JP2022121053A - Water treatment system and water treatment method - Google Patents

Abstract

To provide a water treatment system and a water treatment method which are configured to, when membrane filtration treatment of water to be treated is carried out to obtain purified water, hardly cause membrane clogging, thereby enabling reduction of maintenance work.SOLUTION: A water treatment system 101 comprises: a flocculant addition part 500 which adds a flocculant to water to be treated; a membrane filtration part 600 which is provided downstream of the flocculant addition part and which carries out membrane filtration of the water to be treated having the flocculant added thereto; and other water treatment parts (a biotreatment part 300, an ozone treatment part 400) which are provided upstream of the flocculant addition part. The other water treatment parts are provided with a pH adjustment part 700 for adjustment of a pH of the water to be treated.SELECTED DRAWING: Figure 1

Description

The present invention relates to a water treatment system and a water treatment method for obtaining purified water such as reclaimed water by performing membrane filtration on treated water such as sewage water, other various types of waste water, raw water from tap water, and the like.

In order to effectively utilize water resources, techniques for obtaining reclaimed water by membrane filtration of various types of waste water have been developed.

For example, in Patent Document 1 below, an oxidation treatment step of adding ozone to the water to be treated and oxidizing the water to be treated, and a reverse osmosis membrane treatment step of treating the water that has undergone the oxidation treatment step with a reverse osmosis membrane wherein a pH adjuster is added to the water to be treated so that the pH of the water in the oxidation treatment process or the outflow water from the oxidation treatment process is 8 to 10. A treatment method is described. In addition, it is stated that when the concentration of organic substances in the water to be treated is high, it is preferable to subject the water to be treated to coagulation-sedimentation treatment or biological treatment prior to the ozone oxidation treatment in order to efficiently perform the oxidation treatment with ozone. It is

JP-A-2005-230731

However, in the method described in Patent Document 1, the coagulation-sedimentation treatment is only mentioned as a preferred embodiment and is not essential. Therefore, floc formation in the coagulation-sedimentation treatment may not be effective due to pH fluctuations of the water to be treated, and clogging may easily occur in the reverse osmosis membrane treatment process. Accordingly, the present invention provides a water treatment system and a water treatment method that make it difficult for membrane clogging to occur when water to be treated is subjected to membrane filtration to obtain purified water, thereby reducing maintenance work. for the purpose.

In order to achieve the above object, one of the water treatment systems of the present invention includes a flocculant addition section for adding a flocculant to water to be treated, and a flocculant addition section provided downstream of the flocculant addition section, where the flocculant is added. and another water treatment unit provided upstream of the coagulant addition unit, wherein the other water treatment unit adjusts the pH of the water to be treated. A pH adjusting part is provided.

Another water treatment system of the present invention includes an ozone treatment unit that performs ozone treatment on water to be treated, a coagulant addition unit that adds a coagulant to the water to be treated after the ozone treatment, and the coagulant a membrane filtration unit that membrane-filters the water to be treated to which is added; a pH measurement unit that measures the pH of the water to be treated; and based on the pH measured by the pH measurement unit, the water to be treated after the ozone treatment and a dissolved ozone concentration control device for controlling the amount of ozone injected in the ozone processing section so that the concentration of dissolved ozone in the ozonizer falls within a predetermined range.

According to the water treatment system of the present invention, clogging of the membrane is less likely to occur when the water to be treated is subjected to membrane filtration to obtain purified water, and maintenance work can be reduced.

BRIEF DESCRIPTION OF THE DRAWINGS It is explanatory drawing which shows one Embodiment of the water treatment system of this invention. It is a flowchart which shows the pH adjustment procedure in the same embodiment. It is an explanatory view showing other embodiments of the water treatment system of the present invention. It is a flowchart which shows the dissolved ozone concentration adjustment procedure in the same embodiment. It is an explanatory view showing other embodiments of the water treatment system of the present invention. It is a flowchart which shows the adjustment procedure of pH and dissolved ozone concentration in the same embodiment.

In order to achieve the above-mentioned object, the present inventors have conducted intensive research, and as a result, performed membrane filtration after performing coagulation sedimentation treatment, and pH adjustment in the water treatment unit provided upstream of coagulation sedimentation treatment. or by adjusting the dissolved ozone concentration, clogging of the membrane filtration portion can be effectively suppressed, and the present invention has been completed.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.

