JP2003010877A - Activated sludge treatment method for sewage and its apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an activated sludge treatment method for sewage which can improve decomposition performance of modified sludge and of sewage, thereby reducing the volume of activated sludge and inhibiting misseparation of solid and liquid to stably obtain treated water of high water quality at a low cost, and its apparatus. SOLUTION: The sewage is dividedly introduced into aeration tanks 1a, 1b, etc., from a sewage dividedly introducing channel 4a to be mixed with the activated sludge and aerated by aerators 6a, 6b, etc. While carrying out a biological reaction in such a way, the mixed liquid 20 in the tanks flow sequentially from an aeration tank 1a side in the preceding stage to an aeration tank 1d side in the latter stage, and the mixed liquid 20 in the last-stage aeration tank 1d is fed to a solid-liquid separator 2 through a transfer passage 11 for carrying out solid-liquid separation. A part of the separated sludge is retuned to the first-stage aeration tank 1a as returned sludge through a sludge return passage 8, and the other part of the separated sludge is withdrawn to a modifying device 3 through a withdrawing passage 12 as withdrawn sludge. The withdrawn sludge is modified to easily biodegradable sludge, and the modified sludge is supplied to the first-stage aeration tank 1a through a modified sludge supply passage 9.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of treating sewage by a plurality of aeration treatment steps, and more particularly to a method and apparatus for treating sewage to reduce the volume of sewage.

[0002]

2. Description of the Related Art As a treatment of sewage, aerobic biological treatment by an activated sludge method is widely used. In the activated sludge treatment method, a large amount of excess sludge is generated due to biological growth, but since this excess sludge has undergone biological treatment, it is difficult to biodegrade and difficult to dehydrate, so its disposal is difficult. .
In order to reduce the amount of sludge generated in such activated sludge treatment, the activated sludge is modified to be easily biodegradable by ozone treatment etc. and supplied to the aerobic biological treatment process, and the modified sludge is used as a substrate. Has proposed a method for reducing the volume of generated sludge.

FIG. 2 is a flow chart showing a conventional activated sludge treatment device. In FIG. 2, 1 is an aeration tank, 2 is a solid-liquid separation device such as a precipitation tank, 3 is a reforming device such as an ozone treatment device, 4
b is a raw water injection passage, 5 is an air supply passage, 6 is an aeration device, 7 is a treated water extraction passage, 8 is a sludge return passage, 9 is a reformed sludge supply passage, 10
Is an excess sludge discharge channel.

FIG. 2 is shown in Japanese Unexamined Patent Publication No. 6-206088, in which raw water such as organic waste water is injected into the aeration tank 1 from the raw water injection passage 4b, mixed with activated sludge, and aerated from the air supply passage 5. Air is sent to the device 6 for aeration, and organic substances are decomposed by aerobic biological reaction. The mixed liquid 20 is sent from the transfer passage 11 to the solid-liquid separation device 2 for solid-liquid separation, the separated liquid is taken out as treated water from the treated water take-out passage 7, and part of the separated sludge is aerated as returning sludge from the sludge returning passage 8. Return to tank 1. A part of the separated sludge is drawn out from the drawing path 12 and subjected to a modification treatment such as ozone treatment in the reforming device 3 to be easily biodegradable,
The modified sludge is supplied from the modified sludge supply passage 9 to the aeration tank 1.
When excess sludge is generated, it is discharged from the excess sludge discharge path 10.

In the above treatment, organisms grow due to biological reactions and the amount of activated sludge increases. At this time, when activated sludge larger than the amount of sludge that grows is extracted and modified and supplied to the bioreaction system, the easily converted biodegradable modified sludge is biodegraded in the aeration tank 1, so that the activated sludge is The volume can be reduced, and in some cases, excess sludge can be reduced to substantially zero.

However, when the sewage is treated by the above treatment method, the microorganisms in the sludge are killed by the reforming treatment, reformed into easily biodegradable components and returned to the aeration tank 1, so that the aeration tank 1 The sludge load becomes high, and the treated water quality may become unstable due to insufficient decomposition of organic matter in the modified sludge, especially at low water temperatures in winter. In addition, undegraded inert organic sludge may accumulate in the aeration tank 1 and the sludge settling property in the solid-liquid separator 2 may deteriorate.

