JP2001232160A - Membrane filter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a membrane filter which copes easily with the fluctuation of a property of raw water and the good and undesirable injection states of hypochlorite and by which efficient membrane filtration is carried out over a long period of time. SOLUTION: This membrane filter has a drain pipeline 9 for discharging wastewater and a pipeline 16 for injecting a hypochlorite when a membrane module is periodically cleaned physically. The filter has furthermore a residual chlorine concentration sensor 12 for sampling the wastewater from the pipeline 9 and measuring the residual chlorine concentration in waste water and a pressure sensor 17 arranged on the way of the pipeline 16. The filter is constituted so that the cleaning frequency of the membrane module and/or the time taken to inject the hypochlorite when backward washed are automatically controlled according to the value measured by the sensor 12 when the injection state of hypochlorite is judged to be good with the sensor 17.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing public water by filtering river water, well water, lake water and the like as raw water and filtering the raw water using a membrane module. The present invention relates to a membrane filter for performing physical cleaning.

[0002]

2. Description of the Related Art Conventionally, in a membrane filtration apparatus for performing filtration using a membrane module, after performing filtration for a certain period of time, physical cleaning is performed in order to wash and remove stains due to turbidity adhering to the membrane surface. In the physical cleaning, dirt on the membrane is removed by allowing treated water to permeate from the back surface of the membrane by a backwash pump (hereinafter, referred to as backwashing). At this time,
To prevent biological fouling of the membrane surface in the backwash water, a certain concentration of hypochlorite such as sodium hypochlorite (usually,
(About 3 to 5 ppm) for a certain period of time (about 20 to 30 seconds). Further, usually, the frequency of back washing and the injection time of hypochlorite are determined by a timer, and the washing is performed under constant conditions. As described above, when the frequency of backwashing and the injection time of hypochlorite are constant, the quality of raw water deteriorates (for example, a sudden increase in turbidity due to heavy rain, a large amount of algae, etc.), and turbidity on the membrane surface is caused. The quality load increases, and under the previous backwash conditions, the generation of biological fouling cannot be sufficiently suppressed, and the operating pressure of the membrane increases, which may hinder the operation of the entire membrane filtration facility. . In addition, in addition to the deterioration of the raw water condition as a factor that causes biological fouling, gas generated by gasification of hypochlorous acid or mixing of air into a part of a hypochlorite injection pipe to be injected at the time of backwashing. A stagnation portion is generated, which causes poor injection of hypochlorite, and chlorine may not reach the membrane surface.

[0003]

DISCLOSURE OF THE INVENTION The present invention relates to a membrane filter which can easily deal with fluctuations in the properties of raw water and / or the quality of hypochlorite injection, and can carry out efficient membrane filtration over a long period of time. It is intended to provide a device.

[0004]

SUMMARY OF THE INVENTION The present invention relates to a membrane filtration apparatus provided with a drain pipe capable of draining when periodically performing physical cleaning of a membrane module. It is equipped with a residual chlorine concentration sensor that measures chlorine concentration, and the cleaning frequency of the membrane module and / or the injection time of hypochlorite during backwashing are automatically controlled according to the sensor value. It is intended to provide a membrane filtration device. The present invention also provides a membrane filtration device provided with a hypochlorite injection tube, wherein a pressure sensor is provided in the middle of the injection tube.

[0005] The present invention further provides a membrane filtration device provided with a drain pipe and a hypochlorite injection pipe capable of draining when periodically performing physical cleaning of the membrane module. Equipped with a residual chlorine concentration sensor that measures the residual chlorine concentration in the wastewater, and a pressure sensor in the middle of the hypochlorite injection pipe, which determines that the hypochlorite injection state is good. The cleaning frequency of the membrane module and / or according to the residual chlorine concentration sensor value.
Another object of the present invention is to provide a membrane filtration device wherein the injection time of hypochlorite during backwashing is automatically controlled.

[0006]

Next, the present invention will be described more specifically with reference to the drawings. FIG. 1 is a system diagram of a membrane filtration device showing one embodiment of the present invention. The membrane filtration device shown in FIG. 1 mainly includes a raw water tank 1, a membrane module 2, a backwash water tank 3, and a hypochlorite tank 4. Raw water is sent to the membrane module 2 by a pump 5 via a valve 6. The filtered water filtered here flows out from the filtered water outflow pipe 7. When the membrane filtration device is operated, backwashing of the membrane module 2 is performed at a constant frequency, and water in the backwash water tank 3 is permeated from the back surface of the membrane module 2 by the backwash pump 8. At this time, hypochlorite, for example, sodium hypochlorite is added to the backwash water from the hypochlorite tank 4 by the hypochlorite injection pump 18.
The chlorine concentration of the backwash water to which hypochlorite is added is 3-5p
pm is common. Backwash wastewater is supplied to the membrane module 2
From the drain pipe 9 through a drain valve 10.

