JP3525458B2 - Aerobic treatment of organic wastewater - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for aerobically treating an organic effluent, and more particularly to a method for treating an organic effluent which can suppress the generation of excess sludge.

[0002]

2. Description of the Related Art In an aerobic treatment method in which an organic effluent is treated under aerobic conditions by utilizing the action of aerobic microorganisms, such as an activated sludge treatment method, a large amount of surplus sludge that is difficult to dehydrate is produced. Generate and its processing 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.

[0003] One of the aerobic treatment methods is a complete oxidation method. This method is a method in which the sludge load is reduced and aerobic treatment is performed in the same manner as in a normal method. Since the amount of self-digestion of the sludge increases with respect to the amount of the sludge multiplication, excess sludge can be extremely reduced. However, this method requires a low tank load, and is not practical when the amount of drainage is large.

On the other hand, a normal aerobic treatment is performed,
A method for reducing the volume of generated excess sludge has been used. As such sludge volume reduction methods, anaerobic digestion and aerobic digestion are generally used. These are methods in which an anaerobic digester or an aerobic digester for sludge is provided separately from an aerobic treatment device for organic wastewater to digest sludge under anaerobic or aerobic conditions.

However, in these methods, only about 50% of the treated sludge is decomposed, and the remainder is discharged as digested sludge. This digested sludge is a biologically inert substance, cannot be further reduced in volume, and must be incinerated or discarded.

As a method of reducing the volume of excess sludge, there has been proposed a method in which excess sludge is subjected to physicochemical treatment such as ozone treatment, and then guided to an aerobic digester to perform aerobic digestion (Japanese Patent Publication No. Sho-Kyoaki). No. 57-19719). However, in this method, the digestion rate of aerobic digestion is increased by ozone treatment or the like, but since it is not essentially different from the conventional aerobic digestion method, excess sludge cannot be eliminated, and a separate sludge digestion apparatus is required. Another drawback is that it is necessary.

On the other hand, the excess sludge generated by the aerobic treatment of the organic effluent is hydrolyzed and solubilized by adding an alkali and heating, and the aerobic treatment apparatus after neutralizing the decomposed liquid. A method for treating excess sludge has been proposed (Japanese Patent Publication No. 49-11813). However, in this method, since the hydrolysis product of the excess sludge is added as the BOD load of the raw water, the amount of sludge in the aeration tank also increases. For this reason, it is necessary to dispose a part of the excess sludge, and this method is also merely a means for reducing the volume of the excess sludge, and the volume reduction rate is low. If the amount of sludge to be hydrolyzed is increased in order to reduce the amount of excess sludge generated, the amount of activated sludge involved in aerobic treatment will decrease, resulting in lower treatment efficiency, and in addition to the difficulty of living organisms in the decomposition products. There is a problem that decomposable organic substances cannot be decomposed.

[0008]

SUMMARY OF THE INVENTION An object of the present invention is to provide an organic compound capable of suppressing the production of excess sludge and reducing the difficulty of biodegradable organic matter generated by decomposition without reducing load and treatment efficiency. It is to propose a method for aerobic treatment of effluent.

[0009]

SUMMARY OF THE INVENTION The present invention is a method for aerobically treating an organic effluent. In the presence of activated sludge containing (1) aerobic microorganisms, a method for aerobic treatment of organic waste liquid, with a longer SRT by Rukoto by supporting an active sludge to the carrier, good
A certain amount of activated sludge is held in the aerobic treatment tank to maintain a certain activity.
Activated sludge maintained in the aerobic treatment system by performing aerobic treatment while maintaining the amount of sludge generated by assimilation of BOD in organic effluent more than self-decomposition of activated sludge Activated sludge separated from the carrier in a state where the amount increases
Among the floating activated sludge containing, pull the amount greater than the growth amount of sludge from good <br/> aerobic treatment system, the extracted sludge is introduced into solubilizing treatment to aerobic treatment system by ozone treatment, the production of excess sludge An aerobic treatment method for an organic wastewater, characterized in that it is suppressed. (2) The method according to the above (1), wherein a larger amount of suspended activated sludge than the amount of the proliferating sludge is withdrawn from the aerobic treatment system in a state of a tank solution or a concentrated sludge.

