JP2005313078A - Water treatment method and water treatment system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a water treatment method and a water treatment system which can most efficiently perform decomposition treatment of an organic matter in water to be treated, and treatment for reducing a trihalomethane generating capacity, reduce the injection of useless ozone gas without increasing running costs of the system, and suppress the generation of by-products, such as bromate ion, which cannot be removed even by activated carbon treatment and chlorine treatment at the subsequent stage. <P>SOLUTION: The concentration of dissolved organic carbon in raw water is measured by an organic carbon analyzer 10 before introduction of the raw water into an ozone treatment pond 4, an ozone injection controller 11 determines the amount of ozone injected into the ozone treatment pond 4 from an ozone absorption rate corresponding to the measured dissolved organic carbon concentration, from a predetermined relation between a dissolved organic carbon concentration and an ozone absorption rate. Thereby a minimum ozone injection rate conformable to water quality of the raw water and required for the decomposition treatment of the organic matter and the treatment for reducing the trihalomethane generating capacity can be obtained. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a water treatment method and a water treatment system for performing water treatment based on ozone injection into water to be treated, such as water purification treatment, sewage treatment, industrial wastewater treatment, and food wastewater treatment.

  In water treatment at a water purification plant, groundwater or river surface water is introduced into a landing well as raw water, and flocculant is first injected into the raw water in a coagulating sedimentation basin to form a floc, and coagulation sedimentation processing is carried out. . After that, the supernatant water is guided to the sand filtration pond to remove the suspended matter, and finally, a disinfecting treatment is performed by injecting a disinfecting chlorine agent to supply it to demand.

  However, in recent years, water pollution due to industrial wastewater, domestic wastewater, etc. has progressed, and pollution of water source water quality has become a social problem. Specifically, it has been pointed out that upstream rivers contain trace amounts of persistent substances such as musty odors, organic compounds such as humic substances, agricultural chemicals, dioxins, and environmental hormones. .

  Note that humic substances are a type of polymer compound composed of various organic compounds that are decomposed by microorganisms such as plants. In other words, it is an organic substance produced in the process of oxidizing cellulose and lignic acid such as trees, causing river coloring and a causative substance of carcinogenic trihalomethane, which is a by-product of chlorine disinfection.

  In addition, pollution is further progressing on the downstream side of the river, and in addition to these pollutants, pollution by various chemical substances such as ammonia, organochlorine detergents, synthetic detergents, and dyes is spreading.

  The above-described conventional water purification treatment methods can not only cope with the removal of such pollutants, but also increase the amount of trihalomethane produced by chlorination due to the increase in humic substances that are precursors of trihalomethane. Also, with the increase in ammonia, chlorine and ammonia produce chloramine by reaction, consuming more chlorine than necessary. For this reason, as a result of the increase in the chlorine injection amount, the production amount of trihalomethane is increased. Trihalomethane is a substance that has been pointed out to be carcinogenic, and it is necessary to remove trihalomethane precursors such as humic substances in the water treatment process before chlorine injection.

  Therefore, water treatment plants incorporating an advanced water purification system combining ozone treatment and granular activated carbon treatment or biological activated carbon treatment are increasing as a treatment method capable of decomposing and removing various pollutants that cannot be removed by conventional treatment processes. . The ozone treatment uses an ozonized gas in which a part of oxygen is ozonized by discharge (silent discharge) using air or oxygen as a raw material in an ozone generator, and this ozonated gas is brought into contact with water to be treated. Oxidizing and decomposing pollutants in treated water with strong oxidizing power of ozone.

  In particular, advanced water purification systems combining ozone treatment and granular activated carbon or biological activated carbon are widely used, and the previous ozone treatment decomposes and removes pollutants that cannot be treated by conventional water purification methods. In particular, odorous substances, decomposition of chromaticity components, oxidation and insolubilization of iron and manganese, and organic substances including organic halogen compounds are decomposed. And adsorption is performed when the latter stage is granular activated carbon, and when it is biological activated carbon, it is further decomposed and removed by microorganisms.

  In water purification plants that have introduced an ozone treatment system as an advanced water treatment system, it is necessary to inject ozone gas enough to oxidatively decompose the target substance to be treated. However, excessive ozone gas injection not only increases the power cost for generating ozone, but also increases the concentration of dissolved ozone in the ozone-treated water.

  When dissolved ozone concentration is high, the problem of shortening the lifetime of the biological activated carbon of the latter stage arises. Further, when bromine ions are contained in the raw water, problems such as the formation of bromate ions, which are pointed out as carcinogenic as a byproduct of ozone treatment, occur.

  Therefore, it is necessary to control the injection amount of the ozonized gas so that both the dissolved ozone concentration in the ozone-treated water and the removal rate of the substance to be treated become optimum values. As a method of controlling the ozonized gas injection amount, the ozone injection rate is controlled constant so that the ozone injection rate is constant with respect to the amount of treated water introduced, or the dissolved ozone concentration at the ozone treatment pond outlet becomes a constant value. Known are dissolved ozone concentration constant control to be controlled, exhaust ozone concentration constant control to control the ozone concentration discharged as unreacted ozone to a constant value, and the like.

  In each of these control methods, each set value for constant control is obtained by conducting an experiment in advance to obtain the reaction characteristics between the water to be treated and ozone. And other water purification plant data, and the operator changes it manually if necessary. In general, from the viewpoint of injecting ozone without excess or deficiency, constant dissolved ozone concentration control is often employed. With this method, the dissolved ozone concentration in the treated water can be controlled so as to be in a concentration range in which the amount of bromate ions generated does not increase, and the formation of bromate ions can be easily suppressed (see, for example, Patent Document 1).

