JPH08112600A - Combined septic tank - Google Patents

Abstract

PURPOSE: To provide a combination septic tank which makes it possible to stably obtain highly treated water, eliminates the need for specialized and high- leveled knowledge for operation and management, decreases the amt. of the initially settled sludge and excess sludge to be discharged, eliminates the need for a substrate for denitrification and pH control chemicals and is capable of reducing electric power consumption including driving power for aeration. CONSTITUTION: The SSs in living waste water are disintegrated by a solid disintegrating means P1 and is subjected to anaeration treatment in a liquefying tank 1 and are further treated in a UASB type anaeration tank 2. The anaerobically treated water is subjected to a nitrifying treatment in a nitrifying tank 3. The nitrified water is partly circulated to the anaeration tank 2 and the remaining part thereof is subjected to a sepn. of solid from liquid. The high-quality treated water is easily and efficiently obtd. by applying the UASB type anaeration tank to the combination septic tank in such a manner.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a combined septic tank, and more particularly, it is a combined septic tank for advanced treatment of domestic wastewater, which is an effective treatment means for easy energy management and less discharge of excess sludge. , UASB type (upflow type sludge blanket type) anaerobic tank is incorporated.

[0002]

2. Description of the Related Art Conventionally, a combined septic tank has been put into practical use as an apparatus for purifying household wastewater (wastewater discharged from kitchen, laundry, bath, etc.) and human waste in an undeveloped sewer system. There are various scales of combined septic tanks, for example, 5
A treatment amount of about 13 m ³ / day is used for household wastewater discharged from a house or facility of about 0 people, and a treatment amount of about 130 m ³ / day is used for 500 people.

By the way, since about 70% of the causes of pollution in public water bodies such as lakes and seas in Japan are occupied by domestic wastewater, as a part of pollution countermeasures, maintenance of merged septic tanks in undeveloped sewerage areas. Is being done. In particular, from the viewpoint of preventing eutrophication, the combined septic tank is intended for advanced treatment of nitrogen and phosphorus in addition to BOD. Treatment methods include anaerobic / aerobic activated sludge method, batch activated sludge method, intermittent aeration method, etc. In addition, many methods that incorporate nitrification, denitrification, and coagulation sedimentation have been certified by the Building Standards Law Construction Ordinance, and each has its own implementation effect.

[0004]

However, most of these treatment methods have excellent functions from the viewpoint of advanced treatment of nitrogen and phosphorus, but they are solved from the viewpoint of maintenance and energy saving. There are remaining issues to be solved. In particular,
It is requested to solve the following problems.

A high level of technology is required to operate the treatment facility. Many treatment methods require advanced operating conditions based on public sewage treatment and industrial wastewater treatment technology, and operators with specialized knowledge are required to perform maintenance. In particular, in removing nitrogen, it is necessary to adjust the residence time, load amount, sludge amount, circulation ratio, addition of denitrification substrate, pH control, etc. within appropriate ranges.

Maintenance such as discharge of excess sludge and chemical replenishment is required. The installation location of the combined septic tank will be in mountainous areas where it is difficult to install public sewers, agricultural and fishing villages on remote islands, or resort areas that are used only depending on the season.
Therefore, maintenance such as equipment inspection, chemical replenishment, water tank cleaning, and discharge of accumulated sludge is done at most about several times a year, especially in a small-scale septic tank that targets less than 50 people in half a year. It is necessary to make it about once. However, in the current treatment facility, the discharge of first settling sludge and excess sludge,
It is necessary to frequently perform maintenance such as replenishment of denitrification substrate (mainly methanol) and neutralizing agent (mainly caustic soda), backwash SS of filtration device and discharge of coagulated sediment sludge.

Aeration power is large and energy saving is insufficient. Since BOD and nitrogen removal mainly consist of long-term aeration, contact aeration, and intermittent aeration, aeration power is large and energy cost is high.

Therefore, the functions required of the combined septic tank are:
While stably obtaining high-grade treated water, the above problem has been solved, that is, it does not require specialized high-level knowledge for operation management, and the amount of initial sludge and excess sludge is small,
It does not require a denitrifying substrate or a pH adjusting chemical, and on top of that, the amount of electric power used including aeration power can be reduced.

