JP3325474B2 - Sewage treatment method and circulating nitrification denitrification method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for treating sewage by an activated sludge method and a method for circulating nitrification and denitrification. When air is blown into sewage such as sewage and agitated, various microorganisms propagate using organic matter in the sewage to form flocculent floc. This is called activated sludge, and is composed of non-biological inorganic substances in addition to microorganisms such as bacteria, protozoa and metazoans.

When activated sludge is mixed with sewage in the presence of oxygen, organic matter in the sewage is adsorbed by the activated sludge, oxidized and assimilated by the metabolic function of the microorganisms constituting the activated sludge, and a part of the activated sludge is converted into activated sludge. Is converted. In the activated sludge method, oxygen is supplied by blowing air or stirring the water surface with a machine in a biological reaction tank, that is, aeration.
The activated sludge is maintained in a floating state by the water flow in the reaction tank generated at this time.

[0003]

2. Description of the Related Art FIG. 1 shows a conventional sewage treatment apparatus using an activated sludge method. The illustrated sewage treatment apparatus has a basic configuration in which a sedimentation basin 1, a biological reaction tank 2, and a final sedimentation basin 3 are arranged in this order, and a submersible aerator for aeration and an aeration tube (not shown) are immersed in the reaction tank 2. It is. Raw water (sewage) first flows into the sedimentation basin 1 from the left end of the figure, and after first removing coarse solids in the sedimentation basin 1, flows into the biological reaction tank 2, where the activated sludge generated by the biological reaction described above. The treated water in a mixed liquid state in which the flocs are suspended flows into the final sedimentation basin 3, where the activated sludge is precipitated to perform solid-liquid separation, and the supernatant is discharged as treated water. The activated sludge settled in the final settling basin 3 is supplied to the reaction tank 2 by the pump P.
The waste is returned inside and part of it is discharged to the outside as excess sludge and disposed of.

[0004] However, the conventional activated sludge method has the following problems. (1) Activated sludge floc (suspended material (S
There is a limit to the separation capacity of SS in the treatment to remove suspended solid (S: suspended solid)) in the final sedimentation basin, especially when the inflow load fluctuates, when the biological function decreases in winter, or when the inflow load increases in the combined treatment facility. When the bulking occurs, the quality of the treated water deteriorates.

(2) When high treated water quality is required, equipment such as a rapid filter and a strainer is required after the final sedimentation basin. (3) It is necessary to return activated sludge from the final sedimentation basin. (4) Troubles such as scum generation and sludge floating (when nitrification progresses) may occur in the final sedimentation basin.

(5) The final sedimentation basin itself requires a large installation area. Next, FIG. 9 shows a typical example of a conventional nitrification denitrification apparatus. In the illustrated nitrification denitrification apparatus, a first settling basin 1, a reaction tank 2 and a final settling basin 3 are arranged in this order.
A submersible aerator for aeration (not shown), an aeration tube, a stirrer, and the like are arranged therein. The reaction tank 2 is composed of an oxygen-free tank (denitrification tank) 21 on the upstream side and an aerobic tank (nitrification tank) 22 on the downstream side. The flow into the gas tank 22 is performed by an overflow A that exceeds the upper end of the weir 23.

[0007] Raw water (sewage) is first settled from the left end of the figure.
And first, coarse solids are precipitated and removed in the sedimentation basin 1. In the recirculation type nitrification and denitrification process, the inflow water from the first settling basin 1 and the returned sludge from the final settling basin 3
1, while a part of the nitrification mixture in the aerobic tank 22 is circulated to the oxygen-free tank 21 through the conduit B. In the aerobic tank 22, the inflowing ammoniacal nitrogen is oxidized to nitrite or nitrate nitrogen, and in the anoxic tank 21, these oxidized nitrogens are reduced to nitrogen gas by the oxidation reaction of the organic matter in the influent water. You. After nitrification and denitrification in the reaction tank 2, the supernatant separated and settled in the final settling basin 3 is discharged as treated water.

[0008] Standard municipal sewage does not require the addition of a hydrogen donor (such as methanol) for denitrification or an alkaline agent (such as sodium hydroxide) for adjusting pH.
These need to be considered depending on the quality of the incoming water. Since a part of the organic matter in the sewage is decomposed and removed by the denitrification reaction, the oxygen supply amount for removing the BOD can be reduced as compared with the nitrification-promoting activated sludge method.

