JP2003024985A - Dentrification apparatus and dentrification method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To perform high load treatment by efficiently propagating ANAMMOX bacteria and holding the propagated ANAMMOX bacteria to high concentration in the system, in performing the biological denitrification of raw water containing ammonia nitrogen and nitrous nitrogen by the ANAMMOX bacteria being autotrophic denitrifying bacteria using ammonia nitrogen as an electron doner and nitrous nitrogen as an electron acceptor. SOLUTION: The denitrified treated liquid of a denitrification tank 1 holding the ANAMMOX bacteria is subjected to membrane separation in a membrane separator 3 to obtain treated water. Both of or either one of the concentration of ammonia nitrogen and the concentration of nitrous nitrogen in the denitrified treated liquid separated in the membrane separator 3 is set to 0-3 mg/l.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to an autotrophic denitrifying microorganism in which raw water containing ammoniacal nitrogen and nitrite nitrogen is used as an electron donor for ammoniacal nitrogen and an electron acceptor for nitrite nitrogen. The present invention relates to a denitrification device and a denitrification method for biological denitrification by the action of

[0002]

2. Description of the Related Art Conventionally, as a method for removing nitrogen in water, nitrifying bacteria oxidize ammoniacal nitrogen to nitrite nitrogen or nitrate nitrogen, and then denitrifying bacteria by adding an electron donor such as methanol. A method is known in which nitrate nitrogen or nitrate nitrogen is reduced to nitrogen gas to remove nitrogen from water.

This method requires more oxygen than the oxidizing power required to oxidize ammoniacal nitrogen to nitrogen gas, and thus requires a large amount of oxygen, and the energy cost for supplying this oxygen to microorganisms is high. Expensive. In addition, there is a cost to add an organic substance such as methanol as an electron donor for the denitrification reaction, and denitrifying bacteria that ingested this organic substance and proliferated become excess sludge, so that the disposal cost of the waste is also increased. There is a problem of being expensive. In particular, nitrate nitrogen is in a more oxidized state as compared with nitrite nitrogen, so the cost of oxygen supply for this is also high, and more electron donors are needed to reduce it. There is also a large amount of excess sludge.

On the other hand, in recent years, under anoxic conditions, ammonia nitrogen is used as an electron donor and nitrite nitrogen is used as an electron acceptor to react them with each other to produce nitrogen gas. A denitrification method using nitrifying microorganisms has become known (Microbiology 142 (1996), p2187-21.
96 etc.). Hereinafter, this reaction is referred to as an ANAMMOX reaction, and this autotrophic denitrifying microorganism group is referred to as an ANAMMOX bacterium. According to this method, it is possible to oxidize ammoniacal nitrogen using the oxidizing power of nitrite nitrogen, so nitrogen can be removed with the same amount of oxygen consumption as the theoretical amount, thus saving energy. can do. Further, since it is not necessary to add an organic substance such as methanol, the cost for that can be saved. This microorganism is an autotrophic bacterium. Compared with bacteria that denitrify using organic matter, the amount of excess sludge generated per reducing nitrite nitrogen is one-fifth or less, and the amount of waste generated There is also an advantage that can be significantly reduced.

When carrying out this denitrification reaction, nitrite nitrogen may be generated by oxidizing a part of the ammoniacal nitrogen in the wastewater, or by mixing with other wastewater containing nitrite nitrogen. You may.

As a form of a biological denitrification tank using ANAMMOX bacteria, raw water is passed upward through a column packed with a carrier suitable for adhering microorganisms such as sand, synthetic resin and gel, and nitrogen compounds are formed on the surface of the carrier. A method is used in which microorganisms are brought into contact with each other to progress the denitrification reaction. In this case, a carrier having a large specific surface area is preferable, and a particle size of 0.1 to 1 is particularly preferable.
Shapes of about 0 mm, such as granules, strings, cylinders, and gears, are known. The carrier is preferably gently flowing in water, and is made to flow by a gas generated by denitrification, a gas injected from the outside, a stirrer, or the like.

On the other hand, the activated sludge is used to remove organic matter and nitrogen in the wastewater, the treated water containing almost no SS is taken out from the treated solution of the activated sludge, and the concentrated microorganisms are returned to the reaction tank. As one of them, a membrane separation method is known. This method uses microfiltration (M
F) or ultrafiltration (UF) membrane is used, SS is 0
It has the advantage that about 2 mg / L of clear treated water can be taken out. Further, since the microorganism concentration in the reaction tank can be usually increased to 5,000 to 35,000 mg / L for operation, there is also an advantage that a large load per reaction tank volume can be taken.

When the membrane separation method is adopted for BOD removal, the volumetric load of the reaction tank is usually 0.5 to 2 kg-BOD / m ³
/ Day, the nitrification load when adopted in the nitrification / denitrification method is 0.1 to 0.5 kg-N / m ³ / day, and the denitrification load is 0.1 to 1.0 kg-N / m ³ / day. The range of is often used. Also, the retention time of the sludge in the reaction tank (SR
T) is usually 5 to 100 days, especially 10 depending on the load.
~ 50 days is adopted.

[0009] In this case, in order to prevent clogging of the membrane surface, the suspension concentrated on the membrane surface is usually provided by applying a water flow (cross flow) of about 5 to 400 cm / sec in a direction parallel to the membrane surface. The material is diffused and continuously filtered. As means for giving a cross flow, there are known a pump, a method of utilizing a water flow generated by aeration, a means of moving, for example, rotating the membrane itself to generate a relative water flow. In order to obtain the transmembrane pressure difference (hereinafter also referred to as “filtration pressure difference”) that is the driving force for membrane filtration, the positive pressure or the negative pressure generated by the pump is used, the head difference is used, or Both are used.

[0010] Depending on the type of membrane, a backwashing operation is carried out in which the sludge adhering to the membrane surface is peeled off by periodically backwashing a gas such as washing water or air. In addition, by continuing membrane filtration, membrane contamination that cannot be completely removed by crossflow or backwash occurs, filtration resistance increases, filtration differential pressure increases or membrane flux (permeation flux) decreases, and You cannot get the amount of water. In this case, physical cleaning is performed to physically remove contaminants on the film surface with a sponge ball or spray, or an alkali such as caustic soda, an acid such as sulfuric acid, oxalic acid, citric acid, or sodium hypochlorite. Chemical cleaning is performed to remove contaminants by dissolving or decomposing the contaminants on the film surface using an oxidizing agent such as hydrogen peroxide solution. Such physical cleaning or chemical cleaning is usually performed about once every 2 to 10 months.

The cause of membrane contamination is cake contamination in which sludge attached to the membrane surface becomes a dehydrated cake and adheres firmly, and high molecular weight organic matter that flows in from raw water or is produced by microorganisms.
Those that do not pass through the membrane are gel contamination in which the membrane surface is concentrated and gelled, and slime contamination due to the growth of microorganisms in the form of slime on the membrane surface.

Further, since the separation membrane deteriorates in about 2 to 10 years and does not exhibit a predetermined performance, it needs to be replaced regularly.

By the way, the maximum specific growth rate of ANAMMOX is about 0.065 day ^-1 (1.06 per day).
It grows 5 times slower and it is very difficult to secure a large amount of bacterial cells. On the other hand, ANAMMOX that exists in the natural world
Since the amount of bacteria is very small, it is necessary to sufficiently grow the bacterial cells in order to start up the denitrification device using the ANAMMOX bacteria. For this purpose, the ANAMMOX bacteria can be grown to the maximum in an ideal environment. It is necessary to allow the ANAMMOX bacterium, which has grown near the speed and has grown, to remain in the system efficiently.

In order to grow the ANAMMOX bacterium at the maximum rate, it is necessary to sufficiently supply substances such as ammoniacal nitrogen, nitrite nitrogen, and carbonate radicals, which are substrates for this bacterium, but they must be attached to a carrier. When grown, it is difficult to penetrate the substrate to the inside of the attached biofilm, and thus the growth rate is slower than the maximum rate, which is inefficient. Further, in order to penetrate the substrate deep inside the biofilm, it is necessary to maintain the substrate concentration in the liquid at a high level. On the other hand, if the substrate, especially nitrite nitrogen, is present at a high concentration, AN
There is also a problem that the AMMOX bacterium is inhibited, and it does not proliferate or is killed, which has the opposite effect. Also, when operating as an actual denitrification device, the ANAMMOX on the carrier surface
Since the maximum load cannot be applied until the bacteria grow sufficiently, the start-up is slow. In order to avoid this
It is possible to add a carrier with sufficient adherence of AMMOX bacteria to the denitrification tank, but for this purpose, it is necessary to pre-culture ANAMMOX bacteria in a reaction tank of the same size as the denitrification device to be operated. Therefore, the cost of the culture device is high and the installation space is required. In addition, cultured ANAMMO
The cost of transporting X bacteria is also high.

Further, a problem in growing the ANAMMOX bacteria on the surface of the carrier is that a part of the ANAMMOX bacteria on the surface of the carrier is always exfoliated into the liquid and flows out to the treated water. Especially, finally, the surface of the carrier is ANAMMO.
Saturated with X bacteria, the amount of ANAMMOX bacteria that grows and the amount of ANAMMOX bacteria that exfoliate will be balanced.
As the amount of adhered NAMMOX bacteria increases, the amount of peeling also increases, and the growth rate of the ANAMMOX bacteria and the accompanying increase in denitrification capacity are apparently lower than the above-mentioned 0.065day ^{- 1} . In fact, the inventor
Granules mainly composed of methanogenic bacteria
An attempt was made to grow by attaching OX bacteria to the grown AN.
The proportion of AMMOX bacteria remaining in the system was 10 to 75%, and the amount of bacteria flowing out of the system increased with the growth of ANAMMOX bacteria.

