JP4513368B2 - Sewage treatment method and apparatus - Google Patents

Description

  The present invention relates to a method and apparatus for anaerobic biological treatment of sewage after anaerobic biological treatment when the sewage flow rate is less than or equal to a predetermined flow rate. The present invention relates to a sewage treatment method and apparatus that are reduced in number.

  In the sewage treatment method in which sewage is aerobically treated by aerobic treatment and then settled and separated, and part of the sludge is returned to the biological treatment unit, anaerobic treatment is performed before the aerobic treatment. It is well known that the settling property of activated sludge is improved.

In JP-A-5-192688, in an activated sludge treatment apparatus for sewage in which sewage is anaerobically treated in an anaerobic tank and then aerobically treated in an aerobic tank, a buffer tank is provided in parallel with the anaerobic tank in the previous stage. Providing anaerobic tank effluent and buffer effluent both to the aerobic tank; determining the diversion ratio between the anaerobic tank and the buffer tank based on the oxygen utilization rate in the aerobic tank; It is described that even when the sewage flow rate suddenly increases, the load on the anaerobic tank and the aerobic tank is prevented from rapidly increasing.
JP-A-5-192688

  In the activated sludge treatment method in which sewage is treated with aerobic organisms and then solid-liquid separated in the final sedimentation basin (final settling), the anaerobic treatment is carried out before the aerobic treatment, so However, when the sewage flow rate increases due to rainfall or the like, the amount of sludge outflow from the anaerobic organism treatment section increases, and the sludge enters the outflow water from the final settlement. In the sewage treatment method disclosed in JP-A-5-192688, the oxygen utilization rate of the aerobic tank is measured, and the diversion ratio between the buffer tank and the anaerobic tank is controlled based on the result. When this increases, a control delay occurs, and a large amount of sludge flows out of the sedimentation basin.

  An object of the present invention is to solve the above-mentioned conventional problems and to provide a sewage treatment method and apparatus in which sludge outflow from final settlement is small even when the sewage flow rate is rapidly increased due to rainfall or the like.

In the sewage treatment method of the present invention, after sewage is precipitated, the supernatant water is biologically treated in a biological treatment unit, the treated liquid is solid-liquid separated into treated water and sludge, and a part of the separated sludge is biologically treated. In the sewage treatment method to be returned to the inlet side of the part, as the biological treatment part, a pre-stage biological treatment part capable of both anaerobic treatment and aerobic treatment and a post-stage biological treatment part for aerobic treatment are provided. When the flow rate of the supernatant water is equal to or lower than a predetermined flow rate, the front biological treatment unit is placed in an anaerobic treatment state, and the entire amount of the supernatant water is circulated in this order through the front biological treatment unit and the rear biological treatment unit, When the flow rate of the supernatant water exceeds the predetermined flow rate, the pre-stage biological treatment section is brought into an aerobic treatment state, and a part of the supernatant water is circulated in this order through the pre-stage biological treatment section and the post-stage biological treatment section. The remainder of the supernatant water is not passed through the previous biological treatment section. It is characterized in that to flow into the processing unit.

In addition, as an aeration member for performing an aerobic treatment in this pre-stage biological treatment unit, air is blown into the inside and a cylindrical support body having a passage for guiding the air to the outer peripheral surface, and the support body A thing provided with the elastic envelope which surrounds the outer periphery, and the slit for air blowing provided in this envelope is suitable .

Sewage treatment apparatus for the onset Ming, a primary sedimentation, and any biological treatment also possible preceding biological treatment tank anaerobic and aerobic accept supernatant water from the primary sedimentation, the front stage biological treatment tank In a sewage treatment apparatus having an aerobic post-stage biological treatment tank that accepts the biological treatment water and a final sedimentation basin that accepts the biological treatment water of the post-stage biological treatment tank, the supernatant water from the first sedimentation basin has a predetermined flow rate or less. Sometimes, the pre-stage biological treatment tank is placed in an anaerobic treatment state, and the whole amount of the supernatant water is circulated in this order through the pre-stage biological treatment section and the post-stage biological treatment section, and the supernatant water from the first sedimentation basin is When the flow rate is exceeded, the pre-stage biological treatment tank is made aerobic, and the predetermined flow rate of the supernatant water is circulated in this order through the pre-stage biological treatment section and the post-stage biological treatment section, and the remaining portion of the supernatant water Is passed through the previous biological treatment tank. In which it characterized in that a means for guiding the subsequent biological treatment tank without.