There is a two-stage circulation system for improving the nitrogen removal rate. In this system, a set of anoxic tanks and aerobic tanks is arranged in two stages in series, and the inflow water is step-flowed into the anoxic tanks of each stage, so that a high M is achieved.
This enables LSS concentration and long SRT. By such an operation, it is possible to receive the effluent from the nitrification tank in the preceding stage in the anoxic tank in the subsequent stage, and it is possible to obtain a high nitrogen removal rate.

However, the above-mentioned conventional recirculation type nitrification and denitrification process has problems in the following points (1) to (4). (1) It is necessary to keep the MLSS concentration in the reaction tank higher than the activated sludge method at 2,000 to 3,000 mg / L. Therefore, the load on the solids flowing into the final sedimentation basin increases, so that the water area load is reduced. There is a need.

[0011] Therefore, it is not possible to apply this process using an existing final settling basin due to excessive load. (2) If the treated water SS is large, it is necessary to install a filter at the latter stage of the reaction tank. (3) Return sludge operation in the final sedimentation basin is required.

(4) Sludge floats due to denitrification gas in the final sedimentation basin. To solve these conventional problems, Japanese Unexamined Patent Publication (Kokai) No. 5-185078 discloses a bag-like shape formed by sealing the periphery of a laminated water-permeable sheet with a water-permeable porous material for maintaining an interval interposed therebetween. Is disposed above the aeration unit in the aeration tank and is immersed and disposed in the treated water, and a suction pipe for drawing out the filtered water with a low suction force due to a lower head difference than the filter body is led out of the aeration tank. A filtration device for an aerated tank has been proposed.

[0013] However, even if the filtration device proposed above is used,
When there is a sudden drop in water temperature or a change in water quality, there is a problem that good treated water quality cannot be stably obtained.

[0014]

SUMMARY OF THE INVENTION The present invention solves the problems associated with solid-liquid separation by the final settling basin in the conventional activated sludge method using the above-mentioned proposed filtration device, and further stably improves the performance. It is an object of the present invention to provide a sewage treatment method by an activated sludge method and a circulating nitrification and denitrification method capable of obtaining treated water quality.

[0015]

SUMMARY OF THE INVENTION The above object is attained by the present invention.
According to the invention, there is provided a hollow filter body having an inflow portion made of a water-permeable support material as at least a part of a peripheral wall, and an outflow portion as an opening, wherein activated sludge and turbidity are formed on the support material. A filtration body that forms a filtration membrane made of quality and performs filtration,
In the sewage treatment method by the activated sludge method of immersing and disposing in at least one of the biological reaction tank and the final sedimentation basin, and withdrawing the treated water from the filter through the outflow port due to the head difference from the subsequent tank, This is achieved by a sewage treatment method characterized by adding a flocculant to at least one of raw water or a biological reaction tank.

According to a second aspect of the present invention, there is provided a biological reaction tank having an oxygen-free zone on an inflow side of treated water and an aerobic zone on an outlet side of treated water. A circulating nitrification denitrification method for circulating a part of the nitrification mixed solution in the region to the oxygen-free region to remove nitrogen in the water to be treated, wherein at least a part of a peripheral wall is formed of a water-permeable supporting material. The filtered hollow filter body is immersed in at least one of the aerobic region and the subsequent final sedimentation basin to form a filtration membrane made of nitrified sludge and turbidity on the support material, and the head difference from the subsequent tank In the circulating nitrification and denitrification method of causing treated water to flow into the filter body through the filtration membrane and extracting the treated water from the filter body, in the raw water or biological reaction tank to be treated Circulating nitrification denitrification characterized by adding a flocculant to at least one of them Also be achieved by law.

As the water-permeable supporting material constituting the filter used in the first and second inventions of the present application, a metal, synthetic resin or ceramic net, a nonwoven fabric, a woven fabric, a membrane, or a porous material may be used. It is convenient. Among them, metal mesh,
It is preferable to use a synthetic resin non-woven fabric in the form of a sheet.

