JP2006175342A - Method of cleaning filter medium and filter system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of cleaning a filter medium capable of removing deposits thoroughly from the medium with no limitation on the range of utilization of treated water and little lowering of the treating efficiency and a filter system employing the method. <P>SOLUTION: The method is employed in cleaning a filter medium 18 by causing a part of treating water after filtering to pass in the direction opposite to the filtering direction with respect to the medium 18 and has a process of adding, before filtering, a disinfectant to raw water to be used in cleaning. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a filter medium cleaning method and a filtration system for filtering an object to be filtered, and in particular, waterworks for construction work, sewage, river water, lake water, coagulated sediment supernatant, various process intermediate water, and recovered water in a papermaking process. Various filtration water levels, various wastewaters, treated water in biological treatment, liquid containing valuables, liquor or oil, etc. Related to the filtration system.

  Conventionally, when purifying an object to be filtered by filtration, a filtration device for filtering by sand filtration or membrane filtration has been used. There are various types of objects to be filtered, gas phase, liquid phase, and solid phase, but here, explanation will be made by paying attention to the object to be filtered. Moreover, it is liquid filtration object, Comprising: An unfiltered thing is also called raw | natural water or untreated water, and the thing after filtration may be called treated water. Recently, a long fiber filtration device that filters a liquid using a large number of long fiber filter media is sometimes used. This long fiber filter medium has the features of a large specific surface area, small filling rate and low filtration resistance, and is attracting attention as a filter medium that can perform high-speed and high-capacity filtration. It is used for processing. For example, Patent Documents 1 to 3 disclose long fiber filtration devices using this long fiber filter medium.

  When filtration is performed for a long time in a filtration device using such a filter medium, suspended substances in raw water accumulate on the filter medium and the filtration performance deteriorates (especially increases the filtration resistance). In some cases, so-called backwashing is performed in which a suspended liquid is passed in the opposite direction to remove the accumulated suspended matter. Since a part of the long fiber filter medium is fixed to the strainer, it can be backwashed at high speed, and the washing time (backwashing time) is short. About washing | cleaning of the filter medium by backwashing, it is disclosed by patent document 4, for example.

  However, if the filtration is further continued, deposits derived from microorganisms, other organic substances, metals, and the like begin to adhere to the filter medium. It is difficult to remove the deposits and the like even if the above-described normal cleaning is performed. Therefore, in order to effectively remove or prevent such deposits derived from microorganisms, sterilization washing is generally performed.

In this sterilization cleaning, for example, there is a method in which a small amount of sodium hypochlorite is always added to raw water (see, for example, Patent Document 5). In addition, there is a type in which a chlorine-based disinfectant is added to a liquid for backwashing (also referred to as backwashing water) to perform backwashing (see FIG. 3). In this case, the addition amount of the bactericide is adjusted so that the residual chlorine concentration in the waste water after backwashing is 0.5 to several mg / L. In addition, as a liquid for backwashing, a part of treated water may be used.
Japanese Patent Publication No. 5-12002 JP 2003-265907 A JP-A-63-315110 JP-A-2-157007 Japanese Patent Laid-Open No. 7-241549

  However, in the case where sodium hypochlorite is constantly added to the raw water, there is a problem that chlorine remains in the treated water, although the effect of preventing adhesion of adhered substances and the like is high. Therefore, the use range of such treated water is limited.

  Moreover, in the case of adding a chlorine-based disinfectant to backwash water, there is a problem that the filter medium can contact the disinfectant only during the backwash time. In general, the longer the contact time between the sterilizing agent and the filter medium, the higher the sterilizing ability, that is, the ability to remove deposits, etc., but if the backwash time is about 4 to 6 minutes, sufficient deposits are removed. I can't. On the other hand, if the contact time between the disinfectant and the filter medium is lengthened, that is, the backwash time is lengthened, the water treatment efficiency is lowered accordingly.

  The present invention has been made in view of the above circumstances, and does not limit the range of use of treated water, and does not substantially reduce the treatment efficiency. It is an exemplary problem to provide a filter medium cleaning method capable of removing kimono and the like and a filtration system using the method.

  In order to solve the above-described problem, a filter medium cleaning method as an exemplary aspect of the present invention is to wash a filter medium by passing a part of the filtration target after filtration in a direction opposite to the filtration direction with respect to the filter medium. It is a washing | cleaning method, Comprising: It has the process of adding a disinfectant before filtration only with respect to the filtration object used for washing | cleaning, It is characterized by the above-mentioned.

