JP2003340208A - Water cleaning method and apparatus therefor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a water cleaning method which provides an excellent turbidity removing effect even at the time of low turbidity when a polymeric flocculant is used, eliminating the problem of over-blocking generable when the polymeric flocculant is used and enabling stable water cleaning treatment, and an apparatus therefor. <P>SOLUTION: An inorganic flocculant is injected in raw water and the polymeric flocculant is succeedingly injected therein to perform flocculation and sedimentation treatment, and filter treatment is subsequently performed. In this water cleaning treatment method, the drift current of flocs after the injection of the polymeric flocculant is measured and the injection amount of the polymeric flocculant is controlled on the basis of the measured result. In this water cleaning treatment method, flocs formed by flocculation and sedimentation treatment is returned. The water cleaning treatment apparatus is also disclosed. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a suitable method and apparatus for purifying water using a polymer flocculant, and more particularly to preventing filtration clogging that occurs when a polymer flocculant is used. The present invention relates to a method and an apparatus capable of obtaining an excellent coagulation treatment effect in a coagulation-sedimentation step using a polymer coagulant.

[0002]

2. Description of the Related Art Conventionally, in water purification treatment, an inorganic coagulant such as a sulfuric acid band or polyaluminum chloride (PAC) is injected into water to be treated (hereinafter also referred to as “raw water”) containing suspended substances, and suspended. The suspended substance was removed by forming aggregate flocs incorporating turbid substances and allowing the aggregate flocs to settle. However, in recent years, eutrophication of lakes and rivers has progressed and algae have grown. These algae have poor cohesive properties and adversely affect the sand filtration process. A large amount of inorganic coagulant is required to coagulate the grown algae, and the addition of a large amount of inorganic coagulant makes the treated water acidic, which makes it unsuitable as drinking water. Further, the amount of sludge derived from the inorganic coagulant also increases, and there is a problem that the cost of treating this sludge increases.

In order to improve the settling property of flocs caused by an inorganic flocculant in water purification treatment, it has been studied to use an anionic polymer flocculant together, but the following problems have been pointed out. That is, the polymer coagulant injected in the water purification process is solid-liquid separated together with the generated flocs and most of it is removed, but a part thereof remains on the treated water side together with the fine flocs. This residual polymer coagulant may be adsorbed on the filter material in the sand filtration tower in the subsequent step and cause filter clogging.

As means for preventing clogging by a polymer flocculant, a method of injecting a coagulant blocking agent, a degree of floc formation after injection of an inorganic flocculant is measured, and the degree of flocculation of the polymer flocculant is measured according to the degree of floc formation. A method of determining the injection rate, measuring the flowing current in the floc generation tank during wastewater treatment, obtaining the surplus amount or deficiency of the coagulant based on the measured flowing current, and controlling the injection amount of the coagulant, etc. is there.

[0005]

However, the above method also has the following problems. The method of injecting the coagulant blocking agent may increase the processing cost. In the method of measuring the degree of floc formation after injection of the inorganic flocculant and determining the injection rate of the polymer flocculant according to the degree of floc formation, the fine floc in which the suspended substance and the inorganic flocculant are well bonded is used. Even if the coagulant is formed, if the polymer coagulant is not effectively used for coagulation of the coarse floc, the risk of filter clogging still remains, so it is not enough to manage the degree of floc formation after injection of the inorganic coagulant. is there. Further, in the method of measuring the flowing current in the floc generation tank and controlling the injection amount of the coagulant based on the measured flowing current, the suspended substance and the coagulant react with each other in just proportion and electrically neutral The purpose is to control the amount of coagulant so that, in the water purification treatment, good neutralization results are not always obtained in terms of electrical neutralization. There is no suggestion of any effect on the degree or filtration.

In view of the above-mentioned problems, the present inventors have obtained an excellent effect of removing turbidity even when the turbidity is low when a polymer flocculant is used, and use the polymer flocculant. As a result of diligent study to solve the problem of filtration blockage that may occur in some cases and to develop a method capable of stable water purification treatment,
The present invention has been completed.

