JPS5929320B2 - Phosphate stripping of sewage - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides an activated sludge solution for treating raw or treated phosphate-containing sewage to obtain a substantially phosphorus-free effluent that is returned to natural water resources. :Relating to sewage treatment law.

In the activated sludge systems commonly used today,
The sewage is subjected to conventional screening and pre-sedimentation methods, then mixed with activated sludge that has been recycled from the settling tank to form a mixture, and this mixture is subjected to aeration or aeration.

While aerating the mixture, the organic matter present causes aerobic decomposition of the solids and a high degree of removal of BOD is achieved.

Phosphates are present in organic wastes and detergents, and are not captured by conventional sewage treatment methods and are therefore carried along with the effluent to natural water resources such as lakes and rivers. is being released.

Such phosphates have been attributed to overpressure iodification or eutrophication of the water causing unsightly algal blooms and severe pollution problems.

In the activated sludge sewage treatment method, the mixed liquid is aerated first.
It is known to cause phosphate to be taken up or absorbed by the microorganisms present.

US Pat. No. 3,236,766 discloses a method for removing phosphates from sewage using this phenomenon.

According to this method of the U.S. patent, the pH of the raw sewage is maintained in the range of about 6.2 to about 8.5, adjusted as necessary, and the sewage is mixed with activated sludge to form a mixture. However, the mixed liquid has a low oxygen content that can be dissolved therein (both 0.3
Aeration is maintained at ~/l and the phosphate-enriched sludge is separated from the mixture to yield a substantially phosphate-free effluent.

The phosphate-enriched sludge is treated to reduce its phosphate content before it is recycled to mix with influent sewage.

This content reduction is accomplished by holding the phosphate-enriched sludge in anaerobic conditions for several hours.

Several other methods have been proposed to reduce the phosphate content of phosphate-enriched sludge after the aeration step in activated sludge sewage treatment processes.

Thus, for example, U.S. Pat. Discloses contacting and stirring in the tank for a sufficient time to transfer the phosphate material from the sludge to the aqueous phase.

The low phosphate content aqueous medium used in this tank is water added from an external source to leach the phosphates from the sludge.

After the soluble phosphates have been leached from the sludge into the aqueous medium, the mixture is passed to a settling tank where the phosphate-enriched aqueous medium is added to the phosphate-depleted sludge (ph
osphate-depleted sludge).

This method requires the addition of a significant amount of water from an external source and requires two separation tanks, a phosphate elution tank and a settling tank, to separate the soluble phosphates from the sludge. Therefore, such a method requires a large capital investment.

Accordingly, one object of the present invention is to provide an improved method for reducing the phosphate content of phosphate-containing sewage in activated sludge sewage treatment processes.

Another object of the present invention is such an improved method comprising an improved phosphate stripping treatment operation of phosphorus-enriched sludge, thus improving the efficiency of phosphate removal from sewage. The object of the present invention is to provide a method for reducing phosphate content.

Further objects and advantages of the invention will be apparent from the claims and the following description.

In summary, the present invention relates to an activated sludge process for treating raw or treated phosphate-containing sewage to obtain a substantially sludge-free effluent.

The method of the present invention involves aerating a mixture comprising phosphate-containing influent sewage material and activated sludge in an aeration zone to reduce the BOD content of the sewage material and to allow the microorganisms present to absorb the phosphates. include.

The phosphate-enriched sludge is then separated from the mixture in a settling zone to provide a substantially phosphate-free effluent.

The separated phosphate-enriched sludge is passed through a phosphate stripping zone (hereinafter sometimes simply referred to as the stripping zone or stripper) where it settles to form a supernatant liquid in the upper portion of the stripping zone. , and also forms settled sludge in the lower part.

At least a portion of the settled sludge is maintained under anaerobic conditions for a sufficient period of time to release phosphate into the liquid phase of the settled sludge.

