JPH11333494A - Method and apparatus for biological dentrification of waste water - Google Patents

Abstract

PROBLEM TO BE SOLVED: To modify biological sludge to an easily biodegradable one by a simple modifying treatment to enhance the utilization efficiency of org. matter at a time of the utilization of the modified sludge as a hydrogen donor in a denitrification process to reduce the vol. of sludge thereby and to reduce the amt. of org. matter added from the outside. SOLUTION: Biological sludge is withdrawn to a modifying treatment tank 16 from a biological denitrification treatment system 10 including a denitrification tank 1 and a nitration and solid-separation tank 2 is modified to an easily biodegradable state by ozone treatment, heat treatment, an acid and alkali treatment or the like and the modified sludge is subjected to acid fermentation in an acid fermentation tank 18 to be introduced into the denitrification tank 1 and org. matter formed by acid fermentation is used as a hydrogen donor to perform denitrification treatment.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for removing biological nitrogen from wastewater containing nitrogen by biological nitrification and denitrification.

[0002]

2. Description of the Related Art As a method for treating wastewater containing ammoniacal or organic nitrogen compounds, there is a biological nitrification and denitrification treatment method. This method uses activated sludge for COD in wastewater,
While decomposing the BOD component, converting the organic nitrogen compound into ammonia nitrogen, nitrifying (oxidizing) the ammonia nitrogen to nitrate or nitrite nitrogen by nitrifying bacteria, and reducing it to nitrogen gas by denitrifying bacteria to remove nitrogen gas It is a method of nitriding.
In this treatment method, a method is also provided in which a denitrification tank is provided in a preceding stage, a nitrification solution and separated sludge are returned to a denitrification tank, mixed with raw water, denitrified, and simultaneously decomposed BOD components.

[0003] A general aerobic biological treatment method for treating an organic wastewater under aerobic conditions by utilizing the action of aerobic microorganisms, such as the activated sludge treatment method constituting the above treatment system, comprises: Since the processing cost is low and the processing performance is excellent, it is widely used in general. However, since a large amount of hardly dewaterable excess sludge is generated, a processing method for reducing the volume of the sludge is performed.

As a treatment method for reducing the volume of such sludge, in a general aerobic treatment method, sludge is extracted from an aeration tank or a sedimentation tank, and the extracted sludge is subjected to ozone treatment, heat treatment, acid or alkali treatment. There has been proposed a method in which the sludge is reformed to be easily biodegradable by a reforming treatment, and the reformed sludge is returned to an aeration tank for biodegradation (for example, Japanese Patent Application Laid-Open No.
No. 116686). In such a method, the reformed sludge is BO
Since the load of the aeration tank is used as the D source, the sludge is multiplied using this as a substrate, and the amount of new sludge multiplied is about 1 / of the reformed sludge.
It is set to 3. For this reason, it is necessary to reform and return a large amount of sludge, and in order to reduce the amount of surplus sludge to zero, it is necessary to reform three times the amount of surplus sludge.

[0005] Also in the biological nitrogen removal method, a method has been proposed in which sludge is modified to be easily biodegradable by a modification treatment and introduced into a denitrification step (for example, Japanese Patent Application Laid-Open No. Hei 8-1190).
In the biological nitrogen removal method, when nitrate or nitrite generated in the nitrification step is reduced by the action of the denitrifying bacteria in the denitrification step and converted into nitrogen gas, it is necessary for nitric acid respiration of the denitrification bacteria. It is necessary to add an electron donor (hydrogen donor). When an organic substance such as methanol is added as the hydrogen donor, the treatment cost increases and excess sludge increases.

[0006] Japanese Patent Application Laid-Open No. Hei 8-1190 discloses that in such a biological nitrogen removal method, in order to reduce the volume of sludge, when sludge is returned to be easily biodegradable by ozone treatment and returned. This is a method in which the amount of an organic substance added from the outside is reduced by being introduced into the denitrification step and used as a hydrogen donor.

[0007] By the way, in general, methods for modifying sludge to be easily biodegradable include ozone treatment, heat treatment, acid treatment, alkali treatment and the like, all of which make biosludge having poor biodegradability biodegradable. However, reforming is usually performed so as to enable treatment with a long residence time as in the activated sludge treatment method, and is not modified until it is decomposed into low-molecular compounds.