In the sewage treatment method of the present invention, most of the year is when the flow rate of the supernatant water is equal to or lower than the predetermined flow rate, and the supernatant water is anaerobically treated after being anaerobically treated. The sludge produced has good sedimentation properties .

In the present invention, when the supernatant water flow rate exceeds a predetermined flow rate, a part of the supernatant water is circulated to the preceding biological treatment section, and the remaining portion is passed through the preceding biological treatment section without passing through the previous biological treatment section as in the first invention. Introduce to the department. Also in this case, the activated sludge with good sedimentation formed when the solid content concentration in the effluent from the latter biological treatment section is low and the supernatant water flow rate is below the predetermined flow rate is retained. A treated water having a low solid content is obtained.

In inventions of this, when the upper supernatant water flow exceeds a predetermined flow rate, it performs aerobic treatment even in front biological treatment unit. Thus will be aerobic treatment of BOD components even in front biological treatment section is carried out, the solubility BOD concentration in the treated water is low down.

In inventions of this, when performing aerobic treatment in the preceding paragraph biological treatment unit performs air diffusion from the air diffuser member provided in the preceding stage biological treatment unit. This aeration member is not used (vented) when the previous biological treatment section is in an anaerobic treatment state, and there is a possibility that sludge is solidified inside and clogged when not in use. Therefore, the air diffuser is preferably a structure that does not allow water to enter inside when it is not ventilated. Specifically, air is blown into the inside and a cylindrical shape having a passage that guides the air to the outer peripheral surface. And the elastic enveloping body surrounding the outer periphery of the supporting body, and the air blowing slit provided in the enveloping body are suitable.

Hereinafter, the present invention will be described in more detail with reference to the drawings. FIG. 1A is a system diagram of a sewage treatment method and apparatus according to a reference example , and FIG. 1B is a system diagram of a sewage treatment method and apparatus according to an embodiment of the present invention.

  In FIG. 1A, sewage is introduced into a first sedimentation basin (primary sedimentation) 1 and separated into solid and liquid, and supernatant water is introduced into a first tank 3 for anaerobic treatment as a pre-stage biological treatment section via a pipe 2. Is done. The first tank 3 is provided with a stirrer 4. The water that has been anaerobically treated in the first tank 3 is introduced into the second tank 5 as a post-stage biological treatment unit, and is subjected to aerobic treatment by aeration from the aeration tube 6. The water subjected to aerobic treatment is introduced into a final sedimentation basin (final sedimentation) 7 and subjected to solid-liquid separation treatment, and the supernatant water flows out as treated water. Part of the sludge settled in the final sedimentation 7 is returned to the first tank 3 through the sludge return pipe 8, and the excess sludge is discharged as excess sludge from the pipe 8a.

  When the supernatant water flow rate is equal to or lower than the predetermined flow rate, the whole supernatant water is anaerobically treated in the first tank 3 and then aerobically treated in the second tank 5 according to the above flow. Since it is generally due to rainfall that the supernatant water flow rate exceeds the predetermined flow rate, the aerobic tank (second tank) is used for the most part of the year after anaerobic treatment. Sedimentation of sludge in the effluent of tank 5) will be good.

  When the supernatant water flow rate exceeds a predetermined flow rate, a part of the supernatant water is directly introduced into the second tank 5 via the bypass pipe 9 branched from the pipe 2 without passing through the first tank 3. The pipe 9 is provided with a flow rate adjusting valve 10.

  The flow rate of the supernatant water exceeding the predetermined flow rate is generally due to rain. Therefore, the water flowing through the bypass pipe 9 is diluted with rain water and has a very low solid content. Therefore, the mixed liquid flowing into the second tank 5 from the first tank 3 is diluted with the supernatant liquid flowing in by bypass, the solid content concentration becomes low, and the flow rate flowing out from the second tank 5 increases, but the outflow Since the solid content concentration in water is low, the solid content load of the final sediment 7 does not increase greatly, and the solid content concentration in the treated water from the final sediment 7 is also low, which is not much different from that before rainfall. The sedimentation property of sludge is also well maintained by a temporary change in the processing flow.

FIG. 1 (b) shows an embodiment of the present invention.

