JP2007222830A - Treatment method of nitrogen-containing organic wastewater, and treatment apparatus for it - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a treatment method of nitrogen-containing organic wastewater enabling stable removal of nitrogen, capable of reducing the amount of generated excess sludge and excellent in economy in the method of biologically treating the nitrogen-containing organic wastewater to remove nitrogen, and a treatment apparatus for it. <P>SOLUTION: The apparatus comprises a denitrification tank 2 into which the nitrogen-containing organic wastewater flows, a nitrification tank 3 into which a liquid from the denitrification tank 2 flows, an immersion type membrane separator 5 provided by immersing it in the nitrification tank 3 and a circulation flow path 4 for circulating a liquid inside the nitrification tank 3 to the denitrification tank 2, and further comprises a sludge solubilization device 7 for solubilizing the sludge removed from the denitrification tank 2 and/or the nitrification tank 3. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a treatment method for treating nitrogen containing organic wastewater with activated sludge to remove nitrogen in the wastewater, and a treatment facility therefor.

  Conventionally, in biological nitrogen removal methods consisting of a nitrification process and a denitrification process, sludge that has been crushed or solubilized has been used as a hydrogen donor for denitrifying bacteria in the denitrification process. For example, Patent Document 1 discloses a method of performing centrifugation after alkali treatment and returning the separated liquid to the denitrification step.

  However, the nitrifying bacteria that play an important role in the nitrification process have a relatively slow growth rate, and if it is intended to stably hold the nitrifying bacteria in the system, it is necessary to increase the aerobic solid residence time, Since the amount of crushing and solubilization cannot be increased, as a result, there has been a problem that the effect of weight reduction by solubilization of sludge is lowered. Conversely, increasing the ratio of sludge for crushing and solubilization to the amount of sludge in the nitrification tank and shortening the aerobic solid residence time makes it difficult to retain nitrifying bacteria in the system, especially in the low temperature period. As a result, there has been a problem that the nitrogen concentration of the treated water becomes high.

  For this reason, it is usually appropriate to set the sludge concentration in the nitrification tank to about 1,000 mg / L to 4,000 mg / L, greatly reducing the generation of excess sludge and simultaneously removing nitrifying bacteria in the system. However, there is a method of increasing the nitrification tank in order to stably maintain the nitrification tank, and there is a problem that the equipment cost becomes high and the installation area becomes large.

  Furthermore, when the sludge concentration in the nitrification tank is increased, the solid load in the final sedimentation basin is increased, and particularly when a fine grinding machine such as a wet-medium agitating mill is used as a sludge crushing means. The sludge flocs tend to disperse, making it difficult to separate the sludge. It is conceivable to reduce the water area load of the final sedimentation basin as a means to solve this, but for that purpose, it is necessary to enlarge the final sedimentation tank, resulting in high equipment costs and large installation area. There was a problem.

  On the other hand, a membrane separation activated sludge method that removes fine suspended solids and installs a submerged membrane separator in a nitrification tank instead of a precipitation tank for the purpose of improving water quality and reducing the scale of facilities. Is known, for example, from Patent Document 2.

However, in such a membrane separation activated sludge method, the fine suspended solids concentration of the treated water can be kept low, but the amount of sludge generated cannot be reduced as compared with the case where solid-liquid separation is performed using a sedimentation tank.
Japanese Patent Publication No.59-48677 JP 2001-29994 A

  The present invention is a method for removing nitrogen by biologically treating nitrogen-containing organic wastewater, enabling stable nitrogen removal, and reducing the amount of generated excess sludge, which is excellent in economic efficiency. An object of the present invention is to provide a method for treating nitrogen-containing organic wastewater and a treatment facility therefor.

  As a result of intensive investigations to solve the above problems, the present inventors have extracted some sludge from the denitrification tank and / or nitrification tank, solubilized it, and returned it to the denitrification tank and / or nitrification tank. The present inventors have found that the above-mentioned problems can be solved by solid-liquid separation using a membrane separation apparatus immersed in the present invention.

