JPH11156396A - Waste water treatment method and apparatus therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a waste water treatment method wherein the use amt. of a chemical soln. or charge energy is reduced and a treatment time is short and excessive sludge is reduced in waste water treatment due to activated sludge. SOLUTION: In a waste water treatment method having a process for treating waste water with activated sludge and a process subjecting sludge containing treated water after the treatment of waste water to solid-liquid separation to take out the separated water, a process wherein a part of the separated sludge obtained by the solid-liquid separation or the whole thereof is aerobically subjected to sludge decomposition treatment in the presence of microorgansisms under an alkali condition is provided.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for treating wastewater and sludge which decomposes wastewater-treated sludge by using microorganisms to reduce or eliminate sludge volume, and an apparatus used for the method.

[0002]

2. Description of the Related Art A typical method of biological treatment of wastewater is an activated sludge method in which BOD components are decomposed into microorganisms under aerobic conditions, and sedimentation / separation is performed at a later stage. In this method, a part of the settled sludge is returned to the aeration tank, but a part of the sludge needs to be treated as excess sludge after solid-liquid separation in a settling tank or the like.

[0003] Surplus sludge is partly reused as a soil conditioner or compost material, but most is treated as industrial waste. However, due to cost and environmental considerations, methods other than disposal are required. As one of the methods, for example, an anaerobic or aerobic digestion method by an organism is conventionally known. In the anaerobic treatment method, anaerobic microorganisms such as methanogens decompose organic components in sludge to generate methane and carbon dioxide. This method has the advantage that the sludge can be reduced and the energy resources can be recovered at the same time. However, the sludge needs to stay for 10 to 30 days, which causes problems such as an increase in the size of the facility. The aerobic treatment method also requires a long residence time, but has a problem such as a low weight reduction rate, and is hardly used recently.
Further, a method of chemically or physically pretreating the sludge and then anaerobically or aerobically treating the microorganism with a sludge is also being studied. This is a method aimed at shortening the treatment time by the microorganisms at the subsequent stage by forcibly pretreating the sludge. For example, Japanese Patent Application Laid-Open Nos.
Japanese Patent Laid-Open No. 19789 discloses a method of treating sludge cell walls with ozone and then reducing the volume of sludge in an aerobic tank.
Japanese Patent Publication No. 8-76200 is expected to reduce the volume by crushing the cell wall of sludge with ultrasonic waves. In addition, Japanese Unexamined Patent Publication
Japanese Patent No. 8496 discloses an aerobic treatment after adding an alkali or a mineral acid to sludge, treating the sludge under an alkaline condition or an acidic condition. JP-A-4-326998,
Japanese Unexamined Patent Publication No. 5-345200 discloses a method in which a sludge is made alkaline and heated at the same time as a hot alkali treatment is carried out to promote solubilization, followed by anaerobic treatment near neutrality.
Further, JP-A-8-229595 and JP-A-8-243
No. 595 discloses a method of solubilizing sludge by heating. Japanese Patent Application Laid-Open No. 9-136097 discloses a method in which aeration is carried out in the presence of aerobic microorganisms under alkaline conditions, and the solution is returned to the biological treatment step. It is an object of the present invention to provide a sludge volume reduction technology that can reduce the volume of sludge compared to the conventional technology.Basically, sludge volume reduction is performed in the process of aeration in the presence of aerobic microorganisms under alkaline conditions. Without
This method is aimed at solubilization.

However, the conventional method using sludge destruction such as ultrasonic waves and ozone requires high equipment and running costs, and the method of adding an acid or alkali requires the cost of chemicals used, equipment and chemicals for neutralization. Further, a more innovative method is desired, for example, a method of heating to a higher temperature raises a problem of an increase in cost for heating. In addition, after these chemical or physical pre-treatment, in the method of anaerobic or aerobic microorganism treatment,
Even if the volume can be reduced very slightly in the pretreatment tank, at least a pretreatment tank and a microorganism treatment tank are required, which requires more space, and the microorganism treatment tank is returned as an activated sludge tank. In this case, the load on the activated sludge tank is greatly increased.Therefore, there is a problem that it can be applied only when there is enough processing capacity in the activated sludge tank. A method that can be performed is desired.

