JPH0819789A - Method and apparatus for aerobic treatment of organic waste solution - Google Patents

Abstract

PURPOSE:To provide a method and apparatus for the aerobic treatment of an org. waste soln. capable of subjecting a reaction soln. to membrane separation in a high flux while preventing the clogging of a separation membrane to obtain treated water of high quality to enable the reutilization of water and capable of reducing the vol. of excessive sludge without lowering load and treatment efficiency. CONSTITUTION:An org. waste soln. 13 is introduced into an aerobic treatment tank 1 to be subjected to aerobic treatment and this reaction soln. is subjected to membrane separation in a membrane separator 12 to be separated into a filtrate 12b and a conc. soln. 12c and the reaction soln. or the conc. soln. is introduced into an ozone treatment tank to subject activated sludge to ozone treatment and the ozone treated sludge is introduced into the aerobic treatment tank 11.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and apparatus for aerobically treating organic waste liquid, and more particularly, to a method and apparatus for aerobically treating organic waste liquid which can be easily separated by membrane separation and which can suppress the production of excess sludge. It is about.

[0002]

2. Description of the Related Art An aerobic treatment method, such as an activated sludge treatment method, which treats an organic waste liquid under aerobic conditions by utilizing the action of aerobic microorganisms, produces a large amount of hardly dehydratable excess sludge. However, the processing is difficult. Conventionally, in such an aerobic treatment system, sedimentation separation is performed to separate the treatment liquid and the sludge, but since solid-liquid separation is poor, a large device is required, and sludge in the treated water is required. , It was not possible to obtain reusable treated water.

On the other hand, when a membrane separation device such as ultrafiltration or microfiltration is used to separate such sludge, clogging is severe and high flux (membrane permeation flux) cannot be obtained, which is practical. There wasn't. Although excess sludge was disposed of, it is difficult to secure a disposal site for it, and it is necessary to reduce the volume of sludge.

As a method for reducing the volume of excess sludge, a method has been proposed in which excess sludge is treated with ozone and then introduced into an aerobic digester to perform aerobic digestion (Japanese Patent Publication No. 57-197).
No. 19). However, this method increases the digestion rate of aerobic digestion by ozone treatment, but since it is essentially the same as the conventional aerobic digestion method, the volume reduction rate of sludge is about 50% of the treated sludge as in the conventional method. However, there is a drawback that a device for digesting sludge is required separately.

[0005]

DISCLOSURE OF THE INVENTION The object of the present invention is to enable the membrane separation with a high flux, to suppress the production of excess sludge without lowering the load and treatment efficiency, and in some cases to remove excess sludge. An object of the present invention is to propose a method and apparatus for aerobic treatment of organic waste liquid which can reduce the generation to zero.

[0006]

The present invention is the following method and apparatus for aerobic treatment of organic waste liquid. (1) In the method of aerobically treating organic waste liquid in the presence of activated sludge containing aerobic microorganisms, a step of separating a reaction solution of an aerobic treatment system into a permeate and a concentrate, An aerobic treatment method for an organic waste liquid, which comprises a step of subjecting the reaction solution or the concentrated solution to ozone treatment and a step of introducing the ozone treatment solution into an aerobic treatment system. (2) An aerobic reaction tank that aerobically treats the organic waste liquid in the presence of activated sludge containing aerobic microorganisms, and the reaction solution of this aerobic reaction tank is separated into a permeate and a concentrate. An apparatus for treating an organic waste liquid, comprising: a membrane separation device for performing an ozone treatment on the reaction liquid or the concentrated liquid; and an ozone treatment device for introducing the ozone treatment liquid into an aerobic reaction tank.

In the aerobic treatment method of organic waste liquid, a certain amount of activated sludge containing aerobic microorganisms is held in the aerobic treatment system,
The organic waste liquid is introduced here and brought into contact under aerobic conditions, and the BO in the liquid to be treated is subjected to a biooxidation reaction by aerobic microorganisms.
Decompose D. At this time, the BOD in the liquid to be treated is assimilated and the activated sludge grows. As an aerobic treatment tank used for such an aerobic treatment system, an aeration tank for activated sludge treatment is generally used, but the aerobic treatment tank is not limited to this.