The released phosphate-containing anaerobic sludge is brought into contact with a lower soluble phosphate content medium (the supernatant liquid of the stripping zone or the liquid phase of the phosphate-enriched sludge entering the stripping zone). to transfer the soluble phosphate in the anaerobic sludge liquid phase to the lower soluble phosphate content medium, thereby enriching the supernatant in the upper part of the stripping zone with phosphate. Close.

At least a portion of the anaerobic sludge is recycled from the phosphate stripping zone to the aeration zone as the activated sludge.

As used herein, the term "sludge" means a solid-liquid mixture characterized by a solid phase of sludge and an associated liquid phase.

The term "lower soluble phosphate gold content medium" refers to an aqueous medium containing soluble phosphate at a lower concentration than the anaerobic sludge containing released phosphate with which the medium comes into contact. or a water-containing medium.

According to the present invention, a phosphate-enriched sludge that has phosphate present within the cells of the sludge microorganisms, i.e., biological solids, provides phosphate to the microorganisms in the settling sludge in the stripping zone. The sludge is maintained under anaerobic conditions for a sufficient period of time to release into the liquid phase.

The resulting anaerobic sludge containing released phosphate is contacted with a lower soluble phosphate content medium.

The purpose of such contact is to transfer soluble phosphate from the anaerobic sludge and ultimately to the supernatant in the stripping zone, thereby achieving phosphate enrichment of the supernatant in the stripping zone. It is something.

According to the invention, the transfer of soluble phosphate from such an anaerobic sludge can be done directly by contacting the anaerobic sludge with a supernatant liquid, or, for example, by placing the anaerobic sludge in a This can be done indirectly, such as by contacting the phosphate-enriched sludge that is sent to the ripping zone.

In the absence of such a contact/transfer step, the released soluble phosphate in the anaerobic sludge (particularly in the settled sludge in the lowest part of the stripping zone) is removed from the sludge layer within the same stripping zone. It takes a considerable amount of time to move to the supernatant liquid.

Under such conditions, if the sludge is removed from the stripping zone and recycled to the aeration zone before a sufficient amount of soluble phosphate is transferred to the supernatant, the aeration zone contains: Excess amounts of soluble phosphate will be recycled, reducing the phosphate removal efficiency of the overall process.

The present invention eliminates such problems and thus proves that high phosphate removal efficiencies can be achieved in practical operations.

FIG. 1 is a schematic flowchart of an activated sludge process according to one embodiment of the present invention in which an anaerobic sludge containing released phosphate is contacted with a phosphate-enriched sludge that is sent to a stripping zone. It is a sheet.

FIG. 2 shows that a portion of the supernatant liquid in the phosphate stripping zone is removed from the zone and returned to the stripping zone for contact with an anaerobic sludge layer containing released phosphate. 2 is a schematic flow sheet of an activated sludge process according to another embodiment of the invention, but introduced below the anaerobic sludge bed.

Referring now to the drawings, FIG. 1 depicts an exemplary process system in accordance with the present invention.

The raw phosphate-containing sewage inlet stream 1 is passed through conventional sieving and fines removal equipment, optionally subjected to a first settling treatment in a first settling tank 2, and from said settling tank via pipe 3. The first sludge is removed.

The sewage that has undergone the first sedimentation treatment is mixed with recycled activated sludge, which will be described later, to form a mixed liquid, and is further passed through a pipe 4 to an aeration tank 5.

In the aeration tank, the mixture is made aerobic (i.e., such that there is a measurable amount of dissolved oxygen present in the mixture) in at least a portion of the tank.
Aerate for 1 to 8 hours at a rate sufficient to hold.

During aeration, the microorganisms present absorb phosphates and also consume organic substances present in the sewage.

A high degree of BOD removal is achieved with the aeration process.

After aeration, the mixed liquid is fed to the second settling tank 6.

In this second settling tank, the phosphate-enriched sludge settles and is separated from the mixed liquor by straining.

This sludge contains a significant portion of the phosphates present in sewage.

The substantially phosphate-free effluent is discharged via line 7 to be treated in a conventional manner.