  That is, in the first aspect of the present invention, the nitrogen-containing organic wastewater is introduced into the denitrification process, the liquid after the denitrification process is introduced into the nitrification process, and a part of the nitrification liquid after the nitrification process is introduced into the denitrification process. In a biological nitrogen removal method in which a part of the nitrification liquid is circulated and solid-liquid separated to obtain treated water, the solid-liquid separation is performed by a membrane separation apparatus, and sludge is removed from the denitrification process and / or the nitrification process. The gist of the present invention is a method for treating nitrogen-containing organic wastewater, which is characterized by returning to the denitrification step and / or the nitrification step after part extraction and solubilization treatment.

  The second aspect of the present invention is a denitrification tank into which nitrogen-containing organic wastewater flows, a nitrification tank into which liquid from the denitrification tank flows, a submerged membrane separation apparatus provided by being immersed in the nitrification tank, and a tank of the nitrification tank A nitrogen-containing nitrogen stream characterized by comprising a circulation channel for circulating the internal liquid to the denitrification tank, and a sludge solubilizer for solubilizing sludge extracted from the denitrification tank and / or nitrification tank The organic wastewater treatment facility is a gist, preferably, the sludge solubilizer is the above-mentioned nitrogen-containing organic wastewater treatment facility which is a wet medium stirring mill, and preferably, in the nitrification tank. The nitrogen-containing organic wastewater treatment facility is provided with a sludge concentration meter for measuring the sludge concentration.

  According to the present invention, since the sludge concentration in the nitrification tank can be maintained at a high concentration by using the submerged membrane separator, it is possible to stably remove nitrogen without substantially reducing the activity of nitrifying bacteria. In addition, the use of a sludge concentration meter installed in the nitrification tank makes it possible to easily control the aerobic solid residence time to a predetermined time or more, thereby achieving more stable nitrogen removal. . In the present invention, since treated water is obtained by the submerged membrane separation apparatus, SS in the treated water can be lowered, and accordingly, components such as BOD and COD have better treated water quality compared to the activated sludge method having a sedimentation tank. Can be obtained economically. Furthermore, according to the present invention, since sludge is partially extracted and solubilized from the denitrification tank and / or nitrification tank and then returned to the denitrification tank and / or nitrification tank, the amount of surplus sludge generated can be stabilized. Can be reduced.

In the conventional biological nitrogen removal method having a final sedimentation basin, the sludge concentration in the nitrification tank is usually about 1,000 mg / L to 4,000 mg / L. In a facility with a sludge generation rate of 4 kg / day at 100 m ³ / day, the sludge solubilization amount is 12 kg / day, the SS and surplus sludge amount in the treated water is 0 kg / day, and aerobic solids to retain nitrifying bacteria When the material residence time is 10 days, the required nitrification tank volume is 40 m ³ when aeration is performed for 24 hours per day. Therefore, if the denitrification tank and the nitrification tank have the same volume, a total volume of 80 m ³ is required. On the other hand, according to the present invention, for example, when the sludge concentration is 15,000 mg / L, the volume of the nitrification tank is 8 m ³ , and if the denitrification tank and the nitrification tank have the same volume, the total volume is 16 m ³ . Well, the volume can be reduced in proportion to the inverse of the sludge concentration in the nitrification tank.

  The nitrogen-containing organic wastewater to be treated in the present invention is not particularly limited as long as it contains organic matter treated by a normal activated sludge method. Sewage, human waste, food manufacturing industry wastewater Industrial wastewater, sludge, etc.

The processing method of the present invention will be described below with reference to the drawings.
In FIG. 1, nitrogen-containing organic waste water 1 (hereinafter referred to as waste water) first flows into a denitrification tank 2 in which a denitrification step is performed. Here, stirring is preferably performed, and molecular nitrogen is removed from nitrate nitrogen or nitrite nitrogen by the action of denitrifying bacteria in the tank during a predetermined residence time in the tank. The waste water containing ammonia nitrogen is sent to the nitrification tank 3 where the nitrification process is performed next. Here, the waste water is aerated, and the waste water in the tank is passed through a predetermined retention time in the tank under aerobic conditions. The organic matter is decomposed by the biological reaction of activated sludge and nitrated or nitrified by the action of nitrifying bacteria. Next, with a pump or the like installed in the nitrification tank 3, a part of the nitrification liquid returns from the nitrification tank 3 to the denitrification tank 2 through the circulation channel 4 and circulates in the system.

