JP2000005798A - Method for concentrating sludge - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for concentrating sludge capable of concentrating the sludge drawn from a waste mud pond to almost constant sludge concn. throughout the year. SOLUTION: In a method concentrating the sludge, raw water taken from river, etc., is subjected to water purifying treatment, then the sludge generated by being precipitated at a bottom part of the waste mud pond 7 is supplied to a membrane concentrating device 8 using an org. ultrafilter membrane to execute membrane treatment and the sludge is concentrated to 5-10% solid concn. The method is independent of seasonal influence, and high concentration ratio and stable treatment are assured.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for concentrating sludge in a water treatment plant, and more particularly, to a method for concentrating sludge which is applicable to existing water purification equipment and uses an ultrafiltration membrane as a membrane module. It is about.

[0002]

2. Description of the Related Art FIG. 4 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 by the landing well 31, it is led to a chemical mixing pond 32 to which a coagulant is added and mixed, and the floc forming pond 33 causes the suspended components in the raw water to coagulate. 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, is further subjected to chlorination, and is supplied as tap water. The settled sludge pulled out from the bottom of the settling tank 34 is sent to a sludge tank 37, then concentrated by gravity settling in a concentration tank 38, and then supplied to a dehydrator 39. Further, the backwash wastewater discharged by the backwash operation periodically performed in the filtration pond 35 is sent to the drainage pond 40,
It is separated into settled sludge and supernatant water. Settling sludge is drainage pond 3.
7 and the supernatant water is returned to the landing well 31 together with the separated water obtained in the sludge tank 37 and the concentration tank 38.

[0004] Next, a method of condensing sludge in a water purification plant is as follows.
For example, it is disclosed in JP-A-8-257600. This will be described with reference to FIG. First, the raw water was landed on well 41
After receiving the water, the flocculant is added to and mixed into a chemical mixing pond 42, and the floc forming pond 43 is used to coagulate the suspended components in the raw water. And separated into solid and liquid into settled sludge and supernatant water. The supernatant water is sent to a sand filtration pond 45, and the filtered water is subjected to chlorine sterilization to obtain clean water.

The purified sludge and concentrated sludge from the chemical sedimentation basin 44 and the drainage basin 49 are sent to a membrane module 46 using a ceramic inorganic membrane. Utilized as water or the like, the membrane-concentrated sludge is sent to a thickener 47 to be concentrated, and the concentrated sludge is supplied to a dehydrator 48 for dehydration. This sludge concentration method is
This is a method in which purified water sludge is pressed into an internal pressure type membrane module to perform membrane filtration, and the membrane concentrated sludge concentrated by the membrane module 46 is intermittently supplied to the thickener 47 by physical washing and concentrated to a concentration at which dewatering is possible.

[0006]

The sludge concentration method in the water treatment plant shown in FIG. 4 has a disadvantage that the concentrated sludge concentration obtained in the concentration tank 38 is susceptible to seasonal fluctuations. Even so, it is at most 4% and drops to about 2% in winter. As described above, according to the conventional concentration method using the concentration tank 38, the dehydrator 3
The volume and the solids concentration of the concentrated sludge mixture supplied to 9 significantly fluctuate. Therefore, conventionally, the processing capacity of the dehydrator 39 needs to be adjusted to the winter season when the concentration of the concentrated sludge is the lowest, and the processing capacity of the dehydrator 39 is set to be capable of processing a large-capacity, low-concentration concentrated sludge mixed liquid. It is not economical to increase the size of the equipment.

In the method for concentrating sludge in a water purification plant shown in FIG. 5, purified water sludge is injected into an internal pressure type membrane module 46 to perform membrane filtration, and the membrane concentrated sludge concentrated by the membrane module 46 is physically washed. Intermittently thickener 47
And concentrated to a dewaterable concentration. In this method of concentrating sludge, since a ceramic inorganic membrane is used as the membrane module 46, the membrane may be damaged when the membrane module is replaced. In addition, since the physical cleaning interval is set to 2 hours or more in the dead-end type filtration operation, 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 for concentrating sludge, the membrane-concentrated sludge is supplied to the thickener 47, gravity-concentrated and solid-liquid separated, and then the final sludge is taken out. There is a problem that it is difficult.

The present invention has been completed as a result of intensive studies in order to overcome the above-mentioned problems, and concentrates sludge drawn from a sludge pond 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.

[0009]

According to the present invention, in order to solve the above-mentioned problems, according to the first aspect of the present invention, raw water taken from a river or the like is subjected to water purification treatment and then settles at the bottom of a mud pond. The sludge is supplied to a membrane concentrator using an organic ultrafiltration membrane to perform a membrane treatment to reduce the solid concentration of the sludge to 5 to 10%.
This is a method for concentrating sludge, characterized in that the sludge is concentrated.
In this configuration, the method for concentrating sludge in the water purification treatment is a method for concentrating sludge using a membrane concentrating device using a membrane module, and a high concentration rate and stable treatment can be performed without being affected by seasonal effects.

According to a second aspect of the present invention, in the method for concentrating sludge according to the first aspect, the organic ultrafiltration membrane used in the membrane concentrator has a molecular weight cutoff of 5,000 to 500,000.
It is a sludge concentration method characterized by the following. In this configuration, the use of an ultrafiltration membrane with a smaller pore size than the microfiltration membrane prevents the infiltration of sludge into the pores,
It is possible to suppress clogging of the membrane, and it is expected that the membrane filtered water also has a secondary effect of obtaining water of very high quality as compared with the case of the microfiltration membrane. When an ultrafiltration membrane having a molecular weight cut-off of 5,000 or less is used, there is a drawback that the operating pressure increases and the processing cost increases. Further, when an ultrafiltration membrane having a molecular weight cut-off of 500,000 or more is used, sludge infiltrates into the pores of the membrane, which causes clogging of the membrane and increases membrane permeation performance after chemical washing. Also has the disadvantage of being reduced. From the above, it is preferable to adopt a molecular weight cut-off of the organic ultrafiltration membrane of 5,000 to 500,000.

[0011] The invention of claim 3 is a method for concentrating sludge according to claim 1, wherein the membrane treatment by the membrane concentrating layer is performed by an internal pressure type cross flow system. . In the membrane concentrator, as a filtration method,
External pressure type or internal pressure type dead end filtration (total filtration)
In this case, the concentrated sludge adhering to the membrane surface causes clogging in a relatively short period of time, and requires frequent chemical cleaning with an acid or alkali, which is not economical. Therefore, in this configuration, the cross-flow system is used in which the concentrated sludge attached to the membrane surface is separated and circulated, whereby clogging of the membrane is suppressed and the frequency of chemical cleaning is reduced. At that time, if water is passed using an external pressure type or internal pressure type membrane module,
When the power of the circulating pump is the same, the internal pressure type can set the membrane flow velocity higher than the external pressure type, so that sludge accumulation on the membrane surface is reduced and clogging of the membrane is suppressed. Can be. From the above, it is preferable to employ an internal pressure type cross flow method as the filtration method of the membrane concentrator.

[0012]

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 backwashing operation that is periodically performed in a chlorine disinfection device 6 that injects liquid chlorine or sodium hypochlorite and sterilizes, a sludge pond 7 that receives sediment sludge drawn out from the bottom of the sedimentation pond 4, and a filtration pond 5. It comprises a drain pond 10 for receiving the backwash wastewater discharged by the above, a membrane concentrator 8 for condensing sludge, and a dehydrator 9 for dewatering membrane condensed sludge.

As shown in FIG. 2, the membrane concentrator 8 comprises a circulation tank 11, a stirrer 12, a circulation pump 13, and a membrane module 14, a backwash means 22 and a membrane filtration water tank 23 for storing membrane filtration water. It has. Numerals 15 to 21 are pipes, and V is a balf.

Next, regarding water purification treatment of rivers, etc., FIG.
This will be described with reference to FIG. After the raw water is received by the landing well 1, a flocculant is added and guided to the chemical mixing pond 2 for mixing, and the suspended components in the raw water are flocculated in the floc forming pond 3. 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 further passes through the chlorination device 6.
And supplied to customers as tap water.

The settled sludge extracted from the bottom of the settling tank 4 is sent to a sludge tank 7, and the sludge separated in the sludge tank 7 is sent to a membrane thickening device 8 to be concentrated. The membrane filtered water obtained from the membrane concentrator 8 is returned to the landing well 1. The membrane-concentrated sludge that is intermittently or continuously withdrawn from the membrane concentrator 8 is sent to a dehydrator 9 and dewatered. In addition, filtration pond 5
The backwashing is periodically performed, and the backwash wastewater discharged by the backwashing operation is sent to the drainage pond 10, where it is separated into sludge and supernatant water. The sludge from the drain pond 10 is sent to the sludge pond 7, and the supernatant water is combined with the supernatant water from the sludge pond 7 and the membrane concentrator 8.
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 pond 10 are sent to the sludge basin 7, and the sludge separated in the sludge basin 7 is sent to the membrane concentrating device 8 using the membrane module to be concentrated. And
This concentrated sludge is sent to the dehydrator 9 to be dehydrated.

Next, the membrane concentrator 8 will be described in detail with reference to FIG. Sludge from waste sludge 7
5, it is supplied to a circulation tank 11 equipped with a stirrer 12 of the membrane concentrator 8. The settled sludge in the circulation tank 11 is passed through a pipe 16 by a circulation pump 13 to a membrane module 14.
After being sent to the membrane treatment, the circulated sludge is returned to the circulation tank 11 through the pipe 17. On the other hand, membrane filtered water is
After being sent to the membrane filtered water tank 23 through 8, the water is returned to the landing well 1 via a pipe. In addition, the membrane module 14
Is periodically back-washed by a back-washing operation, and back-washing water is passed through the pipe 19 by the back-washing means 22.
4 and is washed, and the membrane backwash wastewater is supplied to the pipe 2
0 is returned to the circulation tank 11. Circulation tank 1
In 1, the concentrated sludge is withdrawn through the pipe 21 intermittently or continuously by operating the valve V,
It is sent to the dehydrator 9.

The membrane module 14 has a molecular weight cutoff of 5,
000 to 500,000 organic ultrafiltration membranes are used, and the backwash means 22 of the membrane module is backwashing water using raw water or membrane filtered water, backpressure washing using pressurized gas or Perform them in combination.
On the other hand, the filtration method in the membrane concentrator 8 is a cross-flow system in which the concentrated sludge adhering to the membrane surface is separated and circulated, thereby suppressing clogging of the membrane module and reducing the frequency of chemical cleaning. . 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 the most preferable as the filtration method in the membrane concentrator 8.

[0018]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, an embodiment of a method for concentrating sludge according to the present invention will be shown, and will be described in comparison with existing equipment. In addition,
The present invention is not limited to the following examples.

(Example) In this example, river water was used as raw water, and the raw water was treated according to the flow of the coagulation sedimentation / filtration treatment shown in FIG. The sediment sludge in the sedimentation basin 4
And the backwash wastewater from the filtration pond 5 was sent to the drainage pond 10, and the sludge separated in the drainage pond 10 was sent to the sludge pond 7. The sludge separated in the sludge pond 7 was supplied to the membrane concentrator 8 and concentrated by an internal pressure cross-flow method as a filtration method. The concentration of sludge supplied to the membrane concentrator 8 is 1.1%
The membrane concentrator 8 used had the specifications shown in Table 1.

In this embodiment, as the membrane module 14,
The ultrafiltration membrane shown in Table 1 was used, and as a comparative example,
The microfiltration membrane shown in Table 2 is used for the membrane module 14. FIG. 3 shows a comparison result between the present embodiment and a comparative example.
The average filtration pressure of the membrane concentrator 8 is shown as a daily change,
The horizontal axis in the figure is the number of days of water passage, and the vertical axis shows the average filtration pressure. In addition, this average filtration pressure refers to the membrane concentrator 8
Shows the pressure obtained by subtracting the membrane outlet pressure from the average value of the membrane inlet pressure and the circulation pressure.

[0021]

[Table 1]

As is apparent from FIG. 3, in the present embodiment, the increase in the average filtration pressure is slower when the ultrafiltration membrane is used as the membrane module 14 than when the microfiltration membrane is used. This indicates that the interval until chemical cleaning becomes longer. Of course, even when a microfiltration membrane is used for the membrane module of the comparative example, it goes without saying that the method for concentrating sludge is superior to the method for concentrating sludge by the gravity type concentrator shown in FIG.

[0023]

[Table 2]

Next, as a comparative example of the present embodiment and existing equipment (a method of concentrating sludge by a gravity type concentrator in FIG. 4), Table 3 shows the final sludge concentration and concentration ratio, and each concentration. The dewatering performance obtained by performing a dewatering test on the sludge was shown.
As is clear from Table 3, this example shows that the present example is superior to the existing equipment in sludge concentration. 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.

[0025]

[Table 3]

[0026]

As described above, according to the method for concentrating sludge of the present invention, sludge having a substantially constant solid matter concentration (5 to 10%), which is not significantly affected by seasonal fluctuation, is always supplied to the dehydrator. Since it can be driven and the dewatering time in the dewatering machine can be greatly shortened, it is possible to reduce the size of the dewatering machine in comparison with the capacity of the dewatering machine in the case of the conventional method of concentrating sludge by a gravity type concentrator. Has an effect.

Further, by using an ultrafiltration membrane having a molecular weight cut-off of 5,000 to 500,000 by using an internal pressure type cross flow system as the membrane concentrator, a rapid increase in the average filtration pressure can be eliminated. Therefore, continuous water flow to the membrane concentrator is possible, and clogging due to sludge does not occur in a relatively short period of time, and the interval between chemical cleaning operations is increased, thereby reducing costs and labor for chemical cleaning operations. It has effects such as being able to.

[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 an example of a membrane concentrator according to the present invention.

FIG. 3 is a diagram showing operation results of an example.

FIG. 4 is a system diagram for explaining a conventional water purification treatment and sludge concentration method.

FIG. 5 is a system diagram for explaining a conventional water purification treatment and a sludge concentration method.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Landing well 2 Chemical mixing pond 3 Floc forming pond 4 Sedimentation pond 5 Filtration pond 6 Chlorine disinfection device 7 Drainage pond 8 Membrane concentrator 9 Dehydrator 10 Drainage pond 11 Circulation tank 12 Stirrer 13 Circulation pump 14 Membrane module 22 Backwash Means 23 Membrane filtration water tank

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 4D006 GA06 GA07 HA04 HA18 JA53A JA56A JA57A JA63A KA12 KA16 KC03 KC12 KC13 KC14 KC16 KD11 KD17 MA01 MA33 MB02 MB05 MC29 MC39 PB04 PB22 PB23 PC51 4D059 AA31 BE38BE BEBEBE25BE30CB EB01

Claims (3)

[Claims] Claims: 1. After purifying raw water taken from a river or the like, sludge generated by settling at the bottom of a sludge pond is supplied to a membrane concentrator using an organic ultrafiltration membrane to perform membrane treatment. And concentrating the solid content of the sludge to 5 to 10%. 2. The method for concentrating sludge according to claim 1, wherein the molecular weight cut off of the organic ultrafiltration membrane used in the membrane concentrator is 5,000 to 500,000. Concentration method. 3. The method for concentrating sludge according to claim 1, wherein the membrane treatment by the membrane concentrating device is performed by an internal pressure type cross flow system.