JPH1133364A - Back washing of hollow fiber membrane filter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make a special back washing circuit unnecessary by causing tap water to flow in a direction opposite to a filtration direction by using tap water pressure within a cake filtration range in a waste water filtration by a hollow fiber membrane filter. SOLUTION: A large number of hollow fiber membranes 2 curved in a loop and having both ends bundled and fixed at one point are installed in a filter 1. During filtration operation, solenoid valves 5, 8 are opened and valves 6, 7 are closed and waste water is fed from a pump 3 to the filter 1 so as to extract a filtrate through the solenoid valve 8 outside by effecting filtration from an outer side of the hollow fiber membranes 2 to an inner side. If filtration speed decreases or filtration pressure rises owing to accumulation of filtered bacteria and turbidity substances in the waste water on an outer face of the hollow fiber membrane 2, the solenoid valves 6, 7 are opened and the valves 5, 8 are closed so as to feed tap water from the valve 7 to the filter 1 and the tap water is caused to flow in a reversed direction from the inner side of the hollow fiber membrane 2 to the outer side, and substances blocking the outer face of the fiber membrane 2 is separated and discharged outside via the valve 6. A special back washing circuit is not required and a facility can be made simple and economical.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a backwashing method for restoring the filtration performance when filtering wastewater such as industrial wastewater, domestic wastewater, and these activated sludge treatment liquids with a filter comprising a hollow fiber membrane. More particularly, the present invention relates to a simple backwashing method using tap water as it is as a backwashing means.

[0002]

2. Description of the Related Art Backwashing of hollow fiber membranes is a well-known technique. Examples of the backwashing liquid include clarification free of clogging substances of various hollow fiber membranes such as a filtrate, a liquid containing a drug, and air. Fluids have been used.

In order to effectively recover the filtration performance,
Usually, it is necessary to flow the backwash fluid at a speed higher than the filtration speed, and a fluid circuit including a dedicated pump or the like is required to flow the backwash fluid at a high speed from the direction opposite to the filtration direction to the hollow fiber membrane. Was.

[0004] However, in applications where it is not necessary to use a clear fluid as the backwash fluid, it is not economical to use a fluid circuit including a pump or the like for the backwash or a special fluid.

[0005]

When the main purpose of filtration is not necessarily required to be higher than that of tap water, such as sterilization and removal of turbidity components in wastewater, etc. No special clear backwash is required. On the other hand, tap water itself has a high pressure, does not contain viable bacteria, and is a liquid having no water quality problems in normal use.

In view of the above situation, the present invention seeks to solve the problem by simply backwashing a hollow fiber membrane filter using tap water as it is as a means for backwashing a hollow fiber membrane filter used for drainage filtration. The point is to provide a method.

[0007]

In the case of microfiltration or ultrafiltration used for such a purpose, a pressure of about 200 kPa or less is generally used as a filtration pressure, and usually a pressure of 200 kPa or more is maintained. It is possible to use the tap water as it is as the backwash liquid.

[0008] That is, the present invention provides a method for filtering drainage water using a hollow fiber membrane filter, wherein tap water is supplied from a direction opposite to the filtration direction using tap water pressure in the range of cake filtration. Method for backwashing the membrane filter ". In this case, it is preferable to flow tap water from the inside to the outside of the hollow fiber membrane at the time of back washing, and the pore diameter of the hollow fiber membrane is 0.0
It is preferably from 1 to 0.5 μm.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, embodiments of the present invention will be described in detail and concretely with reference to the accompanying drawings. FIG. 1 is a schematic view of a typical embodiment of the present invention, wherein reference numeral 1 denotes a filter, 2 denotes a hollow fiber membrane, 3 denotes a pump, 4 denotes a pressure gauge, 5 to 8
Indicates electromagnetic open / close valves.

The filter 1 is provided with a large number of hollow fiber membranes 2 which are folded in a loop shape and both ends of which are converged and fixed at a location.

During the filtration operation, the electromagnetic switching valves 5 to 8
The valves 5 and 8 are opened and the valves 6 and 7 are opened and closed so that the valves 6 and 7 are closed. Drainage is sent from the pump 3 to the filter 1. It is taken out to the outside.

When bacteria and turbid components in the filtered waste water accumulate on the outer surface of the hollow fiber membrane 2, the filtration speed gradually decreases and the filtration pressure increases. For example, in an operation of filtering at a constant filtration speed (constant speed filtration), the pressure gradually increases. In many cases, the filtration pressure increases in proportion to the filtration time at the beginning of filtration, and then rapidly rises out of the proportional relationship.

