JPH07232175A - Removing method of phosphorus in water - Google Patents

Abstract

PURPOSE:To attain a high removing effect of phosphorus and to prevent a generation of a hardly concentrating and dehydrating sludge by adding the slurry of particles consisting of ferric hydroxide and/or aluminum hydroxide to a phosphorus-containing raw water to subject the slurry to a biological treatment and subjecting an effluent water to solid-liq. separation treatment to obtain a treated water. CONSTITUTION:The slurry (a) prepared by suspending particles consisting of ferric hydroxide and/or aluminum hydroxide good in settling and concentrating properties is added to sewage 1 at a liq. injecting point 10 of a raw water supply pipe 20 and flows into an aeration tank 2 of an activated sludge process together with the sewage 1. Then, when the activated sludge and the slurry (a) are brought into contact with the sewage 1 while being fluidized and suspended by an air discharged from a diffusing member 5, BOD in the sewage 1 is subjected to the biological treatment and removed, and phosphorus in the sewage is sufficiently removed by the slurry (a). Then, a mixture of the activated sludge and a flock formed from the slurry (a) are settled and separated in a sedimentation basin 3 and the sewage is separated into a clarified treated water 4 highly removed in phosphorus, BOD and SS and a settled sludge 17.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for removing phosphorus containing water, and more particularly to a method for effectively removing phosphorus in organic wastewater such as sewage and various industrial wastewater by a new technical idea. .

[0002]

2. Description of the Related Art A technique for removing phosphorus from organic sewage called a coagulant-added activated sludge method has been known. In this technology, an iron-based or aluminum-based inorganic coagulant such as PAC, Alum, ferric chloride, and ferric polysulfate is added to the aeration tank of the process for biologically treating organic wastewater such as sewage by the activated sludge method. This is a technique of adding as a solution to form a precipitate (flock) of ferric phosphate or aluminum phosphate, and removing this floc together with the activated sludge by precipitation, and has the following characteristics. If there is an existing activated sludge facility, phosphorus can be removed and the construction cost is low simply by providing a chemical injection facility to add an inorganic coagulant to the aeration tank. The phosphorus removal rate is excellent, and a removal rate of 90% or more can be easily obtained.

However, the "coagulant-added activated sludge method" has not been widely used because of the following major drawbacks. That is, when an iron-based or aluminum-based inorganic coagulant such as iron phosphate, ferric hydroxide, aluminum phosphate, or aluminum hydroxide is used, a large amount of sludge is generated, and the generated sludge is difficult to concentrate. (Hereinafter, it may be referred to as bulky.) However, since it is difficult to dehydrate, it is a serious drawback that the disposal of sludge is extremely troublesome.

[0004]

As a result of investigating the cause of the above-mentioned drawbacks of the conventional coagulant-added activated sludge method, the present inventors have found that iron-based or aluminum-based sewage containing phosphorus-containing organic sewage. Although a high phosphorus removal rate can be obtained by directly adding the inorganic coagulant, the precipitate (flock) of the produced iron phosphate, ferric hydroxide, aluminum phosphate or aluminum hydroxide is hard to concentrate and It is difficult to dehydrate, and it is completely impossible to control the sedimentation concentration such as improving the concentration dehydration property of flocs by the method of directly adding these coagulants to the wastewater. We have found the fact that a large amount of concentrated and dewaterable sludge is produced.

As a result of extensive studies to solve this drawback, the conventional idea of directly adding an iron-based or aluminum-based inorganic coagulant to wastewater was abolished, and i) an iron-based or aluminum-based inorganic Prior to adding the coagulant to the organic wastewater, a slurry having an improved sedimentation / concentration property was prepared from an iron-based and / or aluminum-based inorganic coagulant in advance.
i) It was concluded that a treatment method of adding the slurry whose sedimentation concentration is controlled to organic wastewater to generate flocs having good sedimentation concentration and thus concentration and dehydration properties is necessary. The present invention utilizes the advantages of the coagulant-added activated sludge method, while establishing a new technology that completely solves the drawbacks of the conventional coagulant-added activated sludge method, and does not generate hardly concentrated or hardly dehydrated sludge. It is an object of the present invention to provide a new technique for efficiently removing phosphorus.

