JPH11221407A - Filtration apparatus for sea water - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the performance of a filtration apparatus without using a chemical agent and consequently to prolong the durable operation time of a dialysis apparatus by employing a filtration material having respectively specified effective diameter and zeta potential. SOLUTION: The sea water to be subjected to filtration may include not only salt water taken out of a sea but also water taken out of a salt lake, under ground, or the like and these waters may be diluted with fresh water or concentrated by dissolving a salt. A filtration apparatus for filtering water through a layer filled with a granular material such as sand and actuvated carbon may be employed. The effective mesh diameter of a filtration material is controlled to be not smaller than 0.23 mm and not larger than 0.27 mm. Sand called as Soma siliceous sand derived from a stratum covering Kashima machi, Haramachi city, Odaka machi, and Namie machi of Soma city Fukushima prefecture is preferable and also sand having zeta potential at 34 mV or higher is preferable. The thickness of the layer of the filtration material is sufficient to be about 20 cm or thicker and preferably 50 cm or thicker. Filtration can be carried out at a flow rate as low as about 5 m/h or lower and as high as about 10-30 m/h.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a filtration device for treating seawater supplied to a dialysis device in order to extend the operation period of an ion exchange membrane electrodialysis device (hereinafter referred to as a "dialysis device").

[0002]

2. Description of the Related Art A dialysis apparatus is used in various fields such as a field of concentrating seawater to obtain salt and a field of desalinating seawater to obtain fresh water. This device has a structure in which an anion and a cation exchange membrane are alternately arranged between a cathode and an anode through a chamber frame, and a concentration chamber and a desalination chamber are formed alternately by the ion exchange membrane and the chamber frame. It has become. Each chamber must be narrow to reduce electrical resistance, and in addition to having a spacer to maintain uniform spacing and uniform flow distribution, suspensions and colloids in seawater When contaminants such as substances and microorganisms are present, they accumulate in a dialysis device such as a membrane surface or a spacer with the elapse of operation time, and the flow pressure loss increases to increase the pressure at the inlet of the desalting chamber (hereinafter referred to as PD
i)), and if the operation is further continued, the supply amount decreases, and finally the film is broken by scale deposition due to water decomposition. In order to prevent this, every time PDi reaches a reference value, the operation is stopped, and it is necessary to disassemble the membrane group and clean the inside. However, considering the decrease in operation rate due to washing, the labor cost of dismantling washing, artificial membrane breakage that occurs during washing, etc., it is possible to improve the capacity of the filtration device for seawater treatment supplied to the dialysis machine. The essential measures are to reduce the amount of contaminants accumulated in the dialyzer and extend the period until the PDi reaches the reference value, that is, the operation period of the dialyzer.

[0003] Conventional filtration has an effective diameter of 0.4 to 0.6 mm.
-Stage filtration using sand of sand as a filter medium (JP-A-48-74652)
There is also a two-stage filtration method in which fibers are used as the second-stage filter medium (Japanese Patent Laid-Open No. 52-32173). In order to reduce the power cost, they have become narrower, the amount of contaminants accumulated in the dialysis machine has increased, and the continuous operation period of the dialysis machine has been shortened. There is also a strong demand for further extending the continuous operation period of the dialysis device in order to reduce costs.

There is also a method of adding a chemical such as coagulation filtration and chemical injection filtration. However, in the case of producing food, it is preferable for consumers not to add additives to raw materials and the like, that is, to use a so-called non-additive. It is rare.

[0005]

SUMMARY OF THE INVENTION An object of the present invention is to improve the performance of a filtration device by specifying a filter medium without using a chemical or the like in order to extend the operation period of the dialysis device.

[0006] Even if the quality of the filtered water is improved, it is meaningless if the pressure loss of the filtration becomes large and the filtration operation is practically impossible. Therefore, it is necessary to consider the prevention of an excessive rise in the pressure loss.

[0007]

Means for Solving the Problems Regarding the mechanism of filtration,
It is a complex of sieving, sedimentation on filter media, electro-adsorption, inertial motion, Van der Waals force, etc., and it is extremely complicated due to the influence of filter material contamination and so on. It is difficult to handle properly. In addition, the accumulation mechanism of contaminants in the dialysis machine, which is important in determining the water quality specifications of the drainage water, is a complex of sieving, electric adsorption, inertial motion, van der Waals force, etc. The theoretical complexity of such contaminant accumulation is difficult due to the extreme complexity. However, the present inventor has conducted intensive studies on the improvement of filtration performance while keeping in mind the increase in pressure loss of filtration, and as a result, if a specific filtration device is used, the amount of contaminants accumulated in the dialysis device is reduced, and The present inventors have found that the continuous operation period can be greatly extended, and have made the present invention based on this finding.