When a large amount of activated sludge is reformed to further increase the volume reduction rate, the sludge retention time (SRT) in the aeration tank 1 may be shortened and the treated water quality may be deteriorated. For example, in order to satisfactorily remove nitrogen and maintain the treated water quality, it is important not to wash out nitrifying bacteria, and the SRT of the aeration tank 1 must be maintained according to the water temperature. Further, SRT is an important factor for the decomposition of hardly decomposable organic substances, and if the SRT is short, the treated water COD may deteriorate.

As a method of lengthening the SRT, an aeration tank 1 is used.
It is easy to increase the capacity, but it is not realistic because it increases the site area and construction cost. In order to lengthen the SRT without increasing the capacity of the aeration tank 1, it is sufficient to increase the sludge concentration in the tank. However, the higher the sludge concentration, the more difficult the solid-liquid separation in the solid-liquid separation device 2, and the carry-over of the sludge may occur depending on the sludge property, which may rather deteriorate the quality of the treated water. Therefore, there is a demand for a method of lengthening the aeration tank SRT without imposing a heavy economic burden and without sacrificing the stability of the solid-liquid separation device 2.

By the way, in the sewage treatment facility, the treated water amount is often much smaller than the designed water amount at the beginning of service. Depending on the connection status of the sewer pipeline, a period of less than half the design water volume may continue for a while. When the amount of water is small in this way, the amount of organic matter loaded in the aeration tank may deviate from the proper range for biological treatment, leading to deterioration of water quality due to excessive aeration and the like. In order to deal with this, when there are multiple series of processing facilities, the number of series is usually reduced to operate. When there is only one treatment facility, the number of treatments cannot be reduced, so the amount of air is reduced and the aeration device is operated intermittently to support low-load operation. However, there is a limit to these measures, and there is a demand for effective utilization of facilities to obtain good treated water quality even when the amount of treated water is small immediately after the start of operation.

[0010]

The object of the present invention is to improve both the decomposition performance of the modified sludge and the decomposition performance of the sewage, thereby reducing the volume of the activated sludge and preventing solid-liquid separation obstacles. It is an object of the present invention to propose a method and an apparatus for treating activated sludge of sewage, which can suppress and stably obtain treated water of high quality at low cost.

[0011]

The present invention is the following method and apparatus for treating activated sludge of sewage. (1) While mixing sewage with activated sludge and performing aeration,
A plurality of aeration processing steps provided so as to pass sequentially,
Separate sewage injection process that divides sewage into multiple aeration processes, solid-liquid separation process that separates the mixed liquid of the latter aeration process into separated sludge and separated liquid, and part of the separated sludge in the previous stage. The sludge return process, which is returned to the aeration treatment process, and part of the separated sludge that has undergone solid-liquid separation in the mixed liquid or solid-liquid separation process of the aeration process are easily biodegradable and the modified sludge is aerated in the previous stage. A method for treating activated sludge containing sewage, which comprises a reforming step of supplying the treatment step. (2) While mixing sewage with activated sludge and performing aeration,
A plurality of aeration tanks that are connected in series so as to pass sequentially, a sewage split injection path that divides and injects sewage into a plurality of aeration tanks, and a mixed solution in the aeration tank in the subsequent stage as separation sludge and separation liquid. A solid-liquid separator for solid-liquid separation, a sludge return path for returning a part of the separated sludge to the aeration tank at the previous stage, and a part of the separated sludge for solid-liquid separation by the mixed liquid in the aeration tank or the solid-liquid separator An activated sludge treatment device for sewage, which includes a reformer that is biodegradable and that supplies the reformed sludge to the aeration tank in the previous stage.

The target of the treatment in the present invention is so-called sewage, and concrete examples thereof include urban sewage, agricultural sewage collected, septic tank sewage, etc. Industrial wastewater does not belong to the treatment target.

