KR100391009B1 - System for Additional Removal of Nitrogen and Phosphorus from Treated Wastewater - Google Patents

Abstract

The present invention relates to a biological treatment system for sewage, and in particular, to be installed in an existing activated sludge process or nitrogen / phosphor removal single sludge process to improve the removal rate of organic matter, nitrogen and phosphorus.

Anaerobic tank / DPB tank (1), aerobic tank (2), anaerobic tank (3), acid fermentation tank (4), storage tank (5) and final sedimentation basin (6). ); Primary sludge is fed to the acid fermentation tank 4; A part of the sludge is supplied from the final settling basin 6 to the anaerobic tank 3, and the aeration liquid is discharged through the final settling basin 6 through the anaerobic tank / DPB tank 1 and the aerobic tank 2; The primary sludge is combined with the sludge returned from the final settling basin (6) in the anaerobic tank (3) via the acid fermentation tank (4) and the storage tank (5), and then again with the aeration liquid in the anaerobic tank / DPB tank (1). A system for discharging through the final settling basin (6) via a DPB tank (1) and an aerobic tank (2).

Description

System for Additional Removal of Nitrogen and Phosphorus from Treated Wastewater}

The present invention relates to a biological treatment system for sewage, and more particularly, to a system for improving the removal rate of organic matter, nitrogen and phosphorus by being installed in addition to an existing activated sludge process or nitrogen / phosphorus removal single sludge process.

Biological nitrogen / phosphorus simultaneous removal systems developed to date are roughly classified into a pre-denitrification process characterized by internal transport and a post-denitrification process characterized by supplying carbon sources from the outside.

The denitrification process includes the modified Badenpo 5-stage process, VIP process, UCT process, and A ₂ / O process, and the actual residence time of the reaction tank is reduced because the internal return of about 2 to 5 times the inflow flow rate is reduced. It has the disadvantage of increasing the facility cost and operating cost, such as the large volume and the large-capacity pump facility. In addition, the phosphorus removal rate is low, which makes it difficult to maintain anaerobic conditions, and in order for biological phosphorus release to occur smoothly, organic matters that are easily biodegradable should be present. This is because biological phosphorus release becomes difficult. Above all, due to the characteristics of Korean sewage with low C / N ratio, it is difficult to remove nitrogen and phosphorus to a satisfactory level only with organic matter contained in sewage.

On the other hand, the post-denitrification process has the advantage of high nitrogen and phosphorus removal rates, but the organic material in the influent cannot be used as a carbon source for the denitrification process, so it has to be dependent solely on an external carbon source, resulting in a high operating cost.

The post-denitrification process varies depending on the type of external carbon source. When methanol or a similar compound is used as the external carbon source, the operation is excellent in stability, high nitrogen removal rate and simple process. On the other hand, it uses very little internal carbon source, so it is expensive to operate.

When acid fermentation of food waste is used as an external carbon source, an additional process for acid fermentation is required, which makes the process complicated and difficult to operate. In addition, when the acid fermentation solution is added in an excessive amount, there is a concern that the nitrogen removal rate may be reduced due to the ammonia contained in the acid fermentation solution.

It is an object of the present invention to provide a system for improving the removal rate of organic matter, nitrogen and phosphorus by additionally installing it in an existing activated sludge process or nitrogen / phosphor removal single sludge process.

1 is a schematic process diagram of a first embodiment according to the present invention.

Explanation of symbols on the main parts of the drawings

1: anaerobic tank / DPB group 2: angi group

3: anaerobic tank 4: acid fermentation tank

The system of the present invention for achieving the above object consists of an anaerobic tank / DPB tank (1) and an aerobic tank (2) and an anaerobic tank (3), an acid fermentation tank (4), a storage tank (5) and a final settling basin (6). From the aeration liquid is supplied to the anaerobic tank / DPB tank 1, the primary sludge is supplied to the acid fermentation tank 4, and a part of the sludge is supplied from the final settling basin 6 to the anaerobic tank 3; The aeration liquid is combined with an acid fermentation solution flowing from the anaerobic tank / DPB tank (1) from the anaerobic tank (3) to remove nitrogen and then discharged through the aerobic tank (2) through the final settling basin (6), and the primary sludge is an acid fermentation tank ( 4) and through the storage tank (5) to join the sludge conveyed from the final settling basin (6) in the anaerobic tank (3), acid fermentation occurs, and after phosphorus release has been achieved in the anaerobic tank / DPB tank (1) again joined with aeration liquid It is characterized in that it is discharged through the final sedimentation basin (6) via / DPB tank (1) and aerobic tank (2).

The configuration of the present invention will be described in detail with reference to FIG. 1 while following the flow of aeration liquid and primary sludge supplied from an existing process.

The aeration liquid (nitric oxide) containing nitrate nitrogen and nitrite nitrogen supplied from the existing process flows into the anaerobic tank / DPB tank (1), and the acid fermentation solution from the anaerobic tank (3) and the anaerobic tank / DPB tank (1) The nitrogen is removed using the organic acid contained in the acid fermentation solution. The effluent from the anoxic tank / DPB tank (1) from which nitrogen was removed flows into the aerobic tank (2) and the dissolved oxygen (DO) is increased to 2 mg / l or more due to aeration to improve sludge sedimentation, and then the final settling basin (6). Solids are separated and discharged.

On the other hand, the primary sludge supplied from the existing process is acid fermented and solid-liquid separated in the acid fermentation tank (4), and then stored in the storage tank (5) is introduced into the anaerobic tank (3). The acid fermentation broth containing the organic acid flowing into the anaerobic tank is combined with the sludge returned from the final settling basin (6), and the phosphorus is discharged from the anaerobic tank (3), and then introduced into the anaerobic tank / DPB tank (1) and joined with the aeration liquid. Then, phosphorous intake is made by denitrifying phosphorus removal bacteria (DPB) and flows into the aerobic tank (2). After entering the aerobic tank, the phosphorus is further ingested in the aerobic tank. In general, phosphorus removal is released by phosphorus-removing microorganisms, accumulating phosphorus under anaerobic conditions, and phosphorus ingested under aerobic conditions. The phosphorus is removed as the process is repeated. However, DPB ingests phosphorus even under anoxic conditions because phosphorus intake in aerobic conditions uses oxygen as an electron acceptor, whereas denitrification and dephosphorylation are performed simultaneously using nitrate or nitrite nitrogen as an electron acceptor under anoxic conditions. .

Next, the role of the reactor constituting the present invention will be described in more detail.

In the anoxic tank / DPB tank (1), denitrification occurs by combining the aeration liquid (nitric oxide water) and the acid fermentation liquid flowing through the anaerobic tank (3) from the existing process. Nitrate nitrogen and nitrite nitrogen are removed using the organic acid contained in the acid fermentation solution as an electron donor. In addition, intake of phosphorus occurs by DPB in which PHB is accumulated in the anaerobic tank 3. In this case, nitrate nitrogen and nitrite nitrogen contained in the aeration liquid are used as the electron acceptor.

In the aerobic tank 2, the DO is increased to 2 mg / l or more, thereby improving sludge settling in the final settling basin 6. In addition, intake of phosphorus using oxygen as the electron acceptor occurs. DO is raised by conventional aeration.

In the anaerobic tank 3, the secondary sludge returned from the final sedimentation basin 6 and the acid fermentation liquor flowing from the acid fermentation tank 4 join. Here, PHB accumulation and phosphorus release by the phosphorus-removing microorganisms contained in the conveying sludge occur, and using an organic acid having a simple structure and easy decomposition is much more efficient than using organic matter in waste water. For this reason, the acid fermentation solution is introduced into the anaerobic tank 3, which is a phosphorus release tank, which is a characteristic difference of the present invention.

In the acid fermentation tank (4), the primary sludge introduced in the existing process is acid fermented. Mainly acetic acid, butyric acid, propionic acid, etc. are produced. These organic acids are biologically decomposed quickly and more easily, and phosphorus and nitrogen removal microorganisms can be used. The residence time is about 1 to 2 days and the solid solution is separated and the supernatant is stored in the storage tank (5) and supplied to the anaerobic tank (3). The acid fermentation mixed liquor can be efficiently separated using a dehydration device or a micro sieve. Adding a small amount of flocculant improves solid-liquid separation.

In the final sedimentation basin 6, the mixed liquor flowing from the aerobic tank 2 is separated into solid-liquid, and the supernatant is finally discharged. The settled sludge is returned to the anaerobic tank (3) and the shear of the existing process.

The configuration of the present invention will become more apparent from the following examples.

<Example>

(1) reaction system

In addition to the existing process (A ₂ / O process), a system consisting of anoxic tank / DPB tank (1) = 8 l, aerobic tank (2) = 4 l, anaerobic tank (3) = 2 l, and acid fermentation tank (4) = 2 l respectively Five experiments were performed.

The aeration liquid of the A ₂ / O process was fed to the anaerobic tank / DPB tank at 4 L per hour, and the primary sludge was collected separately from the sewage treatment plant and fed to the acid fermentation tank at 40 ml per hour (1% of the aeration solution). In the anoxic tank / DPB tank, anaerobic tank and acid fermentation tank, agitator was installed. The sludge of the final sedimentation basin was returned 50% to the aerobic tank of the existing process and 50% to the anaerobic tank.