In the present invention, in the step of carrying out aerobic treatment by such an aerobic treatment system, the reaction liquid (mixed liquid) of the aerobic treatment system (aerobic treatment tank) is subjected to membrane separation by a membrane separation device to obtain a permeated liquid. And separate into a concentrated solution. As a membrane separation device, an ultrafiltration (UF) membrane, a microfiltration (MF) membrane, a reverse osmosis membrane (RO) membrane or the like having any separation membrane can be used, but the UF membrane and the MF membrane are preferable. . Such a membrane separation device may be provided inside the aerobic treatment tank or outside the aerobic treatment tank. By membrane separation, activated sludge and other solids in the reaction solution are concentrated on the concentrated solution side, and the permeated solution can be reused as treated water.

On the other hand, in the ozone treatment system (ozone treatment device), the reaction liquid of the aerobic treatment system or the concentrated liquid concentrated by the membrane separation device is subjected to ozone treatment to hydrolyze the activated sludge and other solid substances to thereby form low molecular weight compounds. It is biodegradable and introduced into the aerobic treatment system. Since the low molecular weight compound obtained by such ozone treatment is converted into BOD, it is assimilated as BOD in the aerobic treatment system and undergoes biodegradation. This prevents clogging of the separation membrane in the membrane separation device, increases the flux, and reduces the volume of excess sludge.

In this case, the activated sludge having a larger amount than the sludge that proliferates due to the assimilation of BOD in the liquid to be treated is withdrawn from the aerobic treatment system, is ozone-treated, and is returned to the aerobic treatment system. Apparent growth can be suppressed. As a result, the amount of excess sludge is reduced, and depending on the conditions, the amount of excess sludge generated can be reduced to zero.

FIG. 1 is a schematic diagram for explaining the principle of sludge volume reduction. In the figure, 1 is an aerobic treatment system and 2 is an ozone treatment system. The aerobic treatment system 1, like an activated sludge treatment device, is a treatment system that aerobically decomposes organic waste liquid by contacting it with activated sludge, and an aerobic treatment tank and a membrane separation device are separately provided. Is shown as an overall processing system including these. The ozone treatment system 2 is a device that reacts ozone-containing gas with the drawn sludge that is drawn in the state of a reaction solution or a concentrated solution, oxidatively decomposes it, and converts it into BOD.

The aerobic treatment system 1 of FIG. 1 holds a certain amount of activated sludge 3a for performing aerobic treatment. When the liquid to be treated 4 is introduced into the aerobic treatment system 1 and subjected to aerobic treatment, the BOD contained in the liquid to be treated 4 is assimilated into the activated sludge 3a, and a new sludge 3b is generated due to the multiplication thereof. To do. On the other hand, the activated sludge 3a in the system is self-decomposed, and the self-decomposed portion 3c disappears. So in steady state,
The difference between the generated sludge 3b and the self-decomposition 3c grows as the grown sludge 3d.

In the conventional volume-reducing method, the multiplied sludge 3d generated here was discharged outside the system as excess sludge to reduce the volume, so 50% of the sludge was further discharged as digested sludge. Alternatively, in Japanese Examined Patent Publication No. 49-11813, B is obtained by hydrolyzing the breeding sludge 3d discharged as excess sludge.
Although it is converted to OD and returned to the aerobic treatment system 1, in this treatment method, BOD added as a hydrolysis liquid newly generates generated sludge, and excess sludge is generated by continuing the treatment.

The case of treating with the ozone treatment system 2 instead of hydrolysis is shown by the broken line 5 in FIG.
When ozone is treated and returned to the aerobic treatment system 1, BOD generated by the ozone treatment is converted into sludge, and another generated sludge 3e is generated. Must be discharged. In this way, the sludge volume reduction rate in the case where ozone of the expanded sludge 3d is returned to the aerobic treatment system is 30 to 40% by weight of the expanded sludge 3d, which is lower than that in the case of anaerobic or aerobic digestion.