[0006]

The above-mentioned object of the present invention can be achieved by the method for removing phosphorus in wastewater according to the present invention. That is, (1) a slurry whose sedimentation concentration is controllable is prepared from particles of ferric hydroxide and / or aluminum hydroxide, and the slurry is added to raw water containing phosphorus, and then the raw water is added to a living organism. A method for removing phosphorus in water, which comprises leading to a treatment step, solid-liquid separation of the effluent of the biological treatment step, and using the separated water as treated water, (2) an acidic solution of iron salt and / or aluminum salt An alkaline agent is added to increase the pH of the solution of the iron salt and / or aluminum salt, and the resulting particles of ferric hydroxide and / or aluminum hydroxide produce a slurry whose sedimentation concentration is controllable. It is characterized in that after preparing and adding the slurry to raw water containing phosphorus, the raw water is led to a biological treatment step, the outflow water of the biological treatment step is subjected to solid-liquid separation, and the separated water is treated water. Removal of phosphorus in water Law. (3) Ferric hydroxide produced by adding a Mg-based or Ca-based alkaline agent to an acidic solution of an iron salt and / or an aluminum salt to increase the pH of the iron salt and / or aluminum salt solution And / or particles of aluminum hydroxide are used to prepare a slurry whose sedimentation concentration is controllable, and the slurry is added to raw water containing phosphorus, and then the raw water is introduced into a biological treatment step, and the raw water of the biological treatment step is added. It is achieved by a method for removing phosphorus in water, characterized in that the effluent water is subjected to solid-liquid separation, and the separated water is treated water.

That is, the core of the technical idea of the present invention is iron hydroxide whose precipitation concentration dehydration property is controlled from an iron-based or aluminum-based inorganic coagulant under reaction conditions in which characteristics such as particle size can be controlled, By generating aluminum hydroxide particles, dispersing and suspending the particles in water, and preliminarily preparing a slurry having good sedimentation concentration and excellent concentration / dehydration properties, and adding the prepared slurry to wastewater, sedimentation is performed. The technical idea is to generate flocs with good concentration, to adsorb and remove phosphorus to a high degree, and to prevent generation of sludge that is difficult to concentrate and dehydrate.

Here, the sedimentation-concentration property of the slurry is a characteristic evaluated by the volume occupied by the precipitation particles when the particles in the slurry are sedimented for a certain period of time. For example, the evaluation of the sedimentation-concentration property of the slurry. Of the Sludge Volume Index
(Hereinafter referred to as SVI value). SV
The I value is the volume of sludge occupied by 1 g of solid matter in milliliters after the slurry was filled in a graduated cylinder and allowed to stand for 30 minutes. “Controllable sedimentation concentration” means that an appropriate sedimentation concentration index (for example, SVI value) can be reproduced. Further, the concentration / dehydration property of the slurry is a property related to the syneresis property of the particles when the particles in the slurry or the like are subjected to solid-liquid separation from the dispersion medium by filtration or centrifugal sedimentation. What is the sedimentation concentration and concentration dehydration of the slurry?
Although the characteristics are not always parallel, the flocculating and concentrating properties of flocs produced by the addition of the iron-based or aluminum-based flocculant slurry of the present invention are in a parallel relationship with each other, and the flocs having good sedimentation-concentrating properties are constituted. The concentrated dehydration property of the iron hydroxide or aluminum hydroxide particles is good. That is, the particles have good syneresis, and the treated water is easily separated.

[0009]

