JP2000140878A - Waste water treating device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To stabilize the water quality of treated water in a water treating process and also to enable the efficient solid-liq. separation of sludge. SOLUTION: The treating device is composed of the biological reactor 1 for obtaining solution 12 by biologically treating water 10 to be treated, a centrifugal separator 2 executing concentration or dehydration to obtain dehydrated cake 14 and separated liq. 13, a introducing means 4 introducing a part of the solution 12 to the centrifugal separator 2, the precipitation separation tank 3 separating the solution to sludge 17 and treated water 16, a transfer means 6 transferring the remainder of the solution 12 to the precipitation separation tank 3 and a joining means 5 joining the separated liq. 13 to the solution 12 in the transfer means 6.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a biological wastewater treatment apparatus using a centrifuge used for sludge treatment and the like.

[0002]

2. Description of the Related Art In the conventional centrifugal separation of sludge associated with wastewater treatment, to efficiently concentrate and dewater sludge, (1)
Excess sludge extraction from the final sedimentation site, (2) concentration treatment,
Generally, processes of (3) storage, (4) dehydration treatment, and (5) disposal outside the system are common. In this process, a dehydration treatment is performed on the high-concentration sludge after the concentration treatment. The reason for adopting such a process is that the properties of the sludge to be subjected to the conventional sludge treatment were adapted to the dehydration treatment of this process.

That is, in the sludge dewatering treatment, the VTS defined by the organic matter content (%) relative to the TS (total evaporation residue: mg / l) of the sludge affects the dewatering efficiency. In addition, the concentration and dehydration tend to deteriorate. And, the sludge to be subjected to the conventional dehydration treatment has a low VTS and has good concentration and dehydration properties.

However, in recent years, general sludge has a high VTS, and therefore has poor concentration and dewatering properties.
Since sludge properties deteriorate (rot) due to long-term storage, improvement and improvement of the dewatering capacity and concentration capacity of the sludge treatment apparatus have been desired.

[0005] Therefore, as a countermeasure against the deterioration of the concentration and dewatering properties of the sludge to be subjected to the dehydration treatment, a “liquid mixture in a biological reaction tank (aeration tank, microorganism suspension treatment tank, activated sludge treatment tank, etc.)” is taken. A method of directly dewatering (mixed wastewater and sludge) in a fresh state (direct dehydration) is being adopted. In this method (direct dehydration), since the dehydration treatment is performed before the deterioration of the sludge properties due to long-term storage starts, a dehydrated cake having a low water content and a separated liquid having good water quality can be obtained. Therefore, direct dewatering is very effective for sludge treatment.

A conventional wastewater treatment apparatus for performing direct dehydration, as shown in FIG. 4, for example, is a biological reaction tank 21, a centrifugal dehydrator 22, and a sedimentation separation tank 23 such as a sedimentation basin. It is composed of In the centrifugal dehydrator 22,
Although a centrifugal concentrator may be used in some cases, a case of a centrifugal dehydrator will be described below.

The operation of the wastewater treatment device will be described as follows.

[0008] The water to be treated 1 is stored in a biological reaction tank 21 such as an aeration tank.
0, and after a predetermined residence time, the mixed solution 18 that has completed the biological reaction is transferred to the precipitation separation tank 23. In the sedimentation separation tank 23, the retained liquid mixture 18 is solid-liquid separated into the sedimentation sludge 17 and the separation liquid 16 with time. Settling sludge 1
7 is returned to the biological reaction tank 21, and the separated liquid 16 is treated water 1
It is discharged as 6 or sent to the next step. Centrifugal dehydrator 22
Dehydrates the mixed liquid 12 collected from the biological reaction tank 21,
Separation liquid 13 and dewatered cake (dewatered sludge) 14 are separated. The separated liquid 13 is returned directly to the biological reaction tank 21 or returned to the inflow portion of the biological reaction tank 21 or the like. Dehydrated cake 14
Is appropriately disposed of outside the system.

The operation in the centrifugal concentrator is performed in the same manner.

However, since the mixture from the biological reaction tank has a low sludge concentration (0.1% to 1.0%), if the mixture is directly dewatered with a conventional centrifugal dehydrator as it is, the sludge treatment amount (water volume) Load) cannot be increased. Therefore, there has been a problem that it is not possible to obtain a solid processing amount equivalent to that of the conventional high-concentration sludge dewatering.