Here, the amount of the nitrifying liquid to be circulated is usually set to 1 to 5 times the amount of waste water introduced, and is set so as to achieve the target nitrogen removal rate.
In the present invention, the nitrification liquid is also introduced into a submerged membrane separation device 5 provided by being immersed in the nitrification tank 3, and the liquid that has permeated the membrane is discharged out of the system as treated water 6. The submerged membrane separation device 5 receives gravity or the suction pressure of the suction pump device to filter the liquid in the nitrification tank 3, and the treated water is discharged out of the system by the gravity or suction pump device.

  In the present invention, a part of the sludge is further extracted from the denitrification tank 2 and / or the nitrification tank 3, introduced into the sludge solubilizer 7, and the solubilized sludge is returned to the denitrification tank 2 and / or the nitrification tank 3 again. To do. Specifically, for example, a part of the sludge in the denitrification tank 2 and / or the nitrification tank 3 is sent to the sludge solubilizer 7 using a sludge supply pump, solubilized to improve biodegradability, and the denitrification tank 2 and Returned to the nitrification tank 3.

  As the amount of sludge to be solubilized such as crushing in the sludge solubilizer 7, the amount of sludge solidified by assimilation of the BOD of the sewage and part of the sludge solubilized will become sludge again by biological treatment. In view of the amount of growth, it may be set as appropriate so as to achieve the target reduction rate. Usually, about 2 to 4 times the amount of excess sludge generated when the sludge is not solubilized is solubilized. It is preferable.

Further, the time zone for returning the solubilized sludge is preferably at night when the amount of wastewater inflow is small and the organic content for denitrification is small.
At this time, either the denitrification tank 2 or the nitrification tank 3 may be used as a tank for extracting the sludge, but the sludge concentration in the nitrification tank 3 is usually higher than that of the denitrification tank 2, so that the sludge solubilizer 7 becomes compact. Also, the nitrification tank 3 is preferable because it can be operated efficiently. The tank for returning the solubilized sludge may be either the denitrification tank 2 or the nitrification tank 3, but when returned to the denitrification tank 2, the solubilized sludge should be used effectively as an organic substance for denitrification. Therefore, the denitrification tank 2 is preferable.

Such treatment is performed, and the generated sludge is discharged from the nitrification tank 3 or the denitrification tank 2 as excess sludge 8.
Next, a description will be given of a first example of equipment that can suitably carry out the above-described treatment method based on FIG. 2. The nitrification tank 3 includes a submerged membrane separation device 5 and an aeration device 9 in the tank, and a flow path from the denitrification tank 2 to the nitrification tank 3 and a circulation flow path from the nitrification tank 3 to the denitrification tank 2 4. There are a flow path between the sludge solubilizer 7, the denitrification tank 2 and the nitrification tank 3.

  In FIG. 2, in the denitrification tank 2, waste water flows in and circulating liquid flows in from the nitrification tank 3, and nitrate nitrogen and nitrite nitrogen contained in the circulating liquid are removed as nitrogen gas by the action of denitrifying bacteria. This tank is removed. In the denitrification tank 2, a stirrer 10 is preferably installed to stir the liquid in the tank. Examples of the stirring device 10 used here include an underwater mixer and an underwater pump.

  The nitrification tank 3 is a tank into which the liquid from the denitrification tank 2 is introduced, in which ammonia nitrogen is nitrified into nitrate or nitrite nitrogen by a biological reaction by nitrifying bacteria. The nitrification tank 3 is provided with a circulation pump device 11 for returning a part of the liquid in the tank to the denitrification tank 2, whereby the sludge liquid is circulated between the denitrification tank 2 and the nitrification tank 3. Become. The amount of liquid to be circulated is preferably set to be several times (about 1Q to 5Q) of the amount of normal wastewater introduced (daily average amount of sewage Q), depending on the target nitrogen removal rate.

