JPH10137767A - Treatment of waste water - Google Patents

Abstract

PROBLEM TO BE SOLVED: To quicken sedimentation and to decrease a tank area of a sedimentation tank by mixing a specified quantity of flocculated products settled on the sedimentation tank at a flocculant addition process to new treating waste water or to a process before the flocculant addition process. SOLUTION: An inorganic flocculant 4 is added to waste water at a first reaction tank 2, stirred with an agitator 3, and small-sized flocculated products 5 are formed. Next, a polymer flocculant 9 and the flocculated products 12 returned from the sedimentation tank 11 are added at a second reaction tank 7 and stirred. This mixture is fed to the sedimentation tank 11 and guided with a guiding plate 11B to grow diameters of the flocks and settle a floating component in the waste water. The supernatant 13 from which the floating component is settled and removed is fed to a next process, and the settled flocculated products 12 are introduced into a flock tank 17. One portion of the flocculated products 12 is returned to the second reaction tank 7 through a return pipe 18 by a return pump 18A. Thus, flocculating molecules become larger with the polymer coagulant 9 and speeds of the flocculation and sedimentation can be made faster.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for treating wastewater, and more particularly, to a technique for treating wastewater containing suspended components generated from a painting process, for example.

[0002]

2. Description of the Related Art Conventionally, for removing a suspended component of wastewater containing fine SS (floating substance) such as wastewater in a coating process, a wastewater 100 is sent to a reaction tank 101 as shown in FIG. 102 and stirred by a stirrer 103 to form fine aggregates (fine flocs) 104. Thereafter, the wastewater 100 containing the fine flocs 104 is sent to the settling tank 106 via the liquid sending pipe 105. The polymer flocculant 107 is injected into the wastewater 100 in the middle of the liquid feeding pipe 105. The wastewater 100 into which the polymer flocculant 107 has been injected is led to the sedimentation tank 106. As shown in FIG.
Reference numeral 6 denotes a storage tank having an open top, and wastewater 100 into which a polymer flocculant 107 has been injected is supplied from a central supply pipe 106A.
It is guided laterally by the lower guide plate 106B. Supply pipe 10
6A and the diameter of the fine flocs 104 of the wastewater 100 guided by the guide plate 106B are grown by the polymer flocculant 107, and the sedimentation rate of the grown flocs is increased by the sedimentation tank 106.
Is controlled so as to be larger than the water area load (upward flow velocity), and aggregates 108 of suspended components are precipitated and separated from the wastewater 100, and the supernatant 109 is sent to the next step. The aggregate 108 precipitated in the sedimentation tank 106 is stored in the floc tank 111 via the pump 110 by the pump.
The aggregate 108 in the flock tank 111 is supplied to the feed pump 112A.
Then, it is sent to the next process via the transfer pipe 112 and disposed.

[0003]

However, since the wastewater 100 to be treated has a low concentration of suspended components, the contact between the suspended components is low, and the floc diameter growth is poor, so that the floc sedimentation rate is low. For this reason, there was a problem that the area load of the water in the sedimentation tank 106 could not be increased, and the area of the sedimentation tank 106 had to be increased.

Accordingly, an object of the present invention is to form a flocculating agent in wastewater having a floating component by adding an aggregating agent to form a floating component flocculate and remove the sediment. It is an object of the present invention to provide a wastewater treatment method capable of reducing the tank area.

[0005]

According to a first aspect of the present invention, there is provided a method for treating wastewater, comprising the steps of: adding a flocculant to wastewater containing a floating component; In a method for treating wastewater that precipitates in a sedimentation tank to obtain a supernatant, a predetermined amount of the aggregate that has settled in the sedimentation tank is
It is characterized in that the wastewater to be newly treated is mixed in a coagulant adding step or a step before that.

[0006] According to this treatment method, the suspended components in the wastewater are aggregated by the flocculant. Since the wastewater to be treated has aggregates in the sedimentation tank, they are combined to form aggregates (flocs) having a large diameter. Since this aggregate has a large diameter, a large water area load can be obtained, and the sedimentation in the sedimentation tank is quick.

In order to achieve the above object, a method for treating wastewater according to the second aspect of the present invention is characterized in that the flocculant added to the wastewater is a polymer flocculant.

According to this treatment method, the suspended components in the wastewater are aggregated by the polymer flocculant. The polymer flocculant and the aggregate in the sedimentation tank are mixed with the wastewater, and the aggregate of the floating components in the wastewater is combined with the aggregate in the sedimentation tank to form a large-diameter aggregate (floc). This aggregate has a large diameter, and the water area load is large, and the sedimentation in the sedimentation tank is fast.

According to a third aspect of the present invention, there is provided a method for treating wastewater, wherein the wastewater is of a water quality containing a low-concentration suspended component, and the addition of the coagulant comprises adding an inorganic coagulant to the wastewater;
Next, a polymer coagulant and a predetermined amount of the coagulated substance precipitated in the sedimentation tank are added.

