JPH09262594A - Method and apparatus for controlling injected amount of ozone in high-degree water purifying treatment - Google Patents

Abstract

PROBLEM TO BE SOLVED: To control the optimum injected amt. of ozone on-line by separating an org. substance oxidatively decomposed by ozone into a substance to be removed and other substance and modeling the effect of the other substance on the reaction of the substance to be removed with ozone by an item capable of being made on-line. SOLUTION: When the injected amt. of zone in high-degree water purifying treatment of raw water for tap water is controlled, the flow rate of water to be treated flowing in an ozone contact basin is measured by a flowmeter 3 and the concn. of a coexisting substance therein is measured by a UV meter 4 and the water temp. and pH thereof are respectively measured by a water temp. meter 5 and a pH meter 6 and these measurement results and an assumed value of the injected amt. of ozone gas are inputted to a computer 9 and the concn. of a dissolved offensive smell substance after ozone treatment is calculated. This calculated value is set to an index to determine the injection amt. of ozone gas. At this time, a modified ozone reaction model formula of which the relative reaction speed constant is represented by 1+r.Cs2 (wherein Cs2 is the concn. of a dissolved substance to be oxidized and r is a proportion constant) is used and the concn. of an offensive smell substance is inputted to the model formula to obtain a proper ozone amt.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ozone injection amount control method and control device in advanced water purification treatment in which ozone gas is injected to decompose and remove organic substances contained in raw water for tap water. INDUSTRIAL APPLICABILITY The present invention is suitable as a method for controlling an ozone injection amount when performing advanced water purification treatment in a water purification plant.

[0002]

2. Description of the Related Art Currently used water purification systems are processes centered on rapid filtration. That is, tap water taken from a river is purified in a sedimentation basin, sent to a mixing basin to add chemicals to agglomerate fine suspended substances, put in another sedimentation basin to precipitate aggregates, and then filtered. After the pond, chlorine is added in a chlorine pond to sterilize it and supply it to customers as tap water.

In this process, insoluble substances can be removed, but dissolved organic substances such as odorous substances and toxic substances cannot be removed.

Therefore, so-called advanced water purification treatment has been drawing attention in which odorous substances and toxic substances are decomposed by utilizing the oxidizing power of ozone, and further sent to the activated carbon layer for adsorption removal. In clean water treatment with ozone, ozone gas generated by corona discharge of an ozone generator is blown as fine bubbles from a diffuser in an ozone contact pond and dissolved in water, and the oxidative power of the dissolved ozone causes odorous substances, toxic substances and other organic substances To remove.

Since ozone gas can be generated electrically, it is easy to adjust and control the injection amount. However, there are the following problems.

Generating ozone requires a great deal of power cost. Therefore, it is necessary to control the ozone gas concentration and the ozone injection rate according to the quality of water flowing into the ozone contact pond. However, automatic control of the ozone injection amount cannot be performed because there is no method and apparatus for measuring the concentration of the odorous substance or toxic substance to be removed online. Currently, the empirical method is to keep the ozone injection rate constant, or manually increase the ozone injection rate only when the concentration of odorous substances and toxic substances becomes high, or to dissolve it in the treated water flowing out from the ozone contact pond. The mainstream method is to control the ozone injection amount so that the ozone concentration becomes constant.

Under the circumstances, a method for controlling the ozone injection amount has been actively researched, but the current situation is that no reliable method has been found yet. Regarding the method of controlling the amount of injected ozone, JP-A-6-269786 and JP-A-6-269786
JP-A-6-63570, JP-A-3-56196, JP-A-6-792
No. 90, etc. Of these, JP-A-6-269
Japanese Patent No. 786 describes that an appropriate amount of ozone for musty odor substances is obtained using a predetermined algorithm, and an amount of appropriate ozone required for decomposition of musty odor substances is calculated based on a relative reaction rate constant.