[0018]

First, as a premise of the present invention, the following effects are obtained by sewage treatment using a filter. That is, the first of the present application
In the sewage treatment method of the present invention, the above filter is immersed and disposed in at least one of the biological reaction tank and the final sedimentation basin, and a part or all of the solid-liquid separation conventionally performed in the final sedimentation basin is performed by the filter. Performed by

In the circulating nitrification and denitrification method of the second invention of the present application, the above-mentioned filter is immersed in at least one of the aerobic region of the biological reaction tank and the final sedimentation basin, and is conventionally performed in the final sedimentation basin. Part or all of the solid-liquid separation that has been performed is performed by a filter. At this time, since the filtration is performed by extracting the treated water from the filter through the outlet due to the head difference from the succeeding tank, the power for driving the water to be treated is not particularly required.

With the above structure, the present invention performs solid-liquid separation by filtration instead of flotation separation. Therefore, it is possible to eliminate all of the above-mentioned conventional problems (1) to (5) associated with solid-liquid separation by using a final sedimentation tank. it can. That is, the present invention can solve the above-mentioned problems (1) and (2) because a high treated water quality can be obtained beyond the limit of solid-liquid separation by flotation, and the final settling basin is simplified or omitted. So the above problem can
(3) to (5) can be eliminated.

In addition to the above premise, the most important feature of the present invention is that a coagulant is added to raw water to be treated or into a biological reaction tank (or in an aerobic region thereof). By adding a flocculant, flocculation of the activated sludge is promoted, and a good filtration membrane (biological membrane or dynamic membrane) is formed on the support material. Still another great advantage of the present invention is that the effect of removing phosphorus by the flocculant can be obtained at the same time.

That is, the coagulant used in the present invention has been generally used for removing phosphorus in the activated sludge method. The mechanism of phosphorus removal in the activated sludge process is based on a reaction in which trivalent metal ions react with phosphate ions in sewage to form poorly water-soluble phosphates. This reaction is represented by the following formula. M ³⁺ + PO ₄ ^3- → MPO ₄ ↓ Usually, an aluminum salt or an iron (III) salt which forms a precipitate near neutrality is used as a flocculant.

The phosphorus removal process based on such a principle requires three steps of mixing a flocculant with sewage, floc formation, and sedimentation. In the activated sludge method, mixing and floc formation are performed by a flow in a biological reactor,
A floc is produced in harmony with the biological floc, which is sedimented and separated in the final sedimentation basin. The coagulant applicable to the present invention may be any as long as it is applicable to the activated sludge method, and typical examples include aluminum sulfate, polyaluminum chloride (PAC), ferric chloride, and ferrous sulfate. is there.

The coagulant is added at the end (downstream end) of the reaction tank when an aluminum salt or a ferric salt is used as the coagulant, and when the ferrous salt is used as the coagulant. Is a position where ferrous iron can be oxidized to ferric iron at the end of the reactor. In general, the amount of sludge generated by the addition of a flocculant is about 5 times the amount of aluminum added when an aluminum salt is used as a flocculant, and 3.5 times as much as iron when an iron salt is used. About twice as many SSs occur.

[0025]

The present invention will be described in more detail with reference to the following examples. Embodiment 1 FIG. 2 shows an example of a sewage treatment apparatus for performing the method of the first invention of the present application. The part corresponding to FIG.
The same reference numerals as in the figures are used.

The illustrated sewage treatment apparatus initially comprises a settling basin 1,
The biological reaction tank 2 and the buffer tank 4 are arranged in this order, and the reaction tank 2 has a basic configuration in which a set of filter bodies 5 is immersed and arranged in addition to an underwater aerator for aeration and an aeration tube (not shown). . Raw water (sewage) is the first settling pond from the left end of the figure.
After the coarse solid content is first settled and removed in the sedimentation basin 1, it flows into the biological reaction tank 2, and becomes the treated water in the mixed liquid state in which the activated sludge floc generated by the biological reaction floats, Due to the head difference from the subsequent buffer tank 4, it is sucked into the filter body 5 and flows thereinto, where it is separated into solid and liquid by filtration,
The water is discharged through the buffer tank 4 as treated water. The head difference required for filtration is stably maintained by the water level in the buffer tank 4.