  In the advanced water purification system that introduced the conventional ozone treatment system, the raw water is coagulated and settled, then the ozone treatment, removal of soluble components with granular activated carbon (biological), and the finishing treatment in the filtration pond. There is a medium ozone treatment system. In addition to this, there is a post-ozone treatment system in which the raw water is subjected to coagulation sedimentation and sand filtration to remove turbidity, and then the soluble components are removed with ozone and granular activated carbon (biological) in the subsequent stage.

  Here, the case of the post-ozone treatment method will be described. After the raw water is introduced into the landing well, a flocculant and, if necessary, a pH adjuster are injected at the inlet of the coagulation sedimentation basin. For this reason, the suspended matter of clay, bacteria and algae in the raw water is aggregated in advance in the coagulation sedimentation basin and separated as floc. Then, after removing the turbidity remaining in the sand filtration pond, it is introduced into the ozone treatment pond. The treated water ozone-treated in the ozone treatment pond is inserted into the activated carbon treatment pond (granular or biological activated carbon), and the treatment target substance remaining here is decomposed and removed. Finally, a chlorine agent for disinfection is injected at the entrance of the water purification pond.

  In general, an ozone treatment pond includes an ozone contact tank in which ozonized gas is injected into contact with water to be treated and contacted and mixed in a plurality of stages. Moreover, the residence tank for ensuring the reaction time of ozone and to-be-processed water is installed in the back | latter stage of these ozone contact tanks. Further, there is provided an exhaust ozone treatment device for decomposing and removing exhausted ozonized gas discharged from the ozone contact tank in an unreacted state.

  An ozone diffusing tube is installed in the lower part of each ozone contact tank, and ozonized gas is supplied from the ozone generator and injected as bubbles into the ozone contact tank. A dissolved ozone concentration meter is installed at the treated water outlet of the ozone treatment pond, and the output of the dissolved ozone concentration meter is input to the ozone injection control device to control the amount of ozonized gas injected into the ozone contact tank.

  In the above configuration, the raw water from which suspended substances have been removed in the previous stage flows into the ozone treatment pond as treated water. Ozonized gas is injected into each ozone contact tank in the ozone treatment pond from an air diffuser provided in the lower part, and is injected into the water to be treated as bubbles. Ozone is dissolved in the water to be treated by gas-liquid contact between the ozonized gas bubbles and the water to be treated, and an oxidation reaction with the solute causes a low molecular weight organic polymer compound that is a trihalomethane precursor, mainly humic substances. , Deodorization by decomposition of 2-methylisoborneol (2-MIB), geosmin and the like is achieved.

  In the treated water treated with ozone, the dissolved ozone concentration is measured by a dissolved ozone concentration meter installed at the outlet of the ozone treatment pond, and the measured value is input to the ozone injection control device. In the ozone injection control device, the amount of ozonized gas injected from the ozone generator to the ozone contact tank based on the difference between the preset dissolved ozone concentration set value and the measured value of the dissolved ozone concentration meter (in the ozonized gas) The ozone concentration and / or the injection flow rate, or both), that is, the ozone injection rate for the water to be treated.

  Of the ozonized gas, the ozonized gas discharged in an ozone contact tank without being dissolved is discharged from the upper vapor phase of the ozone treatment pond, detoxified by the exhaust ozone treatment device, and then released into the atmosphere. If there is a large amount of unreacted ozone, the generated ozone is lost. Dissolved ozone concentration in the ozone-treated water is also a loss of generated ozone. Therefore, it is necessary to reduce the generation of wasteful ozone by injecting the minimum amount of ozone in accordance with the change in the properties of the material to be treated.

  However, in practice, it is difficult to perform feedback control while confirming changes in the substance to be treated in the water to be treated. Therefore, the dissolved ozone concentration setting value of the ozone injection control device is determined so that a little more ozone is always injected. ing.

  Moreover, if undissolved ozonized gas bubbles enter the dissolved ozone concentration meter, the measured value becomes unstable. Therefore, the numerical value obtained by dividing the ozonized gas absorption amount (difference between the injected ozone amount and the discharged ozone amount) by the organic carbon concentration (TOC) in the water to be treated instead of the dissolved ozone concentration is within a certain range. There has been proposed a control method (see, for example, Patent Document 2).

  In this case, as a method of measuring the TOC in the water to be treated, a method is generally used in which the total carbon concentration (TC) and inorganic carbon concentration (IC) of the sample are measured, and the TOC is obtained by subtracting the IC from the TC. Yes. In this method, the measurement time for one sample takes about 15 to 30 minutes. In Patent Document 2, the TOC of the treated water inflow portion of the ozone treatment pond is measured, but in this case, there is a problem that a time difference occurs in the control due to the measurement time and real-time control is difficult.

  On the other hand, as a method of performing feedback control while confirming the quality of the water to be treated, a method of performing feedback control by measuring ultraviolet absorbance in treated water oxidized and decomposed by ozone has been proposed (for example, see Patent Document 3). .

  In this case, a wavelength of about 260 nm is used for ultraviolet rays that are generally used as an indicator of the organic substance concentration. However, when dissolved ozone is present in the ozone-treated water, the ultraviolet absorption wavelength of ozone is about 254 nm, which is very close to the measurement wavelength of organic matter concentration, so it cannot be measured accurately due to the influence of dissolved ozone. As a result, there is a problem that the ozone injection amount cannot be accurately controlled.

  Further, when bromide ions are present in the water to be treated, bromate ions are generated as a by-product by the reaction with ozone. This bromate ion has been pointed out to be carcinogenic and is regulated worldwide. That is, the guideline value by the World Health Organization (WHO) is 25 μg / L, and the control value by the US Department of Environmental Protection is 10 μg / L.

