JP3299936B2 - Sludge treatment method and system - 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 treating organic wastewater, and more particularly to a method for efficiently and appropriately concentrating sludge generated by biological treatment.

[0002]

2. Description of the Related Art Conventionally, organic waste liquids such as night soil and domestic wastewater have been treated with various suspended substances (S) contained therein.
After the process of removing S) is performed, the water is discharged into a river or the like. As such a system for treating organic sludge, for example, a system as shown in FIG. 5 is used. In this system, first, the waste liquid raw water to be treated is subjected to a biological treatment for decomposing water-soluble components such as BOD and COD in the waste liquid by activated sludge in an aeration tank through a flow control tank. Then, in the final sedimentation basin, the flocs of the activated sludge are separated and discharged. The sludge from the final sedimentation tank is mainly returned to the aeration tank, but part of the sludge is concentrated as excess sludge in the gravity type thickening tank. In the gravity type concentration tank, the desorbed liquid is returned to the flow rate adjustment tank, and the concentrated sludge is sent to the sludge storage tank and stored therein. The sludge stored in the sludge storage tank is appropriately subjected to dehydration treatment, or is transported to another treatment facility for treatment at a facility without dehydration treatment equipment, and is treated.

[0003]

In the case of waste liquid treatment, the amount of suspended substances contained in the waste liquid is not constant.
Fluctuations in waste water quality, water volume, water temperature, etc. If such load fluctuations are large, fluctuations in the quality and quantity of the generated sludge are also large. In the gravity type thickening tank, sludge is concentrated by gravity sedimentation, so it takes a long time to concentrate the sludge,
Concentration may be insufficient. In particular, sludge, which is difficult to concentrate by gravity, has been increasing recently. For this reason, when the quality and quantity of the sludge transferred from the final sedimentation basin to the gravity type thickening tank change, a situation in which the treatment in the gravity type thickening tank cannot be completed in time may occur. When the capacity of the gravity type thickening tank is exceeded, it is dealt with by stopping the extraction of the sludge from the final sedimentation tank to the gravity type thickening tank and temporarily storing the sludge in the aeration tank or the final sedimentation tank. However, if such sludge accumulates, the processing conditions of the entire system may be disrupted, and flocs may flow out from the final sedimentation basin. In addition, if the separation in the gravity type concentration tank is insufficient, the concentration in the sludge storage tank will be low, the dewatering efficiency of the post-treatment will decrease, and the amount of transfer by the vacuum truck will increase, which will be uneconomical. .

For this reason, mechanical concentration methods such as centrifugal concentration, flotation concentration, and granulation concentration are generally employed as means for further concentrating gravity-type concentrated sludge or alternative means. However, the mechanical concentration method generally requires an expensive apparatus and a large treatment capacity. Therefore, in a treatment facility with a small sludge treatment amount, it is necessary to temporarily store sludge and then perform intermittent concentration. For this reason, there is a disadvantage that the sludge is easily anaerobic, rots, and the concentrated state is deteriorated, and on the contrary, human labor is required. Also, as a method of concentrating a small amount of sludge, there are known some methods of adding a flocculant to sludge and concentrating the sludge by a screen. In these methods, generally, a screen is filtered after a strong agglomerated sludge is prepared by adding a stirring tank at the time of or after the addition of a flocculant or by using a line mixer. This is because, until recently, a screen with a slit width of less than 1 mm has not been manufactured, or in a screen filtration method other than the screen-lifting method, if the coagulated sludge is not strong, the floc-like coagulated sludge breaks during filtration and passes through the screen. Therefore, it was necessary to make strong coagulated sludge. Further, it is necessary to add a large amount of a coagulant in order to produce strong coagulated sludge. However, as a result, flocculants remain in the liquid passing through the screen and adversely affect biological treatment after the liquid is returned,
In some cases, the concentration of the separated coagulated sludge becomes 5% or more, which makes it difficult to handle the subsequent transportation of the concentrated sludge. In addition, when a rotary drum screen or a drop bar screen other than the scoop-up screen is used, there is a problem that the screen is clogged due to entanglement of hair and the like. More recently, as described in Japanese Patent Application Laid-Open No. 9-38699, a sludge concentration method by membrane treatment has been studied. However, if the concentration of the concentrated sludge is too high, the treatment efficiency may be rather deteriorated. There is. The present invention has been made to solve the above-mentioned problem, and a small amount of a cationic polymer flocculant is added to surplus sludge generated in the activated sludge method, and the coagulated sludge is separated by using a scraping screen. Accordingly, it is an object of the present invention to provide a processing method and a processing system for efficiently and economically separating concentrated sludge having an appropriate concentration.

