JP2009214073A - Treatment method for nitrogen-containing organic wastewater and treatment apparatus therfor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a cost-effective treatment method for nitrogen-containing organic wastewater capable of reducing the amount of excess sludge generated in performing activated sludge treatment for nitrogen-containing organic wastewater to be cleaned and of stably removing nitrogen, and a treatment apparatus employed for the method. <P>SOLUTION: In the treatment method for nitrogen-containing organic wastewater, solid-liquid separation for treated liquid is performed after nitrogen-containing organic wastewater is treated in an activated sludge treatment tank. The separated water is released as treated water to return the separated sludge to the activated sludge treatment tank. A portion or all of the sludge returned to the activated sludge treatment tank is concentrated in a membrane separation sludge concentration tank having a sludge densitometer. Thereafter, solubilization treatment is performed for a portion of the concentrated sludge to be returned to the activated sludge treatment tank, while the remaining of the concentrated sludge is extracted out of the sludge concentration tank to the outside as excess sludge. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a treatment method and a treatment apparatus for treating and purifying nitrogen-containing organic wastewater by activated sludge, and more specifically, it is possible to reduce the amount of surplus sludge generated in the activated sludge treatment tank, The present invention relates to a method and apparatus for treating nitrogen-containing organic wastewater that can stably remove nitrogen in wastewater.

  Conventionally, in biological nitrogen removal methods comprising 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. A method is known in which the alkali treatment is followed by centrifugation, and the separated liquid is returned to the second denitrification step (see, for example, Patent Document 1).

  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, For this purpose, the amount of crushing and solubilization cannot be increased, resulting in a problem that the effect of reducing sludge is reduced. Conversely, increasing the ratio of sludge for crushing and solubilization to sludge in the nitrification process to shorten the aerobic solid residence time makes it difficult to keep nitrifying bacteria in the system, especially during low water temperatures. As a result, there has been a problem that the nitrogen concentration of the treated water becomes high.

  Moreover, extraction of excess sludge outside the system is usually performed by gravity concentration or mechanical concentration of the separated sludge separated in the solid-liquid separation tank or the sludge in the activated sludge treatment tank. However, in gravity concentration, the concentration of excess sludge drawn out by the sludge residence time in the tank changes greatly, and even in the case of mechanical concentration, it is difficult to maintain the same concentration stably or to reproduce it. The exact amount of excess sludge extraction could not be known.

Therefore, it has been a difficult problem to control the sludge crushing and solubilization amount and the excess sludge extraction amount in order to stably and maximize nitrogen removal and sludge reduction.
Japanese Patent Publication No.59-48677

  The present invention solves such a problem, and reduces the amount of excess sludge generated when treating and purifying nitrogen-containing organic wastewater by activated sludge and is economically capable of stably removing nitrogen. It is an object of the present invention to provide an organic wastewater treatment method that excels in quality and an apparatus used for the method.

  As a result of intensive investigations to solve such problems, the present inventor economically performs sludge solubilization treatment by concentrating sludge in a membrane separation type sludge concentration tank, and measures its concentration. In addition, the present inventors have found that the above-described problems can be solved by extracting excess sludge from the sludge concentration tank to the outside of the system, and have reached the present invention.

  That is, according to the first aspect of the present invention, after treating nitrogen-containing organic wastewater in an activated sludge treatment tank, the treatment liquid is subjected to solid-liquid separation, and the separated water is discharged as treated water. The separated sludge is fed to the activated sludge treatment tank. In the method of treating nitrogen-containing organic wastewater to be returned, a part or all of the sludge to be returned to the activated sludge treatment tank is concentrated after the sludge is concentrated in a membrane separation type sludge concentration tank having a sludge concentration meter. A method for treating nitrogen-containing organic wastewater, wherein a portion of sludge is solubilized and returned to the activated sludge treatment tank, and the remainder of the concentrated sludge is drawn out of the system as excess sludge from the sludge concentration tank. Preferably, when the nitrification capacity in the activated sludge treatment tank is reduced, the sludge concentration tank is aerobic by aeration and a part or all of the sludge in the sludge concentration tank is allowed. Solubilize It is a process method of the nitrogen-containing organic waste water to be returned to the no bioreactor tank.

