JP7133339B2 - Nitrogen treatment method - Google Patents

Description

TECHNICAL FIELD The present invention relates to a nitrogen treatment method for wastewater, and more particularly to a nitrogen treatment method for biologically denitrifying nitrogen components contained in wastewater.

Wastewater containing nitrogen components causes eutrophication in enclosed water areas, which is one of the causes of water pollution. Therefore, in some sewage treatment facilities and wastewater treatment facilities, nitrogen treatment is performed in which nitrogen components contained in wastewater are decomposed and removed using microorganisms.

Conventionally, as a method for biologically nitrogenizing wastewater containing nitrogen components, nitrification-denitrification treatment in which nitrification treatment and denitrification treatment are combined has been widely used. In the nitrification and denitrification treatment, ammonia nitrogen contained in the water to be treated is oxidized to nitrate nitrogen by nitrifying bacteria, and then the nitrate nitrogen is converted to molecular nitrogen by denitrifying bacteria.

On the other hand, in recent years, the anaerobic ammonium oxidation (ANAMMOX) method has been put to practical use. The anaerobic ammonium oxidation method is a method of co-denitrifying ammonia and nitrite by anaerobic ammonium-oxidizing bacteria. According to the anaerobic ammonium oxidation method, ammonium nitrogen and nitrite nitrogen in the water to be treated are converted into molecular nitrogen and some nitrate nitrogen by an anaerobic ammonium oxidation reaction.

The anaerobic ammonium oxidation reaction is a reaction performed by autotrophic anaerobic ammonium oxidizing bacteria using ammonia as a hydrogen donor, so there is no need to supply organic substances such as methanol, which has the advantage of reducing operating costs. . Also, since there is no need to oxidize nitrite nitrogen to nitrate nitrogen, costs associated with aeration are also reduced. In addition, since anaerobic ammonium-oxidizing bacteria exhibit a high denitrification rate and a small amount of growth, it is possible to reduce the scale of facilities without impairing treatment efficiency, and there is also the advantage that the amount of excess sludge is reduced.

Wastewater containing nitrogen components often contains ammoniacal nitrogen. On the other hand, in the anaerobic ammonium oxidation reaction, ammonium ions and nitrite ions react at a ratio of about 1:1.3. Therefore, in the anaerobic ammonium oxidation method, nitrite-type nitrification, in which part of the ammonium nitrogen is oxidized to nitrite nitrogen, is performed in advance before the anaerobic ammonium oxidation reaction.

Nitrogen treatment methods by anaerobic ammonium oxidation include a single-tank method in which nitrite-type nitrification and anaerobic ammonium oxidation are performed in one tank, and an ammonium oxidation tank in which nitrite-type nitrification is performed and an anammox reaction in which anaerobic ammonium oxidation is performed. It is roughly divided into a two-tank type that uses tanks.

The single-tank method includes the CANON method, which is performed under aeration limited to a low oxygen concentration, the OLAND method, which is performed under conditions limited to a low oxygen concentration, and anaerobic ammonium-oxidizing bacteria inside a carrier to which nitrifying bacteria are adhered and immobilized. There are a SNAP method, which is carried out by proliferating, an SBR method, which is carried out by a semi-batch method, and the like.

As for the two-tank type, there is a one-pass type in which the entire amount of the water to be treated is introduced into the ammonia oxidation tank and part of the ammonia nitrogen is partially nitrite, and a part of the water to be treated is introduced into the ammonia oxidation tank. There is a bypass method in which all of the ammoniacal nitrogen is converted to nitrite, the remainder is bypassed, and then combined.

Conventionally, no pure culture system of anaerobic ammonium-oxidizing bacteria has been established, and anaerobic ammonium-oxidizing methods mainly use sludge that has been acclimatized or sludge obtained by enriching and culturing seed sludge. Since anaerobic ammonium-oxidizing bacteria grow very slowly, when the concentration of organic matter in the water to be treated is high, heterotrophic microorganisms, which grow at a high rate, proliferate predominantly, making it difficult for anaerobic ammonium-oxidizing bacteria to grow. Therefore, regarding the nitrogen treatment by the anaerobic ammonium oxidation method, measures to remove or dilute the organic substances contained in the water to be treated in advance have been studied.

For example, Patent Document 1 discloses a treatment for reducing the concentration of organic matter contained in wastewater by methane fermentation, a treatment for converting ammonium nitrogen into nitrogen gas by anammox bacteria, nitrification of ammonium nitrogen, and nitrate nitrogen/nitrite. A wastewater treatment method is described in which any one of activated sludge treatments for denitrification of nitrate nitrogen is applied based on the concentration of organic substances in the wastewater.

In addition, in Patent Document 2, organic matter is aerobically removed by non-agglutinating bacteria, solid-liquid separation is performed using pressure flotation treatment, and then part of ammonia nitrogen is converted to nitrite nitrogen. A wastewater treatment method is described in which untreated water that has been oxidized and contains ammonia nitrogen and nitrite nitrogen is denitrified by autotrophic denitrifying bacteria.

Further, in Patent Document 3, organic matter in wastewater is removed in an oxygen-free tank to generate nitrous acid, and then treated water is generated by anaerobically denitrifying the nitrous acid and ammonia. A wastewater treatment process is described in which residual ammonia is oxidized before being recycled back to an oxygen-free tank. In the anoxic tank, organic matter in the waste water is removed by nitrite respiration or nitrate respiration.

Japanese Patent No. 5862082 Japanese Patent No. 5186420 Japanese Patent No. 3858271

When nitrogen treatment of wastewater is performed using the anaerobic ammonium oxidation reaction, if the concentration of organic substances in the water to be treated is lowered by performing activated sludge treatment or the like before the anaerobic ammonium oxidation reaction, the concentration of organic substances will decrease. Since anaerobic ammonium-oxidizing bacteria easily propagate in the untreated water, the activity of the anaerobic ammonium-oxidizing reaction is stabilized, and a relatively high nitrogen removal rate can be obtained.