In the method for aerobically treating an organic wastewater, a fixed amount of activated sludge containing aerobic microorganisms is held in an aerobic treatment system,
Here, an organic wastewater is introduced and brought into contact under aerobic conditions, and the BOD in the liquid to be treated is decomposed by the oxidizing action of aerobic microorganisms. At this time, the BOD in the liquid to be treated is assimilated, and the activated sludge multiplies.

Conventionally, in order to keep a certain amount of activated sludge in the aerobic treatment system, the same amount of activated sludge as the amount of sludge multiplied by assimilation of BOD is discharged as surplus sludge. Volume reduction is underway. Therefore, even if the excess sludge is decomposed by hydrolysis or the like and returned to the aerobic treatment system, the excess sludge is generated.

In the present invention, the activated sludge is carried on a carrier to carry out aerobic treatment, and a part of the suspended activated sludge in the liquid to be treated,
In particular, floating activated sludge larger than the amount of sludge multiplied by assimilation of BOD in the liquid to be treated is withdrawn from the aerobic treatment system, solubilized by ozone treatment, and returned to the aerobic treatment system, whereby activated sludge is reduced. Suppresses apparent growth. As a result, the amount of excess sludge decreases, and the amount of excess sludge can be reduced to zero depending on conditions.

As a carrier for supporting the activated sludge, a granular or massive fluid carrier such as sponge or sand can be charged and used, and a porous material such as a honeycomb tube, a corrugated plate, or a string-like contact material can be used. It can also be used by filling in a fixed bed type. The activated sludge adheres to the carrier and is carried by carrying out the aerobic treatment together with the suspended activated sludge by putting these carriers into the aerobic treatment tank. The carrier supporting such activated sludge is held by a screen or the like so as not to flow out of the aerobic treatment tank. The activated sludge adhering to the carrier is partly peeled off by propagation and becomes floating activated sludge.

In the present invention, a part of the suspended activated sludge including the activated sludge which does not adhere to the carrier and the separated activated sludge is withdrawn from the aerobic treatment system, solubilized, and returned to the aerobic treatment system.
As a means of solubilization, ozone treatment is performed , and sludge is
Convert to degradable.

In the aerobic treatment using no carrier, that is, in the aerobic treatment in which the aerobic treatment is carried out only with the floating activated sludge, the suspended activated sludge is larger than the amount of the sludge multiplied by the assimilation of BOD in the liquid to be treated. Is extracted from the aerobic treatment system, and is solubilized and returned to the aerobic treatment system, thereby reducing the amount of excess sludge. That is, the amount of sludge that grows due to the assimilation of BOD in the liquid to be treated corresponds to the amount of excess sludge in the related art. Therefore, if a larger amount of suspended sludge is extracted and solubilized and returned, the amount of excess sludge decreases. Then, when the amount of suspended sludge that is sufficient to reduce the amount of sludge that grows from the BOD generated by solubilization to zero is extracted and solubilized and returned, the amount of excess sludge generated becomes zero.

However, in such a method, since the amount of the extracted sludge increases, the amount of the activated sludge involved in the aerobic treatment decreases, and the treatment efficiency may decrease. Therefore, in the present invention, the activated sludge is loaded by loading the carrier into the aerobic treatment tank, the carrier is prevented from flowing out of the aerobic treatment tank, the activated sludge necessary for the aerobic treatment is retained, and the suspended sludge can be pulled out. By solubilizing and returning to the aerobic treatment system, the treatment efficiency of the aerobic treatment is increased, and the amount of excess sludge is reduced.