In the conventional coagulation-sedimentation method, for example, chlorinated sewage in the aeration tank for biological treatment is treated with the second chloride.
Since an inorganic flocculant solution such as iron, poly-iron sulfate, aluminum sulfate, and poly-aluminum chloride is directly added, a flocculated precipitate of ferric phosphate and aluminum phosphate is rapidly produced in the aeration tank. In this case, the following precipitation reaction, that is, M ³⁺ + PO ₄ ^3- → MPO ₄ ↓ −−−− (1) M ³⁺ + 3OH ⁻ → M (OH) ₃ ↓ −− (2) (where , M ³⁺ represents Fe ³⁺ or Al ³⁺ ), and at the same time phosphorus is removed, the reaction causes extremely difficult concentration and hardly dehydrating MPO ₄ or M.
A precipitate of (OH) ₃ is produced. In the conventional method, since the inorganic coagulant liquid is directly added to the phosphorus removal target water (here, sewage containing phosphorus), a small amount of inorganic coagulant is added to a large amount of pH-neutral phosphorus-containing wastewater. Therefore, the formation of MPO ₄ and M (OH) ₃ precipitates rapidly proceeds in the neutral pH range, and the formation of MPO ₄ and M (OH) ₃ precipitates with good concentration and dehydration properties is achieved. Is impossible.

On the other hand, in the present invention, an apparatus for adding an alkaline agent to the aqueous solution of the inorganic coagulant is added before the precipitation reaction by adding the inorganic coagulant consisting of an acidic aqueous solution of iron salt and aluminum salt to the sewage. Since a slurry having good sedimentation / concentration property and good concentration / dehydration property is prepared in the apparatus before being added to the sewage and the prepared slurry is added to the aeration tank, in the slurry preparation apparatus, M ³⁺ + 3OH ⁻ → M (OH) ₃ ↓ −− (2) The reaction proceeds in an environment in which the environment of low pH changes to neutral pH, and precipitation of M (OH) _{3 with} good sedimentation concentration and dehydration property Can be produced with good reproducibility, and by adding this slurry to the aeration tank, flocs with good sedimentation / concentration / dehydration properties can be produced even in the presence of activated sludge in wastewater, and phosphorus can be efficiently dephosphorized.

As an alkaline agent added to the flocculant in the slurry preparation device, Mg (O) other than NaOH is used.
H) ₂ , MgO, Ca (OH) ₂ , CaO, CaCO ₃
When an alkali such as the above is used, a precipitate of M (OH) _{3 having} a better sedimentation concentration and dehydration property can be generated. In the present invention, the production of a slurry whose sedimentation concentration is controllable means
For example, as described above, the precipitate obtained by the method of adding an alkaline agent in advance to an acidic aqueous solution of an iron salt or an aluminum salt is dispersed / suspended in water to obtain a slurry having good sedimentation-concentrating properties and good concentration / dehydration properties. It means stable and reproducible preparation.

In the present invention, as means for producing a precipitate of ferric hydroxide and / or aluminum hydroxide having good sedimentation / concentration and dehydration properties, an aqueous solution of polyiron sulfate (abbreviated as polyiron) and aluminum sulfate is used as Mg (OH). ) ₂ or Ca (OH)
_The manufacturing method neutralized by ₂ is the simplest in operation,
Most preferred for the present invention. In addition, as another manufacturing method, an aqueous solution of a ferrous salt is oxidized with an oxidizing agent such as air, oxygen, ozone, or hydrogen peroxide to produce Fe (O 2
H) ₃ particles can also be obtained to obtain precipitated particles having good sedimentation / concentration and dehydration properties. Disperse / suspend the particles from the precipitated particles with good sedimentation and dehydration properties in water,
A slurry with good sedimentation and concentration properties and with good concentration and dehydration properties can be prepared stably and with good reproducibility, and by using the slurry with good concentration and dehydration properties together with sewage such as sewage into an aeration tank having activated sludge, phosphorus It is possible to obtain an aggregate containing activated sludge and having a small SVI value (about 50 or less) and good sedimentation / concentration property while removing the above. The above is the operation of the present invention.

Next, sewage will be cited as a typical example of phosphorus-containing organic wastewater, and a specific embodiment of the present invention will be described with reference to FIG. In FIG. 1, 2 is an aeration tank of the activated sludge process which is a typical example of the biological treatment process. Sewage 1 is supplied to the aeration tank 2 through a raw water supply pipe 20. The biological treated water treated in the aeration tank 2 is the water supply well 2
From 1 through a settling basin 3 (which is an example of a kind of solid-liquid separation step), clarified treated water 4 flows out of the system through a treated water outflow pipe 22. Here, the biological treatment process (aeration tank 2) is, of course,
It may be a biological treatment process, and the process can be set aerobically or anaerobically. Further, as the solid-liquid separation section, in addition to the settling tank 3, known solid-liquid separation means such as a membrane separation device, a sedimentation separation device or a centrifugal separation device can be appropriately used.

