JP3201095B2 - Method and apparatus for removing phosphorus from water - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a system for removing phosphorus by injecting chemicals into a digested sludge dewatered filtrate, in which the amount of dissolved oxygen is measured by measuring the phosphorus concentration and the amount of dissolved oxygen in the inflow water. The present invention relates to a method and an apparatus for removing phosphorus in water.

[0002]

2. Description of the Related Art Phosphorus is an element widely existing in the ground and is contained in natural water. However, since phosphorus is contained in large amounts in human waste, sludge, fertilizers, etc., these are mixed into natural water. Often. Phosphorus in water is orthophosphate,
There are various forms such as metaphosphate, pyrophosphate and polyphosphate, and organic phosphorus compounds such as phosphate esters and phospholipids. Phosphorus forms are divided into three types: phosphate ion form phosphorus, hydrolyzable phosphorus and total phosphorus, and these are further divided into soluble and insoluble.

[0003] All of these various phosphorus compounds are finally converted into orthophosphoric acid by pretreatment, and are measured by utilizing a reaction peculiar to phosphate ions, and are expressed in terms of the amount of phosphorus. Phosphorus itself plays an important role in the growth of living organisms,
And it is an essential element in biological treatment such as sewage,
On the other hand, phosphorus contributes to the promotion of eutrophication in lakes and seas, and the increase of phosphorus compounds in water is not preferable.

On the other hand, in the anaerobic digestion means of sewage sludge, a phenomenon in which phosphorus is dissolved from the solid phase is observed, and therefore, the liquid phase of digested sludge has a relatively high concentration, for example, 100 to 300 mg · P.
It is known to contain about / l of phosphate ion form phosphorus. The above-mentioned phosphate ion-form phosphorus is a phosphate ion in water represented by the amount of phosphorus (P).

As a method for biologically removing nitrogen and phosphorus simultaneously, an anaerobic-aerobic activated sludge method is known as a modification of the conventional activated sludge method. As shown in FIG. 2, the anaerobic-aerobic activated sludge method is a method in which a biological reaction tank is provided with anaerobic tanks 1a, 1b and D without dissolved oxygen (abbreviated as DO).
Oxygen-containing aerobic tanks 2a, 2b and 2c are separated from each other, and the anaerobic tanks 1a and 1b are used to stir the inflow water 3 by an agitation mechanism 10 in an anoxic state to remove denitrification by denitrifying bacteria in activated sludge. Then, by supplying air from the blower 5 to the air diffuser 4 disposed inside the aerobic tanks 2a, 2b, 2c, oxidative decomposition of organic matter by activated sludge in the presence of oxygen by aeration and nitrification bacteria The nitrification of ammonia is performed.

The nitrification liquid in the last aerobic tank 2c is fed into the anaerobic tank 1a by using the nitrification liquid circulation pump 6, whereby the denitrification effect is promoted. Phosphorus in water is anaerobic tank 1a,
It is released in 1b and is taken in activated sludge and removed in the aerobic tanks 2a, 2b, 2c. 7 is the final sedimentation basin,
The supernatant 50 of the final sedimentation basin 7 is discharged after passing through a disinfection tank or the like (not shown), and a part of the sludge settled in the final sedimentation basin 7 is returned to the anaerobic tank 1a by the sludge return pump 8. The other sludge is sent from the surplus sludge pump 9 to a surplus sludge treatment device (not shown) for treatment.

[0007] Such an anaerobic-aerobic activated sludge treatment apparatus can obtain the same effect as the organic matter removing effect achieved by the ordinary standard activated sludge method, and has a higher removal rate of nitrogen and phosphorus than the activated sludge method. Is achieved.

On the other hand, the present applicant has previously filed Japanese Patent Application No.
No. 91713 proposes a device for removing phosphorus from a dehydrated filtrate shown in FIG. This will be briefly described as follows.
Is discharged as treated water 15 from the first settling basin 12 through the aeration tank 13 and the final settling basin 14, while the initial settling sludge 16 of the first settling basin 12 and the excess sludge 17 of the final settling basin 14 are sludge thickening tanks. It is sent to 18.

