JP5333953B2 - Nitrogen removal system and nitrogen removal method of dehydrated filtrate - Google Patents

Description

  The present invention relates to an activated sludge treatment of ammonia nitrogen, which is contained in a large amount of filtrate when anaerobic digested sludge is dehydrated, and in particular, a nitrification tank and an oxygen-free tank are installed at the subsequent stage of the dehydrator to form nitrogen in a water treatment process. The present invention relates to a nitrogen removal system and a nitrogen removal method for dehydrated filtrate that reduce a load.

Conventionally, sludge containing organic matter and activated sludge are mixed by aeration to oxidize to nitrite nitrogen and nitrate nitrogen, and the treatment method to reduce nitrite nitrogen or nitrate nitrogen to nitrogen gas in an oxygen-free tank is It is known.
Then, by the circulatory nitrification and denitrification method, the denitrifying bacteria use organic matter to reduce oxidizing nitrogen to nitrogen gas, and the nitrifying bacteria in the aerobic reaction tank oxidize ammonia nitrogen to nitrite nitrogen and nitrate nitrogen Sludge treatment is also known.
Also, an anaerobic-aerobic activated sludge method removes phosphorus from sludge containing organic matter, and an activated sludge treatment method that simultaneously removes nitrogen and phosphorus in a three-tank anaerobic-anoxic-aerobic tank. Is well known.

Then, activated sludge treated with an anaerobic-aerobic or anaerobic-anoxic-aerobic activated sludge treatment apparatus is added with acetic acid in a reaction tank to release phosphorus, and the concentrated sludge is solid-liquid separated with a dehydrator. A method for treating organic sludge is disclosed in Patent Document 1.
In addition, the sewage from the anaerobic treatment device of the anaerobic-aerobic activated sludge method is supplied to the aerobic treatment device to treat high-concentration organic waste liquid, and the effluent is supplied to the dehydrator to form the SS component and the separated liquid. Separation, the separation liquid is allowed to flow into a nitritation apparatus, aeration is performed, pH is adjusted by adding an alkali component or acidic component, and a part of ammoniacal nitrogen is converted to nitrogen nitrite. Patent Document 2 discloses a method for treating organic waste water that performs a denitrification reaction to release nitrogen gas and adds magnesium and an alkaline component to remove phosphorus in a dephosphorization step.

JP 2006-263515 A (paragraph numbers 0013 to 0018, FIG. 1) JP 2007-117948 A (paragraph numbers 0027 to 0030, FIG. 1)

In the method of treating organic sludge described in Patent Document 1, the activated sludge treated in the reaction tank is such that nitrogen and phosphorus are removed well, but since the target stock solution is raw sludge, the content of ammoniacal nitrogen There are not many.
The treatment method of high concentration organic waste water described in Patent Document 2 is treated by an anaerobic-aerobic activated sludge method, and ammonia nitrogen and phosphorus contained in a large amount of solid-liquid separated effluent are removed to remove high concentration organic wastewater. Although wastewater treatment is performed satisfactorily, many chemicals of magnesium and alkali components are required.
The dehydrated filtrate after the anaerobic digestion treatment contains a lot of ammonia nitrogen, and the nitrogen load in the water treatment process may be excessive.
For the purpose of removing ammonia nitrogen contained in a dehydrated filtrate, which is a conventional problem, the present invention provides a nitrogen removal system and a nitrogen removal method for a dehydrated filtrate by providing a nitrification tank and an oxygen-free tank at the subsequent stage of the dehydrator. provide.

The gist of the dewatered filtrate nitrogen removal system of the present invention is that the sludge containing organic matter is first flowed into the sedimentation basin, and the digested sludge treated in the aerobic reaction tank and the anaerobic digestion tank is subjected to solid-liquid separation with a dehydrator. In the sludge treatment system that temporarily stores the dehydrated filtrate in the adjustment tank, a nitrification tank is provided after the adjustment tank, an intermittent aeration and a stirrer are provided in the nitrification tank, and oxygen-free annexed to the nitrification tank While installing a stirrer in the tank and installing an extraction pump that draws the supernatant of the nitrification tank into the anoxic tank and an exchange pump that alternately replaces the sewage in the nitrification tank and the anoxic tank, Processes dehydrated filtrate containing ammonia nitrogen. If dewatered filtrate is supplied by alternating sewage, appropriate organic matter is supplied to the nitrification tank to suppress pH drop and sludge decomposition. Can be prevented.
Ammonia nitrogen contained in the dehydrated filtrate of the nitrification tank can be oxidized to nitrate nitrogen and nitrous nitrite by stirring and intermittent aeration. The supernatant after nitrification is supplied to the anoxic tank and nitrogen gas is removed by denitrifying bacteria. Can be reduced to
Nitrogen contained in the dehydrated filtrate that may become excessive can be removed, and the nitrogen load in the water treatment process can be reduced.

