JPH0788497A - Method and apparatus for removing phosphorus in water - Google Patents

Abstract

PURPOSE:To provide a dephosphorization method and apparatus in which the dephosphorization function is maintained without troubles by dephosphorizing the dewatering filtrate of digested sludge even when DO in inflow water is elevated with the decrease in phosphorus concentration in water to be treated. CONSTITUTION:A dissolved oxygen meter 40 and a flow meter 41 are installed in inflow water 11; a dewatering filtrate temporary storing tank is equipped with a pH meter 43, a pH feedback controller 44, and an alkali injection device 45. A polymeric coagulant is injected to concentrated digested sludge which was digested in an aerobic-anaerobic tank 42, and the sludge is dewatered with a dewaterer 25. The reagent injection ratio is calculated on the basis of the stoichiometric relationship between phosphorus and a dephosphorization reagent obtained from the data on the phosphorus concentration in the dewatering filtrate and the dissolved oxygen in the inflow water. The final reagent injection ratio is determined by multiplying the calculated reagent injection ratio by the data on the flow rates of the dewatering filtrate and the inflow water. In this way, the treatment to make phosphorus insoluble is conducted by injecting the reagent to make phosphorus insoluble to the dewatering filtrate, providing the dephororization method and apparatus.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention is directed to a digested sludge dehydration filtrate, and in a system for removing phosphorus by chemical injection, the phosphorus concentration and the dissolved oxygen amount of inflow water are measured to control the chemical injection amount. The present invention relates to a method and apparatus for removing phosphorus in water.

[0002]

2. Description of the Related Art Phosphorus is a widely existing element in the earth and is also contained in natural water. However, since phosphorus is contained in large amounts in human waste, sludge, fertilizer, etc., phosphorus is mixed in natural water. In many cases. Phosphorus in water is orthophosphate,
It exists in various forms such as metaphosphates, pyrophosphates, polyphosphates, and organic phosphorus compounds such as phosphates and phospholipids. The form of phosphorus is classified into three types, that is, phosphate ion-type phosphorus, hydrolyzable phosphorus, and total phosphorus, which are further divided into soluble and insoluble.

All of these various phosphorus compounds are finally converted to orthophosphoric acid by pretreatment, measured using the reaction peculiar to phosphate ions, and expressed as the amount of phosphorus. Phosphorus itself plays an important role in the growth activity of organisms,
Moreover, although it is an essential element in biological treatment of sewage,
On the other hand, phosphorus is one of the factors that promote eutrophication in lakes and sea areas, and an increase in phosphorus compounds in water is not preferable.

On the other hand, in the anaerobic digestion means for sewage sludge, a phenomenon in which phosphorus is dissolved from the solid phase is observed, so that the liquid phase of the digested sludge has a relatively high concentration, for example, 100 to 300 mg · P.
It is known to contain phosphate ion phosphorus of about 1 / l. The above-mentioned phosphate ion type phosphorus is a phosphate ion in water expressed by the amount of phosphorus (P).

As a biological method for simultaneously removing nitrogen and phosphorus, an anaerobic-aerobic activated sludge method is known as a modification of the conventional activated sludge method. The anaerobic-aerobic activated sludge method is, as shown in FIG. 2, that the biological reaction tanks are anaerobic tanks 1a, 1b and D which do not have dissolved oxygen (usually abbreviated as DO).
It is divided into aerobic tanks 2a, 2b and 2c in which O exists, and the anaerobic tanks 1a and 1b are used to agitate the inflowing water 3 by an agitation mechanism 10 under anoxic conditions to denitrify the denitrifying bacteria in the activated sludge. Then, by supplying air from the blower 5 to the air diffuser 4 arranged inside the aerobic tanks 2a, 2b, 2c, oxidative decomposition of organic matter by activated sludge and nitrifying bacteria in the presence of oxygen by aeration. Nitrification of ammonia is performed.