A part of the surplus sludge 17 is returned to the aeration tank 13, and the supernatant 19 of the sludge concentration tank 18
The sludge 21 in the sludge thickening tank 18 is first returned to the sedimentation basin 12 together with the return water 20, and is sent to the sludge digesting tank 22 for anaerobic digestion. This sludge digestion tank 22
The coagulant is injected into the digested sludge 23 from the polymer coagulant injecting device 24 to perform the coagulation treatment. As this flocculant, a polymer flocculant having no phosphorus removing ability is employed.

After the coagulation, the dewatered cake 26 is obtained by a dehydrator 25, and the dehydrated filtrate of the dehydrator 25 is sent to a dehydrated filtrate temporary storage tank 29 via a dehydrated filtrate discharge pipe 28. At this time, the dehydrated filtrate sampled from the dehydrated filtrate discharge line 28 is supplied to the automatic phosphorus concentration measuring device 31 to automatically measure the phosphorus concentration, and the measured value is converted into an electric signal, and the chemical injection control arithmetic device 33 At the same time, the flow rate of the dehydrated filtrate is measured by the flow meter 32, and the measured value is similarly converted into an electric signal and input to the chemical injection control arithmetic unit 33.

The chemical injection control arithmetic unit 33 calculates a chemical injection rate based on the stoichiometric relationship between the phosphorus and the phosphorus removing chemical from the data on the phosphorus concentration of the dehydrated filtrate, and calculates the chemical injection rate by the flow meter 32. The final chemical injection rate is determined by multiplying the data of the measured flow rates, and the chemical injection into the dehydrated filtrate temporary storage tank 29 is performed by driving the chemical injection device 34 based on the final chemical injection rate. Then, the dehydrated filtrate is stirred with the driving of the stirring mechanism 30, and the phosphorus insolubilization treatment is performed.

[0012] The dehydrated filtrate thus treated is supplied to the precipitation tank 3.
5, and the precipitate 36 insolubilized by the injection of the chemical is withdrawn from the bottom of the tank, returned to the dehydrator 25, and dehydrated again. The supernatant 3 of the precipitation tank 35
7 is returned to the sedimentation basin 12 as return water 20 together with the supernatant 19.

The means for removing phosphorus by injecting a chemical into the dewatered filtrate of digested sludge 23 reduces the amount of chemical sludge generated due to poor dehydration as compared with a means of injecting a chemical directly into aeration tank 13. Has the effect of

[0014]

However, among such conventional phosphorus removing means, the anaerobic-aerobic activated sludge method shown in FIG. When the DO of the inflow water becomes high as described later, the anaerobic state cannot be maintained satisfactorily, and there is a concern that the ability to remove phosphorus may be reduced. As described above, there is a problem that phosphorus excessively taken into an organism is redissolved from a solid phase, and a relatively high concentration of phosphate ion-type phosphorus is contained in a liquid phase of digested sludge. In the method of coagulating and dehydrating using a polymer flocculant that does not have the ability to remove phosphorus, the dehydrated filtrate is first returned to the sedimentation basin as return water. Cause the phosphorus concentration of
There is a problem that the load on the water treatment system is increased and the phosphorus concentration of the discharge water cannot be reduced.

As a method for removing phosphorus by injecting a chemical based on a biological phosphorus removing method, means for directly injecting a chemical into an aeration tank or means for injecting a chemical into secondary treatment water or return water are available. It is conceivable, however, that it is technically difficult to inject the chemicals without excess or deficiency according to the phosphorus concentration. However, there is a problem in that the amount of injected chemical is insufficient, and when the phosphorus concentration is low, the injection of the chemical becomes excessive and the chemical is wasted.

On the other hand, as shown in FIG. 3, the phosphorus concentration of the dehydrated filtrate is measured, and a chemical is injected based on the stoichiometric injection rate according to the phosphorus concentration to insolubilize the phosphorus. The effect of reducing the load on the water treatment system due to the return water is obtained by removing it, but if the DO of the inflow water increases, the phosphorus removal capacity of the anaerobic-aerobic tank may decrease. The problem remains.

