JP2002018488A - Method and apparatus for treating wastewater - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method and apparatus for treating wastewater whereby the quality of membrane-separated sludge is improved; the concentration dependence of filtration pressure in membrane separation is reduced and so is the formation of a cake layer on a membrane surface; and thus, the membrane separation performance can be enhanced. SOLUTION: This method for treating wastewater comprises a biological treatment step wherein wastewater is biologically treated in a biological treatment apparatus; a flocculation treatment step wherein an inorganic flocculant is added while an active sludge is kept remaining in a treated liquid obtained in the biological treatment step without subjecting the treated liquid to solid- liquid separation and the pH of the treated liquid is adjusted to 4.5-6.5; a membrane separation step wherein the treated liquid obtained by the flocculation treatment in the flocculation treatment step and containing the active sludge and a flocculated sludge is subjected to membrane separation; and a return step wherein at least a part of the sludge separated in the membrane separation step is returned to the biological treatment apparatus.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method and an apparatus for treating sewage for treating sewage such as human waste and septic tank sludge generated from a septic tank.

[0002]

2. Description of the Related Art As a method for treating sewage such as human waste or septic tank sludge generated from a septic tank, for example, Japanese Patent Publication No. 6-67.
Japanese Unexamined Patent Publication No. 520 and No. 9-314193 are known.

In the treatment method disclosed in Japanese Patent Publication No. 6-67520, a coagulant is added to human wastewater in advance and coagulated and dewatered in a coagulation tank and a dehydrator, and the obtained separated liquid is subjected to biological treatment in a biological treatment tank. Then, the treatment liquid is subjected to membrane separation by an ultrafiltration membrane, and the water permeated through the membrane is discharged out of the system.

In the treatment method disclosed in Japanese Patent Application Laid-Open No. 9-314193, a coagulant is added to a septic tank sludge in advance, coagulated and dewatered in a first coagulation tank and a dehydrator, and urine is mixed with the obtained separated liquid. After the biological treatment in the biological treatment tank, the treated liquid is subjected to solid-liquid separation in the sedimentation tank, and then the inorganic flocculant is added to the supernatant separated liquid in the second flocculation tank, and the flocculated sludge is subjected to membrane filtration using an ultrafiltration membrane. Separated and the permeated water is discharged out of the system.

[0005]

[Problems to be solved by the invention]
In the treatment method disclosed in No. 7520, since activated sludge subjected to biological treatment is subjected to membrane separation by an ultrafiltration membrane, the filtration pressure is dependent on the activated sludge concentration in the membrane separation equipment,
There is also a problem that the filtration pressure rises rapidly with the increase of the permeation flux. Therefore, at the time of treatment, it is necessary to maintain an appropriate activated sludge concentration and to select an appropriate permeation flux so that the filtration pressure does not rise sharply, and this involves various restrictions in membrane separation.

In the treatment method disclosed in Japanese Patent Application Laid-Open No. 9-314193, the coagulated sludge generated by adding an inorganic coagulant is subjected to membrane separation by an ultrafiltration membrane. However, it became easy to form a cake layer on the film surface, and frequent film cleaning was required.

Therefore, the present invention improves the properties of sludge to be subjected to membrane separation, and alleviates the concentration dependency of filtration pressure during membrane separation and the formation of a cake layer on the membrane surface, thereby improving membrane separation performance. It is an object of the present invention to provide a method and an apparatus for treating sewage that can be performed.

[0008]

A wastewater treatment method according to the present invention comprises a biological treatment step of biologically treating wastewater in a biological treatment facility, and a treatment liquid without solid-liquid separation of the treatment liquid obtained in the biological treatment step. Add the inorganic flocculant while leaving activated sludge in the solution, and
A coagulation treatment step of adjusting coagulation to 4.5 to 6.5, and a membrane separation step of membrane-separating a treatment liquid in which activated sludge and coagulation sludge obtained by coagulation treatment in the coagulation treatment step are mixed. And returning the sludge separated in the membrane separation step to the biological treatment facility.

