JPS60206493A - Simultaneous removal of nitrogen and phosphorus in sewage - Google Patents

Abstract

PURPOSE:To perform the simultaneous removal of nitrogen and phosphorus by such a simple process that a high COD solution is introduced into an aerobic tank and the supernatant solution separated in the aerobic tank and precipitated sludge are respecitvely taken out as treated water and excessive sludge. CONSTITUTION:Raw sewage (a) is flowed into a water channel 15 in the vicinity of the opening provided to the top part of said water channel 15 from a sewage supply pipe 20 and enters an anaerobic tank 12 through the water channel 15 while mixed with recirculated activated sludge and a recirculation liquid in an aerobic tank 11. In the anaerobic tank 12, NO2-N and NO3-N are denitrified by the action of denitriding bacteria utilizing org. substances present in the raw sewage. The supernatant solution separated in the upper layer part in the aerobic tank 11 is flowed in a trough 21 while overflows the upper end of the aerobic tank 11 in an amount corresponding to the inflow of new raw sewage and subsequently taken out to the outside through a treated water take-out pipe 22. Activated sludge taking in excessive phosphorus is discharged from the excessive sludge take-out pipe 23, provided to the bottom part of an aerobic zone.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for simultaneously removing nitrogen and phosphorus from domestic wastewater by biological treatment, and also relates to a method for simultaneously removing nitrogen and phosphorus from domestic wastewater, which is generally used in the treatment of organic wastewater.

The activated sludge treatment method is an aerobic process and is effective in removing organic matter, so various modified methods have been developed around the standard activated sludge method and are now widely used. . However, compared to organic matter, nitrogen and phosphorus are not removed sufficiently, and when treated water is discharged into closed water bodies, it causes eutrophication, causing great damage to fisheries and fisheries.

In recent years, methods for removing these nutrient salts have been developed, such as the biological circulation denitrification method for nitrogen removal, and the coagulation-sedimentation method using metal salts, Ca salts, etc. for phosphorus removal. has been put into practical use. However, this method of removing phosphorus generates a large amount of sludge, and this sludge is difficult to dewater, causing problems in its treatment, and the use of chemicals imposes a heavy economic burden.

Therefore, biological dephosphorization methods are attracting attention as a method for solving this problem.

The processing steps of the conventional biological dephosphorization method are shown in FIG. The main equipment consists of an anaerobic tank 1, an aerobic tank 2, and a settling tank 3. Activated sludge is treated anaerobically (dissolved oxygen D) in the presence of organic matter.
o and the presence of nitrate/nitrite nitrogen NOx-N)
As a result of repeated aerobic cycles, dephosphorizing bacteria that accumulate excessive phosphorus become prioritized. In this biological dephosphorization method, when certain microorganisms are exposed to anaerobic conditions, they hydrolyze polyphosphorus stored in intracellular polyphosphorus granules into orthophosphoric acid, and use the energy obtained at this time to remove organic matter. On the contrary, IJ phosphate is released outside the cells and temporarily increases the concentration of phosphate in the liquid, but when it is next exposed to aerobic conditions, it decomposes the organic matter taken in. This energy is used to take advantage of the property of ingesting more phosphorus than was released in the anaerobic tank 1. Therefore, phosphorus is removed by pulling out the sludge that has taken in too much phosphorus from the settling tank.

Furthermore, when denitrification is used together, as shown in Figure 2, a denitrifying rosewood 4 is provided between the anaerobic tank 1 and the aerobic tank 2, and the nitrification liquid (NOx-N The same applies hereinafter) is internally circulated to the denitrifying rosewood 4 to convert nitrate nitrogen or nitrite nitrogen into N! Remove by reducing to gas.

In addition, in order to further enhance the denitrification effect, as shown in Fig. 3, a nitrogen tank 5 is provided between the aerobic tank 2 and the settling tank 3, and a hydrogen donor such as methanol is added here. Furthermore, a re-aeration tank 6 is provided to remove residual methanol.

These known methods have the following problems.

■ Since there is no oxygen supply in the sedimentation tank 3, if the sludge remains for a long time, it will become anaerobic, and phosphorus will be re-released from the sludge as orthophosphoric acid, deteriorating the quality of the treated water. In order to prevent this, it is necessary to maintain a high Do in the aerobic tank 2 and to
It is necessary to keep the sludge level low.

■ Because the treatment process is complex, sludge return pumps, circulation pumps, etc. are required, and electricity consumption is high.

■ In aerobic IA2, the pH decreases as nitrification progresses, so neutralization treatment by adding an alkaline agent may be necessary.