[0007]

In order to solve the above problems, the present invention has the following constitution. (1) In a water purification method in which an inorganic coagulant is injected into the water to be treated, and then a polymer coagulant is injected to perform coagulation-sedimentation treatment, followed by filtration treatment, coagulation after injection of the polymer coagulant. A water purification method characterized by measuring the flow current of flocs and controlling the injection amount of the polymer flocculant based on the measurement result. (2) In a water purification method in which an inorganic coagulant is injected into the water to be treated, and then a polymer coagulant is injected to perform coagulation-sedimentation treatment, followed by filtration treatment, coagulation flocs before injection of the polymer coagulant. Of the flocculant floc after injection of the polymer flocculant,
A water purification method characterized in that the injection amount of a polymer coagulant is controlled based on the measurement result. (3) In the water purification method in which an inorganic coagulant is injected into the water to be treated, and then a polymer coagulant is injected to perform the coagulation-sedimentation treatment, and subsequently the filtration treatment is performed, the flocs generated by the coagulation-sedimentation treatment are inorganic. A water purification method characterized by returning the coagulant to the water to be treated before it is injected.

(4) A flocculant which receives the water to be treated and has a flocculant mixing tank having an inorganic coagulant injection means and a polymer flocculant is injected into the fine flocs produced in the flocculation mixing tank. In a water purification device that has a floc formation tank for enlarging and strengthening, a settling tank for solid-liquid separation of enlarging flocs, and a sand filtration tower for discharging the solid-liquid separated sedimentation treated water to the outside of the system, polymer A flowing current meter for measuring a flowing current of a giant floc in a floc formation tank after injecting a flocculant, or a flowing current of a fine floc before injecting a polymer flocculant and a flowing current of the giant floc after injecting a polymer flocculant, and A water purification treatment device, comprising: a polymer coagulant injection control means for controlling an injection amount of the polymer coagulant based on a measurement result of a streaming ammeter.

(5) Coagulation mixing tank having an inorganic coagulant injecting means for receiving water to be treated for purification treatment, and macro flocculant by injecting a polymer coagulant into fine flocs produced in the coagulation mixing tank A floc formation tank that has a floc formation tank for solidification and solidification, a sedimentation tank for solid-liquid separation of giant flocs, and a sand filtration tower that discharges the solid-liquid separated precipitation treatment water to the outside of the system. And / or a means for returning the settling flocs of the settling tank to the coagulation / mixing tank and / or the water to be treated.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be specifically described below. The water purification equipment to which the present invention can be applied is an ordinary equipment that has been put into practical use, and examples thereof include water purification equipment having a cross-flow type precipitation equipment and water purification equipment having a high-speed coagulation sedimentation equipment. Both slurry circulation type and sludge / blanket type can be applied as the high-speed coagulation / sedimentation facility. Note that components having the same function are denoted by the same reference symbols throughout the drawings for describing the embodiments.

FIG. 1 is a diagram showing an embodiment of the present invention. The figure shows an example of a water purification facility with a cross-flow type sedimentation facility.
Raw water 1 is sent to a coagulation and mixing tank 3 through a raw water introduction pipe 2. The inorganic coagulant 4 is injected into the coagulation / mixing tank 3, and the turbidity in the raw water reacts with the inorganic coagulant 4 by rapid agitation here to form fine flocs.

The inorganic coagulant used in the present invention includes:
Generally, an iron-based or aluminum-based inorganic coagulant that has already been used as a coagulant can be used. Specific examples thereof include a sulfuric acid band, polyaluminum chloride (PAC), aluminum chloride, polyferric sulfate (polyiron), ferric chloride, and mixtures thereof. The injection amount of these inorganic coagulants depends on the water quality of the raw water, but is in the range of 1 to 1000 mg / liter.

The water 6 containing fine flocs produced in the flocculation and mixing tank 3 is sent to a floc formation tank 7. In the floc forming tank 7, a polymer flocculant is injected, and the floc is mixed in the flocculation and mixing tank 3 more slowly and slowly, so that the fine flocs are enlarged by the polymer flocculant.

