JPH07229891A - Analysis of ozone treatment characteristics and membrane treatment of ozone-treated water - Google Patents

Abstract

PURPOSE:To remove a precursor substance having trihalomethane forming capacity by successively filtering ozone-treated water by a ultrafiltration membrane having two or more of preset mol.wt. fractionation stages and measuring the water quality control items of the obtained conc. soln. to evaluate ozone treatment characteristics. CONSTITUTION:Ozone gas from an ozone generator is diffused into water to be treated in an ozone treatment tank and sterilization, deodorizing and decoloration are performed by its oxidizing power and sterilizing power. This ozone treated water is filtered with an ultrafiltration membrane having many mol.wt. fractionation stages wherein MW is 300K, 50K, 30K, 10K, 3K, 1K and 0.5K. Subsequently, water quality control items such as dissolved organic carbon, chemical oxygen demand, ultraviolet absorbancy at a wavelength of 260nm, the residual ratio change of trihalomethane forming capacity or the like are measured. By this constitution, the ozone treatment for ensuring objective water quality can be effectively controlled. Especially, when an ultrafiltration membrane of 0.5K is used, a precursor substance having trihalomethane forming capacity can be almost removed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for analyzing ozone treatment characteristics in an ozone treatment apparatus as an advanced water treatment method and a membrane treatment method for removing a precursor having a trihalomethane-forming ability from ozone-treated water. is there.

[0002]

2. Description of the Related Art The current water supply penetration rate in Japan is about 94.7.
%, And the maintenance system for maintaining cleanliness of tap water has reached one of the highest levels in the world. This is obvious from the fact that tap water can be safely consumed anywhere in the country.

Generally, in order to purify raw water taken from a river or the like, a coagulant is injected into and mixed with raw water in a coagulating sedimentation tank,
Suspended substances (sand, clay,
Organic substances such as algae) are aggregated, precipitated, and separated. This process incorporates chlorine treatment for the purpose of algicidal treatment and removal of chromaticity components such as iron and manganese.

On the other hand, with the recent development of various industries, pollution of natural waters with chemical substances is progressing, and it is a reality that it is difficult to cope with this. For example, THM (trihalomethane) countermeasures caused by disinfection by-products such as chlorine treatment,
Problems such as contamination of raw water and groundwater by pesticides used in fields and golf courses, and generation of off-flavor due to the growth of odorous algae in closed water areas (Masanori Ando, Toyaku Magazine, 15- 10, 55, 1993).

Particularly in the case of the above-mentioned THM, the U.S.M. S. In 1979, the EPA established a rule that the total trihalomethane concentration in tap water should be 0.1 mg / l or less. In Japan as well, in 1981, the immediate control target value for trihalomethane was set to 0.1 mg / l on an annual average of all THMs (edited by Kenji Tanbo, water supply and trihalomethane, Gihodo Publishing, 1983).
See year). In addition, in 1992, the standard for tap water quality was established based on the control target value of trihalomethane, and the standard was established for each of the four trihalomethane substances (Biotreatment Technology Subcommittee, 57th regular meeting materials, 1
993).

THM is one in which three hydrogen atoms of methane (CH ₄ ) which is the simplest hydrocarbon are replaced by halogen atoms such as chlorine, iodine and bromine, and among them, it is expressed in tap water. Chloroform occupies the largest proportion, and four trihalomethane compounds of bromodichloromethane, dibromochloromethane, and bromoform are summed up and defined as the total trihalomethane content. It has been confirmed that chloroform of the four types is a carcinogen.

[0007] The THM generated in tap water is said to be generated by pre-chlorination or chlorine addition for disinfection using as a precursor a humic substance which is a naturally occurring organic coloring component or a stable organic substance similar thereto. The most representative of such precursors are humic acids and fulvic acids, which are the main components of what is called peatland colored water. These components are stable metabolic wastes resulting from the metabolic activity of microbial communities and appear in high-color wastewater from human waste treatment plants as well as in effluents of general sewage treatment plants.