[0008] That is, the present invention relates to a filtration device using a filter having an effective diameter of 0.23 or more and 0.27 mm or less, and a filtration device for seawater in which the zeta potential of the filter is 34 mV or more.

Here, the effective diameter means a particle size corresponding to a size of a sieve through which 10 wt% of the total amount passes through a filter medium. Specifically, the filter medium is sieved with a sieve of each opening,
Find each pass rate. The vertical axis shows the result,
The horizontal axis is drawn on a piece of grid paper with a sieve opening to draw a grain size accumulation curve. A horizontal line is drawn from the 10 wt% point on the vertical axis in the figure, and a vertical line is drawn down from the intersection with the curve to the horizontal axis to determine the intersection. This value is the effective diameter. The uniformity coefficient refers to the ratio between the particle size corresponding to the size of the sieve through which 60 wt% of the total amount obtained by the same method passes and the effective diameter. Measurement of specific surface area is B
According to the ET method.

[0010] Sand, anthracite, activated carbon,
There are natural products such as garnet and man-made products, but preferably cheap and durable sand is suitable.

Any kind of sand may be used, but silica sand is preferred, and more preferably Soma, Kashima, Haramachi, Kodaka, Fukushima prefectures, which is called Soma silica sand.
It is good to use quartz sand from the stratum extending to Namie town.

It has also been found that the use of a filter having a zeta potential of 34 mV or more as a filter medium dramatically increases the operation period of the dialysis apparatus. This is probably because most of the suspension has a negative charge. The measuring method was such that a streaming potential and a pressure were measured by a streaming potential method, and calculated by the following formula.

Zeta potential = 1.15 × 10 ¹⁰ × η / ε ×
κ / R × E / P (where η: viscosity coefficient [g / cm · sec] ε: dielectric constant [−] κ: conductivity [1 / cm] R: resistance of flowing liquid [Ω] E: flowing potential [MV] P: Pressure [g / cm ² ]) The fluid is a 1 mM KCl aqueous solution, and the test temperature is 21 to 22.
° C.

There are many opinions that the filtration performance should be evaluated based on the quality of the filtrate. Generally, the measurement of turbidity and the measurement of living things are known. Examples of the measurement of turbidity include a light scattering method such as a dry weight method such as JIS0102 and an integrating sphere photoelectricity method, an MF value, and an F value.
The filtration rate method such as I value and the measurement of organisms include plankton number and chlorophyll amount. The relationship between the quality of the drainage water and the operation period of the dialysis device, which is the object of the present invention, depends on the fact that the accumulation mechanism of contaminants in the dialysis device is uncertain as described above. However, there is often no clear relationship at present when the water quality became clearer at that time. Therefore, the operation period of the dialysis device was directly used as the evaluation method, specifically, the period from the start of operation until PDi reached the reference value of 1.00 kgf / cm ² .

[0015]

BEST MODE FOR CARRYING OUT THE INVENTION The seawater to be filtered is not only salt water collected from the so-called sea, but also salt water collected from salt lakes and underground. May be higher.

The filtration device may be of any type that purifies the solution by passing the solution through a layer filled with particulate matter such as sand or activated carbon. That is, a method of supplying seawater such as a pressure type rapid filtration pond, a gravity type rapid filtration pond, an upward flow filtration pond, a downward flow filtration pond,
There is no limitation on the direction in which seawater is supplied, such as horizontal flow filtration, or the type of automatic operation, such as a valveless filter, harding filter, or green leaf filter.

Although there are many combinations of the number of stages of filtration and the structure of the filter layer, the filter medium of the present invention may be used for a part thereof, and it is not necessary that all of the filter medium be used. The number of filtration stages and the configuration of the filter layer may be appropriately determined depending on the properties of seawater to be treated. For example, one-stage single-layer filtration not only using the filter medium of the present invention as a filter medium, but also two-stage filtration using the filter medium of the present invention only in the second stage, one-stage multi-layer filtration having a small particle size Alternatively, the filter medium of the present invention may be used. In the case of seawater along the coast of Japan, it would be better to use the filter medium of the present invention in the second stage in the two-stage filtration or use the filter medium of the present invention in the layer of the filter medium having a small particle size in the one-stage multilayer filtration.

