JPH119908A - Operation method of sand filtration/ozonation apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To contrive reduction of exhaust ozonation load by using an exhaust ozone gas discharged from an ozone oxidation treatment as an air lift gas of a sand filtration treatment in a method wherein foul water containing a suspending substance and an organic substance is purified by moving-bed sand filtration and ozone oxidation treatment. SOLUTION: Raw water 20 to be filtered is made to flow from a bottom part of a sand filtration tank 10 and is discharged as filtration treatment water 21b from a top part of the tank before entering a top part of an ozone reaction tank 16, and then the water is extracted as treatment water 22 from the bottom part of the tank. During this period, ozone gas 24 is blown through an aeration pipe 17 from a bottom part of the ozone reaction tank 16 and concentrations of organic substances and coloring constituents are reduced by oxidation capacity of the ozone gas 24. Exhaust ozone gas 25 which has not undergone reaction and discharged from the top part of the ozone reaction tank 16 is introduced in a gas blower pipe 14 in a sand filtration tank 10 by a blower 15 and is allowed to be discharged as exhaust gas 27 from the top part of the sand filtration tank 10 via an air lift pipe 12 and treated by an exhaust ozonation apparatus 18 before being emitted.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to the treatment of sewage containing a floating substance and an organic substance, and more particularly, to a method for treating secondary sewage water, which efficiently removes the floating substance and the organic substance, Sand filtration effective to reduce processing load
The present invention relates to an operation method of an ozone combination treatment device.

[0002]

2. Description of the Related Art Generally, a water treatment process in a sewage treatment plant comprises a sedimentation basin, a primary treatment plant for a primary sedimentation basin, a microbial reaction tank called an aeration tank or an aeration tank, and a secondary treatment plant for a final sedimentation basin. You.

[0003] The function of the primary treatment plant is to remove coarse foreign matters suspended in the influent water and suspended substances which settle by gravity. The secondary treatment plant uses a variety of microorganisms called activated sludge to remove soluble organic matter in the sewage, and removes suspended substances that could not be treated in the primary treatment plant to produce clear treated water. ing. Furthermore, in order to improve the quality of the secondary treatment water, there is a method in which a facility for sand filtration, ozone treatment, and activated carbon treatment is disposed after the secondary treatment plant. These facilities are called tertiary or advanced treatment plants.

An example of the altitude processing will be described with reference to FIG.
The secondary treatment water from the final sedimentation basin of the secondary treatment plant is passed through a sand filtration tank to remove floating substances that could not be removed by the secondary treatment in the sand layer in the sand filtration tank. Next, the secondary treatment water is put into an ozone reaction tank, and organic substances that cannot be filtered are removed. In this treatment process, the ozone gas injected from the bottom of the ozone reaction tank is brought into gas-liquid contact with the secondary treatment water, and the treated water is discharged from the bottom of the ozone reaction tank and the ozone gas discharged from the top of the ozone reaction tank.

[0005] This treatment removes the chromaticity, odor, or organic substances remaining in the secondary treatment water (cited reference: ozonation of sewage treatment water, The 4th Annual Meeting of the Japan Ozone Association Annual Study Meeting) Lectures 1995). In addition, as a sand filtration operation method, there are a transfer type in which the filtration step and the washing step are continuously performed in one tank, and a batch type in which suspended matter is removed by repeating the filtration step and the washing step.

In the transfer type, the filtration and washing steps are performed while moving and circulating a sand layer in a tank. In the filtration step, the sand layer to which suspended matter (hereinafter referred to as SS) adheres is transferred by, for example, an air lift. Wash and transfer the washed sand to the filtration step.

On the other hand, in the ozone treatment, a part of the ozone gas injected into the ozone reaction tank is discharged as exhaust ozone gas. It is common to install an exhaust ozone gas treatment device in the exhaust ozone treatment, but it is a treatment system that combines an aerobic filter bed filled with a bioadhesive carrier and an ozone reaction tank.
A method in which the exhausted ozone gas discharged from the ozone reaction tank is guided to the aerobic bed and the oxygen in the exhausted ozone gas is utilized (Japanese Patent Publication No. 7-1).
No. 99 publication).

[0008]

The problems of the prior art described above are as follows. First, in the cited document, in the treatment of the ozone gas discharged from the ozone reaction tank, it is necessary to provide a treatment device filled with a catalyst. And equipment equivalent to an ozone reactor. Further, in Japanese Patent Publication No. 7-199, exhausted ozone gas is blown into an aerobic filter packed with a bioadhesive carrier as a waste gas. There is a concern.

[0009] Further, the washing step for regenerating the filter layer in the sand filter tank is important, and a method of backwashing with water or washing with air is known (Japanese Sewage Works Association Advanced Treatment Facility Design Manual, draft H6).

In the transfer type sand filtration tank, filtration is performed at the bottom of the tank.
Washing is performed at the top of the tank. Air is blown into an air lift pipe installed at the center of the tank, and sand and water are sent to the top of the tank by the air, and the sand flows down from the top of the tank. At this time, sand is washed using a part of the treated water filtered at the bottom of the tank. Therefore, it is necessary to supply air for air lift by a compressor or the like. Further, although the sand layer is washed with water or air, if organic suspended matters in the secondary treatment water are retained in the filter layer, algae and protozoa gradually propagate in the filtration tank. For this measure, it was necessary to add a chemical such as hydrogen peroxide or sodium hypochlorite to suppress the propagation of organisms.

On the other hand, the ozone in the ozone gas injected into the ozone reaction tank is not consumed in its entirety, but is discharged outside the system as exhausted ozone gas. Since ozone gas is a harmful substance, it is converted into oxygen and discharged through a processing device filled with a catalyst or the like.

An object of the present invention has been made in view of the above-mentioned problems of the prior art, and can solve the problems of sand filtration and ozone treatment by operating a combination of sand filtration and ozone treatment. An object of the present invention is to provide an operation method of a sand filtration / ozone treatment device.

[0013]

In order to achieve the above object, according to the present invention, waste ozone gas from an ozonation apparatus is introduced as an air lift air source for moving sand in a sand filtration tank. On the other hand, when viewed from the ozone treatment side, the load of the exhaust ozone gas treatment is reduced because the exhaust ozone gas is continuously used for the sand filtration treatment.

In the present invention, the object of the present invention can be attained by adopting a combination system in which sand is filtered in the first stage and ozone is processed in the second stage. That is, in the transfer type sand filtration tank, the sand layer is moved and circulated, and the filtration step and the washing step are operated continuously, and compressed air must be continuously supplied as an air lift. On the other hand, in the ozone treatment, ozone is continuously injected, and therefore, the discharged ozone gas is also continuously discharged. As described above, as a result of combining the opposing operations of requiring gas supply in the sand filtration process and disposal of the exhaust gas on the ozone treatment side, it is possible to effectively operate the processing devices of the sand filtration tank and the ozone reaction tank. When the waste ozone gas thus disposed is used as an air lift gas for sand filtration, compressed air is not required, and since the sand is transferred by the waste ozone gas, propagation of organisms is suppressed. Furthermore, chemicals for suppressing the propagation of organisms are not required. In addition, the exhausted ozone gas comes into contact with the raw water for filtration, and the ozone treatment proceeds even in the sand filtration tank, which has a synergistic effect of reducing the chromaticity and the concentration of organic substances.

[0015]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below with reference to FIG.

The raw water for filtration (secondary treated water) 20 is supplied to the sand filtration tank 1.
0 and flows out from the tank top as filtered water 21b. The filtered water 21b is then passed to the ozone reactor 16
From the top of the tank and taken out as treated water 22 from the bottom of the tank. On the other hand, ozone gas is blown from the bottom of the ozone reaction tank 16 through the diffuser 17. The ozone gas that has not been reacted with the blown ozone gas is discharged as ozone gas 25 from the top of the ozone reaction tank 16.

Next, the exhausted ozone gas 25 is supplied to the blower 1
5 introduces the gas into the gas injection pipe 14 in the sand filtration tank 10. The gas injection pipe 14 is connected to the inside of the bottom of the air lift pipe 12, and the ozone gas 26 sent into the air lift pipe 12 flows out from the top of the sand filtration tank 10 as an exhaust gas 27, and the exhaust ozone gas treatment device 18 And then discharged out of the system.

Next, the operation of the embodiment constructed as described above will be described. In the filtration step, SS in the raw filtered water 20 flowing from the bottom of the sand filtration tank 10 is captured in the sand layer 11 by filtration and adhesion in the sand layer. The raw water from which the SS component has been removed flows out from the top of the sand filtration tank 10 and becomes filtered water 21b, and enters the ozone gas reaction tank 16 in the latter stage. The filtered water flowing into the ozone reaction tank comes into countercurrent contact with the ozone gas 24 injected from the bottom of the ozone reaction layer 16 in the tank. At that time, components such as organic matter and chromaticity in the treated water are reduced in concentration by the oxidizing power of the injected ozone gas, and flow out as treated water 22.

On the other hand, the ozone in the injected ozone gas is not partially consumed in the reaction tank 16 but is discharged from the top of the tank as exhausted ozone gas 25. Blower 1
5, the gas is introduced into the air lift pipe 12 through the gas injection pipe 14 in the sand filtration tank 10. The suction gas also sucks up the sand and water at the bottom of the sand filter tank 10 when moving up the air lift pipe.

The sand that has risen in the air lift pipe enters the filter medium washer 13 and flows down by its own weight. The sand is brought into countercurrent contact with a part of the filtered water 21a filtered by the sand layer 8, and the sand that has flowed down by its own weight is brought into contact therewith. Is washed. The washed sand further flows down to form a sand layer 8. As described above, the sand as the filter medium is continuously circulated and moved, and the filtration step and the washing step are continuously repeated.

The washing water that has passed through the filter material washing device 13 is discharged out of the system as washing waste water 23, and
Most of the filtered water 21b that has not entered into 3 flows into the ozone reaction tank 16 in the subsequent stage. The exhausted ozone gas 26 used as the air lift gas is supplied to the air lift tube 12.
Since it is mixed and stirred with the sand and the raw water for filtration, ozone treatment also proceeds in the air lift tube, and there is also an effect of removing organic substances, chromaticity, and the like in the filtered water 26. Therefore, the residual ozone in the exhaust ozone gas 27 is consumed, most of the exhaust ozone gas 25 from the top of the sand filtration tank 10 becomes oxygen, and the load on the exhaust ozone gas treatment tank 18 is greatly reduced.

Next, the effectiveness of the present invention will be described based on specific demonstration data. The operation conditions of the sand filter tank and the ozone reaction tank treatment device were as follows: treated water volume: 5 L / min, ozone injection concentration: 2
0 mg / L Ozone injection rate: 20 mg / L Ozone gas amount:
8 NL / min.

Effect (1) Ozone content in exhausted ozone gas Table 1 shows the ozone exhaustion reduction status in the sand filtration tank 10 under the above operating conditions. In the same table, the ozone content in the exhausted ozone gas discharged from the ozone reaction tank was set to 100 in the conventional method.
On the other hand, when the exhaust ozone gas of the present invention is used as an air lift gas for the sand filtration tank (using the entire amount of the exhaust ozone gas),
The ozone content of the sand filter tank was reduced to 20.

[0024]

[Table 1]

Effect (2) Suppression of Propagation of Organisms in the Sand Layer As described above, when the washing operation for sand layer regeneration is performed by washing with water or empty, algae and protozoa proliferate. As a result, the flow resistance of the sand layer is increased, and the filtration operation is adversely affected, for example, the filtration loss is increased. As a countermeasure, chemicals are continuously injected into the filtered raw water to control the progress of organisms. Then, as a situation of propagation of organisms in the sand layer, the time-dependent change of filtration loss in the present invention and the conventional method was examined.

The operating conditions are (1) when the exhausted ozone gas of the present invention is used for an air lift, (2) when a conventional chemical injection method (sodium hypochlorite) is used, and (3) no chemical injection. There are three cases. The results are shown in FIG.

When no chemical injection was performed, the filtration loss gradually increased, whereas when the method of the present invention and the injection were used, the increase in filtration loss was suppressed. That is, in the present invention using the exhausted ozone gas, the same effect of suppressing the propagation of organisms as in the case of chemical injection was recognized. When sodium hypochlorite (effective chlorine concentration 10%) is used as a chemical, the amount of filtered water is 60 m ^3.
Although about 0.5 L / hr is injected with respect to / hr, according to the present invention, no chemical is required, and injection equipment is not required.

As a method for cleaning the sand layer, the entire sand layer may be immersed in hydrogen peroxide. However, in this method, a complicated process is required such that the waste liquid treatment of the used hydrogen peroxide and the re-cleaning of the sand layer must be repeated several times before use. These also become unnecessary in the present invention.

Effect (3) Water Quality of Sand Filtration Treatment Water FIG. 4 is a bar graph showing the result of comparing the water qualities of the sand filtration treatment water. Water quality items are chromaticity, SS content and COD,
The comparison was made between (1) raw filtered water, (2) air as the air lift gas source (conventional method), and (3) the method of the present invention using the exhausted ozone gas as the air lift gas source. The comparison method is
For each water quality item, the concentration in the filtered raw water was set as the standard 100.

As a result, the chromaticity had a slight removal effect of 90 in the conventional method, but was reduced to about 50 in the present invention, and the introduction of exhaust ozone was effective in removing the chromaticity component.
Next, the SS content was reduced to about 5 in both the conventional method and the method of the present invention by sand filtration, which was almost the same effect. Also, CO
D was 92 in the present invention, compared with 92 in the conventional method, and introduction of exhaust ozone was effective in removing organic components.

Effect (4) Number of Bacteria in Sand Filtration Water As a study of the number of bacteria in sand filtration water, the number of E. coli was measured. FIG. 5 shows the results of comparison of the number of E. coli in the conventional method and the method of the present invention, where the number of E. coli in the filtered raw water is 100. As a result, the SS content was captured by passing through the sand layer, and E. coli was also reduced to 90 to some extent. On the contrary,
With the introduction of the exhausted ozone of the present invention, it is reduced to 10 and it is clear that the exhausted ozone greatly contributes to the sterilization.

Effect (5) Chromaticity of Ozonated Water FIG. 6 shows the chromaticity of ozonated water. The conventional method uses air as an air lift gas, and the present invention uses exhaust ozone gas as a comparison.
The display method was set at 100 based on the conventional method. As a result, in the present invention, the chromaticity becomes 50 or less at an ozone injection rate of about 5 mg / L. On the other hand, in the conventional method, the ozone gas injection rate needs to be about 20 mg / L to reduce the chromaticity according to the present invention.

Effect (6) COD of Ozonated Water FIG. 7 shows the COD state of ozonated water. The display method of the result was set to 100 in the conventional method. As a result, in the present invention, 8
0 was used as a reference, and was reduced to 60 at an ozone injection rate of about 10 mg / L. On the other hand, in the conventional method, the ozone injection rate needs to be 20 mg / L to achieve 60.

Although the present invention has been described with reference to an example in which a sand filtration tank is provided in the first stage and an ozone reaction tank is provided in the second stage, the present invention is applicable to a case in which an ozone reaction tank is provided in the first stage and a sand filtration tank is provided in the second stage. It is possible to obtain the effect of

[0035]

According to the present invention, as an advanced treatment of the sewage secondary treatment water, a combination of a sand filtration treatment and an ozone treatment is used, and the ozone gas discharged from the ozone reaction tank is used for the sand filtration. The processing amount of ozone gas was significantly reduced. Furthermore, it is effective in improving the quality of the water subjected to the sand filtration treatment, which in turn leads to the improvement in the quality of the discharged water, which is effective in improving the aquatic environment.

[Brief description of the drawings]

FIG. 1 is a configuration diagram showing an entire embodiment of the present invention.

FIG. 2 is a configuration diagram showing a conventional example.

FIG. 3 is a diagram showing suppression of biological action in a sand layer.

FIG. 4 is a view showing the water quality of sand filtration treatment water.

FIG. 5 is a diagram showing a bactericidal effect.

FIG. 6 is a diagram showing the quality of ozonated water.

FIG. 7 is a diagram showing the quality of ozonated water.

[Explanation of symbols]

10: sand filter tank, 11: sand layer, 12: air lift tube,
13: sand washer, 14: gas blower pipe, 15: gas blower, 16: ozone reaction tank, 17: diffuser pipe, 18: exhaust ozone gas treatment tank, 20: raw filtered water, 21a: filtered water, 21b: filtration Treated water, 22: treated water, 23: washing water, 24: injected ozone, 25: exhausted ozone gas, 26: blow-in gas for air lift, 27: exhaust gas of sand filter tank, 2
8. Processing gas.

Claims (3)

[Claims] 1. A combined apparatus for transferring sewage water containing a floating substance and an organic substance to a bed-type sand filtration and an ozone oxidation treatment, wherein an ozone gas discharged from the ozone oxidation treatment is air-lifted by the transfer-type sand filtration processing. A method for operating a sand filtration / ozone treatment device, wherein the method is used for gas. 2. The sand filtration and ozone treatment according to claim 1, wherein the first stage is a moving bed type sand filtration process, the second stage is an ozone oxidation process, or the first stage is an ozone oxidation process, and the second stage is a moving bed type sand filtration process. How to operate the device. 3. The method for operating a sand filtration / ozone treatment apparatus according to claim 1, wherein the ozone gas / sand / inflow water is stirred and mixed by an air lift operation.