However, in the method of Patent Document 1, it is necessary to analyze the Kjeldahl nitrogen concentration and the COD/N ratio of the wastewater in advance, so the operation of the treatment apparatus becomes complicated, and a treatment tank such as a methane fermentation treatment tank is installed. In such a case, the equipment becomes large-sized and the equipment cost increases. In addition, in the method of Patent Document 2, it is necessary to perform solid-liquid separation treatment after decomposing organic matter, so the equipment cost and operating cost of the treatment apparatus increase, and downsizing of equipment may be hindered.

In the method of Patent Document 3, organic matter is removed by nitrous acid respiration or nitric acid respiration in the anoxic tank, but when the nitrite concentration or nitric acid concentration of the treatment liquid returned to the anoxic tank decreases, the organic matter decomposes. is likely to be insufficient. The concentration of nitrous acid and nitric acid in the treated liquid returned to the oxygen-free tank depends on the nitrification rate and nitrogen removal rate. may not.

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a nitrogen treatment method for efficiently treating wastewater containing nitrogen components and organic matter at low cost.

In order to solve the above-mentioned problems, the nitrogen treatment method according to the present invention is a nitrogen treatment method for denitrifying nitrogen components contained in wastewater. An anaerobic ammonium oxidation treatment process in which sludge is converted into molecular nitrogen, and in the anaerobic ammonium oxidation treatment process, ammonium nitrogen and nitrite nitrogen are co-denitrified using ammonium nitrogen as a hydrogen donor. using a fixed-bed reactor holding a filler in which the microbial sludge containing ammonia-oxidizing bacteria and heterotrophic microorganisms that decompose organic matter contained in the water to be treated is immobilized; The anaerobic ammonium-oxidizing bacteria and the heterotrophic microorganisms are separated from each other by causing concentration polarization of organic matter and dissolved oxygen in the direction of water flow, and the subject is exposed under anoxic conditions that do not increase the dissolved oxygen concentration. Treat the treated water.

According to the present invention, wastewater containing nitrogen components and organic substances can be efficiently treated at low cost.

BRIEF DESCRIPTION OF THE DRAWINGS It is a schematic diagram which shows an example of the wastewater treatment apparatus used for nitrogen treatment. It is a schematic diagram which shows the other example of the wastewater treatment apparatus used for nitrogen treatment.

A nitrogen treatment method according to one embodiment of the present invention will be described below with reference to the drawings. In addition, the same code|symbol is attached|subjected about the structure which is common in the following each figure, and the overlapping description is abbreviate|omitted.

The nitrogen treatment method according to the present embodiment relates to a method for denitrifying nitrogen components contained in wastewater (water to be treated) by biological treatment. This nitrogen treatment method includes at least an anaerobic ammonium oxidation treatment step of converting ammonia nitrogen and nitrite nitrogen contained in the water to be treated into molecular nitrogen by microbial sludge.

In the nitrogen treatment method according to the present embodiment, in the anaerobic ammonium oxidation treatment process, water to be treated is treated using a fixed-bed reactor in which a filler in which microbial sludge is immobilized is held. According to the fixed-bed reactor, anaerobic ammonium-oxidizing bacteria and heterotrophic microorganisms can be propagated in different areas within the treatment tank. Therefore, even if the water to be treated contains organic matter in addition to the nitrogen component, it can be treated efficiently in a single tank.

FIG. 1 is a schematic diagram showing an example of a wastewater treatment apparatus used for nitrogen treatment.
The nitrogen treatment method according to this embodiment can be carried out using a wastewater treatment apparatus 100 as shown in FIG. A wastewater treatment apparatus 100 shown in FIG. A tank 5 , a microbial sludge 6 , an air diffuser 7 , a treated water tank 8 and a cleaning pump 9 are provided.

The wastewater treatment apparatus 100 is an apparatus for nitrogenizing wastewater (water to be treated) containing nitrogen components by an anaerobic ammonium oxidation method, and is a two-tank type in which nitrite-type nitrification and anaerobic ammonium oxidation are performed in separate reaction tanks. It is said that Since the anaerobic ammonium oxidation tank 1 that performs the anaerobic ammonium oxidation treatment is a fixed-bed reactor, the wastewater treatment apparatus 100 treats anaerobic ammonium-oxidizing bacteria and aerobic heterotrophic microorganisms. The decomposition of organic matter and the anaerobic ammonium oxidation can be performed in a single tank by propagating them in different regions within the tank.

When the water to be treated contains organic matter, heterotrophic microorganisms, which grow at a fast rate, proliferate predominantly, and anaerobic ammonium-oxidizing bacteria, which grow at a slow rate, do not propagate easily, resulting in a decrease in anaerobic ammonium oxidation activity. It tends to be destabilizing. On the other hand, in the fixed-bed reactor, organic matter contained in the water to be treated causes heterotrophic microorganisms to proliferate on the upstream side of the treatment tank, while anaerobic ammonium-oxidizing bacteria proliferate on the downstream side, where the concentration of organic matter is low. Therefore, even if the water to be treated contains organic substances, highly active and stable anaerobic ammonium oxidation activity can be obtained on the downstream side in the treatment tank.

Examples of the water to be treated include wastewater discharged from business establishments such as sewage treatment facilities, semiconductor factories, metal smelters, and chemical manufacturing facilities. The wastewater may contain nutrients such as phosphorus, carbon, and heavy metals in addition to ammoniacal nitrogen and organic matter. Moreover, the wastewater may be subjected to activated sludge treatment, denitrification treatment by heterotrophic denitrifying bacteria, dephosphorization treatment, etc., before the nitrification treatment performed in the ammonia oxidation tank 1 .

