JPH1119421A - Method of backwashing filter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To sharply reduce the quantity of water to be used for backwashing, to shorten backwashing time, to increase washing performance and to enable to reduce the concentration of suspended matter in treated water immediately after washing by adding a flocculant to washing water in a final process for backwashing. SOLUTION: To the upper part of a column filter 12 of an upstream flow type filter, a washing water inlet pipe 18 whose one end is connected to a treated water tank 16 through a backwashing pump 17 is connected at the other end thereof. To perform backwashing, treated water in the treated water tank 16 is allowed to flow in from the upper part toward the lower part of a filter bed 11. The washing water inlet pipe 18 is provided with a flocculant adding means 20, and in a final process for backwashing, by allowing washing water to which the flocculant is added to flow in, the finishing washing is performed. In this way, by the action of the flocculant added to the filter bed, the remaining suspended matter in the bed become bulky flocs, which are caught by the filter medium. Thus by a small quantity of washing water, treated water of good quality can be obtained immediately after washing.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a filter device for performing sewage treatment, sewage discharged from factories of various industries, etc., or a filter device capable of backwashing a filter material of a biological filtration device with a small amount of water. Backwashing method.

[0002]

2. Description of the Related Art Conventionally, for example, in the treatment of sewage treatment and industrial wastewater of various industries, an upflow filtration device in which raw water flows upward from below, and a downward filtration device in which raw water flows downward from above. Various filtration devices such as a countercurrent filtration device are used, and the filter medium used in such a filtration device needs to be periodically cleaned. In the case of washing such a filter medium, generally, a backwashing method in which washing water is introduced from a direction opposite to the raw water and air bubbling is employed.

[0003] Fig. 3 shows an upflow filter using a floating filter medium as an example of a filter. In such a filtration device,
A raw water inflow pipe 14 in which a raw water pump 13 is interposed is connected to a lower part of a filtration tower 12 having a filtration layer 11 formed of a filter medium. On the other hand, a treated water outflow pipe 15 is connected to the upper part of the filtration tower 12, and the treated water outflow pipe 15 is connected to a treated water tank 16.
It is connected to the. In addition, the upper end of the filtration tower 12 is connected to the other end of the washing water inflow pipe 18 whose one end is connected to the treatment water tank 16 via the backwash pump 17. Tube 19 is connected.

[0004] Therefore, when backwashing the upward flow filtration device, the treated water in the treated water tank 16 flows from the upper part to the lower part of the filtration layer 11 by the backwash pump 17, and then the rinse water To finish wash. In such a backwash, the filter medium is developed downward by washing the floating filter medium in a downward flow, and suspended substances and excess sludge can be efficiently discharged downward without opposing gravity.

[0005]

However, in order to obtain good treated water having a low SS concentration immediately after backwashing by the above-described backwashing method, it is necessary to reduce the amount of water contained in the filter medium by 2 to 4 in the finishing washing step of backwashing. There is a problem that twice the amount of rinse water is required.

Also, since a large amount of washing water is used, it takes a long time to perform the operation, and there is a problem that the operation efficiency is low.

[0007] In view of such circumstances, an object of the present invention is to provide a method for backwashing a filtration device which can obtain treated water having a low SS concentration immediately after backwashing with a small amount of washing water. .

[0008]

According to the present invention, there is provided a method for backwashing a filtration layer of a filtration apparatus, comprising the steps of: introducing washing water into the filtration layer in a direction opposite to the flow of raw water; A backwash method for a filtration device, comprising: a first step of washing the filtration layer by flowing in; and a second step of subsequently flowing washing water to which a coagulant has been added.

Here, for example, 80 to 95% of the SS trapped in the filtration layer in the first step is discharged.

The washing water used in the second step is:
For example, it is 0.5 to 1.5 times the amount of water retained in the filtration layer.

Further, it is preferable that the flow of the washing water to which the flocculant is added is performed in a direction opposite to the flow direction of the raw water.

In the present invention, the first step may be carried out in the same manner as in a normal backwashing method. Generally, the first step is water washing with washing water flowing in a direction opposite to the raw water, and bubbling of air. Are repeated alternately several times. By this first step, 80 to 9 of SS trapped in the filter medium
The cleaning time is set so that 5% is removed by cleaning.

In the next second step, finishing washing is performed by flowing washing water to which a coagulant has been added. However, due to the action of the coagulant added to the filter layer, the residual SS in the layer becomes coarse flocs. As a result, high quality treated water quality can be obtained immediately after washing with little water washing.

Here, the backwashing method of the present invention will be described using a model.

For the sake of simplicity, consider a model in which all captured SS are separated and floating. Assuming that the SS concentration in the layer at this time is C, the relationship between the amount of washing water and the SS concentration after backwashing when washing in a completely mixed state is as shown in FIG. Although the SS concentration is reduced to 0.10 C after backwashing at 2.3 times the amount of retained water, it is 4.6 to obtain a treated water quality of 0.01 C.
Double dose is required. It is extremely inefficient to obtain an SS concentration of 0.01 C or less after backwashing by passing washing water.

On the other hand, as in the method of the present invention, for example, 2.
At the time of washing with 3 times the amount of washing water, a flocculant is added and washed. As the flocculant diffuses into the filtration layer, the SS in the layer
Is flocculated by a flocculant and captured by the filtration layer. Approximately one-time amount of washing water is required for diffusion of the flocculant, but good treated water quality can be obtained by using a total of 3.5-times amount of washing water.

Since the mixing state at the time of washing varies depending on the filter medium particle size, the length of the filtration layer, and other washing conditions, the amount of washing water does not always correspond to the above-mentioned perfect mixing model, but the basic principle is common and the separated When about 80 to 95% of the SS is discharged, a flocculant is added, and 0.5 to
The same effect can be obtained if 1.5 times the amount of washing water is passed.

The coagulant may be added by a method capable of diffusing into the filtration layer, but is preferably added to the washing water and supplied together with the washing water.

The washing at the time of adding the flocculant may be performed from any direction. However, if the washing is performed from the filtration layer outlet side, that is, from the direction opposite to the inflow direction of the raw water, the flocculation floc is surely formed near the filtration layer outlet. Therefore, the effect of reducing the concentration of the treated water SS can be further enhanced.

In the present invention, the flocculant is preferably a polymer flocculant such as an anionic polymer or a cationic polymer, but may be an inorganic flocculant, and any of those commonly used can be used. .

The amount of the coagulant to be added varies depending on the type of the coagulant and the like.
It is about 10 to 10 mg / L (liter).

The flow direction of the raw water in the filtration device to which the method of the present invention is applied may be an upward flow or a downward flow, and the filter medium may be settled or floatable.

[0023]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present embodiment will be described below.

FIG. 1 shows an upflow filtration device used in this embodiment.
Shown in

The upflow filtration device used in this embodiment is the same as that described in the section of the prior art except that the washing water inflow pipe 18 connected to the upper part of the filtration tower 12 has a coagulant addition means 20. Therefore, the same members are denoted by the same reference numerals, and redundant description will be omitted.

Hereinafter, an embodiment using this filtering device will be described.

(Embodiment) In this embodiment, a filter medium having an average particle size of 3.5 m was placed in the filtration tower 12 of the above-described upward flow filtration device.
m, a filter medium made of polypropylene having a density of 0.5 g / cm ³ and a filtration layer 11 having a filtration layer length of 3.0 m was used.

After processing food wastewater as raw water through the filtration layer 11 at a filtration LV of 5 m / h for 12 hours, the following backwashing was performed.

In the first step, water washing at LV = 30 m / h for 2 minutes and air washing at LV = 20 m / h for 2 minutes were repeated eight times.

Next, in the second step, a cationic polymer acrylamide-dimethylaminoethyl methacrylate copolymer (Kurita Kogyo Co., Ltd .: Crifix CP604) as a coagulant was added at a ratio of 0.5 mg / L. Water washing was performed at LV = 30 m / h using the washed water.

FIG. 2 shows the result of measuring the SS concentration of the treated water by flowing the washing water after the completion of the back washing.

(Comparative Example) The operation was performed in the same manner as in the above-mentioned Example, except that no coagulant was added to the washing water in the second step of the backwashing. After the backwash, the washing water was flowed to measure the SS concentration of the treated water, and the results are shown in FIG.

(Test Results) As shown in FIG. 2, the SS concentration of the treated water was 13 mg / L immediately after washing in the example to which the flocculant was added. On the other hand, in the comparative example in which the flocculant was not added, the concentration was 47 mg / L, and it was further 1.9 until the treated water SS concentration reached the same level as when the flocculant was added.
Double water flow was required. Comparing the total amount of washing water when this amount of flowing water is included in the amount of washing water, it is 5.2 times in the comparative example in which no flocculant is added, whereas it is 3.2 times in the example in which the flocculant is added. It was confirmed that the amount of washing water could be reduced by 38% by employing the method of the present invention.

[0034]

As described above, according to the present invention,
By adding a flocculant in the final step of backwashing, the amount of water used for backwashing can be significantly reduced. At the same time, the backwashing time can be shortened, and the working efficiency can be improved. Further, there is an effect of improving the cleaning performance, and the SS concentration of the treated water can be reduced immediately after the cleaning.

[Brief description of the drawings]

FIG. 1 is a schematic diagram of a filtration device used in one embodiment of the present invention.

FIG. 2 is a diagram showing test results of Examples and Comparative Examples of the present invention.

FIG. 3 is a schematic diagram showing an example of a filtration device according to the related art.

FIG. 4 is a diagram showing the relationship between the amount of backwash water and the SS concentration after backwash.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 11 Filtration layer 12 Filtration tower 13 Raw water pump 14 Raw water inflow pipe 15 Treated water outflow pipe 16 Processing water tank 17 Backwash pump 18 Cleaning water inflow pipe 19 Cleaning water drainage pipe 20 Coagulant addition means

Claims (4)

[Claims] 1. A method for backwashing a filtration layer of a filtration device, comprising: a first step of washing the filtration layer by flowing washing water and air into the filtration layer in a direction opposite to a flow direction of raw water. A method for backwashing a filtration device, comprising: a step; and, thereafter, a second step of flowing washing water to which a coagulant has been added. 2. The method according to claim 1, wherein 80 to 95% of the SS trapped in the filtration layer in the first step is discharged. 3. The method according to claim 1, wherein the washing water used in the second step has a water content of 0.5 to 0.5% of the retained water amount of the filtration layer.
A method for backwashing a filtration device, wherein the amount is 1.5 times the amount. 4. The method according to claim 1, wherein the flow of the washing water to which the coagulant is added is performed in a direction opposite to a flow direction of the raw water.