JP2001259653A - Water treating device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To effectively reutilize sludge containing aluminum. SOLUTION: Precipitated sludge in an inclined-plate precipitation tank 22 is concentrated in a concentration tank 30, and is aerated in a concentrated sludge storage tank 32, then is mixed with sulfuric acid by a line mixer 36. Then, the sludge treated with the acid is treated by a cyclone 42 to remove large solids. The acid treated sludge containing small solids is returned to a mixing tank 10 and is reutilized as a flocculant.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a water treatment apparatus for obtaining treated water by subjecting raw water to coagulation and sedimentation treatment using an inorganic aluminum coagulant.

[0002]

2. Description of the Related Art Conventionally, there is a water treatment plant which treats surface water such as river water or lake water as raw water, purifies the raw water, and supplies it as tap water or the like. In such a water treatment plant, a coagulation sedimentation process using an aluminum-based coagulant is widely adopted. Then, in order to effectively use the aluminum-based flocculant, the flocculation and settling sludge is treated with an acid to dissolve and recover aluminum hydroxide and reused as a flocculant. For example, a method of converting sludge into a coagulant admixing tank for coagulation and sedimentation has been proposed.

[0003] By such a method, the coagulant can be effectively used, and the amount of the coagulant used can be reduced. Also, the amount of sludge generated can be reduced.

[0004]

However, in the regeneration band method, the acid-treated sludge is concentrated by gravity, and the supernatant in which the aluminum hydroxide is dissolved is returned to the coagulant mixing tank.
There is a problem that a relatively large gravity concentration tank is required. Further, in the method for converting into a sludge auxiliary, a gravity concentration tank is not required, but there is a problem that solids in acid sludge returned to the flocculant mixing tank consume the flocculant.

[0005] The present invention has been made in view of the above problems, and has as its object to provide a water treatment apparatus capable of performing an appropriate coagulation treatment using coagulated sludge.

[0006]

According to the present invention, there is provided an aggregating / separating means for subjecting raw water to an aggregating treatment using an inorganic aluminum aggregating agent, followed by a solid-liquid separation to obtain treated water; An acidifying means for adding acid to the treated sludge and acid-treating the sludge; and a partial separating means for partially separating solids in the acid-treated sludge. The sludge from which the material is partially separated is supplied to the coagulation separation means.

[0007] In this way, the sludge that has been partially separated from the acid-treated sludge is returned to the coagulation separation treatment means. Therefore, in the coagulation separation process, an appropriate solid substance is added, and an effective coagulation process can be performed.

Preferably, the partial separating means is a cyclone. The cyclone can separate solids with a simple device, and can partially remove solids when acid-treated sludge is treated. In addition, since a solid having a large particle diameter is preferentially separated, a sufficient number of solids can be added to raw water, and an effective coagulation treatment can be performed.

[0009]

Embodiments of the present invention (hereinafter referred to as embodiments) will be described below with reference to the drawings.

FIG. 1 is a diagram showing the overall configuration of a water treatment apparatus according to this embodiment. Raw water, such as river water and lake water,
First, it flows into the mixing tank 10. A flocculant from a flocculant storage tank 12 is supplied to the mixing tank 10 by a flocculant pump 14. The flocculant is an inorganic aluminum flocculant such as PAC. The mixing tank 10 is provided with a stirrer 16 for rapidly stirring the raw water and the coagulant. In the mixing tank 10, the coagulant-mixed water mixed with the coagulant flows into the coagulation tank 18. The flocculation tank 18 is provided with a slow stirring machine 20, which slowly mixes the flocculant-mixed water so that the flocculated floc is united and coarsened.

Next, the flocculant-mixed water after the slow stirring from the flocculation tank 18 flows into the inclined plate sedimentation tank 22. The inclined plate sedimentation tank 22 is divided into an inlet side and a discharge side by a partition plate 22a, and a sedimentation part 22b having a deep tank depth is formed on the inlet side. The lower part of the sedimentation part 22b is a sludge storage part 22c for storing the sedimentation sludge. A large number of inclined plates 22d are arranged on the discharge side to form inclined plate settling portions 22e. The coagulant-mixed water flows into the sedimentation section 22b, where it is subjected to sedimentation treatment, passes under the partition plate 22a, and passes through the inclined plate sedimentation section 22e in an upward flow. Then, the inclined plate 2 of the inclined plate settling portion 22e
When passing through 2d, further sedimentation treatment is performed, and sludge sediments toward the tank bottom. Since the tank bottom of the inclined plate settling portion 22e is inclined so as to become deeper toward the sludge storage portion 22c, the settled sludge moves to the sludge storage portion 22c by gravity and is stored therein. Then, the supernatant water that has passed through the inclined plate sedimentation section 22 e flows out of the inclined plate sedimentation tank 22.