Then, the nitrifying solution in the last-stage aerobic tank 2c is fed into the anaerobic tank 1a by using the nitrifying solution circulating pump 6, whereby the denitrifying effect is promoted. Phosphorus in water is anaerobic tank 1a,
It is released in 1b and taken in and removed by the activated sludge in the aerobic tanks 2a, 2b, 2c. 7 is the final sedimentation pond,
The supernatant 50 of the final settling basin 7 is discharged after passing through a disinfecting tank or the like (not shown), and a part of the sludge settled in the final settling basin 7 is returned to the anaerobic tank 1a by a sludge returning pump 8. Other sludge is sent from the excess sludge pump 9 to an excess sludge treatment device (not shown) for treatment.

[0007] Such an anaerobic-aerobic activated sludge treatment device has the same effect as the organic substance removal effect achieved by the ordinary standard activated sludge method, and has a higher removal rate for nitrogen and phosphorus than the activated sludge method. Is achieved.

On the other hand, the present applicant has previously filed Japanese Patent Application No. 5-
No. 91713 proposed a device for removing phosphorus in dehydrated filtrate shown in FIG. To briefly explain this, inflow water 11
While being discharged from the first settling tank 12 as treated water 15 via the aeration tank 13 and the final settling tank 14, the first settling sludge 16 of the first settling tank 12 together with the surplus sludge 17 of the final settling tank 14 is a sludge thickening tank. It is sent to 18.

A part of the excess sludge 17 is returned to the aeration tank 13, and the supernatant 19 of the sludge thickening tank 18 is
It is first returned to the settling tank 12 together with the return water 20, and the thickened sludge 21 in the sludge thickening tank 18 is sent to the sludge digesting tank 22 for anaerobic digestion treatment. This sludge digestion tank 22
The coagulant is injected into the digested sludge 23 from the polymer coagulant injection device 24 to be subjected to the coagulation treatment. As the coagulant, a polymer coagulant having no phosphorus removing ability is adopted.

After the flocculation, the dehydrated cake 26 is obtained by applying it to the dehydrator 25, while the dehydrated filtrate of the dehydrator 25 is sent to the dehydrated filtrate temporary storage tank 29 via the dehydrated filtrate discharge conduit 28. At this time, the dehydrated filtrate sampled from the dehydrated filtrate discharge conduit 28 is supplied to the phosphorus concentration automatic measuring device 31 to automatically measure the phosphorus concentration, and the measured value is converted into an electrical signal to control the chemical injection control computing 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 calculation unit 33 calculates the chemical injection rate based on the stoichiometric relationship between phosphorus and the chemicals for phosphorus removal from the data relating to the phosphorus concentration of the dehydrated filtrate, and the flow rate meter 32 calculates this chemical injection rate. The final chemical injection rate is determined by multiplying the measured flow rate data, and the chemical injection device 34 is driven based on the final chemical injection rate to inject the chemical into the dehydrated filtrate temporary storage tank 29. Then, as the stirring mechanism 30 is driven, the dehydrated filtrate is stirred to perform the phosphorus insolubilization treatment.

The dehydrated filtrate treated in this way is used in the precipitation tank 3
The precipitate 36 that has been sent to the tank 5 and insolubilized by the injection of the above chemicals is withdrawn from the bottom of the tank and returned to the dehydrator 25, where it is again dehydrated. Supernatant liquid 3 of this settling tank 35
7 is returned as return water 20 together with the supernatant 19 to the sedimentation tank 12.

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

[0014]

However, among such conventional phosphorus removing means, the anaerobic-aerobic activated sludge method for biologically removing nitrogen and phosphorus shown in FIG. When the DO of the inflow water becomes high as in the latter case, the anaerobic state cannot be maintained well, and the phosphorus removal ability may be deteriorated. Further, the sludge treatment means by anaerobic digestion is As described above, there is a drawback that phosphorus excessively ingested by the organism is redissolved from the solid phase and the liquid phase of the digested sludge contains a relatively high concentration of phosphate ion-type phosphorus. Further, in the method of coagulating and dehydrating using a polymer coagulant that does not have the ability to remove phosphorus, the dehydrated filtrate is first returned as it is to the settling tank as return water, so that the high phosphorus concentration of the dehydrated filtrate is high in the water treatment system. Cause increase of phosphorus concentration of
There is a problem that the load on the water treatment system becomes high and the phosphorus concentration in the discharged water cannot be reduced.