[0008]

SUMMARY OF THE INVENTION According to the present invention, the amount of ozone injected can be calculated online by modeling the relative reaction rate constant, which varies depending on the type and concentration of the dissolved substance dissolved in the inflow water, with an online measurable item. An object is to provide a control method and a control device for the ozone injection amount that can be determined.

[0009]

According to the present invention, an organic substance which is oxidatively decomposed by ozone is divided into a substance to be removed and a substance other than that, and a substance other than the substance to be removed reacts with ozone and the substance to be removed. By modeling the effect on the above with items that can be online, the optimum ozone injection amount can be controlled online.

The present invention inputs the measured water quality of treated water and the assumed amount of ozone gas injection into an ozone reaction model equation modeled using a relative reaction rate constant representing the reaction rate of ozone and an odorous substance. In this method, the concentration of dissolved odor substance after ozone treatment is calculated, and the amount of ozone gas injection is determined using the calculated amount as an index.
r · Cs2, where Cs2 is the concentration of dissolved substances that are oxidized,
r is a proportionality constant), and an improved ozone reaction model formula is provided, and the ozone gas injection amount is determined by this improved ozone reaction model formula.

As the value of Cs2, the ultraviolet absorption luminosity before ozone injection can be used.

The ozone reaction model formula is, as shown in FIG. 1, the amount of change in dissolved ozone concentration, the amount of change in vapor phase ozone concentration, the amount of change in dissolved odorous substance concentration after ozone treatment, and the coexistence after ozone treatment. It is desirable to use the ozone reaction model formula of the simultaneous equations of four elements for calculating the change amount of the substance concentration.

The ozone injection amount control device of the present invention comprises an ozone generation amount control computer having an ozone reaction model equation modeled by using a relative reaction rate constant representing the reaction rate of ozone and an odorous substance. By inputting the measured water quality of the treated water and the assumed value of the ozone gas injection amount into the model formula, the dissolved odorous substance concentration after ozone treatment is calculated, and the ozone gas injection amount is determined using this calculated value as an index. In order to control the amount of ozone generation, the improved ozone reaction model formula, in which the relative reaction rate constant of the ozone reaction model formula is represented by (1 + r · Cs2, where Cs2 is the concentration of the dissolved substance to be oxidized, and r is a proportional constant) It is characterized by having a computer.

When the ozone injection amount is determined by the method of the present invention, the odorant concentration is input to the ozone reaction model formula, but the odorant concentration hardly changes on a daily basis. Can be used.

In the improved ozone reaction model formula of the present invention, not only the odorous substance is removed but also the proportional constant r is changed depending on the substance to be removed by ozone oxidation, so that the ozone generation amount can be controlled.

[0016]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below in the case where the target odorous substance to be removed by ozone is limited to 2-MIB (dimethylisoborneol).

The ozone gas injected into the ozone contact pond dissolves from the gas phase to the liquid phase. The dissolved ozone concentration at that time is
It is calculated by applying the model shown in Expression (1).

[0018]

[Equation 1]

Here, C1: dissolved ozone concentration, C1 *:
Saturated dissolved ozone concentration (mg / L), KL: overall mass transfer coefficient (1 / m · min), a: gas-liquid contact area (m ² ) per unit contact tank.

The symbols in the formulas shown below represent the following.

T: water temperature (° C.), V: contact tank volume (m ³ ), dB: bubble diameter (m), VB: bubble rising speed
(m / min), Qg: Inflow gas amount (Nm ³ / min), H: Effective depth of contact tank (m), S: Partition coefficient, Kde: Self-decomposition reaction coefficient (1 / mm) of dissolved ozone, Cs: Odorant (2
-MIB) concentration (mg / L), Cs2: dissolved substance concentration (mg / L) that is oxidized, pH: pH, Kox: 2-MI
Oxidative decomposition coefficient of B (1 / min / mg / L), Kr: 2-MI
B unit amount Oxidation required ozone amount (g · O ₃ / g · 2-MI
B), Kr2: Unit amount of dissolved substance to be oxidized Oxidation required amount of ozone (g · O ₃ / g · dissolved substance), Kox ′: Oxidative decomposition coefficient in the presence of coexisting substance (1 / min / mg / L) ), K
ox2: Oxidation reaction coefficient of coexisting substance (1 / min / mg /
L), R: Relative reaction rate constant, r: Proportional constant (1 / mg /
L), OH: Udon of hydride ion (mol / L).