The present inventor uses the carrier as described above to
As a result of studies to solve the problem in the case of growing NAMMOX bacteria, it was found that it is also possible to grow and use ANAMMOX bacteria in suspension. In this case, since the bacterial cells form relatively small flocs with a particle size of 0.1 mm or less, the permeation of the substrate does not limit the growth and the growth is not hindered. Denitrification can be performed. In addition, the bacterial cells thus grown can be concentrated to a high concentration for operation by precipitating them over time or by using a mechanical concentrating means. Supply is also easy.

As described above, in order to grow the ANAMMOX bacteria in suspension and remove nitrogen, the cells after the reaction are separated from the treated water, and the concentrated cells are transferred to the reaction tank again. Need to bring back. As the separation / concentration means for this purpose, precipitation, centrifugal concentration, filtration, pressure floating concentration, etc. can be considered as in the case of activated sludge, but the method by precipitation is the cheapest and the operation is simple.

FIG. 6 shows a denitrification device using a settling tank for the separation of ANAMMOX bacteria. This denitrification device is mainly composed of a denitrification tank 1 and a sedimentation tank 2. The denitrification tank 1 is provided with a stirrer 1M, and the sedimentation tank 2 has a feed well 2F into which a denitrification treatment liquid flows and a mud collecting unit. Rake 2M is provided. The denitrification tank 1 and the precipitation tank 2 have a closed structure, and a denitrification gas discharge pipe 15A for discharging the denitrification gas from each of the tanks 1 and 2,
15B and 15 are provided.

Raw water is introduced into the denitrification tank 1 through a raw water inflow pipe 11, is subjected to denitrification treatment, and is then transferred to a settling tank 2 through a communication pipe 12 for precipitation separation. The separated liquid separated in the settling tank 2 is discharged out of the system as treated water through the treated water outflow pipe 13.
The separated sludge is returned to the denitrification tank 1 by a sludge return pipe 14 equipped with a pump P.

The volume of the denitrification tank 1 is determined so that the ammonia nitrogen load is, for example, 0.1 to 2 kg-N / m ³ / day. The area of the settling tank 2 is determined so that the water area load is, for example, 1 to 20 m / day with respect to the inflowing raw water amount.

[0021]

However, when the present inventor attempted to separate flocs containing ANAMMOX bacteria by precipitation, part of them precipitated, but part of them floated, and
Since the separation could not be performed well, the ANAMMOX bacteria could not be maintained at a high concentration in the system, and the performance of the denitrification tank could not be maintained high. In addition, the apparent specific growth rate is 0.035 to 50 even if good separation can be achieved.
0.055 day ^-1 and propagated ANAMMOX
The proportion of the bacteria remaining in the system was 55 to 85%.

By the way, the anammox bacterium loses its activity when nitrite nitrogen is present at a high concentration and is inhibited. The concentration at which this inhibition starts is 50 to 200 mg / L, and the higher the concentration, the more severe the inhibition. In the case of being hindered by such nitrite nitrogen, or in an appropriate pH range of 6 to
Under conditions that are unsuitable for the growth of bacteria, such as when the pH value is out of the range of 9 or when water containing dissolved oxygen is touched, the biofilm method makes it easy for ANAMMOX to peel off and precipitate. In the tank, the amount of outflow to treated water is higher than usual. On the other hand, in order to recover from such an inhibitory environment, it is important to remove the cause of inhibition as soon as possible, and for that purpose, the nitrite nitrogen is 200 mg / L or less, preferably 50 mg / L or less and the pH is 6 to 9 , Preferably 6.5 to 8.5, dissolved oxygen 0 to 0.1 mg / L, preferably 0 to 0.05 mg / L water is used to replace the inside of the ANAMMOX reaction tank, and an environment where ANAMMOX bacteria are not inhibited It is desirable to do.

However, in the conventional method using a biofilm or the method using precipitation separation, since it is difficult to separate the microorganism from the treated water at the same time as the inhibition, water having no inhibitory effect as described above is used. Trying to replace it, ANAMMOX
Since bacteria will flow out at the same time, promptly ANAMMO
There is a drawback that the inhibitor in the X reaction tank cannot be removed.

The present invention solves such a problem, and
AMMOX bacteria are grown in suspension to perform biological denitrification,
Efficiently isolate the ANAMMOX bacteria from the denitrification treatment liquid,
A denitrification device and a denitrification device that can perform efficient biological denitrification by maintaining a high concentration of ANAMMOX bacteria in the system, and can quickly remove the inhibitor even if it accumulates in the system The purpose is to provide a method of nitrification.

[0025]

A denitrification apparatus of the present invention has an inlet for raw water containing ammoniacal nitrogen and an outlet for a treatment liquid, and uses ammoniacal nitrogen as an electron donor and nitrite A denitrification tank that biologically denitrifies in the presence of nitrite nitrogen by the action of a denitrifying microorganism that uses nitrogen as an electron acceptor, and the effluent of the denitrification tank or the liquid in the denitrification tank is membrane-separated to perform the denitrification. It is characterized by comprising a membrane separation means for separating microorganisms and treated water.

The denitrification method of the present invention uses raw water containing ammoniacal nitrogen as an electron donor with ammoniacal nitrogen,
A denitrification step of biologically denitrifying in the presence of nitrite nitrogen by the action of a denitrifying microorganism having nitrite nitrogen as an electron acceptor, and a treatment liquid of the denitrifying step is subjected to membrane separation to remove the denitrifying microorganism. In a denitrification method having a membrane separation step of separating into sludge containing water and treated water, either or both of the concentration of ammonia nitrogen and the concentration of nitrite nitrogen in the treatment liquid of the denitrification step of separating in the membrane separation step Is 0 to 5 mg / L.

The present inventor has repeatedly studied to efficiently separate the ANAMMOX bacteria from the denitrification treatment liquid, and
When using a membrane separation means to separate flocs containing bacteria,
Outflow of SS completely disappeared, and specific growth rate was 0.06
An ideal value of ^{0 to} 0.065 day ^-1 is obtained,
In addition, the ratio of the propagated ANAMMOX bacteria in the system is 9
Since it is 5% or more, it has been found that it is optimal to use a membrane separation means to efficiently grow the ANAMMOX bacteria, and the present invention has arrived at the denitrification device of the present invention.

That is, when solid-liquid separation of ANAMMOX bacteria is carried out using a settling tank, a part of ANAMMOX bacteria flows out into the treated water, and the reason why the amount of ANAMMOX bacteria cannot be effectively increased is that ANAMMOX bacteria. It is considered that the flocculation ability of the bacteria was weak, and the sedimentation separation was difficult because the dispersed cells that were not incorporated into the flocs had a slow sedimentation rate.

On the other hand, the weak floc forming ability was presumed to be due to the small amount of colloid-like substances secreted out of the cells. Therefore, the present inventor can reduce gel contamination derived from a polymer colloidal substance, which is a problem in membrane separation of activated sludge and the like, in the case of ANAMMOX bacteria by utilizing such characteristics of ANAMMOX bacteria, We thought that stable membrane filtration could be performed.

In practice, the membrane separation means was used for solid-liquid separation of ANAMMOX bacterium, and the amount of the substance, which was blocked by the membrane separation, of the colloidal substances produced outside the cells was centrifuged. When the difference in TOC concentration between the supernatant and the membrane-permeated water was evaluated, it was found that this value was 5 mg / L or less, and it was confirmed that the production of colloid-like substances was slight. When the membrane separation method is applied to ordinary activated sludge, this value is about 20 to 300 mg / L, and particularly when it is 100 mg / L or more, gel contamination on the membrane surface occurs violently.

Further, if it is a membrane separation means, ANAMMO
Even when the sedimentation property is extremely deteriorated due to the inactivation of X bacteria, it is possible to quickly discharge only the treated water without causing the ANAMMOX bacteria to flow out. Therefore, even when the inhibitor accumulates in the tank, by providing a means for supplying water having no inhibitory effect and operating it together with the membrane separating means, the inhibitor in the system can be quickly washed out,
The inside of the ANAMMOX reaction tank can be quickly returned to a non-inhibitory environment.

However, when the membrane separating means was used, the presence of deposits on the membrane surface was observed as the operation was continued. Since this adherent had a red color similar to that of ANAMMOX bacteria, the suspended ANAMMOX
Bacteria were concentrated on the surface of the film and caked, or A on the surface of the film
It was estimated that NAMMOX bacteria grew in a slime form.

On the other hand, since the filtration pressure difference showed a rapid rise, it was necessary to perform chemical cleaning once every 2 to 4 weeks in order to perform stable membrane filtration.