For this reason, when sludge that has been modified to be easily biodegradable is supplied to the denitrification step, the rate of use as an electron donor is low, and the utilization efficiency in the denitrification reaction is not very high. That is, easily biodegradable sludge contains a large amount of high-molecular organic matter (such as broken cell membranes) that constituted microorganisms. After the molecule has been degraded, the degraded compound is taken up by the microorganism,
It needs to go through the process of being metabolized. Naturally, even in the denitrification reaction, the biodegradable sludge is used as an electron donor after being depolymerized and taken up by microorganisms, and is not used as a high molecular compound as it is.

However, the hydrolysis rate is relatively slow,
It takes 1-2 days for complete hydrolysis. On the other hand, the reaction time (residence time) of the denitrification step is usually several hours, and may be 30 minutes or less in an intermittent aeration method or the like.
Therefore, the above method has a problem that the organic matter in the easily biodegradable sludge sent to the next step without being completely hydrolyzed in the denitrification step is not effectively used. The ratio of the unused organic matter is estimated to be as high as 20 to 60%, and it can be considered that if the organic matter can be effectively used, the efficiency can be further improved. It is also conceivable to decompose organic substances into low molecules in the reforming treatment, but this requires a large amount of ozone, heat, acid, alkali, etc., and is not practical.

Usually, an aerobic step (BOD) is provided after the denitrification step.
Oxidation or nitrification reaction), but the rate of hydrolysis of high-molecular organic matter is higher in an aerobic environment than in a denitrification environment. It is hardly expected to return to the denitrification process again with the above. Thus, when the unused organic matter is sent to the next step, that is, the BOD oxidation step or the nitrification step,
Since the remaining organic matter is oxidatively decomposed by microorganisms as a load, a large amount of aerated air is required, and there is a problem that the amount of sludge multiplication becomes large.

On the other hand, there is also known a method in which biological sludge is subjected to acid fermentation, then subjected to ozone treatment, modified to be easily biodegradable, and returned to the biological treatment step (Japanese Patent Laid-Open No. 7-88495). However, the acid fermentation in this method is merely performed to adjust the pH to a value suitable for ozone treatment, and the sludge subjected to ozone treatment is returned to the biological treatment system as it is. Also has the same problem as described above.

[0012]

SUMMARY OF THE INVENTION An object of the present invention is to convert organic sludge into easily biodegradable one by a simple reforming treatment, and to use the organic sludge as a hydrogen donor in a denitrification step. It is an object of the present invention to provide a method and an apparatus for removing biological nitrogen from wastewater, which can reduce the volume of sludge and reduce the amount of organic substances added from the outside.

[0013]

SUMMARY OF THE INVENTION The present invention is a method and apparatus for removing biological nitrogen from wastewater. (1) In a method for removing biological nitrogen from wastewater including a denitrification step, a step of extracting a part of biological sludge generated in a treatment system, a reforming step of reforming the extracted sludge to be easily biodegradable, A method for removing biological nitrogen from wastewater, comprising: an acid fermentation step of acid-fermenting sludge-treated sludge; and a transfer step of introducing the acid-fermented sludge to a denitrification step. (2) Biological nitrogen removal treatment system including a denitrification tank, extraction means for extracting a part of biological sludge from the treatment system, reforming treatment tank for reforming the extracted sludge to be easily biodegradable, and acidification of the reformed sludge An apparatus for removing biological nitrogen from wastewater, comprising an acid fermenter for fermentation and a transfer means for introducing acid fermentation sludge into a denitrification tank.

The wastewater to be treated according to the present invention is wastewater containing a nitrogen compound such as ammoniacal, organic, nitric, nitrite, etc., and it is particularly suitable for the treatment. The wastewater contains nitrogen compounds, and may further contain organic substances and other impurities. Examples of such wastewater include night soil, sewage, food wastewater, and the like. Among these wastewaters, wastewater having a BOD / N ratio of 4 or less, preferably 0.1 to 2 is preferable as a treatment target.

In the present invention, such wastewater is treated in a biological nitrogen removal treatment system having a denitrification tank to biologically remove nitrogen. The above treatment system includes an organic matter decomposing step for decomposing organic substances in addition to a denitrifying step, a nitrification step for oxidizing ammoniacal or organic nitrogen to nitric acid or nitrite nitrogen, and a method for separating sludge and treatment liquid. Although a solid-liquid separation step and the like are included, each of these steps may be performed independently, or a plurality of steps may be performed simultaneously or with a time delay.

