JP2002136981A - Method for cleaning secondarily treated water of sewage - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for cleaning secondarily treated water of sewage constituted by combining ozone treatment, biological membrane filtering treatment and permeable membrane filtering treatment, and to perform the removal of ammonia nitrogen and the oxidative decomposition of an organic substance in biological membrane filtering treatment and to further prevent the fouling of the membrane by the organic substance in permeable membrane filtering treatment to enable filtering operation in high filtering flux. SOLUTION: In the method for cleaning secondarily treated water of sewage, preozone treatment is applied to secondarily treated water (3) of sewage in a low ozone injection ratio and biological membrane filtering treatment is next applied thereto and the ozone residual ratio of inflow water is made zero to facilitate the removal of ammonia nitrogen or the oxidative decomposition of the organic substance. Thereafter, the secondarily treated water is treated in a high ozone injection ratio and permeable membrane filtering treatment is performed in the presence of dissolved ozone, and back pressure water washing and air scrubbing are also performed at the same time. Filtering operation is enabled in high filtering flux by forcibly discharging a fouling substance to make regenerated water having stable quality.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for purifying secondary sewage treatment water, and more particularly to a method for purifying ozone by dividing an ozone treatment step into a pretreatment and a posttreatment, and reducing the ozone injection rate in the pretreatment. In the biofiltration membrane treatment step of the process, the residual ozone is reduced to zero, the oxidative decomposition of organic substances in the biofiltration membrane step is facilitated, and after post-treatment with ozone, the separation is performed with a permeable membrane having an ozone resistant membrane. Regarding new improvements.

[0002]

2. Description of the Related Art A sewage system for purifying secondary sewage treated water of this type, which has been conventionally used, to obtain treated water (regenerated water).
As a method for purifying the next treated water, JP-A-7-185546 and JP-A-10-30957 shown in FIGS.
Publication No. 6 can be cited. That is, the first of FIG.
In the prior art, the reference numeral 1 indicates an ozone generator 2
Is an ozone reaction tank which receives supply of ozone from the reactor and feeds raw water 3 as sewage secondary treatment water. In this ozone reaction tank 1, an ozone injection rate of 5 to 15 mg / l is used to convert organic substances into organisms using ozone. Easy to decompose. In the biofilm filtration tank 4 next to the ozone reaction tank 1, an aerobic biological carrier filtration layer 5 is provided.
To supply air from the blower B to oxidatively decompose organic substances that have become biodegradable by aeration. A first filtration unit 6 using a UF membrane next to the biofilm filtration tank 4 filters undecomposed organic substances that could not be oxidized and decomposed in the biofilm filtration tank 4, and a second filtration unit 7. The small-diameter turbid components that could not be completely filtered by the first filtration unit 6 are filtered to obtain treated water as reclaimed water.

[0003] Next, in the second conventional example of FIG.
The ozone reaction tank having the same configuration as that shown in FIG.
The turbid and colloidal substances are removed by a 001 to 1 μm film, and in the next retention tank 10, a reducing agent is injected to lower the ozone concentration to 0.2 mg / l. Next biological activated carbon tank 1
In 1, biologically decomposed organic substances, ammoniacal nitrogen, and the like are biologically treated to obtain treated water 8.

[0004]

The conventional method for purifying the secondary sewage water has the following problems because it has been configured as described above. That is, since there is only one ozone reaction tank, the amount of injected ozone must be increased in order to exhibit a sufficient ozone effect. However, a large amount of ozone remains in the solution, which hinders the oxidative decomposition of organic substances during biological treatment, making it difficult to perform sufficient biological treatment. Further, in the first conventional example shown in FIG. 5, the UF membrane was subjected to fouling of the organic substance, and it was difficult to continue stable filtration for a long time.

[0005] The present invention has been made to solve the above-described problems. In particular, the ozone treatment step is divided into pretreatment and posttreatment, and by reducing the ozone injection rate in the pretreatment, In the biofilm filtration process in the subsequent step, the residual ozone is reduced to zero, and the removal of ammonia nitrogen and the oxidative decomposition of organic substances in the biofilm filtration process are facilitated.
An object of the present invention is to inject a required amount of ozone in a post-treatment, thereby preventing fouling due to an organic substance in a permeable membrane, and enabling a stable filtration operation.