  The produced bromate ions are difficult to remove by the subsequent activated carbon treatment (granular or biological), and in order to reduce the bromate ions, it is necessary to suppress the production during the ozone treatment. The amount of bromate ions produced by ozone treatment is proportionally dependent on the product (CT value) of bromide ion concentration in the water to be treated, dissolved ozone concentration, and retention time (reaction time) of the water to be treated in the ozone treatment pond.

  In an actual water purification plant, the residence time depends on the amount of treated water in the plant because the size of the ozone treatment pond does not change. However, it is difficult to change the amount of treated water appropriately for ozone treatment. Therefore, a method of suppressing the formation of bromate ions by adjusting the dissolved ozone concentration in the treated water is effective.

  Here, in the conventional ozone water treatment control system based on the constant control of the dissolved ozone concentration, the set value of the dissolved ozone concentration must be set to a low value in order to suppress the production of bromate ions. However, if the set value is too low, it approaches or falls below the lower limit of measurement of the dissolved ozone concentration meter. In this case, the measurement value of the dissolved ozone concentration meter varies greatly and the error is large, and the ozonized gas injection amount cannot be accurately controlled.

  Moreover, in order to suppress the production of bromate ions, it is necessary to lower the ozone injection rate by lowering the set value of the dissolved ozone concentration, but lowering the ozone injection rate is the object of decomposition by the original ozone. As a result, the ability to decompose odorous substances, chromaticity substances, trihalomethane precursors, etc. will be reduced, and the ozone injection rate cannot be lowered more than necessary. For these reasons, it is difficult to determine each set value for controlling the ozone gas injection amount in the conventional system, and it is impossible to deal with the fluctuation of the raw water quality in real time.

  Furthermore, one of the purposes of water treatment plants adopting advanced water treatment ozone treatment is to decompose trihalomethane precursors, but the main trihalomethane precursor humic substances have a fast decomposition reaction rate by ozone. And there are slow ones. The ratio varies depending on the type of raw water, season, and weather. Decomposition of humic substances with a fast decomposition reaction rate proceeds preferentially even at low dissolved ozone concentrations, but the dissolved ozone concentration is increased so that it decomposes to humic substances with a slow decomposition reaction rate, that is, the amount of ozone gas injected (ozone If the injection rate is increased, by-products such as bromate ions that cannot be removed by the subsequent activated carbon treatment or chlorination increase.

In addition, when humic substances having a slow decomposition reaction rate are subjected to ozonolysis halfway, the trihalomethane generating ability is increased. That is, ozonolysis of humic substances having a slow decomposition reaction rate means that unnecessary ozone is injected from the viewpoint of reducing trihalomethane production ability, resulting in an increase in operating cost.
JP 2000-288661 A JP 2000-288561 A JP-A-11-207368

  In this way, in the water treatment facility that combines ozone treatment and biological activated carbon treatment, it is possible to efficiently perform the decomposition treatment of organic matter in the water to be treated and the reduction treatment of trihalomethane production ability, and reduce wasteful ozone gas injection. In addition, it is difficult to control the injection of the minimum ozone necessary to suppress the generation of by-products such as bromate ions that cannot be removed by the subsequent activated carbon treatment or chlorination treatment.

  It is an object of the present invention to reduce the wasteful ozone gas injection that increases the operating cost of equipment and can reduce the wasteful ozone gas injection that can most efficiently perform the decomposition treatment of organic matter in the water to be treated and the reduction of trihalomethane production ability, and the activated carbon in the latter stage An object of the present invention is to provide a water treatment method and a water treatment system that can suppress the production of by-products such as bromate ions that cannot be removed even by treatment or chlorination.

  The water treatment method according to the present invention is a water treatment method in which suspended substances are removed from raw water, then ozone treatment is performed in an ozone treatment pond, and after the ozone treatment, activated carbon treatment is performed in the activated carbon treatment pond. Is introduced into an organic carbon concentration meter after removing suspended substances, and the dissolved organic carbon concentration of raw water is measured. From the relationship between the dissolved organic carbon concentration and ozone absorption rate obtained in advance, The amount of ozone injected into the ozone treatment pond is determined based on the ozone absorption rate corresponding to the measured concentration of dissolved organic matter in the raw water.

  In the method of the present invention, the ratio between the dissolved organic carbon concentration of the raw water and the fluorescence intensity of the raw water at the entrance of the ozone treatment pond is obtained, and the amount of ozone injected into the ozone treatment pond is controlled based on the value of this ratio. To do.

  In the method of the present invention, the fluorescence intensity of the raw water at the entrance portion of the ozone treatment pond and the fluorescence intensity of the treatment water at the exit portion of the ozone treatment pond are respectively measured, and the fluorescence of the treatment water with respect to the fluorescence intensity of the raw water A ratio of intensity is obtained, a ratio that becomes a boundary of reaction to ozone injection based on a decrease characteristic of the ratio with respect to a change in ozone absorption amount is obtained in advance, and a ratio that becomes the boundary is obtained by measuring the fluorescence intensity. As a target value for the above, the amount of ozone injected into the ozone treatment pond may be controlled.

  Further, in the method of the present invention, the ozone treatment pond has a plurality of ozone contact tanks which are separated so as to communicate with each other and are supplied with ozone individually, and fluorescence at the inlet and outlet of each ozone contact tank is provided. The fluorescence intensity decrease rate in each ozone contact tank is determined from the difference in intensity, and the ozone injection rate for each ozone contact tank is determined according to the fluorescence intensity decrease rate, and the determined injection rate is set as a target value. The amount of ozone injected into the ozone contact tank may be controlled.