  In the present invention, a submerged membrane separator 5 is provided in the nitrification tank 3, and an air diffuser 9 is disposed below the submerged membrane separator 5. The type of the submerged membrane separation device 5 is not particularly limited. For example, the submerged membrane separation device 5 includes a plurality of filtration membrane cartridges arranged in parallel at predetermined intervals, and the aerated air ejected from the diffuser 9 is a gas-liquid mixed phase flow. It is preferable to wash the membrane surface by crossflow along the membrane surface.

  The treated water that has permeated the filtration membrane by the submerged membrane separation device 5 is taken out of the system by gravity or the suction pump device 12. As the suction pump device 12, it is preferable if the amount of treated water can be adjusted in the range of 1Q to 3Q with respect to the daily average sewage amount Q of wastewater received in the denitrification tank 2. Further, the submerged membrane separation device 5 can be preferably used as long as it has a filtration membrane area and a treatment capacity of the number of membrane cartridges capable of taking out treated water that is three times the daily average sewage amount Q at the maximum.

  In the present invention, the nitrification tank 3 is preferably provided with a sludge extraction pump 13 for discharging excess sludge out of the system and a sludge supply pump 14 for sending sludge to the sludge solubilizer 7.

Note that there may be a plurality of nitrification tanks 3 as described above. In this case, the liquid from the denitrification tank 2 is allowed to flow in parallel.
In the present invention, it is preferable that the nitrification tank 3 is provided with a sludge concentration meter 15 for measuring the sludge concentration. Examples of the sludge concentration meter 15 include various methods such as a transmitted light method, a scattered light method, a microwave method, and an ultrasonic method. Further, an instrument having a correlation with the sludge concentration such as a viscometer may be used, and of course, the measurement may be made by hand analysis. The sludge concentration meter 15 is preferably installed in both the denitrification tank 2 and the nitrification tank 3, but may be installed on one side to obtain a correlation and use the value. When the sludge concentration meter 15 is installed on one side, it is preferable to install it on the nitrification tank 3.

  In the treatment facility of the present invention, the sludge solubilizer 7 is installed to solubilize a part of the sludge existing in the denitrification tank 2 and / or the nitrification tank 3. In order to send the sludge in the tank to the sludge solubilizer 7, the sludge supply pump 14 is preferably immersed in the denitrification tank 2 and / or the nitrification tank 3. Sludge that has been subjected to solubilization treatment such as crushing is returned to the denitrification tank 2 and / or the nitrification tank 3 again. At this time, as described above, the tank for extracting the sludge may be either the denitrification tank 2 or the nitrification tank 3, but the sludge concentration in the nitrification tank 3 is usually higher than that of the denitrification tank 2, so that the sludge solubilizer is used. The nitrification tank 3 is preferred because 7 is compact and can be operated efficiently. The tank for returning the solubilized sludge may be either the denitrification tank 2 or the nitrification tank 3, but when returned to the denitrification tank 2, the solubilized sludge should be used effectively as an organic substance for denitrification. Therefore, the denitrification tank 2 is preferable.

  The sludge solubilizer 7 used in the treatment facility of the present invention is not particularly limited as long as it can solubilize sludge. For example, a wet medium agitating mill, ultrasonic wave, homogenizer, In addition to mechanical crushing processing devices such as mixers, chemical solubilization processing devices such as oxidants and alkali treatments, devices using methods for crushing and solubilizing sludge with heat treatment devices, etc. can be mentioned alone, Or they can be used in combination.

  Among these apparatuses, the wet-medium agitating mill is preferable as a sludge crushing and solubilizing apparatus because it is easy to handle and is excellent in that the generation of persistent organic substances is small.

  In addition, in the apparatus which uses an oxidizing agent for sludge solubilization, in the case of treating the sludge in the denitrification tank 2, more oxidizing agent is required to make the anaerobic sludge aerobic. It is better to treat the sludge in the nitrification tank 3.

Hereinafter, the wet medium stirring mill will be described in detail.
Examples of the crushing medium (beads) used include beads such as glass, alumina, and zirconia, and beads having a true specific gravity of 2.0 to 7.0 are preferable. If the true specific gravity is less than 2.0, microorganisms cannot be sufficiently crushed, and even if the true specific gravity is greater than 7.0, the sludge crushing effect is hardly improved and the power required for stirring increases. It is not preferable.

