JP3663178B2 - Sewage treatment method by intermittent aeration using a membrane diffuser. - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for purifying sewage such as sewage, industrial wastewater, and domestic wastewater. More specifically, when the sewage whose amount of drainage varies is activated sludge treatment or biofilm contact oxidation treatment, a specific aeration pipe is arranged in the sewage to perform intermittent aeration with fine bubbles, and a small amount of airflow over a long period of time. The present invention relates to an economical water treatment method that removes contaminants such as BOD components in the sewage by diffusing with energy and without blocking the holes of the diffusing tube.
[0002]
[Prior art]
Conventionally, a method for purifying sewage containing 10 mg / L or more of BOD components such as sewage, factory effluent, domestic sewage, etc., by putting the sewage into a water tank and blowing air into the water from an air diffuser and aeration. There is an activated sludge method in which the dissolved oxygen concentration is maintained at a high level by bringing the aerobic bacteria and microorganisms into the water to propagate and proliferate to reduce the BOD component. Also, a biofilm that purifies water by adhering and growing aerobic bacteria and microorganisms on the surface of a carrier by immersing a biofilm carrier such as an organic or inorganic fiber, film, or plate in the water tank and diffusing it. There is a catalytic oxidation treatment method.
[0003]
Usually, these activated sludge methods and biofilm contact oxidation methods are used for water treatment by continuously flowing wastewater and sewage from factories that operate continuously for a long time day and night into the aquarium. A diffuser tube having a hole having a diameter of several centimeters or more and a diffuser tube that generates fine bubbles having a diameter of several millimeters are used. Generally, the air diffuser having a hole having a diameter of several centimeters or more and an air outlet can purify water by growing and floating microorganisms by aerating large bubbles from a metal pipe or nozzle and stirring the water vigorously. Therefore, it is used in the activated sludge treatment method. On the other hand, the method of aerating fine bubbles with a diameter of several millimeters is efficient in diffusing oxygen from the bubbles into water, and can increase the dissolved oxygen concentration in water with a small amount of air compared to the above method. Attention has been paid to the advantage that the blower can be made smaller and energy consumption such as electric power can be saved. In particular, when fine bubbles are continuously diffused to wastewater that generates a certain amount of sewage continuously day and night, a number of slit holes are provided in materials such as ethylene propylene diene rubber (EPDM), polyurethane, and nitrile rubber. In addition, membrane diffuser tubes with a high pressure loss of 5000 Pa or more are frequently used for activated sludge treatment and biofilm contact oxidation treatment methods.
[0004]
[Problems to be solved by the invention]
However, when applying the membrane diffuser pipe having a large number of slits to sewage such as factory effluent that operates during the day and does not operate during the night, or general household effluent that is generated in large quantities only during a specific time period, When the amount is reduced, the BOD component, which is a nutrient for aerobic bacteria and microorganisms in the treated water, is insufficient, but the dissolved oxygen concentration in the water is excessive and the work of the aerobic bacteria and microorganisms is reduced, so the purification of water does not progress much. There was a problem. Therefore, in the time when there is almost no discharged sewage, such as at night or on holidays, when the factory operation is stopped or when household activities are reduced, the air supply to the air diffuser placed in the sewage in the tank is stopped, and the factory operation and household We perform intermittent aeration to resume aeration as life becomes active. However, in this intermittent aeration, the slit hole of the diffuser tube repeats the intermittent aeration, which makes it difficult to diffuse due to sludge and bacteria in a short period of time. The problem that it must be performed frequently, and when the diffuser of the membrane air diffuser having slit holes is resumed, a large load is applied to the air blower and the blower energy is increased. Therefore, there has been a demand for an economically inexpensive method for purifying sewage due to stable intermittent aeration over a long period of time.
[0005]
Therefore, the object of the present invention is to solve the above-mentioned conventional problems, and to arrange sewage such as sewage, factory effluent, and domestic effluent into the aquarium and perform the activated sludge treatment and biofilm contact oxidation treatment in the aquarium. It is an object of the present invention to provide a water purification method for removing pollutants such as BOD in the sewage stably over a long period of time by intermittently diffusing with less blowing energy without blocking the diffusive holes of the diffusing pipe.
