JP4587559B2 - Method and apparatus for removing nitrogen from sludge return water - Google Patents

Description

【００５７】
【発明の効果】
以上のように本発明によれば、生物付着担体を活性汚泥と併用し、硝化槽のＭＬＤＯを所定の低い範囲に維持するようにしたことにより、脱窒槽で脱窒と生汚泥の可溶化とを進行させることができるとともに、硝化槽で硝化と脱窒とを同時に進行させることができ、生汚泥を最大限に利用することが可能になり、従来に比べて生汚泥必要量の低減を実現できる。
【図面の簡単な説明】
【図１】本発明の汚泥返流水中の窒素除去方法が行われる下水処理場の処理フローを示す説明図である。
【図２】図１に示した処理フローの内、汚泥返流水中の窒素除去工程を詳細に示した説明図である。
【図３】本発明の汚泥返流水中の窒素除去方法を例示する装置構成図である。
【図４】本発明の汚泥返流水中の窒素除去方法を例示する他の装置構成図である。
【符号の説明】
20 造粒脱リン処理液（汚泥返流水）
22 脱窒槽
24 硝化槽
25 硝化循環液
27 沈殿槽（汚泥分離返送系）
28 返送汚泥
29 脱窒素処理水
31 破砕生汚泥
33 送泥ポンプ
34 生物付着担体
37 ＯＲＰ計
38 散気装置
39 ＤＯ計
40 コンプレッサ
41 制御装置[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method and apparatus for removing nitrogen in sludge return water that removes nitrogen from sludge return water returned to a water treatment system.
[0002]
[Prior art]
A large amount of organic sludge generated in water treatment facilities such as sewage treatment plants is processed through processes such as concentration, digestion, and dehydration, and the separated liquid generated in each treatment process is returned to the water treatment system. Yes. However, since ammonia nitrogen and orthophosphoric acid phosphorus are contained at high concentrations in the return water, the load accompanying the return causes deterioration of the quality of treated water in the water treatment system.
[0003]
In water treatment facilities that perform biological denitrification and biological dephosphorization at the same time, there is a case where denitrification and dephosphorization deteriorate due to insufficient BOD in the water treatment system due to the load of ammonia nitrogen and orthophosphoric acid phosphorus from the return water. Not a few. On the other hand, in water treatment facilities that carry out coagulation dephosphorization without biological dephosphorization, there is little discharge of phosphorus during anaerobic digestion of sludge, and the phosphorus content in the dehydrated filtrate of digested sludge is low. Therefore, the load on the water treatment system can be reduced by taking a measure for reducing ammonia nitrogen. That is, the phosphorus concentration in the return water varies depending on whether biological dephosphorization is being performed in the water treatment system or whether coagulation dephosphorization is being performed.
[0004]
When the phosphorus concentration is high, phosphorus in the return water can be recovered as magnesium ammonium phosphate particles by the technique disclosed in, for example, Japanese Patent Publication No. 7-12477. In this case, the phosphorus load of the water treatment system is reduced to about It can be reduced by 40%.
[0005]
Ammonia nitrogen can be nitrified to about 90% into nitrate nitrogen by a technique using a bioadhesive carrier as disclosed in JP-A-9-75992 and JP-A-9-167875. Denitrification after nitrification can be carried out by a method using raw sludge that has been first separated and separated in a settling basin as a BOD source for denitrification, which was proposed by Japanese Patent Application Laid-Open No. 11-104693. . Japanese Patent Laid-Open No. 11-104693 describes a compact processing method using a carrier, but the carrier separation screen is clogged by the fiber contained in the raw sludge, and the raw material as a BOD source is clogged. Since the properties of sludge change seasonally, the present applicants further disclosed in Japanese Patent Application No. 11-326210 a raw material in which the fiber content was cut by crushing with a stone mill crusher to increase the soluble BOD. It proposes a more desirable method of using sludge.
[0006]
[Problems to be solved by the invention]
However, raw sludge can be used as a BOD source as described above, and can be recovered as energy by converting it to methane gas in an anaerobic digester, and the fiber content in it improves the dewaterability of the sludge. Therefore, it is desirable that the amount of raw sludge used for the treatment of sludge return water is small. However, although the amount of raw sludge used can be reduced by adding the process of increasing soluble BOD using the above-mentioned stone mill type crusher, the effective utilization is still low when viewed from the total BOD in raw sludge. Increasing the degree and reducing the amount used has been a problem.
[0007]
[Means for Solving the Problems]
As a result of diligent research to solve the above problems, the present inventors maintain the MLDO in the nitrification tank at a low concentration and reduce the residence time of the crushed raw sludge when removing nitrogen from the sludge return water using the crushed raw sludge as a BOD source. The present inventors have found that the amount of raw sludge used can be reduced by adjusting the amount.
[0008]
  That is, the present invention allows the sludge return water returned from the sludge treatment system for treating sludge generated in the water treatment system to flow into the nitrification tank and the denitrification tank sequentially.Then, a part of the nitrification liquid flowing out from the nitrification tank is circulated and returned to the denitrification tank, the sludge is separated from the remainder of the digestive liquid flowing out from the nitrification tank, and the separated sludge is returned to the denitrification tank.When biologically nitrifying and denitrifying, sludge return is performed by crushing raw sludge settled and separated in the first sedimentation basin of the water treatment system and adding it as a BOD source to the nitrification solution nitrified in the nitrification tank. A method for removing nitrogen from running water, wherein in the nitrification tank, a bioadhesive carrier is introduced, and the dissolved oxygen concentration in the liquid mixture in the tankTo 1-5 mg / LPerform nitrification under controlled conditionsAnd the retention time of the crushed raw sludge in the nitrification tank and denitrification tank is 1 to 10 daysIt is characterized by that.
[0009]
  Moreover, the present invention is characterized in that in the above-described method for removing nitrogen in the sludge return water, a bioadhesive carrier is introduced into the denitrification tank.
  The present invention further includes a denitrification tank charged with activated sludge, a nitrification tank having aeration means and charged with activated sludge and a bioadhesive carrier, and a sludge treatment system for treating sludge generated in a water treatment system. Sludge return water returned to the water treatment system sequentially flows into the denitrification tank and the nitrification tank, and a water supply system for circulating and returning a part of the nitrification liquid flowing out from the nitrification tank to the denitrification tank, and the water treatment system A raw sludge injection means for injecting the crushed raw sludge crushed from the raw sludge separated and separated in the first settling basin into the circulation return path from the nitrification tank to the denitrification tank, and the remainder circulated and returned to the denitrification tank A sludge return system that separates sludge from the nitrification liquid and returns the separated sludge to the denitrification tank, a dissolved oxygen concentration meter that measures the dissolved oxygen concentration of the mixed liquid in the nitrification tank, and the in-vessel mixing of the nitrification tank The dissolved oxygen concentration of the liquid1-5mg / LControl means for controlling the amount of air diffused by the air diffuser so as to be maintained at the same time and controlling the amount of raw sludge injected by the raw sludge injecting means to a predetermined amount.In addition, the residence time of the crushed raw sludge in the nitrification tank and the denitrification tank is controlled for 1 to 10 days.A device for removing nitrogen from sludge return water.
[0010]
According to the above configuration, in the denitrification tank, the oxidized nitrogen contained in the sludge return water and the nitrification liquid flowing in through circulation return from the nitrification tank in the former stage or from the nitrification tank in the latter stage is crushed raw sludge by the activated sludge. Is reduced and denitrified in the state of using as a BOD source (hydrogen donor). At this time, since the crushed raw sludge is decomposed as denitrification proceeds, BOD derived from SS of the crushed raw sludge is also converted to S-BOD, and a tendency for S-BOD to increase is recognized. As much as possible.
[0011]
In the nitrification tank, ammonia nitrogen, activated sludge, and crushed raw sludge with a high S-BOD content are brought in by sludge return water and denitrification liquid flowing in from the previous denitrification tank or circulating return from the latter denitrification tank. Since the dissolved oxygen concentration (MLDO) of the liquid in the nitrification tank is controlled within a predetermined low range, a system is formed in which nitrification and denitrification proceed simultaneously in an aerobic atmosphere. That is, in the aerobic atmosphere near the activated sludge in the floating state and near the surface of the bioadhesive carrier, nitrification reaction that oxidizes ammonia nitrogen and hydrolysis of crushed raw sludge (solubilization of BOD derived from SS) occur. In the anaerobic atmosphere inside the carrier, S-BOD having a high concentration due to the inflow from the denitrification tank is supplied, and a denitrification reaction occurs.
