JP2008086949A - Volume reduction method of excess sludge - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for simply reducing a volume of excess sludge. <P>SOLUTION: In a treatment tank for bringing organic sewage and activated sludge into contact with each other to biologically treat them, the activated sludge slurry drawn out of the treatment tank is passed through a dissolving vessel filled with a trichloroisocyanuric acid molded material, the packed bed of the trichloroisocyanuric acid molded material is brought into contact with activated sludge to kill the activated sludge in the slurry at a ratio of 50-100% and the slurry is returned to the treatment tank to adjust a volume reduction ratio of the excess sludge to a range of 10-60%. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a method for reducing excess sludge in a wastewater treatment facility.

  In wastewater treatment facilities, the activated sludge method is widely adopted as a microorganism treatment method for organic sewage containing sewage, human waste and organic substances (hereinafter referred to as sewage). This method generally consists of an aeration operation that purifies sewage by bringing sewage into contact with activated sludge, which is an aggregate of microorganisms, and a precipitation operation that separates the treated water and activated sludge. Therefore, activated sludge more than can be accommodated in the aeration tank, that is, excess sludge is generated.

In the activated sludge method, the batch activated sludge method in which the aeration operation and the precipitation operation are performed in one treatment tank, and the two operations of the aeration operation and the precipitation operation in each treatment tank (aeration tank and precipitation tank). A continuous activated sludge process is known.
The former method is advantageous in that the apparatus is simple, the equipment cost is low, and the maintenance is easy, and is suitable for small-scale processing facilities. The latter is complicated in treatment operation and requires equipment and maintenance costs, but it is suitable for large-scale treatment facilities because it can treat a large amount of sewage continuously and has high treatment efficiency. ing.

  By the way, the treatment of surplus sludge requires great costs for dehydration, storage, transportation, incineration, etc., so reduction and reuse of the sludge is required, and a treatment method that does not burden the environment is eagerly desired. ing.

  As a method for reducing the amount of such excess sludge, various methods have been studied. For example, in Patent Document 1, in a continuous activated sludge method, activated sludge slurry is extracted from an aeration tank, and hypochlorite is added to the slurry. A method for reducing excess sludge has been proposed, characterized by adding hypochlorite such as sodium chlorate and calcium hypochlorite to organic matter that can be digested by microorganisms and then treating the microorganisms. ing.

  However, since sodium hypochlorite is an aqueous solution, there is a difficulty in that the equipment cost increases because a liquid supply device whose supply amount can be controlled is necessary or a storage tank dedicated to sodium hypochlorite is required. . Although calcium hypochlorite is solid, it has the advantage of being easy to handle, but because of its high solubility in water, it dissolves quickly when brought into contact with the activated sludge slurry extracted from the aeration tank. Therefore, there is a problem that it is difficult to control the amount of dissolution, and as a result, excessive active chlorine is generated.

  Patent Document 2 discloses a method of bringing activated sludge slurry into contact with chlorinated isocyanuric acid in order to prevent bulking of activated sludge, but (a) it is more soluble than trichloroisocyanuric acid having low solubility. Highly active sodium dichloroisocyanurate and potassium are preferably used. (B) Low concentration of active chlorine is generated to kill only filamentous bacteria that cause bulking without killing activated sludge. The present invention is completely different from the present invention in that it has to be controlled, and (c) there is no description regarding reduction of excess sludge.

Japanese Patent Laid-Open No. 2002-126895 JP-A-4-126593

  This invention is made | formed in view of the said situation, and it is providing the method of reducing excess sludge simply.

  As a result of earnest test research to solve the above-mentioned problems, the present inventors have found that the activated sludge slurry extracted from the treatment tank is trichloro-treated in a treatment tank in which organic sewage and activated sludge are brought into contact with each other. By passing through a dissolver filled with isocyanuric acid molded product, the packed bed of trichloroisocyanuric acid molded product and activated sludge are brought into contact, and then the slurry is returned to the treatment tank to achieve the intended purpose. As a result, the present invention has been completed.

