JP3474476B2 - Sewage treatment method - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a sewage treatment method , and more particularly to a sewage treatment method capable of decomposing nitrogen compounds contained in sewage . 2. Description of the Related Art With the improvement of sewers, water quality of polluted rivers and the like has been restored, and sewerage facilities have become more and more important in order to maintain them. Under such circumstances, sewage treatment nationwide has mainly focused on the removal of organic pollutants represented by indicators such as conventional BOD (biochemical oxygen demand) and SS (suspended matter). Recently, there has been a shift to advanced treatment with the addition of nitrogen, a substance that causes eutrophication of enclosed water bodies, which has become a problem in recent years. At present, as a method for removing nitrogen content in sewage, a method in which nitrogen compounds such as ammonia in sewage are oxidized by nitrifying bacteria, and then reduced by denitrifying bacteria to remove nitrogen contained in sewage as nitrogen gas. Can be considered. [0003] However, when nitrogen is removed using the above-mentioned method, the rate of growth of nitrifying bacteria for oxidizing nitrogen compounds is low, and the number of nitrifying bacteria in the treatment tank is small. , The residence time of the sewage had to be lengthened. Therefore, in a series of sewage treatment facilities, the amount of sewage treated per hour is fixed, so the size of the treatment tank must be increased, and the problem of securing land for the treatment tank and construction of facilities requires a large amount of cost. Had occurred. The present invention has been made in view of such circumstances, and an object of the present invention is to provide a sewage treatment method capable of realizing an improvement in the concentration of microorganisms in a treatment tank and efficiently performing a decomposition treatment of a nitrogen compound. According to the present invention, there is provided a sewage treatment method for decomposing a nitrogen compound contained in sewage introduced into a treatment tank. An aeration tank, and a part or all of the aeration tank,
The outer surface is modified to be hydrophilic, and actively supports microorganisms including nitrifying bacteria on the outer surface, and has pores having a diameter of 10 to 1000 nm from the inner cavity toward the outer surface. through pores by arranging a large number of hollow fibers may supply oxygen required for growth of the microorganisms, oxygen hollow inside thread
Gas, and the pH of the sewage is adjusted to 6 according to the progress of nitrification.
Sewage while adding an alkaline agent to maintain ~ 9
Nitrate ion or nitrite ion
Further, the nitrate ion or nitrite ion is
Microorganisms mainly containing denitrifying bacteria are carried in part or all
Into the oxygen-free tank where the hollow fibers are placed,
Release the nitrogen gas from the sewage ; and
Inside the hollow fiber of the tank, an organic gas that becomes an inert gas or nutrient
Things have been introduced . [0007] Embodiments of the present invention will be described below with reference to the accompanying drawings to provide an understanding of the present invention. Here, FIG. 1 is an explanatory diagram of a hollow fiber in which microorganisms are positively supported, FIG. 2 is a schematic explanatory diagram of a sewage treatment facility using a sewage treatment device according to the first embodiment of the present invention, and FIG. Is a schematic explanatory view of the sewage treatment apparatus, and FIG. 4 is a schematic explanatory view of a sewage treatment facility using the sewage treatment apparatus according to the second embodiment of the present invention. First, a description will be given of a hollow fiber (referred to as a bioreactor 10) that carries microorganisms including nitrifying bacteria or denitrifying bacteria used in an embodiment of the present invention.
As shown in FIG. 1, a hollow fiber 11 made of, for example, polyethylene, polysaphon, Teflon, cellulose, or the like has a diameter of about 1 mm and a diameter of 300 to 400 inside.
A pore 12 (having a diameter of 10 to 10) having a cavity of about μm and through which gas can penetrate from the cavity toward the outer surface.