[0005]

One of the problems in the activated sludge system is the generation of excess sludge.
An object of the present invention is to provide a method for decomposing sludge generated by wastewater treatment using microorganisms without requiring long-time treatment and without requiring a large amount of heat energy, and reducing or eliminating sludge volume. It is to propose a device for that.

[0006]

The object of the present invention is achieved by the following constitution. That is, 1. "A method for treating wastewater, comprising a step of treating wastewater with activated sludge, and a step of solid-liquid separating sludge containing treated water after treating the wastewater, and a step of taking out the separated water. A method for treating wastewater, comprising a sludge decomposition step of treating a part or all of the separated sludge obtained by separation with a microorganism capable of aerobically decomposing sludge under alkaline conditions. 2. 2. A method for treating the wastewater, wherein the temperature of the sludge decomposition treatment is 40 ° C. or higher. 3. The method for treating any one of the wastewaters described above, wherein the condition of the sludge decomposition treatment is pH 8 to 13. 4. The method for treating wastewater as described above, wherein the condition of the sludge decomposition treatment is pH 9 to 12. 5. A method for treating any of the wastewaters described above, wherein part or all of the treated sludge that has undergone the sludge decomposition treatment is sent to a wastewater treatment step using a second activated sludge. "As a wastewater treatment step using the second activated sludge,
The method for treating wastewater as described above, wherein the wastewater treatment step also uses a wastewater treatment step using a first activated sludge for treating wastewater. 7. 7. A method for treating any of the wastewaters described above, wherein a solid-liquid separation step is provided between the sludge decomposition step and the wastewater treatment step using the second activated sludge. "Wastewater inlet, wastewater treatment means containing first activated sludge communicating with the wastewater inlet, solid-liquid separation means connected to the wastewater treatment means, and separated water connected to the liquid side of the solid-liquid separation means." And a wastewater treatment apparatus having sludge decomposing means communicating with the separated sludge side of the solid-liquid separation means, wherein the sludge decomposing means removes microorganisms capable of aerobicly decomposing sludge under alkaline conditions. Wastewater treatment device characterized by containing. " 9. The apparatus for treating wastewater, wherein the sludge decomposing means has means capable of maintaining a treatment temperature at 40 ° C. or higher. 10. Any one of the wastewater treatment apparatuses described above, further comprising a wastewater treatment unit configured to communicate with the sludge decomposition unit using second activated sludge. "The wastewater treatment apparatus described above, wherein the wastewater treatment means containing the first activated sludge is also used as the wastewater treatment means using the second activated sludge."

Further, a wastewater treatment method having at least wastewater treatment means using activated sludge and means for solid-liquid separation of sludge from the wastewater treatment means using activated sludge,
Part or all of the separated sludge from the solid-liquid separation means,
A method for treating sludge, comprising a sludge decomposing means for treating with a microorganism capable of aerobicly decomposing sludge under alkaline conditions. "The sludge treatment method characterized in that the treatment temperature in the sludge decomposition means is 40 ° C. or higher.", "The alkaline condition in the sludge decomposition means is pH 8 to 13. Any of the above-mentioned sludge treatment methods. ”,“ Any or all of the treated sludge from the sludge decomposition means is sent to a second aerobic activated sludge wastewater treatment means. Sludge treatment method. "," The sludge treatment method characterized in that the second aerobic activated sludge wastewater treatment means is also used as the first activated sludge wastewater treatment means. ""A method for treating any one of the above-mentioned sludges, wherein a solid-liquid separation means is provided between the sludge decomposing means and the wastewater treatment means using activated sludge."

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail.

In the treatment of organic wastewater by the activated sludge treatment method, wastewater comprising at least a step of wastewater treatment with activated sludge and a step of solid-liquid separation of sludge containing liquid generated by the wastewater treatment with activated sludge. In the processing method, the present invention can be applied. That is, after the solid-liquid separation, the sludge is decomposed, so that an effective sludge volume reduction can be realized.

