JP2010179298A - Low-speed filtration apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a low-speed filtration apparatus that is excellent in biological treatment performance and can remove various hazardous substances. <P>SOLUTION: The filtration apparatus includes a filtration tank 2 and a pretreatment tank 3. The pretreatment tank 3 is equipped with an air supplying unit 4 that supplies air to raw water sent into the pretreatment tank 3. The filtration tank 2 is made of a transparent material excellent in heat resistance, cold resistance and shock proof, and includes a raw water intake 12 near its upper end that takes in the raw water sent from the pretreatment tank 3, a fine-sand layer 9 that is made of sand of a particle size of 0.08 to 0.29 mm in the filtration tank 2 and stacked so that upper layer has smaller sand, a net 10 made of stainless steel having a mesh size of about 0.1 mm to cover the top of the fine-sand layer 9 in the filtration tank 2, and a treated water outlet 13 at the bottom of the filtration tank 2. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a slow filtration device for producing drinking water and the like.

  In general, a slow filtration device and a rapid filtration device are known as filtration devices that generate water taken from rivers or underground (hereinafter referred to as “raw water”) as drinking water. In the old days, slow filtration devices with slow filtration speed compared to rapid filtration devices were the mainstream, but slow filtration devices have slow filtration speeds as described above, and the filtration sand layer is clogged when the water source is heavily contaminated. There is a problem that the filtration capacity is lowered, and further, with the increase of the population and the development of the industry, a rapid filtration apparatus having a large filtration capacity has been used. However, although the rapid filtration device has a large filtration capacity, it uses chemicals such as chlorine, so the treated water smells chemicals, and the substances contained in the water taken from the water source react with the chemicals to cause carcinogenic substances. There is a problem such as the generation of Cryptos contamination that does not work with chlorine, and there is also a problem that the filtration rate is slow, but a slow filtration device that can make safe water as drinking water It is being reviewed.

  Specifically, the slow filtration device is configured so that the water to be treated passes slowly through the filtered sand layer, and microorganisms adhering to the sand wall remove the dirt of the water to be treated. In general, sea sand, mountain sand, river sand or the like having a uniform particle size is used as the filtration sand of the slow filtration apparatus.

  By the way, there is a standard for the washing turbidity of the filtration sand, the washing turbidity should be 30 degrees or less, and the adhesion of organic impurities, germs and other contaminants should be as small as possible. Then, in this conventional slow filtration device and slow filtration method, sea sand, mountain sand, river sand is used as it is as a filtration sand layer, so that the specified washing turbidity is obtained, organic impurities, germs, and other contaminants are obtained. It took a considerable amount of time and effort to wash until it was removed.

  Therefore, organic impurities, germs and other contaminants attached to the sand used for the filtered sand layer are efficiently removed so that the water obtained through the filtered sand layer can be safely used as drinking water. An apparatus disclosed in Patent Document 1 is known as such a slow filtration apparatus.

  In the slow filtration device disclosed in Patent Document 1, a raw water supply unit is provided at the upper part of a filtered water tank having a predetermined height and diameter, and a filtered water take-out part is provided at the lower part. In the slow filtration apparatus equipped with a filtration tank made of baked sand after repeated washing with baked washing water at a predetermined temperature, the filtration tank comprises an upper first filtration layer and a lower second filtration layer. The first filtration layer is formed of baked sand having a particle size of 0.15 mm to 0.29 mm, and is configured to form a microbial membrane on the surface of the baked sand of the first filtration layer. A plurality of filter cloths are laid on the first filter layer so that they can be taken out in order from the top, and the upper first filter layer is formed of baked sand having a particle size of 0.15 mm to 0.29 mm. Protozoa that cannot be removed with chlorine (cryptos) Rijiumu, Sai cross polar, Giardia) with trapping like, dioxin hardly soluble in water, it is intended to primarily capture at the top of the first filter layer. In addition, by filtering raw water with a filtration membrane made of baked sand, a microbial membrane (slime) is formed on the surface of the sand, and not only turbidity and bacteria in the water but also harmful due to the natural purification power and decomposition action by microorganisms By removing the components of mold odor from the components, it is possible to obtain safe drinking water for the human body that greatly exceeds the standard value of the water quality test. Moreover, since large impurities can be removed in advance by the filter cloth provided on the first filter layer, clogging of the first filter layer made of baked sand having a very small particle size can be suppressed as much as possible. A plurality of filter cloths are provided, and clogged filter cloths can be taken out in order from the top, so the filter cloth can be used for a long time after being replaced once, enabling continuous operation over a long period of time. It is to become.