In the present invention, a trichloroisocyanuric acid molded product that releases active chlorine is used as a disinfectant, and the method of adding trichloroisocyanuric acid is a means for bringing activated sludge into contact with the packed layer of the trichloroisocyanuric acid molded product. The amount of excess sludge generated can be reduced more easily than the first (first invention).
Moreover, by reducing the kill rate of activated sludge to 50 to 100% and adjusting the reduction rate of excess sludge to a range of 10 to 60%, reduction of excess sludge is achieved without deteriorating the quality of treated water. (Second invention). Furthermore, by making the major axis of the molded product of trichloroisocyanuric acid 5 to 100 mm, the activated sludge and the trichloroisocyanuric acid molded product can be efficiently contacted (third invention).

The best mode for carrying out the present invention will be described below. Symbols appearing in the specification of the present application are as follows.
・ BOD (Biochemical
Oxygen Demand): Biochemical oxygen demand / MLSS (Mixed
Liquor Suspended Solids): Activated sludge concentration in activated sludge slurry

FIG. 1 shows a schematic flow diagram of a treatment process when the present invention is applied to a batch activated sludge method. In a treatment tank 1, an aeration operation and a precipitation operation are performed. First, the sewage 2 flows into the treatment tank 1 and is mixed with the activated sludge, whereby the activated sludge slurry 3 is prepared. Moreover, the air supplied from the air blower 11 is ejected from the diffuser pipe 12 provided at the bottom of the treatment tank 1 to aerate the activated sludge slurry. Under such aerobic conditions, activated sludge digests organic matter contained in the sewage.
At this time, the activated sludge slurry 3 is continuously extracted from the treatment tank 1 by the pump 13 and supplied to the dissolver 20 filled with the trichloroisocyanuric acid molded product. Then, the activated sludge comes into contact with the packed bed filled with the trichloroisocyanuric acid molded product and is killed, and the microorganisms are converted to an organic material in a digestible state. Next, the activated sludge slurry that has been killed is returned to the treatment tank 1.

  After the purification of the sewage is completed, the aeration operation and the killing process are stopped, and the sedimentation operation is performed in which the activated sludge slurry is allowed to stand and the supernatant water and the concentrated sludge are separated. In addition, even if it is during precipitation operation, you may perform a killing process as needed. After completion of the precipitation operation, the supernatant water is discharged out of the system as treated water 4.

FIG. 2 shows a schematic flow diagram of a treatment process when the present invention is applied to a continuous activated sludge method. Sewage 2 continuously flows into the aeration tank 5 and is mixed with the activated sludge. Slurry 3 has been prepared. Further, the air supplied from the air blower 11 is ejected from the air diffuser 12 provided at the bottom of the aeration tank 5 to aerate the activated sludge slurry 3. Under such aerobic conditions, activated sludge digests organic matter contained in the sewage.
The activated sludge slurry 3 is continuously extracted from the aeration tank 5 and supplied to the precipitation tank 6. In the sedimentation tank 6, the activated sludge slurry 3 is allowed to stand, so that it is separated into treated water 4 (supernatant water) and concentrated sludge slurry 7. The treated water 4 is out of the system, and the concentrated sludge slurry 7 is pumped 13. A part is discharged out of the system as surplus sludge slurry 9, and the rest is supplied as return sludge slurry 8 to a dissolver 20 filled with a trichloroisocyanuric acid molded product. The sludge is killed by contact with the packed bed of the trichloroisocyanuric acid molded product, and microorganisms are converted to an organic material that can be digested. Next, the returned sludge after the killing process is returned to the aeration tank 5.
In such a continuous activated sludge method, when the killing process is continued and the operation of the sewage treatment reaches a steady state, the amount of concentrated sludge generated in the settling tank decreases, and the excess discharged to the outside of the system Sludge has also been reduced.

  The shape of the packed layer is not limited as long as the packed layer formed by filling the trichloroisocyanuric acid molded product into the dissolver is filled to the extent that adjacent molded products are in contact with each other. However, in order to reduce the variation in contact efficiency as much as possible, as shown in FIG. 3 (A) or (B), the distance between the inlet side and the outlet side with respect to the flow direction of the activated sludge slurry. It is preferable to fill a trichloroisocyanuric acid molded product with as little gap as possible in a dissolver having a constant.