(First embodiment)
1 and 2 show a first embodiment of the water treatment system of the present invention.

As shown in FIG. 1, the water treatment system 101 in this embodiment obtains reclaimed water by treating water to be treated which is obtained from a final sedimentation tank 200 of a sewage treatment plant.

However, the water to be treated is not limited to the sewage treated water as described above. etc. can also be used.

This water treatment system 101 includes a biological treatment section 300 , an ozone treatment section 400 , a coagulant addition section 500 and a membrane filtration section 600 . The configuration of each processing unit will be described below in order.

The biological treatment unit 300 includes a biofilm filtration tank 301 having a biofiltration membrane formed by growing organisms on a filter medium to form a biofilm on the surface of the filter medium. As the filter medium, any filter medium that is used in normal biological filtration membranes for water treatment can be used without limitation. can be done. Organisms live on the surface of the filter medium, decompose organic matter derived from the water to be treated, and biologically remove it. The water to be treated obtained from the final sedimentation tank 200 of the sewage treatment plant is introduced through the pipe 201 into the biological membrane filtration tank 301 of the biological treatment unit 300, passes through the biological filtration membrane and is biologically treated, and then passes through the pipe 302. It is sent to the ozone processing section 400 . A pH meter 202 for measuring the pH of the water to be treated may be provided on the pipe 201 connecting the final sedimentation tank 200 and the biological treatment section 300 .

The ozone treatment section 400 includes an ozone contact tower 401 and an ozone generator 402 . The ozone generator 402 is not limited as long as it generates ozone by a silent discharge method, an ultraviolet method, a chemical generation method, an electrolysis method, or the like, but the silent discharge method is preferable for obtaining a large amount of ozone. The ozone generator 402 generates ozone of a predetermined concentration when the power is turned on, and blows the ozone into the water to be treated from the air diffuser 403 provided in the ozone contact tower 401 . The water to be treated comes into contact with ozone introduced from the ozone generator 402 in the ozone contact tower 401 . In the present invention, the means for contacting the water to be treated with ozone is not particularly limited, and may be either an upward flow type or a downward flow type. A method of ejecting ozone or a method of blowing ozone as fine bubbles (nanobubbles, microbubbles) using an ejector may be used. The ozone modifies the surface properties of the solid matter floating in the water to be treated, resulting in an effect of improving coagulation in the subsequent coagulant addition section 500 . The water to be treated that has been ozonized in the ozone treatment section 400 is sent to the coagulant addition section 500 through the pipe 404 . A dissolved ozone concentration meter 405 for detecting the concentration of dissolved ozone in the water to be treated after the ozone treatment may be provided in the pipe 404 .

The coagulant addition unit 500 has a coagulant tank 501 , a coagulant storage tank 502 , and a pump 503 for injecting the coagulant into the coagulant tank 501 through a pipe 504 . Examples of types of flocculants that can be used include PAC (polyaluminum chloride), ferric chloride, aluminum sulfate, polymer flocculants, and PSI (polysilica iron flocculants). The water to be treated passes through a rapid stirring section, a slow stirring section, etc. provided in the coagulation tank 501, and is mixed with a coagulant to form coagulated flocs. A line mixer may be used as the aggregating means. The water to be treated that has undergone coagulation treatment in the coagulant addition section 500 is sent to the membrane filtration section 600 through the pipe 506 . A pH meter 505 for measuring the pH of the water to be treated in the aggregation tank 501 may be provided.

The membrane filtration unit 600 is provided with a separation membrane (not shown), and the flocs formed in the coagulant addition unit 500 are filtered and removed by the separation membrane to obtain clean treated water that can be used as reclaimed water. . As the separation membrane, for example, an MF membrane or a UF membrane can be used. Since good flocs are formed in the previous stage, the membrane surface is less likely to be clogged. The material of the membrane may be a polymer membrane or a ceramic membrane, and the membrane shape may be a monolithic type, a tubular membrane, a honeycomb membrane, a hollow fiber membrane, a flat membrane, or the like. Also, the membrane may be of internal or external pressure type. Furthermore, the membrane filtration method may be a dead end filtration method or a cross flow method.