  In this embodiment, instead of the first tank 3, a first tank 13 including a stirrer 4 and an air diffuser 11 is provided as a pre-stage biological treatment unit. Other configurations are the same as those in FIG.

  In the flow of FIG. 1 (b), when the supernatant water flow rate is equal to or lower than the predetermined flow rate, the same processing as in FIG. 1 (a) is performed. That is, the entire amount of the supernatant water is sent to the first tank 13. Moreover, in the 1st tank 13, aeration is not performed at all and the 1st tank 13 becomes an anaerobic tank like the 1st tank 3. FIG. Therefore, since the whole amount of sewage is subjected to an aerobic treatment after being subjected to an anaerobic treatment, the sludge settling property at the final settling 7 is improved.

  When the supernatant water flow rate exceeds the predetermined flow rate, a part of the supernatant water is directly introduced into the second tank 5 through the bypass pipe 9 as in FIG.

  The processing in FIG. 1B is different from the processing in FIG. 1A because when the supernatant water flow rate exceeds a predetermined flow rate, air is diffused from the air diffusing pipe 11 and the first tank 13 An aerobic process is performed. When the aerobic treatment is performed in the first tank in this way, the water flowing to the second tank 5 through the first tank 13 is subjected to the aerobic treatment over two stages, and the treated water flowing out from the final settling 7 The soluble BOD concentration of the is reduced. In this case, anaerobic treatment is not performed in the first tank 13, but the supernatant water is anaerobically treated after being anaerobically treated during a period in which the supernatant water flow rate is equal to or lower than a predetermined flow rate. As described above, the solubility BOD concentration in the treated water is lower than that in FIG.

FIG. 1 (b) is a simple configuration example of the sewage treatment method of the present invention, and the present invention can take other modes such as a configuration in which tanks are provided in multiple stages. 2 (a) and 2 (b) show that the former biological treatment section and the latter biological treatment section are each composed of two tanks, FIG. 2 (a) relates to a reference example , and FIG. 2 (b) shows the present invention. According to the embodiment.

  In FIG. 2A, the effluent from the first tank 3 is introduced into the anaerobic tank 3A having the stirrer 4 and subjected to the second stage anaerobic treatment, and then introduced into the aerobic tank 5A. This effluent is treated and introduced into the second tank 5. When the supernatant water flow rate from the first sedimentation 1 is less than or equal to the predetermined flow rate, the supernatant water is not branched to the bypass pipe 9, and when the supernatant water flow rate exceeds the predetermined flow rate, a part of the supernatant water passes from the pipe 2 to the bypass pipe 9. Through the second tank 5. The other configuration in FIG. 2A is the same as that in FIG. 1A, and the same reference numerals denote the same parts.

  This sewage treatment method shown in FIG. 2 (a) also has the same effects as those shown in FIG. 1 (a). In addition, the quality of treated water improves by performing anaerobic treatment and aerobic treatment in multiple stages.

  In FIG. 2 (b), the entire amount of the effluent from the first tank 13 is introduced into a tank 13A equipped with the stirrer 4 and the air diffuser 11 as in the first tank 13, and the effluent from the tank 13A is aerobic. Introduce into tank 5A. The outflow water from the aerobic tank 5A is introduced into the second tank 5.

  Also in FIG. 2 (a), when the supernatant water flow rate from the initial sedimentation 1 is equal to or lower than the predetermined flow rate, the supernatant water is not branched to the bypass pipe 9, and the tanks 13 and 13A are not diffused and anaerobic treatment is performed. .

  When the supernatant water flow rate exceeds a predetermined flow rate, a part of the supernatant water is introduced into the second tank 5 from the bypass pipe 9. And the tanks 13 and 13A are diffused from the diffuser tube 11, and perform aerobic treatment. The other structure of FIG.2 (b) is the same as FIG.1 (b), and the same code | symbol has shown the identical part.

This sewage treatment method in FIG. 2B also provides the same operational effects as in FIG. In addition, the solubility BOD density | concentration of treated water will become low by performing an aerobic process in multistage further. In FIG. However, there may be one tank or three or more tanks. The latter biological treatment section may also be one tank or three or more tanks.

  In FIGS. 2 (a) and (b), a part of the supernatant water is introduced only from the bypass pipe 9 into the second tank 5, but it may be introduced into the tank 5A or only into the tank 5A. Also good. Although not shown, when the latter biological treatment section is composed of three or more tanks, the supernatant water may be divided and injected into only a part of these tanks in addition to the first tank 13. The supernatant water may be divided and injected into the tank.

