JPH02157005A - Treatment apparatus for flocculating settling - Google Patents

Abstract

PURPOSE:To provide a flocculating settling treatment apparatus for effecting favorable settling treatment by providing a means for returning sludge and a means for adding acid. CONSTITUTION:Raw water introduced through a raw water feed line 1 is stirred and mixed with flocculants supplied by means of a flocculant feeder 12 so as to effect flocculation reaction. By effecting the growth and settling of flocculated flocs, sludge is collected at the bottom of a flocculating settling tank 3 disposed at the rear stage of a flocculant mixing tank 2, while treated water 15 is discharged to a water treatment system at the rear stage through an overflow passage. The sludge collected at the bottom of the flocculating settling tank is suitably discharged to a flocculated sludge concentration tank 5 through a sludge discharge pipe 4 to be further concentrated to about tenfold concentration. The concentrated sludge is then sent to a flocculated sludge treatment apparatus 14 from the bottom of the tank 5 through a concentrated sludge discharge line 6 so as to be subjected to a disposal treatment.

Description

Detailed Description of the Invention (Industrial Field of Application) The present invention relates to a coagulation-sedimentation facility for separating suspended solids in raw water into solid and liquid by a coagulation-sedimentation method, and more specifically, the present invention relates to a coagulation-sedimentation facility that separates suspended solids in raw water from solid to liquid by a coagulation-sedimentation method. This invention relates to coagulation and sedimentation equipment that improves the effectiveness of coagulation and sedimentation treatment by being reused in the system.

(Background of the Invention and Prior Art) In general, water purification treatment involves adding an aluminum-based coagulant to raw water introduced into treatment equipment to coagulate suspended matter contained in the raw water, resulting in coagulation and sedimentation. A typical method is known in which coagulated flocs are grown and precipitated in a tank, and the precipitated sludge is collected and treated. In such water purification treatment, it is generally required to sufficiently remove suspended solids contained in raw water and to reduce equipment operation costs. Various techniques have been proposed in the past.

One of them is the reuse of flocculants.

In other words, the sludge generated by coagulation and sedimentation treatment of suspended solids in raw water contains flocculants added to the raw water, for example in the form of aluminum hydroxide, so this aluminum content can be recovered. It is beneficial to reuse it as a flocculant.

This method is generally called the reproduction band method, and has been actually practiced in the past. The regeneration band method involves sludge settling and collecting sludge in sludge treatment equipment, adding strong acids such as sulfuric acid or hydrochloric acid to adjust the pH of the sludge to around 2, and removing the aluminum hydroxide contained in this sludge. AN (0)1)
3, remove the supernatant liquid containing dissolved aluminum, recover aluminum ions t,13- from this supernatant liquid, and reuse it as a flocculant.By reusing this flocculant, This method is characterized by a reduction in the amount of flocculant used and a reduction in the total amount of sludge to be treated.

In addition to the above-mentioned reuse of the flocculant, improvements aimed at improving the flocculating effect have also been proposed. A method of improving the balance between the flocculant and the substance to be flocculated to improve the flocculation reaction is also known. This method is said to be effective when the target is raw water with low turbidity or when the purpose is to remove color.

By the way, among these methods, the above-mentioned reproduction band method is
Although it has the advantage of significantly reducing the amount of newly added flocculant used, the amount of aluminum contained in the supernatant varies depending on the amount and quality of flocculated sludge, so it is difficult to adjust the injection amount to optimize the flocculation reaction. There is a problem that control becomes difficult, and in order to increase the recovery rate of aluminum, the above-mentioned
Since the pH is around 2, there is a problem that many other heavy metals such as iron contained in the sludge are dissolved, and the heavy metals gradually accumulate depending on the number of times the flocculant is recycled and reused.

On the other hand, the above method of adding kaolin or bentonite as a flocculation aid to improve the flocculation reaction is not effective due to the low turbidity of the water, and the flocculation reaction is not effective or the flocculated flocs have poor settling properties. Although it is effective in improving
Since these kaolin and bentonite are discharged as part of sludge, there is a problem in that the amount of waste increases and, as a result, the cost of water purification treatment increases.

(Problems to be Solved by the Invention) The present invention solves the various problems described above, and enables economical treatment by reducing the amount of flocculant injection for coagulation and sedimentation treatment as much as possible in water purification treatment. The purpose of this invention is to provide a flocculation and sedimentation treatment facility that can improve the flocculation reaction and the sedimentation properties of flocculated flocs, thereby realizing good sedimentation treatment.

