JPS61125490A - Treatment of organic waste water - Google Patents

Abstract

PURPOSE:To remove stably phosphorus from feed water by preventing the outflow of the sludge having the larger BOD quantity from a water way for treating sewage into a settling basin owing to an increase in the BOD load of the feed water. CONSTITUTION:The feed water is passed through an absolute anaerobic tank 14 and is introduced into the water way 11 for treating sewage which has a water circulator 16 and aerators 17, 172 and forms flatly a closed circuit. The sludge discharged from said water way is introduced into the settling basin 13 and the water treated in the basin 13 is discharged to the outside of the system. At least part of the settled sludge is returned to the tank 14 from which the sludge is introduced together with the feed water again into the above- mentioned water way. The sludge from said water way is post-aerated by a post-aerator 18 in the mid-way of introducing the same into the basin 13. As a result not only the nitrogen can be effectively removed but also the outflow of the sludge having the large BOD quantity from the water way 11 into the settling basin owing to the fluctuation of the BOD load (more particularly the increase of the BOD load) of the feed water is prevented. The stable removal of phosphorus is thus made possible.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a method for treating organic wastewater, and particularly to a method for removing nitrogen and phosphorus from wastewater.

[Technical background of the invention and its problems]

In recent years, the oxidation ditch method (00 method) has been attracting attention as a sewage treatment facility for small and medium-sized businesses. The reasons why the 00 method is attracting attention are: ■ It is an energy-saving system; ■ It is possible to omit the sedimentation tank in the previous stage; ■ It is easy to maintain; ■ It is resistant to load fluctuations; ■ It generates little sludge. etc.

On the other hand, in recent years there has been a movement to regulate nitrogen and phosphorus, which are the causes of pollution, in closed water bodies such as lakes and inner bays, with the aim of preventing eutrophication, and some regions have already implemented emission controls. . In order to quickly respond to such situations,
The applicant has already developed biological denitrification using a combination of an anaerobic tank and OD.
(Special Application No. 174328/1982)
. This method will be explained with reference to the wastewater treatment apparatus shown in FIG. 1 in the figure is an oxidation ditch tank in which a partition plate 2 is arranged in the center. Such a partition plate 2
By arranging this in the ditch tank 1, a planar closed circuit is formed in the ditch tank 1. In the ditch tank 1, an underwater blower 3 for the purpose of water circulation and an aeration pipe 4 as an aerator for supplying oxygen are arranged. The underwater blower 3 and the aeration pipe 4 are separated, and the ditch tank 1 is
This allows the formation of an anaerobic zone A and an aerobic zone B, which are indicated by diagonal lines. Further, the ditch tank 1 is connected to a sedimentation tank 5. This sedimentation tank 5 is connected to an absolute anaerobic tank 6, and the anaerobic tank 6 is connected to the ditch tank 1. Note that it is necessary to install a submersible propeller or the like in the absolute anaerobic tank 6 to provide a flow velocity that prevents the sludge from settling.

In the above-mentioned apparatus, the raw water 7 is treated with NOx (tilil
! , nitrous acid) is introduced into the absolute anaerobic tank 6.
The sludge returned from the settling tank 5 in the absolute anaerobic tank 6
After that, the mixed liquid is introduced into the ditch tank 1 at the position of the underwater propeller 3. A mixed solution of raw water and returned sludge introduced into the ditch tank 1 circulates within the same type 1. At this time, the mixed liquid of raw water and returned sludge is introduced from anaerobic zone A to aerobic zone B, where a sludge formation reaction takes place, resulting in N1-1
4-N is oxidized to produce NOx. Furthermore, a denitrification reaction proceeds in the anaerobic zone using the BOD component in the raw water as an organic carbon source, and the generated NOx becomes nitrogen gas and is released into the atmosphere. The sludge generated by biological activity in the ditch tank 1 is introduced into the settling tank 5, where the treated water 9 is discharged outside the system, and the settled sludge is returned to the absolute anaerobic tank 6 as return sludge 8.
will be returned to. Through this circulation of ditch tank 1 → sedimentation tank 5 → absolute anaerobic tank 6 → ditch tank 1, anaerobic → aerobic stress is applied to the sludge, and phosphorus is removed biologically.