Apparatuses constituting such a treatment system include a denitrification tank for a denitrification step, an aeration tank for an organic matter decomposition step, a nitrification tank for a nitrification step, and a solidification tank for solid-liquid separation. Although a liquid separation tank can be provided, it is also possible to adopt a configuration in which a plurality of steps are performed simultaneously or with a time lag by using these tanks. For example, an aeration tank and a nitrification tank can be shared, and a solid-liquid separation tank can also be accommodated therein. The denitrification tank can also be used as an aeration tank and / or a nitrification tank. For example, by using an intermittent aeration tank, an organic matter decomposition step and a nitrification step can be performed during aeration.
At the time of non-aeration, a denitrification step can be performed. Known solid-liquid separation methods such as sedimentation separation, filtration separation, flotation separation, centrifugation, and membrane separation can be employed. The aeration tank for decomposing organic substances can be omitted when the content of organic substances in the raw water is small, and the nitrification tank can be omitted when nitrogen is nitric acid or nitrite nitrogen.

In the treatment by the above-mentioned treatment system, wastewater as the water to be treated is treated under aerobic or anaerobic conditions in the organic matter decomposition step, and COD and BO in the wastewater are treated with activated sludge.
In addition to decomposing the D component, the organic nitrogen compound is converted to ammonia nitrogen, and in the nitrification process, the ammonia nitrogen is nitrified (oxidized) to nitric acid or nitrite nitrogen under aerobic conditions by nitrifying bacteria. It is the same as the conventional one in that nitrate or nitrite nitrogen is reduced under anaerobic conditions by denitrifying bacteria and denitrified. In such a nitrogen removal system, the combination or the number of each step can be freely set according to the wastewater.For example, a denitrification tank is provided in the former stage, and the nitrification liquid and the separated sludge are returned to the denitrification tank and mixed with the raw water, B with denitrification
It is also possible to adopt a method of removing OD and then nitrification and denitrification, or a method of combining aerobic treatment and anaerobic treatment as an organic matter decomposition step.

The present invention is particularly effective when wastewater having a low BOD / N ratio of 4 or less in the raw water is subjected to nitrification and denitrification. In particular, after reducing and removing nitrogen components in the wastewater by microorganisms,
It is effective in a membrane separation type activated sludge treatment method in which solid-liquid separation of microorganisms and treated water is performed by membrane separation. This is because the apparatus that decomposes excess sludge that has been easily biodegraded as in the present invention in the same treatment system that treats raw water requires more load on the treatment system than a treatment system that simply treats raw water. Because you do. On the other hand, it is important for an apparatus that performs a nitrification reaction to ensure an SRT (sludge residence time) of a certain value or more in order to smoothly advance the nitrification reaction. In order to treat such a large load with the same SRT as before, it is necessary to secure more microorganisms in the reaction tank, so that the capacity of a biological reaction tank such as a denitrification tank or a nitrification tank is increased. Or increase the concentration of sludge held in the biological reaction tank. In this case, if the solid-liquid separation is performed by membrane separation, solid-liquid separation is possible even when the sludge concentration is high, and the apparatus can be downsized.

In the present invention, a part of the biological sludge generated in the above-mentioned treatment system is withdrawn and modified to be easily biodegradable.
Furthermore, it is acid fermented and introduced into a denitrification tank. For this reason, as a nitrogen removal device, extraction means for extracting biological sludge from the treatment system,
A reforming treatment tank for reforming, an acid fermentation tank for acid fermentation, and a transfer means for transfer are provided for easy biodegradability.

Examples of the biological sludge to be drawn out for treatment include sludge generated in an organic matter decomposition step, a nitrification step, a denitrification step, a solid-liquid separation step, or an optional step associated therewith, and these are concentrated. It may be in a state or a sparse state, and can be pulled out from any position. These extracted sludges may be subjected to a reforming treatment as they are, or may be further concentrated to a higher concentration by a centrifuge. The amount of biological sludge to be withdrawn may be basically the amount necessary to use it as a source of organic matter during denitrification, but in systems where excess sludge is generated in large quantities, sludge is larger than the amount discharged as excess sludge. By extracting the amount and performing the reforming treatment, the volume of sludge can be reduced, and in some cases, the amount of excess sludge can be reduced to zero.

Any method can be adopted as a reforming treatment method for modifying the extracted sludge to be easily biodegradable.
For example, reforming treatment by ozone treatment, reforming treatment by acid treatment, reforming treatment by alkali treatment, reforming treatment by heat treatment, high-pressure pulse discharge treatment, grinding treatment by mill such as ball mill, colloid mill, etc. Modified treatment or the like can be employed. Among these, the reforming treatment by ozone treatment is preferable because the treatment operation is simple and the treatment efficiency is high. The degree of the modification treatment may be such that microorganisms in the biological sludge are killed and cell membranes and cell walls are destroyed and lysed, and it is not necessary to reduce the molecular weight.

