JPH06190395A - Biological dephosphorization of phosphorus-containing waste fluid - Google Patents

Abstract

PURPOSE:To biologically dephosphorize a phosphorus-containing fluid by a simple apparatus and operation even if no aeration treatment process is provided. CONSTITUTION:A fluid to be trated to which acetic acid is added from an org. matter adding passage 8 is introduced into a phosphorus discharge tank 1 from a supply passage 5 and mixed with return sludge to be held to an aerobic state to discharge phosphorus from sludge. The mixed fluid in the phosphorus discharge tank 1 is introduced into a denitrifying and dephosphorizing tank 2 and nitrous acid and/or nitric acid are added to the tank 2 from an addition passage 10 and an anaerobic state is kept to perform denitrification and dephosphorization. The mixed fluid in the denitrifying and dephosphorizing tank 2 is subjected to solid-liquid separation in a solid-liquid separation tank 3 and a part of separated sludge is returned to the phosphorus discharge tank 1 from a sludge return passage 4 and the remainder thereof is discharged as excess sludge.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a biological dephosphorization method for phosphorus-containing effluent.

[0002]

2. Description of the Related Art Conventionally, in order to perform a biological dephosphorization treatment on an effluent containing phosphorus, the anaerobic treatment device is first anaerobically treated, and this anaerobic treatment liquid is aerated in an aeration tank. For biological dephosphorization of waste liquid containing phosphorus and nitric acid and / or nitrous acid, first, anaerobic treatment is performed by an anaerobic treatment device, this anaerobic treatment liquid is denitrified by a denitrification device, and further this denitrification treatment is performed. The liquid is aerated in the aeration tank (for example, Japanese Patent Publication No. 3-1039).
No. 5). As described above, conventionally, aeration treatment is required when treating any phosphorus-containing drainage liquid.

As another method, there is a method in which a biological denitrification step is combined with dephosphorization by addition of a flocculant or crystallization. In this case, aeration treatment is not required, but phosphorus is physicochemically removed by adding a flocculant, etc.,
No biological dephosphorization is performed.

[0004]

SUMMARY OF THE INVENTION An object of the present invention is to provide a biological dephosphorization method for phosphorus-containing effluent capable of biological dephosphorization without aeration treatment.

[0005]

The present invention relates to a phosphorus releasing step of releasing phosphorus from sludge in the presence of an organic substance, and sludge releasing phosphorus in this phosphorus releasing step in the presence of (nitrite) ions. The denitrification and dephosphorization step of absorbing phosphorus and performing denitrification and dephosphorization, the solid-liquid separation step of solid-liquid separation of the sludge that has absorbed phosphorus in this denitrification and dephosphorization step, and the solid-liquid separation step A sludge returning step of returning a part of the sludge to the phosphorus releasing step, and a treated liquid introducing step of introducing a treated liquid containing phosphorus to the phosphorus releasing step or the denitrification / dephosphorization step. And a biological dephosphorization method for phosphorus-containing wastewater.

In the present invention, "(nitrite)" means "nitrite and / or nitric acid" and "(nitrite) ion" means "nitrite ion and / or nitrate ion". "... acid (salt)" means "... acid and / or ... acid salt"
Means The drainage to be treated in the present invention is a phosphorus-containing drainage containing phosphorus and may contain organic matter, nitrate ions, nitrite ions, or the like. Phosphorus is generally contained in the form of phosphoric acid, phosphate or the like.

The phosphorus release step is a step in which microorganisms in the returned sludge release phosphorus accumulated in the body in the presence of organic matter under anaerobic conditions. As the organic substance to be present in the phosphorus releasing step, a phosphorus-containing drainage liquid to be treated can be supplied. As the organic substance, lower organic acids (salts) such as acetic acid (salt) and butyric acid (salt) are preferable. Even if the organic acid (salt) does not exist in the effluent, the organic acid (salt) can be generated by self-digestion of sludge, decomposition of raw water SS, and the like. When treating the drainage liquid in which the organic substance does not exist, it is necessary to add the organic substance separately. For the drainage supplied to the phosphorus release step,
It is necessary that (nitrite) nitrate ion is not present.

The denitrification and dephosphorization step is a step in which the sludge that has released phosphorus in the phosphorus release step absorbs phosphorus under anaerobic conditions in the presence of (nitrite) ions to perform denitrification and dephosphorization. As (nitrite) nitrate ion to be present here, (sub)
An effluent containing nitrate ions can be supplied to the denitrification and dephosphorization step. Examples of the effluent containing (nitrite) ions include a fertilizer factory effluent and a nitrification treatment solution of an ammoniacal nitrogen-containing effluent. When treating an effluent that does not contain (nitrite) ions as the liquid to be treated, the liquid to be treated is supplied to the phosphorus release step, and (nitrite) (salt) is added separately to the denitrification and dephosphorization step. There is a need to. Examples of the (nitro) nitric acid (salt) added here include sodium and potassium salts of (nitro) nitric acid. Organic matter is also required in the denitrification and dephosphorization step, but the organic matter adsorbed by sludge in the phosphorus release step or the organic matter contained in the effluent can be used.

The solid-liquid separation step is a step of performing solid-liquid separation of a mixed solution containing sludge that has accumulated phosphorus in the denitrification and dephosphorization step into sludge and separated liquid. The separated liquid separated here is discharged as a processing liquid. The sludge returning step is a step of returning a part of the separated sludge to the phosphorus releasing step as return sludge.

The treatment liquid introducing step is a step of introducing the phosphorus-containing waste liquid as a treatment liquid into the phosphorus releasing step or the denitrification and dephosphorization step. When the phosphorus-containing waste liquid does not contain (nitrite) ions, it is introduced into the phosphorus releasing step, and when it contains (nitrite) ions, it is introduced into the denitrification and dephosphorization step.

In the biological dephosphorization method of the present invention, biological dephosphorization can be performed by a biological treatment method using suspended sludge, but biological dephosphorization is performed by a biological treatment method using attached sludge such as a fixed bed or a fluidized bed. You can also do it. In the former case,
The steps are switched by moving the floating sludge between the steps, but in the latter case, the steps are switched by changing the order of liquid passage to each step as shown in JP-A-58-61886.

Further, aerobic treatment for giving dissolved oxygen to the treatment liquid may be performed after the solid-liquid separation step. The aerobic treatment device in this case does not need to use a large-scale device such as an aeration device for removing organic substances.

[0013]

The biological dephosphorization method of the present invention is as follows. First, by introducing returned sludge into the phosphorus releasing device and maintaining it in an anaerobic state in the presence of organic matter, the microorganisms in the sludge release phosphorus accumulated in the body and anaerobically decompose the organic matter. Therefore, when the phosphorus-containing waste liquid as the liquid to be treated is supplied to the phosphorus release step, the organic matter in the waste fluid is decomposed here, and the surplus organic matter is adsorbed in the sludge, and the organic matter is removed in this step. .

When a mixed liquid containing sludge that has released phosphorus by the phosphorus releasing device is introduced into a denitrification and dephosphorization device and maintained in an anaerobic state in the presence of (nitrite) ions, microorganisms in the sludge become (sub) The combined oxygen of nitrate ions is used as an oxygen source to decompose organic matter absorbed in the body or organic matter in liquid. As a result, (nitro) nitrite nitrogen is converted to nitrogen gas for denitrification, and phosphorus is absorbed and removed by microorganisms in the sludge. Therefore, in this step, phosphorus, nitrogen and organic substances are removed.

The mixed liquid containing the sludge that has absorbed phosphorus in the denitrification and dephosphorization device is separated in the solid-liquid separation device into the sludge that has accumulated phosphorus and the separation liquid from which phosphorus has been removed. Is discharged. Part of the separated sludge is returned to the phosphorus discharge device as return sludge, and the rest is discharged as excess sludge.

A preferred treatment method for treating the phosphorus-containing wastewater containing no (nitrite) ions in such a biological dephosphorization apparatus is to introduce the treated liquid from the treated liquid introducing device into the phosphorus releasing device. , It mixes with the returned sludge and maintains anaerobic condition to release phosphorus from the sludge. Then, the mixed solution of the phosphorus releasing device was introduced into the denitrification and dephosphorization device,
Denitrification and dephosphorization are performed by adding nitrous acid (salt) and maintaining an anaerobic state. The mixed liquid of the denitrification / dephosphorization device is subjected to solid-liquid separation by a solid-liquid separation device, part of the separated sludge is returned from the sludge return device to the phosphorus release device as return sludge, and the rest is discharged as excess sludge. The separated liquid is discharged as a processing liquid.

Further, a preferable treatment method in the case of treating the phosphorus-containing waste liquid containing (nitrite) ions is to introduce the liquid to be treated from the liquid introducing device to the denitrification and dephosphorization device, and
By mixing with the liquid mixture from the phosphorus release device and maintaining an anaerobic state, denitrification and dephosphorization are performed, and phosphorus is adsorbed in the sludge. The mixed liquid of the denitrification and dephosphorization device is subjected to solid-liquid separation by a solid-liquid separation device, a part of the separated sludge is returned from the sludge return device to the phosphorus release device as return sludge, and the rest is discharged as excess sludge. Phosphorus is released from the sludge by maintaining the returned sludge returned to the phosphorus release device in an anaerobic state in the presence of organic matter. In the process of repeating the denitrification dephosphorization process and the phosphorus release process, the separated liquid separated by the solid-liquid separation device is discharged as a treatment liquid.

In the present invention, the mechanism of dephosphorization and denitrification is not clear, but it is presumed to be roughly as follows. That is, in the present invention, it is speculated that a microorganism having both dephosphorization and denitrification functions releases phosphorus and absorbs and denitrifies phosphorus in an aerobic cyclic environment due to anaerobic-bound oxygen. In this case, the microorganisms in the sludge use the energy generated by the hydrolysis of the polyphosphoric acid stored in the body to decompose the organic matter in the effluent and release orthophosphoric acid in the phosphorus releasing step.

When denitrifying and dephosphorizing the sludge that has released phosphorus, the microorganisms that have released phosphorus decompose organic matter by utilizing the bound oxygen of the (nitrite) ion, thereby converting the (nitrite) ion into nitrogen gas. At the same time as conversion and denitrification, phosphorus is taken up into the body and accumulates in the form of polyphosphoric acid, so dephosphorization also progresses. Ingestion of phosphorus by these microorganisms prepares for an anaerobic environment in the phosphorus release step, and by repeating the environmental change of the phosphorus release step-denitrification dephosphorization step,
Sludge becomes an excessive intake of phosphorus. By repeating the phosphorus release treatment under the anaerobic condition and the denitrification treatment under the anaerobic condition in this way, phosphorus in the effluent is removed together with the denitrification. The phosphorus thus removed is discharged outside the system by discharging excess sludge.

[0020]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a flow chart showing a method for treating a phosphorus-containing drainage liquid containing no (nitrite) ion in the example. In the figure,
1 is a phosphorus release tank, 2 is a denitrification dephosphorization tank, 3 is a solid-liquid separation tank,
Reference numeral 4 is a sludge return passage, and 5 is a treated liquid supply passage.

A sludge return passage 4, a liquid to be treated supply passage 5 and a transfer passage 6 are connected to the phosphorus release tank 1, and the agitator 7 gently agitates the mixture to keep it in an anaerobic state for phosphorus release treatment. ing. An organic substance addition passage 8 is connected to the liquid to be treated supply passage 5.

The denitrification and dephosphorization tank 2 has the same anaerobic structure as the phosphorus release tank 1, is connected to the transfer paths 6 and 9 and the nitric acid etc. addition path 10, and is gently stirred by an agitator 11 to anaerobically. It is designed to maintain its condition.

The solid-liquid separation tank 3 is connected to a transfer passage 9, a treated liquid take-out passage 12 and a sludge take-out passage 13 for solid-liquid separation by sedimentation separation. The sludge take-out path 13 branches into the sludge return path 4 and the surplus sludge discharge path 14, and a part of the separated sludge is pumped by the pump 15 through the sludge return path 4 to the phosphorus release tank 1
It will be sent back to.

