JP2002177963A - Water cleaning treatment system and water cleaning method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a water cleaning treatment system and treatment method which decrease the amount of the effluent sludge from a drinking water treatment plant and decrease the manganese recovered in a regenerated flocculating agent. SOLUTION: Hydrochloric acid or sulfuric acid is injected into the slurry-like settled sludge generated when raw water is cleaned by injecting the flocculating agent consisting of an aluminum compound as an essential component into the raw water, by which the sludge is separated to a solution eluted with the aluminum compound and thick sludge. The solution is subjected to alkaline reaction separation treatment of adding an alkaline compound exhibiting strong alkalinity of a pH>=13 to the solution to regulate the solution to pH 4.5 to 6.5 and separating the deposit consisting essentially of the aluminum hydrate deposited by this regulation from the solution, then the regenerated flocculating agent essentially consisting of the aluminum chloride or aluminum sulfate obtained by using the deposit consisting essentially of the separated aluminum hydrate as raw material is injected into the raw water, by which the raw water is subjected to flocculation treatment. The thick sludge separated by the dissolution and separation treatment and the solution separated by the alkaline reaction separation treatment is subjected to neutralization treatment then to dehydrating treatment.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a water purification system and a water purification method, and more particularly to a water purification system in which a coagulant mainly composed of an aluminum compound is injected into raw water, subjected to coagulation treatment and supplied for drinking water and the like. The present invention relates to a system and a water purification treatment method.

[0002]

2. Description of the Related Art In a drinking water treatment plant (hereinafter sometimes referred to as a water purification plant) for obtaining drinking water to be supplied to beverages or the like from raw water taken from a river or the like, a water treatment flocculant (hereinafter referred to as a water treatment coagulant) is used in the water treatment process. , May be simply referred to as a flocculant). As such a coagulant, a coagulant mainly containing an aluminum compound is widely used. Conventionally, a new flocculant was used as this flocculant, but it was necessary to carry in the flocculant from outside the water purification plant, and the cost of chemicals was high. Further, in recent years, environmental problems have been highlighted, and disposable flocculants are becoming a problem. For this reason, a water purification system for collecting and reusing a flocculant has been studied.
No. 198 proposes a water purification treatment method shown in FIG. In the water purification treatment method shown in FIG. 2, raw water taken from a river or the like is injected into a mixing pond 100 with a coagulant containing an aluminum compound as a main component. The suspension is settled to form a slurry-like settling sludge, and the supernatant is sent to the rapid filtration pond 115. The filtered water filtered by the rapid filtration pond 115 is sterilized by chlorine in a sterilization tank 116 and supplied as clean water. On the other hand, the slurry-like sedimentation sludge settled in the sedimentation tank 103 is gravity-sedimented in the sludge sedimentation tank 104 to be concentrated first-stage sludge, and then the centrifugal separator 106
, To obtain a second-stage concentrated sludge which was further concentrated. The water separated by the sludge concentration tank 104 and the centrifugal separator 106 is returned to the mixing pond 100.

[0003] The second dewatering process performed by the centrifugal separator 106
The second-stage concentrated sludge is put into the acid treatment tank 108, and while the concentrated sulfuric acid is injected and stirred, the aluminum compound in the second-stage concentrated sludge is converted into aluminum sulfate. The solution containing aluminum sulfate is dehydrated by the centrifugal separator 110, stored in the regenerating flocculant storage tank 112, and injected again into the mixing pond 100 as the regenerating flocculant. On the other hand, the acidic residual sludge dewatered by the centrifugal separator 110 is neutralized by injecting caustic soda, and stored in the sludge storage tank 114.
To make a dewatered cake.

[0004]

According to the water purification treatment method shown in FIG. 2, the flocculant injected into the raw water can be regenerated and injected again as a flocculant, and the problem of disposable flocculants can be solved. There is. However, the slurry-like sedimentation sludge settled in the sedimentation basin 103 contains a high concentration of a manganese compound in addition to the aluminum compound as a main component. This is because naturally-occurring manganese compounds contained in raw water are concentrated in sludge. The manganese compound reacts and dissolves with sulfuric acid in the acid treatment tank 108,
It is also contained in the solution containing aluminum sulfate as a main component separated by the centrifugal dehydrator 110. Therefore, a manganese compound is also contained in the regenerated coagulant using such a solution. Although the concentration of the manganese compound in the regenerated coagulant is initially low, the manganese compound in the regenerated coagulant gradually accumulates because it is collected and circulated with the aluminum compound. On the other hand, since manganese is a metal harmful to the human body, a coagulant containing manganese at a high concentration cannot be used as a water treatment coagulant in a water purification plant. Therefore, in the water purification treatment method shown in FIG. 2, it is necessary to constantly measure and monitor the amount of manganese in the regenerated coagulant, and it is necessary to periodically purge the regenerated coagulant so that the amount of manganese in the regenerated coagulant is less than the specified value. Required.

[0005] As described above, a water purification treatment method that requires constantly monitoring the amount of manganese in the regenerated flocculant is not practical. However, the conventional sedimentation basin 103
The slurry-like sediment sludge precipitated in
8, the efficiency of dewatering in the pressurized dehydrator 118 can be greatly improved and the amount of waste sludge discarded from the water treatment plant is reduced in the water purification method shown in FIG. it can. Accordingly, an object of the present invention is to improve the efficiency of dewatering treatment of slurry-like sedimentation sludge generated when purifying raw water, to reduce the amount of waste sludge discarded from a water treatment plant, and to be recovered in a regenerated flocculant. It is an object of the present invention to provide a water purification system and a water purification method capable of reducing manganese as much as possible.

