JPS5939199B2 - Biological denitrification method of wastewater - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a biological denitrification method for wastewater, and provides a treatment method that is particularly suitably applied to the biological denitrification process for human waste wastewater. .

Conventionally, the biological denitrification method for human waste wastewater involves contacting the wastewater with activated sludge under aerobic conditions in an aeration tank or nitrification tank, and the ammonia nitrogen contained in the wastewater is removed by the joint action of various nitrifying bacteria. is converted into nitrite nitrogen (NO2-N) and nitrate nitrogen (NO3-N), and then this mixed solution or precipitated supernatant is biologically reduced by nitrate respiration by denitrifying bacteria in a denitrification tank. Then, nitrite nitrogen and nitrate nitrogen are decomposed and removed, or a large amount of the nitrated species effluent is circulated and returned to the first denitrification tank together with the raw wastewater, and the nitrated detection effluent is treated with denitrifying bacteria. After reducing and decomposing the nitrite nitrogen and nitrate nitrogen in the water, the ammonia nitrogen contained in the raw wastewater before mixing is converted into nitrite nitrogen and nitrate nitrogen by the joint action of various nitrifying bacteria. oxidation (and then further led to a second denitrification tank, where nitrite nitrogen and nitrate nitrogen are decomposed and removed by the biological reduction action of denitrifying bacteria in the presence of an organic carbon source (BOD source). It has been adopted.

However, denitrifying bacteria that use nitrite nitrogen and nitrate nitrogen produced by the action of nitrifying bacteria in the nitrification tank as final electron acceptors are facultative anaerobic heterotrophic bacteria;
In order to obtain the energy necessary to reduce nitrite nitrogen in the denitrification tank, the presence of an organic carbon source as a hydrogen donor is an essential condition.

However, in the nitrification process, that is, in the effluent from the nitrification tank, there is extremely little organic carbon source as a hydrogen donor that can be used by denitrifying bacteria. Denitrification will be incomplete unless a source is artificially provided.

Therefore, nitrite nitrogen or nitrate nitrogen can be produced as a source of organic carbon by: (1) obtaining the intracellular storage substances of denitrifying bacteria, (2) obtaining the inflow substrate of sewage, and (2) obtaining it from addition from the outside world. There is a method of biological reduction.

However, when using a supply means based on the above method, the following disadvantages occur.

In other words, the main disadvantages are: 1) A method of reductively decomposing nitrite nitrogen and nitrate nitrogen through bacterial autooxidative respiration (endogenous respiration), using the intracellular storage substances of denitrifying bacteria as an organic carbon source. In the case of
In the denitrification tank, the growth rate of denitrifying bacteria decreases and the number of dead cells increases, so the denitrification rate also slows down, and as a result, a large denitrification tank is required. 2. Organic carbon source is used as wastewater inflow substrate. When using the method of adding wastewater equivalent to the amount of organic carbon required to reductively decompose nitrite nitrogen and nitrate nitrogen to the denitrification tank, the ammonia nitrogen contained in the wastewater is removed by the action of denitrifying bacteria. 3) The organic carbon source is added from the outside world and the growth and proliferation of denitrifying bacteria is caused by extracorporeal respiration. In the case of a method that aims to reduce nitrite nitrogen and nitrate nitrogen in a short period of time by increasing denitrification activity and reducing nitrite nitrogen and nitrate nitrogen within a short period of time, the denitrification tank has a significantly smaller volume than the required volume of the denitrification tank described in 1 above. Although reduced, organic carbon is required in excess of the stoichiometric amount required to reduce nitrate nitrogen and nitrite nitrogen.

For example, when methanol is used as this organic carbon, a large amount of methanol (2.5 kg or more) is usually required for 1 kg of nitrate nitrogen, so the operating cost associated with denitrification is reduced by the amount of nitrogen flowing into the denitrification tank. The concentration of nitrate nitrogen and nitrate nitrogen increases significantly in proportion to the concentration. 4. When denitrification is carried out in a conventional method in two stages as in JP-A-51-8754, for example, in the first denitrification tank. N02-N and N03-N in the nitrification mixture circulating from the nitrification tank
is denitrified by the action of denitrifying bacteria, and N02-N and N03-N, which remain in the second denitrifying tank, are supplemented by endogenous respiration of denitrifying bacteria or in the presence of an organic carbon source added from outside the system. Therefore, in order to increase the nitrogen removal rate in the first denitrification tank, the stoichiometric carbon to nitrogen ratio (BOD/N03- It is necessary to increase the nitrogen removal rate determined by N23-5) and the circulation ratio of the nitrification mixture to wastewater, which increases the operating cost required for liquid circulation.

