JP3248233B2 - Activated sludge treatment method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an activated sludge treatment method for aerobically treating organic wastewater, and more particularly to an activated sludge treatment method capable of reducing the amount of excess sludge generated.

[0002]

2. Description of the Related Art Activated sludge treatment as an aerobic treatment method for organic wastewater involves introducing raw water into an aeration tank together with return sludge, performing aeration treatment, and separating aerated liquid into solid and liquid to form a separated sludge. This is a method of returning the part to the aeration tank. This method can efficiently decompose organic substances at a relatively low cost, but generates a large amount of surplus sludge that is difficult to dehydrate, and it is difficult to treat the sludge.

[0003] Methods of reducing the amount of excess sludge in activated sludge treatment are roughly classified according to their functions as follows. 1) Increasing the sludge concentration in the aeration tank and increasing the SRT to increase the amount of sludge to be self-decomposed and reduce the amount of excess sludge. 2) Increasing the temperature of water in the aeration tank increases the amount of self-decomposing sludge and reduces the amount of excess sludge. 3) Organisms other than activated sludge, such as protozoa and anaerobic bacteria, are grown in the aeration tank, and the sludge is decomposed by the microorganisms. 4) Excess sludge is separately subjected to physical treatment under high temperature and high pressure and chemical treatment such as an enzymatic agent and an oxidizing agent to decompose the sludge. Further, the eluate at the time of decomposition is treated with activated sludge.

In the method 1), the amount of self-decomposition of the sludge increases, but depending on the properties of the sludge, the solid-liquid separation in the solid-liquid separation tank becomes insufficient, and a large amount of sludge may be mixed into the treated water. There is. In addition, it is necessary to greatly increase the ventilation amount of the aeration tank, and there is a problem that the running cost increases.

The above method 2) is most effective as a method for increasing the rate of self-decomposition of sludge, and can be applied to sludge of various properties. However, actually increasing the temperature of water in an aeration tank is not particularly high-temperature drainage. Not as practical as possible. Even if the water temperature is increased, there is a problem that the air flow increases due to the increase in the water temperature, the running cost increases, the sludge tends to be dispersed, and the treatment efficiency decreases.

Although the effects of the above methods 3) and 4) are sufficiently recognized, there is a problem that the processing flow and the equipment become complicated, and the running cost of the ventilation power, heat source, chemicals, etc., is greatly increased. There is. As described above, in the conventional method, at present, the advantage of reducing the running cost by reducing the excess sludge is not fully utilized.

On the other hand, Japanese Patent Application Laid-Open No. 55-34175 discloses a method in which excess sludge is heat-treated at 60 to 100 ° C. and then aerobically digested. But with this method,
Since the heating temperature is high, the cells are destroyed and the COD in the liquid becomes high, and thus a dedicated digester is required.

[0008]

SUMMARY OF THE INVENTION An object of the present invention is to solve the above problems by reducing the amount of excess sludge generated without reducing the load on the aeration tank, the processing efficiency and the processing performance. Another object of the present invention is to propose an activated sludge treatment method which is easy to operate and has a small increase in running cost.

[0009]

According to the present invention, raw water is introduced into an aeration tank together with return sludge, subjected to aeration treatment, aerated liquid is separated into solid and liquid, and a part of the separated sludge is returned to the aeration tank as return sludge. In the activated sludge treatment method, a part of the returned sludge is
This is an activated sludge treatment method characterized by returning to an aeration tank after aeration at ~ 55 ° C.

In the present invention, the activated sludge treatment method employed is such that raw water is introduced into an aeration tank together with return sludge, subjected to aeration treatment, aerated liquid is separated into solid and liquid, and a part of the separated sludge is returned as return sludge. The method includes a standard activated sludge treatment method including only these steps, a modified aeration such as a step aeration, and a modification such as a combination with an aerobic treatment and a nitrification denitrification method.

In the present invention, when a part of the separated sludge generated when the raw water is aerated by the activated sludge treatment method and solid-liquid separated is returned to the aeration tank as return sludge, the entire returned sludge is directly used in the aeration tank. Instead of returning the sludge to the aeration tank without heating and aeration, the amount of returned sludge required to maintain the MLSS in the aeration tank is returned to the aeration tank without heating, and the remaining returned sludge is heated and aerated in the heating aeration tank. , Return to aeration tank.

The temperature of the heating and aeration in the heating and aeration tank is 35.
To 55 ° C, preferably 35 to 40 ° C. The residence time is desirably 10 to 100 hours, preferably 12 to 72 hours. The amount of returned sludge to be heated and aerated is determined by the MLS in the aeration tank.
S, but generally 10-30 of returned sludge
% Is preferable. Heating in the heating aeration tank is usually performed by steam, a heater, or the like, but can also be performed by using a heat exchanger with hot water, high-temperature drainage, or high-temperature anaerobic treated water.

