. 1, the waste treatment system 1 includes a reformer 2, a methane fermentation tank 4, and a water quality measuring device 6.

[0012] The waste W is, for example, municipal waste. Municipal waste mainly consists of food waste, paper waste, plastic waste, and contains a small amount of metal. Note that the present disclosure is not limited to municipal waste as the waste W. The waste W may have a higher water content than municipal waste, such as sludge generated by treating wastewater from factories or agricultural waste.

[0013] The reformer 2 hydrolyzes the waste W. The reformer 2, for example, directly receives the waste W from a vehicle or a plant that has collected the waste W and batch - hydrolyzes the waste W with steam. The hydrolysis of the waste W in the reformer 2 may be wet hydrolysis in which steam contacts the waste W to heat the waste W, or dry hydrolysis in which steam does not contact the waste W and indirectly heats the waste W. By hydrolyzing the waste W, the waste W is refined, the high - molecular components contained in the waste W are reduced to low - molecular components. Further, volatile fatty acids (VFA) such as acetic acid increase. Also, the organic nitrogen contained in the waste W is decomposed, increasing the ammonia - nitrogen (NH4 - N).

[0014] The reformed product X, which is the waste W hydrolyzed by the reformer 2, is to be supplied to the methane fermentation tank 4. The reformed product X contains a liquid and a solid. In one embodiment, the reformed product X has a high water content and is in a slurry state, for example, sludge.

[0015] The methane fermentation tank 4 reduces the molecular weight of the reformed product X supplied from the reformer 2 by microorganisms. More specifically, the methane fermentation tank 4 generates methane gas, which is a valuable substance, by reducing the molecular weight of the reformed product X through the biological action of microorganisms.

[0016] In some embodiments, as illustrated in FIG. 1, the methane fermentation tank 4 is provided with a circulation line 8 that takes out a part of the content Y1 of the methane fermentation tank 4 to the outside and returns it to the methane fermentation tank 4 again. This circulation line 8 connects an outlet 10 formed at the lower part of the methane fermentation tank 4 and an inlet 12 formed at an upper part located above the lower part of the methane fermentation tank 4. The circulation line 8 takes out a part of the content Y1 of the methane fermentation tank 4 to the outside of the methane fermentation tank 4 through the outlet 10. And through the inlet 12, a part of the content Y1 of the methane fermentation tank 4 flowing through the circulation line 8 is returned to the methane fermentation tank 4. Thus, by circulating a part of the content Y1 of the methane fermentation tank 4 through the circulation line 8, the content Y1 of the methane fermentation tank 4 is stirred.

[0017] The water quality measuring device 6 measures the acid consumption or alkali consumption of the content Y1 of the methane fermentation tank 4 and the concentration of the components contained in the content Y1 of the methane fermentation tank 4 by titration. Such a water quality measuring device 6 includes, as illustrated in FIG. 1, a sample acquisition device 14, a reaction tank 16, a dropping part 18, an antifoaming agent supply part 20, and a pH measuring device 22.

[0018] The sample acquisition device 14 acquires the content Y1 of the methane fermentation tank 4 from the methane fermentation tank 4 without filtration. In the form illustrated in FIG. 1, the sample acquisition device 14 includes a sample supply line 15 that connects the circulation line 8 and the reaction tank 16. The sample supply line 15 branches from the circulation line 8 and is configured such that a part of the content Y1 of the methane fermentation tank 4 flows from the circulation line 8 toward the reaction tank 16. A filtration device such as a filter is not provided in the sample supply line 15, and the sample acquisition device 14 supplies a part of the content Y1 of the methane fermentation tank 4 to the reaction tank 16 as a sample Y2 without filtration.

[0019] The reaction vessel 16 has a reaction chamber 17 inside into which the sample Y2 is supplied. The reaction vessel 16 is configured such that the amount of sample Y2 stored in the reaction chamber 17 is a predetermined amount. In the embodiment illustrated in Figure 1, the water quality measuring device 6 further includes a dilution unit 24 for supplying dilution water Y5, which can dilute the sample Y2, to the reaction chamber 17. For example, the sample Y2 supplied from the sample acquisition device 14 is diluted 2 times before measuring the acid consumption of the sample Y2. The dilution unit 24 is, for example, a dilution nozzle connected to a water supply. In this disclosure, when dropping is started, the 2-fold diluted sample Y2 is weakly alkaline, for example, pH 8. In some embodiments, the water quality measuring device 6 measures the acid consumption of the sample Y2 without diluting the sample Y2 supplied from the sample acquisition device 14. With such a configuration, by keeping the sample Y2 undiluted, the influence of ion dissociation of components contained in the sample Y2 and changes in gas-liquid equilibrium on the measurement values ​​can be suppressed.

[0020] The dropping section 18 is configured to dropwise dispense titrant Y3, whose concentration is predetermined, into the reaction chamber 17. Such a dropping section 18 is, for example, a dropping nozzle attached to the top surface of the reaction chamber 17. Titrant Y3 is, for example, an aqueous solution of sodium hydroxide or sulfuric acid.

[0021] The foam suppressant supply unit 20 is configured to supply the foam suppressant Y4 to the reaction chamber 17. Such a foam suppressant supply unit 20 is, for example, a foam suppressant supply nozzle attached to the upper surface of the reaction chamber 17. The foam suppressant Y4 may suppress the generation of foam itself, or it may break the foam that has been generated. The foam suppressant Y4 is, for example, an oil-based defoamer, a surfactant-based defoamer, or an alcohol-based defoamer.

[0022] The pH measuring device 22 measures the hydrogen ion concentration (pH) of the sample Y2 in the reaction chamber 17.

[0023] In some embodiments, the water quality measuring device 6 further includes a stirring device 26 for stirring the sample Y2 in the reaction chamber 17. The stirring device 26 includes a gas nozzle that supplies gas G to the reaction chamber 17 and stirs the sample Y2 by aeration. In another embodiment, the stirring device 26 includes a rotor located in the reaction chamber 17 and rotated by magnetic force, and the sample Y2 is stirred by the rotation of the rotor.

[0024] <First Embodiment> (composition) In the waste treatment system 1 illustrated in Figure 1, a water quality measurement method will be described in which the acid consumption of a pH 8 sample Y2, and the concentrations of volatile fatty acids and ammonia nitrogen contained in this sample Y2 are measured by titration. Figure 2 is a flowchart of the water quality measurement method according to the first embodiment.

[0025] As illustrated in Figure 2, the water quality measurement method includes a target pH setting step S1, a pH range setting step S2, titration solution supply steps (S7, S9, S11, S13), alkalinity calculation step S8, and concentration calculation steps (S12, S14). In the first embodiment, as illustrated in Figure 2, the water quality measurement method further includes a sample supply step S3, a dilution step S4, a foam suppressant supply step S5, aeration start step S6, a degassing step S10, and aeration stop step S15.

[0026] In the first embodiment, the titration solution supply step includes a first sulfuric acid supply step S7, a second sulfuric acid supply step S9, a first sodium hydroxide aqueous solution supply step S11, and a second sodium hydroxide aqueous solution supply step S13. The concentration calculation step includes a volatile fatty acid concentration calculation step S12 and an ammonia nitrogen concentration calculation step S14.

[0027] In step S1, the target pH corresponding to sample Y2 is set. The target pH is a value set based on the influence function I that affects the rate of methane gas production in the methane fermentation tank 4.

