JP3104313B2 - Membrane separation device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a membrane separation device, and more particularly to a membrane separation device capable of maintaining a high filtration rate of a membrane module and obtaining treated water at a high recovery rate.

[0002]

2. Description of the Related Art In recent years, with the development of membrane separation technology, treatment methods by membrane filtration have been adopted in various technical fields. For example, membrane filtration in fields such as turbidity and sterilization has been widely used, but the concentration range of applicable raw water has been expanded with the development of cross-flow type membrane modules. This is because the use of a cross-flow type membrane module allows the membrane filtration to be continued without reducing the filtration rate to a level that cannot be used even if the turbidity of the raw water fluctuates. .

For this reason, for example, UF (ultrafiltration) membranes and MF (ultrafiltration) membranes are used instead of flocculation, sedimentation, and filtration as pretreatments for separating RO (reverse osmosis) water from river water, industrial water, and clean water.
(Microfiltration) Membrane filtration with a membrane has made it possible to simplify the pretreatment process.

Further, it is contained in semiconductor cleaning wastewater.
Trace TOC components (isopropyl alcohol, methanol
Aerobic fluidized bed biological treatment equipment
(Bio-filter)
Bacteria (10 ⁶ Unit / ml level)
Removal means for removing bacteria after effluent water is sterilized with chlorine
As a result, membrane filtration can be applied. However
And the membrane permeated water discharged from such a process
Inexpensive treatment by sending water to ultrapure water production equipment
Thus, it was possible to suppress the growth of viable bacteria in the next step.

By the way, in such a membrane filtration application,
The turbidity of raw water fluctuates extremely. For example, when river water or industrial water is used as raw water, turbidity fluctuates significantly due to rainfall in addition to seasonal fluctuations. In the case where semiconductor cleaning wastewater is treated with an aerobic fluidized bed biological treatment apparatus as raw water, the concentration of bacterial cells flowing out (this is the concentration of suspended solids) is proportional to the fluctuation of the TOC concentration in the wastewater. Also fluctuates.

However, in the above-mentioned raw water, the fluctuation of the turbidity is often maintained almost in the low concentration (low turbidity) range. As described above, in most cases, the turbidity fluctuation of the raw water is in a low turbidity range.
The treatment is performed with the discharge rate of membrane concentrated water kept constant.

Similarly, even in the case of raw water which may fluctuate even in high turbidity, the conventional cross flow filtration employs an operation of continuously or intermittently discharging a fixed amount of concentrated water. ing. For this reason, even when the turbidity of the raw water fluctuates to a high turbidity, a relatively large amount of concentrated water is conventionally discharged in a constant amount so as not to excessively concentrate and lower the filtration rate. Therefore, conventionally, in many cases, regardless of the quality of the raw water, the recovery rate of the treated water (membrane permeated water) (= (1-concentrated water discharge water amount / raw water amount) × 100).
Is maintained at about 90%, the concentrated water discharge rate (= (concentrated water discharged water amount / raw water amount) × 100) is 10%, and even if the raw water has low turbidity and the recovery rate can be increased, This value is fixed.

Heretofore, there has been proposed a method of measuring the turbidity of concentrated water to monitor the turbidity of raw water and the degree of contamination of the membrane module. However, this method is intended to prevent the contamination of the membrane module. In addition, the amount of raw water is adjusted or the membrane is washed in accordance with the turbidity of the concentrated water, but the recovery rate of the treated water is not controlled.

[0009]

As described above, in the prior art, even when the quality of raw water is relatively high and the recovery rate can be increased, the recovery rate is kept at a constant level, and the treated water is recovered at a high rate. There was a drawback that it could not be obtained at a rate.

The present invention solves the above-mentioned conventional problems, maintains the filtration rate of the membrane module at a high level without lowering the filtration rate, and minimizes the amount of concentrated water to be discharged, thereby achieving high recovery of treated water. It is an object of the present invention to provide a membrane separation device obtained at a high efficiency.

[0011]

The membrane separation device of the present invention comprises:
A membrane module having a separation membrane, a turbidity meter for detecting the turbidity of the membrane concentrated water discharged from the membrane module, and comparing the detected value of the turbidity meter with a set value, A discharge means for controlling the discharge amount of the membrane concentrated water from the membrane module so as to keep the turbidity of the water constant.

[0012]

By providing a turbidity meter on the discharge side of the concentrated membrane water of the membrane module, it is possible to accurately detect turbidity even in the case of low-concentration raw water that could not be detected in raw water. You. That is, for example, when operating at a recovery rate of 90%, the concentration ratio is 10 times. Therefore, even when the raw water turbidity is 0.2 degrees and lower than the detection limit, it is provided on the discharge side of the membrane concentrated water of the membrane module. The turbidity meter can detect the turbidity of the membrane concentrated water as 2 degrees.