An air diffusing member 5 is arranged below the aeration tank 2, and air is supplied to the air diffusing member 5 from an air diffusing blower 6 through an air supply pipe 23. Sludge 1 settled and separated in settling tank 3
7 is returned from the bottom of the settling tank 3 to the aeration tank 2 by the sludge return pump 7 through a part of the sludge return pipe → sludge return pipe 24, and the other part through the sludge transfer pipe 25. The excess sludge 9 is sent to the sludge tank 18 and stocked.

The slurry (a), which is prepared by dispersing and suspending particles of ferric hydroxide and / or aluminum hydroxide, which is a feature of the present invention, and which has a controllable sedimentation and concentration property, is a reaction equipped with a stirrer 16. The slurry is prepared in the slurry preparation unit 30 including the tank 15 and the alkaline liquid supply pipe 28, and the slurry supply pipe 2
Slurry constant quantity supply pump 19 to raw water supply pipe 20 via 6
Is supplied quantitatively by. 11 is an acidic aqueous solution of an iron salt and / or an aluminum salt, and the acidic liquid tank 32
Is stored in the tank, and the acid solution is supplied in a fixed amount from the pump 14
Liquid is supplied to the reaction tank 15 via the acidic liquid supply pipe 27 provided with. Further, 12 is an alkaline liquid, which is stocked in an alkaline liquid tank 33, and is then supplied to the reaction tank 15 via an acidic liquid supply pipe 28 equipped with a constant amount supply pump 13 for the acidic liquid.

In the conventional coagulant-added activated sludge method, in FIG. 1, PAC, Alum, ferric chloride, poly This is a technique of directly adding an acidic liquid of an iron-based or aluminum-based inorganic coagulant such as ferric sulfate to the aeration tank 2, and the slurry preparation unit 30 surrounded by a dotted line in FIG.
It did not have a process like.

On the other hand, as will be described below, in the present invention, the existence or nonexistence of the steps within the dotted frame of FIG. 1 makes a very significant difference. That is, the slurry (a) prepared by suspending particles of ferric hydroxide and / or aluminum hydroxide having good sedimentation and concentration properties in the sewage 1 is continuously supplied at the injection point 10 of the raw water supply pipe 20. Aeration tank for activated sludge process with sewage added intermittently or intermittently 2
When the activated sludge and the slurry (a) are brought into contact with the sewage while being fluidized and suspended by the air discharged from the air diffusing member 5, the BOD in the sewage is biologically treated and removed, and at the same time, the sewage is converted into sewage. The contained phosphorus is highly adsorbed and removed by the slurry (a). Next, the mixture of activated sludge and flocs generated by the slurry (a) was mixed with the sedimentation tank 3
And is separated into precipitates and separated into the clarified treated water 4 from which phosphorus, BOD and SS have been highly removed and the settling sludge 17.
Most of the returned sludge 8 of the settled sludge 17 is returned to the aeration tank 2 by the sludge return pump 7 through the returned sludge pipe 24. In addition, the other part of the settled sludge 17 is drawn out of the system in an amount corresponding to the surplus activated sludge generated by the biological treatment of the sewage, passes through the transfer sludge pipe 25, and becomes the sludge as the surplus activated sludge 9. It is sent to the sludge tank 18 where the dehydration process is performed and is dehydrated.

Although a small amount of slurry is mixed in the surplus activated sludge 9, since the slurry has a good concentration and dehydration property as described above, it can be easily dehydrated, and the conventional coagulant-added activated sludge is used. It does not have the disadvantage of sludge, which has a markedly poor dehydration property.

As described above, in contrast to the conventional coagulant-added activated sludge method, the slurry preparation section 30 surrounded by a dotted line in FIG.
It is a surprising effect that the drawbacks of the prior art can be completely solved and the advantages can be utilized only by adding such simple equipment and process. The reason why such a great effect appears is due to a fundamental difference between the conventional technology and the technical idea of the present invention. In the prior art, attention is paid only to removing phosphorus, and the MPO ₄ and M (O
There is a technical defect in that the sedimentation concentration of the H) ₃ precipitate is indifferent and, in fact, the sedimentation concentration cannot be controlled at all.

