JP2007061786A - Aerobic treatment method of organic drainage - Google Patents

Abstract

【Task】
It is to propose an aerobic treatment method for organic drainage that can prevent deterioration of treated water transparency even when the amount is reduced by ozone treatment.
[Solution]
The organic waste liquid is introduced into the aeration tank, the aerobic biological treatment process in which aerobic biological treatment is performed in the presence of activated sludge containing aerobic microorganisms, and the liquid mixture in the aeration tank is separated into solid and liquid, and the separated liquid is processed. A solid-liquid separation process that discharges as liquid and returns at least a part of the separated sludge to the aeration tank; In the aerobic treatment method of organic drainage having a storing step of storing and a returning step of returning the stored sludge to the aeration tank,
In the storage step, the ozone-treated sludge is stored under alkaline conditions.
[Selection] Figure 3

Description

The present invention relates to a method for biologically treating organic wastewater in the presence of activated sludge containing aerobic microorganisms, and more particularly to a method for biologically treating organic wastewater that can reduce excess sludge in an aerobic biological treatment system. .

The aerobic biological treatment method that treats organic wastewater under aerobic conditions using the action of aerobic microorganisms, such as the activated sludge treatment method, has low treatment costs and excellent treatment performance. Although widely used in general, a large amount of hardly dewatering excess sludge is produced. This excess sludge is treated B
It reaches about 30 to 60% of the OD amount, and its processing is difficult. Conventionally, such excess sludge has been disposed of by disposal, but it is difficult to secure the disposal site, and it is necessary to reduce the amount of sludge.

In order to reduce the amount of sludge, Japanese Patent Application Laid-Open No. 8-155482 discloses an aerobic property of organic waste liquid that is subjected to oxidative decomposition and storage of activated sludge extracted from an aerobic treatment system with ozone and then biologically treated aerobically. A treatment method is described, and it is disclosed that the amount of excess sludge can be reduced by ozone treatment, and in some cases, the generation of excess sludge can be reduced to zero. In this method, the sludge is treated with ozone to oxidatively decompose and store to form BOD, which is aerobically treated to reduce sludge.
Japanese Patent Laid-Open No. 8-155482

However, when the treatment is carried out by such a method, the treated water transparency tends to be lower than in the case where the reduction by ozone treatment is not performed. The cause is that when the sludge is converted to BOD by ozone treatment, a partly ultra-refractory biodegradable component is generated, and this is discharged into the treated water without being biodegraded in the aerobic treatment, and an increase in COD is recognized. Although not possible, it is considered that the degree of transparency is low. Such a refined, hardly biodegradable component not only has a bad appearance of treated water, but also has a problem of increasing the load of coagulation sedimentation treatment and activated carbon treatment as post-treatment.

The purpose of the present invention is to reduce sludge in order to solve the above problems,
It is to propose an aerobic treatment method for organic drainage that can prevent deterioration of treated water transparency.

The present invention introduces organic drainage into an aeration tank, and aerobic biological treatment process for aerobic biological treatment in the presence of activated sludge containing aerobic microorganisms, and a liquid mixture of the aeration tank are solid-liquid separated, A solid-liquid separation step of discharging the separation liquid as a treatment liquid and returning at least a part of the separated sludge to the aeration tank; an ozone treatment process of extracting a part of the mixed liquid or separation sludge in the aeration tank and performing ozone treatment; In the aerobic treatment method of organic drainage having a storage step of storing ozone-treated sludge and a return step of returning the stored sludge to the aeration tank,
The storage step is an aerobic treatment method for organic drainage characterized by storing ozone-treated sludge under alkalinity.

In the present invention, the organic effluent to be treated is a effluent that is treated by a normal aerobic biological treatment method, but may contain a non-biodegradable organic or inorganic substance. Such organic effluents include sewage, human waste, food factory effluents and other industrial effluents.

In the aerobic biological treatment in the present invention, an organic aerobic biological treatment is performed in the presence of activated sludge containing aerobic microorganisms. In such a process, the organic waste liquid is mixed with activated sludge in an aeration tank and aerated, and the mixed liquid is solid-liquid separated in a solid-liquid separator, and a part of the separated sludge is returned to the aeration tank. The aerobic biological treatment in the sludge treatment method is common, but other treatments obtained by modifying this may be used.

