JP3493769B2 - Aerobic treatment of organic wastewater - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for biologically treating an organic effluent in the presence of biological sludge containing aerobic microorganisms, and more particularly, to a method for treating waste water in an aerobic biological treatment system. The present invention relates to a biological treatment method for organic wastewater capable of reducing sludge volume. [0002] An aerobic biological treatment method for treating an organic effluent under aerobic conditions by utilizing the action of aerobic microorganisms, such as an activated sludge treatment method, has a low treatment cost. Because of its excellent processing performance, it is widely used in general, but generates a large amount of hardly dewaterable surplus sludge. This surplus sludge reaches about 30 to 60% of the amount of the treated BOD, and its treatment is difficult. Conventionally, such excess sludge has been dumped and disposed of. However, it is difficult to secure a disposal site and sludge volume reduction is required. In order to reduce the volume of sludge, Japanese Patent Laid-Open Publication No.
No. 088 describes a method for aerobically treating an organic effluent which is subjected to oxidative decomposition of activated sludge withdrawn from an aerobic treatment system with ozone and then aerobic biological treatment. It is disclosed that the degree of volume reduction is improved and, in some cases, the generation of excess sludge can be reduced to zero. In this method, sludge is treated with ozone and oxidatively decomposed into BOD, which is aerobicly treated to reduce the volume of sludge. However, when the treatment is performed by such a method, the COD of the treated water tends to be higher than when the volume is not reduced by the ozone treatment. It is considered that the cause is that, when converted into BOD by the ozone treatment, a part of the hardly biodegradable component is generated, which flows out into the treated water without being biodegraded in the aerobic treatment and is detected as COD. Such a hardly biodegradable component is slight when the BOD of the liquid to be treated is low, but when the BOD of the liquid to be treated is 100 mg / l or more, the increase in COD may be 10 mg / l or more, There is a problem that the load of the coagulation sedimentation treatment or the activated carbon treatment as the post-treatment is increased. An object of the present invention is to propose an aerobic treatment method for organic wastewater which can reduce the volume of sludge and prevent deterioration of treated water quality in order to solve the above problems. It is to be. [0006] The present invention is a method for aerobic biological treatment of organic wastewater in an aeration tank in the presence of biological sludge containing aerobic microorganisms, wherein the BOD is 100 m.
g / l or more of an organic effluent is introduced into an aeration tank, and an aerobic biological treatment step of performing aerobic biological treatment in the presence of biological sludge containing aerobic microorganisms; A solid-liquid separation step of discharging the separated liquid as a treatment liquid and returning at least a part of the separated sludge to the aeration tank, and an ozone treatment step of extracting and ozone-treating a part of the mixed liquid or the separated sludge in the aeration tank. , Storing ozone-treated sludge ,
Transforms the produced biodegradable components into biodegradable.
And an aerobic treatment method for organic wastewater, comprising a return step of decomposing residual ozone and returning the ozone to an aeration tank. The organic effluent to be treated in the present invention is an organic effluent having a BOD of 100 mg / l or more.
Alternatively, the effluent contains an organic substance that is treated by an ordinary aerobic biological treatment method, but may contain a hardly biodegradable organic substance or inorganic substance. Such organic effluents include sewage, night soil, food factory effluents and other industrial effluents. In the aerobic biological treatment of the present invention, the organic effluent is subjected to aerobic biological treatment in the presence of biological sludge containing aerobic microorganisms. In such treatment, the organic wastewater is mixed with activated sludge in an aeration tank and aerated, the mixed liquid is separated into solid and liquid by a solid-liquid separator, and a part of the separated sludge is returned to the aeration tank. Aerobic biological treatment in the sludge treatment method is general, but other treatments modified from this may be used. In the present invention, a part of the biological sludge is extracted from the treatment system in such aerobic biological treatment, and the extracted sludge is subjected to ozone treatment. When extracting biological sludge, it is preferable to extract a part of the separated sludge separated by the solid-liquid separator, but it may also be possible to extract the mixed sludge from the aeration tank. When extracting from the separated sludge, part or all of the part discharged as excess sludge can be extracted as extracted sludge,
In addition to excess sludge, it is preferable that a part of the sludge returned to the aeration tank as return sludge is further extracted and subjected to ozonation. In this case, the amount of excess sludge can be reduced, and depending on conditions, excess sludge may be used. Can be reduced to zero. This will be described in detail later. 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:
It is preferable to add an inorganic acid such as sulfuric acid, hydrochloric acid or nitric acid to the biological sludge as a pH adjuster, adjust the biological sludge by acid fermentation treatment, or combine them.