  Furthermore, in the method of the present invention, the dissolved oxygen concentration of the treated water at the ozone treatment pond outlet is measured, and the amount of ozone injected into the ozone treatment pond is limited so that the dissolved oxygen concentration does not exceed the set value.

  In the water treatment system according to the present invention, a part of raw water is introduced through a filter for removing suspended solids, and an organic carbon concentration meter for measuring the dissolved organic carbon concentration of the raw water, Ozone injection control device for determining the amount of ozone injected into the ozone treatment basin based on the ozone absorption rate corresponding to the measured concentration of dissolved organic matter in the raw water based on the relationship between the organic carbon concentration and the ozone absorption rate It is characterized by comprising.

  Further, in the water treatment system of the present invention, a fluorescence analyzer for measuring the fluorescence intensity of the raw water is provided at the entrance of the ozone treatment pond, and the ozone injection control device is used for the dissolved organic carbon concentration of the raw water and the ozone treatment pond. It has the function of obtaining the ratio of the raw water fluorescence intensity at the entrance and controlling the amount of ozone injected into the ozone treatment pond based on the value of this ratio.

  In the water treatment system of the present invention, a fluorescence analyzer that measures the fluorescence intensity of raw water at the entrance of the ozone treatment pond and a fluorescence analyzer that measures the fluorescence intensity of the treated water at the exit of the ozone treatment pond are provided. The injection control device has a function for obtaining the ratio of the fluorescence intensity of the treated water to the fluorescence intensity of the raw water from the fluorescence intensity of the raw water and the fluorescence intensity of the treated water measured by the respective fluorescence analyzers, and the ozone absorption obtained in advance. Using the ratio that becomes the boundary of the reaction to ozone injection based on the decreasing characteristic of the ratio with respect to the change in quantity, the ratio that becomes the boundary is set as the target value for the ratio obtained by the measurement of the fluorescence intensity, and the ozone to the ozone treatment pond And a function of controlling the injection amount.

  In the water treatment system of the present invention, the ozone treatment pond has a plurality of stages of ozone contact tanks that are separated so as to communicate with each other and are individually supplied with ozone. The ozone injection control device has a function for obtaining the fluorescence intensity reduction rate in each ozone contact tank based on the difference in fluorescence intensity between the inlet and outlet of each ozone contact tank, and these fluorescence intensity reduction rates. The ozone injection rate for each ozone contact tank may be obtained according to the above, and the ozone injection rate to each ozone contact tank may be controlled using the obtained injection rate as a target value.

  Furthermore, in the water treatment system of the present invention, a dissolved ozone concentration meter that measures the dissolved oxygen concentration of the treated water is provided at the outlet of the ozone treatment pond, and the ozone injection control device prevents the dissolved oxygen concentration from exceeding a set value. The structure which has a function which restrict | limits the ozone injection amount to an ozone treatment pond may be sufficient.

  According to the present invention, the dissolved organic carbon concentration of raw water is measured, and from the relationship between the dissolved organic carbon concentration obtained in advance and the ozone absorption concentration, it corresponds to the measured dissolved organic carbon concentration of the raw water. Because the amount of ozone injected into the ozone treatment liquid is determined based on the ozone absorption rate, the most effective is the degradation of organic matter in the water to be treated and the reduction of trihalomethane production capacity, which suits the quality of the raw water. The minimum ozone injection rate that can be obtained can be obtained.

  In addition, when the amount of ozone injected into the ozone treatment pond is controlled based on the ratio of the dissolved organic carbon concentration of the raw water and the fluorescence intensity of the raw water at the entrance of the ozone treatment pond, sudden changes in the quality of the raw water On the other hand, the ozone injection amount can be quickly controlled.

  Further, the ratio of the fluorescence intensity of the treated water relative to the fluorescence intensity of the raw water is obtained in advance, the ratio that becomes the boundary of the reaction with respect to the ozone injection is obtained in advance, and the ozone injection amount is controlled with the ratio that becomes the boundary as the target value. A substance with a fast reaction rate can be reliably decomposed, and useless injection of ozone gas into a substance with a slow reaction rate can be prevented.

  In addition, for each ozone contact tank in the ozone treatment pond, if the fluorescence intensity reduction rate in each ozone contact tank is determined and the ozone injection rate is determined according to the fluorescence intensity reduction rate, each ozone contact tank The optimal ozone injection amount control for the tank can be performed.

  Furthermore, a dissolved ozone concentration meter is installed at the outlet of the ozone treatment pond, and the ozone injection amount is limited so that the dissolved oxygen concentration of the treated water does not exceed the set value, thereby reliably preventing excessive ozonated gas injection. be able to.

  Hereinafter, an embodiment of a water treatment method and a water treatment system according to the present invention will be described in detail with reference to the drawings.

  FIG. 1 is a block diagram showing a processing flow of an advanced water purification system introduced with an ozone treatment system. In FIG. 1, reference numeral 1 denotes a landing well, from which raw water is introduced from a water source such as a river (not shown). Reference numeral 2 denotes a coagulation sedimentation basin, and raw water is introduced from the landing well 1, and a coagulant and, if necessary, a pH adjusting agent are injected by a drug injection device 7 at the inlet portion. In the coagulation sedimentation basin 2, suspended substances such as clay, bacteria, and algae in the raw water are aggregated in advance and separated as flocs, and the turbidity remaining in the subsequent sand filtration pond 3 is removed. That is, suspended substances in the raw water are removed by the coagulation sedimentation basin 2 and the sand filtration basin 3.