Accordingly, the present invention solves the problems of the conventional apparatus for removing phosphorus in water, and reduces the phosphorus concentration of the treated water by removing phosphorus from the dehydrated filtrate. It is an object of the present invention to provide a method and an apparatus for removing phosphorus, which can perform the phosphorus removal ability even when the DO of the inflow water rises.

[0018]

According to the present invention, in order to achieve the above object, the influent water is introduced into an anaerobic-aerobic sludge digestion tank for treatment, and a polymer flocculant is injected into the concentrated digested sludge. And then dehydrated by a dehydrator, measure the phosphorus concentration of the dehydrated filtrate, and calculate the final chemical injection rate based on the stoichiometric relationship between the phosphorus and the phosphorus removing chemical from the phosphorus concentration data, Based on this final chemical injection rate, chemicals are injected from the chemical injection device into the dehydrated filtrate temporary storage tank, and the phosphorus insolubilization treatment is performed. In the method for removing phosphorus, a dissolved oxygen meter and a flow meter are attached to the inflow water, and a pH meter and a pH meter are added to the dehydrated filtrate temporary storage tank.
A feedback control device and an alkali injection device are provided, and a chemical injection ratio based on the stoichiometric relationship between the phosphorus and the phosphorus-removing chemical is calculated from data on the phosphorus concentration of the dehydrated filtrate and dissolved oxygen in the inflow water. The final chemical injection rate is determined by multiplying the chemical injection rate by the data on the flow rates of the dehydrated filtrate and the inflow water, and the phosphorus insolubilization treatment is performed by injecting the phosphorus insolubilizing reagent into the dehydrated filtrate based on the final chemical injection rate. To provide a method and apparatus for removing phosphorus in water.

Calcium sulfide is used as the phosphorus insolubilizing reagent. If the concentration of dissolved oxygen in the influent water is low and the amount of calcium ions required for removing phosphorus is insufficient, slaked lime is replenished. Further, the pH value in the dehydrated filtrate temporary storage tank is measured by the pH meter, and the sodium hydroxide solution is injected into the dehydrated filtrate temporary storage tank from the alkali injection device so that the pH value is about 8 by the pH feedback control device. I have to do it.

[0020]

According to the method and apparatus for removing phosphorus in water,
The DO of the influent water is measured by the dissolved oxygen meter and the flow rate is measured by the flow meter, and the digestion treatment is performed by the anaerobic-aerobic tank, and then the polymer flocculant is injected into the digested sludge to perform the coagulation treatment. After the coagulation, the dehydrated filtrate is sent to a dehydration filtrate temporary storage tank and temporarily stored therein by being subjected to a dehydrator.

At this time, the phosphorus concentration of the dehydrated filtrate sampled from the dehydration filtrate discharge line of the dehydrator is automatically measured by an automatic measuring device. The chemical injection rate is calculated based on the stoichiometric relationship between the chemical and the phosphorus removal chemical, and the chemical injection rate is multiplied by the flow rate data measured by the flow meter for the dehydrated filtrate and the flow rate of the inflow water to obtain the final chemical injection rate. The rate is determined, and a phosphorus insolubilizing reagent is injected from the chemical injection device into the dehydrated filtrate based on the final chemical injection rate, and the phosphorus insolubilization treatment is performed.

During the above operation, the pH value in the dewatered filtrate temporary storage tank is measured by the pH meter, and the sodium hydroxide solution is injected from the alkali injection device so that the above-mentioned pH value is about 8 by the pH feedback control device. You.

The precipitate thus insolubilized by the chemical treatment is returned to the dehydrator and dehydrated again, and the supernatant is returned to the water treatment system as return water.

[0024]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to FIG. 1, a specific embodiment of a method and an apparatus for removing phosphorus in water according to the present invention will be described in detail by attaching the same reference numerals to the same constituent parts as those of the conventional art. .