The supply of organic matter and the drainage of treated water consist of a return pump that returns the supernatant or sewage from the anaerobic tank to the aerobic reaction tank before the dehydrator, and sewage containing organic matter from the first sedimentation basin in the anaerobic tank. It is equipped with a water pump to supply it, and can supply organic matter as nutrient source necessary for denitrification from the sewage in the first sedimentation basin.

The gist of the nitrogen removal method of dehydrated filtrate in the activated sludge treatment of the present invention is that sludge containing organic matter is first flowed into a settling basin, and digested sludge treated in an aerobic reaction tank and an anaerobic digester is solidified by a dehydrator. In the sludge treatment system that performs liquid separation and temporarily stores the dehydrated filtrate in the adjustment tank, a nitrification tank that performs intermittent aeration downstream of the adjustment tank, and an oxygen-free tank in which the supernatant is introduced from the nitrification tank and stirred In addition, a certain amount of dehydrated filtrate stored in the adjustment tank is sent to the nitrification tank and agitated while stirring, and the ammonia nitrogen contained in the dehydrated filtrate is nitrified, which is necessary for nitrification. After a lapse of time, the stirring and aeration of the nitrification tank are stopped, and a certain amount of supernatant containing a large amount of nitrate nitrogen and nitrite nitrogen that has been nitrified is supplied to the anoxic tank and reduced to nitrogen gas, Sewage in nitrification tank and anoxic tank after nitrification treatment The denitrifying bacteria grown by intermittent aeration are supplied alternately to the anoxic tank, maintaining an appropriate concentration of organic matter in the nitrification tank, and preventing the nitrification tank from lowering its pH and decomposing sludge flocs. By supplying oxygen and nitrifying bacteria, ammonia nitrogen contained in the dehydrated filtrate can be oxidized to nitrate nitrogen and nitrite nitrogen. Sedimentation can be improved.
The stirred and mixed sludge in the nitrification tank and the oxygen-free tank can be alternately exchanged to supply organic matter to the nitrification tank while maintaining a uniform MLSS concentration, and the sludge floc can be prevented from being decomposed.
The supernatant liquid containing nitrate nitrogen and nitrite nitrogen in the nitrification tank can be supplied to the anoxic tank and reduced to nitrogen gas by denitrifying bacteria.

In the intermittent aeration method, intermittent aeration is performed in a 60-minute cycle with stirring so that the dehydrated filtrate flowing into the nitrification tank does not become excessive aeration, and the upper limit of dissolved oxygen in the tank is reduced to 2 mg / L or less. While maintaining the concentration at pH 5 or higher, replace the sewage in the nitrification tank and anoxic tank with a volume of about one-fifth of the nitrification tank once a day. Is maintained at about 6,000 mg / L, so that nitrifying bacteria and denitrifying bacteria can be cultured. The dehydrated filtrate flowing into the nitrification tank does not become excessively aerated, making it easy to adjust the nitrification tank aeration. It becomes.
By putting oxygen-free conditions in the nitrification tank, there is no generation of microorganisms harmful to water treatment such as actinomycetes, and sludge sedimentation can be improved. The MLSS concentration in the nitrification tank and the anoxic tank becomes appropriate while maintaining a low aeration state.

Discharge of treated water after denitrification treatment is performed after the time required for denitrification of the anaerobic tank has elapsed, stirring of sewage is stopped, gravity concentration is performed, and a certain amount of supernatant liquid intermittently flows from the nitrification tank The same amount of the denitrified supernatant is returned to the aerobic reaction tank in front of the dehydrator, and treated water containing the grown nitrifying bacteria and denitrifying bacteria can be supplied.

To supply organic matter necessary for denitrification, a certain amount of sewage is returned to the aerobic reaction tank in front of the dehydrator while stirring in the anaerobic tank, and a certain amount of sewage containing the organic matter in the first sedimentation basin is returned to the anaerobic tank. 2 to 4 times a day to ensure a COD concentration of 30 to 40 mg / L necessary for denitrification, and by introducing the sewage water in the first sedimentation basin, organic substances necessary for denitrification can be secured, Denitrifying bacteria can reduce nitrate nitrogen to nitrogen gas using organic matter.

The denitrated filtrate nitrogen removal system and the nitrogen removal method according to the present invention are configured as described above, and when deaerating anaerobic digested sludge, a large amount of ammonia nitrogen contained in the dehydrated filtrate after sludge treatment. Since the nitrification tank with intermittent aeration and a stirrer and the oxygen-free tank with the stirrer was used as a two-tank removal system, the nitrification tank that performs intermittent aeration puts oxygen-free conditions during operation As a result, a low aeration state is achieved, denitrifying bacteria grow, and generation of microorganisms harmful to water treatment such as actinomycetes can be suppressed, and sludge sedimentation can be improved.
The organic matter that is the source of nutrients in the anaerobic tank can be secured by first putting the sewage in the sedimentation basin.
The nitrification tank can maintain a uniform MLSS concentration by exchanging a certain amount of sewage with the oxygen-free tank, and can prevent the sludge floc from being decomposed. The nitrification tank and the oxygen-free tank have no new sludge, and the sludge is extracted. Do not need.
A lot of ammonia nitrogen contained in the dehydrated filtrate is removed, and the nitrogen load on the water treatment can be reduced.

It is a flowchart of the nitrogen removal system of the dehydrated filtrate which concerns on this invention. This is an experimental device for a nitrogen removal system for dehydrated filtrate that is equipped with a high-concentration water treatment tank and a low-concentration sludge treatment tank.

The nitrogen removal system and nitrogen removal method of the dehydrated filtrate according to the present invention will be described in detail with reference to the drawings. FIG. 1 is a flowchart of the nitrogen removal system, and sewage containing organic matter that flows into the sedimentation tank 1 first. The separated water and the suspended matter are transferred to the aerobic reaction tank 2, and the precipitated sludge that has settled on the bottom of the tank is extracted into the adjustment tank 3. The separated water containing the organic matter flowing into the aerobic reaction tank 2 decomposes the organic matter in the activated sludge into nitrogen components by aeration.
The aerobically treated water is transferred to the final sedimentation basin 4 and the supernatant is sterilized by the sterilization apparatus 5 and discharged. A part of the sedimented and concentrated sedimentary sludge is returned to the aerobic reaction tank 2 as activated sludge, and the rest is extracted as excess sludge to the adjustment tank 3.
Precipitated sludge and excess sludge collected in the adjustment tank 3 are transferred to the anaerobic digestion tank 6, where organic matter in the sludge is decomposed by denitrifying bacteria to reduce the amount.
The digested sludge subjected to anaerobic treatment is supplied to a dehydrator 7 such as a screw press, and is solid-liquid separated into a dehydrated filtrate and a dehydrated cake.

As shown in FIG. 1, the adjustment tank 8 which temporarily stores the dehydrated filtrate separated into solid and liquid by the dehydrator 7 is installed, and the intermittent aeration 9 and the stirrer 10 are provided in the subsequent stage of the adjustment tank 8. A nitrification tank 11 and an oxygen-free tank 13 provided with a stirrer 12 are provided side by side. An extraction pump 14 for extracting a certain amount B of the supernatant liquid of the nitrification tank 11 between the nitrification tank 11 and the anoxic tank 13 and the agitators 10 and 12 of the nitrification tank 11 and the anoxic tank 13. An exchange pump 15 for alternately replacing the sewage having a uniform concentration in the tank is installed.
The oxygen-free tank 13 is provided with a return pump 16 that extracts a certain amount B of the supernatant and returns it to the front part of the aerobic reaction tank 2. In order to maintain the MLSS concentration (the amount of activated sludge suspended solids) in the anaerobic tank 13, the agitator 12 is stopped and gravity concentration is performed, and a certain amount B of the supernatant is extracted and returned to the aerobic reaction tank 2.
In order to secure the organic matter necessary for denitrification of the anaerobic tank 13, a water supply pump 17 that supplies the anaerobic tank 13 is initially installed in the settling basin 1, the SS of the first settling basin 1 is as small as possible, and the organic matter is A certain amount A of sewage is supplied to the anoxic tank 13 from many locations.