Another object of the present invention is that it is particularly effective in improving coagulation and sedimentation in raw water with low turbidity, thereby reducing the amount of flocculant added and reducing the amount of coagulation aids such as kaolin and hentonite mentioned above. It is an object of the present invention to provide a flocculation and sedimentation treatment facility that is capable of reducing or omitting the amount of added flocculant and flocculation aid, and can prevent an increase in the amount of sludge generated due to the addition of flocculant or flocculation aid. In recent years, reducing the amount of sludge generated has become one of the important technical issues from the perspective of pollution prevention. Although the amount of coagulant greatly affects the difficulty of processing, by realizing the objective of reducing the amount of coagulant added, processing can be facilitated.

Still another object of the present invention is to provide a coagulation-sedimentation treatment facility that does not cause any adverse effects due to the accumulation of heavy metals.

Another object of the present invention is to provide a coagulation-sedimentation treatment facility that can be suitably used when the water source is river water, lake water, or marsh water, whose water quality tends to fluctuate depending on the season or the weather. In other words, river water or lake water is often used as a water source for coagulation sedimentation treatment in water supplies, etc., but the characteristics of such water sources are: - The turbidity is low for boat fishing, but when the water increases due to rain or snow melting. It is known that turbidity increases. In this case, when the turbidity increases, good coagulation and sedimentation can be observed by adding an appropriate amount of flocculant, but when the turbidity is low, the balance between the flocculating substances and the flocculant in the raw water is poor, and flocs with poor settling properties are generated, resulting in the formation of flocs. There is a problem of deteriorating water quality. In such a case, the present invention makes it possible to provide a coagulation-sedimentation treatment facility that does not require the addition of large amounts of suspended solids such as the above-mentioned kaolin and bentonite as coagulation aids.

(Means for Solving the Problems) A feature of the present invention, which has been made to achieve the above-mentioned various objects, is that sludge containing both insoluble aluminum hydroxide and suspended solids, which are flocculated substances, is One of the features is that the suspended matter in the raw water is returned to the stirring system (or the previous stage thereof) which coagulates the suspended matter in the raw water by adding a flocculant containing A1. The sludge may be returned in part or in its entirety, or the amount to be returned may be changed and controlled as appropriate in consideration of seasonal fluctuations, weather, and the like.

The stirring system for adding the flocculant to the raw water is not necessarily required for boat fishing as a flocculant mixing tank equipped with stirring means.
In short, the object of the present invention is achieved by returning the sludge before the system that performs the flocculation reaction in the flocculation and sedimentation treatment equipment.

Another feature of the present invention is that a mineral acid such as hydrochloric acid is added to the returned sludge in order to ionize the aluminum hydroxide contained therein. The amount of acid added is such that the aluminum hydroxide contained in the sludge is ionized into Al3+ or aluminum polyions, etc., and this acts as a flocculant after the sludge is returned. It is appropriate to add the aluminum hydroxide at a pH of 3 to 4 so as to dissolve about 30 to 80% of the aluminum hydroxide. If the amount of acid added is increased, the dissolution rate of aluminum hydroxide will increase, but there is a problem that heavy metals will also be dissolved.

By returning such sludge, the dissolved aluminum and undissolved aluminum contained in the sludge returned to the stirring system (or its previous stage) will once again have the effect of a flocculant, and the suspended solids contained in the sludge will becomes a flocculating substance, which interacts with the flocculating substance contained in the raw water and contributes to flocculation and precipitation.

As a result, compared to the conventional coagulation-sedimentation method, it is possible to reduce the amount of coagulation-sedimentation agent added and to produce coagulated flocs with good sedimentation properties.

The coagulation-sedimentation treatment equipment of the present invention, which returns the sludge containing ionized aluminum and suspended solids as described above, exhibits excellent effects particularly in low-turbidity raw water with a raw water turbidity of 10 degrees or less. In other words, when using such low-turbidity raw water, the conventional method for boat fishing was to add about 5 ppm of kaolin or bentonite as a coagulation aid, but with the treatment equipment of the present invention, such The external addition of flocculation aids is now virtually unnecessary or can be significantly reduced, and for low turbidity raw water, conventional flocculants such as aluminum sulfate or polyaluminum chloride can be
Compared to the previous case where it was necessary to add 0 to 50 ppm,
In the equipment of the present invention, this is substantially unnecessary, or can be reduced to about 10 ppm at most.