By controlling the discharge amount of the membrane concentrated water so as to keep the turbidity of the membrane concentrated water at a predetermined value, the recovery rate of the treated water can be increased.
That is, when the quality of the raw water is relatively good and the turbidity is low, the turbidity of the membrane concentrated water is naturally lower than the set value. In this case, it is possible to increase the concentration ratio, reduce the discharge amount of the membrane concentrated water, and increase the recovery rate of the treated water. If the turbidity of the raw water changes and the turbidity increases, and the turbidity of the membrane concentrated water becomes higher than the set value, the concentration ratio is reduced to increase the discharge amount of the membrane concentrated water, Lower the recovery rate.

As described above, according to the membrane separation device of the present invention, the membrane filtration speed and the treated water are controlled by controlling the optimum amount of the membrane concentrated water discharge in response to the fluctuation of the raw water promptly. The treated water can be obtained at a high recovery rate without lowering the water quality.

[0015]

Embodiments of the present invention will be described below in detail with reference to the drawings. 1 and 2 are system diagrams each showing an embodiment of the present invention. 1 and 2
In the drawings, members having the same functions are denoted by the same reference numerals.

The membrane separation apparatus shown in FIG. 1 includes a raw water tank 1, a circulating water tank 2, a membrane module 3, a turbidity meter 4, a membrane concentrated water discharge valve 5, a computer 6, and a spare membrane separation apparatus 7. A pipe 11 for introducing raw water into the raw water tank 1;
12 is a pipe for introducing raw water from the raw water tank 1 into the circulating water tank 2,
Reference numeral 3 denotes a pipe provided with a pump 13A for supplying water in the circulating water tank 2 to the membrane module 3, and reference numeral 14 denotes an extraction pipe of the membrane module 3, which is provided with a turbidity meter 4 on the way. The pipe 13 is provided with a bypass pipe 17 having a pump 17A.
15 is a pipe for circulating the membrane concentrated water to the circulating water tank 2,
A discharge valve (automatic valve) 5 for the membrane concentrated water and a discharge pipe 16 branched from the discharge valve 5 are provided on the way. Reference numeral 18 denotes a pipe for extracting permeated water of the membrane module 3 as treated water. The computer 6 is linked to the discharge valve 5, the turbidity meter 4, the pump 17A of the bypass pipe 17 and the spare membrane separation device 7, and replaces the detection value of the turbidity meter 4 with an electric signal.
The opening and closing (opening degree) of the discharge valve 5 and the operation of the pump 17A and the spare membrane separation device 7 are controlled. That is, the discharge valve 5 and the computer 6
This constitutes a discharge unit for controlling the discharge amount of the membrane concentrated water from the membrane module 3. The spare membrane separation device 7
Is configured such that water in the circulating water tank 2 is introduced by piping not shown.

In the membrane separation apparatus of the present embodiment, the raw water is supplied by the pipe 11, the raw water tank 1, the pipe 12, the circulating water tank 2, the pump 1
The membrane permeated water is supplied to the membrane module 3 through a pipe 13 having 3A, and the permeated water is discharged from the pipe 18 as treated water to the outside of the system. On the other hand, the membrane concentrated water is circulated to the circulating water tank 2 via the pipes 14 and 15. During this time, the required amount of membrane concentrated water is discharged out of the system via the discharge valve 5 and the pipe 16.

In such a membrane separation process, the turbidity of the membrane concentrated water extracted from the membrane module 3 is measured by the turbidimeter 4, and the detected value is sent to the calculator 6.
The calculator 6 replaces the detected value of the turbidity meter 4 with an electric signal, compares the detected value with a set value, and when the detected value of the turbidity meter 4 is lower than the set value, turbidity of the membrane concentrated water. The opening degree of the discharge valve 5 is adjusted so that the concentration ratio is increased to increase the degree, that is, the discharge amount of the membrane concentrated water is reduced. Conversely, turbidity meter 4
If the detected value is higher than the set value, the concentration ratio is reduced to reduce the turbidity of the membrane concentrated water, that is, the opening of the discharge valve 5 is adjusted so that the discharge amount of the membrane concentrated water is increased. I do. In adjusting the opening of the discharge valve 5, a signal is issued from the computer 6 as necessary to operate the pump 17A of the bypass pipe 17 to increase the membrane surface flow rate or to operate the spare membrane separation device 7. Then, the raw water exceeding the processing capacity of the membrane module 3 is supplied to the spare membrane separation device 7 for processing.

According to such a membrane separation device, it is possible to control the discharge amount of the membrane concentrated water to the minimum necessary according to the quality of the raw water without lowering the filtration speed.
The recovery rate of treated water is greatly improved.

The membrane separation apparatus shown in FIG. 2 has the same configuration as the membrane separation apparatus shown in FIG. 1 except that there is no piping for forming a circulation line for the concentrated membrane water, a bypass pipe, and a spare membrane separation apparatus. ing. 2A is an intermediate water tank.

