Water treatment method and water treatment apparatus

Abstract

To provide a water treatment method and a water treatment apparatus which can efficiently obtain treated water having a water quality satisfying a sewage discharge standard from treatment object water containing septic tank sludge or excrement-based sludge with an apparatus having a smaller size.SOLUTION: A water treatment method includes: supplying a separated liquid obtained by solid-liquid separating sludge containing at least either septic tank sludge or excrement-based sludge into an aeration treatment tank 2 storing a biological carrier; setting two or more aeration conditions including at least an aeration condition of nitrification promotion treatment for promoting nitrification and an aeration condition of denitrification promotion treatment for promoting denitrification with a smaller aeration amount than that of the aeration condition of the nitrification promotion treatment, as the aeration conditions in the treatment tank 2 as to perform the nitrification promotion treatment and the denitrification promotion treatment in the treatment tank 2; performing the biological treatment, switching the aeration conditions so as to alternately switch the nitrification promotion treatment and the denitrification promotion treatment in the treatment tank; and diluting, so as to satisfy a sewage discharge standard, biologically-treated water obtained by the biological treatment.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a water treatment method and a water treatment apparatus, and more particularly to a water treatment method and a water treatment apparatus suitable for application to water treatment for treating septic tank sludge and night soil sludge and discharging treated water into a sewer.

Background Art

[0002] In order to discharge treated water obtained by treating raw water containing septic tank sludge and night soil sludge into a sewer, it is only necessary to satisfy the sewage discharge standards, which are generally less strict than the discharge standards into public water areas. For example, the discharge standards into public water areas are BOD (biochemical oxygen demand) of 10 mg / L, T-N (total nitrogen) of 10 mg / L, and SS (suspended solids) of 10 mg / L, while the sewage discharge standards are BOD of 600 mg / L, T-N of 240 mg / L, and SS of 600 mg / L.

[0003] As a conventional treatment method, for example, there is a method of removing garbage (night soil residue) contained in night soil and diluting it to the discharge standard for discharge. In this case, the dilution ratio is generally about 10 to 20 times, and the dilution water volume and the sewage discharge volume become excessive.

[0004] As another treatment method, there is a method of separating night soil and the like by a dehydrator into solid and liquid, and diluting the dewatered separation liquid for sewer discharge. In this case, since the components such as BOD, SS, and nitrogen in the dewatered separation liquid are significantly reduced compared to the defecated night soil, the dilution ratio can generally be about 4 to 8 times. However, since there are fluctuations in the water quality of the dewatered separation liquid, there is a problem that the dilution water volume also varies greatly depending on the water.

[0005] In addition, the method of solid-liquid separation of excrement and urine using a dehydrator will ultimately result in discharging 6 to 9 times the amount of the inflow, so the effect of reducing the sewage discharge volume is limited. Furthermore, in solid-liquid separation, it is difficult to remove soluble components. Therefore, when excrement and urine contain a large amount of soluble components, the water quality of the dewatered separation liquid deteriorates, and it may be necessary to increase the dilution water volume. There may also be cases where the discharge standard cannot be satisfied due to the regulation of the discharged water volume.

[0006] As another method for more reliably reducing the dilution water volume and the discharged water volume, a method combining solid-liquid separation and biological treatment can be considered. For example, Japanese Patent Application Laid-Open No. 61-50691 (Patent Document 1) describes a method in which the solid-liquid separated solid-liquid fraction of septic tank sludge is mixed with excrement-based sewage, the mixed liquid is subjected to coagulation treatment, and then the separated liquid is subjected to biological treatment.

Prior Art Documents

Patent Documents

[0007]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0008] The method described in Patent Document 1 does not describe the discharge destination of the biologically treated water. However, since it is described that the BOD of the treatment liquid in Example 1 can be treated to 10 mg / L or less, it can be said that it is a treatment method premised on discharging into public water areas.

[0009] However, for the treated water discharged into the sewer, the water quality for the purpose of discharging into public water areas as mentioned in Patent Document 1 is not required. On the other hand, in the water treatment that combines solid-liquid separation and biological treatment as described in Cited Document 1, there is a problem that it is difficult to perform half-hearted treatment to meet the sewage discharge standards. For example, when performing nitrification and denitrification treatment as biological treatment, methods such as treating about 60% of nitrogen instead of the total amount, or performing denitrification treatment on only 60% of the total ammonia nitrogen contained in the dewatered separation liquid after fully nitrifying it can be considered.

[0010] However, when treating about 60% of nitrogen, about 40% of nitrate nitrogen will remain. Therefore, denitrification will occur again when the anaerobic state is reached in the subsequent sedimentation tank, and the generated nitrogen gas may cause the sludge to float, and solid-liquid separation may not be sufficiently performed in the sedimentation tank. If solid-liquid separation cannot be performed in the sedimentation tank, the MLSS (mixed liquor suspended solids concentration) in the nitrification and denitrification tank cannot be maintained, and the treatment itself will deteriorate.

[0011] When fully nitrifying the ammonia nitrogen contained in the dewatered separation liquid, the water tank capacity may become too large, the aeration volume required for nitrification may become too large, and the addition of hydrogen donors such as methanol and ethanol required for denitrification may be necessary. As a result, the equipment and operation costs become too high for the required treated water quality.

[0012] As another method for efficiently treating septic tank sludge and night soil sludge, a method of performing rough treatment by biological treatment using the activated sludge method until the water quality of the treated water becomes less than the sewage discharge standards and then diluting and discharging it into the sewer can also be considered. However, a large water tank capacity is required for biological treatment using the activated sludge method, and the aeration volume for coping with a higher BOD load also becomes too large. Therefore, it cannot be said that it is a means with good treatment efficiency.

[0013] In view of the above problems, the present invention provides a water treatment method and a water treatment apparatus capable of efficiently obtaining treated water with a water quality that satisfies the sewage discharge standards from treated water containing septic tank sludge or night soil sludge with a smaller device.

Means for Solving the Problems

[0014] As a result of intensive studies by the inventors to solve the above problems, it has been found that it is effective to supply the separation liquid obtained by solid-liquid separation of sludge containing septic tank sludge or night soil-based sludge into a treatment tank equipped with a biological membrane, and to set two or more aeration conditions in the treatment tank for treatment.