Phosphate enriched sludge is removed from settling tank 6 by pipe 8.

A portion of the sludge can be transported as waste, while the remaining portion is passed through the stripper 9 in contact with the anaerobic sludge containing a high concentration of soluble phosphates that has been recycled from the stripper 9. Ru.

Within the phosphate remover stripper, phosphate-enriched sludge settles to form a supernatant liquid in the upper portion of the stripping zone and also to form a settled sludge.

At least a portion of the settled sludge is maintained under anaerobic conditions for a sufficient period of time to cause microorganisms in the anaerobic sludge to release phosphates associated with the anaerobic settled sludge.

Phosphate elutes from the anaerobic sludge solids into the liquid phase.

The mechanism of this processing will be explained in detail later.

The phosphate enriched supernatant liquid produced in the IJ tube 9 is passed by tube 10 to the phosphate precipitator 11.

In this precipitator, a phosphate precipitating agent such as an aluminum or iron salt or lime mixes with the phosphate-enriched supernatant to precipitate the phosphates.

The precipitated phosphate is transferred to pipe 1 to mix with the raw sewage in pipe 1.
2.

The sludge solids present in the stripper 9, which contain large amounts of phosphate within the cells of the organic matter in the sludge, separate from the aqueous phase of the sludge and settle to the bottom of the stripper. .

The solid particles in the sludge, containing intracellular phosphate, thus settle into the settled sludge layer of the stripper 9.

There is a density gradient in the settled sludge layer, and the sludge density at the bottom of the sludge is higher than that at the top.

In the practice of the present invention, at least a portion of the settled sludge is subjected to anaerobic conditions for a period of time sufficient to cause phosphate to be released into the liquid phase of the anaerobic settled sludge, i.e., dissolved in a measurable amount. Oxygen is kept essentially absent in the liquid phase of the sludge.

The residence time of the sludge within the stripping zone required for phosphate release depends in part on whether the phosphate-enriched sludge being passed through the stripping zone is aerobic or anaerobic. Ru.

For example, it has been found that the absorption rate of dissolved oxygen (by the microorganisms present) in the second settling zone of a conventional activated sludge plant is quite high, for example on the order of 20-30 ppm/hr.

With such high absorption rates, the dissolved oxygen of the mixture that has been discharged from the previous aeration step can be depleted in this settling zone, so much so that the sludge underflow withdrawn from the settling zone is anaerobic. .

As applied to the present invention, such anaerobic phosphate-enriched sludge, which is separated from the mixed liquor and passed to the stripping zone, is equal to or less than the total volume of settled sludge in the stripping zone. is kept under anaerobic conditions,
It also allows the sludge residence time in the stripping zone required for phosphate release to be relatively short.

When the sludge removed from the second settling zone and passed to the stripping zone is anaerobic, the residence time and resting state of the sludge in the settling zone is such that the phosphate in the second settling zone is must be maintained so that they cannot be released or mixed to the extent that they impair the effluent output from the process).

On the other hand, when the phosphate-enriched sludge being passed to the stripping zone is aerobic, a relatively long sludge residence time in the stripping zone is required to achieve the required phosphate release. .

In such a case, the upper part of the settled sludge in the stripping zone is aerobic, and only the lower part of the settled sludge is anaerobic.

Under such conditions, as the solids in the sludge containing intracellular phosphate migrate to the bottom of the settling sludge layer,
Due to the anaerobic conditions in this part of the sludge layer, organic matter releases phosphate into the liquid phase of the sludge in the form of water-soluble phosphate ions.

In the stripping zone of this system, the concentration of soluble phosphate is initially highest in the lower part of the sludge layer.

In carrying out the present invention, the residence time of the sludge in the IJ tube is 2 to 30 hours.

As mentioned above, a considerable amount of time is required for the soluble phosphate to be released by the settling solids and to migrate from this settled solids layer to the supernatant liquid.