In the present invention, the sludge that is flocculated and settled and returned is flocculated and
It is possible to return the sludge directly from the sedimentation tank, but the sludge must be sent back to the sludge thickening tank.
It is desirable to concentrate the product to about 10% before returning it in order to reduce the amount returned. Furthermore, for sludge return, a sludge storage tank may be installed in the middle of the return system, in which case sludge is drawn out from the sludge thickening tank etc. intermittently, and sludge is returned and injected into the stirring system etc. continuously. There are advantages to doing so.

The surplus of the flocculated and precipitated sludge may be appropriately scraped, treated by a known method, and disposed of as industrial waste. In the equipment of the present invention, although the amount of suspended solids circulating within the system increases due to sludge return, the amount of flocculant added or the amount of flocculated materials can be reduced or eliminated, so it should be disposed of as surplus sludge. It also has the advantage of reducing the amount.

(Function) By having the above configuration, the ionic aluminum contained in the returned sludge acts as a flocculant, and the coexisting suspended matter becomes a flocculating substance, and similarly, the ionic aluminum contained in the returned sludge acts as a coagulant. The flocculent substances that are eaten are also taken in for coagulation and sedimentation treatment, resulting in a significant reduction in the amount of flocculant injection and generation of flocculation flocs with good sedimentation properties compared to conventional coagulation and sedimentation methods. .

(Example) The present invention will be described below based on embodiments shown in the drawings.

In this figure, 2 is a flocculant mixing stirring tank, which stirs and mixes the raw water introduced from the raw water introduction pipe 1 and the flocculant injected from the flocculant storage tank 13 by a flocculant injection device 12 such as a pump, Let the coagulation reaction take place.

A coagulation-sedimentation tank 3 is disposed downstream of the flocculant mixing tank 2, and sludge is collected at the bottom of the tank 3 through the growth of flocs and sedimentation, and the treated water 15 is passed through an overflow channel (as shown in the figure). It is discharged into the downstream treated water system.

The sludge collected at the bottom of the flocculation/sedimentation tank is appropriately drawn out to the flocculated sludge concentration a15 by the flocculated sludge withdrawal pipe 4, and the sludge is further concentrated about 10 times. From the bottom of the flocculated sludge thickening tank 5, the flocculated sludge is intermittently fed to the flocculated sludge treatment device 14 by the flocculated sludge feed pump 7 through the flocculated sludge withdrawal pipe 61, so that excess sludge can be disposed of.] In addition, a sludge return system is provided which is connected to the flocculant mixing tank 2 so that the thickened sludge can be returned to the flocculant mixing and stirring tank 2 through the thickened and flocculated sludge withdrawal pipe 62 by the thickened and flocculated 5 sludge pump 72. ing.

A branch path from the acid injection pump 8 for adding acid from the acid storage tank 9 is connected to the sludge return system. Further, downstream of the confluence of this branch route, a stirring device 10 is arranged to appropriately stir the added acid and sludge, and a pH meter 11 is installed to detect the pH of the sludge due to acid addition. It is installed in the sludge return system.

According to the coagulation-sedimentation treatment equipment configured as described above, coagulation and
The aluminum hydroxide contained in the sludge that has been settled and collected can be melted and ionized with acid and reused as a flocculant for raw water, and the suspended solids contained in the sludge can be transferred to the flocculation mixing tank. By returning the water, the balance between the flocculant and the flocculated substance can be adjusted, and therefore, in the case of water with relatively low turbidity, flocs with poor sedimentation properties are not generated as in the case of conventional methods. Although kaolin, bentonite, etc. were added as substances to be agglomerated, the examples of the present invention have the advantage that such addition of kaolin, etc. is not necessary.

Due to these characteristics, the device of the present invention is particularly effective as a flocculation and sedimentation treatment facility for water with relatively low turbidity, and the balance between flocculant and specific flocculating substances can be easily maintained by adjusting the amount of sludge returned. This makes it extremely useful when the water source is a water system where water quality is likely to change due to weather or seasonal fluctuations.

(Effect of the invention) According to the present invention, the following effects (1) to (4) can be obtained.

■Suspended substances such as kaolin and bentonite, which are flocculation aids conventionally added to improve flocculation effect, can be eliminated.

■Since the flocculant in the sludge re-agglomerates, the amount of flocculant used is significantly reduced.

■As a result of the reduction in the amount of flocculant used, the amount of aluminum hydroxide produced by the injection of flocculant is reduced, and the total amount of flocculated sludge generated is reduced.

■As a result of reducing the content of aluminum hydroxide in flocculated sludge, the dewaterability of the sludge improves and sludge treatment costs are reduced.

2 is an overview-example diagram; FIG.

