JP2006055852A - Cleaning method and equipment for filter element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a cleaning method and equipment for a filter element of a solid-liquid separator of biologically treated waste water which makes it possible to stably obtain a filter Flux nearly similar to an initial value for a long period of time in cleaning the filter element by idle cleaning in filtration using the water-permeable filter element. <P>SOLUTION: The cleaning method for the filter element is a solid-liquid separation method of filtering the liquid mixed with the activated sludge from a bio-reaction tank for aerobically treating raw water by the activated sludge by forming a dynamic filter layer of sludge on the surface of the filter element in a filtration separating tank installed with the water-permeable filter element to obtain filtrate and returning the waste water of back washing to the bio-reaction tank after completely returning the liquid mixed with the activated sludge to the bio-reaction tank in washing the filter element or at the point of time the filtration separating tank is filled with the filtrate. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to sewage treatment, and particularly relates to washing of water-permeable filter used for solid-liquid separation of activated sludge and concentration of excess sludge, and is used for treatment of organic industrial wastewater and domestic wastewater. The present invention relates to a method and apparatus for cleaning a water-permeable filter.

  Conventionally, in water treatment with activated sludge, solid sludge separation of activated sludge has to be performed in order to obtain treated water. Normally, a method is used in which activated sludge is introduced into a sedimentation basin, the sludge is sedimented by gravity sedimentation, and the supernatant is discharged from the sedimentation basin as treated water. In this case, there is a need for a sedimentation basin that has a sufficiently large sedimentation area to settle the activated sludge and can secure a sufficiently long residence time, which is a factor in increasing the size of the processing apparatus and increasing the installation volume. Yes. Moreover, when activated sludge deteriorates sedimentation property, such as bulking, sludge flows out from a sedimentation basin and causes deterioration of treated water.

In recent years, a method of performing solid-liquid separation of activated sludge by membrane separation instead of a sedimentation basin has been used. In this case, a microfiltration membrane or an ultrafiltration membrane is generally used as the solid-liquid separation membrane.
At that time, suction or pressurization by a pump is required as a filtration separation means, and since it is usually performed at a pressure of several tens of kPa to several hundred kPa, the power of the pump is large and the running cost is increased. In addition, clear treated water having no SS is obtained by membrane separation, while permeation flux is low, and it is necessary to periodically wash the medicine in order to prevent membrane contamination.

  Recently, as a method of solid-liquid separation of activated sludge by membrane separation, a method has been proposed in which a filter body made of a breathable sheet such as a nonwoven fabric is immersed in an aeration tank to obtain filtered water with a low head pressure. In this method, clear filtered water is obtained by filtration separation means in which the flow of the activated sludge mixed liquid is set so that a sludge dynamic filtration layer is formed on the surface of the filter body. In this method, as a means for washing the filter body when the filtration flux is lowered, aeration is performed from an air diffuser installed at the lower part of the filter body, so that a sludge dynamic filtration layer formed on the surface of the filter body can be easily obtained. Since it exfoliates, it is said that a stable filtered flux is obtained.

However, in the method in which the filter body is immersed in an aeration tank and washing is performed by washing with air only when the filtration flux is lowered, it is recognized that the filtration flux gradually decreases. That is, with the increase in the number of treatment days, the filtration flux immediately after the flushing gradually decreased compared to the initial value. In addition, the recovery rate indicating the ratio with respect to the initial value is similarly decreased, and the degree of the decrease is increased as the number of times of washing is increased. When the filter is immersed in an aeration tank, when the sludge dynamic filtration layer formed on the filter surface is not completely removed by air washing, fine sludge flocs adhere to the filter surface and accompany long-term filtration. The surface of the filter body is clogged by the refinement of the attached sludge. In addition, in the initial filtration from immediately after the washing to the formation of the dynamic filtration layer, the sludge that has passed through the surface of the filter body is accumulated inside and gradually concentrated over time, so that the filtration resistance increases and the filtration flux Cause a significant decrease in
As a result, a good cleaning effect cannot be obtained by empty washing, and the drop in the filtration flux increases with the elapsed time, making it difficult to obtain a stable treatment.

  The present invention has been made in view of the above-described conventional problems, and the inside of a water-permeable filter body is back-washed with water to obtain a filtration flux almost the same as the initial value stably over a long period of time. In addition, an object of the present invention is to obtain a method and an apparatus for cleaning a filter body of a solid-liquid separation apparatus for biologically treated sewage that can obtain stable water quality.

The present inventors have made various studies on methods for always forming a uniform dynamic filtration layer on the surface of the filter body regardless of the lapse of processing time due to the above-mentioned problems.
And if the inside of the filter body is back-washed with filtered water from the treatment water tank or chemical cleaning liquid, the surface of the filter body and fine flocs inside the body that could not be completely removed by normal air washing, or biological slums are easy. It was confirmed that it was possible to wash it off.
The present invention has been made based on such knowledge and has the following configuration.

(1) The activated sludge mixed liquid from the biological reaction tank that performs the treatment with activated sludge aerobically by flowing raw water is supplied to the filtration separation tank in which the water-permeable filter is installed, and the filtration separation tank is used for the filtration. In the solid-liquid separation method of the activated sludge mixed liquid, the sludge dynamic filtration layer is formed on the body surface to obtain filtered water by filtration, and the filtered activated sludge mixed liquid is returned to the biological reaction tank. After the activated sludge mixture in the filtration / separation tank is completely returned to the biological reaction tank, or when the filtration / separation tank is filled with filtered water, the inside of the filter body is back-washed with water, A method for washing a filter body, which is returned to a biological reaction tank.
(2) Water backwashing into the filter body is characterized in that filtered water or chemical cleaning liquid is allowed to flow into the backwash line at the top of the filter body, and backwash drainage is discharged from the water intake line at the bottom of the filter body. 1) The washing | cleaning method of the filter body of description.

(3) The activated sludge mixed liquid is supplied from a biological reaction tank in which raw water is introduced and aerobically treated with activated sludge, and has a water-permeable filter body. In a solid-liquid separation device for an activated sludge mixed liquid using a filtration separation tank that forms a sludge dynamic filtration layer to obtain filtered water, below the water-permeable filter body that has formed a dynamic filtration layer immersed in the filtration separation tank An air-washing air diffuser for air-washing and piping for returning the activated sludge mixed liquid in the filtration / separation tank to the biological reaction tank, or piping from the treated water tank to fill the filtration / separation tank with filtered water After the activated sludge mixed liquid in the filtration separation tank is completely returned to the biological reaction tank or when the filtration separation tank is filled with filtered water, the treated water is introduced into the filter body from the treatment water tank. With backwash water line connected to send Cleaning device of the filtering body and having a backwash unit comprising a backwash drain line for discharging the backwash waste water from the interior of said filtration body.
(4) The backwash unit allows filtered water or chemical cleaning liquid to flow from the backwash water line at the top of the filter support part, and discharges backwash drainage or drainage from the bottom backwash drainage line. The apparatus for washing a filter body according to (3), wherein the filter body is back-washed from a water-permeable spacer provided in contact with the inside of the filter body.

  According to the present invention, in a solid-liquid separation method of a sludge mixed liquid that uses a water-permeable filter and forms a sludge dynamic filtration layer on the surface of the filter to obtain filtrate, a filter module that is immersed in a filtration separation tank. On the other hand, after all the sludge mixed liquid in the filtration separation tank has been returned to the biological reaction tank on a regular basis, using the filtered water of the treated water tank, if the water is back-washed inside the filter module, it adheres to the filter surface. Fine sludge particles can be easily dropped, and sludge accumulated in the filter body can be discharged to the outside by backwashing. As a result, both the surface resistance due to the sludge fine particle blockage on the surface of the filter body and the internal resistance due to the accumulation of sludge inside the filter body can be reduced, and the filtration flux recovers to almost the initial value.

  In water backwashing, filtered water is injected into the backwash line at the top of the filter body, drained backwash water is discharged from the intake line at the bottom, and returned to the biological reaction tank to facilitate sedimentation of the sludge inside the filter body Since the sludge can be discharged and the sludge is not deposited again inside the filter body, a stable filtration flux can be obtained at all times. Further, when the chemical cleaning liquid is used as the backwashing water during the water backwashing, even if the biological slam adheres to the surface of the filter body, it can be easily washed off. That is, it is possible to suppress the decrease in the filtration flux due to the biological slam adhesion accompanying long-term filtration.