In the aeration treatment step of the present invention, organic substances and the like are aerobically removed by the action of organisms while aerating the sewage as described above in the presence of activated sludge. This biological reaction is a reaction in which a heterotrophic microorganism decomposes by assimilating an organic substance in the case of an organic substance, and is a reaction in which nitrification is caused by an ammonia-oxidizing bacterium in the case of ammonia.

In the aeration tank according to the present invention, sewage is mixed with activated sludge so that the sludge passes sequentially while performing a biological reaction.
A plurality of aeration tanks are connected in series and provided. Although each aeration tank may be independent, one aeration tank can be formed by partitioning with a partition. In this case, it is preferable that the mixed liquid in the tank pass through the upper part of the partition wall, but it may pass through other parts.

The sewage split injection passage in the present invention is provided so as to split and inject sewage into a plurality of aeration tanks. In this case, it is preferable to provide each aeration tank so as to perform divided injection into each of the first to final aeration tanks, but the injection into some aeration tanks may be omitted.

The solid-liquid separator according to the present invention performs solid-liquid separation of the mixed liquid in the aeration tank by precipitation separation, filtration separation, etc., and discharges the separated liquid as treated water, and at least a part of the separated sludge to the preceding aeration tank. Configure to return. As an activated sludge treatment system including such an aeration tank, a sewage split injection path, and a solid-liquid separation device, organic waste liquid is mixed with activated sludge in an aeration tank and aerated, and the mixed liquid is solidified in a solid-liquid separation device. A step-feed type activated sludge treatment method in which liquid is separated and a part of the separated sludge is returned to the aeration tank is generally used, but other treatment methods modified from this may be used.

In the present invention, a part of the activated sludge (biological sludge) from the treatment system in such activated sludge treatment is extracted, and the extracted sludge is modified to be easily biodegradable to aerate the modified sludge in the preceding stage. A reforming process to be supplied to the processing step is performed. When extracting the activated sludge, it is preferable to extract a part of the separated sludge separated by the solid-liquid separation device, but the mixed liquid may be extracted from the aeration tank. When extracting from separated sludge, part or all of the part discharged as excess sludge can be extracted as extracted sludge, but in addition to excess sludge, part of the return sludge returned to the aeration tank as return sludge It can also be pulled out and modified. In this case, the amount of excess sludge discharged to the outside of the system can be reduced, and in some cases, it can be reduced to zero. When withdrawing the mixed liquid from the aeration tank, it is preferable to withdraw it from the aeration tank at the subsequent stage.

As a modification treatment method for modifying the drawn sludge into a property in which organisms are easily decomposed, any method can be used as long as it is a method of adding chemicals and / or energy to the drawn sludge so as to be easily biodegradable. Can be adopted. For example, modification treatment by ozone treatment, modification treatment by hydrogen peroxide treatment, modification treatment by acid treatment, modification treatment by alkali treatment, modification treatment by heat treatment, high pressure pulse discharge treatment, ball mill, colloid mill, etc. Milling treatment with a mill, modification treatment combining these, and the like can be adopted. Of these, the modification treatment by ozone treatment is preferable because the treatment operation is simple and the treatment efficiency is high.

For the ozone treatment as the reforming treatment, the drawn sludge drawn from the activated sludge 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 carried out in an acidic region of pH 5 or less, the oxidative decomposition efficiency becomes high. The pH adjustment at this time is preferably carried out by adding an inorganic acid such as sulfuric acid, hydrochloric acid or nitric acid to the activated sludge as a pH adjusting agent, adjusting the activated sludge by acid fermentation treatment, or a combination thereof. . p
When the H adjuster is added, the pH is preferably adjusted to 3 to 4, and when the acid fermentation treatment is performed, the pH is preferably adjusted to 4 to 5.