  In FIG. 1 and FIG. 2, the dissolver filled with the trichloroisocyanuric acid molded product is provided in the return line of the activated sludge slurry, but as a simple method, a measuring rod (not shown) usually installed in the return line It is also possible to form a packed bed by introducing a trichloroisocyanuric acid molded product between the weirs that divide the interior of the container. Moreover, the method etc. which hang | suspended the cage | basket or net-like bag filled with the trichloroisocyanuric-acid molded product at the final drop (not shown) of the return line installed in the upper part of the water surface of the processing tank 1 or the aeration tank 5 are mentioned.

  Trichloroisocyanuric acid is a compound classified as a chlorinated isocyanuric acid compound, but this chlorinated isocyanuric acid compound is a chemically stable solid compound that can be easily handled and dissolved in water. In this case, hydrolyzed active chlorine having a bactericidal property is released, and the stability of the active chlorine is excellent, and the bactericidal effect lasts for a long time. It is widely used as a disinfectant and disinfectant for effluent water from facilities, as well as algae and anti-algae agents such as cooling water for machinery.

  Examples of the chlorinated isocyanuric acid compound include trichloroisocyanuric acid, dichloroisocyanuric acid, sodium dichloroisocyanurate and its hydrate, potassium dichloroisocyanurate, and the like.

By the way, trichloroisocyanuric acid has the highest effective chlorine content of about 90% among chlorinated isocyanuric acid compounds, and its solubility in water is as low as 1.2 g and its dissolution rate is slow. Therefore, a small amount of active chlorine over a long period of time. Is preferably used in the practice of the present invention.
On the other hand, the sodium salt and potassium salt of dichloroisocyanuric acid have a low effective chlorine content of about 60%, but the solubility in water is about 25 g and the dissolution rate is fast, so that it is used for supplying high concentration active chlorine. Although it is used, in the practice of the present invention in which the activated sludge is continuously contacted, the amount of active chlorine supplied to the activated sludge slurry becomes excessive and the chemical cost increases, which is not suitable.
On the other hand, calcium hypochlorite can also dissolve in water to generate active chlorine, and those with an effective chlorine content of 60% or more are called advanced bleaching powders and are used for the same applications as chlorinated isocyanuric acid. Widely used. However, this calcium hypochlorite is also not suitable for practicing the present invention for the same reason as described above, because it has a solubility in water of about 21 g and a high dissolution rate.

The shape of the trichloroisocyanuric acid molded product used in the present invention is not limited, and may be any shape as long as it does not cause inconvenience during molding and practical use. For example, in the case of a cylindrical tablet, a powder Or granular trichloroisocyanuric acid can be molded under a tableting pressure of about 500 to 1500 kg / cm ² using a normal tableting machine. In the case of briquettes, granulation of a biaxial roll method Using a machine, it can be molded under a press pressure of roll pressure (static pressure) of 4 to 5 t.
Moreover, it is preferable that the major axis of the trichloroisocyanuric acid molded product is 5 to 100 mm (weight is 5 to 1000 g). If it is smaller than 5 mm, the activated sludge slurry may clog when passing through the packed bed of the trichloroisocyanuric acid molded product. If it is larger than 100 mm, the void portion in the packed layer may be clogged. The contact efficiency decreases, and there is a risk that sludge cannot be killed sufficiently.

  When the present invention is applied to general wastewater treatment using the activated sludge method, the generation of excess sludge can be reduced at a rate of 10 to 60% within a range that does not deteriorate the quality of the treated water.

  EXAMPLES Hereinafter, although an Example and a comparative example demonstrate this invention concretely, this invention is not limited to these. In addition, the analysis method of the killing rate of activated sludge and the reduction rate of excess sludge implemented in the Example and the comparative example is as follows.

[Destruction rate of activated sludge]
Measure the oxygen utilization rate (A) of the activated sludge before contact with trichloroisocyanuric acid and the oxygen utilization rate (B) of the activated sludge after the contact with each other. The sludge kill rate (% by weight) was calculated.
Killing rate (% by weight) = [1- (oxygen utilization rate (B) / oxygen utilization rate (A))] × 100
The oxygen utilization rate was measured in accordance with the method described in “Sewage Test Method, Japan Sewerage Association, 1997 Edition”.