One feature of the water treatment system of the present invention is that pH The reason is that the adjusting section 700 is provided. In the present invention, the meaning of providing a pH adjustment unit in another water treatment unit is limited to a place where water treatment is performed in another water treatment unit (for example, the biofilm filtration tank 301, the ozone contact tower 401, etc.). It does not mean that it is intended to include a mode provided before and after a portion (for example, piping) of a portion of the water treatment unit where water treatment is performed.

In this embodiment, a pH adjuster 700 is provided in the pipe 302 that connects the biological treatment section 300 and the ozone treatment section 400 . The pH adjusting unit 700 includes a pH adjusting agent tank 701, a pump 702 for adding the pH adjusting agent in the pH adjusting agent tank 701 to the water to be treated passing through the pipe 302 through the pipe 703, and the pH of the water to be treated passing through the pipe 302. a pH controller 705 that acquires the pH value measured from the pH meter 704 and sends a control signal to the pump 702 based on the pH value to adjust the amount of the pH adjuster to be added; have.

In this embodiment, the pipe 302 connecting the biological treatment unit 300 and the ozone treatment unit 400 is provided with the pH adjustment unit 700. The pH adjustment unit 700 is, for example, the final sedimentation tank 200 It can also be provided in the pipe 201 (at arrow A in FIG. 1) connecting to the biological treatment section 300 . Moreover, it can also be provided in places where water treatment is performed, such as the biofilm filtration tank 301 and the ozone contact tower 401 .

Next, the control flow of the pH control device 705 in this embodiment will be explained based on FIG. As shown in FIGS. 1 and 2, pH meter 704 measures the pH value (STEP 01). Next, the pH controller 705 determines whether or not the pH value is within a predetermined range (STEP 02). If the pH value is within the predetermined range, the pH control device 705 terminates the process (END), and if the pH value is not within the predetermined range, proceeds to STEP 03, operates the pump 702, and disconnects the pipe 302. A pH adjuster is added to the water to be treated which passes through.

Next, pH meter 704 measures the pH value again (STEP 04), and pH controller 705 determines whether the pH value is within a predetermined range (STEP 05). If the pH value is not within the predetermined range, the pH controller 705 returns to STEP03 and adds the pH adjuster again (STEP03). If the pH value is within the predetermined range, the pump 702 is stopped (STEP06), and the process is terminated (END). In this way, the pH control device 705 repeats the processes of STEP03, STEP04, and STEP05 when the pH value is not within the predetermined range, thereby finally adjusting the pH value of the water to be treated within the predetermined range. .

The range of pH values determined in STEP 02 above, in other words, the range of pH values in which the water to be treated is adjusted by the pH adjusting unit 700 is preferably pH 6.0 to 6.8, and pH 6.3 to 6.8. 8 is more preferred. If the pH value is within the above range, the effect of preventing clogging of the membrane during membrane filtration after the flocculation step can be satisfactorily obtained.

In addition, when the pH adjustment unit 700 is provided in the pipe 302 leading to the ozone treatment unit 400, the acquisition of the pH value in STEP 01 is provided in the pipe 404 (arrow B in FIG. 1) passing through the ozone treatment unit 400. A value measured by a pH meter can also be used.

Next, one embodiment of the water treatment method of the present invention using the water treatment system 101 will be described. In this embodiment, the water to be treated taken out from the final sedimentation tank 200 of the sewage treatment plant is introduced into the biofilm filtration tank 301 of the biological treatment section 300 through the pipe 201 . When the water to be treated passes through the biological filtration membrane of the biological membrane filtration tank 301, the contained ammonia and nitrous acid are nitrified to nitric acid, and coarse solids are removed (these are the “biological treatment steps”). ).

The water to be treated is then sent to the ozone treatment section 400 through the pipe 302 . At this time, the pH of the water to be treated passing through the pipe 302 is measured by the pH meter 704, and based on the measured value, the pH controller 705 operates the pump 702 according to the control flow shown in FIG. amount of pH adjuster is added to the water to be treated. As a result, the water to be treated is adjusted to a predetermined pH value (the above "pH adjustment step").