  In this invention, backwashing is performed in washing, and the filtered object (treated water) after filtration is used as the backwashing water. Since the bactericidal agent is added only to the raw water used as the backwash water, the raw water used as the treated water does not contain the bactericidal agent. Therefore, the use range of treated water is not limited.

  Furthermore, since a bactericidal agent is added to the raw water for backwashing, the bactericidal agent is filtered both when it passes through the filter medium in the filtration direction and when the backwash water passes through the filter medium in the direction opposite to the filtration direction. Can contact. Therefore, the contact time between the filter medium and the disinfectant can be extended without reducing the water treatment efficiency, and the effect of removing the deposits and the like on the filter medium is improved.

  The filter medium may be a long fiber filter medium. In the case of a long fiber filter medium, deposits derived from microorganisms, other organic substances, metals, etc. are more likely to adhere to the portion where the filter medium is fixed, and the backwash time is short because of its characteristics. Accordingly, when the filter medium cleaning method of the present invention is applied to this long fiber filter medium, the effect of removing deposits and the like can be further improved with a short backwash time.

  The disinfectant may be a chlorine agent. As this chlorinated disinfectant, for example, sodium hypochlorite, chlorine dioxide, chloramine and the like are applicable.

  In the addition step, a chlorinating agent may be added so as to have a chlorine concentration of 1 mg / L or more and 50 mg / L or less with respect to the object to be filtered. The addition of a chlorinating agent within this concentration range is most desirable from the viewpoints of the effect of removing deposits and the like, and the processing cost.

  It is desirable to have a step of detecting the concentration of the sterilizing agent to be filtered after washing and a step of controlling the addition amount of the sterilizing agent so that the detection result is 0.5 mg / L or more. If the concentration of the sterilizing agent in the wastewater after adding the sterilizing agent to the raw water used for backwashing and using the treated water as backwashing water is 0, for example, the amount of the added sterilizing agent should be removed It means that there is a shortage with respect to the amount. Therefore, it is possible to obtain a sufficient removal effect by detecting the concentration of the bactericide in the backwash water and adding the bactericide so that the drainage contains 0.5 mg / L or more of the bactericide. Can do. Note that the bactericidal agent may be added only to the raw water used for backwashing, or may be added again to the backwashing water after passing through the filter medium.

  It is further desirable to have a step of passing the filtration target in the direction opposite to the filtration direction after a predetermined time has elapsed after the filtration of the filtration target used for washing is completed. For example, by setting the predetermined time to 4 to 5 minutes, the contact time between the disinfectant and the filter medium can be further increased, and the deposits and the like can be more effectively removed.

  The filtration system as another exemplary aspect of the present invention is a backwashing unit that allows a part of the filtration target after filtration to pass through the filter medium in a direction opposite to the filtration direction, and a filtration target used for backwashing. Only having a disinfectant addition means for adding a disinfectant before filtration.

  In this invention, backwashing is performed in washing, and the filtered object (treated water) after filtration is used as the backwashing water. Since the bactericidal agent is added only to the raw water used as the backwash water, the raw water used as the treated water does not contain the bactericidal agent. Therefore, the use range of treated water is not limited.

  Furthermore, since a bactericidal agent is added to the raw water for backwashing, the bactericidal agent is added to the filter medium both when it passes through the filter medium in the filtration direction and when the backwash water passes through the filter medium in the reverse direction of the filtration direction. Can touch. Therefore, the contact time between the filter medium and the disinfectant can be extended without reducing the water treatment efficiency, and the effect of removing the deposits and the like on the filter medium is improved.

  Further objects and other features of the present invention will become apparent from the preferred embodiments described below with reference to the accompanying drawings.

  According to the present invention, the use range of treated water is not limited, and the treatment efficiency is hardly lowered, and the contact time between the filter medium and the disinfectant can be lengthened. Deposits and deposits on the filter medium can be removed. As a result, the frequency of cleaning with the bactericide can be greatly reduced.

[Embodiment]
Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a block diagram showing a schematic configuration of a filtration system S that uses a filter medium cleaning method according to an embodiment of the present invention. In this filtration system S, so-called backwashing is performed in which a part of treated water after filtration is passed through the filter medium 18 in a direction opposite to the filtration direction to wash the filter medium 18. This filtration system S has a raw water supply unit 1, a filtration unit 2, and a drainage unit 3 and is generally configured.