From such a background, recently, for the purpose of reducing the THM precursor, an advanced water purification system combining ozone treatment and activated carbon treatment instead of chlorine treatment has been actively studied. . Specifically, a method of performing ozone treatment with an ozone treatment tower, removing chromaticity components, etc. with a biological filtration tower, then filtering with a sand filtration pond, etc. and sending it to a water purification pond is adopted. It effectively sterilizes, deodorizes and decolorizes by utilizing its oxidative power and bactericidal power. In particular, by performing the ozone treatment before the biological activated carbon treatment, it is possible to improve the tolerance for load fluctuation and the life of the activated carbon.

[0009]

As a conventional method for analyzing qualitative changes in ozone treatment characteristics, Sephadex G is usually used.
A means for putting soft gel such as 25 into a cylindrical body and filtering is adopted, but this method has a molecular weight cut-off range of MW 5
Since it is as narrow as K or less and the fractionation amount is as small as about 5 ml, dissolved organic carbon (DOC) and chemical oxygen demand (C
There is a problem that it is not possible to sufficiently examine water quality control items such as ODcr,) and trihalomethane production capacity (THMFP).

Further, as a method for controlling ozone treatment, generally, a simple control method such as a control in which the amount of emitted ozone is proportional to the amount of treated water, a control in which the injected ozone concentration is constant or a control in which the exhaust ozone concentration is constant, etc. Is adopted, and the actual situation is that the control based on the analysis of the qualitative change in the ozone treatment characteristics is not carried out. In such a method, there is a possibility that excess or deficiency of ozone may occur due to disturbance such as fluctuation of inflow water quality and fluctuation of water temperature, and it is difficult to obtain stable treated water quality.

Further, conventionally, the removal of components in the suspended matter region has been targeted, such as a microfiltration method (MF method) or an ultrafiltration method (UF).
Direct filtration is known. Turbidity and ss component (Suspended solid, suspended solids in water) are almost 100%, chromaticity is 50-90%, coliform bacteria is 100%, general bacteria and Although 99.5% or more of subordinate bacteria are removed, the present situation is that the removal of precursors having THMFP is not considered.

In view of the above problems, the present invention secures the target water quality when ozone-treating the water to be treated and detects and analyzes the qualitative change of THMFP, and based on this analysis result. An object of the present invention is to provide a method of analyzing ozone treatment characteristics and a method of treating ozone-treated water with a film, which makes it possible to carry out an optimal operation of the ozone treatment tank and remove precursors having THM generation ability. To do.

[0013]

In order to achieve the above object, the present invention sequentially diffuses ozone gas obtained by an ozone generator into the water to be treated in an ozone treatment tank, and oxidizes and sterilizes the ozone gas. In an ozone treatment apparatus adapted to perform sterilization, deodorization and decolorization using force, first, according to claim 1, ozone-treated water is sequentially filtered using an ultrafiltration membrane having a plurality of preset molecular weight fractions. Then, a method for analyzing ozone treatment characteristics is provided, in which the water quality control items of the obtained concentrated liquid are measured to evaluate the ozone treatment characteristics.

As an index for evaluating the ozone treatment characteristics, dissolved organic carbon (DOC), chemical oxygen demand (CO
Dcr), UV absorbance (E2 at 260 nm wavelength)
60) and each water quality control item of the residual rate change of the trihalomethane production ability, the MW is 3 as the cut-off molecular weight in multiple stages.
00K or higher, 50-300K, 30-50K, 10-3
0K, 3-10K, 1-3K, 0.5-1K, 0.5K
Classify into molecular weight fractions below.

Further, according to claim 4, the precursor for trihalomethane-producing ability is decomposed by ozone treatment, and the ozone-treated water is subjected to ultrafiltration using a membrane having a molecular weight cutoff of 0.5 K to produce trihalomethane. Provided is a method for treating a film of ozone-treated water with a film so as to remove a precursor substance having a hydrogen atom.