  The particle size of the crushing medium is preferably 0.05 to 2.0 mmφ, particularly preferably 0.25 to 1.0 mmφ. If the particle size of the beads is larger than 2.0 mmφ, it is not preferable because the gap between the beads becomes large and it becomes difficult to crush microorganisms such as bacteria of several μm to several tens μm constituting the sludge. Further, if the particle size of the beads is smaller than 0.05 mmφ, it is difficult to separate the beads at a bead separating portion such as a screen.

  The bead filling rate is preferably 50 to 100%, particularly 70 to 90% from the viewpoint of crushing effect and power consumption, and the disk (pin) tip peripheral speed is 3 to 30 m / second, particularly 5 to 20 m / second. preferable. Further, the direction of the mill chamber may be either a vertical type or a horizontal type, and examples of the stirring device for stirring the crushing medium include a disk type, a pin type, and a pin disk type.

  The sludge residence time in the wet medium stirring mill treatment is appropriately set depending on the sludge concentration to be introduced and the crushing medium to be used, and is not particularly limited, but is usually preferably 20 seconds to 20 minutes, particularly 30 seconds to 10 minutes are preferred. If the residence time is shorter than 20 seconds, there is a possibility that the sludge is not sufficiently crushed, and even if it is longer than 20 minutes, only the power consumption increases and the crushing effect is not improved so much.

  Moreover, as processing temperature, 60 degrees C or less is preferable, and 4-40 degreeC is especially preferable. When the treatment temperature is higher than 60 ° C., a part of the sludge component is thermally denatured to become a hardly decomposable substance, which is not preferable because the quality of the treated water may be deteriorated.

  Usually, the temperature of sludge crushed by mill treatment rises by about 10-30 ° C compared to the sludge before treatment. Therefore, when the temperature is high and the treatment temperature is 60 ° C or higher as in summer, cooling water is used. It is preferable to cool it.

  In addition, after the mill treatment is completed, it is desirable to wash the mill chamber with water in order to easily start the next operation. As the water to be washed, tap water, treated water, sewage, or the like may be used. The amount and time of water to be washed may be set as appropriate, but it is preferable to wash until the sludge concentration in the washing water is 1% by weight or less.

  If the sludge flows in the wet medium agitation mill treatment, the sludge crushing effect is not greatly affected by the sludge concentration. Therefore, the concentration of sludge to be crushed is preferably higher if the sludge flows.

  Therefore, when a precipitation tank is used for solid-liquid separation, the sludge concentration of the separated sludge after solid-liquid separation is usually as low as about 0.2 to 1% by mass. In order to smash sludge economically, it is desirable to concentrate the separated sludge using a sludge concentrator.

  However, in the present invention, since the sludge concentration in the nitrification tank 3 is usually as high as 1% by mass or more, it is usually unnecessary to concentrate these sludges using a sludge concentrating device, and the installation space of the entire facility can be reduced. And is economical.

  As described above, by using the treatment equipment of the present invention, the treatment method of the present invention can be carried out. At this time, nitrifying bacteria having a slow growth rate are stably retained in the system, In order to sufficiently remove nitrogen, it is preferable to control each condition in the system so that the aerobic solid residence time in the nitrification tank 3 is not less than a predetermined time. In order to facilitate the calculation, it is preferable that the tank for extracting excess sludge and the tank for extracting solubilized sludge are usually the same tank.

By the way, in the advanced treatment facility design manual (draft) (Japan Sewerage Association 1994), the aerobic solid residence time (θ _XA ) is expressed by the following formula (1). In order to keep the aerobic solid in the system, the aerobic solid retention time (θ _XA ) needs to satisfy the following formula (2). It is shown that the time (θ _XA ) satisfies the water temperature and the relational expression (3).

θ _XA = θ _X · t _A / t Equation (1)
θ _XA ; Aerobic solid residence time (days)
θ _X ; solids residence time (days)
t _A ; nitrification tank residence time (hours)
t: Activated sludge tank (denitrification tank + nitrification tank) residence time (hours)
θ _XA = 1 / μ Equation (2)
μ: Specific growth rate of nitrifying bacteria (function of water temperature T (° C)) (1 / day)
θ _XA = δ · 20.6e ^(−0.0627T) (3)
δ: Correction coefficient for fluctuation of influent TN 1.2-1.5
T: Water temperature T (° C)
Here, in the present invention, in order to reduce the amount of sludge generation as compared with the normal activated sludge method, normally, about 2 to 4 times the amount of excess sludge generation when not sludge solubilization is solubilized. Therefore, since most of the solubilized sludge is killed, the aerobic solid residence time is shortened.

