JP2791053B2 - Wastewater treatment method - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for treating wastewater. In particular, it relates to a stable wastewater treatment method.

(Conventional technology) In the wastewater treatment process, the microbial treatment tank is one of the most important devices, but rainwater etc. may flow into this tank and cause a higher load than the planned treatment capacity. Management of the treatment tank can often be difficult. In particular, in a combined sewage treatment plant in an urban area that employs the activated sludge method, bulking and floating development of sludge are often observed in the final sedimentation basin. Conventionally, various measures have been proposed to prevent such development, but these can be broadly classified into the following two.

The first is a method of increasing dissolved oxygen in a microorganism treatment tank. In this method, aeration is performed using oxygen or air having a high oxygen concentration, or liquid oxygen is injected into returned sludge to increase dissolved oxygen in the aeration tank. However, in any of the above methods, the supplied oxygen often escapes without being sufficiently consumed for purification of sewage, so that not only the expected effect is not obtained but also a large amount of oxygen is required and practically Had a problem. In addition, there is a method to increase the amount of dissolved oxygen by creating fine air bubbles by finely diffusing the holes, but this tends to cause clogging of the diffusing holes, which requires a laborious work to remove them. Needed.

The second method is to supply fine granules for increasing the weight of sludge to a microorganism treatment tank and settle the sludge to prevent a bulking phenomenon and a floating phenomenon. However, although this method is effective for removing suspended organic substances, it is still insufficient for removing soluble organic substances.

(Problems to be Solved by the Invention) In the treatment of wastewater by the activated sludge method, the present invention solves the problem of bulking and flotation of sludge without requiring a large amount of oxygen and efficiently dissolving organic substances. It is intended to be solved by a well-removed method.

(Means for Solving the Problems) The present invention relates to a method for treating wastewater by an activated sludge method in the presence of a granular material.
9μm siege with 10% or less siege or 10% or less of 149μm siege or 10% or less of 149μm siege The granules composed of a mixture with the silicic acid granules are suspended in treated water or a part of wastewater pretreated in a first settling basin, and adhered to fine bubbles formed by a part of the wastewater. Is supplied to the aeration tank of the sewage treatment apparatus, and then subjected to an aerobic treatment in accordance with a conventional method, where a part of the separated sludge is returned to the aeration tank as return sludge and excess sludge is removed. A wastewater treatment method (claim 1), wherein the wastewater is discharged and dewatered, and wherein the silicic acid-based powdery granules are at least one of converter slag, blast furnace slag, shirasu, Kanto loam, and zeolite The method for treating wastewater according to claim 1, which is A. Hereinafter, these inventions are further described.

The present invention increases the amount of dissolved oxygen in an aerobic microorganism treatment tank by flowing fine bubble particles having carbon-based powder particles attached to the wastewater inlet of an aeration tank in activated sludge treatment of wastewater. And the sludge generated is made heavy, thereby preventing the bulking phenomenon and the floating phenomenon of the sludge,
Thus, it is intended to efficiently and stably treat wastewater. Next, the invention of the present application will be described with reference to the process drawings.

FIG. 1 shows a typical wastewater treatment process according to the present invention. In the figure, reference numeral 1 denotes inflow sewage. This influent sewage is, for example, a lean urban sewage with a BOD of 200 ppm or less. The inflowed sewage 1 is first guided to a sand basin 2 where sand in the sewage is removed, and then sent first to a sedimentation basin 3 where suspended matter is removed. The pretreated sewage is then sent to the aeration tank 4. However, in the present invention, when the above-mentioned pretreated sewage flows into the aeration tank 4, the fine bubble particles 5 are supplied to the aeration tank 4 together with the sewage. Here, the fine bubble particles 5 supplied to the aeration tank together with the sewage are obtained by adhering powder particles to fine bubbles.