The filter medium has an effective diameter of 0.23 to 0.27 m.
m or less. Soma silica sand, which is produced from the strata of Soma, Kashima, Haramachi, Kodaka and Namie in Fukushima Prefecture, is preferred. Further, those having a zeta potential of 34 mV or more are preferable.

The layer thickness of the filter medium may be 20 cm or more, preferably 50 cm or more.

The filtration speed is determined from the type of filtration, the amount of filtration, and the filtration area. That is, from low speed of 5 m / h or less to 10
Applicable to high speeds of up to 30 m / h.

[0021]

Next, the present invention will be described in more detail with reference to Examples and Comparative Examples.

Example 1 Seawater was treated using the filter medium of the present invention only in the second stage of the two-stage filtration, and the solution was passed through an electrodialysis apparatus.

First-stage filter Filtration method Gravity-type rapid filtration Valveless filter Filtration speed 8 m / h Filter material Takahagi silica sand Specific surface area 0.2 m ² / g Effective diameter 0.45 mm, Equivalent coefficient 1.6 Particle size distribution 710 μm 62.0 Passage of 600 μm (wt%) 36.2 Passage of 425 μm (wt%) 9.2 Layer thickness 500 mm (Gravel was spread 100 mm under it for the purpose of leak prevention etc.) Second-stage filter Filtration method Gravity type rapid filtration Valveless filter Filtration speed 15 to 25 m / h Filter material Soma Silica 5 Specific surface area 1.0 m ² / g Zeta potential 35 mV Component Si: 42.9%, Al: 1.80%, K: 1. 53%, Fe: 0.188% Effective diameter 0.26 mm, Uniformity coefficient 1.9 Particle size distribution 600 μm passage (wt%) 100.0 425 μm passage (wt%) 50.1 300 μm passage (wt 27.7 250 µm pass (wt%) 9.8 212 µm pass (wt%) 3.6 Layer thickness 700mm (For the purpose of leak prevention, etc. (The gravel was spread 100 mm.) Thickness of the desalting chamber of the dialyzer: 0.55 mm ± 0.03 mm Drainage supply rate in the desalting chamber: 7.6 cm / sec.
The period until f / cm ² is not known because PDi has not yet reached the reference value at the time of filing the present invention,
After 500 days of operation, the PDi rise was almost 0.0
kgf / cm ² .

The pressure loss of the second stage filtration is 0.65 kgf /
When the pressure exceeds ² cm ^{2, the} amount of drainage water decreases and the operation of the dialysis apparatus is hindered. Therefore, 0.65 kgf / cm ² was set as the pressure drop upper limit of the second filtration. In this implementation, the pressure loss was 0.4 kgf / cm ² at the maximum, which was lower than the upper limit. Note that the filtration was washed every 15 hours and returned to the initial pressure.

Example 2 In the two-stage filtration, seawater was treated under the same conditions as in Example 1 except that the particle size of the filter material in the second stage was different.

Second-stage filter Filter material Soma silica sand No. 5 Effective diameter 0.27 mm, uniformity coefficient 1.6 Particle size distribution 600 μm passage (wt%) 96.4 425 μm passage (wt%) 61.6 300 μm passage (wt%) 18.5 250 μm passage (wt%) 7.7 212 μm passage (wt%) 4.5 Result PDi is 1.00 kg of the reference value from the start of operation of the dialysis device.
The period until f / cm ² is not known because PDi has not yet reached the reference value at the time of filing the present invention,
After driving for 200 days, the PDi rise was almost 0.0
kgf / cm ² .

[0027] The pressure loss of the second stage filtration is 0.4 k at the maximum value.
gf / cm ² , which is below the upper limit.

Comparative Example 1 In the two-stage filtration, seawater was passed under the same conditions as in Example 1 except that the place of origin, the particle size, the thickness of the sand layer, and the thickness of the leak prevention layer of the second-stage filter medium were changed.