The ozone treatment can be carried out by bringing the drawn sludge or the acid fermentation treatment liquid as it is, or if necessary concentrating it with a centrifuge or the like, adjusting the pH to 5 or less, and contacting it with ozone. As a contact method, a method of introducing sludge into an ozone treatment tank and blowing ozone, a method of mechanical stirring, a method of utilizing a packed bed, and the like can be adopted. As the ozone gas, ozone-containing gas such as ozonized oxygen or ozonized air can be used. The amount of ozone treated sludge per _{0.002~0.1g-O 3 / g-SS} , preferably it is desirable to _{0.03~0.08g-O 3 / g-SS} . Activated sludge is oxidatively decomposed by ozone treatment,
Converted to BOD component.

In the hydrogen peroxide treatment as the reforming treatment, the drawn sludge drawn from the activated sludge treatment system is introduced into the reforming tank and hydrogen peroxide is mixed. The amount of hydrogen peroxide used is 0.001
And _{0.2g-H 2 O 2 / g} -SS. At this time, it is preferable to add an acid such as hydrochloric acid to the drawn sludge to adjust the pH to 3 to 5, and in this case, the amount of hydrogen peroxide used is 0.001 to 0.001.
It is preferably 0.07 g-H ₂ O ₂ / g-SS. In order to accelerate the reaction, heating may be performed or a catalyst such as ferrous ion may be added.

In the acid treatment as a reforming method, the drawn sludge drawn from the activated sludge treatment system is introduced into a reforming tank, and a mineral acid such as hydrochloric acid or sulfuric acid is added thereto to adjust the pH to 2.5 or less, preferably pH.
It may be allowed to stay for a predetermined time under an acidic condition of 1-2. The residence time is, for example, 5 to 24 hours. At this time, it is preferable to heat the sludge, for example, to 50 to 100 ° C., since the reforming is promoted. By such treatment with acid, the sludge becomes easily biodegradable and can be easily decomposed and removed by returning it to the aeration tank.

In addition, in the alkali treatment as a sludge reforming method, the drawn sludge drawn from the activated sludge treatment system is introduced into a reforming tank, and alkali such as sodium hydroxide or potassium hydroxide is added to the sludge in an amount of 0.1. Add about 1% by weight and let it stay for a predetermined time. The residence time is about 0.5 to 2 hours, and the sludge is easily biodegradable. At this time, heat the sludge,
For example, heating to 50 to 100 ° C. is preferable because reforming is promoted.

The heat treatment as a reforming method can be carried out by the heat treatment alone, but it is preferably carried out in combination with the acid treatment or the alkali treatment. When the heat treatment is performed alone, 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 allowed to exist between a positive electrode such as a tungsten / thorium alloy of 10 mm, preferably 4 to 8 mm, and a negative electrode of stainless steel, and an applied voltage is 10 to 50 kV, preferably 20 to
40 kV, pulse interval 20-80 Hz, preferably 40
The pulse discharge is performed at -60 Hz, and the sludge can be treated while being sequentially circulated.

The modified sludge thus modified to be easily biodegradable is introduced into the aeration tank of the first stage, preferably the first stage, and subjected to activated sludge treatment to be assimilated by microorganisms and decomposed. The sludge may be dividedly injected into the aeration tank at the latter stage. The final activated aeration tank activated sludge had a VSS / SS ratio of 0.2 to 0.
7, preferably 0.3-0.6, MLVSS 500-
10000 mg / l, preferably 1000-5000 m
By controlling so that the sludge is maintained at g / l, the activated sludge treatment can be performed without deteriorating the sedimentation property and the dehydration property of the sludge.

In the present invention, sewage is split-injected into a plurality of aeration tanks from the sewage split-injection passage, mixed with activated sludge to cause a biological reaction, and the mixed liquid is sequentially passed from the aeration tank in the first stage to the aeration tank in the second stage. Then, the latter-stage mixed liquid is subjected to solid-liquid separation by a solid-liquid separation device. Then, the separated liquid is taken out as treated water, a part of the separated sludge is returned from the sludge return path to the aeration tank in the previous stage as returned sludge, and the other part is drawn out as reformed sludge into a reformer to improve biodegradability. Quality treatment is performed and the modified sludge is supplied to the previous aeration tank.