The wastewater treatment apparatus of the present invention further comprises a biological treatment means for biologically treating wastewater, an inorganic coagulant added to the treatment liquid from the biological treatment means, and a pH of the treatment liquid of 4.
A coagulation treatment means for performing coagulation treatment by adjusting to 5 to 6.5; a flow path for sending the treatment liquid from the biological treatment means to the coagulation treatment means with activated sludge remaining in the treatment liquid; A membrane separation means for membrane-separating the treatment liquid in which the activated sludge and the coagulated sludge are mixed from the means, and a flow path for sending the treatment liquid in which the activated sludge and the coagulated sludge are mixed from the coagulation treatment means to the membrane separation means. And return means for returning at least a part of the sludge separated by the membrane separation means to the biological treatment means.

[0010] According to the method and the apparatus, the contaminated sewage is biologically treated in the biological treatment step by the biological treatment means. The biologically treated treatment liquid is sent from the biological treatment means to the coagulation treatment means through the flow path, with the activated sludge remaining in the treatment liquid without solid-liquid separation.
Then, in the coagulation treatment step by the coagulation treatment means, an inorganic coagulant is added to the treatment liquid in which the activated sludge remains, and the pH is adjusted to an acidic state of 4.5 to 6.5. For example, a phosphorus compound, a hardly decomposable organic substance, or the like that is difficult to be subjected to aggregation treatment. Thereafter, the treatment liquid in which the activated sludge obtained by the coagulation treatment and the coagulated sludge are mixed is sent to the membrane separation means through the flow path, and the membrane is separated in the membrane separation step by the membrane separation means, and the membrane separation liquid is separated. It is discharged out of the system. As described above, since the coagulation treatment is performed without separating the biologically treated treatment liquid into solid and liquid, the sludge to be subjected to membrane separation is a so-called coagulation activated sludge in which activated sludge by biological treatment and coagulation sludge by coagulation treatment are mixed. State. Therefore, the coagulation activated sludge does not easily form a cake layer on the membrane surface, but the activated sludge whose filtration pressure depends on the concentration of sludge in the membrane separation equipment and the filtration pressure depends on the concentration of sludge in the membrane separation equipment. Although it does not depend on it, it has an intermediate property with coagulated sludge that a cake layer is easily formed on the membrane surface, and the property of sludge is improved. As a result, the concentration dependency of the filtration pressure is reduced, and the formation of the cake layer on the membrane surface is reduced, and the membrane separation performance can be improved. In addition, there is no need to perform solid-liquid separation of the treatment liquid after the biological treatment, and the treatment can be simplified. Further, at least a part of the sludge separated in the membrane separation step by the membrane separation means is returned to the biological treatment means in the return step by the return means, and is subjected to biological treatment. Thereby, in the biological treatment step by the biological treatment means, the concentration of the activated sludge used for the treatment can be maintained at a high concentration. As a result, biological treatment can be suitably performed, and the size of the biological treatment equipment can be reduced. Further, since the returned sludge has an extra inorganic coagulant that has not been subjected to the coagulation treatment, the inorganic coagulant added in the coagulation treatment can be saved.

In the method for treating wastewater of the present invention, the biological treatment step may include a pH adjusting step of adjusting the pH of the wastewater in the biological treatment facility. In the sewage treatment apparatus of the present invention, the biological treatment means may include a pH adjusting means for adjusting the pH of the sewage. In this way, wastewater is efficiently biologically treated.

In the method and apparatus for treating wastewater of the present invention, the inorganic coagulant may include an iron-based coagulant.

[0013]

Embodiments of the present invention will be described below with reference to the accompanying drawings. Note that the same components are denoted by the same reference numerals, and redundant description will be omitted.

FIG. 1 is a flow sheet schematically showing an apparatus for treating human wastewater (hereinafter referred to as “treatment apparatus”) according to a preferred embodiment of the present invention. Here, the human wastewater refers to human waste and septic tank sludge generated from the septic tank.

As shown in FIG. 1, a treatment apparatus 10 includes a coagulation dehydration equipment (coagulation dehydration means) 1 for coagulating and dewatering human wastewater.
1 is provided. The coagulation dewatering equipment 11 includes a coagulation tank 12
And a dehydrator 13. A line L <b> 0 through which the human wastewater flows in is connected to the coagulation tank 12. The coagulation tank 12 is provided with a polymer coagulant adding device (not shown) for adding a polymer coagulant such as a cationic polymer to the inflowed human wastewater. The coagulant was added to the line L0.
It is also possible to omit the coagulation tank 12 by directly injecting it into the tank.

The coagulation tank 12 is connected via a line L1 to a dehydrator 13 for dehydrating and separating the human wastewater subjected to coagulation in the coagulation tank 12 into dehydrated sludge and a separated liquid. The dehydrator 13 is provided with a dewatered sludge take-out means 14 for discharging the dewatered sludge out of the system.

Further, a biological treatment facility (biological treatment means) 15 for biologically treating the separated liquid separated in the dehydrator 13 via a line L2 (flow path) is connected to the dehydrator 13. The biological treatment equipment 15 includes an aeration unit (not shown) for supplying oxygen such as air and a pH control unit for measuring and controlling the pH in order to efficiently treat the separated liquid introduced from the dehydrator 13 with activated sludge. Is provided.

In the biological treatment equipment 15, the coagulation is performed via the line L3 (flow path) without passing through a solid-liquid separation means such as a sedimentation tank or a membrane for solid-liquid separation of the biologically treated treatment liquid. The mixing equipment (aggregation processing means) 16 is connected.
The flocculation and mixing equipment 16 includes an activated sludge mixture having a high concentration of suspended solids (SS) sent through the line L3 and an inorganic flocculant, for example, an iron-based compound such as ferric chloride and polyiron sulfate. An inorganic coagulant adding device (not shown) for adding a coagulant or an aluminum-based coagulant such as a sulfate band or polyaluminum chloride is provided. In addition, a quantitative feeder (carbonaceous adsorbent addition means) 17 for adding a carbonaceous adsorbent to the activated sludge mixture is connected to the coagulation and mixing equipment 16. As the carbonaceous adsorbent, for example, powdered activated carbon and granular activated carbon are used. Of these, usually 10 to 5 having high fluidity
Powdered activated carbon having a particle size of about 0 μm is preferably used. It is preferable that the fixed-quantity feeder 17 is connected to the coagulation and mixing equipment 16 that facilitates the stirring and mixing of the powdered activated carbon, but may be connected to the biological treatment equipment 15 and a membrane separation equipment 18 described later. In addition, in the middle of the line L3 or a line L4 described later.
(The flow path) may be connected in the middle. Further, the coagulation mixing equipment 16 is provided with a pH control means (not shown) for measuring and controlling the pH in order to secure an optimum pH for coagulation.

Further, the line L4
A membrane separation facility (membrane separation means) 18 is connected via the. In the membrane separation equipment 18, any of a rotating flat membrane, a submerged flat membrane, and a tubular membrane can be used. Further, as the type of the membrane, any of an ultrafiltration membrane, a microfiltration membrane and the like can be used. A return sludge return means (return means) 19 for returning a part of the separated sludge to the biological treatment equipment 15 is connected to the membrane separation equipment 18, and excess sludge is converted into excess sludge as excess sludge. The surplus sludge return means 20 for returning the sludge is connected.

The membrane separation equipment 18 is connected to an activated carbon adsorption equipment (activated carbon treatment means) 21 via a line L5. Further, the activated carbon adsorption equipment 21 is provided with a line L for discharging the treated liquid subjected to the activated carbon treatment as treated water out of the system.
6 are connected.

Next, a method of treating urine-based sewage using the treatment apparatus 10 having the above-described configuration will be described.

First, human wastewater flows into the coagulation tank 12 via the line L0. The human wastewater is raw human wastewater, but the human wastewater which has been removed by a removing means such as a screen may be allowed to flow. Coagulation tank 1
A polymer flocculant, such as a cationic polymer, is added to the human wastewater flowing into the wastewater from a polymer flocculant addition device (not shown), and a suspended solid (SS), an oil component, a heavy metal compound, etc. in the human wastewater is added. Are aggregated (coagulation dehydration step).

Then, it is sent to the dehydrator 13 via the line L1 and separated into dehydrated sludge and a separated liquid (coagulation dehydration step). The dewatered sludge dewatered and separated here is discharged out of the system by the dewatered sludge take-out means 14 and disposed of by incineration or soil reduction. As described above, before performing the biological treatment, the wastewater of the human waste is subjected to the coagulation and dehydration treatment in advance to reduce the concentration of the organic matter and the suspended substance (SS), thereby reducing the load on the biological treatment.

The separated liquid obtained from the dehydrator 13 is
It is sent to the biological treatment facility 15 via the line L2. In the biological treatment facility 15, nitrification denitrification treatment is performed by nitrifying bacteria, nitrifying bacteria, and denitrifying bacteria in the activated sludge and the returned sludge returned from the returned sludge returning means 19 in the subsequent stage, and the biochemical in the human wastewater is performed. Components such as oxygen demand (BOD), chemical oxygen demand (COD), and total nitrogen (TN) are reduced (biological treatment step). At this time, the optimal p
In order to secure H, it is preferable to perform pH adjustment using an alkali by a pH adjusting means (not shown) so that the pH becomes 6.5 or more. In the biological treatment equipment 15, the returned sludge is returned to activate the activated sludge (cell concentration).
Is preferably maintained at a high concentration of about 5 to 20 g / l. Thereby, size reduction of the biological treatment equipment 15 is achieved.

Thereafter, the treatment liquid having a high concentration of suspended solids (SS), which has been retained in the biological treatment equipment 15 for a predetermined time and biologically treated, is transferred to the coagulation and mixing equipment 16 via the line L3 without being subjected to solid-liquid separation. Sent. Here, an inorganic coagulant is added from an inorganic coagulant addition device (not shown), and a phosphorus compound (TP) or a hardly decomposable organic substance caused by COD, which is hardly treated by biological treatment, is subjected to coagulation treatment (coagulation treatment step). . In addition, the concentration of the suspended solids in the treatment liquid in which the activated sludge sent to the coagulation and mixing apparatus through the line L3 remains as obtained in a normal biological treatment (activated sludge treatment) of 5000 mg / l to 20,000 mg / l. It is preferable that the concentration of the suspended substance is determined. This means that the concentration of the suspended substance is 5000mg
If the ratio is less than / l, the ratio of activated sludge in the coagulated activated sludge to be separated by membrane becomes too small, and the activated sludge tends to hardly exhibit the properties of the activated sludge. If the concentration is more than 20,000 mg / l, the ratio of the coagulated sludge in the coagulated activated sludge to be subjected to membrane separation becomes too small, and the coagulated activated sludge tends to hardly exhibit the properties of the coagulated sludge. In addition, in the coagulation mixing equipment 16, in order to secure the optimum pH for coagulation,
The pH is adjusted by a pH adjusting means (not shown) using an alkali or an acid. The optimum pH varies depending on the inorganic coagulant used, but is preferably about pH 4.5 to 6.5.

The processing liquid in the coagulation mixing equipment 16 includes:
Activated carbon powder is added from the fixed-quantity feeder 17, and organic substances such as high-molecular-weight proteins that may hinder membrane filtration in the subsequent membrane separation are adsorbed and removed (carbonaceous adsorbent addition step). Thereby, the membrane separation performance in the subsequent membrane separation can be improved. COD in sludge mixture
Organic substances such as color and chromaticity components can also be adsorbed and removed, so that when activated carbon treatment is performed at a later stage, the treatment is simplified, or equivalent to the case where activated carbon treatment is performed without activated carbon treatment Water quality can be obtained.

Next, the treatment liquid subjected to the coagulation treatment is supplied to the line L
4 and is sent to the membrane separation equipment 18 to be subjected to membrane separation into sludge and a membrane separation liquid (membrane separation step). In this embodiment,
Since the biologically treated liquid is subjected to coagulation without solid-liquid separation, the sludge to be membrane-separated is a state of so-called coagulated activated sludge in which activated sludge by biological treatment and coagulated sludge by coagulation are mixed. Become. Therefore, in the case of flocculation activated sludge, a cake layer is not easily formed on the membrane surface, but activated sludge in which the filtration pressure (differential pressure between membranes) depends on the concentration of sludge in the membrane separation facility, Although it does not depend on the concentration of sludge in the inside, it has an intermediate property with coagulated sludge that a cake layer is easily formed on the membrane surface, and the properties of sludge are improved. As a result, the concentration dependency of the filtration pressure is reduced,
The formation of the cake layer on the membrane surface is eased, and the membrane separation performance can be improved.

Part of the flocculated activated sludge separated by the membrane is:
The sludge is returned to the biological treatment facility 15 via the return sludge return means 19 (return step). Thereby, the concentration of the activated sludge used for the biological treatment can be maintained at a high concentration, and the biological treatment can be suitably performed.
5 can be reduced in size. Further, since the inorganic flocculant that has not been subjected to the coagulation treatment remains in the returned sludge, the inorganic coagulant added in the coagulation treatment can be saved.

The excess sludge is returned to the excess sludge return means 2.
And returned to the coagulation tank 12 through the zero. Thereby, the sludge that has grown too much can be discharged out of the system together with the dewatered sludge by the coagulation and dewatering means 11.

The membrane separation liquid is sent to the activated carbon treatment facility 21 via the line L5. Here, organic substances such as COD and chromaticity components remaining in the membrane separation solution are adsorbed on activated carbon,
It is removed from the membrane separation solution (activated carbon treatment step). As a result, the efficiency of removing organic matter from human wastewater is improved, and a high-level purification treatment is performed.

Then, the treatment liquid subjected to the activated carbon treatment is discharged out of the system via the line L6, and discharged to a river or the like.

Hereinafter, the contents of the present invention will be specifically described with reference to examples.

[0033]

(Embodiment 1) A processing apparatus 10 as shown in FIG.
Then, the night soil and the septic tank sludge having the properties shown in the table of FIG.
The sewage sewage was mixed and treated. Biological treatment equipment 1
5 used a general floating activated sludge treatment facility. As the membrane of the membrane separation equipment 18, a rotating flat membrane having a membrane area of 1.5 m ² was used. As a type of the membrane, a membrane formed of a polysulfone-based polymer and having a molecular weight cut off of 750000 was used. Further, the temperature condition was set between 20 and 30 ° C. In the first embodiment, the powdery activated carbon was not added from the fixed-quantity feeder 17.

First, about 0.5 m ³ / day of human waste, about 0.5 m ³ / day of septic tank sludge and about 0.2 m ³ / day of water are converted into about 0.01 m ^{3 of} excess sludge returned by the excess sludge return means 20. ³ / da
The mixture was introduced into the coagulation tank 12 together with y, and about 1 to 2% of the cationic polymer was added in terms of SS weight. Then, the treatment liquid subjected to the aggregating treatment by stirring and mixing was dehydrated by the dehydrator 13. And about 1.21 m ³ / da of the obtained dehydrated separation liquid
y is flowed into the biological treatment facility 15 together with about 4.8 m ³ / day of returned sludge returned from the returned sludge return means 19,
Activated sludge treatment was performed. Then, about 6.0 m ³ / day of the activated sludge treatment liquid that had been subjected to the activated sludge treatment was sent to the coagulation mixing equipment 16 via the line L3 without solid-liquid separation. Then, FeCl _{3 is} used as an inorganic coagulant in the coagulation mixing equipment 16.
Was added as iron ions at a concentration of about 500 mg / l, and about 6.0 m ³ / day of the coagulated treatment liquid was sent to the membrane separation equipment 18. In the membrane separation equipment 18, the above-mentioned membrane is used to perform membrane separation into the flocculated activated sludge and the membrane separation liquid, and about 1.2 m ³ / day of the obtained membrane separation liquid is passed through the line L5 to the activated carbon treatment equipment 21. Sent to Then, the activated carbon treated liquid subjected to the activated carbon treatment was discharged out of the system as treated water from a line L6. In this case, the concentration of the flocculated activated sludge in the membrane separation equipment 18 is about 1
It was 5 g / l and the transmembrane pressure was about 13 kPa.

Next, in this operating state, the permeation flux (1
The amount (m ³ ) of the membrane separation liquid that can be filtered with the m ²
The pressure was changed between 2.0 m ³ / m ² · day, and the transmembrane pressure (filtration pressure) in that case was measured as needed to examine the relationship between the permeation flux and the transmembrane pressure. Further, the same experiment as above was carried out also when the concentration of the flocculated activated sludge in the membrane separation equipment 18 was maintained at about 12 g / l, and the relationship between the transmembrane pressure (filtration pressure) and the flocculated activated sludge concentration was determined. Examined.

FIG. 3 shows the relationship between the permeation flux of the membrane separation liquid and the transmembrane pressure (filtration pressure) when the flocculation activated sludge concentration in the membrane separation equipment 18 is about 12 g / l and 15 g / l, respectively. Shows the relationship. In the case where Example 1 was performed, the frequency of cleaning of the membrane of the membrane separation equipment 18 was about once every two months.

The state of treatment of human wastewater in each part of the apparatus when the first embodiment is performed is shown in the table of FIG.

(Comparative Example 1) In Example 1, the relationship between the transmembrane pressure and the permeation flux in the case of membrane separation of coagulated activated sludge in which coagulated sludge and activated sludge are mixed was examined.
In order to examine the relationship between the transmembrane pressure and the permeation flux when only activated sludge is subjected to membrane separation, or when only coagulated sludge is subjected to membrane separation, and to compare with the case where the activated sludge is subjected to membrane separation, The following experiment was performed using the same film as in Example 1.

The treatment of human wastewater was performed in the apparatus 30 shown in FIG. In Comparative Example 1, after performing the biological treatment, the treatment liquid containing only the activated sludge is subjected to membrane separation in the first membrane separation equipment 33, and the obtained membrane separation liquid is subjected to coagulation and mixing equipment 35. The coagulation treatment is performed, and the processing liquid containing only the coagulated sludge is subjected to membrane separation again in the second membrane separation equipment 36. Here, the membranes of the two membrane separation facilities 33 and 36 were the same as those in Example 1 for comparison, the membrane area of the first membrane separation facility 33 was 1.5 m ^2, and the second Membrane separation equipment 36
Was 1.5 m ² .

First, human waste (SS = 9700 mg / l) about 0.5 m ³ / day, septic tank sludge (SS = 1500 mg / l)
About 0.5m ³ / day and about 0.2m ³ / day of water
0, the sludge is returned to the receiving storage facility 31 and then returned by the return sludge return means 38 (SS = 1500
0 mg / l) about 4.7 m ³ / day and coagulation dewatering equipment 34
(SS = 21)
(0 mg / l) and flowed into the biological treatment facility 32 via the line L1 together with about 0.6 m ³ / day to carry out biological treatment. Then, a biologically treated treatment solution (SS = 12000 mg /
1) About 6.5 m ³ / day was sent to the first membrane separation facility 33 via the line L2, and the activated sludge and the membrane separation liquid were separated into membranes. Then, about 1.3 m ³ / day of the obtained membrane separation liquid was sent to the coagulation mixing equipment 35 via the line L5. The first
Activated sludge (SS =
About 0.5 m ³ / day of a part of 15000 mg / l) is sent to the coagulation dewatering equipment 34 via the line L4. In this coagulation and dewatering treatment facility 34, together with about 0.1 m ³ / day of coagulated sludge (SS = 10000 mg / l) sent from the second membrane separation equipment 36, the cationic polymer is contained in about 1 to 2% by weight of SS. After being added to a certain extent and subjected to coagulation treatment, the mixture is dehydrated by a dehydrator to be separated into dehydrated sludge and a separated liquid. About 1.3 m ³ / day of the membrane separation liquid sent to the coagulation mixing apparatus 35, about 5 m ² of FeCl ₃ as iron ion as an inorganic coagulant was used.
Approximately 1.3 m ³ /
Day (SS = 1000 mg / l) was sent to the second membrane separation equipment 36 via the line L6. In the second membrane separation facility 36, membrane separation was performed on the coagulated sludge and the membrane separation solution, and the obtained membrane separation solution was sent to the activated carbon treatment facility 37 via the line L8 at about 1.2 m ³ / day. Then, the activated carbon treatment liquid subjected to the activated carbon treatment was discharged out of the system from line L9 as treated water. In this case, the concentration of the activated sludge in the first membrane separation equipment 33 was about 15 g / l, and the transmembrane pressure was about 12 kPa. Further, the concentration of the coagulated sludge in the second membrane separation equipment 36 was about 10 g / l, and the transmembrane pressure was about 8 kPa.

Next, in this operating state, the permeation flux of the membrane of each of the membrane separation equipments 33 and 36 is adjusted to 0.0 to 2.0 m ³ / m ^2.
-It was changed during the day, and the transmembrane pressure (filtration pressure) in that case was measured as needed to examine the relationship between the permeation flux and the transmembrane pressure.

The same experiment as above was carried out when the activated sludge concentration in the first membrane separation equipment 33 was maintained at about 11 g / l, 16 g / l and 21 g / l, and the transmembrane pressure difference was measured. The relationship between (filtration pressure) and the activated sludge concentration was examined. FIG.
In the case where the activated sludge concentration in the first membrane separation device 33 is about 11 g / l, 16 g / l and 21 g / l, respectively, the permeation flux of the membrane separation liquid and the transmembrane pressure (filtration pressure) Shows the relationship.

The concentration of the coagulated sludge in the second membrane separation equipment 36 was 6 g / l, 13 g / l, 19 g / l, and 23 g / l.
The same experiment was performed as described above, and the relationship between the transmembrane pressure (filtration pressure) and the coagulated sludge concentration was examined.
FIG. 5 shows the permeation flux of the membrane separation liquid and the difference between the membranes when the coagulated sludge concentration in the second membrane separation device 36 is about 6 g / l, 13 g / l, 19 g / l, and 23 g / l, respectively. It shows the relationship with the pressure (filtration pressure).

The frequency of cleaning the membrane of the first membrane separation facility 33 in the case of performing the comparative example 1 is about once every March, and the frequency of cleaning the membrane of the second membrane separation facility 36. Was about once a month.

The following can be understood from the above results.

That is, as shown in FIG. 4, when activated sludge is separated using a membrane, the transmembrane pressure difference is 0.8
It can be seen that the temperature rises sharply at 以上 1.4 m ³ / m ² · day or more, that filtration with a higher permeation flux is difficult, and that the transmembrane pressure strongly depends on the activated sludge concentration. Therefore, when pure activated sludge is subjected to membrane separation, it is necessary to maintain an appropriate activated sludge concentration, and to select an appropriate permeate flux so that the transmembrane pressure does not rise sharply. It can be seen that various restrictions are involved. However, in the membrane separation of activated sludge, the frequency of washing the membrane is only about once in March, and it can be seen that continuous operation for a long time is possible.

Further, as shown in FIG. 5, when coagulated sludge is separated using a membrane, it can be seen that the transmembrane pressure does not depend on the coagulated sludge concentration and that filtration can be performed with a small transmembrane pressure. . Therefore, it can be seen that the operation with a higher permeation flux is possible as compared with the case where the activated sludge is subjected to membrane separation, and that there are fewer restrictions on membrane separation. However, in membrane separation of coagulated sludge,
Since it is easy to form a coagulated sludge cake layer with the filtration, it is necessary to wash the membrane about once a month, which indicates that long-term continuous operation is difficult.

On the other hand, when the flocculated activated sludge is subjected to membrane separation as in Example 1, as shown in FIG. 3, the concentration dependency of the transmembrane pressure difference is reduced as compared with FIG. It can be seen that the operation at is possible. In addition, the frequency of membrane cleaning is about once every two months, and the frequency of cleaning is higher than when pure activated sludge is separated by membrane. However, the cleaning frequency is higher than when pure coagulated sludge is separated by membrane. Frequency is low.

As described above, conventionally, activated biological sludge is subjected to membrane separation using a membrane when biological treatment is performed, and aggregated sludge is subjected to membrane separation using a membrane when aggregate treatment is performed. Separation was considered to be common sense in view of treatment efficiency and the like, but in the present invention, this common sense is deliberately broken, and membrane activated coagulated sludge in which activated sludge generated by biological treatment and coagulation treatment and coagulated sludge are mixed is separated. By doing so, the advantageous effects described above could be obtained. That is, the coagulation activated sludge to be subjected to membrane separation has both properties of conventional activated sludge and coagulation sludge, and the properties of the sludge to be subjected to membrane separation are improved, so that the concentration of filtration pressure during membrane separation is improved. It can be seen that the dependence on the degree of dependence is reduced and the formation of a cake layer on the film surface is reduced, thereby improving the membrane separation performance.

Further, it is not necessary to separate the treatment liquid into solid and liquid after the biological treatment, which not only simplifies the treatment but also improves the quality of the treated water as shown in the table of FIG.
It can be seen that advanced purification processing has been performed.

[0051]

According to the present invention, the properties of sludge to be subjected to membrane separation are improved, the concentration dependency of filtration pressure during membrane separation is reduced, and the formation of a cake layer on the membrane surface is reduced. It is possible to provide a wastewater treatment method and apparatus capable of improving the separation performance.

[Brief description of the drawings]

FIG. 1 is a flow sheet showing an apparatus for treating human wastewater according to an embodiment of the present invention.

FIG. 2 is a flow sheet showing an apparatus for treating human wastewater for implementing Comparative Example 1.

FIG. 3 is a graph showing the relationship between the permeation flux and the transmembrane pressure when the flocculated activated sludge is subjected to membrane separation in Example 1.

FIG. 4 is a graph showing the relationship between permeation flux and transmembrane pressure when activated sludge is subjected to membrane separation in Comparative Example 1.

FIG. 5 is a graph showing the relationship between the permeation flux and the transmembrane pressure when the coagulated sludge is subjected to membrane separation in Comparative Example 1.

FIG. 6 is a table showing the treatment status of human wastewater in the case of Example 1.

[Explanation of symbols]

10 treatment apparatus, 11 coagulation dehydration equipment, 12 coagulation tank,
13 ... dehydration tank, 15 ... biological treatment equipment, 16 ... coagulation and mixing equipment, 17 ... quantitative feeder, 18 ... membrane separation equipment, 19 ... return sludge return means, 21 ... activated carbon treatment equipment, L2, L3
L4 ... line.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) C02F 9/00 504 C02F 9/00 504E B01D 21/01 102 B01D 21/01 102 C02F 1/44 C02F 1 / 44 F 1/52 ZAB 1/52 ZABE 3/12 3/12 DFS 11/02 11/02 11/14 11/14 BF term (reference) 4D006 GA06 GA07 HA21 HA41 HA82 KA01 KB13 KB22 MA02 MA03 MC62 PB08 PC63 4D015 BA19 BA23 BB05 CA03 DA04 DA05 DA16 DA17 EA13 EA37 FA26 4D028 AC01 AC04 BC19 BC28 BD17 4D059 AA02 BA01 BE55 BE57 BE70 DA16 DA17 DA23 DA24 DB11

Claims (6)

[Claims] A biological treatment step of biologically treating sewage in a biological treatment facility; and inorganic coagulation while the activated sludge remains in the treatment liquid without solid-liquid separation of the treatment liquid obtained in the biological treatment step. A coagulation treatment step of adding the agent and adjusting the pH of the treatment liquid to 4.5 to 6.5 to perform coagulation treatment; and the activated sludge and coagulation sludge obtained by the coagulation treatment in the coagulation treatment step, A membrane separation step of membrane-separating the mixed treatment liquid, and a return step of returning at least a part of the sludge separated in the membrane separation step to the biological treatment facility,
Wastewater treatment method including: 2. The wastewater treatment method according to claim 1, wherein the biological treatment step includes a pH adjustment step of adjusting a pH of the wastewater in the biological treatment facility. 3. The method for treating sewage according to claim 1, wherein the inorganic coagulant includes an iron-based coagulant. 4. A biological treatment means for biologically treating sewage, and an inorganic coagulant is added to the treatment liquid from the biological treatment means, and the pH of the treatment liquid is adjusted to 4.5 to 6.5 for coagulation. A flocculation treatment means to be treated; a flow path for sending the treatment liquid from the biological treatment means to the coagulation treatment means with activated sludge remaining in the treatment liquid; and an activated sludge from the coagulation treatment means and flocculation. Membrane separation means for membrane-separating a treatment liquid in which sludge is mixed, a flow path for sending a treatment liquid in which activated sludge and coagulated sludge are mixed from the coagulation treatment means to the membrane separation means, and the membrane separation means Return means for returning at least a part of the sludge separated by the above to the biological treatment means. 5. The sewage treatment apparatus according to claim 4, wherein the biological treatment means has a pH adjusting means for adjusting a pH of the sewage. 6. The sewage treatment apparatus according to claim 4, wherein the inorganic coagulant includes an iron-based coagulant.