[0010] Solid-liquid separated sludge mainly refers to excess sludge and returned sludge discharged from sewage treatment plants, human waste treatment plants, and other treatment facilities, but also includes organic waste discharged from the above facilities. The present invention can be sufficiently applied to any water to be treated such as wastewater or treated water having a large BOD load.

Means used in the step of wastewater treatment with activated sludge include an aeration tank and a fixed filter bed. In the present invention, although not particularly limited, an aeration tank is preferred.

As a means of the solid-liquid separation step, precipitation in a precipitation tank is most widely practiced. Other centrifugation,
A method using membrane separation is also possible. There is also a method of using a sludge concentration tank after solid-liquid separation in a precipitation tank.

The sludge separated in the solid-liquid separation step is introduced into sludge decomposition treatment means, and the sludge is decomposed by microbial treatment under alkali and aerobic conditions. Theoretically, no excess sludge is generated. However, in actual excess sludge, in addition to inorganic SS components, hardly decomposable organic components that are difficult to decompose are present and may accumulate in the system. It is preferable to dispose it. Of course, a part of the solid-liquid separated sludge may be returned to the means for the activated sludge wastewater treatment step in the preceding stage, as is performed in the ordinary activated sludge treatment method.

The method of alkalizing in the present invention includes, but is not limited to, for example, addition of sodium hydroxide, potassium hydroxide, calcium hydroxide, magnesium hydroxide, sodium carbonate, sodium hydrogen carbonate and the like. The amount of addition depends on the type, temperature and condition of the sludge, but may be any amount that can achieve pH 8 or more, and may be added in a solid state or an aqueous state.

The treatment pH is preferably 8 or more. When the pH is 8 or more, solubilization of sludge can be performed more efficiently than when only heating is performed. However, if the pH is too high, the chemical solution cost is high and the growth of microorganisms becomes difficult. Therefore, in the present invention, pH 8 to 13 and more preferably pH 9 to 12 are preferable.

The temperature condition is suitably from 40 ° C. to 80 ° C. Generally, temperature conditions considered to be preferable for the propagation of microorganisms are around room temperature.
It is 30 ° C, and at most 35 ° C. However, in the present invention, high efficiency of decomposition was obtained at a high temperature, which is considered unfavorable for the propagation of microorganisms, that is, at 40 ° C. or higher. Although the details are unknown, it is speculated that at high temperatures, the growth of microorganisms that do not contribute to sludge decomposition is suppressed, and the activity of microorganisms that contribute to sludge decomposition is activated. Further, focusing on the effect of promoting the solubilization of sludge by heat, when the temperature is lower than 40 ° C., it is insufficient. When the temperature is higher than 80 ° C., the energy cost for maintaining the temperature is high and the energy cost is high. The activity of microorganisms that can perform sludge treatment as much as possible becomes difficult. The most efficient in terms of compatibility between the growth of microorganisms and energy cost is that the temperature is 40 to 70 ° C, more preferably 45 to 65 ° C, but if it is set according to the nature of the microorganisms contributing to decomposition. good. Therefore, it is desired that the sludge decomposing means has means capable of maintaining the temperature at 40 ° C. or higher. Further, a method may be employed in which the concentration of the sludge to be decomposed is appropriately adjusted so that the heat generated during the decomposition and the heat radiation from the tank are well balanced to maintain an appropriate temperature.

The microorganism to be used is pH 8 or more and 4
The microorganism is not particularly limited as long as it can grow under the condition of 0 ° C. or higher and can use a sludge component as a nutrient source. Microorganisms that can grow under these conditions can be obtained relatively easily from general soil, river water, sludge, etc., unless one or both of the pH and temperature are extremely high. In addition, in the case of sludge treatment by these microorganisms, the addition of inorganic salts such as potassium phosphate, dipotassium phosphate, magnesium sulfate, and ammonium nitrate can sometimes increase the growth, but it is not always necessary. Absent.

In the present invention, aerobic conditions are preferred as conditions for performing sludge treatment with microorganisms under alkaline conditions. As an oxygen supply source therefor, other than ordinary air, an oxygen gas or an oxygen-enriched gas may be used. The oxygen supply source is supplied by a method such as stirring, aeration stirring, and air lift, but is not limited to these. Unless the dissolved oxygen is extremely low, the rate of decomposition is not limited.