On the other hand, in wastewater treatment of sewage and the like, since the load variation of the inflow sewage is large, the influence on the allowable treatment amount is large. That is, in the case of the illustrated example, when the separated liquid 13 generated by the direct dehydration is returned to the biological reaction tank 21 at the time of the peak of the inflow sewage, the total amount of the inflow of the biological reaction tank 21 is increased. There has been a problem that stable water quality of the treated water 16 cannot be maintained due to a reduction in the residence time at 21 or an outflow of sludge in the sedimentation separation tank 23 due to an increase in solid (sludge) load.

[0012] Further, the separated liquid generated by the dehydration treatment by the centrifugal dehydrator or the concentration treatment by the centrifugal concentrator is usually returned to the biological reaction tank or the like. This leads to an increase in the load of the tank (return water load), which also affects the properties of the treated water flowing out of the sedimentation separation tank.

[0013]

SUMMARY OF THE INVENTION An object of the present invention is to stabilize the quality and volume of treated water in a water treatment process and to enable efficient solid-liquid separation of sludge.

It is another object of the present invention to provide a wastewater treatment apparatus which directly dehydrates a mixed solution having a low sludge concentration and obtains a solids treatment amount equivalent to that of the prior art.

[0015]

In order to achieve the above object, according to the present invention, a mixed solution in a biological reaction tank is directly dehydrated (solid-liquid separation) using a centrifugal separator, and the separated solution is subjected to biological separation. After combining with the mixed solution in the advancing means from the biological reaction tank instead of the reaction tank, the mixture is put into a precipitation separation tank. Specifically, the wastewater treatment apparatus of the present invention includes a biological reaction tank for biologically treating wastewater, which is water to be treated, and a sedimentation for solid-liquid separation of a mixed solution in the biological reaction tank into sludge and treated water. A separation tank, a transfer means for transferring the mixed liquid to the sedimentation separation tank, a centrifugal separator for concentrating or dehydrating a part of the mixed liquid and discharging concentrated sludge or dewatered sludge, and centrifuging the mixed liquid. And a merging means for merging the separated liquid separated by the centrifugal separator with the advancing means.

A centrifugal dehydrator capable of obtaining a sufficient solids treatment amount as in the conventional high-concentration sludge dewatering is used even when the low-concentration mixed liquid is directly dewatered. Specifically, the centrifugal separator used in the wastewater treatment device of the present invention includes a rotatable outer body bowl and an inner body screw,
The difference between the rotation speeds can be adjusted.

In the present invention, the mixture in the biological reaction tank is
It is directly introduced into the centrifuge from the biological reaction tank, or is introduced into the centrifuge from the means for advancing to the precipitation separation tank. Since this mixture is mainly composed of fresh activated sludge, solid-liquid separation in a centrifuge is good. In addition, since the separated liquid generated by centrifugation is returned to the inflow section (advancing means) of the sedimentation separation tank, the return water load to the biological reaction tank is eliminated. Furthermore, since the separated liquid containing almost no solid matter is mixed with the mixed liquid flowing into the sedimentation separation tank, the load of the solid matter in the sedimentation separation tank can be reduced by thinning the mixed liquid.

[0018]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to FIG. 1, the configuration of a wastewater treatment apparatus according to the present invention includes a biological reaction tank 1 for receiving wastewater, which is water to be treated, and a part of the mixed solution from the biological reaction tank 1. Centrifugal separator 2, receiving means 4 from biological reaction tank 1 to centrifugal separator 2, sedimentation / separation tank 3 for receiving mixed liquid from biological reaction tank 1, and advection from biological reaction tank 1 to sedimentation / separation tank 3 Means 6 and merging means 5 for merging the separated liquid from the centrifuge 2 with the mixed liquid from the biological reaction tank 1.

The biological reaction tank 1 is usually an activated sludge treatment tank, but may be a biological treatment tank based on a microorganism suspension method using a special microorganism such as yeast.