In the present invention, a part of the activated sludge is extracted from the treatment system in such aerobic biological treatment,
This extracted sludge is treated with ozone. When extracting activated sludge, it is preferable to extract a part of the separated sludge separated by the solid-liquid separator, but it may be extracted from the aeration tank in a mixed liquid state. 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 sludge returned to the aeration tank as return sludge Further, the ozone treatment is preferably performed by drawing out. In this case, the generation amount of excess sludge can be further reduced, and the generation amount of excess sludge can be reduced to zero depending on conditions.
This point will be described in detail later.

When the ozone treatment is performed in an acidic region having a pH of 5 or less, the oxidative decomposition efficiency is increased. PH at this time
This adjustment is preferably performed by adding an inorganic acid such as sulfuric acid, hydrochloric acid or nitric acid as a pH adjuster to the activated sludge, adjusting the activated sludge by an acid fermentation treatment, or a combination thereof.
When adding a pH adjuster, it is preferable to adjust pH to 3-4, and when performing an acid fermentation process, it is preferable to carry out so that pH may become 4-5.

The ozone treatment can be performed by adjusting the drawn sludge or the acid fermentation treatment solution as it is, or if necessary by concentrating it with a centrifuge, etc., and then adjusting the pH to 5 or less and bringing it into contact 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 using a packed bed, or the like can be employed.
In addition to ozone gas, ozone-containing gas such as ozone-containing air or ozonized air can be used as ozone. The amount of ozone used is 0.03 to 0.07 g-O ₃ / g-VSS, preferably 0
. It is desirable to _{004~0.06g-O 3 / g-VSS} . The activated sludge is oxidatively decomposed by ozone treatment and converted into a BOD component.

As an ozone treatment device for ozone treatment, an ozone treatment tank for contacting ozone with sludge in a sludge-containing liquid to cause an oxidation reaction, and a device having means for returning the ozone treatment liquid to the aeration tank Any configuration of devices can be used. If sludge tends to settle in the ozone treatment tank, or if there is more sludge that settles than the floating sludge, the sludge-containing liquid and the ozone-containing gas are preferably contacted in parallel flow. This improves the contact efficiency between sludge and ozone. On the other hand, when the sludge tends to float in the ozone treatment tank, or when there is more sludge that floats than the sedimented sludge, it is preferable to make contact in countercurrent, which improves the contact efficiency.

Foaming occurs when ozone treatment is performed by blowing ozone-containing gas into the ozone treatment tank. In order to prevent troubles caused by the foaming, a liquid spraying means for defoaming can be provided in the ozone treatment tank. As the liquid spraying means, an apparatus configured to draw out the liquid in the tank containing sludge in the ozone treatment tank and spray this drawn liquid on the liquid surface in the ozone treatment tank as defoaming water.

Also, as an ozone treatment tank, a liquid phase contact area is formed in which ozone-containing gas is blown into a liquid-phase sludge-containing liquid at the lower part of the tank to bring it into gas-liquid contact, and foamed foam is brought into contact with the ozone-containing gas at the upper part. When an ozone treatment tank configured to form a contact area is used, the ozone treatment efficiency is further increased. The height of the liquid phase contact area is 0.2 to 3 m, preferably 0.5 to 1.5 m.
And
The height of the foam contact area may be at least 1 m higher than the liquid surface of the sludge-containing liquid in the liquid phase contact area,
The height is preferably 1 to 10 m, more preferably 2 to 5 m.

The foam contact area can be filled with a foam holding member, whereby the inner diameter of the ozone treatment tank is large and foam is difficult to be retained, or the activated sludge concentration is low and the sludge containing liquid is difficult to foam. Even in the case, the foam can be efficiently held, and the ozone treatment efficiency can be increased. The foam holding member may be of any structure that can hold the foam, but preferably has a partition plate structure such as a honeycomb or lattice.

Provide the above-mentioned liquid spraying device above the foam contact area in the ozone treatment tank, and use industrial water, final treatment liquid, drawn liquid from the ozone treatment tank, or mixed liquid of drawn liquid and liquid to be treated as a foam layer. The foam contact area can be maintained at a predetermined height by suppressing excessive foaming. In this case, when using a drawing liquid or a mixed liquid of a drawing liquid and a liquid to be processed,
This is preferable because the sludge concentration in the tank liquid does not decrease and the nozzles are not clogged. Since the foam contact area of the ozone treatment tank is only filled with foam, the strength of the ozone treatment tank may be smaller than that of an apparatus that fills the tank with the liquid to be treated, resulting in a low-cost ozone treatment apparatus.