The anaerobic ammonium oxidation tank 1 is a fixed-bed reactor holding a filler 2 in which microbial sludge is immobilized. The fillers 2 forming the fixed bed are held in a cylindrical treatment tank, and the water to be treated flows through the gaps between the fillers 2 . Microbial sludge containing anaerobic ammonium-oxidizing bacteria and microbial sludge containing heterotrophic microorganisms are immobilized on the filler 2 .

The anaerobic ammonium oxidation tank 1 has an inlet in the upper part of the treatment tank and an outlet in the lower part of the treatment tank as shown in FIG. It is An ammonia oxidation tank 5 is connected to the inlet via a pipe having a supply pump 3 and a pH adjuster 4 . The treated water treated in the ammonia oxidation tank 5 is pH-adjusted as necessary and introduced into the anaerobic ammonia oxidation tank 1 by the supply pump 3 .

The ammonia oxidation tank 5 is a treatment tank that performs a nitrite-type nitrification treatment for oxidizing ammonia nitrogen contained in the water to be treated into nitrite nitrogen. The ammonia oxidation tank 5 holds microbial sludge 6 for biologically treating the water to be treated. Further, the ammonia oxidation tank 5 is equipped with an air diffuser 7 for aerating the water to be treated.

The microbial sludge 6 is sludge containing bacteria, protozoa, etc., and contains nitrifying bacteria. Usually, the nitrifying bacteria group includes ammonia-oxidizing bacteria (AOB) classified into the genus Nitrosomonas, the genus Nitrosococcus, the genus Nitrosospira, the genus Nitrosolobus, etc., and the nitrobacter (Nitrobacter). ), Nitrospina, Nitrococcus, Nitrospira, etc., with nitrite-oxidizing bacteria (NOB).

Microbial sludge 6 is immobilized on a fluidized bed carrier in FIG. However, the microbial sludge used in the ammonia oxidation tank 5 is entrapped and immobilized inside the carrier, entrapped and immobilized on the surface of the carrier, adhered and immobilized on the carrier, and self-granulated. It may be in either a state of forming granules or a state of suspended sludge suspended in water. In addition, the immobilized microbial sludge may be used in any form of fixed bed, fluidized bed and moving bed.

Carrier materials include mono (meth) acrylates, di (meth) acrylates, tri (meth) acrylates, tetra (meth) acrylates, urethane (meth) acrylates, epoxy (meth) acrylates, polyvinyl alcohol , vinylon, polyethylene glycol, polypropylene glycol, acrylamide, polyethylene, polypropylene, ethylene vinyl acetate copolymer, polyvinyl chloride, polyamide such as aramid and nylon, polyester, rayon, glass, activated carbon, etc. can.

The shape of the carrier is cubic, rectangular parallelepiped, plate-like, spherical, disk-like, cylindrical, porous, sponge-like, fiber-like, cloth-like, coin-like, lotus root-like, chrysanthemum-like, and the like. be able to. The size of the carrier is not particularly limited, and can be, for example, 3 mm square.

The air diffuser 7 includes, for example, a diffuser and an air diffuser that generate air bubbles, an air blower that supplies air, a compressor that compresses the air, and an air pipe that sends air from the blower to the diffuser and the air diffuser. The amount of aeration for the water to be treated may be controlled to be constant, or may be variably controlled according to the concentration of ammonium nitrogen, the concentration of nitrous nitrogen, and the like, so as to achieve the desired nitrification rate.

The pH adjuster 4 is provided to adjust the pH of the water to be treated with anaerobic ammonium oxidation treatment. The pH adjusting device 4 is composed of, for example, a pH adjusting agent tank that stores the pH adjusting agent, a chemical injection pump that supplies the pH adjusting agent to the water to be treated, and the like. As the pH adjuster, for example, an alkaline pH adjuster such as sodium hydrogen carbonate or sodium hydroxide can be used. The treated water treated in the ammonia oxidation tank 5 is adjusted to have an acidified pH near neutrality.

The anaerobic ammonium oxidation tank 1 includes an organic matter treatment that decomposes organic matter contained in the water to be treated, and an anaerobic ammonia that co-denitrifies ammonium nitrogen and nitrite nitrogen contained in the water to be treated through an anaerobic ammonium oxidation reaction. and oxidation treatment. Organic matter treatment is performed by heterotrophic microorganisms retained in the filler 2 on the upstream side (inlet side) of the treatment tank. The anaerobic ammonium oxidation treatment is performed by anaerobic ammonium oxidizing bacteria retained in the filler 2 on the downstream side (outflow side) of the treatment tank.

Since the anaerobic ammonium oxidation tank 1 is a fixed bed reactor, when the water to be treated containing organic substances flows in, the concentration of organic substances increases on the upstream side of the treatment tank, and on the packing material 2 located on the upstream side, Heterotrophic microorganisms multiply. Organic matter and dissolved oxygen contained in the water to be treated are consumed by the heterotrophic microorganisms, and the water to be treated in which the concentrations of organic matter and dissolved oxygen are reduced flows downstream. Therefore, even if the water to be treated contains organic matter and dissolved oxygen, the anaerobic ammonium-oxidizing bacteria can reliably grow on the filler 2 positioned downstream in the treatment tank.

The microbial sludge used in the fixed bed reactor is entrapped and immobilized inside the carrier, entrapped and immobilized on the surface of the carrier, adhered and immobilized on the carrier, or self-granulated. It is preferably in a state of forming granules. That is, a carrier or granules can be used as the packing material 2 of the fixed bed. When such a filler 2 is filled in the treatment tank, it becomes difficult for the water to be treated to mix and diffuse due to the filler layer formed by the filler 2 itself. Therefore, concentration polarization of organic matter and dissolved oxygen can be easily generated without partitioning the inside of the fixed bed reactor.