[0028] According to our findings, the rate at which methane gas is produced from acetic acid by biological action by microorganisms is dominated by pH and is greatly influenced by the pH influence function I shown in equation (1). In equation (1), pH UL This is the upper limit of pH at which pH inhibition does not occur. LL This is the pH at which the reaction rate decreases to 5% of its maximum value due to pH inhibition. UL If the value is 7 or greater, the lower equation of equation (1) is adopted, the influence function I = 1, and the rate of methane gas production does not decrease. On the other hand, pH UL If the value is less than 7, the upper equation of equation (1) is adopted, the biological activity by microorganisms slows down, and the rate of methane gas production decreases sharply. In the first embodiment, the target pH is set to pH 7. TIFF0007906580000001.tif70170

[0029] In pH range setting step S2, a pH range corresponding to the components contained in sample Y2 is set. The pH range is set for each component whose concentration is to be measured. In the first embodiment, as described above, the modified product X is produced by the hydrolysis of waste W and contains both volatile fatty acids and ammonia nitrogen. That is, sample Y2 contains both volatile fatty acids and ammonia nitrogen. The pH range includes a first pH range corresponding to volatile fatty acids and a second pH range corresponding to ammonia nitrogen. The first pH range is pH 2.8 to 6.8. The second pH range is pH 7.8 to 10.8.

[0030] The first pH range is described below. The volatile fatty acids contained in sample Y2 exist in the form of volatile fatty acids (acetic acid, propionic acid) or volatile fatty acid ions (acetate ions, propionate ions). The acid dissociation constants of acetic acid and propionic acid under standard conditions (temperature of sample Y2 is 25 degrees Celsius) are both approximately 4.8. Below pH 2.8, the majority of the volatile fatty acids in sample Y2 exist in the form of acetic acid and propionic acid, and above pH 6.8, the majority exist in the form of acetate ions and propionate ions. The lower limit of the first pH range is the value at which the majority of the volatile fatty acids in sample Y2 exist in the form of acetic acid and propionic acid. The upper limit of the first pH range is the value at which the majority of the volatile fatty acids in sample Y2 exist in the form of acetate ions and propionate ions. The titrator Y3 (aqueous sodium hydroxide solution) added dropwise while sample Y2 is within the first pH range is used for the chemical reaction between the volatile fatty acids and volatile fatty acid ions.

[0031] The second pH range is explained below. The ammonia nitrogen contained in sample Y2 exists in the form of ammonia or ammonium ions. The acid dissociation constant of ammonia nitrogen under standard conditions is approximately 9.3. In sample Y2, the majority of ammonia nitrogen exists in the form of ammonium ions below pH 7.8, and the majority exists in the form of ammonia above pH 10.8. The lower limit of the second pH range is the value at which the majority of ammonia nitrogen contained in sample Y2 exists in the form of ammonium ions. The upper limit of the second pH range is the value at which the majority of ammonia nitrogen contained in sample Y2 exists in the form of ammonia. The titrant Y3 (aqueous sodium hydroxide solution) added dropwise while sample Y2 is within the second pH range is used for the chemical reaction between ammonia and ammonium ions.

[0032] In the first embodiment, the target pH setting step S1 and the pH range setting step S2 are performed in that order, but the disclosure is not limited to this form. The pH range setting step S2 and the target pH setting step S1 may be performed in that order, or the pH range setting step S2 and the target pH setting step S1 may be performed in parallel with each other.

[0033] In the sample supply step S3, once the target pH and pH range are set, the sample Y2 is supplied to the reaction chamber 17. When the sample supply step S3 is completed, the supply of sample Y2 to the reaction vessel 16 is stopped, for example, by closing a valve provided in the sample supply line 15. In some embodiments, the water quality measurement method further includes a drainage step before the sample supply step S3 in which the liquid stored in the reaction chamber 17 is drained.

[0034] In the dilution step S4, sample Y2 is diluted before the titrator supply step. In the first embodiment, the dilution step S4 involves supplying dilution water Y5 to the reaction chamber 17 after the sample supply step S3 is completed. Sample Y2 is adjusted to, for example, pH 8.

[0035] In the foam suppressant supply step S5, once the supply of dilution water Y5 to the reaction chamber 17 by the dilution step S4 is complete, the foam suppressant Y4 is supplied to the reaction chamber 17 from the foam suppressant supply unit 20. In the aeration start step S6, once the supply of dilution water Y5 to the reaction chamber 17 by the dilution step S4 is complete, the supply of gas G to the reaction chamber 17 from the agitator 26 (gas nozzle) is started. The aeration start step S6 may be performed after the foam suppressant supply step S5, or it may be performed in parallel with the foam suppressant supply step S5.

[0036] In the first sulfuric acid supply step S7 (titrate supply step), sulfuric acid (titrate Y3) is supplied to sample Y2 after both the target pH setting step S1 and the pH range setting step S2 have been performed. In the first embodiment, the first sulfuric acid supply step S7 is performed after the aeration start step S6 has been performed. Sulfuric acid is added dropwise to sample Y2 from the dropping section 18 until the pH of sample Y2 in the reaction chamber 17, as measured by the pH measuring device 22, reaches the target pH of pH 7.

[0037] In alkalinity calculation step S8, after the supply of sulfuric acid to sample Y2 is started by the first sulfuric acid supply step S7, the alkalinity (acid consumption) of sample Y2 is calculated based on the amount of sulfuric acid supplied to sample Y2 until the pH of sample Y2 changes from pH 8 to pH 7. In some embodiments, the amount of sulfuric acid supplied to sample Y2 until the pH changes from pH 8 to pH 7 may be the acid consumption itself.

[0038] In the second sulfuric acid supply step S9 (titrate supply step), sulfuric acid is supplied to sample Y2 until the pH of sample Y2 in the reaction chamber 17, as measured by the pH measuring device 22, falls below the lower limit of the first pH range (less than pH 2.8). In the first embodiment, sulfuric acid is added to sample Y2 from the dropping section 18 until the pH reaches 2.

[0039] In the degassing step S10, carbon dioxide is degassed from sample Y2 after the alkalinity calculation step S8. In the first embodiment, carbon dioxide is degassed from sample Y2 after the pH of sample Y2 falls below the lower limit of the first pH range in the second sulfuric acid supply step S9. Specifically, carbon dioxide is degassed from sample Y2 by gas G supplied from the stirring device 26 to the reaction chamber 17. The concentration of carbon dioxide in gas G is lower than the concentration of carbon dioxide in sample Y2.

[0040] Figure 3 is a graph showing the relationship between the supply amount of sodium hydroxide aqueous solution and the pH of sample Y2 in the first embodiment. In Figure 3, the horizontal axis represents the supply amount of sodium hydroxide aqueous solution, and the vertical axis represents the pH of sample Y2. In the graph shown in Figure 3, a virtual line 50 is formed that passes through the plot (pH) corresponding to the supply amount.

[0041] In the first sodium hydroxide aqueous solution supply step S11 (titrate supply step), the sodium hydroxide aqueous solution (titrate Y3) is supplied to the sample Y2 after both the target pH setting step S1 and the pH range setting step S2 have been performed. In the first embodiment, the first sodium hydroxide aqueous solution supply step S11 is performed after the degassing step S10 has been performed. As illustrated in Figure 3, the sodium hydroxide aqueous solution is added dropwise from the dropping section 18 to the sample Y2 until the sample Y2, which has a pH of 2, reaches the upper limit of the first pH range (pH 6.8).