In the above treatment, the modified sludge supplied to the aeration tank of the first stage is mixed with the return sludge and decomposed by a biological reaction in the process of passing from the aeration tank of the first stage to the second stage, and the easily biodegradable component concentration is gradually increased. descend. By separately injecting sewage into a plurality of aeration tanks, the aeration tanks are decomposed, the load on the aeration tanks in the subsequent stages is reduced, and the decomposition efficiency is increased. Therefore, the organic matter removing performance of the modified sludge and the organic matter removing performance of the sewage are both high, and high quality treated water can be obtained. Further, the volume of the activated sludge is reduced by the decomposition of the modified sludge, and the volume reduction rate is increased by increasing the amount of drawn-out sludge to be larger than the multiplication amount, and the amount discharged as surplus sludge can be substantially zero.

In the present invention, since the aeration tank is divided into a plurality of stages and the sewage is dispensed to each aeration tank to treat the activated sludge, the aeration tank capacity is not increased and the solid load of the solid-liquid separator is increased. The aeration tank SRT can be lengthened without having to do so. Moreover, since the returned sludge and the modified sludge are returned to the aeration tank in the previous stage,
Compared with the conventional method, the MLSS concentration in the parts other than the final aeration tank can be increased, and the MLSS concentration in the final aeration tank can be the same level. Therefore, the sludge holding amount in the entire aeration tank can be increased, the SRT can be lengthened to obtain treated water of high water quality, and the solid load on the solid-liquid separation device does not increase. Separation failure does not occur.

The larger the number of division stages, the greater the amount of activated sludge retained in the aeration tank. However, considering the complexity of the equipment, etc.
Usually, about 2 to 5 steps is preferable. In the case where the amount of sewage to be treated is small, it is possible to omit the divisional injection into a part of the aeration tank in the previous stage. As a result, even if the amount of treated water at the beginning of service at the sewage treatment facility is small, it can be easily dealt with.

In the treatment of the present invention, the reformed sludge can be dividedly injected into a plurality of aeration tanks connected in series, but the reformed sludge is less biodegradable than the organic matter in the sewage. It is preferable to inject the entire amount into the aeration tank in stages. However, when treating sewage containing organic substances that are less biodegradable than the modified sludge, such sewage may be injected into the aeration tank at a stage before the modified sludge. In the above-mentioned activated sludge treatment, the activated sludge in the plurality of aeration tanks is sequentially diluted by the sewage to be dispensed, so that the sludge concentration becomes low from the first stage to the second stage.

In the above treatment method, the electron acceptor for treating the activated sludge is not limited and may be molecular oxygen or bound oxygen (eg nitric acid). In the present invention, since it is intended to form a gradient in the sludge concentration in the aeration tank by the sewage and the returned sludge to increase the amount of sludge retained in the tank, it is preferable to adopt the floating method as the activated sludge treatment method. The amount of sludge retained can be further increased by adding a carrier to which microorganisms can adhere and increase the floor.

[0033]

EFFECTS OF THE INVENTION According to the present invention, the modified sludge and the returned sludge are supplied to the aeration tank at the preceding stage, and the sewage is dispensed into a plurality of aeration tanks. It is possible to improve both the decomposition performance of the above, and thereby to reduce the volume of the activated sludge and stably obtain the treated water of high quality. In this case, since the amount of sludge retained in the aeration tank in the first stage can be increased, sewage and excess sludge can be decomposed with high performance, and the sludge concentration in the aeration tank in the second stage can be kept low, resulting in solid-liquid separation failure. Hateful. In addition, since the amount of activated sludge retained in the aeration tank as a whole can be increased to increase the SRT, it is possible to stably obtain high-quality treated water at a low cost without increasing the aeration tank capacity.

[0034]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below. FIG. 1 is a flow chart showing the activated sludge treatment device of the embodiment, and the same reference numerals as those in FIG. 2 indicate the same or corresponding portions.

