JPH10309576A - Water treatment by ozone resistant membrane - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prolong the regeneration cycle of activated carbon by adding ozone into raw water, filtering by using a ozone resistant membrane and treating the filtrate with the activated carbon. SOLUTION: A subject raw water is supplied from a raw water tank to an external pressure type module at the rate of about 3 m<3> /hr by a pump and ozone using air as a starting material is introduced from an ozone ejecting port of an ejector system attached between the outlet of the pump and the module. The external pressure type module, which has, for example, about 1800 pieces of yarns having about 0.1 μm pore diameter and put in an about 3 inch diameter casing and has about 7.0 m<2> membrane surface area is made to about 1.8 m<3> /hr.module, 0.5 kg/cm<2> a clean water flow flux. Then, the concentration of ozone just before the inlet of the module is made to about 3.5 ppm. The resultant filtrate is retained in a tank and is introduced into an activated carbon vessel after the remaining ozone is decomposed with sodium thiosulfate. The, activated carbon uses, for example, a charcoal type and the thickness is made to 1 m. The degraded module is regenerated by ozone ejecting and an improved COD value is attained.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for purifying water using a filtration membrane, in which the membrane is filtered at a high filtration rate by an ozone-resistant membrane in the presence of ozone, and the microorganism is easily treated by ozone oxidation. The present invention relates to a method for purifying water that can efficiently and highly treat water by a synergistic effect of a combination of ozone treatment, membrane filtration, and activated carbon treatment, in which membrane filtered water is used to reduce soluble organic matter with activated carbon.

[0002]

2. Description of the Related Art Conventionally, a method of purifying water is to sterilize the raw water withdrawn by first adding chlorine or sodium hypochlorite to prevent the growth of microorganisms and the adverse effects thereof in the purification process, This is a coagulation sedimentation method in which a flocculant corresponding to the amount is added, the suspended substance is flocculated and separated by sedimentation, the overflowed floc is separated in the next sand filtration step, and the raw water is clarified. When the amount of suspended solids in the raw water is small, there are a method of line-mixing the flocculant and filtering it with sand, and a method of floating under pressure. Recently, a technique to replace the above method by an ultrafiltration (UF) method or a microfiltration (MF) method has been developed, and practical use has begun in small-scale water supply and the like.

[0003]

However, the coagulation-sedimentation method removes protozoa such as cryptosporium which are present in very small amounts in raw water required for the level of turbidity required in the recent semiconductor industry and waterworks. However, these requirements have not been satisfied. In addition, recent membrane separation methods have been spotlighted as a technology that can cope with the level of turbidity and protozoa and bacterium, which are disadvantages of the coagulation sedimentation method, but their use is limited from the viewpoint of economy. Have been. Furthermore, in membrane separation by the UF method or the MF method, the removal of soluble organic substances (DOC) and chromaticity is at an insufficient level for semiconductor applications and the like. Therefore, there is a need for a thorough removal of suspended matter, removal of DOC, and the emergence of a new process that is more excellent in terms of hygiene or economy.

[0004]

As a result of various studies on such a problem, it has been found that a combination of a membrane filtration method in the coexistence of ozone or in the presence of ozone and a flocculant, and a treatment of the filtered water with activated charcoal, makes it possible to use each element technology. It has been found that a novel water treatment process that achieves a synergistic effect and satisfies economic requirements can be provided, and has completed the present invention. That is, the present invention provides: a water treatment method in which ozone is added to raw water, filtered using an ozone-resistant membrane, and then the filtered water is treated with activated carbon. Another feature is that ozone is added in an amount that causes 0.05 ppm or more to remain in the filtered water. Another feature is that a coagulant capable of coagulating suspended substances contained in raw water is added before adding ozone to raw water. Another characteristic is that the ozone resistant film is a fluororesin film. Another characteristic is that the activated carbon is a microbial activated carbon.

Hereinafter, the present invention will be described in detail. (A) Characteristics of the hybridized membrane filtration process of the present invention, etc. Issues in the prior art (i) Issues in membrane filtration 1) Conventionally, filtration by the membrane filtration method results in suspended substances in raw water and pore size of the membrane used. A certain component of the organic substance having the above size is blocked by the film, and a so-called concentration polarization or cake phase occurs. At the same time, organic matter in the raw water clogs the membrane or adsorbs to the network inside the membrane. As a result, the flux of the resulting membrane is reduced from a fraction to a few tens of minutes compared to the flux of the clarified water, the cost of membrane filtration is often increased, and economically impractical. .