On the other hand, a larger amount of the extracted sludge 3f than the propagated sludge 3d is extracted from the aerobic treatment system 1, ozone-treated in the ozone treatment system 2 and converted into BOD, and the ozone-treated sludge 6 is converted into the aerobic treatment system. By returning the value to 1, another 3 g of produced sludge is produced from BOD produced by ozonolysis. In this case, the difference between the drawn sludge 3f and the produced sludge 3g is the mineralized portion 3h.
Becomes

[0016] Here, by treating the extracted sludge 3f in an amount larger than that of the propagated sludge 3d with ozone, and converting it into BOD,
Compared with the case where only the propagated sludge 3d is decomposed by ozone, the mineralized portion is increased and the sludge volume reduction rate is increased. Breeding sludge 3
3d of drawn sludge so that d and the mineralized portion 3h become equal
When the amount of is determined, the surplus sludge becomes substantially zero. When the amount of the grown sludge 3d is larger than that of the mineralized portion 3h, the difference becomes a substantially increased portion 3i, and the excess sludge 7 is discharged out of the system. Reference numeral 8 is a treatment liquid of the aerobic treatment system 1.

In the aerobic treatment system 1, the biological treatment tank capacity is V, the activated sludge concentration is X, the sludge yield is Y, the treated liquid flow rate (treatment liquid flow rate) is Q, and the organic matter concentration of the treated liquid is C.
i, organic concentration of treated liquid is Ce, concentration of biologically treated organic substance is (Ci-Ce), sludge self-decomposition constant is Kd, excess sludge discharge amount is q, extraction amount to ozone tank is Q ', ozone treatment is performed. The mass balance is expressed by the following equation [1], where k is the rate at which the sludge is reconverted to activated sludge.

[Formula 1] V dX / dt = Y Q (Ci−Ce) −V Kd X−q X−Q′X + k Q′X [1]

In the formula [1], V dX / dt is the amount of change of the activated sludge 3a in the aerobic treatment system 1, YQ (Ci-Ce) is the amount of produced sludge 3b, and V Kd X is the amount of self-decomposition 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 produced sludge.

Where Q (Ci-Ce) / V = LV (tank load), q /
V = 1 / SRT (excess sludge retention time ratio), Q '/ V = θ (circulation ratio of activated sludge to ozone treatment system), (1-k) = δ (mineralization rate) Then, the equation [1] is simplified as the following equation [2].

[0020]

[Formula 2] Y LV / X = Kd + 1 / SRT + δθ [2]

In an ordinary aerobic treatment system in which the ozone treatment system 2 does not exist, the third term (δθ) in the equation [2] does not exist, so when the sludge load is constant, the excess sludge amount (X / SRT) is decided. On the other hand, in the treatment system in which the ozone treatment system is combined, as is apparent from the equation [2], the volume of the excess sludge is reduced by the value of the third term. 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 the excess sludge (1 / SRT = 0). is there.

FIG. 2 is a graph showing the relationship between the ozone injection rate and the mineralization rate δ in the drawn sludge, FIG. 3 is a graph showing the relationship between the circulation ratio θ and the sludge activity, and FIG. 4 is the ozone injection rate and the ozone-treated sludge. It is a graph which shows the relationship with the biodegradation rate of.

The parameters of the third term in the above equation [2] are the mineralization rate δ and the circulation ratio θ, of which δ is the ozone injection rate into the sludge of 0.03 g-O ₃ / g
At −SS or higher, the steady value is around 0.5, and thus the apparent volume reduction rate of sludge is determined in proportion to θ in this region.

On the other hand, the circulation ratio θ is as shown in FIG.
It does not affect sludge activity up to about 0.5 day ^-1 .
This means that even if 1/2 or less of the activated sludge 3a retained in the aerobic treatment system 1 is circulated to the ozone treatment system 2 as the extracted sludge 3f per day, the sludge activity of the aerobic treatment system 1 is maintained. It means that.

Therefore, the upper limit of the circulation ratio θ is set to 0.5 day ^-1 . When θ is zero, the complete oxidation method is used, but 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 grown sludge 3d, the volume reduction rate is the same as that of the conventional method. In normal aerobic treatment, S
The RT is 10 days and the sludge extraction rate is 0.1 day ^-1 . In the present invention, since the extracted sludge 3f, which is larger than the propagated sludge 3d, is circulated, the lower limit of θ on the circulation is set to a value exceeding 0.1 day ^-1 , but 0.2 d ^-1 or more is preferable, and particularly, 0. If 3day ^-1 , no excess sludge is generated 100
% Volume reduction is possible.