[0006]

According to the present invention, there is provided a method for purifying secondary sewage water, comprising the steps of pre-ozonating the secondary sewage water to convert organic substances remaining in the secondary sewage water into biodegradable water. A second step of oxidatively decomposing the organic substance which has become biodegradable by the biofilm filtration treatment, and a second step of performing ozone reaction at a rate higher than the ozone injection rate of the first step by the ozone reaction treatment. A third step of sterilizing bacteria, inactivating and removing chromatic components by treating at an injection rate, and then removing the inactivated bacteria and insolubilized chromatic components by permeable membrane filtration. And a fourth step of trapping and removing the treated water to obtain treated water. The first step is to eliminate residual ozone in the second treated water at the biofilm filtration inlet of the second step. Ozone injection rate The third step in the transmissive membrane filtration inlet of the fourth step, the dissolved ozone is method for purifying sewage secondary treatment water to leave 1 to 1.5 mg / l. The fourth step of the permeable membrane filtration treatment is the method for purifying the sewage secondary treatment water using a permeable membrane module made of an ozone-resistant material that enables filtration in the presence of dissolved ozone.
Further, in the fourth step of performing the permeable membrane filtration, the bacteria and the insoluble chromaticity component (particulate matter) inactivated by the third step of performing the ozone reaction are captured and filtered by a permeable membrane module, The particulate matter is periodically discharged using physical cleaning means (after simultaneously performing back-pressure water cleaning and air scrubbing, and forcibly discharging treated water remaining in the permeable membrane module before starting the filtration operation). In addition, the method for purifying sewage secondary treatment water enables the continuous operation of the permeable membrane module for a long period of time.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of a method for purifying secondary sewage water according to the present invention will be described below with reference to the drawings. The same or equivalent parts as those in the conventional example will be described using the same reference numerals. In FIG. 1, reference numeral 1A denotes a pre-ozone injection tank, and raw water 3 composed of sewage secondary treatment water is used as pre-ozone treatment in this pre-ozone injection tank 1.
A, and downstream of the pre-ozone injection tank 1A,
Biofilm filtration tank 4, ozone reaction tank 1 for post-ozone treatment
And a permeable membrane module 9, and ozone 2a and 2b from the ozone generator 2 are supplied to the pre-ozone injection tank 1A and the ozone reaction tank 1, respectively.

Next, a process of performing a purification process using the above-described configuration of FIG. 1 will be described with reference to a process diagram of FIG. In FIG. 2, when the raw water composed of the secondary sewage water is supplied to the pre-ozone injection tank 1A, the ozone injection rate 1
Ozone 2 injected from ozone generator 2 at ~ 5 mg / l
Due to a, the organic substances remaining in the raw water 3 change to biodegradable. At the pre-ozone outlet, a pre-ozone treatment step 1Aa in which the ozone concentration becomes zero and the biological treatment reaction is not hindered in the next biofilm filtration tank 4 is performed. The pre-ozone injection tank 1A usually has a volume of about several minutes of residence time.

Next, the treated water sent from the above-mentioned pre-ozone injection tank 1A is supplied to a well-known biofilm filtration tank 4 and supplied with air from a blower B while aerating the air.
By passing through this biofilm filtration tank (not shown, but using a granular filtration layer of anthracite, ceramics, activated carbon, etc.), organic substances that have already become biodegradable in the previous process are oxidatively decomposed. A biofilm filtration process step 4a is performed. In this biofilm filtration tank 4, ammonia nitrogen can be converted to nitrate nitrogen. Therefore, even if sodium hypochlorite is added to retain residual chlorine in a later step, ammonia nitrogen and chlorine are combined. Chloramine formation can be suppressed, and generation of this chloramine odor can be prevented.

Next, ozone 2b from the ozone generator 2 is supplied to the treated water sent from the biofilm filtration tank 4, and is subjected to an ozone reaction in the ozone reaction tank 1. In the ozone reaction treatment step 1a, sterilization or inactivation treatment of bacteria such as Escherichia coli and protozoa, removal of chromaticity, and reduction of COD are performed. In this ozone reaction treatment step 1a, in order to prevent clogging of a permeable membrane, which will be described later, in addition to the sterilization or inactivation treatment of the bacteria and protozoa, the removal of chromaticity, and the reduction of COD, It is necessary to have an ozone injection rate at which the dissolved ozone in the treated water at the outlet of the tank 1, that is, the influent water flowing into the permeable membrane module 9 is kept at about 1 to 1.5 mg / l.