According to the present invention, in a solid-liquid separation method of a sludge mixed liquid that uses a water-permeable filter body (hereinafter also simply referred to as “filter body”) and forms a sludge dynamic filtration layer on the surface of the filter body to obtain filtered water, Treat the water-permeable filter module immersed in the filtration / separation tank after returning the sludge mixture in the filtration / separation tank to the biological reaction tank or filling the filtration / separation tank with filtered water. By using the filtered water in the aquarium and backwashing the inside of the filter body module, fine sludge particles adhering to the surface of the filter body can be easily removed, and sludge accumulated inside the filter body can be removed by backwashing. It can be discharged to the outside.
As a result, both the surface resistance due to sludge fine particle blockage on the filter body surface and the internal resistance due to accumulation of sludge inside the filter body can be reduced, and the filtration flux is almost restored to the initial value.

In addition, “water backwashing” as used herein refers to the filtration that passes from the surface of the water-permeable filter body to the inside of the filter body, and supplies the wash water to one end inside the filter body to allow the inside of the filter body to be washed. An operation for discharging washing wastewater from the other end inside the filter body.
In the present invention, there are the following two points for the purpose of backwashing the inside of the filter body.
(B) The cleaning water is allowed to pass from the inside of the filter body through the surface of the filter body, and the fine sludge floc adhering to the inside of the surface is peeled off. (B) Discharge sludge that has entered the filter body to the outside together with cleaning water before it accumulates inside. In this latter case, it is difficult and unreasonable to pass the invading sludge from the inside through the surface of the filter body, and it is unreasonable. It was.

In the present invention, the following two cases are set as the state of the filtration separation tank when performing water backwashing.
1) When the sludge mixture in the filtration separation tank is completely returned to the biological reaction tank (time point).
2) When the filtration separation tank is filled with filtered water.
In the case of this case 1), there is no residue of filtered water inside the filter body, and it is almost hollow, so it is not subject to the resistance of water that occurs when the filter separation tank is filled with water. The flow rate of backwash water flowing through the filter is large, and the sludge accumulated inside the filter body and the sludge adhering to the inner surface of the filter body can be efficiently separated and completely discharged to the outside, that is, the biological reaction tank. . In this case, if the amount of backwash water is about several times the volume of the filtrate water chamber inside the filter body, a good cleaning effect can be obtained, so that it can be handled with a small amount of backwash water.
In case 2), the filtration separation tank is filled with water, so that fine sludge flocs adhering to the surface of the filter body are dissolved, and the adhesive force on the surface of the filter body is weakened. At this time, if backwash water is supplied to the inside of the filter body, sludge adhering to the surface of the filter body can be easily peeled off and discharged into the biological reaction tank together with the backwash waste water. The sludge accumulated in the filter body is also diluted by the infiltration of the filtration separation tank into the filter body, and the sludge accumulated by the backwash water supply is easily discharged into the biological reaction tank along with the backwash drainage. Can do.

Water backwashing injects filtered water into the backwash line at the top of the filter body, discharges backwash wastewater from the bottom water intake line, and returns it to the biological reaction tank, making it easy to remove accumulated sludge inside the filter body. Since the sludge can be discharged and the sludge is not deposited again in the filter body, a stable filtration flux can be obtained at all times.
Further, when the chemical cleaning liquid is used as the backwash water during the water backwashing, even if the biological slam adheres to the surface of the filter body, it can be easily washed off. The fall of the filtration flux by the biological slam adhesion accompanying long-term filtration can be suppressed.
As the chemical cleaning solution, any of hypochlorous acid aqueous solution, alkaline aqueous solution, acid aqueous solution, ozone aqueous solution, hydrogen peroxide aqueous solution and the like can be used. The selection of chemical cleaning liquid and the frequency of cleaning are determined from the sludge to be treated and the state of contamination, and it is preferable to carry out the cleaning once every few days to several months.

If the water-permeable filter is a sheet-like body having a water-permeable and pressure-resistant porous surface, the same effect can be obtained by using any of nonwoven fabric, woven fabric, metal net, and the like. And as a filter body shape, any of a plane type, a cylindrical type, and a hollow type can be used, and a plurality can be bundled and used as a module filter body.
Moreover, as a filter body module structure, it is desirable for the support plate holding a water-permeable filter body to be as hollow as possible. There is a backwash water inflow pipe through which the backwash water can be injected into the support plate at the top of the filter module, and the intake pipe for obtaining filtered water is installed at the bottom of the filter module, and the discharge line for backwash drainage is It is desirable to have a structure that is connected to a water intake pipe and can return backwash wastewater to the biological treatment tank by switching bubbles during backwashing.
As the target sludge that can be filtered and separated by the water-permeable filter body, any of activated sludge, agglomerated sludge, initial settling sludge, and the like are possible. It can also be used for solid-liquid separation of drainage with high SS and river water.