As the polymer coagulant to be injected, known anionic, nonionic and cationic polymer coagulants can be mentioned. Examples of the anionic polymer flocculant include a polyacrylamide partial hydrolyzate, a copolymer of an anionic monomer, and a copolymer of an anionic monomer and a nonionic monomer such as acrylamide. Examples of the anionic monomer include acrylic acid, methacrylic acid, itaconic acid, maleic acid, fumaric acid, vinyl sulfonic acid, allyl sulfonic acid, methallyl sulfonic acid, styrene sulfonic acid, 2-allylamide ethane sulfonic acid, 2-acrylamido-2. -Methylpropanesulfonic acid, 2-methacrylamidoethanesulfonic acid, 2-methacrylamido-2
-Methylpropanesulfonic acid, 2-acryloyloxyethanesulfonic acid, 3-acryloyloxypropanesulfonic acid, 4-acryloyloxybutanesulfonic acid,
Examples thereof include 2-methacryloyloxyethanesulfonic acid, 3-methacryloyloxypropanesulfonic acid, 4-methacryloyloxybutanesulfonic acid, and metal salts or ammonium salts of these alkali metals and alkaline earth metals. These anionic monomers may be used alone or in combination of two or more. Examples of the nonionic monomer include acrylamide, methacrylamide, methacrylonitrile, vinyl acetate and the like. These nonionic monomers may be used alone,
You may use it in combination of 2 or more type. Preferred copolymers are acrylamide / acrylic acid salt copolymers and acrylamide / 2-acrylamido-2-methylpropanesulfonic acid copolymers. The nonionic polymer flocculant is a polymer or copolymer of the above nonionic monomers, preferably polyacrylamide.

The injection amount of the polymer coagulant is 0.05 to 0.5.
Although the object of the present invention can be achieved with mg / l, it is preferable that the total is 1 mg / l or less at the maximum.
Further, since the regulated value in use is 0.00005 mg / liter or less of the residual acrylamide monomer in the treated water, the acrylamide monomer in the product is theoretically 0.
It is important to keep it to 005 wt% or less.

Most of the flocs, which have been enlarged by the polymer flocculant, are recovered as sludge by solid-liquid separation in the subsequent settling tank 13. Generally, the sedimentation tank 13 is provided with an inclined plate and an inclined pipe inside. The precipitated treated water that has undergone solid-liquid separation is sent to the sand filtration tower 15 where it is treated with a filter medium and purified water 1
It becomes 6. Quartz sand and anthracite are the most common filter media. As mentioned above, most of the flocs are sedimentation tank 13
The turbid matter in the raw water that was not captured by the flocs and the flocs that did not settle in the settling tank 13 are separated by the filter medium in the sand filtration tower 15 although they are separated by. The floc aggregated only with the inorganic coagulant does not adhere to the filter medium because the viscosity of the inorganic coagulant itself is not so high, and even if it adheres to the filter medium, the floc can be easily removed by backwashing. On the other hand, the flocs aggregated with the polymer flocculant adhere to the filter medium due to the viscosity of the polymer flocculant, and cause filter clogging.

The most important feature of the present invention is to measure the streaming current of the floc after the injection of the polymer coagulant in order to solve the problem of filtration blockage which may occur when the polymer coagulant is used. The point is to control the injection amount of the polymer coagulant based on the measurement result. Flow current is measured by flow ammeter 1
1 is used.

A schematic diagram of the streaming ammeter 11 is shown in FIG. A piston 21 that is moved up and down by a motor 22 is provided inside the cylinder 20. There is a predetermined clearance between the piston 21 and the inner wall of the cylinder 20. The sample water containing the flocs that entered from the sample water inlet 23 is the piston 2
A shearing force is applied within the above-mentioned clearance by the vertical movement of 1, and the shearing force causes the colloidal particles attached to the surface of the floc to be separated from the floc. The flowing current generated at this time can be detected by the amplifying rectifier circuit 25 as a flowing current value corresponding to the charge density on the floc surface. For example, in flocs aggregated with polyaluminum chloride (PAC), a large amount of aggregated substances of aluminum hydroxide are attached to the surface of the aggregated flocs, so that many positively charged particles are present. Therefore,
The flow current value after coagulation with the inorganic coagulant is higher than that of raw water (on the positive side). Further, the flowing current value increases in proportion to the injection amount of the inorganic coagulant.

On the other hand, the floc produced by using the anionic polymer flocculant has a large amount of negative charges because the polymer flocculant which is an anionic substance adheres to the surface of the floc. For this reason, the streaming current value becomes lower (becomes negative) than the streaming current value after aggregation with the inorganic coagulant. Therefore, by measuring the flowing current value of the floc after the injection of the polymer flocculant, it is possible to determine the excess or deficiency of the polymer flocculant. The streaming current value decreases in proportion to the injection rate of the polymer flocculant. Further, the streaming current value decreases in proportion to the anionic strength of the polymer coagulant. That is, if the injection amount of the polymer coagulant is the same, the flow current value of the polymer coagulant having a strong anionic property is largely decreased, and the flow current value of the nonionic or the polymer coagulant having a weak anionic property is small.