Finally, the treated water sent from the ozone reaction tank 1 has a well-known M having a pore diameter of 0.45 μm or less (the chromaticity component does not decrease to 5 degrees or less when the pore diameter is greater than this diameter).
A permeable membrane module 9 using a permeable membrane made of an F membrane is subjected to a permeable membrane filtration step 9a to remove bacteria, protozoa, and turbid components that have been sterilized or inactivated in the previous step.
By adding sodium hypochlorite 20 to the final treated water 8, it can be used as reclaimed water. Since ozone remains at a concentration of about 1 mg / l in the treated water supplied to the final permeable membrane module 9, the ozone passing through the permeable membrane did not completely decompose and adhere to the permeable membrane. Self-cleaning, which filters while oxidizing organic substances, is performed. The pores of the permeable membrane are not easily clogged, and high filtration flux (about 5 m /
Days) is possible. Although most of the chromaticity components are oxidatively decomposed in the ozone reaction tank 1, the remaining chromaticity components are trapped by the permeable membrane module 9 as particulate matter by setting the pore size to 0.45 μm or less. . As shown in FIG. 3, the trapped particulate matter is washed by simultaneously performing back pressure water washing and air scrubbing with a washing interval of 10 to 20 minutes. Immediately after the simultaneous cleaning of the back pressure water and the air scrubbing is completed, the treatment water remaining in the permeable membrane module 9 is forcibly discharged to the outside of the permeable membrane module 9. The discharge time is 40 to 60 seconds. Since ozone remains as a material of the permeable film, an ozone-resistant film such as polyvinylidene fluoride (PVDF) having ozone resistance is used.

Next, an embodiment which was actually performed will be described. Example Raw water quality Color degree 40 degrees, BOD (ATU added) 11 mg / l Number of coliform bacteria 3050 / ml, COD 24 mg / l Ozone injection rate Pre-ozone treatment 5 mg / l Ozone reaction treatment 15 mg / l Biofilm filtration filter media Anthracite Particle size 3 mm layer thickness 2 m Water flow rate 100 m / day Gas-liquid ratio 2 (aerated air volume / treated water volume) Material of permeable membrane PVDF (pore diameter 0.1 μm) Simultaneous cleaning of back pressure water cleaning and air scrubbing is performed for 30 seconds every 10 minutes Then, forced drainage of retained water in the permeable membrane module 9 was performed for 60 seconds, and continuous operation could be performed without chemical cleaning for 3 months or more at a filtration flux of the permeable membrane module 9 of 5 m / day. As a result, at the outlet of the ozone reaction tank 1, the level of the quality of water used as the landscape water and the hydrophilic water is barely attained.
The water quality standards for training landscape water and hydrophilic water were fully cleared.

Each of the above steps 1Aa, 4a, 1a,
It is clear that the state in which the water quality in 9a is purified is stepwise purified as shown in the characteristic diagram of FIG.

The reduced states of ammonia nitrogen and nitrite nitrogen in each of the steps 1Aa and 4a are as shown in Table 1 below.

[0015]

[Table 1]

The ozone injection rate and the change in chromaticity in the above-mentioned ozone reaction treatment step 1a are as shown in Table 2 in Table 2 below.
A decrease in chromaticity is observed in water treated by filtration with a permeable membrane having a pore diameter of 1 to 0.45 μm.

[0017]

[Table 2]

[0018]

The method for purifying secondary sewage water according to the present invention is configured as described above, so that the following effects can be obtained. That is, the ozone treatment of the raw water is divided into two systems of pretreatment and posttreatment, and the ozone injection rate in the pretreatment ozone treatment step is set to a level sufficiently lower than the injection rate of the posttreatment, so that the ozone treatment during the preozone treatment is performed. Is consumed, and the ozone concentration becomes almost 0 mg / l at the entrance of the biofilm filtration tank, and the removal of ammonia nitrogen, organic substances, and the like is more reliable than before. In addition, after biofilm filtration, ozone treatment is performed, and permeable membrane filtration is performed in the presence of dissolved ozone, and immediately after simultaneous back pressure water washing and air scrubbing, forced drainage is performed to remove particulate matter through the permeable membrane. By discharging from the module, it was possible to operate continuously for a long time without chemical washing even at a high filtration flux (5 m / day). According to this method, it is possible to efficiently produce treated water that can sufficiently satisfy the water quality standards as reclaimed water such as toilet water, landscape water, and hydrophilic water.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram showing a method for purifying sewage secondary treatment water according to the present invention.