In FIG. 1, a plurality of aeration tanks 1a, 1b,
1c and 1d are partitioned by partition walls 13a, 13b and 13c, and the mixed liquid 20 is connected in series so as to flow over the upper portions of the partition walls 13a, 13b and 13c,
A transfer path 11 communicates with the solid-liquid separation device 2 from the last-stage aeration tank 1d. The sewage split injection path 4a is provided in each aeration tank 1a, 1
b ... is contacted and the same sewage is dispensed to each. The aeration device 6 is provided in each of the aeration tanks 1a, 1b.
a, 6b, 6c, 6d are provided and are connected to supply air from the air supply passage 5. The solid-liquid separator 2 is connected to a treated water take-out passage 7 for taking the separated liquid as treated water at the upper part, and the sludge return passage 8 and drawn sludge for returning the separated sludge as the returned sludge to the first aeration tank 1a from the lower part. As a result, the withdrawal path 12 for withdrawing is connected to the reforming apparatus 3, and further, the excess sludge discharge path 10 for discharging the excess sludge to the outside of the system is connected as necessary. The reforming device 3 communicates so that the extracted sludge is easily biodegradable by ozone treatment and the modified sludge is supplied from the modified sludge supply passage 9 to the first-stage aeration tank 1a.

In the activated sludge treatment method using the above-mentioned apparatus, the sewage is aerated from the sewage split injection path 4a, respectively.
Are separately injected and mixed with activated sludge, and air is supplied from the air supply path 5 to aerate from the aeration devices 6a, 6b. It is preferable that the sewage is divided and injected evenly according to the aeration tanks 1a, 1b ..., However, it is also possible to provide a difference in the dispensing amount. While carrying out the biological reaction in this manner, the mixed solution 20 in the tank is sequentially passed from the aeration tank 1a side of the first stage to the aeration tank 1d side of the second stage, and the mixed solution 20 of the last aeration tank 1d is transferred from the transfer path 11. It is sent to the solid-liquid separation device 2 for solid-liquid separation. Then, the separated liquid is taken out from the treated water outlet 7 as treated water, a part of the separated sludge is returned from the sludge returning passage 8 to the first-stage aeration tank 1a as returning sludge, and the other part is taken out as drawn-out sludge. 12
The modified sludge is extracted to the reforming device 3 to be easily biodegradable, and the modified sludge is supplied from the modified sludge supply passage 9 to the first-stage aeration tank 1a. When excess sludge is generated, it is discharged from the excess sludge discharge path 10 to the outside of the system.

In the above treatment, the reformed sludge supplied to the first-stage aeration tank 1a is mixed with the return sludge and decomposed by biological reaction in the process of passing from the first-stage to the final-stage aeration tanks 1a to 1d. The concentration of easily biodegradable components gradually decreases. The sewage is decomposed in each tank by dividing and injecting it into the multi-stage aeration tanks 1a, 1b ..., The load on the aeration tank 1d in the subsequent stage is reduced, and the decomposition efficiency is increased. Therefore, the organic matter removing performance of the modified sludge and the organic matter removing performance of the sewage are both high, and high quality treated water can be obtained. The volume of activated sludge is reduced by the decomposition of the reformed sludge, and the volume reduction rate is increased by increasing the amount of drawn-out sludge to be larger than the multiplication amount, and the amount discharged as excess sludge from the excess sludge discharge path 10 becomes substantially zero. You can also do it.

The sludge retention amount can be increased in the aeration tank as a whole, and the SRT can be lengthened to obtain treated water of high water quality. Further, since the mixed liquid 20 in the aeration tank 1d in the latter stage with a small load is subjected to solid-liquid separation by the solid-liquid separation device 2, the solids load of the solid-liquid separation device 2 does not increase, and solid-liquid separation obstacles occur. Does not happen. When biologically inert sludge, for example inorganic sludge, accumulates, only a small amount of excess sludge can be discharged.

[0039]

EXAMPLES Examples and comparative examples of the present invention will be described below.

Example 1 Sewage was treated with activated sludge under the following conditions using the apparatus shown in FIG. As the aeration tank, an aeration tank that was evenly divided into four stages was used. Further, ozone treatment was performed as the modification treatment.