2) Therefore, when filtration is performed in the presence of an oxidizing agent such as ozone, the filtration can be performed while decomposing organic substances attached or clogged on the membrane, and an extremely high flux can be obtained. That is, in the membrane filtration in the presence of ozone, since organic substances attached to the membrane are repeatedly attacked by ozone passing through the membrane, filtration is performed while always performing self-cleaning, and as a result, a high flux is obtained. It becomes a possible filtration method.

3) This filtration method is disclosed in, for example, Japanese Patent No. 2,5
No. 70,496. In the above publication,
In order to increase the filtration flux and improve the water quality by combining ozone and / or a flocculant with membrane filtration, a method of filtering by adding powdered activated carbon or a flocculant to raw water has been proposed.
In addition, this method is still insufficient for obtaining a highly treated and constant water quality such as for drinking.

(Ii) Problems with ozone treatment Conventionally, soluble organic matter (usually,
Humic substances and fluoic acid, which are hardly decomposed by microorganisms), are oxidized by reacting with ozone. The BOD value of water is rather high due to contact with ozone. This is because the double bond in the humic molecule is oxidized by ozone and becomes an aldehyde, a carbonyl group, a carboxylic acid group, etc.
This is because organic substances that have not been digested by microorganisms are now easily digested. Another reason is that microbial digestion similarly occurs because the macromolecule is reduced in molecular weight. When water with a BOD value increased by ozone treatment is used for water supply, it is necessary to increase the amount of added chlorine to suppress the growth of microorganisms, but the water quality deteriorates, so post-treatment with granular activated carbon is required. It becomes.

(Iii) Problems with activated carbon treatment 1) In Japanese Patent No. 2,570,496, powdery activated carbon is added to raw water to adsorb organic substances in order to improve water quality. The powdered activated carbon has the disadvantage that it is blocked by the membrane and is concentrated, resulting in new concentrated waste. In addition, suspended and colloidal substances in raw water are adsorbed on powdered activated carbon,
The active site does not always effectively adsorb soluble organic matter. If the amount of the organic matter is large, the amount of the powdered activated carbon to be added increases, and the limit of the membrane concentration comes earlier, and there is a possibility that the amount of collected drainage may decrease. 2) On the other hand, activated carbon provided with a membrane facility at the preceding stage is capable of reliably removing suspended substances and colloidal substances by membrane filtration, so that the active sites on the surface are reduced due to contamination due to such adhesion. Disappears. Therefore, the regeneration cycle of the activated carbon can be extended, which is economically effective.

[0010] The method of the present invention basically comprises adding ozone to raw water,
This is a water treatment method in which filtration is performed using an ozone-resistant membrane, and then the filtered water is treated with activated carbon. 1) According to the method of the present invention, by connecting an organic matter removal process to a membrane filtration process and performing hybridization,
It has achieved a revolutionary effect over running the unit process alone.

2) In the present invention, before the treatment in the activated carbon tank, ozone is preferably self-decomposed in a retention tank, or 0.2 ppm with a reducing agent such as sodium thiosulfate.
Is then decomposed, and then treated in a tank having activated carbon in which microorganisms are propagated on activated carbon, that is, bioactive carbon (BAC) provided with activation ability as a floor.
In particular, when the microorganism-coated activated carbon is used, humic substances and the like can be oxidized by the ozone treatment and organic substances which are easily digested can be decomposed. Therefore, a microbial digestion function is imparted to the adsorption of activated carbon, and a more highly treated water quality can be obtained. In addition, it is possible to reduce ammonia which is difficult to treat with ozone by digesting it with microorganisms.

3) In the method disclosed in Japanese Patent No. 2,570,496, since ozone and activated carbon coexist, microorganisms cannot grow and have no effect. Moreover,
When the method of the present invention is applied to waterworks, there is no need for a previous chlorine disinfection process and no trihalomethane formation.
Further, since the COD value is low, the concentration of chlorine used for disinfection can be low, and the generation of trihalomethane can be suppressed as much as possible. 4) As described above, the method of the present invention is a hybrid process consisting of raw water → (addition of a coagulant if necessary) → addition of ozone → ozone resistant membrane → microbial activated carbon treatment, and each unit process is mutually fused. However, this is an epoch-making process that can exhibit more effects than the unit process and can perform highly efficient and advanced processing.

(B) Ozone treatment Introduction of ozone 1) Ozone may be ozone alone or ozonized air. The introduction of ozone into a storage tank such as a tank for storing raw water may be performed through an air diffuser provided at an appropriate position in the tank. good. Further, ozone may be injected by an ejector method or a line mixing method in the middle of a pipe for guiding raw water from a tank to an ozone-resistant film. 2) Addition of ozone sterilizes and removes microorganisms in raw water that normally inhabit raw water such as rivers and lakes, for example, protozoa such as viruses, bacteria, molds, and cryptosporidium.

Ozone Concentration 1) When purifying water by ozone-resistant membrane filtration, the ozone injection concentration for increasing the filtration speed, sterilizing microorganisms and removing odorous substances is generally 0.05 ppm or more. . If the ozone concentration is too high, the economic efficiency is reduced. Therefore, 1 to 10 ppm, preferably 2 to 5 ppm is good. 2) The contact time of raw water with ozone is as long as organic substances and ozone water attached to the surface of the membrane structure are continuously filtered and supplied.
It is not necessary to pay particular attention to the contact time. Usually 1-20m
g / L, preferably 2 to 10 mg / L, at an injection rate of 0.1 g / L.
The contact time is generally 5 to 30 minutes, preferably about 5 to 20 minutes.

(C) Materials of the ozone-resistant film 1) The ozone-resistant film is not particularly limited as long as it is a filter film which does not deteriorate by ozone. For example, an inorganic film such as ceramic; polyvinylidene fluoride (P) having ozone resistance
VdF), polytetrafluoroethylene (PTFE) membrane, ethylene-tetrafluoroethylene copolymer (ETFE)
An organic film such as a film and a fluorine-based resin film such as a polyfluoroacrylate (PFA) film can be used, but a polyvinylidene fluoride film is preferably used. 2) As the pore diameter provided in such an ozone-resistant membrane, a pore diameter range from UF to MF can be used, but the point of pursuing economic efficiency, which is a weak point of the membrane filtration method, and the water permeability of the membrane are fundamental. The use of MF is good because of its high cost. For example, a desirable pore diameter is 0.001 to 1 μm, preferably 0.05 to 1 μm.

(D) Combined Use of Coagulant 1) During membrane filtration, when the pore size of the membrane is in the MF region, the pore size increases, so that viscous substances, bacteria, and the like in raw water enter the membrane. In particular, clogging with a viscous substance cannot be washed by a normal membrane filtration method. Therefore, in a membrane filtration method using an MF membrane, it is generally preferable to use a flocculant such as polyaluminum chloride (PAC). When the use of a flocculant is not necessary, the pore size of the membrane is 0.1 μm or less, and in the case of a membrane having a pore size larger than that, unless a flocculant is added to coarsen a minute suspended substance, flow due to clogging occurs. The bundle tends to decrease and the life of the membrane tends to shorten.

2) When coarsening is performed by using a coagulant together,
It is possible to use an MF membrane having a pore diameter of about 4 to 1 μm, and good economics can be obtained with a high flux. As described above, when a coagulant is used in combination, an organic suspended substance or a high-molecular substance is taken into the coagulant and contact with ozone is reduced, so that an effect that the necessary amount of ozone can be reduced by almost half can be expected. 3) The amount of the coagulant to be added needs to be an amount capable of coagulating a suspended substance contained in raw water, and is generally 1 to 100 mg.
/ L of raw water, preferably 2 to 50 mg / L of raw water.

(E) Post-Treatment with Activated Carbon In the post-treatment with activated carbon, one of the steps of the present invention, the filtrate permeated through the ozone-resistant membrane is introduced into a tank containing granular activated carbon,
Post-processing. As the activated carbon, microorganism-coated activated carbon can be preferably used. That is, the treatment is performed in a tank having activated carbon obtained by propagating microorganisms on activated carbon, that is, bioactive carbon (BAC) provided with activation ability as a floor. In particular, when the microorganism-coated activated carbon is used, humic substances and the like are oxidized by ozone treatment, and organic substances which are easily digested can be removed. Therefore, a microbial digestion function is imparted to the adsorption of activated carbon, and a more highly treated water quality can be obtained. In addition, it is possible to reduce ammonia which is difficult to treat with ozone by digesting it with microorganisms.