Japanese Patent No. 3406258

  However, recently, environmental pollution problems caused by yellow sand have been taken up as cross-border pollution. The yellow sand particles contain a lot of harmful substances such as ammonium ions and sulfate ions that may have originated from the soil, and are thought to be drowning in river water and groundwater, which are the basis of drinking water. According to the slow filtration device disclosed in Patent Document 1, most harmful substances can be removed, but volatile harmful substances such as trichlorethylene and tetrachloroethylene adhering to the yellow sand particles are aerated. It is impossible to process. This volatile toxic substance is not limited to yellow sand particles, but may be contained in the waste water from the plating factory. If it enters river water or groundwater, it cannot be processed until it reaches drinking water. Currently.

  The object of the present invention is to solve such problems, and in addition to removing volatile harmful substances such as trichlorethylene and tetrachloroethylene, various harmful substances can be removed, and the fossil soil accumulated in the slow filtration device. An object of the present invention is to provide a slow filtration device that can remove muddy substances such as those without stopping the operation and is excellent in microbial treatment effect.

  The slow filtration apparatus according to claim 1 of the present invention includes a pretreatment tank and a filtration tank, and an air supply unit for supplying air to the raw water fed into the pretreatment tank is provided in the pretreatment tank. The filtration tank is made of a material with excellent heat resistance, cold resistance, and earthquake resistance such as transparent acrylic and polycarbonate, and a raw water intake is provided near the upper end to take in the raw water sent from the pretreatment tank. The support sand layer laminated so that the particle size becomes smaller toward the upper side in the inside of the filtration tank, and 0.08 to 0.29 mm smaller than the particle size of the sand of the uppermost support sand layer on the support sand layer A fine sand layer is provided which is made of sand with a particle size as large as the upper side, and the stainless steel net with a mesh size of about 0.1 mm is fine inside the filtration tank. Set up to cover the top of the sand layer Is the provided raw water withdrawal port at the lower position than the raw water inlet to the filtration tank, characterized in that a treated water outlet at the lower end of the filtration tank.

  In the slow filtration device according to claim 2, the amount of oxygen is increased by the air supplied from the air supply unit in the pretreatment tank, and the raw water adjusted to a water temperature of 20 to 22 ° C. is fed into the filtration tank. It is characterized by that.

The slow filtration device according to claim 3 is characterized in that a net having a mesh size of about 0.1 mm is attached to the upper surface of the upper water intake port through which raw water is fed into the pretreatment tank.
The slow filtration device according to claim 4 has a cylindrical shape in which the upper end is open and the lower end is closed so that there is a space between the inner surface of the pretreatment tank and the inner wall of the pretreatment tank. Equipped with a muddy substance removal device consisting of a net with a mesh size of about 0.1 mm so that the outer wall of the case is formed and the side wall around this case is covered from the outside. In the pretreatment tank, an air supply unit is provided at the inner bottom of the casing, and a raw water intake port for taking in raw water fed from the casing is provided near the upper end of the filtration tank.

  As described above, in the slow filtration device of the present invention, the filtration tank is made of a material having excellent heat resistance, cold resistance, and earthquake resistance such as transparent acrylic and polycarbonate. It is configured not to be affected by the air temperature. For example, the raw water adjusted to a water temperature of about 20 to 22 ° C. is present in the filtration tank, the filtration tank is transparent, and the amount of collected light is increased. By supplying air, there is a large amount of oxygen in the raw water, so that the environment for breeding microorganisms in the filtration tank 2 is established, and microorganisms in the raw water are captured and gradually propagated on the fine sand layer to form a microbial membrane. To do. This microbial membrane can exert an effect of removing not only turbidity and bacteria in the water but also harmful components to moldy odor components by natural purification power and decomposition action by microorganisms. In addition, protozoa (Cryptosporidium, Cyclic Polar, Cyclosporal, which cannot be removed with chlorine by the uppermost part of the fine sand layer made of sand having a particle size of 0.08 to 0.29 mm and laminated so that the particle size becomes smaller toward the upper side (Giardia) can be captured, and dioxins that are hardly soluble in water can be captured. In addition, the removal of the muddy substance deposited on the upper side of the net can be performed at the muddy substance suction port via the suction pump, while removing the muddy substance accumulated on the upper side of the net at the muddy substance suction port, Continuous operation is possible without stopping the supply of raw water from the raw water intake. In addition, volatile harmful substances such as trichlorethylene and tetrachlorethylene present in raw water are decomposed by supplying air from the air supply section in the pretreatment tank, and the safety standard for turbidity is set. Treated water that is safe for the human body can be obtained as clear drinking water. In addition, it is possible to reduce the inflow into the filtration tank by precipitating iron having a large specific gravity contained in the raw water in the pretreatment tank. Furthermore, when river water or groundwater is used as raw water, even when a large amount of polluted mud is contained in river water or groundwater, the mesh size on the upper side of the treatment section in the filtration tank is 0. Since the sludge-like substance in the raw water can be removed by the net of about 1 mm, the amount of the sludge-like substance precipitated in the treatment section in the filtration tank is greatly reduced, and the filtration efficiency can be improved.

It is a partial notch front view of the slow filtration apparatus in the 1st Embodiment of this invention. It is a top view of the same pretreatment tank. It is a schematic explanatory drawing of the slow filtration apparatus in the 2nd Embodiment of this invention. It is a perspective view of the muddy substance removal apparatus used for the filtration tank of the slow filtration apparatus in the 3rd Embodiment of this invention. It is sectional drawing of the same muddy substance removal apparatus. It is a partially cutaway front view of the pretreatment tank of the slow filtration device. It is a top view of the same pretreatment tank.

Embodiments of the present invention will be specifically described below with reference to the drawings.
First, the first embodiment will be described with reference to FIG. 1 and FIG. 2. In the figure, 1 is a slow filtration device, and this slow filtration device 1 includes a cylindrical filtration tank 2 and a filtration tank 2. It comprises a cylindrical pretreatment tank 3 for pretreating the raw water to be fed. The pretreatment tank 3 is provided with an air supply part 4 at the inner bottom for pretreatment of raw water fed into the filtration tank 2, and air is ejected from the tips of a plurality of pipes 4 a of the air supply part 4. The raw water sent to the pretreatment tank 3 is agitated to aerate volatile harmful substances such as trichlorethylene and tetrachloroethylene present in the raw water. In addition, an activated carbon layer (not shown) is provided in the pretreatment tank 3, and volatile harmful substances released into the air in the pretreatment tank 3 are captured by activated carbon and released to the outside atmosphere. The release is stopped. Further, in the pretreatment tank 3, iron having a large specific gravity contained in the raw water is precipitated to reduce the inflow into the filtration tank 2. The sediment accumulated at the bottom of the pretreatment tank 3 is removed from a removal port 5 formed at the bottom of the pretreatment tank 3.

  Next, the filtration tank 2 is made of a material having excellent heat resistance, cold resistance, and earthquake resistance, such as transparent acrylic and polycarbonate, and the maximum diameter is formed at the lowest end inside the filtration tank 2. A crushed stone layer 6 having a size of about 15 to 20 mm, a boulder gravel layer 7 having a particle size of about 10 to 15 mm located on the crushed stone layer 6, and a particle size located on the boulder gravel layer 7 A supporting sand layer 8 having a size of 0.3 to 1 mm, and a particle size smaller than the minimum particle size of the sand of the supporting sand layer 8 on the supporting sand layer 8, specifically a particle size of 0.08 to 0.29 mm A fine sand layer 9 is provided which is made of sand having a size of 5 and is laminated so that the particle size becomes smaller toward the upper side. As for the thickness of the crushed stone layer 6, the gravel layer 7, the supporting sand layer 8, and the fine sand layer 9, the crushed stone layer 6 and the gravel layer 7 are about 50 mm, the supporting sand layer 8 is about 100 mm, and the fine sand layer 9 is about 250 mm. Is set to The sand used for the supporting sand layer 8 has a particle size of 0.3 to 1 mm, but the supporting sand of the supporting sand layer 8 is laminated so that the particle size decreases toward the upper side. .

  Thus, in the filtration tank 2 in which the crushed stone layer 6, the gravel layer 7, the supporting sand layer 8, and the fine sand layer 9 are provided in a laminated state from the bottom, the mesh size is about 0.1 mm on the fine sand layer 9. The stainless steel net 10 is placed so as to cover the uppermost layer of the fine sand layer 9. When the net 10 is made of a wire having a thin wire diameter and the strength against water pressure is insufficient, the wire 10 is thicker than the wire diameter constituting the net 10 on the net 10 as shown in the drawing. And a reinforcing net 11 made of stainless steel having a mesh size of about 0.3 mm. In this way, the net 10 placed on the fine sand layer 9 serves to receive mud substances such as fossil soil contained in the raw water supplied from above the filtration tank 2.

  In the figure, 12 is a raw water intake provided in the vicinity of the upper end of the filtration tank 2 to take in the raw water treated in the pretreatment tank 3, 13 is a treated water outlet provided at the lower end of the filtration tank 2, and 14 is A raw water extraction port provided in the middle of the filtration tank 2 at a position between the raw water intake port 12 and the net 11.

  In the above-described configuration, the pretreatment tank 3 is supplied with, for example, groundwater pumped from the ground as raw water, and heavy iron or the like sinks to the bottom of the pretreatment tank 3, and small iron or light fossil mud with a low specific gravity or the like. A substance or the like is fed into the filtration tank 2. In the pretreatment tank 3, air is spouted from the ends of a plurality of pipes 4 a of the air supply unit 4 to stir the raw water, and aerated and decomposed by volatile harmful substances such as trichlorethylene and tetrachlorethylene present in the raw water. The volatile harmful substances released into the air in the pretreatment tank 3 are captured by activated carbon to stop the release to the outside atmosphere. Further, when air is ejected in the pretreatment tank 3, frictional heat of air is generated in the air supply unit 4, and the temperature of the raw water can be raised by the air heated by the frictional heat. Usually, the temperature of the groundwater (raw water) pulled up from the underground is about 14 ° C., and the temperature of the ground water (raw water) can be raised to nearly 20 ° C. by blowing out heated air. The temperature of the groundwater (raw water) sent from the pretreatment tank 3 to the filtration tank 2 is preferably about 20 to 22 ° C. for the propagation of microorganisms, and the temperature of the groundwater (raw water) heated by blowing out air is 20 to 20 ° C. When the temperature does not reach 22 ° C., the temperature of the raw water is adjusted to about 20-22 ° C. by using another temperature adjusting means. Furthermore, the amount of oxygen in the raw water can be increased by blowing out air in the raw water of the pretreatment tank 3 and feeding the air.

  In this way, the raw water having a high specific gravity removed from the pretreatment tank 3 and heated to increase the amount of dissolved oxygen is fed into the transparent filtration tank 2 using a pump (not shown) as necessary. It is. The raw water sent to the filtration tank 2 passes through the nets 11 and 10, passes through the fine sand layer 9, the supporting sand layer 8, the gravel layer 7 and the crushed stone layer 6, and the filtered treated water is taken out from the treated water outlet 13. It is. By the way, the filtration tank 2 is made of a transparent material having high heat resistance and cold resistance, and is configured so that the water temperature in the filtration tank 2 is not affected by the outside air temperature, and is adjusted to a water temperature of about 20 to 22 ° C. Microorganisms in the filtration tank 2 due to the presence of the raw water in the filtration tank 2, the filtration tank 2 being transparent, having excellent heat resistance and cold resistance, and excellent translucency, and having a large amount of oxygen in the raw water. The environment for breeding is prepared, microorganisms in the raw water are captured on the fine sand layer 9 below the net 10 and gradually propagate to form a microorganism film. This microbial membrane can remove not only turbidity and bacteria in the water, but also harmful components to moldy odor components by natural purification and decomposition by microorganisms. In addition, mud substances such as fossil soil contained in the raw water are received by the net 10 having a mesh size of about 0.1 mm, and are deposited on the net 10. The muddy substance deposited on the net 10 is lifted by lifting the net 11 that overlaps the net 10 from the net 10 when it is confirmed that the water treatment speed has decreased due to an increase in the amount of accumulated muddy substance. In the state, it is sucked by the muddy substance suction port 15 through a suction pump (not shown) and taken out of the filtration tank 2. At that time, the amount of raw water contaminated on the net 10 is reduced by opening the raw water extraction port 14 and reducing the amount of raw water existing on the fine sand layer 9 at the uppermost level up to the level of the raw water extraction port 14. Become. Then, while removing the muddy substance accumulated on the net 10 at the muddy substance suction port 15, continuous operation can be performed without stopping the supply of the raw water from the raw water intake port 12. The raw water in the filtration tank 2 contains a large amount of oxygen, and the microbial film generated in an algal form due to oxygen adhering to the propagated microbial film floats up and is discharged from the raw water extraction port 14. . Therefore, clogging due to the microbial film on the net 11 is prevented.

  As described above, according to the present slow filtration device, at the uppermost part of the fine sand layer 9 made of sand having a particle size of 0.08 to 0.29 mm and stacked such that the particle size becomes smaller toward the upper side. It captures protozoa (Cryptosporidium, Cyclos Polar, Giardia) and the like that cannot be removed by chlorine, and also captures dioxins that are hardly soluble in water at the top of the fine sand layer 9, and deposited on the net 10 Mud substances and the like are removed by a suction pump. At that time, the muddy substances accumulated on the net 10 are removed from the raw water intake port 12 while being removed by the mud substance suction port 15 through the suction pump. Continuous operation is possible without stopping the supply of raw water. Furthermore, volatile harmful substances such as trichlorethylene and tetrachlorethylene present in the raw water are decomposed by supplying air from the air supply unit 4 in the pretreatment tank 3, and the turbidity safety standard Safe drinking water can be obtained for the human body as drinking water that has been cleared.

  By the way, in this embodiment, the raw water to be treated by the slow filtration device is groundwater pumped up from the underground, but the raw water to be treated is not necessarily groundwater, even river water, factory wastewater, etc. good. Since river water changes its temperature depending on the season, it may not be possible to adjust the temperature of the raw water to about 20-22 ° C. with the frictional heat generated by the air supply unit 4. What is necessary is just to adjust the temperature of raw | natural water to about 20-22 degreeC using a temperature control means together. Anyway, the temperature of the raw water in the filtration tank 2 may be maintained at about 20 to 22 ° C.

  Further, a stainless steel net having a mesh size of about 0.1 mm may be interposed between the upper end of the supporting sand layer 8 and the lower end of the fine sand layer 9 in the same manner as the net 10, whereby the fine sand layer It is possible to reliably stop 9 sand from sinking into the supporting sand layer 8.

  Furthermore, by stacking the above-described transparent filtration tank 2 in the vertical direction, so-called multistage type, it is possible to solve the problem that a wide site of a slow filtration device is conventionally required to increase the amount of water treatment, In addition, even when the transparent filtration tanks 2 are arranged in the horizontal direction, the amount of collected light to each filtration tank 2 is not reduced by increasing an appropriate interval, and the throughput of water is increased even in a narrow place without reducing the filtration efficiency. Can do.

  And this slow filtration apparatus processes raw water with a large amount of oxygen adjusted to a water temperature of about 20-22 ° C. in the filtration tank 2 which is transparent, heat-resistant and cold-resistant as described above, and propagates microorganisms. By preparing the environment, even if the thickness of the filtration layer comprising the fine sand layer 9 and the supporting sand layer 8 provided in the filtration tank 2 is reduced, an excellent treatment effect as a slow filtration device can be obtained. As a result, the filtration tank 2 The height can be lowered, and the overall height can be lowered even when stacked in a multistage manner as described above.

  As described above, the first embodiment has been described. However, as in the second embodiment shown in FIG. 3, when the raw water fed into the pretreatment tank 3 contains a large amount of contaminated mud, A stainless steel net 17 having a mesh size of about 0.1 mm is attached to the front surface of the treatment tank 3, for example, the upper surface of the river water intake 16, and most of the muddy substances are removed by the net 17. It is also possible to draw river water from the water inlet 16 and send it to the pretreatment tank 3. In the second embodiment, the other configuration is the same as that of the first embodiment. In this manner, by attaching the net 17 having a mesh size of about 0.1 mm to the upper surface of the river water intake 16, the polluted mud is not contained in the raw water sent to the pretreatment tank 3. Almost no polluted mud substances are contained in the raw water that is hardly contained and then sent to the filtration tank 2, so environmental hormones and various chemical substances contained in the raw water are treated by biological treatment in the filtration tank 2. It is removed efficiently. In addition, since a muddy substance adheres and accumulates on the net | network 17, it is necessary to remove the muddy substance adhering to the net | network 17 regularly.

  Furthermore, as in the third embodiment shown in FIGS. 4 to 7, the upper end is opened and the lower end is closed so that the space between the inner surface of the pretreatment tank 3 and the inner surface of the pretreatment tank 3 is about 10 cm. A cylindrical body 18 in which an infinite number of holes 18a 'are formed in a peripheral side wall 18a, and a size of a mesh mounted on the casing 18 so as to cover the peripheral side wall 18a of the casing 18 from the outside. You may make it equip with the muddy substance removal apparatus 20 which consists of the stainless steel net | network 19 whose length is about 0.1 mm. An air supply unit 4 is provided at the inner bottom of the housing 18. Further, a removal port 21 for removing the sediment accumulated on the bottom of the housing 18 is provided at the bottom of the housing 18. Other configurations are the same as those of the first embodiment.