That is, the microorganisms used in such activated sludge absorb phosphorus under aerobic conditions and discharge phosphorus under anaerobic conditions.

This anaerobic discharge of phosphorus is promoted by the presence of BOD as an organic carbon source in the system and inhibited by the presence of NOx. For this reason, in Kouki Zettai Kiki Tank 6,
Due to the presence of 800 in the raw water, phosphorus is sufficiently discharged from the microorganisms in the returned sludge, and when the mixed solution of raw water and returned sludge introduced into the ditch tank 1 enters the aerobic zone B, the phosphorus is absorbed by the microorganisms. The phosphorus is introduced into the sedimentation tank 5 in a state in which it has been absorbed. This sedimentation tank 5 is normally an anaerobic layer, but in a state where there is almost no BOD and no anaerobic biological reaction is progressing, microorganisms hardly discharge phosphorus. Therefore, phosphorus is not contained in the treated water 9 again and is not discharged. By applying anaerobic to aerobic stress to the sludge such as phosphorus discharge in the absolute anaerobic tank 6 and phosphorus absorption in the ditch tank 1, the returned sludge is directly transferred to the ditch tank 1 without installing the absolute anaerobic tank 6. The amount of phosphorus accumulated in sludge can be significantly improved compared to the method in which phosphorus is introduced into the sludge for treatment. Then, the sludge with increased phosphorus content is discharged outside the system as surplus sludge 10 and is treated separately.

In the above-mentioned method, since an aerobic zone is formed in the ditch tank and an anaerobic zone is formed in the subsequent stage thereof, the oxygen supply (aeration) by the aeration w4 cannot be increased arbitrarily. Therefore, when raw water with a high BOD concentration flows into the ditch tank 1 through the absolute anaerobic tank 6 due to fluctuations in the BODffi of the raw water, BOD removal with the nuclide 1 is not performed sufficiently, and the sludge with a high BOD is transferred to the settling tank 5. There, a discharge reaction of phosphorus by microorganisms occurs, and the amount of phosphorus in the treated water 9 increases.

[Purpose of the invention]

The present invention aims to provide a method for treating organic wastewater that can prevent sludge with a large amount of BOD from being discharged from a sewage treatment channel to a settling pond due to an increase in the BOD load of raw water.

[Summary of the invention]

The present invention introduces raw water through an absolute anaerobic tank into a sewage treatment waterway that has a water circulator and an aerator and forms a closed circuit on a plane, and introduces sludge flowing out from the waterway into a settling tank. The treated water in the pond is discharged out of the system, and at least a portion of the settled sludge is returned to the absolute anaerobic tank and is reintroduced to the waterway together with the raw water for circulation. The method is characterized in that post-aeration is performed during the introduction of the sediment into the sedimentation tank.

Hereinafter, the present invention will be explained in detail with reference to FIG.

FIG. 1 is a schematic diagram showing one embodiment of an apparatus used for organic wastewater treatment of the present invention. This device is roughly divided into an oxidation ditch tank 11 as a sewage treatment waterway, a settling tank 13 connected to this ditch tank 11 via piping 12a and into which sludge from the ditch tank 11 flows, and this settling tank. 13 via piping 12t), and piping 12G
At the same time, raw water and return sludge are transferred to pipe 1.
Absolute anaerobic tank 14 supplied from 2d to the ditch tank 11
It is composed of.

A partition plate 15 is arranged in the center of the ditch tank 11, and the partition plate 15 forms a planar closed circuit in the same type 11. Further, inside the ditch tank 11, there are an underwater propeller 16 for the purpose of water circulation and two first and second aeration pipes 1 as an aerator for supplying oxygen.
71 and 172 are arranged respectively. By separating the underwater propeller 16 and each diffuser pipe 171, 172, and arranging each diffuser pipe 171, 172 at an appropriate position,
The ditch tank 11 can be formed into an anaerobic zone A and an aerobic zone B, which are indicated by diagonal lines. Each of the diffuser pipes 171 and 172 is connected to a blower (not shown). Also, the arrangement that connects the ditch tank 11 and the sedimentation tank 13! A post aeration tank 18 having a third aeration pipe 173 is interposed in the aeration tank 12a. A blower (not shown) is connected to this diffuser pipe 173. Note that a stirring propeller 19 and the like are installed in the absolute anaerobic tank 14 to provide a flow rate that does not allow the sludge to settle.

A return pump 20 is installed in the pipe 12b that returns the sludge from the settling tank 13 to the absolute anaerobic tank 14.

Further, a branch pipe 21 for discharging sludge to a surplus tank is connected to the pipe 12b. These piping 1
2b and the branch pipe 21 are provided with first and second electromagnetic valves 221 and 222, respectively, which are opened and closed by a controller (not shown).

Next, a treatment method will be explained with reference to the above-mentioned wastewater treatment apparatus.

First, raw water is introduced from the sedimentation tank 13 through the pipe 12c to the absolute anaerobic tank 14 to which sludge is returned by the return pump 23 and the pipe 12b, and the mixed liquid of raw water and returned sludge is introduced into the pipe 12.
It is supplied to the ditch tank 11 through d. Ditch tank 11
The mixed liquid introduced into the ditch tank 1 is circulated by an underwater propeller 16 in a closed circuit partitioned by a partition plate 15 in the ditch tank 1 . At this time, the mixed liquid is transferred from anaerobic zone A to aerobic zone B.
The nitrification reaction takes place in the aerobic zone A, and NH4
-N is oxidized to generate NOx. Furthermore, a denitrification reaction proceeds in the anaerobic zone using the BOD component in the raw water as an organic carbon source, and the generated NOx becomes nitrogen gas and is released into the atmosphere.

Next, the sludge in the ditch tank 11 flows into the settling tank 13 through the pipe 12a and the post-aeration tank 18. In this way, the sludge in the ditch tank 11 is flushed with air (It) through the aeration pipe 173.
After aeration 11118 is supplied, sedimentation tank 13
By introducing raw water with a high 800 load into the ditch tank 11 through the absolute anaerobic tank 14, even if BOD is not sufficiently removed here and sludge with residual BOD flows out from the ditch tank 11. , the post-aeration tank 18
Since BOD is removed while passing through the aeration tank 18 (that is, after the aerobic state), it is possible to prevent sludge containing BOD from flowing into the settling tank 13. Moreover, by passing the sludge through the after-air tank 18, the settling tank 13 into which the cough sludge is introduced can be brought into an aerobic state. As a result, BO is added to the sedimentation tank 13.
It is possible to suppress the discharge of phosphorus by microorganisms due to the inflow of D and the anaerobic state, and it is possible to prevent the phosphorus concentration from increasing due to discharge of phosphorus that has accumulated in the sludge into the treated water.

In the settling tank 13 into which the sludge has been introduced, treated water is discharged outside the system, and a portion of the settled sludge is returned to the absolute anaerobic tank 14 via the piping 12b and the return pump 20. Through this circulation of the ditch tank 11 → settling tank 13 → absolute anaerobic tank 14 → ditch tank 11, anaerobic → aerobic stress is applied to the sludge, and as described above, phosphorus is biologically accumulated in the sludge.

Then, the sludge with increased phosphorus content is discharged from the branch pipe 21 to the surplus tank and is treated separately.

Therefore, according to the present invention, even if the raw water increases by 80 DjM, the mixed liquid with a large amount of BOD is prevented from flowing out from the ditch tank 11 to the sedimentation tank, and nitrogen and phosphorus are effectively removed. A method for treating organic wastewater can be provided.

In addition, in the above method, a diffuser pipe was used as an aerator, but
It is not limited to this. For example, a similar effect can be achieved using a mechanical system (aerator, water wheel, etc.).