FIGS. 3 to 6 show the arrangement of a set of filter bodies 5 in the biological reaction tank 2 of the sewage treatment apparatus of the present invention. FIG.
4 is a plan view, FIG. 4 is a sectional view taken along line IV-IV in FIG.
3 is a sectional view taken along line V-V in FIG. 3, and FIG.
It is sectional drawing in VI. The reaction tank 2 has a middle partition 2A at the center thereof, and a range of an intermediate depth excluding an upper layer portion and a lower layer portion is separated into right and left. The to-be-treated water initially introduced by the to-be-treated water introduction pipe 1A from the sedimentation basin 1 is maintained at a water level 2W higher than the upper end 2AU of the intermediate partition 2A.
That is, in the tank 2, an upper layer portion between the water level 2W of the water to be treated and the upper end 2AU of the partition wall 2A is in communication with the water to be treated. Further, the water to be treated is also communicated between the lower end 2AL of the partition 2A and the bottom surface 2B of the tank 2.

Area to the right of intermediate partition 2A of tank 2 (FIG. 6)
In FIG. 3, a number of aeration tubes 6 are immersed and arranged side by side over almost the entire length of the tank 2 (FIGS. 3 and 5). The filter body 5 is a set of four filter bodies 5 arranged side by side in the thickness direction, and a downstream portion (FIG. 6) of a left section (FIG. 6) opposite to the aeration tube 6 with the intermediate partition wall 2A in the tank 2 interposed therebetween. 3 and 4).

The water to be treated from the first sedimentation basin 1 shown in FIG. 2 passes through the inlet pipe 1A (FIGS. 3 and 5) and passes through the right end of the upstream end of the biological reaction tank 2 (the left side in FIGS. 3 and 5). Area (FIG. 6), and the ascending flow (arrow F)
1), it crosses over the partition 2A in the direction of arrow F2, enters the left area where the filter 5 is located, and becomes a downward flow (arrow F3),
While forming a swirling flow of a cycle of diving below the partition wall 2A and returning to the right area, the inside of the tank 2 is changed from an upstream portion to a downstream portion (FIGS. 3 to 5).
From the left to the right).

FIG. 7 is an enlarged sectional view of a portion of the filter 5 shown in FIG. The arrow F3 in FIG. 7 indicates the downward flow of the water to be treated shown in FIG. One set of four filter bodies 5 has a support member 52 having a predetermined range of apertures and thicknesses in close contact with the side surface of a structural member 51. Structural member 51
Is a flat hollow body, the upper end is closed and the lower end is opened as an outlet 54, and a number of inlets 51A are provided on the side.
Is open. On the support material 52, a filtration membrane, which will be described in detail later, is formed by activated sludge. The water to be treated is separated into solid and liquid by the above-mentioned filtration membrane when passing through the support material 52, and the permeated portion flows into the inside of the filter body 5 through the inlet 51A on the side of the structural member 51, and the outlet 54 at the lower end. From the outlet pipe 55 and is led to a subsequent tank or conduit.

As shown in FIG. 8, the activated sludge and turbid matter are concentrated on the supporting material 52 to form a filtration membrane. For simplicity of illustration, the structural member 51 is omitted in FIG.
In the present embodiment, the filter body 5 is disposed in the downward flow portion F3 of the swirl flow F of the water to be treated. Next, an example of a result of performing sewage treatment by the sewage treatment apparatus of the present embodiment having the arrangement shown in FIG. 2 will be described.

Raw water was BOD180mg / L, SS13
The sewage was 0 mg / L. A filter having a side surface area of 40 cm × 40 cm is immersed and arranged in the downstream part of the swirling flow of the water to be treated in the downstream part of the biological reaction tank having an effective volume of 1 m ³ ,
At the daily permeation flow rate, the treated water was taken out under natural flow. As a support material of the filter, a nonwoven fabric made of polyester having a mesh size of 40 μm and a thickness of 0.3 mm was used. The head difference (loss head) was 20 cm. The effective volume of the final settling basin was 500 L.

Ferric polysulfate as a coagulant was continuously charged into the reaction tank by a chemical injection pump at an addition amount of 7 mg / L as iron. As a result, the quality of the treated water obtained is BOD
8 mg / L, SS 5 mg / L, and TP 1.5 mg / L. For comparison, the treatment was performed under the same conditions as above except that no coagulant was added.