An object of the present invention is to provide a combined septic tank which can satisfy all the above functions required for the combined septic tank.

[0010]

The combined septic tank of the present invention comprises:
A liquefaction tank having a solid material crushing means for introducing sewage of domestic system and anaerobic treatment, a UASB type anaerobic tank for introducing effluent water from the liquefaction tank for methane gasification, and treatment of the anaerobic tank A nitrification tank in which water is introduced and subjected to nitrification treatment, a solid-liquid separation means for performing solid-liquid separation on the treated water in the nitrification tank, and a circulation means for circulating a part of the treated water in the nitrification tank to the anaerobic tank,
It is characterized by comprising.

[0011]

[Function] As a treatment method satisfying some of the above-mentioned functions required for the combined septic tank, there is an anaerobic treatment which is widely applied in organic industrial wastewater treatment. It is generally said that the wastewater suitable for anaerobic treatment is a high-concentration wastewater having a BOD of several thousand mg / liter or more. However, by keeping the anaerobic bacteria at a high concentration in the reaction tank, the BO
Anaerobic treatment is possible even with low-concentration wastewater of D100-200 mg / liter. Further, the operating water temperature of the anaerobic reaction tank is preferably a temperature condition around 35 ° C., but it has been proved by many researchers that the temperature can be sufficiently treated even at around 20 ° C. by adjusting the load amount. Furthermore, it has been revealed that SS components in wastewater and organic excess sludge generated from a treatment facility are decomposed by anaerobic treatment if mechanically cut and sufficiently liquefied.

However, conventionally, the anaerobic treatment has not been positively adopted in the combined septic tank. It is considered that this is because the technology for keeping the anaerobic bacteria at a high concentration in the reaction tank has not been sufficiently established.

By the way, as a method for retaining anaerobic bacteria in the reaction tank, there are an anaerobic filter bed and an anaerobic biofilm filtration method in which the anaerobic bacteria are adhered and immobilized on the surface of a filter medium or a packing material, and the anaerobic bacteria are biologically self-organized. A typical example is the UASB method of granulating and holding it as fine granule-like sludge. Among these, in the anaerobic filter bed and biofilm filtration system, when a large amount of SS component is contained in the liquid to be treated, the SS adheres to the filter material or the filler to cause a clogging phenomenon, and the filter material or the filler layer is appropriately added. Need to backwash. Therefore, the mechanism may be complicated and maintenance may be complicated. On the other hand, the UASB method does not require a filter material or a filler layer, and sludge is flowing, so there is no concern of blockage even when SS or activated sludge flows in, and therefore the backwash mechanism is not required The equipment is simple and maintenance is easy.

The biggest problem of this UASB system is the setting of conditions under which granulated sludge can grow stably. However, even if it is difficult to grow the granulated sludge in the combined septic tank treatment facility, the surplus granulated sludge generated from the treatment plant that uses the UASB method is put into the reaction tank. By doing so, U can be easily
It is possible to launch the anaerobic treatment of ASB method to the stable operation range. At present, this means of introducing the granulated sludge has been proved to be effective in many industrial wastewaters.

The most important features of anaerobic treatment are energy saving and reduction of excess sludge generation. Further, by setting the operating load lower than the load amount commensurate with the water temperature of the waste water, pH adjustment in the reaction tank becomes unnecessary. Further, the anaerobic treatment continues for more than half a year, and even if the inflow of wastewater is stopped, the activity of the anaerobic bacteria remains, and even if new wastewater flows in, normal treatment can be performed in a short period of time. Utilizing this characteristic, anaerobic treatment is used for industrial wastewater treatment of seasonal operation, for example, beet sugar mill wastewater treatment. As described above, the anaerobic treatment is an effective treatment method because the operation management is easy.

From the above viewpoints, the present inventors can apply the UASB type anaerobic treatment to the combined septic tank facility, and the application of the UASB type anaerobic treatment is required for the combined septic tank described above. They have found that all the functions are realized, and have completed the present invention.

Hereinafter, the operating method and processing mechanism of the combined septic tank of the present invention will be described in detail with reference to the drawings.