  The raw water supply unit 1 is for supplying a liquid (raw water) as an object to be filtered to the filtration unit 2. The raw water pump 5 for pumping the raw water from the raw water tank 4 where the raw water is stored, A flow meter 6 for measuring the flow rate is attached. A disinfectant addition means 8 is connected to the downstream of the flow meter 6 in the middle of the raw water pipe 1a. The sterilizing agent adding means 8 is for adding the sterilizing agent only to the portion of the raw water used as the backwash water, and has a sterilizing agent tank 8a and a sterilizing agent pump 8b. As the disinfectant, chlorine-based disinfectants such as sodium hypochlorite, chlorine dioxide, chloramine, etc. are used. Of course, any other effective microorganism disinfectant is applicable as well as chlorine-based disinfectants.

  A backwash water drain pipe 10 is connected to the raw water pipe 1a so that drainage when backwashing described later can be performed can be discharged. The backwash water drain pipe 10 is provided with a chlorine concentration meter 12 for measuring the disinfectant concentration (chlorine concentration) in the drained water after backwashing. The raw water pipe 1a and the backwash water drain pipe 10 are provided with valves V1 and V2, respectively, so that the flow paths during the raw water treatment and backwash washing can be switched.

  The filtration unit 2 is generally configured by including a filtration tank 14 that stores the supplied raw water, a strainer 16 and a filter medium 18 that are disposed in the filtration tank 14.

  The strainer 16 is for passing raw water and preventing the filter medium 16 from flowing out. A filter medium 18 is fixed to the strainer 16. The filter medium 18 is a long fiber filter medium, and one end of the fiber is fixed to the strainer 16 and the other end is a free end. The raw water supplied into the filtration tank 14 is filtered while moving from the free end side of the filter medium 18 to the fixed end side, and becomes treated water and is discharged from the filtration tank 14 to the drainage section 3. Yes.

  The filtration tank 14 is provided with a level switch 20 that transmits a signal when the raw water stored in the filtration tank 14 reaches a certain amount. When a signal from the level switch 20 is received, control means (not shown) closes the valve V1 and stops the supply of raw water. This control means controls the operation of the entire filtration system S. For example, the valves V1 and V2 are opened and closed, the detection result is received from the chlorine concentration meter 12, and the supply amount by the raw water pump 5 and the sterilizing agent pump 8b. Make adjustments.

  The drainage section 3 has a drainage pipe 22 and a treated water tank 24 and is generally configured. The terminal end of the drain pipe 22 reaches the treated water tank 24 so that the treated water after filtration is stored in the treated water tank 24.

  The treated water tank 24 is divided into a water tank 24 a and a water tank 24 b by dividing the inside by a partition plate 25. The end of the drainage pipe 22 is piped to guide the treated water to the water tank 24a. When the water tank 24a reaches a predetermined amount of water, the treated water overflows from the water tank 24a and starts to be stored in the water tank 24b. It has become.

  The treated water stored in the water tank 24a is then led to a subsequent processing apparatus (not shown) for use in various applications. The treated water stored in the water tank 24b is for use as backwash water for backwashing. This backwash water is returned again to the filtration unit 2 from the water tank 24b by the backwash supply pipe 26 and the backwash pump 28 (backwashing means). A sterilizing agent tank 30 and a sterilizing agent pump 32 are connected to the backwashing supply pipe 26 so that the sterilizing agent can be added to the backwashing water.

  At the time of backwashing, air can be supplied into the filtration tank 14 by the washing blower 34. Thereby, stirring efficiency can be improved and deposits, deposits, and the like on the filter medium 18 can be effectively removed.

  Next, the operation of this filtration system will be described.

  First, the raw water is filtered. At this time, the valves V1 and V3 are opened, and the valves V2 and V4 are closed. Raw water is sucked up from the raw water tank 4 by the raw water pump 5 and sent to the filtration tank 14. The flow rate of the raw water is adjusted by the control means controlling the operation of the raw water pump 5 based on the measurement result of the flow meter 6. Here, the bactericide adding means 8 does not add a bactericide to the raw water. When filtered by the filter medium 18 in the filtration tank 14, the treated water is stored in the water tank 24 a through the drain pipe 22. The treated water stored in the water tank 24a is led to a subsequent processing apparatus and used for various purposes. Since the sterilizing agent adding means 8 does not add the sterilizing agent, the use range of the treated water is not limited.