[0015] In one aspect, a water treatment method according to an embodiment of the present invention completed based on the above findings is to supply a separation liquid obtained by solid-liquid separation of sludge containing at least one of septic tank sludge and night soil-based sludge into an aeration treatment tank containing a biological carrier, and in the treatment tank, a nitrification promotion treatment for promoting nitrification and a denitrification promotion treatment for promoting denitrification are performed. Two or more conditions of the aeration conditions in the treatment tank are set, including at least the aeration conditions for the nitrification promotion treatment and the aeration conditions for the denitrification promotion treatment with an aeration amount less than that of the nitrification promotion treatment. The aeration conditions are switched so that the nitrification promotion treatment and the denitrification promotion treatment alternate in the treatment tank, and biological treatment is performed. The biologically treated water obtained by the biological treatment is diluted to meet the sewage discharge standards. This is a water treatment method.

[0016] In one embodiment, the water treatment method according to an embodiment of the present invention intermittently supplies the separation liquid to the treatment tank.

[0017] In another embodiment, the water treatment method according to an embodiment of the present invention, in the denitrification promotion treatment, at least one of flowing the separation liquid into the treatment tank from the lower part, stirring with a stirrer, or performing aeration is carried out to flow the separation liquid accommodated in the treatment tank.

[0018] In one aspect, a water treatment apparatus according to an embodiment of the present invention includes a solid-liquid separation device that separates sludge containing at least one of septic tank sludge and night soil sludge into separated sludge and separated liquid, a treatment tank that houses a biofilm for biologically treating the separated liquid and performs a nitrification promotion treatment for promoting nitrification and a denitrification promotion treatment for promoting denitrification on the separated liquid, control means for setting and controlling the aeration conditions of the treatment tank to at least two or more conditions of the aeration conditions for the nitrification promotion treatment and the aeration conditions for the denitrification promotion treatment so that the nitrification promotion treatment and the denitrification promotion treatment are alternately performed in the treatment tank, and a dilution tank for diluting the biologically treated water treated in the treatment tank so as to meet the sewage discharge standards.

[0019] In another embodiment, a water treatment apparatus according to an embodiment of the present invention includes a separated liquid supply pipe connected to the lower part of the treatment tank and capable of supplying the separated liquid into the treatment tank so as to generate a liquid flow in the treatment tank.

Advantages of the Invention

[0020] According to the present invention, it is possible to provide a water treatment method and a water treatment apparatus capable of efficiently obtaining treated water having a quality that satisfies the sewage discharge standards from treated water containing septic tank sludge or night soil sludge with a smaller-sized apparatus.

Brief Description of the Drawings

[0021]

Figure 1

Figure 2

Embodiments for Carrying Out the Invention

[0022] Hereinafter, embodiments of the present invention will be described with reference to the drawings. The embodiments shown below are examples of apparatuses and methods for embodying the technical idea of the present invention, and the technical idea of the present invention does not specify the structure, arrangement, etc. of the components as follows.

[0023] <Water Treatment Method> The water treatment method according to an embodiment of the present invention includes performing biological treatment using a biofilm (biological carrier) on a separation liquid obtained by solid-liquid separation of sludge containing at least one of septic tank sludge and night soil sludge, and diluting the biologically treated water obtained by the biological treatment so as to meet the sewage discharge standards.

[0024] As the raw water, a separation liquid obtained by solid-liquid separation of sludge containing at least one of septic tank sludge and night soil sludge can be used. Typically, a dewatered separation liquid of septic tank sludge, night soil sludge, or a mixture thereof can be preferably used. When mixing septic tank sludge and night soil sludge, a mixed liquid of septic tank sludge and night soil sludge may be solid-liquid separated, but it is preferable to perform solid-liquid separation separately on septic tank sludge and night soil sludge, and mix the respective separation liquids obtained by the solid-liquid separation.

[0025] For the solid-liquid separation treatment, various solid-liquid separation devices can be used. Among them, it is preferable from the viewpoints of equipment and operation costs to perform solid-liquid separation of the raw water into separated sludge and a separation liquid using a dehydrator. It is also preferable to perform a concentration treatment on the raw water before the solid-liquid separation treatment. As the concentration method, both gravity concentration and mechanical concentration are effective concentration methods.

[0026] By performing a concentration treatment with the addition of a polymer flocculant before the solid-liquid separation treatment, the sludge concentration (TS) of the concentrated sludge can be concentrated to about 10 to 12 mass% at maximum, whereby the treatment device can be made compact. If a dehydration treatment is further performed on the concentrated sludge concentrated to a high concentration using a dehydrator, a dewatered sludge (separated sludge) with a low water content of 70% or less can be obtained, and thus a more remarkable sludge volume reduction effect can be obtained. Since the calorie of this dewatered sludge with a low water content is high, self-ignition without auxiliary fuel is possible in the incineration treatment, resulting in energy savings and low costs.

[0027] Typical raw water quality is not limited to the following, but for example, BOD is 600 - 2000 mg / L, T-N is 240 - 1000 mg / L, and more typically T-N is 240 - 700 mg / L. The treated water quality of the biologically treated water before dilution obtained by the biological treatment described later is BOD of 200 - 1500 mg / L and T-N of 240 - 600 mg / L.

[0028] The separation liquid is supplied into a treatment tank equipped with a biofilm with microorganisms attached to the surface of the carrier, and biological treatment using the biofilm method is performed in the treatment tank. The biofilm method according to this embodiment can be roughly classified into those that require a regular cleaning process of the carrier and those in which the amount of biofilm is autonomously controlled during the treatment. The former includes the biofilm filtration method and the like. The latter includes the sprinkling filter method, the fluidized carrier method, the rotating disk method, and the fixed bed method (contact oxidation method). Among them, as the biological treatment according to the embodiment of the present invention, it is preferable to use a type of biofilm method in which the amount of biofilm is autonomously controlled during the treatment, and this is defined as the "non-blocking type biofilm method" in this specification.

[0029] Among them, in this embodiment, an aerated biofilm method that performs biological treatment including the contact oxidation method (fixed bed method) using a fixed bed carrier or the fluidized carrier method using a fluidized carrier in an aeration treatment tank (hereinafter also referred to as the "treatment tank") containing a biological carrier is preferably used. The "aerated biofilm method" means a biological treatment in which the biological carrier contained in the treatment tank is fluidized while diffusing air in the treatment tank using aeration means. Examples of the aerated biofilm method suitable for this embodiment are shown below.

[0030] -Contact oxidation method (fixed bed method)- The contact oxidation method is a method of obtaining biologically treated water by immersing a fixed bed carrier in the liquid contained in the treatment tank, performing aeration while passing the separation liquid, and decomposing the organic matter in the separation liquid while forming a biofilm on the surface of the carrier. Since the treatment is performed by the biofilm attached to the carrier, it is not necessary to control the amount of sludge by return compared to the activated sludge method and the like, and maintenance management becomes easy. The BOD volume load is 0.1 - 1.0 kg-BOD / m 3 / d is preferred. When operating at a high load, the biofilm may grow excessively and the contact material may become clogged. Also, as the T-N load, 0.06 - 0.3 kg-N / m 3 / d is preferred.