However, such frequent chemical cleaning not only takes time and cost, but also accelerates the deterioration of the membrane and increases the membrane replacement cost. That is, one of the main causes of deterioration of the film is a chemical reaction caused by contact with the cleaning chemical liquid, and the life of the film becomes shorter as the cleaning frequency increases. Further, the increase in the frequency of chemical cleaning also poses a problem in the treatment of waste chemicals generated in membrane cleaning. This waste chemical contains a large amount of dissolved organic matter from the film surface, and an oxidizing agent such as sodium hypochlorite remains. Acids such as oxalic acid and citric acid are organic substances themselves.

When the membrane filtration means was applied to the activated sludge, it was easy to treat these waste chemicals with the activated sludge. That is, organic substances such as oxalic acid and citric acid eluted from the membrane surface can be easily removed by the organic matter removal ability of the activated sludge, and an oxidizing agent such as sodium hypochlorite is also added to the activated sludge. If so, it reacts with a part of the bacterial cells, easily loses its oxidizing power and is neutralized. However, A
Since NAMMOX bacteria do not have the ability to remove organic substances, they cannot process waste chemicals, and if such a large amount of organic substances are added, they will exert an inhibitory effect on ANAMMOX bacteria and lose their denitrifying ability. Further, an oxidizing agent such as sodium hypochlorite also has a strong inhibitory effect on ANAMMOX bacteria. The oxidative power of sodium hypochlorite is lost by sterilizing ANAMMOX bacteria, but unlike activated sludge, since ANAMMOX bacteria take a long time to grow, the activity of ANAMOX bacteria inactivated by sodium hypochlorite is low. Is not easily recovered. Thus, ANAMM
In the membrane separation of OX bacteria, the waste chemical generated by the chemical cleaning of the membrane cannot be treated in the system like in the case of activated sludge, and it is necessary to discharge it to the outside of the system for disposal. ,
There is a problem that it takes more labor and cost.

Further, since the membrane separation device is expensive, it cannot be said that it is advantageous from the viewpoint of cost, but in addition to this, as described above, the frequent labor of chemical cleaning and Considering cost and high membrane replacement cost, AN
The cost reduction effect by using AMMOX bacteria is low.

It is considered that the membrane contamination during the membrane separation of the ANAMMOX bacteria is due to the proliferation of the ANAMMOX bacteria on the membrane surface to form slime. According to the inventor's observation, AN
AMMOX bacteria tend to attach especially at high flow rates,
A large amount of ANAMMOX slime adhered not only to the membrane surface but also to the wall surface of the water tank and the wall surface of the water pipe to the membrane separation device.

However, the present inventors have discovered that this slime contamination is unlikely to occur when the concentration of at least one of the ammonia nitrogen concentration and the nitrite nitrogen concentration is low.

That is, the reason why the adherence of the ANAMMOX bacteria is strong is that the movement of the ANMMOX bacteria to other places by the flow of water is carried out from the optimum habitat because the habitat of the ANAMMOX bacteria in nature is limited. This is probably because it is particularly necessary to resist this and stay in an environment suitable for growth. On the other hand, since it is disadvantageous for the ANAMMOX bacterium to remain in a place without a substrate, it is considered that the adhesion phenomenon does not occur in such a place, and rather, the peeling is rather positive. Therefore, if one of the substrates, ammoniacal nitrogen and nitrite nitrogen, is small, slime attachment due to the growth of ANAMMOX bacteria on the membrane surface is prevented. And
The present inventor has conducted further studies and specified the concentration of a substrate capable of preventing membrane contamination. As a result, the concentration of either ammoniacal nitrogen or nitrite nitrogen is 0 to 5 mg / L, preferably 0 to 2 mg / L. When L, it was found that the membrane contamination by ANAMMOX slime can be prevented and the frequency of chemical cleaning can be reduced, and the denitrification method of the present invention was reached.

Since the denitrification method of the present invention reduces membrane contamination, the cost for chemical cleaning of the membrane and the membrane replacement cost are reduced. Therefore, the membrane separation method should be adopted at a practical cost. Is possible.

[0041]

Embodiments of the denitrification apparatus and denitrification method of the present invention will be described in detail below.

The denitrification apparatus of the present invention is mainly composed of a denitrification tank for holding ANAMMOX bacteria and a membrane separation apparatus for membrane-treating the denitrification treatment liquid in this denitrification tank.

The denitrification tank according to the present invention is a means for supplying wastewater or solution containing nitrite nitrogen and wastewater or solution containing ammonia nitrogen, or wastewater or solution containing ammonia nitrogen and nitrite nitrogen. It is preferable to provide a supply means, preferably a stirring means for gently stirring the inside of the denitrification tank, for example, a stirrer, a submersible pump, or a gas blowing means.

It is preferable that a pH detecting means is provided in the denitrification tank, and a means for supplying an acid or an alkaline agent or both is provided if necessary. The acid used is hydrochloric acid,
Sulfuric acid, carbonic acid and the like are preferable, and as the alkali, sodium hydroxide solution and the like are preferable.

Further, the denitrification tank is usually of a closed structure so that air is not mixed therein, and the denitrification gas generated by the denitrification reaction is discharged to the outside through a check valve or a water seal part in order to prevent backflow of air from the outside. It

Further, since scum is often generated in the upper part of the denitrification tank, it is preferable to provide a scum crushing means, and a foam cutting cutter for crushing the floating scum is provided near the water surface or near the water surface. It is effective to stir the water surface by stirring with a stirring blade, or to cause the swirling flow in the water tank to sufficiently entrain sludge that floats and concentrates near the water surface into the denitrification tank. Particularly, as a means for causing the swirling flow, it is preferable to blow an anaerobic gas, and in this case, it is easy to blow the denitrifying gas in the upper part of the denitrification tank into the denitrification tank by pressurizing it with a blower or a compressor. The amount of gas blown is 1 to 5 with respect to the bottom area of the denitrification tank
0 Nm ³ −gas / m ² −bottom surface / hr is preferable, and more preferably 2 to 20 Nm ³ −gas / m ² −bottom surface / hr.
The degree is good. The gas may be blown continuously or intermittently, but only when scum occurs intermittently about 1 to 50 times a day, more preferably about 4 to 20 times, and the blowing time per one time is 1 to 60 minutes, preferably Is preferably performed for about 3 to 30 minutes. It is preferable to partition the gas blowing part with a baffle plate or the like and partition the rising part and the descending part from the viewpoint of the stirring effect and the defoaming effect.

It is particularly preferable to install a submerged membrane in the rising water flow due to the gas lift action generated at this time to carry out the membrane separation, as this saves power. Also, when the liquid inside the denitrification tank is taken out to the outside and is circulated through a membrane separation device installed outside the tank to perform membrane separation, the concentrated liquid returned to the reaction tank breaks down the scum on the water surface, It is also preferable to blow the concentrated liquid sideways or downward on the water surface so that the scum is rolled into the denitrification tank and is stirred to save the power.

On the other hand, as the material of the separation membrane of the membrane separator for separating the denitrification treatment liquid in the denitrification tank, polyethylene, polypropylene, polyolefin, polysulfone, polyethersulfone, polyamide, PVDF (polyvinylidene fluoride), PTFE. (Polytetrafluoroethylene), ceramic, non-woven fabric, etc. can be used regardless of the material, but especially hydrophilic material is ANAMMO.
It is suitable for preventing membrane contamination due to the attachment of X bacteria.

The types of separation membranes are hollow fiber membranes, tubular membranes,
Any form such as flat membrane may be used.

The membrane separation system may be any of a dead end filtration system, a cross flow filtration system, a submerged membrane system and a dynamic filtration system. Particularly, the cross flow filtration system and the submerged membrane system are used in the denitrification tank as described above. It is suitable because it can be used also as a stirring or scum crushing means.

As the pressure for membrane separation, both positive pressure and negative pressure using a pump or water pressure can be used, but when the permeate becomes negative pressure on the membrane surface, denitrifying gas is generated from the permeate. , The pressure in the permeate flow path becomes non-uniform due to the accumulation of bubbles in the flow path, and when the permeate is discharged by the pump, the pump entrains air to reduce the membrane separation efficiency. When the liquid is discharged with a siphon, the siphon breaks easily. Therefore, it is preferable that the permeate side is operated at a positive pressure.

For chemical cleaning of the membrane, an alkaline solution such as sodium hydroxide solution, an oxidizing agent such as sodium hypochlorite and hydrogen peroxide, an acid such as hydrochloric acid, sulfuric acid, citric acid and oxalic acid, and various surfactants. For example, various chemicals that are usually used for cleaning the membrane can be used. In particular, since the ANAMMOX bacterium is weak against the presence of oxygen, it is preferable that the cleaning chemical contains 1 mg / L or more of dissolved oxygen in order to efficiently remove the ANAMMOX bacterium that adheres to the film and causes the film contamination.
More preferably, it contains 3 mg / L or more of dissolved oxygen. Further, bubbling with an oxygen-containing gas or backwashing with air is also effective. Dissolved oxygen is most effective when used in combination with other drugs, but dissolved oxygen alone has a membrane fouling recovery effect.

The present invention is particularly excellent in that it efficiently proliferates the ANAMMOX bacterium, and the AN proliferated by this apparatus is used.
By using sludge containing AMMOX bacteria with other equipment,
It can also be useful for shortening the startup time of other devices, for temporarily increasing the processing capacity of other devices, and for recovering the processing capacity that has deteriorated due to a trouble or the like.