In the ozone treatment section 400, the ozone generator 402 generates ozone, and the ozone is blown into the water to be treated from the air diffuser 403 of the ozone contact tower 401 to perform the ozone treatment. Since the pH of the water to be treated is adjusted to a predetermined range, ozone is decomposed and radicals are easily generated. Therefore, the surface property of the fine solids contained in the water to be treated is modified, and the flocculation in the subsequent flocculant treatment step can be enhanced (the above is the "ozone treatment step").

The water to be treated that has been ozonized in the ozone treatment section is sent to the coagulation tank 501 of the coagulant addition section 500 through the pipe 404 . A coagulant is added to the coagulant tank 501 by a pump 503 from a coagulant storage tank 502 . The water to be treated passes through a rapid stirring section, a slow stirring section, and the like provided in the coagulation tank 501, and is mixed with a coagulant to form coagulant flocs (the above "coagulant addition step"). At this time, the pH of the water to be treated is adjusted to a predetermined range, and the surface properties of the fine solids contained in the water to be treated are modified in the ozonation step, making it easier for the fine solids to aggregate. Therefore, the formation of flocs is excellent.

The water to be treated is then sent to the membrane filtration unit 600 through the pipe 506 . In the membrane filtration unit 600, the water to be treated is filtered by the separation membrane, and aggregated flocs contained in the water to be treated are removed by the separation membrane. As a result, fine solid matter in the water to be treated is removed from the water that has passed through the separation membrane, resulting in clean water that can be used as reclaimed water. This treated water is taken out through the pipe 601 (the above "membrane filtration process").

As described above, in this embodiment, the pH value of the water to be treated is adjusted to a predetermined range in the pH adjustment step, so that in the ozone treatment step, ozone is decomposed to facilitate the generation of radicals. It is possible to effectively modify the surface properties of the fine solids contained in the water to be treated, thereby enhancing the flocculation in the subsequent flocculant treatment step. As a result, it is possible to improve the formation of aggregated flocs in the coagulant treatment step.

As a result, the filtration amount in the membrane filtration unit is increased, the transmembrane differential pressure increase speed is decreased, and maintenance intervals such as chemical cleaning of the separation membrane of the membrane filtration unit 600 are lengthened, thereby reducing the labor, time and cost of maintenance. can do.

In the present invention, as other water treatment units, at least one of a biological treatment unit 300 that treats water to be treated with a biological filtration membrane and an ozone treatment unit 400 that performs ozone treatment on water to be treated, The pH adjusting section 700 is preferably provided in at least one of the biological processing section 300 and the ozone processing section 400 .

(Second embodiment)
3 and 4 show a second embodiment of the invention. In addition, the same code|symbol is attached|subjected to the substantially same part as 1st Embodiment, and the description is abbreviate|omitted.

As shown in FIG. 3, the water treatment system 102 of this embodiment differs from the above-described first embodiment in that it does not have the pH adjuster 700 and is provided with a dissolved ozone concentration control device 406. ing.

In this embodiment, based on the pH value measured by the pH meter 704 provided in the pipe 302 connecting the biological treatment unit 300 and the ozone treatment unit 400, the dissolved ozone concentration control device 406 controls the ozone generator 402 The supplied ozone injection amount is controlled. That is, the ozone treatment unit 400 has an ozone contact tower 401, an ozone generator 402, and a dissolved ozone concentration control device 406. The dissolved ozone concentration control device 406 supplies ozone from the ozone generator 402. By controlling the amount, the amount of ozone injected into the water to be treated passing through the ozone contact tower 401 is controlled.

When the pH of the water to be treated is lower than a predetermined value, the amount of radicals generated by ozone decomposition in the ozone treatment section 400 tends to decrease. Moreover, when the pH of the water to be treated is higher than a predetermined value, the flocculating effect of the flocculating agent tends to decrease. In any of the above cases, the concentration of dissolved ozone can be increased to increase the amount of radicals generated, thereby enhancing the effect of modifying the surface properties of fine solids contained in the treated water. Therefore, in this embodiment, the dissolved ozone concentration that can effectively modify the surface properties of fine solids in the water to be treated at a certain pH is determined by the pH of the water to be treated and the membrane filtration at the dissolved ozone concentration in the water to be treated. The relationship between the transmembrane pressure increase rate in the process is investigated in advance, and the dissolved ozone concentration of the water to be treated is controlled according to the pH of the water to be treated so that the transmembrane pressure increase rate is within a predetermined range. I'm trying

A control flow in the dissolved ozone concentration control device 406 will be described with reference to FIG. First, the pH meter 704 measures the pH value of the water to be treated passing through the pipe 302 (STEP 11), and the dissolved ozone concentration control device 406 determines whether the pH value is within a predetermined range (STEP 12). When the pH value is within a predetermined range, the decomposition of ozone favorably generates radicals, and the flocculating effect of the flocculant is maintained favorably. The density control device 406 ends the processing (END).