The present invention will be described more specifically with reference to the drawings.
FIG. 1 is a flow sheet showing an example of a treatment method according to the present invention for a group groundwater.
As shown in FIG. 1, inflow raw water 1 flows into a biological reaction tank 2, and aerobic treatment with activated sludge is performed by supplying air from the aeration blower 4 to the aeration pipe 3 in the biological reaction tank 2. The activated sludge mixed liquid is supplied to the filtration separation tank 10 from the sludge supply pump 5. The activated sludge mixed liquid that has flowed into the filtration separation tank 10 is filtered from the water-permeable filter 11 at a head pressure ΔH, opens the filtered water intake valve 17, is discharged through the filtered water intake pipe 14, and flows into the treated water tank 15. The treated water 21 is taken out. In addition, the sludge mixed liquid after filtration is returned to the biological reaction tank 2 as the sludge circulating liquid 19.

As a washing method for the filter body 11, during the filtration body immersion, the filtration flux is usually stabilized by air washing. At this time, it is carried out by sending air from the air washing blower 9 to the air washing air diffuser 8 below the filter body once every several hours.
Water backwashing using filtered water is performed periodically at a frequency of once every several weeks. At the time of water backwashing, the mixed liquid sludge in the filtration tank 10 is temporarily returned to the biological reaction tank 2 from the sludge mixed liquid pump 5 by switching between the sludge mixed liquid supply valve 6 and the sludge mixed liquid transfer valve 7, and then reversely mixed. The washing pump 12 is activated, and the treated water (filtered water) 21 in the treated water tank 15 is supplied into the filter body 11 through the backwash line 13 above the filter body 11.
The backwash drainage is discharged from the intake pipe below the filter body 11, the backwash drainage return valve 16 is opened, and returned to the biological reaction tank 2 through the backwash drainage return line 18. In this case, the filtered water intake valve 17 is closed. In addition, at the time of this water backwashing, the backwash waste water which comes out to the surface from the inside of the filter body 11 and is discharged | emitted by the filtration separation tank 10 is always returned to the biological reaction tank 2 from the sludge liquid mixture pump 5. .
If the sludge mixed liquid of the biological reaction tank 2 is again supplied to the filtration separation tank 10 after the backwashing operation is completed, the filtrate from the water-permeable filter 11 can be continuously obtained through the filtered water intake valve 17.

  In FIG. 2, 10 is a filtration separation tank, 13 is a backwash water line, 22 is a backwash drainage line, and the cylindrical filter body (woven fabric) 11 is placed on the spacer 24 of the filter support part 23. It is loosely fitted. The backwash water flows from the backwash water line 13 to the backwash drainage line 22 and flows through the spacer 24 while washing away the sludge accumulated inside the filter body (woven cloth) 11 and the sludge particles adhering to the surface, and the filter body. The sludge inside the slag flows out from the backwash drainage line 22 together with the wash sewage, and the sludge particles adhering to the surface of the filter body 11 flow out to the outside with the backwash water from the inside of the filter body 11. Flow down to the bottom.

  The present invention will be specifically described below with reference to examples. However, the present invention is not limited to this example.

Example 1
(Processing method)
About the collective groundwater, it processed by the processing method by this invention represented with the flow sheet shown in FIG.
The quality of the groundwater is as shown in Table 1.
In the biological reaction tank that treats the groundwater with activated sludge, the MLSS of activated sludge was about 3500 mg / liter. The activated sludge mixed solution exiting from the biological reaction tank was guided to the filtration / separation tank shown below to obtain treated water.
The quality of the treated water obtained in the filtration separation tank is as shown in Table 1.

(Filtration separation tank)
As the filtration separation tank, a solid-liquid separation tank having an effective area of 0.3 m ² and an effective volume of 0.6 m ³ was used. Five flat woven fabric filter bodies having an effective area of 1 m ² / sheet were immersed in the filter separation tank 10 as a filter module. The material of the woven fabric was made of polyester, having an opening of 200 mesh and a thickness of 0.09 mm. The average head pressure during filtration was about 10 cm.
Table 2 shows the processing conditions of the filtration / separation tank.
Table 3 shows the conditions for washing the filter body with air and backwashing with filtered water.

(Processing result)
FIG. 3 shows the course of the filtration flux in this example.
The MLSS of the activated sludge to be treated is about 3500 mg / liter, and the filtration flux can be maintained at 4.2 to 4.8 m / d during the treatment period of 2 months, and backwashing with filtered water once every 2 weeks. Was added to obtain a stable filtered flux. In addition, the turbidity of filtered water was around 5 degrees on average during the treatment period, and it was clear.