For this purpose, it is preferable to provide an apparatus for storing sludge containing ANAMMOX bacteria. As this storage device, it has a closed structure that maintains an oxygen-free environment,
It is more preferable to have a stirrer such as a stirrer or a gas stirrer, and to further include a pH adjusting means for adjusting pH fluctuation during storage. Furthermore, during storage, ANAMMO
It is also effective to provide a means for replenishing ammonia nitrogen and nitrite nitrogen in order to maintain the activity of X bacteria. In addition, since it is more preferable to concentrate the sludge to increase its concentration when it is carried out, it is more effective to provide the concentration means. Concentration means include means for discharging the supernatant liquid after sedimentation of sludge, means for discharging sludge concentrated below, means for generating fine bubbles for floating concentration of sludge, membrane separation and centrifugation. And the like, but a structure in which the membrane separation means as a constituent element of the denitrification device of the present invention can be used may be used. It is also preferable to adjust the water temperature as necessary, and a suitable water temperature is 5 to 40 ° C, more preferably 10 to 25 ° C.

Further, the denitrification tank as a constituent element of the denitrification apparatus of the present invention can also be used as a container for storing sludge, and in this case, the membrane separation means of the denitrification method of the present invention,
It is preferable that the allowance ratio for increasing the sludge concentration is 10 to 200%, and more preferably 20 to 100%. As a method of taking a margin ratio in the membrane separation means, a method of increasing the membrane area, a method of accelerating the circulation flow velocity or bubble flow on the membrane surface, a method of operating a spare membrane separation device, a method of using a spare denitrification tank, etc. Is mentioned.

Such means may be temporary means used when it is necessary to carry out sludge.

The apparatus of the present invention preferably has a residence time of 0.5 so that if a high concentration of an inhibitor such as nitrite nitrogen is accumulated in the denitrification tank, it can be quickly washed away.
It is preferable to provide a means capable of supplying water from which dissolved oxygen has been removed in -12 hours, and more preferably in 1-6 hours. It is necessary to use water having a nitrite nitrogen concentration of 200 mg / L or less, preferably 50 mg / L or less. As a means for removing dissolved oxygen, introduction of an oxygen absorber or bubbling with an anaerobic gas can be used.
These means can be used in an airtight water tank communicating with the MOX denitrification tank. The size of this airtight water tank is preferably 1 to 60 minutes for the above-mentioned amount of water,
More preferably, it should be 5 to 30 minutes, but a long residence time exceeding this range because a water tank installed for other purposes is diverted does not particularly hinder the practice of the present invention. Further, this deoxidizing means can be shared with the deoxidizing means of raw water.

In the denitrification method of the present invention, one or both of the concentration of ammonia nitrogen and the concentration of nitrite nitrogen of the denitrification treatment liquid supplied to the membrane separation means are 0 to 5 mg / L, particularly preferably 0. Membrane separation is performed at ˜2 mg / L.

In the denitrification treatment with ANAMMOX bacteria, nitrate nitrogen is produced. Therefore, in the usual case, a denitrification device for removing nitrate nitrogen is provided at the subsequent stage of the biological denitrification device according to the present invention. The treated water from the membrane separator is further denitrified. In this denitrification process, nitrite nitrogen is also removed at the same time. Therefore, even if nitrite nitrogen remains in the treated water, it can be removed by the denitrification device at the subsequent stage, but if ammonia nitrogen remains, a nitrification denitrification device for removing the remaining ammonia nitrogen should be installed. In the present invention, it is preferable to maintain the ammoniacal nitrogen at a lower concentration than the nitrite nitrogen, from the viewpoints of improving the quality of treated water in the latter stage and simplifying the configuration of the apparatus. Therefore,
In general, it is preferable to perform the treatment so that the concentration of ammonia nitrogen in the denitrification treatment liquid for membrane separation is 0 to 5 mg / L, preferably 0 to 2 mg / L.

In order to effectively carry out such a method of the present invention, the ammonia nitrogen concentration and / or the nitrite nitrogen concentration in the feed water to the membrane separation device are monitored to reduce the ammonia nitrogen concentration. If the concentration of ammonia nitrogen in the supply water seems to be high in the case of keeping, the operation of decreasing the load of ammonia nitrogen flowing into the denitrification device or increasing the load of nitrite nitrogen is performed to reduce the nitrite nitrogen concentration. If the concentration of nitrite nitrogen in the feed water is high when it is kept low, the operation of reducing the load of nitrite nitrogen flowing into the denitrification device or increasing the load of ammonia nitrogen may be performed.

Even when either the concentration of ammonia nitrogen or the concentration of nitrite nitrogen in the water supplied to the membrane separation device is sufficiently low, the residual concentration of the other is large, and when the total nitrogen concentration is high, it is insufficient. It is desirable to reduce the total nitrogen concentration by increasing the nitrogen load on the operating side or reducing the nitrogen load on the excess side.

When the membrane separation device of the denitrification device is an immersion type membrane separation device immersed in the denitrification tank, the concentration is monitored by measuring the concentration of the liquid in the denitrification tank in which the membrane separation device is immersed. Just watch. When the denitrification treatment liquid in the denitrification tank is subjected to membrane separation with a membrane separation device outside the denitrification tank, for example, the concentration of the denitrification treatment liquid transfer pipe from the denitrification tank to the membrane separation device or the concentration in the denitrification tank is monitored. Just do it. The ammonia nitrogen concentration and nitrite nitrogen concentration in the sludge supplied to the membrane surface can be considered to be almost the same as that of the membrane permeate water, so monitoring the concentration of the membrane permeate water may be used instead. .

Such load adjustment is performed in A in the denitrification tank.
If the NAMMOX reaction rate or the ratio of ammonia nitrogen to nitrite nitrogen in the raw water flowing in is known, or if it can be easily estimated, it may be possible to use only a desktop calculation without performing such concentration measurement. it can.

The monitoring of the above-mentioned concentration is carried out at regular intervals by manual or automatic water quality analysis, preferably automatic water quality analysis. The measuring means for this is not particularly limited, the measuring means by the flow injection method, the measuring means by the ion electrode, the measuring means by the ultraviolet analyzer,
Any of simple analysis means such as water quality test paper and other conventionally known measurement means can be used.

When the water quality of the raw water and the operating conditions of the denitrification tank are stable, the same state can be usually maintained for a certain period of time after once adjusting the ammonia nitrogen concentration and / or the nitrite nitrogen concentration. Therefore, it is not always necessary to adjust the load every day, and in some cases it may not be necessary to adjust the load for about half a year.

In the denitrification method of the present invention, it is particularly preferable to arrange two or more denitrification tanks in series in order to stably maintain the ammoniacal nitrogen concentration and / or the nitrite nitrogen concentration of the membrane separation feed water. In this case, it is advisable to apply a higher sludge load to at least one tank than to the mud supply tank to the membrane separation device or the membrane dipping tank. In this case, from the quality of the treated water in the denitrification tank with this high load, the current ANAMM possessed by ANAMMOX bacteria
The OX reaction rate can be calculated, and the quality of treated water in the mud feed tank or the membrane immersion tank to the membrane separation device can be predicted from this value, which is preferable. In particular, in a denitrification tank under a sludge load higher than the sludge load in the sludge supply tank or the membrane immersion tank to the membrane separation device, either the ammonia nitrogen concentration or the nitrite nitrogen concentration of the denitrification treatment liquid is 3 mg. If / L or less, it can be expected that the nitrogen concentration of these in the mud supply tank or the membrane dipping tank to the membrane separation device is also 3 mg / L or less. However, other nutrients, carbonates, p
Whether conditions such as H and temperature are constant between these denitrification tanks,
The environment of the mud supply tank or the membrane immersion tank to the membrane separation device is more ANA
It is better to have an environment suitable for the MMOX reaction.

Further, it is important to keep the amount of sludge discharged to the outside of the system small in order to keep the nitrogen removal capacity high while maintaining the nitrogen concentration in the denitrification method of the present invention. The sludge retention time (SRT), which is a value obtained by dividing the amount of sludge discharged per day by the retained amount, is 16 days or longer, preferably 20 days or longer, and particularly preferably 30 to 300 days. For example, when the SRT is 18 days, there is a possibility that the concentration range of nitrogen of the present invention may easily be exceeded due to a load fluctuation of about 10%, and thus careful concentration monitoring and load adjustment are necessary. On the other hand, if the SRT is set to 30 days, for example, a load fluctuation of about 40% can be tolerated.
If 100 is 100 days, a load fluctuation of about twice can be allowed.

In the present invention, the sludge concentration in the denitrification tank is 1 to 40 kg / m ³ as the suspended solid concentration (SS), and particularly ³ to 2
0 kg / m ³ is preferred. Especially, sludge concentration of 3-10
If it is operated at kg-SS / m ³ , the contamination of the membrane can be further reduced, the frequency of chemical cleaning of the membrane is reduced,
The life of the membrane is extended, the membrane replacement cost is reduced, and the flux of the membrane can be set high, so that the required membrane area is reduced and the membrane cost can be reduced.