The closing mechanism of the hollow fiber membrane 2 is considered to shift from cake filtration in which the blocking substance accumulates on the membrane surface to standard blocking or intermediate blocking filtration in which the blocking substance enters the inside of the membrane during this time. Can be As can be readily imagined, it is difficult to remove the occluding substance that has entered the interior of the membrane by backwashing. Therefore, backwashing should be performed while the filtration mechanism is in the range of cake filtration.

The open / close states of the electromagnetic open / close valves 5 to 8 at the time of back washing are such that the valves 6 and 7 are open and the valves 5 and 8 are closed. Tap water, which is a backwash liquid, is sent from the valve 7 to the filter 1. Then, the tap water accumulates on the outer surface of the hollow fiber membrane 2 while the tap water having a pressure higher than the filtration pressure flows from the inside to the outside of the hollow fiber membrane 2 in a direction opposite to the filtration direction more rapidly than the filtration speed. The clogging substances such as bacteria and turbid components are peeled off and released outside through the valve 6.

When a hollow fiber membrane having pores for removing bacteria and turbid components or smaller is backwashed with tap water, scale components (mainly hydroxides such as Si, Al, Ca, Fe, etc.) in the tap water are removed. ) And dead bacteria are also trapped in the hollow fiber membrane, so that it is necessary to consider that these may block the hollow fiber membrane simultaneously with the backwash. In other words, backwashing with tap water must be included in the category of cake filtration.

The pore size of the hollow fiber membrane 2 that can be used in the present invention is:
It is desirable that the thickness be about 0.01 μm or more so that the filtration operation can be performed at a pressure not exceeding the tap water pressure. In addition, since the main purpose of the filtration of the present invention is to remove bacteria and remove turbid components, it is preferable that the thickness is about 0.5 μm or less.

When the same amount is filtered, the accumulated amount of the occluding substance on the membrane surface is inversely proportional to the membrane area. Therefore, the filtration surface should be on the outer surface side of the hollow fiber membrane having a large surface area.

The inner diameter of the hollow fiber membrane 2 is about 300 μm so that tap water can effectively flow through the entire hollow fiber membrane during backwashing.
That's it. If the inner diameter of the hollow fiber membrane 2 is smaller than 300 μm, the pressure loss increases, so that most of the backwash liquid flows out of the hollow fiber membrane near the entrance, and only a small amount flows away from the entrance, and the backwash effect is reduced. Become scarce.

For the same reason, the length of the hollow fiber membrane 2 must be rationally set with respect to the inner diameter.
It should be about 70 cm or less for μm and about 15 cm or less for 300 μm.

The present invention can be applied to any hollow fiber membrane filter satisfying these conditions.

When filtration is started again after backwashing, the initial filtrate contains the substance in tap water captured by the hollow fiber membrane at the time of backwashing. Therefore, the present invention is used for applications in which these substances do not pose a particular problem. Such a typical use is filtration of natural water or filtration of wastewater, and the main purpose of the filtrate is to be sterile or contain no turbid components. More specifically, when filtering river or lake water as pretreatment of drinking water,
This is the case where the activated sludge treatment liquid of industrial wastewater or domestic wastewater is filtered to be discharged to sewage or the like or reused as washing water or cooling water instead of drinking. In addition, as a special example, the present invention can be applied to sterilization filtration of so-called 24-hour bath water.

Next, an example of circulating and filtering bath water using the filter 1 will be described with reference to FIGS. The filter 1 is in the form of a cartridge as shown in FIG.
Used as 1.

The circulating filtration apparatus for bath water is constructed as shown in FIG. 2, wherein A denotes a bathtub, B denotes a forced circulation means, C denotes a purification means, and D denotes a heating means. The forced circulation means B includes a circulation pump (the pump 3
Bathtub A
The hot water is sucked from the bath, the water to be sucked is sent to the purifying means C and the heating means D, and discharged into the bathtub A again. Further, the purifying means C is provided with bath water of about 40 ° C. (water to be treated) sucked from the bathtub A by the forced circulation means B.
The purifying means C is a filter for purifying and purifying the hot water in the bathtub A at all times. The hollow fiber membrane type filter C1 which can be backwashed by an external pressure filtration method is used as a main component of the purifying means C. Further, the heating means D heats the water to be treated which is circulated so as to maintain the bath water in the bathtub A at a predetermined temperature, and directly or indirectly uses a ceramic heater or a double sheathed heater. The temperature of the bath water is maintained at a set temperature within a range of about 35 to 45 ° C. by a heating method.

