JPS6048196A - Method for removing phosphorus from organic waste liquid - Google Patents

Abstract

PURPOSE:To remove stably the phosphorus with high efficiency by releasing a part of phosphorus contained in returned activated sludge into a soln. to form a liquid mixture contg. high-concn. soluble phosphorus, and removing the phosphorus chemically from a part of the mixture. CONSTITUTION:The phosphorus is substantially removed by separating the flow with a distribution vessel 2. Namely the amt. of entrained soluble phosphorus is decreased by the amt. corresponding to the amt. of the phosphorus introduced into a chemical phosphorus removing stage. Since the activated sludge in an aeration tank 5 has surplus capacity for removing phosphorus after reabsorbing the entrained soluble phosphorus, the phosphorus can be removed surely even with the comparatively small-capacity aeration tank 5. A liquid mixture 39 flowing out from the aeration tank is introduced into the final settling pond 10 wherein the activated sludge is separated by settling and concentrated to obtain a treated liquid 40. At least a part of the activated sludge which is separated by settling and concentrated is returned to an anaerobic tank 1 and treated as returned sludge 32.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a method for removing phosphorus together with BOD from organic wastewater containing particularly low concentrations of phosphorus, such as municipal sewage.

[Prior art]

Municipal sewage and organic industrial wastewater are generally treated using the standard activated sludge method, but nitrogen and phosphorus, which are present in excess compared to BOD, cannot be sufficiently removed, and lakes and oceans, which are the receiving water bodies for the treated liquid, cannot be sufficiently removed. This is causing eutrophication in the area, causing severe damage to the fishing and tourism industries.

A technique for removing phosphorus, most of which exists as soluble phosphoric acid Cpo41-3, is the coagulation-precipitation method, but the phosphorus concentration in the liquid to be treated must be sufficiently low to be effective in preventing eutrophication. This requires a large amount of flocculant,
This itself is a huge economic burden, and at the same time it brings about difficulties in the treatment and disposal of the coagulated and settled sludge that is generated along with it and is difficult to dewater. As an alternative to the flocculation-sedimentation method, which has these disadvantages, the effective phosphorus removal technologies are (1) "catalytic dephosphorization method" that applies the principle of U ore formation, and (2) activated sludge. There are two methods that have been modified to remove BOD and phosphorus at the same time, using phosphorus metabolism by special microorganisms: the ``biological dephosphorization method.'' This biological dephosphorization method is further divided into "dephosphorization side activated sludge method" and "
It is divided into two methods: anaerobic-aerobic activated sludge method.

Among these, the catalytic dephosphorization method is essentially a technology suitable for high-concentration phosphorus-containing wastewater, and even when applied to low-concentration phosphorus-containing wastewater such as urban sewage, it still achieves highly efficient phosphorus removal. To do this, a large amount of calcium agent is required, and alkalinity adjustment is important, making this technology unsuitable for treating wastewater containing low concentrations of phosphorus, such as urban sewage.

The biological membrane phosphorization method uses microorganisms that perform a special phosphorus metabolism, which can be called dephosphorizing bacteria, as the dominant species among activated sludge microorganisms by installing an anaerobic tank in any of the conventional activated sludge systems. This method involves culling the microorganisms to remove phosphorus as well as organic matter, and in some cases also performs denitrification.

Phosphorus in the liquid to be treated is absorbed into the activated sludge in the aeration tank of the normal activated sludge method, and the returned sludge or a portion of the returned sludge from the final settling tank is made into an anaerobic state (more precisely, a non-breathable state). The returned sludge is guided to a maintained thickening tank-like dephosphorization tank, where the returned sludge is reconcentrated and at the same time phosphorus is released from the sludge. The activated sludge dephosphorization method, in which the concentrated supernatant liquid contained in the dephosphorization tank is treated by the lime coagulation sedimentation method, has the disadvantage that the return sludge must remain in the dephosphorization tank for a very long time. Since the returned sludge is left in an anaerobic state for a long time, activated sludge microorganisms other than dephosphorizing bacteria are likely to die and decompose, and there are operational difficulties such as abnormal foaming occurring when the returned sludge is returned to the aeration tank.

In the case of normal activated sludge microorganisms, a small-capacity anaerobic tank that does not tolerate the presence of 02 or NOx- is installed in front of the aeration tank, and here the liquid to be treated and the activated sludge returned from the final settling tank are mixed by contact. By utilizing the special phosphorus metabolism and organic matter metabolism of dephosphorizing bacteria contained in activated sludge, phosphorus is removed from activated sludge while allowing at least a portion of the BOD of the treated liquid to be absorbed into activated sludge in a non-oxidative manner. The resulting mixed solution containing a high concentration of soluble phosphorus is led to the subsequent aeration tank, where the BOD remaining on the solution side and the intracellular organic matter ingested and stored in the activated sludge are biooxidized. At the same time, the present inventors have used experiments and theory to develop the anaerobic-aerobic activated sludge method, which attempts to reabsorb the phosphorus present in the solution, including the phosphorus contained in the liquid to be treated, into the activated sludge. According to recent knowledge, unless BOD substances are added as chemicals, if the BOD:IJ ratio contained in the liquid to be treated is below a certain value, complete phosphorus removal cannot be achieved even if the sludge is operated at a fairly short daily sludge period. However, if the sludge days ◆ are increased, phosphorus removal becomes insufficient.

[Purpose of the invention]

A first object of the present invention is to provide a method that can stably and highly efficiently remove phosphorus even from a liquid to be treated having a small BOD-nilin ratio by combining it with a chemical phosphorus removal method. The second objective is to provide a method for concentrating low concentration phosphorus contained in a liquid to be treated into a small volume liquid using activated sludge as a medium using simpler facilities and easier operation.