Based on the biological phosphorus removal method, a method of directly injecting a chemical into an aeration tank or a means of injecting a chemical into secondary treated water or return water is used as a method of depositing and removing phosphorus by injecting a chemical. It is conceivable, however, that it is technically difficult to inject chemicals just enough depending on the phosphorus concentration, and if a certain amount of chemicals is simply injected, or if the phosphorus concentration is high in the constant injection rate flow rate proportional injection control means. However, if the phosphorus concentration is low and the phosphorus concentration is low, the chemicals will be excessively injected and the chemicals will be wasted.

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

Therefore, the present invention solves the problem of such a conventional apparatus for removing phosphorus in water and reduces phosphorus concentration in treated water by removing phosphorus from the dehydrated filtrate. It is an object of the present invention to provide a phosphorus removing method and apparatus that do not hinder the phosphorus removing ability even when the DO of inflow water rises.

[0018]

[Means for Solving the Problems] In order to achieve the above object, the present invention introduces influent water into an anaerobic-aerobic sludge digestion tank for treatment, and injects a polymer flocculant into the concentrated digested sludge. Then, dehydration treatment with a dehydrator, measuring the phosphorus concentration of the dehydrated filtrate, calculating the final chemical injection rate based on the stoichiometric relationship between phosphorus and chemicals for phosphorus removal from the data on the phosphorus concentration, Based on this final chemical injection rate, chemicals are injected from the chemical injection device into the dehydrated filtrate temporary storage tank, and after the phosphorus insolubilization treatment is performed, the dehydrated filtrate is treated as return water by the water treatment system again in water. In the method for removing phosphorus, while a dissolved oxygen meter and a flow meter are attached to the inflow water, a pH meter and a pH are stored in the dehydrated filtrate temporary storage tank.
A feedback control device and an alkali injection device are provided, and the chemical injection rate based on the stoichiometric relationship between phosphorus and the chemicals for phosphorus removal is calculated from the data on the phosphorus concentration of the dehydrated filtrate and the dissolved oxygen of the inflow water. Determine the final chemical injection rate by multiplying the chemical injection rate by the data related to the flow rates of dehydrated filtrate and inflow water, and perform the phosphorus insolubilization treatment by injecting the phosphorus insolubilizing reagent into the dehydrated filtrate based on this final chemical injection rate. A method and apparatus for removing phosphorus in water are provided.

Calcium sulfide is used as the phosphorus insolubilizing reagent, and slaked lime is supplemented when the dissolved oxygen concentration of the inflowing water is low and the calcium ions required for removing phosphorus are insufficient. 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 am doing it.

[0020]

According to such a method and apparatus for removing phosphorus in water,
The DO of the inflowing water is measured by the dissolved oxygen meter and the flow rate is measured by the flow meter, and the digestive sludge is digested by the anaerobic-aerobic tank. By being applied to a dehydrator after aggregation, the dehydrated filtrate is sent to and temporarily stored in the dehydrated filtrate temporary storage tank.

At this time, the phosphorus concentration of the dehydrated filtrate sampled from the dehydrated filtrate discharge pipe of the dehydrator is automatically measured by an automatic measuring device, and the phosphorus concentration is measured from the phosphorus concentration data of the dehydrated filtrate and the DO of the inflow water. The chemical injection rate is calculated based on the stoichiometric relationship between the chemicals for phosphorus removal and the chemicals for phosphorus removal, and the chemical injection rate is multiplied by the flow rate data measured by the flowmeter of the dehydrated filtrate and the flowmeter of the inflow water to make the final chemical injection. The rate is determined, and the phosphorus insolubilizing reagent is injected from the chemical injecting device into the dehydrated filtrate based on the final chemical injecting rate to perform the phosphorus insolubilizing treatment.

At the time of the above operation, the pH value in the temporary storage tank for the dehydrated filtrate 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. It

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 A concrete embodiment of a method and apparatus for removing phosphorus in water according to the present invention will be described in detail below with reference to FIG. .

In the figure, 11 is inflow water, 12 is the inflow water 11
Is the first settling basin into which the dissolved oxygen meter 40 and the flow meter 41 are attached. 42 is an anaerobic-aerobic tank, 14 is a final settling tank, 18 is a sludge thickening tank, 22
Is a sludge digestion tank, 24 is a polymer coagulant injection device, 25 is a dehydrator, and 29 is a dehydration filtrate temporary storage tank.
The dehydrated filtrate discharge pipe line 28 derived from 5 is connected to the dehydrated filtrate temporary storage tank 29. 30 is a stirring mechanism, 31 is an automatic phosphorus concentration measuring device for 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 temporary dehydrated filtrate storage tank 29, and 35 is a precipitation tank.

In the chemical injection control calculation device 33, the phosphorus concentration automatic measuring device 31, the flow meter 32 and the DO of the inflow water 11 measured by the dissolved oxygen meter 40 and the flow rate of the inflow water 11 measured by the flow meter 41. Each data of is input. Furthermore, a pH meter 43 is installed in the dehydration filtrate temporary storage tank 29, and the pH feedback control device 4 is installed in the pH meter 43.
4 and an alkali injection device 45 for the dehydration filtrate temporary storage tank 29.

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

The thickened sludge 21 in the sludge thickening tank 18 is sent to the sludge digesting tank 22 in the next stage and subjected to anaerobic digestion treatment. Then, the coagulant is injected into the digested sludge 23 of the sludge digestion tank 22 from the polymer coagulant injecting device 24 to undergo the coagulation treatment. As the coagulant, a polymer coagulant having no phosphorus removing ability is adopted. After the flocculation, the dehydrated cake is applied to the dehydrator 25 to obtain the dehydrated cake 26, while the dehydrated filtrate of the dehydrator 25 is
Dehydration filtrate temporary storage tank 2 via dehydration filtrate discharge conduit 28
It is sent to 9.

At this time, the dehydrated filtrate sampled from the dehydrated filtrate discharge conduit 28 is supplied to the phosphorus concentration automatic measuring device 31 to automatically measure the phosphorus concentration, and the measured value is converted into an electric signal to control the chemical injection. 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 calculation unit 33.

The chemical injection control calculation unit 33 calculates the chemical injection rate based on the stoichiometric relationship between phosphorus and the chemical for phosphorus removal from the data on the phosphorus concentration of the dehydrated filtrate and the DO of the inflow water 11, and this chemical is calculated. Flow rate 32 and inflow water 11
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 device 34 is driven based on this final chemical injection rate to inject the chemical into the dehydrated filtrate temporary storage tank 29. Done. Then, as the stirring mechanism 30 is driven, the dehydrated filtrate is stirred to perform the phosphorus insolubilization treatment.

As the phosphorus insolubilizing reagent, a sulfuric acid band or slaked lime is usually used, but in this embodiment, calcium sulfide CaS is adopted in place of the above reagent. The reaction formula when this calcium sulfide is used 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 causes dissolved oxygen to disappear as shown in equation (1), and Ca ²⁺ ions (2) ), The phosphorus ion is removed by reacting with the phosphate ion and precipitating and separating as insoluble hydroxyapatite Ca ₅ (OH) (PO 4) _{3 in} the neutral to weakly alkaline region. Therefore, even when the DO of the inflow water becomes high as after raining, the DO in the inflow water disappears by the addition of calcium sulfide CaS as the phosphorus insolubilizing reagent,
Anaerobic-In an aerobic tank, the anaerobic state of the anaerobic tank is maintained in good condition, and there is no fear that the phosphorus removal ability of the treated water will deteriorate.

[0033] Further, CaS and thiosulfate ions produced by the reaction of DO S ₂ O ₃ ^- becomes the electron donor denitrification in the anaerobic tank, the nitrogen removal efficiency is enhanced.

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 the pH feedback control device 44 adjusts the above pH value to about 8 from the alkali injecting device 45 to the sodium hydroxide. Na
The OH solution is injected.