In the ozone treatment as the reforming treatment, the extracted sludge extracted from the aerobic biological treatment system may be brought into contact with ozone, and the sludge is reformed to be easily biodegradable by the oxidizing action of ozone. When the ozone treatment is performed in an acidic region having a pH of 5 or less, the efficiency of oxidative decomposition increases. The pH adjustment at this time is as follows:
An inorganic acid such as sulfuric acid, hydrochloric acid or nitric acid can be added to the biological sludge as a pH adjuster. However, it is preferable to adjust by adding an acid fermentation sludge in a later step, and these may be used in combination. When adding a pH adjuster, the pH should be 3 ~
It is preferable to adjust the pH to 4, and in the case of returning the acid fermentation sludge, it is preferable to return the acid fermentation sludge in an amount of 0.5 to 3 times the amount of the extracted sludge to adjust the pH to 4 to 5.

[0023] Ozone treatment is performed by drawing sludge or acid fermentation.
Concentrate the liquid as it is or, if necessary, with a centrifuge
After adjusting the pH to 5 or less, contact with ozone
Can be performed. As a contact method,
A method and machine for introducing sludge into an ozone treatment tank and injecting ozone
Method using mechanical stirring, method using packed bed, etc. are adopted
Wear. Ozone includes ozone gas and ozone-containing air.
Ozone-containing gas such as air or ozonized air can be used.
The amount of ozone used is 0.002-0.05g-O _Three/ G-
VSS, preferably 0.005 to 0.03 g-O_Three/ G
-VSS is desirable. Biofouling due to ozone treatment
Mud is oxidatively decomposed and converted to easily biodegradable BOD components
Is done.

In the acid treatment as the reforming treatment, the extracted sludge extracted from the aerobic biological treatment system is led to a reforming tank, and hydrochloric acid,
A mineral acid such as sulfuric acid is added, and pH 2.5 or less, preferably p
What is necessary is just to stay for a predetermined time under the acidic condition of H1-2. The residence time is, for example, 5 to 24 hours. On this occasion,
It is preferable to heat the sludge, for example, to 50 to 100 ° C., since reforming is promoted.

In the alkali treatment as the sludge reforming treatment, the extracted sludge drawn from the aerobic biological treatment system is led to a reforming tank, and alkali such as sodium hydroxide and potassium hydroxide is added to the sludge at 0.1%. What is necessary is just to add 1 to 1% by weight and to stay for a predetermined time. The residence time is about 0.5 to 2 hours, and the sludge is reformed to be easily biodegradable. At this time, heat the sludge,
For example, heating to 5 to 100 ° C. is preferable because reforming is promoted.

The heat treatment as the reforming treatment can be performed alone, but is preferably performed in combination with an acid treatment or an alkali treatment. When heat treatment is performed alone, for example, the temperature may be 70 to 100 ° C., and the residence time may be 2 to 3 hours.

The high-voltage pulse discharge process is performed with an electrode interval of 3 to
Sludge is present between a positive electrode of 10 mm, preferably 4 to 8 mm such as a tungsten / thorium alloy, and a negative electrode of stainless steel or the like, and an applied voltage of 10 to 50 kV, preferably 20 to 40 kV, and a pulse interval of 20 to 80 Hz, preferably Performs pulse discharge at 40 to 60 Hz, and can perform treatment while circulating sludge sequentially.

The acid fermentation is carried out by subjecting the modified sludge modified as described above to anaerobic treatment in the presence of sludge containing acid-producing bacteria. In this step, the modified sludge is kept in the acid fermentation tank at a pH of 3 to 9, preferably 4 to 6, and kept for 2 hours to 10 days, preferably 0.5 to 4 days under a condition where oxygen is not supplied. It is performed by The acid fermentation tank may be a complete mixing type (single-stage, multi-stage), a plug flow type, or an intermediate type, but usually a one-stage or two-stage complete mixing tank can be used. Although the treatment may be carried out continuously or batchwise, it is usually preferred to carry out the treatment continuously. In addition, in order to prevent an excessive decrease in pH of the acid fermenter, it is preferable to control the pH by injecting an alkali substance such as sodium hydroxide by a pH controller. At the start-up of acid fermentation, quick start-up is possible by introducing bio-sludge, which is not biodegradable, as a seed fungus.

[0029] By acid fermentation of the modified sludge, the high biodegradable sludge obtained by decomposing biological sludge is decomposed by acid-producing bacteria and converted into low molecular organic acids such as acetic acid, propionic acid and butyric acid. When such acid fermentation sludge is introduced into a denitrification tank, low-molecular-weight organic acids are rapidly used as hydrogen donors, and nitric acid or nitrite nitrogen is reduced to nitrogen gas and removed by the action of denitrifying bacteria. Low molecular organic acids decompose.