In the present invention, the amount of excess sludge is reduced by setting the amount of suspended activated sludge withdrawn from the aerobic treatment system to be larger than the amount of sludge proliferating by assimilation of BOD in the sludge to be treated. When the suspended sludge is extracted so that the amount of sludge proliferating by assimilation of BOD generated by solubilization becomes zero, the amount of surplus sludge becomes zero. Withdrawal of suspended activated sludge for solubilization may be withdrawn from an aerobic treatment tank such as an aeration tank in the state of a liquid in the tank, or may be withdrawn in a state of concentrated sludge from a sludge separation tank such as a precipitation tank. . The drawn sludge may be concentrated to a high concentration by a centrifugal separator and subjected to a solubilization treatment.

By using the carrier as described above, the aerobic microorganisms carried on the carrier are not subjected to the solubilization treatment, so that a certain amount of activated sludge is always held in the aerobic treatment tank. As a result, even if the amount of suspended sludge increases or decreases due to fluctuations in the solubilization conditions, a constant activity is maintained. Therefore, the aerobic treatment is less affected by the solubilization treatment,
Stable processing becomes possible.

Since the sludge attached to the carrier has a longer SRT than the suspended sludge, a trace amount of the hardly biodegradable COD component generated by the solubilization treatment can be efficiently biodegraded. Further, the SRT becomes longer, for example, 5
Days or more, it is also possible to retain nitrifying bacteria, and in an aerobic treatment system, in addition to decomposing organic matter, nitrification can be performed simultaneously, and biological nitrification and denitrification treatment can be performed. This is advantageous when performing.

FIG. 1 is a schematic diagram for explaining the principle by which the generation of excess sludge can be suppressed in the present invention. In the figure, 1 is an aerobic treatment system and 2 is a solubilization treatment system. The aerobic treatment system 1, like an activated sludge treatment device, is a treatment system in which organic wastewater is brought into contact with activated sludge to decompose aerobically, and comprises an aeration tank (aerobic treatment tank), a sludge separation unit, Are sometimes provided separately, but are shown as a whole processing system including these. The solubilization treatment system 2 is a device that solubilizes the extracted sludge and converts it into BOD.

The aerobic treatment system 1 of FIG. 1 holds a fixed amount of activated sludge 3a for performing aerobic treatment. When the liquid 4 to be treated is introduced into the aerobic treatment system 1 and subjected to the aerobic treatment, the BOD contained in the liquid 4 to be treated is assimilated into activated sludge 3a, and the sludge 3b is newly generated by the multiplication thereof. I do. On the other hand, the activated sludge 3a in the system loses its self-decomposed component 3c by self-decomposition. Therefore, in the steady state,
The difference between the generated sludge 3b and the self-decomposed component 3c proliferates as the proliferating sludge 3d.

In the conventional volume reduction method, the proliferating sludge 3d generated here is discharged outside the system as surplus sludge and volume reduction is performed, so that 50% of the sludge is further discharged as digested sludge. Alternatively, in Japanese Patent Publication No. 49-11813, the proliferating sludge 3d discharged as surplus sludge is hydrolyzed and solubilized and returned to the aerobic treatment system 1, but in this treatment method, it is added as a hydrolysis liquid. The BOD newly generates generated sludge, and surplus sludge is generated by continuing the treatment.

The case where the sludge 3d conventionally discharged as surplus sludge is treated by the solubilization treatment system 2 is shown by a broken line 5 in FIG. 1. However, the propagation sludge 3d is solubilized and subjected to an aerobic treatment system. When set back to 1, BOD generated by solubilization
Is converted into sludge, and another generated sludge 3e is generated, and this amount becomes substantial sludge multiplication and must be discharged as surplus sludge. Thus, the sludge volume reduction rate when solubilizing the proliferating sludge 3d and returning it to the aerobic treatment system is 30 to 40% by weight of the proliferating sludge 3d, which is lower than that in the case of anaerobic or aerobic digestion.

In the present invention, the extracted sludge 3f is treated in the aerobic treatment system 1
The solubilized sludge 6 is returned to the aerobic treatment tank of the aerobic treatment system 1 by being solubilized by the solubilization system 2 and converted into BOD. Thereby, another 3 g of generated sludge is generated from the BOD generated in the solubilization treatment. In this case, the extracted sludge 3
The difference between f and the generated sludge 3g is the mineralized portion 3h.