[0005]

The problems and causes of the prior art were examined in detail, and by combining a method of adding a cationic polymer flocculant with a scraping screen having an appropriate screen width, etc. The present inventors have found that it is possible to efficiently separate coagulated sludge having an appropriate concentration, and have reached the present invention. That is, the method for treating sludge of the present invention is applied to excess sludge generated in biological treatment of organic wastewater,
A method for treating sludge having a step of adding a cationic polymer flocculant and separating into a flocculant sludge and a filtrate with a scraping-up screen, without adding a cationic polymer flocculant, without performing a stirring treatment. And separating excess sludge with a screen. At this time, after adding the cationic polymer flocculant to the excess sludge, it is desirable to transfer the excess sludge in a laminar flow state to a scraping-up screen. In this method, before adding the cationic polymer flocculant to the excess sludge, the excess sludge is concentrated in a gravity concentration tank, or as excess sludge, organic wastewater is generated by membrane separation type activated sludge treatment. Activated sludge can be used directly. The sludge treatment system of the present invention includes an aeration tank for biologically treating organic wastewater, a scraping screen for separating excess sludge generated in the aeration tank into coagulated sludge and a filtrate, and the scraping screen. A sludge treatment system having a flocculant adding means for adding a cationic polymer flocculant to the excess sludge, the sludge treatment system being attached to a pipe for transferring surplus sludge to the surplus sludge. The pipe for transferring the sludge to the screen for lifting the sludge is for transferring the excess sludge in a laminar flow state. As the scraping-up type screen, a screen having a slit width of 0.3 to 1 mm is desirable. As a treatment system for this sludge, a gravity-type thickening tank for concentrating excess sludge is interposed between an aeration tank and a scraping screen, or a membrane separation type activated sludge aeration tank is used as an aeration tank. be able to.

[0006]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described below, but it should be understood that the present invention is not construed as being limited thereto.

[Embodiment 1] In the waste liquid treatment method of the present embodiment, as shown in FIG. 1, first, raw waste water to be treated is introduced into a flow control tank. Then, the sludge is treated in an aeration tank with activated sludge and led to a final sedimentation basin to separate and separate sludge. Waste liquid is aeration tank, BOD, COD in waste liquid by activated sludge
After the water-soluble components such as are decomposed, flocs of the activated sludge are settled and separated in the final sedimentation basin. The treated water is discharged, and the sludge settled in the final sedimentation basin is returned mainly to the aeration tank, but part of the sludge is transferred to the gravity type thickening tank as excess sludge. In the gravity type concentration tank, the sludge pulled out from the bottom is passed through the raw sludge tank, then a sludge floc is formed by adding a cationic polymer flocculant, and separated into flocculated sludge and filtrate by a scraping screen. I do.

The reason why the cationic polymer flocculant is used as the flocculant to be added is that the inorganic flocculant and the anionic or nonionic polymer flocculant are formed into flocculated sludge that can be separated by a scraping screen. Because it is difficult. As the cationic polymer flocculant, any one may be used as long as it can make sludge into flocs of an appropriate size. For example, polyamine, condensation polymer flocculants such as polyethyleneimine, and polyacrylamide Mannich Modified or degraded Hoffman, polyamidine polymer flocculant, tertiary inorganic acid homopolymer of dimethylaminoethyl (meth) acrylate (hereinafter abbreviated as DM), homopolymer of quaternary salt such as methyl chloride of DM Copolymers of the polymer and the above tertiary or quaternary salt of DM with acrylamide and other copolymerizable vinyl monomers can be used. The shape of the polymer flocculant is not limited to liquid, emulsion, dispersion and powder. The amount of the cationic polymer flocculant used depends on the properties of the excess sludge and the type of the polymer flocculant, but is 0.2 to 1 part by weight based on 100 parts by weight of the suspended solid (SS) in the excess sludge. Is preferable, and 0.3 to
0.8 parts by weight is particularly preferred. If the amount is less than 0.2 parts by weight, the formation of flocs becomes insufficient. If the amount is more than 1 part by weight, the floc is redispersed, the cationic polymer flocculant remaining in the filtrate has an adverse effect on biological treatment, and the flocculant cost is too high, which is uneconomical. It is not preferable.