The pH range determined in STEP 12 is preferably pH 6.0 to 6.8, more preferably pH 6.3 to 6.8.

Then, the dissolved ozone concentration control device 406 proceeds to STEP 13 when the pH value is not within the predetermined range. In STEP 13, as described above, from the relationship between the rate of increase in transmembrane pressure, the pH of the water to be treated, and the concentration of dissolved ozone in the water to be treated, which has been obtained in advance, Obtain (in other words, calculate) the required dissolved ozone concentration. Then, the ozone generator 402 is operated to inject ozone into the ozone contact tower 401 (STEP 14). The relationship (hereinafter referred to as correspondence) among the transmembrane pressure increase rate, the pH of the water to be treated, and the concentration of dissolved ozone in the water to be treated, which has been obtained in advance, can be expressed in a table format, a function format in a memory (not shown) of the dissolved ozone concentration control device 406 .

Here, the reason why the transmembrane pressure increase rate is referred to when calculating the dissolved ozone concentration will be described. In order to operate the membrane filtration device stably, it is desirable that the transmembrane differential pressure rise rate is low. In order to reduce the transmembrane pressure increase rate, the dissolved ozone concentration should be increased to suppress the clogging of the membrane filtration section. However, increasing the dissolved ozone concentration increases the operating cost of the membrane filtration device.

Therefore, after weighing the stable operation and operating cost of the membrane filtration device, the inventors found that when stable operation of the membrane filtration device is prioritized over the operating cost, the rate of increase in the transmembrane pressure difference is reduced. The ozone concentration (amount of ozone to be injected) determined to be high is determined. On the other hand, the inventor determines the required ozone concentration to be low when prioritizing the operating cost of the membrane filtration device over stable operation.

A case where the correspondence relationship is defined in the form of a function will be exemplified. The following relational expressions are determined with reference to the results of various experiments or the results of actual machine operation.

When the transmembrane pressure-like speed may be higher than the first speed (operating cost is prioritized), the correspondence relationship is defined as the following (Equation 1).

Dissolved ozone concentration in the water to be treated (required dissolved ozone concentration) = a1 x pH value of the water to be treated + b1 (Formula 1) where a1 and b1 are constants.

On the other hand, when the transmembrane pressure-like velocity is to be suppressed to the first velocity or less (stable operation is prioritized), the correspondence relationship is defined as the following (Equation 2).

Dissolved ozone concentration in water to be treated = a2 x pH value of water to be treated + b2 (Formula 2) However, if a1 and a2 are positive constants, a2 is a constant greater than a1, and b2 is a constant greater than b1. .

The above formulas (1) and (2) are examples, and various modifications are possible according to the results of various experiments or the results of actual operation.

Thereafter, the dissolved ozone concentration meter 405 measures the dissolved ozone concentration (STEP 15), and the dissolved ozone concentration control device 406 determines whether or not the measured value of the dissolved ozone concentration is within the calculated dissolved ozone concentration range (STEP 16). ). The dissolved ozone concentration control device 406 terminates the process (END) when the measured value of the dissolved ozone concentration is within the above range, and returns to STEP 14 to inject ozone again when it is not within the above range. The dissolved ozone concentration control device 406 repeats the processes of STEP15 and STEP16 to adjust the dissolved ozone concentration of the water to be treated that has been subjected to ozone treatment to within the calculated dissolved ozone concentration range.

In this way, the water to be treated that has been ozonized so that the dissolved ozone concentration falls within the calculated range is sent to the coagulant addition section 500 through the pipe 404 . Since the rest of the configuration is the same as that of the first embodiment, description thereof will be omitted.

