JP2001198591A - Bulking inhibitor for activated sludge and bulking inhibition method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To stably and economically inhibit the bulking of the sludge generated in the settling tank (basin) used in the activated-sludge process. SOLUTION: At least the cement composition component is incorporated as the bulking inhibitor of activated sludge. The inhibitor is allowed to act as the weight increasing agent of the cement composition component based on the fundamental characteristic that the true specific gravity of the component consisting essentially of the calcium salt such as calcium silicate and calcium aluminate is large enough to improve the setting property of sludge, and further the bulking is inhibited immediately and continuously by utilizing the time lag in the supply of plural kinds of calcium salts different in hydration reaction rate.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an activated sludge process which is a technique for treating organic waste water. More specifically, an anti-bulking agent and anti-bulking of activated sludge that can stably and economically prevent sludge bulking that occurs in a final sedimentation tank (pond) used for solid-liquid separation in the activated sludge method. About the method.

[0002]

2. Description of the Related Art At present, an activated sludge method (or an activated sludge treatment method) is widely used as a technique for treating organic waste water. In this activated sludge method, in an aeration tank installed in a wastewater treatment system, wastewater (wastewater) is brought into contact with activated sludge to oxidize and decompose organic substances in the wastewater by the action of microorganisms in the activated sludge. In the sedimentation tank, the activated sludge is settled and separated into solid and liquid, and the treated water overflows from the final sedimentation tank and is discharged outside the system, and the concentrated activated sludge in the final sedimentation tank is returned to the aeration tank. Wastewater treatment technology.

One of the important technical problems of the activated sludge method is prevention of a bulking phenomenon in a settling tank. That is, the SVI (the value obtained by dividing the volume percentage of the sludge portion in which the mixture was put into the cylinder and sinking) by the sludge concentration was 15
Prevention of the swelling (swelling) phenomenon of sludge showing 0 mL / g or more is an important issue of the activated sludge method.

The activated sludge method, as described above, is a method of solid-liquid separation of the activated sludge, which finally exerts a water purification action, and the treated water, and discharging only the treated water. If this occurs, the sedimentation of the sludge will be hindered and the sludge interface in the final sedimentation tank will be high, making it difficult to separate the sludge from the treated water. Mixing) will cause deterioration of the quality of the treated water.

[0005] Recently, the frequency of occurrence of the bulking phenomenon has increased due to the fact that the load of BOD on sludge has increased and wastewater treatment has been performed in a range where the sludge concentration is high. More permanent measures against bulking are desired.

Therefore, various techniques have been conventionally proposed to prevent such bulking. The main prior arts are (1) a technique of disinfecting (suppressing the growth) of filamentous bacteria that cause a bulking phenomenon by adding chlorine, hydrogen peroxide, or the like to a sedimentation tank, and (2) an iron such as FeCl _3. Technology to settle sludge by adding salt or aluminum salt, (3)
Technology to forcibly settle sludge by adding polymer flocculant, etc. (4) Technology to promote settling of sludge by adding weight agent such as kaolin, earth and sand, slaked lime, (5) in activated sludge Examples thereof include a technique of independently adding an inorganic powder containing calcium as a main component and a technique of adding it together with a predetermined floc-forming bacterium.

[0007]

However, the prior arts (1) to (5) have the following technical problems. First, the technique of (1) in which chlorine, hydrogen peroxide, or the like is added to the sedimentation tank is used for bulking other than bulking by filamentous bacteria (filamentous bulking) (bulking by sludge dispersion, bulking by sludge dispersion, high viscosity bulking, etc.). Cannot be expected to be effective.

[0008] In addition, if the amount and place of addition are inappropriate, activated sludge is formed, and other bacteria that are effectively involved in water purification are sterilized, resulting in a reduction in purification ability, In some cases, the effect was difficult to obtain, and the control for preventing bulking was delicate and difficult.

Next, (2) iron salts, aluminum salts, etc.
The technique of (3) has a low effect on severe bulking, and the technique of (3) in which a polymer flocculant is added,
Low persistence of anti-bulking effect. Moreover, (2),
The technique (3) has a problem in that the cost increases.