As shown in FIG. 4, the biodegradability of the ozone-treated sludge tends to deteriorate in a region where the ozone injection rate into the sludge is low, and remarkably decreases below 0.02 g-O ₃ / g-SS. Therefore, the lower limit of ozone injection rate is 0.02
and _{g-O 3 / g-SS} , the upper limit is not restricted, preferably from cost aspects and _{0.2g-O 3 / g-SS} .

From the above results, the maximum value of the third term δθ in the equation [2] is 0.5 × 0.5 = 0.25 day ⁻¹ . Therefore, even if the SRT in a normal aerobic treatment system is under operating conditions for 4 days, that is, for operating conditions in which 1/4 of the total sludge is discharged as surplus sludge per day, this sludge is treated by the ozone treatment system 2
By circulating the waste sludge to the operation (1 / SRT = 0), the excess sludge 7 is not discharged.

Since the sludge activity of the activated sludge in the aerobic treatment system 1 decreases at a stage where the ozone injection rate is low, it is necessary to perform the ozone treatment on the drawn sludge extracted from the aerobic treatment system 1. The place where sludge is drawn from the aerobic treatment system is
Either an aerobic treatment tank or a membrane separation device may be used. When extracting from an aerobic treatment tank, a relatively small amount of sludge can be extracted although the concentration is low. When it is drawn out as a concentrated liquid of a membrane separation device, the sludge amount tends to be inconsistent although the concentration is high.

[0029]

Embodiments of the present invention will be described below. FIGS. 5 and 6 are flow sheets showing an aerobic treatment apparatus for organic waste liquid of each example, FIG. 5 shows an example in which the membrane separation apparatus is provided outside the aerobic treatment tank, and FIG. 6 shows membrane separation. The example which the apparatus provided in the aerobic processing tank is shown.

In FIG. 5, the aerobic treatment system 1 is composed of an aerobic treatment tank 11 and a membrane separation device 12. The aerobic treatment tank 11 has a liquid passage 13 and a liquid return passage 14 to be treated.
And an air diffuser 15 is provided at the bottom, and an air supply path 16 is in communication. A communication path 17 having a pump P ₁ communicates with the membrane separation device 12 from the aerobic treatment tank 11. The membrane separation device 12 is divided into a permeate chamber 12b and a concentrate chamber 12c by a separation membrane 12a.
The processing liquid passage 18 communicates with b, the concentrated liquid withdrawal passage 19 communicates with the concentrated liquid chamber 12c, and the return liquid passage 14 branches.
As the membrane separation device 12, a device having an arbitrary separation membrane module such as a tubular type, a spiral type, or a hollow fiber type can be used.

The ozone treatment system 2 has an ozone treatment tank 21, a withdrawal liquid passage 22 branching from a concentrate withdrawal passage 19 and an exhaust ozone passage 23 are connected to the upper part, and an ozone supply passage 24 and an ozone treatment sludge passage 25 are provided. Contact the bottom. The ozone treatment sludge passage 25 is provided from the ozone treatment tank 21 to the aerobic treatment tank 11
Have been contacted. 20 is a surplus sludge discharge channel.

In the method of treating organic waste liquid by the above-mentioned treatment apparatus, in the aerobic treatment system 1, the organic waste liquid is introduced from the liquid passage 13 to be treated into the aerobic treatment tank 11 and returned from the return liquid passage 14. The returned sludge in the concentrated liquid and the activated sludge in the aerobic treatment tank 11 are mixed, and the air supplied from the air supply passage 16 is diffused from the diffuser 15 to perform aerobic treatment. As a result, the organic matter in the waste liquid is separated by the biooxidation reaction. A part of the reaction liquid (mixed liquid) in the aerobic treatment tank 11 is taken out from the communication path 17 and pressurized by the pump P ₁ to obtain the membrane separation device 1
By conducting to 2 and performing membrane separation, a permeate and a concentrate are separated. Here, the permeated liquid that has permeated the separation membrane 12a is discharged as a treated liquid from the treated liquid passage 18, and the concentrated liquid in which activated sludge and other solids are concentrated is drawn out from a concentrated liquid outlet passage 19,
A part of it is returned to the aerobic treatment tank 11 from the return liquid passage 14.