[Structure of the invention]

In the present invention, a liquid to be treated and returned activated sludge are contacted and mixed in a state where dissolved oxygen, nitric acid, and nitrous acid are substantially absent, and a part of the phosphorus contained in the returned activated sludge is removed. Release the soluble phosphorus into the solution to produce a mixture rich in soluble phosphorus, and introduce a portion of the mixture to a chemical phosphorus removal process to remove the soluble phosphorus in the solution. At least a part of the chemically phosphorus-removed liquid and the remainder of the mixed liquid are treated with at least one of oxygen, nitric acid, and nitrous acid.
A method for removing phosphorus from an organic waste liquid, which comprises contacting and mixing the organic matter in the liquid with biological oxidation treatment, while absorbing soluble phosphorus into activated sludge and using a part of it as the returned activated sludge. It is.

〔Example〕

As an example of an embodiment of the present invention, FIG. 1 shows a typical flow sheet when the present invention is applied to an activated sludge method whose main purpose is to remove organic matter and phosphorus.

FIG. 2 shows a flow sheet when applied to a cyclic nitrification-denitrification method that also includes nitrogen removal.

Next, the features of the present invention will be described in more detail while explaining the embodiment shown in FIG.

The liquid to be treated 31 such as urban sewage that has passed through the initial settling tank (not shown) is maintained in an anaerobic state together with the return sludge 32 that is returned from the final settling tank 10 which is the final solid-liquid separation step. They are led to sex tank 1 and mixed and contacted. Here, "anaerobic state" means that dissolved oxygen [DO] and NOx-
(Nitric acid or nitrous acid) is also substantially absent and microorganisms cannot perform respiratory metabolism.
Although the specific concentration of x- is not specified, the redox potential (:0
RP) is preferably kept below a concentration that should be -130 mV or below. The returned sludge 32 often contains NOx.
- may be included, and if it is a small amount of NOx -, it will be consumed immediately when mixed with the liquid to be treated 31 and there will be no problem, but if it is contained in a large amount, it will impair the anaerobic state of the anaerobic tank 1. Undesirable. As a countermeasure against this, one method is to lengthen the residence time of the settled sludge in the final settling tank 10, but a return sludge storage tank 23 with no aeration or with a weak aeration force is installed in the return sludge route, and the return sludge is removed there. I hope that there is a way to make nitrogen work. If NOx- still gets mixed in, divide the anaerobic tank 1 into two or more compartments as shown in the example shown, or make the tank longer in the flow direction lζ, and change the mixing type of the mixed liquid in the tank to a pseudo plug flow. What is necessary is to devise measures to realize an anaerobic state at least in the latter half of the anaerobic tank 1. Of course, in this case, a part of the BOD of the liquid to be treated (mixed liquid in the tank) is consumed for denitrification, and the selection power against dephosphorizing bacteria is weakened accordingly. Therefore, eradicating the influx of NOx is the most desirable countermeasure. As for the structure of the anaerobic tank, the technology that has been used for denitrification tanks of the nitrification and denitrification method can be directly applied. Although an airtight structure is preferable in order to prevent 02 from being mixed in from the atmosphere and to prevent the dispersion of odor components contained in the liquid to be treated, it is not necessary to be limited thereto. As for the stirring technology required for mixed contact, gas stirring 9 mechanical stirring, liquid flow stirring, etc., which have been used in the venting tank, can be used.

In an activated sludge method facility in which the anaerobic tank 1 and the subsequent aeration tank 5 are connected to each other with the above conditions, activated sludge containing dephosphorizing bacteria as the main microbial species is easily produced. This activated sludge ingests at least a part of the BOD contained in the liquid to be treated in the anaerobic tank 1 in a non-oxidative manner, and stores it as intracellular organic matter. granules) is released as soluble phosphorus outside the cell, that is, on the pale side.

Phosphorus release from the activated sludge in the anaerobic tank 1 is coupled with BOD intake, so it is carried out quickly and reliably.

When urban sewage is used as the liquid to be treated, approximately five times the amount of phosphorus in the liquid to be treated can be released within two hours, although there are some differences depending on the conditions, and the soluble phosphorus concentration of the mixed liquid can be released within two hours. The phosphorus concentration in the sludge increases to about 6 times the liquid phosphorus concentration, and the phosphorus content in the sludge decreases accordingly. That is, the anaerobic tank effluent mixed liquid 33 obtained in this way is the sum of the phosphorus-released activated sludge that has released phosphorus and has a low phosphorus content i, the amount of released phosphorus, and the amount of phosphorus in the liquid to be treated. Contains corresponding soluble phosphorus.

Then, this anaerobic tank outflow mixed liquid 33 flows down to the distribution tank 2, where it is divided into a mainstream mixed liquid 34 and a branched mixed liquid 35, which flow directly down to the aeration tank 5. The divided mixed liquid 35 is led to the intermediate settling tank 3, which is an intermediate solid-liquid separation step, where it is separated into a separated liquid 36 containing concentrated phosphorus and an accompanying phosphorus containing a relatively small amount of soluble phosphorus. Released intermediate thickened sludge 3
7 is obtained. This intermediate solid-liquid separation operation may be not only gravity sedimentation concentration but also mechanical sedimentation concentration using a pressure flotation separator, a centrifugal sedimentation machine, or the like. However, since the activated sludge produced by the activated sludge method or the nitrification-denitrification method has extremely good sedimentation and concentration properties, ordinary gravity sedimentation and concentration is sufficient. The intermediate thickened sludge 37 obtained in the intermediate settling tank 3 flows down to the aeration tank 6 via the intermediate thickened sludge pump 4, and the separated liquid 36 is sent to a chemical phosphorus removal process.