In the figure, reference numeral 11 denotes inflow water, and 12 denotes inflow water 11
Is a first settling pond into which water flows, and a dissolved oxygen meter 40 and a flow meter 41 are attached to the inflow water 11. 42 is an anaerobic-aerobic tank, 14 is a final sedimentation basin, 18 is a sludge thickening tank, 22
Is a sludge digestion tank, 24 is a polymer flocculant injection device, 25 is a dehydrator, and 29 is a dehydration filtrate temporary storage tank.
The dewatered filtrate discharge pipe 28 derived from 5 is connected to a dehydrated filtrate temporary storage tank 29. 30 is a stirring mechanism, 31 is a device for automatically measuring the phosphorus concentration of the dehydrated filtrate, 32 is a flow meter, 33
Is a chemical injection control arithmetic unit for the dehydrated filtrate, 34 is a chemical injection device for the dehydrated filtrate temporary storage tank 29, and 35 is a precipitation tank.

The chemical injection control arithmetic unit 33 includes an automatic phosphorus concentration measuring device 31, a flow meter 32, a DO measured by the dissolved oxygen meter 40 of the inflow water 11, and a flow rate of the inflow water 11 measured by the flow meter 41. Are entered. Further, a pH meter 43 is provided in the dewatered filtrate temporary storage tank 29, and the pH feedback controller 4
4 and an alkali injection device 45 for the dehydrated filtrate temporary storage tank 29 are provided.

The basic operation of this embodiment will be described below. That is, DO is measured by the dissolved oxygen meter 40 before the inflow water 11 first flows into the sedimentation basin 12, and then the anaerobic-
While being discharged as treated water 15 via the aerobic tank 42 and the final sedimentation basin 14, the initial sludge 16 of the first sedimentation basin 12 and the excess sludge 17 of the final sedimentation basin 14 together with the sludge concentration tank 18
Sent to. Part of the surplus sludge 17 is returned to the anaerobic tank side of the anaerobic-aerobic tank 42, and the supernatant 19 of the sludge concentration tank 18 is returned to the sedimentation basin 12 together with the return water 20.

The concentrated sludge 21 in the sludge thickening tank 18 is sent to the next-stage sludge digestion tank 22, where the anaerobic digestion treatment is performed. Then, a flocculant is injected into the digested sludge 23 of the sludge digestion tank 22 from the polymer flocculant injecting device 24 to perform a flocculation treatment. Note that a polymer flocculant having no phosphorus removing ability is used as the flocculant. Then, after the aggregation, the dehydrated cake 26 is obtained through the dehydrator 25, while the dehydrated filtrate of the dehydrator 25 is
Dehydration filtrate temporary storage tank 2 via dehydration filtrate discharge line 28
It is sent to 9.

At this time, the dehydrated filtrate sampled from the dehydrated filtrate discharge line 28 is supplied to an automatic phosphorus concentration measuring device 31 to automatically measure the phosphorus concentration, and this measured value is converted into an electric signal to control chemical injection. The flow rate of the dehydrated filtrate is measured by the flow meter 32 at the same time as the flow rate of the dehydrated filtrate. The measured value is similarly converted into an electric signal and input to the chemical injection control calculation device 33.

The chemical injection control arithmetic unit 33 calculates the chemical injection rate based on the stoichiometric relationship between the phosphorus and the phosphorus removing chemical from the data on the phosphorus concentration of the dehydrated filtrate and the DO of the influent water 11. Flow rate 32 and inflow water 11 at injection rate
The final chemical injection rate is determined by multiplying the data of the flow rate measured by the flow meter 41 of the above, and the chemical injection into the dehydrated filtrate temporary storage tank 29 is performed by driving the chemical injection device 34 based on the final chemical injection rate. Done. Then, the dehydrated filtrate is stirred with the driving of the stirring mechanism 30, and the phosphorus insolubilization treatment is performed.

Usually, a sulfuric acid band or slaked lime is used as a phosphorus insolubilizing reagent. In this embodiment, calcium sulfide CaS is used instead of the above reagent. The reaction formula when using this calcium sulfide is as follows.