[Reduction rate of excess sludge]
The MLSS concentration after killing treatment in the test zone was measured, and the amount of excess sludge generated in the test zone was calculated from the difference from the MLSS concentration before killing treatment. Similarly, the amount of excess sludge generated in the control plot was determined, and the reduction rate (% by weight) of the excess sludge was calculated from the difference in the amount of surplus sludge generated between the test plot and the control plot.

[Reference Example 1]
As a preliminary test, the relationship between the supply amount of trichloroisocyanuric acid and the kill rate of activated sludge was investigated.
A predetermined amount of trichloroisocyanuric acid (manufactured by Shikoku Kasei Kogyo Co., Ltd., trade name “Neochlor 90”, powder product, effective chlorine content 90%) is added to the activated sludge slurry and stirred for 2 hours. Part was collected and the kill rate of activated sludge was determined. The obtained test data is as shown in the line graph of FIG. 4, and the kill rate of activated sludge increased as the amount of trichloroisocyanuric acid added to the activated sludge slurry increased. The addition amount of trichloroisocyanuric acid shown on the horizontal axis is the ratio (%) of the addition amount (effective chlorine equivalent weight) of trichloroisocyanuric acid to the activated sludge amount (dry weight) in the activated sludge slurry.
In the practice of the present invention, it is not preferable that the supply amount of trichloroisocyanuric acid to the activated sludge exceeds the necessary amount (minimum amount) of trichloroisocyanuric acid at which the kill rate of the activated sludge reaches 100%.
Even if the killing rate reaches 100%, if excessive trichloroisocyanuric acid is supplied, the amount of trichloroisocyanuric acid used increases, the chemical cost increases, and when it is returned to the aeration tank, it is activated chlorine in the aeration tank. May remain and adversely affect the microbial treatment of sewage.

[Example 1]
Two wastewater treatment test apparatuses for the test shown in the flow of FIG. 1 were installed in the dredged sewage treatment plant for the test zone and the control zone, and an excess sludge reduction test was conducted.
The activated sludge slurry 50L which was extract | collected from the aeration tank of the processing place and MLSS density | concentration was adjusted to 5000 mg / L was thrown into the processing tank. Next, while aeration with a blower, the activated sludge slurry was extracted with a metering pump, and the slurry was trichloroisocyanuric acid tablet (trade name “Neochlor Mini”, diameter 15 mm, weight 2.5 g, manufactured by Shikoku Kasei Kogyo Co., Ltd.) After passing through a cylindrical dissolver (φ10 cm × height 15 cm) filled with an effective chlorine content of 90% to bring the packed bed of trichloroisocyanuric acid tablets into contact with activated sludge, the solution was returned to the treatment tank.
In addition, as a blank test, the dissolution apparatus of the test device for the control group was not filled with the trichloroisocyanuric acid tablet and was left empty, and a weight reduction test was performed under the same conditions as in the test group. . The wastewater treatment conditions in these tests are as shown in Table 1.

The discharge rate of the metering pump is set to the minimum so that the kill rate of the activated sludge after passing through the dissolver is 100%, and then the kill treatment time is adjusted with a timer to set the amount of treated sludge per day to 4 L (treatment rate: 8% / day). Under these conditions, the test apparatus was operated for 5 days, and then the amount of excess sludge generated after the operation was completed and the BOD of treated water (supernatant water after 2 hours of aeration stop) were measured.
The test results obtained were as shown in Table 2.

[Example 2]
Excess sludge reduction test was carried out in the same manner as in Example 1 except that the sludge was newly replaced and the amount of treated sludge per day was set to 8 L (treatment rate: 16% / day).
The test results obtained were as shown in Table 2.

[Examples 3 to 4]
Adjust the discharge rate of the metering pump so that the sludge kill rate before and after passing through the dissolver is 80%, and the amount of treated sludge per day is 4L (treatment rate: 8% / day) or 8L (treatment rate: 16%) Excess sludge reduction test was carried out in the same manner as in Example 1 except that it was set to / day).
The test results obtained were as shown in Table 2.

[Examples 5 to 6]
Adjust the discharge rate of the metering pump so that the sludge kill rate before and after passing through the dissolver is 60%, and the amount of treated sludge per day is 4L (treatment rate: 8% / day) or 8L (treatment rate: 16%) Excess sludge reduction test was carried out in the same manner as in Example 1 except that it was set to / day).
The test results obtained were as shown in Table 2.

