JPH0732919B2 - Sludge concentration method - Google Patents

Description

TECHNICAL FIELD The present invention relates to an improvement in a sludge concentration method used for efficiently concentrating sludge generated from a sewage treatment plant or the like.

(Prior Art) Standard sewage treatment at a sewage treatment plant, etc. is carried out by using a pump to draw out mixed raw sludge of initial sludge and excess sludge returned from the final settling basin as shown in FIG. It is carried out by a method of gravity concentration by sending it to a concentration tank. However, in recent years, the amount of organic substances in sewage has increased,
Since organic substances adhering to the surface of sludge hinder gravity concentration, such factors as reduced concentration, increased settling time, increased equipment scale, floating sludge due to sludge decay, reduced dewatering capacity and increased dehydrated cake water content. It causes various problems.

Therefore, recently, as shown in Fig. 6, a dilution cleaning method has been developed in which mixed raw sludge is introduced into a dilution tank to wash the sticky substances derived from organic substances adhering to the surface, and then to perform gravity concentration. It has been implemented at some sewage treatment plants. However, in the past, the method of diluting to a certain ratio was adopted, so if the concentration of sludge flowing into the diluting tank is low, it will be overdiluted and it may take time rather than gravity concentration thereafter, and it will flow into the diluting tank. When the concentration of the sludge that fluctuates fluctuates, the concentration of the diluted sludge that flows into the gravity concentrator also fluctuates, and there is a problem that the receiving load becomes unstable and a stable concentration effect cannot be obtained.

(Problems to be Solved by the Invention) The present invention solves the above-mentioned problems of the prior art, and enables sludge containing a large amount of organic matter to be efficiently gravity-concentrated and does not become over-diluted. This was completed for the purpose of a sludge concentration method that can obtain a stable concentration effect even when the sludge concentration changes.

(Means for Solving the Problem) The present invention made to achieve the above object is to provide a method for concentrating sludge by diluting a mixed raw sludge first drawn from a settling tank in a diluting tank and then gravity concentrating it. The concentration of sludge is detected by a densitometer installed in the middle of the transfer pipe, the extraction pump is stopped when the concentration falls below the set value, and when the concentration exceeds the set value, the flow rate measured together is calculated. It is characterized in that the dilution water pump is controlled to dilute 1.5 to 2.5 times and then preconcentrated to supply to the gravity concentration tank while maintaining the concentration after preconcentration in the range of 0.7 to 1.5%.

Next, the present invention will be described in more detail with reference to the block diagram of FIG.

Also in the present invention, sewage is first introduced into the sand basin (1),
After removing coarse floating contaminants and sand / mud in the wastewater, the sediment / sedimentation of sand / mud and suspended solids is first performed in the settling tank (2). Then, the supernatant water is biologically treated by the activated sludge method in the aeration tank (3) to promote coagulation and oxidation of the soluble organic matter, and further separated into the supernatant water and the sludge by the final settling tank (4). This sludge is first returned to the settling basin (2) and aeration tank (3) by the pump (5). The mixed raw sludge, which is a mixture of the initial sludge and the excess sludge drawn from the first settling basin (1), is transferred to the dilution tank (8) by the drawing pump (6) through the transfer pipe (7), Here, the organic substance on the surface of the sludge is washed by being diluted with the dilution water supplied from the dilution water tank (9) by the dilution water pump (10).