[0042] In step S12, the volatile fatty acid concentration calculation step, the concentration of volatile fatty acids contained in sample Y2 is calculated based on the amount of sodium hydroxide solution supplied to sample Y2 from the start of supplying the sodium hydroxide solution to sample Y2 until the pH of sample Y2 changes from the lower limit to the upper limit of the first pH range (i.e., the amount of sodium hydroxide solution supplied to sample Y2 until the pH of sample Y2 changes from pH 2.8 to pH 6.8).

[0043] In the second sodium hydroxide aqueous solution supply step S13 (titrate supply step), the sodium hydroxide aqueous solution is supplied to the sample Y2 until the pH of the sample Y2 in the reaction chamber 17, as measured by the pH measuring device 22, exceeds the upper limit of the second pH range (pH 10.8). In the first embodiment, as illustrated in Figure 3, the sodium hydroxide aqueous solution is added dropwise to the sample Y2 from the dropping section 18 until the pH reaches 12.

[0044] In step S14, the ammonia nitrogen concentration is calculated based on the amount of sodium hydroxide solution supplied to sample Y2 from the start of supplying the sodium hydroxide solution to sample Y2 until the pH of sample Y2 changes from the lower limit to the upper limit of the second pH range (i.e., the amount of sodium hydroxide solution supplied to sample Y2 until the pH of sample Y2 changes from pH 7.8 to pH 10.8). Hereafter, this amount of sodium hydroxide solution will be referred to as the concentration calculation titration volume V2.

[0045] In the aeration stop step S15, after calculating the concentration of ammonia nitrogen contained in the sample Y2, the supply of gas G from the agitator 26 to the reaction chamber 17 is stopped. In other words, gas G is supplied to the reaction chamber 17 from the aeration start step S6 to the aeration stop step S15. In some embodiments, the water quality measurement method further includes a washing step after the ammonia nitrogen concentration calculation step S14 and before the aeration stop step S15, in which the inside of the reaction chamber 17 is washed with nitrogen-containing water, such as pure water or ammonia water.

[0046] Let v1 be the supply rate of sulfuric acid in the first sulfuric acid supply step S7 (first substep). Let v2 be the supply rate of sodium hydroxide aqueous solution in substep S11a (second substep) of the first sodium hydroxide aqueous solution supply step S11, from pH 2 to pH 2.8. Let v3 be the supply rate of sodium hydroxide aqueous solution in substep S11b (third substep) of the first sodium hydroxide aqueous solution supply step S11, from pH 2.8 to pH 6.8. Let v4 be the supply rate of sodium hydroxide aqueous solution in substep S13a (second substep) of the second sodium hydroxide aqueous solution supply step S13, from pH 6.8 to pH 7.8. Let v5 be the supply rate of sodium hydroxide aqueous solution in substep S13b (third substep) of the second sodium hydroxide aqueous solution supply step S13, from pH 7.8 to pH 10.8. Let v6 be the supply rate of the sodium hydroxide aqueous solution in substep S13c of the second sodium hydroxide aqueous solution supply step S13, from pH 10.8 to pH 12. In the first embodiment, v2, v4, and v6 are each faster than v1, v3, and v5.

[0047] (Effects / Actions) The operation and effects of the water quality measurement method according to the first embodiment will now be explained. As described above, in methane fermentation, when the pH of the contents Y1 of the methane fermentation tank 4 falls below 7, the biological activity of microorganisms slows down, and the rate of methane gas production decreases sharply. For this reason, general alkalinity levels such as the amount of acid consumed (P alkalinity) when the contents Y1 of the methane fermentation tank 4 are neutralized to pH 8.3 or the amount of acid consumed (total alkalinity) when the contents are neutralized to pH 4.8 result in low accuracy in evaluating the state of the methane fermentation tank 4 (the state of microorganisms).

[0048] According to the first embodiment, by setting the target pH to pH 7, the amount of acid consumed by sample Y2 until the pH reaches 7 can be measured. Therefore, the accuracy of evaluating the state of the methane fermentation tank 4 can be improved. Furthermore, by setting a first pH range and a second pH range, the concentrations of volatile fatty acids and ammonia nitrogen contained in sample Y2 can also be obtained, thereby further improving the accuracy of evaluating the state of the methane fermentation tank 4.

[0049] In some embodiments, the first pH range is pH 4.3 to 5.3. As mentioned above, the acid dissociation constants of acetic acid and propionic acid under standard conditions are both approximately 4.8. Therefore, in the pH range of 4.3 to 5.3, the influence of ions other than acetate and propionate ions is suppressed (in other words, the change in pH of sample Y2 is dominated by acetate and propionate ions). Thus, by setting the first pH range to pH 4.3 to 5.3, the accuracy of measuring the concentration of volatile fatty acids contained in sample Y2 can be improved.

[0050] In some embodiments, the second pH range is between pH 8.8 and 9.8. As mentioned above, the acid dissociation constant of ammonia nitrogen under standard conditions is approximately 9.3. Therefore, in the pH range between 8.8 and 9.8, the influence of ions other than ammonia and ammonium ions is suppressed (in other words, the change in pH of sample Y2 is dominated by ammonia and ammonium ions). Thus, by setting the second pH range to between pH 8.8 and 9.8, the accuracy of calculating the concentration of ammonia nitrogen contained in sample Y2 can be improved.

[0051] If sample Y2 contains carbon dioxide, the accuracy of measuring the concentration of volatile fatty acids and ammonia nitrogen in sample Y2 may decrease. Specifically, the carbon dioxide in sample Y2 exists in one of three forms: carbon dioxide, bicarbonate ions, or carbonate ions. The first-stage acid dissociation constant (the acid dissociation constant between carbon dioxide and bicarbonate ions) under standard conditions is approximately 6.3. Therefore, in the supply (dropping) of sodium hydroxide aqueous solution from the lower limit (pH 2.8) to the upper limit (pH 6.8) of the first pH range in the first sodium hydroxide aqueous solution supply step S11, the sodium hydroxide aqueous solution is used in the chemical reaction between carbon dioxide and bicarbonate ions. Consequently, the concentration of volatile fatty acids in sample Y2 may be measured higher than it actually is. Similarly, the second-stage acid dissociation constant (the acid dissociation constant between carbon dioxide and bicarbonate ions) under standard conditions is approximately 10.3. Therefore, in the supply (dropping) of sodium hydroxide aqueous solution from the lower limit (pH 7.8) to the upper limit (pH 10.8) of the second pH range in the second sodium hydroxide aqueous solution supply step S13, the sodium hydroxide aqueous solution is used in the chemical reaction between bicarbonate ions and carbonate ions. Consequently, there is a risk that the concentration of ammonia nitrogen contained in sample Y2 will be measured higher than it actually is.

[0052] In the first embodiment, the water quality measuring device 6 measured the acid consumption of sample Y2 at a temperature of 25 degrees Celsius, but the temperature of sample Y2 is not limited to 25 degrees Celsius. In some embodiments, the water quality measuring device 6 is configured to maintain the temperature of sample Y2 at a predetermined temperature, and the first pH range and the second pH range are corrected based on the predetermined temperature.

