JP2003094075A - System and method for treating water - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve a system and a method for treating water for decomposing a difficult-to-decompose organic matter in water by an oxidation promotion treatment utilizing ozone/ultraviolet rays. SOLUTION: The system for treating water is provided with an ozone addition means (an ejector 3 to which an ozone generator 8 is connected), an ultraviolet irradiation means 4, and a gas/liquid separating vessel 5 having a pressure adjusting means 6 and a liquid level adjusting means 7. An unreacted ozone is separated from a mixed fluid after irradiating the ultraviolet rays in the gas/liquid separating vessel 5, and a pressure of an ozone/raw water mixed fluid in the ultraviolet irradiation means 4 is stabilized by regulating the pressure of the gas separated in the gas/liquid separating vessel 5 and the liquid level of the treatment water. As a result, the oxidation promotion treatment can be stably performed, and the unreacted ozone after treatment can efficiently be reused at low cost.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a water treatment apparatus and method, and more particularly to a water treatment apparatus and method suitable for treating raw water containing hardly decomposable organic substances such as dioxins. Is.

[0002]

Conventionally, in order to decompose persistent organic substances such as dioxins contained in wastewater, ozone is dissolved in the wastewater and irradiated with ultraviolet rays to generate OH radicals to oxidize the organic matter. An accelerated oxidation treatment that decomposes is considered (Japanese Patent Laid-Open No. 2001-70962 etc.).

For example, by dissolving ozone gas generated by an ozone generator using PSA in raw water treated through a sand filtration tower, an activated carbon tower, and a biological activated carbon tower, and irradiating the raw water with ultraviolet rays by an ultraviolet irradiator. It is possible to oxidatively decompose the hardly decomposable organic matter contained in. At this time, the ozone addition pressure is limited by the ozone gas supply pressure (about 0.1 MPa at maximum) of the ozone generator, and the ozone addition is performed at a pressure lower than this or by using an apparatus such as an ejector.

Since the raw water to be treated usually contains a radical scavenger which is a reaction inhibitor in the oxidative decomposition of organic substances by ozone / ultraviolet rays, ozone is added to the raw water in advance before the accelerated oxidation treatment. Pre-ozone treatment is often used to remove radical scavengers.

Further, in order to further reduce the concentration of organic substances in water, there are cases where these devices are arranged in a circulation line and a back pressure valve is provided at a predetermined position in the flow path to repeatedly carry out the accelerated oxidation treatment.

[0006]

By the way, in the above-mentioned accelerated oxidation treatment, not all of the ozone gas supplied to the raw water is converted into OH radicals by the irradiation of ultraviolet rays, but the exhaust ozone / treated water mixture after irradiation of ultraviolet rays is mixed. The fluid is
Usually, about 10 to 20% of the supplied ozone amount remains unreacted ozone. This unreacted ozone is usually released into the atmosphere at atmospheric pressure or a slight negative pressure, but for the purpose of cost reduction, it has been attempted to recover unreacted ozone and reuse it for accelerated oxidation treatment or pre-ozone treatment. Has been done.

However, in order to reuse the recovered ozone for the accelerated oxidation treatment and the pre-ozone treatment, the ozone must be under a pressurized state, and thus it is not possible to achieve a sufficient cost reduction effect. That is,
A pressurizing fan is generally used as a means for pressurizing ozone, but due to the chemical nature of ozone, it is necessary to take explosion-proof measures for the pressurizing fan, which is rather costly. It is also possible to provide a blower in the exhaust ozone gas line or supply an ejector to the ozone reuse destination with a pump. However, these methods all require power for pressurization, and power means is required. Costs increase due to installation of the equipment and energy supply to the equipment.

Further, in the conventional method, the treatment conditions in the accelerated oxidation treatment are likely to be unstable. In particular, when the accelerated oxidation treatment is repeatedly performed in the circulation line, the raw water and the treated water circulate in the circulation route while the pressure of the raw water keeps changing, so the treatment conditions may change due to the influence of ozone or unreacted ozone supplied to the raw water. Therefore, it becomes very difficult to stably perform the accelerated oxidation treatment.

The present invention has been made in view of the above problems of the prior art, and when decomposing a hardly decomposable organic substance in water by an accelerated oxidation treatment utilizing ozone / ultraviolet, a stable oxidation treatment is performed. It is an object of the present invention to provide a water treatment apparatus and method that enable efficient implementation and efficient and inexpensive reuse of unreacted ozone after treatment.