If the sludge is removed and recirculated to the aeration zone before a sufficient amount of soluble phosphate is transferred to the supernatant, the aeration tank will have an excess amount of soluble phosphate recycled, but phosphate removal efficiency of the whole process decreases.

Preferably no more than 75% of the soluble phosphate released in the stripper is recycled to the aeration tank along with the recycled activated sludge.

According to one embodiment of the invention, the anaerobic sludge containing a significant portion of the soluble phosphate released in the stripper 9 is removed from the stripper and divided into two parts.

One part of this high soluble phosphate content sludge is
Raw sewage and pipe 4 on the way to the aeration tank
Another portion of the anaerobic, high soluble phosphate content sludge is recirculated via pipe 13 for mixing within the stripper. It is recirculated via pipe 14 to contact and mix with the sludge on its way to 9.

The sludge taken out from the second settling tank 6 contains intracellular phosphate in its solid phase, and the liquid phase, which may constitute 98 to 99% of the sludge, contains almost no soluble phosphate. or none at all, soluble phosphate is transferred from the high soluble phosphate content anaerobic sludge coming from tube 14 to the liquid phase of phosphate enriched sludge.

The tubes 13 and 14 are removed from the stripper, respectively.
Each portion of the high soluble phosphate content anaerobic sludge passed through constitutes about 25-75% of the total amount of high soluble phosphate content sludge removed from the stripper and discharged within the stripper. Preferably, at least 25% of the soluble phosphate is removed from the IJ collar into tube 10 along with the supernatant liquid.

Alternatively, the high soluble phosphate content sludge portion in tube 14 may be placed directly into the stripper 9 but within the stripper 9 such that the soluble phosphate comes into contact with and transfers to the supernatant liquid in the stripper. It can be introduced onto the sludge layer.

In the embodiment of the invention shown in FIG. 2, the phosphate-containing influent sewage material is introduced into the sewage treatment system by line 15, and the phosphate-reduced supernatant liquid from line 34, described in more detail below. mixed with.

This incoming sewage and recirculating sludge in pipe 24 is passed to an aeration zone where the mixture formed from the sewage material and the recirculating activated sludge is aerated to reduce the BOD content of the sewage and remove any microorganisms present. Incorporates phosphate.

In practice, the aeration zone can be of the conventional type using air as the oxidant or oxidant in an open aeration chamber.

Alternatively, aeration may be performed by J. R. McWhhirter (McWh.
U.S. Patent No. 3,547,813 for i r ter ) et al.
No. 3,547,815.

There, at least one closed covered aeration chamber is used, and in the aeration chamber the liquid being treated is
The presence of activated sludge, in intimate contact with the oxygen-enriched gas from the overlying gas space, dissolves the oxygen necessary for aerobic biological activity.

Such oxygenation systems can achieve comparable or higher overall treatment rates at biological suspended solids loads that are several times higher than conventional air aeration systems, and within aeration residence times that are several times shorter than conventional air aeration systems. It has been found to be very effective in carrying out the present invention.

The aerated mixture is directed from the aeration zone into tube 17 and passed to second settling zone 18 .

In this settling zone, the phosphate-enriched sludge is separated from the mixed liquor to yield a substantially phosphate-free effluent.

The effluent is discharged from this system into pipe 19.

The separated phosphate-enriched sludge is passed from the second settling zone via tube 20 to a phosphate stripping zone 21.

In this stripping zone, the phosphate-enriched sludge settles to form a supernatant liquid in the upper part 22 of the stripping zone and also to form a settled sludge.

At least a portion of the settled sludge within the stripping zone is maintained under anaerobic conditions for a period sufficient to release phosphate into the liquid phase of the anaerobic sludge in the same manner as previously described.

The anaerobic sludge contacting step is carried out in this system by taking the supernatant liquid from the stripping zone into a tube 25 and transferring a portion of it to a tube 26 with a pump means 27 disposed in the middle.
This is accomplished by recirculating the flow into the lower part of the stripping zone.

The supernatant liquid in the diversion tube 26 is reintroduced to the phosphate stripping treatment zone by a sparging means 28, which may include a multi-headed stationary nozzle, for example.

Dissolution in the anaerobic sludge is thus transferred to the upper flow recirculated supernatant and subsequently to the bulk volume of the supernatant in the upper part of the IJ topping zone. A countercurrent aqueous solution of phosphate is established.

In this contactor, any dissolved oxygen content of the stripping zone supernatant, such as may result from passing an aerobic phosphate-enriched sludge from a second settling zone to a phosphate treatment zone, is It is clear that the contacting flow in tube 26 is also passed to the lower part of the IJ coupling zone.

The introduction of such dissolved oxygen causes phosphate to be reincorporated by microorganisms in the precipitated solid layer into which the contacting stream is introduced that have already released the phosphate into the associated liquid phase.

This effect should be localized in the immediate vicinity of the introduction means so as not to adversely affect the anaerobic conditions of the anaerobically settled sludge volume within the IJ pinning zone.

In other words, the dissolved oxygen content of the supernatant liquid should be controlled by appropriate design.

The supernatant portion removed from the stripping zone into line 25 but not diverted into line 26 as recirculating contacting medium is directed to a rapid mix tank 29.

In said tank, the supernatant liquid which has not been diverted is rapidly mixed (by means not shown) with a phosphate precipitant, such as lime, which has been introduced into the same tank by pipe 30.

The supernatant liquid-phosphate precipitant mixture is then passed by tube 31 to a flocculator tank 32 where the precipitant-treated phosphate is precipitated and removed from the system as chemical sludge waste into tube 33. taken out.

The phosphate depleted supernatant effluent from condenser tank 32 is recycled into pipe 34 to be combined with the sewage influent in pipe 15 entering the process.

The anaerobic sludge contact system described above transfers a significant amount of the phosphates released into the anaerobic sludge to the supernatant liquid in the upper part of the stripping zone and thereby removes the phosphate from the bottom of the stripping zone to the supernatant liquid in the upper part of the stripping zone. The anaerobic sludge withdrawn within the aeration zone has a phosphate content sufficiently reduced to allow for a high degree of phosphate removal from the sewage water in the aeration zone.

In practicing the present invention, contact between the anaerobic sludge portion having a high soluble phosphate content and the supernatant in the stripper is maximized to elute the soluble phosphate into the supernatant. In order to achieve this, measures other than those described by way of example can be used.

For example, two or more stripper tanks may be used.

One tank is kept relatively undisturbed and the sludge is kept under anaerobic conditions so that the microorganisms release its phosphate content.

On the other hand, in the other tank, the microorganisms have already released their phosphate content, so the tank is agitated to mix the anaerobic sludge layer containing the soluble phosphates with the supernatant liquid. be done.

This vigorous agitation is stopped after the supernatant liquid has dissolved away a substantial amount of soluble phosphate from the sludge solids, thus allowing the solids to settle out.

After the solids have settled, the supernatant liquid containing virtually all the soluble phosphates in the tank is removed and passed through a phosphate precipitator, and the phosphate-depleted sludge is
This is recycled to mix with the raw sewage that is on its way to the aeration tank.

The tank is then filled with sludge from the second settling tank.

The sludge is allowed to settle and becomes anaerobic and is maintained under anaerobic conditions.

Meanwhile, in the first tank, the previously described process of vigorously agitating the anaerobic sludge and supernatant, allowing it to settle and removing the phosphate-enriched supernatant is repeated.

In other words, the two tanks are held at a phase difference of 180° from each other.

Another means to remove soluble phosphate from the anaerobic sludge is to introduce fresh sludge from a second settling tank to the bottom of the stripping zone so that it diffuses upward through the anaerobic sludge; However, the soluble phosphate contained in the lever layer is to be dissolved and removed.

Another means of maximizing contact between the supernatant and the anaerobic sludge layer containing high concentrations of soluble phosphate in the stripper is to intermittently vigorously agitate the contents of the stripper to The purpose is to disperse the sludge layer into the supernatant liquid.

The supernatant liquid thereby elutes the phosphates from the sludge solids.

This allows the contents of the stripper to settle.

During agitation and settling, no recirculated sludge is removed from the bottom of the IJ collar.

Agitation can be accomplished by introducing non-oxygen-containing gas to the bottom of the stripper 9.

Also, different parts of the anaerobic sludge layer can be raised above the settled sludge layer and then allowed to settle again.

During this precipitation, the soluble phosphates are eluted by the supernatant.

While this is occurring, another portion of the anaerobic sludge layer can be removed from the stripper for recirculation to the aeration tank.

Any such process can be performed continuously or intermittently.

Thus, if, for example, the anaerobic sludge removed from the stripper is recirculated through line 14 for one hour out of every five hours of operation, there will be sufficient soluble phosphate in the system of FIG. Transfer can be achieved.

The following example illustrates the unique benefits of the present invention compared to conventional equipment in achieving high total phosphate removal from phosphate-containing sewage without the anaerobic sludge contact technique feature. .

EXAMPLE ■ In this test, a process system of a type similar to that illustrated in FIG. 2 was first operated in a prior art manner without the anaerobic sludge contact of the present invention.

The system is then modified in accordance with the present invention in a manner substantially similar to that described above in connection with FIG. operated using.

In both experiments of this comparative evaluation test, the influent sewage was mixed with the recycled activated sludge to form a mixture which was then aerated in an aeration zone to allow the microorganisms present to absorb the phosphates.

The phosphate-enriched sludge was then separated from the mixture in a second clarifier to obtain a substantially phosphate-free effluent.

The separated phosphate-enriched sludge was passed through a stripping zone where it was allowed to settle to form a supernatant liquid in the upper portion of the stripping zone and to form a settled sludge.

The settled sludge was held under anaerobic conditions for a sufficient time to release phosphate into the liquid phase of the sludge and yield a phosphate-enriched supernatant.

The resulting phosphate-enriched supernatant liquid is removed from the IJ pulling zone and mixed with a phosphate precipitant (lime) in a rapid mixing tank, and the resulting phosphate precipitate is converted into a chemical sludge in a flocculation tank. The phosphate depleted supernatant was removed as waste and recycled to the inlet sewer.

The settled sludge was removed from the stripping zone and recycled to the influent sewage as the activated sludge described above.

The first comparative evaluation test operated according to the teachings of the prior art.
In the experiment, the supernatant liquid removed from the upper part of the IJ stripping zone was not recirculated or reintroduced into the stripping zone.

All of the supernatant liquid removed from the upper section was treated with phosphate precipitant and recycled to the inlet drain.

As explained by the system in FIG.
7 is schematically shown as being disposed in a recirculation tube communicating with the stripping zone supernatant discharge tube 25 and terminating in the lower part of the stripping zone;
It was not activated and did not direct any flow into the recirculation line.

In a second experiment of a comparative evaluation test operated in accordance with the present invention, the process system was operated as above, except that the recirculation pump was used to remove lower soluble phosphorus from the stripping zone supernatant drain. A partial flow diversion of the acid-containing supernatant liquid was activated and introduced below the anaerobic sludge in the stripping zone.

In this way, a countercurrent aqueous flow of soluble phosphate in the anaerobic sludge is established, whereby phosphate is transferred to the eluent supernatant and subsequently to the supernatant in the upper part of the IJ tupping zone. to the liquid resulting in phosphate enrichment of the supernatant liquid.

The test period for the first experiment without anaerobic sludge contact was 8 days of continuous operation, and the test period for the second experiment with anaerobic sludge contact was 10 consecutive days.

The data obtained from the comparative evaluation test of the above strains are listed in the table below.

Such material shows that the method of the present invention (material shown in column A) is significantly better in phosphate removal efficiency than the system taught by the conventional method (material shown in column B). It's proven.

As shown by the data, flow rate of influent sewage, recirculation flow rate of phosphate-enriched sludge, lower stripping zone flow rate, upper stripping zone flow rate, mixed liquid suspended solids under aeration, solids suspended under aeration, mixed liquid volatile suspended solids,
The process parameters of each system, including effluent biochemical oxygen demand (BOD5) and effluent biochemical oxygen demand (BOD, ), all have strictly corresponding measurements.

Therefore, the entries in the table regarding the phosphate concentrations measured in the selected process streams in both systems, i.e. phosphate in the influent sewage, phosphate in the effluent, % total phosphate removed, stripper bottom layer. The phosphate in the stream and the phosphate in the stripper supernatant are transferred to the supernatant in the stripping zone by contacting the released phosphate-containing anaerobic sludge with a lower soluble phosphate content medium. The process of the present invention, which involves the ultimate transfer and enrichment of the supernatant, reduces the total amount of phosphates removed from the treated sewage (8
7%), demonstrating a significant improvement over the conventional process (16.7%) which did not use such an anaerobic sludge contacting step.

It is readily apparent that the reason for the significant difference in phosphate removal between these systems is based on comparing the phosphate stripper underflow and supernatant phosphate concentrations in these systems.

Process carried out according to the present invention (materials to be posted in column A)
Then, the phosphate concentration in the flow below the stripper is 4687
nII/l, and the concentration in the stripper supernatant is 35 μ/l, whereas in the conventional process the corresponding phosphate concentration in the stripper underflow is 68 μl/l.
5~/l and stripping zone supernatant liquid 4.9/l
It was l.

Such material shows that in the conventional process, the phosphate released by the anaerobic sludge remained in the settled sludge layer and did not move significantly into the supernatant liquid of the stripping zone, whereas in accordance with the present invention, The results show that the process achieved significantly higher total phosphate removal than the conventional process, and at the same time significant phosphate transfer.

Example ■ Raw sewage containing approximately 1100 ppm solids and approximately 10 ppm total phosphates [approximately 1,000,000 gallons 7 days (gpd)]
) was passed through conventional sieving and fines removal equipment and mixed with recycled activated sludge (about 100,000 gpd) containing about 50 ppm of soluble phosphate.

This mixture was pumped to an aeration zone and aerated for 6 hours at a rate of 2 ft'' of air per gallon of sewage.

The effluent mixture from the aeration zone was fed to a second settling tank.

The purified, substantially phosphate-free effluent was discharged to the effluent stream after chlorination at a rate of approximately 1,000,000 gpd.

The mixture of precipitated phosphate-enriched sludge is approximately 21,000
It was removed from the second settling tank at a rate of 0 gpd.

A portion of this sludge (approximately 100,100 O0) was transported as waste sludge, and the remaining portion was passed through an anaerobic phosphate stripper where it was kept under anaerobic conditions for approximately 10 hours.

The anaerobic conditions within this stripper induced significant intracellular phosphate release by the microorganisms.

The sludge was concentrated and allowed to settle under slow mechanical stirring.

This agitation is not sufficient to drive the phosphates that can be leached from the sludge layer into the supernatant liquid at a rate fast enough to make the process reasonably efficient.

Thus, dissolved phosphates released by microorganisms tend to remain in the anaerobic settling sludge.

Anaerobic sludge was removed from the bottom of the stripper at a rate of 200,000 gpd.

A portion of this anaerobic sludge (100,000 gpd
) is recycled to mix with the incoming raw sewage, and the remaining portion (100,000 gpa) is mixed with existing anaerobic sludge removed from the second settling tank and routed to the stripper. I recirculated it as much as possible.

Thus, the soluble phosphates contained in the anaerobic sludge portion are transferred to the liquid phase of the anaerobic sludge, and thereby the soluble phosphates are dispersed in the supernatant liquid in the stripper tank. .

Approximately 50p of soluble phosphate is extracted from this stripper tank.
Phosphate-enriched supernatant containing pm (100,000 g
pd) was removed and fed to a chemical precipitation tank where lime was added and mixed to form a phosphate precipitate.

The precipitated phosphorus was recycled and mixed with the flowing sewage.

In the aeration zone, the soluble phosphates introduced from the stripper along with the recirculated sludge were absorbed by the microorganisms present in the sludge along with the phosphates contained in the influent sewage.

Although we have described various exemplary embodiments of the present invention using supernatant liquor and phosphate-enriched sludge as the lower soluble phosphate content media, for example, the feed from an aeration tank to a second settling tank may be Other media, such as a portion of the aerated mixture taken from the stream in transit, may be used to contact the anaerobic sludge containing released phosphate according to the method of the present invention. is clear.

Thus, while preferred embodiments of the invention have been described in detail, it will be appreciated that other embodiments are contemplated as falling within the scope of the invention by mere modification of the disclosed features. Good morning.

[Brief explanation of drawings]

Figure 1 shows an anaerobic sludge containing released phosphate.
1 is a schematic flow sheet of an activated sludge process according to one embodiment of the invention, contacting phosphate enriched sludge that has been passed through a stripping zone. FIG. 2 shows that a portion of the supernatant liquid in the phosphate stripping zone is removed from the zone and brought back into the stripping zone for contact with the anaerobic sludge layer containing the released phosphate. 1 is a schematic flow sheet of an activated sludge process according to another embodiment of the present invention, introducing below the anaerobic sludge layer. Explanations of the symbols representing the main parts of these attached figures are as follows. 2: First settling tank, 5: Aeration tank, 6:
2nd sedimentation tank, 9 Ni Stripper-111: Sedimentator, 1
6: Aeration zone, 18: Second sedimentation zone, 22:
Phosphate stripping zone, 29: rapid mix tank, 32: condenser.

Claims (1)

[Claims] 1. A mixed solution containing phosphate-containing influent sewage material and activated sludge is aerated in an aeration zone to remove B of the sewage material.
reducing the OD content and allowing the microorganisms present to take up phosphate, and separating this phosphate-enriched sludge from the mixture in a settling zone to obtain a substantially phosphate-free effluent; passing the phosphate-enriched sludge through a phosphate stripping zone and settling the sludge to form a supernatant liquid and a precipitated sludge above the stripping zone, and subjecting at least a portion of the precipitated sludge to anaerobic conditions. and introducing and contacting the supernatant liquid of the stripping zone with the anaerobic sludge containing the released phosphate, holding the phosphate for a sufficient time to release the phosphate into the liquid phase of the precipitated sludge; Thereby, the soluble phosphate in the anaerobically settled sludge liquid phase is transferred to the supernatant liquid, enriching the overlay liquid in the upper part of the stripping zone with phosphate, and A method of treating activated sludge wastewater comprising recycling at least a portion of the activated sludge from the phosphate stripping zone to the aeration zone. 2 Aerate the mixed liquid containing phosphate-containing influent sewage material and activated sludge in an aeration zone to remove B of the sewage material.
reducing the OD content and allowing the microorganisms present to take up phosphate, and separating this phosphate-enriched sludge from the mixture in a settling zone to obtain a substantially phosphate-free effluent; passing the phosphate-enriched sludge through a phosphate stripping zone and settling the sludge to form a supernatant liquid and a precipitated sludge above the stripping zone, and subjecting at least a portion of the precipitated sludge to anaerobic conditions. and retaining the phosphate for a sufficient period of time to release the phosphate into the liquid phase of the precipitated sludge, and transporting at least a portion of the released phosphate-containing anaerobic sludge to the stripping treatment zone. contacting the phosphate-enriched sludge on its way to the stripping zone, thereby transferring the soluble phosphates in the anaerobic sludge liquid phase into the phosphate-enriched sludge liquid phase above the stripping zone. A method for treating activated sludge wastewater comprising enriching a portion of the supernatant with phosphate and recycling at least a portion of the anaerobic sludge as the activated sludge from the phosphate stripping zone to the aeration zone. .