JPH06114400A - Concentration of sludge - Google Patents

Abstract

PURPOSE:To enhance concn. effect and solid recovery and to exert no effect on sludge properties by sedimenting the sludge generated in the water treatment process of a sedimentatrion basin and concentrating the sedimented sludge by the separation due to a precise filter membrane. CONSTITUTION:Sewage 1 is introduced into a first sedimentation basin 2 and the coarse solid in the sewage is removed. This sewage flows in an aeration tank 3 and the suspended solid matter and soluble org. matter in the sewage are removed. The sewage from which the suspended solid matter and the soluble org. matter are removed in the aeration tank 3 flows in a post-stage final sedimentation basin 4 and the activated sludge in the sewage is recovered in the poststage sedimentation basin 4 and a part thereof is supplied to the aeration tank 3 as return sludge 5 and the remainder thereof is stored in a storage tank 8 as excessive sludge 7 to be conc. by a membrane separation part. The initial sedimented raw sludge 6 generated in the first sedimentation basin 2 is allowed to flow in the final sedimentation basin 4 and mixed with the sludge of the final sedimentation basin as excessive sludge 7. A precise filter membrane 9A is provided to the membrane separation part 9 to concentrate the excessive sludge 7.

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 generated in water treatment such as sewage treatment and various industrial wastewater treatment.

[0002]

2. Description of the Related Art Conventional sewage sludge concentration includes gravity concentration, pressure flotation concentration, centrifugal concentration and the like, and Table 1 shows an outline of these methods.

[0003]

[Table 1]

In these conventional methods, the solid concentration of sludge of 1.5% is 2-2.5% by gravity concentration, 3.5-4% by pressure floating concentration, and 4-4.5 by centrifugal concentration. It is concentrated to about%. In actual use, 80% or more is gravity concentration, followed by centrifugal concentration and pressure floating concentration.
In recent years, the adoption of the latter two has increased.

[0005]

The conventional sludge concentration methods such as gravity concentration, pressure floating concentration and centrifugal concentration have the following basic problems. (1) The solid-liquid separation function and the concentration function are unstable (Each method is susceptible to changes in sludge properties, and gravity concentration, which accounts for the majority, is extremely large.) (2) Solids recovery rate Is low (70-80% by gravity concentration,
80-85% by pressure floatation, 85-90% by centrifugal concentration). (3) The water quality of the concentrated separated liquid is not good. The concentrated separated liquid is returned to the water treatment process, but the quality of the water is not good, so the load on the water treatment process (biological treatment) cannot be ignored, and as a return water load, it is a basic problem of sewage treatment plants. It is listed as one.

[0006] The major cause of the basic problem of such a conventional sludge concentration method is (a) that the solid-liquid separation function is not sufficiently high. (B) Solid-liquid separation and concentration functions are easily affected by changes in sludge properties. Therefore, there is a demand for a sludge concentrating method which has a high solid-liquid separation function and whose solid-liquid separation / concentration functions are not affected by changes in sludge properties.

The present invention is intended to provide a sludge concentration method which can solve the above problems.

[0008]

The method for concentrating sludge according to the present invention is characterized in that sludge generated in a water treatment step is precipitated in a settling basin and the precipitated sludge is concentrated by microfiltration membrane separation. .

[0009]

[Function] The membrane separation methods for liquid separation include microfiltration membrane separation (membrane pore size μ order) and ultrafiltration membrane separation (membrane pore size Å order). These membrane separations have the following basic features. There is. (1) High solid recovery rate (1 depending on the membrane pore size selection
00%). (2) The solid-liquid separated water quality is good due to the high solids recovery rate. Furthermore, soluble substances are also blocked to some extent depending on the choice of membrane pore size. (3) The concentration function is hardly affected by the properties of the target liquid because it is a type of forced concentration in which solids are blocked by the membrane.

Therefore, it can be expected that the above-mentioned membrane separation solves the basic problems of the conventional sludge concentration method described in the section "Problems to be solved by the invention". But,
The issue in application is whether or not the concentration function can be maintained at the same level as or higher than existing methods.

The present inventor has conducted a number of experiments and found that microfiltration is more suitable than ultrafiltration as a membrane separation applied to a sludge concentration method, and that even in microfiltration, existing selections have been made by appropriately selecting the membrane pore size. It was found that the sludge has a concentration function equal to or higher than that of the sludge concentration method.

FIG. 2 shows the result of the membrane separation test of sewage sludge carried out by the present inventor. In FIG. 2, ultrafiltration is shown as UF and microfiltration is shown as MF, and FIG. 3 shows a schematic diagram of the test apparatus. As shown in FIG. 3, this test apparatus is provided with a stock solution storage tank a having a heater e for temperature control and an effective solution amount of 300 ml, and a circulation pump b for supplying the stock solution in the storage tank a to a membrane separation section c. There is. The stock solution in the stock solution storage tank a supplied to the membrane separation section c by the circulation pump b is separated into the membrane permeated water and the concentrated circulation solution by the membrane d attached to the membrane separation section c, and the concentrated circulation solution is stored in the stock solution storage tank a. Will be returned. The membrane d mounted on the membrane separating portion c can be changed in various ways.

The membranes used in the above test apparatus are (i) ultrafiltration membrane molecular weight cutoff of 40,000 (material polyacrylonitrile), 100000 (material polyethersulfone) (ii) microfiltration membrane pore diameter 0.1, 0.2, 0.45 μm
(Material polysulfone). The test method and conditions are as follows. After putting the sample liquid (gravity concentrating tank inlet sludge collected from City A sewage treatment plant, sludge concentration 16500 to 17900 ppm) into the stock solution storage tank a, a predetermined permeation pressure (4.0 kg / cm ² G) was obtained with N ₂ gas. It is a batch test in which the membrane permeated water is discharged over time while the concentrated liquid that has been set and concentrated in the membrane separation section c is continuously circulated.

After the start of the batch test, the "cumulative amount of permeated water" was measured every predetermined time, and after the permeation was completed, the solid concentration (SS) of the collected permeated water was analyzed. The concentration of concentrated sludge is
The cumulative membrane permeation water amount (V _u ) at which the membrane permeation flux was extremely reduced was used and calculated from the solid balance by the formula C _U = C _o V _o / (V _o −V _u ). Here, Cu: concentrated sludge concentration (%), C _o : target sludge concentration (%), V _o : initial sample liquid amount (milliliter) As shown in FIG. 2, which is the result of the above test conducted by the present inventor. , MF is higher in concentrated sludge concentration than UF, MF
However, there is a membrane pore diameter (0.2 μm) that maximizes the concentration of concentrated sludge, and if MF with a membrane pore diameter of 0.1 to 0.2 μm is applied, it will be 3.5 to 4%, which is gravity concentration among existing concentrations, It was found that a concentration function equivalent to or higher than the pressure floating concentration was obtained. In addition, the solid recovery rate is 1 for both UF and MF.
It was found to be 00%.

Based on the above test results, in the present invention, the sludge generated by the water treatment in the sedimentation basin is precipitated, and the microfiltration membrane (MF) separation is used in concentrating the precipitated sludge. As described above, according to the present invention, by having the above-mentioned configuration, while maintaining a concentration function equal to or higher than that of the conventional sludge concentration method, a solid-liquid separation function having a high solid recovery rate and a stable solid-liquid separation function can be obtained. Can be maintained.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT An embodiment of the present invention will be described with reference to FIG. In this example, the concentration step of sludge treatment generated from sewage treatment is performed by microfiltration membrane (MF) separation.

The sewage 1 first removes coarse solids in the settling tank 2 and then flows into the aeration tank 3 to remove floating solids and soluble organic substances in the aeration tank 3. The mixed solution from which the floating solids and soluble organic substances have been removed in the aeration tank 3 flows into the final settling tank 4 in the latter stage, and the activated sludge in the mixed solution is recovered in the final settling tank 4 in the latter stage, and part of it The returned sludge 5 is stored in the aeration tank 3, and the rest is stored in the storage tank 8 as excess sludge 7, and then concentrated in the membrane separation unit 9. The first settling sludge 6 generated in the first settling basin 2 is caused to flow into the final settling basin 4, and the first settling sludge 6 is mixed with the final settling basin sludge to be treated as surplus sludge 7. A microfiltration membrane 9A is attached to the membrane separation section 9 so that the excess sludge 7 is concentrated by the microfiltration membrane 9A.

In the membrane separation section 9, the membrane permeated water 11 and the concentrated sludge 10 which are concentrated separated liquids are generated, and the membrane permeated water 1
1 is sent to the aeration tank 3, and the concentrated sludge 10 is sent to the dehydrator 12. In the dehydrator 12, the concentrated sludge 10 is dehydrated into a dehydrated sludge 13, and this dehydrated sludge 13 is sent to a sludge treatment unit in a subsequent stage.

In the present embodiment, as described above, the initial sludge 6 generated in the first settling tank 2 and the sludge generated in the final settling tank 4 in the subsequent stage are sent to the membrane separation section 9 as excess sludge 7. It is then concentrated by separation with the microfiltration membrane 9A. Therefore, as described in detail in the "Action" column, this example maintains a concentration function equal to or higher than that of the conventional sludge concentration method, while maintaining a high solid recovery rate and a stable solid-liquid separation function. can do.

[0020]

INDUSTRIAL APPLICABILITY According to the present invention, sludge generated by water treatment is settled in a settling basin and the settled sludge is concentrated by microfiltration membrane separation. As a result, the solid recovery rate is high, and a stable solid-liquid separation function that is not affected by the properties of sludge can be maintained.

[Brief description of drawings]

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

FIG. 2 is a graph showing the test results using an ultrafiltration membrane and a microfiltration membrane.

FIG. 3 is a configuration diagram of a test apparatus used in the test.

[Explanation of symbols]

 1 Sewage 2 First settling tank 3 Aeration tank 4 Final settling tank 5 Return sludge 6 Initial sludge sludge 7 Excess sludge 8 Storage tank 9 Membrane separation section 9A Microfiltration membrane 10 Concentrated sludge 11 Membrane permeate 12 Dehydrator 13 Dewatered sludge

Claims (1)

[Claims] 1. A method for concentrating sludge, which comprises sludge sludge generated by water treatment in a settling basin and concentrating the precipitated sludge by microfiltration membrane separation.