JPS5845797A - Anaerobic digestion of highly-concentrated organic waste water - Google Patents

Abstract

PURPOSE:To enhance the efficiency of anaerobic digesting reaction, by anaerobically digesting highly-concentrated organic waste water in a first digesting vessel, concentrating digestive fluid from the first digesting vessel with a centrifugal concentrator, and returning the concentrated liquid to the first digesting vessel. CONSTITUTION:Highly-concentrated organic waste water (a) such as night soil is anaerobically digested in a first digesting vessel 1, the resulting digestive fluid is concentrated by a centrifugal concentrator 2 without being brought into contact with oxygen in air, and at least a part of the concentrated liquid is returned to the first digesting vessel 1 while the remainder is discharged as excess sludge (e). As a result, a condition in each vessel comes to the optimum for digestion, so that the efficiency of digestion is remarkably improved. Consequently, the method can be applied for difficulty decomposable stroma-contg. waste water or highly-loaded operation, and the reduction of the total volume can make the size of installation small.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for anaerobically digesting highly concentrated organic wastewater such as human waste.

In the anaerobic digestion method applied to highly concentrated organic wastewater, the substrate and anaerobic bacteria are brought into contact with each other by heating and stirring.
Treatment is carried out by: promoting the decomposition of substrates and the production of metabolic products such as methane gas, and separating the sludge containing a large amount of anaerobic bacteria from the desorbed liquid. This method C
A part of the underlying processing process is shown in FIG. The raw water is first subjected to anaerobic digestion treatment in the first digestion tank 1, and then sent to the second digestion tank, where the digested sludge and the desorbed liquid are separated. The desorbed liquid is then sent to the next treatment step, and a portion of the digested sludge is returned to the first digestion tank 1. In the conventional method, the separation between the digested sludge and the desorbed liquid is achieved by the sedimentation separation effect caused by standing still, so the separation effect is often not sufficient even after a long residence time, and the desorbed liquid There is also a drawback that a large amount of solid matter flows out. In particular, if the substrate in the liquid to be treated is difficult to decompose and the growth rate of anaerobic bacteria is slowed down, the flow of bacteria into the desorption liquid may lead to overload of the digestion process and cause a decrease in digestion efficiency. Become. Furthermore, if the sedimentation separation time is unnecessarily prolonged in order to prevent the outflow of bacteria, the frequency of scum generation may be increased and gas generation may be suppressed.
Other drawbacks arise, such as the accumulation of solids such as sand mixed in the liquid to be treated, reducing the effective volume of the paddle.

An object of the present invention is to provide an anaerobic digestion method that can increase the efficiency of the anaerobic digestion reaction and reduce the burden of subsequent processing without the above-mentioned drawbacks.

Next, an example of the steps of the method of this invention will be explained with reference to the drawings. In FIG. 2, reference numeral 1 indicates the first digester, 2 indicates the centrifugal P:A1m compressor, and 3 indicates the second digester.
It communicates with the upper part of the first digestion tank 1 via.

Highly concentrated organic wastewater such as human waste is first introduced into the first digestion tank 1 and digested under anaerobic conditions to perform methane fermentation, and the digested liquid is centrifugally filtered and concentrated 82. A part of the sludge is returned to the first digestion tank 1, and the remainder is discharged as surplus sludge. Also, the r liquid is the second
Digested sludge is sent to the cypress, where it is further digested and the digested sludge is separated by precipitation. The desorbed liquid generated here is sent to the subsequent treatment process, and the digested sludge is discharged as surplus sludge together with the concentrated liquid from the centrifugal filtration thickener 2. however,
The second digestion tank 6 may not be provided.

An example of a specific structure of the centrifugal filtration concentration 82 is shown in FIG. In FIG. 2, a basket 13 supported by a rotating shaft 12 is accommodated in a housing 11 having an airtight structure, and a P cloth 14 is arranged along the inner surface of the basket 13. A mechanical seal 15 is provided between the rotating shaft 12 and the housing 11 to maintain airtightness within the housing 11. The digestive fluid to be treated is supplied to the supply pipe 1.
6 and is supplied to the center of the P cloth 14. Since the rotating basket 13 and the P cloth 14 have an upside-down truncated conical shape and are rotating at high speed, the liquid in the digestive juices passes through the small holes of the R cloth 14 and the basket 13 due to the action of centrifugal force. The solid content is released into the P liquid chamber 17 in the radial direction, and the solid content moves on the P cloth 14 in the direction away from the center of rotation C (upward in FIG. 3) due to the action of centrifugal force. The concentrate is discharged into the separated concentrate chamber 19. As a result, solid-liquid separation of the digestive fluid is efficiently performed, the concentrated liquid containing a large amount of digested sludge is taken out via the pipe 20, and the P liquid is sent to the second digestion tank 3 via the pipe 21.

Furthermore, the inside of the housing 11 is connected to the first
Since it communicates with the upper part of the digestion tank 1, it is filled with gas mainly composed of methane gas generated in the first digestion tank. Therefore, the liquid passing through the centrifugal filtration concentration 1124' does not come into contact with oxygen in the air.

The reference numeral 22 indicates a cleaning pipe provided with a large number of nozzles 23, which is used to interrupt the work and perform cleaning when the P cloth 14 or the like becomes clogged.

In order to carry out methane fermentation efficiently in the first digestion tank 1, it is important to maintain the microbial concentration in the tank at a high level, to reliably maintain anaerobic conditions, and to stir well. According to this invention, the digestive fluid taken out from the first digestion tank 1 is concentrated in the centrifugal compressor 2 and then returned, so that the solids concentration in the first digestion tank 1 is maintained at a high level (for example, M
L88 can be maintained at 4 degrees or higher, and sufficient stirring can be performed. In addition, since the inside of the centrifugal filtration concentrator 2 is kept airtight, air will not get mixed in and the activity of methane-producing bacteria will not be inhibited. Since the generated P liquid undergoes digestion and precipitation treatment in the second digestion tank 6, there is no problem in processing the R liquid even if some solid matter is mixed in.Therefore, a somewhat coarse mesh material is used as the P cloth 14. This reduces the chance of clogging and allows for stable continuous operation.Furthermore, even if cleaning water is supplied to the pipe 22 during operation, the cleaning waste water will be a concentrated liquid. The medium ζ= is not mixed in and is discharged together with the P solution, so ・return concentrated liquid)
There is no effect.

As described above, according to the present invention, the digestive juice from the first digestion tank is concentrated using a centrifugal superconcentrator, and the concentrated liquid is returned to the first digestion tank, so that the conditions in each digestion tank are becomes optimal for digestion, and digestion efficiency is greatly improved. Therefore, it can handle wastewater containing difficult-to-decompose substances and high-load operation, and it is also possible to downsize the equipment by reducing the total capacity.Furthermore, the desorbed liquid, such as 88 and BOD, can be reduced in concentration. As a result, the load on the secondary processing system is reduced.

[Brief explanation of the drawing]

Fig. 1 is a flow sheet showing the steps of a conventional anaerobic digestion method, Fig. 2 is a flow sheet showing an example of the steps of this invention method, and Fig. 3 is a schematic diagram of the centrifugal filtration concentrator used in this invention. FIG. 1... First digestion tank, 2... Centrifugal filtration and concentration device, 6.
...Second digestion tank, 4.Communication pipe, 11.Housing, 12.Rotating shaft, 16.j.basket, 14.
... P cloth, 15... Mechanical seal, 16... Supply pipe, 17... r liquid chamber, 18... Partition wall, 19...
...Concentrate chamber, 26...nozzle. Patent applicant Nishihara Environmental Health Research Institute Co., Ltd.

Claims (1)

[Claims] (1) High-concentration organic wastewater is anaerobically digested in the first digestion tank, and the digested liquid is reduced by centrifugation and over-water reduction without contacting with oxygen in the air. A method for anaerobic digestion of highly concentrated organic wastewater, characterized in that a portion of the wastewater is returned to the first digestion tank. 1) The high-concentration organic compound as described in Claim 1, characterized in that the P solution from the centrifugal filtration and concentration machine is supplied to a second digestion tank for anaerobic digestion, and the digested sludge is separated by sedimentation. Methods of anaerobic digestion of wastewater.