In the illustrated membrane filtration device, a sampling valve 11 is provided on a drain pipe 9, and a residual chlorine concentration sensor 12 is connected to the drain valve 9. At the same time as the drain valve 10 is opened, the sampling valve 11 is opened to supply a drain sample to the residual chlorine concentration sensor 12. When the operation of the membrane module 2 is performed normally and no biological fouling occurs on the membrane surface, the residual chlorine in the backwash wastewater is detected at a normal value (0.5 to 1.5 ppm). If biological fouling occurs, the residual chlorine in the backwash effluent drops significantly (0-0.3 ppm).

If the value measured by the residual chlorine concentration sensor 12 is below a certain set value, it is determined that the membrane module has caused biological fouling, and the membrane module is used for eliminating or improving biological fouling. Increase the frequency of backwashing of the filtration device (typically once every 20-60 minutes) or extend the hypochlorite injection time (typically 20-30 seconds). These operations can be performed by receiving a decrease signal of the residual chlorine concentration sensor 12 in the control panel and switching to a preset backwash frequency and hypochlorite injection time. Further, the occurrence of biological fouling is suppressed by the above operation, and when the value of the residual chlorine concentration sensor 12 returns to a normal value, the backwash frequency and the hypochlorite injection time are returned to the initial set values again. .

When the membrane module is backwashed, hypochlorite is injected into the backwash water by the injection pipe 16 through the hypochlorite injection pump 18 as described above.
A gas stagnant part is formed in a part of the injection pipe 16 by gasification of hypochlorous acid or mixing of air, which may cause hypochlorite injection failure and chlorine may not reach the membrane surface.
To prevent this, the injection pipe 16 is provided with a pressure sensor 17, which measures the injection pressure. If this value exceeds a normal pressure (2 kg / cm ² or less), it is determined that the pressure in the injection pipe 16 has been abnormally increased due to gas stagnation or the like, and a warning is displayed on the control panel. Even if the residual chlorine concentration sensor value drops, if this pressure sensor value is high,
The frequency of backwashing and the injection time of hypochlorite are not changed.
The backwash frequency and the hypochlorite injection time are changed only when the value of the pressure sensor 17 is normal and the value of the residual chlorine concentration sensor 12 decreases.

As a method of measuring the residual chlorine concentration of the backwash wastewater, instead of sampling the wastewater from the drain pipe 9 and measuring the residual chlorine concentration with the residual chlorine concentration sensor 12, the wastewater is once received in the drainage pit 13 and sampled therefrom. The wastewater can be sent to the residual chlorine concentration sensor 15 by the pump 14 for measurement. When the residual chlorine concentration in the wastewater decreases, the output of the hypochlorite injection pump 1 is increased instead of changing the backwashing frequency and the setting of the chlorine injection time, thereby increasing the concentration of biological fouling. A ring suppressing effect can be provided.

[0011]

According to the membrane filtration apparatus of the present invention, the means for automatically detecting the occurrence of biological fouling in the membrane module and suppressing the biological fouling at an appropriate time (such as an increase in the frequency of backwashing and Extension of hypochlorite injection time). According to the membrane filtration device of the present invention,
It is possible to distinguish between the phenomenon of lowering the residual chlorine concentration in wastewater due to biological fouling, the phenomenon of lowering the residual chlorine concentration due to malfunction of the hypochlorite injection pump, or the occurrence of both phenomena. And efficient membrane filtration can be performed over a long period of time.

[Brief description of the drawings]

FIG. 1 is a system diagram of a membrane filtration device showing one embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Raw water tank 2 Membrane module 3 Backwash water tank 4 Hypochlorite tank 7 Filtration water outflow pipe 9 Drain pipe 11 Sampling valve 12 Residual chlorine concentration sensor 13 Drain pit 14 Sampling pump 15 Residual chlorine concentration sensor 16 Injection pipe 17 Pressure sensor

Claims (3)

[Claims] 1. A membrane filtration device provided with a drain pipe capable of draining when a membrane module is periodically physically cleaned, wherein drain water is collected from the drain pipe and the residual chlorine concentration in the drain water is measured. A membrane filtration device comprising a sensor, wherein the washing frequency of the membrane module and / or the injection time of hypochlorite during backwashing are automatically controlled according to the sensor value. 2. A membrane filtration device having a hypochlorite injection tube, wherein a pressure sensor is provided in the middle of the injection tube. 3. A membrane filtration device provided with a drain pipe capable of draining when periodically performing physical cleaning of a membrane module, and a hypochlorite injection pipe. Equipped with a residual chlorine concentration sensor for measuring the residual chlorine concentration of, further equipped with a pressure sensor in the middle of the hypochlorite injection pipe, when this pressure sensor determines that the hypochlorite injection state is good, A membrane filtration device wherein the frequency of washing the membrane module and / or the injection time of hypochlorite during backwashing are automatically controlled according to the residual chlorine concentration sensor value.