JP3340311B2 - Operating method of water treatment equipment using immersion type membrane filtration 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 method for operating a water treatment facility using a submerged membrane filtration device.

[0002]

2. Description of the Related Art Conventionally, when arsenic is contained in raw water in water purification treatment, water treatment, groundwater treatment, etc., coprecipitation using an aluminum-based or iron-based coagulant, activated alumina, chelate, etc. Arsenic is removed by an exchange / adsorption method using a resin or the like.

[0003] In the case of performing the coprecipitation method, raw water containing arsenic is introduced into a rapid stirring tank, and while stirring rapidly, an aluminum-based flocculant such as polyaluminum chloride or a sulfuric acid band (or ferrous chloride such as ferric chloride) is used. And a pH adjuster to adjust the pH to an appropriate value to precipitate aluminum (or iron) hydroxide and coprecipitate arsenic therewith. Then, the treated water containing sediment in the rapid stirring tank is introduced into the floc forming tank, and floc is formed by slow stirring, and the treated water containing floc is sequentially introduced into the sedimentation basin and the sand filtration pond. As a result, arsenic-free treated water is obtained by separating flocs.

In the case of performing the exchange / adsorption method, for example, the activated alumina adsorption method, the raw water is adjusted to pH 5 to 6 with an acid, and then introduced into an adsorption column filled with activated alumina to convert arsenic in the raw water into activated alumina. After adsorbing and neutralizing the acidic treated water flowing out of the adsorption tower with an alkali, the treated water is guided to a sand filtration pond to separate turbidity, thereby obtaining arsenic-free treated water.

[0005]

However, the above-mentioned co-precipitation method is a skilled technique for adjusting the injection amount of a chemical such as a flocculant in response to fluctuations in the quality of raw water in order to maintain a stable quality of treated water. Is necessary, and the amount of injected chemical is large. In addition, the processing steps are complicated, and a large device installation space is required.

In addition, the exchange / adsorption method has a complicated treatment process, and requires pH adjustment of raw water as a pretreatment as described above in order to obtain an arsenic removal rate of 80% or more. When the adsorption capacity of the catalyst decreases, it needs to be regenerated. In addition, this method uses raw water with high turbidity (1).
0 or more).

The present invention solves the above-mentioned problems, and does not require a skilled technician or a large installation space for an apparatus, and reduces the amount of injected chemicals so that arsenic can be efficiently removed. It is the purpose.

[0008]

In order to solve the above-mentioned problems, a method for operating a water treatment facility using a submerged membrane filtration device according to the first aspect of the present invention comprises: The mixed water to which a chemical for precipitating arsenic or an adsorbent for adsorbing arsenic is added flows into the membrane filtration tank, or the raw water flows into the membrane filtration tank, and the chemical or adsorbent is added to form a mixed water. The arsenic in the water was precipitated or adsorbed by the adsorbent, and the mixed water in the membrane filtration tank was solid-liquid separated by the immersion membrane filtration device installed in the tank, and passed through the membrane surface of the immersion membrane filtration device. When the membrane filtered water is taken out of the tank, the amount of membrane filtered water taken out with respect to the amount of water flowing into the membrane filtration tank is set to 99% or more, and a high concentration of arsenic is obtained by maintaining a high concentration of chemicals or adsorbent in the membrane filtration tank. Promotes precipitation or adsorption of In which was to so that.

According to a second aspect of the present invention, there is provided a method for operating a water treatment facility using a submerged membrane filtration device, wherein an oxidizing agent is added to the raw water or the raw water is subjected to ozone treatment in the above-mentioned configuration. Arsenic is oxidized to pentavalent arsenic ions.

[0010] According to the above-mentioned structure, the amount of membrane water taken out of the membrane filtration tank is reduced by 99%.
As described above, precipitation or adsorption of arsenic can be promoted by keeping the added chemical or adsorbent at a high concentration in the membrane filtration tank and making the most of the ability of the chemical or adsorbent. . As a result, the amount of the chemical or the adsorbent can be reduced, and the fluctuation of the raw water quality can be widely dealt with. Therefore, it is possible to obtain the membrane filtered water having a stable treated water quality by operating at a constant amount.

According to the second aspect of the invention, the arsenic removal rate can be improved by previously oxidizing arsenic in the raw water to pentavalent arsenic ions.