■ °If nitrogen and phosphorus are removed simultaneously, the nitrogen removal rate is 50%.
It's only ~60 inches.

This invention was made to solve the problems of the conventional simultaneous nitrogen and phosphorus removal method as described above, and removes nitrogen and phosphorus while circulating a mixed solution between an anaerobic tank and an aerobic tank. At this time, the mixed liquid in the anaerobic tank is extracted, oxygen is dissolved in it, this high-Do liquid is introduced into the aerobic tank, and the supernatant liquid and precipitated sludge separated in the aerobic tank are used as treated water and surplus, respectively. The object of the present invention is to provide a method for removing nitrogen and phosphorus that can be removed simultaneously in a simple process without adding any chemicals by removing them as sludge.

The steps of this invention method will be explained with reference to FIG. In the figure, 11 is an aerobic tank, 12 is an anaerobic tank, 13 is a bubbler, and 14 is a settler.

The inside of the aerobic tank 11 is connected to the bottom of the anaerobic tank 12 via a water channel 15 that opens near its upper end.
The inside of bubbler 2 is connected to the lower end of bubbler 13 via a water channel 16 that opens near its upper end. At the bottom of the bubbler 13, a diffuser pipe 18 is provided which sucks the oxygen-containing gas sent through the water channel 1.7 into the liquid in the bubbler 13. Further, the top of the bubbler 13 communicates with the top of the settler 14, and the bottom of the settler 14 is connected to the bottom of the aerobic atmosphere 4111 via the water channel 19.

Note that 20 is a sewage supply pipe, 21 is a trough, 22 is a treated water takeoff pipe, 23 is an excess sludge takeout pipe, and 24 is an exhaust gas takeoff pipe.

That is, the apparatus shown in FIG. 4 has a circulation path from the aerobic tank 11, which returns to the aerobic tank 11 via a water channel 15, an anaerobic tank 12, a water channel 16, a bubbler 13, a settler 14, and a pipe 19. The movement of the liquid within the circulation system path is performed by the upwelling force given to the liquid in the bubbler 13 when the oxygen-containing gas blown into the bubbler 13 from the aeration pipe 18 becomes bubbles and rises inside the bubbler 13. .

The oxygen-containing gas blown into the bubbler 13 is air or a highly concentrated oxygen gas that has a higher oxygen content than air. When air is used, the gas separated from the liquid in the bubble 2-13 and settler 14 is transferred to the exhaust gas outlet pipe 2.
However, if high concentration oxygen gas is used, the gas taken out from the exhaust gas extraction pipes 2 and 4 may still have a high oxygen content. It is desirable to return it to the source of high concentration oxygen gas for reuse.

In the example of FIG. 4, raw sewage flows from the sewage supply pipe 2o into the vicinity of the top opening of the waterway 15, and flows through the waterway 15 while being mixed with the circulating activated sludge and circulating liquid that have risen inside the aerobic tank 11. After that, it enters the anaerobic tank 12. The inside of the anaerobic tank 12 forms an anaerobic zone in which the supply of oxygen is cut off, and therefore the liquid mixture consisting of sewage and activated sludge transferred from the aerobic tank 11 is placed under anaerobic conditions. As a result, No2-N (nitrite nitrogen) and NOs-N (nitrate nitrogen) generated by nitrification in the aerobic tank 11 are
Denitrification occurs through the action of denitrifying bacteria that utilize organic matter present in raw sewage. Note that the flowing raw sewage may be injected into any part of the route from the aerobic zone to the anaerobic zone.

Regarding phosphorus, in the anaerobic tank 12, polyphosphorus stored in intracellular polyphosphorus granules is hydrolyzed into orthophosphoric acid and released into the liquid, as described above.

The mixed liquid that has remained in the anaerobic zone for a predetermined time is transferred to the anaerobic tank 12.
The acid is sucked into the pipe 16 at the upper end, enters the pumper 13, rises in the bubbler 13 together with the oxygen-containing gas blown from the diffuser pipe 18, and then descends in the settler 14. and bubble separation. The bubble-free mixed liquid with high DO flows into the aerobic tank 11 from the bottom through the water channel 19.

The high DO mixture that has flowed into the aerobic tank 11 slowly rises through the aerobic zone formed inside the aerobic tank 11, during which time it undergoes the following steps: 1) Adsorption and oxidation of organic matter.

2) Nitration of ammonia nitrogen.

3) Excessive intake of phosphorus.

will be held.

The mixed liquid that has reached the upper end of the aerobic tank 11 is sucked through the opening of the water channel 15 and sent to the anaerobic tank 12 again.