In the ozone treatment tank, sludge reacts with ozone to be oxidatively decomposed and converted into a BOD component. At this time, a part of the biodegradable component is generated, and it is difficult to biodegrade even if it is returned to the aeration tank and subjected to aerobic biological treatment, but in the present invention, the ozone-treated sludge is stored under alkaline conditions. Alter sludge to make it easily biodegradable. Ozone-treated sludge gradually changes in quality after the end of ozone treatment, so that soluble COD increases and biodegradable components decrease even when no biological reaction is involved. Residual ozone in ozone-treated sludge is also decomposed during storage. At that time, the soluble COD increases even with the pH of the ozone treatment, and the hardly biodegradable components decrease, but the effect is remarkable when stored under alkaline conditions. The pH during storage is 7 to 11, preferably 8 to 10.

Although storage can be performed at any place, for example, if it is stored in a mixed state with the liquid to be treated, it is not necessary to provide a new device, but since a lot of alkali is required, a storage tank for ozone treatment sludge is provided. It is preferable to provide a new one because it requires less alkali for pH adjustment. The storage time is about 15 minutes to 2 hours, preferably about 30 minutes to 1 hour.

After the ozone treatment, the sludge stored and altered under alkaline conditions is introduced into the aeration tank of the aerobic biological treatment process and subjected to the aerobic biological treatment. As a result, the readily biodegradable component converted into BOD by the ozone treatment and the hardly biodegradable component once become easily degradable component, and the easily biodegradable component generated by alteration due to storage under alkalinity is easily biodegraded and removed. As a result, a decrease in the treated water transparency is prevented, a high treated water quality is obtained, and the amount of sludge discharged from the entire system is reduced. Residual ozone in the ozone-treated sludge is decomposed during storage, so that there is no inhibitory effect on organisms in the activated sludge.

In this case, the sludge weight loss rate increases as the amount of sludge to be ozone-treated increases. However,
Since sludge grows when biodegrading organic matter in ozone-treated sludge, surplus sludge cannot be reduced to zero by simply treating excess sludge with ozone. When excess sludge is drawn out and ozone treatment is performed, the amount of excess sludge generated from the entire system can be made zero. In this case, if the amount of sludge to be treated with ozone increases, the biological treatment performance may decrease. In such a case, a carrier for supporting sludge is provided in the aeration tank to maintain a certain amount of sludge. By doing so, the biological treatment performance can be maintained high.

In the aerobic treatment step, the supply amount of sludge supplied to the ozone treatment and the discharge amount of excess sludge discharged outside the system are controlled, and the VSS / SS ratio and MLVSS of the activated sludge in the aeration tank are maintained at predetermined values. As a result, the amount of excess sludge can be reduced without degrading the biological treatment performance, and the settling and dewatering properties of the activated sludge in the aeration tank can be improved. Thereby, the separation operation in the solid-liquid separator is facilitated, and the dewatering treatment of the generated excess sludge is facilitated. That is, the VSS / SS ratio of the activated sludge in the aeration tank is 0.2 to 0.7, preferably 0.3 to 0.6, and MLVSS is 500 to 10,000 mg / l, preferably 1000 to 50.
By controlling so that it may be maintained at 00 mg / l, the sedimentation property and dewatering property of sludge can be improved. As a general tendency, the smaller the VSS / SS ratio, the higher the specific gravity of the sludge, and the better the sedimentation and dewatering properties.

The principle of sludge reduction in the present invention will be described with reference to the drawings. FIG. 1 is a schematic diagram for explaining the principle of sludge reduction. In the figure, 1 is an aerobic biological treatment system and 2 is an ozone treatment system. The aerobic biological treatment system 1 is a treatment system that aerobically decomposes organic waste liquid by contacting it with activated sludge, like an activated sludge treatment apparatus, and an aeration tank and a solid-liquid separation device are provided separately. However, it is shown as a whole processing system including these. The ozone treatment system 2 has an ozone treatment tank that reacts ozone-containing gas with the drawn sludge drawn in the state of a mixed liquid or a concentrated liquid, oxidatively decomposes it into BOD, and a storage tank that stores the ozone treated sludge. These are shown as the entire processing system including these.

In the aerobic biological treatment system 1 of FIG. 1, a certain amount of activated sludge 3a is held in order to perform aerobic biological treatment. When the treatment liquid 4 is introduced into the aerobic biological treatment system 1 and the aerobic biological treatment is performed, the BOD contained in the treatment liquid 4 is assimilated into the activated sludge 3a, and newly generated sludge 3b is generated by the multiplication. Produces. On the other hand, the activated sludge 3a in the system is self-decomposed and self-decomposed 3
c disappears. Therefore, in the steady state, the difference between the generated sludge 3b and the self-decomposition component 3c is the breeding sludge 3d.
Proliferate as.