By such a coagulation sedimentation treatment, the sedimentation treatment water from the inclined plate sedimentation tank 22 has a considerable amount of suspended solids removed. This settling water is
It flows into the filter 24. The filter 24 is a gravity-type quick filter having a sand filter layer. In this example, the filter layer consists of an upper layer of anthracite and a lower layer of sand. It is also preferable to additionally mix a flocculant with the settling water flowing into the filter 24. And
The filtered water from the filter 24 is stored in a treated water tank 26 and then distributed. In addition, this treated water tank 26
The treated water in the inside is supplied to the filter 24 by the backwash pump 28 in an upward flow, and the filter layer in the filter 24 can be backwashed.

The sludge settled in the sludge storage section 22c of the inclined plate settling tank 22 is introduced into the thickening tank 30. The concentration tank 30 stores the sedimentation sludge, performs gravity concentration, and discharges the separated water out of the system. On the other hand, the concentrated sludge in the thickening tank 30 is partially discharged as surplus sludge, and the remainder is supplied to a sludge storage tank 32 that is aerated and stirred by air from a blower to make the concentrated sludge aerobic. Once stored. The concentrated sludge in the sludge storage tank 32 is supplied to a concentrated sludge pump 34.
Is returned to the mixing tank 10 via the line mixer 36, and the acid (acid solution) from the acid storage tank 38 is added to the concentrated sludge supplied to the line mixer 36 by the acid pump 40. Therefore, in the line mixer 36, the concentrated sludge is mixed with an acid by stirring to dissolve the aluminum hydroxide to form aluminum ions. In this example, sulfuric acid is used as the acid, but hydrochloric acid or the like can also be used.

Here, the amount of the acid added always keeps the pH of the sludge to which the acid is added (acid-treated sludge) at 3 or less (for example, 2.5
(A range of 3.0 to 3.0). However, the acid addition amount may be a fixed amount with respect to the sludge amount, or may be a fixed amount with respect to the solid matter amount in the sludge.

The acid-treated sludge is supplied to the cyclone 42. The cyclone has a conical cylindrical shape whose inner surface is reduced in diameter toward the bottom, and an outlet for treated water is provided at an upper portion, and an outlet for solids is provided at a bottom portion. The acid-treated sludge that is the water to be treated flows into the cyclone 42 at a predetermined speed in the circumferential direction. The acid-treated sludge moves in a circular motion along the inner surface of the cyclone, and solid-liquid separation is performed using centrifugal force.Some solids move downward and the amount of solids decreases at the top. Is obtained. Therefore,
The treated water is discharged from the treated water discharge port at the top, and the solids are discharged from the treated water discharge port at the bottom.

Here, the cyclone 42 is small and capable of processing a relatively large amount, but the solid matter separation capacity is not so high. Therefore, it is most suitable for removing sand and the like contained in water, but when acid-treated sludge is treated, large solids can be separated, but small solids remain in the treated water as they are. Therefore, a considerable amount of solid matter is contained on the treated water side. For example, when the acid-treated sludge is treated by the cyclone 42, the solids separating ability is such that solids having a particle size of 30 μm or more can be separated. Usually, the particle size of sludge is distributed in a range of several μm to several tens of μm, and 80 to 90% of the particle size is 30 μm or less. Therefore, in the cyclone 42, about 10 to 20% of the solid matter in the acid-treated sludge is separated and removed as a solid matter, but 80 to 90% remains on the treated water side.

The removal rate of solids in the cyclone 42 is preferably 50% or less, more preferably 20% or less.

Then, the treated water containing aluminum ions containing the solid matter is supplied to the mixing tank 10. Therefore, an acidic liquid containing aluminum ions, which contains a certain amount of solid content, is returned to the mixing tank 10,
It is mixed with raw water and fresh flocculant.

Here, the aggregation efficiency in the aggregation treatment is G
CT is used as an index. G is the stirring intensity, C is the solid (number) concentration, and T is the stirring time. Therefore, the greater the number of solids, the higher the aggregation efficiency. If the raw water contains many solids, no additional solids need be added due to the presence of solids in the raw water. However, some water sources do not contain as much solids. Therefore, the coagulation effect can be improved by adding a certain amount of solid matter.

On the other hand, when the entire amount of the acid-treated sludge is supplied to the mixing tank 10 as in the sludge-assisting method, the amount of solid matter is too large and an additional coagulant is required.

As in the present embodiment, by partially removing solids having a large particle size, a sufficient number of solids can be added to raw water, and effective coagulation can be performed. .

The solid separated by the cyclone 42 is treated together with the excess sludge from the concentration tank 30.

[0023]

EXAMPLE An experiment was conducted using the apparatus shown in FIG. The experimental conditions are shown below.

<Experimental conditions> Raw water flow rate: 1000 m ³ / D Mixing tank 10: residence time: 4 minutes Inclined plate sedimentation tank 22: sedimentation tank with upward flow inclined plate, residence time: 40 minutes, rising speed: 5 cm / min · raw water turbidity: 8-30 degrees & raw water pH: 7.2.about.7.5-coagulant: PAC10~30mg / l, PAC (polyaluminum chloride): Compounds _Al 2 _O 3: 10% · mixing tank Sludge injection rate: 4-6 L / m ³ -treated water amount (sludge concentration 2%) Acid injection rate: sulfuric acid 2-6 mL / L-concentrated sludge, sulfuric acid: 7
_5% H 2 _{SO 4.}

<Experimental Results> To raw water having a turbidity of 8 ° C., 15 mg / L of PAC was added as a coagulant in the mixing tank 10, and the coagulated sediment sludge obtained in the inclined plate sedimentation tank 22 was solidified in the concentration tank 30. Gravity concentrated to 2%. After the concentrated sludge is aerated in the concentrated sludge storage tank 32 and then returned to the mixing tank 10, the concentrated sludge is 4 to 6 L / m2.
^{To 3} was added 75% sulfuric acid at 2 to 6 mL / L-sludge.

Then, the acid-treated sludge is added to cyclone 42
After removing some of the solids, the mixing tank 1
Returned to 0. In the case of this example, since the solids having a particle size of 30 μm or more were about 15%, the solids removal rate in the cyclone 42 was almost 15%. Then, the acid-treated sludge from which the solids were partially removed was returned to the mixing tank 10.

As a result, a new P
In addition to AC, acid-treated sludge containing aluminum ions is added, and this is slowly stirred in the flocculation tank 18, then settled in the inclined plate sedimentation tank 22, and further filtered in the filter 24 to obtain treated water. Was done.

As a result, good treated water having a turbidity of 0.1 or less was always obtained while maintaining the recovery of aluminum (Al) at 90% or more.

"Other Configurations" In the above example, the inclined plate sedimentation tank is used, but the inclined plate is not always required.
The filter 24 may be a pressure type filter, and various types of filter media may be used. Sludge thickening tank 3
For 0, other types such as a floating separation type can be adopted. Further, instead of the line mixer 36, a stirring tank using an ordinary stirrer may be provided.

As a device for removing a part of solid matter from the acid-treated sludge, a cyclone 42 is preferable.
It is not limited to this. For example, gravity precipitation,
A part of the solid may be removed by filtration. Furthermore, it is also possible to subject a part of the acid-treated sludge to solid matter separation processing without treating the entire amount thereof, and return the remaining part to the mixing tank 10 as it is. According to this method, an arbitrary amount of solid can be returned to the mixing tank 10 by adjusting the solid separation amount.

[0031]

As described above, according to the present invention,
After partially removing solids from the acid-treated sludge, the sludge is returned to the coagulation separation treatment means. Therefore, in the coagulation separation process, an appropriate solid substance is added, and an effective coagulation process can be performed.

A cyclone is a simple device,
This can be used to efficiently perform partial separation of solids.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating an overall configuration of an apparatus according to an embodiment.

[Explanation of symbols]

10 mixing tank, 18 coagulation tank, 22 inclined plate sedimentation tank, 2
4 filter, 30 sludge thickening tank, 32 thick sludge storage tank,
36 line mixer, 38 acid storage tank, 42 cyclone.

Continued on the front page F term (reference) 4D015 BA04 BA15 BA19 BB05 CA14 DA04 DC02 EA03 EA07 EA32 FA02 FA03 FA12 FA16 FA19 FA25 FA28 4D059 AA06 BE31 BE39 BF12 BH00 BH04 BH07 CC05 DA32 DA33 EB05 4D062 BA04 BA15 DA04 EA05 EA05 FA02 FA03 FA12 FA16 FA19 FA25 FA28

Claims (2)

[Claims] 1. An aggregating / separating means for performing an aggregating treatment on raw water by using an inorganic aluminum aggregating agent and then performing a solid-liquid separation to obtain treated water;
Acid treatment means for treating the sludge with acid, and partial separation means for partially separating the solid matter in the acid-treated sludge, wherein the solid matter is partially separated by the partial separation means. A water treatment apparatus for supplying sludge to the coagulation separation means. 2. The water treatment apparatus according to claim 1, wherein said partial separation means is a cyclone.