JP2003285059A - Control method of ozone supply in water treatment using ozone oxidation and membrane filtration - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a control method of ozone supply in water treatment using ozone oxidation and membrane filtration which can realize stable water treatment with a required minimum amount of injected ozone without the deterioration of filtration performance and reduce the running cost. <P>SOLUTION: In water treatment where one cycle comprises membrane filtration treatment after the ozone treatment of water to be treated and washing of a filtration membrane performed at every prescribed membrane filtration treatment time, dissolved ozone in water treated by membrane filtration is measured at every prescribed time after starting the membrane filtration treatment in the above one cycle, an increase/decrease amount of ozone supply at every prescribed time after starting the membrane filtration treatment in the next cycle is preset based on a difference between the above measured value and the predetermined target value of dissolved ozone, and the amount of ozone supply at every prescribed time after starting the membrane filtration treatment in the next cycle is controlled to the value corrected by the above increase/decrease amount. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for controlling ozone supply in water treatment using ozone oxidation and membrane filtration, which is carried out to separate and remove pollutants contained in water.

[0002]

2. Description of the Related Art As a method for removing pollutants in water to be treated, a water treatment method utilizing membrane filtration is well known. In the water treatment using this membrane filtration, as the water treatment operation is continued, an adhered layer of pollutants is generated on the surface of the membrane, clogging, fouling such as flow path clogging due to solid matter occurs, and filtration performance is improved. There is a problem of decline. Therefore, there is a problem that a stable amount of treated water cannot be obtained, or the frequency of chemical cleaning of the membrane must be increased in order to obtain a stable amount of treated water.

In recent years, in order to prevent the above-mentioned deterioration of the membrane treatment performance, a water treatment method has been proposed in which ozone oxidation treatment is carried out before the membrane filtration treatment and ozone is left on the membrane surface for filtration. According to this method, since ozone remains on the film surface, it is possible to oxidize and remove the film and the substances attached to the film by ozone, and it is possible to prevent deterioration of the film performance.

However, in the above-mentioned water treatment method utilizing ozone oxidation and membrane filtration, it is difficult to control the concentration of dissolved ozone in the membrane filtration water to a predetermined value, and therefore even when there is a fluctuation. Since it was necessary to add an excessive amount of ozone so that the concentration of dissolved ozone exceeds the target, it was desired to reduce the ozone supply amount as much as possible from the viewpoint of effective use of ozone.

On the other hand, Japanese Patent Laid-Open No. 2000-107777.
In the publication, as a water treatment method for reducing the ozone supply amount, the dissolved ozone concentration in the membrane-filtered water is continuously measured, and the dissolved ozone concentration in the membrane-filtered water falls within a predetermined range based on the measured value. A method of controlling the ozone supply amount so as to achieve the above is disclosed.

[0006]

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention
In the method described in Japanese Patent No. 777, the dissolved ozone concentration is monitored to control the ozone supply amount at that time. However, in reality, the response speed of the ozone supply amount change and the change of the dissolved ozone concentration accompanying it is slow, there is a time lag, and the filtered water at the time of backwashing and air washing does not flow to the dissolved ozone concentration detector. It is difficult to keep the ozone concentration constant because it is difficult to keep the ozone concentration constant due to the lack of time and the sudden change of the dissolved ozone concentration due to the recovery of the film contamination by the physical cleaning. It was

The present invention has been made in view of the above-mentioned problems of the prior art, and ozone oxidation and membrane filtration capable of realizing stable water treatment without deteriorating the filtration performance by a necessary minimum ozone supply amount. It is an object of the present invention to provide a method for controlling ozone supply in water treatment using water.

[0008]

That is, according to the present invention, after subjecting the water to be treated to ozone oxidation, a membrane filtration treatment is carried out, and further, the filtration membrane is washed at a predetermined membrane filtration treatment time for one cycle. Then, the dissolved ozone concentration in the membrane filtration treated water is measured, and based on this measured value, ozone oxidation and membrane filtration for controlling the ozone supply amount are performed so that the dissolved ozone concentration in the membrane filtration treated water is within a predetermined range. In the ozone supply control method for water treatment used, the dissolved ozone concentration in the membrane-filtered water is measured every predetermined time after the start of the one-cycle membrane filtration process, and the measured value and the predetermined dissolved ozone concentration target value are used. Based on the difference between the two values, the increase / decrease amount of the ozone supply amount for each predetermined time after the start of the membrane filtration process of the next cycle is set in advance, and the ozone supply for the predetermined time after the start of the membrane filtration process of the next cycle is set. Amounts, there is provided a supply control method of the ozone in the water treatment using ozone oxidation and membrane filtration, wherein the controller controls such that a value obtained by correcting the increment or decrement.