(2) aeration liquid and primary sludge sample

The amount of aeration was treated by inflow of sewage from Gayang Environmental Office in Gangseo-gu, Seoul by A ₂ / O process, and the first sludge was collected from Seongnam Environmental Office in Seongnam, Gyeonggi-do.

The aeration liquid is described in [Table 1] and the primary sludge in [Table 2], respectively.

Item Aeration pH 6.4 to 7.2 DO (mg / L) 1.8 to 2.5 Alkalinity (mgCaCO ₃ / L) 60 to 110 MLSS (mg / L) 2,500 ~ 3,400 SCOD _Cr (mg / L) 12 to 28 SBOD ₅ (mg / L) 8 to 16 Ammonia (mgN / L) 2 to 4 Nitrite + Nitrate (mgN / L) 6 to 8 S-P (mg / L) 1.1 to 2.5

Item Primary sludge pH 5.3 to 6.2 ORP (mV) -233 to -38 Alkalinity (mgCaCO ₃ / L) 425-1,570 TS (mg / L) 16,000-39,000 VS (mg / L) 11,650 ~ 21,450 TSS (mg / L) 15,900-34,800 VSS (mg / L) 11,400-18,700 TCOD _Cr (mg / L) 22,300-45,000 SCOD _Cr (mg / L) 2,300-4,340

The characteristics of the liquid phase (acid fermentation solution added to the anaerobic tank) separated by acid fermentation of the primary sludge of [Table 2] for 48 hours is shown in the following [Table 3].

Item Acid Fermentation Solution in Anaerobic Tank TCOD _Cr (mg / L) 2,400-2,800 SCOD _Cr (mg / L) 2,100-2,600 VA 1,670-1710 TKN 210 to 230 T-P 25-28

As a result of treating the aeration liquid of [Table 1] with the system of this invention, the characteristics of the outflow water were as [Table 4]. (Total stay time = 3.0 hours)

Item Treated water property Alkalinity (mgCaCO ₃ / L) 118-135 TCOD _Cr (mg / L) 14-21 SCOD _Cr (mg / L) 11-15 SBOD ₅ (mg / L) 2 to 4 TKN (mgN / L) 1 to 3 Ammonia (mgN / L) 1 to 2 Nitrite + Nitrate (mgN / L) 2-3 T-P (mg / L) 0.5 to 0.8

Comparing the nitrogen and phosphorus components of the aeration liquid in [Table 1] and the effluent in [Table 4], the ammonia nitrogen and nitrate nitrogen were reduced to about 1/2, and the phosphorus was reduced to 1/2 to 1/3. Able to know. This means that if the effluent of the conventional denitrification process is further treated with the system of the present invention for 3 hours, nitrogen and phosphorus can be further removed by 50% or more.

SCOD _{Cr was} also reduced from 12 to 28 mg / l to 11 to 15 mg / l it can be seen that a considerable amount of organic matter was removed. It is interpreted that some organic matter contained in the aeration liquid is used in addition to the organic acid supplied from the acid fermentation tank in the denitrification process.

By simply installing the system of the present invention in an existing facility or restructuring the existing process, the insufficient denitrification efficiency of the total denitrification process can be drastically improved.

In addition, by acid-fermenting the primary sludge to supply the organic acid to the carbon source can solve the disadvantage of the post-denitrification process that must be supplied separately from the external carbon source.

Claims (2)

Anaerobic tank / DPB tank (1), aerobic tank (2), anaerobic tank (3), acid fermentation tank (4), storage tank (5) and final settling basin (6). Primary sludge is supplied to the acid fermentation tank 4, and a portion of the sludge from the final settling basin 6 is supplied to the anaerobic tank 3; The aeration liquid is combined with an acid fermentation solution flowing from the anaerobic tank / DPB tank (1) from the anaerobic tank (3) to remove nitrogen and then discharged through the aerobic tank (2) through the final settling basin (6), and the primary sludge is an acid fermentation tank ( 4) and through the storage tank (5) and the sludge conveyed from the final settler (6) in the anaerobic tank (3) to acid fermentation and phosphorus release, and then to the aeration liquid in the anoxic tank / DPB tank (1) again to the aerobic tank Nitrogen / phosphorus additional removal system, characterized in that it is discharged through the final sedimentation basin (6) via / DPB tank (1) and aerobic tank (2). The nitrogen / phosphorus further removal system according to claim 1, wherein a coagulant dispensing device is added to the acid fermentation tank to improve the solid-liquid separation performance of the acid fermentation tank and promote phosphorus removal.