In a fixed-bed reactor, when concentration polarization of organic matter and dissolved oxygen occurs in the water flow direction of the water to be treated, the respective habitats of anaerobic ammonium-oxidizing bacteria and heterotrophic microorganisms are divided upstream and downstream in the treatment tank. separated into two sides. Even if the water to be treated contains organic matter and dissolved oxygen, heterotrophic microorganisms on the upstream side of the treatment tank consume the organic matter and dissolved oxygen, and anaerobic ammonium-oxidizing bacteria propagate on the downstream side of the treatment tank. Therefore, highly active and stable anaerobic ammonium oxidation activity can be obtained.

The filler 2 of the carrier has an appropriate shape such as cubic, rectangular parallelepiped, plate-like, spherical, disk-like, cylindrical, porous, sponge-like, fibrous, cloth-like, coin-like, lotus root-like, and chrysanthemum-like. can be As the carrier, a cubic, rectangular parallelepiped, or other resin pellet carrier is particularly preferably used because it has a large holding amount of microbial sludge, a large specific surface area, and is easy to fill into a fixed-bed reactor. The size of the carrier is not particularly limited, and can be, for example, 3 mm square. The carrier material can be the same as the carrier of the ammonia oxidation tank 1 .

The carrier filler 2 has a specific gravity of at least less than 1 g/cm ³ and is preferably sedimentary. If the packing material 2 is a sedimentary carrier, when the packing material 2 is directly packed in the fixed bed reactor, the water to be treated will not easily flow even if it is passed through. Therefore, it is possible to clearly separate the habitats of anaerobic ammonium-oxidizing bacteria and heterotrophic microorganisms into the upstream side and the downstream side in the treatment tank to obtain highly active and stable anaerobic ammonium-oxidizing activity. can.

The filling rate of the filler 2 is preferably 60% or more, more preferably 70% or more, and still more preferably 80% or more per filling layer. Also, the filling rate is preferably 90% or less. As the volume of the packed bed, an apparent volume calculated from the effective height in the water flow direction of the water to be treated is used. Such a high filling rate makes it difficult for the water to be treated to be agitated by the carriers or granules filled as the filler 2 . Therefore, by separating the respective habitats of anaerobic ammonium-oxidizing bacteria and heterotrophic microorganisms in the direction of flow of the water to be treated, highly active and stable anaerobic ammonium-oxidizing activity can be obtained. Moreover, since the total surface area of the filler 2 is increased, a high denitrification rate can be obtained.

As the filler 2, a kind of immobilized anaerobic ammonium-oxidizing bacteria and heterotrophic microorganisms may be held in a fixed bed reactor, or the filler 2 immobilized with anaerobic ammonium-oxidizing bacteria and The filler material 2 on which the trophic microorganisms are immobilized may be separated in the water flow direction of the water to be treated and held in the fixed bed reactor. When one type of filler 2 is stored all at once, preparation of the carrier or granules becomes easy, but a long period of acclimatization is required. On the other hand, when the filler 2 holding heterotrophic microorganisms is arranged upstream and the filler 2 holding anaerobic ammonium-oxidizing bacteria is arranged downstream, the habitat can be separated in a short acclimatization time. can.

The carrier or granules as the filler 2 may be directly accommodated in the fixed-bed reactor, or may be accommodated in a container having openings, and the container may be charged into the fixed-bed reactor. As the container, for example, a sieve-like container such as a strainer type or colander type can be used. When the filler 2 is stored in the container, it may be densely packed so that the fillers 2 are in contact with each other, or may be sparsely packed so that the fillers 2 are less likely to come into contact with each other. If the filling rate per container is low, the filler 2 can flow within the container, making it difficult to separate the habitats of the anaerobic ammonium-oxidizing bacteria and the heterotrophic microorganisms, but preventing clogging in the treatment tank. be.

The fixed bed reactor is preferably a piston flow treatment tank. In the case of the piston flow type, compared with the case of the complete mixing type, the water to be treated is difficult to diffuse and mix. The water to be treated flows at a highly uniform linear velocity, and concentration polarization of organic matter and dissolved oxygen is likely to occur. A highly active and stable anaerobic ammonium oxidation activity can be obtained by clearly separating it from the downstream side.

In the fixed-bed reactor, the inside of the treatment tank may be partitioned into a plurality of compartments by perforated plates, partition plates, gabion or the like. When the inside of the treatment tank is partitioned in the direction in which the water to be treated flows, the position of the filler 2 does not change significantly even when the water to be treated flows. habitat can be clearly separated to obtain highly active and stable anaerobic ammonium oxidation activity. In addition, since the filler 2 in the upstream compartment and the filler 2 in the downstream compartment are not mixed, high-speed stirring by the stirrer becomes possible, and a high denitrification rate can be obtained.

A treated water tank 8 is provided to receive treated water treated in the anaerobic ammonium oxidation tank 1 . A portion of the treated water treated in the anaerobic ammonium oxidation tank 6 is transferred to the treated water tank 8 and temporarily stored. The treated water in the treated water tank 8 is returned to the anaerobic ammonium oxidation tank 6 by the cleaning pump 9 at any time. The cleaning pump 9 can physically clean the packing material 2 by causing the treated water pressurized to a higher pressure than the supply pump 3 to flow into the fixed bed reactor through an inlet opening below the packing material 2 . .

Next, an example of the nitrogen treatment method according to the present embodiment will be specifically described by taking nitrogen treatment by an anaerobic ammonium oxidation method using the wastewater treatment apparatus 100 as an example.

Nitrogen treatment by the anaerobic ammonium oxidation method consists of a nitrification process in which ammonium nitrogen contained in the water to be treated is oxidized with microbial sludge to produce nitrite nitrogen, and and an anaerobic ammonium oxidation treatment step of converting the ammonium nitrogen and nitrite nitrogen into molecular nitrogen by an anaerobic ammonium oxidation reaction.

