JPS6366599B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a water purification method for removing nitrogen-containing compounds from water by a biochemical nitrification-denitrification method. Biological nitrification and denitrification method oxidizes organic nitrogen and ammonia nitrogen contained in water to nitrite or nitric acid in an aerobic atmosphere through the action of nitrifying bacteria, and then provides hydrogen to these in an anaerobic atmosphere. In this method, the nitrogen is reduced to molecular nitrogen through the action of denitrifying bacteria. The hydrogen donor referred to here is a BOD source derived from organic substances such as methanol, acetic acid, sugars, and organic substances contained in wastewater. Also,
These changes are shown by the following equation. NH ⁺ ₄ +1.5O _2Nitrite bacteria――――→ NO ₂ +H ₂ O +2H ⁺ NO ^- ₂ +0.5O _2Nitrate bacteria――――→ NO ^- ₃ NO ^- _3Hydrogen donor denitrifying bacteria――――→ 0.5N ₂ +2H ₂ O +OH ^- NO ^- _2Hydrogen donor denitrifier ---→ 0.5N ₂ + _H2O ⁺ OH -Organic nitrogen is generally decomposed into ammonia nitrogen and decomposed by the above reaction. be. Traditionally, such biochemical water purification methods have involved a process of oxidizing and removing BOD in water under aerobic conditions and oxidizing ammonia to nitrite or nitric acid (nitrification process), and a process of oxidizing ammonia to nitrite or nitric acid under anaerobic conditions. A treatment process consisting of nitric acid or a process of reducing nitric acid to molecular nitrogen (denitrification process) is provided, and a treatment tank and a precipitation tank are provided for each process, and after the ammonia is completely treated in the nitrification tank, the denitrification tank is installed. This is a method of treating nitrous acid or nitric acid with When water contains a large amount of BOD sources, a process to oxidize and remove the BOD sources (BOD treatment process) is provided before the nitrification tank. In such a purification method, when ammonia in water is oxidized to nitrite or nitric acid during nitrification treatment, the pH in the treatment tank decreases, so an alkaline agent must be added to adjust the pH. Furthermore, when the concentration of nitrite or nitric acid in the treatment tank increases, the nitrification rate of ammonia decreases. For this reason, it is not possible to increase the ammonia concentration in water, and water containing a high concentration of ammonia requires a large amount of dilution water. On the other hand, in denitrification treatment, there are almost no organic substances in the water flowing into the denitrification tank, so methanol, acetic acid, and sugars, which do not contain nitrogen atoms, are used as hydrogen donors to reduce nitrite or nitric acid to molecular nitrogen. of organic material must be added to the tank. As mentioned above, such a purification method requires a large amount of an alkaline agent and an expensive organic substance, and when water contains a high concentration of nitrogen-containing compounds, a large amount of dilution water is required, which increases operating costs. In the case of water containing a large amount of BOD sources, a BOD oxidation treatment process must be performed before the nitrification treatment process, which poses problems such as the treatment process becoming complicated. In order to solve these problems, the following methods have been used. That is, when performing nitrification treatment by bringing sludge containing nitrifying bacteria and denitrifying bacteria into contact with water in a suspended state, denitrification treatment is performed without completely nitrifying ammonia nitrogen,
This is a water purification method that removes ammonia nitrogen by repeating these steps (Japanese Unexamined Patent Application Publication No. 1973-
38357). In addition, when nitrification treatment and denitrification treatment are repeated using the same method, ammonia nitrogen is removed by using the BOD source contained in the water as an organic substance necessary for denitrification treatment. method (Toya et al., Water and Wastewater 15 1058.1973). By using these purification methods, the amount of alkaline agent added during nitrification treatment can be significantly reduced.
In particular, the latter method is excellent because it can simultaneously purify nitrogen-containing compounds and BOD sources without reducing the amount of organic substances added during denitrification treatment or without adding them at all. . Currently, in order to implement these purification methods, a nitrification tank, a denitrification tank, and a sedimentation tank are installed, water containing nitrifying bacteria and denitrification bacteria is circulated between the nitrification tank and the denitrification tank, and water is removed from the sedimentation tank. These bacteria must be brought into contact with the water in suspension in each tank, while returning the bacteria. For this reason, if the concentration of these bacteria in the tank is high, it will be difficult to separate the bacteria from purified water in the sedimentation tank.