In order to make the fine particles 6 adhere to the fine bubbles to form the fine bubbles 5, a part 7 of the sewage pretreated in the sedimentation basin is first collected and sent to the granular suspension tank 8. 20
Add and suspend at 100 g / m ³ sewage ratio. Next, the suspension is introduced into a high-pressure tank 9, and air compressed to, for example, 3 kg / cm ² or more is sent from one side to the high-pressure tank by a compressor 10 to form the air-dissolved suspension. Tank 9
It is formed by removing this from the pipe 11 and placing it under reduced pressure. In FIG. 1, the fine bubble particles 5 thus formed are guided to the bottom of the aeration tank 4 and discharged from the bottom into the aeration tank. The fine bubble particles are preferably sent out from the lower part of the aeration tank 4 as described above. For this purpose, in addition to the supply in the illustrated manner, the flow of sewage flowing into the aeration tank 4 adopts a downward flow. If you have
If supplied to the inflow sewage inlet of the aeration tank 4, it may be sent to the bottom of the tank along with the flow of the inflow sewage. Aeration is performed in the aeration tank 4 by an ordinary method, and normal aerobic treatment is performed. However, here, since the fine bubble particles 5 are added as described above, the dissolved oxygen amount in the aeration tank is increased, and the oxygen deficiency in the aerobic treatment is released. The treated water subjected to the aerobic treatment is led to the final sedimentation basin 12 where the separated sludge 13 is extracted, while the treated water 14 of the supernatant is discharged to rivers and the like. A part of the separated sludge 13 is returned as return sludge 15 before the aeration tank 4 and added to the treated sewage 1. The surplus sludge 16 is sent to a sludge thickening tank 17, where it is sent to a dehydrator 18 for dehydration. The drainage 19 from the dehydrator 18 is first settled in the sedimentation basin 2
Will be returned before The sludge that has been dewatered is then disposed of by incineration and the like in accordance with ordinary methods.

The granules used in the present invention may be pure carbon-based granules or a mixture of carbon-based granules containing at least 60% of carbon-based granules and silicic acid-based granules. is there. As the carbon-based powder, any one of coal and carbonized coal is used,
Further, as the silica-based powder, converter slag, blast furnace slag, shirasu,
One or more of Kanto loam and zeolite. These powders have a particle size of 10% or less in a 149 μm sieve residue. Such particulate material is a said been to adhere to fine air bubbles as of fine bubbles particles, the amount of particulate material is set to be in the range of 20 to 100 g / m ³ with respect to sewage using Good to do. The water used for forming the fine bubble particles may be treated water in addition to the water pretreated by the initial precipitation as described above. .

Usually, the introduction of the fine bubble particles into the aeration tank may be performed as needed during operation of the apparatus. For example, when a bulking phenomenon or the like occurs or is likely to occur under a high load state of the device, fine bubbles are introduced, and then when this recovers normally, the introduction of the fine bubbles into the aeration tank is stopped. What is necessary is just to drive only by a device.

(Effects of the Invention) According to the present invention described above, even if the load fluctuation occurs in the inflow sewage, the dissolved oxygen in the microorganism treatment tank can be kept high correspondingly, and the normal operation can always be performed. Can be done. For this reason, in the aeration tank, the priority species of microorganisms are changed from filamentous fungi to protozoa, and the bulking phenomenon and floating of sludge can be prevented. Also,
The use of the powdered particles can greatly reduce the generation of odor in the aeration tank.

 Hereinafter, the present invention will be further described with reference to Examples.

Example 1 An experiment was conducted using activated sludge collected from a sewage treatment plant in the city of A where a bulking phenomenon had occurred, and primary settling water. The activated sludge, water depth 50cm, length 100cm, width 20cm
, And from the one end of the aeration tank, the same initial treatment water for the first settling of 100 mg / BOD as described above was continuously supplied at a rate of 0.8 m ³ / day. At the same time, the fine bubble particles were discharged from five places on the bottom of the aeration tank on the sewage inflow side. The fine bubble particles were formed as follows.