When the amount of suspended solids flowing into the denitrification tank is large, the amount of suspended solids other than ANAMMOX bacteria increases, and S
Since the ANAMMOX reaction rate per S decreases, it is necessary to keep the SS concentration high accordingly. In order to avoid this problem, it is effective to perform solid-liquid separation on the upstream side of the denitrification tank to remove SS or to remove BOD to reduce the amount of heterotrophic bacteria growing in the denitrification tank. Is. However, if there is no space to install these pretreatment devices, or if these pretreatments are difficult due to technical and economic reasons, the decrease in membrane separation capacity due to the increase in SS concentration may cause This can be supplemented by increasing the capacity of the device above normal.

When it is desired to keep a large amount of bacterial cells in preparation for carrying out the ANAMMOX bacteria, the SS in the denitrification tank is also used.
It is desirable to keep the concentration high. When the membrane concentration is insufficient due to the high SS concentration, it is preferable to operate a spare membrane separator or install a temporary membrane separator. It is also effective to stop the inflow of relatively low-concentration inflow drainage and select high-concentration drainage for passage. In addition, ANAMMO in sludge
In order to increase the proportion of X bacteria particularly, it is also effective to increase the concentration of ANAMMOX bacteria in the denitrification tank by adding a solution containing relatively high concentrations of ammonia nitrogen and nitrite nitrogen.

In the denitrification tank of the present invention, it is possible to coexist with a denitrifying bacterium having a nitrate denitrifying ability other than ANAMMOX bacteria. In this case, the concentration of residual nitrate nitrogen can be reduced, The removal rate is improved. For this reason,
The subsequent denitrification treatment process can be miniaturized or omitted. In the case of organic substances, the amount of the electron donor added to carry out this denitrification reaction is 0.5 as COD _{Cr with} respect to the sum of nitrate nitrogen flowing from raw water and nitrate nitrogen generated in the system. ˜3 times, more preferably 1.5 to 2.5 times, it is preferable to add 0.5 to 1.7 times the amount of sulfur in the case of sulfide, similarly to the sum of nitrate nitrogen. In this case, 0.8 to 2.2 times is preferable. Thus, when the electron donor is added from the outside, ANAMM is added in the tank.
When the sludge concentration is increased by increasing the number of cells other than OX bacteria, or when the sludge is drawn out so that the sludge concentration does not increase, the concentration of ANAMMOX bacteria decreases and ANAMMOX
The reaction rate decreases.

However, since the membrane separation means is used to separate the sludge, the membrane area is increased even if the sludge concentration is increased,
By increasing the membrane surface velocity, increasing the gas scrubbing amount on the membrane surface, lowering the membrane flux, increasing the backwash frequency, and increasing the chemical cleaning frequency, this increases the cost of the membrane separation device. However, it is possible to cope with an increase in sludge concentration, and in some cases, it may be more advantageous than providing a separate denitrification tank as a post-treatment.

Since these denitrifying bacteria may also denitrify nitrite nitrogen, which is a substrate of ANAMMOX bacteria,
After completion of the MMOX reaction, it is preferable to add an electron donor to denitrify. For this purpose, the period during which nitrite nitrogen is mainly supplied and the period during which electron donors are mainly supplied for denitrifying nitrate nitrogen are mainly divided, or they are added to separate denitrification tanks. Is good.

In this case, the concentration of nitrate nitrogen in the mud feed tank or the membrane dipping tank to the membrane separator is 1 to 10,000 mg /
L is preferable, and more preferably 5 to 2,000.
It is preferably 0 mg / L. When the concentration of nitrate nitrogen is lower than this range, the film is contaminated, and the COD concentration of the treated water is deteriorated and the odor is generated. This is because heterotrophic bacteria and organic matter in the liquid start to decompose, and sulfide ions and organic acids are produced, and these spoilage products kill some of the ANAMMOX bacteria and further promote spoilage. It is presumed that this is because the spoilage product causes clogging of the membrane and deterioration of the treated water. In order to increase the concentration of nitrate nitrogen, decrease the electron donors that flow in, decrease the amount of denitrifying bacteria that flow in, discharge the denitrifying bacteria in the tank to reduce the concentration, and It is possible to take measures such as increasing the load to increase the amount of nitrate nitrogen produced, or introducing a liquid containing nitrate nitrogen. The most desirable means is to reduce the amount of electron donors flowing in.If electron donors are added for denitrification, the amount of organic substances added should be reduced. When a donor is included, it is desirable to reduce the organic matter by using a biological treatment device, a filtration device, a coagulation / separation device, an activated carbon adsorption tower, or the like. In order to increase the nitrate nitrogen concentration, the next preferable means is to reduce the inflowing denitrifying bacteria amount, and for this purpose, a device having an SS removing capacity such as a biological treatment device, a filtration device or a coagulation separation device is used. Can be used.

The denitrification device of the present invention is an ANAMMOX.
Since it is particularly good at growing bacteria, it can function as a device for removing nitrogen in wastewater while using the ANAMM of other devices.
It is also useful as a supply source for supplying sludge having OX activity. When it is desired to increase the amount of sludge in order to supply the ANAMOX sludge of another device, the nitrite nitrogen of the denitrification treatment liquid used for membrane separation should be sacrificed at the expense of temporarily promoting membrane contamination. 5 to 3,0 for all ammoniacal nitrogen
00 mg / L, particularly preferably 10-1,000 mg / L
By setting it to L, it is also possible to promote the growth of ANAMMOX bacteria. However, high concentration of nitrite nitrogen is
Since it has an inhibitory effect on OX bacteria, the upper limit of the nitrite nitrogen concentration is preferably 200 mg / L or less, more preferably 50 mg / L or less.

In the present invention, the raw water to be treated is
Water containing ammoniacal nitrogen and nitrite nitrogen, which may contain organic matter and organic nitrogen, but these must be decomposed in advance to the extent of becoming ammoniacal nitrogen before denitrification treatment. Preferably, when the dissolved oxygen concentration is high, it is preferable to remove the dissolved oxygen as needed. Further, the raw water may be a mixture of a liquid containing ammoniacal nitrogen and a liquid containing nitrite nitrogen.
For example, wastewater containing ammoniacal nitrogen can be subjected to aerobic treatment in the presence of nitrifying bacteria, and a portion of the ammoniacal nitrogen, preferably 50 to 70% of which is partially oxidized to nitrous acid, can be used as raw water. . Further, a part of the wastewater containing ammoniacal nitrogen is subjected to aerobic treatment in the presence of nitrifying bacteria, the ammoniacal nitrogen is oxidized to nitrite, and the mixture with the rest of the wastewater containing ammoniacal nitrogen is used as raw water. Is also good.

Generally, sewage, human waste, sludge digestion and desorption liquid, other industrial wastewater, landfill leachate, and other wastewater containing ammonia nitrogen, organic nitrogen and organic matter are often treated. In this case, these are subjected to aerobic or anaerobic treatment to decompose organic substances, decompose organic nitrogen into ammonia nitrogen, and further carry out partial nitration or a part of nitrite is used as raw water. It is preferable.

The specific configuration of the denitrification device of the present invention will be described below with reference to the drawings.

1 to 3 are system diagrams showing an embodiment of the denitrification device of the present invention.

The denitrification device of FIG. 1 mainly comprises a denitrification tank 1 and a membrane separation device 3. Raw water is introduced into the denitrification tank 1 through a raw water inflow pipe 21 equipped with a flow meter 21F and a flow rate adjusting valve 21V. The denitrification tank 1 is provided with a stirrer 1M, and
A baffle plate 1B that prevents entrapment of denitrifying gas from below is provided on the wall surface at the bottom of the tank. Then, from the portion enclosed by the baffle plate 1B, the sludge feeding pump P _1, denitrified liquid is taken out, fed to the membrane separation unit 3 via Kyudorokan 22. As the mud supply pump P ₁ , a pump suitable for transferring sludge, such as a snake pump or a centrifugal pump, is used, but a snake pump is suitable because of its small mechanical impact on sludge. The mud supply pump P ₁ is equipped with a transmission or a flow rate adjusting valve is provided on the discharge side so that the discharge capacity can be adjusted. Mud supply pipe 2
2 is provided with a flow meter 22F and a pressure gauge 22P.

The denitrification tank 1 is provided with a level switch 1L so that when the water level is low, the amount of raw water or diluted water input is increased or the flow rate of membrane filtration is decreased, for example, the flow rate of permeate is controlled by a valve. To reduce the amount of permeated liquid by lowering the flow rate and / or pressure to feed mud, and conversely reduce the input amount of raw water or diluted water when the water level is high, or increase the flow rate of membrane filtration. Such an operation is performed, for example, to increase the opening degree of the valve on the permeate side, or to increase the flow rate and / or the pressure for supplying mud to increase the permeate amount. The water level may be adjusted by intermittently supplying the raw water or operating the membrane separation device 3. Further, the interval of intermittent operation may be changed in association with the water level.

The denitrification tank 1 has an airtight structure in order to avoid mixing of air, and the denitrification gas generated by the denitrification reaction is discharged from the system through the denitrification gas discharge pipe 25. The denitrifying gas discharge pipe 25 is provided with a check valve 25V and a backflow preventing means such as a water seal. Since it may be difficult to keep the denitrification tank 1 completely airtight, the pressure in the denitrification tank may be higher than the atmospheric pressure, and for example, maintained at 1 to 10 kPa, so that the inclusion of air may be prevented. The denitrification tank 1 is provided with pH adjusting means and, if necessary, temperature adjusting means.