[0012]
In this way, the crushed raw sludge is efficiently solubilized and used to the maximum as T-BOD, so that the amount of raw sludge used can be reduced as compared with the conventional case. When a bioadhesive carrier is also introduced into the denitrification tank, microorganisms can be kept at a high concentration in the denitrification tank, and the denitrification efficiency can be increased.
[0013]
As the bioadhesive carrier, a BOD or a carrier that flows in the tank by a bubble ejected from an air diffuser such as an air diffuser installed in the lower part of the nitrification tank or by a stirring means generally installed in the denitrification tank is used. It is desirable in terms of contact efficiency with nitrogen and oxygen. At least the bioadhesive carrier to be introduced into the nitrification tank needs to be a porous carrier that allows microorganisms to permeate and adhere to the core, and is preferably capable of utilizing capillary action.
[0014]
Considering the residence time of raw sludge in the tank, it is not possible to completely consume the total BOD, especially the BOD component derived from SS of raw sludge, by circulating it with activated sludge. It is important to increase the utilization by. The sludge residence time required for this varies depending on the water temperature, but requires about 1 to 10 days. It is about 1 to 3 days in the high water temperature period and about 3 to 6 days in the low water temperature period. One-pass is possible if such sludge residence time can be secured, but it is not practical because a tank capacity corresponding to the sludge residence time is required, and circulation is necessary.
[0015]
If the sludge retention time is too short, the effective utilization of raw sludge will be low, and the amount of input to the denitrification tank will have to be increased. If the sludge residence time is too long, hydrolysis and oxidation of organic nitrogen derived from raw sludge will progress too much, so that the nitrogen content of the solubilized raw sludge will not be nitrified in the nitrification tank, and there will be a lot of ammonia nitrogen in the treated water Will remain. Moreover, since SS of raw sludge increases more than the proliferation of activated sludge and the ratio of raw sludge in floating sludge becomes high, it is not preferable. The greater the amount of raw sludge input, the higher the proportion of raw sludge.
[0016]
In other words, in order to keep the ammonia nitrogen elution amount low and to keep the activated sludge ratio high, it is necessary to reduce the sludge retention time without excessively adding raw sludge, In order to reduce the input amount of raw sludge and increase the effective utilization, there is a conflicting aspect that a long sludge residence time is required.
[0017]
For this reason, it is necessary to control the input amount while ascertaining the situation where raw sludge is solubilized and used for denitrification. That is, in the denitrification tank, it is important to link the monitoring of the progress of denitrification and the input of raw sludge. The total BOD of raw sludge is about 5000 mg / L with no seasonal variation, and the soluble BOD is about 1500 to 2500 mg / L depending on the state of crushing and seasonal variation, so theoretically raw sludge can be used if the total BOD can be used effectively The amount can be reduced to about 1/3.
[0018]
For this purpose, the raw sludge is crushed to help solubilization. According to the crushing process, the amount of ammonia nitrogen is hardly increased, and the soluble BOD can be increased mechanically. As the crusher, for example, a stone mill crusher can be used. The sludge residence time can be shortened by using the wet mill bead method (described in Japanese Patent Application No. 11-326210), which is considered to have the highest solubilization rate after crushing with a stone mill.
[0019]
If the crushing treatment is not performed, the carrier can not be used because fibers are mixed, and the biological reaction can be performed only with activated sludge, so denitrification in the nitrification tank cannot be expected. It is necessary to complete the treatment in the denitrification tank. Therefore, there is a decrease in solubilization speed due to the absence of crushing treatment, a decrease in biological treatment capacity due to the absence of a carrier, and an increase in organic nitrogen and ammonia nitrogen due to biological solubilization. It is assumed that the denitrification tank must be made 6 times larger and the nitrification tank about 2.5 times larger than the case where it is performed.
[0020]
Moreover, the utilization rate of the crushed raw sludge is raised by using floating activated sludge together with a bioadhesive carrier. The utilization rate of raw sludge is considered to be related to the residence time as described above, and it is thought that it can be used more effectively than the one-pass by recycling, but the raw sludge is solubilized only with the raw sludge and the bioadhesive carrier. Under the influence of the phenomenon, the nitrification ability may decrease. On the other hand, when floating activated sludge exists, activated sludge acts as a BOD adsorption medium, buffers it so as to minimize the influence on nitrification, and flows into the denitrification tank while adsorbing BOD, Increase the use of BOD.