1... Raw water introduction pipe 2... Coagulant mixing tank 3
...Coagulation sedimentation tank 4...Coagulated sludge extraction pipe 5...
・Flocculated sludge thickening tank 6. 62... Concentrated flocculation sludge withdrawal pipe 71.72... Concentrated flocculation 5 Sludge feed pump 8... Acid injection pump 9... Acid storage tank 10... Stirring device
11...12...Flocculant injection device 13...
Coagulant storage tank 14... Coagulated sludge treatment device 15... Treated water raw water inlet pipe Coagulant mixing stirring tank Coagulating sedimentation tank Coagulating sludge drawing pipe Coagulating sludge thickening tank Concentrating coagulating sludge drawing pipe Concentrating coagulating sludge sludge pump Acid injection Pump Acid Reservoir Stirring Device Flocculant Injection Device Procedural Amendment March 1990 1, Incident Indication Showa 1, 3rd Patent Application First R Ko 3? No. 6 ζ 飄; Agent address: 330 Marunouchi Building, 2-6-2 Marunouchi, Chiyoda-ku, Tokyo Amendments The following matters in the specification and drawings of this application will be amended.

Record The scope of claims is amended as shown in the attached sheet.

2. On the 5th line from the bottom of the 4th page ``The method says Uchi J.'' "Method no Richi" I corrected.

7th line from the bottom of page 5 It says "Water purification treatment cost" Corrected to ``increase in water treatment costs.''

On page 11, lines 5-4 from the bottom It says "eaten in raw water" Corrected to ``Contained in raw water.''

On page 14, line 10 It says "sludge return" Corrected to "return sludge."

On the 6th line from the bottom of page 15, the phrase "Agricultural shrinkage flocculation sludge pump" has been corrected to read "Thickened flocculation sludge pump."

7. On the 4th line from the bottom of page 15 It says "rll..." rll...pH meter".

8. Correct the drawing as shown in the attached sheet.

Claims: A flocculation and sedimentation treatment facility having a stirring system that flocculates suspended solids in raw water by adding a flocculant containing IAρ, and a treatment system that flocculates the flocculated suspended solids and collects them as sludge. A sludge return system for returning at least a part of the sludge that has been settled and collected is provided to the stirring system or a path for introducing raw water into the stirring system, and in the middle of the sludge return system, there is a Ati (
1. A coagulation and precipitation treatment facility, characterized in that it is provided with acid addition means for ionizing oH) 3.

2 Claim characterized in that the stirring system for coagulating the suspended solids is formed as a flocculant mixing tank that adds and stirs a flocculant to the introduced raw water, and the returned sludge is returned to this flocculant mixing tank. The coagulation and sedimentation treatment equipment described in 1.

3. Is the means of adding acid to the returned sludge the same as the returned sludge? nun p
The coagulation sedimentation treatment facility according to claim 1 or 2, characterized in that the coagulation sedimentation treatment facility is H3-4.

The coagulation and sedimentation treatment equipment according to any one of claims 1 to 3, characterized in that it is intended for raw water with a turbidity of 10 degrees or less.

Raw water introduction pipe Coagulant mixing tank Coagulation sedimentation tank Coagulated sludge drawing pipe Coagulated sludge thickening tank Concentrated flocculation sludge drawing pipe Concentrated flocculation sludge pump acid injection pump acid storage tank Stirring device pH meter Flocculant injection device 15: Treated water

Claims (1)

[Scope of Claims] 1. A flocculation system having a stirring system that flocculates suspended solids in raw water by adding a flocculant containing Al, and a treatment system that flocculates the flocculated suspended solids and collects them as sludge. In the sedimentation treatment equipment, a sludge return system for returning at least a portion of the sludge collected by sedimentation is provided to the agitation system or a path for introducing raw water into the agitation system, and in the middle of the sludge return system, Al(O) contained in the returned sludge
H) A coagulation-sedimentation treatment facility characterized by being provided with acid addition means for ionizing _3. 2 Claim characterized in that the stirring system for coagulating the suspended solids is formed as a flocculant mixing tank that adds and stirs a flocculant to the introduced raw water, and the sludge is returned to the flocculant mixing tank. The coagulation and sedimentation treatment equipment described in 1. 3 The means for adding acid to the returned sludge adjusts the returned sludge to pH
3. The coagulation and sedimentation treatment equipment according to claim 1 or 2, wherein the coagulation and sedimentation treatment equipment is characterized in that: 4. The coagulation and sedimentation treatment equipment according to any one of claims 1 to 3, which is intended for raw water with a turbidity of 10 degrees or less.