The purpose of the present invention is to eliminate the disadvantages 1 to 4 mentioned above in the conventional biological membrane nitrogen method for wastewater, which performs denitrification in two stages, as disclosed in JP-A-51-8754, and to reduce maintenance and management costs. It's about trying.

The purpose of the present invention is to adsorb wastewater as it is or after diluting it into activated sludge that has been stabilized by returning it to the internal respiratory phase through oxidation, and then separate the adsorbed sludge into an appropriate amount of clean water. Alternatively, by washing with washing water such as denitrified water, ammonium present in the sludge is desorbed and diffused from the activated sludge interface into the washing water, and then separated again.
This is achieved by collecting organic adsorbed sludge containing almost no ammonium, introducing it into a second denitrification tank, and using it as a hydrogen donor for denitrifying bacteria.

The embodiment of the present invention will be described with reference to the drawings. The wastewater is introduced into the adsorption tank 1 through the pipe A as it is or after being diluted appropriately, and is sufficiently oxidized in the stabilization tank 9 and returned to the internal respiratory phase. Activated sludge microorganisms ((C5H7NO
2) When mixed with an appropriate amount of n), organic carbon compounds (CxHyOz) contained in sewage are adsorbed and accumulated on activated sludge microorganisms within a short period of time due to the following biological adsorption reaction, so they are precipitated. When the sludge is introduced into tank 2 and solid-liquid separated into adsorbed sludge and liquid, 60 to 90% of the BOD component, which is a source of organic pollution in the sewage, is adsorbed and coagulated on the activated sludge interface and separated from the sewage.

After the adsorption and accumulation reaction of organic matter by activated sludge microorganisms such as denitrifying bacteria, this separated activated sludge is led to washing tank 3 and washed with an appropriate amount of fresh water supplied from pipe B while being moderately stirred. At the same time, ammonium mixed in the separated activated sludge quickly dissolves and diffuses into the washing water, but on the other hand, it aggregates due to the viscous substances secreted by the activated sludge, and is stored and accumulated in the BOD component adsorbed and retained at the biological interface and in the biological body. BOD
By gentle stirring and mixing, the components easily dissolve in the washing water and are retained at the biological interface without being diffused. When this is led to the precipitation tank 4 and allowed to settle, a highly concentrated organic substance containing almost no ammonium is produced. It is separated into adsorbed sludge and a liquid containing ammonium.

The precipitated and separated organic adsorbed sludge is recovered and led to the second denitrification tank 7 through a pipe 12 in order to be used as a carbon source for denitrification bacteria in the second denitrification tank.

On the other hand, the liquid separated in the settling tank 2 is transferred to the first
The washing liquid flows out from the settling tank 4 through the pipe 13, an appropriate amount of nitrification detection effluent is returned to the first denitrification tank 5 from the return pipe 14, and is returned from the return pipe 15. The mixture is sufficiently stirred and mixed with an appropriate amount of activated sludge under anaerobic conditions, and the nitrite nitrogen and nitrate nitrogen in the mixed solution are decomposed into nitrogen gas or nitrogen oxide gas by the biological reduction action of denitrifying bacteria.

In this case, the ratio of the mixed liquid circulating from the nitrification tank 6 to the wastewater flowing into the first denitrification tank 5 (circulating liquid ratio) is such that the stoichiometric ratio of carbon to nitrogen required for denitrification is B as carbon.
When OD is determined using nitrate nitrogen as nitrogen, BOD
/No3-N=3~5, so BOD/ of inflow raw water
It is necessary to adjust the range to fit what is required from N.

In addition, the theoretical circulation permeation rate determined from the target nitrogen removal rate (α1) is as follows: (where d: dilution water volume ratio, r: return sludge ratio), the closer the nitrogen removal rate α is to the critical nitrogen removal rate α, the greater the becomes large, and the power cost associated with liquid circulation increases.

Therefore, in order to reduce A, it is essential to reduce α.

The reason why BOD in the inflow raw water is adsorbed and removed and recovered in the adsorption tank 1 prior to the denitrification process is to reduce the critical nitrogen removal rate in the first denitrification tank 5 and to reduce A.