FIG. 2 is a process chart showing a method of the configuration of FIG. 1;

FIG. 3 is a configuration diagram showing back pressure water washing and air scrubbing means in a permeable membrane filtration treatment step in FIG. 2;

FIG. 4 is a characteristic diagram showing a change in water quality in the present invention.

FIG. 5 is a configuration diagram illustrating a purification method according to a first conventional example.

FIG. 6 is a configuration diagram illustrating a purification method according to a second conventional example.

[Explanation of symbols]

 1a Ozone reaction treatment step 1Aa Pre-ozone treatment step 2a Ozone 3 Sewage secondary treatment water 4a Biofilm filtration treatment step 8 Treated water 9a Permeation membrane filtration treatment step

Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat II (reference) C02F 1/50 510 C02F 1/50 510A 510E 520 520C 531 531R 550 550H 560 560E 560H 3/02 3/02 A 9/00 501 9/00 501B 502 502E 502R 503 503C 504 504A 504E (71) Applicant 000000033 Asahi Kasei Co., Ltd. 1-2-6 Dojimahama, Kita-ku, Osaka-shi, Osaka (71) Applicant 000183369 Sumitomo Precision Industries, Ltd. Amagasaki, Hyogo 1-10 Fuso-cho (72) Inventor Takuya Onizuka 5-48-16 Sakuragaoka, Setagaya-ku, Tokyo Waterworks Co., Ltd. (72) Inventor Shizuo Takeda 5-48-16 Sakuraoka, Setagaya-ku, Tokyo Waterworks Co., Ltd. (72) Inventor Yohei Imoto 5-48-16 Sakuragaoka, Setagaya-ku, Tokyo Waterworks Co., Ltd. (72) Keiichi Sone 2-1-1 Nishi-Shinjuku, Shinjuku-ku, Tokyo Tokyo Metropolitan Sewer Within the Bureau (72) Inventor Takashi Ueno 2-81-1, Nishi-Shinjuku, Shinjuku-ku, Tokyo Inside the Tokyo Metropolitan Sewerage Bureau (72) Inventor Naoo Ogasawara 3-5-2, Nihonbashi Ningyocho, Chuo-ku, Tokyo (72) Inventor Kazuaki Sugimoto 3-5-4 Ningyo-cho, Nihonbashi, Chuo-ku, Tokyo Inside the Water Development Promotion Center (72) Inventor Yoshihiko Mori 2-1 Samejima, Fuji City, Shizuoka Prefecture Asahi Kasei Kogyo Co., Ltd. 72) Inventor Takashi Kono 1-10 Fuso-cho, Amagasaki-shi, Hyogo F-term (reference) in Sumitomo Precision Industries, Ltd. 4D003 AB02 BA02 CA10 FA04 FA06 4D006 GA07 KA01 KA02 KA03 KB21 KB22 KC03 KD21 MB11 MC29 PB08 PB70 PC62 4D050 AA15 AB03 AB06 BB02 BD06 CA09 CA17

Claims (3)

[Claims] 1. A first step (1Aa) of pre-ozone treatment of sewage secondary treatment water (3), a second step (4a) of biofilm filtration treatment, and a third step of ozone reaction treatment (1a) and a fourth step (9a) of performing a permeable membrane filtration treatment to obtain a treated water (8). A method for purifying secondary treated water, wherein the first step (1Aa) comprises: Ozone is injected into the secondary treatment water (3), and the ozone injection rate at the biofilm filtration inlet of the second step (4a) is set to zero residual ozone. The third step (1a) is a biofilm filtration treatment Inject ozone into the water,
A method for purifying sewage secondary treatment water, wherein dissolved ozone is set to 1 to 1.5 mg / l at a permeable membrane filtration inlet in the fourth step (9a). 2. A fourth step (9a) of the permeable membrane filtration treatment.
The method for purifying secondary sewage treatment water according to claim 1, wherein a permeable membrane module (9) made of a material having ozone resistance that enables filtration in the presence of dissolved ozone is used. 3. A fourth step (9a) of performing the permeable membrane filtration treatment.
The sewage according to claim 1 or 2, wherein the particulate matter from the third step (1a) of the ozone reaction treatment is periodically discharged from the permeable membrane module (9) by using a cleaning means. A method for purifying secondary treated water.