[0053] An example of correction for the first and second pH ranges according to several embodiments will be described. Figure 9 is a graph showing the relationship between the acid dissociation constant and temperature. Figure 9 shows the acid dissociation constant pK1 (pK1 = -logK1) for acetic acid and the acid dissociation constant pK2 (pK2 = -logK2) for ammonia nitrogen. As shown in Figure 9, the acid dissociation constant changes with temperature. The acid dissociation constant pK1 for acetic acid increases slightly as the temperature increases. The acid dissociation constant pK2 for ammonia nitrogen decreases as the temperature increases.

[0054] In the first embodiment described above, the first pH range is defined as having the acid dissociation constant of acetic acid under standard conditions (approximately 4.8) as the median value, with a predetermined value (2.0) added to this median value as the upper limit, and a predetermined value (2.0) subtracted from this median value as the lower limit. As shown in Figure 9, the acid dissociation constant of acetic acid is determined by temperature. When the temperature of sample Y2 is 55 degrees Celsius, the acid dissociation constant of acetic acid is 4.85, and the first pH range is corrected to a pH of 2.85 to 6.85, which is obtained by adding or subtracting a predetermined value (2.0) from 4.85. The predetermined value in the first pH range is constant regardless of temperature. With this correction, the temperature dependence of acetic acid is taken into consideration because the first pH range is corrected based on the temperature of sample Y2. Therefore, the accuracy of calculating the concentration of acetic acid contained in sample Y2 can be improved. Although the explanation used acetic acid as the volatile fatty acid as an example, propionic acid may be used instead of acetic acid, or both acetic acid and propionic acid may be included.

[0055] In the first embodiment described above, the second pH range is defined as having the acid dissociation constant of ammonia nitrogen under standard conditions (approximately 9.3) as the median value, with a predetermined value (1.5) added to this median value as the upper limit, and a predetermined value (1.5) subtracted from this median value as the lower limit. As shown in Figure 9, the acid dissociation constant of ammonia nitrogen is determined by temperature. When the temperature of sample Y2 is 55 degrees Celsius, the acid dissociation constant of ammonia nitrogen is 8.45, and the second pH range is 6.95 to 9.95, obtained by adding or subtracting a predetermined value (1.5) from 8.45. The predetermined value in the second pH range is constant regardless of temperature. The predetermined value in the first pH range and the predetermined value in the second pH range may be the same or may be different. With such correction, the second pH range is corrected based on the temperature of sample Y2, so the temperature dependence of ammonia nitrogen is taken into consideration. Therefore, the accuracy of calculating the concentration of ammonia nitrogen contained in sample Y2 can be improved.

[0056] According to the first embodiment, the concentration of volatile fatty acids contained in sample Y2 is calculated based on the amount of sodium hydroxide solution used to change the first pH range from the lower limit to the upper limit, after carbon dioxide has been removed from sample Y2 by the degassing step S10. Similarly, the concentration of ammonia nitrogen contained in sample Y2 is calculated based on the amount of sodium hydroxide solution used to change the second pH range from the lower limit to the upper limit, after carbon dioxide has been removed from sample Y2 by the degassing step S10. Therefore, the decrease in accuracy of measuring the concentration of volatile fatty acids and the ammonia nitrogen due to the presence of carbon dioxide in sample Y2 can be suppressed.

[0057] In the first sodium hydroxide aqueous solution supply step S11, substep S11a corresponds to a preparatory stage for performing substep S11b. Therefore, in substep S11a, it is not necessary to supply the sodium hydroxide aqueous solution as carefully as in the first sulfuric acid supply step S7 and substep S11b. Similarly, in the second sodium hydroxide aqueous solution supply step S13, substep S13a corresponds to a preparatory stage for performing substep S13b. Therefore, in substep S13b, it is not necessary to supply the sodium hydroxide aqueous solution as carefully as in the first sulfuric acid supply step S7 and substep S13b. According to the first embodiment, by making v2 and v4 faster than v1, v3 and v5, the time required to measure the alkalinity of sample Y2 and the concentrations of volatile fatty acids and ammonia nitrogen contained in sample Y2 by titration can be shortened.

[0058] In the first embodiment, the case in which sample Y2 is the contents of the methane fermentation tank 4 was described as an example, but the disclosure is not limited to this form. For example, sample Y2 may be the contents of a saccharification tank that produces sugars as valuable products from carbohydrates such as starch and cellulose, or the contents of a composting device that produces compost by composting carbohydrates. In some embodiments, sample Y2 is the contents of a fermentation tank in which modified product X, obtained by hydrolyzing waste W, is broken down into smaller molecules by microorganisms.

[0059] While the water quality measurement method according to the first embodiment measured the acid consumption of sample Y2, this disclosure is not limited to this embodiment. In some embodiments, the water quality measurement method according to this disclosure measures the alkali consumption of sample Y2 and the concentration of components contained in sample Y2 by titration. The water quality measurement method according to this disclosure does not limit the target pH to pH 7, but the target pH can be arbitrarily set according to sample Y2. Similarly, the water quality measurement method according to this disclosure does not limit the pH range to a first pH range (pH 2.8 to pH 6.8) or a second pH range (pH 7.8 to pH 10.8), but the pH range can be arbitrarily set according to the component whose concentration is to be measured.

[0060] <Second Embodiment> A water quality measurement method according to a second embodiment of this disclosure will now be described. In the second embodiment, the method for calculating the concentration of ammonia nitrogen differs from that of the first embodiment. The other components are the same as those described in the first embodiment. In the second embodiment, components that are the same as those of the first embodiment are denoted by the same reference numerals, and their detailed descriptions are omitted.

[0061] In the second embodiment, in the ammonia nitrogen concentration calculation step S14, the concentration calculation titration volume V2 is calculated based on the change in pH of sample Y2 in a second pH range due to the supply of sodium hydroxide aqueous solution (titrate Y3).

[0062] As illustrated in Figure 3, the portion 52 of line 50 from pH 7.8 to pH 10.8 can be considered to extend in a straight line. Therefore, by obtaining the slope of portion 52, the concentration calculation titration volume V2 can be calculated. In the second embodiment, the slope of portion 52 is calculated from two plots 52a and 52b located at different positions in portion 52. Plot 52a is pH 7.8, and plot 52b is a value other than pH 7.8 and pH 10.8.

[0063] The operation and effects of the water quality measurement method according to the second embodiment will now be explained. According to the second embodiment, the concentration calculation titration volume V2 is calculated before the sodium hydroxide aqueous solution is actually supplied up to the concentration calculation titration volume V2, and the concentration of ammonia nitrogen contained in the sample Y2 is calculated based on this calculated concentration calculation titration volume V2. Therefore, the time required for measuring the ammonia nitrogen concentration can be shortened.

[0064] In some embodiments, the volatile fatty acid concentration calculation step S12 calculates the amount of sodium hydroxide aqueous solution supplied to sample Y2 until the sample Y2 changes from pH 2.8 to pH 6.8, based on the amount of pH change of sample Y2 in a first pH range due to the supply of sodium hydroxide aqueous solution (titrate Y3).

[0065] <Third Embodiment> A water quality measurement method according to a third embodiment of this disclosure will now be described. The water quality measurement method according to the third embodiment is modified by adding a calibration curve setting step S16 to the water quality measurement method according to the first embodiment. In the third embodiment, components that are the same as those of the first embodiment are denoted by the same reference numerals, and their detailed description is omitted. In some embodiments of the water quality measurement method, a calibration curve setting step S16 is added to the water quality measurement method according to the second embodiment.

