JPH08192176A - Separate injection type ozone contact method - Google Patents

Abstract

PURPOSE: To correspond to the use of highly conc. ozone by branching the passage of raw water into two passages and injecting ozone only into the raw water flowing through one passage to dissolve the same in raw water and allowing this water to meet with the raw water of the other passage to form mixed flow and sending the mixed flow to a stagnation tank to stagnate the same for a definite time before discharging the stagnated water as treated water. CONSTITUTION: Raw water 3 flows in the system from an introducing port 19 to be branched at a branch point 20 to flow toward an ozone dissolving part 17 to reach an ozone dissolving device 21 and the ozone gas sent from an ozone generator 7 is injected into raw water to be mixed therewith. The raw water 3 issued from the ozone dissolving device 21 meets with the raw water 3, which enters from the introducing port 19 to straightly advance through piping without advancing toward the ozone dissolving part 17 at the branch point 20, at a confluent point 22 to be mixed therewith to reach a mixing device 23 such as a barrier plate or a line mixer. Subsequently, the mixed raw water 3 flows in a stagnation part 18 to be stagnated for a definite time and is sent to the outside of the system as treated water from a discharge port 24.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a descending dissolution type ozone reaction tank for sterilizing water, deodorizing water, and oxidizing organic substances using ozone.

[0002]

2. Description of the Related Art In recent years, ozone is diffused in water by utilizing the characteristic that ozone has a strong oxidizing power next to fluorine, so that sterilization, decolorization, deodorization, and removal of organic or inorganic substances by oxidation are performed. Water treatment is widely used. In particular, in the water supply in the suburbs of cities, the damage of offensive odor caused by the water intake source is widespread, and the strong oxidizing power of ozone exerts a great effect in removing this offensive odor. The introduction of advanced processing using is being promoted.

An ozone treatment apparatus for reacting such ozone with organic matter in water treated by ozone (hereinafter referred to as raw water) supplies an ozone generator for generating ozone mainly from electric energy and raw water. It is composed of a water pump, a reaction tank for proceeding the reaction, and an exhaust ozone treatment facility for decomposing the exhaust ozone discharged unreacted from the reaction tank. Generally, the contact method of raw water and ozone is to remove ozone from the lower part of the reaction tank. A bubble column method that blows out as bubbles is used. In recent years, most of them have used a countercurrent contact method in which raw water is supplied from the top of the reaction tank in the bubble column to face ozone gas.In large-scale water purification plants, etc., a crossflow with multiple countercurrent contact ponds connected in series is used. A countercurrent multi-stage contact pond is used.

FIG. 3 is a schematic diagram showing the structure of a cross-flow countercurrent multistage contact basin, including the various devices attached thereto. In FIG. 3, several partition plates 2 are provided in the ozone contact pond 1, and the flow of water is shown by the arrows in FIG. 3, but the raw water 3 is an inlet port at one end of the ozone contact pond 1. 4 flowed in, flowed down in the ozone contact pond 1, moved up between the partition plates 2 and flowed down again, and finally, from the discharge port 5 at the other end of the ozone contact pond 1 as treated water 6 Taken out.

Then, the ozone gas generated by the ozone generator 7 outside the ozone contact pond 1 is introduced from the bottom of the ozone contact pond 1 and brought into contact with the raw water 3 as fine bubbles 9 by the air diffuser 8. Of the ozone injected at this time, unreacted ozone is decomposed by the exhaust ozone treatment facility 10 and released into the atmosphere. These ozone treatment devices require contact time for sufficiently performing an oxidation reaction on raw water. Therefore, when the amount of treated water is large, a large-volume ozone contact pond is required, and when it is introduced into a water purification plant in the suburbs of a city with a large water supply population, large-scale equipment is required. The need for large-scale equipment means
It is not preferable from the economical point of view and becomes a major factor that hinders the introduction of a water treatment apparatus using ozone. Therefore, the ozone treatment apparatus is required to have a high ozone absorption rate and a sufficient organic substance removal efficiency.

[0006] Here, the ozone absorption rate means that of the injected ozone gas, it is dissolved or decomposed in raw water in the reaction tank,
It is the ratio of ozone consumed and is expressed by the following formula.

[0007]

[Equation 1] The removal efficiency is the ratio of water pollutants in the raw water decomposed and removed in the reaction tank, and is represented by the following formula. Typical odorants are water pollutants.

[0008]

[Equation 2] Generally, the higher the ozone absorption rate and the removal efficiency, the better the processing efficiency of the ozone reaction tank.

