JPH0149555B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention saves energy by nitrifying ammonia contained in wastewater, which causes water pollution, to NO ₂ ^- using nitrifying bacteria attached to the medium. , the purpose is to provide a method for efficiently removing resources while saving resources. [Technical background of the invention] Biological denitrification method uses the action of nitrifying bacteria (nitrite bacteria, nitrate bacteria) to nitrify nitrogen compounds into NOx (NO ₂ , NO ₃ ) under aerobic conditions. After (oxidation),
It uses the action of denitrifying bacteria to reduce and remove NOx to _N2 gas under anaerobic conditions. The reaction process until the completion of denitrification is expressed stoichiometrically as shown in the following equation. Nitrification reaction (aerobic conditions) NH ₄ ⁺ +1.5O ₂ →NO ₂ ^- +2H ⁺ +H ₂ O
Nitrite bacteria...(1) NO ₂ ^- +0.5O ₂ →NO ₃ ^-Nitrate bacteria...(2) Denitrification reaction (anaerobic conditions) NO ₃ ^- +H ₂ →NO ₂ ^- +H ₂ O Denitrification bacteria...(3 ) NO ₂ ^- +1.5H ₂ →0.5N ₂ ↑＋OH ^- +H ₂ O
Denitrification bacteria...(4) The conditions for the nitrification reaction described above, like other aerobic microbial reactions, are that dissolved oxygen, water temperature, and pH are maintained appropriately, but the nitrification reaction requires the removal of carbonaceous compounds. Unlike the case of oxidation, as shown in equation (1), it is a live acid reaction that generates 2 equivalents of H ⁺ per 1 equivalent of ammonia, so as nitrification progresses, the pH decreases. However, the optimal pH range for nitrifying bacteria is 7.8.
~8.8, and nitrification almost stops when the pH drops to about 5. Therefore, in order for the nitrification reaction to proceed smoothly, the pH of the wastewater must be maintained near neutrality. As shown in equations (1) to (4) above, it is necessary to supply oxygen for nitrification and a hydrogen donor for denitrification, but when treating a large amount of nitrogen contained in wastewater, This has become a major problem in terms of the cost of oxygen supply power, the consumption of valuable industrial chemicals such as methanol used as a hydrogen donor, and alkaline agents for pH control, and the operating costs of denitrification treatment equipment. In the nitrification process of denitrification treatment equipment, ammonia is usually nitrified to NO ₃ , but the above (1) to (4)
As can be seen from the equation, denitrification treatment by stopping nitrification with NO ₂ requires less oxygen supply for nitrification and less hydrogen donor supply for denitrification, which is advantageous in terms of operating costs. In other words, the amount of oxygen for _NO2 type nitrification is
NO ₃ type nitrification requires 3/4 (1.5O ₂ /2O ₂ ), and the amount of hydrogen donor consumed for NOx reduction is 3/5 (1.5H ₂ /2.5H ₂ ) of _{NO 3 .} Enough. in this way,
Despite the obvious advantages of _NO2 -type nitrification denitrification treatment, most of the actual denitrification treatments are
It is carried out using NO ₃ type nitrification. This is because it is extremely difficult to maintain NO ₂ type nitrification in a denitrification treatment equipment. However, PH
and a report that the higher the ammonia concentration, the more likely _NO2 type nitrification is to occur (Journal of Japan Sewage Works Association Vol. 7, No.
74, 1970/7, Yasunori Toya, "Research on biological denitrification methods (1)"). It can be easily inferred from the following chemical equilibrium equation that this is because free NH ₃ inhibits the activity of nitrate bacteria that nitrifies NO ₂ to NO ₃ . NH ₄ ⁺ +OH ^- →NH ₃ +H ₂ O...(5) NH ₃ : Free ammonia From this equation (5), the higher the ammonia concentration and pH, the higher the free NH ₃ concentration, and the condition range for NO ₂ type nitrification. However, it is difficult to carry out nitrification under such conditions due to the nitrogen removal rate and the cost of supplying an alkali agent, and it has not been carried out yet. [Object of the Invention] An object of the present invention is to provide a method for nitrifying ammonia in an ammonia-containing aqueous solution while controlling the NO ₂ type nitrification format, which is preferable from the viewpoint of energy saving and resource saving. shall be. [Structure of the Invention] The present invention provides a method for nitrifying ammonia by sequentially passing an ammonia-containing aqueous solution through two nitrification tanks containing nitrifying bacteria attached to a medium, in which the flow direction of the ammonia-containing aqueous solution is This is a biological nitrification method for ammonia-containing wastewater, which is characterized in that the pH of the nitrification tank on the side into which the ammonia-containing aqueous solution is first introduced is controlled to be maintained within the range of 8.5 to 10.5. Next, one embodiment of the present invention will be described with reference to the drawings. In Figure 1, ammonia-containing wastewater is filled with a microbial adhesion medium from wastewater introduction pipe 1, and has a pH of
Ammonia is introduced into nitrification tank 2, where the pH is maintained at 8.5 to 10.5, and after a part of the ammonia (usually about 50% or more) is nitrified, it is also filled with a microbial adhesion medium, and the PH
is introduced into the nitrification tank 3, which is maintained near neutrality, and the remaining ammonia is nitrified. At this time, valves 4, 8, and 7 are opened, valves 5, 9, and 6 are closed, and the treated water is normally led to the next denitrification process through the treated water discharge pipe 10. Next, open valves 5, 9, and 6, and open valves 4 and 6.
By closing 7 and 8, the flow of the waste water 1 is switched, and the waste water 1 is first introduced into the nitrification tank 3, and the pH of the nitrification tank 3 is adjusted to 8.5 to 10.5.
After a part of the ammonia in the wastewater (usually about 50%) is nitrified in the tank, it is introduced into the nitrification tank 2, where the pH is maintained at around neutrality or higher, and then the treated water is treated. The water is normally led to the next denitrification process via a water discharge pipe. The wastewater inflow route is switched every certain number of days, and ammonia is nitrified to NO ₂ ^- by this switching. This is because nitrification tanks 2 and 3 are alternately maintained at a high pH, during which time NO ₂ ^- is converted into NO ₃ ^-
This method takes advantage of the fact that only the nitrifying bacteria that nitrify NO ₂ - to NO 3 - have their activity inhibited and do not recover their ability to oxidize NO 2 ^- to NO ₃ ^- for a certain number of days. Therefore, the switching point is determined by manually or automatically analyzing the concentration of NO ₂ ^- and/or NO ₃ ^- in the nitrification water, and when the concentration of NO ₂ ^- becomes lower than a predetermined value or when the concentration of NO ₃ ^- becomes lower than a predetermined value. It is certain to switch when the density becomes higher than a predetermined value. Oxygen may be supplied to the nitrification process either by using air or by using pure oxygen. When plug flow is formed in the nitrification process, in order to nitrify high-concentration ammonia, it is preferable to circulate the effluent water of nitrification processes (tanks) 2 and 3 respectively to dilute the ammonia. The alkaline agent 12 for control may be injected into the circulation line 11. On the other hand, when the nitrification tanks 2 and 3 are of a complete mixing type, there is no need to circulate the water flowing out from each tank, and the alkaline agent is preferably directly injected into the nitrification tank whose pH is to be adjusted by the alkaline agent. Furthermore, in the nitrification step of adjusting the pH to 8.5 to 10.5, _NO2 type nitrification can be performed even if the pH is intermittently maintained within the range of 8.5 to 10.5. Next, examples of the present invention will be described. In carrying out the experiment, nitrification was carried out using an apparatus having the flow shown in FIG. The conditions for implementation are as follows. ◎Nitrification process A, B2 towers Fixed bed fluidized bed using sand as a medium, completely mixed type, no nitrification water circulation equipment, alkaline agent is directly injected into the nitrification process ◎Nitrification process A, B 10 each, total 20 ◎Setting PH Raw water Inflow nitrification process 8.5 Nitrified water outflow nitrification process 7.0 ◎ NH ₃ -N concentration and flow rate of raw water See Table 1 ◎ Air introduction amount 1.0 m ³ /day to each of towers A and B

〔Effect of the invention〕

As described above, according to the present invention, nitrification and denitrification can be improved into an economically superior method as described below. Since the amount of oxygen supplied for nitrification is small, the cost of oxygen supply power can be reduced. When performing denitrification, the amount of alcohol added can be reduced.

[Brief explanation of drawings]

Fig. 1 is a flow diagram for explaining one embodiment of the present invention, and Fig. 2 shows the elapsed time in the embodiment, the raw water injection process switching point, and the amount of water in the treated water.
It is a figure which shows the relationship of _NO2 ^-- N. 1... Raw water introduction pipe, 2, 3... Nitrification tank, 12...
...Alkaline agent.

Claims (1)

[Claims] 1. In a method of nitrifying ammonia by sequentially passing an ammonia-containing aqueous solution through two nitrifying tanks containing nitrifying bacteria attached to the medium, the flow direction of the ammonia-containing aqueous solution is alternately switched, and the ammonia-containing aqueous solution is A biological nitrification method for ammonia-containing wastewater, characterized by controlling the pH of the nitrification tank where the ammonia is first introduced to be maintained within the range of 8.5 to 10.5.