  If filtration is continued, sediment of suspended substances, microorganism-derived deposits, and the like gradually start to occur in the filter medium 18, and the filtration resistance increases and the filtration efficiency decreases. Then, when the treated water in the water tank 24a reaches a predetermined amount and overflows and the treated water starts to be stored in the water tank 24b, the bactericide pump 8b adds the bactericide inside the bactericide tank 8a to the raw water. At this time, it is desirable from the viewpoint of cleaning efficiency to add a disinfectant so that the concentration in the raw water is 1 mg / L to 50 mg / L.

  The raw water containing the bactericide reaches the filtration tank 14, passes through the filter medium 18, and reaches the water tank 24 b from the drain pipe 22. Since the raw water contains a bactericidal agent, microorganisms in the filter medium 18 are sterilized, and microorganism-derived deposits and the like are reduced. Since the disinfectant and the filter medium 18 are brought into contact with each other even during raw water filtration, the contact time between them can be increased. In addition, since the treated water after filtration containing the bactericidal agent is stored in the water tank 24b instead of the water tank 24a, the bactericidal agent is not mixed into the treated water stored in the water tank 24a.

  In the present embodiment, when the treated water in the water tank 24a reaches a predetermined amount of water, the treated water overflows into the water tank 24b, and the addition of the bactericide is started at that timing. However, of course, the filtration resistance of the filter medium 18 is measured, and when the filtration resistance reaches a certain level or more, it is determined that the filter medium 18 should be washed, and the treated water is switched to be stored in the water tank 24b by a drainage switching means (not shown). You may add a disinfectant to.

  When a certain amount of treated water is stored in the water tank 24b, a physical (that is, normal) backwash process is started. At this time, it is desirable to start the backwashing process after elapse of a predetermined time, for example, 4 to 5 minutes after the filtration process is stopped. Thereby, the contact time between the sterilizing agent and the filter medium 18 can be ensured for a longer time, and the effect of removing deposits and the like is further improved.

  In the backwash process, the valves V1 and V3 are closed and the valves V2 and V4 are opened. The treated water (backwash water) is pumped from the water tank 24 b by the backwash pump 28 and sent to the filtration tank 14. At this time, backwash water is supplied from the downstream side to the upstream side of the filter medium 18 (that is, in the direction opposite to the filtration direction). Furthermore, in order to enhance the stirring effect, the cleaning blower 34 is operated to send air into the filtration tank 14. Thereby, the suspended substances deposited on the filter medium 18 are peeled off from the filter medium 18 and discharged through the backwash water drain pipe 10. In addition, since the bactericide is added to the backwash water, the effect of removing microorganism-derived deposits, other organic substances, metals, and the like attached to the filter medium 18 can also be obtained.

  The chlorine concentration meter 12 measures the chlorine concentration in the waste water after backwashing. If the chlorine concentration remains at 0.5 mg / L or more, there is no problem, but if it is less than that, it is judged that the amount of added disinfectant is insufficient with respect to the amount of deposits to be removed. To do. Then, based on the measurement result, the control means drives the sterilizing agent pump 32 to further add the sterilizing agent from the sterilizing agent tank 30 to the backwash water. Of course, the addition of the sterilizing agent by the sterilizing agent pump 32 may be performed by a certain amount.

  As mentioned above, although preferable embodiment of this invention was described, this invention is not limited to these, A various deformation | transformation and change are possible within the range of the summary.

  A comparative experiment was performed under the following three conditions using a small experimental apparatus. First, in the case of the first condition, chlorine (disinfectant) was added only to the backwash water to perform backwash (conventional method). In the case of the second condition, a certain amount (10 mg / L) of sodium hypochlorite is added to the raw water used as the backwash water, followed by filtration. In contrast, backwashing was performed by adding sodium hypochlorite so that the residual chlorine concentration in the backwash wastewater was 0.5 to 1.0 mg / L (Invention (1) No pause). In the case of the third condition, filtration and backwashing were all carried out under the same conditions as in the second condition except that backwashing was started after a rest time of 5 minutes after filtration (Invention (2) with rest). And the time-dependent change of initial filtration resistance in these cases was investigated.

  Secondary raw water (water after biological treatment and precipitation treatment) was used as raw water, and the filtration rate was LV = 1000 m / day. In the conventional method, the backwashing was started when the filtration resistance reached 1,000 mmaq. On the other hand, in the inventions (1) and (2), when the filtration resistance reaches 950 mmaq, sodium hypochlorite is added to the raw water so as to be 10 mg / L, and after the backwash water is filtered, the reverse is performed. Washing started.

  In the invention (2) provided with a rest time, when the filtration resistance reaches 950 mm, sodium hypochlorite is added to the raw water so as to be 10 mg / L, and after the backwash water amount is filtered, the rest time = An immersion time of 5 minutes was provided, and then backwashing was started. The conditions for backwashing are: water and air simultaneous backwashing is performed for 4 minutes at a water flow rate LV = 100 m / h and an air flow rate LV = 400 m / h, and then water-only water backwashing is performed at a water flow rate LV = 100 m. / H for 2 minutes.

  The long fiber filtration system used in the experiment of the conventional method is the same as that shown in FIG. 3, and the long fiber filtration system used in the experiments of the inventions (1) and (2) is the one shown in FIG. A summary of the experimental results is shown in FIG.

  When the filter medium is new and the filtration speed is LV = 1000 m / day, the initial filtration resistance (also referred to as filtration resistance) is 0 mm, and the initial filtration resistance (the filtration resistance at the time when filtration is started after backwashing) .) Reached 300 mmaq, and chemical cleaning with high concentration of chlorine was performed. As shown in FIG. 3, in the conventional method, the number of times of chemical cleaning was 3 times during the operation days of 240 days, 2 times in the case of the invention (1), and 1 time in the case of the invention (2).

  Chemical cleaning with high-concentration chlorine is performed according to the following procedure. (1) Stop the filtration device after backwashing. (2) Sodium hypochlorite is introduced from the upper part of the filtration tank 14 so that the effective chlorine concentration is 500 mg / L. (3) Air cleaning is performed for 30 seconds at a flow rate of LV = 400 m / h. (4) After leaving for 2 hours, drain by drain. (5) Perform backwashing. Backwashing consists of a 4 minute wash with water and air followed by a 2 minute wash with only water.

It is a block diagram which shows schematic structure of the filtration system using the washing | cleaning method of the filter medium which concerns on embodiment of this invention. It is a graph which shows the experimental result of the Example of this invention. It is a block diagram which shows schematic structure of the conventional filtration system.

Explanation of symbols

S: Filtration system V1, V2, V3, V4: Valve 1: Raw water supply part 1a: Raw water piping 2: Filtration part 3: Drainage part 4: Raw water tank 5: Raw water pump 6: Flow meter 8: Disinfectant addition means 8a, 30: Disinfectant tank 8b, 32: Disinfectant pump 10: Backwash water drain pipe 12: Chlorine concentration meter 14: Filtration tank 16: Strainer 18: Filter medium 20: Level switch 22: Drain pipe 24: Treated water tanks 24a, 24b: Water tank 25: Partition plate 26: Backwash supply pipe (part of backwash means)
28: Backwash pump (part of backwash means)
34: Cleaning blower

Claims (7)

A washing method for washing the filter medium by passing a part of the filtration target after filtration with respect to the filter medium in a direction opposite to the filtration direction,
It has the process of adding a disinfectant | microbicide before filtration only with respect to the filtration object used for the said washing | cleaning, The washing | cleaning method of the filter medium characterized by the above-mentioned.   The method for cleaning a filter medium according to claim 1, wherein the filter medium is a long fiber filter medium.   The method for cleaning a filter medium according to claim 1, wherein the bactericide is a chlorine agent.   The method for cleaning a filter medium according to claim 3, wherein, in the adding step, the chlorine agent is added so as to have a chlorine concentration of 1 mg / L or more and 50 mg / L or less with respect to the object to be filtered. Detecting the concentration of the bactericide to be filtered after the washing;
The method for cleaning a filter medium according to claim 1, further comprising a step of controlling an addition amount of the bactericide so that the detection result is 0.5 mg / L or more.   The method for washing a filter medium according to claim 1, further comprising a step of passing the filtration object in a direction opposite to the filtration direction after a predetermined time has elapsed after the filtration of the filtration object used for the washing is completed. Backwashing means for passing a part of the filtration target after filtration with respect to the filter medium in a direction opposite to the filtration direction;
A filtration system comprising: a bactericidal agent addition means for adding a bactericidal agent before filtration only to a filtration target used for the backwashing.

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