[0032]

[Formula 1] _{3O 2 + 4CaS → 2S 2 O} 3 - + 4Ca 2+ ··············· (1) 3HPO 4 2+ 5Ca 2+ + 4OH - → Ca 5 (OH) ( PO ₄ ) ₃ + 3H ₂ O (2) Calcium sulfide CaS dissipates dissolved oxygen as shown in equation (1), and Ca ²⁺ ion becomes (2 The phosphorus is removed by reacting with phosphate ions according to the formula to precipitate and separate as insoluble hydroxyapatite Ca ₅ (OH) (PO 4) _{3 in} a neutral to weakly alkaline region. Therefore, even when the DO of the influent becomes high as after rain, the DO in the influent disappears due to the addition of calcium sulfide CaS as a phosphorus insolubilizing reagent,
In the anaerobic-aerobic tank, the anaerobic state of the anaerobic tank is favorably maintained, and there is no fear that the phosphorus removal ability of the treated water is reduced.

The thiosulfate ion S ₂ O ₃ ⁻ generated by the reaction between CaS and DO becomes an electron donor in the denitrification reaction in the anaerobic tank, and the nitrogen removal efficiency is improved.

At the time of the above reaction, the pH value in the dehydrated filtrate temporary storage tank 29 is measured by the pH meter 43, and sodium hydroxide is supplied from the alkali injection device 45 by the pH feedback control device 44 so that the pH value is about 8. Na
An OH solution is injected.

Specifically, the injection rate of calcium sulfide CaS as the phosphorus insolubilizing reagent is calculated by calculating the amount of dissolved oxygen entering the water treatment system from the DO of the influent water 11 and the amount of the influent water, and calculating the equivalent amount of CaS. And the value obtained by dividing by the filtrate throughput. If this is expressed by a formula,

[0036]

I _CaS = DO _IN × Q _IN × K _CaS-DO / Q _FIL (3) here

[0037]

_{Embedded image} I _CaS ; Injection rate of CaS (ppm) DO _IN ; Dissolved oxygen concentration of influent (ppm or mg / l) Q _IN ; Influent water (m ³ / hr) Q _FIL ; ³ / hr) K _CaS-DO ; Do equivalent conversion coefficient of _CaS (K _CaS-DO = 4 × 7
2/3 × 16 = 6.0) The addition of CaS causes dissolved oxygen to disappear and Ca ²⁺
The ions have the effect of reacting with phosphorus to precipitate as hydroxyapatite, but when the dissolved oxygen concentration of the influent is low, the amount of CaS added is small, and the calcium ions required to remove phosphorus are insufficient. . In such a case, slaked lime is replenished. The slaked lime injection rate is determined by measuring the phosphorus concentration of the dehydrated filtrate, multiplying the phosphorus concentration by the filtrate treatment amount, and calculating the amount of phosphorus in the dehydrated filtrate. Ion and equivalent phosphorus are subtracted, and equivalent Ca
Determined by calculating the amount of (OH) ₂ . If this is expressed by a formula,

[0038]

Embedded image _{I Ca (OH) 2 = PO} 4 -P FIL × Q FIL × K P-Ca (OH) 2 -I CaS × K CaS-Ca (OH) 2 / Q FIL ······· (4) here

[0039]

_{Embedded image} I _{Ca (OH) 2} ; Ca (OH) ₂ injection rate (ppm) PO ₄ -P _FIL ; PO ₄ -P concentration of dehydrated filtrate (ppm or mg / l) Q _FIL ; (M ³ / hr) K _{P-Ca (OH) 2} ; Ca (OH) ₂ equivalent conversion coefficient of PO ₄ -P (K _{P-Ca (OH) 2} = 5 × _74/3 × 31 = 4.0) I _CaS CaS injection rate (ppm) K _{CaS-Ca (OH) 2} ; Ca (OH) ₂ equivalent conversion coefficient of _CaS (K _{CaS-Ca (OH) 2} = 74/72 = 1.03).

The dehydrated filtrate treated in this way is supplied to the precipitation tank 3
5, and the precipitate 36 insolubilized by the injection of the chemical is withdrawn from the bottom of the tank, returned to the dehydrator 25, and dehydrated again. The supernatant 3 of the precipitation tank 35
7 is returned to the sedimentation basin 12 as return water 20 together with the supernatant 19.

The measuring means of the above-mentioned automatic phosphorus concentration measuring device 31 is described in Japanese Patent Application No. 4-31 proposed by the present applicant.
Although the apparatus based on the titration method disclosed in No. 7590 may be adopted, the principle of this measurement will be briefly described. A sample is introduced into an aggregating / separating tank, and a solid is aggregated by injecting an aggregating agent. Using the inserted funnel, only the liquid is slowly suctioned to make a sample solution, and a predetermined amount of the solution is precipitated in the reaction tank by injecting a phosphorus insolubilizing reagent,
After suctioning and removing only the liquid using an automatic vacuum filtration mechanism arranged below the reaction tank, the precipitate was dissolved with concentrated hydrochloric acid,
After volatilizing dissolved carbonic acid by aeration of nitrogen gas, distilled water is added to make a sample solution for titration, and the alkali is titrated with a conductive buret. This is for calculating the concentration of phosphate ion-type phosphorus. According to this apparatus, when a high concentration of phosphorus in a sample is measured, the sample is measured without dilution and all operations can be automated.

[0042]

As described above in detail, according to the method and the apparatus for removing phosphorus in water according to the present invention, the digested sludge after digestion by the anaerobic-aerobic tank is converted into a polymer flocculant. After the coagulation treatment by the injection of water, the water is dehydrated by a dehydrator, and the dehydrated filtrate of this dehydrator is sent to a dehydrated filtrate temporary storage tank and temporarily stored, and the phosphorus concentration of the dehydrated filtrate is automatically measured by an automatic measuring device. Measured,
Data on the phosphorus concentration of this dehydrated filtrate and DO of influent water
A chemical injection rate based on the stoichiometric relationship between phosphorus and the phosphorus removal chemical is calculated from the above, and the chemical injection rate is multiplied by the flow rate data measured by the flow meter of the dehydrated filtrate and the flow rate of the inflow water. The final chemical injection rate is determined, and the phosphorus insolubilizing reagent is injected into the dehydrated filtrate from the chemical injection apparatus based on the final chemical injection rate, and the phosphorus insolubilization treatment can be performed.

Accordingly, since the dehydrated filtrate is not returned to the water treatment system as it is, the phosphorus concentration of the treated water can be effectively reduced, and the dehydrated filtrate of the digested sludge discharged from the anaerobic-aerobic tank is removed. The return water containing does not increase the load of phosphorus on the water treatment system, and can cope with phosphorus discharge regulations.

During the above operation, the pH value in the dewatered filtrate temporary storage tank is measured by the pH meter, and the sodium hydroxide solution is injected from the alkali injection device so that the pH value is about 8 by the pH feedback control device. You. By performing such a chemical injection control, it becomes possible to inject the chemical without excess or deficiency in accordance with the phosphorus concentration of the dehydrated filtrate, and in particular, there is obtained an effect that the chemical is not wasted due to excessive injection of the chemical. Can be

Even when the DO of the inflow water becomes high, especially after rainfall, the DO in the inflow water disappears due to the addition of calcium sulfide as a phosphorus insolubilizing reagent. The anaerobic state of the anaerobic tank in the above can be maintained well, and a decrease in the ability of the treated water to remove phosphorus can be effectively prevented.

It is known that the concentration of soluble phosphorus in the above-mentioned dehydrated filtrate varies depending on the digestion state. Therefore, the measurement of the phosphorus concentration can be used as a guide for judging the digestion state. In particular, when the concentration of soluble phosphorus is abnormally low, it can be considered that digestion is insufficient.

Therefore, according to the present invention, by removing phosphorus from the dehydrated filtrate in a conventional sewage sludge treatment apparatus or the like, a great effect of effectively reducing the phosphorus concentration of the treated water is exhibited.

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing an entire processing apparatus to which a phosphorus removal method according to the present invention is applied.

FIG. 2 is a schematic diagram showing an example of a conventional anaerobic-aerobic activated sludge treatment method.

FIG. 3 is a schematic diagram showing an example of a conventional sewage sludge treatment apparatus which is a premise of the present invention.