When a pH adjuster is added, the pH is preferably adjusted to 3 to 4, and when an acid fermentation treatment is performed, the pH is preferably adjusted to 4 to 5. The ozone treatment can be carried out by adjusting the pH of the extracted sludge or acid fermentation treatment solution to 5 or less as it is or, if necessary, concentrating it with a centrifugal separator or the like, and bringing it into contact with ozone. As a contact method, a method of introducing sludge into the ozone treatment tank and blowing ozone, a method of mechanical stirring, a method of using a packed bed, and the like can be adopted. As ozone, ozone-containing gas such as ozone-containing air and ozonized air can be used in addition to ozone gas. The amount of ozone _{0.002~0.05g-O 3 / g-VSS} , preferably it is desirable to _{0.005~0.03g-O 3 / g-VSS} . The biological sludge is oxidatively decomposed by the ozone treatment and is converted into a BOD component. As an ozone treatment apparatus for ozone treatment,
Any device having an ozone treatment tank for contacting ozone with sludge in the sludge-containing liquid to cause an oxidation reaction and a device having a means for returning the ozone treatment liquid to the aeration tank can be used. be able to. If the sludge is likely to settle in the ozonation tank, or if there is more sludge to settle than the floating sludge, it is preferable that the sludge-containing liquid and the ozone-containing gas are brought into contact in parallel, Thereby, the contact efficiency between sludge and ozone is improved. On the other hand, when the sludge is likely to float in the ozone treatment tank, or when the amount of the sludge that floats is larger than that of the settling sludge, it is preferable that the sludge is brought into contact with the countercurrent, thereby improving the contact efficiency. When the ozone treatment is performed by blowing the ozone-containing gas into the ozone treatment tank, foaming occurs. To prevent troubles caused by the foaming, a liquid spraying means for defoaming can be provided in the ozone treatment tank. . As a liquid spraying means,
It is preferable to use an apparatus configured to withdraw the liquid in the tank including the sludge in the ozonation tank and to spray the extracted liquid as defoaming water on the liquid surface in the ozonation tank. As an ozone treatment tank, a liquid-phase contact area is formed at the lower part of the tank where an ozone-containing gas is blown into a liquid-phase sludge-containing liquid to make gas-liquid contact, and the foamed foam and the ozone-containing gas are formed at the upper part. The use of an ozonation tank configured to form a foam contact area to be contacted further increases ozonation efficiency. Liquid phase contact area height is 0.2-3
m, preferably 0.5 to 1.5 m. The height of the foam contact area may be at least 1 m above the liquid level of the sludge-containing liquid in the liquid phase contact area, but is preferably 1 to 10 m, more preferably 2 to 5 m. The foam contact area can be filled with a foam holding member, so that the inside diameter of the ozone treatment tank is large and it is difficult to hold the foam, or the concentration of biological sludge is low and the sludge-containing liquid is hard to foam. Even in the case of properties, foams can be efficiently retained, and ozone treatment efficiency can be increased. The foam holding member may have any structure as long as it can hold the foam, but preferably has a honeycomb-shaped or lattice-shaped partition plate structure. The above-mentioned liquid spraying device is provided above the foam contact area in the ozone treatment tank, and is used to supply industrial water, a final treatment liquid, a withdrawal liquid from the ozone treatment tank, or a mixture of the withdrawal liquid and the liquid to be treated. Spraying can be performed toward the foam layer, thereby suppressing excessive foaming and maintaining the foam contact area at a predetermined height. In this case, it is preferable to use a drawing liquid or a liquid mixture of the drawing liquid and the liquid to be treated, because the sludge concentration of the liquid in the tank does not decrease and the nozzle or the like does not block. 