In controlling the injection amount of the polymer coagulant by the flow current, the flow current value that can be optimally controlled varies depending on the raw water state, the type and injection amount of the inorganic coagulant, and the type and injection amount of the polymer coagulant. I can not say unequivocally because it does,
When the flowing current value (stable value) in the state where the polymer coagulant is injected and there is no filtration blockage and stable operation is possible in advance, and the flowing current value drops by about 50% from this stable value It can be determined that the polymer coagulant is excessive. Therefore, when the operation is continued in such a state, the floc of flocs containing the excess polymer flocculant flows out to the filtration pond,
It will cause a sudden filter blockage. In this case, it is necessary to reduce the injection amount of the polymer coagulant so that the streaming current value approaches the stable value.

Further, in the present invention, it is possible to control the injection amount of the polymer coagulant by comparing the streaming currents before and after the polymer coagulant injection. Even in this case, the streaming current value that can be optimally controlled varies depending on the raw water state, the type and injection amount of the inorganic coagulant, and the type and injection amount of the polymer coagulant. When the flowing current value decreases about twice as much as the flowing current value before injection,
It can be determined that the polymer flocculant is excessive.

On the other hand, when the turbidity of the raw water is low, the turbidity is small, so the number of nuclei for floc formation is reduced, the number of collisions of the flocs with each other is reduced, and the turbidity can be reduced even if a polymer flocculant is used in combination. The effect may not be seen. Furthermore, it is considered that the number of nuclei for floc formation is small and the amount of residual polymer coagulant that could not contribute to the formation of flocs increases, which also causes filtration clogging.

Another most important feature of the present invention is that flocs produced in the coagulation sedimentation treatment are returned to the raw water before the coagulation sedimentation treatment in order to achieve both the above-mentioned prevention of filter clogging and reduction of turbidity. It is to be characterized.
The returned flocs are flocs produced in the floc formation tank after the injection of the polymer flocculant, or flocs produced in the floc formation tank after the injection of the polymer flocculant are sedimented in the sedimentation tank (hereinafter, (Referred to as precipitation flocs). Since these flocs already retain the polymeric flocculant on the surface and still have the ability to flocculate, the ability of the flocs to collide with each other to form a larger floc is compared to the case where the flocs are not returned. Have.
In addition, since the number of collisions between the flocs increases, the amount of fine flocs reaching the sand filtration tower can be drastically reduced without being made huge and without being settled in the sedimentation basin, so that it is possible to prevent the duration of filtration from being shortened. In addition, the effect of reducing the amount of newly injected polymer coagulant can be expected.

When returning the settling flocs, it is better to avoid sending back the settling flocs completely settled and concentrated in the settling tank. When the flocs are completely precipitated and concentrated, it is difficult to adjust the concentration of the suspended matter to the target when returning, and the amount of inorganic coagulant or polymer coagulant newly injected may increase. . Further, by concentrating, the effective part of the polymer flocculant retained on the surface of the flocs disappears completely, and the floc forming ability also disappears.

The flock may be returned to either the raw water or before the polymer flocculant is injected. The flocs can be returned to the raw water introduction pipe 2 and the coagulation / mixing tank 3 from the flocculation tank 7 or the settling tank 13 using the floc return pipe 18a shown in FIG. 3, for example. In particular, when the turbidity of raw water is low and the suspended matter is small, it is effective to return the raw water. The amount of flocs to be returned is not particularly limited, but optimal conditions may be set by monitoring the floc state in the flocculation and mixing tank 3 and the floc formation tank 7, or the turbidity of the precipitated treated water.

When practicing the present invention, if clay particles such as kaolin or fine sand or fine sand are mixed with the returned flocs, the flocs become stronger and heavier, so that the turbidity-eliminating effect is more exerted. Therefore, it is preferable. The clay inorganic fine particles and the fine sand may be mixed in any place in the flock return pipes 18a and 18b, but immediately before returning the extracted flocs to the raw water introduction pipe 2 or the coagulation / mixing tank 3. It is also possible to separately provide a means for injecting clay inorganic fine particles or fine sand at the point of returning to the raw water introducing pipe 2 or the coagulating and mixing tank 3 instead of the flock returning pipes 18a and 18b.

[0027]

The present invention will be described in more detail with reference to the following examples. The experiment was performed using the apparatus shown in FIG.