[0006]
[Means for solving the problems]
As a result of intensive studies to achieve the above object, the present inventors have found that when intermittent air is diffused using a membrane air diffuser having a slit hole, the slit hole of the air diffuser is blocked when the blower is stopped. This is because the sludge flows backward in the trachea or the sludge gets caught in the slit hole, and the tendency is that the air diffuser of the membrane with high surface energy becomes larger with aerobic bacteria and microorganisms attached to the membrane surface, slit hole and its surroundings, In addition, it has been found that the longer the slit hole is, the more easily sludge is trapped and the more easily the blockage occurs. In addition, the load of the blower at the time of resuming the air diffuser is larger than that at the steady state, but it is recognized that the load can be reduced if the pressure loss of the air diffuser is lowered, and a slit hole having an appropriate length is provided with an appropriate surface energy. It has been found that a diffuser tube using a membrane with a low pressure loss does not cause clogging of the slit hole, and can intermittently diffuse stably for a long period of time with a small blowing energy.
[0007]
That is, the present invention is when treating activated sludge treatment or biofilm catalytic oxidation by introducing the wastewater to a water tank, a slit hole length of the surface energy soil water was used following the membrane 35 mN / m is from 0.4 to 0 It consists of a water treatment method in which an aeration tube made of a membrane having a pressure loss of 0.8 mm and a pressure loss of 1000 to 4000 Pa (Pascal) is arranged and intermittently diffused.
[0008]
The present invention is characterized in that the membrane having a surface energy of 35 mN / m or less is silicone rubber or EPDM.
[0009]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the implementation of the present invention will be described in detail.
Intermittent aeration The intermittent aeration in the present invention is defined as the repeated starting and stopping of aeration. Normal intermittent aeration diffuses when the amount of sewage flowing into the tank increases, and repeats the repetition of stopping the aeration when there is almost no inflow, hourly, daily and weekly, monthly and combinations of them Do it. For example, when air is diffused in the daytime when the amount of sewage flowing into the tank increases, the air diffuser is stopped for a long time, or it is repeated for a long time at night. If the day of the holiday, such as holidays, is low or stops, the inflow will be low or will not be diffused for a long time, or if the inflow is low for a week or more due to holidays or holidays of the year This may be the case when the aeration is stopped and repeated for many years. Furthermore, the intermittent air diffuser is used in an industrial water treatment when a large number of the air diffuser pipes disposed in the water tank are intermittently diffused or when the water tank exceeds the treatment capacity into which sewage flows continuously. In the case of activated sludge treatment or biofilm contact oxidation treatment, intermittent aeration is performed to save energy related to blowing.
[0010]
Membrane air diffuser The membrane air diffuser used in the present invention preferably has a shape suitable for evenly disposing at the bottom of the water tank for activated sludge treatment or biofilm contact oxidation treatment, and is preferably rectangular or disk-shaped or cylindrical. Is. A rectangular shape or a disc shape is a concentric rectangle, a disk type having an air chamber 3 for equalizing pressure as shown in FIG. Insert a pipe 5 made of resin such as polypropylene or acrylonitrile butadiene styrene (ABS) for feeding air into a tube 8 in which slit holes 9 are arranged at intervals in the length direction of the membrane, It is a cylindrical shape as shown in FIG. 2 in which the membrane is fixed to the pipe with metal bands 6 and 7. The size of the disk type is 20 to 75 cm in diameter, the size of the cylindrical type is 20 to 75 cm in length, and the tube diameter is 5 to 20 cm. Therefore, it is not preferable.
[0011]
The membrane air diffuser used in the present invention is preferably one using a membrane having a surface energy of 35 mN / m or less in which a large number of slit holes are arranged. When the surface energy exceeds 35 mN / m, aerobic bacteria and microorganisms adhere to the membrane slit hole and its surroundings while the aeration is stopped, and are not removed even when the aeration is resumed. It is not preferable because the air diffuser tends to be clogged. Examples of the material having a surface energy of 35 mN / m or less include ethylene / propylene rubbers such as EPM (ethylene / propylene rubber) and EPDM (ethylene / propylene diene rubber), and silicone rubber. . Silicone rubber membranes have excellent compression set characteristics, so there is no sag in the hole due to repeated opening and closing of the slit hole due to intermittent air diffusion over a long period of time, and it remains in the same state as a new product and is not easily clogged. Particularly preferred.
[0012]
The slit hole of the air diffuser used in the present invention is a thin plate having a thickness of 2 to 4 mm, and a slit, a cutter, a laser or the like is penetrated in the thickness direction. Usually, the slit hole is formed by the elasticity of the membrane. Although it is in a closed state, when air is supplied to the air diffuser and pressurized, the slit is opened and air is blown out to form uniform fine bubbles. The length of the slit hole is preferably 0.4 to 1.0 mm. When the slit hole length is less than 0.4 mm, it is not preferable because the hole is likely to be blocked by fine dust in the blown air. If the slit hole is larger than 1.0 mm, the opening will vary in the length direction of the slit hole at the time of air diffusion, and it is easy to create a part where the air goes out and a part where the air does not come out. Since it tends to proliferate or get caught, it is not preferable. In particular, the length of the slit hole is preferably 0.5 to 0.8 mm in consideration of blockage by dust in the blown air and uniform opening of the slit hole in the diffused air. The slit hole interval in the length direction and the width direction of the slit hole is preferably 1 to 5 mm because coalescence of fine bubbles during aeration can be prevented.