The permeate of the membrane separator 3 is the treated water outflow pipe 23.
Is discharged outside the system. The treated water outflow pipe 23 is provided with a flow rate adjusting valve 23V and a flow meter 23F. Also,
A sampling pipe 26 having an on-off valve 26V is provided so as to branch to the treated water outflow pipe 23, and the sampling water is sent to an ammonia nitrogen concentration and nitrite nitrogen concentration measuring device for water quality control as needed. And a concentration measurement is made. As the concentration measuring means, the above-mentioned means for monitoring the concentration of the denitrification treatment liquid can be used. Since the permeated liquid of the membrane separation device 3 does not contain SS, it is not necessary to perform the SS removal operation in advance for this measurement, and the analysis can be performed easily and easily.

The concentrated liquid (concentrated sludge) of the membrane separation device is returned to the denitrification tank 1 through the concentrated sludge return pipe 24. The concentrated sludge return pipe 24 has a flow rate adjusting valve 24V, a pressure gauge 24P,
A flow meter 24F is provided.

The concentrated liquid is discharged laterally, obliquely downward or downward near the water surface of the denitrification tank 1. This improves the stirring condition near the water surface of the denitrification tank 1 and prevents the scum from floating.

The denitrification device of FIG. 2 is provided with two membrane separation devices and a sludge storage tank 4 for storing the ANAMMOX sludge. In FIG. 2, FIG.
The members having the same functions as the members shown in FIG.

In the membrane separation device 5 as the second membrane separation device, the denitrification treatment of the denitrification tank 1 is performed by the second mud feed pump P ₂ via the second mud feed pipe 32 branched from the mud feed pipe 22. The liquid is introduced, the permeate of the membrane separation device 3 is taken out from the second treated water outflow pipe 33, and the concentrated liquid is returned to the second concentrated sludge return pipe 34.
It is configured so that it can be returned to the denitrification tank 1 via. 22V and 32V are open / close valves, and 33V and 34V
V is a flow control valve. 32F, 33F and 34F are flowmeters and 32P and 34P are pressure gauges.

In this denitrification device, either one of the membrane separation device 3 and the second membrane separation device 5 is operated, and, for example, when cleaning one of the membrane separation devices or when exchanging the membrane, the other membrane separation device is operated. It is also possible to operate both, and both are operated so that the denitrification treatment liquid in the denitrification tank 1 is operated by two membrane separation devices 3, 5
It is also possible to perform membrane separation treatment with.

The sludge storage tank 4 is the same as the denitrification tank 1 with the agitator 4
It is provided with M and a baffle plate 4B, and has an airtight structure, and is configured to draw out sludge containing ANAMMOX bacteria from the denitrification tank 1 through the pipe 31 and store the extracted sludge while appropriately stirring. P ₃ is a sludge drawing pump, 31 F is a flow meter, and 31 V is a flow rate adjusting valve. A sludge extraction pipe 35 having an on-off valve 35V is provided in a portion of the sludge storage tank 4 surrounded by the baffle plate 4B, and the sludge extraction pipe 35 is connected to a mud supply pipe to the second membrane separation device 5. ing. Further, a pipe 36 branched from the concentrated sludge return pipe 34 of the second membrane separation device 5 is provided. Three
6V is a flow control valve. 37 is a gas vent pipe,
A check valve 37V is provided. The sludge storage tank 4 can be provided with a pH adjusting means and a temperature adjusting means as required.

The sludge stored in the sludge storage tank 4 is for the purpose of storing a larger amount of sludge, for the purpose of transporting a larger amount of sludge, or for reducing the collection cost of a disposal company when disposing of sludge. Concentration can be performed for the purpose such as.

When sludge is concentrated, the sludge storage tank 4
After stirring inside is stopped and the sludge is allowed to settle naturally, the supernatant liquid in the upper part is discharged or the concentrated sludge settled in the lower part is taken out. Further, the sludge can be concentrated using the second membrane separation device 5, and in this case, the sludge in the sludge storage tank 4 is fed to the second membrane separation device 5 through the pipes 35 and 32. Then, the membrane separation treatment is performed, the permeated liquid is discharged to the outside of the system through the pipe 33, and the concentrated sludge is returned to the sludge storage tank 4 through the pipes 34 and 36 to concentrate the sludge in the tank.

Although the sludge storage tank 4 is provided with a level switch 4L, in order to concentrate such sludge,
It is preferable to provide, for example, two or more water level control points on the level switch 4L. In this case, the automatic control can start the concentration operation when the upper water level control point is reached and stop the concentration operation when the lower water level control point is reached.

The denitrification device of FIG. 3 uses an immersion type membrane separation device as a membrane separation device. This membrane immersion denitrification tank 6
The inside is partitioned by a baffle plate 6B, an immersion membrane 7 such as a flat membrane type or an external pressure type hollow fiber membrane is provided in the area partitioned by the baffle plate 6B, and an air diffuser 8 is provided below this.
6L is a level switch.

The membrane immersion denitrification tank 6 has an airtight structure so that air is not mixed therein, and the denitrification gas generated by the denitrification reaction is discharged through the pipe 42. In this pipe 42, the pipe 4
3 is branched, and a part of the denitrifying gas is sent to the diffuser pipe 8 by the gas blowing blower 43B and is diffused from below the submerged film 7. 42V ₁ , 42
V ₂ is an open / close valve, 43 V is a gas flow rate adjusting valve, and 43 F is a blown gas flow meter.

Raw water is introduced into the membrane immersion denitrification tank 6 through the pipe 41 by the raw water pump P ₄ and is denitrified. The denitrification treatment liquid in the membrane immersion denitrification tank 6 is subjected to membrane separation treatment by the immersion membrane 7, and the permeated liquid is taken out as treated water through the pipe 44 by the treated water pump P ₅ . 44P is a pressure gauge, 44V is a flow rate adjusting valve, and 44F is a flow meter.

The sludge concentrated in the membrane immersion denitrification tank 6 is drawn out of the system through the pipe 45 by the sludge drawing pump P _{6 as} needed.

In this denitrification device, accumulation of sludge on the membrane surface of the submerged membrane 7 is prevented by the gas flow due to air diffusion from the air diffusion pipe 8. The treated water is taken out by sucking the permeate side of the immersion membrane 7 with the treated water pump P ₅ , but at this time, since a swirling flow is generated in the membrane immersion denitrification tank 6, scum-like sludge near the water surface. Are involved in this swirling flow, uniformly dispersed in the tank, and efficiently contribute to the ANAMMOX reaction. Further, since the inside of the tank is effectively agitated by the swirling flow generated when the treated water is taken out as described above, another agitating means is often not required.

[0098]

EXAMPLES The present invention will be described more specifically with reference to Comparative Examples and Examples below.

Comparative Example 1 Approximately 5 g of ANAMMOX bacterium, which was prepared by filling a cylindrical USB reaction vessel having an inner diameter of 0.3 m with about 20 L of granules mainly composed of methane bacteria and separately culturing by the fill-and-draw method.
Was thrown in. Synthetic wastewater containing 200 mg / L of ammonia nitrogen, 280 mg / L of nitrite nitrogen, 300 mg / L of sodium bicarbonate and a trace amount of calcium ion, magnesium ion and other trace elements as raw water was previously supplied to this reaction tank by nitrogen gas. Deoxygenated water was passed through. From this raw water, ANAMMOX bacteria produce about 22 mg / L as VSS in anoxic environment, and other bacteria produce only negligible amount.

Raw water was passed through the lower part of the USB reaction tank to grow ANAMMOX bacteria, and nitrogen was removed. The reaction tank was installed in a thermostatic chamber at 30 ° C. GSS (Gas Solid Separator; Gas Solid Separa) is a separator for the purpose of gas separation and granule sedimentation separation above the USB reaction tank.
tor), and the treated water is circulated from the settling part of the GSS and merged with the raw water so that the rising flow velocity inside the USB reaction tank is 1
Water was passed so that the flow rate would be m / hr (1.7 m ³ / day). The amount of raw water introduced was initially 5 L / day, and thereafter, the amount of raw water introduced was increased so that ammoniacal nitrogen remained at 5 mg / L or more. After the raw water and the circulating water were combined, the pH was adjusted to 7.5 with a pH adjusting tank and led to the lower part of the reaction tank. Further, the upper part of the reaction tank was sealed, the denitrifying gas was discharged to the outside, and water was sealed to prevent air from flowing backward.

As a result, the VSS concentration flowing into the treated water was 2 to 8 mg / L up to the volumetric load of ammoniacal nitrogen of 1.5 kg / m ³ / day (150 L / day of raw water). Further, when the volume load was around ³ kg / m ³ / day, the outflowing VSS was 14 to 17 mg / L.

That is, the ratio of the amount of bacterial cells flowing out to the amount of bacterial cells produced is 1 to 4 at the initial stage of startup when the load is relatively low.
On the other hand, it became clear that when the load increased, it reached about 80%.

Comparative Example 2 A denitrification tank volume of 1 L and a precipitation tank volume of 0.5 as shown in FIG.
L, settling tank area 50 cm ^TwoUsing the equipment of
Soil mainly composed of ANAMMOX bacteria cultivated by the draw method
Put the mud into the denitrification tank so that the VSS becomes 1000 mg / L.
Ammonia nitrogen concentration 100mg / L, nitrite nitrogen
Elementary concentration 140 mg / L, sodium bicarbonate 200 mg /
L and trace amounts of calcium and magnesium ions
The synthetic wastewater containing other trace elements of
Oxygenated water was passed as raw water. Acid free from this raw water
Approximately 11 mg of ANAMMOX bacteria as VSS in the natural environment
/ L is produced, and other bacteria produce only negligible
Absent.