As a result, the quality of the treated water obtained was BOD 8 m
g / L, SS 5 mg / L, and TP 0.2 mg / L. As described above, by adding the flocculant according to the present invention, the removal of phosphorus was promoted while the BOD and SS were kept at the same level. The addition method in which the flocculant is stored in the storage tank and charged by the chemical injection pump as in this embodiment is efficient and reliable.

The coagulant may be added continuously or intermittently. However, in the case of continuous charging, the removal of phosphorus and stable processing can be continuously performed, but in the case of intermittent charging, the effect of removing phosphorus is effective only for a certain period after the charging. Intermittent dosing can also be used in which dosing is performed only when the phosphorus removal action is reduced or when the treatment is deteriorated. [Example 2] Using the same apparatus as in Example 1, the treatment was carried out while varying the quality of the raw water. That is, BOD3 of raw water
00 mg / L and supply for 2 days, then return to BOD 180 mg / L for 3 days, and again BOD 300 mg / L
L and fed for 2 days to exacerbate the activated sludge.

As in Example 1, ferric polysulfate was added as a coagulant in an amount of 7 mg / L in terms of iron, and was continuously charged into the reaction tank by a chemical injection pump. As a result, the obtained treated water quality was BOD 8 mg / L, SS 5 mg / L, T-
P was 0.2 mg / L. For comparison, the treatment was performed under the same conditions as above except that no coagulant was added.

As a result, the quality of the treated water obtained was BOD 15
mg / L, SS 15 mg / L, and T-P 1.7 mg / L. As described above, by adding the coagulant according to the present invention, good treated water quality was stably obtained even when the water quality of the raw water fluctuated, and the phosphorus removing effect was also obtained.
[Embodiment 3] Fig. 10 shows an example of a circulating nitrification denitrification apparatus for performing the method of the second invention of the present application. Portions corresponding to those of the conventional device in FIG. 9 are denoted by the same reference numerals.

The illustrated nitrification and denitrification apparatus initially comprises a sedimentation basin 1,
The reaction tank 2 and the buffer tank 4 are arranged in this order, and the reaction tank 2
A submersible aerator for aeration (not shown), an aeration tube, a stirrer, and the like are arranged therein. The reaction tank 2 is composed of an oxygen-free tank (denitrification tank) 21 on the upstream side and an aerobic tank (nitrification tank) 22 on the downstream side. The flow into the gas tank 22 is overflow A over the weir 23
It is performed by

Further, in the aerobic tank 22 of the reaction tank 2,
The filter 5 is immersed. Raw water (sewage) first flows into the sedimentation basin 1 from the left end of the figure, and first precipitates coarse solids in the sedimentation basin 1. While the influent from the first settling basin 1 and the returned sludge from the final settling basin 3 are allowed to flow into the anoxic tank 21, a portion of the nitrification mixture in the subsequent aerobic tank 22 is circulated to the anoxic tank 21 by the conduit B. I do. In the aerobic tank 22, the inflowing ammoniacal nitrogen is oxidized to nitrite or nitrate nitrogen, and in the anoxic tank 21, these oxidized nitrogens are reduced to nitrogen gas by the oxidation reaction of the organic matter in the influent water. You. The water to be treated after nitrification and denitrification is
After being separated into solid and liquid by filtration with the filter 5 immersed in the aerobic tank 22, it is discharged as treated water through the buffer tank 4. The head difference required for filtration is stably maintained by the water level in the buffer tank 4.

FIGS. 11 to 14 show the arrangement of a set of filter bodies 5 in the reaction tank 2 of the circulating nitrification and denitrification apparatus of the present invention. 11 is a plan view, FIG. 12 is a sectional view taken along line IV-IV in FIG. 11, FIG. 13 is a sectional view taken along line V-V in FIG.
FIG. 14 is a sectional view taken along line VI-VI in FIG. In FIGS. 11 to 14, the circulation conduit B is not shown.

