JPH0745038B2 - Downflow filtration method and device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of application] The present invention is capable of extremely effectively filtering out SS from water containing suspended particles (SS). The present invention relates to a novel filtration method and device capable of extremely effectively removing SS from wastewater by filtration.

The term "filtration" used here includes ordinary filtration and a filtration treatment method in which filtration is performed while supplying air or the like as in the case of biochemical treatment.

[Conventional technology]

In order to increase the treatment efficiency of the immersion filter bed method in the case of biochemical treatment, it is necessary to allow organic wastewater to pass through at a high filtration rate, and a filter medium and its filter medium for slowing the increase of filtration resistance. There is a need for an improved device for filling and filtering.

An aerobic immersion biological filter bed apparatus as shown in FIG. 3 is known as a concrete apparatus for the immersion filter bed method. This device is a tank
An immersion filter bed 32 made of granular filter material such as anthracite or chamotte is provided under the water surface of 31, and an air diffusing pipe 33 is provided under the immersion filter bed 32, and an organic wastewater introduced from a raw water supply pipe 35 is supplied. The immersion filter bed 32 is circulated in a downward flow, and aerobic biological treatment is performed in the immersion filter bed 32.

Ancillary equipment of this equipment is settling basin 34, treated water storage tank 3
8. Washing waste water storage tank 40 is installed.

This device is a submerged filter bed composed of a granular mineral filter material such as anthracite, chamotte, or artificial or natural lightweight aggregate under the water surface of a tank 31 while supplying organic wastewater in a downward flow. Is removed by filtration. However, when using this conventional device, SS and BOD of several hundred mg /
When the sewage of the above is passed, SS is trapped on the surface layer of the submerged filter bed such as anthracite and the biofilm grows excessively, causing severe clogging, resulting in a rapid increase in filtration resistance, It has been found that the impermeability is impaired shortly after the start of water and the submerged filter bed 32 must often be washed.

A filter device using sponge-like particles as a filler is disclosed in JP-A-60
It is described in JP-A-147207 and is publicly known.

A brief description of this conventional technique will be given with reference to FIG. 2. In the filtration tank shown in the figure, water-passing members 7 such as nets are provided in the upper, middle, and lower three stages, and sponge-like granular materials are contained therein. Filled with filler.

An organic wastewater supply pipe 2 is provided in the lower part of the tank, and the organic wastewater is injected as an upward water flow from there, thus,
SS is removed by filtration while the sponge-like granular material is pressed. The filtered treated water is sent to the treated water storage tank from the filtered water outflow pipe 3 at the upper part of the tank.

Furthermore, at the bottom of the tank, there is a cleaning water supply pipe (also for supplying organic wastewater), and the air for cleaning the filter medium can also be sent from the cleaning air pipe, causing clogging of the filter medium. At this time, cleaning water and cleaning air are sent to clean the filter medium, and the waste water after cleaning is discharged to the outside from the cleaning waste water outflow pipe 8 in the upper part of the tank.

That is, in this technique, the sponge-like granular filler is pressed against the lower surface of the upper net by the upward flow of organic wastewater, and the upward-flow SS filtration is performed in a state in which the sponge-like granular material is considerably compressed. It is a technology. However, as a result of a supplementary test conducted by the present inventor, it was recognized that the filtration according to this conventional technique has a serious drawback in that the filter medium is rapidly clogged and the filtration resistance is rapidly increased.

The reason is that since the sponge-like granular material is filtered in a compressed state, the porosity of the filter material layer becomes small, and SS
It was found that the particles were captured only on the lower surface of the sponge layer and so-called volumetric filtration was not performed. (Here, the volumetric filtration means filtration in a situation in which SS is trapped over the entire thickness direction of the filtration layer.) In addition, in this conventional technique, water and air are mixed in order to perform cleaning. Although the method of supplying from the lower part is used for cleaning, when air is supplied from the lower part, the pressure of rising bubbles compresses it to the lower surface of the upper mesh, sponge-like particles do not move at all, and cleaning is successful. It turned out that there is a drawback that cannot be done.

[Problems to be Solved by the Invention]

An object of the present invention is to pass water containing SS through the water through a filter layer filled with a filter medium, effectively remove SS, and obtain filtered water with extremely low SS, and by using SS in the filter medium. It is an object of the present invention to provide a filtration method that does not cause clogging and can withstand a long filtration process, and an apparatus suitable for the filtration method.

