JPS6129794B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for biologically treating wastewater containing organic substances, such as fishery processing wastewater, human waste wastewater, and agricultural processing wastewater.

As is well known, as a biological treatment method for this type of wastewater, the activated sludge method, which consists of the steps shown in FIG. 1, has been used for a long time. In this method, wastewater is once stored in adjustment tank A, and after operations such as equalizing liquid properties, adding nutrients, and adjusting pH are performed as necessary, a certain amount of wastewater is continuously transferred to aeration tank B. Supply water. While the wastewater remains in the aeration tank B for a certain period of time, the organic substances in the wastewater are oxidized and decomposed by aerobic bacteria that are actively activated by the air sent in from the blower C, forming activated sludge (floc). , wastewater is sent to sedimentation separation tank D together with this activated sludge. Then, in the sedimentation separation tank D, the activated sludge and supernatant liquid are separated by residence for a certain period of time,
The supernatant liquid is discharged as treated water. On the other hand, a part of the settled activated sludge is returned to the aeration tank B by the sludge pump E and used for circulation, maintaining the activated sludge concentration in the aeration tank B and making it useful for oxidative decomposition by aerobic bacteria. There is. The remaining activated sludge returned to the aeration tank B is drawn out of the circulation system as surplus sludge and separated into liquid and solid by a sludge dehydrator F, etc., and the solid is disposed of by landfilling, dumping, etc.

In this type of activated sludge method, wastewater
When the BOD concentration is high, oxidative decomposition by aerobic bacteria does not proceed satisfactorily, so the predetermined BOD
When treating wastewater that exceeds the concentration using the activated sludge method, it is necessary to add a large amount of dilution water to reduce the BOD concentration. As the amount of wastewater due to this diluted water increases, aeration tank B etc. becomes larger and operation management becomes more complicated. This is accompanied by various drawbacks, such as an increase in the power cost of the blower C as the volume increases. Furthermore, although various adjustments of wastewater are carried out in adjustment tank A, sudden changes in the components and concentration of wastewater,
If there is a change in weather conditions or other physical and chemical conditions, the survival conditions for bacteria in the treatment system will change accordingly, making it impossible to perform smooth wastewater treatment. The drawback was that it required a great deal of effort to stabilize the liquid and produced a bad odor.

This invention was made in view of the above circumstances, and aims to reduce operating costs, downsize the equipment, and simplify operation management by treating wastewater extremely efficiently regardless of the BOD concentration. The purpose is to improve the stability of the treatment system, perform smooth wastewater treatment, and prevent the generation of bad odors.

The feature of this invention is that wastewater containing organic substances is sent in order from the adjustment tank to the anaerobic tank and then to the coagulation separation device, and in the coagulation separation device, the sludge is coagulated by adding a coagulant to purify the wastewater. In the anaerobic tank, aeration and agitation suitable for the proliferation of anaerobic bacteria including facultative anaerobic bacteria including Lactobacillus genus bacteria are carried out, and a part of the wastewater is separately taken out and C/ Adjustment of N ratio, addition of inorganic substances,
After aeration and agitation, the wastewater is returned to the aeration tank to promote the activation of bacteria in the wastewater and to stabilize the wastewater treatment system.

The method of this invention will be explained in detail below with reference to FIG.

In this invention method, wastewater is divided into a regulating tank 1, an anaerobic tank 2,
Coagulation separation device 3 and higher-order treatment process 4 if necessary
This process is followed by purification treatment.

The anaerobic bacteria that act in this wastewater treatment system are facultative anaerobic bacteria with partially aerobic properties, including bacteria of the genus Lactobacillus, such as genus Pediococcus, genus Streptococcus. , Bacillus
Any anaerobic bacterial group including bacteria belonging to the genus etc. may be used. Such anaerobic bacteria are introduced into the anaerobic tank 2 of the wastewater treatment system before the system starts operating, and from then on, those that have grown naturally in this layer 2 are used.

Any kind of wastewater, such as fishery processing wastewater, accumulated human waste wastewater, agricultural processing wastewater, or any other wastewater containing organic substances, can be treated by the method of the present invention.

This wastewater is first collected in the adjustment tank 1, where operations such as equalizing the liquid, adding nutrients, and adjusting the pH are performed as necessary. After the water has been retained for a predetermined period of time, a certain amount of water is continuously or all at once supplied to the anaerobic tank 2.

