JPH1119694A - Sludge concentration method - Google Patents

Abstract

(57) [Summary] [PROBLEMS] To provide a sludge concentration method capable of always concentrating sediment sludge drawn out from a sedimentation tank to a substantially constant sludge concentration throughout the year. SOLUTION: This is a method for concentrating sludge in the coagulation sedimentation / filtration treatment of raw water taken from a river or the like, and sends the settled sludge generated by settling at the bottom of a sedimentation basin 4 to a sludge basin 6,
Is supplied to a membrane concentrating device 7 using a membrane module to perform a membrane treatment, to condense the solid content of the sludge to 5 to 10%, and send the sludge to a dehydrator 8 for treatment. A stable treatment with a high concentration rate can be performed without being affected by the season.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for condensing settled sludge extracted from a sedimentation basin in a water treatment plant.

[0002]

2. Description of the Related Art FIG. 6 shows a processing flow in an existing water purification plant which performs a conventional coagulation sedimentation / filtration treatment. The processing flow will be described with reference to FIG. First, after the raw water is received at the landing well 31, the raw water is guided to a chemical mixing pond 32 to which a coagulant is added and mixed, and the suspended components in the raw water are coagulated in the floc forming pond 33. The water to be subjected to the coagulation treatment is supplied to the sedimentation basin 34, where it is separated into settled sludge and supernatant water.

[0003] The supernatant water obtained in the sedimentation basin 34 passes through a filtration basin 35 and is further subjected to chlorination to be supplied as tap water. The settled sludge drawn out from the bottom of the settling tank 34 is sent to a sludge tank 36, where it is concentrated by gravity sedimentation in a concentration tank 37 and then supplied to a dehydrator 38.
Further, the backwash drainage discharged by the backwash operation periodically performed in the filtration pond 35 is sent to the drainage pond 39 and separated into settled sludge and supernatant water. The settled sludge is supplied to the sludge pond 36, and the supernatant water is returned to the landing well 31 together with the separated water obtained in the sludge pond 36 and the concentration tank 37.

[0004]

As described above, the conventional method for concentrating sludge in a water treatment plant has a disadvantage that the concentration of concentrated sludge obtained in the concentration tank 37 is susceptible to seasonal fluctuations. Is at most 4% and drops to about 2% in winter. For this reason, the volume and solids concentration of the concentrated sludge mixture supplied to the dehydrator 38 fluctuate significantly depending on the season. For this reason, the processing capacity of the dehydrator 38 needs to be adjusted to the winter season when the concentration of the concentrated sludge is the lowest.
It is necessary to be able to treat a low-concentration mixed sludge mixture, which is not economical due to the large size of the equipment.

Regarding the method of concentrating the settled sludge, for example,
It is disclosed in JP-A-8-257600. This method of concentrating the settled sludge can be dewatered by injecting purified water sludge into an internal pressure type membrane module, performing membrane filtration, and supplying the membrane concentrated sludge concentrated by the membrane module to a thickener intermittently by physical washing. This is a method of concentrating to a concentration.

In this method for concentrating the settled sludge, since a ceramic inorganic membrane is used as the membrane module, the membrane may be damaged when the membrane module is replaced. In addition, since the physical washing interval is set to 2 hours or more in the dead-end filtration operation, there is a disadvantage that the settled sludge adheres to the membrane surface and causes clogging in a relatively short time. It is necessary to perform chemical cleaning with acid or alkali. Therefore, there is a problem that the cost and labor for the chemical cleaning operation are increased, leading to an increase in cost. Furthermore, ceramic membranes are expensive and have the drawback of increasing maintenance costs. In this method of concentrating settled sludge, the membrane sludge is supplied to a thickener, gravity-concentrated and solid-liquid separated, and then the final sludge is taken out. Is difficult.

The present invention has been completed as a result of intensive studies in order to overcome the above-mentioned problems, and the present invention concentrates settled sludge drawn from a sedimentation tank to a substantially constant sludge concentration throughout the year. It is an object of the present invention to provide a method for concentrating sludge that can be performed.

[0008]

Means for Solving the Problems The present invention has been made to solve the above-mentioned problems. According to the invention of claim 1, in the method for condensing sludge in the coagulation sedimentation / filtration treatment of raw water taken from a river or the like, A method for concentrating sludge, comprising supplying sedimented sludge generated by sedimentation at the bottom of a sedimentation basin to a membrane concentrating device using a membrane module to perform membrane treatment, thereby concentrating the solid content of the sludge to 5 to 10%. It is. In this configuration, a sludge concentration method using a membrane concentration device with a membrane module corresponds to the sludge concentration method in the water purification treatment,
Without being affected by the season, the concentration rate is high and stable processing can be performed.

Further, the invention of claim 2 is the sludge concentration method according to claim 1, wherein two or more kinds of organic membranes having different membrane filling rates are used as membrane modules used in the membrane concentrator. This is a characteristic method of sludge concentration. According to a third aspect of the present invention, in the method for concentrating sludge according to the first aspect, two or more types of organic membranes having different membrane inner diameters are used as membrane modules used in the membrane concentrator. It is a method of concentration. In these configurations, the optimum average filtration pressure is obtained by changing the membrane filling rate of the enrichment rate membrane module according to the sludge concentration. In addition, when the concentration of sludge supplied to the membrane concentrator is high, a single-stage system may be used using one type of organic membrane, but when the concentration of sludge is low, the power cost of the circulation pump can be reduced as much as possible. In order to reduce the amount, the use is made of two or more types of organic membranes having different membrane packing ratios and inner diameters of the membranes, so that the sludge has a multistage configuration in which the solid concentration is increased stepwise.

[0010] In a fourth aspect of the present invention, in the sludge concentrating method according to the first, second or third aspect, the membrane treatment by the membrane concentrating apparatus is performed by an internal pressure type cross flow system. This is a concentration method. In the membrane concentrator, dead-end filtration of external pressure type or internal pressure type is used as a filtration method.
In the case of the (total filtration) method, clogging occurs in a relatively short time due to the concentrated sludge adhering to the membrane surface, and frequent chemical cleaning with an acid or alkali is required, which is not economical. Therefore, in this configuration, the cross-flow method of separating and circulating the concentrated sludge attached to the membrane surface,
Film clogging is suppressed and the frequency of chemical cleaning is reduced. At that time, when water is passed using an external pressure type or internal pressure type membrane module, if the power of the circulation pump is the same, the internal pressure type can set the membrane surface flow rate higher than the external pressure type, The accumulation of sludge on the membrane surface is reduced, and clogging of the membrane can be suppressed. From the above, it is preferable to employ the internal pressure type cross flow method as the filtration method of the membrane concentrator.

[0011]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a water purification treatment system diagram for explaining an embodiment of a sludge concentration method according to the present invention. In the figure, a landing well 1 for receiving raw water, a chemical mixing pond 2 for adding and mixing a flocculant to raw water, a floc forming pond 3 for flocculating reaction, a sediment for solid-liquid separation into settled sludge and supernatant water. Pond 4, Filtration pond 5, which completely removes fine flocs not solid-liquid separated in sedimentation pond 4.
A sludge pond 6 for receiving sediment sludge drawn out from the bottom of the sedimentation pond 4, a drainage pond 9 for receiving backwash wastewater discharged by a backwashing operation periodically performed in the filtration pond 5, and a sludge concentration. It comprises a membrane concentrator 7 and a dehydrator 8 for dewatering the membrane concentrated sludge.

FIG. 2 is a diagram showing an example of the membrane concentrator 7 in the present invention. In FIG. 1, the membrane concentrator comprises a circulation tank 10, a stirrer 11, a circulation pump 12, and a membrane module 13, and includes a backwash means 21 and a membrane filtrate tank 22 for storing membrane filtrate. 14 to 20 are pipes, and V is a valve.

First, referring to FIG. 1, water purification treatment of a river or the like will be described. After receiving water at a landing well 1, a flocculant is added to a chemical mixing pond 2 for mixing. Aggregate suspended components in raw water. The water to be subjected to the coagulation treatment is supplied to the sedimentation basin 4 and solid-liquid separated into sedimentation sludge and supernatant water. The supernatant water obtained in the sedimentation basin 4 passes through the filtration basin 5 and is further subjected to chlorination to be supplied as tap water.

The settled sludge withdrawn from the bottom of the settling tank 4 is sent to a sludge tank 6, and the sludge separated in the sludge tank 6 is sent to a membrane thickener 7 for concentration. The membrane filtered water obtained from the membrane concentrator 7 is returned to the landing well 1. Membrane concentrator 7
The more concentrated or continuously withdrawn membrane concentrated sludge is sent to the dehydrator 8 to be dehydrated. In addition, filtration pond 5
The backwash wastewater discharged by the backwash operation periodically performed in the above is sent to a drainage pond 9 and separated into sludge and supernatant water. Sludge from the drainage pond 9 is sent to the drainage pond 6,
From the wastewater pond 6 and the membrane concentrator 7
Is returned to the landing well 1 together with the membrane filtered water. Thus, the settling sludge from the settling basin 4 and the sludge from the drainage basin 9 are sent to the sludge basin 6, and the sludge separated in the sludge basin 6 is concentrated by the membrane concentrating device 7 using the membrane module. The concentrated sludge is sent to the dehydrator 8 to be dehydrated.

The settling sludge will be described in more detail.
1 is supplied to the circulation tank 10 provided. The settled sludge is passed through the piping 15 by the circulation pump 12 and is passed through the membrane module
After being sent to the membrane treatment, the circulating water is returned to the membrane filtered water tank 22 through the pipe 17. On the other hand, the membrane filtered water is sent to the pipe 17 and then returned to the landing well 1 via the pipe. Further, in the backwashing operation which is periodically performed, membrane backwash drainage obtained by washing the inside of the membrane module through the pipe 18 by the backwash means 21 is returned to the circulation tank 10 via the pipe 19. You. In this way, the circulation tank 10
After the sludge concentrated in the above is drawn out intermittently or continuously by the valve V through the pipe 20, the dewatering machine 8
Sent to

The membrane concentrating device 7 employs a membrane module made of an organic membrane such as a microfiltration membrane or an ultrafiltration membrane. The backwashing means for the membrane module may be backwashing using raw water or membrane filtrate. This is performed by back pressure cleaning using a pressurized gas or a combination thereof.

On the other hand, the filtration method in the membrane concentrator 7 is as follows.
By using a cross-flow method in which concentrated sludge adhering to the membrane surface is separated and circulated, clogging of the membrane module can be suppressed, and the frequency of chemical cleaning can be reduced. At that time, when water is passed using an external pressure type or internal pressure type membrane module, if the power of the circulation pump is the same, the internal pressure type can set the membrane surface flow rate higher than the external pressure type, Sludge accumulation on the membrane surface is reduced, and clogging of the membrane is suppressed. From the above, the internal pressure type cross-flow method is most preferable as the filtration method in the membrane concentrator 7. Of course, the filtration method in the membrane concentrator 7 is not limited to the internal pressure type cross flow method.

Further, the processing system of the membrane concentrator 7
When the concentration of sludge supplied to the membrane concentrator 7 is as high as 2% or more, a single-stage system may be used using one type of organic membrane. However, when the concentration of sludge is as low as 2% or less, circulation is performed. In order to reduce the power cost of the pump as much as possible, a multistage system in which the solid concentration of sludge is increased stepwise by using two or more types of organic membranes having different membrane filling rates and membrane inner diameters may be used. The membrane filling rate of the membrane concentrator 7 is 20 to
70%, and the membrane inner diameter of the hollow fiber of the membrane module is 1
A membrane module that is 〜4 mm may be used.

[0019]

[Embodiment] Hereinafter, an embodiment of a method for concentrating sludge according to the present invention will be described, and the present embodiment will be described in comparison with existing equipment. The present invention is not limited by the following examples. (Example 1) In this example, a river was used as raw water, and the raw water was treated and purified according to the flow of coagulation sedimentation / filtration shown in FIG. The sediment sludge from the sedimentation basin 4 is sent to the sludge basin 6, the backwash drainage from the filtration basin 5 is sent to the drainage basin 9,
The sludge separated in the drainage pond 9 is sent to the drainage pond 6. The sludge separated in the sludge pond 6 was supplied to a membrane concentrating device 7 using an internal pressure tube type membrane module, and concentrated by an internal pressure type cross flow system as a filtration system. The sludge concentration supplied to the membrane concentrator 7 was 2.0%, and the membrane concentrator 7 was an internal pressure tube type membrane module having the specifications shown in Table 1. Table 2 shows the processing results of the present embodiment and the existing equipment. In addition, PVDF in Table 1 indicates polyvinylidene fluoride which is a fluororesin.

[0020]

[Table 1]

FIG. 3 shows the change over time in the average filtration pressure due to clogging of the membrane module in the membrane concentrator 7, where the horizontal axis represents the number of days of water passage and the vertical axis represents the average filtration pressure. . The average filtration pressure indicates a pressure obtained by subtracting the membrane outlet pressure from the average value of the membrane inlet pressure and the circulating water pressure of the membrane concentrator 7.

In Table 2, the final sludge concentration and concentration ratio of each of the present embodiment and the existing equipment, and the dewatering performance of the test results obtained by the dehydrator are shown. As is clear from Table 2, this example shows that the present example is superior to the existing equipment in the concentration of sludge. For example, even if the dewatering time was 1/3 or less of the existing equipment, the water content of the dewatered cake was almost the same.

[0023]

[Table 2]

Example 2 In this example, as in Example 1, raw water was treated and purified according to the flow of coagulation sedimentation / filtration shown in FIG. The sludge separated in the sludge pond 6 was supplied to a membrane concentrating device 7 using an inner tube membrane module and concentrated. The sludge concentration supplied to the membrane concentrator 7 is 0.9
%, And the membrane concentrator 7 was an internal pressure tube type membrane module, and the one having the specifications shown in Table 3 was used.

[0025]

[Table 3]

Incidentally, PVDF in Table 3 is an abbreviation for polyvinylidene fluoride which is a fluororesin. Table 4 shows the results of the treatment according to the present embodiment and the existing equipment. FIG. 4 shows the daily change of the average filtration pressure in the membrane concentrator 7. Table 5 shows the final sludge concentration and concentration ratio of the membrane concentrated sludge obtained by the sludge concentration method of the present example and the concentrated sludge obtained by the existing equipment, and a dewatering test of each concentrated sludge. The obtained dehydration performance was shown.

[0027]

[Table 4]

(Embodiment 3) In this embodiment, a river is used as raw water and treated according to the flow of coagulation sedimentation / filtration treatment shown in FIG. The mixture was supplied to the concentrating device 7 and concentrated, and dewatered by the dehydrator 8. The sludge concentration supplied to the membrane concentrator 7 was 1.3%. The membrane concentrator 7 was an internal pressure tube type membrane module, and a membrane module having the specifications shown in Table 5 was used. Table 6 shows the processing results of the present embodiment and the existing equipment. PVDF in Table 5 is an abbreviation for polyvinylidene fluoride which is a fluororesin.

[0029]

[Table 5]

FIG. 5 shows the change over time of the average filtration pressure in the membrane concentrator 7. Table 6 shows the final sludge concentration and concentration ratio of the membrane concentrated sludge obtained by the sludge concentration method of the present embodiment and the concentrated sludge obtained by the existing equipment, and the concentration of each of the present embodiment and the existing equipment. It shows the dewatering performance obtained by performing a dewatering test on sludge.

[0031]

[Table 6]

From the above, the following has become clear. First, in this example, as is clear from FIGS. 3 to 5, it was shown that the average filtration pressure in the membrane concentrator did not increase and water could be stably passed. Further, as is clear from Tables 2, 4 and 6, the sludge concentration ratio obtained by the sludge concentration method of the present invention increases to 2.4 to 3.6 times that of the existing equipment, and dewatering is performed. The dewatering time by the machine is reduced to 27 to 30% of that of the existing equipment, indicating that concentrated sludge excellent in dewatering properties can be obtained. In addition, it is clear that the dependence on the season of sludge concentration can be almost neglected in the membrane concentrator using the membrane module.

[0033]

As described above, according to the method for concentrating sludge of the present invention, sludge having a solid concentration (5 to 10%) which is substantially unaffected by seasonal fluctuations and is almost always constant. And the time required for the dehydrator in the dehydrator can be greatly reduced, so that the capacity of the dehydrator in the case of the conventional gravity type concentrator method can be reduced.

Further, since the membrane concentrator is subjected to membrane treatment by the internal pressure type cross flow system, continuous water flow is possible without a sharp rise in the average filtration pressure, and sedimentation sludge is clogged in the concentrator in a relatively short time. As a result, the interval between chemical cleaning operations is increased, and the cost and labor required for the chemical cleaning operation can be reduced.

Further, in order to perform membrane treatment of the settled sludge by the membrane concentrator, the quality and quantity of the concentrated sludge injected into the dehydrator are almost constant, so that the capacity of the dehydrator is low and large in winter. This has the effect that it can be made smaller than the capacity of the dewatering machine after the conventional sludge concentration treatment, which had to accept the capacity of concentrated sludge.

[Brief description of the drawings]

FIG. 1 is a system diagram for explaining an embodiment of the present invention.

FIG. 2 is a system diagram for explaining a membrane concentrator according to the present invention.

FIG. 3 is a diagram showing operation results of Example 1.

FIG. 4 is a diagram showing operation results of Example 2.

FIG. 5 is a diagram showing an operation result of Example 3.

FIG. 6 is a system diagram showing a conventional water purification treatment and sludge concentration method.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Landing well 2 Chemical mixing pond 3 Floc formation pond 4 Sedimentation pond 5 Filtration pond 6 Drainage pond 7 Membrane concentrator 8 Dehydrator 9 Drainage pond 10 Circulation tank 11 Stirrer 12 Circulation pump 13 Membrane module 14-20 Pipe 21 Backwash Means 22 Membrane filtered water tank

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁶ Identification code FI B01D 71/34 B01D 71/34 C02F 1/44 C02F 1/44 H 1/52 1/52 Z

Claims (4)

[Claims] 1. A method for concentrating sludge in coagulation sedimentation / filtration treatment of raw water taken from a river or the like, wherein the sedimentation sludge generated by sedimentation at the bottom of a sedimentation basin is supplied to a membrane concentrator using a membrane module to perform membrane treatment. A method for concentrating sludge, wherein the sludge concentration is increased to 5 to 10%. 2. The method for concentrating sludge according to claim 1, wherein two or more types of organic membranes having different membrane filling rates are used as membrane modules used in said membrane concentrating apparatus. . 3. The method for concentrating sludge according to claim 1, wherein two or more types of organic membranes having different membrane inner diameters are used as a membrane module used in the membrane concentrating device. 4. The method for concentrating sludge according to claim 1, 2 or 3, wherein the membrane treatment by the membrane concentrating device is performed by an internal pressure type cross flow system.