The high molecular organic matter after the microorganisms in the extracted sludge have been killed and destroyed is subjected to acid fermentation in advance.
When it is hydrolyzed and converted to low molecular weight, it is rapidly converted into a substrate that can be effectively used in the denitrification step. Therefore, the organic matter utilization rate in the easily biodegradable sludge in the denitrification step increases, and
The above is also possible. Therefore, the amount of organic substances such as methanol added from the outside is reduced. The amount of surplus sludge is reduced by the decomposition of the extracted sludge, and the activated sludge is used for denitrification, so that the load on the organic matter decomposition step is small, and therefore the amount of new sludge multiplied is also reduced.

That is, the BOD / N ratio in the raw water is 4 or less,
Particularly when denitrifying wastewater of 2 or less, methanol or the like is added as a hydrogen donor because it is not enough to simply use BOD in raw water as a hydrogen donor for the denitrification reaction. In the present invention, as the hydrogen donor, the biological sludge which has been very easily used for the denitrification reaction by the reforming treatment and the acid fermentation can be effectively used, so that the amount of the chemical added as the hydrogen donor is significantly reduced. be able to. In this case, an increase in the load on the treatment system due to the biodegradable biosludge and a decrease in the load on the treatment system due to a reduction in the amount of chemicals such as methanol as a hydrogen donor are offset. For wastewater of 0.5 or less, there is no need to increase the sludge concentration or increase the size of the reaction tank as compared with the conventional method, so that efficient treatment can be performed at low cost.

[0032]

According to the present invention, the modified sludge is subjected to acid fermentation and introduced into the denitrification step. Therefore, a simple reforming treatment can be performed without strengthening the reforming conditions such as increasing the amount of injected ozone. Thus, the biological sludge can be easily biodegradable, and the biosludge can be reduced in molecular weight by a simple operation of acid fermentation to increase the utilization efficiency as a hydrogen donor. For this reason, the sludge can be reduced in volume and the amount of organic substances added from the outside can be reduced, so that the amount of newly generated sludge can be reduced and nitrogen can be efficiently removed with a small device.

[0033]

Embodiments of the present invention will be described below with reference to the drawings. 1 to 3 are system diagrams showing biological nitrogen removing apparatuses according to different embodiments. FIG. 1 shows that if the nitrogen removal rate can be relatively low, FIGS.
Applies when high.

In FIG. 1, reference numeral 1 denotes a denitrification tank, 2 denotes a nitrification / solid-liquid separation tank, both of which are connected by a communication path 3 and a return path 4. A treatment water channel 6 is connected to the solid / liquid separation tank 2, and these constitute a treatment system 10. The denitrification tank 1 has a stirrer 7 and a motor M
It is driven by _one . An immersion type membrane separation device 9 is provided in a guide cylinder 8 provided in the nitrification / solid-liquid separation tank 2, and a process having a suction pump P ₁ in a permeate liquid chamber 12 of a permeable membrane 11 provided therein. Waterway 6 is in communication. An aeration device 13 is provided at a lower portion of the guide tube 8, and an air passage 14 communicates therewith. The sludge return path 4 pump P ₂ is provided.

In order to extract the biological sludge from the treatment system, the extraction passage 15 communicates with the reforming treatment tank 16 via the pump P _3, and the acid fermentation tank 1 communicates with the reforming treatment tank 16 via the communication passage 17.
From 8, a transfer path 19 communicates with the denitrification tank 1. An ozone treatment tank is used as the reforming treatment tank 16, and an ozone supply path 22 is connected to the ozone blowing device 21. Agitator 23 is driven by the motor M ₂ provided in the acid fermentation tank 18. Reference numeral 24 denotes a medicine injection path provided as necessary, reference numeral 25 denotes a return path, and reference numeral 26 denotes a drainage path.

The processing by the above-described device is performed as follows. First, raw water is introduced from the raw water channel 5 into the denitrification tank 1, the nitrification liquid and the returned sludge are returned from the return line 4, and the mixture is gently stirred by the stirrer 7 to come into contact with the denitrifying bacteria in an anaerobic state to perform biological denitrification. Do. As a result, nitric acid and nitrite nitrogen in the nitrification liquid are reduced to nitrogen gas and denitrified, and low-molecular organic substances contained in raw water are decomposed. If the hydrogen donor is insufficient, a low-molecular-weight organic substance such as methanol is supplied from the chemical injection path 24.