[0066] Figure 4 is a flowchart of the water quality measurement method according to the third embodiment. As illustrated in Figure 4, the water quality measurement method further includes a calibration curve setting step S16 which is performed before the first sulfuric acid supply step S7. In the third embodiment, the calibration curve setting step S16 is performed before the target pH setting step S1.

[0067] In calibration curve setting step S16, a calibration curve is set that shows the correspondence between the concentrations of components contained in sample Y2 and the supply amount of titrant Y3. In the third embodiment, a first calibration curve L1 is set that shows the correspondence between the concentration of volatile fatty acids contained in sample Y2 and the supply amount of sodium hydroxide aqueous solution. In addition, a second calibration curve L2 is set that shows the correspondence between the concentration of ammonia nitrogen contained in sample Y2 and the supply amount of sodium hydroxide aqueous solution. In other words, both the first calibration curve L1 and the second calibration curve L2 are set in calibration curve setting step S16. In some embodiments, only one of the first calibration curve L1 and the second calibration curve L2 is set in calibration curve setting step S16.

[0068] An example of how to set up the first calibration curve L1 will be described. Figure 5 is a flowchart of how to set up the first calibration curve L1. As illustrated in Figure 5, the method for setting up the first calibration curve L1 includes a first sample preparation step S161, a first sample supply step S162, a first plot addition step S163, and a first calibration curve creation step S164.

[0069] In the first sample preparation step S161, a first sample 60 is prepared in which the concentration of volatile fatty acids is within the range of 9500 ppm to 10500 ppm. For example, the concentration of volatile fatty acids in the first sample 60 is 10000 ppm.

[0070] In the first sample supply step S162, an aqueous sodium hydroxide solution (titrate Y3) is supplied to the first sample 60. This aqueous sodium hydroxide solution is the same as the aqueous sodium hydroxide solution supplied to sample Y2 in the first aqueous sodium hydroxide solution supply step S11 and the second aqueous sodium hydroxide solution supply step S13, respectively.

[0071] Figure 6 is a graph showing the relationship between the supply amount of sodium hydroxide aqueous solution and the concentration of volatile fatty acids in the third embodiment. The graph shown in Figure 6 includes a first coordinate system 62 where the horizontal axis is the supply amount of sodium hydroxide aqueous solution and the vertical axis is the concentration of volatile fatty acids.

[0072] In the first plot addition step S163, a first plot 64 corresponding to the concentration of volatile fatty acids (10,000 ppm) contained in the first sample 60 is added to the first coordinate 62. Then, in the first calibration curve creation step S164, a straight line passing through the first plot 64 and the origin O of the first coordinate 62 is created as the calibration curve for volatile fatty acids (first calibration curve L1).

[0073] An example of how to set up the second calibration curve L2 will be described. Figure 7 is a flowchart of how to set up the second calibration curve L2. As illustrated in Figure 7, the method for setting up the second calibration curve L2 includes the second sample preparation step S165, the second sample supply step S166, the second plot addition step S167, and the second calibration curve creation step S168.

[0074] In the second sample preparation step S165, a second sample 70 is prepared with a known concentration of ammonia nitrogen, which falls within the range of 4500 ppm to 5500 ppm. For example, the concentration of ammonia nitrogen in the second sample 70 is 5000 ppm.

[0075] In the second sample supply step S166, an aqueous sodium hydroxide solution (titrate Y3) is supplied to the second sample 70. This aqueous sodium hydroxide solution is the same as the aqueous sodium hydroxide solution supplied to sample Y2 in the first aqueous sodium hydroxide solution supply step S11 and the second aqueous sodium hydroxide solution supply step S13, respectively.

[0076] Figure 8 is a graph showing the relationship between the supply amount of sodium hydroxide aqueous solution and the concentration of ammonia nitrogen in the third embodiment. The graph in Figure 8 includes a second coordinate system 72 in which the horizontal axis represents the supply amount of sodium hydroxide aqueous solution and the vertical axis represents the concentration of ammonia nitrogen.

[0077] In the second plot addition step S167, a second plot 74 is added to the second coordinate 72, corresponding to the concentration of ammonia nitrogen (5000 ppm) contained in the second sample 70. Then, in the second calibration curve creation step S168, a straight line passing through the second plot 74 and the origin O of the second coordinate 72 is created as the calibration curve for ammonia nitrogen (second calibration curve L2).

[0078] In step S12, the volatile fatty acid concentration is calculated based on the amount of sodium hydroxide solution supplied to sample Y2 until the pH of sample Y2 changes from pH 2.8 to pH 6.8, and the first calibration curve L1. Specifically, the concentration of volatile fatty acids corresponding to the amount of sodium hydroxide solution supplied to sample Y2 is obtained from the first calibration curve L1.

[0079] In the ammonia nitrogen concentration calculation step S14, the ammonia nitrogen concentration is calculated based on the concentration calculation titration volume V2 and the second calibration curve L2. Specifically, the ammonia nitrogen concentration corresponding to the concentration calculation titration volume V2 is obtained from the second calibration curve L2.

[0080] The operation and effects of the water quality measurement method according to the third embodiment will be described. According to the third embodiment, compared to the case where the first calibration curve L1 and the second calibration curve L2 are not used, the measurement accuracy of the concentration of volatile fatty acids and the measurement accuracy of the concentration of ammonia nitrogen contained in the sample Y2 can be improved.

[0081] When measuring the concentration of volatile fatty acids, it is desirable to have high measurement accuracy around 10,000 ppm. This is because when the concentration of volatile fatty acids exceeds 10,000 ppm, the demolecularization of the modified product X by microorganisms is inhibited. According to the third embodiment, the calibration curve for volatile fatty acids (first calibration curve L1) is a straight line that passes through the first plot 64 of the first sample 60, where the concentration of volatile fatty acids is 10,000 ppm, and the origin at the first coordinate 62, thus improving the measurement accuracy of the concentration of volatile fatty acids around 10,000 ppm.

[0082] Furthermore, this disclosure is not limited to the first sample 60 having a volatile fatty acid concentration in the range of 9500 ppm to 10500 ppm. In some embodiments, the first sample preparation step S161 prepares a first sample 60 having a volatile fatty acid concentration in the range of 19000 ppm to 21000 ppm.

[0083] When measuring the concentration of ammonia nitrogen, it is desirable to have high measurement accuracy around 5000 ppm. This is because when the concentration of ammonia nitrogen exceeds 5000 ppm, the demolecularization of the modified product X by microorganisms is inhibited. According to the third embodiment, the calibration curve for ammonia nitrogen (second calibration curve L2) is a straight line that passes through the second plot 74 of the second sample 70, where the ammonia nitrogen concentration is 5000 ppm, and the origin at the second coordinate 72, thus improving the measurement accuracy of the ammonia nitrogen concentration around 5000 ppm.

[0084] Furthermore, this disclosure is not limited to the case where the concentration of ammonia nitrogen contained in the second sample 70 falls within the range of 9500 ppm to 10500 ppm.