[0006]

Means for Solving the Problems The inventors of the present invention have studied to solve the above-mentioned problems. As a result, sulfuric acid was added to a precipitated sludge containing a manganese compound to dissolve an aluminum compound, and then a saturated aqueous solution was added to the aqueous sulfuric acid solution. PH of about 7 ~
PH 4 to 6 by adding a weakly basic inorganic compound exhibiting 11
And by precipitating the aluminum compound again,
It has been found that a flocculant containing aluminum sulphate as a main component having a very low manganese content can be obtained from a sludge containing a high concentration of a manganese compound. For this reason, in the water purification system shown in FIG. 2, a weakly basic inorganic compound having a pH of about 7 to 11 is added to the solution containing aluminum sulfate stored in the regenerating flocculant storage tank 112 to adjust the pH to 4. As a result, an attempt was made to reuse the precipitated aluminum compound as a regenerated coagulant. However, it has been found that the flocculating effect of the regenerated flocculant containing aluminum sulfate as a main component, which is recovered from the precipitated sludge and regenerated, is inferior to that of a commercially available flocculant.

[0007] For this reason, the present inventors examined the cause of the inferiority of the regenerated flocculant containing aluminum sulfate as a main component recovered and regenerated from the precipitated sludge as compared with a commercially available flocculant. Although iron compounds were also contained at a high concentration, it was found that, in the recovery method discussed above, the iron compounds were also removed simultaneously with the removal of the manganese compounds in the settled sludge. On the other hand, iron is a metal that is harmless to the human body, and iron ions have a flocculating effect, so it is possible to leave iron in the regenerated flocculant to improve the flocculating effect of the regenerated flocculant injected into raw water. is there. Based on such findings, the present inventors have further studied and found that after adding sulfuric acid to the precipitated sludge containing the iron compound and the manganese compound to dissolve the aluminum compound, caustic soda was added to the aqueous sulfuric acid solution. By precipitating aluminum hydrate, it is possible to leave iron while removing manganese, and even with a regenerated flocculant containing aluminum chloride as a main component recovered and regenerated from the precipitated sludge, commercially available aluminum chloride can be used. The present inventors have found that a coagulation effect similar to that of a water treatment coagulant as a main component can be exhibited, and have reached the present invention.

That is, according to the present invention, in a water purification system in which a coagulant mainly composed of an aluminum compound is injected into raw water and subjected to coagulation treatment to supply drinking water or the like, a slurry generated when the raw water is purified is used. Dissolving and separating treatment means for injecting hydrochloric acid or sulfuric acid into the sedimentation sludge to separate into a solution in which the aluminum compound in the sedimentation sludge is dissolved and concentrated sludge; An alkali compound exhibiting alkalinity is injected, and the solution is adjusted to pH 4.5 to 6.5 to precipitate a precipitate mainly composed of aluminum hydrate, and is separated into the precipitate and the solution. Separation means, aluminum chloride using as a raw material a precipitate mainly composed of aluminum hydrate separated by the alkali reaction separation means A coagulant regenerating means for regenerating a coagulant containing aluminum sulfate as a main component, a coagulant regenerated by the coagulant generating means, a coagulant injection means for injecting into the raw water and performing a coagulation treatment, A purified water treatment comprising: performing a neutralization treatment on the concentrated sludge separated by the dissolution separation treatment means and the solution separated by the alkali reaction separation means; In the processing system.

Further, the present invention has been developed in purifying raw water when injecting a coagulant mainly composed of an aluminum compound into raw water and performing coagulation treatment to obtain purified water to be supplied to drinking water or the like. Hydrochloric acid or sulfuric acid is injected into the slurry precipitation sludge, subjected to a dissolution separation treatment for separating a solution in which the aluminum compound in the precipitation sludge is dissolved and a concentrated sludge, and the solution separated by the dissolution separation treatment is subjected to a pH of 13 or more. After injecting an alkali compound exhibiting alkalinity, adjusting the solution to pH 4.5 to 6.5, and subjecting the precipitate containing aluminum hydrate as a main component to an alkaline reaction separation treatment for separating the precipitate from the solution, Obtained using as a raw material a precipitate mainly composed of aluminum hydrate separated by the alkali reaction separation treatment, aluminum chloride or aluminum sulfate as a main component The regenerated coagulant is injected into the raw water and subjected to coagulation treatment, and the concentrated sludge separated by the dissolution separation treatment and the solution separated by the alkali reaction separation treatment are neutralized, followed by dehydration treatment. It is also a water purification method characterized by applying.

In the present invention, there is provided a sedimentation separation means for sedimenting and separating the slurry-like precipitation sludge into concentrated sludge and water, returning the separated water to raw water, and supplying the concentrated sludge to the dissolution separation treatment means. This makes it possible to reduce the amount of processing in each processing unit after the dissolution separation processing unit. Also, by providing a concentrated sludge dewatering treatment means for directly dehydrating a part of the concentrated sludge separated by the sedimentation separation treatment means, when the raw water becomes extremely turbid due to heavy rain, etc., and the concentrated sludge amount is extremely large. Even so, by directly dehydrating a part of the concentrated sludge, the load in the flocculant recovery step can be made constant, and a regenerated flocculant of stable quality can be recovered.

According to the present invention, the regenerated coagulant recovered from the slurry-like settling sludge generated when purifying raw water can contain as little manganese compounds as possible and also have a large iron content. . For this reason, even if the regenerated coagulant is used repeatedly, the manganese compound can be prevented from gradually accumulating in the regenerated coagulant, and the coagulability exhibited by the regenerated coagulant is equal to or higher than that of a commercially available water treatment coagulant. Moreover, since the aluminum compound is substantially removed from the slurry-like settling sludge and then subjected to the dehydration treatment, the treatment is easier and the dewatering treatment is easier than when the slurry-like precipitation sludge is directly dehydrated. The amount of waste sludge to be discarded from the water treatment plant can be reduced.