(About 00 nm). The bioreactor 10
Microorganisms 13 containing nitrifying bacteria or denitrifying bacteria are supported on the outer surface of the hollow fiber 11 in the form of a thin film via a hydrophilic polymer. A method for manufacturing the bioreactor 10 will be described below. First, since the surface of the hollow fiber 11 is strong, low-temperature plasma treatment is performed on the surface to introduce a hydrophilic group such as an amino group, a carboxyl group, or a hydroxyl group, and the surface is modified to be hydrophilic. Microorganisms 13 containing nitrifying bacteria or denitrifying bacteria are immobilized thereon via a hydrophilic polymer such as polyvinyl alcohol (PVA). It is preferable to freeze and fix with a hydrophilic polymer such as polyvinyl alcohol in order to strengthen the fixation. In the bioreactor 10 as described above, for example, when microorganisms including nitrifying bacteria that are aerobic bacteria are carried as the microorganisms 13, oxygen is supplied from the inside of the hollow fiber 11, and a nutrient source (medium) is supplied from the outside. Therefore, the growth of microorganisms including nitrifying bacteria can be promoted. Next, a sewage treatment facility 16 having sewage treatment apparatuses 14 and 15 according to the first embodiment will be described with reference to FIGS. 2 and 3 together with the flow of sewage. The sewage treatment device 14 uses hollow fibers carrying microorganisms containing nitrifying bacteria, and the sewage treatment device 15 uses hollow fibers carrying microorganisms containing denitrifying bacteria. In the sewage treatment facility 16 shown in FIG. 2, drainage from houses, factories, etc., and sewage such as rainwater are first removed from a large settling basin (not shown) by a large sediment and sediment.
Flowed into. The sewage flowing into the first sedimentation basin 17 is slowly flown in the first sedimentation basin 17, during which the sediment included in the sewage, which tends to settle, is precipitated. The sewage in which the solids have settled is discharged to a sewage treatment device
Sent to The sewage treatment device 15 is for treating sewage treated by a sewage treatment device 14 described later. The sewage first sent from the sedimentation basin 17 is hardly treated here, and the next sewage treatment device is not used. 14. As shown in FIG. 3, the sewage treatment apparatus 14
A part or all of an aeration tank 18 as an example of a treatment tank is loaded with one or two or more bundles of hollow fibers 19 having a length of, for example, about 2 m carrying microorganisms (mainly nitrifying bacteria) (specifically, Tens or more). The bundle of hollow fibers 19 (about 50 to 1000 in this case) is assembled in a cylindrical container 20 having an end portion thereof solidified with resin and having a large number of holes 21. Aeration tank 18
Soaked (soaked). In this container 20, a pipe 21a is placed from above (or from below).
Is used to introduce air, which is an example of a gas containing oxygen, so that oxygen can pass through the inside of the hollow fiber 19. In the sewage treatment device 14, the microorganisms in the sludge containing a large amount of aerobic microorganisms (hereinafter referred to as activated sludge) and the aerobic bacteria carried on the hollow fibers 19 are used to remove fine suspended matter and organic matter contained in the sewage. Decompose. At the same time, nitrifying bacteria (and nitrifying bacteria in the activated sludge) mainly supported by the hollow fiber 19 oxidize nitrogen compounds in the sewage, for example, ammonia (nitrification), and form nitrate ions (NO ₃ ).
^-), nitrite (NO ₂ ^-) to convert the like. Here, the pH of the sewage in the sewage treatment apparatus 14 decreases with the progress of nitrification. To prevent this, an alkaline agent such as sodium carbonate is added to adjust the pH to a constant pH, for example, pH 6 to 10.
It is preferable to keep it at about 9. In the sewage treatment apparatus 14, a hollow fiber 19 in which microorganisms including nitrifying bacteria are positively supported is disposed in a part or the whole thereof, so that the oxidation of nitrogen compounds can be promoted. At the same time, decomposition of organic substances can be promoted at the same time. The number of the hollow fibers 19 carrying microorganisms including nitrifying bacteria may be adjusted in consideration of the size of the aeration tank 18. That is, it is desirable to adjust the number of the hollow fibers 19 in consideration of the residence time of the sewage in the aeration tank 18 so that nitrogen in the sewage can be sufficiently oxidized (and organic substances can be sufficiently decomposed). Further, when the concentration of nitrogen compounds in the sewage is low, etc., the efficiency of the aeration treatment is increased by reducing the ratio of nitrifying bacteria carried on the hollow fiber 19 and carrying more aerobic bacteria which decompose organic substances, for example. It is also possible. The sewage treated by the sewage treatment device 14 is returned to the sewage treatment device 15 again by a pump (not shown). In the sewage treatment device 15, for example, a bundle of, for example, about 2 m long hollow fibers 22 carrying microorganisms (mainly) including denitrifying bacteria is supported on a part or all of an oxygen-free tank which is an example of a treatment tank. Are arranged in the vertical direction at one or two or more (specifically, several tens or more). This bundle of hollow fibers 22 includes a plurality or a large number of hollow fibers 22 (here, 50 to 100).
The ends are solidified with resin in a bundled state and are incorporated in a cylindrical container having a large number of holes. Since the sewage returned to the sewage treatment device 15 contains nitrate ions, nitrite ions and the like, these are reduced here and released from the sewage as nitrogen gas.
Here, since hollow fibers 22 in which microorganisms including denitrifying bacteria are positively supported are arranged in a part or the whole of the anoxic tank, reduction of nitrate ions, nitrite ions and the like is promoted. be able to. Also, the denitrifying bacteria present here are
Organic substances and the like contained in the sewage sent from the first sedimentation basin 17 can be used as a nutrient source. In addition, it is also possible to introduce an inert gas such as nitrogen or an organic substance (alcohol or the like) serving as a nutrient into the hollow fiber 22. Next, the sewage from which nitrogen has been removed by the sewage treatment device 15 passes through the sewage treatment device 14 and passes through the final sedimentation basin 23.
Sent to. Here, the activated sludge that has become easier to settle is settled at the bottom. Then, the supernatant liquid in the final sedimentation basin 23 is sent to the next disinfection tank 24, where the pathogen is killed by sodium hypochlorite, and the treated water is released to the sea with improved sanitary safety. In the sewage treatment plant 16 described above, nitrogen compounds such as ammonia are rapidly oxidized in the sewage treatment device 14, and nitrogen oxides are also rapidly reduced in the sewage treatment device 15 and released as nitrogen gas. Therefore, nitrogen can be efficiently removed from sewage. Further, in the sewage treatment facility 16 according to the present embodiment, since the aeration tank 18 is used in the sewage treatment apparatus 14, it is not necessary to provide a special oxidation treatment tank for nitrogen compounds.
Moreover, since the nitrogen compound can be efficiently oxidized by arranging the hollow fibers 19 that actively support the microorganisms including nitrifying bacteria, the nitrogen compound can be decomposed without increasing the volume of the existing aeration tank. It can be performed. Also,
Also in the sewage treatment device 15, since the concentration of microorganisms in the anoxic tank can be increased and nitrate ions, nitrite ions and the like can be efficiently reduced, the capacity of the anoxic tank can be reduced. A sewage treatment facility 27 having a sewage treatment apparatus 26 according to a second embodiment of the present invention will be described.
The same components as those in the sewage treatment facility 16 are denoted by the same reference numerals, and description thereof is omitted.
As shown in FIG. 4, the sewage treatment plant 27
7. It has a sewage treatment device 26, a final sedimentation basin 23, and a disinfection tank 24. The sewage treatment device 26 vertically orients a bundle of hollow fibers 28 carrying microorganisms including nitrifying bacteria in a part or all of an aeration tank as an example of a treatment tank (specifically, Dozens or more). This hollow fiber 28
Supports more aerobic bacteria such as those present in activated sludge than the hollow fiber 19. The bundle of the hollow fibers 28 includes a plurality or a large number (here, 50 to 1) of the hollow fibers 28, similarly to the hollow fibers 19 according to the first embodiment.