[Explanation of symbols]

 11 ... inflow water 12 ... first sedimentation basin 14 ... final sedimentation basin 16 ... initial sedimentation sludge 17 ... surplus sludge 18 ... sludge concentration tank 20 ... return water 21 ... concentrated sludge 22 ... sludge digestion tank 24 ... polymer coagulant injection device 25 ... dehydrator 28 ... dehydrated filtrate discharge line 29 ... dehydrated filtrate temporary storage tank 31 ... phosphorus concentration automatic measuring device 32, 41 ... flow meter 33 ... chemical injection control arithmetic unit 34 ... chemical injection device 35 ... sedimentation tank 40 ... dissolved oxygen Total 42: Anaerobic-aerobic tank 43 ... pH meter 44 ... pH feedback control device 45 ... Alkaline injection device

Continuation of the front page (58) Field surveyed (Int. Cl. ⁷ , DB name) C02F 3/30 C02F 11/00-11/20 C02F 1/58

Claims (4)

(57) [Claims] 1. Influent water is introduced into an anaerobic-aerobic sludge digestion tank for treatment, and a polymer flocculant is injected into concentrated digested sludge and then dewatered by a dehydrator to reduce the phosphorus concentration of the dehydrated filtrate. Measure and calculate the final chemical injection rate from the data on the phosphorus concentration based on the stoichiometric relationship between phosphorus and the phosphorus removing chemical, and temporarily store the dehydrated filtrate from the chemical injection apparatus based on the final chemical injection rate. Injecting a chemical into a tank, performing a phosphorus insolubilization treatment, and then treating the dehydrated filtrate as return water by a water treatment system again in a water removal method, wherein a dissolved oxygen meter and a flow meter are used for the inflow water. In addition, a pH meter, a pH feedback control device, and an alkali injecting device are provided in the dehydrated filtrate temporary storage tank, and phosphorus is determined from data on the phosphorus concentration of the dehydrated filtrate and dissolved oxygen in the inflow water. The final chemical injection rate is determined by calculating the chemical injection rate based on the stoichiometric relationship with the chemical for removal of the chemical, and multiplying the chemical injection rate by the data on the flow rates of the dehydrated filtrate and inflow water. A method for removing phosphorus in water, comprising: injecting a phosphorus insolubilizing reagent into a dehydrated filtrate based on the rate to perform a phosphorus insolubilization treatment. 2. Calcium sulfide is used as the phosphorus insolubilizing reagent, and slaked lime is replenished when the concentration of dissolved oxygen in the inflow water is low and calcium ions required for removing phosphorus are insufficient. The method for removing phosphorus in water according to claim 1. 3. The pH value in the temporary storage tank for dehydrated filtrate is measured by the pH meter, and the pH is controlled by the pH feedback control device from the alkali injection device to the temporary storage tank for dehydrated filtrate so that the pH value is about 8. 3. The method for removing phosphorus in water according to claim 1, wherein a sodium solution is injected. 4. An anaerobic-aerobic sludge digestion tank for treating influent water, a dehydrator for injecting a polymer flocculant into concentrated digested sludge and a dehydration treatment, and measuring the phosphorus concentration of the dehydrated filtrate. A chemical injection control arithmetic unit for calculating the final chemical injection rate based on the stoichiometric relationship between phosphorus and the phosphorus removing chemical from the data on the phosphorus concentration, and a dehydration filtrate from the chemical injection apparatus based on the final chemical injection rate. A submersible phosphorus removing device comprising a chemical injection device for injecting a chemical into a temporary storage tank, wherein a dissolved oxygen meter and a flow meter are attached to the inflow water, while a pH meter and a pH meter are provided in the dehydrated filtrate temporary storage tank. A feedback control device and an alkali injection device are provided to determine the chemical injection rate based on the stoichiometric relationship between the phosphorus and the phosphorus removal chemical from data on the phosphorus concentration of the dehydrated filtrate and the dissolved oxygen in the inflow water. The final chemical injection rate is determined by multiplying the chemical injection rate by the data on the flow rates of the dehydrated filtrate and the inflow water, and a phosphorus insolubilizing reagent is injected into the dehydrated filtrate based on the final chemical injection rate. A device for removing phosphorus in water.