In the filter device of the above two examples, one is a filter device in the immersion filter bed method used in the biochemical treatment of organic wastewater that is widely used, the filter medium is fixedly packed in layers, This filter layer is called an immersion filter bed (simply a filter bed). However, here, since it is more generally applied to the case where SS-containing water is filtered in a filter layer filled with a filter medium, it will be referred to as a fixed-packing layer. The filtration layer in the filtration device when water is filtered in step 1 will be referred to as a packed bed.

By the way, the conventional aerobic immersion biological filter bed apparatus has various drawbacks as described below, and realization of a filter bed apparatus having more excellent performance is desired.

If the treated organic wastewater contains a large amount of SS such as sewage, a sedimentation basin should be provided in front of the filter bed to remove most of the SS in advance. Otherwise,
Clogging rapidly progresses at the surface layer of the filter bed, the filtration resistance rises sharply, and water cannot pass. The frequency of backwashing the filter bed also increases dramatically several times a day. Moreover, the sedimentation speed in the sedimentation basin is at most about 30 m / day or less, and the design must be made on the premise of the conditions, so the installation area of the sedimentation basin must be taken large and the construction cost is high.

When treating sewage, even if a settling basin is installed in the previous stage to remove most of SS, the SS remains to some extent, so the filtration rate (LV) in the filter bed is set to a small value of 20 to 30 m / day. If this is not possible, and if the filtration rate is higher than this, the filter bed will be clogged, the filtration resistance will rise rapidly, and the filter bed will have to be backwashed several times a day. The condition that the filtration rate is 20 to 30 m / day is the limit necessary for backwashing once a day.

When backwashing the filter bed, the filter bed volume (V _H ) of 2.5-3
Although it is necessary to use a doubling of the amount of washing water, in the conventional device in which the filtration rate cannot be set to a large value, the filter bed volume in the filter bed must be large in order to treat a predetermined amount of organic wastewater. Since it was unavoidable, a large amount of washing water was needed. Since treated water is usually used as the washing water, the amount of treated water finally obtained is small.

To describe these relationships by formulas, if the filter bed horizontal cross-sectional area is S, the filter bed height is H, and the treated amount of organic wastewater is Q, V _H and LV are expressed by the following formulas. It

V _H = S * H LV = Q / S From these two equations, V _H = (Q / LV) H, and if LV becomes a small value, V _H becomes large, and as a result, the amount of washing water used increases. It will be.

Further, in the above-mentioned prior art, SS contained in organic wastewater
Method to devise a filter material for the filtration of, that is, by using a sponge-like granular material as the filter material as an upflow water flow
Although a technique of filtering SS has been tried, the filter according to this conventional technique has not been able to improve the filtration rate because the filter material is rapidly clogged and the filtration resistance of the packed bed is increased.

The object of the present invention is, for example, to completely solve the above disadvantages in the method of treating organic wastewater using a submerged biological filter bed, water containing SS in general, specifically organic wastewater at an extremely large filtration rate. It is an object of the present invention to provide a novel filtration method that can be processed through a packed fixed bed and can be highly purified, and a filtration device for enabling the same, and more specifically, an SS trapping capacity of the packed filtration bed. It is an object of the present invention to provide a novel filtration method and a filtration medium and a filtration device for enabling the same, which are large in size and can be easily and effectively washed.

[Means for Solving the Problems]

The above-mentioned problems are as follows: 1) A filling / fixing layer of an open-cell type porous elastic body is formed in a tank, and organic sewage is supplied from an organic sewage supply unit above the filling / fixing layer to obtain the filling / fixing layer. A filtered water outflow section is provided at the bottom of the tank to let the filtered water flow out, and the organic wastewater level in the tank is set to a position below the upper end interface of the packed fixed bed, and the position above the packed fixed bed is set. It is characterized in that a water-passing member is stretched through a space, and when the filling and fixing layer is washed, washing water is supplied from a lower portion of the filling and fixing layer, and washing drainage is discharged from above the water-passing member. Downflow filtration method.

2) A filling / fixing layer of an open-cell type porous elastic body is formed in the tank, an organic sewage supply unit is provided above the filling / fixing layer, and a filtered water outflow unit is provided below the filling / fixing layer. The organic wastewater level in the tank is set to a position lower than the upper end interface of the packed fixed bed, and a water-permeable member is stretched above the packed fixed bed through a space to form a lower part of the packed fixed bed. A downflow type filtering device, wherein a wash water supply part is provided in the above, and a wash drainage outflow part is provided above the water passage member.

3) A filling and fixing layer of granular solid having a specific gravity larger than that of the porous elastic body and smaller than the particle diameter is provided below the filling and fixing layer in the tank. The downward flow type filtration device according to the item 2).

Is solved by using.

The present invention has reviewed the fact that a treatment device using a conventional aerobic biological filter bed forms a biological filter bed with a granular filter medium, for example, sand, activated carbon or anthracite, and as a result of repeated research, the above-mentioned conventional immersion. It was recognized that the biological treatment method using the filter bed and the immersion filter bed have a drawback that they are composed of granular minerals such as anthracite having a small porosity of about 50% at the time of filling. It became so.

Considering this, in the biological treatment method using the immersion filter bed, even if the supplied organic sewage is passed through at a high speed with a downward flow, the filter medium is wide and efficiently. When contacting causes a biological reaction, the BOD is rapidly reduced, and if the SS is promptly removed and the filter medium is not clogged, the wastewater can be treated at a high speed. As a result of various examinations and experimental investigations on a packed fixed bed using a large number of types of filter media, it has a large void (pore) on the surface and inside, that is, an open-cell type porous elastic body such as plastic. It was confirmed that by introducing a new concept in the construction of the filter layer, such as the filling and fixing layer composed of small pieces of sponge (urethane foam, etc.), clogging will not occur and wastewater treatment will be possible at a high speed. The present invention has been reached.

An open-cell type porous elastic body (hereinafter, sometimes simply referred to as “a porous elastic body”) has pores that are open cells and have voids inside, and when compressed like a sponge, it contracts and when compressed it stops. Anything that restores the original state can be used.

In the present invention, it is extremely important to configure the packed fixed bed immersion filter bed with a porous elastic body. This is because, for example, sponge is a porous elastic body that is usually made of plastics, so its specific gravity is light as close to 1.0, so the density at the time of filling is very small, and the porosity is 95% or more. This is because the pore size of the porous portion can be increased in this way, and thus a large amount of SS of organic wastewater can be captured. In addition, the pores on the surface and inside of the porous elastic body can also greatly contribute to significantly increase the SS trapping amount.

The porous elastic bodies and granular solids used for constructing each submerged filter bed and filtration tank have physical properties such as size, bulk density, and specific gravity, as well as their shape, which greatly influences the treatment, and is important. It becomes a factor.

The particle size of the porous elastic body is 10 to 30 mm, preferably 15 to 20 mm, and the shape thereof can be various shapes such as prismatic, spherical, and granular, and prismatic is preferable. Its specific gravity is 0.9 to 1.2, but since it is porous, the apparent specific gravity may be 0.8 or less even when it contains water, so the apparent specific gravity of the filter medium is 0.8 to 1.2.
Is preferred.

[Action]

The structure of the filtration tank and the mode of treatment of the present invention will be described below with reference to FIG. 1, and the operation of the present invention will be described based on that.

The filtration tank 1 determines the water level of the organic waste water supply unit 2, the washing waste water outflow unit 8, the porous water-passing member 7 (net etc.) for preventing the outflow of the porous elastic body A, and the water level of the organic waste water in the tank from the top. It is equipped with a filtered water outflow part 3, a lower support member 4, a cleaning water supply part 5, a cleaning air supply part 6 and a filtered water outflow valve 9. Although not shown, as another embodiment of the filtration layer, a packed bed of granular solid (sand, anthracite, activated carbon, etc.) having a large specific gravity and a small specific gravity in the lower part of the packed fixed bed made of the porous elastic body A is used. May be provided. In the figure, B is the upper end interface of the packed and fixed layer composed of the porous elastic body A, C is the water level of the organic wastewater in the tank, and the layer between B and C, that is, the air of the packed and fixed layer composed of the porous elastic body A. The exposed layer was E, the filtered water outflow water level was D, and the space between the upper end interface B of the packed fixed layer and the porous water-permeable member 7 was F.

The filtration tank 1 is filled with a porous elastic body A such as urethane foam to form a fixed filling layer. Organic sewage containing SS such as sewage is supplied from the organic sewage supply unit 2 at the top of the tank. The filtered water outflow part 3 is installed in the lower part of the tank and stands up to determine the outflow water level of the filtered water at the position C.

The most important component of the present invention is the positional relationship between the outflow water level C of this filtered water and the upper interface B of the packed fixed layer filled with the porous elastic body A, and at least the outflow water level of the filtered water at the start of filtration. The upper interface B of the packed fixed layer is set at a higher position than C.

With this setting, the upper part of the filling and fixing layer of the porous elastic body A is exposed to the air without being immersed in the organic waste water at least at the start of filtration.

When organic sewage is supplied to the exposed portion of the packed fixed bed, the organic sewage first passes through the exposed portion E of the packed fixed bed, and then passes through the dipping filter bed in a downward flow to be filtered. In this respect, it has a new idea concept that has never existed before.

The exposed portion E of the packed fixed layer does not have the exposed portion E, and when the fixed bed made of the porous elastic body A is entirely immersed in the organic wastewater, the porous elastic body A is particularly apparent. For polyurethane foams with a specific gravity of less than 1.0, the packed bed floats entirely in organic wastewater. On the other hand, when there is the exposed portion E, the exposed portion E containing water prevents the floating of the filling and fixing layer and stabilizes the filling and fixing layer. Here, the thickness of the layer of the exposed portion E of the packed fixed bed should be sufficient to remove SS in the organic wastewater, prevent floating of the fixed bed, and stabilize the packed fixed bed. Good.

The porous elastic body A of the packed fixed layer exposed in the air is
Although many thin capillaries are filled with water, air is present in the capillaries with relatively large pore diameters and voids between the porous elastic bodies A, and the supplied organic wastewater is filtered water. Accompanied by organic sewage due to the suction effect of the spill
Even if a large amount of SS is captured, the increase in filtration resistance of the fixed bed is small, and therefore a large amount of SS can be captured in this exposed layer.

In this way, as the organic sewage flows downward, first, the SS having a coarse particle size is captured while flowing down the exposed portion E of the packed fixed bed, and then flows into the submerged packed bed, During the downward flow, SS having a small particle size is trapped inside the porous elastic body and in the voids between them. At this time, the porous elastic body A in the tank is not so compressed by water pressure or its own weight and is gently filled, so that the porosity of the filtration layer is large and the filtration resistance is increased or decreased.

The organic sewage flowing down as a downward flow in the filter tank finally becomes clear filtered water and flows out from the filtered water outflow pipe.

Then, as the operation of the filtration device of the present invention is continued for a long time, the filtration resistance gradually increases, the water level in the tank rises, the packed fixed bed is compressed due to water pressure, and the exposed part of the packed fixed bed is submerged. Therefore, the filter tank is washed when the water level reaches a predetermined level (usually set to about 1 mH ₂ O).

The porous elastic body A can be effectively washed by performing the following procedure, for example, to wash the filtration device.

First, the inflow of organic waste water is stopped, and the filtered water outflow valve 9 is closed.

Cleaning water (the filtered water of the present invention is stored and used) is supplied from the cleaning water supply unit 5 to raise the water level C in the tank to slightly below the upper porous water-passing member 7.

The blower is driven and the cleaning air is supplied to cause a violent upward flow of bubbles in the tank to violently disturb the porous elastic body A. (At the so-called slugging state) At this time, since there is the space F, the porous elastic body A can freely move.

Next, wash water is supplied, and water and air are simultaneously washed to wash out the captured SS. If this operation is continued for 5 to 10 minutes, the SS will be washed out almost completely and the filtration tank will return to a clean state, so stop the washing water and air, open the filtered water outflow valve 9 and supply the organic waste water. , The washing operation is completed.

Next, another preferred embodiment of the present invention will be described. That is, in the lower part of the packed layer made of a porous elastic body, compared with the particle size and specific gravity of the porous elastic body, a filter material made of granular solid having a small particle size and a large specific gravity (for example, anthracite, sand, granular activated carbon, By providing a packed layer of artificial lightweight aggregate, chamotte, zeolite, etc.), the SS of filtered water can be constantly kept to 10 mg / or less, which is suitable when advanced treated water is required. .

Such a concept of a multi-layer filter bed in which a packed bed made of a porous elastic body is used as an upper packed bed is a new concept that has not been known so far.

In addition, when a filtration treatment is performed and an oxygen-containing gas is supplied from the lower part of the packed layer made of a porous elastic body, a microbial film develops on the surface and inside of the filter medium, and since the microbial film is rich in the adsorptivity of colloidal SS, Since the filtration effect is further improved, it is extremely suitable for removing SS in organic wastewater by filtration.

〔Example〕

Based on the present invention, the result of a filtration experiment for sewage will be described. However, this specific embodiment of the filtration experiment is intended to facilitate understanding of the embodiment of the filtration treatment of the present invention, and does not limit the filtration method or apparatus of the present invention.