[0031] There are no particular restrictions on the material and specific shape of the carrier in the contact oxidation method, and any device can be used. As the material of the carrier, polyethylene, plastic, etc. can be used, and as the shape, any shape such as tube type, string type, net type, flat plate type, ball type, etc. can be adopted.

[0032] The specific surface area of the carrier in the contact oxidation method is 50 - 200 m 2 / m 3 , preferably 70 - 150 m 2 / m 3 is preferred. The porosity of the carrier is preferably 97 - 99.5% from the viewpoint of both preventing blockage and achieving the above specific surface area, and preferably 97.5 - 99%.

[0033] Generally, when performing treatment by the contact oxidation method, continuous aeration is basic and switching operation to a low aeration volume is not performed. This is because when the aeration volume is low, the stirring in the tank weakens, and there is a possibility that the raw water may short-circuit and untreated drainage may flow out. On the other hand, in the water treatment method according to the embodiment of the present invention, the contact oxidation method is used as a method for roughly treating the separated liquid with the sludge solid-liquid separated to reduce the load of biological treatment for sewer discharge. Therefore, even if the mixing of the water in the tank becomes insufficient during the time zone of low aeration volume or no aeration, the target treatment can be sufficiently achieved. Furthermore, in order to further improve the mixing in the tank, at least one of flowing the raw water from the lower part of the treatment tank, performing stirring by a stirrer, or performing aeration can be carried out to promote the in-tank flow of the separated liquid accommodated in the treatment tank, so that more stable treatment can also be realized.

[0034] -Fluidized Carrier Method- The fluid carrier method is a method of obtaining biologically treated water by accommodating a carrier in a treatment tank and allowing the carrier to flow in the liquid in the treatment tank, thereby bringing microorganisms into contact with organic substances, oxygen, etc. in the water to be treated. The treatment tank using the fluid carrier method may be newly installed, or a carrier, an air diffuser, etc. may be introduced into an existing storage tank. There are no particular restrictions on the carrier used for the fluid carrier, but typical examples include the following.

[0035] Any carrier can be used as long as microorganisms can adhere to it and it can flow by aeration. As the material of the carrier, any carrier can be used as long as it can flow by aeration. For example, plastics (polyurethane (PU), polyethylene (PE), polyethylene glycol (PEG), polyvinyl alcohol (PVA)), wooden chips, sand, etc. are used. The shape of the carrier can be sponge-like, gel-like, solid, etc.

[0036] The shape of the carrier can be any shape such as spherical, cubic, cylindrical, honeycomb-like, etc. Among them, by using a binding and immobilization carrier that attaches microorganisms to the outer surface of the carrier, microorganisms suitable for the environment in the treatment tank can be attached to the carrier, and it is less affected by fluctuations in the properties of the influent water, enabling more stable biological treatment.

[0037] The structure of the carrier preferably has a structure that takes into account the contact efficiency between the carrier and the raw water in both the nitrification promotion treatment that promotes nitrification and the denitrification promotion treatment that promotes denitrification in the treatment tank. For example, in order to efficiently carry out the nitrification promotion treatment, it is preferable to use a carrier with a large specific surface area in order to increase the contact efficiency between nitrifying bacteria and oxygen. On the other hand, since denitrification treatment does not require contact with oxygen, in order to carry out the denitrification promotion treatment, it is preferable to have a carrier structure in which the voids inside the carrier are filled with microorganisms.

[0038] Therefore, the specific surface area of the carrier suitable for the nitrification promotion treatment and the denitrification promotion treatment is 50 - 5000 m 2 / m 3 , preferably 100 - 3000 m 2 / m 3It is preferably set to be such that even after the voids of the carrier are filled with sludge, a specific surface area of 50 m 2 / m 3 or more can be maintained. The porosity of the carrier (i.e., the volume of the voids of the carrier ÷ the volume calculated from the outer dimensions of the carrier) is preferably 50 to 99%, desirably 70 to 99%. The effective diameter of the carrier is preferably 3 to 10 mm that can be stably separated by a screen for separating the carrier.

[0039] The specific gravity of the carrier is preferably 1.00 to 1.10 g / cm 3 so that the carrier can flow quickly and uniformly in the treatment tank even when intermittent aeration or micro-aeration is performed in the treatment tank. Further, it is preferably 1.01 to 1.05 g / cm 3 for better performance.

[0040] The filling rate of the carrier is preferably 10 to 50% by volume (V%) such that the carrier can be uniformly mixed and flowed, and more preferably 20 to 40% by volume (V%). By setting the filling rate to 20% by volume or more, a large amount of microorganisms can be retained in the tank, and by setting it to 40% by volume or less, appropriate voids can be created to maintain good fluidity.

[0041] It is also possible to fill two types of carriers in the treatment tank for nitrification promotion treatment and denitrification promotion treatment. In that case, as the carrier for nitrification promotion treatment, it is preferable to fill a carrier with a relatively large specific surface area, and as the carrier for denitrification promotion treatment, it is preferable to fill a carrier with a relatively high porosity and filling rate. Although not limited to the following, for example, as the carrier for nitrification promotion treatment, a specific surface area of 100 m 2 / m 3 or more, desirably 300 m 2 / m 3The above carrier is filled at 20 to 35% by volume based on the tank capacity, and it is preferable to fill, as the carrier for denitrification promotion treatment, a carrier having a porosity of 70% or more, preferably 85% or more, at 5 to 20% by volume based on the tank capacity. By using such a carrier, the carrier can be fluidized in the treatment tank even by micro-aeration, intermittent aeration, or supply of the separated liquid into the treatment tank, and the denitrification treatment can be suitably advanced.

[0042] The BOD volumetric load is 0.1 to 2.0 kg-BOD / m 3 / d, preferably 0.2 to 1.0 kg-BOD / m 3 / d. Also, the T-N load is 0.03 to 0.7 kg-N / m 3 / d, preferably 0.06 to 0.3 kg-N / m 3 / d. The fluidized carrier method has a higher load and less risk of clogging compared to the contact oxidation method. In the treatment tank, activated sludge may be further added in addition to the fluidized carrier. By adding activated sludge to the treatment tank, fluctuations in the properties of the biologically treated water due to fluctuations in the properties of the raw water can be suppressed, and more stable treatment can be performed.