Also in the membrane separation apparatus of this embodiment, the turbidity detection value of the membrane condensed water detected by the turbidimeter 4 is compared with a set value by the computer 6 and the membrane is determined according to the comparison result. Good results can be obtained by controlling the opening and closing (opening degree) of the discharge valve 5 of the concentrated water to adjust the discharge amount of the membrane concentrated water.

The membrane separation apparatus shown in FIGS. 1 and 2 is an embodiment of the present invention, and the present invention is not limited to the illustrated one. As shown in FIG. 1, in a device having a circulation line for membrane concentrated water, the turbidity meter may be installed at any part of the circulation line. Further, in order to control the discharge amount of the membrane concentrated water, a discharge pump may be provided in addition to the discharge valve.

The control of the discharge amount of the membrane condensed water by the membrane separation apparatus of the present invention may be either intermittent control or continuous proportional control, and is appropriately determined according to the scale of the apparatus and required accuracy. Is done.

The effects of the present invention will be described more specifically with reference to experimental examples and comparative experimental examples. Experimental Example 1 Bacteria detached from biofilter (10 ⁶ cells / ml
The experiment was conducted by applying the membrane separation device of the present invention as a membrane separation device for removing bacterial cells after effluent water containing (level) was sterilized with chlorine. The relationship between the TOC at the inlet of the biofilter and the turbidity of the effluent was as follows.

[0025]

[Table 1]

The filtration rate of the UF membrane when the cross-flow filtration is performed at an average membrane surface flow rate of 0.3 m / s is constant when the turbidity of the circulating water is 7 degrees or less, and is 3.8 m ³ / m ² · d. (25
° C, Kg / cm ² ). Here, when the inlet TOC of the bio-filter was changed in two stages as follows, the discharge amount of the membrane concentrated water was controlled so as to keep the turbidity of the membrane concentrated water constant at 7 degrees. AM 10:00 to PM 10:00 → TOC: 4.0 mg / l PM 10:00 to AM 10:00 → TOC: 2.1 mg / l As a result, the average daily enrichment ratio is 16.7 times and the recovery rate is 94%. And the filtration speed is 3.8m ³ / m ² · d
(25 ° C., Kg / cm ² ).

Comparative Experimental Example 1 For comparison, in Experimental Example 1, the discharge amount of the membrane concentrated water was set to a constant amount so that the concentration ratio was 10 times and the recovery rate was 90% without controlling by turbidity. After discharging,
The filtration speed is 3.8 m ³ / m ² · d as in the above-mentioned present invention.
(25 ° C., Kg / cm ² ).

Experimental Example 2 In Experimental Example 1, when the average filtration rate was 2 m ³ / m ² · d, the membrane area was set so that the planned water volume could be treated.
The discharge amount of the membrane concentrated water was controlled so that the turbidity of the membrane concentrated water was kept constant at 14 degrees. As a result, the average concentration ratio per day was 33.3 times, the recovery rate was 97%, and the operation rate of the pump was increased to 83%.

Comparative Experimental Example 2 In Experimental Example 2, the membrane concentrated water was discharged at a constant rate so that the concentration ratio was 20 times and the recovery rate was 95% without controlling by turbidity. The operation rate of the pump was 68%.

Experimental Example 3 In Experimental Example 1, when the average filtration rate was 3 m ³ / m ² · d, the membrane area was set so that the planned water volume could be treated.
The discharge amount of the membrane concentrated water was controlled so that the turbidity of the membrane concentrated water was kept constant at 14 degrees. When the water level in the circulating water tank became high, the membrane surface flow rate in the cross-flow filtration was increased to 0.5 m / s. As a result, the average daily enrichment rate was 33.3 times, the recovery rate was 97%, and the planned water volume could be treated.

Comparative Experimental Example 3 In Experimental Example 3, the membrane concentrated water was discharged at a fixed amount so that the concentration ratio was 20 times and the recovery rate was 95% without controlling by turbidity. At 9:00 PM, the water level in the circulating water tank reached a high water level, making it impossible to treat.

[0032]

As described in detail above, according to the membrane separation device of the present invention, the minimum required membrane concentration water can be obtained without reducing the filtration rate, depending on the quality of the raw water, that is, the turbidity of the raw water. It is possible to control the discharge amount so as to increase the recovery rate of the treated water and the operation efficiency of the apparatus, and to perform an efficient membrane separation process.

[Brief description of the drawings]

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

FIG. 2 is a system diagram showing another embodiment of the membrane separation device of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Raw water tank 2 Circulating water tank 3 Membrane module 4 Turbidity meter 5 Discharge valve of membrane concentrated water 6 Computer

Claims (1)

(57) [Claims] A turbidity meter for detecting the turbidity of membrane concentrated water discharged from a membrane module provided with a separation membrane, and a detection value of the turbidity meter is compared with a set value. And a discharge means for controlling the discharge amount of the membrane concentrated water from the membrane module so as to keep the turbidity of the membrane concentrated water constant.