[0021]
  Furthermore, in order to increase the effective utilization of raw sludge, a dissolved oxygen concentration meter is installed in the nitrification tank to control the MLDO concentration. When activated sludge and bioadhesive carrier are used in combination, MLDO of the mixed solution in the nitrification tank is 1 to 5 mg / L.It is necessary to control, Preferably 2 to 4 mg / L, more preferably 2 to 3 mg / L. When MLDO is higher than this range, organic nitrogen contained in raw sludge is converted to ammonia nitrogen, which is combined with the quantitative influence of raw sludge, leading to deterioration of treated water quality. When MLDO is lower than this range, the nitrification performance of the activated sludge that is maintained at a high concentration by the bioadhesive carrier is not sufficiently exhibited, leading to deterioration of the treated water quality.
[0022]
In addition, in order to avoid excessive input of raw sludge, measures such as measuring the oxidation-reduction potential (ORP) of the mixed liquid in the denitrification tank with an ORP meter and maintaining it within a predetermined low range are taken. The input amount of raw sludge is controlled so that the ORP of the mixed liquid in the denitrification tank is −100 mV or less, preferably −150 to −350 mV, more preferably −170 to −240 mV. If the ORP is higher than this, the reduction reaction is less likely to occur, so NOx-N, which is oxidized nitrogen, remains, and the denitrification effect is reduced. When ORP becomes lower than this, it means that raw sludge is excessively charged, and organic nitrogen derived from raw sludge increases.
[0023]
However, the control value by the sensor generally tends to make the indicated value unstable. In particular, since the ORP has a large variation in data, it is not suitable for wastewater with small concentration fluctuations such as sludge return water to be treated here. It seems to be appropriate to use it as a guideline, and actually inject a fixed amount by using a timer while comparing with the water quality. Sludge return water and raw sludge have seasonal variations, although there are few, it is optimal to create multiple types of timer control patterns that take into account each seasonal variation and control the sludge injection rate accordingly.
[0024]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below with reference to the drawings.
FIG. 1 shows a treatment flow in a water treatment facility equipped with a water treatment system and a sludge treatment system. In the water treatment system, the influent raw water 1 is first introduced into the biological reaction tank 3 after removing impurities and sand in the sedimentation basin 2 and biologically removed organic matter, nitrogen and phosphorus, and finally the final sedimentation basin 4 It flows out as treated water 5 after passing through.
[0025]
The raw sludge 6 precipitated in the first settling basin 2 and the excess sludge 7 precipitated in the final settling basin 4 are guided to the sludge treatment system and processed. That is, the raw sludge 6 is guided to the gravity concentration tank 8 to be the concentrated raw sludge 9, and the excess sludge 7 is guided to the mechanical concentration tank 10 to be the concentrated excess sludge 11. The concentrated excess sludge 11 and a part of the concentrated raw sludge 9 are guided to the anaerobic digestion tank 12 and subjected to anaerobic digestion, and the volume is reduced as methane gas is generated.
[0026]
The anaerobic digested sludge 13 is guided to a dehydrator 14 and separated into a dehydrated cake 15 and a dehydrated filtrate 16. The dehydrated cake 15 is carried out of the system, and the dehydrated filtrate 16 is returned to the water treatment system as sludge return water. Washed away. The gravity concentrated separation liquid 17 separated in the gravity concentration tank 8 and the mechanical concentrated separation liquid 18 separated in the mechanical concentration tank 10 are also returned to the water treatment system.
[0027]
At that time, ammonia nitrogen and phosphate phosphorus are released from the concentrated raw sludge 9 and the concentrated surplus sludge 11 in the anaerobic digestion tank 12, and these nutrient salts become dehydrated filtrate 16 when the anaerobic digested sludge 13 is dehydrated. In order to shift, the dehydrated filtrate 16 is first guided to the granulation dephosphorization apparatus 19 where the phosphorous phosphorus is crystallized by adding magnesium and recovered as fertilizer, and the granulation dephosphorization treatment liquid 20 is removed from the nitrogen. Led to. However, phosphorus removal treatment such as coagulation dephosphorization may be performed in a water treatment system. In this case, the phosphorus concentration is not so high even after anaerobic digestion, so anaerobic digestion solution 21 (and dehydrated filtrate 16). Is directly introduced into the nitrogen removal step.