[0019]

The present invention will be illustrated by the following examples, which do not limit the scope of the present invention. (Example 1) (1) River surface water Turbidity: 10 to 20 degrees COD value: 6 to 8 ppm Water temperature: 16 ° C. (2) Water purification process Raw water → ozone treatment → 0.1 μm PVdFMF membrane filtration → retention tank → activated carbon treatment

(3) An external pressure type module (membrane area: 7.0 m ² , clear water flow) in which the target raw water is supplied to a raw water tank, and 1800 threads having a pore diameter of 0.1 μm are accommodated in a 3-inch diameter PVC casing by a pump. Bundles: 1.8 m ³ / hour module; 0.5 kg / cm ² ) are supplied at a rate of ³ m ³ / hour. An ejector-type ozone injection port is provided between the pump outlet and the module to introduce ozone using air as a raw material. The ozone concentration immediately before the module entrance was 3.5 ppm.

For a constant flow rate filtration, the set flux is 1.7 m ³ /
When the module and the module were set at 16 ° C., the average filtration pressure was 0.5 kg / cm ² , which was stable for two months.
The filtration speed was 5.8 m / day high flux. 1.3m ³
The amount of circulating water per hour was returned to the raw water tank, and the raw water tank was supplied with 1.7 m ³ / hour of the surface drainage of the river. The ozone concentration in the filtered water was set to 0.2 ppm, and the ozone concentration at the pump outlet was linked. Module is 30 minutes in 20 minutes
It was backwashed with filtrate from the filtrate tank at a rate of seconds, and the backwash drainage was discharged out of the membrane filtration system. At this time, the COD value of the drainage water was 4 to 5.5, indicating a decrease of about 1/3.

The filtrate was retained in a 0.7 m ³ tank, the residual ozone was decomposed with sodium thiosulfate, and then led to an activated carbon tank. Activated carbon was charcoal-based and had a thickness of 1 m.
The COD value at the activated carbon outlet after two months is 0.3-0.8 pp
m. When the ozone injection is stopped in this device, the module flux decreases to 0.35 m ³ / h / module,
The stable area has been reached. At this time, the filtration speed was a value of 1.2 m / day, the molecular weight cut off was 13,000, which was the same value as that of the PAN UF membrane. When the injection of ozone was started again at this point, the module returned to 1.7 m ³ / hour / module in one hour.
When the ozone injection was stopped, the COD value was 5.2 ppm.

(Embodiment 2) 0.4 μm to the apparatus of Embodiment 1
Was replaced with a PVdF membrane module (membrane area: 7.0 m ² ). 25 ppm of a flocculant PAC was added to the raw water tank, and the pH was adjusted to 7 with NaOH. The PAC was charged, the suspended material was agglomerated, and ozone was introduced. The water temperature at this time was about 20 ° C. Ozone concentration on the filtered water side is 0.2
Ozone was introduced from the ozone generator to the raw water supply line so as to be ppm. The ozone concentration at this time is 2-2.5p
pm. By adding PAC, the concentration of ozone injected into the raw water could be reduced.

The circulating supply rate was 4.5 cm ³ / hour, the set water amount of the module was 2.5 m ³ / hour at 20 ° C., and the concentrated circulating water was 2.0 m ³ / hour. At this time, the average filtration pressure was 0.4 kg / cm ² , and the filtration pressure remained stable.
The flux at this time was as high as 8.5 m / day. At this time, the COD value of the raw water was 6.8 ppm, and the COD value of the filtrate was 2.7 ppm. The COD value at the outlet of the microorganism activated carbon tank was 0.5 ppm.

[0025]

According to the method of the present invention, since the addition of ozone and the treatment with activated carbon are combined, the amount of soluble organic matter in raw water can be reduced. Further, in the present invention, the coagulant is added at the time of the ozone treatment, so that the amount of added ozone can be reduced and the filtration speed can be improved. In short, the following effects can be expected. (B) Providing a high-efficiency process with a high flux, (b) Providing a simplified water purification process, and thus maintaining good maintenance. (C) Good treated water quality (combination of ozone, membrane treatment and activated carbon treatment), (d) space saving, and (e) suppression of trihalomethane generation. (F) By adding ozone, viruses, bacteria,
Protozoa such as molds and Cryptosporidium are sterilized and filtered off, so that measures against microorganisms in the filtrate are thorough.

Continued on the front page (51) Int.Cl. ⁶ Identification code FI C02F 9/00 502 C02F 9/00 502H 503 503A 504 504B 504E

Claims (1)

[Claims] 1. A water treatment method comprising adding ozone to raw water, filtering using ozone-resistant membrane, and treating the filtered water with activated carbon.