In order to treat the phosphorus-containing effluent with such a biological dephosphorization apparatus, first, in the phosphorus releasing tank 1, the organic substance addition passage 8 is provided.
The liquid to be treated to which a lower organic acid (salt) has been added is introduced from the liquid to be treated supply passage 5, and the returned sludge is returned to the sludge return passage 4.
The mixture is agitated by the stirrer 7, and is kept in an anaerobic state, and phosphorus is released with a residence time of about 0.5 to 12 hours. The amount of the lower organic acid (salt) added is preferably 5 to 50 times (weight) the amount of phosphorus to be removed. Lower organic acids (salts) if organics are already present in the effluent
Is unnecessary. Other treatment conditions are the same as the anaerobic treatment conditions adopted in the conventional biological dephosphorization treatment, for example, pH 5-9, water temperature 5-40 ° C., preferably 1
The temperature is preferably 5 to 38 ° C.

The mixed liquid in the phosphorus discharge tank 1 is taken out from the transfer passage 6 part by part and introduced into the denitrification and dephosphorization tank 2, and (nitro) nitric acid (salt) is added from a nitric acid addition passage 10
The denitrification and dephosphorization treatment is performed for a residence time of about 1 to 24 hours.
The (nitrous) nitric acid (salt) is preferably added so as to be 1 or more (molar ratio) with respect to phosphorus in the liquid in the denitrification and dephosphorization tank 2. The other treatment conditions are the same as those used in the conventional biological denitrification treatment, for example, pH 5
-9, preferably 6-8, water temperature 5-40 ° C, preferably 15-38 ° C, sludge concentration 1000-30000 mg / l
Is desirable.

The mixed liquid in the denitrification and dephosphorization tank 2 is taken out part by part from the transfer passage 9 and introduced into the solid-liquid separation tank 3 for solid-liquid separation, and a separated liquid from which organic substances, phosphorus and the like have been removed, Separated into sludge that stores phosphorus. The separated liquid is discharged as a processing liquid from the processing liquid outlet 12.

The separated sludge is taken out from the sludge take-out path 13,
A part of the sludge is returned to the phosphorus release tank 1 from the sludge return passage 4 as return sludge. The remaining part is intermittently discharged as excess sludge from the excess sludge discharge path 14. Sludge return rate is a prescribed ML
The lower the SS is, the more preferable.

In the method shown in FIG. 1, the lower organic acid (salt) is added to the liquid to be treated, but it may be added directly to the phosphorus releasing tank 1. Further, when treating a waste liquid containing a lower organic acid (salt), the organic substance addition passage 8 is unnecessary.

FIG. 2 is a flow chart showing a biological dephosphorization method for phosphorus-containing drainage according to another embodiment. This example is a flow for treating an effluent containing (nitrite) ions and phosphorus. 2, the same reference numerals as those in FIG. 1 indicate the same or corresponding parts.

The phosphorus releasing tank 1 has the same structure as the phosphorus releasing tank of FIG. 1 except that an organic substance adding passage 8 is connected instead of the liquid to be treated supply passage. The denitrification and dephosphorization tank 2 has the same configuration as the denitrification and dephosphorization tank of FIG. 1 except that the liquid to be treated supply path 5 is connected instead of the nitric acid addition channel. Other configurations are the same as those in FIG.

In order to treat the phosphorus-containing effluent with such a biological dephosphorization apparatus, the liquid to be treated is introduced into the denitrification and dephosphorization tank 2 from the liquid to be treated supply line 5 and dephosphorized in the same manner as in FIG. Nitrogen and dephosphorization. The separated sludge separated in the solid-liquid separation tank 3 is returned to the phosphorus release tank 1 from the sludge return passage 4, and a lower organic acid (salt) is added from the organic matter addition passage 8 to maintain the anaerobic state to remove phosphorus. To release. Other operations are the same as in the case of FIG. The liquid to be treated introduced into the denitrification and dephosphorization tank 2 may contain an organic substance, and in this case, the addition of the organic substance from the organic substance addition passage 8 is unnecessary. The denitrification and dephosphorization mechanism in FIG. 2 is the same as that in FIG.