[0028]
In the nitrogen removal step, the denitrification treatment liquid 20 or the anaerobic digestion liquid 21 (hereinafter collectively referred to as the granulation dephosphorization treatment liquid 20) is fed to the denitrification tank 22 and flows out from the denitrification tank 22. 23 is guided to the nitrification tank 24, a part of the nitrification liquid flowing out from the nitrification tank 24 is returned to the denitrification tank 22 as the nitrification circulation liquid 25, and the remaining nitrification liquid 26 is guided to the precipitation tank 27. It is processed in a flow that it is separated into return sludge 28 and denitrified treated water 29. On the other hand, a part of the above-described concentrated raw sludge 9 is crushed by the raw sludge crusher 30, and the crushed raw sludge 31 is put into the denitrification tank 22.
[0029]
Specifically, as shown in FIG. 2, a storage tank 32 and a mud feed pump 33 for stably supplying the crushed raw sludge 31 to the denitrification tank 22 are provided at the subsequent stage of the raw sludge crusher 30. The denitrification tank 22 and the nitrification tank 24 are loaded with a bioadhesive carrier 34 as will be described later, and held in the respective tanks by a carrier separation screen 35. The denitrification tank 22 is provided with a stirrer 36 for stirring the mixed liquid in the tank and an ORP meter 37 for monitoring the oxidation-reduction potential (ORP) of the mixed liquid in the tank. The nitrification tank 24 is provided with an air diffuser 38 that diffuses into the liquid mixture in the tank and a DO meter 39 for monitoring dissolved oxygen (MLDO) in the liquid mixture in the tank.
[0030]
An air supply source such as a compressor 40 for supplying air to the air diffuser 38, the mud pump 33, the ORP meter 37, and the DO meter 39 are connected to the control device 41, respectively. The amount of raw sludge charged is controlled via the mud feed pump 33 based on the measured value, and the amount of air diffused is controlled via the compressor 40 based on the measured value of the DO meter 39.
[0031]
For this reason, in the denitrification tank 22, crushed raw sludge 31 containing activated sludge is charged in an input amount that maintains the ORP of the mixed liquid in the tank within a predetermined range, and the crushed raw sludge 31 is supplied as a BOD source (hydrogen supply). NOx-N, which is likely to occur when excessively charged, due to reduction of the oxidizing nitrogen brought in by the granulated dephosphorization treatment liquid 20 and the nitrification circulating liquid 25 by floating activated sludge and carrier-attached activated sludge. Increases in organic nitrogen from residues and raw sludge are avoided.
[0032]
In the nitrification tank 24, the MLDO of the mixed liquid in the tank is controlled within a predetermined low range, thereby forming a system in which nitrification and denitrification proceed simultaneously in an aerobic atmosphere. That is, as suspended activated sludge, ammonia nitrogen, and crushed raw sludge having a high S-BOD content are brought in by the denitrification treatment liquid 23 from the denitrification tank 22, the vicinity of the suspended activated sludge and the biological adhesion to which the activated sludge has adhered. Near the surface of the carrier, nitrification reaction and hydrolysis of crushed raw sludge (solubilization of BOD derived from SS) occur, and denitrification of S-BOD occurs inside the carrier. Therefore, it is possible to prevent wasteful aerobic decomposition of crushed raw sludge, which is likely to occur when MLDO is high, and generation of ammonia nitrogen, and to prevent nitrification shortage that is likely to occur when MLDO is low.
[0033]
In this way, the crushed raw sludge 31 can be efficiently solubilized and utilized to the maximum to maintain the treated water quality high, and the nitrification circulating liquid 25 containing the crushed raw sludge 31 and the return sludge 28 from the settling tank 27 can be used. By returning to the denitrification tank 22, the input amount of the crushed raw sludge 31 to the denitrification tank 22 can be minimized.
[0034]
The denitrified water 29 separated in the settling tank 27 is discharged or initially refluxed to the settling basin 2. However, since dephosphorization and denitrogenation are sufficient, the load on the water treatment system is small, The treated water quality is kept high.