Overall mass transfer coefficient KLa in equation (1)
Is expressed by the product of the overall mass transfer coefficient KL and the gas-liquid contact area a per unit contact tank. Therefore, known equation (2),
The formula (5) derived from the formulas (3) and (4) is used.

[0023]

[Expression 2] KL = (0.038 · T + 1.22) · 10 ⁻⁴ (2)

[0024]

(Equation 3)

[0025]

(Equation 4)

[0026]

(Equation 5)

C1 * in the equation (1) is the saturated dissolved ozone concentration, and is calculated by the product of the distribution coefficient S and the dissolved ozone concentration Cl as in the equation (6) according to Henry's law. The distribution coefficient S is calculated by the water temperature T from the equation (7).

[0028]

[Equation 6] Cl * = S · Cl (6)

[0029]

(Equation 7)

For the self-decomposition of dissolved ozone dissolved from the gas phase to the liquid phase, the model shown in equation (8) is applied. The self-decomposition reaction coefficient Kde of dissolved ozone is calculated from equations (9) and (10).

[0031]

(Equation 8)

[0032]

[Equation 9]

[0033]

(Equation 10)

Regarding the oxidative decomposition reaction in the case where only dissolved ozone and 2-MIB are present, formula (11) was applied to 2-MIB and formula (12) was applied to dissolved ozone.

[0035]

[Equation 11]

[0036]

(Equation 12)

The 2-MIB oxidative decomposition coefficient Kox is expressed by the equation (1)
Calculated from 3). Further, the 2-MIB unit amount oxidation demand ozone amount Kr is defined as the amount of ozone consumed when the 2-MIB unit amount is oxidatively decomposed, and 1 mol of ozone molecule is 2-
Equation (14) applies, considering that one mole of the MIB molecule is oxidized.

[0038]

(Equation 13)

[0039]

[Equation 14]

In the present invention, organic substances other than 2-MIB are considered as follows. 2 for actual tap water
-In addition to MIB, various organic substances, inorganic substances, metal ions, etc. are contained. Substances other than 2-MIB to be removed are included together with coexisting substances. This coexisting substance promotes or inhibits the oxidative decomposition of 2-MIB depending on the type and concentration of the constituent substances. Therefore, the degree of promotion and inhibition of the oxidative decomposition of 2-MIB is represented by the change in the oxidative decomposition coefficient Kox of the equation (11). Using the relative reaction rate constant, the oxidative decomposition coefficient Kox ′ in the presence of coexisting substances
It is represented by the product of the relative reaction rate constant and Kox. In the present invention,
For convenience, the relative reaction rate constant is represented as R in the equation (15).

[0041]

(Equation 15)

In the actual concentration range of the coexisting substance in the raw tap water, the relative reaction rate constant R and the dissolved substance Cs2 oxidized by ozone can be linearly approximated. Apply the model shown.

[0043]

## EQU16 ## R = 1 + r.multidot.Cs2 (16) Here, the proportional constant r is a value that differs depending on the composition of the coexisting substance, and is therefore identified by the measured value. Therefore, the apparent oxidative decomposition coefficient Kox ′ in the presence of coexisting substances
Is expressed by equation (17).

[0044]

[Equation 17] Kox ′ = R · Kox (17) The apparent oxidative decomposition coefficient Kox ′ is calculated by the equations (11) and (1).
Substituting into Kox in 2), the oxidative decomposition of dissolved ozone and 2-MIB is shown in equations (18) and (19).

[0045]

(Equation 18)

[0046]

[Equation 19]

Regarding the oxidative decomposition of dissolved ozone and 2-MIB in the presence of coexisting substances by substituting equation (17) into equations (18) and (19), equations (20) and (21) Apply the model shown in.