A part of the liquid in the denitrification tank 1 is transferred from the communication path 3 to the nitrification / solid-liquid separation tank 2, where air is sent from the air path 14 and aerated by the aeration device 13 to perform aerobic biological treatment. This decomposes organic substances in the liquid and nitrifies ammoniacal and organic nitrogen into nitric acid and nitrite nitrogen. Then, by suctioning with the pump P _1, solid-liquid separation is performed by the membrane separation device 9, and the permeate is discharged from the treatment water channel 6 as treatment water. Nitrifying solution and concentrated sludge is subjected to denitrification returned from return path 4 by a pump P ₂ in the denitrification tank 1. The aeration device 13 uses the air flow to transmit the permeable membrane 11.
It also functions as a pollution prevention means.

In order to extract the biological sludge from the treatment system 10 and perform the reforming treatment, a pump P is supplied from the nitrification / solid-liquid separation tank 2.
_{3, the} concentrated biological sludge is introduced into the reforming treatment tank 16 through the extraction path 15, and ozone is supplied from the ozone supply path 22,
The ozone is blown from the ozone blowing device 21 to perform ozone treatment, thereby modifying the biological sludge to be easily biodegradable. The amount of drawn sludge can be the whole amount of excess sludge or more. During the ozone treatment, the pH can be adjusted by returning the acid fermentation sludge from the return path 25.

The reformed sludge is introduced into the acid fermentation tank 18 through the communication line 17 and gently stirred by the stirrer 23 to make it contact with the acid-producing bacteria under anaerobic conditions to perform acid fermentation. Even if the bio-sludge not subjected to the reforming treatment is subjected to acid fermentation, the effect of reducing the volume of the sludge is small, a large amount of sludge circulates as it is, and the amount of organic acid generated is small by that amount. Most of them are decomposed by acid fermentation to lower molecular weight, the effect of volume reduction of sludge is large, and the amount of low molecular organic acid generated is also large.

When the acid fermentation sludge containing the organic acid whose molecular weight has been reduced in this way is introduced into the denitrification tank 1 from the transfer path 19, the organic acid having a low molecular weight is used as a hydrogen donor. For this reason, the amount of organic substances such as methanol injected from the chemical injection path 24 is reduced,
In some cases, it can be zero. When excess sludge is generated, the sludge is discharged from the sludge passage 26.

When the modified sludge is returned to the denitrification tank 1 without acid fermentation, the organic matter utilization rate is low because the high molecular organic matter is not used as a hydrogen donor. In addition, since high-molecular organic matter becomes a load on the nitrification / solid-liquid separation tank 2, it is necessary to increase the amount of aeration here, and as a result of decomposition,
The sludge volume-reducing effect is also small because the amount of generated sludge is large. On the other hand, when the acid fermented sludge is returned, the organic matter utilization rate in the denitrification tank 1 increases, and the amount of load in the nitrification and solid-liquid separation tank 2 is small. Can be reduced.

In FIG. 2, a denitrification / nitrification tank 3 comprising an intermittent aeration tank is used instead of the denitrification tank 1 and the nitrification / solid-liquid separation tank 2 shown in FIG.
1 and a solid-liquid separation tank 32 are provided. The denitrification and nitrification tank 31 is provided with an aeration device 33 below the stirrer 7 and is connected to an air passage 34. The solid-liquid separation tank 32 has substantially the same configuration as the nitrification / solid-liquid separation tank 2 in FIG.

In the treatment by the above-described apparatus, first, raw water is introduced into the denitrification / nitrification tank 31 from the raw water channel 5, sludge is returned from the return line 4, air is sent from the air line 34, and intermittent aeration is performed by the aeration device 33. I do. In the aerobic process, the organic matter in the raw water is decomposed and the ammonia and organic nitrogen are nitrified into nitric acid and nitrite nitrogen. Subsequently, when the aeration is stopped and the process proceeds to the anaerobic step, denitrification is performed by maintaining the anaerobic state by gently stirring with a stirrer.

The liquid in the denitrification / nitrification tank 31 is transferred to the solid / liquid separation tank 32 continuously or intermittently, and is subjected to solid / liquid separation by the membrane separator 9. The aeration device 13 may be provided for cleaning the permeable membrane 11, but it is preferable to decompose and nitrify organic substances here. The return of the sludge and nitrification liquid from the return path 4 may be continuous or intermittent, but the return amount is preferably 3 to 5 times the raw water amount.