In the ozone treatment system 2, a part of the extracted concentrated liquid is circulated from the concentrated liquid withdrawal passage 19 through the withdrawal liquid passage 22 to the ozone treatment tank 21, and is brought into contact with ozone supplied from the ozone supply passage 24 so that the ozone is supplied. Treatment is performed to convert activated sludge into BOD. The ozone-treated sludge is returned from the ozone-treated sludge passage 25 to the aerobic treatment tank 11 and aerobically treated as a load. By thus introducing the ozone-treated sludge into the aerobic treatment tank 11 and performing the aerobic treatment, the properties of the activated sludge in the aerobic treatment tank 11 are improved, and the separation membrane 12a in the membrane separation device 12 is clogged. Is prevented, the flux can be increased and the membrane can be separated, and the volume of the excess sludge can be reduced.

In FIG. 6, the membrane separation device 12 is an aerobic treatment tank 1.
1, the aerobic treatment tank 1 is provided in the ozone treatment tank 21.
The in-tank liquid of No. 1 is supplied. Examples of the membrane separation device 12 include JP-A-61-29094 and JP-A-1-293.
No. 103, that is, a plurality of modules 12d having flat membrane-like separation membranes are arranged on the air diffuser 15 so that the membrane surfaces face in the vertical direction, and each module 12d is arranged. It is connected to the treatment liquid passage 18 through a branch passage 18a, and the treatment liquid passage 18 provided with a suction pump P ₂ is used. An extraction liquid passage 22 having a pump P ₃ is connected to the ozone treatment tank 21 from the aerobic treatment tank 11.

According to the method for treating organic waste liquid by the above-mentioned treatment apparatus, aerobic treatment is performed in the aerobic treatment tank 11 as in the case of FIG. 5, but by driving the pump P ₂ to absorb it. A pressure difference is generated between the inside and outside of the membrane surface of the module 12d of the membrane separation device 12, and membrane separation is performed. As a result, the liquid component in the reaction liquid (liquid in the tank) passes through the separation membrane and passes through the processing liquid passage 18.
The activated sludge and other solids are discharged from the reactor and are concentrated in the reaction solution, causing the same phenomenon as returning sludge. Activated sludge and other solid matter attached to the membrane surface are separated by the air rising from the air diffuser 15, and the module 12d maintains a clean membrane surface.

A part of the reaction liquid is introduced into the ozone treatment tank 21 from the extraction liquid passage 22 by the pump P ₃ , and the activated sludge in the liquid is decomposed. Ozone-treated sludge is the ozone-treated sludge path 2.
5 is introduced into the aerobic treatment tank 11 and aerobically treated as a load. As a result, as in the case of FIG. 5, the flux of the membrane separation device 12 increases and the excess sludge is reduced in volume.

5 and 6, V in the above formula [1] is the capacity of the aerobic treatment tank 11, and X is V.
The concentration of total sludge retained in the aerobic treatment tank 11 and the membrane separation device 12, and Q ′ is calculated as the capacity when the sludge concentration of the concentrated liquid in the aerobic treatment tank 11 or in the membrane separation device 12 is converted to X. To be done. As a result, in both cases of FIG. 5 and FIG. 6, the respective values can be determined as the aerobic treatment system 1 as shown in FIG.

In FIG. 5 and FIG. 6, the volume of sludge can be reduced by treating the drawn sludge in excess of the sludge with ozone. However, if the excess sludge is not zero, excess sludge is discharged from the excess sludge discharge path 20. Is discharged to the outside of the system. If the amount of extracted sludge is determined so that the propagated sludge and the mineralized portion are the same, the amount of excess sludge generated becomes zero, and the excess sludge discharge path 20 does not discharge. Even in this case, some sludge can be discharged in a system in which an inorganic substance such as sand is accumulated.