The reaction tank 2 has a weir 23 substantially at the center of its length.
Thereby, an oxygen-free tank 21 and an aerobic tank 22 are separated from each other, and an intermediate depth range excluding an upper layer portion and a lower layer portion is separated left and right by an intermediate partition 2A at the center of the width. First, the water to be treated introduced from the sedimentation basin 1 into the anoxic tank 21 by the introduction pipe 1A is maintained at the water level 2W1 higher than the upper end 2AU of the intermediate partition 2A by the upper end of the weir 23 (FIGS. 12 and 13). ). The water to be treated that has flowed into the aerobic tank 22 by the overflow A over the weir 23 is maintained at a water level 2W2 higher than the upper end 2AU of the intermediate partition 2A but lower than the water level 2W1 in the anoxic tank 21. That is, in the tank 2, both in the anoxic tank 21 and the aerobic tank 22, the water to be treated communicates with the upper layer portion between the water level 2W1 or 2W2 of the water to be treated and the upper end 2AU of the partition wall 2A. In addition, the lower end 2AL of the partition wall 2A and the tank 2
The water to be treated also communicates with the bottom surface 2B.

The area to the right of the intermediate partition 2A of the tank 2 (FIG. 1)
4) In the oxygen-free tank 21, a mechanical stirrer 7 is provided.
A number of aeration tubes 6 are immersed in the aerobic tank 22 (FIGS. 11 and 13). The filter 5 has a thickness of 4
In the aerobic tank 22, the downstream portion (FIG. 14) of the left area (FIG. 14) opposite to the aeration tube 6 across the intermediate partition 2 </ b> A in the aerobic tank 22. (Right side).

The water to be treated from the first settling basin 1 shown in FIG. 10 passes through the inlet pipe 1A (FIGS. 11 and 13), and is located at the right end of the upstream end of the oxygen-free tank 21 (the left side in FIGS. 11 and 13). It is introduced into the section (FIG. 14), and is caused to flow upward (arrow F11 in FIG. 13) in the right section by the stirrer 7, and flows over the partition 2A in FIG.
The flow crosses in the direction of arrow F12 of FIG. 1 and enters the left area to form a downward flow (arrow F13 in FIG. 12), forming a swirl flow of a cycle of dive below the partition wall 2A and return to the right area. Aerobic tank 22
Similarly, the air flows upward in the right area by the aeration tube 6 (arrow F21 in FIG. 13), and flows upward on the partition 2A in FIG.
, A downward flow (arrow F23 in FIG. 12) after entering the left area where the filter 5 is present, and a swirling flow (F in FIG. 14) of diving below the partition wall 2A and returning to the right area.
2) is formed.

As described above, the filter body 5 is disposed in the portion of the downward flow F23 of the swirling flow in the aerobic tank 22, which is a component member of the filter body 5 as described later in detail. This is for stably forming and maintaining the film. FIG. 15 shows an enlarged cross-sectional view of a portion of the filter 5 shown in FIG. The arrow F23 in FIG. 15 indicates the downward flow of the water to be treated shown in FIG. One set of four filter bodies 5 is
The support member 52 is closely fixed to the side surface of the structural member 51. The structural member 51 is a flat hollow body. The upper end is closed, the lower end is opened as an outlet 54, and a number of inlets 51A are opened on the side. On the support member 52, a filtration membrane described in detail later is formed. The water to be treated is separated into solid and liquid by the above-mentioned filtration membrane when passing through the support material 52, and the permeated portion flows into the inside of the filter body 5 through the inlet 51A on the side of the structural member 51, and the outlet 54 at the lower end. From the outlet pipe 55 and is led to a subsequent tank or conduit.

In this embodiment, in the aerobic tank 22, the filter 5 is caused to flow through the downward flow portion F 2 of the swirling flow F of the water to be treated.
3 was placed. Next, an example of a result of processing performed by the apparatus of the present embodiment having the arrangement shown in FIG. 10 will be described. Raw water is BOD160mg / L, SS120mg / L, T-P3
mg / L, T-N 25 mg / L, sewage. The reaction tank 2 having an effective capacity of 1 m ³ was defined as an oxygen-free tank 21 for the first 500 L and an aerobic tank 22 for the second 500 L. A filter having a side surface area of 40 cm × 40 cm was immersed and disposed in the downward flow portion of the swirling flow of the water to be treated in the aerobic tank 22, and the treated water was taken out under a natural flow at a permeation flow rate of 1 m / day. A nonwoven fabric made of polyester having a mesh size of 20 μm and a thickness of 0.4 mm was used as a support for the filter. The head difference (loss head) was 20 cm.