The extraction of the biological sludge from the extraction passage 15, the reforming treatment in the reforming treatment tank 16, and the acid fermentation in the acid fermentation tank 18 are performed in substantially the same manner as in FIG. Acid fermenter 1
It is preferable that only the denitrification step (anaerobic step) be performed for the introduction of the acid fermentation sludge from Step 8 into the denitrification and nitrification tank 31. Sludge may be extracted from the denitrification / nitrification tank 31. By providing a denitrification tank for finishing, or a nitrification tank and a denitrification tank between the intermittent aeration type denitrification and nitrification tank 31 and the solid-liquid separation tank 32, highly treated water can be obtained.

In FIG. 3, a nitrification tank 35 and a second denitrification tank 36 are provided between the denitrification tank 1 and the solid-liquid separation tank 32, and the communication paths 3a,
3b, 3c. The nitrification tank 35 is provided with an aeration device 33 at the lower part, and is connected to the denitrification tank 1 by a return path 4. Second denitrification tank 36 has a stirrer 7a driven by a motor M _3. Return paths 4 a and 4 b having a pump P ₄ from the solid-liquid separation tank 32 communicate with the denitrification tank 1 and the nitrification tank 35. Transfer routes 19 and 19a are connected from the acid fermentation tank 18 to the denitrification tank 1 and the second denitrification tank 36.

In the processing by the above-described apparatus, as in the case of FIG. 1, raw water is introduced into the denitrification tank 1 from the raw water channel, and nitrification liquid is introduced from the return line 4 to perform denitrification. The liquid in the denitrification tank 1 is transferred from the communication path 3a to the nitrification tank 35, where it is aerated by the aerator 33 to decompose and nitrate organic substances. The nitrification liquid is returned to the denitrification tank 1 from the return path 4 by 2 to 10 times the amount of raw water, and is transferred from the connection path 3b to the second denitrification tank 36, where organic substances such as methanol are injected from the chemical injection path 24a as necessary. And denitrification.

The denitrification treatment liquid is supplied to the solid-liquid separation tank 3 from the communication path 3c.
Then, the mixture is transferred to the aeration apparatus 2 and re-aerated by the aeration device 13 and solid-liquid separated by the membrane separation device 9. Sludge from solid-liquid separation tank returns
a and 4b return to the denitrification tank 1 and / or the nitrification tank 35. The amount of returned sludge is preferably 1-2 times the amount of raw water in the denitrification tank 1 and 2-3 times the amount of raw water in the nitrification tank 35.

In order to extract and reform the biological sludge from the treatment system 10, the biological sludge is transferred from the extraction passage 15 to the reforming treatment tank 16, where the sludge is reformed by ozone treatment to be easily biodegradable. To be reformed. The reformed sludge is subjected to acid fermentation in the acid fermentation tank 18 and the denitrification tank 1 and / or
Alternatively, it is introduced into the second denitrification tank 36 and denitrification is performed as a hydrogen donor.

[0050]

Embodiments of the present invention will be described below. In the examples, "L" means liter.

Example 1 and Comparative Example 1 A test was conducted according to the flow shown in FIG. 1 to prove the effect of the present invention. The apparatus used for the test was a denitrification tank 40L and a nitrification / solid-liquid separation tank 40L, and a solid-liquid separation was directly performed by immersing the immersion type membrane separator in the nitrification / solid-liquid separation tank. The immersion membrane used is a hydrophilic polyethylene-based hollow fiber immersion membrane, which is a hollow fiber membrane stretched in a flat plate shape. The film area is 0.5m ²
Was used. This hollow fiber membrane is an MF membrane having a nominal pore diameter of 0.1 μm, and has an outer diameter of 410 μm and an inner diameter of 270 μm. Aeration was performed from the lower part of the membrane separation device, a cross-flow flow rate was given to the membrane surface, and oxygen was supplied to the nitrification / solid-liquid separation tank. The air volume was 100 L / min.

The raw water used in the test was tap water to which sodium acetate was added as a BOD source and ammonium sulfate as a nitrogen source. Raw water concentration is BOD300mg / L, N
It was adjusted to H ₄ -N300mg / L. Phosphoric acid was added so that the concentration of PO ₄ -P became 9 mg / L. An ORP meter was attached to the denitrification tank, and methanol was added in conjunction with the ORP value. Methanol is added when the ORP is -100 mV or more, and between -50 and -100 mV, the OR is increased in proportion to the value of (ORP value +100 mV).
Control was performed such that the higher the P value, the larger the amount of methanol added (proportional control). When the ORP value was -50 mV or more, the amount of methanol added was fixed. The maximum methanol addition was set to be three times the inflow nitrogen load.