The phosphorus concentration contained in the separated liquid 36 is the same as that of the anaerobic tank effluent mixed liquid 3.
The concentration of soluble phosphorus contained in 3 is equivalent to, or slightly higher than, the water quality of the liquid to be treated 31 and the anaerobic tank 1.
subject to the operating conditions of 5 rQ/11 as
When the liquid to be treated is average urban sewage containing phosphorus of about P, a phosphorus concentration of about 25 to 30 m971asP can be expected. As a method for chemically removing phosphorus from the separated liquid 36 containing such a relatively high concentration of phosphorus, a catalytic dephosphorization method is preferable, although the coagulation-precipitation method and other methods are not excluded. The reason for this is that in addition to the two advantages of (1) eliminating the need for sludge treatment and (2) recovering phosphate mineral resources, the catalytic dephosphorization method is particularly suitable for this type of high-concentration phosphorus dissolution. That's why. For example, urban sewage is the liquid to be treated! In this case, although the separated liquid 36 contains a high concentration of phosphorus, its alkalinity is 120.
ml// l as CaCO3, which is lower than phosphorus, and can be easily increased to 90% by simply adding about twice the molar ratio of Cl1(OH)2, without the normally required alkalinity adjustment. % or higher phosphorus removal rate can be expected. Furthermore, even if the alkalinity is adjusted, the amount of water in the separated liquid 36 is 3103 to 25% of the liquid to be treated, so the economic burden is minimal.

Then, the separated liquid 36 is not subjected to alkaline adjustment,
Calcium agent mixing tank 1 via separated liquid supply pump 12
3, where Ca(OJ()2 or CaCA
It is mixed with a calcium agent 14 such as No. 2, and further led to a dephosphorization tower 15. The structure and operation of this dephosphorization tower 15 are as follows:
The technical content that has been proposed for the catalytic dephosphorization method can be used as is. That is, a fluidized bed type dephosphorization tower is used because phosphorus in the separated liquid 36 is concentrated, so that sufficient phosphorus removal is possible even with a fluidized bed type which is easy to maintain. Of course, the type of the dephosphorization tower 16 is not limited to a fluidized bed, but may be a fixed bed or a combination of a fluidized bed and a fixed bed. When the separated liquid 36 is brought into contact with a dephosphorization tower filled with phosphate minerals, the value of the separated liquid is pl (preferably in the range of 6 to 11).

The separated liquid 36 that has undergone phosphorus removal by the chemical method as described above becomes a chemical dephosphorization treatment liquid 38.

This chemical dephosphorization treatment liquid 38 is allowed to flow down to the aeration tank 5 in order to further remove residual BOD and phosphorus, but the mainstream mixed liquid 34 and intermediate thickened sludge 37 also flow into the aeration tank 5 .

In this case, as for the structure and form of the aeration tank 5 and the operational requirements, techniques that have been conventionally used in activated sludge methods can be used. From the viewpoint of the mixing type, the seed shape is preferably a shape that results in a pseudo plug flow rather than complete mixing, both from the viewpoint of preventing short-circuit flow of the inflow liquid and from the viewpoint of producing activated sludge with good sedimentation and concentration properties. Therefore, a rectangular tank that is elongated in the downstream direction or a rectangular tank that has compartments is conceivable. In this case, the mainstream mixed liquid 34
It is preferable that the intermediate thickened sludge 37 and the chemical dephosphorization treatment liquid 38 flow into the farthest point from the aeration and purification outlet to take as long a residence time as possible, but the inflow point of the intermediate thickened sludge 37 and the chemical dephosphorization treatment liquid 38 is not necessarily the inflow point of the mainstream mixed liquid 34. It doesn't have to be the same.

It is preferable to control the - of the aeration tank mixture within the range of 6.5 to 8.5, but a range of 6.0 to 9.0 is permissible.

Dissolved oxygen (BOD) is preferably present at 2 mF//1 or more throughout the tank, but it is unavoidable that the DO is lower than this near the inlet points of the mainstream mixed liquid 34 and intermediate thickened sludge 37. As for the oxygen supply method, all the techniques used in the conventional activated sludge method can be used.

That is, although a diffused aeration system is used in which the air pumped from the blower 16 is blown into the liquid mixture in the form of fine bubbles, mechanical aeration may also be used. An oxygen aeration method that uses oxygen instead of air as an oxygen source can also be used.

When the mainstream mixed liquid 34, the chemical dephosphorization treatment liquid 38, and the intermediate thickened sludge 37 flow into the aeration tank 5 equipped with the equipment and environment described above, the activated sludge contained therein undergoes active respiratory metabolism and is released outside the cells. Biologically oxidizes existing BOD and intracellular stored organic matter, as well as soluble phosphorus existing outside the cells, if
IJ IJ acid begins to accumulate in cells as granules.

The capacity and rate of this soluble phosphorus absorption is proportional to the difference between the critical phosphorus content of the activated sludge and the current phosphorus content. Therefore, immediately after the activated sludge contained in the mainstream mixed liquid 34 and the like and which has already released phosphorus, flows into the aeration tank 51, it violently absorbs soluble phosphorus from the solution side. However, the phosphorus content of activated sludge increases correspondingly. That is, as the phosphorus absorption capacity decreases, the phosphorus absorption rate decreases.

In the conventional anaerobic-aerobic activated sludge method, in which all of the anaerobic tank effluent mixed liquid 33 flows directly into the aeration tank 5, once the amount of phosphorus released in the anaerobic tank 6 has been reabsorbed, the activated sludge Phosphorus absorption is almost saturated, and the amount of phosphorus beyond that, that is, the amount of phosphorus contained in the liquid to be treated 31, is absorbed by the slight increase in the aeration tank 5, that is, the amount of phosphorus absorbed by the excess activated sludge. It has to depend on capacity. For this reason, phosphorus absorption, particularly in the latter half of the aeration tank 5, is slow, and in some cases, phosphorus is not even substantially removed.