Sewage: Sewage after a sand basin (BOD concentration 150
mg / L, Kj-N concentration 25 mg / L) Treatment amount: 1 m ³ / day Sewage division: 1/4 evenly aeration tank: 1 m ³ (HRT 1 day) in all tanks, 4 tanks evenly divided, final Tank MLSS concentration 2500 mg / L Aeration tank water temperature: 14-16 ° C Sludge return rate: 30% Returned sludge concentration: 10800 mg / L Ozone-treated sludge amount: 0.055 m ₃ / day Ozone usage amount: 0.05 g-O ₃ / g -SS

During the test period of 3 months, it was possible to operate without discharging excess sludge. ML of the final stage aeration tank
The SS concentration remained at 2500 ± 300 mg / L, and the sludge volume reduction operation was performed stably. As a result, the SRT of the entire aeration tank was about 10 days, the NH ₄ —N concentration of the treated water was 2 mg / L or less (average 0.8 mg / L), and the nitrification reaction was performed well. The treated water COD _Mn has an average of 9 mg / L (7-
12 mg / L) worked well. Treated water SS is also 5m
It was g / L or less, and sludge did not carry over.

Comparative Example 1 At the same time as Example 1, sewage activated sludge treatment was performed by the apparatus shown in FIG. That is, the same sewage as in Example 1 was used, and the treatment was performed under the same conditions as in Example 1 except that sewage was supplied to an aeration tank that was not partitioned.

As a result, the sludge volume-reducing effect was good, and the MLSS did not increase even without extracting the excess sludge as in Example 1. However, the SRT of the entire aeration tank was 6.5 days on average, which was significantly shorter than that in Example 1.
Therefore, NH ₄ -N is 0.5 to 7 mg / L in the treated water.
(Average 3.5 mg / L) remained and nitrification was unstable. The treated water COD _Mn was 10.5 mg / L on average, which was slightly higher than that in the examples. The treated water SS was good at 5 mg / L or less.

[Brief description of drawings]

FIG. 1 is a flowchart showing an activated sludge treatment device of an embodiment.

FIG. 2 is a flowchart showing a conventional activated sludge treatment device.

[Explanation of symbols]

1, 1a, 1b ... Aeration tank 2 Solid-liquid separator 3 reformer 4a Sewage split injection channel 4b Raw water injection channel 5 air supply 6, 6a, 6b ... Aeration device 7 Treated water outlet 8 Sludge return path 9 Modified sludge supply channel 10 Surplus sludge discharge route 11 Transfer route 12 Withdrawal path 13, 13a, 13b ... Partition walls 20 mixed liquid

Continued front page    F-term (reference) 4D028 AB00 BB06 BC01 BC13 BD01                       BE01 BE08                 4D059 AA03 AA05 BC02 BF01 BF14                       BK12 BK22 CA28 DA32 DA33                       DA43 DA44

Claims (2)

[Claims] 1. A plurality of aeration treatment steps provided so as to sequentially pass while mixing sewage with activated sludge to perform aeration, and a sewage split injection step of separately injecting sewage into a plurality of aeration treatment steps, Mixing the solid-liquid separation process that solid-liquid separates the mixed liquid of the latter aeration process into separated sludge and the separated liquid, the sludge return process that returns a part of the separated sludge to the previous aeration process, and the aeration process Method for sewage activated sludge treatment, including a reforming step in which a part of the sludge separated in the liquid or solid-liquid separation step is subjected to biodegradability and the modified sludge is supplied to the previous aeration treatment step. . 2. A plurality of aeration tanks connected in series so as to sequentially pass while sewage is mixed with activated sludge to perform aeration, and sewage split injection to separately inject sewage into a plurality of aeration tanks. A channel, a solid-liquid separator for solid-liquid separation of the mixed liquid in the aeration tank in the latter stage into separated sludge and the separated liquid, a sludge return path for returning a part of the separated sludge to the aeration tank in the first stage, and mixing of the aeration tank An activated sludge treatment device for sewage, which includes a reformer that reforms a part of the sludge separated by the liquid or solid-liquid separator into a biodegradable substance and supplies the reformed sludge to the aeration tank in the previous stage.