As in Example 1, ferric polysulfate was added as an aggregating agent in an amount of 7 mg / L in terms of iron, and was continuously charged into the reaction tank by a chemical injection pump. As a result, the quality of the treated water obtained was 6 mg / L for BOD, 3 mg / L for SS,
P 0.2 mg / L and T-N 5 mg / L. For comparison, the treatment was performed under the same conditions as above except that no coagulant was added.

As a result, the quality of the treated water obtained was BOD 7 m
g / L, SS4mg / L, T-P1.5mg / L, T-
N5 mg / L. As described above, by adding the flocculant according to the present invention, the removal of phosphorus was promoted while the BOD and SS were kept at the same level. [Embodiment 4] Using the same apparatus as in Embodiment 3, treatment was carried out while varying the quality of raw water. That is, BOD300 of raw water
mg / L and supply for 2 days, then BO for 3 days
The DOD was returned to 180 mg / L, and the BOD was increased again to 300 mg / L and supplied for 2 days to deteriorate the activated sludge.

As in Example 1, ferric polysulfate was added as a coagulant in an amount of 7 mg / L in terms of iron, and was continuously charged into the reaction tank by a chemical injection pump. As a result, the quality of the treated water obtained was 6 mg / L for BOD, 4 mg / L for SS,
P 0.2 mg / L and T-N 6 mg / L. For comparison, the treatment was performed under the same conditions as above except that no coagulant was added.

As a result, the quality of the treated water obtained was BOD14
mg / L, SS15mg / L, T-P1.6mg / L,
T-N was 18 mg / L. As described above, by adding the coagulant according to the present invention, good treated water quality was stably obtained even when the water quality of the raw water fluctuated, and the phosphorus removing effect was also obtained.

[0050]

As described above, according to the sewage treatment method and the circulating nitrification denitrification method of the present invention, the problems associated with the solid-liquid separation by the final settling basin in the conventional activated sludge method are solved. Further, good treated water quality can be obtained stably.
Further, a phosphorus removing effect can also be obtained.

[Brief description of the drawings]

FIG. 1 is a layout diagram showing a conventional sewage treatment apparatus using an activated sludge method.

FIG. 2 is a layout diagram showing an example of a sewage treatment apparatus according to the activated sludge method of the present invention.

FIG. 3 is a plan view showing an arrangement of a filter in a biological reaction tank of the sewage treatment apparatus of the present invention.

FIG. 4 is a sectional view taken along line IV-IV in FIG. 3;

FIG. 5 is a sectional view taken along line VV in FIG. 3;

FIG. 6 is a sectional view taken along line VI-VI in FIG. 3;

FIG. 7 is an enlarged cross-sectional view of a portion of the filter shown in FIG. 4;

FIG. 8 is a cross-sectional view schematically showing a support member.

FIG. 9 is a layout diagram showing a conventional circulation type nitrification and denitrification apparatus.

FIG. 10 is a layout diagram showing an example of a circulating nitrification denitrification apparatus of the present invention.

FIG. 11 is a plan view showing an arrangement of a filter in a reaction tank of the circulating nitrification denitrification apparatus of the present invention.

FIG. 12 is a sectional view taken along line IV-IV in FIG. 11;

FIG. 13 is a sectional view taken along line VV in FIG. 11;

FIG. 14 is a sectional view taken along line VI-VI in FIG. 11;

FIG. 15 is an enlarged cross-sectional view of a part of the filter shown in FIG. 12;

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... First sedimentation basin 1A ... Water introduction pipe from the last sedimentation basin 2 ... Biological reaction tank 21 ... Anoxic tank 22 ... Aerobic tank 23 ... Weir 2A ... Intermediate partition wall 2AU ... Upper end of partition wall 2A 2AL ... Partition wall 2A Lower end 2B ... Bottom of reaction tank 2 2W ... Water level 2W1 ... Water level in anoxic tank 21 2W2 ... Water level in aerobic tank 22 3 ... Final sedimentation basin 4 ... Buffer tank 5 ... Filter 51 ... Structural member 51A ... Inlet 52 ... Support material 53 ... Filtration membrane 54 ... Outlet 55 ... Discharge pipe 6 ... Aeration pipe 7 ... Mechanical stirrer F ... Swirl flow F1 ... Upflow portion of swirl flow F F3 ... Downflow portion of swirl flow F F11, F21 … Upward portion of swirl flow F13, F23… Downward portion of swirl flow