According to the present invention, the dissolved ozone concentration is not monitored and the ozone supply amount at that time is controlled, but the dissolved ozone concentration is measured every predetermined time in one cycle,
By controlling the ozone supply amount for each predetermined time in the next cycle based on that value, the dissolved time is not affected by the time lag due to the slow response speed and the rapid change in dissolved ozone concentration due to physical cleaning. It is possible to make the ozone concentration more constant, prevent clogging of the membrane with the minimum required ozone supply amount, and perform stable water treatment without lowering the filtration performance.

In the present invention, it is preferable to control so that the ozone supply amount between the points at the predetermined time intervals increases or decreases linearly or stepwise. According to this, since the ozone supply amount between each point for each predetermined time is also controlled to be a more preferable concentration, it is possible to make the dissolved ozone concentration more constant while further saving the ozone consumption amount. .

In the present invention, the ozone supply amount can be adjusted by the flow rate of ozone gas or the concentration of ozone gas.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION In the present invention, the control of the ozone supply amount is generally performed by keeping the ozone flow rate constant and changing the supplied ozone concentration so that the dissolved ozone concentration in the membrane filtration water becomes a predetermined value. It is easy to control, but it is also effective to control by changing the supply amount of ozone of the same concentration. In addition, it is generally preferable to supply ozone as ozone gas.

In the present invention, the dissolved ozone concentration in the membrane filtration treated water is measured every predetermined time after the start of one cycle of the membrane filtration treatment. Generally, the measured value and the predetermined dissolved ozone concentration target value are Based on the difference, the increase / decrease amount of the ozone supply amount for each predetermined time after the start of the membrane filtration process in the next cycle is set in advance.

Further, in the present invention, it is preferable to control so that the ozone supply amount between each point for every predetermined time increases or decreases linearly or stepwise. That is, in the present invention, the ozone supply is controlled by setting some points every predetermined time in one cycle. However, not only the ozone supply amount is controlled at each time point but also the ozone supply amount between them is controlled. It is desirable to control the supply amount more appropriately in terms of time.

As one of the methods, there is a method in which the ozone supply amount during that period is linearly increased and decreased to be controlled, and each time point (for example, 5 minutes and 10 minutes after the start of the membrane filtration treatment is set as each time point). At this time, the control is performed so as to increase / decrease in a linear manner for 5 minutes during this time. Further, as another method, a method of controlling the ozone supply amount during that time by increasing or decreasing in stages may be used.
It is controlled to increase or decrease by 0%.

Further, in the present invention, when setting the increase / decrease amount of the ozone supply amount in advance, the increase / decrease ratio of the ozone supply amount at the corresponding elapsed time of the next cycle with respect to the ozone supply amount at the predetermined elapsed time of the previous cycle. It is convenient to set it as (%). Therefore, the increase / decrease rate (%) of the ozone supply amount in the predetermined time after the start of the membrane filtration process in the next cycle is the ozone supply amount in the predetermined time after the start of the membrane filtration process in the previous cycle.
It is preferable to control so as to obtain a value obtained by multiplying by.

Hereinafter, one embodiment of the present invention will be described in more detail with reference to FIG. FIG. 1 shows a system system according to an embodiment of the present invention. In FIG. 1, raw water as raw water to be treated which has flowed into the raw water operation tank 1 is supplied by a raw water pump 2 to a membrane module 4 as a membrane filtration treatment device. On this supply line, the ozone gas generated in the ozone generator 8 is dissolved in the raw water via the static mixer 3. Raw water in which ozone is dissolved is subjected to membrane filtration in the membrane module 4,
Water is supplied to the filtered water tank 7.

A dissolved ozone concentration meter 5 is provided on this line to measure the dissolved ozone concentration in the membrane-filtered water. The treated water in the filtered water tank 7 is supplied to the next process such as activated carbon treatment and, if necessary, post ozone treatment.

For the operation of the membrane filtration treatment apparatus, for example, the raw water operation pump 2 is controlled by a signal from the electromagnetic flow meter 6 to perform constant flow rate filtration. Further, the filtration time for one cycle is set to, for example, 20 minutes, the backwash pump 9 is driven every 20 minutes for backwashing, and then the compressor 10 is driven for air washing.
After that, the raw water pump 2 is driven to perform flushing.

