KR910003004B1 - Biological nitrogen and phosphorus removing method and apparatus - Google Patents

Abstract

The treating method for municipal sewage comprises (a) mixing the effluent water (1) from the primary settler and recycled sludge (2) containing low content phosphorus in a microorganism selecting tank (3) placed before the aeration tank (5) to prevent sludge swelling by controlling the growing condition of microorganism, (b) operating the aeration tank (5) under the favorable condition for the growth of nitrated microorganism to change ammoniac nitrogen to nitric acidic nitrogen, (c) introducing part of sludge (8) to a tank (11) to change NOx into nitrogen gas, (d) washing and removing the discharged phosphorns from tank (13) with water (14), and (e) recycling P-insufficient microorganism to (3).

Description

Biological nitrogen and phosphorus removal method and processing device

1 is a process diagram of the present invention.

Figure 2 is a graph of the change of the sludge volume index according to the experimental period of the present invention.

* Explanation of symbols for main parts of the drawings

1: First settler effluent 2: Direct and low phosphorus mixed conveying sludge

3: microorganism selection tank 4: aeration tank influent

5: aeration tank 6: aeration tank effluent

7: final settler 8: return sludge

9: denitrification tank inflow sludge 10: waste sludge

11: denitrification tank 12: denitrification tank effluent mixture

13: dephosphor 14: washing water

15: dephosphorization supernatant 16: dephosphorization return sludge

17: Low phosphorous conveying sludge 18: Direct conveying sludge

19: gas discharge device 20: chemical precipitation tank

21: chemical coagulant 22: chemical treatment water

23: final settler effluent

The present invention utilizes the metabolism and activity of microorganisms in the treatment of urban sewage, and removes organic matter and removes nutrients such as phosphorus and nitrogen. This is a comprehensive wastewater treatment method that solves the sludge swelling phenomenon, which is the biggest problem in operation, so that three functions can be performed by a relatively simple method. It is also applicable to organic industrial wastewater of less than / L.

In general, organic wastewater such as municipal sewage is mainly removed by the standard activated sludge method in the main secondary treatment process, but nutrients such as nitrogen and phosphorus are not treated well by the standard activated sludge method. Since most of nutrients such as nitrogen and phosphorus are discharged in the treated water as it is, the severity of eutrophication problems in closed water such as lake water or domestic water is not solved.

Therefore, various methods have been applied to the tertiary treatment process to remove nitrogen and phosphorus in addition to organic materials. Recently, the application of the method of removing these nutrients from the secondary treatment process by improving the biological treatment method is increasing. As a method of removing nitrogen by the tertiary treatment method, an ion exchange column that selectively replaces ammonia ions is passed, and ammonia is changed to a free ammonia state by increasing the pH, and then contacted with air in an air stripping tower. There is a method of blowing in the air, and the method of removing nitrogen in the secondary treatment step is a basic process of biological nitrification / denitrification. This is a variation of the standard activated sludge method, which changes ammonia nitrogen to nitrate nitrogen by microorganisms. After nitrification, nitrogen nitrate produced has been established as a method of completely removing nitrogen by converting it into nitrogen gas through denitrification by an active microorganism in an anaerobic state.

On the other hand, as a method of removing phosphorus, it is changed to orth-phosphate state, which is a form of precipitation well through biological treatment process, and aluminum compound, iron compound or lime is chemically removed using chemical treatment method in the tertiary treatment step. In many cases, this method requires a large amount of chemicals, which is not only economical, but also causes dehydration of sludge generated. In addition, when these chemicals are administered in the first treatment step before the second treatment, the removal efficiency of the solid substance is high, but in general, the removal efficiency of phosphorus itself is inferior. Therefore, as one of the economical and high phosphorus removal efficiencies that can be substituted for the chemical precipitation process, the biological removal method using the activity of microorganisms has been considered. The microorganisms release phosphorus in the anaerobic state, and accordingly, the microorganisms which are depleted of phosphorus again remove phosphorus simultaneously with the organic substance by using excessive phosphorus in the process of decomposing the organic substance in the aerobic state.

