JPH0818030B2 - Biological treatment method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of application] The present invention provides a method of removing organic matter or nitrogen from low concentration to high concentration such as river water or lake water with relatively advanced pollution, or sewage / human waste / industrial wastewater. The present invention relates to a biological treatment technology for purifying a contained liquid with microorganisms.

[Conventional technology]

There are many biological treatment technologies since ancient times, and they are still widely used today. Among them, those using a medium for adhering microorganisms have made many technological advances in recent years, and in particular, the method using a granular medium has a very high utility value such as high load operation is possible. Is.

[Problems to be solved by the invention]

However, when the particulate matter is a medium for adhering microorganisms,
Since the porosity is low, it is easily clogged and cleaning is essential.

For example, as in the gravel-to-gravel contact method, a large amount of excess sludge is mixed into the treated water when washed, and when the washing is excessive, the amount of microorganisms is significantly reduced, which causes deterioration of the treatment. As a matter of course, if cleaning is insufficient, clogging occurs immediately and it is difficult to control the degree of cleaning.

Furthermore, as another method for preventing clogging, a method of backwashing using treated water or air has also appeared, but since a large amount of treated water or air is used at one time, the backwash facility becomes huge, Many problems remain, such as having to consider the treatment of cleaning wastewater separately.

The present invention has a drastic solution to the clogging, which is an inevitable and fundamental problem inevitably occurring when the particulate matter is adopted as a medium for adhering microorganisms, and further stabilizes biological treatment. And to provide a method that can be effectively done.

[Means for solving problems]

In the present invention, as a means for solving the above problems, a packed bed of a granular medium for adhering microorganisms is formed as a fixed bed in a tank, and a liquid to be treated is passed through a downward flow to the packed bed. In a biological treatment method of simultaneously performing aerobic biological treatment and filtration treatment, the granular medium is intermittently moved by an air lift, and is transferred upward from a lower part of the packed bed through a transfer path together with a part of the treated water, The transfer amount of the granular medium was changed within the range of 1/4 to 8 times the total amount of the granular medium per day, and the excess biofilm adhering to the granular medium was peeled off by stirring by the air lift during the transfer. After that, it is separated from the granular medium, the separated granular medium is returned to the upper part of the packed bed, and the separated excess biofilm is discharged to the outside of the system.

[Work]

The operation of the present invention will be described below with reference to FIG. 1 showing one embodiment.

The liquid to be treated 1 to be treated flows in from the upper portion of the treatment tank 2 and flows downward in the packed bed 4 formed of the granular medium 3.

The granular medium 3 may be granular, such as sand, gravel, anthracite, activated carbon, lightweight aggregate, plastic material, and artificial stone, as long as it can be transported in water, and the appropriate particle size thereof is a moving state in water. Judging from the above, the particles with a specific gravity of 1-2 have a relatively large particle size of about 3-6 mm and have a specific gravity of 2-3.
It is preferable that the particles have a relatively small particle size of about 1 to 4 mm.

Further, in the packed bed 4, an oxygen-containing gas such as air 5 is introduced by the air diffuser 6 arranged below, and the aerobic state is maintained, and the liquid to be treated 1 is the granular medium 3 of the packed bed 4. Due to the biofilm attached to the surface of the treated water, the aerobic biological treatment and the excess treatment are simultaneously performed, and the biological membrane is gradually purified as it goes down the packed bed 4, and flows out from the treated water outflow pipe 7 as treated water 8.

By the way, in the course of purification, an excessive biofilm is generated and attached to the granular medium 3 due to suspended solids in the liquid 1 to be treated or grown microorganisms. If the above treatment is continued in this state, the voids existing in the packed bed 4 will be occupied by the excessive biofilm, which will generally cause a "clogging condition", making water impassable. Become.

Therefore, the granular medium 3 ′ having excessively attached biofilm is guided from below the packed bed 4 together with part of the treated water 8 to the transfer pipe 9 and separated by the medium transfer device 10 above the packed bed 4. Transferred to device 11. An air lift is used as the medium transfer device 10.

The transfer of the granular medium 3'is carried out intermittently, but the granular medium 3'may depend on the degree of the amount of biofilm attached to the granular medium 3 '.
Change the transfer amount of. That is, the amount of biofilm attached to the granular medium 3 varies depending on the water quality and the amount of water of the liquid to be treated 1,
When the amount of biofilm is large, increase the transfer amount of the granular medium 3 ',
When the amount of the biofilm is small, the driving force of the medium transfer device 10 is increased or decreased (when the air lift is used as the medium transfer device 10, the air supply amount is changed) so as to reduce the transfer amount of the granular medium 3 '. Alternatively, the transfer amount of the granular medium 3'is changed by adjusting the opening degree of a valve provided in the transfer pipe 9, and an appropriate biofilm is always maintained to stabilize the process.

 Further, the transfer of the granular medium 3'will be described.

If the water quality and the amount of water of the liquid to be treated 1 are largely changed, it is necessary to change the transfer amount of the granular medium 3 ′ more than in the case of continuous transfer. In such a case, it is preferable to use a timer or to intermittently operate the medium transfer device 10 by detecting an increase in water flow resistance. It is effective even when it is small. In this case, in particular, the timer can be freely set, and the medium transfer device 10 can be operated at the highest efficiency point, which saves energy.

Further, the transfer amount of the granular medium 3'is preferably in the range of 1/4 to 8 times the total amount of the granular medium 3 per day.
Originally, the transfer amount of the granular medium 3'has a property that should be changed depending on the degree of contamination, in other words, the property of the liquid to be processed 1 and the processing conditions, but there are upper and lower limits for the following reasons. That is, in the case of a relatively clean sample water with a BOD of about 10 mg / hour, the water flow resistance of the packed bed 4 increases by several hours per hour.
It is about mm, and judging from the aspect of capturing SS in the packed bed 4, the transfer amount of the granular medium 3 ′ is 1 / day of the total granular medium 3 per day.
About 10 doses are enough. However, when the experiment was continued for a long period of time, since the biofilm attached to the granular medium 3 had a strong adhesiveness, the granular media were often bonded to each other to form a large lump, which made transfer difficult. As a result of repeating the experiment under various conditions, it was found that the above-mentioned problem does not occur if the transfer amount of the granular medium 3'is 1/4 or more of the total granular medium 3 per day.

On the other hand, in order to prevent the granular media from being combined with each other, the granular media 3 '
When the amount of transfer of the above was extremely increased, it became difficult for organisms to adhere to the surface of the granular medium 3 this time, resulting in a decrease in processing capacity. Therefore, when the upper limit value of the transfer amount was obtained by trial and error, it was found that the decrease in the biofouling amount that would cause the deterioration of the treatment was not observed within 8 times the total amount of the granular medium 3 per day.

Further, FIG. 2 shows an example of a performance curve when an air lift is used as the medium transfer device 10. That is, inner diameter 31mm
× Taking an example of an air lift tube having a height of 2600 mm and an immersion ratio of 1.0, the granular medium 3'cannot be transferred at all when the air supply amount is very small, but when the air supply amount is gradually increased, The 3'transfer amount (lifting amount) also begins to increase. However, even if the air supply is further increased, the lift will level off. That is, this curve is convex upward. Therefore, operating the air lift at the contact point of the straight line passing through the origin has the highest energy efficiency.

Further, in the transfer pipe 9 or the medium transfer device 10, since the granular medium 3'is subjected to strong agitation, excess biofilm attached to the granular medium 3'is peeled off. In particular, since the granular medium 3'is slurried with a part of the treated water 8, the cleaning effect is higher than that in the case of using raw water (the liquid to be treated 1).

In the separation device 11, the washed granular protective body 3 and excess biofilm
12 is separated, the granular medium 3 returns to the upper part of the packed bed 4,
The excess biofilm 12 is discharged outside the tank. The separating device 11 may effectively separate the granular medium 3 and the excess biofilm 12, and may be any combination of a liquid cyclone and a baffle plate, but the granular medium 3 and the excess biofilm 12 may be used.
A method that utilizes the difference in sedimentation speed between and is preferable. Further, the separating device 11 may be installed outside the tank or inside the tank, but it is effective to install it under the water surface in the tank as in the first illustrated example.

When the separation device 11 is installed below the water surface in the tank, the settling speed of the granular medium 3 is generally as fast as about 5 to 20 m / min, so that the packed bed is directly separated from the excess biofilm 12 by gravity. It is possible to easily return to 4, and to omit the pipes and the like from the separation device 11 to the inside of the tank, which are prone to blockage accidents. Also, the separation device 11 is combined with a baffle plate or the like to guide water in the tank. This facilitates the discharge of the excess biofilm 12 out of the tank.

Although the transfer pipe 9 is provided outside the tank in the first illustrated example, it may be provided inside the tank.