In this embodiment, the amount of ozone injected in the ozone treatment unit 400 is controlled in accordance with the pH of the water to be treated, so that the amount of radicals generated by the decomposition of ozone in the ozone treatment unit 400 is maintained well. It effectively modifies the surface properties of fine solids in the water to be treated, improves the formation of flocs in the flocculation process, suppresses clogging in the membrane filtration process, and shortens the maintenance interval of the separation membrane of the membrane filtration unit 600. By lengthening it, maintenance effort, time and cost can be reduced.

In addition, the acquisition of the pH value in STEP 11 uses, for example, a value measured by a pH meter provided in the pipe 404 (at arrow B in FIG. 3) connecting the ozone treatment section 400 and the coagulant addition section 500. can also

(Third Embodiment)
5 and 6 show a third embodiment of the invention. In addition, the same code|symbol is attached|subjected to the substantially same part as 1st Embodiment and 2nd Embodiment, and the description will be abbreviate|omitted.

The water treatment system 103 of this embodiment, as shown in FIG. 2 embodiment.

That is, the pipe 302 connecting the biological treatment part 300 and the ozone treatment part 400 is provided with the pH adjustment part 700 similar to that of the first embodiment. The pH adjusting unit 700 includes a pH adjusting agent tank 701, a pump 702 that adds the pH adjusting agent to the water to be treated passing through the pipe 302 through the pipe 703, and a pH meter 704 that measures the pH of the water to be treated passing through the pipe 302. , and a pH controller 705 that controls the pump 702 based on the pH value measured by the pH meter 704 and adjusts the addition amount of the pH adjuster.

A dissolved ozone concentration control device 406 is provided in the ozone processing unit 400, and the dissolved ozone concentration control device 406 controls the amount of ozone generated by the ozone generator 402 based on the pH value measured by the pH meter 704. Then, the amount of ozone injected into the water to be treated passing through the ozone contact tower 401 is controlled.

A control flow in the pH controller 705 and the dissolved ozone concentration controller 406 will be described with reference to FIG. First, pH meter 704 measures the pH value of the water to be treated (STEP 21), and dissolved ozone concentration control device 406 determines whether the measured pH value is within a predetermined range (STEP 22). If the pH value is within the predetermined range, the dissolved ozone concentration control device 406 ends the process (END).

When the pH value is not within the predetermined range, the dissolved ozone concentration control device 406 controls the relationship between the transmembrane differential pressure increase rate, the pH of the water to be treated, and the dissolved ozone concentration of the water to be treated, which is obtained in advance. , the required dissolved ozone concentration corresponding to the pH value of the water to be treated is obtained. Next, the dissolved ozone concentration control device 406 operates the ozone generator 402 to inject ozone (STEP 24). Thereafter, the dissolved ozone concentration meter 405 measures the dissolved ozone concentration (STEP 25), and the dissolved ozone concentration control device 406 determines whether the measured value of the dissolved ozone concentration is within the calculated dissolved ozone concentration range (STEP 26). ). The dissolved ozone concentration control device 406 ends the process (end) when the measured value of the dissolved ozone concentration is within the calculated dissolved ozone concentration range, and when it is not within the calculated dissolved ozone concentration range, the ozone generator Judging from the output of 402, it is determined whether or not the adjustable upper limit is exceeded (STEP 27).

If the ozone injection amount does not exceed the adjustable upper limit, the dissolved ozone concentration control device 406 returns to STEP 24 and injects ozone again. On the other hand, when the ozone injection amount exceeds the adjustable upper limit, the dissolved ozone concentration control device 406 calculates a pH value corresponding to the dissolved ozone concentration measured in STEP 25 (STEP 28). At this time, the calculated pH value may be replaced with a pH value range having an arbitrarily determined allowable value.

Next, it is determined whether or not the pH value measured in STEP 21 is the pH value calculated in STEP 28 (STEP 29). If the pH value measured in STEP 21 is equal to the calculated pH value, the pH control device 705 terminates the process (END), and if the pH value measured in STEP 21 differs from the calculated pH value, the pump 702 is turned on. The pH adjuster is added to the water to be treated passing through the pipe 302 (STEP 30). After that, the pH meter 704 measures the pH (STEP 31), and the pH controller 705 determines whether the pH value measured in STEP 31 is the calculated pH value (STEP 32). If the pH value is the calculated pH value, the pH control device 705 proceeds to STEP 33, stops the pump 702 (STEP 33), ends the processing (END), and if the pH value is different from the calculated pH value, , return to STEP 30, and add the pH adjuster again. The pH control device 705 adjusts the pH value to the calculated pH value by repeating the processing of STEP30, STEP31, and STEP32.