Specifically, the injection rate of calcium sulfide CaS as the phosphorus insolubilizing agent is calculated by calculating the dissolved oxygen amount entering the water treatment system from the DO of the inflow water 11 and the inflow water amount, and calculating the equivalent CaS amount. Then, the value is divided by the filtrate throughput. If you express this with a mathematical formula

[0036]

_{Embedded image} I _CaS = DO _IN × Q _IN × K _CaS-DO / Q _FIL (3) here

[0037]

_{Embedded image} I _CaS ; CaS injection rate (ppm) DO _IN ; Dissolved oxygen concentration of influent water (ppm or mg / l) Q _IN ; Influent water amount (m ³ / hr) Q _FIL ; Dehydrated filtrate treatment amount (m ³ / hr) K _CaS-DO ； Ca equivalent DO equivalent conversion coefficient (K _CaS-DO ＝ 4 × 7
2/3 × 16 = 6.0) Addition of CaS causes dissolved oxygen to disappear and Ca ²⁺
Ions have the effect of reacting with phosphorus and precipitating as hydroxyapatite, but when the dissolved oxygen concentration of the inflow water is low, the amount of CaS added is small, and the calcium ions required for removing phosphorus are insufficient. . In such a case, slaked lime is replenished, but the injection rate of slaked lime is measured by measuring the phosphorus concentration of the dehydrated filtrate, and the amount of phosphorus in the dehydrated filtrate is calculated by multiplying this by the filtrate treatment amount. Ion and phosphorus equivalent are subtracted, equivalent Ca
Determined by calculating the amount of (OH) ₂ . If you express this with a mathematical 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 in the dehydrated filtrate (ppm or mg / l) Q _FIL ; (M ³ / hr) K _{P-Ca (OH) 2} ; Ca ₄ (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} ; CaS Ca (OH) ₂ equivalent conversion coefficient (K _{CaS-Ca (OH) 2} = 74/72 = 1.03).

The dehydrated filtrate treated in this way is used in the precipitation tank 3
The precipitate 36 that has been sent to the tank 5 and insolubilized by the injection of the above chemicals is withdrawn from the bottom of the tank and returned to the dehydrator 25, where it is again dehydrated. Supernatant liquid 3 of this settling tank 35
7 is returned as return water 20 together with the supernatant 19 to the sedimentation tank 12.

Regarding the measuring means of the phosphorus concentration automatic measuring device 31, the applicant of the present application has previously proposed Japanese Patent Application No. 4-31.
Although the device based on the titration method disclosed in No. 7590 may be adopted, the measuring principle will be briefly described. The sample is taken into the aggregating / separating tank, and the solid matter is agglomerated by injecting the aggregating agent, and the opening is directed downward. Using the funnel inserted as described above, only the liquid is slowly sucked to form a sample solution, and a certain amount of this is precipitated by injecting the phosphorus insolubilizing reagent in the reaction tank,
Only the liquid was sucked and removed using the automatic vacuum filtration mechanism arranged below this reaction tank, and the precipitate was dissolved with concentrated hydrochloric acid,
After volatilizing the dissolved carbonic acid by aeration of nitrogen gas, add distilled water to make a sample solution for titration, perform alkali titration with a conductive burette, and use the formula from the amount of the alkaline solution required for the titration The concentration of phosphate ion-state phosphorus is calculated. According to this device, when measuring a high concentration of phosphorus in a sample, the sample is measured without dilution, and all the operations can be automated.

[0042]

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

Therefore, since the dehydrated filtrate is not directly returned to the water treatment system, 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 can be removed. The contained return water does not increase the load of phosphorus on the water treatment system, and it becomes possible to deal with phosphorus emission regulations.

At the time of the above operation, the pH value in the temporary storage tank of the dehydrated filtrate 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. It By carrying out such chemical injection control, it becomes possible to inject the chemicals just enough according to the phosphorus concentration of the dehydrated filtrate, and there is an effect that the chemicals are not wasted due to excessive injection of the chemicals. To be

Even when the DO of the inflow water becomes high especially after raining, the DO in the inflow water disappears by the addition of calcium sulfide as the phosphorus insolubilizing reagent, so that the anaerobic-aerobic tank The anaerobic state of the anaerobic tank can be favorably maintained and the reduction of the phosphorus removal ability of the treated water can be effectively prevented.

It is known that the concentration of soluble phosphorus in the dehydrated filtrate varies depending on the digested state, and therefore the measurement of the phosphorus concentration can be used as a standard for judging the quality of the digested state. Particularly when the concentration of soluble phosphorus is abnormally low, it can be considered that the digestion is insufficient.