There are three methods that have been developed as a biological removal process of phosphoric acid, postrip, anaerobic / aerobic (A / O) and bardenpho process. Anaerobic-aerobic activated sludge method which connects anaerobic tank and aerobic tank continuously, in normal activated sludge, phosphorus is depleted from microorganism under anaerobic condition, and this is supplemented by aerobic reactor in next stage. It will absorb large amounts of phosphorus. At this time, the content of phosphorus in the sludge that absorbed excessive phosphorus reaches 4-6% in dry amount, so that the phosphorus is removed from the system while removing it in the form of excess sludge. In this method, however, the activated sludge microorganisms are very active in releasing and absorbing phosphorus, but the actual removal of phosphorus is caused by the disposal of excess sludge in the aeration tank, and the effluent mixture of the anaerobic tank is introduced into the aeration tank. Activated sludge, which is less phosphorous by releasing phosphorus, is reactivated in the aeration tank and absorbs less phosphorus than the amount released, but it is limited in its ability to absorb phosphorus. Fluctuation of phosphorus becomes unstable due to changes in water temperature and water quality.

Another method for biological removal is the post-lip method, in which a part of the sludge returned from the final settling of activated sludge method is separated into a dephosphor tank such as a gravity sludge concentration tank to release phosphorus in an anaerobic state, and then phosphorus is concentrated. The supernatant in the solid state is coagulated and precipitated by a chemical coagulant to remove phosphorus and the phosphorus is released and sludge which is insufficient in phosphorus content is returned to the aeration tank to remove phosphorus in excess. However, this post-lip method increases the nitrogen oxide content of sludge flowing into the dephosphorization tank when nitrification is performed in the aeration tank, which inhibits the phosphorus release of microorganisms. Therefore, the contact time is increased to minimize the effect of nitrogen oxide. Since the size of the reaction tank must be increased and the return sludge stays in the anaerobic demineralization tank for a long time, activated sludge microorganisms are killed.

The methods developed above are patented by anaerobic / aerobic phosphorus removal method described above by Korean Patent Application No. 82-1616 (notice 87-107) of Matsuo Yoshidaka, and Gilbert V. Levin et al. Patent 4,141, 822 describes the basic concept of the post-lip method.

On the other hand, the post-lip method removes phosphorus by discharge of dephosphorized supernatant rather than sludge waste, so it is influenced by organic matter / phosphorus (BOD / P) of influent, microbial stay time in aeration tank or phosphorus / volatile suspended solids (P / VSS) ratio. Since it receives less phosphorus, the removal efficiency of phosphorus is stable and it is easy to operate, which has considerable flexibility in removal of phosphorus.

The present inventors installed an anaerobic denitrification tank in front of the dephosphorization tank in order to make use of the characteristics of the post-lip method and to improve the efficiency of nitrogen removal in addition to organic substances and phosphorus, thereby changing nitrogen oxides (NOx) to nitrogen gas (N ₂ ) in the denitrification tank. The present invention was based on the invention that it can be improved by the technology that treats nitrogen at the same time. By eliminating this, it provides a method to remove phosphorus economically and efficiently. In addition, when the nitrification-denitrification reaction is performed to remove nitrogen at the same time, the organic load (F / M ratio) required for the treatment process must be designed and operated at a low level. In many cases, it causes sludge bulking, one of the biggest problems in operation. Therefore, in order to solve this problem, the inventor introduced the concept of a microbial selector and installed a microbial selective tank in front of the aeration tank to mix the direct and low phosphorus mixed carrier sludge with the initial settler effluent for the first time. (Flock) forming microorganisms were selected as the predominant species compared to filamentous microorganisms causing sludge swelling, so that sludge swelling could be prevented.

The present invention controls the growth conditions of microorganisms by controlling the growth conditions of microorganisms by mixing the first settling effluent and the direct and low phosphorus mixed conveying sludge in the microbial selection tank installed in front of the aeration tank. The sludge swelling phenomenon is suppressed by being selected as a dominant species compared to the filamentous microorganism causing the phenomenon, and the aeration tank preferably has an organic load of 0.5 kg BOD / kg MLVSS.d or less to provide favorable conditions for the growth of nitrification microorganisms. By operating below 0.3kg BOD / kg ML SS.d, ammonia nitrogen is converted to nitrate nitrogen, and a part of the return sludge is introduced into the denitrification tank installed in the dephosphorization tank. Nitrogen oxides, along with the removal of nitrogen from the whole, It does not interfere, and it is possible to remove phosphorus efficiently, and the denitrification tank effluent mixture is introduced into the dephosphorization tank, which also provides anaerobic conditions, allowing microorganisms to release phosphorus in the cells, and is released to clean the phosphorus contained in the sludge mixture. Biological nitrogen and phosphorus removal method and treatment apparatus to improve phosphorus aeration efficiency in influent water by washing with water to efficiently absorb phosphorus when microorganisms in a state of phosphorus deficiency are returned to aeration tank through a mass selection tank To provide.

The content of the present invention will be described in detail with reference to the process diagram of FIG. 1 as follows.

The municipal sewage 1 treated first in the initial settler (not shown) is a low phosphorus-containing conveying sludge 17 that is returned after passing through the sludge 18 and the dephosphorization tank 13 directly transferred from the final settler 7. With the microbial selection tank (3) and then mixed in contact with the aeration tank (5) is introduced (4).

The structure and operation of the aeration tank (5) can use the technique used in the general activated sludge method, but it is preferable to connect the four or more reactors in series rather than a fully mixed reactor, the reaction time so that sufficient organic matter removal and nitrification can occur The retention time (or residence time) is maintained at 6-8 hours, and the solid residence time is maintained for at least 5 days for the growth of nitrification microorganisms.

In addition, the dissolved oxygen concentration in the aeration tank 5 is preferably maintained at 2 mg / l or more throughout the aeration tank 5 so as not to interfere with maintaining the anaerobic state in the denitrification tank 11 in the conveying sludge system. The dissolved oxygen concentration of the final reaction tank of the aeration tank (5) should be adjusted, but it is advantageous to supply only enough to maintain the state of mixing or no air supply to the reaction tank. The aeration tank 5 absorbs phosphorus together with organic matter in the mixed solution by active respiration and metabolism of microorganisms constituting activated sludge, uses organic matter as a carbon and energy source, and oxidizes phosphorus to form polyphosphate granules in microbial cells. Start saving.

Some of the conveying sludge 8 which is sedimented and separated from the final settler 7 and returned to the aeration tank 5 passes through the dephosphorization tank 13 to release phosphorus and becomes a microorganism in a state in which phosphorus content is insufficient. It actively absorbs phosphorus and at the same time nitrification occurs by the nitrifying microorganisms in the sludge, and the ammonia nitrogen is converted to nitrate nitrogen through nitrite nitrogen. In this way, the microorganisms grown through the absorption and nitrification of phosphorus and the oxidation of organic matter form activated sludge and are discharged from the aeration tank 5 to be introduced into the lowest settling cell 7, where the sludge is sedimented and the final settling effluent 23. Is discharged as is. The settled concentrated sludge is returned to the microbial selection tank 3, but part of it is disposed of in order to maintain a proper concentration of microorganisms in the aeration tank 5, and the amount of sludge 10 discarded is the sludge residence time in the aeration tank 5. It may be determined to maintain for five days or more, and a portion of the aeration tank effluent 6 and the like discharged from the aeration tank 5 may be discharged to the waste sludge 10.

At this time, a part of the conveying sludge 8 is introduced into the denitrification tank 11, and the denitrification tank inlet sludge 9 is denitrified in an anaerobic state without dissolved oxygen so that nitrogen oxide is changed to nitrogen gas and phosphorus contained in the sludge at the same time. It begins to be released. The amount of denitrification tank inflow sludge (9) which is not directly conveyed to the microbial selection tank (3) out of the total return sludge (8) but undergoes denitrification and dephosphorization is 50% of the total amount of return sludge (8) to maintain a high nitrogen removal rate. As much as possible, the return sludge is subjected to denitrification and dephosphorization as much as possible. The structure of the denitrification tank 11 is hermetically sealed so that complete mixing by the stirrer occurs and the generated nitrogen gas is discharged through the gas discharge device 19 located above the denitrification tank 11.

In the conventional post-lip method, when sludge is not precipitated in the final settler, some amount of oxygen may be introduced into the sludge to be returned. Therefore, it is difficult to maintain an anaerobic state while staying in a dephosphor, or the phosphorus release is interrupted for a long time. As the residence time is required, there is a problem that the facility becomes large, but in the present invention, the denitrification tank 11 is placed in front of the dephosphorization tank 13 to maintain the residence time of the denitrification tank 11 at about 8 hours to proceed with the denitrification reaction. By removing the oxide by converting it into nitrogen gas, the nitrogen oxide in the dephosphorization tank 13 eliminates the factor that prevents the release of phosphorus, and the phosphorus emission can be expected to some extent. Therefore, the function of the denitrification tank 11 is essential and important in the present invention. to be.

As described above, the denitrification tank effluent mixture 12 in which the nitrogen oxide is removed from the denitrification tank 11 and the phosphorus is partially released from the sludge is introduced into the denitrification tank 13 to be solid-liquid separated. At this time, the solid-liquid separation is caused by gravity settling, and the release of phosphorus from the microorganisms continues in the sludge formed under the dephosphorization tank 13, and the released phosphorus is desorbed by washing water 14 flowing in an upward flow through the sludge layer. Phosphorus discharged in the symbolic water in the upper part of the artificial 13 is concentrated to remove phosphorus more efficiently. At this time, the dephosphorized supernatant effluent 15 in which the phosphorus is concentrated is sent to the chemical precipitation tank 20 to form a chemical coagulant (21). After coagulation and precipitation of phosphorus by the chemical treatment water 22 is discharged. Here, the washing water 14 may be used by circulating the first settling effluent 1, the final settling effluent 23, or the chemical treatment water 22, which is a symbol water of the chemical settling tank 20, and the like. Phosphorus treatment water 22, which is a symbol water of the chemical precipitation tank 20 having a low phosphorus concentration, was used. The phosphorus-released activated sludge microorganisms thus discharged from the dephosphorization tank 13 and washed by the washing water 14 are returned to the aeration tank 5 through the microorganism selection tank 3 to contact the initial settler effluent water 1. The microorganisms are actively absorbed by these microorganisms to efficiently remove phosphorus in the initial settler effluent (1).

In the anaerobic-aerobic activated sludge method, all of the phosphorus released from the anaerobic tank flows into the aeration tank and is reabsorbed. Therefore, the phosphorus absorption capacity of the activated sludge becomes almost saturated, and the phosphorus contained in the inlet is slightly reduced by the excess sludge in the aeration tank. While only the increase of is absorbed, the absorption of phosphorus is slowed as a whole, and the removal of phosphorus may not occur efficiently. However, in the present invention, the phosphorus discharged from the dephosphorization tank 13 is used in the state of insufficient phosphorus content by using washing water. By transferring the microorganisms to the aeration tank 5 through the microorganism selection tank 3, the absorption of phosphorus contained in the initial settler effluent 1 can be further increased.

Meanwhile, the dephosphorization tank 13 returns the dephosphorization sludge 16 to about twice as much as the denitrification tank effluent mixture 12 so that sufficient phosphorus release and cleaning can occur, and the sludge residence time is maintained at least 10 hours under anaerobic conditions. It is good. In addition, in order to clean the phosphorus discharged from the dephosphor 13, the inflow rate of the washing water 14 is maintained at 0.1-0.3L / g.SS.

In order to prevent sludge swelling, which is another object of the present invention, in the microbial selection tank (3) installed in front of the aeration tank (5), the initial settling effluent (1) and the mixed transport sludge (2) containing direct and low phosphorus are mixed for a short time. Flock-forming microorganisms that have a low absorption capacity of the substrate and have a higher absorption capacity of the substrate than the filamentous microorganism causing the sludge expansion phenomenon are selected as the dominant species and form a strong floc by breeding in the entire aeration tank 5 to prevent sludge expansion. . The residence time in the microbial selection tank (3) should be less than 30 minutes per tank, the number of microbial selection tanks (3) required to install two or more, and the microbial selection tank (3) to be completely mixed Provide sufficient air to maintain aerobic conditions.