When the nitrification tank 11 and the oxygen-free tank 13 of the dewatered filtrate nitrogen removal system are started up, the excess sludge generated from the final sedimentation tank 4 is diluted with the dehydrated filtrate and supplied to the nitrification tank 11 and the oxygen-free tank 13. The MLSS concentration (the activated sludge suspended solid content) is adjusted to about 3,000 mg / L.
In addition, the organic matter collection destination of the nutrient source may be the supernatant of the first sedimentation basin 1 or the final sedimentation basin 4 of raw sludge.
In the nitrification tank 11, intermittent aeration is performed with intermittent aeration 9 while stirring with the stirrer 10, and in the anoxic tank 13, the oxygen-free dehydrated filtrate is stirred with the stirrer 12, and the ammoniac contained in the dehydrated filtrate. to start the removal of nitrogen _(NH 4 -N).

a. In the oxygen-free tank 13, the sewage is stirred in an oxygen-free state, and after the time necessary for denitrification has elapsed, the agitator 12 is stopped and gravity concentration is performed, and a certain amount of B supernatant is extracted and dehydrated by the return pump 16. It returns to the aerobic reaction tank 2 of the front | former stage of the machine 7.
Treated water from which ammoniacal nitrogen (NH ₄ -N) in the dehydrated filtrate has been removed can be returned.
b. In the nitrification tank 11, intermittent aeration of the dehydrated filtrate is performed, and after the time necessary for the nitrification treatment, the intermittent aeration 9 and the agitator 10 in the nitrification tank 11 are stopped, and the sewage treated with nitrification is concentrated by gravity and separated. A certain amount B of the supernatant is supplied to the anoxic tank 13.
The sewage in the nitrification tank 11 is withdrawn from the supernatant in order to maintain a predetermined MLSS concentration (amount of activated sludge suspended solids).
c. A certain amount B of the dehydrated filtrate stored in the adjustment tank 8 is sent to the nitrification tank 11.

d. The nitrification tank 11 is intermittently aerated and stopped at intervals of about 60 minutes by intermittent aeration 9 while stirring with a stirrer 10 so that dehydrated filtrate containing ammonia nitrogen (NH ₄ -N) does not become excessively aerated. And ammonia nitrogen (NH ₄ -N) is oxidized to nitrate nitrogen (NO ₃ -N) or nitrite nitrogen (NO ₂ -N) by nitrifying bacteria.
e. Ideally, the dissolved oxygen (MLDO) in the nitrification tank 11 is about 0.2 to 0.5 mg / L, but is difficult to adjust.
If the aeration is intermittent aeration for about 60 minutes, the maximum value of dissolved oxygen (MLDO) can be adjusted to about 2 mg / L, and the hydrogen ion concentration can be easily adjusted by maintaining the pH at 5 or more. Become.
The culture time of nitrifying bacteria and denitrifying bacteria can be obtained, the adjustment of aeration in the nitrification tank 11 is facilitated, and the inflowing dehydrated filtrate does not become excessively aerated. By putting oxygen-free conditions in the middle of operation, generation of microorganisms harmful to water treatment such as actinomycetes can be suppressed, and sludge sedimentation can be improved.