[0013]
The pressure loss of the membrane diffuser used in the present invention is preferably 1000 to 4000 Pa. When the pressure loss is less than 1000 Pa, the sewage tends to flow backward and stop the slit hole when the air diffusion is stopped in the intermittent air diffusion. In addition, when the pressure loss exceeds 4000 Pa, in the intermittent aeration, the opening in the length direction tends to be uneven in the slit hole at the time of the aeration, and bacteria and microorganisms that have proliferated when the sludge and the aeration are stopped in a portion that does not open much. It is easy to pinch, and since there is a large difference in the blown energy between the start of the diffuser and the steady state diffuser, it is not preferable because a larger blower must be installed and the cost increases. More preferably, the pressure loss of the membrane diffuser is 1500 to 3000 Pa. In the present invention, the pressure loss is the internal pressure of the diffuser tube when the diffuser tube is arranged in the atmosphere and the air is blown from a large number of slit holes of the diffuser tube.
[0014]
Water treatment method The water treatment method in the present invention is a method of disposing the membrane aeration pipe in the sewage water put in the water tank, and performing the water treatment by intermittent aeration. For example, the amount of inflow during daytime or factory operation is When there is a lot of air, send air to the diffuser to diffuse it, and at the time of the above state where there is almost no drainage, such as at night or when the factory is shut down, all or some of the multiple diffuser installed This is a water treatment method that repeats stopping the aeration.
[0015]
The water tank used for water treatment in the present invention is made of concrete, metal, plastics, fiber reinforced plastics, and a combination of these having a sidewall having a rectangular bottom or a round bottom, and the raw water inlet is the upper part of the tank. Or a known container on one side of the lower part where the treated water outlet faces or near the center of the bottom of the aquarium, and the raw water introduced can be treated with activated sludge or biofilm contact oxidation in the aquarium It is a shape.
[0016]
The size of the aquarium is selected according to the amount of sewage that flows in, the amount of BOD components contained, etc., and is usually used when the amount of water in the aquarium is constantly flowing so that the BOD of the effluent falls below the water discharge standard. A volume of 1 to 24 hours divided by the amount of sewage per hour is appropriate.
[0017]
The arrangement of the air diffuser in the method of the present invention is to install at the bottom of the treated water tank in any case such as activated sludge treatment and biofilm contact oxidation treatment in order to diffuse fine bubbles and efficiently increase dissolved oxygen. In particular, biofilm-catalyzed oxidation in which a biofilm carrier using fibers, fabrics, plates, etc. such as polypropylene, polyethylene, polyvinylidene chloride, etc. or known carbon fibers described in, for example, JP-A-8-290191 is contacted with sewage. In the case of treatment, it is possible to effectively propagate microorganisms and aerobic bacteria by arranging the disk-type air diffuser of the membrane 1 provided with slit holes 2 as shown in FIG. 1 directly below the carrier in the treatment tank. It is preferable because it is possible. In addition, the diffuser tube is installed at the bottom of the aquarium (referred to as full arrangement) so that the membrane surface area of the diffuser is 30% or more of the bottom surface area of the aquarium and is almost evenly distributed (referred to as diffused over the entire surface). It is preferable because the air diffusion efficiency can be increased.
[0018]
The air pressure to be applied to the air diffuser is selected in consideration of the pressure loss of the air diffuser, the water depth at which the air diffuser is disposed, the amount of blown air, and the like. For example, when a disk-type air diffuser having a diameter of 50 cm and a pressure loss of 3000 Pa having a shape as shown in FIG. 1 is disposed at a water depth of 5 m, the air pressure inside the air diffuser is adjusted to a water pressure and a pressure loss of 3000 pa by adjusting the blower. It is preferable to intermittently diffuse air so that the air pressure corresponding to the air volume is added. The amount of air applied to the air diffuser is the capacity of the water treatment tank, the amount of dissolved oxygen and BOD in the treated water flowing into the water treatment tank, the size of the bubbles, the stirring action on the water, and the aerobic property. It is selected in consideration of the amount of bacteria and microorganisms and the propagation / growth rate. Usually, in order to set the dissolved oxygen concentration in the water treatment tank to 3 to 8 mg per liter of water, about 10 per cubic meter of sewage to be treated. ~ 20 cubic meters / hour is preferred.