In general, anaerobic ammonium oxidation treatment is often carried out in a completely mixed flow field using a fluidized bed treatment tank. Since the growth rate of heterotrophic microorganisms is faster than that of anaerobic ammonium-oxidizing bacteria, if the water to be treated contains organic matter, the heterotrophic microorganisms will grow predominantly in the treatment tank, and the anaerobic ammonium-oxidizing activity will increase. is not sufficiently obtained, or it becomes unstable during the anaerobic ammonium oxidation treatment, resulting in an unstable nitrogen removal rate.

Conventionally, in nitrogen treatment by the anaerobic ammonium oxidation method, activated sludge treatment or the like is performed in advance for the purpose of treating organic matter contained in raw water. However, in the method in which activated sludge treatment or the like is performed as an essential pretreatment, the equipment becomes large and the equipment cost increases, so the advantage of the anaerobic ammonium oxidation method may be lost.

Further, the growth of anaerobic ammonium-oxidizing bacteria is inhibited by dissolved oxygen, and since aeration is performed in the activated sludge treatment, it is necessary to remove dissolved oxygen before the anaerobic ammonium-oxidizing treatment. Degassing can be performed by means of forced degassing such as diffusion of nitrogen gas, stirring of the water to be treated, or natural degassing. Equipment becomes complicated and pretreatment takes a long time.

In contrast, in the nitrogen treatment method according to the present embodiment, in the anaerobic ammonium oxidation treatment process, the water to be treated is treated using a fixed bed reactor filled with a filler in which microbial sludge is immobilized. , the efficiency of the anaerobic ammonium oxidation treatment can be made less susceptible to the organic matter concentration and dissolved oxygen concentration of the raw water.

The concentration of total nitrogen and the concentration of ammonium nitrogen in the water to be treated are preferably 1 mg/L or more and 1000 mg/L or less from the viewpoint of avoiding inhibition of anaerobic ammonium oxidation activity. Moreover, from the viewpoint of maximizing the effectiveness of the fixed bed reactor, a low concentration range, in which it is originally difficult to achieve a high nitrogen removal rate, is more preferable. Specifically, the concentration of total nitrogen and the concentration of ammonia nitrogen in the water to be treated are more preferably 10 mg/L or more and 150 mg/L or less.

When the concentration of total nitrogen or the concentration of ammonia nitrogen is high, the water to be treated can be diluted in advance with treated water or the like that has undergone anaerobic ammonium oxidation treatment before the anaerobic ammonium oxidation treatment step. Also, at the time of start-up when it is necessary to acclimatize microbial sludge, diluted water to be treated can be introduced first, and then the concentration of total nitrogen and the concentration of ammonia nitrogen can be gradually increased before the water is passed.

The nitrification treatment step is performed in the ammonia oxidation tank 5 holding the nitrifying bacteria group under aerobic conditions while adding alkali and adjusting the pH as necessary. The water temperature of the water to be treated is preferably 10°C or higher and 40°C or lower. Moreover, the pH of the water to be treated is preferably pH 6 or more and pH 10 or less. The pH of the water to be treated decreases to the acidic side as nitritation of ammonia nitrogen progresses.

The water to be nitrified is preferably adjusted to a dissolved oxygen concentration such that the ratio of the ammonia nitrogen concentration to the nitrite nitrogen concentration is 1:1 to 1:1.5. Normally, the nitrification rate of nitrite-type nitrification falls within an appropriate range by adjusting the dissolved oxygen concentration within the range of 0.5 mg/L or more and 4.0 mg/L or less. If the concentration ratio is adjusted appropriately, the anaerobic ammonium oxidation reaction proceeds efficiently in the case of one-pass treatment, so a high nitrogen removal rate can be obtained.

The anaerobic ammonium oxidation treatment step is performed in the anaerobic ammonium oxidation tank 1 holding anaerobic ammonium-oxidizing bacteria and heterotrophic microorganisms under anoxic conditions, adjusting the pH as necessary. The pH of the water to be treated is preferably pH 6.5 or higher and pH 9 or lower, more preferably pH 7 or higher and pH 8.2 or lower. The water temperature of the water to be treated is preferably 10°C or higher and 40°C or lower, more preferably 15°C or higher and 37°C or lower.

The biochemical oxygen demand (BOD) of the water to be treated is preferably 300 mg/L or less, preferably 150 mg/L or less at the inlet of the anaerobic ammonium oxidation tank 1, which is a fixed bed reactor. It is more preferable to have With such a BOD, organic matter can be sufficiently decomposed in a fixed-bed reactor in which water is passed at a normal flow rate. Even if the residence time is not greatly extended, the concentration of organic substances on the downstream side in the treatment tank is sufficiently lowered, so that highly active and stable anaerobic ammonium oxidation activity can be obtained.

In the anaerobic ammonium oxidation treatment step, the anaerobic ammonium oxidation tank 1, which is a fixed bed reactor, preferably treats the water under oxygen-free conditions without aeration and without increasing the dissolved oxygen concentration. When sufficient dissolved oxygen remains in the water to be treated, heterotrophic microorganisms are likely to proliferate on the upstream side of the treatment tank without aeration. Under conditions where the dissolved oxygen concentration does not increase, the concentration of organic substances in the water to be treated flowing downstream tends to decrease, and anaerobic ammonium-oxidizing bacteria tend to proliferate downstream in the treatment tank. Therefore, according to such an operation, it is possible to efficiently denitrify the treated water containing organic substances and dissolved oxygen after the nitrification treatment at a low cost without deaeration treatment in advance.

In the anaerobic ammonium oxidation treatment step, the treated water treated in the anaerobic ammonium oxidation tank 1, which is a fixed bed reactor, is allowed to flow into the fixed bed reactor through the inlet opening below the filler 2, thereby removing the microorganisms. can be physically washed. By forcing the treated water into the fixed-bed reactor with the cleaning pump 9, it is possible to prevent the packed layer formed by the packing material 2 from clogging with a microbial film or the like.