A case in which the breeding sludge 3d is treated as surplus sludge by the ozone treatment system 2 is shown by a broken line 5 in FIG. 1. When the breeding sludge 3d is ozone treated and returned to the aerobic biological treatment system 1, it is generated by ozone treatment. The BOD to be converted into sludge generates another generated sludge 3e, which becomes a substantial sludge multiplication portion and has to be discharged as surplus sludge. On the other hand, the extracted sludge 3f having a larger amount than the breeding sludge 3d is extracted from the aerobic biological treatment system 1 and is ozone-treated by the ozone treatment system 2 to be converted into BOD. The ozone-treated sludge 6 is converted into the aerobic biological treatment system 1. By returning to, another produced sludge 3g is produced from the BOD produced by ozonolysis. In this case, the difference between the extracted sludge 3f and the produced sludge 3g becomes the mineralized portion 3h.

Here, the extracted sludge 3f having a larger amount than the breeding sludge 3d is treated with ozone and converted into BOD, so that there are more mineralized parts and the sludge reduction rate is higher than when only the breeding sludge 3d is decomposed with ozone. Become. When the amount of the extracted sludge 3f is determined so that the growth sludge 3d and the mineralized portion h are equal, the excess sludge becomes substantially zero. When there is more breeding sludge 3d than the mineralized portion 3h, the difference becomes a substantially increased portion 3i and is discharged out of the system as surplus sludge 7. 8
Is a treatment liquid of the aerobic biological treatment system 1.

The aeration tank capacity in the aerobic biological treatment system 1 is V, the activated sludge concentration is X, the sludge yield is Y, the treatment liquid flow rate (treatment liquid flow rate) is Q, the organic matter concentration of the treatment liquid is Ci, and the treatment liquid. The organic matter concentration of Ce is the biologically treated organic matter concentration (Ci-Ce), the sludge self-decomposition constant is Kd, the surplus sludge discharge amount is q, the withdrawal amount to the ozone treatment tank is Q ', and the ozone treated sludge is When the ratio of reconversion to activated sludge is k, the mass balance is expressed by the following equation [1].
(Equation 1)
V dX / dt = YQ (Ci-Ce) -V Kd X-q X-Q'X + k Q'X [1]
In the equation [1], V dX / dt is the amount of change in activated sludge 3a in the aerobic biological treatment system 1, Y
Q (Ci-Ce) is the amount of generated sludge 3b, V Kd X is the amount of self-decomposition 3c, q X is the amount of excess sludge 7 discharged, Q'X is the amount of extracted sludge 3f, and k Q'X is generated The amount of sludge is 3g. Where Q (Ci−C
e) / V = LV (tank load), q / V = 1 / SRT (excess sludge residence time ratio), Q ′ / V = θ (circulation ratio of activated sludge to the ozone treatment system), (1-k) = Δ (mineralization rate), in the steady state, [1
] Is simplified as the following [2].
(Equation 2)
Y LV / X = Kd + 1 / SRT + δθ [2]
In a normal aerobic biological treatment system in which the ozone treatment system 2 does not exist, the third term (δθ) in the formula [2]
Therefore, surplus sludge (X / SRT) is determined in the second term when the sludge load is constant.
On the other hand, in the treatment system combined with the ozone treatment, the excess sludge is reduced by the value of the third term, as is apparent from the equation [2]. And under the condition that the value of the third term is comparable to the value of the second term, it is possible to set the sludge load to a normal value without discharging excess sludge (1 / SRT = 0). is there.

The parameters in the third term of the above formula [2] are the mineralization rate δ and the circulation ratio θ, where δ is the ozone injection rate with respect to sludge is 0.03 to 0.07 g-O ₃ / g-VSS, Since this is a steady value near 0.5, the apparent reduction rate of sludge is determined in proportion to θ in this region. On the other hand, the circulation ratio θ does not affect the sludge activity up to about 0.5 day ⁻¹ . This means that even if 1/2 of the activated sludge 3a retained in the aerobic biological treatment system 1 per day is circulated to the ozone treatment system 2 as the extracted sludge 3f, the sludge activity of the aerobic biological treatment system 1 is It is meant to be maintained.

Therefore, the upper limit of the circulation ratio θ is set to 0.5 day ⁻¹ . When θ is zero, the complete oxidation system is used. In this case, the load is low and the weight reduction effect is small. When the extracted sludge 3f has the same amount as the breeding sludge 3d, the weight reduction rate is the same value as in the conventional method. In a normal aerobic biological treatment, the SRT is 10 days and the sludge extraction rate is 0.1 day ⁻¹ . In the present invention, breeding sludge 3
When circulating more extracted sludge 3f than d, the lower limit of the circulation ratio θ is a value greater than 0.1Day ^-1, may preferably be 0.2Day ^-1 or more, when a particular 0.3Day ^-1, It is possible to reduce 100% without generating excess sludge.

According to the present invention, the ozone-treated sludge is stored under alkalinity.
Of course, not only the readily biodegradable component converted to OD but also the once degradable component is altered by storage under alkalinity to become a readily biodegradable component, which is returned to the aeration tank and biodegraded and removed.

Next, examples of the present invention will be described. 2 and 3 are flow sheets showing an aerobic treatment apparatus according to another embodiment, and FIG. 2 is an example in which the mixed solution in the aeration tank is treated with ozone.
Shows an example of ozone treatment of the separated sludge of the solid-liquid separator. In FIG. 2, the aerobic biological treatment system 1 includes an aeration tank 11 and a solid-liquid separation device 12. A liquid tank 13 to be treated and a return sludge path 14 are in communication with the aeration tank 11, and an air diffuser 15 is provided at the bottom to communicate with an air supply path 16. A communication path 17 communicates from the aeration tank 11 to the solid-liquid separator 12. The solid-liquid separator 12 communicates with the treatment liquid path 18 and the separated sludge discharge path 19, and the return sludge path 14 branches from the separated sludge discharge path 19. Reference numeral 20 denotes an excess sludge discharge path provided as necessary.

The ozone treatment system 2 includes an ozone treatment apparatus having an ozone treatment tank 21 and a storage tank 22, and a sludge extraction path 23 and a waste ozone path 24 communicate with the ozone treatment tank 21 at the upper part. A pH adjusting agent supply path 25 a communicates with the sludge extraction path 23. The ozone treatment tank 21
An ozone supply path 26 and an ozone treatment sludge path 27 are in communication with the lower part. A pH adjusting agent supply path 25 b and the storage tank 22 communicate with the ozone treatment sludge path 27, and a storage sludge path 28 communicates with the aeration tank 11 from the storage tank 22.

The aerobic biological treatment method of organic waste liquid by the treatment apparatus of FIG. 2 introduces organic waste liquid into the aeration tank 11 from the liquid passage 13 to be treated, and returns the sludge and aeration tank 11 returned from the return sludge passage 14. The aerobic biological treatment is performed by mixing with the activated sludge and diffusing the air supplied from the air supply path 16 from the air diffuser 15. Thereby, the organic matter in the drainage is decomposed by the biooxidation reaction.
A part of the mixed liquid (reaction liquid) in the aeration tank 11 is introduced into the solid-liquid separator 12 through the communication path 17 and separated into a separated liquid and separated sludge by sedimentation separation. The separation liquid is discharged out of the system from the treatment liquid passage 18 as a treatment liquid, the separated sludge is taken out from the separation sludge discharge passage 19, and a part thereof is returned as return sludge from the return sludge passage 14 to the aeration tank 11, and the remainder is surplus. It is discharged out of the system from the excess sludge discharge channel 20 as sludge.

A part of the mixed liquid in the aeration tank 11 is extracted from the sludge extraction path 23 as extraction sludge, and after adjusting the pH to 5 or less by adding an inorganic acid to the extracted sludge from the pH adjusting agent supply path 25a, the ozone treatment tank 21 To introduce. In the ozone treatment tank 21, the ozone supplied from the ozone supply path 26 is brought into contact with the sludge to perform ozone treatment, thereby converting the sludge into BOD. In this case, the ozone injection rate is 0.0
It may be about _{3 to} 0.07 g-O ₃ / g-VSS. The ozone exhaust gas is discharged out of the system from the exhaust ozone path 24.

The ozone treatment liquid is introduced and stored in the storage tank 22 from the ozone treatment sludge passage 27, and the sludge is denatured to convert the hardly biodegradable component into easily biodegradable. At that time, an alkali is added from the pH adjusting agent supply path 25b to adjust the pH to 7 to 11 and store it. The stored sludge is returned from the stored sludge path 28 to the aeration tank 11 and subjected to aerobic biological treatment as a load. In this way, the stored sludge is returned to the aeration tank 11 and subjected to aerobic biological treatment, whereby the BOD component converted by ozone treatment and the readily biodegradable component converted by storage under alkaline conditions are assimilated by microorganisms and decomposed. Removed. Thereby, the excess sludge generated from the aerobic biological treatment system 1 is reduced.

In FIG. 3, a part of the separated sludge separated by the solid-liquid separator 12 is introduced from the separated sludge extraction passage 9 into the ozone treatment tank 21. In the treatment method using the apparatus of FIG. 3, the aerobic biological treatment is performed by introducing the liquid from the liquid passage 13 into the aeration tank 11. A part of the separated sludge separated by the solid-liquid separator 12 is introduced into the ozone treatment tank 21 to perform ozone treatment. The ozone-treated sludge is introduced into the storage tank 22 from the ozone-treated sludge path 27 and stored under alkalinity, and then returned from the stored sludge path 28 to the aeration tank 11. If the separated sludge is ozone-treated as shown in FIG. 3, the ozone treatment efficiency is increased because the ozone treatment is performed in a state where the sludge concentration is high.

2 or 3, the solid-liquid separation tank 12 is a precipitation tank, but it may be a so-called immersion membrane type solid-liquid separation tank in which a separation membrane is immersed in the separation tank.

Hereinafter, the present invention will be described more specifically with reference to examples.

Example 1, Comparative Example 1, Comparative Example 2
The sewage (BOD = 125 mg / l) was subjected to an aerobic treatment using the apparatus shown in FIG. The processing conditions were as follows: The aeration tank 11 is an oxidation ditch type with a BOD tank load of 0.
It was 04g-BOD / liter * day, MLSS6000-9000mg / l. The ozone injection rate was 0.05 g-O ₃ / g-VSS, and the ozone treatment sludge amount was 5% of the retained sludge amount per day. The pH adjustment during the ozone treatment was adjusted to pH 3 with hydrochloric acid. In Example 1, the ozone-treated sludge was introduced into the storage tank, stored at a pH of 9 to 10 for 30 minutes in HRT, and returned to the aeration tank. Comparative Example 1
Then, without adjusting the pH, it was stored in the same HRT and returned to the aeration tank. Comparative Example 2 is an example in the case where ozone treatment is not performed. The processing results are shown in Table 1.

From the above results, Comparative Example 1 in which the ozone-treated sludge was stored without adjusting the pH and returned to the aeration tank had low transparency of the treated water, but Example 1 stored under alkaline was not subjected to ozone treatment. It can be seen that the treated water COD and the degree of transparency equivalent to 2 are obtained, and that sludge is being reduced.

It is a schematic diagram for demonstrating the principle of sludge reduction. It is a systematic diagram which shows the aerobic processing apparatus of an Example. It is a systematic diagram which shows the aerobic processing apparatus of another Example.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Aerobic treatment system 2 Ozone treatment system 3a Activated sludge 3b, 3e, 3g Produced sludge 3c Self-decomposition part 3d Propagation sludge 3f Extraction sludge 3h Mineralization part 3i Increase part 4 Liquid to be treated 6 Ozone treatment sludge 7 Excess sludge 8 Treatment liquid DESCRIPTION OF SYMBOLS 11 Aeration tank 12 Solid-liquid separator 13 Processed liquid path 14 Return sludge path 15 Aeration apparatus 16 Air supply path 17 Connection path 18 Process liquid path 19 Separation sludge discharge path 20 Surplus sludge discharge path 21 Ozone treatment tank 22 Reservoir 23 Sludge extraction path 24 Waste ozone path 25a pH adjuster supply path 25b pH adjuster supply path 26 Ozone supply path 27 Ozone treatment sludge path 28 Storage sludge path

Claims (1)

An aerobic biological treatment step of introducing an organic drainage liquid into an aeration tank and treating the aerobic biological in the presence of activated sludge containing aerobic microorganisms;
Solid-liquid separation of the liquid mixture in the aeration tank, discharging the separation liquid as a treatment liquid, and returning at least a part of the separated sludge to the aeration tank;
An ozone treatment process in which a part of the mixed liquid or separated sludge in the aeration tank is extracted and ozone treated;
A storage process for storing ozone-treated sludge;
In the aerobic treatment method of organic drainage having a return step of returning the stored sludge to the aeration tank,
In the storage step, the ozone-treated sludge is stored under alkaline conditions.

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