Further, in the technique (4) in which kaolin, earth and sand are added, the effect of preventing bulking is unstable, and it is difficult to perform artificial control. In the technique of (5) in which inorganic powder containing calcium as a main component is mixed into activated sludge, although there is a certain effect in preventing the occurrence of bulking, the effect of enhancing cohesiveness to bulking sludge is small and the effect is low. There is a problem in terms of sustainability. As described above, the techniques (1) to (5) are inadequate and have much room for improvement.

Therefore, the present invention provides (1) an immediate effect and sustainability of the anti-bulking effect, (2) a stable anti-bulking effect, and (3) an effect of enhancing cohesiveness to bulking sludge. 4) Does not reduce the microbial activity in sludge, (5) Can cope with various bulking,
(6) It is an object of the present invention to provide a bulking inhibitor and a bulking prevention method having advantages such as low cost (economical).

[0012]

[MEANS FOR SOLVING THE PROBLEMS] To achieve the above object
The present invention employs the following means. First, activated sludge
The anti-bulking agent used in the method generates bulking
It has functions of prevention and improvement (recovery) of sedimentation of bulking sludge.
The additive according to claim 1, wherein the additive needs to be obtained.
In the anti-bulking agent for activated sludge, at least cement
It was configured to contain the components. Here, "Semen
"G" means that it shows curability (hydraulic) when kneaded with water.
"Cement composition component" refers to the raw material
Regardless of the production method, properties as the inorganic bonding agent
Means a composite mineral component with
, Calcium aluminate, calcium sulfate, calcium oxide
Composite inorganic material mainly composed of calcium salt such as calcium
Is a specific cement composition
The purpose is not limited to the components. This cement composition component
The bulking inhibitor contained therein is a calcium salt in the component.
Has a large true specific gravity (approximately 3.0 to 3.2)
It has the characteristics to improve (recover) the sedimentation of sludge.
It works effectively as a weight agent. For comparison,
The following is a supplementary explanation of the true specific gravity of other calcium compounds.
Then, slaked lime is 1.2 to 2.0, and calcium carbonate is 2.
7, calcium silicate is 2.6-3.0,
The true specific gravity of rutland cement is large. Also cement
In the composition, several lime components with different hydration reaction rates
Has the property of containing, for example,
Portland cement, a typical cement, has
Tricalcium iodate (3CaO.SiO_Two), Disilicate
Lucium (2CaO ・ SiO_Two), Tricalcium aluminate
Um (3CaO.Al_TwoO _Three), Tetracalcium iron aluminate
(4CaO.Fe_TwoO_ThreeContains lime components
I have. The hydration rate of these lime components is
Tricalcium> Tricalcium silicate> Dicalcium silicate
Is more dicalcium silicate than tricalcium silicate
Is about 1/20 slower ("Concrete Handbook No. 2
Edition ”, edited by Japan Concrete Institute, 34, 3
See page 5.) In this way, multiple hydration reaction rates differ.
According to the lime component, calcium supply to sludge is inevitable.
There is a difference in paying time,
Provides both durability and anti-bulking effect
The effect of stabilization is exhibited. Further
Is the aluminum oxide contained in the cement composition
(Al_TwoO_Three) And iron oxide (Fe_TwoO_Three) By such
It also has the effect of further increasing the cohesiveness of King sludge
Be conducted.

The anti-bulking agent for activated sludge according to the second aspect is configured to contain an iron salt together with the cement composition component according to the first aspect. In this means, particularly when the amount of the bulking inhibitor added is large, the pH of the aeration tank is excessively inclined to be alkaline, and the ferrous sulfate, ferric sulfate, ferrous chloride, and ferric chloride are used. By adjusting with iron or an iron salt such as ferric polysulfate, the activity of microorganisms in activated sludge is effectively prevented from being reduced. In particular, when the degree of bulking is severe and the amount of cement must be increased, specifically, when the amount of cement exceeds 500 mg / L per aeration tank, iron salt is used. It is desirable to adjust the pH by the combined use of.

In the bulking inhibitor for activated sludge according to the third aspect, the cement composition component according to the first or second aspect is limited to a Portland cement-containing component. In this means, the hydration hardening property of Portland cement, which is a hydraulic silicate calcareous cement, is effectively used. In particular,
Four calcium compounds contained in Portland cement, namely tricalcium silicate, dicalcium silicate,
By utilizing the property of tricalcium aluminate and tetracalcium iron aluminate reacting with water at different hydration rates and hardening while forming fine colloidal hydrates, bulking sludge can be treated for a long time. Agglomerate and maintain sedimentation.

In the method for preventing bulking of activated sludge according to claim 4, the anti-bulking agent according to any one of claims 1 to 3 is added to a wastewater treatment system. in this case,
It is preferable to add the addition portion only to the aeration tank or the return sludge pipe, that is, the portion in the wastewater treatment system where the stirring / mixing action is exhibited, since precipitation and solidification of the added cement are prevented. In addition, in addition to the aeration tank, the cement composition component partially precipitates and solidifies at the bottom of the aeration tank, and the desired effect expected from the initial addition amount is not sufficiently exhibited, and it is necessary to compensate for the addition amount. Therefore, the method of adding the sludge to the returned sludge pipe is more desirable in consideration of cost and work efficiency.

As described above, the anti-bulking agent and the anti-bulking method according to the present invention are characterized in that
Conventionally, measures to prevent bulking, which have been difficult to control and have taken countermeasures, have been made easier to artificially control, so that the occurrence of bulking and the improvement of sedimentation of bulking sludge can be stably performed. Has the technical significance of doing so.

[0017]

BEST MODE FOR CARRYING OUT THE INVENTION The present inventors conducted the following experiments using activated sludge in a sewage treatment plant. A preferred embodiment of the present invention will be described with reference to FIG.

Example 1 First, a 2 L aeration tank was prepared, and activated sludge (MLSS: 1900 mg /
L) as seed sludge and add 2 L of synthetic wastewater
/ Hr flow rate. The components of the synthetic wastewater used were glucose: 100 mg / L, polypeptone: 1
00 mg / L, potassium dihydrogen phosphate: 50 mg / L,
Sodium bicarbonate 100 mg / L, magnesium sulfate: 10 mg / L.

As a result of this experiment, a bulking phenomenon occurred in about one week. Specifically, at the beginning of the experiment, the SVI of the added activated sludge was 115 mL / g, but after one week, the bulking generation standard value of 150 mL / g was obtained.
g of 400 mL / g or more.

Therefore, Portland cement was added as an anti-bulking agent to the aeration tank at a concentration of 1 g / L in the treated water. Immediately after the addition, 170 mL of SVI was added.
/ G and continued operation for one week as it was. As a result, the SVI was reduced to 110 mL / g.

From these results, it is apparent that the swelling (swelling) of the activated sludge was immediately suppressed (the bulking phenomenon was eliminated) and the settling property of the activated sludge was continuously improved (recovered). It is.

This is because calcium salts such as calcium silicate and calcium aluminate, which are the main components of Portland cement, have a large specific gravity, so that the calcium salt hydrated in the sludge functions effectively as a weight agent, It is considered that the sedimentation of sludge was improved.

Further, the inventors of the present invention have further studied the amount of cement to be introduced, and found that the amount is within the range of 1 to 60% by weight, preferably 10 to 50% by weight, based on the activated sludge dry weight.
By setting it within the range, the effect of eliminating bulking became more immediate, and it was also found that the effect was maintained for 5 to 14 days by a single addition.

In Example 1, Portland cement was selected and used as a bulking inhibitor.
If it is a hydraulic cement that has the property of hardening in water,
Basically it is selectable. For example, plain Portland cement, early strength Portland cement, Echihaya strength Portland cement, moderate heat Portland cement, sulfate resistant Portland cement, as well as plain cement such as hydraulic lime, Roman cement, natural cement, alumina cement, and lime mixing Embodiments using mixed cement such as cement and mixed Portland cement are also possible, and these may be used in combination as appropriate. Furthermore, an embodiment in which the hydraulic cement is used in combination with air-hardening cement such as magnesia cement or gypsum or special cement is also applicable.

(Example 2) Next, the present inventors conducted water passage under the same conditions as in the above example, and after one week, added the same amount of Portland cement as in Example 1 to iron salt (secondary chloride). iron)
Was added at 0.2 g / L. As a result, immediately after the addition,
I decreased to 140 mL / g, and one week after the addition, SVI had decreased to 90 mL / g. From this result, by adding an iron salt to the cement composition component, in both the immediate effect of bulking prevention and sustainability,
It has been found that it can be improved over the first embodiment. In addition, it was also clarified that the addition of the cement composition adjusts the pH of the aeration tank to be too alkaline by adding the cement composition component, and thus effectively prevents a decrease in the activity of microorganisms in the activated sludge.

As the iron salt, ferrous sulfate, ferric sulfate, ferrous chloride, ferric chloride, polyiron and the like can be used. 1: 2
The ratio is preferably from 200: 1 to 200: 1, preferably from 2: 1 to 50: 1. In each case, the effect is higher than that of the polymer flocculant.

As described above, the bulking preventing or eliminating action exerted by the cement composition component has both immediate effect and sustainability. Therefore, it is also possible to adopt an embodiment (modification) in which the bulking prevention technology based on the cement composition component is used as the basic technology of the bulking prevention measures. Because, by combining the cement composition component with another bulking inhibitor, the action and effect of using the cement composition component alone and the action and effect of the other bulking inhibitor are added to the type and degree of bulking. This is because artificial control of bulking corresponding to the above becomes possible.

For example, in addition to the effective use of a cement composition component and an iron salt, a combination use of a cement composition component and a polymer coagulant, and inorganic salts other than the cement composition component and an iron salt (for example,
Embodiments (modifications) such as the combined use of an aluminum salt) and the combined use of a cement composition component, an inorganic salt and a polymer coagulant are conceivable.

Specifically, in the embodiment in which the cement composition component and the polymer flocculant are used in combination, the addition of the polymer flocculant makes it possible to more quickly prevent bulking, and means for adding the polymer flocculant alone. The shortage of the effect, which was a drawback of the above, can be enhanced by the cement composition component.

In consideration of the fact that the pH is inclined toward the alkaline side depending on the cement component, cationic polymer flocculants and amphoteric polymer flocculants are more preferable as the polymer flocculant.

The embodiment in which the cement component and the aluminum salt are used in combination is suitable for relatively light bulking, and the embodiment in which the cement component and the inorganic salt and the polymer flocculant are used in combination is suitable for pH adjustment and immediate effect. Both functions can be added.

Here, the mixing ratio of the cement composition component and the polymer coagulant is 1:10 to 1000: 1 by weight, preferably 1: 1 to 100: 1, and in the case of the cement composition component and the aluminum salt, , 1: 2-200: 1, preferably
A ratio of 2: 1 to 50: 1 is preferred.

(Comparative Example 1) When slaked lime (calcium hydroxide. Ca (OH) ₂ ) was added instead of Portland cement under the same water flow conditions as in Example 1 above, the SVI immediately after the addition was 280 mL / g, and the SVI after one week had passed was 250 mL / g.

(Comparative Example 2) When calcium silicate was added in place of Portland cement under the same water flow conditions as in Example 1 above, the SVI immediately after the addition was 220 mL /
g, and the SVI after one week had passed was 160 mL / g.

From the results of Comparative Examples 1 and 2, slaked lime and calcium silicate were found to have an immediate effect as a bulking inhibitor, but their effect was small, and a plurality of lime components and other substances The effectiveness of the anti-bulking agent according to the present invention using a cement composition component characterized by a composite inorganic component containing the same is apparent.

Hereinafter, a specific embodiment of the method for preventing bulking of activated sludge according to the present invention will be described with reference to FIG.

First, the activated sludge method is roughly divided into an aeration step of purifying wastewater (wastewater) to be treated and activated sludge by contacting them under aerobic conditions, and a solid-liquid separation for separating treated water and sludge. And a sludge return step of returning excess sludge from the solid-liquid separation step to the aeration step.

More specifically, the wastewater 1 is first stored in the sedimentation tank 2 after dust and the like are removed by a screen device (not shown) or the like. Then, in the aeration tank 3 provided with a stirring device and an aeration device (not shown), the activated sludge thus introduced is brought into contact with the treated water by aeration.
The organic matter in the wastewater 1 is decomposed, the BOD is reduced, the solid-liquid separation of the activated sludge and the treated water 6 is performed in the final sedimentation tank 4, and the treated water 6 overflowing from above the final sedimentation tank 4 is discharged out of the system. At the same time, a step of returning sludge precipitated and concentrated in the final sedimentation tank 4 to the aeration tank 3 through a return sludge pipe 5 is provided.

Here, in the solid-liquid separation step (final sedimentation tank 4), when bulking occurs due to various causes such as filamentous bulking caused by filamentous bacteria, etc., the bulking inhibitor 7 according to the present invention is used.
Will be added.

However, since the anti-bulking agent 7 is basically composed of a cement composition component having a large true specific gravity as described above, it has the property of being easily precipitated and solidified.

Therefore, in order to make the added anti-bulking agent 7 effective, the anti-bulking agent 7 according to the present invention is limited to a specific portion in the wastewater treatment system where the stirring and mixing action is exhibited. It is desirable to add them.

More specifically, the sludge is added not to the final settling tank 4 but to the aeration tank 3 having a stirring function (see arrow X in FIG. 2) or to the returned sludge pipe 5 in which the returned sludge is flowing. (See arrow Y in FIG. 2) or both are desirably selected and added.

Furthermore, in addition to the aeration tank 3,
Part of the cement component precipitates and solidifies at the bottom, and the desired effect expected from the initial addition amount is not sufficiently exhibited, and it is expected that it is necessary to supplement the addition amount. In consideration of cost and work efficiency, the method of adding the sludge to the return sludge pipe 5 (arrow Y) is more preferable.

[0044]

The anti-bulking agent for activated sludge according to the present invention can utilize the cement component as a weighing agent due to the basic characteristic that the true specific gravity of the cement component is large. Help improve.

In addition, since a plurality of kinds of lime components having different hydration reaction rates contained in the cement composition components cause a time difference in the supply of calcium to the sludge, an advantageous effect having both immediate effect and sustainability can be obtained. The effect can be exhibited. The cohesiveness of bulking sludge can be enhanced by components such as aluminum oxide (Al ₂ O ₃ ) and iron oxide contained in the cement composition components.

In the anti-bulking agent for activated sludge according to the present invention, if the iron salt is added in combination with the cement component, the pH of the aeration tank becomes alkaline especially when the amount of cement added is large. Excessive inclination can be adjusted with an iron salt to effectively prevent a decrease in the activity of microorganisms in activated sludge.

In the anti-bulking agent for activated sludge according to the present invention, a Portland cement component having hydration-hardening properties is employed as a cement component.
Tricalcium silicate contained in Portland cement,
Dicalcium silicate, tricalcium aluminate, and iron tetracalcium aluminate react with water at different hydration rates, and harden while forming fine colloidal hydrates. Aggregation for a certain period of time enables the sedimentation of sludge to be imparted or restored.

According to the method for preventing bulking of activated sludge according to the present invention, an anti-bulking agent containing at least a cement component is added to an aeration tank or return sludge pipe exhibiting a stirring / mixing action. Precipitation and solidification of the added cement can be prevented, so that the bulking prevention action of the cement composition component can be effectively exerted to facilitate the artificial control of bulking, and unnecessary addition is not required. Therefore, it is also advantageous in terms of cost.

As described above, the anti-bulking agent and the anti-bulking method according to the present invention solve all the technical problems in the prior art, and facilitate the artificial control relating to the anti-bulking which is an important issue of the activated sludge method. Can contribute to the development of the water treatment industry in general,
Contribute to improving the water environment.

[Brief description of the drawings]

FIG. 1 is a table summarizing experimental results (table)

FIG. 2 is a simplified process diagram of the activated sludge method showing a place where a bulking inhibitor according to the present invention is added.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Drainage 3 Aeration tank 4 Final sedimentation tank (for solid-liquid separation) 5 Return sludge piping 6 Treated water 7 (including cement component) Bulking inhibitor

Claims (4)

[Claims] 1. An activated sludge bulking inhibitor comprising at least a cement component. 2. The anti-bulking agent according to claim 1, further comprising an iron salt together with the cement component. 3. The anti-bulking agent according to claim 1, wherein the cement composition component is a Portland cement-containing component. 4. A method for preventing bulking of activated sludge, comprising adding the anti-bulking agent according to claim 1 to a wastewater treatment system.