[0043] Similar to the above-described contact oxidation method, generally, when performing treatment by the fluidized carrier method, continuous aeration is basic, and in principle, the switching operation to a low aeration air volume is not performed. This is because when the aeration air volume is low, the agitation in the tank weakens, and there is a possibility that the raw water short-circuits and untreated drainage flows out. On the other hand, the water treatment method according to the embodiment of the present invention uses the fluidized carrier method as a method for roughly treating the separated liquid with the sludge solid-liquid separated to reduce the load of biological treatment for discharging to the sewer. Therefore, even if the mixing of the water in the tank becomes insufficient during the low aeration air volume or non-aeration time zone and the sedimentation of the carrier occurs, the treatment aimed at by this method can be sufficiently achieved. Furthermore, in order to further improve the mixing in the tank, at least one of flowing the raw water from the lower part of the treatment tank, performing agitation by an agitator, or performing aeration can be carried out to promote the flow of the separated liquid accommodated in the treatment tank in the tank, so that more stable treatment can also be realized.

[0044] Furthermore, generally in a process using a fluid carrier, it is more effective to divide the nitrification tank and the denitrification tank and have nitrifying bacteria dominate in the nitrification tank carrier and denitrifying bacteria dominate in the denitrification tank carrier than when both nitrifying bacteria and denitrifying bacteria adhere to a single carrier. Therefore, the one-tank type is rarely adopted. In contrast, in the water treatment according to the embodiment of the present invention, since the purpose is to roughly treat the treated water containing purification tank sludge or night soil-based sludge to meet the water quality standards for sewage discharge, by adopting a method of switching between the nitrification process and the denitrification process in a one-tank type, a water treatment method and a water treatment apparatus capable of efficiently obtaining treated water with a smaller-sized apparatus can be provided.

[0045] According to the water treatment method according to the embodiment of the present invention, by using an aerated biofilm method in which a fixed bed carrier or a fluid carrier is accommodated in a treatment tank, the sedimentation tank set at the latter stage of the biological treatment can be omitted or miniaturized, so that the entire treatment apparatus can be downsized. When the sedimentation tank is omitted, it is not necessary to consider the problem of poor sludge sedimentation due to a part of the BOD component or T-N component of the biologically treated water remaining in the sedimentation tank, so the treatment can be made more efficient. Even when a sedimentation tank is provided at the latter stage of the treatment tank, a compact sedimentation tank is sufficient because only an auxiliary one needs to be installed. Even if a part of the activated sludge flows out due to poor sedimentation, since the carrier is sufficiently retained in the treatment tank, stable treatment can be performed at all times. Furthermore, in a general batch activated sludge method, a certain standing time is required to sediment MLSS to maintain microorganisms and obtain clear treated water, but in this method, since a biological carrier is used, the standing time is unnecessary or only a short time is required, so the load that can be treated can be increased compared to the case of treating with activated sludge.

[0046] In the biological membrane method in which a fixed bed carrier or a fluidized carrier is accommodated in a treatment tank to perform biological treatment, from the viewpoint of ensuring the fluidity of the carrier or the contact efficiency between the raw water and the carrier, oxygen supply by aeration with an in-tank agitation function is performed. However, when nitrification and denitrification are carried out in the same tank, generally, it is difficult to suppress the aeration amount in the denitrification treatment to a low amount suitable for the denitrification treatment. In this embodiment, in biological treatment, since it is sufficient to obtain treated water in which a part of the BOD component and the T-N component remains, by simply operating the aeration amount in the treatment tank, the BOD removal and nitrogen removal of the raw water can be simply and efficiently carried out in a single tank. As a result, treated water with the target treated water quality (for sewage discharge use) can be efficiently obtained with a small facility.

[0047] In the biological treatment according to this embodiment, in the treatment tank, biological treatment is performed by setting two or more aeration conditions in the treatment tank so that a nitrification promotion treatment for promoting nitrification and a denitrification promotion treatment for promoting denitrification are alternately repeated. By setting two or more aeration conditions in the treatment tank and performing the nitrification promotion treatment and the denitrification promotion treatment in a single treatment tank, even when only one treatment tank can be used due to the renovation of existing facilities, the water treatment method according to this embodiment can be applied, so that the economic burden for renovation can be reduced, and treated water suitable for sewage discharge can be obtained more efficiently and stably.

[0048] The aeration conditions in the treatment tank may be set to at least two conditions, one condition for each of the nitrification promotion treatment and the denitrification promotion treatment, the aeration condition for the nitrification promotion treatment and the aeration condition for the denitrification promotion treatment with a smaller aeration amount than the aeration condition for the nitrification promotion treatment. Of course, if necessary, three or more conditions or four or more conditions may be set.

[0049] - Nitrification promotion treatment - In the nitrification promotion treatment, it is preferable to set the aeration conditions so that the dissolved oxygen (DO) in the tank becomes 1.0 to 5.0 mg / L, preferably 2.5 to 4.0 mg / L. Thereby, the nitrification reaction that oxidizes the ammonia nitrogen (NH4-N) contained in the raw water to nitrate nitrogen (NO x - N) can be promoted.

[0050] As the aeration volume, in order for the carrier to flow through the entire tank, it is 0.2 to 0.6 m 3 / m 2 / min, preferably 0.3 to 0.5 m 3 / m 2 / min is preferred. Thereby, the carrier flows through the entire tank, and the reaction efficiency is increased. Preferably, while confirming that the carrier flows through the entire tank at the above-mentioned aeration volume, fine adjustment is performed on the aeration volume so that the set DO can reach the above range, whereby the nitrification promotion treatment according to the present invention can be performed more efficiently.

[0051] When the fluidized carrier method is adopted as the biofilm method, in the nitrification promotion treatment, the carrier flows through the entire tank by aeration, so that the contact efficiency with the raw water is increased and the nitrification ability can be improved. In addition, since the purpose of the nitrification promotion treatment in the present embodiment is rough removal of BOD and T-N, it is not necessary to nitrify the whole amount, and it is sufficient that nitrification is completed up to the target concentration.

[0052] According to the study of the present inventors, it is preferable to adjust the pH so as to maintain the free ammonia concentration of the ammonia nitrogen-containing wastewater in the tank at 1.0 to 10 mg / L, more preferably 2.0 to 10 mg / L. Thereby, while suppressing the growth of nitrite bacteria, ammonia oxidizing bacteria can be preferentially attached to the carrier, and thereby a stable nitrite treatment can be obtained.