Comparative Example 1
Under the same operating conditions as in Example 1, the filtration treatment of the activated sludge mixture was performed without performing regular water backwashing on the inside of the filter module. The course of the average filtration flux in that case is shown in FIG.
The average filtration flux was about 4.8 m / d, which was almost the same as in Example 1 at the start of the treatment. However, after about 10 days from the start of the treatment, the filtration flux dropped rapidly. This is due to sludge fine particles adhering to the surface of the filter body and sludge accumulation inside the filter body.
As a result, even if normal empty washing was carried out once every 4 hours, recovery of the filtration flux was not obtained, and after 20 days from the start of the treatment, the filtration flux was 1.8 m / m or less of half of the initial value. d. After that, it gradually decreased to 1 m / d or less. In addition, filtration water turbidity was always 10 degrees or less, and the big difference with an Example was not recognized.

It is explanatory drawing of the solid-liquid separation apparatus of the biological treatment wastewater containing the washing | cleaning apparatus of the water-permeable filter of this invention. It is explanatory drawing of the backwash process condition of the washing | cleaning apparatus of the filter body of this invention. It is a graph which shows the relationship between the elapsed days of one Example of this invention, and average filtration Flux. It is a graph which shows the relationship between the elapsed days of the comparative example 1, and the average filtration Flux.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Inflow raw water 2 Biological reaction tank 3 Aeration pipe 4 Aeration blower 5 Sludge liquid mixture pump 6 Sludge liquid mixture supply valve 7 Sludge liquid mixture return valve 8 Air washing air diffuser 9 Air washing blower 10 Filtration separation tank 11 Water-permeable filter body 12 Backwash pump 13 Backwash line 14 Filtration water intake pipe 15 Treated water tank 16 Backwash drainage return valve 17 Filtration water intake valve 18 Backwash drainage return line 19 Sludge circulating liquid 20 Waste mud line 21 Treated water 22 Backwash drainage line 23 Filtration Body support part 24 Spacer 25 Woven cloth

Claims (4)

  The activated sludge mixed liquid from the biological reaction tank that performs the treatment with activated sludge aerobically by inflowing raw water is supplied to the filtration separation tank in which the water-permeable filter is installed, and the filtration separation tank is used for the surface of the filter body. In the solid-liquid separation method of the activated sludge mixed liquid in which the sludge dynamic filtration layer is formed and filtered to obtain filtered water, and the activated sludge mixed liquid after filtration is returned to the biological reaction tank, the filter is washed when the filter is washed. After the activated sludge mixed liquid in the separation tank is completely returned to the biological reaction tank, or when the filtered separation tank is filled with filtered water, the inside of the filter body is back-washed with water, and the backwash waste water is removed from the biological reaction tank. A method of cleaning a filter body, characterized by being returned to the factory.   The backwashing of water into the filter body is characterized in that filtered water or chemical washing liquid is allowed to flow into a backwash line at the top of the filter body, and backwash drainage is discharged from the water intake line at the bottom of the filter body. How to wash the filter.   Activated sludge mixed liquid is supplied from a biological reaction tank in which raw water is introduced and aerobically treated with activated sludge, and has a water-permeable filter, and sludge dynamics are applied to the surface of the filter during filtration by the filter. In a solid-liquid separation device for an activated sludge mixed liquid using a filtration separation tank that forms a filtration layer to obtain filtered water, it is disposed below a water-permeable filter body that forms a dynamic filtration layer immersed in the filtration separation tank. Air washing air diffuser for air washing, piping for returning the activated sludge mixed liquid in the filtration separation tank to the biological reaction tank, piping from the treated water tank for filling the filtration separation tank with filtered water, and filtration Connected to send treated water from the treated water tank to the inside of the filter body that operates after the activated sludge mixed liquid in the separation tank is completely returned to the biological reaction tank or when the filtered separation tank is filled with filtered water Backwash water line and Body cleaning device of the filtering body and having a backwash unit comprising a backwash drain line for discharging the backwash effluent from the interior of.   The backwash unit allows filtered water or chemical cleaning liquid to flow from the backwash water line at the top of the filter support part, discharges backwash wastewater or drainage from the backwash drainage line at the bottom, and makes contact with the filter body. 4. The filter cleaning apparatus according to claim 3, wherein the filter body is back-washed from the water-permeable spacer provided in the filter.

Images