  In the present invention, compared to the activated sludge method having a sedimentation tank, the sludge concentration can be increased because of the membrane-separated activated sludge method. Therefore, in order to keep the nitrifying bacteria in the system even in the low water temperature period, It is advantageous to maintain the aerobic solids residence time above a certain level.

  However, as with the activated sludge method with a sedimentation tank, the sludge concentration, sludge solubilization amount, surplus sludge amount, and aeration time are carefully set based on the water temperature and sludge densitometer values. Need to hold.

The calculation of the aerobic solid residence time (θ _XA ) when solubilized is calculated as the sludge that is crushed and solubilized, and the sludge in which the nitrifying bacteria have died is calculated as the sludge that flows out of the system. It is shown by Formula (4).
θ _XA = t _B / 24 · (V _A · X _A ) / (Q _W · X _W + (Q−Q _W ) · X _E + α · Q _M · X _M ) (4)
V _A ; capacity of nitrification tank (m ³ )
X _A : Sludge concentration in nitrification tank (kg / m ³ )
X _W : Sludge concentration of excess sludge (kg / m ³ )
X _M : Sludge concentration of sludge solubilized (kg / m ³ )
X _E ; SS concentration in treated water (kg / m ³ )
Q: Inflow sewage volume (m ³ / day)
Q _W ; excess sludge volume (m ³ / day)
Q _M ; sludge solubilization amount (m ³ / day)
t _B ; Aeration time (hours)
α: Rate of death of nitrifying bacteria by sludge solubilization (-)
Moreover, in this processing equipment, since the treated water is obtained by membrane treatment, the SS concentration of the treated water can be ignored. Therefore, the equation (4) is expressed by the equation (5).
θ _XA = t _B / 24 · (V _A · X _A ) / (Q _W · X _W + α · Q _M · X _M ) (5)
Therefore, in the present invention, the required aerobic solid residence time (day) at T (° C.) is obtained from the formula (3), and the sludge weight of the nitrification tank 3 is set so that the calculated value of the formula (5) becomes longer. It is preferable to operate by setting each value of (V _A · X _A ), sludge solubilized weight (Q _M · X _M ), excess sludge weight (Q _W · X _W ), and aeration time (t _B ). In general, it is preferable to set the calculated value of the formula (5) to be longer than the calculated value of the formula (3) by 2 days or more, and it is more preferable to set the calculated value to be longer than 5 days.

  In the treatment facility of the present invention, when the excess sludge is extracted and the sludge to be crushed is directly extracted from the nitrification tank, the above calculation can be easily performed by measuring the MLSS concentration in the nitrification tank 3. There are advantages.

Next, an example of how to determine each set value in the operating conditions of the present processing equipment is shown below.
(1) Set the amount of sludge solubilization. The sludge solubilization amount is set to a fixed value or is changed according to the influent water amount and the influent water quality. In addition, when the inflow water quality is stable, it may be increased or decreased in proportion to the inflow water amount. Usually, the amount of sludge solubilization may be about 2 to 4 times the amount of excess sludge generated when sludge is not solubilized.

(2) Set the minimum aeration time per day. The minimum aeration time is not particularly limited, but is preferably 6 hours or more per day, and more preferably 8 hours or more.
(3) Set nitrification tank sludge concentration. The set nitrification tank sludge concentration is preferably 10,000 mg / L to 20,000 mg / L, and more preferably 10,000 mg / L to 15,000 mg / L.

  (4) The required aerobic solid residence time (days) is obtained from the water temperature (fixed value or actual measured value) according to the equation (3). When the water temperature is set to a fixed value, it is preferable to use the lowest water temperature of the treatment plant, which is usually about 12 ° C. Further, the value of δ is set to 1.2 to 1.5, but it is preferable to set it to 1.5 in view of the safety side.