  The second aspect of the present invention is an activated sludge treatment tank for treating nitrogen-containing organic waste water, a solid-liquid separation apparatus for separating the treatment liquid into solid and liquid, a membrane separation type sludge concentration tank having a sludge concentration meter, and sludge A nitrogen-containing organic wastewater treatment apparatus characterized by comprising a solubilizer, preferably, the treatment of nitrogen-containing organic wastewater as described above, wherein the sludge solubilizer is a wet medium stirring mill Device.

  According to the present invention, a membrane separation device is used in a sludge concentration tank for solubilization treatment, and solubilization is performed using a sludge concentration meter installed in the tank in order to draw excess sludge out of the system from the sludge concentration tank. The amount of solubilization and the amount of excess sludge can be adjusted at all times while the amount of treatment and the amount of excess sludge are constantly monitored, and the aerobic solid retention time in the activated sludge treatment tank is easily controlled to a predetermined time or more. Therefore, stable nitrogen removal can be achieved, high quality treated water quality can be obtained, and the amount of sludge solubilized treatment is managed, so the amount of excess sludge generated can be reduced stably. it can.

  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.

  In the present invention, as a method for treating nitrogen-containing organic wastewater in an activated sludge treatment tank, a circulation nitrification denitrification method, a step aeration method, a nitrification-endogenous denitrification method, wherein the nitrification step and the denitrification step are performed in different tanks, the same Arbitrary biological denitrification methods such as intermittent aeration performed in the tank are available.

  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) is treated in an activated sludge treatment tank 2 comprising a nitrification step and a denitrification step, and nitrogen removal is performed along with removal of organic substances. In addition, the sludge density | concentration of each tank of an activated sludge process tank is required for calculation of the aerobic solid substance residence time mentioned later, and it is desirable to install and measure a sludge concentration meter.

  Next, the treatment liquid is sent to the solid-liquid separation tank 3 and separated into treated water 4 and separated sludge 5. Part or all of the separated sludge 5 is sent to a membrane separation type sludge concentration tank 7 having a sludge densitometer, and the remaining separated sludge is returned to the activated sludge treatment tank 2 as return sludge 6. The separation sludge 5 is returned from the membrane separation device installed in the sludge concentration tank 7 to the activated sludge treatment tank 2 after the separation liquid 8 has passed through the membrane. Moreover, it is necessary to measure SS concentration of the treated water 4 suitably for calculation of the aerobic solid residence time mentioned later, and it is desirable to install and measure SS concentration meter.

  In the present invention, the concentrated sludge 9 in the sludge concentration tank 7 concentrated by the membrane separator is measured with a sludge densitometer and introduced into the sludge solubilizer 11, solubilized solubilized sludge 12 is The activated sludge treatment tank 2 is returned to. Further, excess concentrated sludge is discharged out of the system as excess sludge 10.

  The amount of sludge to be solubilized such as crushing in the sludge solubilizer 11 includes the amount of solid matter of sludge proliferated by assimilation of the BOD of the sewage, and part of the sludge solubilized to sludge again in the activated sludge treatment process. Therefore, it may be set appropriately so as to achieve the target reduction rate in consideration of the amount of growth, and is usually 1 to 5 times the amount of excess sludge generated when sludge is not solubilized, preferably 2 to 4 It is preferable to solubilize sludge in a double amount, most preferably about 3 to 4 times.

  Further, the time zone for returning the solubilized sludge is preferably performed at night when the amount of inflow of wastewater is small and the organic content for denitrification is small. As a tank for returning the solubilized sludge, the solubilized sludge can be effectively used as an organic substance for denitrification when it is returned to the denitrification tank by the circulation denitrification method or the step aeration method. Nitrogen tanks are preferred. In the intermittent aeration method, it is preferably returned during the denitrification step.