A well-known screen may be used as the scraping-up screen. For example, screens shown in FIGS. 6 and 7 are preferable. In this screen 32, a plurality of slits 36 are formed on the slope 34 along the longitudinal direction, and a plurality of raised teeth 38 whose tips protrude from the inside to the outside are formed from below to above by the power of the motor. The scraping-type screen 32 is installed so as to be immersed in flocculated sludge whose lower part is formed into a floc, so that only the flocculated sludge is scraped upward and the drop plate 40 is moved. From the sludge storage tank. Thus, the coagulated sludge and the filtrate are separated. With such a scraping type screen 32, the separated flocculated sludge is removed outside the system while simultaneously performing the scraping operation of the flocculated sludge and the cleaning between the slits. There is no need for regular cleaning like a screen, and there is virtually no fear of clogging. For this reason,
In the case of a falling bar screen or a drum screen, constant monitoring is required. However, continuous operation can be performed unattended by using a scraping type screen. The slit width of the scraping-up type screen is preferably from 0.3 to 1 mm, particularly preferably about 0.5 mm. If it is wider than 1 mm, the capture rate of the coagulated sludge will be significantly reduced. Also,
If it is less than 0.3 mm, the separability of the coagulated sludge and the filtrate is poor, and as a result, the concentration of the separated coagulated sludge decreases. In addition, the scraping screen separates the coagulated sludge from the water when it is scooped, so that the concentration of the condensed sludge can be kept constant or compared with other screens that separate coagulated sludge in the presence of water. It is easy to drive without clogging.

As shown in FIG. 2, the excess sludge is transferred from the raw sludge tank to a screen using a pump or the like, and the cationic polymer flocculant is added to the excess sludge in the middle of the piping. You. The means for adding the cationic polymer flocculant is not particularly limited, and a mechanism for adding an appropriate amount of the polymer flocculant from the flocculant storage tank to excess sludge in the pipe is employed. However, the present invention is characterized in that forcible stirring and mixing using a stirring device, a mixing device, and the like are not actively performed during the addition or during the period from the addition to the scooping-up screen. When agitation is performed in this step, the particles of the coagulated sludge become finer and pass through a scraping screen, and 1% by weight or more (1% by weight or more based on 100 parts by weight of suspended solids in excess sludge) of cations It becomes uneconomical because a system-based polymer flocculant is required. When 1% by weight or more of a cationic polymer flocculant is added and agitated vigorously, the concentration of the flocculated sludge separated by a scraping screen becomes 5% or more, and then the concentration of the sludge is increased by a pump or the like. Handling becomes rather difficult.

In a pipe for transferring the excess sludge to which the cationic polymer flocculant is added to the screen, it is desirable to transfer the excess sludge in a laminar flow state. In order to transfer to a laminar flow state, the transfer amount of excess sludge,
This is done by adjusting the diameter of the pipe. If the inside of the pipe is not in a laminar flow state but is in a turbulent flow state, the state becomes the same as when a stirring device is used, which is not preferable. According to the sludge treatment system and method of the present embodiment, the concentration of the coagulated sludge separated by the scraping screen is efficiently adjusted to a concentration range of 3 to 5%, which is a viscosity range where handling such as pumping is relatively easy. It can be concentrated. Further, according to this system, an existing sludge treatment system having a gravity type thickening tank and a raw sludge tank can be diverted as it is, and a new capital investment is small.