(Example 1) The experimental conditions are as follows. Raw water flow rate: 100 m ³ / day (lake water) Raw water turbidity: 11 to 15 degrees Raw water pH: 7.6 to 8.3 Inorganic flocculant: PAC 40 to 100 mg / liter Polymeric flocculant: Medium Anionic polymer flocculation Agent 0.1 to 0.
5 mg / liter coagulation mixing tank: Effective volume 200 liters x 2 tanks Flock forming tank: Effective volume 1200 liters x 2 tanks Sedimentation tank = 7000 liters, sand filter tower with sloping plate: Filtration speed 150 m / day filtration layer composition: Anthracite layer Height 400mm, silica sand layer height 4
00 mm

In the apparatus of FIG. 1, the inorganic coagulant (PA
C) was injected into a coagulation / mixing tank of 60 mg / liter, and rapid stirring was performed to form microflocs. Then, a predetermined amount of a polymer flocculant was injected immediately before flowing into the floc forming tank, and slow stirring was performed. The flowing current value was measured immediately after the coagulation and mixing tank outlet and the inflow to the sedimentation tank. Table 1 shows the streaming current value, treated water turbidity, and filtration duration at each polymer coagulant injection amount.

When the injection amount of the polymer flocculant was 0.1 mg / liter and 0.3 mg / liter, the flow current values immediately after the inflow into the sedimentation tank were -18 to -20 mV and -20 to 20 mV, respectively.
At -24 mV, the higher the coagulant injection amount, the lower the value. The filtration duration in each of these cases is 4
It was 8 hours and 46 hours, which was not different from the case where the polymer coagulant was not injected (48 hours), and the state of the filter basin was stable. Further, when the injection amount of the polymer coagulant was set to 0.5 mg / liter, the streaming current value was −33 to −35 mV, the filtration continuation time was significantly shortened to 32 hours, and the polymer coagulant amount was excessive. I decided it was.

As is clear from the above results, when the streaming current value was lower than the stable value by about 50%, the polymer coagulant was excessive and the filtration duration was shortened. Therefore, it is understood that the reduction of the filtration duration can be prevented by measuring the flowing current value of the floc formed by the polymer flocculant.

[0032]

[Table 1]

Example 2 The experiment was carried out using the apparatus shown in FIG. The experimental conditions are as follows. Raw water flow rate: 100 m ³ / day (lake water) Raw water turbidity: 10 to 14 degree Raw water pH: 7.5 to 8.2 Inorganic coagulant: Liquid sulfuric acid band 40 to 100 mg / liter Polymeric coagulant: Weak anion high Molecular flocculant 0.1-0.
5 mg / liter coagulation / mixing tank: Effective volume 200 liters x 2 tanks Flock forming tank: Effective volume 1200 liters x 2 tanks Sedimentation tank: 7000 liters, sand filtration tower with inclined plate: Filtration speed 150 m / day filtration layer composition: Anthracite layer Height 400mm, silica sand layer height 4
00 mm

In the apparatus shown in FIG. 3, an inorganic coagulant (liquid sulfuric acid band) was injected into an 80 mg / liter coagulation / mixing tank,
After rapid stirring to form microflocs, 0.3 mg / liter of a polymer flocculant was injected just before the flow into the floc formation tank, and slow stirring was performed. Immediately after entering the settling tank, the settling flocs were returned to the second coagulation and mixing tank at a rate of 10 liters per minute. Table 2 shows the treated water turbidity and filtration duration.

Examples 3 to 4 and Comparative Examples 1 to 2 Tests were carried out in the same manner as in Example 2 except that the pulling out place, returning place or returning amount of flocs were changed as shown in Table 2. Further, an experiment was carried out in the case where the flocs were not extracted (Comparative Example 1) and the polymer coagulant was not injected (Comparative Example 2). The results are also shown in Table 2. As is clear from the results shown in Table 2, it can be seen that the method for returning flocs of the present invention reduces the turbidity of the precipitation-treated water and can extend the filtration duration.

[0036]

[Table 2]

Example 5, Comparative Example 3 The same experiment as in Example 2 or Comparative Example 1 was repeated except that the polymer coagulant injection amount was changed to 0.1 mg / liter. The results are shown in Table 3. As is clear from the results shown in Table 3, in the method of the present invention, even if the injection amount of the polymer coagulant is decreased, the turbidity of the precipitation-treated water is decreased and the filtration duration time can be extended (Example 5 and (Comparison with Comparative Example 1).