mg/or more) is difficult to maintain. Also,
Since water containing these bacteria is circulated between the nitrification tank and the denitrification tank, these bacteria are placed alternately in an aerobic atmosphere and an anaerobic atmosphere, and their functions are affected. It is not fully demonstrated. For these reasons, treatment efficiency is poor, treatment tends to malfunction due to load fluctuations, etc., and there are disadvantages such as requiring skill in operation and maintenance, and excellent purification methods are not fully utilized. In order to improve these drawbacks, the inventors of the present application have made extensive studies and found that by bringing nitrifying bacteria in the nitrification tank and denitrifying bacteria in the denitrification tank into contact with water while attached to a biological support, It is possible to circulate only water without circulating these bacteria between the nitrification tank and the denitrification tank, and it is possible to maintain a high density of these bacteria in the treatment tank without having to send these bacteria back from the sedimentation tank. The present inventors have discovered that a porous hollow fiber membrane capable of supplying oxygen from within can be advantageously used as a biological support in nitrification treatment, leading to the present invention. That is, the present invention is a method for biochemically purifying water containing nitrogen-containing compounds, in which a hollow fiber membrane is filled in a tank as a support for nitrifying bacteria, and oxygen or a gas containing the same is aerated from inside the tank. This method of purifying water containing nitrogen-containing compounds is characterized by providing a nitrification tank and a denitrification tank filled with a support for denitrifying bacteria in the tank, and circulating water between the nitrification tank and the denitrification tank. Nitrogen-containing compounds are compounds such as ammonium salts such as ammonium hydroxide, ammonium carbonate, and ammonium bicarbonate, urea, amino acids, and proteins that undergo hydrolysis by microorganisms and change into ammonium hydroxide, ammonium carbonate, etc. Examples of water containing nitrogen compounds include wastewater discharged from manufacturing processes such as ammonia synthesis and urea synthesis, human waste, and pig farming wastewater. These may include BOD sources derived from organic substances in addition to nitrogen-containing compounds such as human waste. Furthermore, nitrites and nitrates may also be included. The tank in the present invention is a container equipped with an inlet 2 and an outlet 3 for water as shown in FIG. This is desirable. Further, the support for the nitrifying bacteria is a support for holding the nitrifying bacteria in the tank in an attached state, and a hollow fiber membrane 4 is used. The hollow fiber membrane used in the present invention is usually formed from a spinnable polymeric material such as polyolefin, halogenated polyolefin, polyacrylonitrile, aromatic polyester, aromatic polyamide, etc. It is a porous material that is generally used for ultrafiltration and reverse osmosis, but it is especially suitable for polymer materials with a contact angle of 90° or more with water, such as polytetrafluoroethylene, polyfluoroethylene, etc. Halogenated polyolefins such as vinylidene, polyolefins such as polypropylene, polyethylene, etc. are conveniently used. The outer diameter of the hollow fiber membrane is 0.01 to 3 mm, preferably
It is 0.05 to 1 mm and has a gas permeability of usually 10 to 300000/m ² , hr, atm in a dry state, and such a material can be used appropriately. In addition, the micropores in the wall of the hollow fiber membrane are preferably so small that microorganisms in the water cannot penetrate inside.
Those below 0.5μ are conveniently used. Aerating oxygen or a gas containing oxygen from inside the hollow fiber membrane is carried out by pressurizing air, pure oxygen, or a gas with increased oxygen concentration into the hollow fiber membrane through the air supply pipe 5. The amount of ventilation is controlled by appropriately changing the pressure applied within the hollow fiber membrane. The nitrification tank used in the present invention is a treatment tank that performs biochemical nitrification treatment on ammonia nitrogen contained in water, and consists of a large number of hollow fiber membranes connected at one or both ends to an air supply source. The bundles are filled uniformly into a tank. The air supply source referred to herein is a device for supplying oxygen or a gas containing oxygen, or a container in which such a gas is stored under pressure. The advantage of using such a nitrification tank is that since the hollow fiber membrane is used as a support for nitrifying bacteria and as an oxygen supply means, a very large area of bacteria can be attached per unit volume, and therefore the inside of the tank is bacterial concentration is increased. Furthermore, by increasing the contact area between water and bacteria, contact between water and bacteria can be improved. Furthermore, since oxygen is uniformly supplied from inside the support, an aerobic atmosphere can be maintained throughout the tank. These advantages significantly increase the efficiency of nitrification treatment. The denitrification tank used in the present invention is filled with supports such as honeycomb