[Embodiment 2] Embodiment 2 is the same as Embodiment 1 except that excess sludge is taken out of the sludge line returned from the final sedimentation tank to the aeration tank as shown in FIG. In this case, since the excess sludge is directly collected from the return sludge line, a gravity type thickening tank is not required. [Embodiment 3] In Embodiment 3, as shown in FIG. 4, a membrane separation type activated sludge aeration tank is used as an aeration tank, and the membrane separation type activated sludge aeration tank is used in the membrane separation type activated sludge process. It is the same as Embodiment 1 except that the activated sludge was directly taken out and not passed through the final sedimentation basin and gravity concentration tank. At this time, the raw sludge tank may or may not be installed.
Here, the membrane-separated activated sludge process refers to a process of performing a biological treatment using activated sludge and simultaneously performing a filtration treatment using a separation membrane such as a hollow fiber membrane. The tank is a facility for performing the membrane separation type activated sludge treatment, and is an aeration tank provided with or attached to a filtration device using a separation membrane. In the embodiment 3, since the sludge is always treated under aerobic conditions, it does not become anaerobic or rot, and the coagulation state is hardly deteriorated and odor is hardly emitted. In addition, a gravity-type concentration tank is not required, and if a scraping-up screen is installed above the aeration tank, the filtrate can be returned directly to the aeration tank. Becomes

[0013]

[Example 1] In the sludge treatment system shown in Embodiment 1 described above, sludge treatment was performed by a system not using a raw sludge tank. The excess sludge with a concentration of 10,000 mg / L taken out from the bottom of the gravity type
L / min screen (“NA screen”)
Contour Service Co., Ltd .: slit width 0.5m
m), 0.5 part by weight of a cationic polymer flocculant (“K
M-201G "(manufactured by Diafloc Co., Ltd.).
At this time, a pipe having a diameter (inner diameter) of 8 mm was used in this pipe so that excess sludge was transferred in a laminar flow state. As a result of this treatment, sludge having a concentration of 40,000 mg / L was separated as coagulated sludge on the scraping screen. Screen filtrate has a concentration of 800m
g / L. [Example 2] As in the sludge treatment system of Embodiment 2 described above, excess sludge is taken out from the returned sludge line, and
It was the same as Example 1 except that the sludge was put into the raw sludge tank. Concentration 450 partially removed from returned sludge line
In the middle of the piping for transferring the excess sludge of 0 mg / L to the screen at 4 L / min, 0.5 parts by weight of the cationic polymer flocculant was added to 100 parts by weight of the sludge solids. As a result, a concentration of 3
8000 mg / L sludge was separated as floc-like coagulated sludge. The screen filtrate has a concentration of 500 mg /
It became L.

[Embodiment 3] As in the sludge treatment system of Embodiment 3 described above, the same as in Embodiment 1 except that activated sludge is taken out of the membrane separation type activated sludge aeration tank and directly transferred to a scraping type screen. And A part of the sludge having a concentration of 12000 mg / L taken out of the aeration tank was transferred to the screen at a rate of 4 L / min.
0.5 parts by weight of a cationic polymer flocculant was added to 0 parts by weight. As a result, sludge having a concentration of 42000 mg / L was separated as floc-like aggregated sludge on the scraping screen. The screen filtrate has a concentration of 2
It became 00 mg / L. [Embodiment 4] The slit width of the scraping-up screen is 2 m
Except that m was the same as in Example 1. As a result, the concentration of sludge taken out from the gravity sludge concentration tank was 105
In contrast to 00 mg / L, the concentration of the coagulated sludge separated by the scraping screen was 42000 mg / L. However, since the screen width was large, the amount of separated sludge was small, and many fine coagulated sludges could not be used. The sludge concentration of the filtrate was 6200 mg / L as a result of the passage into the filtrate.

Comparative Example 1 The procedure was the same as in Example 1 except that a line mixer was provided in the middle of the pipe after the addition of the cationic polymer flocculant. As a result, the concentration of sludge taken out from the gravity type sludge thickening tank was 11,000 mg / L, whereas the amount of agglomerated sludge separated by the scraping screen was extremely small, and the concentration of the screen filtrate was 9,800 mg / L. [Comparative Example 2] The amount of the cationic polymer flocculant added was
Comparative Example 1 was performed in the same manner as in Comparative Example 1 except that the amount was 1.5 parts by weight based on 100 parts by weight of the sludge solid content. As a result, since the amount of the polymer flocculant added is large, the concentration of the sludge taken out from the gravity sludge thickening tank is 9800 mg / L, whereas the flocculated sludge separated by the scraping screen is 55000 mg / L. Has a concentration of 300 mg / L. However, since a large amount of a polymer flocculant has been used, not only is economic efficiency low, but also the concentration of the flocculated sludge becomes 5% or more.
Subsequent handling such as transportation by a pump or the like became rather difficult.

