JP3228588B2 - Water purification treatment method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention uses a hollow fiber separation membrane for removing purified fine particles, organic suspended substances and bacteria in surface water such as river water, lake water or pond water to obtain purified water. It relates to a water purification treatment method.

[0002]

2. Description of the Related Art Conventionally, water purification treatment methods for obtaining purified water from surface water such as river water or lake water include coagulation, sedimentation, and sedimentation.
It is common to purify raw water by sequentially performing the steps of sand filtration and disinfection, and a large installation space is required for equipment for the purification. On the other hand, in recent years, the quality of raw water has deteriorated due to the pollution of rivers, etc., and systems such as biological treatment, ozone treatment, and activated carbon treatment have been added to conventional water purification treatment methods to secure safer and more delicious water. The introduction of advanced water purification treatment methods is under study. However, the addition of the above-mentioned treatment system to the conventional advanced water purification treatment method not only causes a further increase in equipment space, but also requires a complicated measurement and control technique and increases the treatment cost. There is a point.

[0003] Under such circumstances, the purpose of the present invention is to provide a water purification treatment method which is much more compact and efficient than conventional water purification equipment. Processing methods that can replace sand filtration have begun to be developed.

[0004] The water purification treatment using the membrane separation technology not only requires the compactness of the apparatus, but also eliminates the necessity of injecting a coagulant or the like, reduces the cost of chemicals, and facilitates operation management and maintenance. It has advantages such as Such a separation membrane for water purification treatment is required not only to have a high permeation rate and not to change with the passage of time, particles suspended in raw water, organic suspended substances, Effective removal of bacteria and viruses is required.

[0005] Microfiltration membranes, which have recently been used in household water purifiers, are characterized by being capable of almost completely stopping suspended particles and bacteria and having a high permeation rate.
Its application to water supply systems is also being considered (Metal Extra Number, April, p. 47 (1991)). However, microfiltration membranes have a relatively large membrane pore size (0.01-1.0 μm) and it is difficult to remove organic substances such as humic substances, which are said to be precursors of organic halogen compounds, from raw water. Most of the humic substances that have permeated the water and the chlorine injected for sterilization react with each other to easily generate trihalomethane, which is known as a carcinogen.

On the other hand, an attempt to completely remove dissolved substances in raw water by using a reverse osmosis (RO) method or a low-pressure reverse osmosis (loose RO) method as a membrane treatment method to obtain cleaner water. (Water Association of Japan, Vol. 58, No. 11
No. 2, p. 1989). However, when trying to remove dissolved substances by the reverse osmosis method, mineral components such as calcium, magnesium, potassium, and sodium are also removed, and there has been a problem that they are not suitable for drinking water. In general, in the reverse osmosis method, the permeation rate is increased by increasing the transmembrane pressure difference. However, such an increase in the pressure increases the power consumption of the water purification treatment, thereby increasing the processing cost. is there.

[0007] Therefore, if the ultrafiltration method is applied to the water purification treatment, suspended minerals and microorganisms are removed while various mineral components from the raw water remain, and the dissolved organic substances such as humic substances are also effective. It is expected that it can be removed.

As an example of removing humic substances using an ultrafiltration method, a report by Taylor et al. On a flat membrane type (Journal
of AWWA, 79 , (8), p. 72 (1987)), but the removal rate was only 40-57%. In addition, when ultrafiltration treatment is performed with a flat membrane using a polyaluminum chloride flocculant together,
It has been reported that a humic acid rejection of 90% can be obtained (Environmental Technology, 11 , 1007 (1990)), but the humic acid rejection of only ultrafiltration in this case was 20% or less.

[0009]

Means for Solving the Problems The present inventors have made intensive studies to achieve the above object, and as a result, completed the present invention.

[0010] That is, the present invention relates to alkaline gold contained in raw water.
99% or more permeation of cations of genus and alkaline earth metals
And inhibits humic acid with a weight average molecular weight of 20,000 by 80% or more.
At the same time, at a transmembrane pressure of 1 kg / cm ² and a temperature of 25 ° C.
Hollow transmission rate of pure water is 150 liters / m ² · hr or more
Using a yarn separation membrane, raw water from surface water as pre-treatment
Water purification characterized by treatment without coagulation treatment
The present invention relates to a chemical treatment method .