[0013]

In the activated sludge treatment method of the present invention, a part of the returned sludge is heated and aerated at a relatively low temperature of 35 to 55 ° C., thereby increasing the self-decomposition rate of the sludge and reducing the sludge capacity. At this time, the BOD does not increase due to cell destruction, and only the autolysis rate of the sludge increases. Although the separation of sludge is deteriorated by the heating and aeration, the separation is improved by performing the aeration treatment in the aeration tank together with the return sludge that is not heated and aerated, thereby reducing the amount of excess sludge generated.

Further, in the present invention, a part of the returned sludge is heated and aerated at a relatively low temperature. Therefore, the present invention can be easily implemented only by providing a small-sized heated aeration tank in an existing apparatus. Also, since the power for ventilation is small, the increase in running cost is small. In the case where 10-20% of the returned sludge is heated and aerated, the heated aeration tank needs only 5-10% of the capacity of the aeration tank. Furthermore, the amount of the heated sludge is small because part of the returned sludge is heated, and even if the heated sludge is returned to the aeration tank, the water temperature of the entire aeration tank does not rise so much, so that the processing performance and the processing efficiency are reduced. Does not drop.

[0015]

Next, an embodiment of the present invention will be described. FIG.
FIG. 2 is a flowchart showing an activated sludge treatment method of an example. In the figure, 1 is an aeration tank, 2 is a solid-liquid separation tank, and 3 is a heated aeration tank.

In the treatment method, first, raw water is introduced into the aeration tank 1 from the raw water supply pipe 4, mixed with the activated sludge in the tank, and aerated by the air diffused from the diffusion pipe 5. The aerated liquid is introduced into the solid-liquid separation tank 2 from the connecting pipe 6 to be separated into solid and liquid, and the separated water is discharged from the treated water pipe 7 as treated water. Solid-liquid separation tank 2
A part of the separated sludge separated in the above is returned to the aeration tank 1 as return sludge, and the remaining part is discharged from the excess sludge discharge pipe 8 outside the system as surplus sludge.

A part of the returned sludge to be returned to the aeration tank 1 is introduced into the heated aeration tank 3 through the connecting pipe 9 and heated and aerated, and the rest is returned to the aeration tank 1 as it is from the returned sludge pipe 10. The returned sludge introduced into the heating aeration tank 3 is heated to a temperature of 35 to 55 ° C. and heated and aerated by air diffused from the diffusion pipe 11. Sludge self-decomposed by heating and aeration is returned to sludge pipe 1
2 to the aeration tank 1. The returned sludge returned from the returned sludge pipes 10 and 12 to the aeration tank 1 is mixed with raw water and aerated to be used for decomposing organic substances in the raw water.

Example 1 The relationship between the self-decomposition rate of activated sludge and the operating water temperature was measured by a coulometer method using glucose assimilation sludge. The results are shown in FIG. From FIG. 2, it can be seen that the rate of increase in the autolysis rate increases with increasing water temperature and reaches a maximum at 55 ° C. In addition, the rate of increase of the autolysis rate is 20 at 35 ° C.
It can be seen that the temperature is about 1.8 times that of the temperature and about 2.7 times the temperature at 55 ° C.

Example 2 In the processing flow shown in FIG. 1, the ratio of the returned sludge heated and aerated in the heated aeration tank 3 and the reduction ratio of the excess sludge at that time are determined by the standard kinetic constant of activated sludge (sludge). Conversion rate,
(Automatic decomposition rate constant, temperature coefficient, etc.). Calculation examples (operating conditions) and calculation formulas are as follows.

(Calculation example) Raw water conditions: water temperature (Q); 1000 m ³ / d water temperature; 20 ° C. BOD (C); 1000 mg / l SS; 0 mg / l aeration tank: BOD load; 1.0 kg-BOD / m ³ · d retention MLSS (M); 4000 mg / l capacity (V); 1000 m ³ returned sludge: returned sludge capacity; 500 m ³ / day returned MLSS; 8000 mg / l heated aeration tank: residence time; 24 hr water temperature; 35 ° C. treatment Water: Discharge rate; 1000 m ³ / day Kinetic constant: Sludge conversion rate (Y); 0.5 g-MLSS / g-BOD Autolysis rate constant at 20 ° C. (Kd (20)); 0.06 g-MLSS / g- MLSS · d Temperature coefficient (θ): 1.05

(Calculation formula for use) Excess sludge amount (ΔSS)

(Equation 1) Autolysis rate constant at T ° C (Kd (T))

(Equation 2)

Under the operating conditions set as described above,
Various ratios of the heated aerated sludge to be heated and aerated in the heated aeration tank are set, and the heating aeration tank 3 capacity, the water temperature in the aeration tank 1, the amount of excess sludge generated (self-decomposition amount) and the heating are set for each ratio Aeration tank 3
The rate of reduction (%) of surplus sludge was calculated with respect to the conventional method without installation. Table 1 shows the results.