A specific system configuration of this circulating filtration apparatus is as follows. A strainer E is provided at a suction port of bath water, and a hollow fiber membrane type filter is provided as a purifying means C downstream of a forced circulating means B via a normal pre-filter F. C1, biological filtering device C2 and sterilizing device C3 are arranged in series, and heating means D
Is arranged. This biological filtration device C2 constitutes a filtration tank using a filtration material made of, for example, porous ceramics or natural stones such as barley stone, Taiseki stone and activated stone, and organic matter is removed by bacteria fixed on the surface of the filtration material. And decompose odors. In addition, an ultraviolet (UV) lamp or an ozone generator can be used as the sterilizing device C3, and the water to be treated sucked and circulated from the bath is irradiated with ultraviolet light, or sterilized by mixing ozone. Things.

As shown in FIG. 3, the hollow fiber membrane type filter C1 has a number of hollow fiber membranes 10 loaded in a synthetic resin storage container 11. This storage container 11
Both are porous cylindrical containers 12 made of heat-resistant synthetic resin,
With the header 13 and the bottom 14, the porous cylindrical container 12
The header 13 and the bottom 14 are formed at the upper and lower ends by bonding, fusion or ultrasonic fusion. The hollow fiber membrane 10 is formed by folding back into a U-shape at the center, and the tip is potted with a thermosetting resin together with the storage container 11. Storage container 1 in contact with this potting material 15
A wedge-shaped projection 16 is formed on the inner peripheral portion of the end portion 1 to supplement the adhesive force. The wedge-shaped protrusion 16 of this embodiment has a shape whose inner edge is expanded so as to have a tapered surface in the vertical direction. The bonding surface of the wedge-shaped projections 16 is subjected to corona discharge treatment to have a critical surface tension of 40 dyn /
cm or more to increase the adhesive strength with the potting material 15.

The water to be treated introduced into the inside through the through hole 17 formed around the storage container 11 and the introduction hole 18 formed in the bottom is filtered through the hollow fiber membrane 10 and the filtrate Spills from the end of the hollow fiber membrane 10 opening into the potting material 15 into the space formed by the potting material 15 and the header 13, and is discharged to the outside through the flow passage 19 provided in the header 13. Because Here, the linear portion 10 a of the hollow fiber membrane 10 is close to the small through hole 17 of the storage container 11, and the loop portion 10 b of the hollow fiber membrane 10 is close to the large introduction hole 18 of the bottom 14. The header 13 has an opening having a flow passage 19 formed in a cylindrical shape, and a single or a plurality of O-rings 20 are mounted around the opening.
Is sealed by the O-ring 20.

In the present embodiment, the housing 21 has an upper lid 23 fitted to the upper end of the outer cylinder 22 with an O-ring 24 interposed therebetween, and a ring-shaped fastening screwed to the upper end of the outer cylinder 22. It has a structure in which the upper lid 23 is detachably attached with the tool 25. An inflow port 27 having a threaded portion on the outer periphery is provided at the center of the bottom surface 26 of the outer cylinder 22 so as to protrude therefrom.
The inlet 28 is connected to the inlet 28. Further, inside the upper lid 23, a cylindrical portion 30 for fitting the mouth of the header 13 is formed, and the hollow fiber membrane type filter C1 is formed.
When the O-ring 20 is accommodated in the housing 21, the O-ring 20 comes into close contact. A plurality of ribs 31,... Are provided vertically below the inside of the outer cylinder 22 to hold the lower portion of the storage container 11 without rattling. An outlet 32 protrudes from the upper end of the upper lid 23, and one end of an outlet pipe 34 is connected to the outlet 32 by a base 33.

[0028]

According to the method for backwashing a hollow fiber membrane filter of the present invention as described above, tap water is used as a backwash means, so that a special backwash circuit including a backwash pump or the like is not required.
Not only is the equipment simple, but it is also economical, so it can be used very effectively for applications that do not require water quality higher than that of tap water as the filtrate.

[Brief description of the drawings]

FIG. 1 is a schematic view showing a method for backwashing a hollow fiber membrane filter with tap water according to the present invention.

FIG. 2 is a simplified arrangement diagram of a bath hot water circulating filtration device.

FIG. 3 is a sectional view showing a specific example of a hollow fiber membrane type filter.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Filter 2 Hollow fiber membrane 3 Pump 4 Pressure gauge 5-8 Electromagnetic switching valve

Claims (3)

[Claims] In the filtration of wastewater by a hollow fiber membrane filter, tap water is supplied from a direction opposite to a filtration direction by utilizing tap water in the range of cake filtration. Washing method. 2. The method for backwashing a hollow fiber membrane filter according to claim 1, wherein tap water is supplied from the inside to the outside of the hollow fiber membrane. 3. The hollow fiber membrane has a pore size of 0.01 to 0.5 μm.
The method for back washing a hollow fiber membrane filter according to claim 1, wherein