(Example-1) As shown in FIG. 1, using the apparatus of the present invention having a diameter of 300 mmΦ, raw sewage (SS96 to 183 mg /, BOD1
Experiments were conducted targeting 65-195 mg /).

Table 1 shows the experimental conditions and the experimental results. As is clear from Table-1, it was confirmed that the present invention has a filtration duration of three times longer than that of the prior art and the cleaning frequency is reduced.

Moreover, (the ratio of the washing wastewater 1 m ³ per organic wastewater 1 m ³ process) washing wastewater generation rate ratio also, the present invention can be greatly reduced to about 1/5 of the prior art, confirmed that easily cleaning of the filter medium Was given.

Next, as a filter medium composition, a multi-layer filter bed was prepared by filling 0.6 m of anthracite having a particle size of 4 to 5 mm in the lower part of the sponge packed bed shown in Table 1, and the above-mentioned groundwater filtration test was conducted.

At a filtration speed of 500 m / day, the filtration duration was 20 to 23 hours, but the SS of the filtered water was reduced to 8 to 10 mg /.

Next, another experiment result will be described.

In the example (invention) of Table-1, as a result of performing downward flow filtration while aerating 1-2 Nm ^{3 of} air bubbles per 1 m ³ of sewage supply from the lower part of the sponge packed bed, the filtration duration was 19 to 21 Hr
Although slightly decreased from the examples of the present invention (invention), the SS of the filtered water was 2 to 4 mg /, and significantly good SS removal was performed. The cause is that a microbial film is generated on the surface and inside of the sponge granular piece due to the supply of air, and this is a fine SS of sewage.
It was thought that this was because the adsorption of the was improved.

〔The invention's effect〕

According to the present invention, the following important effects can be obtained and the drawbacks of the prior art can be solved.

The rate of increase in filtration resistance is small, and the duration of filtration until reaching a certain filtration resistance can be significantly extended compared to the conventional case.

Since the porous elastic body does not have a compressed state on the lower surface of the porous water-permeable member at the interface of the packed layer and has a space F that allows free movement, backwashing of the filter medium is easy and less. Effective cleaning can be performed with the amount of cleaning water. As a result, the amount of waste water to be washed is reduced and the disposal becomes easier.

The SS of the treated water can be further reduced by providing a packed bed of granular solid having a smaller particle size and a larger specific gravity than the packed bed of the elastic porous elastic body under the elastic bed.

[Brief description of drawings]

FIG. 1 is a schematic view of a filtration tank of the present invention having a fixed layer in which a filter material made of a porous elastic material is filled and a part of the upper layer is exposed in the air. FIG. 2 is a schematic diagram of a conventional filtration tank filled with sponge-like particles for treating organic wastewater with an upward flow. FIG. 3 is a schematic diagram showing a biological treatment apparatus having a conventional biological filter bed. Explanation of symbols 1 ... Filtration tank 2 ... Organic sewage supply part 3 ... Filtered water outflow part, 4 ... Lower support member 5 ... Wash water supply part, 6 ... Wash air supply part 7 ... Porous passage Water member, 8 ... Washing wastewater outflow part A ... Porous elastic body B ... Fixed layer upper interface C ... Organic wastewater level in filtration tank D ... Filtered water outflow level E ... Fixed layer exposed part F ... …space

Claims (3)

[Claims] 1. A filling / fixing layer of an open-cell type porous elastic body is formed in a tank, and organic sewage is supplied from an organic sewage supply part above the filling / fixing layer to obtain a filling / fixing layer of the filling / fixing layer. A filtered water outlet is provided at the bottom to let the filtered water flow out, and the organic wastewater level in the tank is set to a position below the upper interface of the packed fixed bed, and a space above the packed fixed bed is provided. A water-permeable member is stretched through the
Washing water is supplied from the lower part of the packed and fixed bed, and washing drainage is caused to flow out from above the water-passing member. 2. A filling / fixing layer of an open-cell type porous elastic body is formed in a tank, an organic wastewater supply unit is provided above the filling / fixing layer, and filtered water flows out below the filling / fixing layer. Is provided, the organic wastewater level in the tank is set at a position lower than the upper end interface of the packed fixed bed, and a water-permeable member is stretched above the packed fixed bed through a space to fix the packed fixed bed. A downflow type filtration device, wherein a wash water supply part is provided in the lower part of the layer, and a wash drainage outflow part is provided above the water passage member. 3. A packed fixed bed of granular solid having a specific gravity larger than that of the porous elastic body and smaller than the particle diameter is provided below the packed fixed bed in the tank. The downflow type filtering device according to claim 2, wherein