[0016]

According to such an ozone treatment characteristic analysis method, the ozone gas obtained from the ozone generator is diffused into the ozone treatment tank for desired sterilization, deodorization and decolorization. By measuring water quality control items after filtering using multiple stages of ultrafiltration membranes, it is possible to sufficiently analyze the qualitative changes in ozone treatment characteristics and achieve the target water quality. It can be effectively used for the control of ozone treatment for ensuring the above.

According to the film treatment method of ozone-treated water according to claim 4, the ozone-treated water decomposes the precursor capable of forming trihalomethane, and the ozone-treated water has a fractional molecular weight of 0.5 K in particular. By performing ultrafiltration using the filtration membrane of No. 2, it is possible to almost remove the precursor having the ability to generate trihalomethane, and a treated water quality that is safe as tap water can be obtained.

[0018]

EXAMPLES Specific examples of the method for analyzing ozone treatment characteristics and the method for treating treated water according to the present invention will be described below. In this example, the molecular weight cutoff was MW 300K, 50.
Using the ultrafiltration membrane divided into multiple stages of K, 30K, 10K, 3K, 1K, and 0.5K, coagulated sediment water before and after ozone treatment is sequentially filtered, and qualitative treatment by ozone treatment is performed based on the molecular weight fraction. The main purpose is to analyze the change and select an ultrafiltration membrane that can remove the THM precursor.

In the ozone treatment defined in this embodiment, ozone gas obtained from an ozone generator is introduced into a diffusing pipe arranged inside the ozone treatment tank by using a blower, and the ozone gas is introduced into the water to be treated in the ozone treatment tank. By dissipating,
This is a method of performing desired sterilization, decolorization, and deodorization.

In this embodiment, first, 4 liters of each of the coagulated sedimentation water and the ozone-treated water is filtered through a 0.22 μm membrane filter to remove the ss component. This is 3.8kg / c
Ultrafiltration was performed under a pressure of m ² (0.7 kg / cm ^{2 in} the case of MW 300K) with a stirring cell equipped with a diamond flow membrane manufactured by Amicon. At this time, the filtration flow rate of purified water, the filtration flow rate of 0.5% bovine serum albumin, and the leakage of albumin from the diaflow membrane were checked to confirm the attachment condition of the diaflow membrane.

The outline and operation of the ultrafiltration device will be described with reference to the schematic view of FIG. That is, N ₂ gas was supplied from the nitrogen gas cylinder 2 into the container 1 containing the sample, the concentrated liquid 3 was sent into the pressure type cell 4 incorporating the ultrafiltration membrane for filtration, and the filtered filtrate 5 was obtained. It is stored in the container 6.

This ultrafilter usually has a function of filtering colloidal particles as well. Generally, a suitable semipermeable membrane is prepared as an ultrafiltration membrane, which is formed into a bag shape. A structure is adopted in which the colloidal particles and the solvent are separated from each other by being attached while being held on a support base. Usually, the size of the mesh of the filtration membrane is set to be a rough standard because it is difficult to filter the components to be filtered.

When the solid-liquid separation effect of this ultrafiltration device is compared with the conventionally used centrifugal separator or the solid-liquid separation method using filter paper, the solid substances remaining in the filtrate in the ordinary centrifugal separator are Hundreds to thousands of mg of ss component /
In the case of using a filter paper, the ss component is several tens to 1,000 mg / l, whereas in the case of using an ultrafiltration device, the remaining ss component can be almost detected. The value cannot be set Moreover, the solid-liquid separation device itself has a simple structure, and the device itself can be automated.

Table 1 shows the ozone treatment conditions for the coagulating sedimentation water.

[0025]

[Table 1]

Next, the ozone-treated water has a molecular weight cut off of MW 3
00K, 50K, 30K, 10K, 3K, 1K, 0.5
Approximately 1 after being filtered sequentially using K's Diaflow membrane
00 ml of concentrated liquid was obtained. Table 2 shows the types of ultrafiltration membranes manufactured by Amicon and the filtration conditions.