  In the treatment method of the present invention, when the nitrification capacity of the activated sludge treatment tank decreases due to a decrease in water temperature such as in winter, the aeration apparatus installed in the sludge concentration tank maintains the inside of the tank in an aerobic state, It is preferable to improve the quality of the treated water by making it suitable for growth and returning it through the concentrated sludge return line 13 to the activated sludge treatment tank without solubilizing part or all of the concentrated sludge. The sludge solubilizer may be returned from the sludge solubilization line without operating part or all of the sludge solubilizer.

  In this way, maintaining the inside of the tank in an aerobic state can be expected to maintain the nitrification ability of nitrifying bacteria and increase the nitrifying bacteria, and the activated sludge treatment without solubilizing and killing the nitrifying bacteria The quality of the treated water can be improved by returning it to the tank. Furthermore, rather than returning without passing through the sludge concentration tank, maintaining the high concentration of sludge in the aerobic state in the sludge concentration tank maintains the nitrification capacity of the nitrifying bacteria in the entire treatment equipment and increases the number of nitrifying bacteria. Can be expected. The aerobic state means that dissolved oxygen is detected in the tank, and as a method for maintaining the inside of the tank in an aerobic state, an aeration apparatus used for cleaning the membrane separation apparatus may be used. The aeration apparatus needs to be capable of aeration so that the dissolved oxygen concentration in the tank is preferably 1 mg / L or more, more preferably 2 mg / L.

  In addition, it is preferable to determine the setting of the dissolved oxygen concentration of a sludge concentration tank in consideration of carrying in of dissolved oxygen to an activated sludge processing tank. Further, when the pH in the tank is extremely lowered, such as 4 or less, due to the dissolution of carbon dioxide gas or a nitrification reaction by aeration, it is preferable to neutralize appropriately considering the influence on the activated sludge treatment tank.

  The second aspect of the present invention is equipment that can suitably carry out the above-described treatment method. The main configuration is an activated sludge treatment tank for treating nitrogen-containing organic wastewater, and a solid solution for separating the treatment liquid into solid and liquid. A liquid separation device, a membrane separation type sludge concentration tank having a sludge concentration meter, a sludge solubilizer, and the like.

  In FIG. 2, a circulating nitrification denitrification method is shown as an example of the activated sludge treatment method. The activated sludge treatment tank 2 includes a denitrification tank 14 and a nitrification tank 15, and the waste water 1 flows into the denitrification tank 14, and the circulating liquid 16 flows from the nitrification tank 15. A tank in which nitrate nitrogen is removed from the system as nitrogen gas by the action of denitrifying bacteria. In the denitrification tank 14, a stirrer 17 is preferably installed to stir the liquid in the tank. Examples of the stirring device 17 used here include an underwater mixer and an underwater pump.

  The nitrification tank 15 is a tank into which the liquid from the denitrification tank 14 is introduced. In the tank, ammonia nitrogen is nitrified into nitrate or nitrite nitrogen by a biological reaction by activated sludge. The nitrification tank 15 is provided with a return flow path 16 for returning a part of the liquid in the tank to the denitrification tank 14, whereby the sludge liquid is circulated between the denitrification tank 14 and the nitrification tank 15. 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. As a method of circulating the sludge water, a circulation pump device 20 is usually arranged in the nitrification tank 15, and the tank water is sent to the denitrification tank 14, and the tank water in the denitrification tank 14 is sent to the nitrification tank 15 under natural flow. However, as another method, a circulation pump is arranged in the denitrification tank 14, the tank water of the denitrification tank 14 is sent to the nitrification tank 15, and the tank water of the nitrification tank 15 is naturally flowed to the denitrification tank 14. It may be circulated.