In the present invention, this problem is solved by dividing the flow using the distribution tank 2. That is, the amount of accompanying soluble phosphorus decreases by an amount corresponding to the amount of phosphorus introduced into the chemical phosphorus removal process. Therefore, even after the activated sludge in the aeration tank 5 has finished reabsorbing its accompanying soluble phosphorus, it still has a surplus in its phosphorus absorption capacity, so phosphorus can be removed reliably even in the aeration tank 5 with a relatively small capacity. , the phosphorus concentration of the treatment liquid 40 is stably low.

Through these functions and operations, the aeration tank effluent mixed liquid 39 formed after soluble phosphorus is absorbed into the activated sludge and BOD is sufficiently biooxidized is the final solid-liquid separation process. The activated sludge is guided to a final settling tank 10, where a treated liquid 40 is obtained while the activated sludge is sedimented, separated and concentrated.

The treatment liquid 4o may be discharged as is, or may be subjected to more advanced treatment if necessary. On the other hand, sedimentation separation a
At least a portion of the shrunken activated sludge is sent to the sludge return pump 1 as return sludge 32! The water is returned to the anaerobic tank 1 for processing. The remainder is discharged outside the system as surplus sludge 41, but if necessary, a part of it may be directly returned to the aeration tank 6 as short-circuit return sludge 42. Although the discharge point of the surplus sludge is set to the final settling tank 1°, it is not necessary to be restricted thereto, and a portion of the liquid mixture flowing out from the aeration tank 6 may be used as the surplus sludge. Further, when sedimentation and concentration is performed in the intermediate sedimentation tank 3, a part of the intermediate concentration sludge 37 may be used as surplus sludge. The surplus sludge obtained in this case is the sludge that has already released enough phosphorus in the anaerobic tank 1, so even if it is left in the surplus sludge thickening tank for a long time, not much soluble phosphorus will be released, and the sludge will not be released from the surplus sludge treatment system. This has the advantage of minimizing the phosphorus backflow phenomenon.

The present invention can also be applied to a nitrification-denitrification method that removes window elements along with BOD. Generally, in the nitrification-denitrification method, it is necessary to lengthen the sludge age in order to prevent the washout phenomenon of nitrifying bacteria, and in the conventional nitrification-denitrification method with an anaerobic tank, the BOD of the liquid to be treated is
Complete dephosphorization cannot be expected unless the J ratio is sufficiently large. However, if the present invention is used, the OD:I
It is also possible to process liquids with a J-ratio. The example in FIG. 2 is an example in which the present invention is applied to a so-called circulating nitrification-denitrification method, and its embodiment and characteristics will be briefly described.

In the example shown in FIG. 2, as in the example shown in FIG. 1, the liquid to be treated 31 and the return sludge 32 flow into the anaerobic tank 1, where they are mixed and contacted. In the example in Figure 2, which assumes complete denitrification, the return sludge 32
Even if NOx- is contained in the anaerobic tank 1, a complete mixing tank is sufficient because the amount is small. The other requirements of the anaerobic tank 1 may be the same as in the example of FIG. 1, and the microbial reactions occurring therein are also the same. The anaerobic tank outflow mixed liquid 33 flowing out from the anaerobic tank 1 becomes the mainstream mixed liquid 34 in the distribution tank 2.
and divided mixed liquid 35, of which divided mixed liquid 35
is sent to the intermediate settling tank 3 which is an intermediate solid-liquid separation step, where it is divided into a separated liquid 36 and an intermediate thickened sludge 37.

That is, the separated liquid 36 is sent to the biological oxidation filter tower 18, which is a biological oxidation treatment step, where it undergoes BOD oxidation removal and preferably nitrification. This operation is preferable when the subsequent dephosphorization tower 15 is used as a fixed bed for catalytic dephosphorization, and this biological oxidation can prevent the generation of microbial slime that causes clogging of the dephosphorization material (phosphate minerals). Fixed bed backwash time intervals can be increased. Further, by performing nitrification at the same time, the alkalinity of the separated liquid 36 can be reduced, and a high phosphorus removal rate can be obtained with a smaller amount of calcium agent. The biological oxidation treatment liquid 18 shows a technical form of an aerated fixed bed in which fine sand is filled and air is sent from the bottom by a blower 19, but there is no need to specify this, and microorganisms are attached to the fine sand etc. Technologies such as an aerated fluidized bed that allows fluidization while being aerated, a sprinkler hearth, and an immersion hearth can also be fully utilized.

The biological oxidation treatment liquid 43 is supplied to the biological oxidation treatment liquid supply pump 12'.
The water is sent to a calcium agent mixing tank 13 via the , where it is mixed with a calcium agent 14 , and then passed to a fixed bed type dephosphorization tower 15 . Here, the liquid that has been cleverly dephosphorized with a phosphorus removal rate of 80% or more, that is, the chemical dephosphorization treatment liquid 38, may be discharged as it is if allowed, but a small amount of water that still remains there may be discharged. In order to completely remove phosphorus and NOx generated in the biooxidation p-passage column 18, the NOx is returned to the circulating nitrification and dechambering facility, which is the main treatment system. In this case, the return point is the nitrification tank 7, but the first denitrification tank 6. Nitrification tank7. Either of the second denitrification tanks 8 may be used.

On the other hand, the mainstream mixed liquid 34 separated in the distribution tank 2 and the intermediate concentrated sludge 3 obtained by sedimentation separation and concentration in the intermediate settling tank 3
7 is also led to a circulating nitrification and denitrification facility. In this case, it is preferable that the mainstream mixed liquid 84 flows into the first denitrification tank 6;
The inflow tank for the intermediate thickened sludge 37 is the first denitrification tank 6. Any of the nitrification tanks 7 may be used.

Dephosphorizing bacteria can also perform denitrification, that is, respiratory metabolism using NOx- as a hydrogen acceptor, and the activated sludge that has released phosphorus flowing into the first denitrification tank 6 is passed from the nitrification tank 7 via the circulation pump 20. Using the NOx- contained in the circulating fluid 44 sent to the N1 denitrification tank 6, ・Bioxidize BOD existing outside the cells and intracellular organic matter while denitrifying it.
At the same time, extracellular soluble phosphorus is absorbed into the cell.

This phosphorus absorption reaction may end in the first decanning tank 6, but the subsequent nitrification tank 7. Second denitrification tank8. Furthermore, the reaeration tank 9
Sometimes it continues until the end. In these phosphorus absorption reactions, only a relatively small amount of soluble phosphorus is involved, so the functions and effects performed are similar to those in the example shown in FIG.

First denitrification tank6. Nitrification tank7. 2nd shedding tank 8. The operating requirements of the six tanks, such as reaeration tank 9, are almost identical to those of the conventional cyclic nitrification decanning process. Although not shown in Figure 2,
A carbon compound may be added to the second denitrification tank 8 as an auxiliary hydrogen donor to promote denitrification. In this case, methanol is the most preferred auxiliary hydrogen donor.

This is because methanol is an inactive substance for dephosphorizing bacteria, so even if it is added in an amount greater than the amount corresponding to the inflowing NOx amount and remains, it will not become a factor promoting phosphorus re-release. Furthermore, in conventional circulating nitrification and decanning methods, when the liquid to be treated is wastewater with a very low BOD:nitrogen ratio, carbon compounds are often added to the first denitrification tank 6, but rather an anaerobic tank is used. should be added to l. This is because the carbon compound becomes a promoter of phosphorus release and, in turn, contributes to the selection of dephosphorizing bacteria. In this case, the carbon compound is preferably ethanol, an organic acid such as acetic acid, a low molecular sugar, etc., instead of methanol.

Do of the nitrification tank 7 is maintained by blowing air from a blower 16. On the other hand, the reaeration tank 9 is a closed tank, and its oxygen supply is carried out by an oxygen generator 21.
This is done by pumping in purified oxygen. There are two advantages to using such oxygen aeration to maintain DO in the reaeration tank 9. The first advantage is that activated sludge is produced which has very good sedimentation and thickening properties (often with an SVI of even less than 50). The advantage of @2 is that the redox potential [
ORP] is slowed down, and the re-release of phosphorus from the activated sludge can be suppressed to a minimum. However, in this case, supplying an excessive amount of oxygen to the reaeration tank 9 to excessively increase the DO of the reaeration tank effluent mixed liquid 46 is not only uneconomical but also leaves Do in the returned sludge 32. Returned sludge 32
If DO remains in the anaerobic tank 1, it may destroy the unbreathable state of the anaerobic tank 1 and impair the selection and selection of dephosphorizing bacteria, which is the basis of this technology. In order to prevent such a situation, a monitor 22 such as an ORP meter or a dissolved oxygen meter is installed in the sludge settling part of the final settling tank 10 or in the middle of the route of the return sludge 32, and the output signal is used to monitor the flow from the oxygen generator 21. There are also measures such as controlling the amount of oxygen supplied. Note that the oxygen supply to the reaeration tank 9 does not need to be oxygen aeration, and a dawn aeration technique using normal air can also be used.

The reaeration tank effluent mixed liquid 45 flowing out from the nitrification and denitrification process as described above is led to the final settling tank 10 which is the final solid-liquid separation process, where the activated sludge is separated by sedimentation to obtain the treated liquid 40. . Most of the precipitated and separated activated sludge is returned sludge 32
While a small portion is sent to the anaerobic tank 1 as surplus sludge 41
is discharged from the system as

In the figure, 51 is a pump for supplying a liquid to be treated, 52 is a pump for a divided mixed liquid, 53 is a pump for supplying a chemical dephosphorization treatment liquid, and 54 is a pump for drawing out excess sludge.

Whether the present invention is applied to an activated sludge process as shown in the example in Figure 1 or to a nitrification-denitrification process as shown in the example in Figure 2, the important design and operational requirements when implementing the present invention are This is the distribution of chemical phosphorus removal amount and chemical phosphorus removal amount.

The amount of phosphorus removed in the anaerobic-aerobic activated sludge method is determined by the amount of surplus sludge generated and the phosphorus content contained in the surplus sludge. On the other hand, since the amount of surplus sludge generated is a function of the amount of BOD removed and the daily sludge age, the relationship between the amount of phosphorus removed and the phosphorus content is as shown in the following equation.

Here, φ: Phosphorus content of excess sludge (1IP-P/%-VSS
:) θ: Sludge daily age [day] ΔP Nilin removal amount [life-P/day] △S: BOD removal amount [Lu〇OD7 days] K: Sludge one-decay coefficient [-/day] Y: BOD sludge conversion Coefficient The biological amount of phosphorus removed in the present invention, that is, the difference between the total amount of phosphorus removed and the amount of chemically removed phosphorus, is also expressed by the following equation similar to equation (2).

Here, ΔP0: chemical phosphorus removal rate (Ij-P/day) The difference between the above equations (1) and (2) means the essential difference between the conventional anaerobic-aerobic activated sludge and the present invention. In other words, when attempting to completely remove phosphorus, the phosphorus content of the surplus sludge produced by the conventional anaerobic-aerobic activated sludge method, that is, the activated sludge at the end of the aeration tank, is In contrast, in the present invention, the phosphorus content can be easily controlled by increasing or decreasing the amount of chemically removed phosphorus.