In this way, the water to be treated that has been ozone-treated so as to have the calculated dissolved ozone concentration range or the calculated pH value is sent to the coagulant addition unit 500 through the pipe 404 . Since other configurations are the same as those of the first and second embodiments, description thereof will be omitted.

In addition, the acquisition of the pH value in STEP 21 uses, for example, a value measured by a pH meter provided in the pipe 404 (at arrow B in FIG. 5) connecting the ozone treatment section 400 and the coagulant addition section 500. can also

In this embodiment, the concentration of dissolved ozone in the water to be treated and the pH of the water to be treated after ozone treatment are adjusted according to the pH of the water to be treated, whereby the amount of radicals generated by decomposition of ozone in the ozone treatment unit 400 is is maintained well, the surface properties of fine solids in the water to be treated are effectively modified, the formation of flocs in the flocculation process is improved, clogging in the membrane filtration process is suppressed, and the membrane By lengthening the maintenance interval of the separation membrane of the filtration unit 600, maintenance effort, time and cost can be reduced.

In the first embodiment, an example in which the biological treatment unit 300 and the ozone treatment unit 400 are provided as other water treatment units has been described. It can also be applied to a system in which either one of them is provided.

Here, as an example, the upper limit of the ozone injection amount is shown as the ozone injection amount that can actually be output, but it may be set to an arbitrary ozone injection amount. Alternatively, the ozone injection amount may be set after bringing the pH value of the water to be treated closer to the target pH value.

Also, in the second embodiment and the third embodiment, examples in which the biological treatment unit 300 and the ozone treatment unit 400 are provided as other water treatment units have been described, but the biological treatment unit 300 is not necessarily required. .

Next, tests conducted on the water treatment system described in the above embodiment will be described.
<Test Example 1> Change in filtration amount due to pH adjustment before ozonation (1) Test method A test was performed by the following method using raw water of pH 5.8 collected from the final sedimentation tank of a sewage treatment plant as water to be treated. .
(a) Adjust the pH before ozonation. That is, sample A is used as raw water (pH is 5.8), B is adjusted to pH 6.2, and C is adjusted to pH 6.7.
(b) Ozone is added until the dissolved ozone concentration reaches 0.3 mg/L.
A flocculant (20 mg PACl/L) is added and a jar test is performed.
(c) Allow to stand for 1 minute.
(d) Filter the supernatant through a disk filter (1 μm, 25 mm diameter) and measure the filtration volume.

(2) Test results Test results are shown in Table 1 below.

Comparing the initial pH from the results in Table 1 above, it can be seen that the filtration amount is increased at pH 6.2 rather than at pH 5.8. It can be seen that when the pH is 6.7, the filtration amount is further increased.

<Test Example 2> Change in Filtration Amount Due to pH Adjustment Before Aggregation (1) Test Method A test was performed by the following method using the same raw water of pH 5.8 as in Test Example 1 as water to be treated.
(a) Ozone is added until the dissolved ozone concentration reaches 0.3 mg/L.
(b) adjusting the pH prior to flocculation; That is, the pH of the sample D remains unchanged (pH 6.2) as naturally changed by the ozone treatment, and the pH of the sample E is adjusted to 6.5.
(c) Add a flocculant (20 mg PACl/L) and perform a jar test.
(d) Allow to stand for 1 minute.
(e) Filter the supernatant through a disk filter (1 μm, diameter 25 mm) and measure the filtration amount.

(2) Test results The test results are shown in Table 2 below.

From the results in Table 2 above, it can be seen that when the pH before aggregation is compared, the amount of filtration increases at pH 6.5 rather than at pH 6.2.

Also, based on the results of Test Example 1 (change in the amount of filtration due to pH adjustment before ozonation) and Test Example 2 (change in the amount of filtration due to pH adjustment before coagulation), both before ozonation and before coagulation, regardless of the adjustment point, It can be seen that the filtration rate increases when the pH is adjusted. However, it can be seen that the adjustment before the ozone treatment enhances the effect.