[0053] In the nitrite treatment, since the reaction can be stopped at NO2-N instead of nitrifying NH4-N to NO3-N as usual, the oxygen utilization efficiency can be increased and the oxygen supply amount can be suppressed. Furthermore, under the denitrification conditions in the subsequent stage, in addition to the dependent denitrification using BOD in the raw water as an electron donor, denitrification by the anaerobic ammonia oxidation reaction between NO2-N and NH4-N also partially proceeds, and the nitrogen removal efficiency can be increased. The free ammonia concentration can be calculated according to formula (1).

[0054]

Equation

[0055] As can be seen from formula (1), the free ammonia concentration is affected by changes in pH, NH4-N concentration, and water temperature. By measuring the changes in pH, NH4-N concentration, and water temperature of the separation liquid in the treatment tank and adjusting the pH so that the free ammonia concentration becomes 1.0 to 10 mg / L based on the measurement results, stable nitritation treatment can be performed.

[0056] -Denitrification promotion treatment- In the denitrification promotion treatment, it is preferable to set the aeration conditions so that the DO in the treatment tank is less than 1.0 mg / L, preferably 0.5 mg / L or less, to promote the denitrification reaction. Under denitrification conditions, aeration may be completely stopped and fluidization by mechanical agitation may be performed, or micro-aeration may be performed within the range where the DO is less than 1.0 mg / L, or a combination of mechanical agitation and micro-aeration may be used. By setting such aeration conditions, although the nitrification rate decreases compared to the nitrification conditions, it is expected that nitrification and denitrification will proceed simultaneously.

[0057] When a fluidized carrier is adopted in the biological treatment in the embodiment of the present invention, the agitation under denitrification conditions is not a problem even if it is to create a flow of water in the tank to increase the contact efficiency between the carrier and the water to be treated rather than to fluidize the carrier throughout the tank, and a part of the fluidized carrier may remain sunken. In the case of the conventional general fluidized carrier method, in order to properly proceed with the treatment, it is ideal to uniformly fluidize the fluidized carrier throughout the tank. On the other hand, in the water treatment method according to this embodiment, since it is for the rough treatment of septic tank sludge or night soil sludge, the target reaction may proceed rather than the degree of fluidization of the fluidized carrier generally required in the fluidized carrier method. Confirmation of the progress of the reaction can be confirmed by sensors such as the ORP meter and NO x -N meter described later. From the viewpoint of facilitating operation management and reducing running costs, it is desirable not to add an electron donor such as methanol from the outside, but depending on the target treated water quality, addition of methanol or the like may be performed.

[0058] When performing agitation by aeration, the aeration volume is, for example, 0.2 m 3 / m2 It may also be below / minute.

[0059] When performing aeration air volume control under micro-aeration conditions, in the control using an inverter, there is a limit to the control lower limit value due to the relationship of the discharge pressure, and precise control may not be possible. Therefore, it is preferable to perform intermittent aeration using a timer of the aeration blower, which enables finer adjustment of the air volume.

[0060] When adjusting the operation time ratio using a timer, if the settings for both the on (aeration operation) time and the off (aeration stop) time are less than 1 minute, it may impose a burden on the blower and it may be difficult to perform stable operation for a long period. In order to reduce the burden on the blower and perform stable treatment so as to be in a state suitable for denitrification, it is preferable that the off time be 5 minutes or more.

[0061] The off time is preferably adjusted so that the DO in the tank becomes 0.5 mg / L or less, so that the progress of nitrification can be more surely stopped. For example, although it depends on the capacity of the blower and the size of the tank, by setting the off time to preferably 5 minutes or more, more preferably 10 minutes or more, the DO in the tank can be made 0.5 mg / L or less, and a period suitable for denitrification can be provided.

[0062] On the other hand, if the off time is set too long, when mechanical agitation is not performed, scale is likely to adhere to the air diffuser, carrier, etc. in the tank during the aeration stop period. The aeration stop time in nitritation treatment is 60 minutes or less, more preferably 45 minutes or less, and even more preferably 30 minutes or less. There is no particular limitation as long as the on time is 1 minute or more. In the on time, it is preferable that the DO be 1 mg / L or more, and when using a fluidized carrier, it is more preferable that the DO be 2.5 mg / L or more. Also, when the dehydrator is not operated on holidays and there is no inflow of raw water, it is possible to promote endogenous denitrification by taking a longer ratio of the aeration stop time under micro-aeration conditions.

[0063] In the denitrification promotion treatment, it is preferable to generate a liquid flow in the raw water contained in the treatment tank by implementing at least one of causing the raw water to flow in from the lower part of the treatment tank, stirring with a stirrer, or performing aeration, so as to fluidize the carrier in the treatment tank. Thereby, the contact efficiency between the fluidized carrier and the raw water can be increased, and the nitrogen removal treatment can be promoted.

[0064] The supply of the raw water to the treatment tank is preferably performed intermittently with a predetermined supply pause period. "Intermittently" means that, for example, there may be a supply pause period of several hours (e.g., 1 to 20 hours), or there may be a supply pause period of several days (e.g., 1 to 7 days). For example, when treating septic tank sludge and night soil sludge, depending on the operating conditions of the treatment facility, etc., there is raw water inflow from 9:00 to 17:00 on weekdays, and there are periods when no raw water flows in during weekdays at night and early morning, on holidays, and on festival days. By supplying the raw water to the treatment tank intermittently in accordance with the operating conditions such as the raw water inflow time of such a treatment facility, a storage tank for storing the raw water can be omitted, contributing to the miniaturization of the entire device. Also, by controlling the aeration conditions in the treatment tank to switch between the aeration conditions for nitrification promotion treatment and the aeration conditions for denitrification promotion treatment in accordance with the timing of this raw water inflow, nitrification and denitrification of the raw water can be performed more efficiently in one treatment tank. For example, by introducing the raw water under denitrification promotion conditions, stopping the introduction of the raw water after confirming the completion of denitrification using sensors such as the set time and ORP described later, and switching to nitrification promotion conditions, the BOD component in the raw water can be effectively used for denitrification, and the amount of oxygen used for BOD oxidation can also be reduced.

[0065] In biological treatment, it is preferable to switch the aeration conditions so that the nitrification promotion treatment and the denitrification promotion treatment performed in one treatment tank alternate. By alternately repeating the nitrification promotion treatment and the denitrification promotion treatment by switching the aeration conditions, rough removal of BOD and T-N in the raw water can be efficiently performed in one treatment tank.

[0066] The switching of the aeration conditions may be carried out manually by the operator or may be automatically controlled using a timer, a sensor, etc. As the switching method, for example, the following methods can be adopted.