That is, in a previously prepared suspension tank, dry-distilled coal having a 149 μm sieve residue of 10% or less was added in a volume ratio of 10
%. This suspension is placed in a high-pressure vessel with a diameter of 20 cm and a height of 1 m.
The pressurized air of No. ² was sent to form a dissolved suspension of the pressurized air, and then the compressed air dissolved suspension was taken out of the high-pressure vessel under reduced pressure to form a fine bubble suspension. .

Next, air was sent to the aeration tank at 16 m ³ / day to continuously perform aeration. The sewage flowing out of the aeration tank was led to a settling tank, and the supernatant was collected as treated water. On the other hand, from the lower part of the sedimentation tank, the sludge was pulled out so that the interface of the settled sludge was raised and the sludge was not mixed with the supernatant. A part of the extracted sludge was returned to the aeration tank on average at 0.2 m ³ / day. Other sludge was retained as excess sludge in the concentration tank for about 12 hours, and then added to the cationic polymer flocculant Kayafloc C-.
566 (trade name of Nippon Kayaku Co., Ltd.) for concentrated sludge at 200mg /
And stirred. Thereafter, a dehydration test was performed using a small belt press tester to obtain a cake.

In these experiments, the dissolved oxygen concentration in the aeration tank, the odor concentration in the aeration tank, the BOD of the treated water, and the content of the dehydrated cake were measured. The odor concentration was measured in accordance with Tokyo Metropolitan Government Pollution Control Ordinance No. 238.

The following three were performed as comparative examples. The same amount of dry-distilled coal was suspended in the primary sedimentation water in the same manner as above,
When it is supplied to the aeration tank in the same manner as above without pressurization (1),
If the treated water in the sedimentation basin is first pressurized under the same conditions as above, and only fine bubbles formed by depressurization are supplied to the aeration tank without using the carbonized coal (2), the carbonized coal is used. An experiment was also performed on the case (3) in which only treated water obtained from the sedimentation tank was pressurized under the same conditions as above, and then only fine bubbles formed by depressurization were supplied to the aeration tank. . All are 1 to
After 2 weeks, the condition was stabilized as shown in Table 1.

 The results are shown in Table 1.

Example 2 The procedure of Example 1 was repeated except that bituminous coal pulverized to a 149 μm sieve residue of 10% or less was used.

The results are shown in Table 2. The results were also obtained for the case where the same amount of bituminous coal was suspended and supplied to the aeration tank without pressurization.

[Brief description of the drawings]

FIG. 1 shows an example of processing steps for carrying out the present invention. 1… Inflow sewage 2… Sand basin 3… First sedimentation 4
…… aeration tank, 5… fine bubble particles, 6… powder, 7…
… A part of sewage, 8… powder suspension tank, 9… high pressure tank,
10 ... compressor, 12 ... final sedimentation basin, 13 ... separated sludge, 14 ... treated water, 15 ... returned sludge, 17 ... sludge concentration tank, 18 ... dehydrator.

──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor Yoshihiko Okada 3-20-8 Azushidai, Sakae-cho, Inba-gun, Chiba (56) References JP-A-63-252594 (JP, A) (58) Fields investigated ( Int.Cl. ⁶ , DB name) C02F 3/12

Claims (2)

(57) [Claims] A method for treating wastewater by an activated sludge method in the presence of a granular material, comprising the steps of:
Granules containing 10% or less of 149 μm sieve or 10% or less of 149 μm sieve with 10% or less of 149 μm sieve or 10% or less of either 149 μm or 10% The granules composed of a mixture with the silicic acid granules are suspended in treated water or a part of wastewater pretreated in a first settling basin, and adhered to fine bubbles formed by a part of the wastewater. Is supplied to the aeration tank of the sewage treatment apparatus, and then subjected to an aerobic treatment in accordance with a conventional method, where a part of the separated sludge is returned to the aeration tank as return sludge and excess sludge is removed. A method for treating wastewater, comprising discharging and dewatering. 2. The method for treating wastewater according to claim 1, wherein the silicic acid-based powder is at least one of converter slag, blast furnace slag, shirasu, Kanto loam, and zeolite.