  Reference numeral 4 denotes an ozone treatment pond, which is connected to the subsequent stage of the sand filtration pond 3, and raw water from which suspended substances have been removed is introduced as water to be treated, and ozone treatment is performed with an ozonized gas injected from the ozone generator 12. An activated carbon treatment pond (granular or biological activated carbon) 5 is connected to the subsequent stage of the ozone treatment pond 4 and adsorbs and decomposes and removes the substance to be treated remaining in the treated water treated with ozone. A purified water pond 6 is provided on the outlet side of the activated carbon treatment pond 5, and a chlorine agent 8 is injected at the entrance for disinfection.

  Reference numeral 10 denotes an organic carbon concentration meter, which is connected to the landing well 1 through a water quality test sample intake pipe attached to the landing well 1 and a filtration filter 9 for removing suspended solids. A part of the sample water is sampled and the organic carbon concentration is measured. Reference numeral 13 denotes a dissolved ozone concentration meter, which samples ozone-treated water through a sample intake pipe for water quality inspection attached to the outlet of the ozone treatment pond 4 and measures the dissolved ozone concentration. Reference numeral 11 denotes an ozone injection control device, to which the measured values of the organic carbon concentration meter 10 and the dissolved ozone concentration meter 13 are input, and the ozone generator 12 is controlled so as to obtain an optimal ozone injection amount based on the respective measured values. Control.

  In the above configuration, the raw water is suspended in the raw water by the coagulation sedimentation basin 2 and the sand filtration pond 3 and flows into the ozone treatment pond 4. For this reason, the organic substance which is the object of ozone treatment in the ozone treatment pond 4 is only a dissolved organic substance. As an index of the dissolved organic substance concentration, there is a dissolved organic carbon concentration (DOC).

  Fig. 2 is a characteristic diagram showing the relationship between the dissolved organic carbon concentration (DOC) and the amount of ozone absorbed by the ozone treatment pond. By using this relationship, the minimum ozone injection amount can be estimated. Can do. Here, the amount of ozone absorption is defined by equation (1).

Ozone absorption amount = injection ozone gas concentration-(dissolved ozone concentration-exhaust ozone gas concentration)
(1)
Here, the measurement of the organic carbon concentration needs to be obtained by measuring the total carbon concentration and the inorganic carbon concentration of the sample as described above, and subtracting the inorganic carbon concentration from the total carbon concentration. The measurement time is about 15 to 30 minutes. In this embodiment, since the raw water collected from the landing well 1 is supplied to the organic carbon concentration meter 10 through the filtration filter 9, the organic carbon concentration meter 10 filters suspended substances in the raw water. Only the dissolved organic carbon concentration (DOC) will be measured. Since the treated water flowing into the ozone treatment pond 4 passes through the coagulation sedimentation basin 2 and the sand filtration pond 3 as described above, by using this time difference, before the treated water flows into the ozone treatment pond 4. In addition, the DOC can be measured.

  The ozone injection control device 11 obtains the ozone injection amount required for the water to be treated flowing into the ozone treatment pond 4 from the relationship shown in FIG. 2 based on the DOC value measured before flowing into the ozone treatment pond 4. The ozone generator 12 is controlled to obtain an optimal ozone injection amount for the treated water.

  A dissolved ozone concentration meter 13 is connected to the outlet of the ozone treatment pond 4, and this measured value output is input to the ozone injection control device 11. In the ozone injection control device 11, the upper limit value of the dissolved ozone concentration of the ozone treated water is set, and when the measured value of the dissolved ozone concentration meter 13 exceeds the set value, the ozone generation is performed so as to decrease the ozone injection amount. The device 12 is controlled.

  According to this embodiment, since the dissolved organic carbon concentration (DOC) can be measured before the water to be treated flows into the ozone treatment pond, the ozone injection amount can be appropriately controlled without a time delay. Can do. As a result, an amount of ozone suitable for the quality of the raw water can be injected, and the organic substance in the treated water can be decomposed and the trihalomethane generating ability can be reduced most efficiently. Moreover, useless ozonization gas injection | pouring can be prevented and the dissolved ozone concentration which remains in process water by excessive ozonization gas injection | pouring does not become high. For this reason, generation | occurrence | production of the by-products which cannot be processed in the activated carbon treatment pond of a latter stage, such as bromate ion produced by reaction of ozone and to-be-processed water, can be suppressed. Furthermore, the amount of ozonized gas injected into the ozone treatment pond can be optimized in real time against seasonal changes in the quality of treated water, fluctuations due to weather, and sudden fluctuations due to unexpected reasons.

  Further, in the above configuration, not only the measured value by the dissolved organic carbon concentration meter 10 but also the dissolved ozone concentration of the ozone treated water flowing out from the ozone treatment pond 4 is measured so that the measured value does not exceed the set value. In addition, the amount of ozonized gas injected into the ozone treatment pond 4 is controlled. As a result, even if the ozonized gas injection amount estimated based on the dissolved organic carbon concentration measurement value and the reaction characteristics of ozone and treated water in the ozone treatment pond 4 differ, Excessive injection into the treatment pond 4 can be prevented. That is, the ozonized gas is excessively injected, the concentration of dissolved ozone remaining in the ozone-treated water increases, and the production of highly toxic by-products caused by the reaction between ozone and the water to be treated can be suppressed.

  Next, the embodiment shown in FIG. 3 will be described. In FIG. 3, the organic carbon concentration meter 10 and the dissolved ozone concentration meter 13 at the outlet of the ozone treatment pond 4 are basically provided for the treatment flow from the landing well 1 to the water purification pond 6 and the ozone injection control device 11. The same as FIG.