[0067] -Switching by time- Since the ratio of the nitrification rate to the denitrification rate is about 1:1 to 1:5, regarding the time ratio of the nitrification promotion treatment - denitrification promotion treatment, by setting it to 1:1 to 5:1, preferably 2:1 to 4:1, it becomes possible to maintain appropriate nitrification time and denitrification time. When using a fluidized carrier in biological treatment, collect the acclimated carrier, and by determining the nitrification rate and denitrification rate through, for example, the following batch test, it becomes possible to manually or automatically set the optimal ratio of nitrification time to denitrification time according to the adhesion status of microorganisms.

[0068] (Batch nitrification test) For example, put 20 vol% of the carrier collected from the treatment tank into a 1 L graduated cylinder, and make up the raw water to a total volume of 1 L. Then, add sodium carbonate so that the alkalinity (mg-CaCO3 / L) is 7 times the ammonia concentration (mg-N / L) of the raw water. After that, start aeration, perform sampling at regular intervals (for example, 0, 30, 60, 90, 120 minutes), and conduct water quality analysis. From the change amount of the NO x -N concentration, calculate the nitrification rate (mg-N / L-carrier / h) per carrier volume.

[0069] (Batch denitrification test) For example, put 20 vol% of the carrier collected from the treatment tank into a 1 L sealable container, and make up the raw water to a total volume of 1 L. Then, add NaNO3 so that NO3-N is 50 - 100 mg / L. After replacing the gas in the container with nitrogen gas, start stirring, perform sampling at regular intervals (for example, 0, 30, 60, 90, 120 minutes), and conduct water quality analysis. From the change amount of the NO x -N concentration, calculate the denitrification rate (mg-N / L-carrier / h) per carrier volume.

[0070] -Control by sensor 1 (feedback control)- As control methods by sensors, pH control, alkalinity control, ORP control, DO control, NH4-N control, NO x -N control, etc., and combinations thereof can be mentioned. For the reasons described below, among them, ORP control and NO x -N control are particularly suitable.

[0071] (pH, Alkalinity Control) In the nitrification promotion treatment, alkalinity decreases and pH decreases along with the nitrification reaction. When nitrification is carried out only with the alkalinity in the raw water without adding alkali, when the alkalinity drops below a certain value, the progress of nitrification stops and the decrease in pH also stops. Therefore, by checking the change over time of pH or alkalinity and regarding the point when the change amount per unit time becomes below a certain value as the point when nitrification is completed, it is possible to switch to the denitrification promotion treatment.

[0072] In the denitrification promotion treatment, alkalinity increases and pH rises along with the denitrification reaction. Therefore, by checking the change over time of pH or alkalinity and regarding the point when the change amount per unit time becomes below a certain value as the point when denitrification is completed, it is possible to switch to the nitrification promotion treatment.

[0073] (ORP Control) In the nitrification promotion treatment, ORP increases along with the oxidation of organic matter and the nitrification of ammonia. Since the slope of the change over time of ORP is different during the period when the oxidation of organic matter and nitrification proceed simultaneously, the period when only nitrification proceeds after the oxidation of organic matter is completed, and after nitrification is completed, by checking the change amount and regarding the point when the change amount per unit time becomes below a certain value as the point when nitrification is completed, it is possible to switch to the denitrification promotion treatment.

[0074] In the denitrification promotion treatment, the inflow of raw water and NO xAs denitrification of -N occurs, the ORP decreases, and when denitrification is completed, the amount of change becomes small. Therefore, when the amount of change per unit time falls below a certain value, it can be regarded as the time point when nitrification is completed, and the nitrification promotion process can be switched to. Compared with pH and DO, ORP control has a wider range of possible values and higher resolution (generally -400 mV to +400 mV), so more accurate control is possible. Also, since it is an index that can comprehensively evaluate the state of organic matter, nitrogen compounds, etc. in the system rather than the concentration of a single substance such as NH4-N or NO x -N, it is a suitable index for evaluating the state in the tank when the purpose is to roughly remove BOD and nitrogen as in this case, and when BOD and nitrogen remain in the tank.

[0075] (DO control) In the nitrification promotion process, when blowing is carried out with the same air volume, after the oxidation of organic matter and nitrification in the tank are completed, the DO becomes higher compared to during the progress of the reaction. By checking the change of DO over time and regarding the time point when DO increases as the time point when nitrification is completed, it is possible to shift to the denitrification promotion process.

[0076] (NH4-N control) In the nitrification promotion process, the time change of the NH4-N concentration increases in the order of the period when nitrification is completed, the period when the oxidation of organic matter and nitrification proceed simultaneously, and the period when the oxidation of organic matter is completed and nitrification is proceeding. By checking this change over time and regarding the time point when the change amount of NH4-N becomes small as the time point when nitrification is completed, it is possible to shift to the denitrification promotion process.

[0077] (NO x -N) In the nitrification promotion process, the time change of the NO x -N concentration increases in the order of the period when nitrification is completed, the period when the oxidation of organic matter and nitrification proceed simultaneously, and the period when the oxidation of organic matter is completed and nitrification is proceeding. By checking this change over time and regarding the time point when the change amount of NO x -N becomes small as the time point when nitrification is completed, it is possible to shift to the denitrification promotion process.

[0078] In the denitrification promotion treatment, the amount of change is large during the period when denitrification is in progress, and the amount of change becomes small when denitrification is completed. By checking this change over time, when the amount of change in NO x -N becomes small, it can be considered that denitrification is completed, and the process can be shifted to nitrification promotion treatment. Control based on the NO x -N concentration is suitable for this embodiment in that the completion point of the denitrification promotion treatment can be confirmed with a single sensor compared to DO control and NH4-N control.

[0079] - Control by sensor 2 (in combination with feedforward)- Since most of the nitrogen components in the raw water are NH4-N, the nitrogen concentration of the raw water can be measured with an NH4-N meter. Therefore, if the target value of the nitrogen concentration of the treated water is determined, the required nitrification-denitrification amount can be calculated from the relationship between the raw water NH4-N concentration and the treated water T-N target concentration. Since the nitrification rate and denitrification rate per unit time can be calculated from the NH4-N concentration or NO x -N concentration in the treatment tank, the time for nitrification conditions and denitrification conditions required to reach the target concentration can be calculated by an arithmetic unit, and the blower can be controlled. As a result, the nitrification time can be minimized, and the aeration air volume can be reduced.