[0038]

[Table 3]

[0039]

EFFECTS OF THE INVENTION According to the present invention, the flow current of coagulation flocs after the injection of the polymer flocculant is measured, and the injection amount of the polymer coagulant is controlled based on the measurement result, which causes a problem in water purification It is possible to prevent the filter clogging due to the polymer coagulant, which can be prolonged, and extend the life of the sand filtration tower. On the other hand, the use of the polymer coagulant allows the precipitated treated water to be treated. It has great effects such as reducing the turbidity of water and purified water. Further, according to the present invention, it is possible to return the flocs generated in the coagulation-sedimentation treatment after the injection of the polymer coagulant, and prevent the filter clogging caused by the polymer coagulant which is a problem in the water purification treatment. It is possible to solve the problem of poor coagulation when the raw water has a low turbidity.

[Brief description of drawings]

FIG. 1 is a schematic explanatory view showing a coagulation-sedimentation treatment apparatus of Example 1 of the present invention.

FIG. 2 is a schematic explanatory sectional view of a streaming ammeter according to the present invention.

FIG. 3 is a schematic explanatory diagram of a coagulation-sedimentation treatment apparatus according to a second embodiment of the present invention.

[Explanation of symbols]

1 raw water 2 Raw water introduction pipe 3 coagulation mixing tank 4 Inorganic coagulant 5 Inorganic flocculant storage tank 6 Water containing fine flock 7 Flock forming tank 8 Polymer flocculants 9 Polymer flocculant storage tank 10 Flock drawn tube 11 Flow ammeter 12 Giant floc-containing water 13 settling pond 14 clear water 15 sand filtration tower 16 clean water 17 Clean water discharge pipe 18a Flock return pipe 18b Flock return pipe 20 cylinders 21 pistons 22 motor 23 Sample water inlet 24 Sample water outlet 25 Amplifying rectifier circuit

Continued front page    F-term (reference) 4D015 BA12 BA21 BA23 BA25 BB09                       BB12 CA14 DA03 DA04 DA06                       DA13 DA16 DB02 DB08 DB12                       DB22 DB30 EA03 EA07 EA32                       FA02 FA16

Claims (5)

[Claims] 1. In a water purification method in which an inorganic coagulant is injected into water to be treated, followed by injecting a polymer coagulant to perform coagulation-sedimentation treatment, and subsequently filtration treatment, after injection of the polymer coagulant. A method for purifying water, characterized in that the flowing current of the floc of flocculation is measured, and the injection amount of the polymer flocculant is controlled based on the measurement result. 2. A water purification method in which an inorganic coagulant is injected into water to be treated, and then a polymer coagulant is injected to perform coagulation-sedimentation treatment, followed by filtration treatment. Measure the flowing current of floc,
Next, a flowing water current of the floc after the injection of the polymer flocculant is measured, and the injection amount of the polymer flocculant is controlled based on the measurement result. 3. A floc produced by the coagulation-sedimentation process in a water purification method in which an inorganic coagulant is injected into the water to be treated, and then a polymer coagulant is injected to perform the coagulation-sedimentation process, followed by filtration. Is returned to the water to be treated before the inorganic coagulant is injected. 4. A floc giant by injecting a water to be treated for purification treatment, a coagulation mixing tank having an inorganic coagulant injection means, and a polymer flocculant injected into the fine flocs produced in the coagulation mixing tank. A floc formation tank that strengthens and strengthens
In a water purification device that has a sedimentation tank for solid-liquid separation of large flocs and a sand filtration tower that discharges the solid-liquid separated sedimentation treated water to the outside of the system, a huge flocculation tank inside the floc formation tank after injection of polymer flocculant A flow ammeter for measuring the flow current of a floc, or a flow current of a fine floc before injection of a polymer flocculant and a flow current of the giant floc after injection of a polymer flocculant, and polymer flocculation based on the measurement result of the flow ammeter A water purification apparatus comprising: a polymer coagulant injection control means for controlling the injection amount of the agent. 5. A floc is enlarged by injecting a water to be treated to be purified, a coagulation mixing tank having an inorganic coagulant injection means, and a polymer flocculant injected into the fine flocs produced in the coagulation mixing tank. In a water purification apparatus having a floc formation tank for solidifying and a flocculation tank, a sedimentation tank for solid-liquid separation of giant flocs, and a sand filtration tower for discharging the solid-liquid separated precipitation treatment water to the outside of the system, a floc formation tank and a And / or a means for returning the settling flocs of the settling tank to the coagulation and mixing tank and / or the water to be treated.