  The solid-liquid separation tank 3 is a tank for separating the water in the activated sludge treatment tank 2 treated with the nitrogen-containing organic waste water into the treated water 4 and the separated sludge 5. Gravity separation is used as a sludge separation method. Or by membrane separation. Part or all of the separated sludge 5 is sent to the sludge concentration tank 7 by the sludge pump 21, and the remaining sludge is returned to the activated sludge treatment tank 2 as return sludge.

  In the present invention, the sludge concentrating tank 7 has a membrane separation type sludge concentrating device 19, and the form of the membrane separation type sludge concentrating device 19 is not particularly limited, but a submerged membrane separation device is suitable. It is. The sludge concentration tank 7 is provided with a sludge concentration meter 18 and an air diffuser 26. In the case of the submerged membrane separator 19, the aerobic state (the situation in which dissolved oxygen exists) in the tank is secured and the membrane is washed. For this purpose, an air diffuser 26 is disposed below. The type of the submerged membrane separation device 19 is not particularly limited. For example, the submerged membrane separation device 19 includes a plurality of filtration membrane cartridges arranged in parallel at predetermined intervals, and the aerated air ejected from the diffuser 26 is a gas-liquid mixed phase flow. It is preferable that the film surface is washed by crossflow along the film surface.

  Concentration of excess sludge and concentration for sludge solubilization are usually performed by other devices such as gravity concentration for concentration of excess sludge, and mechanical concentration for concentration of sludge solubilization. This is economical because it is carried out in a tank.

  With this submerged membrane separator 19, the separation liquid 8 that has passed through the filtration membrane is returned to the activated sludge treatment tank 2 by gravity or a suction pump device 24, but is taken out of the system depending on the processing situation. Become.

  In the present invention, a sludge concentration meter 18 for measuring the sludge concentration is provided in the sludge concentration tank 7. Examples of the sludge concentration meter 18 include various methods such as a transmitted light method, a scattered light method, a microwave method, and an ultrasonic method. Moreover, you may use the instrument which has correlation with sludge density | concentrations, such as a viscometer depending on the case. In addition, it is desirable to install the sludge concentration meter 18 in the activated sludge treatment tank 2, and it is particularly desirable when the sludge concentration in each tank is different, such as the step aeration method, but the sludge concentration in the sludge concentration tank 7 and the concentrated sludge 9, It is possible to estimate the sludge concentration in the activated sludge treatment tank 2 from the sludge amount of the excess sludge 10, the water amount of the treated water 4, the SS concentration of the treated water, the sludge amount of the separated sludge 5, the SS concentration of the separation liquid 8, and the water amount. Since it is possible, the sludge concentration meter of the activated sludge treatment tank 2 may be omitted in consideration of economy when it is provided with the above-described measuring instrument for measuring the amount of water and sludge.

  In the processing apparatus of this invention, the sludge solubilization apparatus 11 is installed in order to solubilize a part of sludge of the sludge concentration tank 7. FIG. In order to send the concentrated sludge in the tank to the sludge solubilizing means, the sludge supply pump 23 is preferably immersed in the sludge concentration tank 7. Sludge that has undergone solubilization treatment such as crushing is returned to the activated sludge treatment tank 2. At this time, as the tank for returning the solubilized sludge, either the denitrification tank 14 or the nitrification tank 15 may be used, but when returned to the denitrification tank 14, the solubilized sludge 12 is effectively used as an organic substance for denitrification. Therefore, the denitrification tank 14 is preferable.

  The sludge solubilizer 11 used in the treatment apparatus of the present invention is not particularly limited as long as it can solubilize sludge. For example, a wet medium agitating mill, an ultrasonic wave, a homogenizer, In addition to mechanical crushing treatment equipment such as mixers, chemical solubilization treatment equipment such as oxidant and alkali treatment, equipment using a method of crushing and solubilizing sludge with heat treatment equipment, etc. can be mentioned alone. Or 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 it hardly generates difficult-to-decompose organic substances.