In the anaerobic tank 2, the wastewater supplied from the adjustment tank 1 is retained and aerated and stirred by air sent from the blower 5. This aeration provides a small amount of dissolved oxygen to the wastewater in order to proliferate facultative anaerobic bacteria including lactic acid bacteria, which are the main anaerobic bacteria living in the wastewater in the anaerobic tank 2. Moreover, since the purpose is to evenly distribute this dissolved oxygen in the wastewater, experience and experiments have shown that weak aeration, which is usually about one-tenth of the amount of aeration in the aeration tank in the conventional activated sludge method, is sufficient. It is clear that This is because if a larger amount of aeration is performed, although the wastewater is sufficiently agitated, the habitat conditions for facultative anaerobic bacteria will be impaired. By performing aeration suitable for these conditions, the inside of the anaerobic tank 2 is free from the lactic acid bacteria that were introduced before the start of operation of the wastewater treatment system, even though the wastewater is continuously supplied and discharged. Anaerobic bacteria, including facultative anaerobic bacteria, proliferate and are maintained at all times.

The wastewater in the anaerobic tank 2, in which anaerobic bacteria including facultative anaerobic bacteria including bacteria of the genus Lactic Acid bacteria live, is guided to the activation tank 7 by the pump 6 to improve the C/N ratio. After adjusting and adding inorganic substances and performing aeration and agitation under the same conditions in the anaerobic tank 2 for a predetermined period of time using air sent from the blower 5, the wastewater in the activation tank 7 is returned to the anaerobic tank 2. . The capacity of this activation tank 7 is usually anaerobic tank 2.
It may be about 1/100 to 1/1,000 of the capacity. or,
The C/N ratio is appropriately selected and adjusted within the range of 10 to 25 depending on the pollutant components of the wastewater. This adjustment of the C/N ratio is performed to activate the anaerobic bacteria contained in the wastewater and speed up their growth rate, but if the C/N ratio is high, it can be lowered by adding nitrogen components such as urea. If the C/N ratio is low, a carbon component such as waste molasses is added. Like the adjustment of the C/N ratio, the addition of inorganic substances is done to activate the anaerobic bacteria contained in the wastewater and increase their growth rate. Add a solution containing about 50% of other necessary salts to about 1/300 to 1/1000 of the volume of the activation tank 7. The standard time for the wastewater to remain in the activation tank 7 is about 10 times the division time of facultative anaerobic bacteria present in the wastewater, specifically about 2 hours and 30 minutes, but depending on the conditions of the wastewater and other factors. Extend or shorten the residence time as necessary for these reasons.
The wastewater in the anaerobic tank 2 is supplied to the activation tank 7 after the predetermined amount described above is supplied at once and subjected to the above-mentioned treatment. So-called batch treatment, in which the wastewater is returned to the atmosphere, is standard, but if the wastewater composition is not particularly suitable for the growth of anaerobic bacteria, a fixed amount may be supplied continuously. As mentioned above, the anaerobic bacteria contained in the wastewater treated in the activation tank 7 have been activated, and the state is most suitable for promoting microbial decomposition of organic matter. By returning the wastewater to the tank 2, the wastewater in the anaerobic tank 2 is brought into a state suitable for promoting microbial decomposition of organic matter, similar to the wastewater returned from the activation tank 7, that is, the anaerobic bacteria in the wastewater are activated. It becomes a state. The batch treatment of the wastewater in the activation tank 7 may be performed continuously depending on the composition of the wastewater, but as the various conditions of the wastewater change, there is a possibility that the treatment system will not be able to operate smoothly. It is also possible to perform the process continuously only once in a while. The temperature of the wastewater in the activation tank 7 needs to be within ±10°C of the temperature of the wastewater in the anaerobic tank 2, but is most preferably within ±30°C.
The temperature is between ℃ and 32℃.

Furthermore, depending on the nature of the wastewater or various circumstances, the regulating tank 1 and the anaerobic tank 2 may be combined into one regulating anaerobic tank that also serves as these two tanks 1 and 2. , which is included in the technical scope of the method of this invention.

In the coagulation separation device 3, wastewater in the anaerobic tank 2 and a flocculant are mixed to produce sludge. If this flocculant is added during the water supply process just before the wastewater is introduced into the coagulation and separation device 3, it will mix well with the wastewater, so that operations such as stirring in the coagulation and separation device 3 can be omitted. The most suitable flocculant is an effective combination of inorganic and organic flocculants, and the combination is adjusted depending on the wastewater conditions. The generated sludge is separated from the liquid part. This separation is the second
In the embodiment shown in the figure, a sedimentation separation tank is used, but the coagulation separation apparatus 3 is not limited to this, and separation methods using other mechanical or physical means are also included. . The liquid part separated from the sludge and the sludge are passed through the sludge dehydrator 8, and the solid part is discharged outside the treatment system.If the pollution concentration is below the regulation value, the remaining liquid part is directly passed outside the treatment system as treated water. However, if it exceeds the regulation value, it is treated in higher-level treatment process 4, such as sand filtration and rotating disks, to bring it below the regulation value, and then it is discharged outside the treatment system as treated water. . The sludge components generated in this higher-order treatment step 4 are mixed with wastewater from the adjustment tank 1 and returned to the anaerobic tank 2. Note that if the water content of the sludge separated from the liquid portion in the coagulation separation device 3 is high, the sludge may be passed through a sludge thickening device (not shown) before being applied to the sludge dehydrator 8. Further, it goes without saying that the aeration in the activation tank 7 including the anaerobic tank 2 may be performed by other means instead of the method of sending air from the blower 5.

As is clear from the above explanation, unlike the conventional activated sludge method, this method adds a flocculant to the wastewater inhabited by anaerobic bacteria, mainly facultative anaerobic bacteria, in the anaerobic tank 2. Just by doing this, the flocculation separation device 3
Since sludge (floe) can be generated in the process, wastewater can be treated regardless of its concentration. Therefore, since there is no need for dilution water to dilute wastewater, it is possible to downsize various devices, simplify operation management, eliminate the need for dilution water supply facilities, etc., and reduce the amount of aeration. Since only a small amount of energy is required, it is possible to reduce operating costs. Furthermore, even if the conditions of the wastewater suddenly change and the wastewater treatment system becomes abnormal, the wastewater adjusted in the activation tank 7 can be returned to the anaerobic tank 2. Since the microorganisms contained in the wastewater in the anaerobic tank 2 are adjusted to an activated state, that is, a state suitable for decomposing organic matter in the wastewater, the wastewater treatment system can be stabilized. . Therefore, compared to conventional methods, it is possible to significantly reduce the effort required to stabilize the system. Furthermore, since facultative anaerobic bacteria include bacteria of the genus Lactic acid bacteria, the action of these bacteria can reduce the occurrence of bad odors in the wastewater treatment system and in the sludge separated by the sludge dehydrator 8. It becomes possible to prevent this.

Examples of the method of this invention will be described below.

Wastewater: Process wastewater such as thawed mackerel and sardine water.

250t/day, COD concentration 300ppm, BOD concentration
900ppm Anaerobic tank...The air volume by the blower is 0.78m ³ /min.

The blower required for this air volume is 1.5KW x 1.

The required air volume in the conventional activated sludge method is 50
As m ³ /BODKg, 250t/day x 0.9Kg x 50m ³ ÷ 24 hours ÷ 60 minutes = 7.8m ³ /min The blower required for this air volume is 11KW x 1.

Coagulation separation device…The COD concentration at the outlet of this device is
The BOD concentration was 60ppm and the BOD concentration was 135ppm, so it was filtered through sand as a higher-level treatment process to reduce it to below the regulatory value and discharged as treated water.

In addition, as a flocculant, liquid sulfuric acid band 7.5%
10 ppm of solution and 0.3 ppm of medium anionic polymer were added.

Next, the wastewater from the anaerobic tank is supplied to an activation tank with a capacity of 1/300 of the anaerobic tank capacity, and aerated under the same conditions as the anaerobic tank, and the C/N ratio is adjusted to 15. Wastewater added with an inorganic solution meeting the above conditions in an amount of 1/400 of the capacity of the activation tank, and retained in the activation tank for approximately 2 hours and 30 minutes at a temperature of 30°C, which is 7°C higher than the temperature of the anaerobic tank. was returned to the anaerobic tank once a day. As a result, compared to the case without this treatment, the sludge production rate in the coagulation separation equipment was approximately 20% lower.
%, the required air flow in the anaerobic tank was reduced by approximately 10%, and at the same time the residence time in each tank was shortened by 15%.
Moreover, no bad odor was generated.

[Brief explanation of the drawing]

FIG. 1 shows a general flow sheet for the conventional activated sludge method, and FIG. 2 shows a flow sheet for the method of this invention. 1... Adjustment tank, 2... Anaerobic tank, 3... Coagulation separation device, 7... Activation tank.

Claims (1)

[Claims] 1 Wastewater containing organic substances is transferred from the adjustment tank to the anaerobic tank.
A biological treatment method for wastewater containing organic substances, in which the wastewater is sequentially sent to a coagulation separation device, and the wastewater is purified by flocculating the sludge by adding a coagulant in the coagulation separation device, and in the anaerobic tank, , performing aeration and stirring suitable for the proliferation of anaerobic bacteria including facultative anaerobic bacteria including Lactobacillus genus bacteria,
A part of the wastewater in the anaerobic tank where anaerobic bacteria including facultative anaerobic bacteria inhabit is taken out to an activation tank and the C/N ratio is adjusted to a range of 10 to 25, and about 50% of activated silicic acid is added. Other necessary salts for base 50
3% of the volume of the activation tank.
After adding 1/100 to 1/1,000 of the amount and performing aeration and stirring suitable for the proliferation of anaerobic bacteria including facultative anaerobic bacteria including Lactobacillus genus bacteria for about 2 hours and 30 minutes, this activation A biological treatment method for wastewater containing organic substances, characterized by returning tank wastewater to an anaerobic tank.