The denitrification tank and the precipitation tank were each sealed, the upper gas phase was communicated, the denitrification gas was guided to the outside, and water was sealed so that air did not flow backward.

A pH meter was installed in the denitrification tank, and the pH was adjusted to 7.5 by introducing carbon dioxide gas as the pH increased.

Raw water was passed at a flow rate of 2 L / day, and the amount of sludge to be returned was 2 L / day.

Then, when the sludge concentration in the denitrification tank was increased, the water flow rate was gradually increased. After about 3 months, the sludge concentration was increased to 2000 mg-VSS / L and the raw water water flow rate was also increased to 4 L / day.

As a result, the volumetric load of ammoniacal nitrogen was reduced to 0.
4 kg-N / m ³ / day, 0.52 kg of nitrite nitrogen
It was confirmed that it was removed up to −N / m ³ / day.
On the other hand, since nitrate nitrogen increased at 0.1 kg-N / m ³ / day, the nitrogen removal rate was 0.82 kg-N.
/ M ³ / day.

During this period, the VSS concentration of the treated water is 2 to 5 mg.
/ L, and the amount of bacterial cells flowing out is 2 to 5 of the amount of bacterial cells produced.
It became clear that it would be comparative.

The water area load in the settling tank at this time is
Since it was sufficiently lower than 1 to 30 m / day as used in an actual apparatus, it was confirmed that the outflow of ANAMMOX bacteria was not a problem of a sedimentation tank, but a characteristic peculiar to floating-proliferating ANAMMOX bacteria.

Example 1 A denitrification process was performed using the denitrification apparatus shown in FIG. However, the baffle plate 1B is not provided in the denitrification tank 1, and the mounting position of the mud supply pipe 22 that takes out the denitrification treatment liquid from the denitrification tank 1 and sends it to the membrane separation device 3 is in the height direction of the denitrification tank 1. It was set to the middle position. Further, the concentrated sludge return pipe 24 for returning the concentrated liquid of the membrane separation device 3 was provided in the in-tank liquid in the denitrification tank 1 so that the concentrated liquid was blown downward. The outside of the denitrification tank 1 was covered with a water jacket, and hot water of 30 to 35 ° C was circulated to maintain the liquid temperature in the denitrification tank at 30 to 35 ° C.

This denitrification device comprises a denitrification tank 1 and a membrane separation device 3.
In terms of mainly being configured by and, the denitrifying device has the same configuration as that shown in FIG. 1, and members having the same functions are designated by the same reference numerals and the description thereof will be omitted.

In the denitrification device of FIG. 4, the permeated liquid of the membrane separation device 3 is taken out from the treated water outflow pipe 23 by the permeated liquid pump P ₇ , but is branched to this treated water outflow pipe 23 and the treated water return pipe 27.
Is provided and the treated water is returned to the denitrification tank 1 as needed. 23S and 27S are solenoid valves. That is, in this denitrification device, the permeate flow rate is controlled by the tube pump P ₇ having a relatively quantitative property in order to keep the membrane flux of the membrane separation device 3 constant. Further, in order to keep the liquid level in the denitrification tank 1 constant while keeping the raw water input amount and the membrane flux constant, when the water level in the denitrification tank 1 is low, it is detected by the level switch 1L, and the treated water return electromagnetic valve 27S is detected.
The permeated liquid is automatically returned to the denitrification tank 1 using. When the water level in the denitrification tank 1 rises, the treated water will be discharged into the treated water discharge solenoid valve 2
It is discharged from 3S.

The denitrification tank 1 has a volume of 5 L, the membrane separator 3 is a flat membrane type membrane separator, and the flat membrane used is a chlorinated polyethylene MF membrane having a nominal pore diameter of 0.4 μm.

The tank liquid in the denitrification tank ₁ is supplied to the membrane separation device 3 by the snake pump P ₁ equipped with a transmission and subjected to membrane separation treatment. In the membrane separation device 3, by squeezing the outlet on the primary side with the ball valve 24V, the average pressure on the primary side (raw water side) of the membrane is set to 100 to 150 MPa, and the secondary side (permeate side) of the membrane is pumped by the tube pump P. _The treated water was obtained by quantitatively sucking in ₇ .

The denitrification tank 1 was agitated by a stirrer 1M,
The internal pH is measured by a pH meter (not shown), and carbon dioxide gas is introduced as the pH rises to adjust the pH to pH 7.5.
Adjusted to. The denitrification tank 1 was sealed, the denitrification gas was guided to the outside, and water was sealed so that air did not flow backward.

Next, the structure of the flat membrane cell of the membrane separation device used in this embodiment will be described with reference to FIG. FIG. 5A is a plan view of the flat film cell 50, and FIG.
It is an enlarged view of the section which follows the BB line of (a).

The upper housing 51 and the lower housing 52 connected by the bolt 50B and the nut 50N form an outer shell. Inside the flat membrane cell 50, a porous metal sintered plate 56 is horizontally arranged, and a flat membrane 53 is arranged on the upper surface of the porous metal sintered plate 56. The upper side of the flat membrane 53 is the liquid to be treated 54, and the lower side of the porous metal sintered plate 56 is the permeate collecting channel 55. The liquid to be treated is introduced into the liquid to be treated 54 from an inlet 57 on one end side in the longitudinal direction of the flat membrane cell 50, and flows out as a concentrated water from a concentrated liquid outlet 58 on the other end side. The liquid to be treated is
While flowing along the flat membrane 53 toward the concentrated liquid outlet 58, the flat membrane 53 performs membrane separation treatment, and the permeated liquid is the porous metal sintered plate 56.
From the permeate flow path of the permeate to the permeate collection channel 55 and the permeate outlet 59.
Is taken out through. The concentrated liquid is taken out from the concentrated liquid outlet 58.

The effective membrane surface of the membrane separation device 3 has a flow passage width of 40 mm.
× The flow path length was 860 mm, and the membrane area was 3.44 × 10 ⁻² m ² . The flow path height on the primary side is 4 mm, and the flow path cross-sectional area is 1.6 × 10 ⁻⁴ m ² . In this membrane separation device 3,
Flow rate of denitrification treatment liquid from denitrification tank 1 is 5 to 19 L / min
As a result, a membrane surface flow velocity of 0.5 to 2 m / sec can be secured, and the permeate flow rate is 10 to 69 L / d.
By setting it as ay, the film flux is 0.3 to ² m ³ / m ²
It can be / day. As described above, the permeated liquid detects the water level in the denitrification tank 1 with the level switch 1L, and when the water level is lower than the predetermined level, it is returned to the denitrification tank 1 to prevent a decrease in the amount of water in the tank, and when the water level is higher than the predetermined level. Was discharged out of the system to be treated water. The same membrane separation device was used in a maximum of two series and in parallel.

As raw water, synthetic wastewater having the same composition as that used in Comparative Example 1 was previously deoxidized with nitrogen gas and introduced into the denitrification tank 1.

At the start of operation of the denitrification device, the separately cultured A
Sludge containing NAMMOX bacteria was put into the denitrification tank 1 so as to have a VSS of 400 mg / L, and the flow of raw water was started at 4 L / day. The membrane surface velocity was 1 m / sec, the membrane flux was 1 m ³ / m ² / day, and the water flow rate was increased after waiting for the ammonia nitrogen in the treated water to be 20 mg / L or less.

As a result, after one month, the sludge in the denitrification tank 1
Reaches VSS 2,500mg / L and the raw water flow rate is 30
L / day, the volumetric load of ammonia nitrogen is 1.2 kg
/ M ^Three/ Day has been reached. VSS of treated water is 1 mg / L
Below 95% or more of the propagated ANAMMOX bacteria
It was confirmed that it remained in the denitrification tank 1. This period
Ammonia content of the denitrification treatment liquid flowing into the membrane separation device 3 during
Nitrogen concentration remained above 10 mg / L, and nitrite nitrogen concentration
The degree remained at 20 mg / L or higher. In addition, the treated water
Monia nitrogen concentration is 12-30mg / L, nitrite nitrogen
The concentration is 25-55 mg / L, and the nitrate nitrogen concentration is 40-
It was 50 mg / L.

On the other hand, the filtration differential pressure initially stayed at 10 kPa or less, but after about 1 week, the filtration differential pressure rapidly increased to 100 kPa after one month. This value is VS
The membrane fouling rate is about 2-3 times higher than that in the case of membrane filtration of S10,000 to 15,000 mg / L of activated sludge, and the fouling rate is further increased particularly when the concentration of ANAMMOX bacteria is higher. When applying such a cross flow filtration method, the upper limit of the filtration differential pressure is 100 to 150 kPa.
The degree is normal, and it is necessary to perform chemical cleaning or the like to recover the membrane contamination before reaching this value. Further, after the filtration differential pressure exceeds 100 kPa, air bubbles are observed in the treated water discharge pipe 23, which makes it difficult to maintain quantitativeness of the amount of treated water discharged, and frequently the tubes are used. It became necessary to adjust the flow rate of pump P ₇ . When the permeated liquid becomes a gas-liquid mixed laminar flow in this way, if the permeated liquid pump is, for example, a spiral pump, problems often occur such that the discharge capacity and the discharge head of the pump are lowered.