f. The nitrification tank 11 has a residence time required for nitrification after the dehydrated filtrate has flowed in, about one day, and while the agitator 10 in the nitrification tank 11 and the agitator 12 in the oxygen-free tank 13 are operated, About one-fifths of sewage is alternately exchanged by the exchange pump 15. The sewage to be replaced has a constant concentration in the tank by the stirrers 10 and 12, and the concentration in the tank does not change when discharged by the replacement pump 15.
g. Organic matter is supplied from the oxygen-free tank 13 to the nitrification tank 11 by exchanging sewage, and the MLSS concentration (active sludge suspended solids amount) in the nitrification tank 11 and the oxygen-free tank 13 is kept uniform at about 6,000 mg / L.
By alternately exchanging sewage in the nitrification tank 11 and the anoxic tank 13 while maintaining a low aeration state, the MLSS concentration (active sludge suspended solids amount) in the nitrification tank 11 and the anoxic tank 13 becomes appropriate.
While maintaining a uniform MLSS concentration, an appropriate organic substance is supplied to the nitrification tank 11 to suppress the pH drop and prevent the sludge floc from decomposing.
h. The residence time of the dehydrated filtrate in the nitrification tank 11 is retained for about one day in order to culture nitrifying bacteria and denitrifying bacteria.
The pH of the nitrification tank 11 decreases due to the nitrification reaction, but the decrease in pH can be suppressed by supplying dehydrated filtrate and exchanging sewage with the anoxic tank 13, and the pH does not become 5 or less by intermittent aeration.
By treating ammonia nitrogen contained in the dehydrated filtrate of the nitrification tank 11 to nitrate nitrogen and nitrite nitrogen, treated water containing the grown nitrifying bacteria and denitrifying bacteria can be supplied to the anoxic tank 13.

i. In the anoxic tank 13, nitrate nitrogen (NO ₃ —N) or nitrite nitrogen (NO ₂ —N) contained in the sewage is reduced to nitrogen gas (N ₂ ) by denitrifying bacteria while stirring with the stirrer 12. .
After a lapse of time necessary for denitrification, the sewage in the anaerobic tank 13 is stirred by the stirrer 12, and a fixed amount A of sewage is returned to the front part of the aerobic reaction tank 2 by the return pump 16. The temperature inside the tank is kept constant by the agitator 12, and the concentration in the tank is not changed by the discharge by the return pump 16.
j. First, a fixed amount A of sewage in a place where the SS in the first sedimentation basin 1 is as small as possible and contains a large amount of organic matter is caused to flow 2 to 4 times a day by the water pump 17. The organic matter as a nutrient source necessary for the sludge in the anaerobic tank 13 is first supplied from the sewage in the settling basin 1 to ensure an organic matter concentration (COD) required for denitrification of 30 to 40 mg / L.
k. A certain amount of B supernatant liquid that has undergone the denitrification process in the anaerobic tank 13 is returned to the aerobic reaction tank 2.
l. There is no increase in sludge due to the nitrogen removal system of the dehydrated filtrate, and no sludge is extracted.
By repeating the above operations a to j, the ammoniacal nitrogen contained in the dehydrated filtrate of the nitrification tank can be oxidized to nitrate nitrogen and nitrite by stirring and intermittent aeration, and the supernatant after nitrification is oxygen-free. It can be supplied to a tank and reduced to nitrogen gas by denitrifying bacteria. Nitrogen excessively contained in the dehydrated filtrate can be removed, and the nitrogen load in the water treatment process can be reduced.

The dehydrated filtrate obtained by solid-liquid separation of anaerobic digested sludge contains a large amount of ammonia nitrogen, and the nitrogen load is excessive in the water treatment step after the sludge treatment. Therefore, in order to reduce the load of the water treatment process, an apparatus for removing ammonia nitrogen was examined.
An experiment was conducted by using a 20 L tank of a high concentration water treatment tank 18 and a low concentration sludge treatment tank 19 shown in FIG.
(1) Experimental apparatus a: A continuous aeration 20 and an agitator 21 were installed in a high-concentration water treatment tank 18, and an intermittent aeration 22 and an agitator 23 were installed in a low-concentration sludge treatment tank 19.