A part or all of the treated sludge reduced in volume by the sludge decomposition means is sent to a second activated sludge wastewater treatment means as required. When the organic components in the treated sludge have been sufficiently removed, the sludge can be discharged to the outside of the system as it is. However, by sending the sludge to the second activated sludge wastewater treatment means, the decomposition of the sludge can be further promoted. Emissions can be reduced. At this time, the wastewater may be returned to the treatment means where the wastewater is treated first without newly providing a wastewater treatment means using the second activated sludge. If the volume of the treated sludge is sufficiently reduced, the sludge can be returned to the first activated sludge wastewater treatment means without applying a high load, so that the equipment can be made compact.

A solid-liquid separating means may be provided between the sludge decomposing means and the activated sludge wastewater treatment means. Part of the solid portion or the liquid portion can be easily withdrawn and disposed of, or returned to the activated sludge wastewater treatment means at the preceding stage.

Since the sludge decomposing means of the present invention decomposes sludge, unlike the method of mainly performing solubilization of sludge, it is solubilized by conventional physical or chemical means or partially mediated by microorganisms. It is essentially different from the solubilized means of solubilisation.

Hereinafter, specific examples of the present invention will be described, but it is needless to say that the present invention is not limited to these examples.

[0023]

The present invention will be described below in more detail with reference to examples.

(Example 1) More than 100 types of soil were collected nationwide, a small amount of soil was suspended in sterilized water, and then returned sludge collected from five sewage treatment plants nationwide was mixed well to form bacterial cells. An exudate was made.

Next, the excess sludge collected from the wastewater treatment plant of the chemical manufacturer is diluted so that the solid content becomes 1 wt%, and potassium diphosphate 0.5 g / l, potassium monophosphate 0.5 g / l, magnesium sulfate 7 A hydrate to be treated having a pH of 10 was prepared by adding 0.2 g / l of hydrate and 10 g / l of sodium carbonate. In the present embodiment, these inorganic salts were added, but they are not essentially required. Further, 95 ml of the liquid to be treated is placed in a 500-ml baffled flask, and 5 ml of the exudate prepared in advance is added and shake-cultured. A part of the liquid is removed and replaced with a new liquid to be treated. Repeated for one month, an accumulation culture of microorganisms capable of decomposing sludge was performed at 30 ° C, 40 ° C, 45 ° C, and 50 ° C.

5 ml of the resulting concentrated culture solution was added to an excess sludge solution diluted to a solid content of 1% by weight and further adjusted to pH 10 with sodium carbonate. The MLSS reduction rate was measured and expressed as a volume reduction rate. In addition, MLSS was measured by the method according to the sewage test method, and the volume reduction rate was calculated from the following formula.

Volume reduction rate = (MLSS1−MLSS2) / MLSS1 × 100 (%) MLSS1: MLSS concentration of sample solution before treatment (g / l) MLSS2: MLSS concentration of sample solution after treatment (g / l) After 2 days, the MLSS volume reduction rate was 30 ° C, 40 ° C,
19%, 35%, 3% when treated at 5 ° C and 50 ° C, respectively.
6% and 41%, and the effect was significant at 40 ° C. or higher.

(Embodiment 2) Activated sludge wastewater treatment means, solid-liquid separation treatment means connected thereto, and a 12-liter activated sludge tank as a container for sludge decomposition treatment means connected to the solid side of the solid-liquid separation means, respectively. A 3-liter sedimentation tank and a 0.8-liter sludge decomposition treatment tank were used. In the sludge decomposition treatment tank, 4 of the sludge decomposing bacteria used in Example 1 was placed.
The enrichment culture at 5 ° C. was injected beforehand.