The phosphorus absorption rate of activated sludge in the aeration tank in the anaerobic-aerobic activated sludge process is proportional to the difference between the critical phosphorus content and the phosphorus content at that point. Therefore, if a high phosphorus absorption activity is to be maintained up to the end of the aeration tank, the phosphorus content of excess sludge should have a relatively large difference from the critical phosphorus content. By doing so, it is possible to generate a treatment solution with a low concentration of phosphorus in a sufficiently stable manner.

Although the present invention does not particularly specify the phosphorus content in excess sludge, it is preferable to suppress the limit phosphorus content to 95% or less, preferably about 80%. In this case, the amount of chemically removed phosphorus is determined by the following equation from equation (1).

Here, φC: Critical phosphorus content CRt-p/Ky-vs s) If the amount of chemically removed phosphorus is determined as described above, by knowing the soluble phosphorus concentration of the separation liquid 36, the flow rate of the separation liquid 36 and the The flow rate of the divided mixed liquid 35 is determined.

Next, specific examples of the present invention will be shown.

The present inventors initially conducted a demonstration test of the conventional anaerobic-aerobic activated sludge method using wastewater from a housing complex for KM employees in City F as the liquid to be treated, but the treatment results were not satisfactory. Therefore, the treatment method was changed to the present invention.

The experimental processing facility has almost the same configuration as the example shown in FIG. The anaerobic tank consists of two cylindrical closed tanks made of hard vinyl chloride arranged in series. 6/min for each type with a motor with a speed reducer
A stirring impeller with 00 rotations is attached. The capacity of each type is 140L, and the total capacity is 280L. The intermediate sedimentation tank is also made of hard vinyl chloride and has a circular clarifier shape. Its diameter is about 280 dragons and its capacity is about 902 dragons. Attached to the bottom is a rake that rotates twice per minute using a motor with a speed reducer. The aeration tank is a rectangular steel plate tank and is nitrided on four sides. The capacity of each compartment is 160Q, and the total capacity is 640jl. Each compartment is equipped with a perforated diffuser tube, through which ventilation is supplied by a small blower. The amount of aeration is 120 to 15017 minutes for the entire aeration tank. The final settling tank is also made of steel plate and is in the form of a circular clarifier, with a diameter of 800mm and a capacity of approximately 300λ. At its bottom is a rake that rotates 0.5 revolutions per minute using a motor with a speed reducer.

Snake pumps were used for the treated liquid supply pump and sludge return pump, and tube pumps were used for the divided mixed liquid pump, intermediate thickened sludge pump, chemical dephosphorization treatment liquid supply pump, and excess sludge extraction pump. . In order to accurately control the sludge amount ◆, excess sludge was pulled out as a mixed liquid from the final compartment of the aeration tank. In this case, the sludge amount ◆ is the ratio of the aeration tank capacity and the daily drawn sludge amount.

A model plant of catalytic dephosphorization method was used as the chemical phosphorus removal facility. In this case, since the amount of separated liquid obtained was small, a fixed-bed desulfurization tower was adopted, but it was still too large for 24-hour water flow, so it was unavoidable to operate it for only a few hours a day.

The separated liquid that is separated and discharged in 24 hours is stored in the 5002 gilite tank and processed within a few hours the next day.The treated liquid is also stored in the 500Q gilite tank and averaged over 24 hours, and then transferred to the first compartment of the tank. It was sent back to .

All samples of the treated liquid and treated liquid used for analysis were collected as composite samples. Samples of the separated solution and chemical dephosphorization solution were collected before and after the catalytic dephosphorization treatment. In addition, samples of the mixed liquid and returned sludge were sampled at approximately 9:00 in the morning.

Using the above-mentioned experimental facility, we operated for a long period of time with sludge days of ◆5.6 days, and we will introduce two experiments related to the present invention.

The flow requirements for the first experiment were as shown in Table 1 and the experiment lasted for 5 weeks.

Table 1 Flow rate requirements for the 1st experiment The average MLSS at the terminal of the aeration tank at this time was 3320 my/n
, ML V S 82830 me/Q.

MLSS and MLVSS of returned sludge are IT, 162 respectively.
00 Da/l and 139001 #/ft. The MLSS and MLVS S of the intermediate thickened sludge were also close to that, 13400 da/2 and 11120 yy/u, respectively.

On the other hand, the model plant for the catalytic dephosphorization method was operated under the conditions shown in Table 2, and the entire discharged separated liquid was treated, and all of it was returned to the aeration tank.

-Table 2 Catalytic dephosphorization process operating conditions Analytical data of the treated liquid, treated liquid, separated liquid, and catalytic dephosphorized liquid obtained during the last 12 days of the 5 weeks of operation under these operating conditions The average values are shown in Table 3.

Result 1. ! It's very satisfying. Aeration tank terminal power)
The phosphorus content of the excess sludge extracted from the
55ffl&-P/,! It was maintained at 9-VSS.

In addition, the phosphorus content contained in the anaerobic effluent mixture is 43
~45η-P/, 9-VSS, which was about 20% lower than that of excess sludge. The phosphorus balance at this time is that the total amount of phosphorus flowing in is 28.
8.9/day, effluent phosphorus amount is 2.297 days, removal rate is 92
%Met. Of the total phosphorus removed in the system [26.6p7 days, 8.3g per day, which is equivalent to 30%, was removed by the catalytic dephosphorization method, so ta, 3. ! ? /
It means that the day has been withdrawn.

The average daily excess sludge drawn is 34 (1/day), so the phosphorus content of the surplus sludge determined from this is 53 m9-P/g-vs.
s, this result is in good agreement with the results of the previous analysis.