As mentioned above, since 60 to 90% of BOD is removed in the adsorption process, α is 70 to 90% smaller than in the known first denitrification-nitrification-second denitrification process, and A is proportionally reduced.
will also become smaller.

Next, ammonium in the liquid in the settling tank 2 and the washing liquid in the settling tank 4 that are led to the first denitrifying tank 5 flow out of the first denitrifying tank 5 as they are because they are not subject to the action of denitrifying bacteria.

Therefore, this mixed solution is then led to the nitrification tank 6, and while the pH of the solution is constantly maintained at 6.5 to 8.5 by the pH controller 10, ammonium is converted into nitrite nitrogen and At the same time as being oxidized to nitrate nitrogen, the BOD component, which is an organic carbon source, is also oxidized and decomposed.

The mixed culture solution treated in this way is then transferred to the second denitrification tank 7.
However, since there is very little organic carbon source in this mixed culture solution for the denitrifying bacteria to acquire the energy necessary to reduce nitrite nitrogen and nitrate nitrogen, it is collected in the settling tank 4. When the organic adsorbed sludge containing almost no ammonium is led from the supply pipe 12 to the second denitrification tank 7 and mixed with the nitrification mixture flowing from the nitrification tank 6, the denitrifying bacteria in the organic adsorbed sludge undergo a respiration reaction as shown in the following equation. The denitrifying bacteria in the nitrification mixture flowing from the nitrification tank 6 contact and collide with the organic matter-adsorbing activated sludge, using the organic carbon compounds adsorbed and accumulated by themselves or other microorganisms as hydrogen donors. Hydrolytic enzymes hydrolyze the organic carbon compounds that are adsorbed on the water and use them as hydrogen donors, converting nitrite nitrogen or nitrate nitrogen in the mixed culture solution into nitrogen gas or nitrogen oxide through the biological reduction action of denitrifying bacteria. It decomposes into gas and dissipates into the atmosphere.

Respiration reactions in the second denitrification tank 7: ■ Nitrite respiration ■ Nitrate respiration H in these equations is given from the hydrolysis reaction of organic carbon compounds, which are hydrogen donors, adsorbed and accumulated by activated sludge microorganisms.

When the amount of adsorbed organic matter is less than the amount of NO□-N or No3-N, denitrifying bacteria oxidize and denitrify their own cytoplasm according to formulas 1, 2, and 2, and obtain energy for life.

The denitrified mixed culture solution is then led to a sedimentation tank 8, where it is separated into activated sludge and denitrified water.

The denitrified water separated in the sedimentation tank 8 is discharged to the outside of the yarn from the pipe C, but a portion of it may also be guided to the washing tank 3 through the return pipe 17 and used as washing water instead of fresh water. .

In addition, a part of the activated sludge separated and concentrated in the sedimentation tank 8 is returned to the return pipe 15 or the first denitrification tank 5, a part is returned to the stabilization tank 9 from the return pipe 16, and the surplus is sent from the pipe to the system. It is discharged outside.

Since the present invention has the above-described process configuration, the following effects can be obtained.

■Organic substances adsorbed and stored by activated sludge microorganisms (denitrifying bacteria, BOD oxidizing bacteria, fungi, etc.)
) is first hydrolyzed and used as energy for the life of the denitrifying bacteria, but since this step does not utilize the endogenous respiration of the denitrifying bacteria, denitrification is continued until the adsorbed and accumulated organic matter is used up. Nitrogen bacteria denitrify through extracorporeal respiration.

Therefore, since nitrogen is removed at the same rate of denitrification as when methanol or the like is added from outside the system, there is no need to increase the volume of the second denitrification tank.

■Since the inflow BOD to the first denitrification tank is reduced by 60 to 90%, the amount of circulating fluid from the nitrification tank can be reduced, and the outflow BOD
Since D is also reduced and the BOD load on the nitrification tank is significantly reduced, the nitrification tank capacity can be reduced by the capacity corresponding to BOD oxidation.

■Since adsorbed sludge contains almost no ammonia nitrogen, it does not increase the nitrogen concentration in the treated liquid.

■Denitrification Since the denitrification reaction is carried out to the extent that the endogenous respiration of the bacteria is suppressed, the decomposition of the bacterial cell cytoplasm is suppressed as much as possible and the elution of ammonia is suppressed.