Either a method of concentrating sludge using a centrifugal concentrator as the centrifugal separator 2 or a method of directly dewatering sludge using a centrifugal dehydrator is selected. Then, in the case of directly dehydrating the centrifugal separator 2 using a centrifugal dehydrator, the obtained dehydrated cake 14 may be disposed of appropriately. When sludge is concentrated using a centrifugal concentrator for the centrifuge 2,
The obtained concentrated sludge 14 may be temporarily stored and sludge treatment may be appropriately performed. If necessary, the concentrated sludge 14 may be returned to the biological reaction tank 1 as returned sludge. The operation of the centrifugal separator 2 may be performed quantitatively over a long period of time, or if the operation is concentrated in a time zone where the wastewater to be treated, that is, the inflow of the water to be treated 10 is large, more stable wastewater treatment can be performed. ,It is valid.

The centrifugal separator used in the wastewater treatment apparatus of the present invention satisfies the same standard (specification) as that of conventional solids even when the sludge to be dewatered has a low concentration like the above-mentioned mixed solution. You can do it.

In general, a centrifugal dehydrator has a rotatable outer shell bowl and an inner shell screw, respectively, so that the differential speed, which is the difference between the rotation speeds of the outer shell bowl and the inner shell screw, can be adjusted. Has become. The mixed liquid supplied to the centrifugal dehydrator is separated into a separated liquid and a dewatered cake by centrifugal force by utilizing a specific gravity difference between water and sludge. In addition, the centrifugal dehydrator has the following characteristics.

(1) During centrifugal dewatering, the smaller the differential speed, the longer the residence time of the mixture in the outer shell bowl, so that the water content of the dewatered cake can be reduced.
SS recovery rate will be worse.

(2) The larger the capacity of the outer bowl, the longer the residence time of the mixed liquid in the outer bowl, so that the solid-liquid separation performance mainly increases and the SS recovery rate can be improved. .

(3) As the rotation speed of the outer bowl increases, the centrifugal force increases and the solid-liquid separation performance increases, so that a reduction in the water content of the dewatered cake and an improvement in the SS recovery rate can be expected. The throughput can also be increased.

Therefore, the centrifugal dehydrator used in the wastewater treatment apparatus of the present invention and corresponding to a low-concentration mixed liquid has the following characteristics utilizing the above characteristics.

(1) Fine adjustment of the speed difference between the outer shell bowl and the inner shell screw (less than 1 rpm, desirably 0.5 rpm)
Degree) can be.

(2) The capacity of the outer shell bowl is increased more than usual.

(3) The rotation speed during the dehydration treatment is increased to increase the solid-liquid separation performance.

With the centrifugal dehydrator having these features,
The low-concentration mixed solution can be sufficiently retained in the outer bowl to perform solid-liquid separation, and the amount of dewatering can be greatly increased. As a matter of course, the present invention can be applied to conventional high-concentration sludge dewatering.

In this centrifugal dehydrator, the processing load is greatly increased as compared with the conventional centrifugal dehydrator, and the quality of the dewatered separated liquid is improved. That is, when a low-concentration mixed solution is treated, dehydration is possible with a water load (treatment amount) 2 to 4 times that of the conventional method, so that a dehydrated cake having a low water content (70 to 85%) is obtained. At the same time, a high SS recovery rate (90% or more) can be achieved, and a separated solution having good water quality can be obtained.

If a centrifugal concentrator having the same configuration and function as the above-mentioned centrifugal dehydrator is used as the centrifugal separator used in the wastewater treatment apparatus of the present invention, a similarly high-quality separated liquid can be obtained.

Therefore, in the above-described wastewater treatment apparatus of the present invention, the mixed solution is introduced into the centrifugal separator from the biological reaction tank (preferably the outflow portion) or its advancing means and directly dehydrated, and the obtained separated solution is subjected to It is configured to supply to the inflow section of the sedimentation separation tank. Thereby, when the water volume (water quality) load on the wastewater treatment facility increases, the solid (sludge) load on the sedimentation separation tank can be significantly reduced.

The introduction means 4 introduces a part of the mixture 12 obtained in the biological reaction tank 1 into the centrifuge 2. Introduction means 4
Is usually introduced quantitatively using a pump or the like. Further, a medicine adding means such as a flocculant may be provided. Further, the mixed solution 12 in the biological reaction tank 1 may be directly collected from the biological reaction tank 1 and introduced into the centrifuge 2, or may be collected immediately after flowing out of the biological reaction tank 1. .