As the biological treatment step in the present invention, in addition to the usual activated sludge method, a biological nitrification denitrification method,
It goes without saying that any biological treatment process such as a biological dephosphorization method may be applied. In particular, when the present invention is applied to the biological dephosphorization method, excellent effects can be obtained. That is, the biological dephosphorization method is a technique for removing phosphorus by excessively accumulating phosphorus in microbial cells, but the phosphorus removal effect is easily affected by disturbances such as water quality fluctuations of raw water,
There is a drawback that a high removal rate of phosphorus cannot be stably obtained. However, when a slurry is added to this biological dephosphorization system, the phosphorus that could not be biologically removed can be adsorbed and removed, so that a high phosphorus removal rate can always be obtained and the addition amount of the slurry can be small. There is an effect. This is because it is only necessary to adsorb a small amount of residual phosphorus that could not be biologically removed.

[0021]

EXAMPLES The hydroxides [M (OH) ₃ ] of the present invention are described below.
Specific examples of the method for controlling the sedimentation and concentration of the particles and the method for removing phosphorus in raw water using a slurry in which the particles are suspended are shown. However, the embodiments of the present invention are not limited to the following description.

Example 1 In order to control the sedimentation / concentration property of a slurry in which hydroxide [M (OH) ₃ ] particles are suspended, the hydroxide [M (O
The method of the present invention for preparing H) ₃ ] particles is as follows: (1) Add Mg (OH) ₂ to the sulphate sulfate to obtain a pH of 5
Neutralize to ~ 6. (2) Add Mg (OH) ₂ to ferric polysulfate to obtain p
Neutralize to H4-6. (3) Add pH 4 by adding Mg (OH) ₂ to ferric chloride.
Neutralize to ~ 6. (4) Ca (OH) on polyaluminum chloride (PAC)
Add ₂ to neutralize to pH 5-6. (5) Add Ca (OH) ₂ to the sulphate soil to adjust the pH to 5
Neutralize to ~ 6. (6) Add Mg (OH) ₂ to ferric polysulfate to obtain p
Neutralize to H4-6. (7) NaOH is gradually added to polyaluminum chloride (PAC) to neutralize it to pH 5-6. (8) Gradually add NaOH to the sulphate to adjust the pH to 5
Neutralize to ~ 6. (9) Gradually add NaOH to ferric polysulfate to obtain p
Neutralize to H4-6. (10) Gradually add NaOH to ferric chloride to adjust pH
Neutralize to 4-6. Is mentioned.

In Table 1, a slurry in which particles of hydroxide [M (OH) ₃ ] prepared by the method described in (1) to (10) above are suspended is placed in a cylinder having a volume of 1 liter. The concentration of concentrated slurry when the slurry was allowed to stand for 1 hour by the sedimentation concentration inspection method in which the particles were allowed to stand for 1 hour was shown.

[0024]

[Table 1]

For comparison, PAC, sulphate, ferric polysulfate and chloride were added to sewage having a pH of 7.2, an SS content of 120 mg / liter and a phosphorus content of 2.6 mg / liter according to the sedimentation concentration test method. Table 2 shows the results of inspecting the sedimentation concentration of the produced slurry when the ferric iron was added in an amount of 2.5 in terms of a metal atom / phosphorus atom (M / P) molar ratio and allowed to stand in a 1-liter cylinder for 1 hour. Shown in.

[0026]

[Table 2]

From the comparison of the inspection results in Tables 1 and 2, the slurry of the present invention for producing the iron-based or aluminum-based metal hydroxide precipitate with controlled sedimentation / concentration properties is compared to the conventional method. It was confirmed that the sedimentation concentration was extremely good.
(The better the concentration / dehydration property is, the better the sedimentation / concentration property is.) Each of the slurries (1) to (10) in Table 1 was added to sewage according to the process of FIG. Processed in a fluid suspension. The results of the sedimentation concentration test and the water treatment results at this time are shown in Tables 3 and 4.