[0012]

FIG. 1 shows an example of a water purification system according to the present invention. In the water purification plant shown in FIG. 1, raw water taken from a river or the like is mixed with a coagulant containing an aluminum compound as a main component in a mixing pond 1, flocculants are suspended in a floc forming pond 2, and then flocculated in a sedimentation pond 3. The suspension is settled to form settled sludge, and the supernatant is sent to the rapid filtration pond 15. The filtered water filtered in the quick filtration pond 15 is sterilized with chlorine in a sterilization tank 16 and supplied as clean water. On the other hand, the slurry-like sediment sludge precipitated in the sedimentation basin 3 is converted into concentrated sludge by sedimentation and separation means. The sedimentation / separation means includes a sludge pond 4, a pump 5, and a first thickener 6 as a sedimentation tank. In this sedimentation separation means, the slurry-like sedimentation sludge discharged from the sedimentation basin 3 to the sludge basin 4 is sent to the first thickener 6 by the pump 5 and separated into supernatant water and first concentrated sludge by gravity sedimentation. The supernatant water separated by the first thickener 6 is returned to the mixing pond 1.

On the other hand, the first concentrated sludge separated by the first thickener 6 contains an aluminum compound from a flocculant or the like injected into the mixing pond 1 as a flocculant. For this reason, the first-stage concentrated sludge is provided to the dissolution separation treatment means. This dissolution / separation treatment means comprises an acid mixing tank 7 with a stirrer and a second thickener 8 as an acid reaction tank and a precipitation tank.
The first-stage concentrated sludge sent from the first thickener 6 to the acid mixing tank 7 is mixed with the injected hydrochloric acid or sulfuric acid while being stirred by the stirrer, and then sent to the second thickener 8.
In the second thickener 8, the aluminum compound in the first-stage concentrated sludge was made water-soluble by reacting it with hydrochloric acid or sulfuric acid, and the supernatant in which the water-soluble aluminum compound was dissolved and the sludge consisting of the undissolved matter settled out. It is separated into second-stage concentrated sludge (hereinafter sometimes referred to as strong acid sludge).

The amount of hydrochloric acid or sulfuric acid injected into the first-stage concentrated sludge sent from the first thickener 6 to the acid mixing tank 7 is equivalent to the amount of aluminum contained in the first concentrated sludge. It is preferable to adjust so that Also,
The aluminum concentration in the supernatant separated in the second thickener 8 is 0.1 to 6% by weight, particularly 1 to 6% by weight in terms of Al ₂ O ₃ , so that the first-stage concentrated sludge amount and the water amount It is preferable to adjust the amount of hydrochloric acid or sulfuric acid. Here, if the aluminum concentration in the supernatant separated by the second thickener 8 is too low, the finally obtained regenerated flocculant becomes unstable,
The coagulation performance of the regenerated coagulant tends to be insufficient.
On the other hand, if the aluminum concentration in the supernatant separated in the second thickener 8 is too high, the viscosity of the slurry composed of the first-stage concentrated sludge and hydrochloric acid or sulfuric acid increases, and the strong acid sludge in the second thickener 8 increases. It tends to hinder the separation operation and the like. The reaction of the aluminum compound in the first concentrated sludge with hydrochloric acid or sulfuric acid is carried out at room temperature to 100 ° C (preferably 50 to 100 ° C).
(95 ° C.).

In the supernatant liquid separated from the second thickener 8, manganese compounds and iron compounds contained in the first-stage concentrated sludge are also dissolved by reacting with hydrochloric acid or sulfuric acid, like the aluminum compounds. . For this reason, the supernatant is subjected to an alkali reaction separation means in order to recover the aluminum compound and the iron compound while removing as much as possible the manganese compound in the supernatant. This alkali reaction separation means includes an alkali reaction tank 9 and a filter 10. Into the alkaline reaction tank 9 to which the supernatant separated in the second thickener 8 has been sent, an alkali compound exhibiting strong alkalinity of pH 13 or more is added to the supernatant as a neutralizing agent, and the supernatant is subjected to pH adjustment.
By adjusting to 4.5 to 6.5, an aluminum hydrate (aluminum hydroxide) and an iron compound can be deposited without substantially depositing a manganese compound. As described above, the pH is adjusted in the alkaline reaction tank 9, and the solution in which aluminum hydrate is precipitated is filtered by the filter 10, and the dehydrated cake containing aluminum hydrate and iron compound and the manganese compound are contained. And separated filtrate. Here, as the alkali compound exhibiting strong alkalinity of pH 13 or more used as a neutralizing agent, caustic soda or caustic potash which can be handled as a solution can be preferably used, and caustic soda is particularly preferable from the viewpoint of chemical cost. Note that a pressure dehydrator can be used as the filter 10, but a filter filter or a suction filter can be used.

When a weakly basic alkali compound such as sodium bicarbonate, calcium carbonate, and magnesium carbonate is used instead of the neutralizing agent, not only manganese but also iron in a hydrochloric acid solution or a sulfuric acid solution is removed. Further, p of the supernatant to which an alkali compound exhibiting a strong alkalinity of pH 13 or more was added.
When H is less than 4.5, the recovery rate of the aluminum contained in the first concentrated sludge decreases. On the other hand, when the pH of the supernatant to which the alkali compound has been added exceeds 6.5, manganese in the supernatant cannot be sufficiently removed. In this way, the detailed reason for separating manganese and iron whose chemical behaviors are similar is not clear, but in general,
The sediment sludge obtained by sedimenting the suspended matter in the sedimentation basin 3 of the water purification plant is produced by treating river water with an aluminum-based coagulant, and the sediment sludge also contains soil-derived components. It is presumed that an alkali compound exhibiting strong alkalinity of pH 13 or more is used as the neutralizing agent.

