JPS6365399B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention is an energy-saving and resource-saving biological nitrification-denitrification method that biologically nitrifies nitrogen in wastewater, which causes water pollution, to NO ₂ ^- and then denitrifies it. It is related to. [Technical background and prior art of the invention] Biological denitrification methods utilize the action of nitrifying bacteria (nitrite bacteria, nitrate bacteria) to convert nitrogen compounds into NOx (NO ₂ , NO ₃ ) After nitrification (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 equipment, ammonia is usually nitrified to NO ₃ , but as can be seen from equations (1) to (4) above, it is better to stop nitrification with NO ₂ and perform denitrification treatment. The amount of oxygen supply for nitrification and the supply of hydrogen donor for denitrification are small, 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 occurs (Journal of the Japan Sewage Works Association vo1.7, 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 these conditions due to the nitrogen removal rate and the cost of supplying an alkaline agent, and it has not been carried out yet. [Object of the Invention] The object of the present invention is to provide a method for controlling the nitrification type of ammonia contained in wastewater to the NO ₂ type nitrification type, which is advantageous in terms of energy saving and resource saving. be. [Structure of the Invention] The present invention is a method for biologically nitrifying and denitrifying ammonia, in which the nitrification process is divided into sections so that a plug flow occurs, and the raw water and returned sludge are kept at a pH of 8.5 to 10.5.
After a part of the ammonia is nitrified by flowing into the inflow end of the nitrification process, the remaining ammonia is nitrified in the nitrification process that follows the inflow end, thereby converting nitrite ions into nitrite ions in the nitrification process. Biological nitrification-denitrification method for ammonia-containing wastewater, characterized in that the nitrite ions are accumulated and then denitrified under anaerobic conditions, and then the denitrification solution is circulated to a nitrification tank following the raw water inlet end. It is. Next, one embodiment of the present invention will be described with reference to the drawings. In FIG. 1, ammonia-containing raw water 1 flows into an inflow end 4 (first nitrification tank) of a nitrification process 3 together with return sludge 2. The nitrification process 3 is divided into sections to prevent mixing of the liquids in the nitrification tanks 4 to 8.
The pH of only the inlet end 4 is maintained at 8.5 or higher.
After a part of the ammonia in the raw water 1 is nitrified at the inflow end 4, the remaining ammonia is transferred to the subsequent nitrification tank 5~
At step 8, it is mixed with the circulating denitrification liquid 9 and nitrified sequentially. It is not necessary to maintain the pH of the subsequent nitrification tanks 5 to 8 on the alkaline side, but if the nitrification activity decreases due to an excessive decrease in pH, the pH may be controlled to about 7.0±0.5. The reason why the denitrification liquid 9 is circulated is to use the alkali content generated during denitrification for neutralizing the subsequent nitrification tanks 5 to 8. By performing nitrification under these conditions, nitrification is produced in nitrification step 3.
Most of NOx ^- (NO ₂ ^- + NO ₃ ^- ) becomes NO ₂ ^- .
Set the pH of inlet end 4 to the same level as that of subsequent nitrification tanks 5 to 8.
Even when set to 7.0±0.5, nitrification is completed, but NO ₂ ^- is hardly accumulated. In order to accumulate a large amount of NO ₂ ^- , it is necessary to maintain the pH at the inflow end 4 at a high level. On the other hand, NO ₂ ^- can be accumulated even if the overall pH of the nitrification process 3 is controlled to 8.5 to 10.5, but in this case, the consumption amount of the alkaline agent 10 for pH adjustment becomes excessive compared to the present invention, and the economic effect is lost. be exposed. In the nitrification step 3, a multistage tank may be used as shown in FIG. 1, but a long and narrow tank in which a plug flow is formed as shown in FIG. 2 may also be used. In addition, in order to induce NO ₂ type nitrification, it is especially important to control the pH at the inflow end 4 to 8.5 to 10.5 in the nitrification process 3, so the subsequent tanks 5 to 8 can be of a single tank complete mixing type. It is. However, it is more reliable and stable to nitrify ammonia sequentially from the inlet end 4 in the flow direction using a multistage tank or a tank in which a plug flow is formed.
_NO2 type nitrification can be performed. NO ₂ ^- generated in the nitrification process flows into a denitrification process 11, where alcohol 13 and the like are added as a hydrogen donor and denitrified. Most of the denitrification liquid is circulated to the subsequent nitrification tanks 5 to 6, and the remainder is discharged via the reaeration tank 14 and the settling tank 15. PH at inflow end is 8.5
However, if NO ₂ ^- in NOx ^- during the nitrification process does not increase, the PH can be temporarily raised to about 9.0 to 10.5, and then set to 8.5 after NO ₂ ^- has accumulated. . However, if the pH is kept above 11.0 for a long period of time, the activity of nitrifying bacteria will be significantly impaired, so care must be taken in this regard. Next, one embodiment of the present invention will be described. In carrying out the process, nitrification and denitrification treatments were carried out using an apparatus having the flow shown in FIG. The conditions for implementation are as follows. Nitrification tank 50 (inflow end 10, subsequent nitrification tank 2nd
～Equally divided into 4 tanks of the 5th tank, each
10) Denitrification tank 50 Raw water The raw water was prepared by appropriately diluting a concentrated solution of 19% NH ₄ Cl and 5% polypeptone. Alkaline agent for pH adjustment NaOH solution Amount of returned sludge Set to the same amount as the raw water inflow Amount of circulating denitrification liquid Set to 3 times the raw water inflow Set PH Inlet end 8.5 Subsequent nitrification tank 3rd tank 7.0 The implementation results are shown in Table 1 .

〔Effect of the invention〕

As described above, according to the present invention, the nitrification and denitrification method can be improved economically as follows. Since the amount of oxygen consumed in nitrification is small, the cost of oxygen supply power can be reduced. Less alcohol is needed for denitrification.

[Brief explanation of drawings]

FIG. 1 is a schematic flow diagram for explaining one embodiment of the method of the present invention, and FIG. 2 is a schematic flow diagram for explaining another embodiment. 1... Raw water, 2... Returned sludge, 3... Nitrification process, 4...
Inflow end (first) nitrification tank, 9... circulating denitrification liquid, 10...
alkaline agent.

Claims (1)

[Claims] 1 In a method of biologically nitrifying and denitrifying ammonia, the nitrification process is divided into sections so that plug flow occurs, and raw water and returned sludge are allowed to flow into the inflow end of the nitrification process where the pH is maintained at 8.5 to 10.5. After nitrifying a portion of the ammonia, the remaining ammonia is nitrified in the subsequent nitrification process at the inlet end, thereby accumulating nitrite ions in the nitrification process, and then the nitrite ions are oxidized under anaerobic conditions. A biological nitrification and denitrification method for ammonia-containing wastewater, which comprises denitrifying the ammonia-containing wastewater and then circulating the denitrification solution to a nitrification tank following the raw water inflow end.