The dissolved ozone concentration in the membrane-filtered water is measured by the dissolved ozone concentration meter 5, the measurement result is sent to the supply ozone concentration control device 11, and the output signal from this control device 11 causes the ozone supply from the ozone generator 8. Control the amount. Normally, the gas flow rate from the ozone generator 8 is constant, and in this case, the supplied ozone concentration is changed so that the dissolved ozone concentration in the membrane filtration water is controlled to a predetermined value.

In the present invention, the amount of increase / decrease in the ozone supply amount is usually about 100% when expressed in terms of the increase / decrease ratio (%) based on the previous output value.
The reason is that it is not necessary to change the output value from the previous value so much, unless there is a drastic change.

Further, in the present invention, after subjecting the water to be treated to ozone treatment, a membrane filtration treatment is carried out, and one cycle of washing the filtration membrane at a predetermined membrane filtration treatment time is usually 15 minutes to It is preferably 60 minutes, and the washing can be performed for about 2 minutes or less.

Further, in the present invention, some points are set as the predetermined time after the start of the membrane filtration process in the above-mentioned one cycle. However, the more the set points are, the stricter the control itself becomes, but the memory capacity of the control device is increased. In consideration of the problem of cost and cost, it is preferable to set the score to about 1 point in about 3 to 7 minutes because the control is easy and practical.

[0024]

EXAMPLE FIG. 2 shows changes with time in dissolved ozone concentration and supply ozone concentration during control in one example of the present invention.
In this example, the target value of the dissolved ozone concentration in the membrane-filtered water is set to 0.5 mg / liter. Further, the filtration time for one cycle is set to 20 minutes, and the backwashing, the air washing, and the flushing are performed every 20 minutes as shown by an arrow P in FIG.

The control method of the embodiment shown in FIG. 2 will be described below. First, after 5 minutes, 10 minutes, 15 minutes, and 20 minutes after the start of the membrane filtration treatment for 20 minutes in one cycle, each of the dissolved ozone concentration values measured by the dissolved ozone concentration meter 5 in the supply ozone concentration control device 11 was measured. Take in. Based on this value, the output value of the ozone generator 8 after 5 minutes, 10 minutes, 15 minutes, and 20 minutes after the start of the membrane filtration process in the next cycle is set. That is, based on the supply ozone concentration in the previous cycle, it is determined how much to increase / decrease.

The supply ozone concentration between these points is controlled so that the supply ozone concentration increases or decreases linearly. Here, the increase / decrease rate (%) is set in advance according to the treatment plant depending on the concentration of dissolved ozone in the membrane filtration water, and for example, an increase / decrease rate as shown in Table 1 below.

[0027]

[Table 1]

According to Table 1, the dissolved ozone concentration is divided into 6 stages before and after the target value of 0.5 mg / liter, and the increase / decrease rate (%) based on the previous output value of the supplied ozone concentration.
Is set. In addition, the difference between the measured value of the dissolved ozone concentration and the predetermined target value of the dissolved ozone concentration is a value obtained by subtracting the target value of 0.5 mg / liter from the value of the dissolved ozone concentration in Table 1.

According to Table 1, for example, the dissolved ozone concentration value in the membrane filtration water 5 minutes after the start of the nth membrane filtration treatment is 0.5.
If it is 48 mg / liter, the output (supply ozone concentration) of the ozone generator 8 is adjusted so that the supply ozone concentration 5 minutes after the start of the membrane filtration process in the next cycle becomes 98% of the previous supply ozone concentration. Control.

Similarly, 10 minutes after the start of the membrane filtration treatment, 1
By performing the same control after 5 minutes and 20 minutes, a predetermined amount of ozone is always left on the film surface, so that the film can be prevented from being contaminated and excessive ozone injection can be avoided.

In FIG. 2,-(-)-indicates the change due to control of the supplied ozone concentration, and-indicates the dissolved ozone concentration varied thereby. Thus, by measuring the dissolved ozone gas concentration for each predetermined time in the previous cycle and controlling the supplied ozone concentration for each predetermined time in the next cycle based on the measured value, the dissolved ozone concentration is made almost constant. Can be kept.