<Test Example 3> Change in Filtration Volume by Adjusting Dissolved Ozone Concentration (1) Test Method A test was performed by the following method using the same raw water of pH 5.8 as in Test Example 1 as water to be treated.
(a) Ozone is added to adjust the dissolved ozone concentration to the calculated concentration. That is, sample D is adjusted to an ozone concentration of 0.3 mg/L, and sample F is adjusted to a dissolved ozone concentration of 0.5 mg/L.
(b) Add a flocculant (20 mg PACl/L) and perform a jar test.
(c) Allow to stand for 1 minute.
(d) Filter the supernatant through a disk filter (1 μm, 25 mm diameter) and measure the filtration volume.

(2) Test results The test results are shown in Table 3 below.

From the results in Table 3 above, it can be seen that when the pH is low and the dissolved ozone concentration increases from 0.3 mg/L to 0.5 mg/L, the filtration amount increases.

101, 102, 103 Water treatment system 200 Final sedimentation tank 201 Piping 202 pH meter 300 Biological treatment unit 301 Biofilm filtration tank 302 Piping 400 Ozone treatment unit 401 Ozone contact tower 402 Ozone generator 403 Air diffuser 404 Piping 405 Dissolved ozone concentration Total 406 Dissolved ozone concentration control device 500 Coagulant addition section 501 Coagulation tank 502 Coagulant storage tank 503 Pump 504 Piping 505 pH meter 506 Piping 600 Membrane filtration section 601 Piping 700 pH adjusting section 701 pH adjusting agent tank 702 Pump 703 Piping 704 pH Total 705 pH controller

Claims (7)

a flocculant addition unit that adds a flocculant to the water to be treated;
a membrane filtration unit that is provided downstream of the coagulant addition unit and performs membrane filtration of the water to be treated to which the coagulant has been added;
and another water treatment section provided upstream of the flocculant addition section,
A water treatment system, wherein the other water treatment part is provided with a pH adjustment part for adjusting the pH of the water to be treated. As the other water treatment unit, at least one of a biological treatment unit that treats the water to be treated with a biological filtration membrane and an ozone treatment unit that performs ozone treatment on the water to be treated,
The water treatment system according to claim 1, wherein said pH adjusting section is provided in at least one of said biological treatment section and said ozone processing section. 3. The water treatment system according to claim 1, wherein the pH adjusting unit adjusts the pH of the water to be treated to 6.0 to 6.8. As the other water treatment unit, an ozone treatment unit that performs ozone treatment on the water to be treated,
3. A dissolved ozone concentration control device for injecting ozone into said ozone treatment unit so that the concentration of dissolved ozone in said water to be treated after said ozone treatment falls within a predetermined range based on the pH of said water to be treated. 4. The water treatment system according to any one of 1 to 3. an ozone treatment unit that performs ozone treatment on the water to be treated;
a flocculant addition unit that adds a flocculant to the water to be treated after the ozone treatment;
a membrane filtration unit that membrane-filters the water to be treated to which the flocculant has been added;
a pH measuring unit for measuring the pH of the water to be treated;
a dissolved ozone concentration control device for injecting ozone into the ozone treatment unit so that the dissolved ozone concentration of the water to be treated after the ozone treatment falls within a predetermined range based on the pH measured by the pH measurement unit; A water treatment system comprising: A flocculation step of adding a flocculating agent to the water to be treated;
A membrane filtration step of membrane filtering the water to be treated to which the flocculant has been added;
and another water treatment step provided upstream from the aggregation step,
A water treatment method characterized in that, in the other water treatment step, the pH of the water to be treated is measured, and the pH is adjusted so that the pH falls within a predetermined range. an ozone treatment step of performing ozone treatment on the water to be treated;
a coagulation step of adding a coagulant to the water to be treated after the ozone treatment;
a membrane filtration step of membrane-filtrating the water to be treated to which the flocculant has been added;
The pH of the water to be treated is measured, and ozone is injected in the ozone treatment step based on the measured pH so that the concentration of dissolved ozone in the water to be treated after the ozone treatment falls within a predetermined range. water treatment method.

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