According to this treatment method, the low-concentration suspended components are formed into small-sized aggregates by the inorganic coagulant. This aggregate becomes a large-diameter aggregate by the polymer flocculant together with the aggregate in the sedimentation tank. This large diameter aggregate precipitates quickly.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The floating component according to the present invention is SS
(Floating substances), floating components such as oil, COD, BOD, turbid components, and coloring substances. The wastewater provided for the treatment of the present invention is water containing the above-mentioned floating components, and can be widely applied regardless of the content of the floating components. Even when the suspended component is fine and has a small content, it can be well precipitated. The flocculant for increasing the diameter of the floc is mainly a polymer flocculant. Aggregation of the floating component forms an aggregate with an inorganic flocculant, which can be made into a larger aggregate with a polymer flocculant. This large-diameter aggregate has a large water area load and tends to precipitate.

As the inorganic coagulant, iron salts, aluminum salts and the like are used. As the polymer flocculant, a polyacrylamide derivative, a polyacrylic acid derivative, or the like is used.

According to the present invention, since the aggregates of the suspended components in the wastewater can be settled quickly, the area of the settling tank can be reduced by that much.

[0014] The present invention can also take the following forms. That is, in the method of treating wastewater in which a flocculant formed by adding a flocculant to wastewater containing a floating component is precipitated in a settling tank to obtain a supernatant, an inorganic flocculant is added to the wastewater. Form an aggregate with an inorganic flocculant, and then add a predetermined amount of the flocculant and a polymer flocculant in the sedimentation tank to wastewater containing the flocculant, and precipitate the flocculant of the polymer flocculant in the sedimentation tank This is a method for treating wastewater.

This treatment method is suitable for treating wastewater containing fine suspended components such as wastewater generated in a painting process.

[0016]

Next, embodiments of the present invention will be described. First, an outline of an apparatus used for carrying out the present invention will be described with reference to FIG. As shown in FIG. 1, the apparatus of the present embodiment mainly includes a first reaction tank 2, a second reaction tank 7, and a precipitation tank 11. In the sedimentation tank 11, aggregates 12 settled on the bottom of the sedimentation tank 11
Agglomerate 12 which is introduced and partially returns to the second reaction tank 7
Return means 15 is connected. Return means 15 of this example
Has a structure in which a part of the aggregate 12 introduced into the floc tank 17 through the introduction pipe 16 of the aggregate 12 is returned to the second reaction tank 7 through the return pipe 18 by the feed pump 18A. Further, the flock tank 17 is provided with a transfer pipe 19 and a feed pump 19A for sending to the next step outside the tank. The feed pump 18A for returning the aggregates 12 is provided in the settling tank 1
By controlling the pump rotation speed by the inverter 18B in proportion to the wastewater amount of No. 2, the feed amount of the returned aggregate 12 is adjusted.

Next, a case where the organic wastewater 1 is treated by the above-described apparatus will be described. As shown in FIG. 1, the wastewater 1 is sent to the first reaction tank 2, and after the inorganic coagulant 4 is added, the wastewater 1 is stirred by the stirrer 3 and mixed. The wastewater 1 to which the inorganic flocculant 4 has been added is a small-diameter floc 5
To form Next, the wastewater 1 containing the aggregates 5 is sent to a second reaction tank 7 via a conduit 6. Wastewater 1 of the second reaction tank 7
, A polymer flocculant 9 and a flocculant 12 from a sedimentation tank 11 are added, and the mixture is stirred by a stirrer 8. After a while, this wastewater 1
Is sent to the sedimentation tank 11. The sedimentation tank 11 is a large-diameter storage tank whose upper part is open, and the wastewater 1 is supplied from a central supply pipe 11A and is guided laterally by a lower guide plate 11B. Information board 1
Wastewater 1 led by 1B grows the diameter of the floc,
Floating components in the wastewater are settled by controlling the sedimentation speed of the floc to be higher than the water area load (upward flow speed) of the sedimentation tank 11. The wastewater 1 in the sedimentation tank 11 is mixed with the aggregate 12 by the second reaction tank 7, so that the polymer flocculant 9
The size of the molecules due to the aggregation of the particles increases, and the precipitation rate of the aggregated molecules can be increased.

The supernatant 13 from which the suspended components have been removed by settling in the settling tank 11 is sent to the next step via a conduit 14, and
Processing for release is performed. On the other hand, the sediment in the sedimentation tank 11, that is, the condensate 12 of the floating component, is introduced into the floc tank 17 through the introduction pipe 16. Agglomerate 12 of floc tank 17
Is returned to the second reaction tank 7 via the return pipe 18 by the operation of the feed pump 18A. The amount of the aggregate 12 returned to the second reaction tank 7 depends on the amount of the supernatant 1 discharged from the precipitation tank 11.
3 is appropriately determined in proportion to the quantity of 3. Further, the aggregates 12 in the floc tank 17 are sent to the next step outside the tank by the operation of the feed pump 19A to be dried and incinerated.

In the process of the apparatus of the present embodiment, the action of condensing floating components of the wastewater 1 will be described as follows with reference to the schematic diagram of FIG. The fine suspended component 1A shown in FIG. 2A in the wastewater 1 supplied to the treatment apparatus of this example is shown in FIG.
As shown in FIG. 2, in the first reaction tank 2, the flocculant aggregates with the inorganic flocculant 4, and becomes a floc F 1 of a small diameter flocculation unit as shown in FIG. 2C. The floc F1 of this small diameter aggregation unit is the second
2 by the polymer flocculant 9 added in the reaction tank 7.
Aggregation occurs as shown in (D), resulting in a polymeric floc F2 as shown in FIG. 2 (E). In the second reaction tank 7, the polymer floc F2 treated in the above step is supplied, so that the newly produced polymer floc F2 and the supplied polymer floc F2, as shown in FIG. Flock F
2 are combined to form an extremely large-diameter floc F3 as shown in FIG. 2 (G). In the case of the above-described conventional processing apparatus, the formation of the floc F2 having the size of L1 shown in FIG. 2E is final because the floc in the wastewater is fine, and no larger floc can be formed. However, according to this example, a floc F3 having an extremely large size L2 shown in FIG. 2G can be formed.

Next, the P discharged mainly in the coating process
The test results when H7 to 8 and SS 6 mg / L wastewater 1 are treated based on the above-described embodiment will be described. In the first reaction tank 2, an inorganic coagulant (for example, aluminum salt) 4 was added in an amount of 150 mg per L of wastewater (the pH was adjusted if necessary). The floc (agglomerate) 5 after the reaction in the first reaction tank 2 was scooped into a beaker and visually observed. As a result, the floc A-1 had a size shown in FIG. 3A.

Next, in the second reaction tank 7, a polymer coagulant (for example, polyacrylamide derivative) 9 was added in an amount of 0.5 mg per L of wastewater, and an agglomerate 12 in the precipitation tank 11 was added. ). Aggregates 12 in the settling tank 11 were added at 3% and 5%. The wastewater 1 to which the polymer flocculant 9 and the aggregate 12 were added and mixed was sampled from the supply pipe 11A, and the floc was visually observed. The floc of the wastewater 1 to which the agglomerate 12 was added by 3% was the size of the floc B-1 shown in FIG.
The floc of the added wastewater 1 had a size shown in FIG.

The control wastewater 1 containing only the polymer flocculant 9 but not the flocculant 12 but the inorganic flocculant 4 was added.
Was the size of the floc D-1 shown in FIG. The flocks shown in FIGS. 3B and 3C correspond to FIG.
The sedimentation rate was faster than the floc of wastewater 1 of the control shown in (D). The sedimentation rate was set to 12
Is about 1.4 times and floc 12 is 5%
The floc when added was about 2.6 times.

[0023]

According to the first to third aspects of the present invention, the water area load of the aggregate of suspended components in the wastewater can be increased, and the sedimentation in the sedimentation tank can be quickly achieved. Therefore, the tank area of the settling tank can be made smaller than before, which is convenient. In the invention of claim 2, the suspended component in the wastewater is:
Together with the added aggregate in the settling tank, the aggregate can be formed by a polymer flocculant. Since this aggregate has a large diameter, a large water area load can be taken, and the sedimentation is quick, the tank area of the sedimentation tank can be made smaller than before. According to the third aspect of the present invention, low-concentration suspended components in wastewater can be formed into large-diameter aggregates, and sedimentation in a sedimentation tank can be achieved quickly.

[Brief description of the drawings]

FIG. 1 is a process diagram of wastewater treatment according to an embodiment of the present invention.

FIG. 2 is a schematic diagram showing agglomeration of suspended components in an example of the present invention.

FIG. 3 is a diagram showing the size of aggregates (flock) in a wastewater treatment test of an example of the present invention.

FIG. 4 is a conventional process diagram of wastewater treatment.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Wastewater 4 Inorganic coagulant 7 2nd reaction tank 9 Polymer coagulant 5,12 Aggregate 11 Sedimentation tank 13 Supernatant

Claims (3)

[Claims] 1. A method for treating wastewater in which a flocculant of a floating component formed by adding a flocculant to wastewater containing a floating component is precipitated in a sedimentation tank to obtain a supernatant, A method for treating wastewater, comprising mixing a predetermined amount of aggregates in a flocculant addition step of wastewater to be newly treated or in a step prior thereto. 2. The method according to claim 1, wherein the coagulant added to the wastewater is a polymer coagulant. 3. The wastewater is water having a low concentration of suspended components, and the step of adding a flocculant comprises adding an inorganic flocculant to the wastewater;
2. The method for treating wastewater according to claim 1, wherein a predetermined amount of the polymer flocculant and the flocculated substance precipitated in the precipitation tank are added.