[0048]

(Equation 20)

[0049]

(Equation 21)

Regarding the oxidative decomposition reaction of the coexisting substance and the dissolved ozone, the formula (2
2), the model shown in Expression (23) is applied.

[0051]

(Equation 22)

[0052]

(Equation 23)

The oxidative decomposition reaction coefficient Kox2 of the dissolved substance oxidized by ozone is identified by an actual measurement value. Further, the dissolved substance unit amount oxidation demand ozone amount Kr2 is determined as follows. Ozone mainly reacts with double bonds and double bonds 1
One ozone is consumed for each piece. There are 2 carbon atoms (12 × 2 = 24 g) forming the double bond and 3 oxygen atoms (16 × 3 = 48 g) forming one ozone molecule. The value.

[0054]

(Equation 24)

The coexisting substance concentration is KMnO here.
₄ (potassium permanganate) consumption will be used. Since the KMnO ₄ consumption represents the total amount of organic substances in water and metal ions that are easily oxidized, it does not contradict the definition of coexisting substances.

As described above, the ozone reaction model formula was improved so that it can be applied to the actual water quality of raw water.
The improved ozone reaction model equation is shown in FIG. Online measurement of KMnO ₄ consumption is not possible for coexisting substance concentration. However, from the actual measurement results, there is a strong correlation between the consumption of KMnO ₄ flowing into the ozone contact pond and the value of ultraviolet absorbance that can be measured online, as shown in FIG. Therefore, the value of the ultraviolet absorbance of ozone-treated water is used as the coexisting substance concentration. In the improved ozone reaction model formula, the ultraviolet absorbance before the ozone injection in the past, the water temperature, the pH, the concentration of dissolved odorous substances before the ozone injection, the inflow water amount, the ozone gas injection amount,
The dissolved ozone concentration and the measured value of the dissolved odor substance after ozone injection are input, and calculation is performed according to the flow shown in FIG.
Is identified. Then, the obtained value of r is modeled by the inflow water quality. Generally, the reaction rate of a chemical reaction depends on the water temperature, p
Since it is affected by H, the value of r also depends on water temperature and pH.
It is thought to change depending on. This time, in our data, it was found that r and the water temperature are correlated as shown in FIG. Therefore, the model shown in Expression (25) is applied to r.

[0057]

(Equation 25)

The method of the present invention will be described below by way of specific examples.

FIG. 5 shows an apparatus to which the method of the present invention is applied. The flow rate of the water to be treated flowing into the ozone contact pond 1 is measured by a flow meter 3, the coexisting substance concentration is measured by a UV meter 4, the water temperature is measured by a water thermometer 5, and the pH is measured by a pH meter 6.

All these measurement results are input to the computer 9 online. The value of r was identified from the measured value from the water thermometer 5, and the amount of change per day was small.
-The MIB is manually input to the computer 9. The set value of the dissolved 2-MIB concentration in the water to be treated flowing out from the ozone contact pond is set in the computer 9. Computer 9
At, the ozone injection rate is changed, the improved ozone reaction model is calculated, and the ozone injection rate is changed until the dissolved 2-MIB concentration in the water to be treated reaches a set value. Based on the obtained calculation results, the ozone flow meter 7 and the ozone meter 8
By controlling the amount of ozonized air from the value of, the ozone generator 2 can be controlled online. The calculation result is stored in the storage device 10.

The method of determining the ozone injection amount and the method of controlling the same in the water purification method using ozone have been described above. In this example, the removal of 2-MIB of the odorous substance was described, but the present invention can be applied to all substances by modeling the above r according to each substance.

[0062]

INDUSTRIAL APPLICABILITY In the present invention, substances contained in tap water other than odorous substances are collectively treated as coexisting substances, and the effect of this coexisting substance on the oxidative decomposition of ozone and the oxidative decomposition of coexisting substances of ozone. By taking into consideration the effect on the above, it became possible to make a model with a value that can be measured online, and it became possible to put into practical use an online control process of the ozone injection amount according to the inflow water quality to the ozone contact pond.