The dewatered cake containing aluminum hydrate (aluminum hydroxide) and an iron compound and substantially free of manganese, which has been dehydrated by the filter 10, is used as a flocculant regenerating means for regenerating the dehydrated cake into a flocculant. Supply. Such a flocculant regenerating means is composed of a reaction tank 11 with a stirrer.
In the reaction tank 11, water and hydrochloric acid or sulfuric acid are injected into the dewatered cake dehydrated by the filter 10 and reacted while mixing. When the dehydrated cake is reacted with hydrochloric acid in the reaction tank 11, a regenerated flocculant whose main component is aluminum chloride can be obtained. When reacting the dehydrated cake with hydrochloric acid, by making hydrochloric acid less than an equivalent amount to aluminum, regenerated coagulation mainly containing polyaluminum chloride (hereinafter sometimes referred to as PAC) represented by the following general formula is used. Agent can be obtained. General formula Al ₂ (OH) _n Cl _(6-n) where 0 ≦ n <6 In the reaction between the dehydrated cake and hydrochloric acid, an appropriate amount of sulfate, for example, anhydrous sodium sulfate (sodium sulfate) is added to hydrochloric acid. By doing so, it is possible to achieve regenerated cohesion mainly composed of PAC having an excellent coagulation effect. The regenerated flocculant containing PAC as a main component is obtained by adding sulfuric acid to the aluminum-containing first-stage concentrated sludge concentrated in the first thickener 6 and collecting the sludge, followed by neutralization with caustic soda to obtain a dehydrated cake. It can also be obtained by reacting with hydrochloric acid. This is because sulfate groups remain in the dehydrated cake. When the dehydrated cake is reacted with sulfuric acid in the reaction tank 11, a regenerated coagulant whose main component is aluminum sulfate can be obtained.

On the other hand, the filtrate filtered by the filter 10 is
The strong acid sludge separated by the thickener 8 is supplied to a neutralization and dehydration treatment means for performing a neutralization treatment and a dehydration treatment. In such a neutralization and dehydration treatment means, since manganese is dissolved in the filtrate filtered by the filter 10, the filtrate is subjected to a neutralization treatment near pH 7 to precipitate and separate as a hydrate. The neutralization of the filtrate of the filtration device 10 and the neutralization of the strong acid sludge separated by the second thickener 8 may be performed in separate processing facilities. It is preferable from the viewpoint of. For this reason, the neutralization / dehydration treatment means comprises a neutralization tank 13 with stirring and a first pressure dehydrator 14. In the neutralization tank 13, while the filtrate filtered by the filter 10 and the strong acid sludge separated by the second thickener 8 are stirred, caustic soda as an alkali is injected to perform a neutralization treatment. The mixture subjected to the neutralization treatment is filtered by the first pressure dehydrator 14, the filtrate is returned to the mixing pond 1, and the dewatered cake is purged from the water purification system as waste sludge outside the system. The amount of the generated waste sludge can be reduced by about 20 to 30% as compared with the case where the first-stage concentrated sludge concentrated by the conventional first thickener 6 is directly dewatered. Moreover, the waste sludge to be purged out of the system is
Since the aluminum compound which causes germination failure of plants is removed, it can be effectively used for horticultural soil and the like. In this regard, conventionally, waste sludge to be purged out of the system contains a large amount of aluminum compounds that cause germination failure of plants, and has an economical effect compared to waste disposal that has been buried as industrial waste. large.

Meanwhile, the regenerated coagulant obtained in the reaction tank 11 has a manganese content of 20 p in a conversion agent converted so that the aluminum component is 10% by weight as Al ₂ O _3.
pm or less (preferably 15 ppm or less), and may be 1 ppm or less. For this reason, the regenerated coagulant can be used in a water purification plant, and is supplied to an injection means for injecting the regenerated coagulant obtained in the reaction tank 11 into the mixing pond 1. Since the regenerated coagulant obtained in the reaction tank 11 is in a liquid state, it can be directly injected into the mixing pond 1. This reaction tank 1
The concentration of the aluminum component in the regenerated coagulant obtained in 1 can be adjusted by the amount of water injected into the reaction tank 11. Here, from the viewpoint of the agglomeration effect of the regenerated coagulant and the stability of the solution in which the regenerated coagulant is dissolved, the aluminum content in the regenerated coagulant is, when the main component is the regenerated coagulant of aluminum sulfate, Al. _The content is preferably 0.5% by weight or more in terms of ₂ O ₃ . On the other hand, when the main component is a regenerated coagulant of polyaluminum chloride, the storage period varies depending on the storage period. For example, when the storage period is about 1 day, it may be 1% by weight or more in terms of Al ₂ O ₃ , and the storage period is 1 week. for degree 2 in terms of Al ₂ O ₃
% By weight. Furthermore, when the regenerated coagulant whose main component is polyaluminum chloride is stored for more than one week, the content is preferably 3% by weight or more.

