JPH01210100A - Anaerobic digestion of sludge - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a method for efficiently performing anaerobic digestion of sludge mainly composed of microorganisms, such as surplus sludge generated in a sewage treatment plant using an activated sludge method. It is something.

[Conventional technology]

In sewage treatment using the general activated sludge method, a large amount of initial settled sludge and surplus sludge are generated. These sludges have extremely high water content and are difficult to dewater by filtration.
As it is, it is difficult to dispose of or use it. Therefore, so-called anaerobic digestion treatment is often performed, which uses microorganisms to biochemically decompose the sludge to reduce the amount of solid matter as much as possible, and to effectively utilize the methane gas generated. However, conventional anaerobic digestion has a VS (organic matter) decomposition rate of about 50 to 55%, which is very inefficient, even with standard mesophilic digestion, that is, the digestion temperature is about 37° C. and the residence time is about 30 days. What is particularly difficult to break down in anaerobic digestion is
This is surplus sludge mainly composed of microorganisms.

Various attempts have been made to improve the inefficient anaerobic digestion of sludge. A typical method is to perform some kind of pretreatment on the sludge prior to anaerobic digestion to destroy the cell walls of organisms in the sludge, such as ultrasonic treatment (Japanese Patent Application Laid-open No. 76200/1983). , a method in which pressurization with methane gas is followed by depressurization treatment (Japanese Unexamined Patent Publication No. 56-40497).

[Problem to be solved by the invention]

An object of the present invention is to provide an efficient sludge anaerobic digestion method that is improved by new means that are based on any of the above-mentioned conventional pretreatment methods.

[Means to solve the problem]

The anaerobic digestion method provided by the present invention is characterized by applying a high voltage pulse to sludge prior to the anaerobic digestion treatment.

When a high voltage pulse is applied to sludge, most of the electrical energy is applied to the cell walls of microorganisms in the sludge and is converted into mechanical membrane compression energy, destroying the cell walls.

As a result, soluble proteins, sugars, nucleic acids, etc., which mainly consist of the cytoplasm, are eluted out of the cells and rapidly undergo anaerobic digestion.

The characteristics of the high voltage pulse necessary (or suitable) to cause the destruction of microbial cell walls as described above vary depending on the microbial concentration of the sludge to be treated, the concentration of coexisting inorganic electrolytes, etc., but generally fall within the following range. be. .

Electric field strength in sludge to be treated: 5 to 50 KV/e+a
Pulse width: 100 μSee or more (preferably 200 to 1000 μSee or more) The pulse waveform is preferably rectangular and about 14 knees, but is not limited to this. Note that depending on the application conditions of high voltage pulses, electrolysis of sludge may occur, but this only increases power consumption and is meaningless for destroying cell walls, so it is equivalent to continuous energization that causes electrolysis. It is desirable to avoid applying such pulses.

A method of applying high voltage pulses to sludge is to insert an electrode plate into a sludge container equipped with a stirring device so that microbial cells receive a high voltage pulse when they enter between the electrode plates. There is a method in which sludge is passed continuously or intermittently and subjected to high voltage pulses. The pulse application time depends on the pulse application method and conditions.
The arrangement is such that substantially all microbial cells in the sludge receive at least one (preferably several) pulses.

After the high voltage pulse treatment, the sludge is mixed with an appropriate amount of seed sludge and subjected to anaerobic digestion using a conventional method.

〔Example〕

After adjusting the concentration of surplus sludge from standard activated sludge collected from a municipal sewage treatment plant so that its organic matter (VS) concentration was 1.0%, it was placed in a 2,000 OOCC container and stirred under the following conditions. High voltage pulse treatment was performed for 20 minutes.

Processing liquid volume: 1,500 cc Electrode Double circular electrode (electrode spacing 4 am) 2 Applied voltage: 10,0 OOV Electric field strength: 25 KV/c
+a Pulse width: 5001ec Pulse interval:
0. After 15 ec digestion, twice the amount of anaerobically digested sludge was added to the sludge as seed sludge, and the sludge was subjected to mesophilic anaerobic digestion for 20 days.

For comparison, the untreated surplus sludge was also subjected to the same anaerobic digestion treatment.

The results are shown in Table 1, and the digestion efficiency was significantly improved by applying the high voltage pulse treatment.

Table 1 Measurement items Example Comparative example Organic matter (VS
) Decomposition rate (%) 55 41 Gas generation amount (m
l, /VS-g) 58th day 225 1301Oth day
330 20015th day 8
375 24520th day 8 4jD
290 Gas composition (%) Methane 61 57C0,333
6 [Effects of the Invention] As is clear from the results of the Examples, according to the present invention, anaerobic digestion of excess sludge can be performed extremely quickly and efficiently. Furthermore, since the high voltage pulse treatment adopted as a pretreatment means for sludge in the method of the present invention is a purely electrical treatment, it is possible to easily adjust the optimum treatment conditions according to changes in the composition of the sludge as long as a power supply is provided. There are advantages in that the processing device can be selected and that the processing device can be small and simple.

Claims (1)

[Claims] When anaerobically digesting sludge mainly composed of microorganisms, such as surplus sludge generated in sewage treatment by the activated sludge method, the sludge is treated by applying a high voltage pulse to the sludge prior to the anaerobic digestion treatment. Anaerobic digestion.