structures, plastic pieces, threads, rotating discs, and hollow fiber membranes that can hold denitrifying bacteria in a state in which they are attached. Any material may be used as long as it can increase the concentration of bacteria in the container, allow good contact between water and bacteria, and keep attached bacteria in an anaerobic atmosphere. Alternatively, a hollow fiber membrane similar to that used in the nitrification tank may be used to supply gas other than oxygen gas, such as methane gas, nitrogen gas, or carbon dioxide gas, from the hollow portion. The advantage of using a treatment tank filled with these bacterial supports is that nitrifying bacteria can be kept in an aerobic atmosphere and denitrifying bacteria can be kept in an anaerobic atmosphere, so their functions can be fully demonstrated. Bacteria can be present at a high density in the tank, and there is no need to send the bacteria back to the sedimentation tank. These advantages increase processing efficiency and significantly facilitate operation. Further, in the present invention, circulating water between the nitrification tank and the denitrification tank means continuously repeating transporting water from the nitrification tank to the denitrification tank and water from the denitrification tank to the nitrification tank. Water circulation is performed using a liquid pump, and the amount of water is adjusted so that the nitrogen source concentration is about 10 to 500 mg/, preferably about 20 to 100 mg/, when water containing nitrogen compounds is diluted with circulating water. do it. By circulating water in this way, nitrous acid or nitric acid produced by oxidation of ammonia in the nitrification tank is reduced to molecular nitrogen in the denitrification tank, and remaining ammonia and ammonia newly produced from nitrogen-containing compounds are nitrified again. It is returned to the tank and oxidized to nitrite or nitric acid. In addition, in the nitrification tank, the PH of the water decreases, while in the denitrification tank, the PH of the water increases, so by circulating the water between both tanks, the water in the nitrification tank can be neutralized without adding an alkaline agent. pH of 7-8
can be kept. Moreover, since even water containing a high concentration of nitrogen-containing compounds is diluted with circulating water, water can be purified without using new dilution water. Furthermore, in the case of water containing a BOD source, by flowing it into the denitrification tank, it can not only be used as a hydrogen donor when reducing nitrite or nitric acid, but also treat the BOD source at the same time. Become. When purifying water containing nitrogen-containing compounds by the method of the present invention, it is first necessary to attach bacteria having the respective functions to the biological supports in the nitrification tank and the denitrification tank. For this purpose, water that initially contains low concentrations of nitrogen-containing compounds is circulated through the treatment equipment while air, pure oxygen, or gas with increased oxygen concentration is aerated in the nitrification tank, and as the purification progresses, the nitrogen-containing compounds are removed. Circulate highly concentrated water. This water supply is
It is preferable to use a denitrification tank for water that contains a BOD source, and a nitrification tank for water that does not contain a BOD source. Furthermore, when the nitrogen concentration in water is 0.3 times or more higher than the BOD source concentration, it is desirable to add an organic substance that does not contain nitrogen-containing compounds as a hydrogen donor to the denitrification tank. Additionally, when the water lacks the nutrients necessary for bacteria to proliferate, it is necessary to add them. In this way, bacterial adhesion formation is achieved in about two months. By adding seed sludge to each treatment tank and adding nitric acid to the denitrification tank, bacterial adhesion can be formed in a shorter period of time, which is advantageous. The adherent bacteria thus formed are stable even under high loads and rapid load changes, and can efficiently purify water. Furthermore, once the bacterial layer on the support has developed beyond a certain level, it falls off as bacterial lumps from the surface layer, but this has good sedimentation properties and can be easily separated and removed. In the present invention, the biological support may be immersed in water, or water may be allowed to flow down onto the surface of the biological support. Furthermore, the liquid may be circulated for each tank. Further, although the method of the present invention has excellent water purification ability by itself, it may be used in combination with other biochemical purification methods or chemical or physical purification methods. The method of the present invention is widely applicable to the purification of water containing nitrogen-containing compounds, has high purification efficiency, allows for miniaturization of equipment, does not require the addition of alkaline agents, and
It is also economical because the BOD source can be used as a hydrogen donor. In addition, since it is easy to operate and maintain, it is easy to apply to small-scale water purification. Examples are shown below. Example 1 Inlet 2 of inflow water as shown in Figs. 1 and 2
Vertical with water outlet 3 at the top and outlet 3 at the bottom.
41,600 hollow fiber membranes made of polypropylene with an outer diameter of 270μ, an inner diameter of 220μ, and a length of 1m are bundled into 400 bundles in a tank 1 measuring 0.1m, width 0.1m, and height 0.7m, each with an open end 7 at the bottom and an open end 7 at the top. A nitrification tank (Fig. 1) and a denitrification tank (Fig. 2) filled in a loop shape so that the bent portion was located were used. The nitrification tank was fixed by hanging the bent part at the upper part with an upper hollow fiber membrane support 6, and the open ends at the lower part were connected to four air pipes 5. The denitrification tank was fixed at both the bent portion at the top and the open end at the bottom so that the hollow fiber membranes were uniformly dispersed within the tank. Using these two tanks, a liquid pump and pipes were connected as shown in FIG. That is, the outlet of the water in the denitrification tank 8 is connected to the suction part of the liquid feed pump 10 via a liquid feed pipe, and this discharge part is connected to the inlet of the water in the nitrification tank 9 via a liquid feed pipe. The liquid feed pipe connected to the water outlet was divided into two parts, one of which was used as the treated water outflow pipe 12, and the other connected to the waste water liquid feed pipe 11, which was connected to the water inlet of the denitrification tank. After first immersing the hollow fiber membrane in the tank in water,
Seed sludge is added to each tank, air is aerated through the air pipe 5 in the nitrification tank, and while water is circulated between both tanks, wastewater to which nitric acid has been added is supplied to prevent the formation of adhesion of denitrifying bacteria and nitrifying bacteria. Figure. In addition, the temperature inside the tank is 25℃, the air ventilation rate is 40/hr,
Amount of circulating water/amount of wastewater supplied = 14, and synthetic wastewater mainly containing peptone, meat extract, and urea was used as wastewater. As bacterial adhesion formation progressed, the amount of nitric acid added was reduced, and after about one month, sufficient bacterial adhesion formation was achieved. Therefore, the wastewater was treated with a residence time of 15 hours in the denitrification tank and nitrification tank. Ammonia nitrogen (NH ⁺ ₄ -N) and organic nitrogen (Org -N) in wastewater and treated water are determined by the Kjeldahl method, and nitrite nitrogen (NO ^- ₃ ) and nitrate nitrogen (NO ^- ₃ -N) are determined by the Kjeldahl method. Aniline acetate method, BOD tester (Taiyo Kagaku Kogyo KK)
(manufactured by). The processing results are shown in Table 1.

[Table] Example 2 Using the same treatment tank as in Example, wastewater was treated using the treatment apparatus shown in FIG. 4. That is, the water outlet of the nitrification tank 9 is connected to the liquid feeding pump 1 via the liquid feeding pipe.
This discharge part is connected to the water inlet of the denitrification tank 8 through a liquid supply pipe, and the liquid supply pipe connected to the water outlet of the denitrification tank is divided into two parts, one of which is processed. The other end was connected to the waste water pipe 11, which was connected to the water inlet of the nitrification tank. Denitrifying bacteria and nitrifying bacteria were attached to each other in the same manner as in Example 1. However, synthetic wastewater mainly containing ammonium carbonate was used as the wastewater, and methanol was added to the denitrification tank from the methanol supply pipe 13 at a ratio of methanol/nitrogen = 2.5. After bacterial adhesion was formed, the wastewater was treated in a denitrification tank and a nitrification tank for a residence time of 15 hours. Analysis of wastewater and treated water was conducted in the same manner as in Example 1. The processing results are shown in Table 2.

【table】 [Brief explanation of drawings]

FIG. 1 and FIG. 2 are specific examples of a nitrification tank and a denitrification tank for carrying out the present invention. FIGS. 3 and 4 show specific process diagrams of an apparatus for carrying out the method of the present invention. 1...Tank, 2...Water inlet, 3...Water outlet, 4
...Hollow fiber membrane, 5...Air supply pipe, 6...Upper hollow fiber membrane support, 7...Hollow fiber membrane open end, 8...Denitrification tank, 9
...Nitrification tank, 10...Liquid sending pump, 11...Waste water sending pipe, 12...Treatment water outflow pipe, 13...Methanol supply pipe.

Claims (1)

[Claims] 1. A nitrification tank in which a hollow fiber membrane is filled as a support for nitrifying bacteria and oxygen or a gas containing it is vented from inside the tank, in a method for biochemically purifying water containing nitrogen-containing compounds. Then, a denitrification tank filled with denitrifying bacteria support was installed.
A method for purifying water containing nitrogen-containing compounds, characterized by circulating water between a nitrification tank and a denitrification tank.