[Brief description of drawings]

FIG. 1 is a diagram showing an improved ozone reaction model formula.

FIG. 2 is a diagram showing a correlation between KMnO ₄ consumption of inflow water of an ozone contact pond and UV absorbance.

FIG. 3 is a flow chart for deriving a proportional constant r from an actual measurement value.

FIG. 4 is a diagram showing a correlation between a proportional constant r and a water temperature of inflow water of an ozone contact pond.

FIG. 5 is a schematic diagram showing a flow of water and an electric signal system of a water purification apparatus to which the method of the present invention is applied.

[Explanation of symbols]

1 ... Ozone contact pond, 2 ... Ozone generator, 3 ... Flow meter,
4 ... UV meter, 5 ... Water temperature meter, 6 ... pH meter, 7 ... Ozone flow meter, 8 ... Ozone meter, 9 ... Computer, 10 ... Storage device.

Front page continuation (72) Inventor Nobuyoshi Yamakoshi 5-2-1 Omika-cho, Hitachi City, Ibaraki Prefecture Hitachi Ltd. Omika Plant, Ltd. (72) Hiroyasu Yasutomi 5-2-1 Omika-cho, Hitachi City, Ibaraki Prefecture Incorporated company Hitachi Ltd. Omika Plant (72) Inventor Shoji Watanabe 7-1, 1-1 Omika-cho, Hitachi City, Ibaraki Prefecture Hitachi Ltd. Hitachi Research Laboratory (72) Inventor Koji Kageyama 7-chome, Omika-cho, Ibaraki Prefecture No. 1 in Hitachi, Ltd. Hitachi Research Laboratory

Claims (4)

[Claims] 1. A method for controlling the amount of injected ozone in advanced water purification treatment in which dissolved odorous substances in water to be treated are decomposed and removed by injecting ozone, and a relative reaction rate constant representing the reaction rate between ozone and odorous substances. Using the ozone reaction model equation including, input the water quality measurement value of the water to be treated and the assumed value of ozone gas injection into this model equation to calculate the dissolved odor substance concentration after ozone treatment, and obtain the calculated value. In the method of determining the ozone gas injection amount as an index, an improved ozone reaction model equation expressing the relative reaction rate constant by (1 + r · Cs2, where Cs2 is the concentration of dissolved substance to be oxidized, and r is a proportional constant) is used. A method for controlling an ozone injection amount, characterized in that an ozone gas injection amount is determined by an improved ozone reaction model formula. 2. The method according to claim 1, wherein the Cs
A method for controlling the amount of injected ozone, characterized by using the ultraviolet absorption luminosity before injection of ozone as the value of 2. 3. The method according to claim 1 or 2, wherein the modified ozone reaction model equation is a change amount of dissolved ozone concentration,
It is characterized in that it is represented by an ozone reaction model formula of a four-way simultaneous equation that calculates the amount of change in vapor phase ozone concentration, the amount of change in dissolved odorous substance concentration after ozone treatment, and the amount of change in coexisting substance concentration after ozone treatment. Ozone injection amount control method. 4. A device for controlling the amount of injected ozone in advanced water treatment, which decomposes and removes dissolved odorous substances in water to be treated by injecting ozone, and is a relative reaction rate constant representing the reaction rate of ozone and odorous substances. A computer for ozone generation control including an ozone reaction model equation including is provided, and the dissolved odorous substance concentration after ozone treatment is input by inputting the water quality measurement value of the treated water and the assumed value of the ozone gas injection amount to the model equation. In the case where the ozone gas injection amount is calculated by using this calculated value as an index, the relative reaction rate constant of the ozone reaction model equation is (1 + r · Cs2, where Cs2 is the concentration of the dissolved substance to be oxidized, and r is Proportional constant)
An ozone injection amount control device comprising a control computer having an improved ozone reaction model formula represented by.