  In FIGS. 1 and 2, each tank is illustrated as being independent, but each tank may be formed by partitioning one tank body.

  Various kinds of diffuser tubes 6 can be used. In the tanks 13 and 13A of FIG. 1B and FIG. 2B, a stirrer with an air supply function can be used as a device having both functions of the stirrer 4 and the diffuser tube 11.

  The diffuser tube 11 used in the tanks 13 and 13A shown in FIGS. 1B and 2B is not vented when anaerobic treatment is performed in the tanks 13 and 13A. When the state where the supernatant water flow rate is equal to or lower than the predetermined flow rate continues, the air diffuser is not vented over a long period of time. Therefore, sludge is solidified inside, and there is a possibility that the air diffuser during the next venting may be hindered. Therefore, the air diffuser 11 is preferably configured so that the sludge in the tank does not enter inside when not vented. FIG. 3 shows an example of an air diffuser having such a sludge invasion preventing characteristic.

  As shown in the figure, a hollow cylindrical support body 21 having one end closed and a connection port 22 connected to the air feeding header 5 at the other end is provided between the both end portions. It has the notch opening part 23 by which the half circumference was cut. An elastic tube (encapsulated body) 24 in which a large number of fine slits 25 are engraved wraps almost the entire length of the outer periphery of the support. Reference numeral 26 denotes a retaining ring for fixing each end of the tube to the outer periphery of each end of the support.

  The slits 25 formed in the tube 24 are negatively connected to the slits 25b arranged at an angle α (30 to 60 °) on the positive side with respect to the circumferential direction E, as shown in FIGS. The slits 25b are arranged at an angle α (30 to 60 °) on the side, the slits 25a and the slits 25b are parallel to each other, and the slits 25b are arranged adjacent to the extending direction of the slits 25a. A pattern in which slits 25a are arranged adjacent to the extending direction is preferable. That is, when the tube 24 supplied with air is expanded into the support body, the slits 25a and 25b have the same angle with respect to the circumferential direction, so that the slits are opened to the same extent, and bubbles are generated uniformly from all the slits. In addition, since all the slits act as effective slits and ventilate evenly, the airflow resistance is reduced, and furthermore, since the airflow per each slit is small, fine bubbles are continuously generated. This is because, since the local weakened portion where the slit direction is concentrated does not occur, the tube generally has a high tensile strength in both the circumferential direction and the axial direction. The tube material is soft vinyl chloride resin, the wall thickness is 0.8 mm, the angle α with respect to the circumferential direction of the slits 25 a and 25 b is 45 °, the length of each slit is 1.0 mm, and the interval between the slits is X = It is preferable that 3.7 mm, Y = 3.2 mm, the length of the tube, and the wall diameter correspond to the length of the support and the outer diameter.

  Therefore, when the connection port 22 of the support 21 is connected to an air supply header (not shown) and air is supplied from the air supply header to the inside of the support 21, the air that exits from the notch opening 23 of the support causes the slit 25. The tube 24 having swells, and all slits carved around the tube are pushed open by air, and air is blown out as bubbles from the entire length of the tube through the slit. When the air supply is stopped, the slit 25 is closed and the sludge does not enter, so that the slit and the inside of the air diffuser are not blocked by the sludge.

Examples , reference examples and comparative examples will be described below.

Reference example 1
In the sewage treatment method shown in FIG. 2A, the area or volume of each tank was as follows.
Initial sedimentation tank area: 100m2
Pre-stage biological treatment section, tank 3 volume: 150 m3
Tank 3A volume: 150m3
Subsequent biological treatment section, tank 5A volume: 300 m3
Tank 5 volume: 300m3
Final sedimentation tank area: 150m2

  The clear sky continued for 2 months. During this period, CODcr was 125 mg / L on average, MLSS was 1400 mg / L in the second tank 5, and the supernatant water flow rate was 160 m3 / Hr.

  The amount of aeration in each tank 5A, 5 was 1.1 m3 / m3 · hr (at 25 ° C.). The flow rate of the bypass pipe 9 was set to zero. The diffuser tube was a porous ceramic tube.