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 inside of the tank with the liquid to be treated, and the cost of the ozone treatment apparatus is reduced accordingly. In the ozone treatment tank, sludge reacts with ozone to be oxidatively decomposed and converted into BOD components. At this time, some biodegradable components are generated, and it is difficult to biodegrade even if it is returned to the aeration tank as it is and subjected to aerobic biological treatment,
In the present invention, the sludge is degraded by storing the ozone-treated sludge to make it easily biodegradable. Ozonized sludge gradually changes in quality even after the end of ozone treatment, and even when biological reactions are not involved, soluble COD increases and hardly biodegradable components decrease. Also, residual ozone in the ozonized sludge is decomposed during storage. The storage can be carried out at an arbitrary place. For example, a storage tank for ozone-treated sludge may be provided. This is preferable because there is no need to provide a simple device. The storage time is about 3 hours to 2 days, preferably about 12 hours to 2 days. The sludge that has been stored and altered after the ozone treatment is introduced into an aeration tank in an aerobic biological treatment step to perform aerobic biological treatment. As a result, the easily biodegradable component that has been converted into BOD by the ozone treatment and the once hardly decomposable component are easily degraded by storage, and the easily biodegradable component is easily biodegraded and removed. Thereby, the outflow of COD is prevented, high treated water quality is obtained, and the amount of sludge discharged from the entire system is reduced. The residual ozone in the ozonated sludge is decomposed during storage, and therefore has no harmful effect on the organisms in the activated sludge. In this case, as the amount of the sludge to be subjected to the ozone treatment is increased, the volume reduction rate of the sludge is increased. However, sludge multiplies when biodegrading the organic matter in the ozone-treated sludge.Thus, simply treating the excess sludge with ozone cannot reduce the excess sludge to zero, but the amount of sludge that grows is apparently zero. When the excess sludge is withdrawn and subjected to ozone treatment, the amount of excess sludge generated from the entire system can be reduced to zero. In this case, when the amount of the sludge to be ozone-treated increases, the biological treatment performance may decrease,
In such a case, the biological treatment performance can be maintained high by providing a carrier for supporting sludge in the aeration tank and maintaining a fixed amount of sludge. In the aerobic treatment step, the VSS / SS ratio and MLVSS of the biological sludge in the aeration tank are controlled to predetermined values by controlling the amount of sludge supplied to the ozone treatment and the amount of excess sludge discharged outside the system. By keeping the volume of the wastewater, the volume of the excess sludge can be reduced without lowering the biological treatment performance, and the sedimentation and dehydration of the biological sludge in the aeration tank can be improved. This facilitates the separation operation in the solid-liquid separation device, and also facilitates the dewatering of the generated excess sludge. That is, V of biological sludge in the aeration tank
SS / SS ratio of 0.2 to 0.7, preferably 0.3 to