  (5) The operation of the sludge solubilizer 7 is started. However, when the calculated value of the formula (5) becomes equal to or shorter than the required aerobic solid residence time (days), the sludge solubilizer 7 is started to operate after increasing the nitrification tank sludge concentration. In addition, since α in formula (5) varies depending on the type of sludge, the sludge solubilization method, and the operating conditions of the sludge solubilizer 7, it is preferable to obtain beforehand by experiment using the sludge of the treatment plant, When the experiment cannot be performed, it is preferable to set α = 1 in view of the safety side.

  (6) When the set nitrification tank sludge concentration is reached, the extraction of excess sludge is started so that the sludge concentration becomes substantially constant. Usually, it is about 0 to 0.5 times the amount of surplus sludge generated when sludge is not solubilized.

(7) When the calculated value of the formula (5) becomes less than the required aerobic solid residence time (days), the aeration time is extended.
(8) Even if the aeration time per day is set to 24 hours due to a decrease in the water temperature, etc., if the calculated value of the formula (5) is less than the required aerobic solid residence time (days), Reduce the sludge solubilization amount so that the residence time (days) of the air solids is reached, or change the sludge solubilization conditions to reduce the killing rate of nitrifying bacteria.

(9) If the calculated value of equation (5) is equal to or longer than the required aerobic solid residence time (days), increase the sludge solubilization amount to the set sludge solubilization amount, or change the sludge solubilization conditions. Change and increase the killing rate of nitrifying bacteria.
(10) Even in the case of the set sludge solubilization amount, the aeration time per day is decreased if the required aerobic solid retention time (days) is reached.

  The above control can be automatically controlled by creating a program. Moreover, it is preferable to control so that the calculated value of Formula (5) is 2 days or more longer than the required aerobic solid residence time (days), and it is more preferable to control to be 5 days or more.

  In this control method, the volume of the nitrification tank is calculated as constant, but in some cases, the volume may be changed by changing the water surface height. Further, when the excess sludge and sludge for sludge solubilization are extracted from the nitrification tank 3, the calculation becomes even easier.

If the aerobic solid retention time is set so as to retain nitrifying bacteria in this manner, the amount of sludge generated can be reduced and nitrogen in the sewage can be removed stably.
If the aerobic solid residence time is set so as to retain nitrifying bacteria in the system, usually organic matter in sewage and sludge sludged or solubilized can be sufficiently decomposed in the tank.

  Moreover, since the phosphorus concentration of treated water usually increases due to a decrease in the amount of sludge generated, a method of removing phosphorus by adding a flocculant such as ferric chloride to the denitrification tank or nitrification tank, It is preferable to carry out a method of removing the flocculant by adding it to the treated water.

By the way, in the processing facility in the first example described above, as a method of circulating the sludge water, the circulation pump device 11 is usually arranged in the nitrification tank 3, the sludge water is sent to the denitrification tank 2, and the tank of the denitrification tank 2 is used. Although the internal water is sent to the nitrification tank 3 under natural flow, the circulation pump device 11 is arranged in the denitrification tank 2 as in the treatment facility in the second example shown in FIG. The water in the tank of the nitriding tank 2 may be sent, and the water in the nitrification tank 3 may be circulated to the denitrification tank 2 under natural flow. Further, in the treatment facility in the second example, the sludge extraction pump 13 and the sludge supply pump 14 are arranged in the denitrification tank 2 together with the circulation pump device 11. Other configurations are the same as those of the processing facility in the first example shown in FIG.
[Example]

Example 1
In the processing apparatus of the present invention comprising a nitrification tank 3 denitrification tank 2 and volume 18m ³ 2 tanks of a processing flow of the volume of 52m ³ as shown in FIG. 3 (illustrated in FIG. 3 1 tank), 98m ³ / day Of domestic wastewater 1 was treated for 196 days. As the immersion type membrane separator 5, an organic flat membrane (0.8 m ² / sheet × 75 sheets / group × 6 units, manufactured by Kubota Corporation) was used. As the sludge solubilizer 7, a wet medium stirring mill (25V-SP, manufactured by Ashizawa Corporation) was used.