[Embodiments of the invention]

Hereinafter, embodiments of the present invention will be described with reference to FIG. 1 mentioned above.

Raw water was treated under the conditions shown below using the wastewater treatment apparatus shown in FIG. 1, and the changes in phosphorus concentration in the raw water and treated water are shown in FIG. 3. In addition, in Figure 3, 50% of water from wastewater treatment is shown.
The changes in phosphorus concentration according to the previously proposed method shown in FIG.

<Conditions for wastewater treatment> ■Raw water (sand treatment tank water) Sedimentation treatment amount: 2 m3/day ■Anaerobic tank residence time: 1 to 2 hours Do: 0 to 0.5II1g/2 ■Ditch tank; Capacity: ditch pipe line 6m in length Blower ON-OFF operation interval: 30 minutes MLSS;
Approximately 4000η/Q BOD load: 0.05Ny/Ky-MLSS-day■
Post-aerator residence time: 2 hours ■ Sedimentation tank residence time: 3 hours Return rate: 100% As is clear from Figure 3, in the method already proposed, if the phosphorus concentration of the inflow raw water is about 31N9/Q or less, the treated water The concentration of phosphorus becomes 0.5118/λ or less, but as the phosphorus concentration of the inflow raw water increases, the water quality of the treated water worsens. On the other hand, in the case of the method of the present invention, treated water with a low phosphorus concentration can be discharged stably even when the phosphorus concentration of inflow raw water fluctuates.

〔Effect of the invention〕

As detailed above, according to the present invention, not only can nitrogen be effectively removed, but also changes in the BOD load of raw water (especially BOD
It is possible to provide a method for treating organic wastewater that can stably remove phosphorus by preventing sludge with a large amount of BOD from flowing out from a sewage treatment waterway (ditch tank) into a settling tank due to an increase in D load.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram showing one form of a wastewater treatment device used in the organic wastewater treatment method of the present invention, and FIG. 2 is a wastewater treatment device used in the organic wastewater treatment method already proposed by the applicant. FIG. 3, which is a schematic diagram of the apparatus, is a characteristic diagram showing changes in the phosphorus concentration of raw water and treated water during wastewater treatment according to this embodiment and the previously proposed method. 11... Oxidation ditch tank, 13...
Sedimentation tank, 14...Absolute anaerobic tank, 16...Water Φ propeller, 171-173...Diffuser pipe, 18...After aerator, 20...Return pump, 221.222...Electromagnetic valve. Applicant's representative Patent attorney Takehiko Suzue Figure 3 Sotsu 5 losses (Japanese) SQ, 121 Showa year, month, day, Japan Patent Office Commissioner Manabu Shiga 1, Indication of case Patent application No. 59-247763 2, Title of invention Organic wastewater treatment method 3, relationship with the case of the person making the amendment Patent applicant (412) Nippon-ei Co., Ltd. 4, agent 7, content of amendment (1) Page 3, lines 14-15 of the specification Multiply by C2,
"Position of the underwater propeller 3 (introduces two rods.") should be corrected to "Introduce it to the starting position of the anaerobic zone." So, "Exhale zone A" should be corrected to "Aerobic zone B." The phrase "The sludge produced by It is corrected as Bonde 20J. (5) In the 9th line, 4th line of the specification (=, the phrase "Ditch tank 1" is corrected as "?' Ditch tank Z1".

Claims (1)

[Claims] The raw water is passed through an absolute anaerobic tank, equipped with a water circulator and an aerator,
The sludge is introduced into a sewage treatment waterway that forms a planar closed circuit, and the sludge flowing out from the waterway is introduced into a settling tank, where the treated water is discharged outside the system, and at least a portion of the settled sludge is In the treatment of organic wastewater that is returned to the absolute anaerobic tank and recycled by being introduced into the waterway together with the raw water, the organic wastewater is subjected to post-aeration while the sludge from the waterway is being introduced into the settling tank. How to treat wastewater.