0.6, the sedimentation and dewatering of sludge can be improved by controlling the MLVSS to be maintained at 500 to 10000 mg / l, preferably 1000 to 5000 mg / l. As a general tendency, as the VSS / SS ratio decreases, the specific gravity of the sludge increases, and the sedimentation and dewatering properties improve. The principle of sludge volume 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 volume reduction. In the figure, 1 is an aerobic biological treatment system,
2 is an ozone treatment system. The aerobic biological treatment system 1 is a treatment system in which an organic effluent is brought into contact with biological sludge to decompose aerobically, such as an activated sludge treatment device, and an aeration tank and a solid-liquid separation device are separately provided. However, it is illustrated as an entire processing system including these. The ozone treatment system 2 has an ozone treatment tank that reacts an ozone-containing gas with the extracted sludge that is extracted in the state of a mixed liquid or a concentrated liquid, and oxidatively decomposes it into BOD, and a storage tank that stores the ozonized sludge. Are shown as an entire processing system including these. The aerobic biological treatment system 1 of FIG. 1 holds a certain amount of biological sludge 3a for performing aerobic biological treatment. When the liquid 4 to be treated is introduced into the aerobic biological treatment system 1 and subjected to the aerobic biological treatment, the BOD contained in the liquid 4 to be treated is assimilated into the biological sludge 3a, and the sludge 3b is newly generated by the multiplication thereof. Is generated. On the other hand, biological sludge 3a in the system
The self-decomposition part 3c disappears by self-decomposition. Therefore, in a steady state, the difference between the generated sludge 3b and the self-decomposed component 3c multiplies as multiplication sludge 3d. The case where the sludge 3d is treated as excess sludge in the ozone treatment system 2 is shown by a broken line 5 in FIG.
When the proliferating sludge 3d is returned to the aerobic biological treatment system 1 by ozone treatment, the BOD produced by the ozone treatment is converted into sludge, and another produced sludge 3e is produced, which becomes a substantial sludge propagation component. Must be discharged as excess sludge. On the other hand, a larger amount of the extracted sludge 3f than the multiplication sludge 3d is extracted from the aerobic biological treatment system 1 and the ozone treatment system 2
To convert it to BOD and return the ozone-treated sludge 6 to the aerobic biological treatment system 1, whereby another 3 g of generated sludge is generated from the BOD generated by ozonolysis. In this case, the difference between the extracted sludge 3f and the generated sludge 3g is the mineralized portion 3h.
It becomes. Here, a larger amount of the extracted sludge 3f than the multiplied sludge 3d is converted to BOD by ozone treatment.
As compared with the case where only the proliferation sludge 3d is decomposed by ozonolysis, the mineralized portion increases and the sludge volume reduction rate increases. Proliferating sludge 3
When the amount of the extracted sludge 3f is determined so that d and the mineralized portion h become equal, the excess sludge becomes substantially zero. When the amount of the proliferating sludge 3d is larger than that of the mineralized portion 3h, the difference becomes a substantial increase portion 3i, and is discharged out of the system as excess sludge 7. Reference numeral 8 denotes a treatment liquid of the aerobic biological treatment system 1. In the aerobic biological treatment system 1, the capacity of the aeration tank is V, the biological sludge concentration is X, the sludge yield is Y, the flow rate of the liquid to be treated (the flow rate of the treatment liquid) is Q, and the organic matter concentration of the liquid to be treated is C.