In the case of a regenerated flocculant whose main component is PAC, the amount of hydrochloric acid added can be adjusted so that the basicity of PAC is 50% or less. At this time, the basicity is preferably set to 15 to 50% in consideration of the coagulation performance of the regenerated coagulant. In the case of a regenerated coagulant having a PAC basicity of less than 15%, the coagulation effect tends to be reduced. If a regenerated coagulant having a PAC basicity of more than 50% is to be obtained,
It tends to gel and decompose easily. As described above, the regenerated coagulant containing PAC having a basicity of about 15 to 50% as a main component exhibits a coagulation effect at least as high as that of a commercially available coagulant containing PAC having a basicity of more than 50% as a main component. be able to. Furthermore, the regenerated flocculant whose main component is aluminum sulfate is also
1000 ppm or more (preferably 3000 ppm or more, particularly preferably 5000 p) in the reduced flocculant converted to be 10% by weight of aluminum sulfate as Al ₂ O _3.
pm or more of iron, and exhibits a coagulation effect at least as high as that of a commercially available regenerated coagulant composed of aluminum sulfate. As described above, it is presumed that iron contained in the regenerated coagulant supplements the coagulation performance of the regenerated coagulant. For this reason, the regenerated flocculant containing PAC as a main component
1000 ppm or more (further 3000 ppm or more, especially 5000 ppm or more) in the reduced flocculant converted so that the polyaluminum chloride becomes 10% by weight as Al ₂ O _3.
It is preferable that iron is contained. Since silica is also considered to effectively act to improve the coagulability of the coagulant, the regenerated coagulant recovered from the sludge of the water purification plant also contains about 500 to 3000 ppm of silica in the reduced coagulant. Is preferred.

The recovered flocculant thus recovered is purified.
Reusable flocculant that can be reused as a flocculant in water
If the amount of coagulant alone is insufficient, use a commercially available coagulant.
You may use together. By the way, sludge generated in water treatment plants
Has a solid content of Al _TwoO_ThreeAbout 2
Contains about 5% by weight of aluminum compound
Is about 5% of the amount of aluminum compound contained.
0% is derived from the flocculant and the remaining 50%
It is thought to be derived from the soil. Furthermore, flocculants
Aluminum compounds derived from water soluble in hydrochloric acid and sulfuric acid
It is present in the form of oxides, and on the other hand,
The coming aluminum compounds are mainly poorly soluble in acids at room temperature.
It is believed to exist in the form of an oxide. Follow
The aluminum recovered from the sludge is mainly agglomerated
It is presumed to be derived from the drug. For this reason, sludge contains
About 50% of the amount of aluminum compounds
By reusing it as a regenerated flocculant
It can be used for circulation, and the flocculant is brought in from outside the water purification plant.
In addition, the problem of disposable flocculants can be solved.

In the water purification system shown in FIG. 1, the first-stage concentrated sludge dewatering means for directly dehydrating a part of the first-stage concentrated sludge separated by the first thickener 6 as the sedimentation separation means is provided. The second pressure dehydrator 12 is provided. In the second pressurized dewatering machine 12, even if the raw water becomes extremely turbid due to heavy rain or the like and a large amount of the first-stage concentrated sludge is generated in the first thickener 6, a part of the first-stage concentrated sludge is removed. By directly performing the dehydration treatment by the second pressure dehydrator 12, the load in the recovery step of the regenerated coagulant can be made constant, and the regenerated coagulant of stable quality can be collected. The water separated by the second pressure dehydrator 12 is returned to the mixing pond 1, and the dewatered cake is purged outside the water purification system, but can be effectively used for horticultural soil and the like.

In the water purification system described above,
Although the liquid regenerated coagulant was injected from the reaction tank 11 into the mixing pond 1, the regenerated coagulant obtained in the reaction tank 11 may be dried to be a powder. As described above, by using the powder as a regenerated coagulant, its storage stability can be improved. In the water purification system shown in FIG. 1, the slurry sludge settled in the sedimentation basin 3 is settled by the sedimentation separation means composed of the sludge pond 4, the pump 5, and the first thickener 6 as a sedimentation tank. Concentrates sludge. However, when the amount of sedimentation sludge settling in the sedimentation basin 4 is small, or in the case of a small-scale water purification plant, the sedimentation / separation means is omitted and the acid mixing tank 7 with a stirrer and the acid reaction tank and the sedimentation tank are used. The settling sludge may be directly supplied to the dissolution / separation processing means constituted by the two thickeners 8.

[0024]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The water purification system according to the present invention will be described in more detail with reference to a model experiment conducted on a beaker scale. Comparative Example 1 Slurry sedimentation sludge precipitated in the sedimentation basin 3 of the water treatment plant A (the aluminum content is 1.3% by weight in terms of Al ₂ O ₃ )
2950 g was subjected to suction filtration using No. 2 filter paper in order to reproduce the state widely practiced in the current water purification plant. 824 g of filtered sludge remained on the filter paper. The water content of the filtered sludge was 84.2% by weight as measured with a moisture meter at 130 ° C./90 minutes (solid content was 130%).
g).