The test examples will be described below. Example 1 Using the apparatus of FIG. 5, COD _Mn 5500 m as a liquid to be treated
g / l human waste was processed. The treatment conditions at this time were: inflow rate of the liquid to be treated 1 m ³ / day, aerobic treatment tank volume 4 m ³ , MLSS
15000 mg / l, the membrane separator inflow 20 m ³ /
Circulation volume of concentrated liquid 18.7 m ³ / day, permeate volume 1 m ³ / day
The ozone treatment amount of the concentrated liquid is 0.3 m ³ / day, and the ozone injection amount is 0.05 (kg-O ₃ / kg-SS). Membrane separation apparatus incorporates a flat membrane module polysulfone UF membrane a fractionation molecular weight of 2,000,000 ⁽² × 10 sheets 0.1 m), is obtained by allowing adjust the separation area 0.1 to 1 m ^2, The operating pressure was 3 kg / cm ² . As a result, the COD _Mn of the treated water was 140 mg / l, the flux of the membrane separation device was 2 m ³ / m ² · day, and the amount of excess sludge generated was zero.

Comparative Example 1 As a result of treating under the same conditions as in Example 1 except that the ozone feed was stopped, the treated water COD _Mn was 140 mg / l,
Flux is 1 m ³ / m ² · day, the amount of excess sludge generated is 5.
It was 5 kg-SS / day.

[0041]

According to the present invention, the reaction liquid of the aerobic treatment system is membrane-separated into the permeated liquid and the concentrated liquid, and the reaction liquid or the concentrated liquid is subjected to ozone treatment to aerobically treat the ozone-treated liquid. Since it was introduced into the system, it is possible to prevent clogging of the separation membrane and perform membrane separation of the reaction liquid with high flux, and also reduce the volume of excess sludge without lowering the load and treatment efficiency, In some cases, it is possible to reduce the generation of excess sludge to zero.

[Brief description of drawings]

FIG. 1 is a schematic diagram for explaining the principle of sludge volume reduction in the present invention.

FIG. 2 is a graph showing a relationship between an ozone injection rate and a mineralization rate.

FIG. 3 is a graph showing the relationship between circulation ratio and sludge activity.

FIG. 4 is a graph showing a relationship between an ozone injection rate and a biodegradation rate.

FIG. 5 is a flow sheet showing the processing apparatus of the embodiment.

FIG. 6 is a flow sheet showing a processing apparatus of another embodiment.

[Explanation of symbols]

 1 Aerobic treatment system 2 Ozone treatment system 3a Activated sludge 3b, 3e, 3g Produced sludge 3c Self-decomposition 3d Proliferation sludge 3f Extracted sludge 3h Mineralized part 3i Increased part 4 Treated liquid 6 Ozone-treated sludge 7 Excess sludge 8 Treatment liquid 11 Aerobic treatment tank 12 Membrane separation device 13 Treated liquid passage 14 Returning liquid passage 15 Air diffuser 16 Air supply passage 17 Connecting passage 18 Treatment liquid passage 19 Concentrated liquid extraction passage 20 Excess sludge discharge passage 21 Ozone treatment tank 22 Extraction liquid Route 23 Waste ozone route 24 Ozone supply route 25 Ozone treatment sludge route

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI Technical display location C02F 9/00 502 ER 503 C 504 A

Claims (2)

[Claims] 1. A method for aerobically treating an organic waste liquid in the presence of activated sludge containing aerobic microorganisms, wherein a reaction solution of an aerobic treatment system is membrane-separated into a permeate and a concentrate. And a step of subjecting the reaction solution or the concentrated solution to an ozone treatment, and a step of introducing the ozone treatment liquid into an aerobic treatment system. 2. An aerobic reaction tank for aerobically treating organic waste liquid in the presence of activated sludge containing aerobic microorganisms, and a reaction solution in the aerobic reaction tank is subjected to membrane separation to obtain a permeated liquid and a concentrated liquid. An apparatus for treating organic waste liquid, comprising: a membrane separation device for separating the reaction liquid or the concentrated liquid; and an ozone treatment device for treating the reaction liquid or the concentrated liquid with ozone and introducing the ozone treatment liquid into an aerobic reaction tank.