  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, it will be difficult to crush microorganisms, and even if the true specific gravity is greater than 7.0, the sludge crushing effect will hardly be improved, and the power required for stirring will increase. 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 crushing effect and power consumption, and the disk (pin) tip peripheral speed is preferably 3 to 30 m / second, particularly 5 to 20 m / second. 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 agitation mill treatment is appropriately set according to 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. However, cooling water is usually not necessary.

  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 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.

  In the wet medium agitation mill treatment, the sludge crushing effect is not greatly affected by the sludge concentration as long as the sludge flows. 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 this method, the separated sludge is concentrated using a membrane separation type sludge concentration tank in order to smash sludge economically. As the concentrated sludge concentration, the higher the amount, the lower the treatment amount, which is economically preferable. However, the higher the sludge concentration, the higher the viscosity, and it becomes difficult to obtain a separation liquid by membrane separation. % Is preferable, and 1.5% by mass to 3% by mass is more preferable.

  As described above, by using the processing apparatus according to the second invention, the processing method of the first invention can be used. At this time, nitrifying bacteria having a slow growth rate can be used. In order to keep it stably in the interior and to sufficiently remove nitrogen, it is necessary to control each condition in the system so that the aerobic solid residence time in the activated sludge treatment tank is not less than a predetermined time. preferable.

  By the way, from the advanced treatment facility design manual (draft) (Japan Sewerage Association 1994), for example, in the circulatory nitrification denitrification method, the aerobic solid residence time (θXA) is expressed by the following equation (1). However, in order to retain nitrifying bacteria in the system, the aerobic solid residence time (θXA) needs to satisfy the following formula (2). In the circulation nitrification denitrification method, It is shown that the aerobic solid residence time (θXA) satisfies the relationship between the water temperature and the relational expression (3).

θXA = θX · tA / t (1)
θXA: Aerobic solids residence time (days)
θX: Solid residence time (days)
tA: Aerobic tank [nitrification tank] Residence time (hours)
t: Biological reaction tank [activated sludge treatment tank] Residence time (hours)
θXA = 1 / μ (2)
μ: Specific growth rate of nitrifying bacteria (function of water temperature T (° C)) (1 / day)
θXA = δ · 20.6e (−0.0627T) Equation (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. As a result, most of the solubilized sludge is killed, and the actual aerobic solid residence time is shortened.

  Therefore, it is necessary to set the sludge concentration, sludge solubilization amount, surplus sludge amount and aeration time with great care based on the water temperature and the sludge densitometer value, and to retain nitrifying bacteria in the system.

The calculation of the aerobic solid retention time (θXA) when solubilization is performed is calculated by calculating the sludge from which nitrifying bacteria have been killed as sludge flowing out of the system among sludge to be crushed and solubilized. It is shown by (4).
θXA = tB / 24 · (VA · XA) / ((QW + α · QM) · XW + (Q−QW) · XE)
...... Formula (4)
VA: Capacity of aerobic tank [nitrification tank] (m3)
XA: Sludge concentration in aerobic tank [nitrification tank] (kg / m3)
XW: Surplus sludge concentration, sludge concentration of sludge solubilized (kg / m3)
XE: SS concentration in treated water (kg / m3)
Q: Amount of inflow sewage (m3 / day)
QW: Excess sludge volume (m3 / day)
QM: Sludge solubilization amount (m3 / day)
tB: Aeration time (hours)
α: Rate of death of nitrifying bacteria by sludge solubilization (-)

  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 (VA · XA) is set so that the calculated value of the formula (4) becomes longer. ), Sludge solubilized weight (QM · XW), surplus sludge weight (QW · XW), and aeration time (tB) are preferably set and operated. In general, it is preferable to set the calculated value of the formula (4) to be longer than the calculated value of the formula (3) by 2 days or more, and more preferable to set it to be longer than 5 days.