(2) Experimental condition a: As a substrate,
The BOD source supplies 40 mL of unadjusted milk (BOD about 78000 mg / L) to the water treatment tank 18 twice a day as a component corresponding to the organic matter contained in the initial sedimentation effluent of the initial sedimentation basin.
As for the nitrogen component, 20 L of dehydrated filtrate of digested sludge (NH ₄ —N of about 500 mg / L) is supplied to the sludge treatment tank 19.
b: The continuous aeration 20 of the high-concentration water treatment tank 18 is set to continuous aeration, and the aeration stop for gravity concentration of the reaction solution is set to 2 h / day.
c: The intermittent aeration 22 of the low-concentration sludge treatment tank 19 performs aeration and stop at 60 minute intervals.
d: The air volume of the continuous aeration 20 and the intermittent aeration 22 is adjusted so that MLDO (dissolved oxygen) is 1 mg / L or less.
e: In order to maintain the MLSS concentration (the amount of activated sludge suspended matter) in the water treatment tank 18 of the water treatment system and the sludge treatment tank 19 of the sludge treatment system, the sludge 4L is appropriately replaced.
f: Water quality measurement: Water quality measurement such as MLDO, MLSS, MLVSS, BOD, COD, chromaticity, etc. is performed.

(3) Operation procedure a: The continuous aeration 20 and the agitator 21 in the water treatment tank 18 and the intermittent aeration 22 and the agitator 23 in the sludge treatment tank 19 are started.
b: After aeration and agitation of the water treatment tank 18 and the sludge treatment tank 19 for 1 hour, the process is stopped to make a supernatant.
c: 4 L of the supernatant liquid of the water treatment tank 18 is removed.
d: 4 L of the supernatant liquid 19 is introduced into the water treatment tank 18.
e: 40 mL of milk is put into the water treatment tank 18 and 4 L of the digested sludge dehydrated filtrate is put into the sludge treatment tank 19.
f: The water treatment tank 18 and the sludge treatment tank 19 are stirred for only one hour in order to ensure oxygen-free conditions.
g: Stirring and aeration of the water treatment tank 18 and the sludge treatment tank 19 are restarted.
h: 4L of the sludge in the water treatment tank 18 and the sludge treatment tank 19 is exchanged after 4 hours.
i: Aeration in the water treatment tank 18 is stopped, 40 mL of milk is added, and aeration is resumed after stirring for 1 hour.
j: Aeration is performed by reducing the air volume at night.

(4) Establishment of low aeration conditions Setting the Aeration Air Volume The air volume of the water treatment tank 18 and the sludge treatment tank 19 was 0.1 to 1.6 L / min. The aeration system was examined for various conditions such as continuous aeration and intermittent aeration for 10 minutes or 1 hour.
Assuming fluctuations in the quality of inflow water and the amount of water, in order to secure MLDO (dissolved oxygen), which is a low aeration condition, to about 0.5 mg / L, 1 hour aeration and 1 hour stop intermittent aeration are the closest conditions. I understood that.
a: Oxidation of organic matter (oxygen respiration, example of glucose)
_{C 6 H 12 O 6 + 6O} 2 → 6CO 2 + 6H 2 O
b: Progress of nitrification (oxygen breathing) NH ₄ ⁺ + 2O ₂ → NO ₃ ⁻ + H ₂ O + 2H ⁺
c: Progress of denitrification (oxygen breathing), (example of glucose)
5C ₆ H ₁₂ O ₆ + 24NO ₃ ⁻ → 30CO ₂ + 18H ₂ O + 24OH ⁻ + 12N ₂

B. As a result of the examination, in intermittent and low aeration, oxygen respiration and nitric acid respiration of the oxygen abc proceed in the system at the same time, organic matter removal and nitrogen removal are performed, and it is considered that pH reduction does not occur.
At this time, MLDO (dissolved oxygen) was about 0.5 mg / L.
The pH decreases as the progress of nitrification proceeds, but at the same time the pH recovers as denitrification proceeds.
However, it has been difficult to set conditions for constantly maintaining MLDO (dissolved oxygen) at about 0.5 mg / L in the presence of fluctuations in flow rate, fluctuations in water quality, progress of reaction in the system, and the like.