The quality of the treated water during this fine weather period was as follows.
SVI (sludge sedimentation) 170 [-]
SS concentration at the outlet of the aeration tank (second tank 5) 1400 [mg / L]
SS concentration of final settled runoff water 2.7 [mg / L]
BOD concentration of final runoff effluent 1.1 [mg / L]
Dissolvable BOD concentration of final sediment runoff water 0.52 [mg / L]

  After that, there was rain and the supernatant water flow increased to 320m3 / Hr. Of that, 200m3 / Hr was sent to the first tank 3, and the remaining 120m3 / Hr was sent directly from the bypass pipe 9 to the second tank 5. It was. Table 1 shows the operation results at this time.

Comparative Example 1
Reference Example 1 sewage treatment apparatus having the same configuration as the juxtaposed and sewage treatment device of Reference Example 1, was operated at the same flow into the sewage flow in the one time. However, in this comparative example 1, the bypass flow rate was set to zero even during rainfall. FIG. 4A shows the flow of the comparative example 1. Table 1 shows the operation results during the rain. In addition, the driving result at the time of fine weather was the same as the case of the reference example 1.

Example 1
Was treated by passing the sewage in Reference Example 1 and the same flow rate sewage treatment apparatus shown in FIG. 2 (b) provided in parallel with sewage treatment apparatus of Example 1. This sewage treatment apparatus has the same configuration as that of Reference Example 1 except that in the sewage treatment apparatus of Reference Example 1 (FIG. 2 (a)), aeration pipes 11 are installed in tanks 3 and 3A to form tanks 13 and 13A, respectively. belongs to. The amount of air supplied to the air diffuser 11 in each of the tanks 13 and 13A was 1.1 m 3 / m 3 · hr (at 25 ° C.). The bypass flow rate during rainfall was the same as in Reference Example 1. Table 1 shows the operation results during rainfall. In addition, the driving result at the time of fine weather was the same as the reference example 1.

Comparative Example 2
In the sewage treatment apparatus provided side by side with the sewage treatment apparatus of Example 1 , the operation was performed at the same time. FIG. 4B shows a flow at this time. Table 1 shows the operation results during rainfall. In addition, it was set as the all tank aerobic operation at the time of fine weather, and 120 m <3> / hr of the supernatant water was sent to the 2nd tank 5 from the bypass piping 9 similarly to Example 1 with the aerobic operation of the whole tank at the time of raining.

Considerations on the results of Example 1 , Reference Example 1, and Comparative Examples 1 and 2 are as follows.
(1) In Comparative Example 1, when the flow rate during rain increased and the flow load of the final sedimentation basin increased, the MLSS concentration at the outlet of the aeration tank was not different from that during fine weather, so the solid load also increased. For this reason, since the aerobic and aerobic operation is performed in fine weather, the sedimentation property of the sludge is good, but SS flows out from the final sedimentation basin. The BOD of the treated water was also increased by the SS-derived BOD component.
(2) In Comparative Example 2, when the flow rate during rain increases and the flow load of the final sedimentation basin increases, the MLSS concentration at the outlet of the aeration tank decreases from that during clear weather due to the bypass feed, and the solid load increases slightly. There was aerobic operation of the entire tank during fine weather, but sludge sedimentation was not good, and SS flowed out from the final sedimentation basin. The BOD of the treated water was also increased by the SS-derived BOD component.
(3) In Reference Example 1, when the flow rate during rain increases and the flow load of the final sedimentation basin increases, the MLSS concentration at the outlet of the aeration tank decreases by a bypass feed than when it is clear, and the increase in solid load is slight. is there. In addition, since the anaerobic and aerobic operation is performed in fine weather and the sedimentation property of the sludge is good, the SS concentration of the treated water is slight. Since the aerobic treatment time was short, the solubility BOD of the treated water was slightly higher than that of the comparative example, but the BOD component derived from SS was kept low, so the BOD of the treated water was comparative example 1 and comparative example. Compared to 2, it was kept low.
(4) In Example 1 , when the flow rate during rainy weather increases and the flow load of the final sedimentation basin increases, the MLSS concentration at the outlet of the aeration tank decreases from that during clear weather due to the bypass feed, and the solid load increases slightly. is there. In addition, since the anaerobic and aerobic operation is performed in fine weather and the sedimentation property of the sludge is good, the SS concentration of the treated water is slight. Moreover, since all the tanks were made into the aerobic tank, the aerobic processing time became long and the solubility BOD of the treated water was suppressed low. Since both the SS-derived BOD component and the soluble BOD component were kept low, the BOD of the treated water was kept very low.