──────────────────────────────────────────────────続 き Continuing from the front page (73) Patent holder 000005083 Hitachi Metals, Ltd. 1-2-1, Shibaura, Minato-ku, Tokyo (73) Patent holder 000001063 Kurita Industries, Ltd. 3-4-1 Nishishinjuku, Shinjuku-ku, Tokyo No. 7 (72) Inventor Hitoshi Daido 2-8-1, Nishi-Shinjuku, Shinjuku-ku, Tokyo Tokyo Metropolitan Government Sewerage Bureau (72) Inventor Noriyuki Tajima 2-2-1 Nishishinjuku, Shinjuku-ku Tokyo Metropolitan Government Tokyo Metropolitan Government Inventor Naoya Takahashi 20-1 Shintomi, Futtsu-shi, Chiba Nippon Steel Corporation Technology Development Division (72) Inventor Mitsuo Kondo 2-6-3 Otemachi, Chiyoda-ku, Tokyo Nippon Steel Corporation (72) Inventor Tetsuo Hasegawa 5200 Mikajiri, Kumagaya-shi, Saitama Hitachi Metals Kumagaya Plant (72) Inventor Mutsuro Nagai 5200 Mikajiri, Kumagaya-shi, Saitama Hitachi Metals (72) Inventor Kazuo Suzuki 3-4-7 Nishi-Shinjuku, Shinjuku-ku, Tokyo Kurita Kogyo Co., Ltd. (72) Inventor Shigeki Sawada 3- 4-7 Nishi-Shinjuku, Shinjuku-ku, Tokyo (56) References JP-A-5-185078 (JP, A) JP-A-1-293196 (JP, A) "Fresh water technology" Vol. 20 No. 2 (1994) Desalination Promotion Center p. 65-68 (58) Field surveyed (Int. Cl. ⁷ , DB name) C02F 3/12 C02F 3/34 101 C02F 3/30

Claims (6)

(57) [Claims] 1. A hollow filter having an inflow portion made of a water-permeable support material as at least a part of a peripheral wall, and an outflow portion as an opening, wherein activated sludge and turbidity are formed on the support material. A filtration body that forms a filtration membrane made of quality and performs filtration,
A sewage treatment method using an activated sludge method in which the treated water is drawn out of the filter through the outflow port due to a head difference from a subsequent tank and immersed in at least one of the biological reaction tank and the final sedimentation tank. A sewage treatment method comprising adding a flocculant to at least one of raw water and a biological reaction tank. 2. A sewage treatment process according to claim 1, wherein said support material is characterized by comprising a metal mesh or nonwoven. 3. An aeration tube is immersed in the biological reaction tank.
And the filter is provided in the aeration tube of the biological reaction tank.
Located on the downflow side of the swirl flow formed by aeration
The sewage treatment according to claim 1 or 2, wherein
Method. 4. A biological reaction tank having an anoxic zone on the inflow side of the water to be treated and an aerobic zone on the outflow side of the treated water, and a part of the nitrification mixture in the aerobic zone is subjected to the anoxic zone. A method of circulating nitrification and denitrification in which nitrogen in the for-treatment water is removed by circulating through a region, wherein a hollow filter body having at least a part of a peripheral wall formed of a water-permeable supporting material is formed in the aerobic region. Alternatively, the filter is immersed in at least one of the subsequent final sedimentation basins, and a filtration membrane composed of nitrifying sludge and turbidity is formed on the support material, and treated into the filtration body through the filtration membrane due to a head difference from the subsequent tank. In a circulating nitrification and denitrification method for inflowing treated water and extracting the treated water from the filter, a coagulant is added to at least one of raw water to be treated or in a biological reaction tank. Circulating nitrification denitrification method. 5. The circulating nitrification denitrification method according to claim 4, wherein said support material is made of a metal net or a nonwoven fabric. 6. An aeration tube is immersed in the biological reaction tank.
And the filter is provided in the aeration tube of the biological reaction tank.
Located on the downflow side of the swirl flow formed by aeration
The circulating nitric acid according to claim 4 or 5, wherein
Chemical denitrification method.