JPH0732917B2 - Pretreatment method for sludge - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial field of application) The present invention relates to an initial sludge generated from a sewage treatment plant, an excess sludge,
The present invention relates to a sludge pretreatment method performed prior to anaerobically treating a mixed raw sludge or the like that is a mixture thereof.

(Prior Art) Various attempts have been made in the past to improve the solubilization rate (VSS reduction rate) by pretreating sludge prior to anaerobic digestion of sewage sludge.
Japanese Patent Laid-Open No. 200-200 discloses a method of crushing flocs by irradiating sludge with ultrasonic waves. However, with such a conventional method, it is difficult to completely atomize a large amount of sludge that is handled in a sewage treatment plant, and there is a drawback in that it is not practical in terms of its pulverization efficiency.

(Problems to be Solved by the Invention) The present invention solves the conventional problems as described above and efficiently and completely atomizes a large amount of sludge before anaerobic digestion, thereby significantly increasing the solubilization rate of sludge. It was completed for the purpose of pretreatment method of sludge that can be improved.

(Means for Solving Problems) In the present invention, before sludge is anaerobically digested, sludge is removed by 40 to 12
It is characterized in that it is heated to 0 ° C., pulverized in this heated state into fine particles, and then sent to the anaerobic digestion step.

In the present invention, the sludge is first heated to 40 to 120 ° C before being anaerobically digested. The heating may be performed rapidly by a heater, or may be performed slowly while being stored in the heating tank for 1 to 24 hours. In any case, the heating temperature is set to 40 to 120 ° C., the effect of the present invention described below is not sufficiently obtained at less than 40 ° C. On the contrary, if it exceeds 120 ° C., it is sufficient in terms of action and effect, It requires a large amount of energy and is uneconomical. Particularly preferred is 50 from the viewpoint of lytic effect.
The temperature range is ℃ or more and 80 ℃ or less from the viewpoint of energy efficiency. When using that heating tank, the residence time in the tank is 70 ° C
Below, it may be 3 to 24 hours, and above 70 ° C may be about 1 to 6 hours.

Next, the sludge is pulverized while being heated to 40 to 120 ° C. and atomized to a particle size of 10 to 20 μm. Any type of grinder can be used as long as it can grind moisture. In the present invention, since the sludge is crushed in such a heated state as described above, the solubility of lipids and the like in the sludge is increased by the heat and the microorganisms in the sludge cause lysis,
The pulverization is performed in a state where the flocs are easily collapsed, and extremely high pulverization efficiency is achieved. In particular, when sludge is retained in the heating tank for a certain period of time before crushing, easily decomposable components that are decomposed by heating in the sludge can be decomposed in the heating tank, and difficult-to-decompose components can be atomized by a pulverizer. Therefore, efficient crushing is possible. At room temperature, the particle size can only be reduced to 30 to 40 μm, and if crushed and then heat-treated, the excellent crushing efficiency of the present invention cannot be achieved. Further, when the material is cooled after heating, the easily decomposable component is again in a difficultly decomposable state, so that a desirable result cannot be obtained. In the present invention, heating and crushing are continuously or simultaneously performed in this manner, but a solid-liquid separation device is installed between the heating means and the crusher, and only solid substances which are not easily solubilized by heating are hard to decompose. If the powder is supplied to the pulverizer, the efficiency of pulverization will be further improved.

The sludge pulverized as described above and having an increased solubilization rate is then sent to the anaerobic digestion step and treated according to a conventional method.

(Example) Example 1 Excess sludge with VSS of 9210 ppm was centrifuged in a 3000 rpm centrifuge, and 30 ml each was placed in a test tube, and 5 ° C, 30 ° C, 50 ° C, 60
The mixture was vigorously stirred for 5 minutes together with 20 g of 2 mm glass beads while being heated to 0 ° C. MLVSS of excess sludge after stirring
Was measured and the result as shown in FIG. 1 was obtained. As is clear from this result, the MLVSS reduction rate is 17% when pulverized under heating at 60 ° C, which is an improvement of 14% compared to the 3% reduction rate when pulverized at room temperature at 30 ° C. Admitted. In order to improve the reduction rate of MLVSS by 14% by the usual digestion method, it is necessary to prolong the retention time of sludge in the digestion tank for about 15 days, and the present invention can significantly reduce the retention time of anaerobic digestion. There is.

Example 2 Excess sludge having a VSS of 14000 ppm and a particle size of 50 to 60 μm was divided into two, one of which was heat-treated at 70 ° C. for 5 hours to 10 to 20 μ at 60 ° C.
m was crushed to m, and the other was crushed at room temperature and then heat-treated at 70 ° C. for 5 hours. For crushing, Supermass Colloider MKZA10-10 manufactured by Masuyuki Sangyo Co., Ltd. was used, and the crushed product was returned to the charging port again for a total of three times of crushing. The results are shown in Table 2, and according to the method of the present invention (shown by ●), the VSS is 1
Although it could be reduced to 0000 ppm, VSS was reduced only to 11000 ppm by the method of the comparative example (shown by ◯) in which heat treatment was performed after pulverization, and the reduction rate was 29% for the former and 21% for the latter. As described above, according to the method of the present invention, the reduction rate of VSS can be significantly improved.

(Effect of the invention) As is apparent from the above description, the present invention improves sludge pulverization efficiency by pulverizing sludge while keeping it heated at 40 to 120 ° C prior to anaerobic treatment of sludge. ,
It has succeeded in greatly improving the solubilization rate in the anaerobic treatment process. Further, since the method of the present invention can be carried out simply by passing the sludge through a heating device and a crushing device, it is suitable for treating a large amount of sludge generated in a sewage treatment plant. Therefore, the present invention is extremely large in that it contributes to the industrial development as a sludge pretreatment method that eliminates the conventional problems.

[Brief description of drawings]

FIG. 1 is a graph showing the relationship between the heating temperature and MLVSS of sludge in the first embodiment of the present invention, and FIG. 2 is the second of the present invention.
5 is a graph showing changes in VSS of sludge in Example of FIG.

Claims (1)

[Claims] [Claim 1] Prior to anaerobically digesting sludge, 40
A pretreatment method for sludge, which comprises heating to ~ 120 ° C, pulverizing in this heated state to atomize, and then sending it to an anaerobic digestion process.