[0019]
The above-described intermittently diffused water treatment method of the present invention can only be effectively applied to activated sludge treatment or biofilm contact oxidation treatment of sewage containing a high BOD component in which the amount of water such as sewage, factory effluent and domestic effluent varies. In addition, it is applied to water such as treated water containing low BOD components after activated sludge treatment or biofilm contact oxidation treatment, and intermittent aeration is performed. Since a certain BOD component and nitrogen compound can be removed very efficiently over a long period of time with a small blowing energy, the replacement work of the diffuser tube and the economic burden associated with the blockage of the diffuser tube are reduced. The water environment of daily life can be maintained cleanly.
[0020]
【Example】
EXAMPLES The present invention will be specifically described below with reference to examples. However, the present invention is not limited to the following examples unless it exceeds the gist. Unless otherwise specified, “%” means “% by weight”.
[0021]
The surface energy in this invention was calculated | required using the liquid surface tension meter (Shimadzu Corporation model DN).
[0022]
Example 1
Activated sludge treatment water tank 22 (water height: 5.25 m, amount of sewage: about 290 m ³ ) caught by overflow weirs 13 and 14 having a width (short side) of 4.0 m, a length (long side) of 14.0 m, and a height of 6 m. An inflow water adjusting tank 15 and a treated water outflow tank 16 each having a raw water inlet 11 and a treated water outlet 12 surrounded by the overflow weir and the concrete outer wall 10 are provided adjacent to both outer sides thereof, and the activated sludge treated water tank 22 At the bottom, the length of the slit holes 9 is 0.7 mm in the silicone rubber 8 having a surface energy of 31.5 mN / m as shown in FIG. 2 (the slit hole interval is 1 mm in the slit hole length direction and the slit hole width direction is Using an activated sludge treatment apparatus in which 168 cylindrical diffuser tubes 20 (membrane tube inner diameter: 10 cm, length: 50 cm) having a pressure loss of 2500 Pa with an interval of 1 mm are uniformly installed, Running time 7:00 to 23:00 field flows factory wastewater is BOD330~350mg / L to discharge at a flow rate of 25 m ³ / time (raw water) to the active sludge treatment tank 22 (MLSS is 12000 mg / L), at the same time, Fine air bubbles 21 are evenly diffused at a flow rate of 7 Nm ³ / min from all the diffuser tubes 20 installed through the pipes 17, 18, and 19 from the blower, and the wastewater is discharged from the factory between 23 and 7 o'clock when the factory stops operating. Since it was not carried out, the process which performs the intermittent air diffusion of stopping the inflow at the same time as stopping the inflow of sewage into the activated sludge treatment tank 22 was performed for one year. As a result, the blast energy at the time of resuming the diffused air in the intermittent air diffuser is almost the same as that in the steady air diffused state with a low energy consumption for one year, and the slit hole of the air diffuser tube is not blocked for one year. Stable intermittent air diffused. Further, the treated water collected in the discharge tank 16 after the activated sludge treatment just before 23:00 before the aeration stop and the discharge tank 16 in the activated sludge treatment tank 22 before 7 o'clock just before the aeration is resumed. As a result of continuously examining the BOD concentration change of the activated sludge water collected in the vicinity for one year, the BOD concentration of the treated water is 5 to 10 mg / L, which is significantly lower than the inflowing raw water. The BOD in water was able to be stably reduced by the air.
[0023]
Example 2
There is a sewage introduction port 24 which is connected to an activated sludge treatment tank of a meat processing factory by a pipe at the bottom so that activated sludge water can be introduced, and has an inner diameter of 50 cm and a height having a discharge port 25 through which treated water 29 is discharged. At the bottom of a cylindrical container 23 made of transparent acrylic resin of 3.5 m, the length of the slit hole 2 is 0.5 mm (circumference) in EPDM rubber 1 having a surface energy of 24.7 mN / m as shown in FIG. Disk-type membrane diffuser 26 (diameter: 30 cm, height: 5 cm) with a slit distance of 1 mm in the direction, a circumferential interval of 1 mm, and a slit hole between the center of the circle and a radius of 5 to 14 cm) and a pressure loss of 2000 Pa 1 piece is placed, and 100 g of carbon fiber 30 (carbon content 4.5%, tensile strength 3950 MPa, tensile elastic modulus 235 GPa, specific gravity 1.77, single fiber straight in the acrylic resin cylindrical container. 7 micrometer) with a weight of 1 mg / denier on the bottom and suspended between 2.5 m from the water surface (water surface height 3.2 m) to the biofilm contact oxidation treatment apparatus for 12 hours a day, The activated sludge water containing 350 to 400 mg / L of BOD component (MLSS is 8000 mg / L) flows in at 50 L / h, and at the same time, the amount of air is ³ Nm ³ / hour (internal pressure) from the blower pipe 27 connected to the blower to the diffuser pipe 26. The microbubbles 28 were diffused at 31430 Pa), and for the next 12 hours, biofilm contact oxidation treatment was performed for 6 months by intermittent aeration that repeatedly stopped the inflow and aeration of the activated sludge water. Collecting inflow raw water and treated water (a) just before stopping the aeration 12 hours after the inflow and aeration of sewage, and just before the start of the aeration 12 hours after stopping both the inflow and aeration of sewage The collection of treated water (b) from the top of the container was performed every day, and the changes during 6 months were examined. As a result, the treated water (a) and the BOD concentration (350 to 400 mg / L) in the influent raw water were compared. Both BOD concentrations in (b) were 5-9 mg / L, the BOD removal efficiency by intermittent aeration was good and could be removed stably, and no blockage of the slit holes of the aeration tube was observed.