  In FIG. 3, in addition to the above-described configuration, fluorescence analyzers 14 and 15 are attached to the inlet and outlet of the ozone treatment pond 4 via sample water intake pipes for water quality inspection, respectively. The fluorescence intensity of sample water sampled from the outlet is measured. The outputs of the fluorescence analyzers 14 and 15 are input to the ozone injection control device 11 together with the measured values of the organic carbon concentration meter 10 and the dissolved ozone concentration meter 13, and the optimum ozone injection amount is obtained based on the measured values. Thus, the ozone generator 12 is controlled.

  Next, the operation of this embodiment will be described with reference to FIGS. FIG. 4 shows the fluorescence intensity measured by selecting the fluorescence wavelength of 425 nm from the fluorescence emitted from the sample water by the fluorescence analyzer 14 on the inlet side of the ozone treatment pond 4 under the condition of the excitation wavelength of 345 nm, and the solubility. It is a figure which shows the relationship with organic substance carbon concentration (DOC). As can be seen from the figure, there is a good correlation between the fluorescence intensity of the water to be treated and the DOC.

  Here, as described above, dissolved organic substances include those having a fast decomposition reaction rate by ozone and those having a slow rate. The ratio varies depending on the type of raw water, season, and weather. The decomposition of an organic substance having a high decomposition reaction rate proceeds preferentially even at a low dissolved ozone concentration. However, increasing the dissolved ozone concentration so that it decomposes to organic substances with a slow decomposition reaction rate, that is, increasing the amount of ozone gas injection increases the amount of by-products such as bromate ions that cannot be removed by subsequent activated carbon treatment or chlorination treatment. End up. For this reason, in the ozone treatment pond 4, the substance having a high decomposition rate is mainly treated, and the remaining substance to be treated is removed by the activated carbon treatment pond 5 provided in the subsequent stage. Even if it does in this way, the soluble organic substance in to-be-processed water can fully be removed.

  That is, if there is a means for monitoring the reaction state of ozone and water to be treated, wasteful ozone injection can be prevented. In this embodiment, fluorescence intensity is used as means for monitoring the reaction state of ozone and water to be treated.

  FIG. 5 is a diagram showing the relationship between the ratio of the treated water fluorescence intensity to the raw water (treated water) intensity and the amount of ozone absorbed absorbed by the ozone treatment pond 4. As can be seen from the figure, as the amount of ozone absorption increases from zero, the substance having a fast reaction rate is first decomposed preferentially and the change in the fluorescence intensity decrease rate is large. When the substance with a fast reaction rate is reduced and only the substance with a slow reaction rate is decomposed, the change in the fluorescence intensity reduction rate becomes small. Therefore, the boundary between the reaction of a substance having a fast reaction rate and the reaction of a slow substance can be experimentally obtained, and the ozone injection amount can be feedback controlled using this boundary as a processing target value.

  That is, the ozone injection control device 11 obtains the ratio of the fluorescence intensity of the treated water to the fluorescence intensity of the raw water (treated water) from the fluorescence intensity measured at the entrance portion and the exit portion of the ozone treatment pond 4, and the ozone absorption amount Based on a decrease characteristic of the ratio with respect to the change in the ratio, a ratio that becomes a boundary of the reaction to ozone injection is obtained in advance, and the ratio that becomes the boundary is set as a target value for the ratio obtained by the measurement of the fluorescence intensity to the ozone treatment pond. The amount of ozone injection is controlled. As a result, a substance having a high reaction rate with respect to the ozone treatment is accurately decomposed, but an increase in the amount of ozone injected for attempting to decompose a substance having a low reaction rate can be prevented.

  Further, according to the measured value of the dissolved ozone concentration meter 13 provided at the outlet of the ozone treatment pond 4, the ozone injection control device 11 determines the ozone injection amount when the dissolved ozone concentration of the ozone treated water exceeds the upper limit value. Since the ozone generator 12 is controlled so as to decrease, excessive ozone injection can be prevented from this.

  According to this embodiment, since the dissolved organic carbon concentration (DOC) can be measured before the water to be treated flows into the ozone treatment pond 4, the ozone injection amount can be controlled without time delay. it can. Furthermore, by measuring the fluorescence intensity of the water to be treated and the fluorescence intensity after the ozone treatment, the progress of decomposition of the substance with a fast reaction rate is monitored by the fluorescence intensity decrease rate, and ozone injection is performed with the fluorescence intensity decrease rate as the control target value. Quantity feedback control can be performed. As a result, not only wasteful ozonized gas injection is prevented, but there is a high toxicity such as bromate ions generated by the reaction between ozone and the water to be treated due to excessive ozonized gas injection, and the secondary activated carbon treatment pond cannot be treated. Product generation can be suppressed. Furthermore, the amount of ozonized gas injected into the ozone treatment pond can be optimized in real time against seasonal changes in the quality of treated water, fluctuations due to weather, and sudden fluctuations due to unexpected reasons.

  In the above configuration, not only the measured value by the dissolved organic carbon concentration meter but also the dissolved ozone concentration of the ozone treated water flowing out from the ozone treatment pond 4 is measured so that the measured value does not exceed the set value. The ozonized gas injection amount into the ozone treatment pond is controlled. As a result, even if the ozonized gas injection amount estimated based on the dissolved organic carbon concentration measurement value and the reaction characteristics of ozone and treated water in the ozone treatment pond are different, excessive ozonized gas Is prevented from being injected into the ozone treatment pond. That is, the production | generation of the highly toxic by-product by excess ozonization gas injection | pouring can be suppressed.

  Next, the embodiment shown in FIG. 6 will be described. This embodiment pays attention to the configuration in the ozone treatment pond 4. In FIG. 6, the ozone treatment pond 4 includes a plurality of ozone contact tanks 16 for injecting ozonized gas into the water to be treated, contacting and mixing, a residence tank 17 for ensuring a reaction time of ozone and the water to be treated, ozone The exhaust ozone treatment device 18 decomposes and removes the exhausted ozonized gas discharged from the contact tank 16 in an unreacted state.