The physical cleaning of the filler 2 may be performed regularly at predetermined time intervals while the water to be treated is subjected to the anaerobic ammonium oxidation treatment, or may be performed irregularly. The development rate of backwashing required for physical washing depends on the linear velocity (LV) of the treated water under the same water temperature, and also varies depending on the size and specific gravity of the carrier or granules. Therefore, it is preferable to determine in advance the relationship between the expansion rate and the linear velocity for each carrier or granule to be used.

According to the nitrogen treatment method described above, since a fixed bed reactor is used in the anaerobic ammonium oxidation treatment process, organic matter can be decomposed upstream of the treatment tank and anaerobic ammonium oxidation can be performed downstream of the treatment tank. In fixed-bed reactors filled with packing materials, the habitats of anaerobic ammonium-oxidizing bacteria and heterotrophic microorganisms are separated, so even if the water to be treated contains organic matter and dissolved oxygen, high activity can be achieved. , a stable anaerobic ammonium oxidation activity can be obtained. In addition, since the fixed bed reactor can hold more microbial sludge than the fluidized bed treatment tank, the denitrification rate per volume of the treatment tank can be easily improved. Therefore, waste water containing nitrogen components and organic matter can be efficiently treated.

Further, according to the nitrogen treatment method described above, the decomposition activity of organic matter by heterotrophic microorganisms and the highly active and stable anaerobic ammonium oxidation activity of anaerobic ammonium-oxidizing bacteria can be utilized in a single treatment tank. can be done. Even if pretreatment such as activated sludge treatment or degassing treatment is omitted or the treatment time for pretreatment is shortened, the decomposition of organic matter and the anaerobic ammonium oxidation reaction can be performed only in a fixed bed reactor. can be done. Therefore, waste water containing nitrogen components and organic matter can be efficiently treated at low cost.

FIG. 2 is a schematic diagram showing another example of a wastewater treatment apparatus used for nitrogen treatment.
The nitrogen treatment method according to this embodiment can also be carried out using a wastewater treatment apparatus 200 as shown in FIG. A wastewater treatment apparatus 200 shown in FIG. , and a solution supply pump 11 . The configurations of the supply pump 3, the pH adjuster 4, the anaerobic ammonium oxidation tank 1, and the filler 2 are substantially the same as those of the wastewater treatment apparatus 100.

The wastewater treatment apparatus 200 is an apparatus for nitrogenizing wastewater (water to be treated) containing nitrogen components by an anaerobic ammonium oxidation method. It is configured to perform anaerobic ammonium oxidation treatment. Since the anaerobic ammonium oxidation tank 1 of the wastewater treatment apparatus 200 is a fixed-bed reactor, anaerobic ammonium-oxidizing bacteria and heterotrophic microorganisms are propagated in different regions of the treatment tank to decompose and decompose organic matter. Anaerobic ammonium oxidation can be performed.

The anaerobic ammonium oxidation tank 1 is a fixed bed reactor filled with a filler 2 in which microbial sludge is immobilized. Microbial sludge containing anaerobic ammonium-oxidizing bacteria or microbial sludge containing heterotrophic microorganisms is immobilized on the filler 2 . The filler 2 forming the fixed bed is held in a cylindrical treatment tank so that the water to be treated can pass through the gaps between the fillers 2 .

The anaerobic ammonium oxidation tank 1 has an inlet at the bottom of the treatment tank and an outlet at the top of the treatment tank as shown in FIG. It is According to the upward flow type, the deposition of microbial sludge on the bottom and the accumulation of nitrogen gas and carbon dioxide produced by microbial sludge in the packed bed are suppressed. Water to be treated is supplied to the inlet through a pipe provided with a supply pump 3 . Also, a solution storage tank 10 is connected via a pipe provided with a solution supply pump 11 . A solution containing nitrite nitrogen, such as a sodium nitrite solution or a potassium nitrite solution, is prepared in the solution storage tank 10 .

To-be-treated water containing ammonium nitrogen and organic matter is supplied to the anaerobic ammonium oxidation tank 1 by a supply pump 3 . Also, a solution containing nitrous nitrogen can be supplied from the solution storage tank 10 by the solution supply pump 11 . The water to be treated containing ammonium nitrogen and the solution containing nitrite nitrogen are mixed and introduced into the anaerobic ammonium oxidation tank 1, where organic matter is decomposed and anaerobic ammonium oxidation is performed.

The water to be treated, which is supplied to the anaerobic ammonium oxidation tank 1, contains nitrite nitrogen such that the ratio of the concentration of ammonia nitrogen to the concentration of nitrite nitrogen is 1:1 to 1:1.5. preferably mixed with a containing solution. By adjusting the concentration ratio to such a value, the anaerobic ammonium oxidation reaction proceeds efficiently, so a high nitrogen removal rate can be obtained. The supply amount of the solution containing nitrite nitrogen is preferably controlled by previously measuring the concentration of ammonia nitrogen in the supplied water to be treated.

The anaerobic ammonium oxidation tank 1 is provided with a circulation line for returning the treated water treated in the anaerobic ammonium oxidation tank 1 into the treatment tank. By returning part of the treated water through the circulation line, the concentration of ammonium nitrogen and the concentration of organic substances in the anaerobic ammonium oxidation tank 1 can be diluted. In addition, in a region where the dissolved oxygen concentration is low, heterotrophic denitrifying bacteria that utilize organic matter can reduce the nitrate nitrogen remaining in the treated water to molecular nitrogen, so the nitrogen removal rate can be increased. can.

It is preferable to return the treated water through the circulation line when the BOD of the water to be treated exceeds 300 mg/L at the inlet of the anaerobic ammonium oxidation tank 1 . By returning under such conditions, the organic matter can be sufficiently decomposed without greatly extending the residence time. When such return is performed, the circulation line is preferably connected to the inflow port of the water to be treated as shown in FIG.