When water purification treatment is performed using the separation membrane of the present invention, useful mineral components (Ca ⁺⁺ , Mg ⁺⁺ ,
Na ⁺ , K ^+, etc.) can permeate the membrane, while humic acid, a harmful trihalomethane precursor, can be removed by more than 80%.
Further, since humic acid having a low molecular weight can be removed, high-molecular-weight organic substances, colloids and suspended fine particles having a size larger than that of humic acid can be almost completely prevented.

Further, since the membrane of the present invention has a hollow fiber structure, the membrane area per volume of the membrane module is large, and thus the permeation amount is large. Furthermore, since backwashing is possible, a decrease in permeation speed can be suppressed.

The term "humic acid having a weight average molecular weight of 20,000" as used herein means a weight average molecular weight in terms of polyethylene glycol by gel chromatography of a solution obtained by adjusting a commercially available humic acid reagent to a concentration of 10 ppm, a pH of 8 and an electric conductivity of 150 μS. 20,000 humic acids.

The hollow fiber membrane of the present invention comprises the above humic acid
% Or more, and as long as 99% or more of alkali metal and alkaline earth metal cations can be permeated, the molecular weight cut off of the membrane is not limited.
Desirably, the membrane is a 000 ultrafiltration membrane.

The inner diameter, outer diameter, length and the like of the hollow fiber membrane are not particularly limited. However, in the internal pressure filtration in which raw water flows inside the hollow fiber membrane, suspended matter in the raw water is reduced by the hollow fiber membrane. The inner diameter is preferably 0.3 to 1.5 mm in consideration of not being clogged inside the flow path and increasing the membrane area per module. In addition, the outer diameter should be 0.5 ~ considering the mechanical strength of the membrane.
2.5 mm is preferred. In order to effectively increase the filtration rate using a hollow fiber membrane having such an inner and outer diameter, the length of the hollow fiber is desirably 0.7 to 1.5 m.

In general, when raw water containing a suspension is filtered through a separation membrane, the suspension fouls the membrane surface, and the filtration rate decreases with time. The hollow fiber membrane of the present invention preferably has a membrane structure capable of effective backwashing in order to remove such fouling substances attached to the membrane surface and improve the filtration rate. That is, in the internal pressure type filtration of the hollow fiber membrane, a hollow fiber membrane having an inner skin structure having the most dense layer inside the membrane cross section is preferable in order to suppress fouling inside the membrane pores. Although a hollow fiber membrane having a structure is preferable, a membrane having an outer skin structure is more preferable because a hollow fiber membrane having an inner skin structure is more preferable since the surface of the membrane is easily scratched and causes defects.

The material of the hollow fiber membrane of the present invention is not limited, but examples thereof include cellulose acetate, aromatic polysulfone, aromatic polyether sulfone, polyacrylonitrile, polyethylene, polypropylene, polyvinyl alcohol, and aliphatic polyamide. Can be used.

[0018]

The present invention will be specifically described below with reference to examples.

Example 1 As a model solution of a mineral component contained in raw water, sodium chloride, potassium chloride, calcium chloride and magnesium chloride were dissolved in ultrapure water, and 0.2% by weight of each was dissolved.
An aqueous solution was obtained. The aqueous humic acid solution was obtained as follows. Commercial humic acid reagent (manufactured by Wako Pure Chemical Industries, Ltd.)
After drying at 110 ° C. for 2 hours, 1.00 g was weighed, added to 100 ml of a 0.1 N sodium hydroxide aqueous solution, vigorously stirred for about 1 hour, and ion-exchanged water was added to make 1 liter.
This solution was filtered through a microfiltration membrane having a pore size of 0.45 μm to remove insoluble components in the solution. Further, while vigorously stirring this solution, while gradually adding an aqueous solution of sodium chloride and an aqueous solution of 0.001 N sulfuric acid to the solution, the concentration was 10 pp.
A humic acid aqueous solution having a conductivity of 150 μS and a pH of 8 was obtained. This humic acid aqueous solution was subjected to gel chromatography,
The absorbance was measured, and the weight average molecular weight of humic acid was determined using monodispersed standard polyethylene glycol. The humic acid used has a weight average molecular weight in terms of polyethylene glycol of about 20,000, and has a wide molecular weight distribution of several hundred to 100,000 or less.

The above-mentioned mineral component solution and humic acid aqueous solution are filled inside various hollow fiber membranes, and the pressure is 1 kg.
While the solution was circulated in the longitudinal direction of the hollow fiber membrane at a rate of 1 cm / s under / cm ² was carried out membrane permeation experiment. The membrane used was a polyethersulfone (PES) hollow fiber membrane manufactured by Daicel Chemical Industries, Ltd .; FUS-0151 (fraction molecular weight 10,000, inner diameter 0.5 mm), FU
S-0382 (fraction molecular weight 30,000, inner diameter 0.8 mm), FUS-1041
(Fraction molecular weight 100,000, inner diameter 0.4 mm), FUS-1581 (fraction molecular weight 50,000, inner diameter 0.8 mm) and Daicel Chemical Industries, Ltd. polyacrylonitrile (PAN) hollow fiber membrane; FUY-
03A1 (fraction molecular weight 30,000, inner diameter 1.0 mm), and all membranes are asymmetric hollow fiber membranes with the finest pore diameters on the inner surface.
The solute concentrations in the undiluted solution and the membrane permeate were measured for the mineral component by electrical conductivity and for humic acid by a total organic carbon meter. Table 1 shows the permeability of various solutes through the various membranes, the permeation rate of pure water at 25 ° C at a transmembrane pressure of 1 kg / cm ^2, and the rejection of humic acid. In each case, 99% or more of the mineral component is permeated, while 80% or more of the humic acid is blocked.

Comparative Example 1 The same mineral solution and aqueous humic acid solution as in Example 1 were mixed with a polyethersulfone hollow fiber membrane FUS-5081 (manufactured by Daicel Chemical Industries, Ltd., molecular weight cut off 500,000, inner diameter 0.8 mm), manufactured by Mitsubishi Rayon Co., Ltd. Polyethylene hollow fiber membrane Stellapore-S (registered trademark, pore size 0.03 μm, equivalent molecular weight cut off 500,000, inner diameter
0.3 mm), and the same membrane permeation experiment as in the example was performed. F
US-5081 has a structure in which sponge-like holes are uniformly laminated, and Stellapore S has a structure in which slit-like holes are uniformly laminated. Table 1 shows the results. The rejection of humic acid by these hollow fiber membranes is as small as several percent or less.

Comparative Example 2 The same mineral solution and aqueous humic acid solution as in Example 1 were used using a cellulose acetate reverse osmosis membrane DRS-97 and a polyamide reverse osmosis composite membrane DRA-98 manufactured by Daicel Chemical Industries, Ltd. The same membrane permeation experiment as in Example 1 was performed. Table 1 shows the results. These membranes allow only a few percent of the mineral components to pass through and block more than 90%.

[0023]

[Table 1]

* 1 Permeability = (permeate solute concentration / stock solution solute concentration) x 100 * 2 PES: polyether sulfone PAN: polyacrylonitrile PE: polyethylene CA: cellulose acetate PA: polyamide

[0025]

The present invention purifies surface water such as river water and lake water,
When the hollow fiber membrane of the present invention is used in a water purification treatment operation for obtaining tap water, a mineral component useful as drinking water permeates from raw water, while humic acid, a precursor of harmful trihalomethane, is largely removed. Can be blocked. In addition, because of the hollow fiber membrane structure, backwashing from the outside to the inside or from the inside to the outside of the membrane can be effectively performed during the filtration period, and the filtration rate can be kept large for a long time.

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-4-290591 (JP, A) JP-A-2-21930 (JP, A) The Chemical Society of Japan, “Chemical Handbook, Applied Chemistry”, Heisei 1991 Published by Maruzen Co., Ltd. on July 10, 2008, p. 1182 (58) Fields investigated (Int. Cl. ⁷ , DB name) B01D 61/00-69/14

Claims (3)

(57) [Claims] The present invention allows 99% or more of cations of alkali metals and alkaline earth metals contained in raw water to permeate and inhibits 80% or more of humic acid having a weight average molecular weight of 20,000 and a transmembrane pressure of 1 kg / cm. ^{2. Using} a hollow fiber separation membrane whose permeation rate of pure water at a temperature of 25 ° C is 150 liter / m ² · hr or more, to treat raw water from surface water without coagulation treatment as pretreatment. Characteristic water purification treatment method. 2. The hollow fiber membrane has an inner diameter of 0.3 to 1.5 mm,
An asymmetric porous material having an outer diameter of 0.5 to 2.5 mm and a length of 0.7 to 1.5 m, and having a dense surface layer at least on the inner surface of the hollow fiber in its cross-sectional structure.
1. The water purification treatment method according to 1. 3. A hollow fiber membrane, cellulose acetate, aromatic polysulfone, aromatic polyether sulfone, polyacrylonitrile, polyethylene, polypropylene, water purification according to claim 1 or 2 wherein is made of polyvinyl alcohol or an aliphatic polyamide Treatment method.