[0085] In some embodiments, the second sample preparation step S165 involves preparing a second sample 70 in which the ammonia nitrogen concentration is in the range of 3800 ppm to 4200 ppm. The methane fermenter 4 may ferment the modified material X by microorganisms under moderate temperature conditions (37°C ± 5°C). In this case, it is desirable to have high accuracy in measuring the ammonia nitrogen concentration around 4000 ppm. According to the method described above, when the methane fermenter 4 undergoes moderate temperature fermentation, the accuracy in measuring the ammonia nitrogen concentration around 4000 ppm can be improved.

[0086] In some embodiments, the second sample preparation step S165 involves preparing a second sample 70 in which the ammonia nitrogen concentration is in the range of 2850 ppm to 3150 ppm. The methane fermenter 4 may ferment the modified material X by microorganisms under high temperature conditions (55°C ± 5°C). In this case, it is desirable to have high accuracy in measuring the ammonia nitrogen concentration around 3000 ppm. According to the method described above, when the methane fermenter 4 undergoes high-temperature fermentation, the accuracy in measuring the ammonia nitrogen concentration around 4000 ppm can be improved.

[0087] In the third embodiment, the calibration curve was a straight line, but the disclosure is not limited to this form, and the calibration curve may be, for example, a curve. In the third embodiment, one plot was attached to the coordinates, but multiple plots may be attached to the coordinates.

[0088] The method for setting the calibration curve is not particularly limited; for example, it may be the absolute calibration curve method or the standard addition method. The absolute calibration curve method involves preparing sample samples of known concentrations and measuring the specific signals of the water quality measuring device 6 to calculate the relationship between concentration and signal and obtain a calibration curve. The standard addition method involves preparing sample Y2, which is the target of water quality measurement, and sample samples of known concentrations obtained by directly adding at least one of volatile fatty acids and ammonia nitrogen to sample Y2, and measuring the specific signals of the water quality measuring device 6 to calculate the relationship between concentration and signal and obtain a calibration curve.

[0089] In the third embodiment, the accuracy of measuring the concentration of components in the sample was improved by setting a calibration curve, but the accuracy of measurement may be improved by other methods. For example, the water quality measurement method may further include a step of setting a correction coefficient K calculated by Z1 / Z2, with 10,000 ppm as the set value Z1, and the amount of titrant Y3 supplied to the sample Y2 from the lower limit to the upper limit of the pH range as the set value Z2. Then, in the concentration calculation step (S12, S14), the concentration of components in the sample Y2 is calculated based on the value obtained by multiplying the amount of titrant Y3 supplied to the sample Y2 from the lower limit to the upper limit of the pH range by the correction coefficient K.

[0090] The contents described in each of the above embodiments can be understood, for example, as follows:

[0091] [1] The water quality measurement method relating to this disclosure is a water quality measurement method that measures the acid consumption or alkali consumption of a sample (Y2) and the concentration of components contained in the sample by titration, The steps include setting the target pH corresponding to the sample (S1), Step (S2) is to set a pH range corresponding to the components contained in the sample, After both the step of setting the target pH and the step of setting the pH range, the step of supplying the titration solution (Y3) to the sample (S7, S9, S11, S13) Step (S8): After starting to supply the titrant to the sample, calculate the amount of acid or alkali consumed by the sample based on the amount of titrant supplied to the sample until the pH of the sample reaches the target pH. The procedure includes the steps (S12, S14) of calculating the concentration of components contained in the sample based on the amount of titration supplied to the sample until the pH of the sample changes from the upper limit to the lower limit, or from the lower limit to the upper limit, after the supply of the titration solution to the sample has begun.

[0092] According to the method described in [1] above, by setting a target pH corresponding to the sample, the amount of acid or alkali consumed by the sample until the pH reaches the target pH can be measured. Furthermore, according to the method described in [1] above, by setting a pH range corresponding to the components contained in the sample, the concentration of the components contained in the sample can also be obtained.

[0093] [2] In some embodiments, the method described in [1] above, The aforementioned sample is the contents of a fermentation tank in which a modified product (X) obtained by hydrolysis of waste (W) is broken down into smaller molecules by microorganisms.

[0094] According to the method described in [2] above, it is possible to measure the amount of acid or alkali consumed by the contents of the fermenter until the pH corresponds to that of the contents of the fermenter, and the concentration of components contained in the contents of the fermenter.

[0095] [3] In some embodiments, the method described in [2] above, The fermentation tank is a methane fermentation tank (4) that reduces the molecular weight of the modified material by microorganisms to produce methane gas. The step of setting the target pH involves setting the target pH based on an influence function (I) that affects the rate of methane gas production in the methane fermentation tank.

[0096] According to the method described in [3] above, the target pH is set based on the influence function, so the acid consumption or alkali consumption of the contents of the methane fermenter can be measured while taking into account the rate of methane gas production. Therefore, the accuracy of evaluating the state of the methane fermenter can be improved compared to measuring general alkalinity (e.g., P alkalinity or total alkalinity).

[0097] [4] In some embodiments, the method described in [3] above, The target pH is pH 7. The step of calculating the acid consumption or alkali consumption of the sample involves calculating the alkalinity of the sample based on the amount of titration supplied to the sample from the start of supplying the titration to the sample until the pH of the sample reaches pH 7.

[0098] According to the inventors' findings, the amount of acid consumed until the pH reaches 7 is a value that can accurately evaluate the state of the methane fermentation tank. The method described in [4] above allows for the calculation of the amount of acid consumed until the pH of the contents of the methane fermentation tank reaches 7, thereby enabling an accurate evaluation of the state of the methane fermentation tank.

[0099] [5] In some embodiments, the method described in any one of [2] to [4] above, The components contained in the aforementioned sample include volatile fatty acids, The aforementioned pH range includes a first pH range of pH 2.8 to 6.8.

[0100] According to the method described in [5] above, the concentration of volatile fatty acids contained in the contents of the fermentation tank can be measured.

[0101] [6] In some embodiments, the method described in [5] above, The first pH range is between pH 4.3 and 5.3.

[0102] The method described in [6] above can improve the accuracy of measuring the concentration of volatile fatty acids contained in the contents of the fermentation tank.

[0103] [7] In some embodiments, the method described in [5] above, The first pH range is corrected based on the temperature of the sample.

[0104] According to the present inventors, the accuracy of calculating the concentration of volatile fatty acids contained in the contents of a fermenter can be improved by correcting the pH range to an appropriate level based on the temperature of the sample. The method described in [7] above is corrected based on the temperature of the sample, so the accuracy of calculating the concentration of volatile fatty acids contained in the contents of a fermenter can be improved.

[0105] [8] In some embodiments, the method described in any one of [2] to [7] above, The components contained in the aforementioned sample include ammonia nitrogen, The aforementioned pH range includes a second pH range of pH 7.8 to 10.8.

[0106] According to the method described in [8] above, the concentration of ammonia nitrogen contained in the contents of the fermenter can be measured.

[0107] [9] In some embodiments, in the method described in [8] above, The second pH range is between pH 8.8 and 9.8.

[0108] The method described in [9] above can improve the accuracy of measuring the concentration of ammonia nitrogen contained in the contents of the fermenter.

[0109]

[10] In some embodiments, the method described in [8] above, The second pH range is corrected based on the temperature of the sample.

[0110] According to the present inventors, the accuracy of calculating the concentration of ammonia nitrogen contained in the contents of a fermenter can be improved by correcting the pH range to an appropriate level based on the temperature of the sample. The method described in

[10] above is corrected based on the temperature of the sample, so the accuracy of calculating the concentration of ammonia nitrogen contained in the contents of a fermenter can be improved.