Furthermore, in the aerobic tank 11, aeration by blowing gas is not performed, and the high DO mixed liquid rises slowly, so that in the tank, the sludge liquid containing a large amount of activated sludge and the sludge liquid located above it are The supernatant liquid separates from each other. In particular, since a large amount of activated sludge is sucked into the waterway 15 from near the opening of the waterway 15, the upward flow rate of the liquid is significantly reduced above the opening surface, making solid-liquid separation more effective. be exposed.

Also, in the process of the mixed liquid rising in the aerobic tank, D.

is highest at the bottom of the aerobic tank 11 and gradually decreases toward the top because it is consumed by biological reactions. This state is effective for nitrification of ammonia nitrogen and subsequent denitrification in the anaerobic tank 12.

The supernatant liquid separated into the upper layer in the aerobic tank 11 overflows the upper edge of the aerobic tank 11 in an amount corresponding to the inflow of new raw sewage, flows into the trough 21, and then flows into the treated water take-out pipe 22. It is then taken out to the outside. Activated sludge that has taken in too much phosphorus is discharged from the excess sludge removal pipe 23 at the bottom of the aerobic zone as necessary. This excess sludge is extracted in an aerobic state, so it stores a large amount of phosphorus, and since it is aerobic, no phosphorus is released.

EXAMPLE Nitrogen and phosphorus were simultaneously removed from standard sewage using the apparatus shown in FIG. 4 under the following operating conditions.

Processing amount: 1~1.5♂/day Circulation t: 12~24nI''/day BOD-8S Load: 01-0.2KtBOD/4S
Table 1 summarizes the properties of raw water and treated water and the removal rate of each component for S-day MLSS: 3000 to 4000 m1F/.

As shown in Table 1, according to the present invention, it is possible to simultaneously remove nitrogen and phosphorus in a simple process without injecting chemicals. Moreover, as is clear from the above results,
Compared to known methods, the nitrogen removal rate is extremely high.
The removal rate of phosphorus is also comparable.

The effects of this invention can be summarized as follows. ■ Nitrogen and phosphorus can be removed simultaneously.

■ No need to add neutralizer or methanol to remove nitrogen.

■ Since sludge is extracted under aerobic conditions, there is no re-release of phosphorus.

■ Since solid-liquid separation is performed under aerobic conditions, there is no impact on treated water due to phosphorus re-release, and water quality is stabilized.

■ Since the aerobic tank has high DOK at the bottom and low DO at the top, it is particularly effective for NHa-H nitrification and denitrification in the anaerobic tank.

■ Liquid circulation was introduced for embarrassment.

Since this is done by the airlift effect of the gas, there is no need for a special circulation device such as a pump, and an energy saving effect can also be obtained.

■ Since no sedimentation pond is required, site area can be saved.

■ Since a large amount of mixed liquid is circulated within the system, it is highly responsive to changes in water quality.

[Brief explanation of drawings]

FIGS. 1, 2, and 3 are system diagrams showing the steps of a conventional sewage treatment method, respectively, and FIG. 4 is a schematic longitudinal sectional view of an apparatus used to carry out the method of the present invention. 11...Aerobic tank, 12...Anaerobic tank, 13...Bubbler, 14...Settler, 18...Aeration pipe, 2o.
... Sewage supply pipe, 21... Trough, 22... Treated water take-out pipe, 23... Excess sludge take-out pipe. Patent applicant: Industrial Development Research Institute Patent applicant: Takuma Co., Ltd.

Claims (1)

[Claims] (1) A mixed solution consisting of sewage and activated sludge is stored in an aerobic zone and an anaerobic zone, respectively, and an oxygen-containing gas is blown into the mixed solution taken out from the anaerobic zone to generate upwelling force. After that, air bubbles are separated to obtain a high-Do mixed solution, and this high-DO mixed solution is introduced into the bottom of the aerobic zone to adsorb and oxidize organic matter, nitrate ammonia nitrogen, and take in excess phosphorus. The supernatant liquid separated in the upper part of the aerobic zone is taken out as treated water,
Excess sludge that has taken in too much phosphorus is extracted from the aerobic zone, and the mixed liquid, which has become low Do while rising in the aerobic zone, is extracted from near the upper end of the aerobic zone and is then transferred to the anaerobic zone. A method for simultaneously removing nitrogen and phosphorus from wastewater, which comprises introducing the raw wastewater into the bottom of the wastewater, denitrifying and releasing phosphorus within the anaerobic zone, and introducing the raw wastewater to any desired location. (2) The method for simultaneously removing nitrogen and phosphorus from wastewater according to claim 1, characterized in that the raw wastewater is introduced into a mixed liquid extraction section in the aerobic zone.