In addition, in Example 1 , when the thing of the structure of FIG. 3 was used instead of the porous ceramic pipe | tube as the diffuser pipe | tube 11, both the BOD density | concentration and soluble BOD density | concentration in treated water decreased by 1 mg / L, and others Almost the same treated water quality was obtained.

Examples 2 and 3
In Example 1 , two tanks 3 and 3A are provided as the pre-stage biological treatment unit, but only one tank 3 is provided as the apparatus of Example 2 , and three tanks of the same type are provided in series. The provided apparatus was used as the apparatus of Example 3 . However, the total volume of the tank of the former biological treatment unit was the same in Examples 1 to 3 .

The devices of Examples 2 and 3 were also installed in parallel with the device of Example 1 , and were operated under the same conditions at the same time.

Sludge sedimentation in the final sedimentation basin during fine weather and SS concentration in the treated water during rainfall were measured. As a result, the settling property (SVI) in fine weather was 250 in Example 2 (1 tank), 170 in Example 1 (2 tanks), and 150 in Example 3 (3 tanks). In addition, the SS concentration during rain was 18 mg / L in Example 2 (1 tank), 8.5 mg / L in Example 1 (2 tanks), and 8.3 mg / L in Example 3 (3 tanks). .

From the comparison of Examples 1 to 3 , it was found that the number of tanks in the former biological treatment section is preferably 2 or more. This is considered to be because activated sludge with good sedimentation is formed by creating a starvation state after a state in which the substrate is excessively present, as will be described later.

Example 4
In Example 1 , the two tanks 5A and 5 are provided as the latter-stage biological treatment unit. However, only one tank 5 is provided as the apparatus of Example 4 . However, the volume of the tank 5 of Example 4 was the same as the sum of the tanks 5 and 5A of Example 1 .

The apparatus of Example 4 was also installed side by side with the apparatus of Example 1 , and was operated under the same conditions at the same time.

Sedimentation of sludge in the final sedimentation basin in fine weather, SS concentration in aeration tank effluent and treated water, and treated water BOD concentration were measured, and sedimentation (SVI) was 240 in Example 4 (one tank). In Example 1 (2 tanks), it was 170. The SS concentration in the aeration tank effluent was 1150 mg / L in Example 4 (1 tank) and 1010 mg / L in Example 1 (2 tanks).

The SS concentration in the treated water was 18 mg / L in Example 4 (1 tank) and 8.5 mg / L in Example 1 (2 tanks). The BOD concentration in the treated water was 10 mg / L in Example 4 (1 tank) and 7 mg / L in Example 1 (2 tanks). The soluble BOD concentration in the treated water was 1 mg / L in Example 4 (1 tank) and 2 mg / L in Example 1 (2 tanks).

As is clear from the comparison between Examples 1 and 4 , when two aerobic tanks were used, SVI was improved compared to when one aerobic tank was used. When two aerobic tanks were used, the aeration tank sludge was diluted in the tank of a small tank size by the untreated water from the bypass pipe 9, so that the SS at the outlet of the aeration tank became smaller. When there are two aerobic tanks, the aerobic contact time between the water from the bypass pipe 9 and the aeration tank sludge is reduced, so the solubility BOD of the treated water deteriorates, but the BOD derived from SS occupies it. Due to the large proportion, the total BOD concentration improved.

Example 5
In the apparatus of Example 1 , the size of the anaerobic tank was changed, and the size of the aerobic tank was fixed. The average flow rate in fine weather is 160 m ³ / Hr. This apparatus was also operated under the same conditions at the same time as Example 1 . FIG. 5 shows the relationship between HRT and sludge sedimentation during fine weather, and FIG. 6 shows the relationship between HRT and final sedimentation outlet SS concentration during fine weather.

  As shown in Fig. 5, when the hydraulic residence time HRT of the anaerobic tank in fine weather is 1.9 [Hr] and 3.0 [Hr], the SVI is very good, and it flows out of the final sedimentation basin when it rains. The SS to do was also low.

  On the other hand, as shown in FIG. 6, when the anaerobic tank HRT was 1.0 [Hr] and 4.0 [Hr], the SVI was relatively poor, and the SS flowing out of the final sedimentation basin was high when it rained. .

