JPH0438477B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] 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. [Prior Art] In sewage treatment using a general activated sludge method, a large amount of initial settling sludge and surplus sludge are generated.
These sludges have a very high water content and are difficult to dewater by filtration, so they are difficult to dispose of or use as they are. 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 extremely inefficient, even with standard mesophilic digestion, that is, a digestion temperature of about 37° C. and a residence time of about 30 days. Excess sludge, which is mainly composed of microorganisms, is particularly difficult to decompose in anaerobic digestion. 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 microorganisms in the sludge. There is a method of pressurizing with methane gas followed by depressurization treatment (Japanese Patent Application Laid-open No. 40497/1983). [Problems 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 novel means different from any of the conventional pretreatment methods described above. [Means for Solving the Problems] 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 are generally as follows: in range. Electrolytic strength in sludge to be treated: 5 to 50 KV/cm Pulse width: 100 μSec or more (preferably 200 to 1000 μSec or more) The pulse waveform is preferably rectangular, 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 continuous energization that causes electrolysis is not recommended. It is desirable to avoid applying pulses that are equal to . As a method of applying high voltage pulses to sludge,
A method in which electrode plates are inserted into a sludge container with an attached stirring device so that microbial cells receive high voltage pulses when they enter between the electrode plates, and the sludge is continuously or intermittently passed between the electrode plates. There are methods such as applying high voltage pulses. Depending on the pulse application method and conditions, the pulse application time is such that substantially all microbial cells in the sludge are
The device is set to receive several pulses (preferably several times). The sludge that has undergone the high voltage pulse treatment 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 of 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 2000 c.c. container, and the following was carried out while stirring. High voltage pulse treatment was performed for 20 minutes under the following conditions. Processing liquid volume: 1500c.c. Electrode: Double circular electrode (electrode spacing 4mm) Applied voltage: 10000V Electric field strength: 25KV/cm Pulse width: 500μSec Pulse interval: 0.1Sec After treatment, double the amount of anaerobic digestion is applied to the sludge. The finished sludge was added as seed sludge and subjected to mesophilic anaerobic digestion for 20 days. For comparison, the untreated excess 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.

〔Effect 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] 1. A sludge characterized by applying a high voltage pulse to the sludge prior to the anaerobic digestion treatment of sludge mainly composed of microorganisms, such as surplus sludge generated in sewage treatment using the activated sludge method. anaerobic digestion method.