[0080] - Addition of nutrients (phosphorus)- In the water treatment method according to the embodiment of the present invention, since biological treatment is employed for the treatment of the separated liquid as the raw water, it may be necessary to supply only the phosphorus necessary for the growth of organisms. Generally, in biological treatment, about 1 mg / L of phosphorus is required for 100 mg / L of BOD, and it is desirable to supply phosphorus so as to satisfy this ratio with respect to the raw water BOD. If the treatment is good, the concentration of phosphorus may be reduced to 1 mg / L or less, preferably 0.7 mg / L or less, more preferably 0.5 mg / L or less before supply.

[0081] In particular, when performing dehydration treatment as a solid-liquid separation treatment for septic tank sludge and night soil sludge, if iron-based or aluminum-based flocculants are used, phosphorus is taken up by the sludge, resulting in a decrease in the phosphorus concentration in the separated liquid and the need for phosphorus addition in some cases. In the rough treatment for BOD and T-N removal, the supply of nutrients such as phosphorus is often overlooked. However, since the lack of phosphorus may also cause almost no BOD removal, it is preferable to supply phosphorus even in the rough treatment. The form of phosphorus to be added is not particularly limited, and there are methods such as adding chemicals such as phosphoric acid and potassium dihydrogen phosphate, or adding a part of the night soil sludge.

[0082] (Dilution ratio) The biologically treated water obtained by the above biological treatment is sent to a dilution tank and mixed with dilution water to be diluted so as to meet the sewage discharge standards. By typically setting the dilution ratio of the biologically treated water to 1 to 4 times, more typically 1 to 3 times, further 1 to 2 times, and further 1 to 1.5 times, the amount that meets the sewage discharge standards can be obtained. The dilution may be carried out constantly or only when necessary to meet the sewage discharge standards. As a result, with a smaller amount of dilution water compared to the conventional method, more efficient and appropriate treatment can be carried out according to the water quality standards for sewage discharge.

[0083] According to this embodiment, by performing the above-described biological treatment, there may be cases where the biologically treated water is treated to such an extent that dilution of the biologically treated water is not required. In that case, it goes without saying that the biologically treated water after the biological treatment using the biofilm method may be directly discharged into the sewer without dilution.

[0084] According to the water treatment method according to the embodiment of the present invention, for the separated liquid obtained by solid-liquid separation of sludge containing at least one of septic tank sludge and night soil sludge, nitrification promotion treatment and denitrification promotion treatment for promoting denitrification are performed. By setting two or more conditions of the aeration conditions in the treatment tank to perform rough removal of BOD and nitrogen and then diluting, treated water that can be discharged into the sewer can be obtained more efficiently and stably with a small amount of dilution water using a small and simple device.

[0085] <Water treatment device> As shown in FIG. 1, the water treatment device according to the embodiment of the present invention includes a solid-liquid separation device 1 that separates sludge containing at least either septic tank sludge or night soil sludge into separated sludge and separated liquid by solid-liquid separation, a treatment tank (aeration treatment tank) 2 that contains a biofilm for biologically treating the separated liquid and performs nitrification promotion treatment and denitrification promotion treatment on the separated liquid, control means 4 that sets and controls the aeration conditions of the treatment tank 2 to at least two or more conditions so that the nitrification promotion treatment and the denitrification promotion treatment are alternately performed in the treatment tank 2, and a dilution tank 3 that dilutes the biologically treated water treated in the treatment tank 2 to meet the sewage discharge standards.

[0086] Various devices can be used for the solid-liquid separation device 1. Among them, it is preferable from the viewpoints of equipment and operation costs to use a dehydrator as the solid-liquid separation device 1. It is also preferable to perform a concentration treatment on the raw water before solid-liquid separation using a concentrator (not shown) in the front stage of the solid-liquid separation device 1.

[0087] As the treatment tank 2, a biofilm with microorganisms attached to the surface of the carrier is accommodated. Typically, a contact oxidation tank containing a fixed bed carrier inside or a fluidized carrier tank containing a fluidized carrier inside can be suitably used as the treatment tank 2 according to this embodiment. The treatment tank 2 may be provided with a stirrer 21 for stirring the separated liquid supplied into the treatment tank 2. The stirrer 21 may be omitted. An aeration means 22 for aerating the inside of the treatment tank 2 is connected to the lower part of the treatment tank 2. The aeration means 22 can be composed of a pump for sending gas into the treatment tank 2, a diffuser pipe (not shown), etc. By the aeration by the aeration means 22, a liquid flow is generated in the separated liquid in the treatment tank 2, and thereby the biofilm (fluidized carrier or fixed bed carrier) in the treatment tank can be made to flow.

[0088] In the treatment tank 2, measuring means 23 for measuring the water quality of the separated liquid in the treatment tank 2 may be arranged. As the measuring means 23, for example, a pH meter, an ORP meter, a DO meter control, an NH4-N concentration meter control, NO x-N concentration meters and combinations thereof can be used. Measuring means 24 for measuring the quality of the separated liquid flowing into the treatment tank 2 may be arranged. As the measuring means 24, for example, a pH meter, an ORP meter, a DO meter control, an NH4-N concentration meter control, NO x -N concentration meters and combinations thereof can be used.

[0089] For example, if the NH4-N concentration of the separated liquid is measured by the measuring means 24, and the NH4-N concentration or NO x -N concentration meter is measured by the measuring means 23, and the target value of the nitrogen concentration of the biologically treated water is determined, the required nitrification and denitrification amounts can be calculated from the relationship between the NH4-N concentrations of the separated liquid and the biologically treated water. Based on this calculation result, the nitrification promotion treatment time and the denitrification promotion treatment time are determined, and by determining the aeration conditions for each treatment, BOD removal and T-N removal from the separated liquid can be efficiently roughly removed.

[0090] The treatment tank 2 preferably includes a separated liquid supply pipe 11 connected to the lower part of the treatment tank 2 and capable of supplying the separated liquid into the treatment tank 2 so as to generate a liquid flow in the treatment tank 2. By configuring the separated liquid supply pipe 11 to be connected to the lower part of the treatment tank 2 and the separated liquid to be supplied from below to above the treatment tank 2, sedimentation of the fluidized carrier or fixed bed carrier accommodated in the treatment tank 2 to the bottom of the treatment tank 2 can be suppressed, the fluidity of the carrier can be increased, and the contact efficiency between the carrier and the separated liquid can be increased. When the height of the treatment tank 2 is set to 1, the separated liquid supply pipe 11 is connected at a height of relatively 0 (tank bottom) to 0.5, more preferably 0 to 0.3, so that the generation efficiency of the liquid flow in the tank due to the supply of the separated liquid can be improved.