Therefore, according to the present invention, by removing the phosphorus from the dehydrated filtrate in the conventional sewage sludge treatment apparatus, the phosphorus concentration of the treated water can be effectively reduced.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing an overall processing apparatus to which a phosphorus removing 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 device which is a premise of the present invention.

[Explanation of symbols]

 11 ... Influent water 12 ... First settling basin 14 ... Final settling basin 16 ... First settling sludge 17 ... Excess sludge 18 ... Sludge thickening tank 20 ... Returning water 21 ... Concentrated sludge 22 ... Sludge digesting tank 24 ... Polymer coagulant injection device 25 Dehydrator 28 Dehydration filtrate discharge pipe 29 Dehydration filtrate temporary storage tank 31 Phosphorus concentration automatic measuring device 32, 41 ... Flow meter 33 ... Chemical injection control calculation device 34 ... Chemical injection device 35 ... Precipitation tank 40 ... Dissolved oxygen Total 42 ... Anaerobic-aerobic tank 43 ... pH meter 44 ... pH feedback control device 45 ... Alkaline injection device

Claims (4)

[Claims] 1. The inflowing water is introduced into an anaerobic-aerobic sludge digestion tank for treatment, and the concentrated digested sludge is injected with a polymer flocculant and then dehydrated by a dehydrator to adjust the phosphorus concentration of the dehydrated filtrate. Measure and calculate the final chemical injection rate based on the stoichiometric relationship between phosphorus and the chemicals for phosphorus removal from the data regarding the phosphorus concentration, and temporarily store the dehydrated filtrate from the chemical injection device based on this final chemical injection rate. In a method for removing phosphorus in water, in which a chemical is injected into a tank and phosphorus insolubilization treatment is performed, and then the dehydrated filtrate is treated again as return water by a water treatment system, a dissolved oxygen meter and a flow meter are added to the inflow water. On the other hand, a pH meter, a pH feedback control device and an alkali injection device were installed in the dehydrated filtrate temporary storage tank, and phosphorus was determined from the phosphorus concentration of the dehydrated filtrate and the data on dissolved oxygen in the inflow water. The chemical injection rate is calculated based on the stoichiometric relationship with the chemicals for removal of water, and the final chemical injection rate is determined by multiplying the chemical injection rate with the data on the flow rates of dehydrated filtrate and inflow water. A method for removing phosphorus in water, which comprises injecting a phosphorus insolubilizing reagent into the dehydrated filtrate based on the rate to perform the phosphorus insolubilizing treatment. 2. When calcium sulfide is used as the phosphorus insolubilizing reagent and slaked lime is replenished when the dissolved oxygen concentration of the inflowing water is low and the calcium ions required for removing phosphorus are insufficient. The method for removing phosphorus from water according to claim 1. 3. The pH value in the dehydrated filtrate temporary storage tank is measured by the pH meter, and the pH is controlled by the pH feedback controller from the alkali injecting device to the dehydrated filtrate temporary storage tank so that the pH value is about 8. 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 inflow water, a dehydrator for dehydrating after injecting a polymer coagulant into concentrated digested sludge, and measuring the phosphorus concentration of this dehydrated filtrate. , A chemical injection control arithmetic unit for calculating the final chemical injection rate based on the stoichiometric relationship between phosphorus and the chemical for phosphorus removal from the data on the phosphorus concentration, and dehydrated filtrate from the chemical injection apparatus based on the final chemical injection rate In a phosphorus removing device in water comprising a chemical injection device for injecting a chemical into a temporary storage tank, a dissolved oxygen meter and a flow meter are attached to the inflow water, while a pH meter and a pH are provided in the dehydrated filtrate temporary storage tank. A feedback control device and an alkali injection device were installed to determine the chemical injection rate based on the stoichiometric relationship between phosphorus and the phosphorus removal chemical from the data on the phosphorus concentration in the dehydrated filtrate and the dissolved oxygen in the inflow water. The final chemical injection rate is determined by multiplying this chemical injection rate by the data on the flow rates of dehydrated filtrate and inflow water, and based on this final chemical injection rate, the phosphorus insolubilization reagent is injected into the dehydrated filtrate to perform the phosphorus insolubilization treatment. An apparatus for removing phosphorus in water, characterized in that