FIG. 1 is a system diagram showing an embodiment of the combined septic tank of the present invention.

In the figure, 1 is a liquefaction tank, 2 is a UASB type anaerobic tank (hereinafter referred to as "UASB reaction tank"), 3 is a nitrification tank, 4
Is a first settling tank, 5 is a flocculation tank, 6 is a flocculant storage tank, and 7 is a second
Settling tank, P ₁ , P ₂ , P ₃ , P ₄ are pumps (however, P
₁ is a pump with a crushing function (hereinafter referred to as "crushing pump")), B is a blower, and 11 to 29 are pipes.

Since the combined septic tank shown in the figure is basically roughly divided into three mechanisms of anaerobic treatment, nitrification treatment and phosphorus removal, each mechanism will be described below. In the following, “L” means “liter”.

[Anaerobic treatment] The anaerobic treatment is carried out in a liquefaction tank 1 for liquefying SS and a UASB reaction tank 2 for carrying out a methane production reaction.

That is, the domestic waste water is introduced into the liquefaction tank 1 through the pipe 11. In the liquefaction tank 1, contaminants (food, paper, dust, sludge (SS), etc.) contained in the wastewater are crushed by the crushing pump P ₁ to a size of about 0.5 to 2 mm, and by the action of microorganisms. It decomposes and liquefies, and organic substances decompose into organic acids.

Incidentally, a part of the treated water in the nitrification tank 3 in the latter stage is circulated in the UASB reaction tank 2, and denitrification treatment is also carried out in the UASB reaction tank 2. Furthermore, the subsequent nitrification tank 3
Excess sludge is completely transferred to the liquefaction tank 1 and is crushed by the crushing pump P ₁ in the same manner as SS of waste water.

The BOD volume load of the UASB reactor 2 is
When the water temperature of the waste water is around 20 ° C, 0.5 Kg-BOD / m ³ · day or less (the residence time is 9 hours or more relative to the amount of domestic wastewater), and in the area where the water temperature is 25 ° C or more, 0.7 Kg-
It is possible to increase to around BOD / m ³ · day (residence time is around 6.4 hours with respect to domestic wastewater discharge).
Water temperature UASB in the reaction vessel 2, by using the pump in water forms as a circulating pump of the crushing pump P ₁ and UASB reactor 2 liquefaction tank 1, warmed by Joule heat generated from the motor or pump , The temperature of the water to be treated can be raised above the water temperature.

On the other hand, the residence time of the liquefaction tank 1 also serves to equalize the flow rate of the water to be treated, and a small-scale facility with less than 50 people needs approximately one day, and a medium- to large-scale facility requires 12 hours or more. It

70% or more of the BOD to be treated is decomposed by the anaerobic treatment in the liquefaction tank 1 and the UASB reaction tank 2, and the anaerobic treated water, that is, the BOD of the treated water in the UASB reaction tank 2 becomes 60 mg / L or less. . Moreover, the is denitrified circulating the treated water nitrification tank in the subsequent stage in the UASB reactor 2, 90% of NO ₃ + NO ₂ -N generated in the nitrification process is denitrified to nitrogen gas.

The nitrifying gas generated from the UASB reaction tank 2 is about 1 m ³ / day in a small-scale facility with less than 50 people.
Even with a large scale of about 500 people, since it is about 10 m ³ / day, the odorous exhaust gas generated from the liquefaction tank 1 and the piping 2
After being blown into the nitrification tank 3 through 7, 28 and 29 to perform biological deodorization treatment, it is suitable to perform atmospheric emission treatment together with aeration exhaust gas.

[Nitrification Treatment] After the anaerobic treatment in the liquefaction tank 1 and the UASB reaction tank 2, the BOD remaining in the treated water in the UASB reaction tank 2 is removed and the nitrogen in the waste water is reduced to NO ₃ +.
A nitrification tank 3 that converts NO ₂ -N is installed,
The treated water in the SB reaction tank 2 is introduced into the nitrification tank 3 through the pipe 14. The nitrification tank 3 is a complete mixing type aeration tank using activated sludge, a fixed bed in which nitrifying bacteria are adhered and fixed to a packing material, or a contact aeration method, but there is no concern of blockage for a long period of time, and vice versa. An aeration tank system that does not require cleaning is suitable. When the contact aeration method is adopted, it is preferable to select, for example, a sponge-like filler having a property of floating in the tank. The load of the nitrification tank 3 is 0.03 Kg-N / when the water temperature of the nitrification tank is set to 20 ° C.
low load near m ³ · day (around 40 hours as retention time)
It is preferable that the setting is made possible because stable nitrification and BOD removal are possible, and troubles such as bulking in the nitrification tank 3 that cause abnormal sludge properties are prevented.