The reason for the preferred HRT is considered as follows.
(1) Microorganisms that grow under aerobic conditions in which a soluble substrate exists are a cause of worsening SVI, and in anaerobic aerobic treatment, create conditions that do not allow the supply of soluble substrates to the subsequent aerobic tank. SVI is said to improve. If the size of the anaerobic tank is small, the solubility is deteriorated because a soluble substrate is supplied to the aerobic tank.
(2) It is known as a selector that selectively proliferates microorganisms having the ability to store a substrate in the body by creating a starvation state in which the substrate does not exist so much after a state in which the substrate exists excessively. These microorganisms are microorganisms that form activated sludge flocs, and as a result, activated sludge with good sedimentation is formed. (Martins et al. 2004). For this reason, when the capacity | capacitance of an anaerobic tank becomes large, since the microorganisms which have the capability to store a substrate in a body do not grow, sludge with good sedimentation property is not formed.

It is a systematic diagram of the sewage treatment method which concerns on embodiment and a reference example . It is a systematic diagram of the sewage treatment method which concerns on embodiment and a reference example . The structure of a diffuser tube is shown, (a) A figure is sectional drawing which made one part a cross section, (b) And (c) figure is an expanded view of a covering body (tube). It is a systematic diagram of the sewage treatment method of a comparative example. It is a graph which shows the relationship between the anaerobic tank HRT and SVI at the time of fine weather. It is a graph which shows the relationship between the anaerobic tank HRT at the time of fine weather, and the last sedimentation tank exit SS.

1 First sedimentation tank 3 First tank 5 Second tank 6,11 Aeration pipe 7 Final sedimentation tank 9 Bypass piping 10 Flow control valve

Claims (4)

After precipitating sewage, the supernatant water is biologically treated in the biological treatment unit, the treated liquid is solid-liquid separated into treated water and sludge, and part of the separated sludge is returned to the inlet side of the biological treatment unit. In the processing method,
As the biological treatment unit, a pre-stage biological treatment unit capable of both anaerobic treatment and aerobic treatment and a post-stage biological treatment unit for aerobic treatment are provided,
When the flow rate of the supernatant water is equal to or lower than a predetermined flow rate, the front biological treatment unit is in an anaerobic treatment state, and the whole amount of the supernatant water is circulated in this order through the front biological treatment unit and the rear biological treatment unit,
When the flow rate of the supernatant water exceeds the predetermined flow rate, the front biological treatment unit is brought into the aerobic treatment state, and a part of the supernatant water is circulated in this order to the front biological treatment unit and the rear biological treatment unit. And the remaining part of the supernatant water is allowed to flow into the subsequent biological treatment section without passing through the previous biological treatment section. In Claim 1 , a diffuser member is provided in the preceding stage biological treatment section, and the diffuser member has a cylindrical support body having a passage through which air is blown and guided to the outer peripheral surface.
An elastic envelope surrounding the outer periphery of the support;
An air blowing slit provided in the envelope;
A sewage treatment method comprising: performing aeration from the aeration member when an aerobic treatment is performed in the upstream biological treatment unit. According to claim 1 or 2, sewage treatment method upper supernatant water is hydraulic retention time of the pre biological treatment unit in the case where the predetermined flow rate or less characterized in that it is a 1.5～3.5Hr. A first sedimentation basin, a pre-stage biological treatment tank capable of accepting both anaerobic and aerobic biological treatment receiving supernatant water from the first sedimentation basin, and an aerobic latter-stage organism receiving biological treatment water in the previous biological treatment tank In a sewage treatment apparatus having a treatment tank and a final sedimentation basin for receiving biological treatment water of the subsequent biological treatment tank,
When the supernatant water from the first sedimentation basin is below a predetermined flow rate, the first biological treatment tank is placed in an anaerobic treatment state, and the whole amount of the supernatant water is circulated in this order through the first biological treatment unit and the second biological treatment unit. When,
When the supernatant water from the first sedimentation basin exceeds the predetermined flow rate, the pre-stage biological treatment tank is made aerobic and a part of the supernatant water is transferred to the pre-stage biological treatment section and the post-stage biological treatment section. A sewage treatment apparatus characterized in that it is circulated in this order, and a means for guiding the remainder of the supernatant water to the subsequent biological treatment tank without passing through the previous biological treatment tank.

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