[0035]
In addition, as the raw sludge crusher 30, a wet mill bead, a stone mill type crusher, etc. can be utilized. The stone mill type crusher is equipped with grindstones at the top and bottom of the container, and the raw sludge thrown into the center is splashed toward the grindstone at the periphery by centrifugal force and sent between the grinding wheels High effect. Wet mill beads are used for further crushing raw sludge crushed with a stone mill crusher. Since the sludge viscosity is reduced by crushing, the stirring of the storage tank 32 and the maintenance management of the mud pump 33 are easy.
[0036]
As the dephosphorization method, in addition to the above-described granulation dephosphorization method using magnesium, a crystallization dephosphorization method using calcium, a coagulation sedimentation treatment method using dolomite ore, etc., a treatment method for removing phosphorus eluted from sludge Is possible. Addition of PAC, polyiron, or the like is a means for preventing phosphorus elution performed in a water treatment system.
[0037]
Examples of the bioadhesive carrier 34 include fiber carriers disclosed in JP-A-9-75992 and JP-A-9-168895, polyester columnar carriers disclosed in JP-A-10-180278, PEG, PVA A spherical, cube-shaped, hollow cylindrical, or columnar carrier made of polypropylene can be used. However, at least in the nitrification tank 24, a porous one that allows activated sludge to penetrate to the center is used.
[0038]
As the carrier separation screen 35, a cylindrical or flat wedge wire screen can be used. It is necessary that the mesh width is finer than that of the carrier, but the mesh width is such that passage of sludge in a floating state is not difficult.
[0039]
If the use of caustic soda is allowed in the nitrification tank 24 where the pH drop occurs in the above-described nitrogen removal step, the order of nitrification-denitrification is reasonable, but in order to refrain from the injection of caustic soda from the viewpoint of running cost. Although the influence of the surplus BOD from the denitrification tank 22 cannot be ignored, the above-described flow for returning to the denitrification tank as the nitrification circulating liquid in the order of denitrification-nitrification is appropriate. However, any flow may be selected.
[0040]
If the order of nitrification-denitrification is used, the BOD of the crushed raw sludge 23 that has been added excessively may exist in the treated water after denitrification. In order to settle and separate activated sludge that may deteriorate in sedimentation due to adhesion of fine nitrogen gas, a re-aeration tank is required after the denitrification tank.
[0041]
At this time, the crushed raw sludge 23 used as a BOD source for denitrification contains a large amount of organic nitrogen, and this organic nitrogen increases the TN of the treated water after denitrification. It is desirable to install a re-aeration tank having nitrification ability instead of an aeration tank for removing BOD. Therefore, the flow is nitrification-denitrification-re-aeration (nitrification).
This processing flow requires one extra tank as compared with the above-described flow of denitrification-nitrification.
[0042]
Hereinafter, the present invention will be described more specifically with reference to examples.
Example 1
In the sludge return water treatment plant, NH_Four-N 200mg / L sludge return water as raw water, raw water inflow 15m^Three/ Day, circulation + return 15m^Three/ Day, by introducing raw sludge of T-BOD 6000-8000 mg / L and S-BOD 1700-2400 mg / L crushed by a stone mill type crusher, a nitrification rate of 93% and a denitrification rate of 85% were achieved. . The processing flow and detailed conditions are as follows.
[0043]
As the nitrogen removal apparatus, a nitrification denitrification apparatus in which a water tank in which a denitrification tank and a nitrification tank were arranged in this order as shown in FIG. 3 was connected in three stages in series was used. In the figure, members having the same functions as those described with reference to FIGS. 1 to 2 are given the same reference numerals as in FIGS. The denitrification tanks 22a, 22b, and 22c are 4.6 m in total.^ThreeThe nitrification tanks 24a, 24b and 24c are 9.3m in total of 3 tanks.^ThreeAs a nitrification denitrification device, the total is 13.9m^ThreeIt is. The bioadhesive carrier 34 is a polyester fiber carrier having a columnar cross section of 6 mm Φ × 8 mmH. 42 shows raw water and 43 shows raw sludge.