The test results will be described below. Example 1 The following effluent was treated by the method of FIG. Acetic acid 100mg
/ L, peptone 50 mg / l, yeast extract 50 mg /
After adjusting the pH of a synthetic effluent containing 1, potassium monopotassium phosphate 20 mg / l, and magnesium sulfate heptahydrate 20 mg / l to pH 6.0, it was introduced into the phosphorus release tank 1 to release phosphorus with a retention time of 2 hours. . The mixed liquid flowing out of the phosphorus release tank 1 was introduced into the denitrification and dephosphorization tank 2, and sodium nitrate was used as nitrogen.
It was added so that the concentration would be mg / l, and denitrification and dephosphorization treatment was performed. The mixed liquid flowing out from the denitrification and dephosphorization tank 2 was introduced into the solid-liquid separation tank 3 to perform solid-liquid separation. The separated liquid was discharged as a treated liquid, the separated sludge was returned to the phosphorus release tank 1 at a return rate of 20% by volume with respect to the liquid to be treated, and the MLSS was kept at about 4500 mg / l. As a result, the PO ₄ -P in the treatment liquid was below the detection limit or 3 mg / l.

Example 2 Nitrate nitrogen 20 mg / l, Nitrite nitrogen 20 mg / l,
A synthetic effluent containing PO ₄ -P 2.5 mg / l and Mg, K was treated by the method of FIG. The synthetic effluent is flown into a denitrification and dephosphorization tank 2 with a capacity of 2400 ml at a flow rate of 500 ml / hr.
It was passed at. 50 mg sodium acetate to the phosphorus release tank 1
/ Hr, peptone 25mg / hr, yeast extract 25mg
/ Hr flow rate. The returned sludge rate is 20% by volume of the treated liquid flow rate, and the MLSS is about 2000 in the phosphorus release tank 1.
It was maintained at 0 mg / l and about 3500 mg / l in the denitrification and dephosphorization tank 2. As a result, PO ₄ -P in the treatment liquid was always 1 mg /
1 or less, NO ₃ -N is 10 mg / l or less, NO _2-
N became 5 mg / l or less.

[0034]

As described above, in the biological dephosphorization method of the present invention, by combining the phosphorus releasing step and the denitrifying step,
It is possible to dephosphorize the phosphorus-containing effluent by the biological dephosphorization method with a simple device and operation without providing an aeration treatment step.

[Brief description of drawings]

FIG. 1 is a flow chart showing a method for treating a phosphorus-containing drainage solution containing no (nitrite) ion in an example.

FIG. 2 is a flow chart showing a method for treating phosphorus-containing drainage containing (nitrite) ions according to another embodiment.

[Explanation of symbols]

 1 Phosphorus release tank 2 Denitrification dephosphorization tank 3 Solid-liquid separation tank 4 Sludge return passage 5 Treated liquid supply passage 6, 9 Transfer passage 7, 11 Stirrer 8 Organic matter addition passage 10 Nitric acid addition passage 12 Treatment liquid take-out passage 13 Sludge removal route 14 Surplus sludge discharge route 15 Pump

Claims (1)

[Claims] 1. A phosphorus releasing step of releasing phosphorus from sludge in the presence of an organic substance, and sludge releasing phosphorus in the phosphorus releasing step to absorb phosphorus in the presence of (nitrite) ions to denitrify and A denitrification and dephosphorization step of performing dephosphorization, a solid-liquid separation step of solid-liquid separation of sludge that has absorbed phosphorus in this denitrification and dephosphorization step, and a part of the sludge separated in this solid-liquid separation step An organism for phosphorus-containing wastewater, comprising a sludge returning step for returning to a discharge step, and a treated solution introducing step for introducing a treated solution containing phosphorus to the phosphorus releasing step or denitrification and dephosphorization step. Dephosphorization method.