[0012]

An embodiment of the present invention will be described below with reference to the drawings. The water treatment equipment shown in FIG.
A processing tank 4 in which a raw water introduction pipe 1, a coagulant injection pipe 2, and an oxidizing agent injection pipe 3 are opened in the upper part of the tank, and a chemical mixed water introduction pipe 5 guided from the processing tank 4 is opened in the upper part of the tank. A membrane filtration tank 7 in which the apparatus 6 is immersed is installed, and a membrane filtration water pipe 8 communicating with the permeation side of the membrane filtration apparatus 6 is provided with a water storage tank 9 opened at the top of the tank. A drain pipe 10 is provided in the lower part of the membrane filtration tank 7, a backwash water pipe 11 led from the water storage tank 9 is opened in the middle of the membrane filtration water pipe 8, and in the middle of the backwash water pipe 11. A chemical injection tube 12 for adding a cleaning chemical such as sodium hypochlorite is open. Reference numeral 13 denotes a stirrer, 14, 15, and 16 denote on-off valves, 17 and 18 denote pumps, and 19 denotes a membrane filtration water discharge pipe.

Although not shown, the membrane filtration device 6 is constituted by, for example, arranging a plurality of external pressure type tubular ceramic membrane elements inside a casing having a liquid passage chamber communicating with the inside of each membrane element. The membrane filtration water pipe 8 is provided so as to communicate with the liquid passage chamber of the casing, and the air diffuser 20 is provided below the membrane element. By driving the pump 17 according to such a configuration, solid-liquid separation is performed in the membrane element, and the membrane filtration water that has passed through the membrane surface flows into the membrane filtration water pipe 8 through the liquid passage chamber, and the membrane of the membrane element The surface is cleaned by a bubble flow supplied through the air diffuser 20.

In such a water treatment facility, raw water is introduced into the treatment tank 4 from the raw water introduction pipe 1 and is stirred by the stirrer 13 while the coagulant such as polyaluminum chloride is supplied from the coagulant injection pipe 2. And a coagulant, such as kaolin or diatomaceous earth, if the raw water does not contain any turbidity, to add 5 to 50 ppm, respectively. If raw water contains trivalent arsenic ions, oxidizer such as sodium hypochlorite, chlorine dioxide, etc. through the oxidizer injection pipe 3 ~ 2mg
/ L. Thereby, while trivalent arsenic ions contained in the raw water are oxidized to pentavalent arsenic ions by the oxidizing agent, these trivalent and pentavalent arsenic ions are precipitated and aggregated by the aggregating agent using the aggregating aid as a core. Let it.

Then, the chemical mixed water 21 containing the sedimentation and coagulant in the processing tank 4 is introduced into the membrane filtration tank 7 through the chemical mixed water introduction pipe 5, and the chemical mixed water 22 in the membrane filtration tank 7 is introduced.
Is separated into solid and liquid by the membrane filtration device 6, and the membrane filtration water 23 that has passed through the membrane surface of the membrane element and flowed into the membrane filtration water pipe 8 is stored in the water storage tank 9, and sediment and turbidity are stored in the membrane filtration tank 7. Let it remain. At this time, the membrane filtration device 6 is operated so that the amount of the membrane filtered water 23 taken out with respect to the amount of the chemical mixed water 21 flowing into the membrane filtration tank 7 is 99% or more, and less than 1% of the inflowed water is drained to the drain pipe 10. , The added coagulant is maintained at a high concentration in the membrane filtration tank 7, and the remaining unreacted arsenic is precipitated and coagulated.

At this time, the ammonia nitrogen contained in the chemical mixture water 22 is oxidized and removed by microorganisms such as nitrifying bacteria naturally occurring in the membrane filtration tank 7, and soluble manganese and iron are oxidized and removed. The membrane filtered water 23 does not contain ammonia nitrogen, soluble manganese or iron because it is subjected to an action such as incorporation into suspended matter.

The membrane filtered water 23 in the water storage tank 9 is taken out through the membrane filtered water outlet pipe 19 as treated water. The membrane washing water 23 is appropriately injected through the backwash water pipe 11 and, if necessary, from the chemical injection pipe 12. It is sent to the filtration device 6, and the membrane element is backwashed.

According to the above-described method, the ability of the coagulant (and the oxidizing agent) is utilized to the maximum extent, so that the amount of the coagulant (and the oxidizing agent) can be reduced and the raw water quality can be widely varied. It is possible to drive with a fixed amount,
Membrane filtered water 23 having stable treated water quality can be obtained.
Therefore, labor saving and unmanned automatic driving are also possible. In addition, since the device configuration is simple and compact, the installation space for the device is reduced.