Moreover, it is preferable to return the treated water through the circulation line when the concentration of ammoniacal nitrogen in the water to be treated exceeds 150 mg/L. By returning under such conditions, the anaerobic ammonium oxidation activity can be stabilized and a high nitrogen removal rate can be obtained. When such return is performed, the circulation line may be connected to the inflow port of the water to be treated as shown in FIG. is preferably connected to

In the anaerobic ammonium oxidation tank 1, which is a fixed-bed reactor, the linear velocity of the water to be treated flowing upward is preferably 20 m/h or less when the filler 2 is a carrier. On the other hand, when the filler 2 is granules, it is preferably 2 m/h or less. At such a linear velocity, it is difficult to mix the upstream filler 2 and the downstream filler 2, so that the habitats of anaerobic ammonium-oxidizing bacteria and heterotrophic microorganisms are clearly separated. be able to.

According to the nitrogen treatment method described above, since a fixed bed reactor is used in the anaerobic ammonium oxidation treatment process, organic matter can be decomposed upstream of the treatment tank, and anaerobic ammonium oxidation can be performed downstream of the treatment tank. . Since the solution containing nitrite nitrogen is mixed with the water to be treated containing ammonia nitrogen, if the water to be treated does not contain nitrite nitrogen or the concentration of nitrite nitrogen is not appropriate, can also be efficiently anaerobic ammonium oxidation. For example, even if the nitrous acid type nitrification treatment is omitted or the nitrification rate in the nitrification treatment is arbitrarily changed, a high nitrogen removal rate can be obtained.

Although the embodiments of the present invention have been described above, the present invention is not limited to the above-described embodiments, and various modifications can be made without departing from the scope of the present invention. For example, part of the configuration of the embodiment can be replaced with another configuration, part of the configuration of the embodiment can be added to another form, or part of the configuration of the embodiment can be added within the scope of the present invention. can be omitted.

For example, in the wastewater treatment apparatus 100 described above, the ammonia oxidation tank 5 is of a one-pass type in which the entire amount of the water to be treated is nitrite-type nitrite, but may be of a bypass type. That is, part of the water to be treated is introduced into the ammonia oxidation tank 5 to oxidize the entire amount of ammonium nitrogen to nitrite nitrogen, and the remainder is diverted to the anaerobic ammonium oxidation tank 1 without nitrite type nitrification. You can merge.

Alternatively, the wastewater treatment apparatus 100 may be operated in an upward flow manner, and the wastewater treatment apparatus 200 may be operated in a downward flow manner. The wastewater treatment apparatus 100 may be provided with a circulation line for returning the treated water treated in the anaerobic ammonium oxidation tank 1 to the anaerobic ammonium oxidation tank 1, or the wastewater treatment apparatus 200 may not be provided with a circulation line. may The pH adjuster 4 may be provided either on the supply side of the anaerobic ammonium oxidation tank 1 or on the circulation line.

Further, the waste water treatment apparatus 100, 200 may be provided with a circulation line for returning the treated water treated in the anaerobic ammonium oxidation tank 1 to the ammonia oxidation tank 5. By returning part of the treated water through the circulation line, the nitrite nitrogen concentration in the ammonia oxidation tank 1 can be diluted.

Further, the fixed bed reactor can be provided with a stirring device for stirring the water to be treated as long as concentration polarization of organic matter and dissolved oxygen is generated. The impeller shape of the stirring device can be, for example, a paddle impeller type, an anchor impeller type, a ribbon impeller type, a gate impeller type, a propeller impeller type, a pincushion impeller type, or the like. The rotation speed (number of rotations) of the stirring device is preferably 200 min ^-1 or less, more preferably 100 min ^-1 or less. Such a slow rate can maintain concentration polarization to separate habitats.

Further, the shape of the fixed bed reactor is not particularly limited. For example, it can have an appropriate shape such as a cylindrical shape, a square tube shape, a polygonal tube shape, and a multiple tube shape. The effective width of the fixed bed reactor (the length of the short side in the treatment tank or the diameter) is at least 30 times the size of the carrier or granules (the length of the long side or diameter). It is preferably 1, more preferably 50 times or more. With such dimensions, the carriers or granules are less likely to be biased in the fixed-bed reactor, so that it is possible to prevent clogging of the packed bed and penetration of the depleted unpacked portion into the packed bed. .

When the non-pellet-like filler 2 is fixed to the fixed bed reactor, the gap between the fillers 2 to be filled in the fixed bed reactor is preferably 0.7 mm or more, and preferably 3 mm or more. more preferred. With such a dimension, it is difficult for the fillers 2 to come into contact with each other, so separation of the microbial sludge, cracking, tearing, etc. of the carrier can be suppressed. As a result of the fact that the filling material 2 is less likely to be damaged, clogging of the filling layer by fragments is also suppressed.

In the wastewater treatment apparatuses 100 and 200, the anaerobic ammonium oxidation tank 1 and the ammonium oxidation tank 5 are provided with an adjustment tank for adjusting the quality and quantity of the wastewater, and an organic substance contained in the wastewater. A biological reaction tank for chemical decomposition, a pre-denitrification tank for previously denitrifying nitrate nitrogen contained in the wastewater, or the like may be provided. Further, a post-denitrification tank or the like for denitrifying the nitrate nitrogen generated by the anaerobic ammonium oxidation reaction may be provided on the rear stage side. A mixing tank for mixing a solution containing nitrate nitrogen may be provided on the upstream side of the wastewater treatment apparatus 200 .

EXAMPLES The present invention will be described in more detail below using examples of the present invention, but the technical scope of the present invention is not limited to these.