  In this way, the configuration in which the muddy substance removing device 20 is installed in the pretreatment tank 3, raw water such as well water that has entered the pretreatment tank 3 outside the muddy substance removing apparatus 20 is contaminated in the raw water. Mud substance enters the housing 18 in a state where the intrusion into the housing 18 is stopped by the net 19, and a heavy iron component or the like in the raw water sinks to the lower end as in the first embodiment. The raw water is heated up and the amount of dissolved oxygen is increased, and the raw water is drawn out from the central portion of the housing 18 and fed into the transparent filtration tank 2.

  In this embodiment, as in the second embodiment, since the contaminated mud substance is hardly contained in the raw water sent to the filtration tank 2, the environmental hormones and various chemical substances contained in the raw water are It is efficiently removed by biological treatment in the filtration tank 2. In addition, since the muddy substance adheres and accumulates on the net 19 of the muddy substance removing apparatus 20, it is necessary to remove the muddy substance adhering to the net 19 by periodically lifting the housing 18 from the pretreatment tank 3. is there.

That is, both the second and third embodiments are intended to remove the polluted mud substances contained in the raw water on the upper side of the filtration tank 2.
Furthermore, it is possible to attach a stainless steel net with a mesh size of about 0.1 mm so as to cover the outside of the tip water intake of the hose for boring groundwater. For example, the raw water is sent to the pretreatment tank in a state where the polluted mud material including fossil soil is removed by the net.

  The slow filtration device of the present invention is a conventional slow filtration device that removes harmful components from raw water such as groundwater and river water, and can obtain treated water that is safe for the human body as drinking water that satisfies the safety standard of turbidity. This is a revolutionary slow filtration device that is not available.

DESCRIPTION OF SYMBOLS 1 Slow filtration apparatus 2 Filtration tank 3 Pretreatment tank 4 Air supply part 4a Pipe 5 Removal port 6 Crushed stone layer 7 Gravel layer 8 Support sand layer 9 Fine sand layer 10,11 Net 12 Raw water intake port 13 Treated water extraction port 14 Raw water extraction Port 15 Mud substance suction port 16 Pull-in port 17 Net 18 Housing 18a Side wall 18a 'Hole 19 Net 20 Mud material removing device

Claims (4)

It consists of a pretreatment tank and a filtration tank, and an air supply unit is provided in the pretreatment tank to supply air to the raw water sent into the pretreatment tank. The filtration tank is made of heat-resistant materials such as transparent acrylic and polycarbonate. It is made of a material with excellent heat resistance, cold resistance, and earthquake resistance, and a raw water intake is provided near the upper end to take in raw water sent from the pretreatment tank, and the particle size becomes smaller in the upper part of the inside of this filtration tank. The support sand layer laminated in this manner, and the sand having a particle size of 0.08 to 0.29 mm smaller than the particle size of the sand of the uppermost support sand layer on the support sand layer, the particle size toward the upper side. Are provided so that a stainless steel net having a mesh size of about 0.1 mm covers the uppermost stage of the fine sand layer. From the raw water intake The raw water withdrawal port provided in a lower position, slow sand filter apparatus characterized in that a treated water outlet at the lower end of the filtration tank. 2. The raw water adjusted to a water temperature of 20 to 22 ° C. is supplied to the filtration tank by increasing the amount of oxygen by the air supplied from the air supply unit in the pretreatment tank. Slow filtration device. The slow filtration apparatus according to claim 1 or 2, wherein a net having a mesh size of about 0.1 mm is attached to the upper surface of the upper water intake port through which raw water is fed into the pretreatment tank. A cylindrical body having an open upper end and a closed lower end so that a gap is formed between the inner surface of the pretreatment tank and the inner surface of the pretreatment tank. Equipped with a muddy substance removal device comprising a net with a mesh size of about 0.1 mm so as to cover the side wall around the case from the outside, and in the pretreatment tank, The slow filtration apparatus according to claim 1 or 2, wherein an air supply section is provided at the bottom, and a raw water intake is provided in the vicinity of the upper end of the filtration tank to take in the raw water fed from the housing.

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