JPS6322879B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention uses nitrate-N produced by oxidizing ammonia and organic nitrogen in wastewater or tap water through aeration.
The present invention also relates to an improvement in a method for denitrifying nitrite-N using a rotating disk type biochemical treatment device anaerobically. Aerating sewage and wastewater using activated sludge
Methods for lowering BOD and purifying wastewater have been used for a long time and are effective, but instead of purifying wastewater by blowing air in an aeration tank, rotating disks and similar items are immersed about half into the septic tank water. By bringing water and air into contact with the media alternately while rotating, the bacteria in the sewage propagate on the disk, and the organic matter in the sewage is decomposed by forming a biofilm.B.
The so-called rotating disk type biooxidation treatment equipment used to lower OD has been rapidly gaining popularity recently due to its compact shape and easy maintenance. Also, very recently, a method has appeared (Patent No. 0911200) in which a cup is attached to the surface of a group of disks and air is sent through it to rotate the rotating body by the buoyancy of the air.
In addition, recent trends in wastewater treatment include the first physicochemical treatment followed by the second aeration tank to reduce BOD.
In addition to the removal of SS, tertiary treatment has begun, that is, removing phosphorus, ammonia, color, odor, etc., and returning the treated water to industrial water. In particular, if treated water containing phosphorus and ammonia is poured into lakes or rivers, abnormal algal blooms will occur due to eutrophication, and if it is poured into the sea, it will cause red tide, and once this occurs, tens of thousands of yellowtails will be destroyed. Fish farm also 1
Frequently, they are completely wiped out in the morning. Therefore, the tertiary treatment of wastewater, that is, the removal of phosphorus and ammonia, has become an extremely important proposition in water treatment. Phosphorus can be easily removed by adding an equivalent amount of lime or aluminum sulfate to the solution as a phosphate with good sedimentation properties, but since ammonia does not have salts that are insoluble in water, it is easily removed. I can't do anything. To remove ammonia, first, ammonia is oxidized from NO ₂ -N to NO ₃ -N by bacteria such as Nitrozomonas and Nitrobacter in an aeration tank. Also, since it is difficult to adjust the pH inside the aeration tank, a nitrification tank is sometimes placed after the aeration tank to carry out nitrification. The nitrified ammonia is then sent to a denitrification tower, where approximately 2.5 to 3.0 times the weight of the nitrogen contained is added using methanol or acetic acid as a hydrogen donor, and denitrification is performed anaerobically in an oxygen-free condition. It is. Normally, the liquid is passed through a tower filled with sand, and denitrification is carried out by the action of bacteria such as Pseudomonas. In the present invention, denitrification is carried out using a gas-driven rotating disk type biochemical treatment device as shown in the cross-sectional view of Figure 3. Initially, the rotating disk was immersed in drip water. The tank was sealed and gradually rotated by a prime mover around a rotating shaft to generate bacterial cells on the rotating disk and carry out the denitrification reaction. However, the bacterial cells mainly adhere to the ends (circumferences) of the rotating disk, and the internal gap surfaces do not function effectively, resulting in the need for frequent cleaning. Therefore, the present inventors focused on the nitrogen that is inevitably generated in this process, and applied the method described earlier in which a rotating disk is driven by air to blow out nitrogen gas at the bottom of the rotating body. At the same time, the tank was sealed and the generated nitrogen was circulated with a blower, which allowed the gas to spread to every corner of the rotating disc body, eliminating the excessive adhesion of bacterial cells. Power was also saved and denitrification efficiency was significantly improved. The flow of denitrification based on the attached drawing,
Let us explain in more detail the structure of the device, the construction and operation of the invention, etc. Figure 1 is an example of a flow sheet for tertiary wastewater treatment using a rotating disk type biochemical treatment device.
(1) is the initial sedimentation tank (2) is the raw wastewater storage tank (3) is the rotating disk type aeration and nitrification tank (4) is the rotating disk type anaerobic denitrification tank (5)
The reaeration tank (6) is the sedimentation tank (7), the phosphorus removal device (8) is the sterilization tank (9), the treated water (10) is methanol. Install an activated carbon adsorption tank. (Not shown) The part to which the present invention relates is the denitrification tank (4). FIG. 2 is a partially cut-away overall view of an example of an apparatus for rotating a rotating disc type biochemical treatment apparatus by gas drive. When the air (gas) coming from the main pipe passes through the pipes 16 and releases air bubbles from the pores 13' of the differential user 13, the air bubbles accumulate in the cup 11 on the entire periphery of the rotating disc group 14, and due to buoyancy, the rotating disc The group gradually rotates in the direction of the arrow. FIG. 3 is a sectional view of one example of the denitrification apparatus of the present invention. This device is a gas-driven rotating disk type biochemical treatment device made into a sealed tank. The denitrification tank 16 has an outer wall 18 and a roof 17, and a group of rotating disks P is connected to the rotating shaft 12 and a bearing in the denitrification tank 16. Supported. Everything is airtight, and one part is vented to the ceiling 22 to vent excess gas.
is attached. NO ₂ -N and NO ₃ -N are decomposed by anaerobic bacteria.
When N ₂ is released _, it accumulates in the space 19 above the denitrification tank 16 . By using the circulation blower 20 to slightly remove the center of the rotating body and blowing it out from the differential user 13 (however, the first step is to send it from the nitrogen cylinder), the air bubbles will rise upward and reach the surface cup 11, as mentioned above. Due to the accumulated buoyant force, the rotating disk group P rotates in the direction of the arrow. The rotating disk group P may be submerged in the water as shown in FIG. 3, but there is no problem even if a portion thereof is exposed above the water surface. The liquid 21 coming from the aeration/nitrification tank 3 (Figure 1) is aerated in the aeration tank and lowers the BOD at the same time.
NH ₃ and organic nitrogen compounds are NO ₂ -N and NO ₃ -N
Since it is airtight, anaerobic bacteria can flourish, and organic matter such as methanol, which is added from step 23, is used as a hydrogen donor to produce NO ₂ -N,
NO ₃ - N is reduced to nitrogen, and some of it becomes carbon dioxide and water. In this case, when the rotary shaft was not driven by gas, biological film excessively adhered to the surface of the rotating disk group, making operation difficult. However, by driving the rotating body by circulating an inert gas such as nitrogen gas according to the present invention, the attached excess bacterial cells are removed by the shear force generated by the aeration, and furthermore, since gas is used for rotation, The gas spreads to the gaps between each disk group, eliminating most of the clogging that occurs in the conventional system. The temperature inside the denitrification tank is preferably 25 to 30°C, and the circulation rate of nitrogen gas is preferably 2 to 6 m ² /min, depending on the size of the tank. PH is acidic at first, but gradually
As NO ₃ NO ₂ decomposes, it approaches neutrality.
For the denitrification reaction, the pH should be around 7, and the pressure should not be too high. After denitrification, the liquid overflows from the outlet 24 and is transferred to the next re-aeration tank 5 (decomposition of excess methanol) and settling tank 6 (Fig. 1), where the SS is settled, then dephosphorized and sterilized. It is also used for industrial water and tap water. This method is used not only to remove NH ₃ organic N from wastewater, but also to remove trace amounts of NH ₃ from clean water. The gas used for the gas drive is optimally nitrogen gas, but carbon dioxide gas or a mixed gas with nitrogen may also be used, or any inert gas that does not contain oxygen and is hygienic and harmless to the bacterial cells may be used. do not have. In this case, nitrogen is a by-product, which is most convenient, and it also has the advantage of being self-sufficient even if there is loss. Example 1 Size of denitrification tank
1600m/mW x 1900m/mL x 1550m/mH Diameter of disc group 1200mmφ Disc surface area 200m ² Number of rotations 4.5rpm Raw water Factory wastewater Retention time 5.0 hours Circulating gas amount 2.2m ³ /min Methanol addition amount 150p.pm Water Temperature 28℃ Cup shape According to attached drawing

[Table] Example 2 Size of denitrification tank
1600m/mW x 1900m/mL x 1550m/mH Diameter of disk group 1200mmφ Disc surface area 200m ² Number of rotations 4.0rpm Raw water River water Residence time 2.0 hours Circulating gas amount 2.0m ³ /min Gas Methanol amount 28mg/Water temperature 25 ℃

[Table] Finally, let us summarize the effects of the present invention. 1. By using nitrogen gas as a by-product, it was possible to drive a group of rotating disks in circulation using the buoyancy of the gas, thereby saving power. 2. Since the inert gas spreads to every corner of the disc gap, denitrification is performed uniformly without excessive biofilm adhering to the disc. 3. Depending on the circulating gas, every corner of the disk can be used for the reaction, resulting in high denitrification efficiency. 4. Cleaning time is significantly reduced compared to conventional methods. Maintenance costs decreased.

[Brief explanation of the drawing]

Figure 1 shows an example of a flow sheet for tertiary treatment of wastewater. FIG. 2 is a partly cut-away overall view of an example of a gas-driven rotating disk type biochemical treatment device. FIG. 3 is a sectional view of one example of a denitrification device according to the present invention. Figure 4 is a side view and sectional view of the cup, and a diagram showing how it is attached to the rotating disk group. Explanation of symbols indicating main parts, 11... Cup, 12... Rotating shaft, 13... Differential user, 14...
Rotating disk group, 15... Gas driven rotating disk type aeration tank, 16... Inert gas driven anaerobic denitrification device, 1
9...Space, 20...Circulation blower, 21...Sewage, 22
... Gas outlet, 23... Methanol inlet, 24... Treated water outlet, P... Rotating disk group (cross section).

Claims (1)

[Scope of Claims] 1. A method for denitrifying nitrate and nitrite nitrogen in clean water or wastewater using a closed rotating disk biochemical treatment device driven by an inert gas. 2. The method for denitrifying nitrate and nitrite nitrogen in clean water or wastewater according to claim 1, wherein the inert gas is a gas mainly composed of nitrogen gas. 3. The method for denitrifying nitrate and nitrite nitrogen in clean water or wastewater according to claim 1, wherein the inert gas is a mixed gas of nitrogen and carbon dioxide. 4. The biochemical treatment device as set forth in claim 1, 2, or 3, which is a biochemical treatment device characterized in that the rotating disk is completely immersed in water or partially exposed above the water surface. A method for denitrifying nitrate and nitrite nitrogen in water or wastewater. 5 Nitrate and nitrite states in clean water or wastewater as set forth in claim 1 or 2 or 3 or 4, characterized in that an inert gas is circulated using a blower. Nitrogen denitrification method.