  Below each ozone contact tank 16, an ozone diffuser 19 is installed, and the ozonized gas from the ozone generator 12 is supplied via the flow rate adjusting valve 20, and as bubbles in the corresponding ozone contact tank 16. Injected. Sample water intake pipes for water quality inspection are attached to the treated water inlet of the ozone treatment pond 4, the lower treated water outlet of each of the three ozone contact tanks 16, and the outlet of the ozone treated pond 4, respectively. The sample water collected from here is guided to the fluorescence analyzers 14, 15, and 21.

  The sample water collected from the ozone treatment pond 4 outlet is also led to the dissolved ozone concentration meter 13. Similarly to each of the above-described embodiments, the sample water collected from the landing well 1 is guided to the organic carbon concentration meter 10 through the filtration filter 9.

  The measured value outputs of the organic carbon concentration meter 10, the fluorescence analyzers 14, 15, 21 and the dissolved ozone concentration meter 13 are input to the ozone injection control device 11, and the optimum ozone injection amount is based on the respective measured values. It is comprised so that the ozone generator 12 and the flow regulating valve 20 may be controlled.

Next, the operation of the present embodiment will be described with reference to FIG. FIG. 7 is a diagram showing changes in the fluorescence intensity decrease rate of sample water collected from the outlet of the ozone contact tank 16 at each stage. In addition, the ozone injection amount with respect to each ozone contact tank 16 shall be substantially equal. In the figure, if the first-stage fluorescence intensity decrease rate is ΔFL1, the second-stage fluorescence intensity decrease rate is ΔFL2, and the third-stage fluorescence intensity decrease rate is ΔFL3, then ΔFL1, ΔFL2, and ΔFL3 are (2), (3), and (4) can be obtained respectively.

  Here, FL0 is the fluorescence intensity of the water to be treated, FL1 is the fluorescence intensity of the first stage outlet, FL2 is the fluorescence intensity of the second stage outlet, and FL3 is the fluorescence intensity of the third stage outlet.

  As can be seen from the figure, as the ozone treatment progresses, the decomposition of the substance with a fast reaction rate is preferentially performed at first, and the change in the fluorescence intensity decrease rate is large. If only the slow-degrading substance is decomposed, the change in the fluorescence intensity decrease rate becomes small. Therefore, the rate of decrease in fluorescence intensity is monitored for each ozone treatment tank at each stage, and the ozone injection rate that allows the most efficient ozone treatment for each stage is experimentally determined in advance, and a processing target value is set for each stage, The generated ozonized gas concentration in the ozone generator 12 and the opening of the gas flow rate adjustment valve 20 can be feedback controlled so that the ozone injection amount changes.

  In the present embodiment, the dissolved organic carbon concentration (DOC) of the raw water sampled from the receiving well 1 through the filtration filter 9 is measured by the organic carbon concentration meter 10, and the ozone injection amount into the ozone treatment pond 4 is measured. The fluorescence intensity (FL0) of the water to be treated is measured by the fluorescence intensity meter 14 connected to the inlet of the ozone treatment tank 4. The ozone injection control device 11 inputs the dissolved organic carbon concentration (DOC) and the fluorescence intensity (FL0) of the water to be treated, and monitors the change in the ratio (FL0 / DOC), so that the raw water quality suddenly changes. Even if the temperature changes, the ozone injection amount can be quickly controlled.

  That is, the ozone injection control device 11 obtains the ratio (FL0 / DOC) between the dissolved organic carbon concentration (DOC) of the raw water and the fluorescence intensity (FL0) of the raw water at the entrance of the ozone treatment pond 4, and this ratio It has a function of controlling the amount of ozone injected into the ozone treatment basin 4 based on the value. For this reason, even when the raw water quality changes suddenly, the ozone injection amount can be quickly controlled.

  Furthermore, also in this case, the dissolved ozone concentration meter 13 is connected to the outlet of the ozone treatment pond 4 and this measured value output is input to the ozone injection control device 11, so that the dissolved ozone concentration of the ozone treated water is When the upper limit value is exceeded, the ozone generator 12 is controlled so as to decrease the ozone injection amount, so that excessive ozone injection can be prevented from this.

  According to the present embodiment, the rate of decrease in fluorescence intensity is monitored for each ozone treatment tank 16 at each stage, and the ozone injection amount is feedback-controlled so that the treatment target value for each stage is set in advance. Can do. In addition, the dissolved organic carbon concentration (DOC) in the raw water is measured, and the change in the ratio of the dissolved organic carbon concentration to the fluorescence intensity of the water to be treated at the inlet of the ozone treatment tank 4 (FL0 / DOC) is monitored. By doing so, even when the raw water quality changes suddenly, the ozone injection amount can be quickly controlled. Furthermore, the dissolved ozone concentration meter 13 provided at the outlet of the ozone treatment pond 4 can be controlled so that the dissolved ozone concentration in the treated water does not exceed the upper limit value, and only unnecessary ozone gas injection is prevented. Therefore, it is possible to suppress the formation of by-products such as bromate ions due to excessive ozonized gas.

It is a block diagram explaining one embodiment of a water treatment system by the present invention. It is a characteristic view explaining the relationship between DOC and ozone absorption density in one embodiment same as the above. It is a block diagram explaining other embodiment of the water treatment system by this invention. It is a characteristic view explaining the relationship between the fluorescence intensity and DOC in other embodiment same as the above. It is a characteristic view explaining the relationship between the amount of ozone absorption and the ratio of the treated water fluorescence intensity with respect to the raw water fluorescence intensity in other embodiment same as the above. It is a block diagram explaining further another embodiment of the water treatment system by this invention. It is a characteristic view explaining the fluorescence intensity decreasing rate in each stage ozone contact tank in other embodiment same as the above.