In equation (4), it is desirable to measure the sludge concentration in the aerobic tank [nitrification tank] as appropriate, but the sludge concentration flowing out from the activated sludge treatment tank is expressed by the following equation (5).
XA '= ((QR + QX) .XR + (Q-QW) .XE) / (Q-QW + QR + QX)
...... Formula (5)
Further, the return sludge concentration and the sludge concentration entering the sludge concentration tank are expressed by the following equation (6) from the sludge concentration in the sludge concentration tank and the sludge concentration in the separated liquid.
XR = ((QM + QW) · XW + QF · XF) / QX (6)
here,
When XF = 0 kg / m3, the sludge concentration flowing out from the activated sludge treatment tank is expressed by the following expression (7) from the expressions (5) and (6). That is, each flow rate and sludge concentration and treatment in the sludge concentration tank It can be calculated from the SS concentration of water, and the sludge concentration in the aerobic tank [nitrification tank] can be estimated from this value.
XA ′ = ((QR + QX) · (QM + QW) · XW / QX + (Q−QW) · XE) / (Q−QW + QR + QX) (7)
XA ': Concentration of sludge flowing out from activated sludge treatment tank (kg / m3)
XE: SS concentration in treated water (kg / m3)
XR: Return sludge concentration, sludge concentration in the sludge concentration tank (kg / m3)
XW: Surplus sludge concentration, sludge concentration of sludge solubilized (kg / m3)
XF: Sludge concentration in the separation liquid (kg / m3)
Q: Amount of inflow sewage (m3 / day)
QR: Return sludge volume (m3 / day)
QX: Sludge concentration tank inflow (m3 / day)
QW: Excess sludge volume (m3 / day)
QM: Sludge solubilization amount (m3 / day)
QF: Water volume of separation liquid (m3 / day)
In addition, the amount of SS in normal treated water is relatively small compared to the amount of excess sludge and solubilized sludge, and when the membrane separation method is used as the solid-liquid separation method of the solid-liquid separation tank, The SS concentration of treated water is negligible.
As described above, in the treatment apparatus of the present invention, since the excess sludge is extracted and the sludge to be crushed is extracted from the sludge concentration tank having the sludge concentration meter, the sludge concentration in the sludge concentration tank is measured. The above calculation can be easily performed.

  Next, an example of how to determine each set value in the operating conditions of this 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. When changing, it is preferable to increase / decrease in proportion to the amount of inflow water. Usually, the sludge solubilization amount may be about 1 to 5 times the amount of excess sludge generated when the sludge is not solubilized.

  (2) Set the minimum aeration time per day for the nitrification tank. 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 1,000 mg / L to 4,000 mg / L when the solid-liquid separation tank is a precipitation tank, preferably 10,000 mg / L to 30,000 mg / L, more preferably 15,000 when the membrane separation method is used. More preferred is mg / L to 30,000 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). In the case where the water temperature is a fixed value, it is preferable to use the lowest water temperature of the treatment plant, 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) Start operation of the sludge concentration tank. The set sludge concentration tank sludge concentration is preferably 10,000 mg / L to 40,000 mg / L, and more preferably 15,000 mg / L to 30,000 mg / L.

  The operation of the sludge solubilizing means 4 is started. However, when the calculated value of the formula (5) is equal to or shorter than the required aerobic solid residence time (days), the sludge solubilization means starts operating after increasing the nitrification tank sludge concentration. Since α in equation (5) varies depending on the type of sludge and the sludge solubilization method, it is preferable to obtain beforehand by experiment using sludge from the treatment plant. It is preferable to set α = 1.

  (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) is less than the required aerobic solid residence time (days), the aeration time of the nitrification tank is extended.

  (8) Even if the aeration time per day in the nitrification tank is set to 24 hours due to a decrease in water temperature, etc., if the calculated value of formula (5) is less than the required aerobic solid residence time (days) By extending the aeration time of the sludge concentration tank, the aerobic state of the sludge in the sludge concentration tank is maintained and the nitrifying bacteria are maintained and increased.