[0028]

[Table 3]

[0029]

[Table 4]

Comparative Example 1 Sewage having the same water quality as shown in Table 3 was used, the same aeration tank was used, and an iron-based or aluminum-based inorganic coagulant (P
AC, sulphate, Alum, poly ferric sulfate, ferric chloride) are each the molar ratio of Fe or Al atom and phosphorus atom (M
/ P) was added to the sewage so as to be 2.5. As a result, the phosphorus concentration in the treated water was 0.05 to 0.13 mg / liter, which means that phosphorus was highly removed regardless of which coagulant was used. However, the excess sludge generation ratio γ is 1.2
The increase was ~ 1.28, which is a significant increase compared to the present invention. This produces FePO ₄ , Fe (OH) ₃ , AlPO ₄ and A
It shows that l (OH) ₃ is hardly concentrated. Here, the excess sludge generation ratio γ refers to when the volume of excess sludge generated when an iron-based or aluminum-based inorganic coagulant is not added to the water to be treated (sewage in the above case) is 1 The generation volume ratio of the excess sludge in Examples and Comparative Examples is shown.

[0031]

According to the phosphorus removing method of the present invention, the following industrially important effects are obtained. 1) A high phosphorus removal effect is obtained, and MPO ₄ and M (OH) ₃ sludge, which are difficult to concentrate and dehydrate, are not generated, and the drawbacks of the prior art can be completely solved. 2) Therefore, the load on sludge treatment is significantly reduced. 3) If there is an existing biological treatment facility, phosphorus can be removed by the simple method of adding the slurry preparation section as shown in Fig. 1, so it is extremely practical and inexpensive to implement. is there.

[Brief description of drawings]

FIG. 1 is a flowchart illustrating an example of a phosphorus removing step of the present invention.

[Explanation of symbols]

 1 Sewage 2 Aeration tank 3 Sedimentation tank 4 Clarification treated water 5 Diffusing member 6 Aeration blower 7 Sludge returning pump 8 Returning sludge 9 Excess sludge 10 Injection point 11 Acidic aqueous solution 12 Alkaline solution 13 Quantitative pump 14 Quantitative pump 15 Reaction tank 16 Stirrer 17 Sludge 18 Sludge tank 19 Metering pump 20 Raw water supply pipe 21 Water supply well 22 Treated water outflow pipe 23 Air supply pipe 24 Sludge return pipe 25 Sludge transfer pipe 26 Slurry supply pipe 27 Acid liquid supply pipe 28 Alkaline liquid supply pipe 30 Slurry preparation Part 32 Acidic Liquid Liquid Tank 33 Alkaline Liquid Liquid Tank (a) Slurry

Claims (3)

[Claims] 1. A slurry having a controllable sedimentation and concentration property is prepared from particles of ferric hydroxide and / or aluminum hydroxide, the slurry is added to raw water containing phosphorus, and then the raw water is treated with a living organism. A method for removing phosphorus in water, which comprises leading to a treatment step, solid-liquid separating the outflow water of the biological treatment step, and using the separated water as treated water. 2. Ferric hydroxide and / or water produced by adding an alkaline agent to an acidic solution of iron salt and / or aluminum salt to increase the pH of the solution of iron salt and / or aluminum salt. A slurry whose sedimentary concentration is controllable by particles made of aluminum oxide is added, and the slurry is added to raw water containing phosphorus, and then the raw water is introduced into a biological treatment step, and the effluent water of the biological treatment step is solidified. A method for removing phosphorus in water, which comprises performing liquid separation and using the separated water as treated water. 3. A hydroxide solution produced by adding a Mg-based or Ca-based alkaline agent to an acidic solution of an iron salt and / or an aluminum salt to increase the pH of the iron salt and / or aluminum salt solution. (2) A slurry whose sedimentation and concentration properties can be controlled is prepared from particles composed of iron and / or aluminum hydroxide, and the slurry is added to raw water containing phosphorus, and then the raw water is introduced into a biological treatment step to carry out the biological treatment. A method for removing phosphorus in water, characterized in that the outflow water of the process is subjected to solid-liquid separation, and the separated water is treated water.