[0111]

[11] In some embodiments, the method described in any one of [1] to

[10] above, The step of calculating the acid consumption or alkali consumption of the sample further includes the step of degassing carbon dioxide from the sample after calculating the acid consumption of the sample (S10), The step of calculating the concentration of the components contained in the sample involves calculating the concentration of the components contained in the sample based on the amount of titration supplied to the sample until the pH of the sample from which the carbon dioxide has been removed changes from the lower limit to the upper limit of the pH range.

[0112] If the sample contains carbon dioxide, the accuracy of measuring the concentration of the components in the sample may decrease. According to the method described in

[11] above, the concentration of the components in the sample is calculated based on the amount of titrant used to change the pH range from the lower limit to the upper limit after the carbon dioxide has been removed from the sample. Therefore, the decrease in accuracy of concentration measurement due to the presence of carbon dioxide in the sample can be suppressed.

[0113]

[12] In some embodiments, the method described in any one of [1] to

[11] above, The step of supplying the titration solution to the sample is: A first substep (S7) involves supplying the titrant to the sample at a first supply rate (v1) from the start of supplying the titrant to the sample until the pH of the sample reaches the target pH, Following the first substep, a second substep (S11a, S13a) is performed in which the titrant is supplied to the sample at a second supply rate (v2, v4) until the pH of the sample reaches the pH range, The process includes, after the second substep, a third substep (S11b, S13b) in which the titrant is supplied to the sample at a third supply rate (v3, v5) until the pH of the sample reaches the upper or lower limit of the pH range, The second supply rate is greater than both the first supply rate and the third supply rate.

[0114] The second substep is a preparatory step for carrying out the third substep and does not require careful supply of the titrant compared to the first and third substeps. According to the method described in

[12] above, the second supply rate is greater than the first and third supply rates, respectively, so that the time required to measure the acid or alkali consumption of the sample and the concentration of components contained in the sample by titration can be reduced.

[0115]

[13] In some embodiments, the method according to any one of [1] to

[12] above, In the step of calculating the concentration of the components contained in the sample, if the amount of titration supplied to the sample until the pH of the sample changes from the upper limit to the lower limit, or from the lower limit to the upper limit, is defined as the concentration calculation titration volume (V2), The titration volume for concentration calculation is calculated based on the change in pH of the sample within the pH range due to the supply of the titrant.

[0116] According to the method described in

[13] above, the titration volume for concentration calculation can be calculated before the titrant is actually supplied to that volume, thereby shortening the time required to measure the concentration of components in the sample.

[0117]

[14] In some embodiments, the method according to any one of [1] to

[13] above, The procedure further includes a step (S4) of diluting the sample before supplying the titrant to the sample.

[0118] The method described in

[14] above can reduce the viscosity of the sample and facilitate stirring of the sample. This can promote the reaction between the sample and the titrant.

[0119]

[15] In some embodiments, the method described in any one of [1] to

[14] above, Prior to the step of supplying the titrant to the sample, the procedure further includes the step (S16) of setting up a calibration curve that shows the correspondence between the concentration of the components contained in the sample and the amount of titrant supplied. The step of calculating the concentration of the components contained in the sample involves calculating the concentration of the components contained in the sample based on the amount of titration supplied to the sample after the supply of the titration solution to the sample begins, until the pH of the sample changes from the upper limit to the lower limit, or from the lower limit to the upper limit, of the pH range, and the calibration curves (L1, L2).

[0120] The method described in

[15] above can improve the accuracy of measuring the concentration of components in a sample compared to the case where a calibration curve is not used.

[0121]

[16] In some embodiments, the method described in

[15] above, The components contained in the aforementioned sample include volatile fatty acids, The step of setting the calibration curve is: The steps include preparing a first sample (60) containing the volatile fatty acid at a known concentration (S161), The step of supplying the titration solution to the first sample (S162), Step (S163) is to plot a first plot (64) corresponding to the concentration of the volatile fatty acid contained in the first sample on a first coordinate system (62) where the horizontal axis is the volume of the titration solution and the vertical axis is the concentration of the volatile fatty acid, The process includes the step (S164) of defining a straight line passing through the first plot and the origin of the first coordinate system as the calibration curve (L1) for the volatile fatty acid.

[0122] According to the method described in

[16] above, a calibration curve can be created to improve the accuracy of measuring the concentration of volatile fatty acids contained in a sample.

[0123]

[17] In some embodiments, in the method described in

[16] , The first sample contains a volatile fatty acid concentration in the range of 9500 ppm to 10500 ppm.

[0124] When measuring the concentration of volatile fatty acids, it is sometimes desirable to have high measurement accuracy around 10,000 ppm. According to the method described in

[17] above, the calibration curve for volatile fatty acids is a straight line that passes through the origin and the first plot of the first sample, in the first coordinate system, where the concentration of volatile fatty acids is in the range of 9,500 ppm to 10,500 ppm. Therefore, the measurement accuracy of the concentration of volatile fatty acids around 10,000 ppm can be improved.

[0125]

[18] In some embodiments, the method described in any one of

[15] to

[17] above, The components contained in the aforementioned sample include ammonia nitrogen, The step of setting the calibration curve is: The steps include preparing a second sample (70) containing a known concentration of ammonia nitrogen (S165), The step of supplying the titration solution to the second sample (S166), Step (S167) involves plotting a second plot (74) corresponding to the concentration of ammonia nitrogen contained in the second sample on a second coordinate system (72) where the horizontal axis is the volume of the titration solution and the vertical axis is the concentration of ammonia nitrogen, The process includes the step (S168) of defining a straight line passing through the second plot and the origin of the second coordinate system as the calibration curve (L2) for ammonia nitrogen.

[0126] According to the method described in

[18] above, a calibration curve can be created to improve the accuracy of measuring the concentration of volatile fatty acids contained in a sample.

[0127]

[19] In some embodiments, the method described in

[18] above, The second sample contains a concentration of ammonia nitrogen in the range of 4500 ppm to 5500 ppm.

[0128] When measuring the concentration of ammonia nitrogen, it is sometimes desirable to have high measurement accuracy for the concentration around 5000 ppm. According to the method described in

[18] above, the calibration curve for ammonia nitrogen is a straight line that passes through the origin and the second plot of the second sample, in the second coordinate system, where the ammonia nitrogen concentration is in the range of 4500 ppm to 5500 ppm. Therefore, the measurement accuracy of the ammonia nitrogen concentration around 5000 ppm can be improved.

[0129]

[20] In some embodiments, the method described in

[18] above, The second sample contains ammonia nitrogen in a concentration range of 3800 ppm to 4200 ppm.

[0130] When measuring the concentration of ammonia nitrogen (when the sample temperature is moderate), it is sometimes desirable to have high measurement accuracy for the concentration around 4000 ppm. According to the method described in

[19] above, the calibration curve for ammonia nitrogen is a straight line that passes through the origin and the second plot of the second sample, in the second coordinate system, where the ammonia nitrogen concentration is in the range of 3800 ppm to 4200 ppm, so the measurement accuracy for the ammonia nitrogen concentration around 4000 ppm can be improved.

[0131]

[21] In some embodiments, the method described in

[18] above, The second sample contains a concentration of ammonia nitrogen in the range of 2850 ppm to 3150 ppm.