[0044]
The raw water 42 having a high ammoniacal nitrogen concentration was divided into three equal parts and allowed to flow into the denitrification tanks 22a, 22b and 22c. Accordingly, in the first-stage denitrification tank 22a, the raw water 42, the circulating nitrification liquid 25 from the third-stage nitrification tank 24c, the return sludge 28 from the settling tank 27, and the raw sludge 43 flow in, and reduction and denitrification occur. The denitrification liquid flows into the nitrification tank 24a, and ammonia nitrogen is oxidized to nitrate nitrogen. In the second-stage denitrification tank 22b, the raw water 42, the nitrification liquid from the first-stage nitrification tank 24a and the raw sludge 43 flow in to reduce and denitrify, and the denitrification liquid flows into the nitrification tank 24b. Ammonia nitrogen is oxidized to nitrate nitrogen. In the third-stage denitrification tank 22c, the raw water 42, the nitrification liquid from the second-stage nitrification tank 24b, and raw sludge 43 flow into the nitrification tank 24c. Ammonia nitrogen is oxidized to nitrate nitrogen. As described above, a part of the nitrification liquid flowing out from the nitrification tank 24c is circulated to the first-stage denitrification tank 22a, and the remaining nitrification liquid is guided to the precipitation tank 27.
[0045]
At this time, an ORP meter, a DO meter, and a controller (not shown) were used to perform ORP control so that the ORP was -170 to -230 mV in the third-stage denitrification tank 22c, thereby controlling the amount of raw sludge injected. . In addition, the amount of aeration was controlled so that the MLDO concentration was 2 to 3 mg / L in the nitrification tank 24c, and aerobic decomposition of BOD was suppressed. Sludge residence time was 2-3 days.
[0046]
As a result, treated water quality is NH_Four-N is 10 mg / L, NO₂-N is 5 mg / L, NO_Three-N was 5 mg / L. Raw water 15m^ThreeThe amount of raw sludge injected into the denitrification tank per day is 0.6-0.8m in total for three tanks^ThreeThe T-BOD / N ratio was about 2, and the S-BOD / N ratio was about 0.5.
[0047]
When methanol is used as the BOD source, the SOD-BOD / N ratio and the T-BOD / N ratio are both lower by using raw sludge as the BOD source than when the BOD / N ratio is about 3. This shows how little raw sludge is used, that is, how effectively raw sludge is used. This is because raw sludge is also separated and recycled in the sedimentation tank, S-BOD is eluted along with the denitrification reaction, and nitrification and denitrification proceed simultaneously in the nitrification tank. Is not wastefully oxidized and decomposed.
(Example 2)
Using a single-stage nitrification denitrification apparatus in which a denitrification tank 22a and a nitrification tank 24a are arranged in this order as shown in FIG._FourThe raw water 42 having the same −N concentration was denitrified. The denitrification tank 22a is 4.6 m so that the total water tank capacity is equivalent to that of the first embodiment.^ThreeThe nitrification tank 24a is 9.3m^ThreeIt was. The properties, ORP, and MLDO control conditions of the raw sludge 43 are the same as those in the first embodiment. In order to obtain a nitrogen removal rate equivalent to that in Example 1 in the flow of Example 2, about 5.1 times of circulation + return was necessary.
[0048]
  As a result, raw sludge52.0m³/ Day required, but the increase in raw sludge input had a slight effect on nitrification, and the treated water quality was NH₄-N is 20 mg / L, NO₂-N is 10 mg / L, NO₃-N was 25 mg / L.
[0049]
(Example3)
  Denitrification was performed under the same conditions as in Example 1 except that the ORP control value was set to a low value of -200 to -260 mV.
[0050]
  As a result, the required amount of raw sludge is 2.0-2.5m.³/ Day, the oxidation of nitrogen from raw sludge could not catch up, and the quality of treated water deteriorated. Treatment water quality is NH₄-N is 40 mg / L, NO₂-N is 10 mg / L, NO₃-N was 20 mg / L.
(Example4)
  NH₄Denitrification was performed under the same conditions as in Example 1 except that the raw water with -N of 100 mg / L was used as the treatment target.
[0051]
As a result, the required amount of raw sludge is ½ that of Example 1 and the quality of the treated water is NH._Four-N is ND (not detected), NO₂-N is ND (not detected), NO_Three-N was 20 mg / L.
[0052]
  More than Example 1₄When raw water with a high -N concentration is to be treated, the water tank capacity of Example 1 cannot cope.
(Example5)
  Denitrification was performed under the same conditions as in Example 1 except that the residence time was shortened to 1.5 days.