  (9) In the case where nitrogen removal deteriorates, the sludge solubilization amount is further reduced so that the required aerobic solid residence time (days) is reached, and the sludge in the sludge concentration tank is partly or entirely contained in the activated sludge treatment tank. Will be returned.

  (10) When the calculated value of the formula (5) is equal to or longer than the required aerobic solid residence time (days), the sludge solubilization amount is increased to the set sludge solubilization amount. Moreover, the aeration time of the sludge concentration tank is returned to the original time.

(11) Even when the set sludge solubilization amount is reached, the aeration time of the nitrification tank per day is reduced if the required aerobic solid retention time (days) or more is reached.
By reducing the aeration time, the running cost of the aeration apparatus can be reduced.

  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 or sludge concentration tank is calculated to be constant. However, in some cases, the volume may be changed by changing the water surface height. In this method, surplus sludge and sludge for sludge solubilization are extracted from the same sludge concentration tank, and aerobic solids residence time can be easily calculated.

  Further, as a method of changing the sludge solubilization amount, the sludge supply speed to the sludge solubilization means 4 may be changed, but since the residence time in the sludge solubilization means 4 changes, the sludge supply speed is changed. It is better to change the processing time per day while keeping it constant.

  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 concentration of phosphorus in the treated water usually increases as the amount of sludge generated decreases, a method of removing phosphorus by adding a flocculant such as ferric chloride to the activated sludge treatment tank, or in the treated water A method of adding and removing a flocculant or the like is preferable.

  As described above, using the treatment apparatus of the present invention, it is possible to reduce the amount of sludge generated by appropriately controlling the amount of sludge in the activated sludge treatment tank, the amount of excess sludge, the amount of sludge solubilized, and the aeration time, Nitrogen and the like in sewage can be removed stably.

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 apparatus of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Nitrogen-containing organic waste water 2 Activated sludge treatment tank 3 Solid-liquid separation tank 4 Treated water 5 Separation sludge 6 Return sludge 7 Sludge concentration tank 8 Separation liquid 9 Concentrated sludge 10 Surplus sludge 11 Sludge solubilization means 12 Solubilized sludge 13 Concentrated sludge Return line 14 Denitrification tank 15 Nitrification tank 16 Circulating fluid 17 Stirrer 18 Sludge concentration meter 19 Sludge concentration device 20 Circulation pump device 21 Sludge pump 22 Sludge concentration meter 23 Sludge supply pump 24 Suction pump device 25 Active sludge treatment tank diffuser 26 Air diffuser

Claims (4)

  After treating the nitrogen-containing organic wastewater in the activated sludge treatment tank, the treatment liquid is solid-liquid separated, the separated water is discharged as treated water, and the separated sludge is returned to the activated sludge treatment tank. In the method, a part or all of the sludge to be returned to the activated sludge treatment tank is concentrated in a membrane separation type sludge concentration tank having a sludge concentration meter, and then part of the concentrated sludge is solubilized. A method for treating nitrogen-containing organic wastewater, wherein the waste sludge is returned to the activated sludge treatment tank, and the remainder of the concentrated sludge is drawn out of the system as excess sludge from the sludge concentration tank.   When the nitrification capacity in the activated sludge treatment tank decreases, the sludge concentration tank is aerobic by aeration and returned to the activated sludge treatment tank without solubilizing part or all of the sludge in the sludge concentration tank The method for treating nitrogen-containing organic wastewater according to claim 1.   It consists of an activated sludge treatment tank for treating nitrogen-containing organic wastewater, a solid-liquid separation device for solid-liquid separation of the treatment liquid, a membrane separation-type sludge concentration tank having a sludge densitometer, and a sludge solubilizer. Nitrogen-containing organic wastewater treatment equipment. The treatment apparatus for nitrogen-containing organic wastewater according to claim 3, wherein the sludge solubilization apparatus is a wet medium stirring mill.