[0027]

[Table 2]

According to Table 2, type YC 05, YM
The molecular weight (MW) is 300 by using seven kinds of ultrafiltration membranes of 1, 3, 10, 30, XM 50,300 in total.
K or more, 50-300K, 30-50K, 10-30
K, 3-10K, 1-3K, 0.5-1K, less than 0.5K can be classified into a total of eight types of molecular weight fractions.

Next, in this example, the sample before and after the ozone treatment was subjected to ultrafiltration based on the above-mentioned molecular weight fractionation of a plurality of stages, and then E260 (UV absorbance at a wavelength of 260 nm) and CODcr (chemical oxygen demand). , DOC
Water quality control items such as (dissolved organic carbon) were measured.

E260 is a Shimadzu spectrophotometer UV-2.
60 was used and DOC was Shimadzu TOC-5000.
And CODcr is Ultra low manufactured by HACH.
range COD reagent 0-40 p
THMFP was measured based on the clean water test method using pm range.

FIG. 2 shows E260 (× 1) based on the above measurement.
It is a graph showing the change of 0 ^-2 ), and according to the figure, the peak of E260 appears at the molecular weight fraction of 1-3K before and after the ozone treatment, but after the ozone treatment, the organic matter at MW of 50K or higher is shown. The removal rate of organic matter was about 60% when the MW was 10 K or less and was almost zero.

The ultraviolet absorbance (UV) is an analytical method utilizing the fact that light is absorbed by a substance in the range of 200 to 400 nm which is the wavelength range of ultraviolet rays, and usually has a wavelength of 26.
Absorbance at 0 nm (E260) and wavelength 370n
Performed using the absorbance at m (E370). It is known that E260 has a high correlation with the amount of permanganate consumed (mg / l), and E370 has a high correlation with the chromaticity.

FIG. 3 shows CODcr (m
It is a graph which shows the result of having measured the change of g), According to the figure, the molecular weight fraction before and behind ozone treatment is 30-50K and 5.
The organic matter removal rates at 0 to 300 K were 75% and 44%, respectively, but the removal rates in the remaining fractions were 9% to 27%, indicating a relatively difficult removal rate.

FIG. 4 is a graph showing changes in DOC (mg / l) before and after ozone treatment based on the above measurement.
It was confirmed that a part of the organic matter at 10K could be reduced to a low molecular weight organic matter having a MW of less than 1K. Usually, in the ozone treatment in the water purification process, the ozone injection rate is as low as 1 to 2 (mg / l), so it is considered that no remarkable reduction in molecular weight occurs.

According to FIGS. 3 and 4, the dissolved organic carbon (T-
DOC mg), chemical oxygen demand (T-CODcr
mg) and the UV absorbance at a wavelength of 260 nm (T-
It can be seen that the measured values in the ozone-treated water are lower than the measured values in any of E260).

Next, FIG. 5 shows that after the ozone treatment, the sample was subjected to ultrafiltration on the basis of the above-mentioned molecular weight fractions, and then THMFP, CHCl ₃ forming ability, CHBrCl ₂ forming ability,
CHBr is a graph showing the ₂ Cl results of the residual ratio changes in product performance as measured, Table 3 shows the results summarized remaining index change THMFP by ozone treatment (Ci / Co%).

[0037]

[Table 3]

C of MW of 300K or more by ozone treatment
The HCl ₃ precursor is preferentially decomposed, and part of the MW0.
Reduced to 5K-1K precursor and CHCl ₃
The production capacity has tripled, and THMF has been correspondingly increased.
It was found that P increased eight times.

The CHBrCl ₂ precursor was also removed on average by about 50%. However, by ozone treatment, MW
CHBr ₂ Cl precursors of 0.5K to 10K tend to be difficult to remove. Further, the CHBr ₃ production ability was not detected in any molecular weight cut-off range.

In particular, in this example, by using an ultrafiltration membrane having a molecular weight cutoff of 0.5 K, the CHCl ₃ production capacity was 1%.
00%, CHBrCl ₂ production capacity is 55.2%, CHBr ₂
It was possible to remove Cl by 38.2% and THM by 75.2%. Therefore, by subjecting ozone-treated water to ultrafiltration using a membrane with a molecular weight cutoff of 0.5 K, TH
It is possible to remove 70% or more of the organic precursors having the ability to generate M, and it is possible to supply safe purified water as tap water.