The sedimentation separation tank 3 is usually a gravity type sedimentation tank, but may be a membrane separation device for solid-liquid separation using a separation membrane.

The transfer means 6 is for transferring the mixed solution 12 flowing out of the biological reaction tank 1 to the precipitation separation tank 3, and may be a natural flow path or a transfer device such as a pump. . In some cases, advection pits and the like may be provided and rectified and distributed. The inflow part (such as a center well) of the precipitation separation tank 3 is also included in the advection means 6.

The joining means 5 joins the separated liquid 13 discharged from the centrifugal separator 2 with the mixed liquid 12 in the transferring means 6, and joins them in a natural flow-down flow path, or transfers by a pump or the like. The facility may be connected to the advection means 6. Further, a merging pit 25 may be provided as shown in FIG. 2 or may be merged at an inflow portion (a center well or the like) of the sedimentation separation tank 3 as shown in FIG. In short, it is only necessary that the separated liquid 13 and the mixed liquid 12 from the biological reaction tank 1 can be joined and mixed.

(Embodiment) An embodiment of the present invention will be described with reference to FIG.

100 mg / l BOD to biological reaction tank 1
(Biochemical oxygen demand), treated water 10 of 80 mg / l SS (suspended matter) was introduced in an amount of 50 m ³ / day. In the biological reaction tank 1, the residence time is about 8 hours and the MLS
The treatment was performed at S (suspended substance concentration) of 1300 mg / l. Part of the mixture 12 flowing out (1 m ³ / hour)
Was supplied to the centrifugal dehydrator 2. Centrifugal dehydrator 2 is 3 hours /
It is operated during the day, and the dewatered cake 14 having a moisture content of 78%, 3
Separation liquid 13 of BOD of 20 mg / l and SS of 20 mg / l
Was mixed with the mixed liquid 12 to be transferred by the joining means 5. The combined liquid 15 was 700 mg / l SS. The residence time in the sedimentation separation tank 3 is about 3 hours,
A treated water 16 having a BOD of 5 mg / l and a SS of 5 mg / l was obtained (Table 1).

Further, as Comparative Example 1, the BOD and SS of the treated water 16 when the operation of the centrifugal dehydrator 2 was not performed without changing the configuration of the wastewater treatment apparatus were measured. Biological reaction tank 1
, Treated water 10 having a BOD of 100 mg / l and an SS of 80 mg / l was introduced in an amount of 50 m ³ / day. In the biological reaction tank 1, the residence time was about 8 hours, and the treatment was performed at an MLSS (suspended substance concentration) of 1300 mg / l. The mixed solution 12 in the biological reaction tank 1 was transferred to the sedimentation / separation tank 3, and the residence time in the sedimentation / separation tank 3 was about 3 hours, thereby obtaining 8 mg / l BOD and 10 mg / l SS treated water 16. (Table 1).

Further, as Comparative Example 2, the BOD and SS of the treated water 16 by the wastewater treatment apparatus having the structure shown in FIG. 4 were measured.

100 mg / l of BO was added to the biological reactor 21.
D, 80 mg / l of SS water to be treated 10 m, 50 m ³ /
Introduced only the amount of the day. In the biological reaction tank 21, the residence time is about 8 hours, and the MLSS (suspended substance concentration) is 1300 mg.
/ L was being processed. A part (1 m ³ / hour) 12 of the mixture was fractionated and supplied to the centrifugal dehydrator 22. The centrifugal dehydrator 22 is operated for 3 hours / day, and the dehydrated cake 14 having a water content of 78% and the separated solution 13 of 3 mg / l BOD and 20 mg / l SS are introduced into the inflow section of the biological reaction tank 21. I returned. 1100 mg of the mixed solution 18 from the biological reaction tank 21
/ L SS. S of mixed liquid 12 in Comparative Example 1
S is 1300 mg / l, and it can be said that the effect of the direct dewatering by the centrifugal dewatering machine 22 is small, as compared with that of S, which is not much reduced. Finally, treated water 1 of 7 mg / l BOD and 9 mg / l SS was discharged from the sedimentation separation tank 23.
6 was obtained (Table 1).

This embodiment is an example of adaptation to sewage. Comparing Example 1 with Comparative Example 1, the quality of treated water is improved during the operation of the centrifugal dehydrator. This is because the operation of the centrifugal dehydrator reduced the solids load on the sedimentation separation tank,
This shows that, in the treatment with sewage or the like, if the dewatering is performed directly when the inflow load increases, the stable quality of the treated water can be maintained.

[0044]

[Table 1]

According to the measurement results of Example 1 and Comparative Example 2 in which the operation time of the centrifugal dehydrator was kept constant at 3 hours / day, a better treated water quality was obtained by the direct dehydration of the present invention than by the conventional direct dehydration. It is understood that it can be done.

In the conventional direct dehydration, the separated liquid from the centrifugal separator is returned to the biological reaction tank. Therefore, in order to achieve the same solid substance load in the precipitation and separation tank as in the direct dehydration of the present invention, a large amount of dehydration treatment is performed. There must be. Further, when a large amount of dehydration treatment is performed, the concentration of microorganisms (MLSS) in the biological reaction tank decreases, which hinders wastewater treatment by biological reaction and deteriorates the quality of treated water.

[0047]

As described above, according to the present invention, the following effects can be obtained.

(1) Stable treated water quality can be obtained even when the inflow load increases.

That is, since the separated liquid from the centrifugal separator does not flow into the biological reaction tank, the microorganism concentration (M
LSS) is not diluted, and the residence time of the water to be treated in the biological reaction tank is sufficiently obtained. In other words, the biological treatment is stable and the quality of the treated water is improved.

(2) Good concentration and dehydration properties are obtained, and no odor is generated.

That is, since the mixed liquid composed of fresh activated sludge and the like is directly dehydrated (concentrated), good solid-liquid separation properties can be obtained. Therefore, the water content of the dehydrated cake decreases, and the chemical injection rate also decreases.

(3) When the amount of inflow water increases, the load of solids on the sedimentation separation tank can be reduced, and good treated water quality can be obtained.

That is, the mixed liquid from the biological reaction tank is diluted with the separated liquid from the centrifugal separator and flows into the sedimentation separation tank, so that the solid (sludge) load is reduced in the sedimentation separation tank such as a sedimentation tank. Is done. Furthermore, the dewatered separation liquid whose water quality has deteriorated is not generated, and the separation liquid having good water quality is sent to the precipitation separation tank, so that the return water load on the biological reaction tank is eliminated.

(4) Direct dewatering by a centrifugal separator does not require complicated operations such as sludge storage and gravity concentration, and equipment such as a storage tank and a thickening tank for treating dewatered cakes and concentrated sludge. Is unnecessary. Therefore, space saving of the wastewater treatment facility can be achieved, and simplification of operation and maintenance can be achieved.

[Brief description of the drawings]

FIG. 1 is a flow sheet showing one embodiment of the present invention.

FIG. 2 is a flow sheet showing one embodiment in which advection pits are used as merging means.

FIG. 3 is a flow sheet showing another embodiment of the present invention.

FIG. 4 is a flow sheet showing a conventional technique.

[Explanation of symbols]

 1, 21 Biological reaction tank 2, 22 Centrifugal separator 3, 23 Precipitation separation tank 4 Introducing means 5 Merging means 6 Transfer means 10 Inflow water 12 Mixed liquid 13 Separated liquid 14 Concentrated liquid / dehydrated cake 15 Mixed liquid 16 Treated water 17 Return Sludge 18 Mixed liquid 25 Transfer pit

Claims (2)

[Claims] 1. A biological reaction tank for biologically treating water to be treated, a sedimentation separation tank for solid-liquid separation of a mixed liquid in the biological reaction tank into sludge and treated water, and a sedimentation separation tank for mixing the mixed liquid. Advancing means for advancing the mixed solution, a centrifugal separator for concentrating or dehydrating a part of the mixed liquid and discharging concentrated sludge or dewatered sludge, an introducing means for introducing the mixed liquid to the centrifugal separator, and a centrifuge. A wastewater treatment apparatus comprising: a joining means for joining the separated liquid separated by the method to the advancing means. 2. The centrifugal separator is a centrifugal dehydrator or a centrifugal concentrator that includes a rotatable outer shell bowl and an inner shell screw, and that can adjust the difference between the respective rotation speeds. The wastewater treatment device according to claim 1.