[0132] When measuring the concentration of ammonia nitrogen (when the sample temperature is high), it is sometimes desirable to have high accuracy in measuring the concentration around 3000 ppm. According to the method described in

[20] above, the calibration curve for ammonia nitrogen is a straight line that passes through the origin and the second plot of the second sample, in the second coordinate system, where the ammonia nitrogen concentration is in the range of 2850 ppm to 3150 ppm, so the accuracy of measuring the ammonia nitrogen concentration around 3000 ppm can be improved. [Explanation of symbols]

[0133] 1. Waste disposal system 2. Modification device 4. Methane fermentation tank 6 Water quality measuring device 60. First sample 62 First Coordinate 64. Plot 1 70. Second sample 72 Second Coordinate 74. Plot 2 I Influence Function L1 First Calibration Curve L2 Second Calibration Curve S1 Objective pH setting step S2 pH range setting step S4 Dilution Step S7 First sulfuric acid supply step S8 Alkalinity Calculation Step S9 Second sulfuric acid supply step S10 Degassing step S11 First sodium hydroxide aqueous solution supply step S12 Step for calculating volatile fatty acid concentration S13 Second sodium hydroxide aqueous solution supply step S14 Step for calculating ammonia nitrogen concentration S16 Calibration curve setting step S161 First Sample Preparation Step S162 First sample supply step S163 First plot addition step S164 Step to create the first calibration curve S165 Second Sample Preparation Step S166 Second sample supply step S167 Second plot addition step S168 Step to create the second calibration curve V2 Concentration calculation titration amount W Waste X modified product Contents of the Y1 methane fermentation tank Y2 sample Y3 titrant

Claims

1. A water quality measurement method for measuring the acid consumption or alkali consumption of a sample, and the concentrations of volatile fatty acids and ammonia nitrogen, which are components contained in the sample, by titration, The aforementioned sample is the contents of a methane fermentation tank, which generates methane gas by hydrolyzing waste materials and then breaking them down into smaller molecules using microorganisms. The steps include setting a target pH corresponding to the sample based on an influence function that affects the rate of methane gas production in the methane fermentation tank, The steps include setting a pH range corresponding to the components contained in the sample, After both the step of setting the target pH and the step of setting the pH range, the step of supplying the titration solution to the sample, After starting to supply the titrant to the sample, the step of calculating the acid consumption or alkali consumption of the sample based on the amount of titrant supplied to the sample until the pH of the sample reaches the target pH, After starting to supply the titrant to the sample, the steps include calculating the concentration of the components contained in the sample based on the amount of titrant supplied to the sample until the pH of the sample changes from the upper limit to the lower limit, or from the lower limit to the upper limit, of the pH range, Equipped with, The target pH is pH 7, and the step of calculating the acid consumption or alkali consumption of the sample is to calculate the acid consumption of the sample based on the amount of titration supplied to the sample from the start of supplying the titration to the sample until the pH of the sample reaches pH 7. The aforementioned pH range corresponds to the aforementioned volatile fatty acids and includes a first pH range of 2.8 to 6.

8. Water quality measurement method.

2. The first pH range is pH 4.3 or higher and 5.3 or lower. The water quality measurement method according to claim 1.

3. The first pH range is corrected based on the temperature of the sample. The water quality measurement method according to claim 1.

4. The pH range includes a second pH range that corresponds to the ammonia nitrogen and is pH 7.8 or higher and 10.8 or lower. A method for measuring water quality according to any one of claims 1 to 3.

5. The second pH range is pH 8.8 or higher and 9.8 or lower. The water quality measurement method according to claim 4.

6. The second pH range is corrected based on the temperature of the sample. The water quality measurement method according to claim 4.

7. The step of calculating the acid consumption or alkali consumption of the sample further includes, after calculating the acid consumption of the sample, a step of degassing carbon dioxide from the sample. The step of calculating the concentration of the component contained in the sample is to calculate the concentration of the component contained in the sample based on the amount of titration supplied to the sample until the pH of the sample from which the carbon dioxide has been removed moves from the lower limit to the upper limit of the pH range. A method for measuring water quality according to any one of claims 1 to 3.

8. The step of supplying the titration solution to the sample is: A first substep involves supplying the titrant to the sample at a first supply rate from the start of supplying the titrant to the sample until the pH of the sample reaches the target pH, A second substep is performed, following the first substep, by supplying the titrant to the sample at a second supply rate until the pH of the sample reaches the pH range, The process includes, after the second substep, supplying the titrant to the sample at a third supply rate until the pH of the sample reaches the upper or lower limit of the pH range, The second supply rate is greater than the first supply rate and the third supply rate, A method for measuring water quality according to any one of claims 1 to 3.

9. In the step of calculating the concentration of the components contained in the sample, if the amount of titration supplied to the sample until the pH of the sample changes from the upper limit to the lower limit, or from the lower limit to the upper limit, is defined as the concentration calculation titration volume, The titration volume for concentration calculation is calculated based on the change in pH of the sample within the pH range due to the supply of the titrant. A method for measuring water quality according to any one of claims 1 to 3.

10. The step of supplying the titrant to the sample further comprises diluting the sample before the step of supplying the titrant to the sample. A method for measuring water quality according to any one of claims 1 to 3.

11. Prior to the step of supplying the titrator to the sample, the method further includes the step of setting up a calibration curve that shows the correspondence between the concentration of the components contained in the sample and the amount of titrator supplied. The step of calculating the concentration of the component contained in the sample involves calculating the concentration of the component contained in the sample based on the amount of titration supplied to the sample and the calibration curve, after the supply of the titration solution to the sample has started and the pH of the sample has changed from the upper limit to the lower limit, or from the lower limit to the upper limit, of the pH range. A method for measuring water quality according to any one of claims 1 to 3.

12. The step of setting the calibration curve is: The steps include preparing a first sample containing the volatile fatty acid at a known concentration, The steps include supplying the titration solution to the first sample, The steps include plotting a first plot on a first coordinate system where the horizontal axis represents the volume of the titration solution and the vertical axis represents the concentration of the volatile fatty acid, and plotting a first plot corresponding to the concentration of the volatile fatty acid contained in the first sample, The process includes the step of defining a straight line passing through the first plot and the origin of the first coordinate system as a calibration curve for the volatile fatty acid, The water quality measurement method according to claim 11.

13. The first sample contains a volatile fatty acid whose concentration is in the range of 9500 ppm to 10500 ppm. The water quality measurement method according to claim 12.

14. The step of setting the calibration curve is: The steps include preparing a second sample containing the ammonia nitrogen at a known concentration, The steps include supplying the titration solution to the second sample, The steps include plotting a second plot on a second coordinate system where the horizontal axis represents the volume of the titration solution and the vertical axis represents the concentration of the ammonia nitrogen, and plotting a second plot corresponding to the concentration of the ammonia nitrogen contained in the second sample, The step includes defining a straight line passing through the second plot and the origin of the second coordinate system as the calibration curve for ammonia nitrogen, The water quality measurement method according to claim 11.

15. The second sample contains ammonia nitrogen in a concentration range of 4500 ppm to 5500 ppm. The water quality measurement method according to claim 14.

16. The second sample contains ammonia nitrogen in a concentration range of 3800 ppm to 4200 ppm. The water quality measurement method according to claim 14.

17. The second sample contains ammonia nitrogen in a concentration range of 2850 ppm to 3150 ppm. The water quality measurement method according to claim 14.

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