[0091] The control means 4 is composed of a general-purpose computer or the like and is connected to the aeration means 22. The control means 4 controls the aeration conditions so that nitrification promotion treatment and denitrification promotion treatment are alternately performed in the treatment tank 2. The control means 4 may be connected to the stirrer 21, and the stirring conditions of the stirrer 21 can also be controlled. Further, the control means 4 may be connected to the measuring means 23 and 24, and the water quality (pH, ORP, DO, NH4-N concentration, NO xBased on the measurement results (such as -N concentration, etc.), the aeration by the aeration means 22 may be controlled. By the control means 4 controlling the aeration in the treatment tank 2 by the aeration means 22 based on the measurement results of the water quality by the measurement means 23 and 24, a more stable biological treatment that can follow the occurrence of water quality fluctuations in the raw water can be performed. The biologically treated water treated in the treatment tank 2 is stored in the dilution tank 3 and diluted with dilution water in the dilution tank 3 to obtain treated water.

[0092] According to the water treatment apparatus according to the embodiment of the present invention, the control means 4 is provided to set and control the aeration conditions in the treatment tank 2 to at least two or more conditions so that the nitrification promotion treatment and the denitrification promotion treatment are alternately performed in the treatment tank 2. As a result, rough removal of BOD and T-N in the solid-liquid separation liquid of the sludge containing purification tank sludge or night soil-based sludge can be performed in one treatment tank 2. Therefore, treated water with a water quality that satisfies the sewage discharge standard can be efficiently obtained from the sludge containing purification tank sludge or night soil-based sludge with a small-sized apparatus.

Example

[0093] Examples of the present invention are shown below. These examples are provided to better understand the present invention and its advantages, and are not intended to limit the invention.

[0094] According to the flow shown in FIG. 2, water treatment according to an example (experimental system), water treatment according to an example, and water treatment according to a reference example (control system) for comparing the effects of water treatment according to an example were performed. The raw water used was the dewatered separation liquid from an actual night soil treatment facility, etc. Appropriate nutrient salts (potassium dihydrogen phosphate (KH2PO4)) were added to the raw water. A representative example of the raw water properties during the experimental period is shown in Table 1.

[0095]

Table 1

[0096] The raw water was set at a BOD volume load of 0.6 kg-BOD / m 3 / d, T-N load of 0.23 kg-N / m 3Water was passed through each test system so that it became / d. The treatment flow of the laboratory test is shown in Fig. 2. Also, as a control system, a comparison was made with a system that performs constant aeration. The carrier was a honeycomb-shaped carrier made of polyethylene (φ25 mm, thickness 4 mm, specific surface area 800 m 2 / m 3 ) and filled 30% by volume with respect to the capacity of each tank.

[0097] The inflow conditions of the raw water and the aeration conditions were set as shown in Table 2 for weekdays (Monday to Friday) and holidays (Saturday and Sunday) respectively. In Table 2, for the "nitrification condition", the aeration amount was set so that the set DO in the treatment tank became 4.0 mg / L, and mechanical stirring was not performed. For the "denitrification (micro-aeration) condition", the aeration amount was set so that the set DO in the treatment tank became 0.2 mg / L, and mechanical stirring was performed.

[0098]

Table 2

[0099] The experimental results are shown in Table 3. The treated water was analyzed for a sample obtained by mixing the treated water for one day. The required dilution ratio was calculated with the discharge standards being BOD: 600 mg / L and T-N: 240 mg / L. In the experimental system where the aeration conditions were switched, although the BOD concentration was slightly higher than that of the control system, the T-N concentration was 320 mg-N / L on average, and the nitrogen removal rate was 52.2%. In the control system where the aeration conditions were not switched, the T-N concentration of the treated water was 648 mg / L on average and almost no nitrogen was removed. The dilution ratio of the dilution water used for sewer discharge was also reduced to 1.3 times in the experimental system.

[0100]

Table 3

[0101] From the above results, by setting at least two or more aeration conditions and switching them so as to alternately repeat nitrification and denitrification, a stable nitrogen removal and a dilution ratio reduction effect were confirmed.

Explanation of Symbols

[0102] 1…Solid-liquid separation device 2…Treatment tank (aeration treatment tank) 3…Dilution tank 4…Control means 11…Separation liquid supply pipe 21…Agitator 22…Aeration means 23…Measuring means 24…Measuring means

Claims

1. A separation liquid obtained by solid-liquid separation of sludge containing at least either septic tank sludge or night soil sludge is supplied into an aeration treatment tank containing a biological carrier, in the treatment tank, the aeration conditions in the treatment tank are set to at least two conditions including the aeration conditions for promoting nitrification and the aeration conditions for promoting denitrification including subordinate denitrification, so that nitrification promotion treatment for promoting nitrification and denitrification promotion treatment for promoting denitrification are performed, the aeration conditions are switched to perform biological treatment so that the nitrification promotion treatment and the denitrification promotion treatment are alternately switched in the treatment tank, the separation liquid is introduced at least during the denitrification promotion treatment, diluting the biologically treated water obtained by the biological treatment at a dilution ratio based on the total nitrogen concentration of the biologically treated water so as to meet the sewage discharge standards characterized by having.

2. The water treatment method according to claim 1, characterized in that the supply of the separation liquid to the treatment tank is performed intermittently.

3. In the denitrification promotion treatment, the separation liquid stored in the treatment tank is caused to flow by performing at least one of causing the separation liquid to flow in from the lower part of the treatment tank, stirring with a stirrer, or performing aeration. The water treatment method according to claim 1 or 2, characterized by this.

4. A solid-liquid separation device that separates sludge containing at least either septic tank sludge or night soil sludge into separated sludge and a separation liquid, a treatment tank that contains a biological film for biologically treating the separation liquid and performs a nitrification promotion treatment for promoting nitrification and a denitrification promotion treatment for promoting denitrification including subordinate denitrification on the separation liquid, control means for setting and controlling the aeration conditions of the treatment tank to at least two conditions including the aeration conditions for the nitrification promotion treatment and the aeration conditions for the denitrification promotion treatment so that the nitrification promotion treatment and the denitrification promotion treatment are alternately performed in the treatment tank, means for supplying the separation liquid into the treatment tank at least during the denitrification promotion treatment, a dilution tank for diluting the biologically treated water treated in the treatment tank at a dilution ratio based on the total nitrogen concentration of the biologically treated water so as to meet the sewage discharge standards characterized by comprising.

5. The water treatment apparatus according to claim 4, characterized in that means for supplying the separation liquid into the treatment tank includes a separation liquid supply pipe connected to the lower part of the treatment tank and capable of supplying the separation liquid into the treatment tank so as to generate a liquid flow in the treatment tank.

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