Although the above steps are not different from the conventional sludge dilution flow shown in FIG. 6, in the present invention, a flow meter (11) and a densitometer (12) are provided in the middle of the transfer pipe (7). The flow rate and the concentration of the mixed raw sludge supplied to the dilution tank (8) are measured, and the calculation result is input to a calculator (13) such as a microcomputer. This calculator (13)
Is connected to the withdrawal pump (6) and the dilution water pump (10), and stops the withdrawal pump (6) if the concentration of the mixed raw sludge to be transferred falls below a set value. For example, 0.5% is adopted as the set value,
It is prevented that 0.5% or less of sludge is supplied to the diluting tank (8) and is excessively diluted. On the other hand, when the concentration of the mixed raw sludge exceeds this set value, dilution cleaning is performed, but in the present invention, it is measured by a flow meter (11) instead of diluting at a constant rate as in the conventional case. After calculating the flow rate and the concentration together, the normal sludge concentration is 0.5 to 2.0%
The dilution water pump (10) is controlled so that the sludge dilution ratio is maintained within the range of 1.5 to 2.5 times. The reason for selecting 1.5 to 2.5 times as the dilution ratio here is that the efficiency of gravity concentration after that becomes lower when the dilution ratio becomes 2.5 times or more, and when it becomes less than 1.5 times, the removal of organic substances is not sufficiently performed and gravity concentration still occurs. This reduces the efficiency of. Pre-concentration of sludge after dilution and washing is because sludge after dilution and washing has an extremely good sedimentation property, and it is usually easily concentrated to 0.7 to 1.5% with a residence time of about 20 to 30 minutes. Because. The concentration is 0.7
% Or less, the capacity of the gravity thickening tank (15) must be extremely increased, which is not preferable. Also 1.5%
If it is below, the concentration property by the gravity concentration tank (15) is deteriorated. In this way, the diluted sludge that has been diluted and washed to remove organic substances while being controlled so that the dilution ratio is 1.5 to 2.5 times is introduced to the preconcentration tank and the concentration after preconcentration is 0.7 to 1.5%.
After that, it is further guided to the gravity concentrating tank (15) and allowed to stand for about 12 to 24 hours to perform gravity concentration until the concentration becomes 2 to 4%. At this time, if the diluted sludge is introduced into the preliminary separation tank (14) to remove the fine particles by overflow for 20 to 30 minutes and then introduced into the gravity concentration tank (15), the gravity concentration tank (15 The stationary time in 15) can be reduced to 70 to 80%, and the total processing time can be greatly shortened. The pre-separation liquid containing fine particles generated from the pre-separation tank (14) is first returned to the sedimentation tank (2) like the separation liquid generated from the gravity concentration tank.

As described above, in the present invention, since diluted washing is performed while controlling the concentration after dilution to be a value within a certain range, the concentration of the reached sludge in the gravity concentration tank (15) after that is determined by the conventional method. 1 to 1.5% higher than that of The graph of FIG. 2 shows the effect of the present invention by plotting the supplied sludge concentration on the horizontal axis and the reached sludge concentration on the vertical axis when gravity concentration is carried out by leaving it in the gravity concentration tank (15) for 24 hours. According to the present invention, the reached sludge concentration by gravity concentration can be increased by up to 1.5% or more as compared with the conventional method in which washing is not performed. In this way, if the sludge concentration can be increased from the conventional 2% to 3.3%,
As shown in Fig. 3, the processing capacity of the post-process dehydrator is 3 kg / m ²
・ Hr to 4.2kg / m ²・ Hr can be improved by 40%, and as shown in Fig. 4, the water content of the dehydrated cake is 67%.
Can be reduced to 64.5%. As a result, the amount of heat required for the incineration process of the dehydrated cake can be significantly reduced, which can greatly contribute to the improvement of the treatment capacity of the entire sewage treatment plant.

(Effect of the invention) As is apparent from the above description, the present invention can prevent excessive dilution by stopping withdrawal when the concentration of mixed raw sludge falls below a set value, and sludge after dilution. Since the dilution water pump is controlled so that the concentration of is maintained within a predetermined range, it is possible to stabilize the acceptance load of the gravity concentration tank. As a result, it is possible to improve the reaching sludge concentration of the gravity separation tank even for sewage with a high content of organic substances, so many practical applications such as improvement of the treatment capacity and management of the sewage treatment plant are possible. The effect can be obtained. Therefore, the present invention is extremely large in that it contributes to industrial development as a method for concentrating sludge that eliminates the conventional problems.

[Brief description of drawings]

FIG. 1 is a block diagram showing the sewage treatment flow of the present invention, FIG. 2 is a graph showing the reached sludge concentration by the present invention and the conventional method, and FIG. 3 is a relation between the sludge concentration and the treatment capacity of the dehydrator. Graph, FIG. 4 is a graph showing the relationship between sludge concentration and water content of the dehydrated cake, FIG. 5 is a block diagram showing a standard flow of sewage treatment, and FIG. 6 is a block diagram showing a conventional sludge dilution flow. . (2): First settling tank, (7): Transfer pipe, (8): Diluting tank, (10): Diluting water pump, (11): Flow meter, (12):
Densitometer, (15): Gravity concentrator.

Claims (1)

[Claims] 1. A method for concentrating sludge, which comprises first diluting mixed raw sludge drawn from a settling tank in a diluting tank and then concentrating it by gravity. The concentration of the mixed raw sludge is detected by a densitometer installed in the middle of a transfer pipe, When the concentration falls below the set value, the extraction pump is stopped, and when the concentration exceeds the set value, the dilution water pump is controlled by calculation with the measured flow rate to dilute 1.5 to 2.5 times and then preconcentrate. The method for concentrating sludge is characterized in that the concentration after preconcentration is supplied to a gravity concentration tank while maintaining the concentration in the range of 0.7 to 1.5%.