Compared with the conventional post-lip method, the present invention described above provides a method of removing the phosphorus which is more stable than the conventional postlip method and removes nitrogen and removes nitrogen. B) removal of nitrogen by denitrification of nitrogen oxides in the denitrification tank (11), and c) suppression of the effects of nitrogen oxide on phosphorus release in the dephosphorization tank (13) by the removal of nitrogen. D) The efficiency of dephosphorization can be further improved by using the washing water 14 in the dephosphorization tank 13, and e) the sludge swelling can be suppressed by the installation of the microorganism selection tank 13.

Example 1

The influent sewage used in this experiment was randomly used daily as domestic sewage and the characteristics of the influent sewage used as sample for 6 months are shown in Table 1.

[Table 1. Characteristics of Influent Sewage] Unit: ㎎ / ℓ

The experimental treatment facility was constructed as shown in Figure 1. The function is as follows.

The size of the microbial selection tank used to prevent sludge swelling due to low organic load was 1/74 of this aeration tank. The volume of the aeration tank was 80L, which was operated at low organic load to proceed nitrification. Air was supplied by Difusser and the flow pattern was Plug Flow. The sedimentation tank was conical and some of the precipitated sludge was returned to the aeration tank through the microbial selection tank as the returning sludge, and some were circulated to the denitrification tank and the dephosphorization tank.

The denitrification tank made four ports to enable volume changes up to 6-40L. The top of the denitrification tank was sealed to prevent air from penetrating, and a stirrer was also installed for complete mixing of the sludge in the denitrification tank. In the dephosphorization tank, sludge that passed through the denitrification tank is introduced, and phosphorus is released from the cells in anaerobic state, and the released phosphorus is discharged from the sludge by the flowing water which is supplied from the sludge. Concentrated.

The operation conditions of the aeration tank were determined as follows to sufficiently proceed with nitrification, and the experiment was performed in two steps as shown in Table 2 and Table 3 to obtain the optimum conditions for the removal of nitrogen and phosphorus.

* Organic load: 0.3㎏ BOD / ㎏ MLVSS.d

* Sludge Transport Rate: 80% of influent

* Hydraulic stay time: 8 hours

First, in step 1, as shown in Table 2, in order to determine the denitrification tank residence time having the highest nitrogen removal rate, the denitrification tank residence time was changed according to the return sludge distribution ratio to determine the optimum denitrification tank residence time for nitrogen removal. In step 2, the cleaning rate is gradually changed from 0.7L / g.SS to 0.1L / g.SS as shown in Table 3 to maintain the optimum denitrification tank residence time determined in step 1 and to determine the minimum amount of cleaning for dephosphorization. Changed.

[Table 2. Phase 1 Experimental Conditions]

[Table 3. Two stage test]

The results of the first stage are shown in Table 4, and the suitable conditions for nitrogen removal are 8 hours of denitrification tank residence time and 3/8 of the return sludge and 5/8 of denitrification and dephosphorization. Was determined. The results of the investigation of the cleaning rate to obtain high phosphorus removal efficiency under these conditions are shown in Table 5. As a result, it can be seen that the phosphorus removal efficiency of 91% can be obtained at the cleaning rate of 0.1-0.3L / g.SS. The cleaning rate 01L / g.SS is to use a flow rate equivalent to 50% of the dewatering influent.

[Table 4. Changes in Nitrogen Removal Rate with Denitrification Tank Retention Time] Unit: (%)

[Table 5. Change of Phosphorus Removal Rate According to Cleaning Rate]

In order to investigate the control of sludge swelling by microbial selection tank, two microbial selection tanks corresponding to 1/74 of the aeration tank volume after operation of the sludge swelling occurred without operating the microbial selection tank were installed. As a result of the installation, the sludge expansion phenomenon is shown in FIG. Sludge swelling can be determined by measuring the Sludge Volume Index, and when the sludge drip index is 150 mg / L or more, it is generally swelled and the sludge is considered to be normal.