According to the present invention, a larger amount of the extracted sludge 3f can be solubilized than the multiplied sludge 3d.
There are many mineralized parts and sludge volume reduction rate is high. Proliferating sludge 3d
When the amount of the extracted sludge 3f is determined so that the amount of the extracted sludge is equal to that of the mineralized portion 3h, the surplus sludge becomes substantially zero. Even in such a case, in the aerobic treatment system 1, since the activated sludge necessary for the aerobic treatment is supported on the carrier, stable treatment is performed. When the proliferating sludge 3d is larger than the mineralized portion 3h, the difference becomes a substantial increase portion 3i, and the excess sludge 7
Is discharged outside the system. Reference numeral 8 denotes a processing solution of the aerobic processing system 1.

In the aerobic treatment system 1, the aerobic treatment tank capacity is V, the activated sludge concentration is X, the sludge yield is Y, the flow rate of the liquid to be treated (flow rate of the treatment liquid) is Q, and the organic matter concentration of the liquid to be treated is Ci, 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, and the withdrawal amount to the solubilization tank is Q ', solubilization. Assuming that the rate at which the treated sludge is reconverted into activated sludge is k, the material balance is expressed by the following equation [1].

(Equation 1)         V dX / dt = Y Q (Ci-Ce) -V Kd X-q X-Q'X + k Q'X [1]

In the equation (1), V dX / dt is the change amount of the activated sludge 3a in the aerobic treatment system 1, Y Q (C
i-Ce) is the amount of generated sludge 3b, V Kd X is the amount of self-decomposition 3c, qX is the amount of surplus sludge 7 discharged, Q'X is the amount of extracted sludge 3f, and k Q'X is the amount of generated sludge 3g. Indicates the amount.

Here, Q (Ci-Ce) / V = LV (tank load), q / V = 1 / SRT (excess sludge residence time ratio),
Q '/ V = θ (circulation ratio of activated sludge to solubilization treatment system),
If (1-k) = δ (inorganization ratio), in a steady state,
Equation [1] is simplified as in the following equation [2].

(Equation 2)       Y LV / X = Kd + 1 / SRT + δ θ [2]

In a normal aerobic treatment system in which the solubilization treatment system 2 does not exist, there is no third term (δθ) in the equation (2). Therefore, when the sludge load is constant, the excess sludge amount (X / SR
T) is determined. On the other hand, in the treatment system in which the solubilization treatment system is combined, as apparent from the equation (2), the volume of the excess sludge is reduced by the value of the third term. Under conditions where the value of the third term is comparable to the value of the second term, the sludge load can be set to a normal value without discharging excess sludge (1 / SRT = 0). is there.

When the ozone treatment is employed as the solubilization treatment, the biodegradability (biodegradation rate) of the ozonized sludge is shown in FIG.
As shown in, tends to deteriorate in low ozone injection rate region to the sludge, considerably decreases below _{0.02g-O 3 / g-SS} . Thus the lower limit of the ozone injection rate is the _{0.02g-O 3 / g-SS} , upper limit is not restricted, preferable from the cost aspects of the _{0.2g-O 3 / g-SS} .

Since the sludge activity of the activated sludge in the aerobic treatment system 1 decreases at a low ozone injection rate, it is necessary to perform ozone treatment on the extracted sludge extracted from the aerobic treatment system 1. The place where sludge is extracted from the aerobic treatment system is
Either an aerobic treatment tank or a sludge separation unit may be used. When the sludge is extracted from the aerobic treatment tank, a relatively fixed amount of sludge can be extracted at a low concentration. When the sludge is extracted from the sludge separation part, the sludge amount tends to be not constant although the concentration is high.