Example 1 Slurry sedimentation sludge settled in the sedimentation basin 3 of the water treatment plant A (the aluminum content is 1.3% by weight in terms of Al ₂ O ₃ )
112 g of 96% sulfuric acid was added to 2950 g, and the mixture was stirred and mixed at 95 ° C. for 120 minutes to react the aluminum compound in the precipitation sludge with sulfuric acid. The slurry reaction solution is
Suction filtration was performed using No. 2 filter paper to separate into 2212 g of filtrate a and 222.5 g of strong acid sludge. The filtrate a obtained
, Gradually add a 20% aqueous solution of caustic soda while stirring,
The final pH was adjusted to 6.3 to precipitate aluminum hydroxide. The solution in which the aluminum hydroxide is precipitated is referred to as N
o.2 Suction filtration was performed using a filter paper, and 613 g of aluminum hydroxide cake (containing 4.3% by weight in terms of Al ₂ O ₃ ) and 202
9 g of filtrate b were obtained. Further, 613 g of the aluminum hydroxide cake was reacted with 79 g of 96% sulfuric acid to obtain 693 g of a liquid regenerated coagulant composed mainly of aluminum sulfate. The obtained regenerated coagulant has an aluminum content of Al
It is 3.8% by weight in terms of ₂ O ₃ and the manganese content is 3p
pm, iron content 3500 ppm, silica content 13
It was 00 ppm. Regarding the contents of manganese, iron, and silica contained in such a regenerated coagulant, in the converted coagulant in which the aluminum content was converted to 10% by weight in terms of Al ₂ O ₃ , manganese was 8 ppm and iron was 8 ppm. 920
It is 0 ppm and silica is 3400 ppm, and can be sufficiently used as a flocculant for water purification treatment. On the other hand, since strong acid sludge is strongly acidic, it is mixed with the filtrate b.
Then, the mixture was neutralized to pH 7 by adding an aqueous solution of sodium hydroxide, and filtered by suction using No. 2 filter paper to separate the cake and the filtrate c.
The water content of 280 g of cake remaining on the filter paper was 65.0% by weight (solid content: 98 g) as measured by a moisture meter at 130 ° C./90 minutes. The cake remaining on the filter paper is reduced by 66% by weight in total weight and 25% by weight in solid content compared to the case of Comparative Example 1. The filtrate c is
It could be returned to the mixing pond 1 at the water purification plant.

Comparative Example 2 Filtrate a (2310 g) obtained in the same manner as in Example 1
20% caustic soda aqueous solution is gradually added to
H7.5, and aluminum hydroxide was precipitated. Further, the solution in which aluminum hydroxide was precipitated was filtered by suction using No. 2 filter paper, leaving 400 g of cake on the No. 2 filter paper. The aluminum hydroxide content in this cake is
It was 6.1% by weight in terms of Al ₂ O ₃ . Further, 440 g of the aluminum hydroxide-containing cake was reacted with 80 g of 96% sulfuric acid to obtain 522 g of a liquid regenerated coagulant composed mainly of aluminum sulfate. The obtained regenerated coagulant had an aluminum content of 5.1% by weight in terms of Al ₂ O ₃ , a manganese content of 2000 ppm, and an iron content of 4200 p.
pm and the silica content g were 1700 ppm.
Also, aluminum sulfate contained in the regenerated flocculant
The contents of manganese, iron, and silica in the reduced flocculant converted to be 10% by weight as Al ₂ O ₃ were such that the manganese content was 3900 ppm, the iron content was 8200 ppm,
And the silica content was 3300 ppm. Thus, the coagulant whose manganese content in the reduced coagulant reaches 3900 ppm cannot be used as a coagulant in a water purification plant.

Comparative Example 3 Filtrate a (2390 g) obtained in the same manner as in Example 1.
20% caustic soda aqueous solution is gradually added to
H4.0, and aluminum hydroxide was precipitated. Further, the solution in which aluminum hydroxide was precipitated was suction-filtered using No. 2 filter paper, leaving 60 g of cake on the No. 2 filter paper. The aluminum hydroxide content in this cake is Al
It was 4.2% by weight in terms of ₂ O ₃ . At this time, the recovery rate of aluminum contained in the sludge was 8%.
And the subsequent operation was stopped due to poor practicality.

Example 2 To 2950 g of the same precipitated sludge as used in Example 1 (the aluminum content was 1.3% by weight in terms of Al ₂ O ₃ ), 3
230 g of 5% hydrochloric acid was added and mixed by stirring at 95 ° C. for 120 minutes to react the aluminum compound in the precipitated sludge with hydrochloric acid. The slurry-like reaction solution was subjected to suction filtration using No. 2 filter paper to separate into 2493 g of filtrate a and 203.0 g of strong acid sludge. To the obtained filtrate a, a 20% aqueous solution of caustic soda was gradually added with stirring to adjust the final pH to 4.8.
And aluminum hydroxide was precipitated. The solution in which the aluminum hydroxide was precipitated was filtered by suction using No. 2 filter paper, and 824 g of aluminum hydroxide cake (Al ₂ O
3.3% by weight in terms of ₃ ) and 2022 g of filtrate b. Further, 824 g of aluminum hydroxide cake, 12 g of anhydrous sodium sulfate (sodium sulfate) and 35% hydrochloric acid were mixed and reacted, and the main component was polyaluminum chloride (PAC).
950 g of a liquid regenerated coagulant consisting of The obtained regenerated coagulant had an aluminum content of 2.8 in terms of Al ₂ O _3.
% By weight, the manganese content was less than 1 ppm, the iron content was 3000 ppm, and the silica content was 1500 ppm. Manganese contained in such a regenerated flocculant,
Regarding the content of iron and silica, the aluminum content is
In the reduced flocculant converted to be 10% by weight in terms of Al ₂ O ₃ , manganese is less than 3.6 ppm and iron is less than 1000 ppm.
The content is 0 ppm and the content of silica is 5000 ppm, and it can be sufficiently used as a coagulant for water purification treatment. On the other hand, since strong acid sludge is strongly acidic, it is mixed with the filtrate b.
Then, the mixture was neutralized to pH 7 by adding an aqueous solution of sodium hydroxide, and filtered by suction using No. 2 filter paper to separate the cake and the filtrate c.
The moisture content of 251 g of the cake remaining on the filter paper was 61.0% by weight (solid content: 98 g) as measured by a moisture meter at 130 ° C./90 minutes. The cake remaining on the filter paper is reduced by 70% by weight in total weight and 25% by weight in solid content as compared with the case of Comparative Example 1. The filtrate c is
It could be returned to the mixing pond 1 at the water purification plant.