[0024]
Comparative Examples 1-4
In carrying out the sewage treatment by intermittent aeration for 6 months, it was the same as Example 2 except that the pressure loss of the EPDM rubber membrane was 5000 Pa (Comparative Example 1), except that the slit hole length was 0.2 mm. 2 (Comparative Example 2), similar to Example 2 (Comparative Example 3) except that the slit hole length is 0.9 mm, and a nylon 6.6 membrane disk having a surface energy of 40.1 mN / m A biofilm contact oxidation treatment was carried out in the same manner as in Example 2 (Comparative Example 4) except that a type air diffuser was used, and changes in blast energy, observation of the closed state of the slit holes, and changes in the BOD concentration of the treated water were examined. As a result, in Comparative Example 1, 1/5 of the slit holes were blocked at the fifth month, and the air could not be sufficiently diffused, and the removal efficiency of BOD was also lowered. Moreover, in Comparative Example 2 and Comparative Example 3, more than 1/4 of the slit holes were blocked after 6 months due to dust clogging or sludge trapped by air blowing, and sufficient air diffusion could not be performed. . Furthermore, in Comparative Example 4, many bacteria and microorganisms adhered to the surface of the diffuser tube, and the slit holes were gradually blocked, and 1/3 was blocked in the sixth month.
[0025]
【The invention's effect】
In the water treatment method of the present invention, when sewage whose amount of wastewater such as factory effluent and domestic effluent varies greatly is activated sludge treatment and biofilm contact oxidation treatment, the surface energy is 35 mN / m or less and the slit hole length is 0.4 to 0.4. Since a membrane air diffuser having a pressure loss of 1.0 mm and a pressure loss of 1000 to 4000 Pa (pascal) is disposed in the treatment tank and intermittently diffused, it is stable over a long period of time without causing a blockage of the slit hole of the membrane, It became possible to treat sewage economically with small blast energy.
[Brief description of the drawings]
FIG. 1 is a schematic diagram of a disk-type air diffuser having slit holes. FIG. 2 is a schematic diagram of a cylindrical air diffuser having slits. FIG. 3 is a schematic side sectional view of an activated sludge treatment apparatus. -Like biofilm contact oxidation treatment equipment schematic side cross-sectional view 【Explanation of symbols】
DESCRIPTION OF SYMBOLS 1, 8 Membrane 2, 9 Slit 3 Air chamber 4 Air supply port 5 Plastic air introduction pipe 6, 7 Fixing band 10 to membrane resin air introduction pipe 10 Concrete wall 11 Raw water inlet 12 Process water outlet 13, 14 Overflow Partition wall 15 Sewage inflow adjustment tank 16 Treated water discharge tanks 17, 18, 19 Air supply pipe 20 Cylindrical air diffuser pipes 21, 28 Fine bubbles 22 Activated sludge treated water tank 23 Transparent acrylic resin cylindrical container 24 Sewage inlet 25 Treatment Water outlet 26 Disc-type membrane diffuser 27 Blower 28 Fine bubbles 29 Treated water 30 Carbon fiber 31 Weight

Claims (1)

In sewage flowing into the water tank, when activated sludge treatment or biofilm contact oxidation is performed, the surface energy of the water tank is 35 mN / m or less, the slit hole length is 0.4 to 0.8 mm, and the pressure loss is 1000 to 1000. A water treatment method comprising disposing an air diffuser using a membrane made of silicone rubber or ethylene propylene diene rubber (EPDM) having a pressure of 4000 Pa (Pascal) to intermittently diffuse air.

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