The synthetic wastewater with a BOD load of 300 ppm was added to 83
The water was supplied to the activated sludge tank at a flow rate of 0 ml / hr, and the wastewater was treated with ordinary activated sludge to obtain MLSS 2 g / l treated water. The treated water was subjected to solid-liquid separation in a sedimentation tank, and the supernatant water having a BOD load of 20 ppm was discharged as separated water to the outside of the system.
In the sludge, MLSS was concentrated to 9 g / l, and 190 ml / hr of this was returned to the activated sludge tank, and 17 ml / h
r was sent to a sludge decomposition treatment tank, the pH was adjusted to 10 with sodium hydroxide, and the mixture was kept at 45 ° C., whereby the MLSS could be reduced to 4 g / l with a residence time of 2 days. Furthermore, this volume-reduced sludge was returned to the activated sludge treatment tank, and the same treatment was continued. As a result, the amount of sludge whose water content was concentrated to 75% was 6 ml / day.

(Comparative Example) Wastewater treatment means using activated sludge,
A 12-liter activated sludge tank and a 3-liter sedimentation tank were used as solid-liquid separation means. BOD load 30
0 ppm synthetic sewage was supplied to the activated sludge tank at a flow rate of 830 ml / hr to perform a usual treatment, and MLSS 2 g / l treated water was obtained. This treated water is solid-liquid separated in a sedimentation tank and
The supernatant water with a D load of 20 ppm was discharged out of the system. In the sludge, MLSS was concentrated to 9 g / l.
As a result of returning the ml / hr to the activated sludge treatment tank, the amount of sludge generated by concentrating the water content to 75% was 21 ml / day.

[0031]

According to the present invention, if a sludge decomposition treatment step is provided in the conventional activated sludge wastewater treatment step, the sludge decomposition treatment can be easily performed, thereby reducing the amount of excess sludge generated. Can be done.

[Brief description of the drawings]

FIG. 1 is a schematic diagram of an apparatus used in Example 2.

FIG. 2 is a schematic diagram of an apparatus used in a comparative example.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Inflow water 2 Activated sludge tank 3 Solid-liquid separation tank 4 Solid-liquid separation supernatant water 5 Pull-out sludge 6 Returned sludge 7 Solid-liquid separation sludge 8 Sludge decomposition treatment tank 9 Return treatment sludge

Claims (11)

[Claims] 1. A method for treating wastewater, comprising: a step of treating wastewater with activated sludge; and a step of solid-liquid separating sludge containing treated water after treating the wastewater, and taking out the separated water. A wastewater characterized by having a sludge decomposition step of treating a part or all of the separated sludge obtained by the solid-liquid separation with a microorganism capable of aerobicly decomposing sludge under alkaline conditions. Processing method. 2. The method for treating wastewater according to claim 1, wherein the temperature of the sludge decomposition treatment is 40 ° C. or higher. 3. The condition of the sludge decomposition treatment is pH 8-13.
The method for treating wastewater according to claim 1 or 2, wherein: 4. The condition of the sludge decomposition treatment is pH 9-12.
4. The method for treating wastewater according to claim 3, wherein: 5. The method for treating wastewater according to claim 1, wherein a part or all of the treated sludge decomposed by the sludge is sent to a wastewater treatment step using a second activated sludge. 6. The wastewater treatment method according to claim 5, wherein the wastewater treatment step using the first activated sludge for treating wastewater is also used as the wastewater treatment step using the second activated sludge. 7. The method for treating wastewater according to claim 5, wherein a solid-liquid separation step is provided between the sludge decomposition step and the wastewater treatment step using the second activated sludge. 8. A drainage passage, a first drainage passage communicating with the drainage passage.
Wastewater treatment means containing activated sludge, solid-liquid separation means connected to the wastewater treatment means, an outlet for separated water connected to the liquid side of the solid-liquid separation means, and communication with the separated sludge side of the solid-liquid separation means A wastewater treatment device having a sludge decomposing means, wherein the sludge decomposing means contains microorganisms capable of aerobicly decomposing sludge under alkaline conditions. 9. The wastewater treatment apparatus according to claim 8, wherein said sludge decomposing means has means capable of maintaining a treatment temperature at 40 ° C. or higher. 10. The wastewater treatment apparatus according to claim 8, further comprising a wastewater treatment unit using a second activated sludge communicating with the sludge decomposition unit. 11. The wastewater treatment apparatus according to claim 10, wherein the wastewater treatment means containing the first activated sludge is also used as the wastewater treatment means using the second activated sludge.