Example 3 To a beaker charged with 2950 g of the same precipitation sludge as used in Example 1 (the aluminum content was 1.3% by weight in terms of Al ₂ O ₃ ), 112 g of 96% sulfuric acid was added and the mixture was heated at 25 ° C. After stirring and mixing for 120 minutes at room temperature to allow the aluminum compound in the settling sludge to react with sulfuric acid, the beaker was allowed to stand still all day and night to separate the supernatant from the gravity-sedimented acid sludge.
A 20% aqueous sodium hydroxide solution was gradually added to 2041 g of the separated supernatant while stirring to adjust the pH to 5.2, and aluminum hydroxide was precipitated. The solution in which the aluminum hydroxide was precipitated was suction-filtered using No. 2 filter paper, and 321 g of an aluminum hydroxide cake (4.7% by weight in terms of Al ₂ O _3).
) And 2067 g of filtrate b. On the other hand, since 1021 g of gravity-sedimented acid sludge is strongly acidic, it is mixed with filtrate b, then neutralized to pH 7 by adding a 20% aqueous solution of caustic soda, and subjected to suction filtration using No. 2 filter paper to obtain cake and filtrate. c. The water content of 469 g of the cake remaining on the filter paper was 76.0% by weight (solid content: 113 g) as measured with a moisture meter at 130 ° C./90 minutes.
The cake remaining on the filter paper was compared to the case of Comparative Example 1,
The total weight is reduced by 43% by weight and the solid content is reduced by 13% by weight. The filtrate c could be returned to the mixing pond 1 of the water purification plant.

Example 4 230 g of 35% hydrochloric acid was added to a beaker charged with 2950 g of the same precipitation sludge as used in Example 1 (the aluminum content was 1.3% by weight in terms of Al ₂ O ₃ ) at 20 ° C. After stirring and mixing for 120 minutes at room temperature to allow the aluminum compound in the settling sludge to react with hydrochloric acid, the beaker was allowed to stand still all day and night to separate the supernatant from the gravity-sedimented acid sludge.
To the separated supernatant (2247 g), a 20% aqueous sodium hydroxide solution was gradually added with stirring to adjust the pH to 6.0 to precipitate aluminum hydroxide. The solution in which the aluminum hydroxide was precipitated was filtered by suction using No. 2 filter paper, and 245 g of an aluminum hydroxide cake (6.0% by weight in terms of Al ₂ O _3).
) And 2036 g of filtrate b. On the other hand, since 933 g of the acid sludge settled by gravity is strongly acidic, it is mixed with the filtrate b, then neutralized to pH 7 by adding a 20% aqueous sodium hydroxide solution, and subjected to suction filtration using No. 2 filter paper to obtain a cake and a filtrate. c
And separated into The water content of 410 g of the cake remaining on the filter paper was 72.2% by weight (solid content: 114 g) as measured by a moisture meter at 130 ° C./90 minutes. The cake remaining on the filter paper is reduced by 50% by weight in total weight and 12% by weight in solid content as compared with the case of Comparative Example 1.
The filtrate c could be returned to the mixing pond 1 of the water purification plant.

Comparative Example 4 112 g of 96% sulfuric acid was added to a beaker charged with 2950 g of the same sludge (the aluminum content was 1.3% by weight in terms of Al ₂ O ₃ ) as in Example 1, and 25 ° C. After stirring and mixing for 120 minutes at room temperature to allow the aluminum compound in the settling sludge to react with sulfuric acid, the beaker was allowed to stand still all day and night to separate the supernatant from the gravity-sedimented acid sludge.
Since 1049 g of the acid sludge subjected to gravity sedimentation is strongly acidic, 1500 g of tap water is added, and then a 10% lime slurry is gradually added with stirring to neutralize the pH to 7, and filtered by suction using a No. 2 filter paper. Separated into cake and filtrate c. The water content of 643 g of the cake remaining on the filter paper was determined by a moisture meter to be 13%.
When measured under the condition of 0 ° C./90 minutes, 72.9% by weight was obtained.
(Solid content: 174 g). The cake remaining on the filter paper was 22% by weight in total weight compared to the case of Comparative Example 1.
Although decreased, the solid content increased by 34% by weight.

Example 5 In Examples 1 to 4, the acid sludge subjected to gravity sedimentation and the filtrate b were mixed, and a 20% aqueous solution of caustic soda was added.
After adding tap water to the acidic sludge in the slurry liquid neutralized to H7, the slurry-like settling sludge of Comparative Example 1, and Comparative Example 4, 10% lime slurry was gradually added to neutralize the pH of the slurry liquid to pH 7. 0.37 g of each was taken and diluted with pure water to a total volume of 15 ml (diluted about 40-fold). Next, suction filtration was performed using a membrane filter having a pore size of 0.45 μm, and the filtration times were compared. The results are shown in Table 1 below.

[Table 1] As is clear from Table 1, the filterability of Examples 1 to 4 is Comparative Example 1 which reproduces a state widely practiced in a current water purification plant.
Is better than the filterability of Further, the filterability of Comparative Example 4 is not inferior to the filterability of Examples 1 to 4, but in Comparative Example 4, as described above, the solid content of the cake remaining on the filter paper increases.

Example 6 The aggregating ability of the regenerated coagulant of Example 1 (a regenerated coagulant mainly composed of aluminum sulfate) with a commercially available coagulant of aluminum sulfate, and the regenerated coagulant of Example 2 (main component) A jar test was conducted on the coagulating ability of a regenerated coagulant composed of polyaluminum chloride and a commercially available coagulant composed of polyaluminum chloride. In this jar test, raw water (turbidity: 1
0.3 °, pH; 7.4, water temperature 25 ° C.), and the added amount of the regenerated coagulant and the commercially available coagulant to the raw water was 2.0 mg / liter in terms of Al ₂ O ₃ when the aluminum component was added. (Raw water).