Filter of the second stage Filter material Silica sand from Takahagi Specific surface area 0.2 m ² / g Zeta potential 33 mV Component Si: 42.7%, Al: 1.70%, K: 1.51%, Fe: 0. 267% Effective diameter 0.45mm, Uniformity coefficient 1.6 Particle size distribution 710μm passage (wt%) 62.0 600μm passage (wt%) 36.2 425μm passage (wt%) 9.2 Layer thickness 500mm (for leak prevention etc.) Result Gravel was spread 100 mm underneath it.) Result It was 30 days after the start of operation that the PDi of the dialysis device reached the reference value of 1.00 kgf / cm ² , which was extremely short compared to Example 1. Was.

Comparative Example 2 In the two-stage filtration, seawater was treated under the same conditions as in Example 1 except that the production area and the particle size of the second-stage filter medium were changed.

Second-stage filter Filter material Takahagi silica sand Specific surface area 2.0 m ² / g Effective diameter 0.15 mm, Equivalent coefficient 1.8 Particle size distribution 300 μm passage (wt%) 73.0 250 μm passage (wt%) 47 2.6 Passage of 212 μm (wt%) 30.1 Passage of 150 μm (wt%) 10.0 Passage of 125 μm (wt%) 5.2 Results Shortly after the start of operation, the upper limit of the pressure loss of the second-stage filter was 0.65 kgf /. The dialysis device could not be operated because the required amount of dialysis could not be filtered because it exceeded cm ² .

Comparative Example 3 In the two-stage filtration, seawater was treated under the same conditions as in Example 1 except that the place of origin, the particle size, and the leak layer thickness of the second-stage filter medium were changed.

Second-stage filter Filter material Takahagi silica sand Specific surface area 2.0 m ² / g Zeta potential 33 mV Effective diameter 0.35 mm, uniformity coefficient 1.6 Particle size distribution 600 μm passage (wt%) 65.2 425 μm passage (wt) %) 22.5 Passing through 300 μm (wt%) 4.6 Layer thickness 700 mm (Gravel was spread 100 mm under it for the purpose of preventing leaks, etc.) Result The PDi of the dialysis device was the standard value of 1.00 kgf / cm ^2. Reached 50 days after the start of operation, which was extremely short as compared with Example 1.

Comparative Example 4 In the two-stage filtration, seawater was treated under the same conditions as in Example 1 except that the production area and the particle size of the second-stage filter medium were changed.

Second-stage filter Filter material Takahagi silica sand Zeta potential 33 mV Effective diameter 0.3 mm, uniformity coefficient 1.6 Particle size distribution 600 μm passage (wt%) 84.0 425 μm passage (wt%) 44.0 300 μm passage (wt%) 10.0 Pass through 250 μm (wt%) 2.8 Pass through 212 μm (wt%) 0.6 Result PDi of the dialysis device reached the reference value of 1.00 kgf / cm ² after 80 days from the start of operation. Yes, extremely short compared to Example 1.

Comparative Example 5 In the two-stage filtration, seawater was treated under the same conditions as in Example 1 except that the layer thickness of the second-stage filter medium was changed.

[0037] Results It was 100 days after the start of operation that the PDi of the dialysis device reached the reference value of 1.00 kgf / cm ² , which was extremely short as compared with Example 1.

Comparative Example 6 In the two-stage filtration, seawater was treated under the same conditions as in Example 1 except that the production area and the particle size of the second-stage filter medium were changed.

Second-stage filter Filter material Silica sand from Iwaki Kunohama Effective diameter 0.22 mm, uniformity coefficient 1.7 Particle size distribution 600 μm passage (wt%) 99.6 425 μm passage (wt%) 73.7 250 μm passage (wt%) 18.1 Pass through 212 μm (wt%) 8.9 Result Immediately after starting operation, the required amount of dialysis could not be filtered because the pressure loss of the second stage filter exceeded the upper limit of 0.65 kgf / cm ^2. The dialysis machine could not be operated.

[0040]

As described above, the filter device of the present invention can greatly extend the operation period of the dialysis device only by using a specific filter medium without using a chemical or the like.

Claims (2)

[Claims] 1. A seawater filtration device characterized by using a filter medium having an effective diameter of not less than 0.23 and not more than 0.27 mm. 2. The filter for seawater according to claim 1, wherein the zeta potential of the filter medium is 34 mV or more.