[0010]

In order to solve the above problems, the water treatment apparatus of the present invention comprises an ozone addition means for adding ozone to raw water containing a persistent organic substance to obtain an ozone / raw water mixed fluid. , An ozone / raw water mixed fluid is irradiated with ultraviolet rays to obtain waste ozone / treated water mixed fluid, and an ultraviolet irradiation means, a pressure adjusting means and a liquid level adjusting means are provided.
The treated water mixed fluid is separated into a gas containing unreacted ozone and the treated water, and the pressure of the gas and the treated water level are adjusted to stabilize the pressure of the ozone / raw water mixed fluid in the ultraviolet irradiation means. And a gas-liquid separation tank that does.

Further, the water treatment method of the present invention comprises an ozone addition step of adding ozone to raw water containing a hardly decomposable organic substance under pressure to obtain an ozone / raw water mixed fluid, and an ultraviolet ray to the ozone raw water mixed fluid. An ultraviolet irradiation step of irradiating to obtain a waste ozone / treated water mixed fluid, and separating the waste ozone / treated water mixed fluid into a gas containing unreacted ozone and treated water, and at the same time, treating the gas pressure and the treated water liquid. A gas-liquid separation step of stabilizing the pressure of the ozone / raw water mixed fluid in the ultraviolet irradiation step by adjusting the position.

In the present invention, ozone is added to raw water containing a hardly decomposable organic substance, and when the organic substance is decomposed by irradiating it with ultraviolet rays, exhaust ozone after irradiation with ultraviolet rays /
By adjusting the pressure of the gas separated from the treated water mixed fluid and the liquid level of the treated water to stabilize the pressure of the ozone / raw water mixed fluid at the time of ultraviolet irradiation, the treatment conditions in ozone / ultraviolet treatment will be sufficient. Since it is stabilized and the ozone dissolution rate in the raw water is maintained at a high level, it is possible to efficiently and reliably oxidatively decompose the hardly decomposable organic matter contained in the raw water.

Further, since the unreacted ozone separated from the exhaust ozone / treated water mixed fluid in this way has a sufficiently high pressure, it can be added without using a pressure fan or the like provided with explosion-proof measures. It can be reused under pressure and a sufficient cost reduction can be achieved.

Therefore, according to the present invention, there is provided a water treatment apparatus and method which enable stable implementation of accelerated oxidation treatment utilizing ozone / ultraviolet rays and efficient and inexpensive reuse of unreacted ozone after treatment. Will be realized.

Further, the water treatment apparatus of the present invention is a pre-ozone treatment for removing radical scavengers contained in raw water by adding unreacted ozone from the gas-liquid separation tank to the raw water before being supplied to the ozone adding means. It may be characterized by further comprising means.

Further, the water treatment method of the present invention is a pre-ozone treatment for removing radical scavengers contained in raw water by adding unreacted ozone from the gas-liquid separation step to the raw water before being supplied to the ozone addition step. It may be characterized by further including a step.

By carrying out the pre-ozone treatment using the unreacted ozone separated from the treated water obtained by the accelerated oxidation treatment as described above, a radical scavenger which is a reaction inhibitor in the oxidative decomposition of hardly decomposable organic substances by ozone / ultraviolet rays. As a result, the decomposition efficiency of the organic substance in the accelerated oxidation treatment can be further enhanced. Further, the required amount of fresh ozone (ozone produced by the ozone supply means) required for the entire apparatus can be sufficiently reduced compared to the conventional one, so that the ozone generation means can be downsized and the power consumption can be reduced. Is realized.

[0018]

BEST MODE FOR CARRYING OUT THE INVENTION Preferred embodiments of the present invention will be described in detail below with reference to the drawings. In the description of the drawings, the same elements will be denoted by the same reference symbols, without redundant description. Further, the dimensional ratios in the drawings do not always match those described.

FIG. 1 is a schematic configuration diagram showing a preferred embodiment of the water treatment apparatus of the present invention. In FIG. 1, a pre-ozone treatment apparatus 11 adds ozone to raw water containing a hardly decomposable organic substance to generate radical scavengers (COD, BOD, Ca ions, Fe ions, Mn) contained in the raw water.
Ions, Al ions, etc.), and the raw water that has been subjected to pre-ozone treatment is sent to and stored in the treated raw water tank 1. In addition, in this embodiment, ozone used in the pre-ozone processing apparatus 11 is supplied from a gas-liquid separation tank 5 described later.