When comparing the above-mentioned method of the present invention with the above-mentioned conventional coprecipitation method, the method of the present invention shows that
When added at mg / L, the content was reduced from 0.03 mg arsenic / L to 0.003 mg arsenic / L or less.
In the coprecipitation method, when a flocculant is added at 20 mg / L,
It was reduced from 0.03 mg arsenic / L to 0.003 mg arsenic / L or less. From these results, it can be seen that according to the method of the present invention, the same arsenic removing effect can be obtained by adding about 1/2 amount of the coagulant as in the conventional coprecipitation method.

This means that the removal amount of the membrane filtration water 23 with respect to the inflow amount of the chemical mixed water 21 into the membrane filtration tank 7 is 99 to 99.
8%, the added powdered activated carbon is 100-
Concentrated 500-fold, for example, when injected at 10 mg / L, concentrated to 1,000-5,000 mg / L,
This is because it accumulates in the tank and is maintained at a high concentration.
An ozone contact tower or the like may be provided in front of the treatment tank 4 instead of the oxidant injection pipe 3 described above, and trivalent arsenic ions in raw water may be oxidized to pentavalent arsenic ions by ozone treatment.

Further, instead of the structure in which the chemical mixed water in which the coagulant and the oxidizing agent are added to the raw water in advance, flows into the membrane filtration tank,
Even if the coagulant is added after the raw water flows into the membrane filtration tank, the ability of the coagulant (and the oxidant) can be maximized as in the case described above.

In the above description, the case where a flocculant is added has been described. However, when an adsorbent having an arsenic adsorption ability, such as powdered activated alumina, a chelate resin, or an ion exchange resin, is added, the same as above is performed. As a result, arsenic can be efficiently removed with a small amount of addition as compared with the conventional adsorption / exchange method. For example, the powdered activated alumina may be added so as to be 5 to 50 ppm. However, depending on the properties of the adsorbent, p
The need for H adjustment and the like is the same as in the prior art.

The configuration of the membrane filtration device is not limited to the above, and membranes of various materials such as an MF membrane and a UF membrane can be used.

[0024]

As described above, according to the present invention, the amount of water flowing into the membrane filtration tank when the mixed water to which the chemical for precipitating arsenic or the adsorbent for adsorbing arsenic is added is subjected to solid-liquid separation by the membrane filtration device. Stable by adding a fixed amount of chemical or adsorbent, which is smaller than before by keeping the added chemical or adsorbent in the membrane filtration tank at a high concentration by setting the extraction amount of membrane filtration water to more than 99% In addition to ensuring the quality of the treated water, labor saving and unmanned automatic operation are possible, and energy saving operation in which the amount of injected chemicals or adsorbents and the amount of power consumption are reduced is possible. Further, since the device configuration is simple, the installation space can be reduced.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram showing an overall configuration of a water treatment facility operated in one embodiment of the present invention.

[Explanation of symbols]

 2 Coagulant injection pipe 3 Oxidant injection pipe 6 Membrane filtration device 7 Membrane filtration tank 21,22 Chemical mixed water 23 Membrane filtration water

────────────────────────────────────────────────── ─── of the front page continued (51) Int.Cl. ⁷ identification mark FI C02F 9/00 504 C02F 9/00 504B ( 72) inventor Toshio Kawanishi Osaka-shi, Osaka Naniwa-ku Shikitsuhigashi chome No. 2 No. 47 Kubota Corporation (56) References JP-A-8-206663 (JP, A) JP-A-6-304573 (JP, A) (58) Fields studied (Int. Cl. ⁷ , DB name) C02F 1 / 44 C02F 9/00

Claims (2)

(57) [Claims] 1. A method in which a mixture of arsenic-containing raw water and a chemical for precipitating arsenic or an adsorbent for adsorbing arsenic is added to a membrane filtration tank, or raw water is introduced to a membrane filtration tank to form the chemical. Alternatively, an adsorbent is added to form a mixed water, and arsenic in the raw water is precipitated or absorbed by the adsorbent, and the mixed water in the membrane filtration tank is solid-liquid by a submerged membrane filtration device installed in the tank. When separating and extracting the membrane filtered water that has passed through the membrane surface of the immersion type membrane filtration device to the outside of the tank,
The removal of membrane filtered water with respect to the amount of water flowing into the membrane filtration tank is set to 99% or more, and by maintaining a high concentration of chemicals or adsorbent in the membrane filtration tank, arsenic precipitation or adsorption is promoted. Method of operating water treatment equipment using a submerged membrane filtration device. 2. The immersion type membrane filtration according to claim 1, wherein arsenic in the raw water is oxidized to pentavalent arsenic ions by adding an oxidizing agent to the raw water or subjecting the raw water to ozone treatment. An operation method of a water treatment facility using the device.