The treated water in the nitrification tank 3 is introduced into the first settling tank 4 through the pipe 15, the supernatant water is discharged through the pipe 16, and a part of the supernatant water is circulated as a circulating liquid through the pipe 20 into the UASB reaction tank 2 for denitrification. The remaining portion is introduced into the coagulation tank 5 through the pipe 21.

The circulating water amount ratio to the UASB reaction tank 2 is
1: 2 to 1: 3 (2 to 3 times the amount of wastewater to be treated that is introduced into the system) is suitable. If this circulation ratio is excessively increased, the ORP in the UASB reaction tank 2 increases, which may adversely affect the anaerobic treatment. By operating the nitrification tank 3 under such conditions, the treated water quality from the nitrification tank 3 is BOD 10 mg / L or less, NH ₄ -N ₅ mg / L.
Hereinafter, it is possible to obtain high water quality of NO ₃ + NO ₂ -N of 10 mg / L or less.

The amount of surplus sludge generated in this nitrification tank 3 is U
30-60 g-SS / m ³ -wastewater per wastewater amount, including the amount of undecomposed SS flowing out from the ASB reaction tank 2, and the excess sludge generated is anaerobically treated through pipes 17 and 19 and is liquefied. It is transferred to the tank 1, pulverized and liquefied by the crushing pump P ₁ , and then decomposed in the UASB reaction tank 2.

A part of the sludge separated in the first settling tank 4 is returned to the nitrification tank 3 as return sludge through the pipes 17 and 18.

[Phosphorus Removal Treatment] The combined septic tank of the present invention is preferably provided with a step of removing phosphorus by subjecting nitrification-treated water to coagulation-precipitation treatment.

That is, in a facility intended for advanced treatment including removal of phosphorus, the treated water from the nitrification tank is dephosphorized, disinfected, and then discharged. As the dephosphorization treatment method,
In addition to the usual coagulation-sedimentation method, biological dephosphorization, crystallization dephosphorization, soil infiltration treatment, etc. are used, but from the viewpoint of practicality, coagulation-sedimentation treatment by adding an aggregating agent such as aluminum salt or iron salt is preferable.

In the illustrated combined septic tank, of the supernatant water from the first settling tank 4, the remaining part circulated to the UASB reaction tank 2 is
It is introduced into the coagulation tank 5 through the pipe 21, and the coagulant in the coagulant storage tank 6 is added through the pipe 22 to cause the coagulation reaction. The coagulation reaction liquid is introduced into the second precipitation tank 7 through the pipe 23, solid-liquid separated, and the treated water is discharged out of the system through the pipe 24. The coagulated sludge is discharged from the system through the pipe 25.

By the above phosphorus removal treatment, P 2 mg is further added.
/ L or less dephosphorized high-quality treated water is obtained.

In the combined septic tank of the present invention, in order to reduce the cost of electric power used for the above-mentioned treatment, it is preferable to actively use late-night electric power, which has a low electric power unit price, for further energy saving. For example, it is possible to store the domestic wastewater in the liquefaction tank from morning to evening, and to process the stored wastewater by using the midnight power from night when the inflow of wastewater is low to early morning. Especially, in small-scale septic tanks with less than 50 people, the basic wastewater to be treated is 12 to 13 m ³
Since it is / day, it can be stored during the day and processed and discharged at night.

[0038]

EXAMPLES The present invention will be described in more detail with reference to the following specific examples. However, the present invention is not limited as long as the gist thereof is not exceeded.
The present invention is not limited to the following examples.