[0041]

As described in detail above, according to the present invention, it is sufficient to measure the water quality control item after filtering the ozone-treated water using the ultrafiltration membrane classified into each molecular weight fraction. It is possible to analyze qualitative changes in various ozone treatment characteristics, and by utilizing the results of this analysis for the control of ozone treatment, it is possible to prevent excess and deficiency of ozone due to fluctuations in inflow water quality and other disturbances, and to perform stable treatment. Water quality can be obtained. In particular, the range of molecular weight cut-off of the ultrafiltration membrane is wide, and the amount of sample collected is relatively large, so that water quality control items for each fraction can be sufficiently examined.

Further, according to the method for treating ozone-treated water according to claim 4, after the precursor capable of forming trihalomethane is decomposed by the ozone treatment, the ozone-treated water is passed through a filtration membrane having a molecular weight cutoff of 0.5K. By using the ultrafiltration, the precursor capable of producing trihalomethane is almost removed,
This produces the effect that safe treated water quality can be obtained as tap water based on ozone treatment.

[Brief description of drawings]

FIG. 1 is a schematic view showing an example of an ultrafiltration method according to this embodiment.

FIG. 2 is a graph showing the results of measuring E260 after ultrafiltration of a sample before and after ozone treatment based on a plurality of stages of molecular weight fractionation.

FIG. 3 is a graph showing the results of measuring CODcr after ultrafiltration of a sample before and after ozone treatment based on a plurality of stages of molecular weight fractionation.

FIG. 4 is a graph showing the results of DOC measurement after ultrafiltration of a sample before and after ozone treatment based on molecular weight fractionation in multiple stages.

FIG. 5 is a graph showing the results of measuring the residual rate change of various trihalomethane-producing ability after performing ultrafiltration on a sample after ozone treatment based on a plurality of stages of molecular weight fractions.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Container 2 ... Nitrogen gas 3 ... Concentrated liquid 4 ... Pressurized cell 5 ... Filtrate 6 ... Container

Claims (4)

[Claims] 1. Ozone gas obtained by an ozone generator is sequentially diffused into water to be treated in an ozone treatment tank, and sterilization, deodorization and decolorization are carried out by utilizing the oxidizing power and bactericidal power of ozone gas. In the treatment equipment, the ozone treatment water is sequentially filtered using an ultrafiltration membrane having a preset number of stages of molecular weight fractions, and the water quality control items of the resulting concentrate are measured to evaluate the ozone treatment characteristics. A method for analyzing ozone treatment characteristics, characterized by: 2. Dissolved organic carbon (DOC) and chemical oxygen demand (CO) are used as indicators for evaluating the ozone treatment characteristics.
Dcr), UV absorbance (E2 at 260 nm wavelength)
60) and the method for analyzing ozone treatment characteristics according to claim 1, wherein each water quality control item of the residual rate change of the trihalomethane production ability is used. 3. The multi-stage molecular weight cutoff having a MW of 300K or more, 50-300K, 30-50K, 10-
30K, 3-10K, 1-3K, 0.5-1K, 0.5
The method for analyzing ozone treatment characteristics according to claim 1, wherein the ozone treatment characteristics are classified into molecular weight fractions less than K. 4. Ozone gas obtained by an ozone generator is sequentially diffused into water to be treated in an ozone treatment tank, and sterilization, deodorization and decolorization are carried out by utilizing the oxidizing power and bactericidal power of ozone gas. In the treatment equipment, the precursor for trihalomethane-forming ability in the water to be treated is decomposed by ozone treatment, and the ozone-treated water is subjected to ultrafiltration using a membrane having a molecular weight cutoff of 0.5 K to obtain the trihalomethane-forming ability. A method for treating a film of ozone-treated water, which comprises removing a precursor substance having: