JPH0468040B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an organic sludge treatment process that is performed prior to dewatering organic sludge such as municipal sewage sludge using a filter press dehydrator, belt press dehydrator, etc. This relates to a method for refining sludge.

(Prior Art) In a dewatering treatment plant for organic sludge, as a pre-process to the dewatering process, there is a refining process in which a polymer flocculant is added to organic sludge and stirred to form flocs. Conventionally, in such a refining process, rapid stirring is performed by rotating stirring blades at a high circumferential speed of, for example, 0.6 to 1.3 m/s in order to rapidly agglomerate the flocs. ,
If it takes a long time to send the sludge to the dehydrator, the flocs once formed are destroyed, which significantly impedes the filterability of the sludge and makes dewatering difficult. In addition, if slow stirring was performed at a peripheral speed of about 0.4 m/s to prevent floc destruction, it would take time for the flocs to coagulate, reducing the efficiency of the entire dehydration treatment plant. .

(Problems to be solved by the invention) The present invention solves these conventional problems,
The flocculation can be completed rapidly,
Moreover, it was completed with the aim of providing a method for refining organic sludge that does not cause the destruction of flocs once formed.

(Means for Solving the Problems) The present invention provides flocculated sludge obtained by adding a polymer flocculant to organic sludge and flocculating it to a capillary suction time measuring device. The capillary suction time value, expressed as the time required for expansion to a predetermined point, is measured, and the capillary suction time value is rapidly stirred until it reaches approximately the minimum value, and then stirred at a slow speed that does not allow the flocs to settle. It is characterized by continuous stirring.

Next, the present invention will be described in more detail with reference to the drawings. Organic sludge is supplied to the inside of a coagulation mixing tank 2 through a supply pipe 1, and a cationic sludge with a molecular weight of 700,000 or less is supplied from a flocculant addition pipe 3. A polymer flocculant is added at a ratio of about 1.5% based on the solid content of the sludge,
Rapid stirring is performed by the rapid stirring blade 4 at a speed of, for example, 32 rpm. During this stirring, a flocculated sludge sample is collected from the sample collection tube 5, and the capillary suction time value (hereinafter referred to as CST value) is collected using a capillary suction time measuring device.
is measured at regular time intervals.

Here, CST is an abbreviation for Capillary Suction Time, and it is the time required for the moist area to expand from 30 mm to 45 mm from the center when sludge is dropped into the center of a specific filter paper. The filtration characteristics of sludge are evaluated based on time. For more information on CST values, see, for example, "About CST as an evaluation index for sludge filterability" published in the Journal of Japan Sewage Works Association, VOL.15, No.168, June 1978 issue.
It is described in a paper by Kasakura, Imaizumi et al.
Although this CST value is small, it means that the filtration properties are excellent. As a result of repeated research on this CST value, the present inventor found that when a polymer flocculant is added to sludge and then stirred, the CST value of the sludge gradually decreases as floc flocculation progresses; The minimum value and the stirring time to reach the minimum value vary depending on the stirring speed, 58 rpm
(peripheral speed 1.03 m/s), CST after reaching the minimum value in 20 to 30 minutes with rapid stirring at 32 rpm (peripheral speed 0.57 m/s)
22 rpm (peripheral speed 0.39) whereas the value increases again
It was found that in the case of slow stirring (m/sec), it takes more than 90 minutes to reach the minimum value, and that the minimum value is maintained even after that.

Therefore, in the present invention, flocculated sludge obtained by adding a polymer flocculant to organic sludge and flocculating it is subjected to a capillary suction time measuring device to measure the CST value. Then, as shown in the third figure, rapid stirring is performed until the CST value reaches almost the minimum value, and then the sludge is transferred to the flocculated sludge holding tank 7 via the overflow pipe 6, and the flocculated flocs are stirred by the slow stirring blades 8. Slow stirring is continued at a speed of, for example, 22 rpm to prevent sedimentation. After shifting to this slow agitation, the sludge is maintained in a state suitable for dewatering treatment, so it can be supplied from the discharge pipe 9 to a filter press dehydrator or belt press dehydrator at any time. It goes without saying that rapid stirring and slow stirring can be performed in the same tank.

(Example) Next, examples of the present invention will be shown.

Pour 1 m ³ of sewage sludge into a 1 m x 1 m x 1.5 m flocculation mixing tank 2, add polymer flocculant at the appropriate chemical injection rate (1.5% per sludge solid content) determined in advance by a jar test, and rapidly stir at 32 rpm. I went there. At the same time, the flocculated sludge was subjected to a capillary suction time measuring device to measure the CST value. Approximately 20 minutes after starting rapid stirring, the CST value reached the minimum value of 17.1 seconds, so the sludge was transferred to the flocculated sludge holding tank 7.
Slow stirring at 22 rpm was performed continuously. after that
The CST value maintains the minimum value as shown in Figure 3,
No destruction of the flocs occurred. The sludge that has passed 30 minutes after shifting to slow stirring is filtered using a filter press dehydrator at a filtration pressure of 4 Kg/cm ² and a filtration time of 10 minutes.
When dehydration was performed under conditions of a compression pressure of 15 Kg/cm ² and a compression time of 10 minutes, a cake with a moisture content of 70.2% was obtained, and the filtration rate at this time was 2.73 Kg・DS/m ²・Hr.
In addition, when rapid stirring at 32 rpm is continued for the same time, the CST value is 18.5 seconds, and when dehydrated under the same conditions, a cake with a moisture content of 72.5% is obtained, and the filtration rate is 2.13 Kg・DS/m ²・It was Hr.

(Effects of the Invention) As is clear from the above explanation, the present invention performs rapid stirring after adding a polymer flocculant to organic sludge, so flocs can be flocculated within a short time, and after that, the flocs can be flocculated slowly. By shifting to rapid agitation, the sludge properties can be maintained in a state suitable for filtration for a long period of time without destroying the flocs once formed. Furthermore, since the timing of switching from rapid agitation to slow agitation is set to the time when the CST value, which accurately represents the filtration characteristics of sludge, is almost at its minimum value, the sludge can be optimized for filtration without relying on intuition or experience as in the past. It is possible to precisely refine the condition. Note that for sludge with the same properties, it is needless to say that it is not necessary to measure the CST value each time, and it is also possible to switch to slow stirring using a timer.

As described above, the present invention is suitable as a refining method as a pre-process for dehydrating organic sludge, and will greatly contribute to the development of industry.

[Brief explanation of the drawing]

Figure 1 is a schematic cross-sectional view of the tempering device used in the implementation of the present invention, and Figure 2 is a CST according to the stirring speed.
Graph showing changes in values. FIG. 3 is a graph showing changes in CST values in the method of the present invention. 2: coagulation mixing tank, 4: rapid stirring blade, 7: flocculating sludge holding tank, 8: slow stirring blade.

Claims (1)

[Claims] 1. Coagulated sludge obtained by adding a polymer flocculant to organic sludge and flocculating it was subjected to a capillary suction time measurement device.
The capillary suction time value, which is expressed by the time required for the wet area to expand to a predetermined point when dropped on filter paper, is measured, and the capillary suction time value is rapidly stirred until it reaches almost the minimum value, and then the flocculation is carried out. A method for refining organic sludge, which is characterized by continuously performing slow agitation to an extent that flocs do not settle.