During this period, the soluble phosphorus contained in the mixed liquid flowing out of the anaerobic tank and the mixed liquid in the first to fourth compartments of the aeration tank was measured and found to be 26.5°10.2 and 4.2, respectively.
, 0.2, and 0.1 ml//l. From this, it is roughly the 31st f of the aeration tank! It is presumed that phosphorus absorption had finished in the I chamber.

In the second experiment, the effect of increasing the amount of chemically removed phosphorus by increasing the amount of separated liquid in the divided mixed liquid was investigated. The flow requirements are shown in Table 4.

Table 4 Flow rate requirements for the second experiment The aeration tank, MLSS, and MLVSS of the returned sludge are not much different from the first experiment, but the sludge concentration of the intermediate thickened sludge has decreased slightly. These are summarized in Table 5.

Table 5: MLSS and MLVSS Although the treatment conditions of the catalytic dephosphorization method were not changed, the amount of treatment increased, so the daily consumption of ca(oH)2 increased to 90 g/day.

The average values of the analytical data of the p42 experiment are shown in Table 6. As you can see, the processing result itself is f:fli
There is almost no significant difference from the experiment. However, the phosphorus content of excess sludge is 42-45 rn9-P/, 9-VSS
It has decreased considerably. Correspondingly, phosphorus release in the anaerobic tank is also slightly lower. However, phosphorus absorption in the aeration tank is faster than in the first experiment. In other words, the dissolved phosphorus concentration contained in the anaerobic tank effluent mixed liquid and the mixed liquid from the aeration compartment 1 to the 4th compartment are each 23.8.
, 5.9 , 0.1 , 0.1゜o, t my7
At i, phosphorus absorption has completed completely in the second compartment.

Through the first and second experiments, Ca(OH) of the catalytic dephosphorization method was
)2 addition rate was fixed at t5oy/4 with respect to the amount of separated liquid. This value is about 2.5 times the mole of phosphorus contained in the separated liquid. When converted to the amount of liquid to be treated, the first experiment was 11 m9/IL as Ca(OH)2.

Table 6 Average analysis data of the second experiment The addition rate of the second experiment was 211 n9/l, both of which were much smaller than when the secondary treated urban sewage water was subjected to direct catalytic dephosphorization treatment.

For comparison, Table 7 shows the treatment results of the conventional anaerobic-aerobic activated sludge method conducted before these experiments. The flow rate conditions of this treatment experiment were also exactly the same as those of the above two experiments.

The phosphorus content of excess sludge at this time is 60 to 611V-P/I
! -VSS did not increase further. In addition, the solubility of the anaerobic effluent mixed liquid and the mixed liquid from the aeration tank m1 compartment to the 4th compartment Table 7 Operation results by conventional anaerobic-aerobic activated sludge method (unit: nyi/IJ) Phosphorus concentration is 30 .2, 14.3, 5.2, 1.
9. At 1.8 my/l, phosphorus absorption occurs at a considerable rate in the first and second compartments, but from the third compartment onward, phosphorus absorption stops despite the presence of a considerable amount of phosphorus. There was a tendency to put it away.

Furthermore, the above-mentioned No. 1. Continuing from the second experiment, the second experiment of the present invention
A third experiment including nitrification and dechambering corresponding to the illustrated example was conducted.

The aeration tank used in the first and second experiments was reused as the nitrification tank, but the first denitrification tank and the second decanning tank with reaeration tank were newly constructed.
I made this. These newly installed tanks are rectangular closed tanks made of steel plates.
Three compartments are each nitrided, and the capacity of each compartment is 1601, for a total of 4801. The last one of the second denitrification tank with reaeration tank
The compartment is also isolated from other compartments regarding the gas phase.
It was used as a reaeration tank using oxygen, and the second compartment was used as a second denitrification tank. The internal liquids in each denitrification tank were stirred and mixed by gas agitation that circulated the generated gas using an air pump. In addition, the reaeration tank performed mixing and stirring and oxygen dissolution at the same time by stirring the gas while supplying oxygen gas from an oxygen cylinder at a constant rate. As a circulation pump from the nitrification tank to the first denitrification tank, Santo 9 Piper'Ii1 is used.
A pump was used. Methanol was used as the auxiliary hydrogen donor to the second denitrification tank, and a small tube pump was used as the supply pump. All other experimental facilities used in the first and second experiments were used as they were. In this experimental facility, unlike the example in Figure 2, the separated liquid was directly treated by the catalytic dephosphorization method without undergoing biological oxidation treatment, and the treated liquid was injected into the first compartment of the nitrification tank.

The third experiment was conducted for 18 weeks using the facility described above.

Among these, the flow rate requirements for about three weeks from which the data introduced here were obtained are shown in Table 8.

@Table 8 Flow rate requirements for the third experiment The sedimentation and concentration properties of the activated sludge obtained in this experiment were extremely good, and the average values of MLSS and MLVSS of the returned sludge were zt5oomg/# and 16,600 my/l, respectively. For this reason, although the return rate was not very high at 35%, the MLSS and MLVSS of the mixed liquid at the end of the nitrification tank were maintained at around 5380 Da/1 and around 4200-4200 Da/1, respectively. On the other hand, MLSS and MLVS of intermediate thickened sludge
S is 189,001 ng/l and 14,500 da/l, respectively.
It was l. Note that among the flow rate requirements for the third experiment, the amount of excess sludge was determined by calculating from the sludge age sufficient to achieve complete nitrification. The sludge age was approximately 13 days based on the amount of sludge held in the nitrification tank. The operating requirements for the catalytic dephosphorization method are as follows. There is basically no difference from the second experiment. However, since the phosphorus concentration of the separated liquid was somewhat high, the injection rate of Ca(OH)2 into the separated liquid was increased to 180 my/l, resulting in a daily consumption of Ca(OH)2 of 9597 days.

Table 9 shows the average values of the analytical data for the treated liquid, the centrifuged supernatant liquid (nitrification liquid) of the mixed liquid at the end of the nitrification tank, the treated liquid 1 separated □ liquid, and the catalytic dephosphorization treated liquid obtained under the above conditions. . The quality of the obtained treated liquid was BOD.

All water quality items, including phosphorus and nitrogen rings, were satisfactory. The phosphorus content in excess sludge is 58η-P/, 1
Although it was higher than before and after it-VSS and the previous two experiments, the first
As shown in Table 0, phosphorus absorption was almost completed at the end of the nitrification tank. Although some phosphorus was released from the sludge in the second denitrification tank, it was completely absorbed in the reaeration tank. Calculating the phosphorus balance, it means that 57% of the inflowing phosphorus was removed by the catalytic dephosphorization method, and the rest was eliminated from the system as phosphorus contained in excess sludge. The reason for the increased reliance on the catalytic dephosphorization method is that in order to achieve complete nitrification, the sludge age has to be controlled to a relatively long number of days, so the amount of surplus sludge has to be kept small. This is because the. Although a confirmation experiment was not conducted, if phosphorus removal by the catalytic dephosphorization method had been omitted in this @3 experiment, the phosphorus concentration in the treated liquid would have been much higher.

The present invention is different from the conventional anaerobic-aerobic activated sludge method (
1) Reduce the phosphorus load without being restricted by the BOD:IJ ratio of the liquid to be treated, (2) freely select the sludge age, and (3) adjust the phosphorus absorption activity of activated sludge to the aeration tank. (4) As a result, a treatment liquid with a sufficiently low concentration of phosphorus can be stably produced. In addition, compared to the conventional catalytic dephosphorization method, phosphate mineral resources can be effectively recovered from the treated liquid with a relatively low concentration of phosphorus with a small amount of calcium agent and without adjusting the alkalinity. It has the following advantages. Therefore, the system as a whole provides an economical and highly efficient method for removing BOD, phosphorus, and in some cases nitrogen as well, as a universal technology for organic wastewater such as municipal sewage containing low concentrations of phosphorus. are doing.

[Brief explanation of the drawing]

The drawings show embodiments of the present invention, and FIGS. 1 and 2 are system explanatory diagrams showing each embodiment of the present invention. 1...Anaerobic tank, 2...Distribution tank, 3.
... Intermediate sedimentation tank, 4 ... Intermediate thickened sludge pump, 5 ... Aeration tank, 6 ... First evacuating tank, 7 ... ...Nitrification tank, 8...Second derooming tank, 9...Reaeration tank, 10...Final settling tank, 11...For sludge return Pump, 12...
... Separated liquid supply pump, 12' ... Biological oxidation treatment liquid supply pump, 13 ... Calcium agent mixing tank, 14 ... Calcium agent, 15 ...・
・Dephosphorization tower, 1g... blower, 18... biological oxidation filter tower, 19... blower, 20...
...Circulation pump, 21...Oxygen generator, 22
...Monitor, 23...Return sludge storage tank,
31... Liquid to be treated, 32... Returned sludge, 33... Anaerobic tank effluent mixed liquid, 34...
Mainstream mixed liquid, 35... Branch mixed liquid, 36...
...Separated liquid, 37...Intermediate thickened sludge, 38...
... Chemical dephosphorization treatment liquid, 39 ... Aeration tank effluent mixed liquid, 40 ... Treatment liquid, 41 ...
・Excess sludge, 42...Short circuit return sludge, 43...
... Biological oxidation treatment liquid, 44 ... Circulating liquid, 4
5... Re-aeration tank outflow mixed liquid, 51...
To-be-treated liquid supply pump, 52... Pump for diverted mixed liquid, 53... Chemical dephosphorization treatment liquid supply pump, 54... Excess sludge drawing pump. Patent Applicant Ebara Infilco Co., Ltd. Agent Patent Attorney Masayuki Takagi Agent Patent Attorney Yori 1) Takatsugu Department Procedural Amendment August 9, 1980 Mr. Manabu Shiga, Commissioner of the Japan Patent Office, Indication 3 of Case, Amendment Relationship with the case of the person who filed the patent Patent applicant address (residence) Name (name) (m) Ebara Infilco Co., Ltd. 4, agent 6, number of inventions increased by amendment 7, subject of amendment Part 4 of specification 8, amendment Hitoshi Nouchi As shown in the attached sheet

Claims (1)

[Claims] 1. The liquid to be treated and the returned activated sludge are contacted and mixed in a state in which dissolved oxygen, nitric acid, and nitrous acid are substantially absent, and the phosphorus contained in the returned activated sludge is A part of the liquid is released into the solution as soluble phosphorus to produce a mixed liquid rich in soluble phosphorus, and a part of the mixed liquid is led to a chemical phosphorus removal process to remove the soluble phosphorus from the liquid. At least a part of the chemically phosphorus-removed liquid and the remainder of the mixed liquid are contacted and mixed with at least one of oxygen, nitric acid, and nitrous acid to biologically oxidize the organic matter in the liquid, A method for removing phosphorus from organic waste liquid, which comprises absorbing soluble phosphorus into activated sludge and using a portion of it as the returned activated sludge. 2. The chemical means is based on the contact arm phosphorus method,
A portion of the mixture was adjusted to pH 6 in the presence of calcium ions.
The method for removing phosphorus according to claim M1, wherein the phosphorus removal method is carried out by contacting and passing through a calcium-containing phosphate mineral within the range of 11 to 11. 3. Phosphorus removal leakage according to claim 1 or 2, wherein a part of the mixed liquid is subjected to a biological oxidation treatment in advance and then treated by the catalytic dephosphorization method.