Table 6 summarizes the removal efficiency of organic substances, nitrogen and phosphorus in the above experimental results.

TABLE A

Comparative Example 1

The results of the operation of the conventional standard activated sludge method with the same aeration tank and the same operating conditions as those of Example 1 are shown in Table 7 below.

TABLE B

Comparing Table 6 of Example 1 and Table 7 of Comparative Example 1, organic matter removal and nitrification showed a similar removal rate to 90% or more, and the removal rates of total nitrogen (TN) and total phosphorus (TP) were shown in Table 6 Compared with each of about 90%, Table 7 shows that the total nitrogen removal rate is about 36% and the total phosphorus removal rate is about 31%, which is superior to the method of the present invention.

Claims (6)

Sewage swelling phenomenon is controlled by controlling the growth conditions of microorganisms by controlling the growth conditions of microorganisms by mixing the initial settling effluent (1) and the mixed and returning sludge containing sludge (2) directly into the microorganism selection tank (3) installed in front of the aeration tank (5). The aeration tank 5 operates under favorable conditions for the growth of nitrifying microorganisms, converts ammonia nitrogen to nitrate nitrogen, and introduces a part of the return sludge 18 into the denitrification tank 11 to reduce nitrogen oxides (NOx) in the anaerobic state. ) To nitrogen gas (N2) to remove nitrogen from the system and prevent the nitrogen oxides from interfering with the release of phosphorus from the dephosphorization tank (13) to effectively remove phosphorus and denitrification tank effluent mixture (12) It enters the dephosphorization tank 13 to provide an anaerobic state so that the microorganisms release phosphorus in the cells, and the released phosphorus is washed and removed using the washing water 14 and the phosphorus is insufficient. Biological nitrogen and phosphorus removal method of transferring the changed microorganisms in the aeration tank (5) via the selected microorganism (3). The microorganism selection tank (3) according to claim 1 is to be at least two, and the residence time is within 30 minutes per tank to supply a sufficient air to maintain the aerobic state and active absorption of the substrate in the microorganism selection tank (3) By setting the conditions so as to induce sludge phenomena at low organic load, while suppressing the growth of filamentous microorganisms with low absorption capacity of substrate and floc forming microorganisms with high absorption capacity are selected as the predominant species, so that they grow in the entire aeration tank (5). The formation of a strong floc prevents sludge swelling, and the aeration tank 5 has an organic load of 0.5 kg ROD / kg MLVSS.d or less suitable for nitrification and a solids retention time (SRT) of 5 days or more, and the dissolved oxygen concentration of the mixed solution 2 Biological nitrogen and phosphorus removal method which can keep sludge in the condition which keeps more than mg / L to change ammonia nitrogen to nitrate nitrogen method. The residence time of the aeration tank (5) is 6-8 hours, the denitrification tank (11) is sealed to maintain the residence time of about 8 hours, the residence time of the dephosphorization tank (13) is more than 10 hours and washing water (14) removes biological organic matter and prevents sludge swelling at a cleaning rate of 0.1-0.3 L / g.SS using the initial sediment effluent, the final sediment effluent or the chemical treatment water 22, which is the symbol water of the chemical sedimentation tank 20, and the like. Method for removing biological nitrogen and phosphorus, characterized in that. A method for removing biological nitrogen and phosphorus by placing a microbial selection tank (3) in front of the aeration tank (5) in organic wastewater treatment. A method for removing biological nitrogen and phosphorus by placing a denitrification tank (11) in front of a dephosphorization tank (13) in organic wastewater treatment. The microbial selection tank 3 is installed in front of the aeration tank 5, and the returning sludge is separated, and a part (1/2 or less) of the returning sludge is directly returned to the aeration tank 5 through the microbial selection tank 3 and the rest is nitrogen and Organic wastewater sewage treatment apparatus characterized in that the denitrification tank (11) installed in front of the dephosphorization tank 13 to go through the denitrification and dephosphorization process for efficient removal of phosphorus.

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