[0032]

Embodiments of the present invention will be described below. 3 and 4 are flow sheets showing an aerobic treatment method of an organic waste liquid according to the embodiment. FIG. 3 shows an example in which sludge is drawn out from an aeration tank and ozone treatment is performed as a solubilization treatment, and FIG. An example is shown in which sludge is extracted from a separation unit and ozone treatment is performed as a solubilization treatment. In the figure, 11 is an aeration tank, 12 is a sludge separation section, 13 is a sponge as a carrier, and 21 is an ozone treatment tank for solubilization.

In the treatment method shown in FIG. 3, first, a sponge 13 is charged, and a liquid to be treated 14 is introduced into an aeration tank 11 holding activated sludge attached thereto.
The air is mixed with the ozone-treated sludge 24 and the floating activated sludge in the aeration tank 11, and air is sent from the air supply pipe 16.
Aeration is performed by aeration from 7 and aerobic treatment is performed. It is desirable that the amount of sponge 13 charged is 5 to 40%, preferably 10 to 30% of the volume of the aeration tank 11. Part of the mixed liquid in the aeration tank 11 is guided to the sludge separating section 12 through the screen 18 so as to prevent the sponge 13 from flowing out, and performs solid-liquid separation. The separated liquid is discharged as the processing liquid 19, separated sludge as a return sludge 15 is returned to the aeration tank 11 by the pump P _1.

On the other hand, floating sludge is drawn out from the aeration tank 11 through the screen 18 as drawn sludge 22, and the pump P ₂
To ozone treatment tank 21 to supply ozone from ozone supply passage 23 and bring it into contact with ozone to perform ozone treatment. The ozone-treated sludge 24 is returned (circulated) to the aeration tank 11 and subjected to aerobic treatment as a load. The ozone exhaust gas is discharged from a discharge ozone passage 25. Here, the extracted sludge 22 is oxidatively decomposed by ozone and converted into BOD and trace amounts of biodegradable COD.

In the treatment method shown in FIG. 4, instead of extracting the floating activated sludge from the aeration tank 11, a part of the separated sludge separated in the sludge separation section 12 is circulated to the ozone treatment tank 21 as the extracted sludge 22 for ozone treatment. I do. Otherwise, processing is performed in the same manner as in FIG.

In each of FIGS. 3 and 4, V in the above equation (1) is the capacity of the aeration tank 11, X is the concentration of the total sludge held in the aeration tank 11 and the sludge separation unit 12 with respect to V, and Q 'Is calculated as the capacity when the sludge concentration of the concentrated sludge in the aeration tank 11 or the sludge separation unit 12 is converted into X. Thus, in each of FIGS. 3 and 4, as shown in FIG. 1, the respective values can be determined as the aerobic treatment system 1.

3 and 4, when the excess sludge is not zero, the excess sludge 20 is discharged out of the system. If more activated sludge than the proliferating sludge is extracted and the amount of the extracted sludge 22 is determined so that the proliferating portion and the mineralized portion are the same, the amount of surplus sludge 20 becomes zero.

Even in such a case, since the aeration tank 11 holds a certain amount of aerobic microorganisms supported on the sponge 13, the aerobic treatment performance does not decrease and stable treatment is performed. Further, the hardly biodegradable COD component generated by the ozone treatment can be efficiently decomposed by the sludge having a long SRT. In a system in which minerals such as sand are accumulated, even when the generation of surplus sludge by propagation is zero, some sludge can be discharged. When the activated sludge carried on the carrier multiplies, the activated sludge is detached from the carrier and becomes floating activated sludge. The activated sludge thus detached is also solubilized in the ozone treatment tank 21.

In the embodiment shown in FIGS. 3 and 4, the sludge separating section 12 is used.
Although a sedimentation tank is shown in the figure, a membrane separation device or another sludge separation device may be used. Further, the aerobic treatment system 1 is not limited to the standard activated sludge treatment, and other aerobic treatment devices can be employed. In addition, activated sludge containing nitrifying bacteria is generated in the aeration tank 11, and oxidative decomposition of BOD and nitrification of ammonia nitrogen are performed. By combining this with a denitrification apparatus, nitrification denitrification can be performed.