C. PH reduction by nitrification and pH recovery by denitrification Conventional standard activated sludge method and OD method lower the pH as nitrification progresses, but at the same time the pH recovers when denitrification proceeds.
The reason why the pH of the treated water does not decrease is considered that nitrification and denitrification occur simultaneously in the treatment system.
The reason why the nitrogen removal rate is higher in the intermittent low-aeration sludge treatment method than in the standard activated sludge method is that denitrification (nitrification respiration) is likely to proceed.
From the experimental results, when nitrification proceeds in the absence of a substrate (milk, glucose, excess sludge, etc.), the pH drops to 5 or less and nitrification stops.
Furthermore, in order to advance nitrification, a buffering agent such as sodium bicarbonate must be added.
NaHCO ₃ + H ⁺ → Na ⁺ + CO ₂ + H ₂ O
In order to prevent the pH from decreasing, crushed oyster shells (CaCO ₃ ) were tried, but no effect was seen.
When the pH was lowered to 5 or less, the sludge was disassembled and the supernatant was suspended.
As a solution, in order to create an oxygen-free condition after adding the substrate, aeration was stopped and only agitation was performed. This is an operating condition called the AO method, and the foaming phenomenon was settled by an experiment using this method. The foaming phenomenon seems to be caused by the outbreak of actinomycetes.
It can be predicted that a decrease in pH and accumulation of nitric acid will occur in a sludge treatment tank in which nitrate respiration is difficult due to a shortage of substrates.
Addition of a substrate such as influent sewage to the sludge aerobic nitrification tank, or the addition of sludge from the sedimentation basin first, it is assumed that nitric acid respiration is promoted, so that alkali supplementation and nitrogen removal are performed. There is a possibility of reducing sludge generation.

D. From the beginning of the experiment to suppress the foaming phenomenon, a foaming phenomenon thought to be caused by actinomycetes occurred in the water treatment tank 18 and the sludge treatment tank 19, and the sludge floc was disassembled. When the foaming phenomenon occurs, the sludge balance due to sludge outflow or the like cannot be obtained. As a solution, aerobic conditions were created after the addition of milk, so aeration was stopped and only stirring was used. This is an operating condition called the AO method, and the foaming phenomenon has subsided through experiments using this method. Incorporation of oxygen-free conditions after low aeration can suppress foaming and improve sedimentation of sludge.
It is considered that intermittent and low aeration can suppress the generation of actinomycetes and improve the sludge sedimentation by putting oxygen-free conditions in the middle of operation.
Based on the above experimental results, the dehydrated filtrate of digested sludge is not returned to the first stage of the water treatment facility, but supplied to the nitrification tank. At the same time, surplus sludge, inflow sewage, initial settling sludge, etc. are slightly added as nitrogen sources. After removal, it can be considered that the excess sludge generation amount decreases if it is returned to the water treatment system.

The nitrogen removal system and the nitrogen removal method of the dehydrated filtrate according to the present invention include a nitrification tank provided with intermittent aeration and a stirrer for removing a lot of ammonia nitrogen contained in the dehydrated filtrate after sludge treatment, Since the anaerobic tank is equipped with two aerobic tanks equipped with a stirrer, the nitrification tank that performs intermittent aeration is in a state similar to low aeration, and the time for nitrifying bacteria and denitrifying bacteria is obtained. By adding conditions, the generation of microorganisms harmful to water treatment can be suppressed, and sludge settling can be improved.
The organic matter of nutrient source in the oxygen-free tank can be secured by first putting sewage in the sedimentation basin, and the nitrification tank can be kept at a uniform MLSS concentration by replacing the sewage with the oxygen-free tank to prevent the sludge floc from decomposing. . Nitrification tanks and oxygen-free tanks do not generate new sludge and do not require sludge extraction.
A lot of ammonia nitrogen contained in the dehydrated filtrate is removed, and the nitrogen load on the water treatment can be reduced.
Therefore, a two-tank nitrification tank is installed after the adjustment tank that temporarily stores dehydrated filtrate in a sludge treatment process such as a sewage treatment plant, a human waste treatment plant, or an industrial wastewater treatment plant. If an oxygen-free tank is installed, a lot of ammonia nitrogen contained in the dehydrated filtrate is removed, and the burden on the water treatment process can be reduced.