■Since adsorbed organic matter is used as a carbon source for denitrifying bacteria, even if the amount of adsorbed sludge added exceeds the range corresponding to the nitrite nitrogen or nitrate nitrogen concentration, the adsorbed BOD source will be the microorganisms. Since it is adsorbed and held in the water, it does not elute into the liquid, and there is no problem of increasing the BOD concentration of the treated water (a problem associated with adding methanol, etc.).

■The adsorption process also captures the BOD source in the inflowing wastewater and uses it as a carbon source for denitrifying bacteria, so BOD is added to the nitrification process.
The outflow of OD sources is reduced, and as a result, bacterial cell synthesis is promoted and the activity of OD oxidizing bacteria is suppressed, and the overall amount of surplus sludge generated can be reduced.

As described above, the present invention utilizes organic carbon compounds contained in wastewater as a hydrogen donor, that is, an organic carbon source required in the second denitrification tank in the biological membrane nitrogen process of wastewater. Therefore, it is possible to significantly reduce the amount of organic compounds used in the second denitrification tank, such as methanol, which is required in large amounts in the conventional method, by not requiring the addition at all, or by adding just enough to compensate. Moreover, since the power cost required for circulating the nitrification mixture can be reduced, maintenance costs can be significantly reduced.

Example 1 Human waste that has been screened to remove foreign contaminants is mixed with water for 5 minutes.
The stabilized activated sludge (oxidation-reduction potential 2
00 mV), the mixture was separated into solid and liquid in a settling tank with a volume of 0.4 d, and the liquid was introduced into a first denitrification tank with a volume of 2.8 m''.

The solid sludge is introduced into a two-stage countercurrent cleaning device with a volume of 0.4 m', where it is washed with approximately the same volume of water as the sludge and used as a hydrogen donor for the denitrifying bacteria in the second denitrification tank. The liquid was introduced into the first denitrification tank.

The liquid content after adsorption treatment and the liquid content after cleaning introduced into the first denitrification tank, the nitrified water with twice the volume of the inflow sewage returned from the 1.4 m" volume nitrification tank, and the enclosure of the returned sludge. The nitrite nitrogen and nitrate nitrogen in the nitrified water are decomposed and removed by the biological reduction action of denitrifying bacteria, and then introduced into the nitrification tank, where the pH of the mixed solution is adjusted to approximately 8 using caustic soda as an alkaline agent. The ammonia nitrogen is sufficiently nitrified while adjusting to Nitrite nitrogen and nitrate nitrogen were decomposed and removed by the biological reduction action of denitrifying bacteria, and the mixed culture solution was introduced into a sedimentation basin with a volume of 1.0771'' and separated into activated sludge and denitrified water.

Part of the activated sludge is returned to the first denitrification tank as return sludge, and part of the activated sludge is returned to a stabilization tank with a volume of 0.7 cm to increase adsorption activity, so that the oxidation-reduction potential is in the range of 110 to 210 mV. I aerated it to make sure.

Next, the results according to the above-mentioned Example 1 of the present invention and the results according to the conventional method are shown in a table as shown below.

The conventional method referred to herein will be explained as follows with reference to some of the attached drawings.

That is, human waste that has been screened to remove foreign contaminants is diluted 10 times with water to a volume of 2.8. The nitrite nitrogen and nitrate contained in the nitrified water are mixed with the nitrified water of twice the volume of the inflowing sewage, which is led to the first denitrification tank 5 through the pipe 14 and returned from the nitrification tank 6. After nitrogen is decomposed and removed by the biological reduction action of denitrifying bacteria, it is introduced into the nitrification tank 6 with a volume of 2.8 m'', and the pH of the liquid is adjusted to 8.0 using caustic soda as an alkaline agent. Ammonia nitrogen was sufficiently nitrified.

Then the volume is 2.8. The nitrite nitrogen and nitrate nitrogen produced in the nitrification tank 6 are decomposed and removed by the biological reduction action of denitrification bacteria while supplying methanol as a hydrogen donor. The mixed culture solution is led to a sedimentation tank 8 with a volume of 1.0 m, where it is separated into activated sludge and denitrified water, and activated sludge with a volume of about 50% of the amount of inflow sewage is returned as return sludge to the first denitrified sludge through a pipe 15. It was returned to nitrogen tank 5.

In addition, in the present invention, the volume of the nitrification tank 6 is set to 6% of the volume of the conventional method, which means that organic pollutants in wastewater are absorbed by 6% in the adsorption process.
Since 0 to 90% is removed, the organic matter/
This is because the nitrogen ratio is kept low, and as a result, the number of nitrifying bacteria increases, and the nitrification reaction rate increases significantly compared to conventional methods.

As is clear from the above results, according to the present invention, only a very small amount of hydrogen donor (for example, methanol) can be used, and the nitrogen removal rate is also excellent.

Example 2 Human waste that has been screened to remove foreign impurities is mixed with water for 5 minutes.
Dilute the wastewater to 2200ppm BOD and 700ppm total nitrogen, and introduce this into an adsorption tank to reduce the amount of wastewater to 10%.
0% volume stabilized activated sludge (redox potential 140mV)
When the liquid was separated into solid and liquid in a settling tank, the BOD in the liquid was reduced by about 80%.

When the separated sludge is washed with approximately equal volume of water in a two-stage countercurrent washing device, ammonium is removed from the adsorption-activated sludge interface by approximately 90%.
% removed, and the BOD concentration of the organic adsorption activated sludge increased approximately 3.5 times compared to the BOD of the sludge before adsorption (stabilized activated sludge).

Next, the liquid after the adsorption treatment and the liquid after washing, the nitrification liquid with a volume three times the volume of these sewage, and the returned sludge with a volume of 50% are led to a first denitrification tank with a volume of 2.8771'', and are subjected to anaerobic treatment. After thorough mixing and contact under the following conditions, the volume is 1.4771.
When aeration is carried out while adjusting the pH of the mixture to approximately 8 using caustic soda as an alkaline agent, the BOD of the wastewater becomes 23.5 ppm, and the ammonia is mostly converted to nitrite nitrogen. and converted to nitrate nitrogen.

Next, this nitrified solution was led to a second denitrification tank with a volume of 2.8771", and only the adsorption activated sludge after washing was added as a hydrogen donor without supplying methanol, and it was brought into contact with denitrifying bacteria under anaerobic conditions. After mixing, this mixed culture solution is led to a sedimentation tank and separated into denitrified water and activated sludge.The total nitrogen in the denitrified water is reduced by approximately 98% in terms of raw human waste, and the BO
D decreased by about 99%.

[Brief explanation of drawings]

The drawings are system diagrams showing embodiments of the present invention. A: Sewage introduction pipe, B: Washing water supply pipe, 1: Adsorption tank, 2: Sedimentation tank, 3
...Cleaning tank, 4...Sedimentation tank, 5...
...First denitrification tank, 6...Nitrification tank, 7...
...Second denitrification tank, 8...Sedimentation tank, 9...
... Stabilization tank, 10 ... pH controller, 11 ... Supernatant liquid pipe, 12 ... Adsorption sludge pipe, 13 ... Washing liquid pipe, 15・・・・・・
・Activated sludge return pipe, 14...Nitrification detection effluent return pipe, 16...Activated sludge conduit, 17...
・Denitrified water pipe, C・・・Denitrified water discharge pipe, D・
... Surplus activated sludge discharge pipe.

Claims (1)

[Scope of Claims] 1. Sewage containing ammonium and nitrification liquid returned from the nitrification tank are introduced into a first denitrification tank, where they are reduced and decomposed by denitrification bacteria, and then introduced into the nitrification tank where they remain. After ammonia nitrogen is oxidized to nitrite nitrogen and nitrate nitrogen by the joint action of various nitrifying bacteria, it is further transferred to a second denitrification tank where it is reductively decomposed by denitrifying bacteria in the presence of an organic carbon source, and then precipitated. In the biological denitrification process in which denitrified water and activated sludge are separated in a pond, the sewage flowing into the first denitrification tank is brought into contact with the activated sludge that has been separated and returned in the settling tank, and the sludge in the sewage is Organic matter is adsorbed to activated sludge and then separated, and the separated sludge is washed with washing water and then re-separated. The organic matter-adsorbing activated sludge obtained is then treated with hydrogen by denitrifying bacteria in the second denitrification tank. A biological denitrification method for wastewater characterized by its use as a donor. 2. The biological denitrification method for wastewater according to claim 1, characterized in that fresh water is used as the washing water. 3. The biological denitrification method for wastewater according to claim 1, characterized in that denitrified water from a settling tank is used as the washing water.