Example 1 By the combined septic tank shown in FIG. 1 (however, the steps subsequent to the coagulation tank were omitted), it was synthesized mainly using dextrin, polypeptone, meat extract, ammonium chloride and monopotassium phosphate. , BOD: 200 mg / L, TOC:
100 mg / L, N: 50 mg / L, P: 10 mg / L
Was treated. The capacity of each tank is 5 for the liquefaction tank.
L, UASB reaction tank was 2 L, nitrification tank was 10 L, and the liquid flow rate was 5 L / day. A small gear pump was installed in the liquefaction tank to constantly mix and stir the liquid in the tank. U
The sludge in the UASB reaction tank that anaerobically treats the beer wastewater was put in the ASB reaction tank, and the sludge in the aeration tank of the municipal wastewater treatment plant was put in the nitrification tank. In the liquefaction tank, assuming the SS contained in the actual domestic wastewater and the surplus sludge in the nitrification tank, the sludge in the aeration tank of the city sewage treatment plant of 50 to 100 mg / L and the filter paper piece are mixed with the synthetic wastewater. The supplied SS was crushed with the gear pump installed and the inside of the tank was stirred. Further, a part of the treated water in the nitrification tank was circulated to the UASB type anaerobic tank at a circulation water amount ratio of 1: 2.

The combined septic tank was operated in a thermostatic chamber at 20 ° C.

As a result of continuous water flow for about 1 month under the above conditions, the BOD of the effluent from the UASB type anaerobic tank was 40 mg / L on average, and the BOD of the nitrification tank treated water was 5 mg.
/ L or less, NH ₄ -N is 3 mg / L or less, NO ₂ + NO
_3- N was 12 mg / L on average.

Furthermore, the circulating water amount ratio of the nitrification tank treated water is 1: 3.
(300% circulation) resulted in NO ₂ + N of treated water
The average amount of O ₃ —N was 8 mg / L.

During this operation, the water flow was stopped, and the water was re-flowed two weeks later, but five days after the re-water flow, the quality of the treated water recovered to the condition before the water flow was stopped.

The above treatment does not incorporate a phosphorus removal step by coagulation and precipitation of the nitrification tank-treated water, but when the sulfuric acid band of 50 ppm was added to the nitrification tank-treated water and sedimentation was performed, P of the obtained supernatant water was obtained. It became 1 mg / L or less.

From the above results, according to the combined septic tank of the present invention, the combined septic tank facility is applied with the anaerobic treatment of the UASB system, which has various features in terms of operation management, treatment equipment, and the like, and is highly advanced. It is clear that treated water is obtained.

[0046]

As described in detail above, according to the combined septic tank of the present invention, the excess sludge generated is only the coagulated sludge for removing phosphorus, and the discharge of the excess sludge is greatly reduced. Since the UASB method, which is easy to operate and does not worry about blockage in the tank, is used, maintenance is easy. By providing a sufficient load for the UASB type anaerobic tank and the nitrification tank, sufficient processing can be performed even at around 20 ° C. Since denitrification is performed in the UASB type anaerobic tank at the same time as the methane generation reaction, the denitrification tank becomes unnecessary. As treated water, BOD: 10 mg / L or less, N: 1
High-quality treated water of 5 mg / L or less can be stably obtained, and P: 2 mg / L or less can also be obtained by incorporating phosphorus removal by coagulation precipitation treatment. With such an effect, it becomes possible to treat domestic wastewater easily and efficiently.

[Brief description of drawings]

FIG. 1 is a system diagram showing an embodiment of a combined septic tank of the present invention.

[Explanation of symbols]

 1 liquefaction tank 2 UASB reaction tank 3 nitrification tank 4 first settling tank 5 coagulation tank 6 coagulant storage tank 7 second settling tank

Claims (1)

[Claims] 1. A liquefaction tank having a solid material crushing means for introducing anaerobic treatment of domestic wastewater, and a UASB type anaerobic tank for introducing effluent from the liquefaction tank to perform methane gasification treatment. A nitrification tank in which the treated water of the anaerobic tank is introduced to perform nitrification treatment, a solid-liquid separation means for solid-liquid separation of the treated water of the nitrification tank, and a portion of the treated water of the nitrification tank is circulated to the anaerobic tank. A combined septic tank comprising: