JP2003103122A - Filtering method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for filtering suspension colloid at a high removal rate. SOLUTION: This filtering method comprises a step to obtain a supernatant liquid by settling the suspension colloid-containing liquid to be treated, a step to filter dynamically the supernatant liquid obtained at the preceding step by a filter medium having substantially uniform pores and a step to store the permeated liquid obtained at the preceding step in a water storage tank.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a filtration treatment method using dynamic filtration.

[0002]

2. Description of the Related Art The biological treatment liquid treated by applying the activated sludge method and the like still contains a large amount of suspended solids, which causes water pollution when discharged directly to rivers. Therefore, the suspended matter is removed by filtration using a non-woven fabric or the like.

In the case of filtration using such a non-woven fabric, since the mesh size is larger than that of a micro filter or the like, so-called dynamic filtration is used to increase the removal rate of suspended matter. This dynamic filtration is a filtration method that deposits suspended solids or flocs (aggregates of suspended solids such as activated sludge) in the pores of non-woven fabrics and nets to form a dynamic membrane, and therefore has a stable filtration capability. In order to maintain the above, rapid formation of a suitable dynamic film and control of the thickness are important.

An object of the present invention is to provide a filtration treatment method suitable as a method for removing suspended matter from a liquid to be treated containing the biologically treated suspended matter.

[0005]

Means for Solving the Problems As a means for solving the above problems, the present invention substantially comprises a step of obtaining a supernatant by subjecting a liquid to be treated containing a suspension to a sedimentation treatment, and a supernatant obtained in the above step. Provided is a filtration treatment method comprising: a step of dynamically filtering with a filter having uniform pores; and a step of storing the permeated liquid obtained in the step in a water storage tank.

The "sedimentation treatment" in the present invention includes either one or both of gravity sedimentation treatment and sedimentation treatment by addition of a flocculant.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION The filtration method of the present invention will be described below with reference to the drawings. FIG. 1 is a conceptual diagram showing a processing flow of a filtration treatment method, and FIG. 2 is a conceptual diagram of a solid-liquid separation device used in FIG. The present invention is not limited to the processing flow shown in FIG. 1, and other processing steps usually performed by those skilled in the art can be added if necessary.

Biologically treated water (water to be treated) treated by the activated sludge method is put in the settling tank 2 of the settling tank 1. In the settling tank 2, the suspension material (SS) is settled to the bottom by gravity settling processing or settling processing of forming flocs by adding a flocculant. The method of sedimentation treatment is selected in consideration of the SS concentration in the water to be treated, the particle size of SS and the like.

The supernatant portion of the settling tank 2 is caused to overflow the partition plate 4 and overflow into the supernatant liquid tank 3. The SS concentration in the supernatant liquid in the supernatant liquid tank 3 is 5 to 5 in order to suitably perform the dynamic filtration in the subsequent step.
100 mg / L is preferable, and 10-50 mg / L is more preferable. 16 is a sludge drawing line.

Next, the pump 31 is actuated, and the supernatant liquid of the supernatant liquid tank 3 is separated from the supernatant liquid line 11 by the solid-liquid separation device 5.
And is subjected to dynamic filtration with a filter body having substantially uniform pores. As the solid-liquid separation device 5 used in this step, the one shown in FIG. 2 can be used.

A required number of filter elements 22 are arranged in the solid-liquid separation tank 21. 18 is a concentrate discharge line, 2
3 is an air diffuser for cleaning the surface of the filtration element 22, and 24 is an overflow line of the solid-liquid separation tank 21. The apparatus of FIG. 2 is a direct immersion type in which the filtration element 22 is immersed in the supernatant liquid.
It is also possible to use an externally installed type in which the module is housed in a housing or the like and is placed outside the solid-liquid separation tank 21.

The filter element 22 is a bag-like member in which a filter body is attached to both sides of a frame body having one or more required number of water collecting pipes. In FIG. 2, one water collecting pipe is a permeate nozzle. Has become. Each permeate nozzle of the plurality of filtration elements 22 is connected to the permeate line 12.

In order to facilitate the formation of a dynamic membrane and maintain a high permeation flux, the filter body should be one having pores having a substantially uniform pore size, for example, a net is preferable.
In addition, the substantially uniform pore diameter means a case where all the pore diameters are completely uniform, and within a range not impairing the object of the present invention, due to a manufacturing error or a change with time due to continuous use. This includes the case where there is an error (for example, an error of about ± several%). Thus, when a net-like material is used as the filter body, since the pore diameters of all the pores are substantially the same, the average pore diameter of the filter body in the present invention is almost the same as the pore diameter of all the pores. Becomes

The net used as the filter body of the filter element 22 preferably has an average pore size of 10 to 50 μm, more preferably 10 to 30 μm.

The net is made of metal fiber or plastic fiber, and the metal fiber is made of iron, silver, copper, copper alloy, titanium, stainless steel, or a base metal plated with silver or copper. However, copper and stainless steel are preferable. Examples of plastic fibers include polyester, polystyrene, polyvinyl chloride, polyvinylidene chloride, polytetrafluoroethylene, poly (meth) acrylic acid ester, viscose rayon, cellulose acetate, polyethylene, polypropylene and other polyolefins, polyethers, polyether esters. Further, these copolymers, blends, crosslinked products and the like can be mentioned, but polyvinylidene chloride, polyester, polyethylene and polypropylene are preferable, and polyester and polyethylene are more preferable.

The dynamic filtration condition is not particularly limited as long as it can form a dynamic membrane, but it is desirable to carry out the filtration operation at a transmembrane pressure difference of about 0.1 to 5 kPa.

Next, the permeated liquid filtered by the solid-liquid separation device 5 is sent from the permeated liquid line 12 to the water storage tank 6 and is stored therein.

When such a filtration operation is continuously performed, excessive SS or flocs (aggregates of SS such as activated sludge) are attached to the surface of the filter body to reduce the filtration ability, so that the back pressure is appropriately adjusted. Wash to remove excess SS or flocs. If the filtration operation time is too long, the detergency of the back pressure cleaning is deteriorated. Therefore, in the present invention, it is desirable to set the filtration time for one time to 5 to 20 minutes and perform the back pressure cleaning during the filtration.

In this back pressure cleaning, the permeate in the water storage tank 6 is sent from the back pressure cleaning line 14 to the back pressure cleaning tank 7 by operating the circulation pump 32, and then the permeate is supplied to the inside of the filter body. By. An acid and / or sodium hypochlorite can be added to the permeated liquid in order to enhance the cleaning property. Further, the method of removing SS on the surface of the filter body by aerating air from the bottom surface of the solid-liquid separation tank 21 with the air diffuser 23 may be combined with back pressure cleaning.

Further, when the filtration operation is continued for a long period of time, scale is adhered and accumulated on the respective pipe walls and inner walls of the supernatant liquid line 11, the permeate liquid line 12 and the water storage tank 6, so that the acid aqueous solution and / or hypochlorous acid It is desirable to wash by flushing with an aqueous sodium acid solution. To wash the scale, an acid or the like is added to the supernatant liquid tank 3, the supernatant liquid line 11, the solid-liquid separation device 5 (solid-liquid separation tank 21), and the concentrated liquid discharge line 18 are added.
Cleaning by the circulation path (circulation path A) in the order of, and the circulation path (circulation path B) by the solid-liquid separation tank 21, the permeate line 12, the water storage tank 6, the back pressure cleaning line 14, and the solid-liquid separation tank 21 in this order. Wash with.

As the acid used for back pressure cleaning and scale cleaning, an organic acid having a chelating action such as citric acid or an inorganic acid such as nitric acid can be used.

If the filtration method of the present invention is applied, 50
SS in the supernatant can be removed with a removal rate of ~ 95%.

The filtration treatment method of the present invention is a treatment of wastewater containing activated sludge, etc. in wastewater treatment plants, etc., treatment of wastewater of various facilities and domestic wastewater, wastewater containing other suspended matter, and purification treatment of rivers, lakes and marshes. Etc. can be applied.

[0024]

The present invention will be described in more detail based on the following examples, but the invention is not intended to be limited by these examples.

Example 1 According to the process flow shown in FIG. 1, the filtration operation was carried out under the following conditions.

Water to be treated (in the settling tank 2): MLSS is 10
00 mg / L of activated sludge liquid supernatant (in the supernatant liquid tank 3): MLSS is 50 mg / L Solid-liquid separation device: As shown in FIG. 2, five plates are vertically arranged in the housing at intervals of 20 mm. A body (a net made of plain woven stainless steel, an effective filtration area of 500 cm ² / sheet, an opening of 37 μm, a wire diameter of 35 μm, an aperture ratio of 27%) is stored. Permeation rate: 10 m / day (transmembrane pressure difference of 1 kPa) Volume filtration operation Filtration operation is performed under such conditions and 0.5 is performed every 10 minutes.
The filter body was back-pressure washed with a permeated liquid (sodium hypochlorite solution having an effective chlorine concentration of 5 mg / L) at 20 m / day for minutes. The water permeation rate after 24 hours was 10 m / day, and the MLSS concentration was 5 mg / L. In addition, every 30 days, the scales of circulation routes A and B were removed using nitric acid. However, 100 ml of 1N nitric acid aqueous solution was added to 1 L of water (supernatant or permeate).

[0027]

EFFECTS OF THE INVENTION According to the filtration method of the present invention, SS can be removed from the supernatant liquid after biological treatment generated in a sewage treatment plant or the like to the extent that it can be discharged into a river.

[Brief description of drawings]

FIG. 1 is a conceptual diagram of a processing flow for explaining a filtration processing method of the present invention.

FIG. 2 is a conceptual diagram of a solid-liquid separation device used in FIG.

[Explanation of symbols]

1 sedimentation tank 2 settling tank 3 supernatant liquid tank 4 partition boards 5 Solid-liquid separation tank 6 water tank 7 Back pressure cleaning tank

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Claims (7)

[Claims] 1. A step of obtaining a supernatant by subjecting a liquid to be treated containing a suspension to a sedimentation treatment, and a step of dynamically filtering the supernatant obtained in the above step with a filter having substantially uniform pores. A filtration method comprising the step of storing the permeated liquid obtained in the above step in a water storage tank. 2. The concentration of suspended matter in the supernatant liquid is 5 to 100 m.
The filtration treatment method according to claim 1, wherein the filtration treatment is g / L. 3. The filtration treatment method according to claim 1, wherein the filter body is a net having an average pore size of 10 to 50 μm. 4. The filtration treatment method according to claim 1, wherein the filtration time is 5 to 20 minutes, and the back pressure washing is performed during the filtration. 5. The filtration treatment method according to claim 4, wherein the surface of the filter is washed by aerating from below the filter during the back pressure cleaning. 6. The filtration treatment method according to claim 4 or 5, wherein as the washing water for the back pressure washing, one in which an acid and / or sodium hypochlorite is added to the permeate is used. 7. A filter body having substantially uniform pores, wherein a step of settling a liquid to be treated containing a suspension to obtain a supernatant liquid is carried out in a sedimentation treatment tank, and the supernatant liquid obtained in the above step is provided with substantially uniform pores. The process of dynamic filtration is performed in the solid-liquid separation tank, and the sedimentation treatment tank and the solid-liquid separation tank are connected by a pipe,
The solid-liquid separation tank and the water storage tank are connected by a pipe, and a pipe connecting the sedimentation treatment tank and the solid-liquid separation tank, a pipe connecting the solid-liquid separation tank and the water storage tank, and Alternatively, the filtration treatment method according to any one of claims 1 to 6, which is washed with an aqueous solution of sodium hypochlorite.