[0032]

As described above, according to the present invention,
After subjecting the water to be treated to ozone oxidation, membrane filtration is performed,
Further, washing the filtration membrane at every predetermined membrane filtration treatment time is set as one cycle, the dissolved ozone concentration in the membrane filtration treated water is measured, and the dissolved ozone concentration in the membrane filtration treated water is determined based on the measured value. In the ozone supply control method in the water treatment using ozone oxidation and membrane filtration to control the ozone supply amount so that it is within the range, the dissolved ozone concentration is measured every predetermined time in one cycle, and based on the value By controlling the amount of ozone supply for each predetermined time in the next cycle, the dissolved ozone concentration can be kept more constant without being affected by the time lag due to the slow response speed and the rapid change in the dissolved ozone concentration due to physical cleaning. It is possible to prevent water from clogging the membrane with the minimum required ozone supply, and to achieve stable water treatment without lowering filtration performance. Can be done, it is possible to avoid excessive ozone injection, it can be reduced operating costs.

[Brief description of drawings]

FIG. 1 is an explanatory diagram showing a system system according to an embodiment of the present invention.

FIG. 2 is an explanatory diagram showing changes over time in dissolved ozone concentration and supply ozone concentration according to an embodiment of the present invention.

[Explanation of symbols]

1: Raw water tank 2: Raw water operation pump 3: Static mixer 4: Membrane module 5: Dissolved ozone concentration meter 6: Electromagnetic flow meter 7: Filtered water tank 8: Ozone generator 9: Backwash pump 10: Compressor 11: Supply ozone concentration control device

   ─────────────────────────────────────────────────── ─── Continued front page    (71) Applicant 000005234             Fuji Electric Co., Ltd.             1-1 Tanabe Nitta, Kawasaki-ku, Kawasaki-shi, Kanagawa (72) Inventor Shoichi Suda             1-2-1, Marunouchi, Chiyoda-ku, Tokyo             Main Steel Pipe Co., Ltd. (72) Inventor Torataro Minegishi             1-2-1, Marunouchi, Chiyoda-ku, Tokyo             Main Steel Pipe Co., Ltd. (72) Inventor Yoshihiko Mori             Asahi Kasei Corporation 2-1 Samejima, Fuji City, Shizuoka Prefecture             Within (72) Inventor Masatoshi Hashino             Asahi Kasei Corporation 2-1 Samejima, Fuji City, Shizuoka Prefecture             Within (72) Inventor Kinzo Isomura             1-3-1 Toranomon, Minato-ku, Tokyo Yutaka Isomura             Mizukiko Co., Ltd. (72) Inventor Kenji Nakatani             1-3-1 Toranomon, Minato-ku, Tokyo Yutaka Isomura             Mizukiko Co., Ltd. (72) Inventor Noriaki Kadokawa             1-1 Tanabe Nitta, Kawasaki-ku, Kawasaki-shi, Kanagawa             Within Fuji Electric Co., Ltd. (72) Inventor Kazutaka Takahashi             1-1 Tanabe Nitta, Kawasaki-ku, Kawasaki-shi, Kanagawa             Within Fuji Electric Co., Ltd. F-term (reference) 4D006 GA02 JA53A JA64A KA02                       KA33 KB30 KC02 KC03 KC13                       KC14 KD21 KE02P KE02Q                       PA01 PB02                 4D050 AA01 BB02 BD03 BD06 BD08                       CA09

Claims (3)

[Claims] 1. Dissolved ozone concentration in water subjected to membrane filtration treatment is defined as one cycle in which treated water is subjected to ozone oxidation treatment, then membrane filtration treatment is carried out, and the filtration membrane is further washed at predetermined membrane filtration treatment times. Is measured, based on this measurement value, so that the concentration of dissolved ozone in the membrane filtration treated water is within a predetermined range,
In the ozone supply control method in water treatment using ozone oxidation and membrane filtration for controlling ozone supply amount, after starting the membrane filtration treatment of the one cycle, the dissolved ozone concentration in the membrane filtration treated water is measured every predetermined time, Based on the difference between this measured value and the predetermined dissolved ozone concentration target value, the increase / decrease amount of the ozone supply amount for each predetermined time after the start of the membrane filtration process of the next cycle is set in advance, and the membrane filtration process of the next cycle is performed. A method for controlling ozone supply in water treatment using ozone oxidation and membrane filtration, which comprises controlling an ozone supply amount at a predetermined time interval from the start to a value corrected by the increase / decrease amount. 2. The ozone supply control in water treatment using ozone oxidation and membrane filtration according to claim 1, wherein the ozone supply amount between each point at each predetermined time is controlled so as to increase or decrease linearly or stepwise. Method. 3. The ozone supply amount is adjusted by the flow rate of ozone gas or the concentration of ozone gas.
The ozone supply control method described above.