Example 1 According to the treatment method shown in FIG. 1, under the conditions shown in Table 1, the circulation ratio of the extracted sludge to the ozone treatment tank 21 (the ratio to the volume of the aeration tank 21) was set to 0%, 10% or 30%. Aerobic treatment of sexual drainage was performed. Using a sponge 13 as a carrier,
20% was added to the volume of the aeration tank 11 and operated continuously for 2 months. The same treatment was carried out only with suspended sludge without adding sponge as a control system. Table 2 shows the results of the treated water quality.

[0041]

[Table 1]

[0042]

[Table 2]

From the results shown in Table 2, the COD _{Mn of the} treatment liquid increased as the sludge volume reduction rate increased in the control system, but in Example 1, the water quality of the treatment liquid hardly changed even when the volume reduction rate increased. You can see that.

[0044]

According to the present invention, activated sludge is supported on a carrier.
Aerobic treatment tank
To maintain a certain amount of activated sludge and maintain a certain level of activity.
Performs anaerobic treatment and produces assimilation of BOD in organic wastewater.
The amount of sludge formed is greater than the activated sludge
Mud is generated and the amount of activated sludge retained in the aerobic treatment system increases.
Activated sludge containing activated sludge separated from the carrier
Aerobic treatment system for more sludge than sewage sludge
The extracted sludge is solubilized by ozone treatment and circulated through an aerobic treatment tank for treatment, so that the production of excess sludge is suppressed without lowering the load and treatment efficiency, and The treatment can be performed stably, and in some cases, the generation of excess sludge can be reduced to zero.

[Brief description of the drawings]

FIG. 1 is a schematic diagram for explaining a principle capable of suppressing the generation of excess sludge in the present invention.

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

FIG. 3 is a flowchart illustrating a processing method according to an embodiment.

FIG. 4 is a flowchart illustrating a processing method according to another embodiment.

[Explanation of symbols]

1 Aerobic treatment system 2 Solubilization system 3a Activated sludge 3b, 3e, 3g Produced sludge 3c Self-decomposition 3d multiplication sludge 3f, 22 drawn sludge 3h mineralized part 3i increase 4, 14 Liquid to be treated 6 Solubilized sludge 7,20 Surplus sludge 8, 19 Treatment liquid 11 Aeration tank 12 Sludge separation unit 13 sponge 15 Return sludge 16 Air supply path 17 Air diffuser 18 screen 21 Ozone treatment tank 23 Ozone supply path 24 Ozone treated sludge 25 Exhaust ozone passage

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-4-305295 (JP, A) JP-A-3-21396 (JP, A) JP-A-4-90896 (JP, A) 19719 (JP, B1) International Publication 93/004988 (WO, A1) (58) Fields investigated (Int. Cl. ⁷ , DB name) C02F 3/02-3/12 C02F 11/00-11/20

Claims (2)

(57) [Claims] 1. A in the presence of activated sludge containing aerobic microorganisms, a method for aerobic treatment of organic waste liquid, to lengthen the SRT by Rukoto by supporting an active sludge to the carrier
While maintaining a certain amount of activated sludge in the aerobic treatment tank
Aerobic treatment is performed while maintaining a certain activity, and the amount of sludge generated by assimilation of BOD in the organic wastewater is larger than the self-decomposition of activated sludge. in a state in which the activated sludge volume held in increases, responsible
Among the floating activated sludge containing activated sludge peeled from the body, the amount greater than the growth amount of sludge withdrawal from aerobic treatment system, the extracted sludge is introduced into solubilizing treatment to aerobic treatment system by ozone treatment, excess sludge An aerobic treatment method for an organic wastewater, characterized in that generation of an organic wastewater is suppressed. 2. The method according to claim 1, wherein a larger amount of the suspended activated sludge than the amount of the proliferating sludge is withdrawn from the aerobic treatment system in a state of a tank solution or a concentrated sludge.