[0016]

[Table 1]

[0017]

According to the present invention, surplus sludge can be efficiently concentrated to an appropriate concentration, and a system that can cope with fluctuations in sludge water quality can be provided. Further, this system can be constructed simply and inexpensively, and can be operated unattended. In addition, the existing sludge treatment system can be effectively used regardless of the presence or absence of the gravity type concentration tank. Also, when a membrane separation type activated sludge aeration tank is used, the sludge is always treated under aerobic conditions, so it does not become anaerobic or decomposed, and the coagulation state deteriorates. Almost no odor or odor. In addition, a gravity type concentration tank is not required, and if a scraping type screen is installed above the aeration tank, the filtrate can be returned directly to the aeration tank, making it possible to make the device extremely compact. Becomes In particular, by setting the slit width of the scraping-up screen to 0.3 to 1 mm, it is possible to increase the capture rate of the coagulated sludge, and to enhance the separability between the coagulated sludge and the filtrate to reduce the concentration of the coagulated sludge. Can be enhanced.

[Brief description of the drawings]

FIG. 1 is a flowchart showing a sludge treatment system according to a first embodiment.

FIG. 2 is a flowchart showing the positions of the scooping-up screen and the cationic polymer flocculant added in Embodiment 1.

FIG. 3 is a flowchart illustrating a sludge treatment system according to a second embodiment;

FIG. 4 is a flowchart illustrating a sludge treatment system according to a third embodiment;

FIG. 5 is a flowchart showing a conventional waste liquid treatment system.

FIG. 6 is a front view showing the scraping-type screen of the first embodiment.

FIG. 7 is a side view showing the scraping-type screen of the first embodiment.

[Explanation of symbols]

 32 scraped-up screen 36 slit

──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Naoya Tanakamaru 1-6-1 Konan, Minato-ku, Tokyo Inside Mitsubishi Rayon Co., Ltd. (72) Inventor Satoshi Miyashita 4-6-1 Sunadabashi, Higashi-ku, Nagoya-shi, Aichi Prefecture No. Mitsubishi Rayon Co., Ltd. Product Development Research Center (72) Inventor Takaaki Takashima 4-160 Sunadabashi, Higashi-ku, Nagoya City, Aichi Prefecture Mitsubishi Rayon Co., Ltd. Product Development Research Laboratory (72) Inventor Kazuo Kuwahara Tama-ku, Kawasaki City, Kanagawa Prefecture Noboru 3816 MRC Techno Research Co., Ltd. Examiner Tadahiro Sanada (56) References JP-A-52-80648 (JP, A) JP-A-4-87607 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) C02F 11/14 ZAB

Claims (8)

(57) [Claims] 1. A method for treating sludge, comprising the step of adding a cationic polymer flocculant to excess sludge generated by biological treatment of organic wastewater and separating the sludge into a flocculated sludge and a filtrate with a scraping screen. A method for treating sludge, wherein after addition of a cationic polymer flocculant, excess sludge is separated by a scooping screen without stirring. 2. The method for treating sludge according to claim 1, wherein after adding the cationic polymer flocculant to the excess sludge, the excess sludge is transferred to a screen of a scraping type in a laminar flow state. 3. The sludge treatment method according to claim 1, wherein the excess sludge is concentrated in a gravity type thickening tank before adding the cationic polymer flocculant to the excess sludge. 4. The sludge treatment method according to claim 1, wherein the excess sludge is activated sludge generated by treating organic wastewater with a membrane separation activated sludge process. 5. An aeration tank for biologically treating organic wastewater, a scraping type screen for separating excess sludge generated in the aeration tank into coagulated sludge and a filtrate, and an excess sludge on the scraping type screen. A sludge treatment system having a flocculant adding means for adding a cationic polymer flocculant to excess sludge, which is attached to a pipe for transferring, and scraping the excess sludge to which the cationic polymer flocculant is added. A sludge treatment system, wherein a pipe for transferring to the fry-type screen transfers the excess sludge in a laminar state. 6. The sludge treatment system according to claim 5, wherein a slit width of the screen is 0.3 to 1 mm. 7. The sludge treatment system according to claim 5, wherein a gravity type thickening tank for thickening surplus sludge is interposed between the aeration tank and the scraping type screen. 8. The sludge treatment system according to claim 5, wherein the aeration tank is a membrane separation type activated sludge aeration tank.