The amount of ozone transferred when ozone is dissolved in water is the difference between the overall mass transfer capacity coefficient (K _L · a), the saturated ozone concentration in water, and the dissolved ozone concentration (concentration gradient). Is the main factor. This saturated ozone concentration is
It is known to depend on the ozone concentration in the gas and the ozone distribution coefficient. Therefore, from the viewpoint of increasing ozone dissolution efficiency by utilizing the water depth pressure of the reaction tank, the water depth of the reaction tank is
Although it is desirable to make the depth as deep as possible, in the above-described countercurrent contact method, gas must be blown against the water depth pressure of the reaction tank, so the actual water depth of the reaction tank was 6 m. A descending dissolution type ozone treatment device was conceived to cope with this.

FIG. 4 is a schematic view showing the structure of the main part of the descending dissolution type ozone processing apparatus, and the same reference numerals are used for the same parts as in FIG. In FIG. 4, this apparatus introduces the raw water 3 from the inlet 12 at the upper part of the reaction tank 11 by the water supply pump 13, and at the same time, the ozone gas generated by the ozone generator 7 is passed through the diffuser 8 to form fine bubbles 9. , Reaction tank 11
Inject into. The raw water 3 becomes a mixed flow with bubbles 9 (ozone gas) and flows down the descending dissolution section 14 of the reaction tank 11. This mixed flow passes through the bottom of the reaction tank 11 and the rising section 15,
The treated water 6 can be distributed from the outlet 16 to the outside of the reaction tank 11. The flow direction of the raw water 3 is indicated by an arrow.
Of the injected ozone gas, unreacted ozone gas is decomposed by the exhaust ozone treatment facility 10 and released to the outside of the system.

Such a descending dissolution type ozone treatment apparatus is
Since the raw water 3 and the ozone gas are simultaneously introduced from the top of the reaction tank 11, there is no need to blow the gas against the water depth pressure, and it is possible to design a reaction tank having a depth of about 30 m, which is deeper than the countercurrent contact method. is there. Further, since the dissolution rate of ozone is high, the ozone absorption rate is 95% or more and the organic matter removal efficiency is 75% or more, which is far higher than the performance of the countercurrent reaction tank.

Generally, when water treatment using ozone is performed in a water purification plant or the like, the ozone injection amount is 1 per 1 L of raw water.
Set to ~ 3 mg. Moreover, since an ozone generator using air as a raw material is usually used, the generated ozone gas concentration is about 20 mg / L, and the gas-liquid ratio (raw water flow rate / ozone gas flow rate) shows a value of 6.6 to 20. . On the other hand, regarding an ozone generator, recently, a high-concentration ozone generator using oxygen as a raw material has been developed, and the ozone generation cost has been reduced to the same level as that of a conventional air raw material. Further, as described above, since the ozone transfer rate from the gas phase to the liquid phase largely depends on the injected ozone gas concentration, it is very desirable from the viewpoint of mass transfer that the ozone gas concentration be high. .

[0013]

However, there are the following problems in using high-concentration ozone. From the viewpoint of hydraulic characteristics (gas-liquid flow mode) of the ozone contact pond, it is not preferable that the amount of ozone air decreases when the injection rate of highly concentrated ozone is constant. In the case of the above-mentioned cross-flow countercurrent multi-stage contact basin, the ozone contact basin originally has the hydraulic characteristic of complete mixing, but when the ozone gas concentration becomes high and the ozone gas flow rate becomes small, mixing due to the rise of bubbles occurs. Also, the stirring effect is reduced, and short-circuit flow and dead water regions are generated. This has been experimentally confirmed by the present inventors, and when the ozone gas flow rate with respect to the raw water flow rate is 1/100 or less (gas-liquid ratio ≧ 100), poor mixing occurs.

On the other hand, the descending dissolution type ozone treatment apparatus described above has a characteristic of gas-liquid co-current extrusion flow, and such a mixing failure does not occur even if the ozone gas air volume decreases. Therefore, in order to use high-concentration ozone, it can be said that the descending dissolution type ozone treatment device is a more suitable contact method than the cross-flow countercurrent multi-stage contact tank. It is not suitable for large-scale water purification facilities because it requires construction technology compared to the flow type. In addition, it is not suitable for use in the suburbs of Japan, where underground use is considerably advanced, in that it requires deep underground digging.

However, it is expected that the ozone generator will become even more efficient in the future and the concentration of ozone generated will increase, so that it is suitable for high-concentration ozone gas, especially for large-scale water treatment facilities using ozone. There is an urgent need to find a method of contact with raw water. The present invention has been made in view of the above points, and an object thereof is to provide a separation injection ozone contacting method that can sufficiently cope with the use of high-concentration ozone and that does not require facility manufacturing costs. Especially.

[0016]

In order to solve the above-mentioned problems, the separation injection ozone contacting method of the present invention divides raw water into two flow passages, and ozone is supplied only to the raw water flowing through one flow passage. It is injected and dissolved, and this water is merged again with the raw water flowing through the other flow path and mixed, and this mixed flow is sent to a retention tank where it is retained for a certain period of time and then discharged out of the system as treated water. The ratio of the ozone flow rate to the raw water flow rate at which ozone is injected and dissolved is at least 0.2 (a gas-liquid ratio of 5 or more).

[0017]

As described above, according to the present invention, the flow of raw water to be brought into contact with ozone is once branched into a separate flow path, and after ozone is injected and dissolved, the raw water of the main stream is re-merged and mixed again. Even if the ozone injection rate is constant by using high-concentration ozone as the water purification equipment, it is possible to obtain a high removal rate of odorous substances, etc., by always maintaining a large gas-liquid ratio without causing poor mixing of raw water and ozone. .

[0018]

[Examples] The inventors of the present invention have conducted extensive studies on a method for injecting high-concentration ozone gas in a large-scale ozone water purification treatment facility through trial manufacture, experiments, and simulations. We have found a method for injecting ozone that can obtain ozone dissolution efficiency and organic matter removal efficiency. The method of the present invention will be described below based on an example.

FIG. 1 is a schematic view showing the structure of the main part of a water treatment apparatus to which the separation injection type ozone contacting method according to the present invention is applied, and the same parts as those in the previous figures are represented by the same reference numerals. Hereinafter, with reference to FIG. 1, a water purification process using ozone will be described together with the configuration of the apparatus. FIG.
In the above, the feature of this apparatus is that it has an ozone dissolving part 17 and a retaining part 18 both surrounded by a dotted line in the system, and a pipe flow path is branched into these two parts so that the raw water 3 flows. That is. First, the raw water 3 flows into the system through the inlet 19, and at the branch point 20 using, for example, a valve, an ozone dissolving section.
It is branched to the 17 side and reaches the ozone dissolving device 21, where the ozone gas sent from the ozone generating device 7 is injected,
Mixed. As the ozone dissolving device 21, an ordinary mixing device such as a bubble column or an ejector is used. Also,
The amount of branching water to the ozone dissolving part 17 side can be arbitrarily determined in consideration of the water quality of the raw water 3 and the treatment scale of the entire equipment, but the amount of branching water to the ozone dissolving part 17 side can be reduced. In this case, the load on the ozone dissolving device 21 is correspondingly reduced, which contributes to a reduction in equipment cost.

Next, the raw water 3 discharged from the ozone dissolving device 21
(Ozone-mixed raw water) enters from the inlet 19 and branches off at 2
At 0, the raw water 3 that does not proceed to the ozone dissolution section 17 side goes straight in the pipe and is mixed and mixed at a confluence point 22 and reaches a mixing device 23 such as a baffle plate or a line mixer to ensure the mixing property. The device 23 is not always necessary depending on the situation. Then, merging mixed raw water 3 is flows into the retention portion 18, retaining portion 18 may comprise retention tank having substantially the same structure as the ozone contact basin 1 shown in FIG. 3, a plurality in the tank The partition plate 2 is installed to have a vertical bypass structure, so that the flow of water in the retention section 18 is made uniform and the occurrence of a short circuit flow is suppressed.

In this way, the raw water 3 mixed with ozone can be sent out of the system as treated water 6 from the outlet 24 after staying in the holding section 18 for a certain period of time. The exhaust ozone treatment facility 10 is the same as that described above. Retention area
The residence time in 18 (retention tank) is required to allow the decomposition reaction of organic substances to proceed, and is set to about 10 to 20 minutes when removing odorous substances, for example. Therefore, the volume of the retention section 18 increases according to the amount of treated water, but unlike the case of the cross-flow countercurrent multi-stage contact pond shown in FIG. 3, the ozone diffuser 8 is not installed and the structure is extremely simple. Therefore, the manufacturing cost can be kept low.

FIG. 2 shows a comparison between the separate injection type ozone contacting method according to the present invention and the conventional ozone contacting method in a cross-flow type countercurrent multistage contact basin in terms of the relationship between injected ozone gas concentration and odorous substance removal rate. It is a diagram. The treatment conditions were the same, and the water depth was 6 m, the contact time was 5 min, and the injection rate was 1.5 mg / L. Since the ozone gas concentration to be injected is changed under the condition that the ozone injection rate is constant, the higher the ozone gas concentration is, the smaller the ozone gas air flow is injected, and the gas-liquid ratio (raw water flow rate / ozone gas flow rate).
Grows. Each curve in FIG. 2 is plotted by ● in the present invention, and plotted by ■ in the conventional method, and the gas-liquid ratio is added to each plotted point.

Further, the amount of branched water to the separation injection type ozone dissolving section 17 (FIG. 1) according to the present invention is 1/10 of the total raw water.
As a result, the gas-liquid ratio is about an order of magnitude smaller than in the case of a cross-flow countercurrent multistage contact basin. As shown by the curves in FIG. 2, the cross-flow countercurrent multistage contact basin shows a higher odorous substance removal rate below the injected ozone gas concentration of around 80 mg / L.
It can be seen that, when g / L or more, the odorous substance removal rate of the separation injection type ozone contacting method becomes high and the superiority increases. This indicates that the separation injection type ozone contact method has a large influence of the gas-liquid ratio in the ozone dissolving part, and the degree varies depending on the water quality of the raw water, but according to the separation injection type ozone contact method of the present invention, It can be seen that higher efficiency of the reaction tank can be obtained as compared with the conventional cross-flow countercurrent multi-stage contact tank by performing the injection operation using the ozone gas with a high concentration and keeping the gas-liquid ratio always high. From FIG. 2, it is effective to maintain the gas-liquid ratio in the method of the present invention at 5 or more.

[0024]

EFFECTS OF THE INVENTION In recent years, the performance of ozone generators has improved, and high concentration ozone has come to be used for water treatment. When high concentration ozone is used, a cross flow countercurrent multi-stage contact pond is used for raw water. Since it is not preferable to use the conventional method as it is because the mixing state of ozone and ozone is bad and the equipment cost of the down dissolution type water treatment equipment is high, a new ozone injection method compatible with high concentration ozone is recommended. Had to develop.

On the other hand, in the separation injection type ozone contact method found by the present inventors, raw water is branched into two flow paths, and ozone is injected and dissolved only in the raw water flowing through one flow path. Water is re-merged with the raw water flowing through the other flow channel and mixed, and this mixed flow is sent to a retention tank where it is retained for a certain period of time and then discharged out of the system as treated water.
When high-concentration ozone is used in a large-scale water treatment facility, even if the ozone injection rate is constant, a high gas-liquid ratio is always maintained and a high removal rate of organic substances is obtained without causing a poor mixing of raw water and ozone. be able to.

As described above, the method of the present invention can effectively use high-concentration ozone by means of a large-scale water treatment facility, and in combination with the expected cost reduction of high-concentration ozone gas generation in the future, low cost and high cost. It is possible to realize a water treatment system that uses ozone with high efficiency, and it can be applied to various water purification facilities.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing a main configuration of a water treatment device to which the method of the present invention is applied.

FIG. 2 is a diagram showing the relationship between the concentration of injected ozone gas and the removal rate of odorous substances, which is shown by comparing the method of the present invention with the conventional method.

FIG. 3 is a schematic diagram showing a main configuration of a water treatment device using a cross-flow countercurrent multistage contact basin.

FIG. 4 is a schematic diagram showing a main configuration of a descending dissolution type ozone treatment apparatus.

[Explanation of symbols]

1 Ozone Contact Pond 2 Partition Plate 3 Raw Water 4 Inlet 5 Outlet 6 Treated Water 7 Ozone Generator 8 Diffuser 9 Air Bubble 10 Waste Ozone Treatment Facility 11 Reaction Tank 12 Inlet 13 Water Pump 14 Descent Dissolving Part 15 Ascending Part 16 Discharge port 17 Ozone dissolution section 18 Retention section 19 Inlet port 20 Branch point 21 Ozone dissolution device 22 Confluence point 23 Mixing device 24 Discharge port

Claims (2)

[Claims] 1. When performing a water treatment for purifying raw water by injecting ozone, the raw water introduced into a pipe system is branched into two flow paths, and only the raw water flowing through an ozone dissolving section formed in one flow path is branched. Ozone is injected and dissolved, and this water is merged again with the raw water flowing through the other flow path and mixed, and this mixed flow is sent to the retention part consisting of a tank with multiple partition plates, where the upper and lower bypass flow As a treated water, the separated contact type ozone contacting method is characterized by discharging the treated water outside the system. 2. The separation injection ozone contact method according to claim 1, wherein the ratio of the ozone flow rate to the raw water flow rate at which ozone is injected and dissolved is at least 0.2 (gas-liquid ratio of 5 or more). Separate injection type ozone contact method.