A circulation line 10 is connected to the treated raw water tank 1, and the raw water in the treated raw water tank 1 is drawn to the circulation line 10 by a circulation pump 2 and returned to the treated raw water tank 1 again. In the circulation line 10, the ejector 3, the ultraviolet irradiation device 4, and the gas-liquid separation tank 5 are arranged in this order along the flow of raw water.

The ejector 3 is connected to an ozone generator 8 having a built-in ozone generating power source (not shown), and the amount of ozone generated can be increased or decreased according to the voltage of this power source. As a result, in the ejector 3, after a predetermined amount of ozone is added to the raw water drawn from the treated raw water tank 1, the ozone / raw water mixed fluid is irradiated with the ultraviolet irradiation device 4
Sent to.

The ultraviolet irradiation device 4 comprises an ultraviolet irradiation tank 4a and an ultraviolet lamp 4b.
The ozone / raw water mixed fluid staying in the area is irradiated with ultraviolet rays from the ultraviolet lamp 4b. As a result, OH radicals are generated in the mixed fluid, and the hardly decomposable organic matter is oxidatively decomposed by the OH radicals. Note that the number of the ultraviolet lamps 4b in FIG. 1 is three, but the number is not limited to this, and may be one, two, or four or more.

The mixed fluid that has passed through the ultraviolet irradiation device 4 is contained in a gas-liquid separation tank 5 and separated into a liquid phase and a gas phase. A pressure adjusting device 6 is provided above the gas-liquid separation tank 5, and a liquid level adjusting device 7 is provided below it. The pressure adjusting device 6 is connected with a pressure measuring device (such as a differential piezoelectric feeder), a PIC (pressure indicating adjusting system) including an indicating controller and a controlling valve, and measures the pressure measured by the pressure measurement value. A constant pressure can be controlled by automatically and continuously giving a matching output from the indicating controller to the control valve (PID control). Further, the liquid level adjusting device 7 is connected to a liquid level measuring device (such as a differential piezoelectric transmitter capable of converting pressure into liquid level), an LIC (liquid level indicating adjusting system) including an indicating controller and a controlling valve. By automatically and continuously giving an output corresponding to the liquid level (converted value from pressure) measured by the liquid level measuring device from the indicating controller to the control valve (P
(ID control), it is possible to control to a constant liquid level. Thus, by the pressure adjusting device 6 and the liquid level adjusting device 7,
A region from the gas phase portion of the gas-liquid separation tank 5 to the ultraviolet irradiation device 4 is water-sealed with a liquid phase, and the pressure adjusting device 6 adjusts the pressure of the gas phase in the gas-liquid separating tank 5 and a liquid level adjusting device. 7
Thus, the liquid level of the liquid phase can be adjusted, and as a result, the pressure of the ozone / raw water mixed fluid in the ultraviolet irradiation device 4 can be adjusted to a desired value.

The gas containing unreacted ozone separated in the gas-liquid separation tank 5 is supplied to the pre-ozone treatment device 11 while being pressurized to a predetermined pressure by the pressure adjusting device 6. On the other hand, the treated water is from the gas-liquid separation tank 5 to the treated raw water tank 1
And is circulated through the circulation line 10 again or discharged from the treated water pump 9 to the outside of the apparatus.

Next, a method for treating raw water containing a hardly decomposable organic substance by using the water treatment apparatus having the above-mentioned structure will be described.

The raw water to be treated in the present invention contains a hardly decomposable organic substance as described above. Specific examples of such a hardly decomposable organic substance include dioxins, organic halogen compounds such as trichloroethylene, and TOC.
(Total organic carbon; all-organic carbon).

Since such raw water usually contains a radical scavenger which is a reaction inhibitor of the oxidative decomposition of hardly decomposable organic substances in the accelerated oxidation treatment by ozone / ultraviolet rays, the raw water is preliminarily converted into raw water in the pre-ozone treatment apparatus 11. It is preferable to perform a pre-ozone treatment in which ozone is added to remove the radical scavenger. This allows
The decomposition efficiency of organic substances in the accelerated oxidation treatment can be further enhanced. Further, when pre-ozone treatment uses unreacted ozone obtained in the gas-liquid separation step to be described later, the required amount of fresh ozone (ozone produced by the ozone supply means) required for the entire apparatus is conventionally reduced. It is preferable in that it is sufficiently reduced. The raw water from which the radical scavenger has been removed in this way is sent to and stored in the treated raw water tank 1.

The raw water in the treated raw water tank 1 is drawn to the circulation line 10 by the circulation pump 2 and mixed with the ozone from the ozone generator 8 in the ejector 3 to produce ozone /
It becomes a mixed fluid of raw water (ozone addition step). The ozone supply pressure from the ozone generator 8 is usually the circulation pump 2
Although the pressure of the raw water is lower than that of the raw water, the use of the ejector 3 allows the raw water to be mixed even if the raw water has a higher pressure than ozone. For example,
When the supply pressure of ozone is 0.1 MPa and the pressure of raw water is 0.3 to 0.4 MPa, 0.2 to 0.3 MP
An ozone / raw water mixed fluid pressurized to a can be obtained, and an ozone dissolution rate of 80 to 90% in the mixed fluid can be achieved. If the pressure of the raw water exceeds the upper limit value, the difference from the ozone supply pressure is too large and the two cannot be mixed sufficiently.

Next, the ozone / raw water mixed fluid is sent to the ultraviolet irradiation device 4 and the mixed fluid retained in the ultraviolet irradiation tank 4a is irradiated with ultraviolet rays from the ultraviolet lamp 4b (ultraviolet irradiation step). As a result, OH radicals are generated from ozone in the mixed fluid, and the oxidizing power of the OH radicals oxidatively decomposes the hardly decomposable organic matter.

The mixed fluid after the ultraviolet irradiation step is treated water purified by oxidative decomposition of organic substances and the ultraviolet irradiation device 4
It is a mixed fluid (exhaust ozone / treated water mixed fluid) with a gas containing unreacted ozone (exhaust ozone gas) that has not been consumed in the process. These are contained in a gas-liquid separation tank 5 and separated into a liquid phase and a gas phase. (Gas-liquid separation step).

At this time, the region from the gas phase portion of the gas-liquid separation tank 5 to the ultraviolet irradiation device 4 is water-sealed with the liquid phase (treated water), and the pressure adjusting device 6 is used.
The pressure of the internal gas phase (exhausted ozone gas) and the liquid level of the liquid phase are adjusted by the liquid level adjusting device 7. Thereby, the pressure of the ozone / raw water mixed fluid in the ultraviolet irradiation device 4 is adjusted to a desired value (preferably 0.2 to 0.3 MPa),
The processing conditions can be stabilized.

The gas containing unreacted ozone separated in the gas-liquid separation tank 5 is pressurized to a predetermined pressure by the pressure adjusting device 6 and supplied to the pre-ozone treatment device 11 in the pressurized state. Thereby, unreacted ozone can be reused efficiently and cheaply in the pre-ozone treatment. On the other hand, the treated water is returned from the gas-liquid separation tank 5 to the treated raw water tank 1 and circulated through the circulation line 10 again, or is discharged from the treated water pump 9 to the outside of the apparatus.

As described above, in this embodiment, when ozone is added to the raw water containing the hardly decomposable organic substance and the organic substance is decomposed by irradiating it with ultraviolet rays, the waste ozone / treated water mixed fluid after the irradiation of ultraviolet rays is added. By adjusting the pressure of the gas separated from and the liquid level of the treated water to stabilize the pressure of the ozone / raw water mixed fluid during UV irradiation, the treatment conditions are sufficiently stabilized and the ozone dissolution rate is high. Since it is maintained at the standard level, it is possible to efficiently and reliably oxidatively decompose the hardly decomposable organic matter contained in the raw water.

Further, since the unreacted ozone thus separated from the exhaust ozone / treated water mixed fluid has a sufficiently high pressure, it can be added without using a pressure-proof fan provided with explosion-proof measures. It can be reused under pressure and a sufficient cost reduction can be achieved.

Further, by performing pre-ozone treatment using unreacted ozone separated from the treated water obtained by the accelerated oxidation treatment, the radical scavenger which is a reaction inhibitor in the oxidative decomposition of the hardly decomposable organic matter by ozone / ultraviolet rays is generated. Not only can it be removed to further improve the decomposition efficiency of the organic matter, but also the required amount of fresh ozone (ozone produced by the ozone supply means) required for the entire device can be sufficiently reduced compared to the conventional method. Therefore, downsizing of the ozone generating means and reduction of power consumption can be realized.

The present invention is not limited to the above embodiment. For example, in the apparatus shown in FIG. 1, the unreacted ozone separated in the gas-liquid separation tank 5 is supplied to the pre-ozone treatment apparatus 11 and reused, but the unreacted ozone is supplied to the ejector 3 to promote the accelerated oxidation. It may be reused as ozone for treatment, or may be reused as ozone used for pre-stage ozone treatment, sludge ozone treatment and the like. The pre-stage ozone treatment mentioned here is a process of decomposing dioxins adsorbed on SS by ozone as a pre-process for removing COD, BOD, and SS (suspended solid content) contained in raw water. The sludge ozone treatment is a treatment for decomposing dioxins concentrated in sludge with ozone.

[0037]

As described above, according to the present invention,
When ozone is added to raw water containing hardly decomposable organic matter and the organic matter is decomposed by irradiating it with ultraviolet rays, the pressure of the gas separated from the waste ozone / treated water mixed fluid after irradiation with ultraviolet rays and the treated water By adjusting the liquid level to stabilize the pressure of the ozone / raw water mixed fluid during UV irradiation, the treatment conditions in the accelerated oxidation treatment are sufficiently stabilized and the ozone dissolution rate is maintained at a high level. It is possible to efficiently and reliably oxidatively decompose the hardly decomposable organic matter contained in the raw water.

Further, since the unreacted ozone separated from the exhaust ozone / treated water mixed fluid in this way has a sufficiently high pressure, the unreacted ozone is discharged from the pressurized fan with explosion-proof measures. It can be reused in a pressurized state without using the above, and a sufficient cost reduction can be achieved.

Therefore, according to the present invention, a water treatment apparatus and method capable of stably performing the accelerated oxidation treatment and efficiently and inexpensively reusing the unreacted ozone after the treatment are realized.

[Brief description of drawings]

FIG. 1 is a flow chart schematically showing a preferred embodiment of a water treatment device of the present invention.

[Explanation of symbols]

1 ... Treated raw water tank, 2 ... Circulation pump, 3 ... Ejector,
4 ... UV irradiation device, 4a ... UV irradiation tank, 4b ... UV lamp, 5 ... Gas-liquid separation tank, 6 ... Pressure adjusting device, 7 ... Liquid level adjusting device, 8 ... Ozone generator, 9 ... Treated water pump, 1
0 ... Circulation line, 11 ... Pre-ozone treatment device.

Claims (4)

[Claims] 1. An ozone adding means for adding ozone to raw water containing a hardly decomposable organic substance to obtain an ozone / raw water mixed fluid, and an ozone / treated water mixed fluid for irradiating the ozone / raw water mixed fluid with ultraviolet rays. And a pressure adjusting means and a liquid level adjusting means for separating the exhaust ozone / treated water mixed fluid into a gas containing unreacted ozone and treated water, and A gas-liquid separation tank for stabilizing the pressure of the ozone / raw water mixed fluid in the ultraviolet irradiation means by adjusting the liquid level of the treated water. 2. A pre-ozone treatment means for adding unreacted ozone from the gas-liquid separation tank to the raw water before being supplied to the ozone addition means to remove a radical scavenger contained in the raw water. The water treatment apparatus according to claim 1, wherein the water treatment apparatus is a water treatment apparatus. 3. An ozone addition step of adding ozone under pressure to raw water containing a persistent organic substance to obtain an ozone / raw water mixed fluid, and irradiating ultraviolet rays to the ozone raw water mixed fluid to discharge ozone / treatment. An ultraviolet irradiation step for obtaining a water mixed fluid, and separating the exhaust ozone / treated water mixed fluid into a gas containing unreacted ozone and treated water, and adjusting the pressure of the gas and the liquid level of the treated water. And a gas-liquid separation step of stabilizing the pressure of the ozone / raw water mixed fluid in the ultraviolet irradiation step. 4. A pre-ozone treatment step of removing unreacted ozone from the gas-liquid separation step to the raw water before being supplied to the ozone addition step to remove a radical scavenger contained in the raw water. The water treatment device according to claim 3, wherein the water treatment device is a water treatment device.