[0053]
As a result, solubilization of raw sludge does not progress, and NH_Four-N is 5 mg / L, NO₂-N is 5 mg / L, NO_Three-To obtain treated water quality with N of 30mg / L, raw sludge is 2.0m^Three/ Day needed.
[0054]
Conversely, when the sludge retention time was increased to 10 days, NH_Four-N is 30 mg / L, NO₂-N is 5 mg / L, NO_Three-N became 5mg / L, NH solubilized too much from raw sludge_Four-N could not be processed and remained.
[0055]
  Example 15The implementation conditions and results are shown in Table 1 below.
[0056]
[Table 1]

[0057]
【The invention's effect】
As described above, according to the present invention, the bioadhesive carrier is used in combination with activated sludge, and the MLDO of the nitrification tank is maintained within a predetermined low range, so that denitrification and solubilization of raw sludge can be achieved in the denitrification tank. Nitrification and denitrification can proceed simultaneously in the nitrification tank, making it possible to maximize the use of raw sludge and reducing the amount of raw sludge required compared to the conventional method. it can.
[Brief description of the drawings]
FIG. 1 is an explanatory diagram showing a processing flow of a sewage treatment plant where a method for removing nitrogen in sludge return water of the present invention is performed.
FIG. 2 is an explanatory diagram showing in detail a nitrogen removal step in sludge return water in the processing flow shown in FIG. 1;
FIG. 3 is an apparatus configuration diagram illustrating a method for removing nitrogen in sludge return water according to the present invention.
FIG. 4 is another apparatus configuration diagram illustrating the method for removing nitrogen in the sludge return water of the present invention.
[Explanation of symbols]
20 Granulated dephosphorization liquid (sludge return water)
22 Denitrification tank
24 Nitrification tank
25 Nitrification circulating fluid
27 Sedimentation tank (sludge separation return system)
28 Return sludge
29 Denitrified water
31 Crushed raw sludge
33 Mud pump
34 Bioadhesive carrier
37 ORP meter
38 Air diffuser
39 DO meter
40 compressor
41 Control unit

Claims (3)

Sludge return water returned from the sludge treatment system that treats sludge generated in the water treatment system to the water treatment system is sequentially introduced into the nitrification tank and denitrification tank, and a part of the nitrification liquid flowing out from the nitrification tank is removed. Circulating and returning to the nitrification tank, separating sludge from the remainder of the digestion liquid flowing out from the nitrification tank, returning the separated sludge to the denitrification tank and biologically nitrifying and denitrifying it, in the first sedimentation basin of the water treatment system A method for removing nitrogen in sludge return water by crushing the separated raw sludge and adding it as a BOD source to the nitrification liquid nitrified in the nitrification tank, and denitrifying the biological sludge in the nitrification tank, The nitrification is performed in a state where the dissolved oxygen concentration of the mixed liquid in the tank is controlled to 1 to 5 mg / L, and the residence time of the crushed raw sludge in the nitrification tank and the denitrification tank is 1 to 10 days. To remove nitrogen in sludge return water.   2. The method for removing nitrogen from sludge return water according to claim 1, wherein a biological adhesion carrier is introduced into the denitrification tank.   From the denitrification tank charged with activated sludge, the nitrification tank charged with activated sludge and bioadhesive carrier having aeration means, and the sludge treatment system for treating sludge generated in the water treatment system to the water treatment system The sludge return water to be returned to the denitrification tank and the nitrification tank is sequentially introduced, and a part of the nitrification liquid flowing out from the nitrification tank is circulated and returned to the denitrification tank, and the first settling basin of the water treatment system. Raw sludge injection means for injecting the crushed raw sludge obtained by crushing the separated raw sludge into the circulation return path from the denitrification tank or the nitrification tank to the denitrification tank, and sludge from the remaining nitrification liquid circulated back to the denitrification tank The sludge return system for separating the separated sludge to the denitrification tank, the dissolved oxygen concentration meter for measuring the dissolved oxygen concentration in the mixed liquid in the nitrification tank, and the dissolved oxygen concentration in the mixed liquid in the nitrification tank Of the aeration means so that is maintained at 1-5 mg / L And control means for controlling the raw sludge injection amount of the raw sludge injection means to a predetermined amount, and the residence time of the crushed raw sludge in the nitrification tank and denitrification tank is controlled for 1 to 10 days. A device for removing nitrogen from sludge return water, which is characterized by

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