[Table 2] As is clear from Table 2, the regenerated flocculants of Example 1 and Example 2 all exhibit a flocculating effect equal to or higher than that of a commercially available flocculant.

[0034]

According to the present invention, manganese recovered in the regenerated coagulant can be reduced as much as possible, and the regenerated coagulant can be recycled. In addition, the efficiency of dewatering treatment of slurry-like sediment sludge generated when purifying raw water can be improved, and the amount of sludge to be discarded from the water treatment system can be reduced to the treatment method widely used in current water treatment plants. Can be reduced in comparison. Furthermore, the sludge to be discarded from the water treatment system has very little aluminum that causes germination failure of plants, so that the sludge can be effectively used as horticultural soil and the like.

[Brief description of the drawings]

FIG. 1 is a schematic diagram illustrating an example of a water purification system according to the present invention.

FIG. 2 is a schematic diagram illustrating an example of a known water purification treatment system.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 mixing pond 2 floc forming pond 3 sedimentation pond 4 drainage pond 5 pump 6 first thickener (sedimentation separation processing means) 7 acid mixing tank 8 second thickener (dissolution separation processing means) 9 alkali reaction tank (alkali reaction separation means) DESCRIPTION OF SYMBOLS 10 Filtration machine (alkaline reaction separation means) 11 Reaction tank (coagulant regeneration means) 12 Second pressure dehydrator 13 Neutralization tank 14 First pressure dehydrator 15 Rapid filtration pond 16 Sterilization tank

Continuing from the front page (72) Inventor Shigemi Ariga 3865-3 Minami-Minawamura, Kamiina-gun, Nagano Prefecture Inside (72) Inventor Shinichi Sano 3865-3825 Minami-minowa-mura, Kamiina-gun, Nagano In-house (72) Inventor Minoru Tanaka 3385-2, Minamiminowa-mura, Kamiina-gun, Nagano Prefecture F-term (reference) 4D015 BA15 BB05 CA14 DA02 DA35 DA39 EA32 FA02 FA03 FA15 FA16 FA23 FA28 4D038 AA01 AB61 BB18 4D059 AA06 AA11 BE15 BE31 BH04 CC10 DA32 DA33 4D062 BA15 BB05 CA14 DA02 DA35 DA39 EA32 FA02 FA03 FA15 FA16 FA23 FA28

Claims (6)

[Claims] 1. A water purification system in which a coagulant composed mainly of an aluminum compound is injected into raw water and subjected to coagulation treatment to supply drinking water and the like, wherein slurry-like sediment sludge generated when purifying the raw water is removed. Dissolving / separating means for injecting hydrochloric acid or sulfuric acid to separate a solution in which the aluminum compound in the settling sludge is dissolved and concentrated sludge; an alkali exhibiting a strong alkalinity of pH 13 or more to the solution separated by the dissolving / separating means An alkali reaction separation means for injecting a compound, adjusting the pH of the solution to 4.5 to 6.5 to precipitate a precipitate mainly composed of aluminum hydrate, and separating the precipitate and the solution; Aluminum chloride or aluminum sulfate using the precipitate containing aluminum hydrate as a main component separated by the alkali reaction separation means as a raw material A flocculant regenerating means for regenerating a flocculant having a main component as a main component; a flocculant regenerating means for injecting the flocculant regenerated by the flocculant generating means into the raw water to perform a flocculating treatment; A water purification treatment system comprising a neutralization and dehydration treatment means for performing a neutralization treatment on the concentrated sludge separated by the treatment means and the solution separated by the alkali reaction separation means and performing a dehydration treatment. . 2. A sedimentation separation means is provided for sedimenting and separating the slurry-like precipitation sludge into concentrated sludge and water, returning the separated water to raw water, and supplying the concentrated sludge to the dissolution separation treatment means. The water purification system according to claim 1. 3. The water purification system according to claim 2, further comprising dewatering means for dewatering the concentrated sludge for directly dewatering a part of the concentrated sludge separated by the sedimentation separation means. 4. A slurry-like sediment generated when purifying the raw water when injecting a flocculant composed mainly of an aluminum compound into the raw water and performing a flocculation treatment to obtain purified water to be supplied to drinking water or the like. Hydrochloric acid or sulfuric acid is injected into the sludge, subjected to a dissolution separation treatment for separating into a solution in which the aluminum compound in the settling sludge is dissolved and a concentrated sludge, and an alkali exhibiting a strong alkalinity of pH 13 or more to the solution separated by the dissolution separation treatment. Inject compound and pour the solution
The aluminum hydrate separated by the alkali reaction separation treatment is subjected to an alkali reaction separation treatment for separating a precipitate containing aluminum hydrate as a main component, which has been adjusted to H 4.5 to 6.5, from the solution. A regenerated coagulant containing aluminum chloride or aluminum sulfate as a main component, obtained by using a precipitate containing a substance as a main component as a raw material, is poured into the raw water and subjected to a coagulation treatment, and is separated by the dissolution separation treatment. And a dewatering treatment after neutralizing the concentrated sludge and the solution separated by the alkali reaction separation treatment. 5. The water purification treatment method according to claim 4, wherein the slurry-like settling sludge is settled and separated into concentrated sludge and water, the separated water is returned to raw water, and the concentrated sludge is subjected to a dissolution separation treatment. 6. The water purification method according to claim 5, wherein a part of the concentrated sludge separated by the sedimentation treatment is directly subjected to a dehydration treatment.