[Example 1]
An entrapping immobilization carrier in which microbial sludge, which is a mixture of anaerobic ammonium-oxidizing bacteria and activated sludge containing heterotrophic microorganisms, was immobilized was prepared. This entrapping immobilization pellet was filled in a reactor having a volume of 0.5 L so as to have a volume of 0.3 L, and this fixed bed reactor was placed in a constant temperature bath at 20°C. Raw water having an ammonia nitrogen concentration of 40 mg-N/L and a BOD of 50 mg/L was prepared so that the ratio of the ammonia nitrogen concentration to the nitrite nitrogen concentration was 1:1 to 1:1.5. After the nitrification treatment, water was passed from the bottom of the reactor so that the hydraulic retention time was 1 hour. The pH of the water to be treated was adjusted to pH 7.6 before the water was passed without performing degassing treatment of the water to be treated or returning the treated water.

When the nitrogen treatment reached steady state, the concentration of ammonia nitrogen was 0.2 mg/L, the concentration of nitrite nitrogen was 0.9 mg/L, and the concentration of nitrate nitrogen was 6 mg/L. The carrier filled in the reactor had a brown color on the lower side into which the nitrified water to be treated flowed, suggesting the possibility that heterotrophic microorganisms were growing there. On the other hand, the red color became stronger toward the upper part of the reactor, confirming the propagation of anaerobic ammonium-oxidizing bacteria.

[Comparative Example 1]
An entrapping immobilization carrier in which microbial sludge, which is a mixture of anaerobic ammonium-oxidizing bacteria and activated sludge containing heterotrophic microorganisms, was immobilized was prepared. This entrapping immobilization pellet was charged into a reactor having a volume of 0.5 L so that the volume became 0.1 L, and this fluidized bed reactor was placed in a constant temperature bath at 20°C. Raw water having an ammonia nitrogen concentration of 40 mg-N/L and a BOD of 50 mg/L was prepared so that the ratio of the ammonia nitrogen concentration to the nitrite nitrogen concentration was 1:1 to 1:1.5. After the nitrification treatment, water was passed from the bottom of the reactor so that the hydraulic retention time was 3 hours. The water to be treated is not degassed or returned, and the water to be treated in the reactor is stirred to the extent that the carrier floats, and the pH of the water to be treated is adjusted to pH 7.6 before the water is passed. did.

When the nitrogen treatment reached steady state, the ammonia nitrogen concentration was 15 mg/L, the nitrite nitrogen concentration was 15 mg/L, and the nitrate nitrogen concentration was 0.6 mg/L. The carriers put into the reactor were brown in color as a whole, suggesting the possibility that heterotrophic microorganisms were proliferating. it wasn't.

As shown by the results of Example 1 and Comparative Example 1, the efficiency of nitrogen treatment differs between the fixed bed reactor that causes concentration polarization and the fluidized bed reactor that causes complete mixing. In the fluidized-bed reactor of Comparative Example 1, anaerobic ammonium-oxidizing bacteria did not propagate sufficiently, and almost no anaerobic ammonium-oxidizing activity was observed. Oxidizing bacteria grew and a high nitrogen removal rate was obtained. Therefore, when the anaerobic ammonium oxidation treatment is performed in the fixed bed reactor, even if the water to be treated contains organic matter, the organic matter can be efficiently denitrified without previously removing the organic matter by activated sludge treatment or the like. It can be said.

1 Anaerobic ammonium oxidation tank (fixed bed reactor)
2 Filling material 3 Supply pump 4 pH adjustment device 5 Ammonia oxidation tank 6 Microbial sludge 7 Aeration device 8 Treated water tank 9 Cleaning pump 10 Solution storage tank 11 Solution supply pump 100 Waste water treatment device 200 Waste water treatment device

Claims (7)

A nitrogen treatment method for denitrifying nitrogen components contained in wastewater,
including an anaerobic ammonium oxidation treatment step of converting ammonia nitrogen and nitrite nitrogen contained in the water to be treated into molecular nitrogen by microbial sludge;
In the anaerobic ammonium oxidation treatment step, anaerobic ammonium oxidizing bacteria co-denitrify ammonia nitrogen and nitrite nitrogen using ammonium nitrogen as a hydrogen donor, and subordinates that decompose organic matter contained in the water to be treated. Using a fixed-bed reactor holding a filler in which the microbial sludge containing nutrient microorganisms is immobilized is used to cause concentration polarization of organic matter and dissolved oxygen in the direction of flow of the water to be treated. A nitrogen treatment method, wherein the habitats of the anaerobic ammonium-oxidizing bacteria and the heterotrophic microorganisms are separated, and the water to be treated is treated under anoxic conditions without increasing dissolved oxygen concentration . 2. The nitrogen treatment method according to claim 1, wherein the microbial sludge is entrapped and immobilized on a carrier, adhered and immobilized on a carrier, or forms granules by self-granulation. . 2. The nitrogen treatment method according to claim 1, further comprising, prior to said anaerobic ammonium oxidation treatment step, a nitrification treatment step of oxidizing ammonium nitrogen contained in the water to be treated with microbial sludge to produce nitrite nitrogen. Prior to the anaerobic ammonium oxidation treatment step, water to be treated containing ammonium nitrogen and a solution containing nitrous nitrogen are mixed and introduced into the fixed bed reactor, and the mixed water to be treated is The nitrogen treatment method according to claim 1, which treats. In the anaerobic ammonium oxidation treatment step, the treated water treated in the fixed bed reactor is allowed to flow into the fixed bed reactor from an inlet opening below the filler to physically wash the filler. The nitrogen treatment method according to claim 1. 2. The nitrogen treatment method according to claim 1, wherein the concentration of total nitrogen in the water to be treated is 10 mg/L or more and 150 mg/L or less. 2. The nitrogen treatment method according to claim 1, wherein said water to be treated has a biochemical oxygen demand of 300 mg/L or less.

Images