(About 000 pieces) in a bundled state, the ends of which are hardened with a resin, and assembled into a cylindrical container having a large number of holes. Air, which is an example of a gas containing oxygen, is introduced into the hollow fiber 28 from above (or from below) the container, and oxygen can pass through the hollow fiber 28. In the sewage treatment plant 27, fine suspended solids and organic matter in the sewage sent to the sewage treatment device 26 are decomposed and settled by the activated sludge and the aerobic bacteria carried on the hollow fibers 28. At the same time, nitrifying bacteria mainly carried by the hollow fibers 28 oxidize nitrogen compounds in the sewage, for example, ammonia, and convert them into nitrate ions, nitrite ions, and the like. As described above, the sewage treatment facility 27
In the above, since the concentration of aerobic microorganisms other than nitrifying bacteria is increased in the aeration tank, the decomposition of organic matter is particularly promoted. Therefore, the volume of the aeration tank can be reduced, and the size of the sewage treatment facility can be reduced. EXAMPLE An experimental apparatus 2 shown in FIG. 5 was used to investigate the ability to decompose nitrogen compounds using the sewage treatment method according to the present invention.
9 was used to conduct an experiment for decomposing (nitrifying) the nitrogen compound NH ₄ . Here, artificial drainage in which an organic substance-containing solution and an inorganic substance-containing solution having the composition shown in Table 1 were mixed was used. [Table 1] The experimental apparatus 29 has two reactors 30 (total volume 3 liters), and the two reactors 30 have hollow fibers 31 (diameter) carrying microorganisms (mainly) including nitrifying bacteria. 1mm, length 1m)
Each book is equipped. Air is supplied to the reactor 30 by the compressor 32 so that the air passes through the inside of the hollow fiber 31. Further, the reactor 30 is set to a constant temperature (for example, about 20 to 30 ° C.) by circulating the liquid in the constant temperature water tank 33. Reference numeral 34 denotes a raw material tank for an organic substance-containing solution, reference numeral 35 denotes a raw material tank for an inorganic substance-containing solution, reference numeral 35a denotes a stirrer, reference numeral 36 denotes a mixer, and reference numeral 37 denotes a constant p for artificial drainage.
A tank containing an alkaline solution for keeping H (about pH 8), reference numerals 38 and 39 indicate pressure gauges, reference numerals 40 to 44 indicate circulation pumps, reference numeral 45 indicates a drainage pump, and reference numerals 46 to 53 indicate valves. The artificial drainage contains an organic substance-containing solution and an inorganic substance-containing solution at 500 ml / h and 50 ml, respectively.
It was mixed at a rate of 00 ml / h,
The artificial drain introduced into the reactor 30 has a BOD of 261
mg / l (ppm), ammonia nitrogen is 34.
It was 4 mgN / liter. The artificial drainage was retained in the experimental device 29 for about 30 minutes. The results are shown in FIGS. FIG.
The nitrification rate over time (mgN / liter-reactor · h) is shown. Here, the nitrification rate refers to the amount of nitrification of ammonia nitrogen per liter of the reactor and per hour. According to FIG. 6, the nitrification rate increased with the lapse of time.
After 0 days, 160 mgN / liter-reactor h
And the nitrification rate is about 93%. This is a very high nitrification rate, indicating that the nitrifying bacteria supported on the hollow fiber 31 proliferated and oxidized the ammonia in the artificial drainage with very high efficiency. The period of 40 days from the start of the experiment was a period required for the bacteria carried on the hollow fiber 31 to adjust, and the nitrification rate was kept constant after 40 days. FIG. 7 shows the change in BOD (ppm) over time. Due to experimental problems, the measurement of BOD was started on the 27th day from the start of the experiment. From FIG. 7, BOD is almost 0p
pm. This indicates that aerobic bacteria other than the nitrifying bacteria carried by the hollow fiber 31 also proliferate and efficiently decompose organic substances. As described above, the present invention has been described with reference to some embodiments. However, the present invention is not limited to the configurations described in the above embodiments, and is described in the claims. It includes other embodiments and modifications that can be considered within the scope of the matters described. For example, it is also possible to provide a separate apparatus for treating a nitrogen compound, such that the sewage treatment apparatus according to the present invention treats sewage in a sedimentation tank and an aeration tank first. Although the hollow fibers are arranged in the sewage treatment apparatus in the vertical direction, they may be arranged in the horizontal direction. According to the sewage treatment method of the present invention, since hydrophilic hollow fibers which positively carry microorganisms composed of nitrifying bacteria are arranged on the outer surface, nitrifying bacteria in the treatment tank are removed. it is possible to increase the concentration of microorganisms, nitrogen compounds
Can promote the oxidation of substances that are contained in sewage.
It is also possible to promote the decomposition of organic substances at the same time .
In addition, since the treatment tank is an aeration tank, aeration treatment and nitrogen
Oxidation can be performed simultaneously, and nitrogen oxidation
It is possible to omit a processing tank for performing only processing. Soshi
The nitric acid produced by the oxidation of the nitrogen compound
Ion and nitrite ions, part or all of which are denitrifying bacteria
A hollow fiber carrying microorganisms containing mainly
Into an oxygen-free tank to convert the gas into nitrogen gas.
Release from inside, and inside the hollow fiber of the anoxic tank,
Introducing inert gas or nutrient organic matter
In this way, nitrate ions and nitrite contained in sewage
Efficient reduction of ions, etc., from sewage as nitrogen gas
It can be removed.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is an explanatory view of a hollow fiber in which microorganisms are positively supported. FIG. 2 is a schematic explanatory diagram of a sewage treatment facility having a sewage treatment device according to the first embodiment of the present invention. FIG. 3 is a schematic explanatory view of the sewage treatment apparatus. FIG. 4 is a schematic explanatory diagram of a sewage treatment facility having a sewage treatment device according to a second embodiment of the present invention. FIG. 5 is an explanatory diagram of an experimental apparatus according to an example of the sewage treatment method of the present invention. FIG. 6 is a graph showing a change in nitrification rate with respect to time. FIG. 7 is a graph showing a change in BOD with respect to time. [Description of Signs] 10: Bioreactor, 11: Hollow fiber, 12: Porous, 1
3: microorganism, 14: sewage treatment device, 15: sewage treatment device, 16: sewage treatment facility, 17: first sedimentation basin, 18: aeration tank, 19: hollow fiber, 20: container, 21: hole, 21
a: pipe, 22: hollow fiber, 23: final sedimentation tank, 24: disinfection tank, 26: sewage treatment equipment, 27: sewage treatment facility, 28:
Hollow fiber, 29: Experimental apparatus, 30: Reactor, 31: Hollow fiber, 32: Compressor, 33: Constant temperature water tank, 34: Raw material tank, 35: Raw material tank, 35a: Stirrer, 36: Mixer, 37: Tank, 38 : Pressure gauge, 39: pressure gauge, 4
0 to 44: circulation pump, 45: drainage pump, 46 to 5
3: Valve

Continuation of front page    (72) Inventor Osamu Koga               1-1, Jonai, Kokurakita-ku, Kitakyushu-shi, Fukuoka               Kitakyushu City Construction Bureau (72) Inventor Kunio Ohara               1-1, Jonai, Kokurakita-ku, Kitakyushu-shi, Fukuoka               Kitakyushu City Construction Bureau                (56) References JP-A-4-371298 (JP, A)                 JP-A-11-162 (JP, A)                 JP-A-7-68287 (JP, A)                 JP-A-57-102294 (JP, A)

Claims (1)

(57) [Claim 1] In a sewage treatment method for decomposing nitrogen compounds contained in sewage introduced into a treatment tank, the treatment tank is an aeration tank, and one of the aeration tanks is provided. In part or all, the outer surface is modified to be hydrophilic, and the outer surface actively supports microorganisms including nitrifying bacteria, and pores having a diameter of 10 to 1000 nm from the inner cavity toward the outer surface. A plurality of hollow fibers capable of supplying oxygen necessary for the growth of the microorganisms through the pores , and an acid is provided in the hollow fibers.
Gas containing nitrogen, and the pH of sewage
While adding an alkaline agent to maintain
The nitrogen compounds contained in the water are converted to nitrate ions or nitrite ions.
And turn on the nitrate and nitrite ions.
Microorganisms containing mainly denitrifying bacteria in part or all of
Into the oxygen-free tank where the held hollow fibers are
Release the nitrogen gas from the sewage ; and
Inert gas or nutrient inside the hollow fiber of oxygen tank
A sewage treatment method characterized by introducing an organic substance .