Considering the above factors, under the operating conditions of this Example 1, the frequency of chemical cleaning was evaluated to be once every 2 to 4 weeks when performing membrane filtration on a practical scale.

On the primary side of this membrane separator 3, a 0.2 wt% sodium hydroxide aqueous solution was dissolved oxygen concentration of 1 mg / L.
When the solution was circulated while maintaining the above conditions, it was confirmed that 90% or more of the film contamination was peeled off by the chemical cleaning for 12 hours and the performance was recovered. On the other hand, in the case of a membrane contaminated with activated sludge, the recovery rate under this condition is about 30 to 70%. The reason why the membrane contamination by the ANAMMOX bacteria was effectively recovered was that the AN attached to the membrane surface due to the presence of dissolved oxygen.
It is considered that the AMMOX bacteria were efficiently decomposed and the exfoliation was promoted.

Example 2 From the conditions of Example 1, the flow rate of raw water was reduced to 25 L / da.
When the operation was performed in the same manner as in Example 1 except that y was set, the ammoniacal nitrogen of the denitrification treatment liquid flowing into the membrane separation device 3 could be dropped to 1 mg / L. After that 1
The water flow rate was increased by 30% every week, and the ammoniacal nitrogen concentration was measured each time. As a result, the ammoniacal nitrogen concentration could be maintained at 3 mg / L or less throughout the period. In particular, the ammonia nitrogen concentration was 1 mg / L or less for several days before increasing the water flow rate. As a result, after 40 days, the VSS concentration in the tank exceeded 10,000 mg / L, and the volumetric load of ammoniacal nitrogen reached ³ kg / m ³ / day.

At this time, the rising speed of the filtration differential pressure is 2 kPa.
Since it was less than / day and was about 0.2 to 1 kPa / day, it was confirmed that the film contamination was effectively suppressed. And the required membrane cleaning frequency is 3 months to 1
It was evaluated as once a year.

On the other hand, at this time, scum-like contamination began to accumulate near the water surface in the denitrification tank 1. The generation of scum may make the sludge distribution in the denitrification tank 1 non-uniform, reduce the contact efficiency between the liquid to be treated and the sludge, and reduce the reaction efficiency, or the sludge may flow out together with the denitrifying gas. Therefore, when the concentrated liquid flow returned from the membrane separation device 3 was improved so as to be horizontally blown out near the water surface of the denitrification tank 1 and the stirring power near the water surface was increased, the amount of scum-like sludge decreased.

Further, the generated denitrifying gas is held and floated.
In addition to the flocs,
Many small bubbles were observed. When this phenomenon is analyzed
The denitrification treatment liquid in the denitrification tank 1 supplied to the membrane separation device 3
Was taken out at the middle height of the wall surface of the denitrification tank 1.
Therefore, the denitrifying gas increased as the volume load increases
This gas is caught in the liquid supplied to the separation device 3 and this gas
Mud supply pump P to storage unit 3 ₁It will be miniaturized by
Pressurized, the denitrifying gas is redissolved in the liquid, and this liquid is denitrifying tank 1
When the pressure is returned to the normal pressure,
Probably because the dissolved denitrifying gas became fine bubbles.
Was determined. These bubbles give buoyancy to the floc and attach it to the water surface.
As it moves closer, it leads to an increase in scum.

Therefore, when the outlet for the denitrification treatment liquid supplied to the membrane separation device 3 is changed to the lower part of the denitrification tank 1 and the baffle plate 1B is provided as shown in FIG. 4, entrapment of denitrification gas is prevented. At the same time, the generation of scum-like sludge was also reduced.

From this result, it is preferable that the denitrification treatment liquid supplied to the membrane separation device is collected from a portion where the denitrification gas is less generated, and especially the vicinity of the collection port is prevented from entraining the denitrification gas generated from below. It turned out that it is better to install a baffle plate. Further, it is more preferable that the denitrification tank, which is a supply source of the denitrification treatment liquid supplied to the membrane separation device, has a low volumetric load to suppress the generation of denitrification gas as much as possible.

The desired volumetric load of this denitrification tank cannot be generally stated because it depends on the shape of the reaction tank, the sludge concentration, the pump type, the flow velocity in the pipe, etc., but for example, the rate at which nitrite nitrogen and nitrate nitrogen are reduced. 0-1.5 kg-N / m ³ / d
ay, more preferably 0.1 to 0.8 kg-N / m ³ /
It is good to use day.

Example 3 In Example 2, the VSS concentration was 10,000 mg / L.
Sludge concentration in the denitrification tank 1 reaches 10,000 mg.
When the operation was performed in the same manner except that the sludge was drawn from the denitrification tank 1 so as to keep / L, an average of 140
mL / day sludge withdrawal was required. At this time, the SRT is calculated to be 36 days. When the raw water concentration was varied in this state, it was found that a maximum load of 50% could be tolerated if the load increased for about 1 day, but there was a tendency that the ammonia nitrogen concentration gradually increased. The practical load fluctuation in which the ammonia nitrogen concentration did not exceed 3 mg / L within one day was about 40%.

The sludge drawn out was filled in another closed reaction tank, gently stirred, and the pH was appropriately adjusted to the range of 6.5 to 9.0, and the water temperature was kept at 15 to 20 ° C. However, 40 g of bacterial cells as VSS could be obtained in one month. When the sludge was further supplied and left standing for 20 hours, about 60% appeared as a supernatant. When this was gently discharged, VSS was about 2
50,000 mg / L sludge was obtained. AN of this sludge
When the AMMOX activity was examined, it was confirmed that the removal rate of ammonia nitrogen was 0.2 kg-N / kg-VSS / day or more, and that it was maintained at a practically sufficient rate even when supplied to other devices. Was done.

The sludge accumulated and concentrated here was able to immediately set up a reaction tank for treating 67 L / day of raw water having the same composition.

[0136]

As described above in detail, according to the denitrification apparatus and the denitrification method of the present invention, by adopting the membrane separation means for separating the sludge containing the ANAMMOX bacteria, the ANAMMOX
Bacteria can be grown at almost the maximum rate, and 95% or more of the propagated ANAMMOX bacteria can be retained in the system, enabling rapid start-up, resistance to load fluctuations, and stable denitrification treatment. Becomes In addition, the propagated ANAMMOX bacteria can be transported at a high concentration and can be used to start up another ANAMMOX reaction tank.

Particularly, in the denitrification method of the present invention, ANAMM
It is possible to effectively prevent membrane contamination due to the attachment of OX bacteria to the membrane surface, and reduce the frequency and frequency of chemical cleaning to reduce the time and cost for chemical cleaning and the waste disposal of cleaning chemicals, and also the life of the membrane. Can be extended to reduce the replacement cost of the membrane.

[Brief description of drawings]

FIG. 1 is a system diagram showing an embodiment of a denitrification device of the present invention.

FIG. 2 is a system diagram showing another embodiment of the denitrification device of the present invention.

FIG. 3 is a system diagram showing another embodiment of the denitrification device of the present invention.

FIG. 4 is a system diagram showing a denitrification device used in Examples 1 to 3.

5 is a diagram showing the configuration of a flat membrane cell of the membrane separator used in Examples 1 to 3, FIG. 5 (a) being a plan view and FIG.
FIG. 5B is an enlarged view of a cross section taken along the line BB of FIG.

FIG. 6 is a system diagram showing a denitrification device using a settling tank as a solid-liquid separation means.

[Explanation of symbols]

1 denitrification tank 2 settling tank 3 Membrane separation device 4 Sludge storage tank 5 Second membrane separator 6 Membrane immersion denitrification tank 7 Immersion film 8 Air diffuser 50 flat membrane cell 53 flat membrane

Continued front page    F-term (reference) 4D006 HA93 KA12 KA43 KA72 KB23                       KC03 KC14 KC16 KD01 KD11                       KD12 KD15 KD16 MA01 MA02                       MA03 MC03 MC22 MC23 MC29                       MC30 MC54 MC62 PA01 PB08                       PC64                 4D040 AA24 AA55 AA61 BB91

Claims (2)

[Claims] 1. An action of a denitrifying microorganism having an inlet for raw water containing ammoniacal nitrogen and an outlet for a treatment liquid, using ammoniacal nitrogen as an electron donor and nitrite nitrogen as an electron acceptor. A denitrification tank for biological denitrification in the presence of nitrite nitrogen, and a membrane separation means for separating the effluent of the denitrification tank or the liquid in the denitrification tank into the denitrifying microorganisms and the treated water. A denitrification device comprising: 2. Biodenitrification of raw water containing ammoniacal nitrogen in the presence of nitrite nitrogen by the action of a denitrifying microorganism using ammoniacal nitrogen as an electron donor and nitrite nitrogen as an electron acceptor. In the denitrification method, the denitrification method comprises: a denitrification step of performing denitrification and a membrane separation step of separating the treatment liquid of the denitrification step into sludge containing the denitrifying microorganisms and treated water. A denitrification method, characterized in that the concentration of ammoniacal nitrogen and / or the concentration of nitrite nitrogen in the treatment liquid in the nitrification step is set to 0 to 5 mg / L.