i, the organic matter concentration of the treatment liquid is Ce, the biologically treated organic matter concentration is (Ci-Ce), the sludge self-decomposition constant is Kd, the surplus sludge discharge amount is q, the extraction amount to the ozone treatment tank is Q ′, and the ozone treatment is performed. Assuming that the rate of the converted sludge converted into biological sludge is k, the material balance is expressed by the following equation [1]. V dX / dt = YQ (Ci−Ce) −V Kd X−q X−Q′X + k Q′X [1] In the formula [1], V dX / dt is an aerobic biological treatment. Amount of change in biological sludge 3a in system 1, YQ (Ci-Ce)
Is the amount of generated sludge 3b, V Kd X is the amount of autolysis 3c, q
X is the amount of surplus sludge 7 discharged, Q'X is the amount of extracted sludge 3f, k
Q'X indicates the amount of 3 g of generated sludge. Where Q (Ci−C
e) / V = LV (tank load), q / V = 1 / SRT (excess sludge residence time ratio), Q '/ V = θ (circulation ratio of biological sludge to ozone treatment system), (1-k) = Δ (inorganization ratio), in a steady state, the equation [1] is simplified as the following equation [2]. YLV / X = Kd + 1 / SRT + δθ [2] In a normal aerobic biological treatment system without the ozone treatment system 2, there is no third term (δθ) in the equation (2), so sludge When the load is constant, the excess sludge (X / S
RT) is determined. On the other hand, in the treatment system combined with the ozone treatment, as apparent from the equation (2), the volume of the excess sludge is reduced by the value of the third term. And the value of the third term is the second
Under conditions comparable to the value of the term, it is possible to set the sludge load to a normal value without discharging excess sludge (1 / SRT = 0). The parameters of the third term of the above equation [2] are the mineralization ratio δ and the circulation ratio θ. Of these, δ is the ratio of ozone injection to sludge of 0.01 g-O ₃ / g-VSS or more. Since the steady value is around 0.5, the apparent volume reduction ratio of the sludge is determined in this region in proportion to θ. on the other hand,
The circulation ratio θ does not affect the sludge activity up to about 0.5 day ⁻¹ . This means that less than 1/2 of the biological sludge 3a held in the aerobic biological treatment system 1 is extracted per day.
It means that the sludge activity of the aerobic biological treatment system 1 is maintained even if the sludge is circulated to the ozone treatment system 2 as f. Therefore, the upper limit of the circulation ratio θ is 0.5 day ⁻¹
It is said. When θ is zero, a complete oxidation method is used. In this case, the sludge load is low and the volume reduction effect is small.
When the amount of the extracted sludge 3f is the same as the amount of the proliferating sludge 3d, the volume reduction rate becomes the same value as the conventional method. In a typical aerobic biological treatment, the SRT is 10 days and the sludge withdrawal rate is 0.1 day ^-1 . In the present invention, the extracted sludge 3 which is larger than the multiplication sludge 3d
When circulating f, 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, excess sludge does not occur 100% volume reduction is possible. Next, embodiments of the present invention will be described. FIG.
And FIG. 3 are flow sheets each showing an aerobic treatment apparatus of another embodiment. FIG. 2 is an example in which a mixed solution in an aeration tank is ozone-treated, and FIG. 3 is an ozone treatment of separated sludge in a solid-liquid separation apparatus. An example is shown. In FIG. 2, the aerobic biological treatment system 1 includes an aeration tank 11 and a solid-liquid separation device 12. A liquid passage 13 to be treated and a return sludge passage 14 communicate with the aeration tank 11, and an air diffuser 15 is provided at the bottom, and an air supply passage 16 communicates therewith. A communication path 17 communicates from the aeration tank 11 to the solid-liquid separation device 12. The solid-liquid separator 12 includes a treatment liquid passage 18 and a separated sludge discharge passage 1.
9, the return sludge passage 14 branches off from the separated sludge discharge passage 19. Reference numeral 20 denotes a surplus sludge discharge passage provided as needed. The ozone treatment system 2 comprises an ozone treatment device having an ozone treatment tank 21 and a storage tank 22. The ozone treatment tank 21 has a sludge extraction passage 23 and an exhaust ozone passage 2.
4 is in contact with the top. The sludge extraction path 23 is connected to an inorganic acid supply path 25. Further, an ozone supply passage 26 and an ozone treatment sludge passage 27 communicate with a lower portion of the ozone treatment tank 21. The ozone-treated sludge passage 27 communicates with the storage tank 22, and a storage sludge passage 28 from the storage tank 22 communicates with the aeration tank 11. In the aerobic biological treatment method for organic effluent by the processing apparatus shown in FIG. 2, the organic effluent is introduced into the aeration tank 11 from the liquid passage 13 to be treated, and the return sludge returned from the return sludge passage 14 It mixes with the activated sludge in the aeration tank 11 and diffuses the air supplied from the air supply path 16 from the diffuser 15 to perform aerobic biological treatment. Thereby, the organic matter in the wastewater is decomposed by the biological oxidation reaction. A part of the mixed liquid (reaction liquid) in the aeration tank 11 is passed through the communication path 17 to the solid-liquid separation device 1.
And separated into a separated liquid and a separated sludge by sedimentation. The separated liquid is discharged out of the system as a processing liquid from the processing liquid path 18, the separated sludge is taken out from the separated sludge discharge path 19, a part of the separated sludge is returned from the returned sludge path 14 to the aeration tank 11 as returned sludge, and the remaining part is surplus. The sludge is discharged from the excess sludge discharge passage 20 to the outside of the system. A part of the mixed solution in the aeration tank 11 is withdrawn as sludge from the sludge withdrawal passage 23, and the pH of the extracted sludge is adjusted to 5 or less by adding an inorganic acid from the inorganic acid supply passage 25, followed by ozone treatment. It is introduced into the tank 21. In the ozone treatment tank 21, the sludge is brought into contact with ozone supplied from the ozone supply passage 26 to perform ozone treatment, thereby converting the sludge into BOD. In this case, the ozone injection rate is 0.005~0.02g-O ₃ /
It may be about g-VSS. Ozone exhaust gas is exhausted ozone passage 24
From the system. The ozonated liquid is introduced into the storage tank 22 from the ozonated sludge passage 27 and stored therein, and the sludge is altered to convert the hardly biodegradable components into easily biodegradable ones. The stored sludge is returned from the storage sludge passage 28 to the aeration tank 11 and subjected to aerobic biological treatment as a load. By returning the stored sludge to the aeration tank 11 for aerobic biological treatment, the BOD component converted by the ozone treatment and the easily biodegradable component converted by the storage are assimilated into microorganisms and decomposed and removed. . Thereby, the volume of 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 separation device 12 is removed from the ozone treatment tank 2 through the separated sludge extraction passage 9.
1 is introduced. The ozonized sludge passage 27 communicates with the liquid to be treated storage tank 22a. 29 is a liquid supply passage to be processed. In the processing method using the apparatus shown in FIG. 3, the processing liquid is supplied from the processing liquid supply path 29 to the processing liquid storage tank 22a, stored, and then introduced into the aeration tank 11 from the processing liquid path 13. Perform aerobic biological treatment. Then, a part of the separated sludge separated by the solid-liquid separation device 12 is introduced into the ozone treatment tank 21 to perform ozone treatment. The ozone-treated sludge is introduced from the ozone-treated sludge passage 27 into the to-be-treated liquid storage tank 22a and stored together with the to-be-treated liquid, and then returned from the to-be-treated sludge passage 13 to the aeration tank 11. If the separated sludge is treated with ozone as shown in FIG.
Since the ozone treatment is performed in a state where the sludge concentration is high, the ozone treatment efficiency is increased, and the apparatus can be effectively used by storing the ozone-treated sludge in the treatment liquid storage tank. FIG. 4 shows that the mixed solution in the aeration tank was treated with ozone at an ozone injection amount of 0.05 g-O ₃ / g-VSS, and the sludge without ozone was treated with 1 mg of NaN ₃ as a biological respiration inhibitor. / L, and the total amount of soluble organic carbon (S.TOC / MLV) in the mixture when allowed to stand at 4 ° C.
6 is a graph showing a change in SS). From FIG. 4, it can be seen that the TOC of the ozone-treated sludge elutes and the sludge is degraded even under the condition where the biological respiration inhibitor does not involve any biological reaction, and the sludge is degraded. It can be understood that it is converted to. Example 1 and Comparative Examples 1 and 2 Peptone: yeast extract = 1: 1 synthetic wastewater (TOC)
= 200 mg / l) was subjected to aerobic treatment by the apparatus of FIG. The processing conditions were as follows: TOC tank load 0.6 g-C / liter.
day, MLSS 3000-4000 mg / l, ozone injection rate 0.05 g-O ₃ / g-VSS, ozone treated sludge amount is 30% of the retained sludge amount per day. In Example 1, the ozone-treated sludge was introduced into a liquid storage tank to be treated, stored for one day in HRT, and returned to the aeration tank. In Comparative Example 1, the sludge was returned directly to the aeration tank without storage. Comparative Example 2 is an example without ozone treatment. Table 1 shows the processing results. [Table 1] From the above results, in the comparative example in which the ozone-treated sludge was returned directly to the aeration tank, the treated water COD was high, but in the stored example 1, the treated water COD was about the same as in the comparative example 2 in which the ozone treatment was not performed. It can be seen that the volume of sludge is reduced. According to the present invention, the BOD is 100 mg /
When an aerobic biological treatment is applied to more than 1 liter of the organic effluent, a part of the mixed liquid or separated sludge in the aeration tank is ozone-treated, the ozone-treated sludge is stored , and the hard-living organisms generated by the ozone treatment are removed.
Converts degradable components to readily biodegradable,
After disassembling the zon, it was returned to the aeration tank,
It is possible to reduce the volume of sludge, convert the hardly biodegradable components generated by the ozone treatment into easily biodegradable components and perform biodegradation, and reduce residual ozone.
Treatment is also possible, thereby preventing deterioration of treated water quality and obtaining high treated water quality.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic diagram for explaining the principle of sludge volume reduction. FIG. 2 is a system diagram showing an aerobic treatment device of an embodiment. FIG. 3 is a system diagram showing an aerobic treatment device of another embodiment. FIG. 4 is a graph showing changes in total soluble organic carbon in a mixed solution. [Description of Signs] 1 Aerobic treatment system 2 Ozonation treatment system 3a Activated sludge 3b, 3e, 3g Generated sludge 3c Self-decomposition part 3d Proliferation sludge 3f Extraction sludge 3h Mineralized part 3i Increased part 4 Liquid to be treated 6 Ozone treated sludge 7 Excess sludge 8 Processing liquid 11 Aeration tank 12 Solid-liquid separator 13 Liquid path to be processed 14 Returned sludge path 15 Air diffuser 16 Air supply path 17 Communication path 18 Processing liquid path 19 Separated sludge discharge path 20 Excess sludge discharge path 21 Ozone treatment Tank 22 Storage tank 22a Liquid to be treated storage tank 23 Sludge extraction path 24 Waste ozone path 25 Inorganic acid supply path 26 Ozone supply path 27 Ozone treated sludge path 28 Storage sludge path 29 Stock solution introduction path

Continuation of the front page (56) References JP-A-6-206088 (JP, A) JP-A-3-21396 (JP, A) JP-A-4-322790 (JP, A) JP-A-4-131193 (JP) , A) JP-A-56-168879 (JP, A) JP-A-55-8883 (JP, A) (58) Fields studied (Int. Cl. ⁷ , DB name) C02F 3/12 C02F 11/00- 11/20

Claims (1)

(1) A method for aerobic biological treatment of an organic wastewater in an aeration tank in the presence of biological sludge containing aerobic microorganisms, wherein the BOD is 100 mg / l or more. An aerobic biological treatment step of introducing an organic wastewater into the aeration tank to aerobic biological treatment in the presence of biological sludge containing aerobic microorganisms, and solid-liquid separation of the mixture in the aeration tank, and separating the separated liquid. A solid-liquid separation step of discharging as a treatment liquid and returning at least a part of the separated sludge to the aeration tank; an ozone treatment step of extracting a part of the mixed liquid or the separated sludge in the aeration tank and performing ozone treatment; Infertility generated by ozone treatment
Converts biodegradable components to biodegradable,
An aerobic treatment method for an organic wastewater, comprising: a return step of decomposing distillate ozone and returning it to an aeration tank.