The nitrification tank water temperature during the period is 18 ° C. to 27 ° C., and the required aerobic solid residence time (days) is 5.7 days to 10.0 days when δ = 1.5 from Equation (3). Met.
On the other hand, from the formula (5), the operation was performed such that α = 0.70 and the aerobic solid residence time (days) was not less than the value obtained from the formula (3). That is, the average operating conditions during the period are as follows. Waste water was allowed to flow into the denitrification tank 2, and sludge in the denitrification tank 2 was supplied to the nitrification tank 3 at 400 m ³ / day by the circulation pump device 11. The sludge in the nitrification tank 3 (sludge concentration 15 g / L) was aerated with a diffuser 9 (19 hours / day), and treated water 6 having the same amount as the amount of wastewater introduced was separated with the submerged membrane separator 5. The remaining nitrification tank sludge was returned to the denitrification tank 2 as an overflow. Further, a part (43 kg / day) of sludge (sludge concentration 12 g / L) in the denitrification tank 2 was supplied to a wet-medium agitating mill as the sludge solubilizer 7 for crushing treatment. Excess sludge was discharged to a sludge storage tank by a sludge extraction pump 13.

Comparative Example 1
In the treatment method of Example 1, wastewater treatment was performed for 131 days in the same manner as in Example 1 except that sludge was not crushed.

  FIG. 4 is a diagram showing the amount of solid sludge generated. In Comparative Example 1, solid sludge was generated at 12 kg / day, whereas in Example 1 in which 3.6 times the solid sludge was processed by the sludge solubilizer, the rate was 5.1 kg / day. The amount of solid sludge generated was decreasing.

  Table 1 shows the quality of waste water and treated water.

表１から実施例１では比較例１と同等の良好な水質が得られていることが分かる。

From Table 1, it can be seen that in Example 1, good water quality equivalent to that of Comparative Example 1 was obtained.

  As described above, in the treatment facility of the present invention, the amount of sludge generated in the nitrification tank, the amount of excess sludge, the amount of sludge solubilized, and the aeration time can be appropriately controlled and stably reduced. Nitrogen in sewage could be removed.

It is a figure which shows the schematic flowchart of the processing method of this invention. It is the schematic which shows the structure of the processing equipment in the 1st example of this invention. It is the schematic which shows the structure of the processing equipment in the 2nd example of this invention. It is a figure which shows the generation amount of the excess sludge in Example 1 and Comparative Example 1.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Nitrogen-containing organic waste water 2 Denitrification tank 3 Nitrification tank 4 Circulation flow path 5 Submerged membrane separation device 6 Treated water 7 Sludge solubilization device 8 Surplus sludge 9 Aeration device 10 Stirring device 11 Circulation pump device 12 Suction pump device 13 Sludge Extraction pump 14 Sludge supply pump 15 Sludge concentration meter

Claims (4)

Nitrogen-containing organic wastewater is introduced into the denitrification process, the liquid that has undergone the denitrification process is then introduced into the nitrification process, a portion of the nitrification liquid that has undergone the nitrification process is circulated to the denitrification process, and a part of the nitrification liquid is recovered. In the biological nitrogen removal method for obtaining treated water by solid-liquid separation, the solid-liquid separation is performed by a membrane separation device, and a part of sludge is extracted from the denitrification step and / or the nitrification step and subjected to a solubilization treatment. A method for treating nitrogen-containing organic wastewater, which is returned to a denitrification step and / or a nitrification step later. Denitrification tank into which nitrogen-containing organic wastewater flows, nitrification tank into which the liquid from the denitrification tank flows in, immersion type membrane separator immersed in the nitrification tank, and circulating nitrification tank liquid to the denitrification tank And a sludge solubilization device for solubilizing sludge extracted from the denitrification tank and / or the nitrification tank, and a treatment facility for nitrogen-containing organic wastewater. The treatment equipment for nitrogen-containing organic wastewater according to claim 2, wherein the sludge solubilizing apparatus is a wet medium stirring mill. The treatment facility for nitrogen-containing organic wastewater according to claim 2 or 3, wherein a sludge concentration meter for measuring the sludge concentration is provided in the nitrification tank.

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