Explanation of symbols

4 Ozone treatment pond 5 Activated carbon treatment pond 9 Suspended substance removal filter 10 Organic carbon concentration meter 11 Ozone injection controller 12 Ozone generator 13 Dissolved ozone concentration meter 14, 15, 21 Fluorescence analyzer 16 Ozone contact tank 20 Ozone Gas flow control valve

Claims (10)

After removing suspended substances from raw water, it is a water treatment method in which ozone treatment is performed in an ozone treatment pond and activated carbon treatment is performed in an activated carbon treatment pond after ozone treatment,
Introducing a part of the raw water into the organic carbon concentration meter after removing suspended substances, measuring the dissolved organic carbon concentration of the raw water,
Based on the relationship between the dissolved organic carbon concentration obtained in advance and the ozone absorption rate, the amount of ozone injected into the ozone treatment pond is calculated based on the ozone absorption rate corresponding to the measured dissolved organic concentration of the raw water. A water treatment method characterized by deciding. A ratio between the dissolved organic carbon concentration of the raw water and the fluorescence intensity of the raw water at the entrance of the ozone treatment pond is obtained, and the amount of ozone injected into the ozone treatment pond is controlled based on the value of this ratio. Item 2. The water treatment method according to Item 1. Measure the fluorescence intensity of the raw water at the entrance portion of the ozone treatment pond and the fluorescence intensity of the treated water at the exit portion of the ozone treatment pond, respectively, and determine the ratio of the fluorescence intensity of the treated water to the fluorescence intensity of the raw water,
Based on a decrease characteristic of the ratio with respect to the change in ozone absorption amount, a ratio that becomes a boundary of reaction to ozone injection is obtained in advance.
2. The water treatment method according to claim 1, wherein the amount of ozone injected into the ozone treatment pond is controlled using the ratio serving as the boundary as a target value for the ratio obtained by the measurement of the fluorescence intensity. The ozone treatment pond has a plurality of stages of ozone contact tanks that are separated so as to communicate with each other and are supplied with ozone individually, and each ozone contact tank has a difference in fluorescence intensity between the inlet and outlet of each ozone contact tank. Obtain the fluorescence intensity decrease rate at
In accordance with the fluorescence intensity reduction rate, an ozone injection rate for each ozone contact tank is determined, and the amount of ozone injected into each ozone contact tank is controlled using the determined injection rate as a target value. Item 4. The water treatment method according to Item 3. 5. The dissolved oxygen concentration of the treated water at the ozone treatment pond outlet is measured, and the amount of ozone injected into the ozone treatment pond is limited so that the dissolved oxygen concentration does not exceed a set value. The water treatment method in any one of. It is a water treatment system that removes suspended matter from raw water, then ozone treatment in an ozone treatment pond, and performs activated carbon treatment in an activated carbon treatment pond after ozone treatment,
An organic carbon concentration meter that introduces a part of the raw water through a filter for removing suspended substances and measures the dissolved organic carbon concentration of the raw water;
Based on the relationship between the dissolved organic carbon concentration and the ozone absorption rate obtained in advance, the amount of ozone injected into the ozone treatment pond is calculated based on the ozone absorption rate corresponding to the measured dissolved organic concentration of the raw water. An ozone injection control device to determine;
A water treatment system comprising: At the entrance of the ozone treatment pond, a fluorescence analyzer that measures the fluorescence intensity of the raw water is installed.
The ozone injection controller calculates the ratio between the dissolved organic carbon concentration of the raw water and the fluorescence intensity of the raw water at the entrance of the ozone treatment pond, and controls the amount of ozone injected into the ozone treatment pond based on the value of this ratio It has a function. The water treatment system of Claim 6 characterized by the above-mentioned. A fluorescence analyzer that measures the fluorescence intensity of raw water at the entrance of the ozone treatment pond and a fluorescence analyzer that measures the fluorescence intensity of treated water at the exit of the ozone treatment pond are provided,
The ozone injection control device
A function for determining the ratio of the fluorescence intensity of the treated water to the fluorescence intensity of the raw water from the fluorescence intensity of the raw water and the fluorescence intensity of the treated water measured by the respective fluorescence analyzers,
Based on the previously determined reduction ratio of the ratio with respect to the change in the amount of absorbed ozone, the ratio that becomes the boundary of the reaction to ozone injection is used, and the ratio that becomes the boundary is set as the target value for the ratio obtained by the measurement of the fluorescence intensity. The water treatment system according to claim 6, further comprising: a function of controlling an ozone injection amount into the ozone treatment pond. The ozone treatment pond has a plurality of stages of ozone contact tanks that are separated so as to communicate sequentially and to which ozone is individually supplied, and a fluorescence analyzer is provided at the inlet and outlet of each ozone contact tank,
The ozone injection control device
A function for obtaining a decrease rate of fluorescence intensity in each ozone contact tank by a difference in fluorescence intensity between the entrance and exit of each ozone contact tank;
According to these fluorescence intensity reduction rates, the ozone injection rate for each ozone contact tank is obtained, and the ozone injection amount to each ozone contact tank is controlled using the determined injection rate as a target value. The water treatment system according to claim 6. A dissolved ozone concentration meter is installed at the outlet of the ozone treatment pond to measure the dissolved oxygen concentration of the treated water.
The ozone injection control device has a function of limiting the amount of ozone injected into the ozone treatment pond so that the dissolved oxygen concentration does not exceed a set value. Water treatment system.

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