[0023]

[Table 1]

As shown in Table 1, under the condition that the raw water temperature is 20 ° C., 20% of the returned sludge is aerated in a heated aeration tank heated to 35 ° C. for 1 day, and then returned to the aeration tank. ,
The reduction rate of the excess sludge was 45% compared to the standard conventional method (when the entire amount of returned sludge was returned to the aeration tank as it was), and the result was 23% when 10% of the returned sludge was heated and aerated. . Further, the water temperature rise of the returned aeration tank body is 1 to 2 ° C., and it is considered that there is no influence on the treatment efficiency and the treatment performance of the activated sludge treatment.

Example 3 In the processing flow shown in FIG. 1, the amount of excess sludge was measured by actually heating and aeration, and it was confirmed whether a result equivalent to the calculation result expected in Example 2 was obtained. As raw water,
BOD 4000mg /
1, TOC (total organic carbon) 2200 mg / l, SS 4
0 mg / l wastewater was used.

In the test apparatus, the main body of the aeration tank 1 is 10 liters.
er, the heating aeration tank 3 is 1 liter and the aeration tank 1
The operating water temperature was adjusted to 25 ° C, and the temperature of the heated aeration tank 3 was adjusted to 37 ° C.
The load of the aeration tank 1 was 1.3 kg-BOD / m ³ · d, the residence time was 3 days (relative to raw water), and the amount of returned sludge was 50% of the raw water amount. The proportion of the heated aerated sludge in the heated aeration tank 3 was 20%, and the residence time was 72 hours. Excess sludge was extracted in order to adjust the MLSS concentration in the aeration tank 1 to 5000 mg / l. MLS in heated aeration tank 3
The S concentration was 9000 to 11000 mg / l.

The following results were obtained as a result of continuous operation for 12 days under the above conditions. Excess sludge amount: average 2.4 g-VSS / d Sludge conversion rate: 0.18 g-MLSS / g-BOD treated water TOC: average 176 mg / l

Comparative Example 1 The same raw water as in Example 3 was used, and a continuous operation was performed for 10 days by the conventional method without installing the heating and aeration tank 3. The operating conditions are as follows: aeration tank operating water temperature is 25 ° C., and load is 1.3 kg / m ^3.
d, Return sludge amount was 50% of raw water amount. The results are as follows. Excess sludge amount: average 4.4 g-VSS / d Sludge conversion rate: 0.33 g-MLSS / g-BOD treated water TOC: average 181 mg / l

From Example 3 and Comparative Example 1, by installing a heated aeration tank, the amount of excess sludge was reduced to 55% as compared with the case where no sludge was installed, and a result almost equivalent to the expected value obtained by calculation was obtained. It is understood that it is possible.

[0030]

As described above, according to the present invention, in the activated sludge treatment method, a part of the returned sludge is aerated at 35 to 55 ° C. and then returned to the aeration tank of the raw water. The amount of excess sludge generated can be reduced at a low running cost with a simple operation without lowering the amount, the processing efficiency and the processing performance.

[Brief description of the drawings]

FIG. 1 is a flowchart showing an activated sludge treatment method of an example.

FIG. 2 is a graph showing the results of Example 1.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Aeration tank 2 Solid-liquid separation tank 3 Heating aeration tank 4 Raw water supply pipe 5, 11 Aeration pipe 6, 9 Communication pipe 7 Treatment water pipe 8 Excess sludge discharge pipe 10, 12 Return sludge pipe

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-4-11994 (JP, A) JP-A-57-1491 (JP, A) JP-A-53-26465 (JP, A) JP-A 52-1994 62962 (JP, A) (58) Field surveyed (Int. Cl. ⁷ , DB name) C02F 3/12

Claims (1)

(57) [Claims] 1. An activated sludge treatment method in which raw water is introduced into an aeration tank together with return sludge and subjected to aeration treatment, and aeration liquid is separated into solid and liquid, and a part of the separated sludge is returned to the aeration tank as return sludge. An activated sludge treatment method comprising aerating a part of sludge at 35 to 55 ° C and returning the sludge to an aeration tank.