[Comparative Example 1]
Except for using dichloroisocyanuric acid sodium tablets (made by Shikoku Kasei Kogyo Co., Ltd., trade name “Neochlor T-20S”, diameter 30 mm, weight 20 g, effective chlorine content 60%) instead of trichloroisocyanuric acid tablets, The excess sludge reduction test was carried out in the same manner as in Example 1.
However, in this test, since the tablet of sodium dichloroisocyanurate has a higher dissolution rate than the tablet of trichloroisocyanurate, the discharge amount of the metering pump was set to the lowest controllable value, but still, The kill rate of the activated sludge after passing through the dissolver was 100%.
The test results obtained were as shown in Table 2. In the activated sludge slurry after passing through the dissolver, active chlorine (effective chlorine equivalent) remained at an average concentration of about 1100 ppm.

[Comparative Example 2]
A comparative example except that calcium hypochlorite tablets (made by Nankai Chemical Co., Ltd., trade name “Nankai Clear”, diameter 30 mm, weight 20 g, effective chlorine content 70%) were used instead of sodium dichloroisocyanurate tablets. The excess sludge reduction test was conducted in the same manner as in 1.
However, in this test, the calcium hypochlorite tablet had a faster dissolution rate than the trichloroisocyanuric acid tablet, so the discharge rate of the metering pump was set to the lowest controllable value. The kill rate of the activated sludge after passing through the dissolver was 100%.
The test results obtained were as shown in Table 2. In the activated sludge slurry after passing through the dissolver, active chlorine (effective chlorine equivalent) remained at an average concentration of about 900 ppm.

  According to the test results shown in Table 2, the higher the kill rate of activated sludge and the higher the rate of killing treatment rate, the higher the excess sludge reduction rate. However, when the reduction rate of excess sludge reached about 70% (Example 2), the treated water became cloudy, the BOD value increased, and the water quality deteriorated. On the other hand, when sodium dichloroisocyanurate and calcium chlorite are used (Comparative Examples 1 and 2), as a result of excessive dissolution, the treated water becomes cloudy and the BOD value increases as described above. Worsened. Therefore, it is preferable to carry out the killing treatment by adjusting the reduction rate of excess sludge to a range of 10 to 60%.

It is a schematic flowchart of the process process at the time of applying this invention to a batch type activated sludge process. It is a schematic flowchart of the process process at the time of applying this invention to a continuous activated sludge process. It is a conceptual diagram showing a mode that an activated sludge slurry passes the dissolver filled with the trichloroisocyanuric acid molded object. It is a line graph which shows the relationship between the supply amount of trichloroisocyanuric acid, and the killing rate of activated sludge.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Treatment tank 2 Sewage 3 Activated sludge slurry 4 Treated water 5 Aeration tank 6 Settling tank 7 Concentrated sludge slurry 8 Return sludge slurry 9 Excess sludge slurry 11 Air blower 12 Air diffuser 13 Pump 20 Dissolver filled with trichloroisocyanuric acid molding

Claims (3)

  In a treatment tank in which organic sludge and activated sludge are brought into contact with each other to perform microbial treatment, the activated sludge slurry extracted from the treatment tank is passed through a dissolver filled with the trichloroisocyanuric acid molded article, thereby forming the trichloroisocyanuric acid molded article. A method for reducing surplus sludge, wherein the slurry is returned to a treatment tank after contacting the packed bed with activated sludge.   In a treatment tank in which organic sludge and activated sludge are brought into contact with each other for biological treatment, the activated sludge slurry extracted from the treatment tank is passed through a dissolver filled with the trichloroisocyanuric acid molded article, thereby forming the trichloroisocyanuric acid molded article. The activated sludge in the slurry is killed at a rate of 50 to 100% by bringing the packed bed into contact with the activated sludge, the slurry is returned to the treatment tank, and the reduction rate of excess sludge is in the range of 10 to 60%. A method for reducing excess sludge, which is characterized by adjusting to the inside. 3. The method for reducing excess sludge according to claim 1 or 2, wherein a major axis of the trichloroisocyanuric acid molded product is 5 to 100 mm.

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