〔Example〕

Next, a comparative example of the present invention and the conventional method will be shown. As a conventional method, backwashing is performed to prevent clogging.
The method shown in No. 889 was used.

In this comparative example, the sewage primary treated water was used as raw water, and the treated water was treated at a treated water amount of 100 m ³ / day and a BOD load of about 3 kg / m ³ · day. Table 1 shows the equipment and Table 2 shows the comparison of the treatment results.

As is clear from Table 1 and Table 2, according to the present invention, auxiliary equipment such as a treated water tank, a waste water storage tank, a backwash pump, and a backwash blower is not required, and the equipment is significantly simplified, while the treatment is performed. The water quality was almost the same for each method, but the difference was significant in the amount of excess biofilm discharged. Compared to the conventional method, the blower flow rate of the packing material transfer blower was about 60% for continuous transfer with two-stage switching, and about 40% for intermittent transfer by a timer, and the amount of excess biofilm discharge was significantly reduced. .

An experiment was also conducted in the case where the amount of air blown by the blower for transferring the filler was not changed and the amount of the filler transferred was always constant. It was Furthermore, when the operation was continued for a long period of time, the treated water quality tended to deteriorate, although this may be due to a decrease in the biomass.

〔The invention's effect〕

As described above, according to the present invention, in the biological treatment in which the particulate matter is adopted as the biological adhesion medium, is formed as a fixed bed, and the liquid to be treated is passed in a downward flow to form the packed bed. In a biological treatment method of simultaneously performing aerobic biological treatment and filtration treatment, the granular medium is continuously or intermittently,
A part of the treated water is transferred upward together with a part of the treated water through a transfer path, and the transfer amount of the granular medium is changed in accordance with the amount of microorganisms adhering to the granular medium, and an appropriate amount is transferred during the transfer. While removing the excess biofilm adhering to the granular medium while maintaining the amount of the biofilm, the particulate medium is separated from the granular medium, the separated granular medium is returned to the upper part of the filling tank, and the separated excess By discharging the biofilm out of the system,
Soluble BOD treatment in wastewater and SS filtration treatment can be performed at the same time, excess biofilm can be separated from the granular medium of the filter medium, and necessary biofilm can be retained on the granular medium. Further, the dispersion medium of this slurry is the same as the treated water, the cleaning effect is higher than that of raw water as the dispersion medium, it is not necessary to use a special water for cleaning, therefore the granular medium It is easy to separate the excess biofilm and the clogging, which has been inevitable in the past, can be prevented, and at the same time, the discharge amount of the excess biofilm can be significantly reduced.

Further, since the transfer amount of the granular medium for exfoliating the excess biofilm can be changed and the microorganisms necessary for the biotreatment can be always maintained appropriately, stable and effective biotreatment can be performed.

In addition, since there is no need to backwash as in the conventional method,
Ancillary equipment required for backwashing can be greatly reduced and extremely rational treatment can be performed.

[Brief description of drawings]

FIG. 1 is a structural explanatory view showing an embodiment of the present invention.
The figure is a diagram showing an example of a performance curve of an air lift. 1 ... Liquid to be treated, 2 ... Treatment tank, 3, 3 '... Granular medium,
4 ... Packed bed, 5 ... Air, 6 ... Air diffuser, 7 ... Treated water outflow pipe, 8 ... Treated water, 9 ... Transfer pipe, 10 ... Medium transfer device, 11 ... Separator , 12 …… Excess biofilm.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Hitoshi Kimura 4720 Fujisawa, Fujisawa City, Kanagawa Prefecture, Ebara Research Institute Co., Ltd. (56) Reference JP-A-61-291099 (JP, A) JP-A-54-115555 (JP, A)

Claims (1)

[Claims] 1. A packed bed of a granular medium for adhering microorganisms is formed as a fixed bed in a tank, and a liquid to be treated is passed in a downward flow to perform aerobic biological treatment and filtration treatment in the packed bed. In the biological treatment method of simultaneously performing the above, the granular medium is intermittently transferred by an air lift from below the packed bed through a transfer path to the upper side together with a part of the treated water, and the transfer amount of the granular medium is 1
The amount is changed within a range of 1/4 to 8 times the total amount of the granular medium per day, and the excess biofilm adhering to the granular medium is peeled off by stirring by the air lift during transfer, and then separated from the granular medium. The method for biological treatment is characterized in that the separated granular medium is returned to the upper part of the packed bed, and the separated excess biofilm is discharged out of the system.