The raw water flow rate was set to 50 to 150 L / d, and was changed according to the processing conditions of the present apparatus to determine the limit processing performance. Caustic soda was added to the nitrification / solid-liquid separation tank in conjunction with a pH meter to adjust the pH to a range of 7.2 to 7.3.
Sludge returned from the nitrification / solid-liquid separation tank to the denitrification tank is 1% of raw water
0 times, that is, 500 to 1500 L / d. Sludge was quantitatively extracted from the nitrification and solid-liquid separation tank, and the SRT in the nitrification and solid-liquid separation tank was maintained on the 15th. That is,
Sludge was drawn out at a flow rate of 2.67 L / d. The extracted sludge was easily biodegraded by ozone treatment in a reforming treatment tank. The ozone injection rate was 0.03 gO ₃ / g VSS.

In Comparative Example 1, the sludge decomposed by biodegradation was directly introduced into a denitrification tank. In Example 1, which demonstrates the effect of the present invention, acid fermentation was performed in an acid fermentation tank, and then supplied to a denitrification tank. The acid fermenter has an effective volume of 2. so that the residence time is one day.
The mixture was made 67 L, sealed without contact with air, and mixed with a stirrer. The pH was adjusted to 5 by adding sodium hydroxide. The treatment was performed under these conditions, and the flow rate was adjusted such that the nitrification tank MLSS was constantly at 10,000 mg / L.

As a result, in the system in which the acid fermentation was not performed in Comparative Example 1, the nitrification tank MLSS concentration was stable at about 10,000 mg / L at a water flow rate of 60 L / d, and the methanol consumption was about 400 mg / l of the raw water. / L. On the other hand, in the system for performing the acid fermentation of Example 1, when the flow rate is 75 L / d, the nitrification tank MLSS concentration is stable at about 10,000 mg / L, and the methanol consumption is about 300 mg / L with respect to the raw water.
It became L. In all systems, the sludge concentration remained unchanged after the flow rate was fixed, and did not show any tendency to increase, so that no excess sludge as waste was generated.
In addition, the denitrification reaction in the denitrification tank proceeded favorably, and the concentration of NOx-N in the supernatant in the tank was 1 mg / L.
It was below.

From the above results, the embodiment of the present invention can be treated with a load 25% larger than that of the comparative example 1 as the conventional method, and at the same time, the amount of methanol used is reduced by about 25%.
It turns out that it can be reduced. At this time, the utilization rate of the reformed sludge for the denitrification reaction is estimated to be about 40% in Comparative Example 1 of the conventional method and about 80% in Example 1 of the present invention. However, since the effect of increasing the treatment capacity and the effect of reducing methanol in the present invention mainly depend on the BOD / N ratio of raw water, these values differ depending on the target wastewater, and generally depend on the adopted flow. The effect is more pronounced in drainage with a lower N ratio.

[Brief description of the drawings]

FIG. 1 is a system diagram showing a nitrogen removing device according to an embodiment.

FIG. 2 is a system diagram showing a nitrogen removing device according to another embodiment.

FIG. 3 is a system diagram showing a nitrogen removing apparatus according to still another embodiment.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Denitrification tank 2 Nitrification and solid-liquid separation tank 3, 3a, 3b, 3c, 17 Connection path 4, 4a, 4b, 25 Return path 5 Raw water path 6 Treatment water path 7, 7a, 23 Stirrer 8 Guide cylinder 9 Membrane separation device 10 Treatment system 11 Permeable membrane 12 Permeate chamber 13, 33 Aerator 14, Air path 15 Extraction path 16 Reformer tank 18 Acid fermentation tank 19, 19a Transfer path 21 Ozone blower 22 Ozone supply path 24, 24a Chemical injection path 26 Drainage passage 31 Denitrification and nitrification tank 32 Solid-liquid separation tank 35 Nitrification tank 36 Second denitrification tank

Claims (2)

[Claims] 1. A method for removing biological nitrogen from wastewater including a denitrification step, wherein a part of biological sludge generated in a treatment system is extracted, and a reforming treatment step of reforming the extracted sludge to be easily biodegradable. A method for removing biological nitrogen from wastewater, comprising an acid fermentation step of acid-fermenting the modified sludge, and a transfer step of introducing the acid-fermented sludge to the denitrification step. 2. A biological nitrogen removal treatment system including a denitrification tank, extraction means for extracting a part of biological sludge from the treatment system, a reforming treatment tank for reforming the extracted sludge to be easily biodegradable, a reformed sludge A biological nitrogen removing apparatus for wastewater, comprising an acid fermentation tank for acid fermentation of urea, and a transfer means for introducing acid fermentation sludge into a denitrification tank.