DESCRIPTION OF SYMBOLS 1 First sedimentation tank 2 Aerobic reaction tank 6 Anaerobic digestion tank 7 Dehydrator 8 Adjustment tank 9 Intermittent aeration 10 Stirrer 11 Nitrification tank 12 Stirrer 13 Anoxic tank 14 Extraction pump 15 Replacement pump 16 Return pump 17 Water feed pump A Fixed amount B Fixed amount

Claims (6)

Sludge containing organic matter is first allowed to flow into the settling basin (1), and the digested sludge treated in the aerobic reaction tank (2) and anaerobic digestion tank (6) is separated into solid and liquid using a dehydrator (7). In the sludge treatment system for temporarily storing the filtrate in the adjustment tank (8), a nitrification tank (11) is disposed after the adjustment tank (8), and intermittent aeration (9) is provided in the nitrification tank (11). In addition to providing a stirrer (10), a stirrer (12) is provided in the anoxic tank (13) attached to the nitrification tank (11), and the supernatant of the nitrification tank (11) is drawn into the anoxic tank (13). An extraction pump (14) to be discharged and an exchange pump (15) for alternately exchanging sewage in the nitrification tank (11) and the anoxic tank (13) are installed, and dehydration containing ammonia nitrogen is performed while intermittent aeration is performed. A nitrogen removal system for dehydrated filtrate, characterized by treating the filtrate. A return pump (16) for returning the supernatant or sewage from the anaerobic tank (13) to the aerobic reaction tank (2) upstream of the dehydrator (7); The nitrogen removal system for dehydrated filtrate according to claim 1, further comprising a water pump (17) for supplying sewage containing organic matter of 1). Sludge containing organic matter is first allowed to flow into the settling basin (1), and the digested sludge treated in the aerobic reaction tank (2) and anaerobic digestion tank (6) is separated into solid and liquid using a dehydrator (7). In the sludge treatment system that temporarily stores the filtrate in the adjustment tank (8), the supernatant is introduced from the nitrification tank (11) that performs intermittent aeration downstream of the adjustment tank (8), and the nitrification tank (11). An anaerobic tank (13) that stirs and stirs in water, and a fixed amount (B) of the dehydrated filtrate stored in the adjustment tank (8) is fed to the nitrification tank (11) and subjected to intermittent aeration while stirring. Nitrification of ammonia nitrogen contained in the liquid is performed, and after the time necessary for nitrification treatment, stirring and aeration of the nitrification tank (11) are stopped, and a large amount of nitrate nitrogen and nitrite nitrogen that have been nitrified is contained. When a certain amount (B) of the supernatant is supplied to the oxygen-free tank (13) and reduced to nitrogen gas, In addition, the sewage in the nitrification tank (11) and the anoxic tank (13) is alternately exchanged after the nitrification treatment, and denitrifying bacteria grown by intermittent aeration are supplied to the anoxic tank (13). A method for removing nitrogen from a dehydrated filtrate, characterized by maintaining an appropriate organic substance concentration and preventing pH reduction of a nitrification tank (11) and decomposition of sludge flocs. In order to prevent the dehydrated filtrate flowing into the nitrification tank (11) from being excessively aerated, intermittent aeration is performed with a 60-minute cycle while stirring, the upper limit of dissolved oxygen in the tank is set to 2 mg / L or less, and the hydrogen ion concentration is reduced. While maintaining the pH at 5 or more, the sewage in the nitrification tank (11) and the anoxic tank (13) is replaced once a day with the capacity of about one fifth of the nitrification tank (11), and the nitrification tank The method of removing nitrogen from the dehydrated filtrate according to claim 3, wherein the MLSS concentrations in (11) and the oxygen-free tank (13) are maintained at about 6,000 mg / L. After the time necessary for denitrification of the anaerobic tank (13), the stirring of sewage is stopped, gravity concentration is performed, and a certain amount (B) of supernatant liquid intermittently flows from the nitrification tank (11) The dehydrated filtrate according to claim 3 or 4, wherein the same amount of the denitrified supernatant is returned to the aerobic reaction tank (2) upstream of the dehydrator (7) in advance. Nitrogen removal method. While stirring in the oxygen-free tank (13), a fixed amount (A) of sewage is returned to the aerobic reaction tank (2) in front of the dehydrator (7), and a fixed amount containing the organic matter in the first sedimentation tank (1) The sewage of (A) is allowed to flow into the anoxic tank (13) 2 to 4 times a day to ensure a COD concentration of 30 to 40 mg / L necessary for denitrification. The method for removing nitrogen from the dehydrated filtrate according to any one of the above.

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